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»ll University Library 
 Medical logic. 
 
 3 1924 012 241 174 
 
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 tine Cornell University Library. 
 
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THE 
 
 SYDENHAM SOCIETY 
 
 INSTITUTED 
 
 MDCCCXLIII 
 
 LONDON 
 
 MPCCCLV. 
 
MEDICAL LOGIC. 
 
 BY 
 
 F. OESTERLEN, M.D. 
 
 TRANSLATED AND EDITED 
 
 G. WHITLEY, M.D. 
 
 LONDON: 
 
 PRINTED FOR THE SYDENHAM SOCIETY. 
 
 M D C C C L V. 
 
I'KINTED BY J. E. ADLAB.D, 
 
 SARlHOLOMKtV CI.OBH. 
 
TRANSLATOR'S PREFACE. 
 
 If the study of Medical Logic be advisable for practitioners 
 in a country such as Germany, where no branch of educa- 
 tion is deficient in metaphysical training, it appeared to the 
 Council of the Sydenham Society that it would be valuable in 
 England, where so little of metaphysics is taught during any 
 portion of a student's career, and where the deficiency of 
 logical accuracy in our medical literature is universally felt 
 and admitted. 
 
 In fulfilling the commission with which the Council has 
 intrusted him, the translator has aimed, not only at render- 
 ing the original faithfully, but also at making it as intelligible 
 as he might to all who are disposed to grapple in earnest 
 witU the subject. He has found his task difficult even for 
 one long acquainted with Germany and the German language, 
 and he fears that his version may, by some persons, be pro- 
 nounced un-English. He has, therefore, thankfully availed 
 himself of the assistance of friends, to get rid, as far as pos- 
 sible, of foreign idioms and expressions, even where it seemed 
 necessary to retain, or to exemplify, foreign modes of thought. 
 
 By such German scholars, however, as will take the trouble 
 of referring to the original treatise, he hopes to be acquitted of 
 anything like carelessness. The author, however solid and accu- 
 
vi TRANSLATOR'S PREFACE. 
 
 rate, is not remarkable either for the clearness or the elegance 
 of his style, and has largely availed himself of that peculiarity 
 of his mother tongue by which new words are created, almost 
 at discretion, to express thoughts and conditions of the mind 
 — words for which no exact equivalent can be found in any 
 other vocabulary. 
 
 G. WHITLEY. 
 
 FlNSBURT; June, 1855. 
 
PREFACE. 
 
 The purpose which this work is intended to fulfil is more 
 fully explained in the Introduction. I shall therefore only 
 say here as much as is necessary to obviate, at the outset, a 
 misunderstanding to which its title might give rise. It can 
 scarcely be necessary, indeed, to assure the reader that Logic, 
 in its ordinary signification, is not here meant, but only the 
 application of certain rules and principles of logic to the study 
 of natural science in general, and of medicine in particular. 
 Our aim, therefore, is a purely practical one — viz., to show, 
 clearly and impressively, the mode in which we must proceed 
 in our observations, investigations, and conclusions, in order 
 that our Theorems and Problems may become more clearly 
 intelligible, and that we may arrive at experimental truths 
 and definite laws in our department of science, as well as at 
 scientific principles of practice. 
 
 The methods and paths by which alone we can arrive at 
 all these ends, and the technical details and peculiarities which 
 encumber them in a study such as ours, have nowhere been 
 set forth, or at least not so that the philosopher, or physician, 
 could derive from them all the advantages and services which 
 he requires at every step : for philosophers and professed logi- 
 
Tiii PREFACE. 
 
 cians have seldom or never touched upon what we have most 
 stood in need of, perhaps because the subject matter — the 
 individual questions and objects with which the natural philo- 
 sopher or physician has to deal — were not sufficiently familiar 
 to them. The latter, on the other hand, seem often not to 
 have closely considered or understood all the processes which 
 they have themselves adopted in their investigations and opera- 
 tions, and by the aid of which they themselves have perhaps 
 arrived, not only at their deductions and theories, but also 
 at their most important discoveries. In short — many con- 
 siderations have concurred to prove that Logic has not always 
 so harmonized and entered into combination with Medicine, 
 or Natural History, as is indispensably necessary for the 
 interests of science. It would seem to me, that philosophy 
 and logic have, on the one hand, by no means given us the 
 precise aid which we require ; and that, on the other, we have 
 not always sought for the support and guidance of a sound 
 logic, where we could scarcely advance safely without it. We 
 may, perhaps, have learnt philosophy, but not to philosophize 
 — we may have learnt logic, but not to form correct opinions 
 and conclusions from observation and investigation. 
 
 But since medicine and the study of natural philosophy 
 have begun to assume a closer relation to each other, and 
 physicians have engaged more frequently in scientific inqui- 
 ries, and advanced from the field of mere empiricism and 
 conjecture to that of comprehension and induction, the desire 
 for scientific methods of inquiry and adequate demonstration 
 has everywhere grown jipon them, and has thereby become a 
 trustworthy guide. Men speak more frequently than hereto- 
 fore of the necessity of a logical mode of proceeding, of a 
 
PREFACE. ix 
 
 correct process of induction^ &c. ; but we have nowhere 
 attained a distinct and complete understanding of all that 
 which we presuppose^ nor have we learnt how to search and 
 investigate in ovir department of science, so as most quickly to 
 arrive at safe principles and conclusions. 
 
 The present has seemed to me, therefore, a seasonable and 
 worthy attempt whereon to venture so far as my powers 
 admit. And the hope of doing some service to my profes- 
 sional brethren, and, through them, to medicine, or even to 
 natural science in general, has been increased by the circum- 
 stance that a period of calm research, in which facts have 
 accumulated, has arrived, free from the excitement which new 
 theories and systems usually produce. The most favorable 
 moment has thus, perhaps, arrived, for making a psychical 
 analysis of the general progress of the human mind; for 
 observing the mind itself in the act of investigation, as 
 well as the mode in which it investigates; and for inquiring 
 why we have hitherto made no further advances in our depart- 
 ment of science, and how we may, with the greatest degree of 
 certainty, do so. 
 
 At this point, however, I wish to obviate the suspicion that 
 the following pages contain nothing more than a pretended 
 elucidation of ideas, and a critique, or that they wiU sweep 
 away the past and leave only a " tabula rasa" for future inves- 
 tigators. The entire aim of this work is rather to endeavour 
 to promote improvement and progress, than to overthrow, or 
 to undo ; nor am 1 called upon to become the judge of my 
 predecessors or contemporaries. It is with results only that 
 we have here to deal, as our progress towards improvement — 
 our future success — depends upon a clearer insight into any 
 
X PREFACE. 
 
 deficiencies in these results, and especially into the causes of 
 such deficiencies or errors, 
 
 If even a Bacon quoted himself as an instance that as a 
 tyro in philosophy one can do much service, much more may 
 a similar excuse be admitted for the author of this work, if 
 his attempt should not fulfil the expectations of his readers. 
 But it is always a difficult task to cement together the de- 
 tached fragments of a subject never yet treated as a whole. 
 It is, however, consolatory to bear in mind, that " he who 
 cannot go to Palestine may still go to Rome," and thus have 
 I, who am self-taught, endeavoured to weigh as exactly and 
 carefully as possible for myself, and^^ to explain, in a manner 
 free from the garb of scholastic philosophy, what has appeared 
 to me to be at once most important and most difficult. 
 Moreover, my guides have been " special," that is, men who 
 have been engaged in one particular study, philosophers on 
 the one hand, as well as naturalists and physicians, both of 
 ancient and modern times, on the other. I am indebted, 
 however, to J. Stuart Mill's excellent work for the greater 
 part, the true pith and thread of my system, and the following 
 is, in a great measure, but an application of his doctrines to 
 the particular questions and objects of our department of 
 science. 
 
 Oesterlen. 
 
 Heidelberg ; September, 1852. 
 
CONTENTS. 
 
 PAGE 
 
 Introduction .... . . 1 
 
 SECTION I. 
 
 Medical Problems in a logical point of view, e. c, in reference to the possibility 
 of solving them. — Topics and Questions with which Logic has to deal, 
 both as a Science and as an Art . . . .31 
 
 SECTION II. 
 
 Of the Methods and Means in general, by which the Naturalist, and especially 
 the Physician, endeavours to attain a perception of Natural Phenomena 
 and Processes, from the study of their Conditions and Laws . . 40 
 
 SECTION III. 
 
 On the Process of Induction, properly so called, or the search, by immediate 
 observation, into the Causal Connection and Laws of the Phenomena and 
 Processes with which we have to do. An inquiry into the simple method 
 of experiment and into the individual steps and means by which it may be 
 facilitated .... . . 82 
 
 I. The observation of the phenomena in question under the greatest pos- 
 sible variety of circumstances and relations . . .92 
 
 II. Comparison of similar Phenomena, &c. with each other ; employment of 
 Analogies . . . . . .97 
 
 III. Application of the Numerical Method, or Statistics . . 106 
 
 SECTION IV. 
 
 Characteristics and Value of the Knowledge which may be acquired by the 
 Observation of Natural Objects, and by immediate Deduction from them. 
 Experience, Empirical Laws, and their Scientific Importance . . 116 
 
xii CONTENTS. 
 
 SECTION V. 
 
 PAGE 
 
 Of the Methods of Investigation and the auxiliary Processes through which 
 alone we can attain to higher and more exact Scientific Knowledge. — 
 Analysis and the Synthetical (Deductive) Method . . • 145 
 
 Progressive Resolution of many and complicated, into fewer and more 
 
 general, Laws. Process of Reduction or Generalization . . 145 
 
 Demonstration of the causal connection of individual phenomena and pro- 
 cesses, and of the laws of operation of individual determining circum- 
 stances and influences. Deduction of the causal connection of the com- 
 plicated processes and influences of medical science . . 152 
 Reduction of numerous apparently heterogeneous phenomenaand processes 
 to one and the same essential process and causal connection. Reso- 
 lution of numerous complex laws into simpler, or more general and 
 higher laws . . . . .192 
 
 SECTION VI. 
 
 On certain Auxiliary Operations and Processes. Observation and Ex- 
 periment. — Hypotheses, Comparison or Analogies, and the Calculation 
 of Probabilities in General — Technicology, Terminology and Definition, 
 Description. — Grouping or Classification .... 222 
 
 I. Observation and Experiment .... 223 
 
 II. Hypotheses, Comparison or Analogies, and the General Calculation 
 
 of Probabilities ..... 266 
 
 III. Language, Terminology and Definition, Description . . 288 
 
 IV. Classification ...... 336 
 
 SECTION VII. 
 
 On Fallacies, their different species, sources, and importance . 353 
 
 I. Errors in the whole Mode of Contemplation, or Conception and 
 
 Judgment ..... 375 
 
 II. Errors in the Discovery of the State of Things . . . 388 
 
 III. Errors in the Comparison and Deduction of General Principles 
 especially in relation to the Causal Connection of certain Things . 399 
 
 C0NCI,USI0N 
 
 420 
 
INTEODUCTION. 
 
 As I feel conscious that the title of my book may, with 
 many readers, lay it open to a degree of doubt respecting its 
 precise purport, I think it desirable to anticipate some of the 
 questions which may naturally arise, by a few words in the 
 way of introduction. 
 
 What, it may be asked, are we to understand by the term 
 Medical Logic ? In what relation does logic stand to medicine 
 and to natural science in general ; and in what degree is the 
 study of it likely to promote and facilitate the peculiar objects 
 such sciences have in view ? Will it assist our investigations 
 into the structure of man ; or may we, by its aid, expect to 
 arrive at a fuller comprehension of natural science in its various 
 branches, and thus be enabled to advance more safely and prac- 
 tically ? Will it afford the physician means whereby to under- 
 stand the condition of his patients more clearly, or endow him 
 with more skill in the treatment of disease, or render him more 
 successful in its prevention ? Such were among the questions 
 which I put to myself and carefully considered, before I could 
 resolve to proceed with this attempt. 
 
 As regards the title "Medical Logic," I might have found 
 many others as fitting, or even more so; but none so 
 
 S ' 
 
3 INTRODUCTION. 
 
 short. It expresses at once the aim of this work ; which is to 
 set forth the importance of a correct application of logic to 
 medical facts and inquiries, and to show the advantages it may 
 render to natural science in so far as logic is connected with 
 such questions. 
 
 I need scarcely remark that we are not here dealing with 
 the ordinary logic of the schools, which I must leave to pro- 
 fessed logicians. In the promotion of the practical object 
 which we have in view, the term " logic " is taken in its widest 
 sense and considered as " the science which acquaints us with 
 the processes by which the mind of man, whether working in 
 direct or indirect channels, may arrive at that establishment of 
 fact in the correct appreciation of nature which constitutes 
 empirical truth." 
 
 For the natural philosopher or physician no more knows 
 by intuition what he needs to understand and learn, than he 
 does anything else throughout nature. He must owe his 
 insight into all these subjects to observation and experiment ; 
 or, in other words, to his experience and the inferences with 
 which it supplies him. By his own efforts, and by many 
 collateral means, he must endeavour to arrive at knowledge; 
 for truth is the philosopher's stone which we all seek and are 
 still, except in miserable fragments, so far from having found. 
 Yet there are certain mental processes, by the aid of which we 
 are able to investigate the actual occurrences in nature; and 
 through these logic is our guide. It teaches us how, by obser- 
 vation, experiment, and inference, we may overcome the 
 obstacles that stand in the way of a clear comprehension of 
 whatever natural phenomena we have to do with, and thus 
 brings us, by a careful induction of processes, to the know- 
 ledge not only of their causal connection with each other, but 
 also of their governing conditions and laws. It further shows 
 us to what extent observation and deduction must be carried, 
 and what requirements they must fulfil, before we can rely 
 upon them as upon acknowledged facts and truths; and 
 explains to us the mode of demonstration by which an assertion 
 or inference, whether drawn from our own particular province 
 of inquiry, or from the wide field of general natural science, 
 may be established as true and proven; and an individual 
 experience be accepted as a permanent truth. It will enlighten 
 
INTRODUCTION. 3 
 
 us in any given case, as to the degree of correctness with 
 which an experiment or a fact has been observed and inter- 
 preted. It will thus enable us to judge whether the con- 
 clusions we are inclined to draw from it (our general abstrac- 
 tions of laws for the science, and of rules for the art), follow 
 strictly in the track of experience : it will also teach us to 
 what extent we are justified in relying on them as on 
 thoroughly demonstrated experimental truths and facts. In 
 short, if it be the object of logic to teach us to think and 
 judge correctly; if it be in all cases the science of exact 
 demonstration, holding up the test whereto to bring our 
 judgment, assertions, and conclusions, then must it (if employed 
 so as to promote our interests and those of natural philosophy 
 in its widest signification,) assist us in finding that which is 
 the especial object of our search. By teaching us to ap- 
 preciate our discoveries, whether real or imaginary, at their 
 exact value, it will enable us to employ them to the fullest 
 advantage, whether in the more immediate service of science, 
 as in elucidating its laws and principles, or in extending the 
 practical application of them, e. g. to the rules of therapeutics. 
 Logic, therefore, in this more special signification, has much 
 to accomplish. It must also be confessed that we are now 
 asking of it services which have not often been demanded of 
 the logic of scholastic philosophy, and such as it has still less 
 frequently rendered. The father of logic, the great Bacon, 
 has complained that the latter is almost useless for discoveries 
 in the sciences, and for the investigation of truth. Men, says 
 a certain Frenchman, have often believed themselves to be pro- 
 found whilst they were only hollow. However this may be, 
 we here take logic and its objects only as they are to be 
 understood in medicine and in natural science in general ; and 
 we therefore give it an acceptation in which philosophers and 
 professed logicians cannot alwaysemployit, because theyare often 
 too little acquainted with all the details and peculiarities of the 
 subjects and objects of investigation with which we are occupied, 
 and, consequently, with our particular wants and difficulties. 
 
 Logic, in this sense of the term, is the appointed cultivator 
 of a soil, more or less crude and barren, wherein it must 
 sow with patience, and in due time it will reap, a sound and 
 nutritious aliment. It then becomes, both to the physician 
 
4 INTRODUCTION. 
 
 and the naturalist, the science of sciences, the "ars artium," in 
 the fullest sense. 
 
 Thus, when we speak of Medical Logic, we simply mean the 
 application of the science in question to our own special 
 province. "We only seek by its aid to explain and develop 
 more clearly the ways and means, the various processes, by 
 which the natural philosopher, the physiologist, and the 
 physician are accustomed to proceed in their investigation 
 of phenomena, occurrences, and influences. It is the pro- 
 vince of Medical Logic to point out how we may best 
 observe, investigate, and experimentally test all those pro- 
 cesses, influences, and occurrences ; those causes, so to speak, 
 and eff'ects, under whose influence man and all living things 
 are born into the world and continue to exist. It must 
 lead us to ascertain the conditions of the living body, and to 
 observe through what peculiar changes it passes from health to 
 disease, and from this again to recovery. This science must 
 determine the exact point to which our observations and 
 experiments ought to lead us ; it must limit the inferences 
 which we' "draw from them in relation to causal connection, 
 and will thus preserve us from building up rash, uncertain 
 conclusions upon generalizations derived from a doubtful, or 
 even erroneous experience, and conduct us, by an exact method 
 of demonstration, to that accurate investigation of nature, 
 which, allowing her to speak for herself, enlightens us as to 
 the real state of things, and so becomes our guide in deducing, 
 with the greatest attainable certainty, those rules by which we 
 must abide in our technical progress as physicians. 
 
 It is not, indeed, from logic, but from the science, what- 
 ever that may be, with which he has to deal, that the natural 
 philosopher or physician must gain the knowledge of the facts 
 and principles he requires; its province is but to guide him in 
 the correct application of them and to enable him to judge 
 whether the processes which are at work, eitlier in his own 
 mind, or in those of others, for the elimination of certain truths, 
 attain to, or fall short of the desired aim. It leads him in the 
 case of any branch of science, to discriminate between the 
 certain, the doubtful, and the erroneous. For we may at all 
 times and in all cases rely upon our investigations, abstractions, 
 deductions, and generalizations, as correct and true, in propor- 
 
INTRODUCTION. 5 
 
 tion as they stand the test of an exact and comprehensive 
 logic ; and should they fall short of its requirements, it will not 
 fail to point out the path by which we may arrive at more 
 certain knowledge and more genuine truth, by providing us 
 with an infallible test to try and prove (whether in observa- 
 tion or deduction), both our own thoughts and those of other 
 men, and by bringing us, through a careful avoidance of error, 
 to a more perfect comprehension of truth. 
 
 But those phenomena and processes in the living body 
 which, under the actioft of the manifold influences of external 
 nature, have ever been the especial object of medical experience, 
 have in their nature nothing isolated, or tending to separate 
 them from the general field of philosophical inquiry. "What 
 we are accustomed to call disease, is but a peculiar change or 
 process in the living organism, under the action of some of 
 those influences from without, which affect the maintenance, 
 loss, and recovery of health ; and these changes are a part — a 
 very small one — of the great whole of nature. A given living 
 being can no more be regarded as perfectly normal and healthy 
 than as perfectly the reverse ; the latter condition would evi- 
 dently be equivalent to death. It may therefore easily be 
 understood why we cannot here confine ourselves to those 
 phenomena and processes which are the special province of the 
 physician. A logic such as medicine is in want of will, in 
 truth, be equally applicable to the whole wide field of na- 
 tural science, and, indeed, to all the so-called experimental 
 sciences ; its doctrines and rules being essentially the same, 
 whether they serve the physician or the physiologist, the physi- 
 cist, chemist, or geologist, in the investigation of his particular 
 objects, phenomena, and processes. Its application to ques- 
 tions and objects in the medico-physiological department is, 
 however, of special importance here. 
 
 After what has just been advanced with regard to the aim 
 and province of logic, as we here understand the term, there 
 can be little doubt of its value to medicine, as well as to na- 
 tural history in general. Whether the problems which these 
 ofl"er it can, in their whole compass, be solved by any one in- 
 dividual, and especially by the author of this work, is a matter 
 of reasonable doubt ; not so the essential nature of the service 
 
6 INTRODUCTION. 
 
 which their solution, if once effected, would render alike to 
 the individual investigator and to the study of natural history 
 and of medicine, whether considered as a science or as an art. 
 Our object here is simply to establish truths and facts, so as 
 to employ them correctly for certain practical purposes. 
 
 And these services acquire a double importance in a study 
 such as medicine, where one of the most valuable possessions 
 of man, his health, is the mediate or immediate object of in- 
 vestigation and treatment ; and where, on the other hand, our 
 comprehension and capability of action* have attained to less 
 certainty and infallibility than in any other department; for 
 even to the present day, it is acknowledged that there is 
 scarcely any department of human knowledge, in which the 
 number of established truths and facts, which no one doubts or 
 attempts to shake, is so small ; in no other field are our rules 
 of action so uncertain and disputed as in medicine, the noblest 
 and most important of all arts. 
 
 The safest data which we possess are individual observations, 
 or empirical propositions in reference to the surface of the 
 living body, and to the occurrence and succession of certain 
 phenomena and processes within it. Of their internal con- 
 nection, on the other hand, and of the essential conditions 
 of their existence, course, and cessation, we know, as yet, next 
 to nothing. We have more or less admissible views and hypo- 
 theses concerning them, but no thoroughly understood and 
 firmly established facts and laws — therefore, no system. And 
 in medicine, as in all cases where personal views and interests 
 uncertain and often arbitrary theories, are defended or at- 
 tacked, we sometimes find a rashness, or even presumption in 
 the hypotheses, and a bitterness between the disputants, such 
 as do not obtain in departments where a scientifically esta- 
 blished, and, consequently, calm insight, has taken the place of 
 mere opinion and subjective, a, priori, conjecture. 
 
 Just as medicine and physiology have entered into closer 
 connection with natural history in general, and with chemistry 
 and physics in particular, so the methods of investigation and 
 the whole process of demonstration in the latter have been 
 more and more adopted in the former. Scientifically educated 
 and thoughtful men now ask themselves other questions, and 
 put their experience and scientific investigations to other'tests 
 
INTRODUCTION. 7 
 
 than they were of old accustomed to do. But through this 
 the discontent of many has but reached a higher pitch. We 
 have seen faith in medicine — as an active agent — shaken on 
 many sides, and a disposition to doubt and question has gained 
 the more ground in proportion as what has been offered has the 
 less corresponded to the demands of the increased intelligence 
 and wider views of the age. A more exact calculation has in 
 so far lowered the standard of our supposed wealth that it has 
 seemed to us to be brought down to poverty itself; and thus 
 one man, in his first excitement, has discarded, perhaps, too 
 much of his previous knowledge, and despaired, more than was 
 reasonable, of the powers of the human mind ; while another 
 has been oppressed in a still higher degree by the responsibility 
 of his duties as a physician, and this through despairing, 
 perhaps, more than was necessaiy, of his art. 
 
 But as one extreme generally calls forth and accompanies 
 another, so has it also been with us. We have seen this 
 scepticism and tendency to critical negation opposed by 
 the greatest confidence, or even arrogance, often combined 
 with the superstitions and mysticism of times long passed 
 away. We have seen the circumspect and, perhaps, too timid 
 physician, who endeavours to instil into his practice a truly 
 scientific spirit, confronted with the boldest speculation, and 
 with the most thoughtless and narrow empiricism : just as we 
 see, in other departments, a boundless and injudicious admira- 
 tion of, and adhesion to what is old, opposed, without discri- 
 mination, to all that is new. 
 
 It can scarcely be doubted, however, that the greater 
 number of these disputes and errors have frequently arisen, 
 less from the insurmountable diflSculties of our subject, than 
 from the want of a better understanding of the actual state of 
 things. We have to blame the deficient employment of the 
 necessary methods of investigation, and to accuse ourselves, in 
 treating so delicate a subject, of a neglect of the doctrines of 
 sound logic. And we must remember, in order to judge of 
 the fitness of the present attempt, that many as are the diffi- 
 culties of our subject, it is less to these difficulties than to our 
 own want of caution, that we are indebted for so many false 
 steps and failures. Against these, a careful logic would arm 
 us, by imparting a clearer insight into nature, and into the 
 
8 INTRODUCTION. 
 
 special requirements and difficulties of our subject, while it at 
 the same time provides us with rules for the critical apprecia- 
 tion of all our experiences and our theories. It not only 
 exacts scientific perception, but also teaches us, D. V,, more 
 aud more to abhor exaggerations and aberrations, in whatever 
 direction they may point ; and these will be the more carefully 
 shunned, the more physicians and physiologists become imbued 
 with, and elevated by its doctrines. 
 
 Many of my readers will perhaps think, that, after all, logic 
 can but assist us to theorize somewhat better than before, or 
 at most to clear up and facilitate our critical examination of 
 the notions and views presented to it. Of what value, it may 
 be urged, will be all the theorizing and speculation through 
 which it would profess to guide us, when we come to practise 
 at the bedside ? Who has not heard so-called practical 
 men say that medicine is a purely empirical science ; that 
 everything depends upon facts and correct experience ; or, 
 perhaps, that the power to cure is the main point ? All argu- 
 ments and theories, they say, do not enable the physician to 
 treat his patients more correctly ; in an art like medicine they 
 rather do harm, or, at best, no positive good. It is there we 
 are in need of experience — facts, and above all, remedies and 
 their correct employment : all the rest is evil. 
 
 Further on I hope to point out what, in medicine and 
 natural science, is the true signification of theory ; and, while I 
 establish a distinction between correct and incorrect speculation, 
 to show how frequently these are confounded. But it is the 
 very fact of this confusion which explains, and in some degree 
 excuses, the mistrust of all theories and so-called systems, and 
 brings contempt upon the idea of methodical progress in our 
 science. It is unfortunate thut there is, perhaps, in no other 
 department, more real ground for such dislike and mistrust 
 than in ours, where all theories and systems have so far proved 
 deficient, and at least, in some degree, erroneous ; and where 
 the very nature of the subject induces a necessity of their 
 appearing less certain in proportion to our success in making 
 them more comprehensive, subtle, and profound. But these 
 false theories, &c., have always returned to their nothingness, 
 and often immediately upon their construction. 
 
INTRODUCTION. 9 
 
 Yet the merely practical man, the so-called empiric, is none 
 the less blameable in his feeling of repulsion and mistrust. 
 Would he, who, on the basis of every insignificant fact, opposes 
 mere experience to theory and speculation, seek to apply that 
 which holds good of monsters and precocious births, to that 
 which is brought forth after the usual manner? He who sees 
 in theory and experience two antagonistic states or tendencies, 
 only proves that he has by no means attained to a clear per- 
 ception of the essential meaning of theory and reasoning. It 
 may be sufficient here to state that the physician who seeks to 
 understand the condition of his patient, and by the aid of 
 such knowledge, to cure his disease, cannot, however earnestly 
 he may endeavour to do so, accomplish this without theorizing. 
 He who doubts this does not even know how impossible it is 
 to reflect upon, i.e., to form for himself any notions of even 
 the simplest vital phenomena and diseased conditions, of the 
 mode of operation of a remedy, or of any other occurrence in 
 nature, without having already theorized and speculated con- 
 cerning it — more or less correctly according to circumstances. 
 Even the savage cannot observe anything in nature around 
 him, i.e., simply recognize it by his senses, without seeking to 
 interpret and to form for himself some notion concerning it. 
 Even he endeavours to determine its origin and the mode of 
 its development; he assumes one thing as an effect, and 
 another as its cause ; though, perhaps, in the end, only some 
 god or demon who, as he imagines, produces and controls it. 
 
 Let us take the case of a patient suffering from inflammation 
 of the lungs, — a disease of frequent occurrence, and com- 
 paratively easy to recognize. The physician does not see this 
 disease, however, any more than he does any other. He infei-s 
 its existence from a number of local or general phenomena ; 
 and traces it through symptoms which he knows have been 
 observed in essentially the same form, combination, and order 
 in other persons suffering from the same disease, But yet 
 he knows next to nothing of the conditions and causal 
 connection — in short, of the exact nature of those phenomena 
 or derangements which, taken collectively, he interprets as and 
 designates "inflammation of the lungs." The most detailed 
 and conscientious investigation of the physical, chemical, and 
 objective, as well as subjective, symptoms in the chest, pulse. 
 
10 INTRODUCTION. 
 
 temperature, blood, excretions, or sensations, &c., in the patient, 
 does not give him the least information on this subject, any 
 more than the post-mortem appearances. And yet, every one 
 who feels any interest in his science will wish to learn, and 
 will therefore reflect, why his patient has been attacked by 
 this disease, and what is its peculiar nature ; what changes or 
 derangements are essential or determining; and which of 
 them, on the other hand, are dependent, comparatively subor- 
 dinate, and accidental. But so soon as he thus reflects at 
 all, and even the most strictly practical man cannot refrain 
 altogether from doing so, he also theorizes, and that, for the 
 moment, very much at random. He entertains, perhaps, cer- 
 tain views concerning the operation of frost, moisture, and 
 what is termed " taking cold," upon the living organism ; and, 
 on the other hand, concerning plethora and similar general 
 predisposing circumstances in his patient. With all this he will 
 soon endeavour to account in some way or other for the de- 
 velopment of the disease. He will further form certain notions 
 concerning the origin of the fever, of the buflSng of the blood, 
 of its accumulation in the parenchyma of the lungs, and of 
 their so-called hepatization, and of the relations these bear to 
 the buffed, or otherwise altered blood, to fever, heat, and other 
 analogous derangements or phenomena. 
 
 And if he now proceeds to the attainment of his chief 
 object, viz. : treatment, he must ask himself how this state of 
 things in his patient may most certainly and quickly be 
 obviated. If he proposes to employ bloodletting, nitre, 
 calomel, or antimony, cold, &c., he must again have known, or 
 at least surmised, something of the properties and effects of 
 those agents. He must expect, for instance, some favorable 
 effect from them upon the composition and circulation of the 
 blood; upon absorption, temperature, innervation, fever, or 
 other derangements in his patient, or he would not, as a 
 strictly practical physician, employ them at all, He must, 
 therefore, have already formed some notion concerning the 
 mode of operation of his remedies in this disease : in short, he 
 must himself have theorized, or others before and for him, and 
 that more or less correctly according to circumstances. 
 
 He who only observes his patients for the purpose of ascer- 
 taining approximately the species of disease, or, perhaps its 
 
INTRODUCTION. 11 
 
 mere denoiaination, and then prescribes his remedies, simply 
 because he knows or surmises, from his own experience, or 
 that of others, that they had done good service in similar 
 cases, — such a one, it is true, does not require much theory. 
 He does not require it so long as he is indifferent to knowing 
 how and why his patients have fallen sick, and what is the 
 nature of their disease. So long as it remains indifferent to 
 him whether he treats his patients solely in accordance with 
 routine rules, or on principles founded upon some compre- 
 hension of the things with which he has to deal as a physician ; 
 so long as he does not strive to understand why he treats his 
 patients in this or that particular way, and whether the means 
 he employs are beneficial or not, he need not either reflect or 
 theorize. To such a one Sismondi's remark applies "that we 
 feel no curiosity concerning things of which we know nothing.'^ 
 He relies simply upon the experience of others, or upon that 
 which he calls his own experience, which, however, a Bacon 
 or a Zimmermann would for the most part have declared to be 
 a dubious or even an erroneous one. No doubt it is, in many 
 respects, quite right to depend upon experience and facts only, 
 but they must be actual facts, not, as they too often are, 
 mere opinions or views. They must be truths founded upon 
 experience, and not, as is so frequently the case, partial 
 truths, — mere errors and illusions. 
 
 The very men who are in the habit of insisting most strongly 
 upon experience, and accustomed most to rest upon the neces- 
 sity of simple facts, without further speculations or theories 
 concerning them, viz. : the so-called exclusive empirics, have 
 often been least able to observe facts positively, (that is to say 
 objectively), and to employ them correctly. They frequently 
 do not even know what observation really is, and how much it 
 includes. What they advance as their positive experience, as 
 actual facts, are more properly their notions of them, and are 
 often but illogical conclusions and interpretations. They con- 
 clude that what they have seen, or believe to have seen, with 
 their own eyes, must be so in all cases, and do not understand 
 that of this very fact, others may take a different view. This 
 explains how one man may regard as an established truth what 
 appears doubtful to another, and to a third even absurd, and 
 opposed to the whole tenor of his experience. They acknow- 
 
12 INTRODUCTION. 
 
 ledge no scientific or theoretical authorityj but substitute for 
 it their yiews at the moment — their ego. To proceed, who 
 has not heard the practical man say that our object is to cure, 
 not to theorize ? In a locomotive engine, the object is to set 
 itself and the carriages in motion ; in a watch, again, the object 
 is to indicate the time ; but no one will assert that the face 
 and hands are the main parts of the machinery of the one, 
 or of the other, thje turning of the wheels, or the rise and 
 fall of the piston. For the patient, it is true, the recovery 
 of his health may be all that he expects from medicine ; to the 
 physician, on the contrary, it is the final result of his know- 
 ledge and power of action, a keystone which presupposes many 
 other things ; a fact, in short, to be made use of, which he 
 will not be able to do, unless he has previously acquired a cer- 
 tain insight into his science and a practical skill in his art, 
 based upon correct experience and precise knowledge. But so 
 long as physicians can appeal to nothing more certain in their 
 practice, in their success or failure, than their experience at the 
 bedside, every new patient, every fresh experience, may shake 
 or contradict their views. They must be content to let every 
 one else, even charlatans, appeal to their experience ; and in- 
 asmuch as the latter can often avail themselves of the same 
 argument, the post hoc propter hoc, which the physician 
 employs for the success of his operations, viz. the recovery of 
 his patients, the sick will necessarily place the same confi- 
 dence in, and award the same thanks to them, as to the most 
 able physician. Science, in the full signification of the word, 
 can, in medicine, mean nothing more or less than the applica- 
 tion, on the part of the practitioner, of a certain knowledge to 
 certain objects. It presupposes, therefore, a certain knowledge 
 and comprehension; or, rather, it is in itself knowledge ar- 
 ranged and employed in the manner best adapted for the attain- 
 ment of his ends, i. e., for practice. It groups for him the 
 doctrines and propositions of his system, and combines them, 
 so as to enable him to found upon them his rules for the 
 treatment of his patients. It is on this account that a sound 
 logic is indispensable to every art, and especially to that of 
 medicine, for, as we cannot conceive of the existence of any true 
 art that is not founded upon knowledge and understanding, 
 so, on the other hand, there can be no more vahd demonstra- 
 
INTRODUCTION. 13 
 
 tion of the accuracy of any knowledge, explanatioUj or theory, 
 than that it furthers art, i. e., practice, as well as insight and 
 comprehension. Thus logic facilitates the physician^s compre- 
 hension and appreciation of a given case of disease and of its 
 treatment, and shields him, on all sides, from error ; as in the 
 words of Bacon : " inter signa nullum magis certum aut nobile 
 est quam quod ex fructibus."^ 
 
 And further, while, as has been said already, the chief stress 
 is laid, and in some degree correctly, upon experience and 
 facts, it is formally asserted that we should confine ourselves 
 entirely to them, and attempt to classify them only. We must, 
 it is said, observe and describe all the phenomena and pro- 
 cesses of health and disease, according to their actual appear- 
 ance, without any subjective aid, whether in the conception or 
 interpretation of them, or in the comparison and classification 
 of them with others. And this must be carried out with a 
 resolute independence of all theoretical views, and without 
 allowing ourselves to be influenced by any dogma, precon- 
 ception, or peculiar mental tendency ; as if this were in any 
 way possible for man in the present state of his intellectual 
 being ! But this idea is most intimately connected with 
 another still more erroneous, — one daily to be met with among 
 the empirics, and even among many of the Coryphaei of 
 medicine — the belief, namely, of its being possible to arrive, by 
 mere observation, and by the collection and accumulation of 
 observations, of so-called experiences and facts, per se, at a 
 certain medical comprehension and science. 
 
 That this is entirely impossible, will, however, be explained 
 at a later period. 
 
 Thus our ancestors, for instance, as well as the uncultivated 
 inhabitants of all countries, constantly observed the wind and 
 the weather, and contemplated the heavenly bodies and their 
 course night after night, for centuries, without thereby ascer- 
 taining anything either of the connection and conditions of 
 the weather, &c., or of the laws of motion of those heavenly 
 bodies and of their own earth, or of the distance and magnitude 
 of the former. Neither have physicians, with all their observation 
 and palpation of their patients during centuries, gained a true 
 insight into their real condition — an insight which we shall 
 ' Novum Organum Scientiarum, etc., lib. i, aphor. 73. 
 
14 INTRODUCTION. 
 
 never obtain by mere observation, whether in the way of 
 auscultation, percussion^ or mensuration; or even by our 
 autopsies and microscopical and chemical examinations, be 
 they ten times as minute and correct as they are at present. 
 These observations, this collection of empirical facts, are no 
 doubt important enough, but only as the first step, — a step 
 which it would be equally erroneous and absurd to regard as 
 the last. Even Bacon, who has in some degree encouraged 
 the error in question by his almost too partial insisting upon 
 observation, positively declares the mere accumulation of obser- 
 vations or empirical facts, to be a " res puerilis."^ He asserts 
 that our gain, in the attempt to deepen our scientific insight by 
 means of such accumulation only, would be about equal to what 
 we should acquire by setting ourselves to learn a diary by heart. 
 
 But the fact of experience being regarded by so many as a 
 substitute for knowledge, — nay, even as being in itself both 
 knowledge and understanding, has further encouraged the 
 illusion of our being already rich in knowledge, while we 
 possess, at the most, but the raw materials, out of which, at 
 some future period, perception and true science may spring. 
 It is not the heaping together of individual experiences and 
 facts, but the understanding of them, that constitutes know- 
 ledge ; and it is because there is in no other department of 
 science such a dearth of this understanding that medical 
 science remains behind all others. We are not deficient in 
 preparatory materials, — for these experience has amply gleaned ; 
 but in that due understanding and arrangement of them, 
 through which alone they can be employed and made available, 
 whether in practice or in the construction of theories. 
 
 Thus, even in the present century some have believed that 
 they had discovered the essential causes and ultimate nature 
 of diseased conditions in certain anatomical changes in the 
 organs : others have found them in certain chemical changes : 
 others, again, in certain derangements of innervation. Yet all 
 of these have rested their assertions upon experience, and 
 appealed to it for their confirmation, but yet have not succeeded 
 in demonstrating the truth of their theories, because, for the 
 reasons already mentioned, it remained an impossibility. 
 
 This erroneous estimate of the value of experience in itself. 
 
 Lib. i, aphor. 102, 105. 
 
INTRODUCTION. 15 
 
 has not only involved a misapprehension of what, in medical 
 science, remains our especial desideratum, but it seems to be 
 the ultimate cause of the further circumstance that we have 
 often omitted first to search for what our understanding and 
 knowledge alone might have established. 
 
 We have only, however, one mode of arriving at the sure 
 understanding of any natural phenomenon or process — e. g., 
 of a disease, or the operation of an influence or a remedy — 
 viz., by bringing these obscure phenomena and processes 
 themselves, as it were, more within the scope of our compre- 
 hension. We must first seek to ascertain their conditions and 
 efi'ects, to trace their causal connection and conformity to fixed 
 laws ; we must be able, by the aid of a carefully constructed 
 theory, to reason consistently concerning them and, above all, 
 we must be provided with scientific demonstrations of the ac- 
 curacy of our views. But if we have once succeeded in the 
 formation of such a theory, we have gained, in that particular 
 department, that of which we must otherwise remain destitute 
 viz., a science. To this goal, the nature of our intellectual being 
 urges us almost instinctively, because the goal itself is a 
 natural one. No one capable of reflection, and possessing an 
 intellect in any degree active, will content himself with the 
 mere observation and sentient perception of any phenomenon 
 or object whatever. He will not only seek, by the aid of per- 
 ception and observation, to intei'pret the phenomena or objects 
 in question, but his observation will pass involuntarily, and in 
 accordance with innate laws of necessity, into a more profound 
 contemplation of them. He reflects upon them, and compares 
 what he observes here with what he has observed elsewhere, 
 noticing their similarity, or their distinguishing features. 
 He strives unconsciously to digest and master, as it were 
 mentally, what he has observed, by seeking for the con- 
 ditions of its development, for its causal connection and 
 laws. Mere observation, however, would not suflBce to 
 satisfy his yearnings. Being conducted by means of the out- 
 ward senses, it can but aid our perception of things exterior, 
 it does but acquaint us with this simple fact — that they appear 
 and present themselves in a certain form. It falls far short, 
 therefore, of such a comprehension of them as our whole na- 
 ture urges us to seek for. This applies also to the phenomena 
 
16 INTRODUCTION. 
 
 and processes in external inanimate nature — e. g., to wind and 
 weather, to light and colour, &c. — as well as to those of 
 living nature, whether in health or disease. 
 
 But while we obey this impulse, and inquire into the con- 
 nection and causes of these phenomena or processes, we must 
 form for ourselves some notion of them, and, as it were, render 
 a certain account of them to our minds — whether a correct or 
 a false one matters not at the moment. The so-called practical 
 man, or empiric, theorizes also at that moment, whether he in- 
 tends and acknowledges it or not. In this sense we may say, 
 and others have already said, that to theorize concerning such 
 things means nothing else than to reflect upon them. But 
 this in all cases presupposes our own subjective co-operation, 
 and in the present state of things, in medicine proper, this can 
 never be carried out without rash hypotheses, and an advance, 
 more or less arbitrary, in our interpretation of what we have 
 observed, in the separation or combination of its individual 
 parts, and in the abstractions or general conclusions with 
 which it furnishes us. 
 
 We have, perhaps, said enough to satisfy the reader, 
 if not convinced beforehand, that in medicine, as well as in 
 the general study of nature, we cannot keep asunder theory 
 and practice, or separate our experience, i. e., our view of the 
 actual state of things — from those our subjective notions 
 concerning them, which aim at their right understanding 
 and explanation. Let us at once admit that all artificial 
 attempts and operations, what is called practice, is itself, funda- 
 mentally, nothing less than the result of theories more or less 
 detailed and comprehensive. For our practice is, after all, but 
 the more or less conscious application, either of our own general 
 views, or of those furnished us by others ; i. e., we take the 
 principles and generalizations deduced from certain individual 
 experiences and cases, and apply them to any given case. 
 We judge of this individual case, we interpret and treat it in 
 one manner or other, conformably to those more general 
 views, or principles and theories, because, without some such 
 a priori groundwork for our operations, we could neither form 
 a correct notion of it nor treat it consistently. Our grounds 
 of action, however, whether sound or otherwise, are furnished 
 
INTRODUCTION. 17 
 
 us by theory, and the sum of them — arranged in a certain 
 form — is, in the end, synonymous with theory itself. This 
 shows us plainly how injurious, in such a study as medicine, 
 the long existing dissention between empirics and theorists 
 must have been to the advance of art as well as of science. 
 This strife between theory and empiricisno, between speculation 
 and sober investigation, exists now, and meets us on either side 
 in its extremest form, just as it has existed for centuries j be- 
 cause it has its root in the different dispositions and tendencies 
 of different men. As nature teaches birds to fly, and other 
 animals to walk or crawl, so the natural tendency of the mind, 
 and subsequent experiences and circumstances, lead one man 
 more especially to speculation and theory, another to the sober 
 and circumspect accumulation of facts, and a third to perform- 
 ance. The position which one man takes, or seeks to take, in 
 the field of thought, conception, and mental combination, 
 another will, perhaps, take in the field of action. If physicians, 
 however, had always clearly understood what theory and expe- 
 rience, science and practice, essentially mean, how they all 
 blend with, and are supported by each other, and can only 
 thrive in intimate connection, many bitter disputes would never 
 have arisen. Reflecting and well-meaning men would have 
 been less ready to place them in opposition, or to be led through 
 an unfounded prepossession for the one, to the undue dispa- 
 ragement of the other. If physicians had always had a clearer 
 comprehension of the questions here at issue, and which, when 
 answered, can alone decide, they would not for the mere sake of 
 what simple experience and practical tact can give, have over- 
 looked the value of theories and the indispensabihty of their 
 services, or have allowed the possibility of deficiencies or errors 
 in them to have diminished the importance of such aid. 
 
 If it is acknowledged that every theory not firmly based 
 upon experience is built upon the sand — and liable to be thrown 
 down by the first wind, and that, from this cause, all theories 
 in the science of life, and especially in medicine, have hitherto 
 been defective, and will, perhaps, always remain so — it is equally 
 certain, that without theory there is no genuine progression. 
 Even the first imperfect attempts to theorize, the first uncer- 
 tain steps towards scientific perception, have rendered infinitely 
 more service to physiology and therapeutics, and furthered the 
 
 2 
 
18 INTRODUCTION. 
 
 progress of the human mind in the dark chaos of investi- 
 gation, more than would ever have been attained by adhesion 
 to simple empiricism. Such theorists and speculators oftenj 
 perhaps, reason too abstractedly, too much a priori ; they may 
 be even dreamers and visionaries. But, in the end, they have 
 always been those who have contributed most to decide the 
 fate and the progress of sciences, and, amongst others, of me- 
 dicine ; for they have laid open nevir veins of knowledge, which 
 the mere empiric, as such, would have been no nearer lighting 
 upon than would the diligent collector and labourer in the 
 sweat of his brow. Every new discovery is a species of creation, 
 almost in the same sense as, for instance, every poetical fiction 
 is. And though such a discovery does not produce the thing 
 itself, but only conveys to our minds the knowledge of its ex- 
 istence, theorists have extracted the honey from the materials 
 often collected by others. If their discoveries have frequently been 
 set down as refuse, some grains of gold have, perhaps, eventually 
 been found therein, some truth worked out, or, at least, the 
 way prepared for doing so. Theorists have often surmised 
 the truth, and led to its discovery through hypothesis and 
 combination, while its demonstration remained for sober and 
 more patient investigators. If, on the other hand, theorists 
 had always understood with sufi&cient clearness that the true 
 object of speculation is not the conception of an idea, not the 
 indefinite surmise and vague assertion of a truth, but the es- 
 tablishment and actual demonstration from experience of a 
 certain connection and conformity in nature, they would have 
 been less averse to labour and investigate for themselves. In 
 becoming aware of the means by which alone they could safely 
 carry out their hypotheses and abstractions, they would have 
 seen the sooner the necessity of investigation in the direction 
 and by the methods through which alone they can furnish 
 themselves with fit materials to work upon ; and instead of 
 being in such haste to make known their views upon first 
 adoption, they would have the rather striven, by adequate in- 
 vestigation, to convert their a priori surmises into infallible 
 truths or laws, and have thus given to theory a higher value 
 than it has hitherto acquired. They VFOuld do well also to 
 bear in mind that with all our philosophy and speculation, 
 when these are left to work alone, we have never arrived at 
 
INTRODUCTION. 19 
 
 genuine truth and perception in the study of nature^ or even at 
 a single discovery, and that they can but guide us by hints 
 and guesses to investigation, and then aid us in forming a 
 correct estimate of its results. 
 
 What has been said will explain why the ancient Egyptians, 
 who regarded every discoverer as worthy of being worshipped, 
 set up infinitely more idols to animals than to men; for 
 animals, by the aid of their instinct, have not only made many 
 discoveries, but have put men upon the track of many more, 
 which human philosophy and speculation would not easily have 
 made. And so it has continued to be to the present day. If 
 we had waited till some one, entering by scientific insight 
 into the proximate and remote conditions, into the essential 
 nature of ague and bronchocele, had hit upon the treatment of 
 them by cinchona, burnt sponge, and iodine; or, conversely, 
 until he had inferred the efficacy of these substances in those 
 diseases, from his insight into their properties, and the mode 
 of their operation, no one would yet, or so far as we can now 
 judge, for centuries to come, have been cured. The very fact 
 that accident, or simple experience, has hitherto furnished 
 medicine with its most importimt, perhaps its only materials 
 for practice, may, in our peculiar department, serve as a good 
 check upon the self-conceit of a priori speculation and philo- 
 sophical abstraction. 
 
 It has been, on the other hand, a no less great and hurtful 
 error on the part of the empirics, and of not a few physicians 
 and natural philosophers, to suppose that they can dispense 
 with the aid of logic in the observation and determination of 
 the materials which experience furnishes ; or in that accurate 
 deduction and generalization in which the scientific appre- 
 ciation of facts and observations consists. For many are of 
 opinion that with a knowledge of the individual facts and 
 doctrines of their particular branch of science, that sort of 
 acumen which goes by the name of common sense and natural 
 tact will furnish aU the rest. Unfortunately, however, the 
 history of medicine — one of the most melancholy of all histories 
 — plainly shows into what errors and exaggerations even those 
 whose " common sense " no one would be inclined to doubt, 
 may nevertheless be led. No man can attain to the logic 
 that we require, or know how to employ it correctly, any 
 
20 INTRODUCTION. 
 
 more than he can understand any art or science — as it were 
 a priori, of himself. 
 
 As we must learn the use of our legs before we can walk 
 properly, so, regarding logic as an instrument, — complicated 
 indeed but useful — we must first understand and be able to 
 manage it properly, before we can employ it to due advantage. 
 In this a man's natural capability may assist him ; he may be 
 able to apply the rules of logic, and to a certain extent suc- 
 cessfully, without being conscious that he employs it at all. 
 But to reap from it all the advantages of which it is capable, 
 he must advance yet further in the copiprehension of its nature, 
 and especially in that of its application. 
 
 I have already endeavoured to point out that many of the 
 impediments to our progress lie less in the intrinsic and inevi- 
 table difficulties of our subject, than in an injudicious choice 
 of ovir objects of investigation, and in an unproductive, if not 
 absolutely erroneous, method of conducting investigation in 
 general. Such failures and aberrations pre-suppose a deficient 
 insight as well into the end in view as into the means by 
 which we propose to attain it, the cause of which we must 
 seek in the want of logical proficiency. In a study such as 
 medicine, we can take no single step ; we can neither observe 
 nor determine anything accurately, nor undertake anything 
 for the cure of disease, without at the same time feeling the 
 necessity of forming some notion or inference, and giving both 
 to ourselves, and, if need be, to others, some explanation of 
 what is before us. But to attempt to accomplish this on the 
 mere ground of experience, and with proofs whose very nature 
 is dubious and fluctuating, must be a rash, and may be a 
 fruitless and purely illusory undertaking. 
 
 Physicians in particular, and many other natural philosophers, 
 do not seem at all times able to track out the difficult and 
 devious paths by which they are accustomed to arrive at what 
 they briefly term their experience. Even in respect to obserr 
 vation, they seem to distinguish less than is to be desired 
 between what is positive, and refers solely to the things them- 
 selves, and what their minds construct out of these given facts. 
 Many cannot even distinguish clearly between the thing 
 observed and their own conception or interpretation of it, but 
 deal with their notions, abstractions, and allegorical phrases as 
 
INTRODUCTION. 21 
 
 if they were tangible realities. It is dangerous, however, as 
 we but too often learn from daily experience, for the mind of 
 man to be left to deal arbitrarily with such an obscure and 
 chaotic subject ; to leave the discovery or non- discovery, the 
 comprehension or non-comprehension of enigmatical phenomena 
 to chance, instead of putting definite and clear questions to 
 nature, and of so arranging everything as to obtain, if possible, 
 decisive answers. Medicine, as it is at present practised at 
 the bedside, does not, it is true, demand abstruse reflection. 
 Almost everything flows from the memory, and from simple, 
 often superficial reminiscences. Most of what is to be done is 
 confined chiefly to the simple sentient perception of certain 
 appreciable phenomena : we are guided (under the influence of 
 proximate conclusions, or mere surmises concerning their con- 
 dition and character) by the combination of these phenomena 
 with each other, or by comparing them with other cases of a 
 similar kind with which we have been furnished by experience. 
 We are accustomed to choose our remedies and treatment 
 without the aid of profound calculation, and only in accordance 
 with general — often arbitrary and vague rules and doctrines, 
 and, in the end, more from memory than from a comprehension 
 of our subject. We might even say, perhaps, that men have 
 expended more acumen and labour upon the interpretation of 
 writings in cypher, or even upon many games, and certainly 
 with more success, than upon the interpretation, prevention, or 
 cure of diseases which may, at any moment, prove fatal to 
 themselves, or to those around them. 
 
 But if any improvement is to be effected in medicine, — if 
 the physician would approach to a certain insight into what 
 he terms health and disease, and jiidge rightly of what con- 
 cerns the maintenance of the one and the cure of the other, 
 he must strive to the utmost to give to medicine a scientific 
 character, and must be, therefore, in the first place, himself 
 convinced both of the necessity and the possibility of doing 
 this. Instead of contenting himself with the fact that phe- 
 nomena vary and run a different course in different patients, 
 — sometimes disappearing under one mode of treatment, some- 
 times under another, he must seek, with unremitting per- 
 severance, to gain positive grounds for his views and active 
 interference, that he may expect in future to be able to give. 
 
23 INTRODUCTION. 
 
 whether to himself or others, a more correct account of them. 
 He must gradually acquire a clearer notion of that in which 
 his knowledge and capability of action consists, and for this he 
 requires a definite idea of the objects submitted to him for 
 examination : he must know their characteristics and weigh 
 their special demands upon his methods of investigation; and 
 to this end he needs a clear insight into the ways and means 
 which can alone lead him to a comprehension of them, and equally 
 into the others which can never render Mm any assistance. 
 What a strange thing is the mind of man ! In proportion to 
 its activity and progress, he is capable of penetrating into the 
 most hidden depths of nature, and of inquiring into her laws ; 
 he calculates with certainty the motions of those distant 
 heavenly bodies which are scarcely discernible by the telescope ; 
 he weighs the earth to which he does not even stand in the 
 relation of the millionth part of an atom, and subjects forces 
 of nature to his will, which his ignorant fellow-man at the best 
 fears and gazes at, as at powers above his control. On the 
 other hand, the same human mind, through want of develop- 
 ment, or through an erroneous employment of its powers, 
 while it receives absurdities as established facts, may overlook 
 the simplest truths, or even declare them to be illusions. 
 
 If we then, as physicians, have any desire to approach 
 nearer to our object — a certain insight into the things with 
 which we have to deal — we must not omit, above all, to pro- 
 ceed methodically, i:e., according to the doctrines and prin- 
 ciples of a sound logic, in our observations and investigations, 
 as well in the scientific appreciation of facts, as in the conclu- 
 sions we draw from them. We must regard this as the first 
 indispensable step towards our end, and be thoroughly con- 
 vinced that this effort is not less important for our practical 
 purposes, as physicians, than for scientific investigation. He 
 who understands nature can alone hope to rule it, because he 
 can only do so by a knowledge of its laws. Such knowledge 
 is, however, very difiScult to acquire, and the main object of 
 our logic here is to make us acquainted with the intricate paths 
 or means through which we may be led to it. The man who 
 possesses a genuine talent for the investigation of nature may, 
 perhaps, dispense, in a certain sense, with its aid and with its 
 methods and laws, but even he can only do so because Ris 
 
INTRODUCTION. 23 
 
 peculiar nature and his instinct make him in a manner inde- 
 pendent of it, by leading him, unconsciously, to employ it 
 correctly. He constructs his own rules, he seeks and discovers 
 his own path. Geniuses are, however, rare, and the mass of 
 ordinary labourers in the field of science probably effect 
 more than individual prodigies. But these will accomplish 
 yet greater and better things, by a more methodical mode 
 of progress, and a stricter adhesion to a correct mental 
 process; and may thus raise themselves from the mass of handi- 
 craftsmen and day-labourers to the rank of scientific investi- 
 gators. 
 
 Every special and methodical attempt at guidance towards 
 this end has, however, hitherto failed. Little as the more 
 general abstractions or doctrines of ordinary philosophy and 
 logic are capable of furthering our ends, the axioms and 
 suggestions that are daily offered to the investigator and phy- 
 sician fall equally short of rendering us any positive service j 
 such, for instance, as these : — that we must observe correctly 
 and impartially ; that we must first interpret our observations, 
 and then draw from them the conclusions to which they legi- 
 timately lead ; that we must avoid all prejudice and one-sided- 
 ness ; and the like trite and trivial instructions. We rather 
 require an exact description of our problems, as they are modi- 
 fied by the peculiar nature ofour branch of study, and of the 
 special objects and questions with which it has to do j we need 
 a detailed explanation of the various ways and means which 
 can lead to the solution of those problems, and of their relative 
 advantages and dangers. In short, as we require the most 
 exact guidance possible for our progress in the investigation of 
 truth, we must, first of all, observe and understand the human 
 mind, as it is accustomed to proceed in the examination of 
 natural objects. 
 
 To fulfil this requirement, as far as may be, is the object of 
 logic, in the sense in which we here understand, and wish to 
 employ it. Its office is evidently, not to discover and divulge 
 the truths and doctrines of any science or art, e.g. of medicine. 
 It no more pretends to unravel at one stroke the mys- 
 teries, enigmas, and questions of our science than to render 
 a stupid man clever. To any one who understands the 
 nature of logic, in the sense which we here attach to it, it will 
 
24 INTRODUCTION. 
 
 be plain enough that an immediate solution of the problems of 
 medicine, or a speedy discovery of many of its truths and laws 
 is not reasonably to be expected. We have had many men, 
 it is true, who have asserted that they could more or less com- 
 pletely accomplish all these tasks, and give to medicine a scien- 
 tific basis, and many more who have brought forward their 
 own theories and doctrines as established truths. But to all 
 who have acquired a clearer comprehension of this subject, it 
 will be evident that every one who pretends to have accom- 
 plished anything of this kind, in the form, for instance, of a 
 system or correct theory, does but mislead himself and others, 
 and may thus be regarded as, in some sort, a deceiver, or as 
 ignorant of the true nature and aim of logic. Medical logic 
 does not profess to acquaint us with the truths, facts, and ex- 
 periences at which our science has already arrived in various 
 branches. Its ofB.ce is not, for instance, to explain the nature 
 of respiration, or digestion, of an inflammation of the lungs, or 
 typhus ; it neither instructs us with regard to their symptoms, 
 nor gives us the reason of their occurrence ; it does not tell us 
 what to set down as cause, what as effect ; it neither enlightens 
 us as to the origin of diseases, nor guides us in their recogni- 
 tion, prevention, or cure. It does but profess to acquaint us 
 with the real value of the ways and means by which we are to 
 acquire an insight into these phenomena and processes, and to 
 warn us of those which promise but fail to impart it. It 
 enables us to judge whether our choice has fallen upon the 
 right methods, by which to proceed in a certain investigation, 
 and gives us data whereby to test the correctness of what phy- 
 siology, for instance, would teach us concerning respiration 
 and digestion, or medical science impart concerning inflamma- 
 tion of the lungs, or typhus fever, and the most efficient 
 mode of treating such diseases. This information would be 
 of considerable value did it aim at nothing higher than the 
 more accurate calculation of probabilities in the case of empi- 
 rical rules, for just such a guide will be needed so long as the 
 most dissimilar, often antagonistic, views and doctrines lay 
 equal claim to truth, recognition, and belief; so long as it is 
 very difficult to decide whether the theory of A, B, or C, may 
 be most correct ; and which are the instructions that may be 
 most safely followed. In like manner, a further insight into 
 
INTRODUCTION. 25 
 
 all the methods and auxiliary means for the attainment of ex- 
 perimental truth, and a suitable guidance in the employment 
 of them, can nowhere be more important than in a study 
 whose difficulty consists, and whose object lies, not merely in 
 observation and deduction, but in the manner in which the 
 mind performs these necessary offiices, and makes for itself a 
 judicious selection among many possibilities. For the necessity 
 of a clearer comprehension of every individual question and 
 case, i.e., of a certain practical logic, is nowhere greater than 
 here, if the investigator is anxious to fulfil all the requirements 
 of his science and of his duty as a practical physician. 
 
 We cannot, it is true, expect that every natural philosopher 
 and physician should be a finished philosopher and logician. 
 But we are justified in demanding so much philosophical insight 
 and proficiency as is necessary for them to proceed according 
 to the rales of true science in their own department ; we may 
 claim a logical acumen sufficiently nice for the correct obser- 
 vation of such facts as may come under their own experience ; 
 sufficiently clear to guide their discrimination of such as they 
 accept upon the testimony of others ; and sufficiently exact to 
 conduct them, in both cases, to a due working out of results. 
 We cannot, perhaps, expect of the physician, any more than of 
 the general natural philosopher, that he should himself solve 
 some even of the most important questions and problems of his 
 department, or that he should understand and know more than 
 his whole science, taken collectively, knows. But we may ex- 
 pect of each individual that he should recognize, above all, 
 what his science ought to know and be able to teach him, if 
 it is really to serve him as a science; that in his own depart- 
 ment he should know, therefore, what, explanation, knowledge, 
 and comprehension, essentially mean. We are also justified 
 in expecting that he should not regard anything as an expla- 
 nation of his questions and problems, or as a comprehension 
 of them, which is not truly such. It would thus, for instance, 
 scarcely be unreasonable to demand of the practical man and of 
 every physician, that he should no longer, as has so frequently 
 been the case, apply to the anatomist, the physiologist, and 
 the chemist, for the explanations and precepts for which he 
 must be indebted to himself, however much he may found 
 them upon his own physiological and chemical knowledge. 
 
26 INTRODUCTION. 
 
 We may demand of him a sufficient insight into his own sub- 
 ject to be aware that no single individual — though he were 
 the greatest and most successful genius — could impart to 
 medicine a scientific form, a knowledge of the conformity of 
 the phenomena and processes submitted to it for investigation^ 
 or to therapeutics a comprehension and a certainty such as, 
 even with the aid of the most diligent and circumspect inves- 
 tigation and labour of all the physicians and natural philoso- 
 phers in existence, is scarcely to be looked for for centuries to 
 come. He would run less risk of being constantly the dupe 
 of those who disseminate, from time to time, their various 
 theories and infallible systems of treatment amongst the me- 
 dical public. And if the physician so frequently laments that 
 little progress is made in medicine; that it has gained but 
 little in scientific and accurate knowledge from the labour of 
 centuries; that his art, instead of acquiring, by cure and 
 prevention, more power over disease, has gradually declined in 
 credit; it might fairly be expected that he would inquire into 
 the reasons of all this, and strive to ascertain why medicine, 
 instead of progressing with its sister arts and sciences, has re- 
 mained in the same position as astrology or alchemy, instead 
 of assuming the scientific character of astronomy or chemistry. 
 He would further seek to understand why his notions of the 
 great majority of his objects, and even his language and tech- 
 nical terms, are obscure, fluctuating, and arbitrary, and are 
 used in a manner befitting, at best, that priesthood with whom 
 his art, amid the dark mysticism of ancient times, originated. 
 
 It is not without good reason that the practical physician 
 complains that quacks of every description, and even unprofes- 
 sional men, participate in the confidence of his patients. What 
 has been thus expressed by the Preacher, has been, with regard 
 to us, the thought of many : ^ " Then said I in my heart, as 
 it happeneth to the fool so it happeneth even unto me : and 
 why then was I more wise ? " Such complaints are, however, 
 evidently useless, and seem the more out of place here as the 
 physician has the remedy in his own hands, and has but to 
 help himself. 
 
 The first step for us all in this direction is, no longer to 
 
 ' Ecclesiastes, chap. ii. Compare Fr. Baconi de Verulam, Opera omnia: de 
 dignitate et augmentis scientiarum, p. 104 i Frankfort, 1664. 
 
INTRODUCTION. 27 
 
 regard our poverty, the reality of which has already been 
 explained, as wealth, or our weakness as strength, but to test 
 whether, besides the natural difficulty of our subject, some 
 blame may not also be fairly cast upon the faultiness of 
 our starting-points and methods, and upon the defective 
 employment of all our auxiliary means. We must seek more 
 and more, by an insight into the peculiar nature of the 
 problems, questions, and objects submitted to our examination, 
 to discover other, perhaps more productive, methods of investi- 
 gation, and to avoid, more carefully than we have yet done, 
 the errors committed by our predecessors. 
 
 But these and similar questions obtrude themselves in every 
 branch of knowledge, and in every art which has hitherto 
 failed to make any safe and notable progress ; for here also it 
 may be said " by their fruits ye shall know them." I can but 
 indulge the hope of in some degree facilitating their answer, 
 and, if I am not so fortunate as to attain to the solution of 
 the problems which medicine, whether as a science or an art, 
 holds out, I may at least stimulate others to aim at, perhaps 
 to accomplish, better things in the paths I shall endeavour to 
 open out. And the result of this attempt, so far from furthering 
 an inclination to scepticism and mere unprofitable criticism, or 
 leading to the depreciation of the healing art, will tend in the 
 precisely contrary direction. The attempt itself has been the 
 further urged upon me by my profound conviction of the 
 infinite value of medicine to our common humanity j and by 
 the firm belief that it can more and more attain its almost 
 god-like end if it did but make the attempt with sufficient 
 earnestness and consistency. But it has seemed to me that 
 the first step, necessary to all that follow it, is this : that 
 medicine should emancipate itself, more than it has yet suc- 
 ceeded in doing, from many of the trammels and swathing- 
 bands of its infancy, and strike out more and more into the 
 paths by which alone it can arrive at its goal, and assume the 
 rank of a more exact science and more serviceable art. 
 
 These paths are by no means new ones, and I, at least, 
 make no pretension to having first discovered, or proposed 
 them. They are fundamentally, mutatis mutandis, those 
 which have been adopted in other natural sciences and arts 
 which have long outstripped our own. I am, however, not 
 
28 INTRODUCTION. 
 
 without the hope of being able to contribute something towards 
 the. better explanation of what, in our peculiar department, yet 
 needs to be investigated and proved; to show what, in a 
 scientific point of view yet remains to be accomplished ; and 
 to indicate the means whereby such ends may be most fitly 
 attained. 
 
 My professional brethren will perhaps not take it amiss that 
 one of their body should attempt, what to the best of my 
 knowledge no one has yet attempted : viz., to explain clearly 
 and simply, without philosophical pretension, what science and 
 precision really mean ; to arrange scientifically and logically 
 for the numerous diligent labourers in the field of medical 
 investigation, all the requirements which every observer and 
 practical physician must fulfil; and especially to attempt to 
 provide them with the ways and means by the aid of which 
 they may best do so. 
 
 This leads to the final question whether our logic can ren- 
 der any service to our younger brethren, and, above all, to 
 the student. I have this point the more at heart from the 
 fact of this attempt being rather intended to serve the younger 
 than the older members of the profession. The former in a,ll 
 cases represent the future, — the future, therefore, of a science 
 or an art. It may even be said, that the past, — so-called 
 older times, are, in a certain sense, the younger, — the first 
 childhood of a science; while, conversely, their subsequent 
 development, i.e., the youngest, — most recent period, repre- 
 sents that science in its riper age. Those who come after us 
 must therefore seek to attain a higher degree of scientific 
 knowledge, than we, their predecessors, have attained to ; and 
 to do this they have but to make the attempt in a serious 
 spirit. They must, above all, accustom themselves to' inves- 
 tigate and appreciate what they meet with at the bedside and 
 elsewhere, more exactly than has hitherto been done. The 
 period of mere belief and arbitrary, more or less unprofitable 
 speculation, appears to have passed away ; and that of positive 
 investigation — of clearer and more dispassionate reasoning — to 
 have taken its place. It can therefore no longer appear 
 indifferent to any one whether or not he has learnt to proceed 
 and judge more correctly in matters and questions of natural 
 science, and especially of medicine : he must feel anxious to 
 
INTRODUCTION. 29 
 
 obtain a finer proficiency in distinguishing the true from the 
 doubtful, and this again from the altogether erroneous : he 
 must aim at obtaining clear and connected explanations of the 
 methods of investigation in his department, and learn, by 
 recognizing his own errors, to shun the rocks upon which 
 thousands before him have made shipwreck. If our prede- 
 cessors had arrived at a truer estimate of this sober, practical 
 logic, they would not have regarded so many impossibilities 
 as possible ; or viewed so many uncertain hypotheses and 
 hollow theories in the light of genuine truths and established 
 facts ; neither should we have been so ready to believe them. 
 
 It is naturally the inexperienced man, the beginner, who is 
 most ready to accept whatever is offered him as established 
 truth, and this cannot but be dangerous in such a study as 
 medicine, where we have scarcely one scientifically ascertained 
 and demonstrated truth, scarcely one established and univer- 
 sally applicable rule for practice; where almost all depends 
 upon the circumspect testing and appreciation of an individual 
 case or question, and much even upon mere instinct. The 
 student, before proceeding to the study of medicine, has, 
 perhaps, become acquainted with other sciences, has learnt to 
 appreciate them, and acquired a certain taste for scientific inves- 
 tigation. He now plunges into the individual special branches 
 of medical science, each of which imparts only its own series of 
 objects and doctrines, and that often drily, and without any 
 allusion to their intrinsic connection. He now feels himself 
 almost crushed by the mass of individual, and apparently trivial 
 facts, amongst which, deficient as they generally are in scientific 
 interest, but little is to be found for comprehension. Or — 
 what is worse — his teachers and authors dispense their vague 
 doctrines, opinions, and a priori abstractions categorically, and 
 vend them to him as so-called science and truth. Their time 
 and, possibly, their inclination fail to point out the paths by 
 which the branch of science in question has arrived at its as- 
 certained results and principles, or to give him a connected 
 explanation of their intrinsic reasons and proofs. 
 
 Thus the clearing away of certain mole-hills from the path 
 of the beginner does but leave whole barren mountains stand- 
 ing in it. His memory is, perhaps, filled with a confiised 
 medley of innumerable facts, but he has yet to learn and 
 
30 INTRODUCTION. 
 
 practise what every natural philosopher and physician especially 
 requires, viz., the habit of clear and circumspect investigation, 
 correctness of insight, and facility in experiment. He has, no 
 doubt, learnt much, but not yet how to seek so that he may 
 find ; he has, perhaps, become acquainted with philosophy with- 
 out learning how to philosophise. Herder complains almost 
 too bitterly when speaking of the Schools (Facultaten) that 
 " youths, on leaving the university, are for the most part per- 
 verted growths ; they have been taught to create their senses 
 and reason a priori, rather than to employ those created for 
 them."^ And if this should, even now, sometimes be the case, 
 the beginner, as well as the more experienced physician and 
 natural philosopher, must, above all, learn to despise and reject 
 the kind of aliment which is offered to him, if he would hope 
 ever to obtain a better and more nutritious one. 
 
 In this respect, also, medical logic may be regarded as de- 
 signed to fill up for the student and embryo natural philoso- 
 pher an important gap in the course and connection of his 
 studies. Its office is to teach him just what his various spe- 
 cial branches of science have failed to teach, and indeed what 
 it was not in their power to impart. It further groups toge- 
 ther for him all those requirements of true natural philosophy 
 and science, which their individual branches must fulfil, and 
 to which they must conform before they can acquire that 
 scientific character to which the progress of their develop- 
 ment tends. This again will naturally recall to the mind 
 that connection of medicine with nature in general, that in- 
 trinsic oneness of all these detached sciences and branches of 
 science, which is so often lost sight of in common life. And 
 yet perception and progress in each of the individual depart- 
 ments can only thrive by constant attention to, and restoration 
 of, their intrinsic oneness ; for as no plant torn from its roots 
 can maintain a healthy state of existence, so medicine can 
 never thrive and expand unless it maintains its natural con- 
 nection with the investigation of the whole field of nature. 
 
 ' Herder's Works; Stuttgard, 1830 ; vol. xvii, p. 207. As this passage clearly 
 admits of more than one reading, the original is annexed : " Die von der Universitat 
 abgehenden Junglinge seyen grossentheils verderbte Gewachse ; man habe da wohl 
 ihre Sinne, ihre Vernunft a priori schaiFen, nicht aber die erschaifenen brauchea 
 gelehrt." 
 
SECTION I. 
 
 MEDICAL PROBLEMS IN A LOGICAL POINT OF VIEW, .. e., IN REFER- 
 ENCE TO THE POSSIBILITY OF SOLVING THEM. —TOPICS AND 
 QUESTIONS WITH WHICH LOGIC HAS TO DEAL, BOTH AS A 
 SCIENCE AND AS AN ART. 
 
 We have already stated, in the Introduction, that the 
 precise object of this work is simply to set forth the means and 
 processes for the attainment of experimental truth in medicine; 
 that it is merely the arrangement of certain rules and prin- 
 ciples for the investigation and due appreciation of the various 
 objects presented to the notice of the physician. To facilitate 
 this object, and more especially to obtain an insight into the 
 nature of the means of its accomplishment, we must first 
 consider what are the phenomena and their mode of occur- 
 rence; or in other words, the objects themselves the investi- 
 gation and comprehension of which is our special aim. For, 
 before we can be in a position clearly to understand the entire 
 process through which the human mind has gone — the method 
 of observation adopted, and the nature of the deductions and 
 generalizations that have been made — in short, the methods 
 of investigation and demons|;ration most appropriate for this 
 department of science, we must ascertain and accurately 
 appreciate what it is that has to be observed, investigated, and 
 proved. We must first of all determine what are the phe- 
 nomena and processes to be recognized, and ascertain their 
 nature, operation, and causal connection. We must scrutinise 
 the nature of the therapeutical operations and influences, ere 
 we can advance any definite propositions in therapeutics. We 
 
32 PROBLEMS OF MEDICINE 
 
 must endeavour to understand the peculiarities of the phe- 
 nomena which modify the methods requisite for their in- 
 vestigation. 
 
 Medicine — in the signification which we attach to it here — 
 is, however, divisible into scientific and practical. Of the 
 latter, the precise object and final aim are the prevention or 
 cure of disease, and the maintenance or restoration of health. 
 Of scientific medicine, the object is the comprehension of all 
 that relates to the invasion and progress of disease, as well as 
 to the period of convalescence, and the plan of treatment. By 
 its study we are to gain a clear insight into all the phenomena 
 occurring from the last moment of health to the time of 
 its restoration. Its first object, therefore, is to acquire a correct 
 knowledge, founded on scientifically accurate experience, of all 
 the conditions and influences which combine to induce disease, 
 or recovery. In other words, it must convey to us a correct 
 perception of the conditions and laws of the maintenance 
 of health, as well as of the various diseases and their cure. 
 Medicine can only be regarded as a science in so far as it 
 demonstrates, or attempts to demonstrate, the natural and 
 regular connection of the phenomena and processes that are 
 presented to our notice, and then gives such explanations of 
 them, and advances such propositions in relation to them, as 
 are founded on experience. As an art, medicine, like every 
 other art, speaks in the imperative. It. tells us what to do and 
 what to leave undone, in order that we may best attain a 
 given object, e. g., the maintenance or restoration of health. 
 As a science, it speaks like every other science, in the in- 
 dicative. It sets forth certain propositions in reference to 
 those phenomena which it is its province to investigate ; it tells 
 us that they have certain definite relations to each other, that 
 they occur in a certain manner, and are subject to certain con- 
 ditions. However much, according to this view, these two 
 branches of medicine may seem to diverge, they are, never- 
 theless, intimately connected. The primary object of thera- 
 peutics, as a practical art, is to prevent, or counteract the 
 influence and deleterious eflfect of all those conditions or agents 
 which induce, or maintain, a state of disease. Should this 
 have been impracticable, or, as too frequently happens, should 
 no such attempt have been made, its next object is to render 
 
IN A LOGICAL POINT OF VIEW. 33 
 
 available all those means, by the aid of which the return of the 
 living being from a diseased to a healthy state may be facili- 
 tated and effected. To do this with any degree of certainty 
 medicine presupposes a knowledge of man and his require- 
 ments, and of the various incidents and influences, external 
 and internal, which affect him and his state of health, and on 
 the co-operation of which the maintenance, loss, or recovery of 
 health depend. It is, therefore, not only necessary to deter- 
 mine precisely how the phenomena and processes of a healthy 
 or diseased organism are manifested externally, i. e., how they 
 are presented to our observation both in reference to characters 
 appreciable by the senses, and to the order of their occurrence, 
 but also and especially to ascertain their essential nature and 
 the conditions to which they are subject. We must, therefore, 
 learn by experience their causal connection with each other, 
 and with the influences of the external world. All this know- 
 ledge, necessary for practice, it is the province of medicine, as 
 a science, to impart. In order to promote this object all the 
 principles or doctrines of scientific medicine must not only 
 be correct in themselves, i. e., conformable to truth, but 
 they must at the same time be such that practical medi- 
 cine can with certainty deduce from them its rules and 
 precepts. 
 
 Medicine was originally something very different from this. 
 It arose, as the offspring of necessity, from the instinctive 
 impulse of man, in common with all animals, to maintain a 
 state of health ; or, when sick, to free himself from his 
 maladies and sufferings. The most ancient designations of 
 medicine, as laTpi/ctj, ars medendi, pharmacology, point out 
 this. Its whole object was purely practical and technical ; its 
 whole substance consisted in a collection of rules and precepts 
 for the preservation or restoration of health, i. e., for the 
 prevention or cure of diseases. All the indications which it 
 could furnish were taken from simple experience, and the 
 observation of the sick ; but we may doubt whether such expe- 
 rience and observation deserved to be so called in many 
 instances. Single cases were collected and compared, in which 
 some mode of treatment or some remedy had seemed bene- 
 ficial ; and the deduction was made, that what had been useful 
 
 3 
 
34 PROBLEMS OF MEDICINE 
 
 in those, might be employed with advantage in other similar 
 cases. 
 
 The sick demanded then, as they do now, nothing more 
 from the men who had collected this experience, and were 
 acquainted with the remedies, than aid in their diseases and 
 freedom from their sufferings. It is owing to the circum- 
 stances that men received, or imagined that they received, such 
 aid, that medicine, from the beginning, has maintained its 
 importance and its credit in the eyes of the public ; i. e., as the 
 art, not as the theory, of healing It was the imperative, not 
 the indicative, which made the impression, as it always does. 
 Medicine was incapable of asserting or proving anything 
 positively, simply because it knew next to nothing of what, or 
 how, it cured. Physicians were also generally at the same 
 time priests, — they were the wisest and ablest men of a nation, 
 as they still are amongst uncivilized people. They were called 
 upon to relieve and restore, as best they might, before they 
 could arrive at any comprehension of what they had to prevent 
 or cure. An individual in danger of dying from hemorrhage 
 was, equally with his professional attendant, unable to wait 
 until the effect of this or that remedy had been established, and 
 still less, until the cause and mode of curing the hemorrhage 
 had been positively and scientifically ascertained. The medical 
 man employed at random the means he had at hand which 
 seemed likely to be of service, e. g., red objects, according to 
 what was called the doctrine of signatures. And because 
 these curative means and manipulations were frequently suc- 
 cessful; because, e. g., the hemorrhage ceased after their 
 employment, they acquired the reputation of remedies, which 
 they have maintained, more or less, to the present day. Thus, 
 in all cases, art has necessarily preceded science, and simple 
 experience true comprehension : this assertion applies alike to 
 medicine and to agriculture, navigation, education, or politics. 
 The whole question for both parties — the patient and phy- 
 sician — was, by what means the health of the former could 
 best be preserved, or disease obviated. This object was to be 
 attained as quickly as possible. For this, both the patient in 
 his need, and the physician in his desire to cure, equally strove. 
 It might in many respects be a logical error on the part of the 
 latter, but it was surrounded by the halo of philanthropy and 
 
IN A LOGICAL POINT OF VIEW. 35 
 
 the desire to relieve. The poetical mythology of Greece shows 
 how great were the respect and gratitude rendered to those 
 who practised the healing art, by the noble origin which is 
 assigned to it in their fables. No less a personage than 
 the god of light himself, Helios or Apollo, who developed 
 and maintains all living nature, is said to have been the 
 father of Esculapius, the god-lilse teacher of the healing art. 
 The same tradition makes Circe to have been the sister of 
 Esculapius ; and even to the present day, conjurors, quacks, and 
 mystics, have continued to be the fellow-craftsmen or the 
 rivals of the physician. 
 
 Gradually, however, the mind of man ceased to content itself 
 with that which had formerly satisfied it, and which had suflBced 
 to do so in the then existing state of things. If his increasing 
 knowledge, for instance, refused to recognise every thing around 
 him as governed by the gods, or by the rude powers of nature, 
 and by accident, he could not rest content, in matters apper- 
 taining to medicine, with simply observing the sick and the 
 phenomena of disease. By observation alone, he could not 
 comprehend the phenomena, nor could he learn anything by 
 such means of their conditions and intimate connection. When, 
 in consequence of the general development of intelligence, the 
 desire was excited to obtain some further insight into the results 
 of simple observation or experience, medicine could not remain 
 exempt from this common impulse and law of the human mind. 
 In this science, as in every other, the mind strove to advance 
 from mere observation and belief, or opinion, to knowledge, and, 
 through this knowledge, to a better practice. Men began to 
 inquire in what mauner, on what account, and by what means, 
 their object was to be attained ; they aspired to a perception of 
 the laws and mutual relations of things, and of their conditions 
 and effects. 
 
 The history of medicine teaches us how, from such a com- 
 mencement in simple empiricism, it has, in the course of cen- 
 turies, acquired a comparatively scientific form, after having 
 passed through phases of superstition, mysticism, alchemy, and 
 the like. It may suffice here to remark, that men gradually 
 arrived at the conviction that the physician could not satisfy 
 the requirements of his art, or the most pressing demands made 
 upon it, without a previous more intimate acquaintance with 
 
36 PROBLEMS OF MEDICINE 
 
 the constitution of man himself, and with the external world 
 with its thousand influences and agents. Physicians became 
 convinced that in medicine, as in other arts, practical success 
 pre-supposed a certain degree of experience; that a man must 
 know and understand many things before he can act with any 
 certainty of success. As the seas, the winds, and the weather 
 gradually engaged more of the attention of the sailor, and man, 
 in his intellectual and moral capacity, occupied the thoughts of 
 the teacher, the moralist, and even the statesman ; so the laws 
 of nature, the conditions of the body in health, and the essence 
 of disease, especially in relation to the means of cure, became 
 by degrees the subjects of scientific investigation with the 
 physician. And as soon as the need of such a study was re- 
 cognized, and physicians had ceased to rest content with ob- 
 serving the more evident effects of disease, and employing at 
 random a few remedies for its cure — as soon as they began to 
 pouder how diseases arose, in what they essentially consisted, 
 how they might best be obviated, and what was the action of 
 the remedies employed — from that moment they required the 
 aid of medical logic. Men's minds were no longer satisfied 
 with simple observation and experience, and the appeal to them 
 was no longer sufficient. Having once endeavoured to arrive 
 at a comprehension of the varying phenomena of the human 
 frame, and the processes going on within it, they formed, from 
 the observations they had made, certain inferences concerning 
 their connection, conditions, and laws, deducing from individual 
 instances more general dogmas and propositions. It was the 
 part of logic to prove that the inferences and deductions were 
 correct, and founded upon experience. History may teach us 
 the manifold errors and contradictions in medicine and natural 
 history which arose during their obscure advance towards the 
 rank of sciences, and the various differences of opinion and dis- 
 putes which have continued to the present day. We must here 
 confine our attention to the present state of medical science, in 
 order to determine what phenomena and processes may be re- 
 garded, at the stage of intellectual development at which man 
 has now arrived, as the legitimate objects of medical investiga- 
 tion — as the problems to be solved in medicine. 
 
 I. An intimate acquaintance with the human, and par- 
 ticularly the living, body was soon recognized as the great 
 
IN A LOGICAL POINT OF VIEW. 37 
 
 object of investigation ; for those changes and processes, to 
 which we give the name of disease, occur in the economy of the 
 body equally with those going on in health, and which are called 
 physiological. To understand the former, it was necessary 
 to put them side by side, and compare them with the latter, for 
 which they are substituted. The first step towards this object 
 being a knowledge of the material structure of the body, in its 
 external (anatomical) form, it was soon found necessary to study 
 its properties, as well with reference to its formal (anatomical), 
 as to its substantive (chemical) elements. This again was the 
 first step — in a higher.,sphere — towards the perception of what 
 we term function, or activity of the individual organs of the 
 body, i.e., towards the perception of the part played by each in 
 the whole series of vital processes. It then became evident 
 that between this condition of health, and what was called dis- 
 ease, between the various processes going on in each, which had 
 hitherto been regarded as unconnected, no line of demarcation 
 could be drawn, simply because none existed. This is true of 
 all the occurrences, and operations to which matter is sub- 
 jected, whether in an animate or inanimate form. We cannot 
 define the boundaries between the various meteorological pheno- 
 mena which constitute good or bad weather — between the dif- 
 ferent states of any substance by which it appears to us to be 
 cold or warm, bright, electric, or magnetic ; neither can we dis- 
 cern the exact limits of the phenomena going on in the living 
 body when it is said, in common language, to be in a state of 
 health or disease. 
 
 As, however, in the other natural sciences, all the objects and 
 phenomena proper to them must be investigated, so also must 
 we investigate and strive to understand the occurrences vphich 
 take place in what we call disease, and their mode of origin in 
 the living body. This task may be divided into several depart- 
 ments and categories, but the real object of investigation is 
 essentially the same in all ; for the so-called physiological and 
 pathological phenomena and processes occur, as has been said 
 already, in the same body, and in the same substances. They 
 will, therefore, depend upon the properties and modes of opera- 
 tion of the organs and elements of the body, being subject to 
 the same essential laws, and only differing in consequence of 
 the changed condition of each. 
 
38 PROBLEMS OF MEDICINE 
 
 II. Such may be said to be the internal aspect of the objects 
 of our investigation, but we must also strive to attain a per- 
 ception of the relations of the living organism to the external 
 world, i. e., to all which exists and occurs without and around 
 it. For, notwithstanding its apparent isolation, its dependence 
 upon the external world could not long escape observation. 
 The first glance must have shown that the phenomena and 
 processes peculiar to the body had their origin and continuance 
 in external influences, which were constantly acting upon it, 
 and a progressive insight into all these mutual relations must 
 have brought with it the conviction, tli^t an exact boundary 
 can no more be drawn between a healthy and a diseased state, 
 than between the beneficial and fostering, or pernicious influence 
 of external agents upon the living organism. The facts that 
 the air we breathe, or the food we eat, may tend to support 
 the body, or to injure it, that electricity may contribute to the 
 cure of disease, or be fatal to life — these facts produce no 
 change in the agents themselves, or in the laws of their action. 
 In the one case, as in the other, they are the same agents and 
 influences, with the same properties, preserving a definite, con- 
 stant conformity to fixed laws in their occurrence, manifesta- 
 tion, and action. If we limit our view to their effects in 
 reference either solely to hygiene, or to getiology (the theory 
 of the causes of disease), the division would be as inadmissible, 
 in a scientific point of view, as the distinction between physio- 
 logy and the theory of disease. To facilitate as much as possi- 
 ble the investigation of the two, it will be necessary to combine 
 them in a higher scientific process including both. 
 
 III. With this great comprehensive aim of investigatilan is 
 associated the further one of studying the properties and modes 
 of action of all the agents and materials which we employ for 
 the cure of disease. That these are used and regarded as 
 remedies on account of certain properties and eff'ects can make 
 no change in the manner of their investigation. We have to 
 learn their properties and consequent relations to the living 
 body, as well as their effects upon it, in order that we may 
 employ them as our means of cure appropriately and intelli- 
 gently. 
 
 This may sufiice for the present to show, in some degree, 
 the series, or kinds of phenomena, incidents, and objects which 
 
IN A LOGICAL POINT OF VIEW. 39 
 
 it is our recognized aim to investigate and comprehend. When 
 any particular process of investigation is demanded by pecu- 
 liarities in the siibject matter, its dependence upon this cir- 
 cumstance will be shown when we come to their detailed 
 consideration. 
 
SECTION II. 
 
 OF THE METHODS AND MEANS IN GENERAL, BY WHICH THE NATU- 
 RALIST, AND ESPECIALLY THE PHYSICIAN, ENDEAVOURS TO 
 ATTAIN A PERCEPTION OF NATURAL PHENOMENA AND PRO- 
 CESSES, FROM THE STUDY OF THEIR CONDITIONS AND LAWS. 
 
 It follows, from what has already been said, that all the 
 objects which we are especially called upon to investigate are, 
 in reality, very similar in their nature. For they are essentially 
 phenomena and processes in the living body, whether it be 
 healthy or diseased, and whatsoever be the mode of their 
 commencement and termination under the influence of various 
 circumstances. As surely as the vitality of the living body is 
 maintained only by the constant and regular continuance of its 
 own processes, and by the aid of a constant cooperation from 
 without, so surely can those changes in the vital processes, 
 which we call diseases, be by possibility, occasioned only by 
 an alteration of vital conditions, and of internal and external 
 influences. And only by the cessation of those changes or 
 derangements affecting the vital processes — ^by the restoration 
 of the normal relations, both external and internal, which are 
 requisite for their healthy performance — can they regain their 
 ordinary state of health, whether by spontaneous recovery or 
 by the help of artificial cooperation on our part. 
 
 According to the present state of our knowledge, we are 
 compelled to assume that these processes in the living body 
 are the results of a specific mechanism, which is invariable for 
 each, and, in its general principles, similar for all of them, just 
 as is the case with the processes in the atmosphere, in all the 
 changes of weather and seasons in different regions. For 
 diseases are, in fact, only certain species of phenomena and 
 processes in the living body, or their results and effects. If, 
 therefore, those which we call vital occur and manifest them- 
 selves conformably to definite laws and in a certain order, the 
 same principle must apply to those to which we give the name 
 
THE STUDY OF NATUEAL HISTORY. 41 
 
 of diseases. Their laws, i. e. the mechanism and exact mode of 
 their origin and occurrence, must coincide with those of the 
 former in all their essential conditions. 
 
 Finally, if it he certain that all the agents and influences of 
 the external world act in their fixed order, and in obedience to 
 definite laws, it is also certain that they cannot have acted 
 otherwise when they have produced a derangement of the vital 
 processes — when they have caused or prevented disease, or even 
 effected its cure. It is eiiually certain that all the efi'ects of 
 these agents and influences in the living body — whether bene- 
 ficial or deleterious — consist in certain definite changes in the 
 body itself, i. e. in some of its parts, tissues, or processes. 
 These changes, therefore, necessarily commence and proceed 
 conformably to the laws of action of the external agents and 
 influences, on the one hand, and to the vital laws and processes 
 on the other. 
 
 Having been convinced of this similarity in the nature of 
 the phenomena and processes which it is our province to inves- 
 tigate, and having clearly recognized the reasons for this 
 conviction, we cannot avoid perceiving that the methods and 
 paths of their investigation must be essentially the same. But 
 they are also the same for each department of natural history, 
 whether the object of study be the heavenly bodies, or our 
 earth, with all that is upon or around it. In each case there 
 are certain things, certain phenomena or occurrences, which 
 we do not understand of ourselves, and of which we can form 
 no idea from merely looking at and observing them ; but they 
 are of such a nature that we may hope to arrive at a compre- 
 hension of them by systematic investigation. Prom this it 
 does not follow that each series of phenomena, processes, &c. 
 belonging to different departments of natural history, or medi- 
 cine, e.ff. the chemical or physiological, the pathological or 
 pharmacological, does not demand, by reason of individual 
 peculiarities, a special mode of investigation ; but the progress 
 of the human mind will always be essentially the same, varying 
 only in comparatively subordinate points, and in the details of 
 the processes adopted. 
 
 All the phenomena and objects with which we have here to 
 deal are recognized through the medium of our senses; in 
 other words, they would not exist for us if we were unable 
 
42 METHODS OF INVESTIGATION IN 
 
 thus to appreciate them. The first indispensable step, there- 
 fore, if we wish to learn anything concerning them, is to 
 observe them, on all sides aad in all the relations discernible 
 by the senses, whether they be such as occur in a healthy or 
 a sick person, or in a dead body, or whether they be pheno- 
 mena connected with the atmosphere or displayed by an 
 electrical machine. The most careful observation of them, 
 indeed, does not suffice to render them intelligible to us : but 
 we learn that they exist and possess certain properties appre- 
 ciable by the senses, we know that certain things have 
 occurred, though their mode of occurrence is incomprehensible 
 to us. They are still covered by a thick veil which the mind 
 seeks to pierce, and must pierce before they can be brought 
 within the range of our comprehension. We may, for in- 
 stance, have observed an animal breathing in a particular way, 
 or crying out and shrinking when a nerve was irritated — we 
 may have observed in a diseased person a cutaneous eruption, 
 an increase of temperature, a rapid pulse, or cough and expec- 
 toration — or in the atmosphere the formation of clouds, rain, 
 wind, or storm. All that we have been able to gather in 
 relation to these phenomena has, however, conveyed to our 
 minds no insight into, or comprehension of, their real nature. 
 For they are not intelligible by the mere sight or touch, 
 neither is the constitution of natural objects such as to be 
 readily comprehended. Instead, however, like the lower ani- 
 mals, of stopping at this point of simply recognizing them as 
 they present themselves, we feel the mental impulse and 
 possess the mental power to acquire, by the aid of manipula- 
 tion, reflection, and investigation, a knowledge of their nature. 
 The interest they excite is proportioned to our acquaintance 
 with them, for we can only deal with them and employ them 
 for our own advantage and that of others, in so^far as we have 
 learnt to understand them. We must not only recognize their 
 reality, but also ascertain by what means they are brought 
 about, and why they are thus and not otherwise, in what manner 
 and order they have occurred, what conditions they are subject 
 to, and what other objects they may themselves modify. In 
 short, we seek to know the causal connection, conformity to 
 fixed laws, and definite order of the phenomena and operations 
 in nature, and nothing else will serve the requirements of the 
 
THE STUDY OF NATURAL HISTORY. 43 
 
 case ; we must know what operations, what causes and influ- 
 ences, we have to deal with, in order to bring them within the 
 scope of our comprehension. 
 
 Mere observation in itself, i. e., all that can be learned by the 
 senses, is insufficient to enable us to do this. All the astronomers 
 in the world, for instance, might have watched the stars night 
 after night as they rose and set, without gathering therefrom 
 anything more concerning the laws of their transit, or the con- 
 ditions of their visible movements, than uncivilized nations have 
 learned up to the present day. Solar eclipses were observed, 
 and the periodicity of their return recognized long before it was 
 known upon what they depended. In a similar manner, we 
 have seen thousands of men afifected with ague, typhus, or in- 
 flammation of the lungs ; we have observed manifold phenomena 
 in them variously grouped, and following a definite order from 
 first to last, and have found certain changes in the bodies of 
 those who have died of these diseases ; but we have never learnt, 
 and never shall learn, from mere observation, what are the con- 
 ditions of these phenomena and changes, and what essentially 
 constitutes disease. Natural historians might continue for cen- 
 turies, as heretofore, to note the variations in height of the 
 barometer and thermometer without thereby alone discovering 
 anything concerning the causal connection, and laws of atmos- 
 pheric pressure and temperature — without learning anything 
 of the still more obscure subject of their possible influence, and 
 mode of action upon human beings in reference to health, or 
 upon the origin and frequency of disease. The physiologist 
 again could not, from the mere observation of respiration in an 
 animal, or of exhalation in a plant, comprehend the exact nature 
 of the process itself. The same holds good in reference to the 
 observation of the phenomena or changes which occur as the 
 efi^ects of our drugs or poisons. We constantly see purging 
 result from rhubarb, and some of the saline substances; vomit- 
 ing from ipecacuanha; or stupefaction and sleep from opium; 
 innumerable cases of ague are cured, under our observation, by 
 cinchona bark or quinine, and of bronchocele by iodine, but we 
 are at present unable to say in what manner, and by what 
 means these results are brought about. 
 
 The most scrupulous observation of any object, or natural 
 phenomenon — e. g., of a healthy function, or of a condition of 
 
44 METHODS OF INVESTIGATION IN 
 
 disease — simply enables us to say that it exists, and has been 
 presented to us in a certain form. We can also examine the 
 subject of our observation with reference to such of its pro- 
 perties as are appreciable by the senses, or with reference to 
 the impressions it makes upon us ; and we can compare it 
 with others in order to acquire a knowledge of their similarities, 
 or differences. We may further ascertain in what order pheno- 
 mena occur, follow each other, and cease, in relation to space 
 and time. All this may, perhaps, satisfy our first curiosity, or 
 even a superficial, aimless thirst for knowledge, but not the 
 comprehensive longings of the mind. It still seeks to learn in 
 what these phenomena essentially consist, and why they have 
 assumed the exact form in which they present themselves to us. 
 In a word, we must discover their causal connection, the mode 
 and mechanism of their origin, their internal arrangement, and 
 their conformity to fixed laws. 
 
 Were all tiiis but once known, the longings of the mind 
 would be satisfied and all the requirements of science ful- 
 filled. 
 
 For the "knowledge" of a thing means here nothing less 
 than the comprehension of the constitution and formation, the 
 conditions and causes of all that we have observed, e. ff., the 
 phenomena and processes occurring in the living body in health 
 or in sickness. We see, or believe that we see, an object 
 before us, but it seems still strange to us, we feel that we are 
 not familiar with it until we have comprehended its consti- 
 tution and origin, and thereby made it our own, our intellec- 
 tual property. The impulse in man to appropriate all things, 
 as far as possible, and render them subservient to his reason — 
 to be master abroad as well as at home, urges him on to under- 
 stand and subject to himself the mysteries of external nature 
 and of his own being and vitality. Thus Virgil sings : 
 
 " Felix qui potuit reram cognoscere causas." 
 
 Man endeavours to discover what nature has concealed from 
 him, and this he can do, more or less, if he undertake it ear- 
 nestly enough, and with the knowledge how he ought to pro- 
 ceed in his attempts. But as the information conveyed by his 
 senses does not enable him to do this, he takes a step further, 
 and properly gives the name of science only to what he has 
 recognized and discovered concerning the objects of his simple 
 
THE STUDY OF NATURAL HISTORY. 45 
 
 observation or experience. Whenever, therefore, a phenomenon, 
 an object of any kind, strikes our senses, the simple observa- 
 tion of it leads naturally to further examination, to its attentive 
 consideration and investigation. We complete and combine 
 almost instinctively, in our minds, what we had observed 
 in an isolated and, perhaps, fragmentary form ; we represent 
 it to ourselves in a certain combination, and assume in it, for 
 the moment, a sort of causal connection. We next seek for 
 the relations in which the phenomenon or object in question 
 stands to other similar phenomena or occurrences, in order 
 that we may arrive at a comprehension of their condition or 
 peculiar effects — in a word — of their causal connection. 
 
 In this further step, which our consciousness and our under- 
 standing demand, we set out with the innate conviction, though 
 not always realized, that every thing which we observe mnst 
 have its causes and laws of action, whether it be a vital phe- 
 nomenon, or a condition of disease, a certain state of the 
 weather, or a conflagration, and having once learnt to reason 
 correctly on such subjects, we feel convinced that among the 
 circumstances which have been observed to accompany or to 
 precede it, some one or other, or, perhaps, several in combina- 
 tion, have given rise to the incident in question. Whether this 
 conviction may be inherent in the human mind, or merely the 
 result of previous experience, or of deductions from that expe- 
 rience — in short, how we may have arrived at it — is of little 
 interest here ; it is enough that *it is felt. 
 
 It is of infinitely more importance to us to know what we 
 are to understand by " cause and effect," in all the natural 
 phenomena and processes ; what, for instance, really consti- 
 tutes cause and effect in what are called the functions of 
 the body, or in diseases and in their origin and cure. 
 A clear understanding of this relation is evidently essential to 
 a successful inquiry into the causal connection, conditions, and 
 laws of any natural phenomenon — e.g., of vital processes — and 
 thus to the attainment of the objects of science. These phe- 
 nomena and processes become more intelligible, and their 
 causal connection unquestionable, when such a relation can be 
 established between them and some other occurrence or cir- 
 cumstance, as would enable us logically to deduce them there- 
 
46 METHODS OF INVESTIGATION IN 
 
 from, or, in other words, to accept the latter as the adequate 
 cause of the former. Thus, the overflow of a river, and con- 
 sequent inundation of its banks become intelligible to us if we 
 hear that heavy rains have fallen in the neighbourhood. The 
 fracture of a bone in A, or the sudden falling down, loss of 
 consciousness, and paralysis of B, would be intelligible if we 
 heard that the former had met with some accident, or that the 
 latter had been the subject of a considerable extravasation of 
 blood into the brain, which we call apoplexy. We should also 
 understand why every animal, and even plant, does and must 
 respire ; why the former gives off carbonic acid, and the latter 
 oxygen, so soon as we knew with what other changes of mate- 
 rial, or other processes in their structure the giving off of cer- 
 tain gases stands connected in such a manner that we can 
 safely regard it as occasioned and modified by them. In the 
 same way, the purgative effects of a substance, such as sulphate 
 of magnesia, would be explained if we knew all the essential 
 modifying changes and processes in the alimentary canal to 
 which its presence gives rise, and which are requisite to cause 
 the purging itself. 
 
 We have now to determine what paths must be taken in 
 order to discover this causal connection, these conditions, of 
 the phenomena and processes which form the subject of inquiry 
 — e.g., of a vital function or of a disease — and thus bring 
 them nearer to our comprehension. 
 
 The first indispensable step towards this end must be, in 
 this, as in every other department of nature, the observation 
 of the phenomena, and the determination of their precise 
 condition. In other words, we must start from our experience 
 concerning them, and carry out the inductive process of rea- 
 soning. Every thing which occurs in nature is so constituted 
 that we cannot attain a full comprehension of it by direct ob- 
 servation alone ; and inasmuch as we should in vain question 
 nature directly concerning it, our object can only be attained 
 by choosing other routes, and sometimes even various by-paths. 
 For this object is not merely to ascertain that certain pheno- 
 mena and processes exist and become known to us by properties 
 appreciable by the senses, but also to discover how they are 
 modified by others ; and to this end we must study the modi- 
 
THE STUDY OF NATURAL HISTORY. 47 
 
 fying circumstances and processes themselves. We have thus, 
 first of all, to ascertain what other phenomena or processes — 
 whether in the external world, or in the interior of the living 
 body itself — constantly precede or accompany that which is 
 the subject of observation. There is, at the outset, only one 
 mode of attaining this object, viz., to observe with care each 
 one individually, as they occur simultaneously, or follow in suc- 
 cession in the case before us. We must, therefore, eudeavour 
 to determine each phenomenon presented by a function such as 
 respiration or by a person labouring under some disease, &c. ; 
 also taking into account the changes in the external world, or 
 in the materials supplied to the body for the purposes of respi- 
 ration or digestion, as well as those occurring in the body itself, 
 from the administration of medicines. In short, our first ofiBce 
 is to determine the exact state of things, and to observe, as 
 correctly and comprehensively as possible, every point in the 
 case before us, since all experience and knowledge of natural 
 objects begins with individual cases. But, to arrive at a proxi- 
 mate insight into the connection and conditions of any given 
 process or phenomenon, it is necessary to compare together 
 numerous examples in which it has been observed to be pre- 
 ceded by or to have accompanied certain others. We have 
 next to make out what has uniformly occurred in all these 
 cases, conjointly or consecutively, and what has not occurred, 
 in order to distinguish constant coincidences from those which 
 are merely accidental. 
 
 Under circumstances favorable to this determination we 
 are justified in concluding from the constancy of the coincidence, 
 that, in all cases, the phenomenon or process in question would 
 find its adequate cause in certain other phenomena, processes, or 
 incidents, e. g., the excretion of carbonic acid in respiration, the 
 existence of paralysis, or the action of a purgative or corrosive 
 substance ; and this is no more than has been established by 
 experience with reference to various facts in medicine. But 
 before this can be assumed, it must be proved that the occur- 
 rence has, in all the cases which we have observed, been brought 
 about by that process or circumstance which we have assumed 
 to be the essential one, and by no other. Having determined 
 this point, we may venture to bring the subject of our investi- 
 gation into causal connection with, and fixed and constant de- 
 
48 METHODS OF INVESTIGATION IN 
 
 pendence on, other plienomeua and processes. For if we have 
 observed a given phenomenon or process to accompany or 
 follow certain others, and if we have, shown that it depends 
 upon them, we may certainly regard them as standing to 
 each other in the relation of cause and effect. And by ful- 
 filling all the requirements in the determination of this 
 fixed causal connection, we not only demonstrate it for the 
 cases immediately bbserved by us, but we establish a law which 
 equally holds good for all cases or instances of the same kind 
 or class ; for we have discovered the invariable order of succes- 
 sion and the conformity to fixed laws of all the phenomena, 
 processes, &c., in question, in the mutual dependent relation in 
 which they stand to each other. This was done, for instance, 
 when it was proved that, in the fall of bodies, their weight) i. e. 
 the attraction of the earth, was the common determining cir- 
 cumstance. It may be said also to have been done with re- 
 ference to certain kinds or series of paralysis which depend upon 
 extravasation of blood into the brain ; and also with reference to 
 the corrosive action of certain substances, which is due to their 
 energetic affinity for, and combination with, certain elements 
 of the organic tissues, such as albumen, water, &c., when brought 
 into contact with them. 
 
 We have thus attained what we call a theory, and indeed a 
 correct one, of these phenomena, or occurrences, i. e., one of 
 such a nature that it explains to us all the processes and phe- 
 nomena of any definite kind or series, and gives us a correct 
 elucidation of their conditions and conformity to fixed laws, 
 as well as of the immutable order of their simultaneous or 
 consecutive occurrence. 
 
 Enough has been said to show the end we must steadily 
 keep in view in the study of natural phenomena, and the 
 method by which we may hope to attain to a comprehension 
 of such as were previously obscure. Our task, therefore, is, 
 to prove from experience in individual cases, and from actual 
 observations and experiments, that they do stand to each other 
 in this fixed relation and causal connection. We shall then 
 be able to advance certain propositions in reference to them, 
 i. e., in reference to the uniformity of certain kinds or series 
 of natural phenomena and processes. 
 
THE STUDY OF NATURAL HISTORY. 49 
 
 The whole method of reasoning by which we seek to make 
 natural phenomena accessible to our comprehension, to arrange 
 them methodically, and make our knowledge of them available, 
 is called the " Inductive Process." It is, as Bacon expresses 
 himself, the " ars interrogandi et interpretandi naturam," the 
 " via a sensu ad intellectum."^ For " omnis interpretatio 
 naturae incipit a sensu, atque a sensuum perceptionibus, et 
 rect^, constanti, et munit^ \ik ducit ad perceptiones intellectus, 
 qu8e sunt notiones verse, et axiomata."^ 
 
 It is essentially the same process in every science which has 
 for its object the attainment of knowledge by the means of 
 special experience, and the examination of individual instances, 
 i. e., a posteriori. The unvarying character of the human 
 mind leads it to adopt, in its struggle for the comprehension 
 of natural phenomena, essentially the same expedients through 
 its whole progress, although they may differ in minor respects 
 with the objects to be investigated, and though they may be 
 applied with very dissimilar results in the various departments 
 of nature. The astronomer, as well as the physicist (Physiker) 
 and geologist — the chemist as well as the physiologist and phy- 
 sician, must all seek to discover, from experience and exact 
 observation, in what the phenomena and processes, with which 
 they have each to deal, essentially consist, and what may be 
 their causes and the effects of certain agents and influences 
 upon them. And only from the results of individual observa- 
 tions of the actual state of things, or from artificial experiments 
 — ^in short, from the empirically ascertained behaviour of the 
 phenomena and processes in question, in a certain number of 
 cases — can any legitimate conclusion be drawn as to the 
 behaviour and conformity to fixed laws of other phenomena 
 and processes of the same kind. 
 
 Our whole course of demonstration consists, therefore — 
 
 I. In the observation of the objects to be investigated in a 
 certain number of cases. 
 
 n. In the comparison of these individual cases or instances 
 with each other, and in extending to all cases of the same kind 
 what we have discovered and established by the aid of such 
 comparison. 
 
 ' Lib. i, aphor. 76. ' Lib. ii, aphor. 38. 
 
 4 
 
50 METHODS OF INVESTIGATION IN 
 
 III. In the deduction therefrom of the "causal connection," 
 the so-called " laws/' which affect this particular series of phe- 
 nomena and processes. 
 
 From the fact, that in all the cases which have come under 
 our observation, any given phenomenon has constantly occurred 
 under certain conditions established by experience, and in 
 consequence of certain processes or influences, we draw the 
 conclusion, that it will invariably recur under the influence and 
 co-operation of the same circumstances. The task to be accom- 
 plished — the difficulty to be overcome — is, to ascertain empiri- 
 cally all the conditions and modifying processes, and to dis- 
 tinguish those which are really essential (constant and deter- 
 mining) from those which are not. If we have accomplished 
 this, we have established what is called a " natural- law" in its 
 most extended signification, and have solved, by induction, the 
 problem which we had to investigate with reference to any 
 particular class of natural phenomena; for we have demon- 
 strated the causal connection, the conformity to fixed laws, and 
 definite order in the relations which certain phenomena and 
 processes bear to each other. And the fact that under the 
 same given circumstances the same thing will always occur, is 
 called a " law." It would, perhaps, be better — because simpler 
 and less ambiguous — to call it a " general natural truth." 
 
 The study of physics, for instance, has demonstrated that the 
 variations of the atmospheric pressure, as indicated by the 
 barometer, as well as the atmospheric currents and winds, have 
 their common cause in the changes and inequality of the tempe- 
 rature of the atmosphere itself; that the motions of all the 
 heavenly bodies are regulated by their mutual attraction. A 
 similar law in chemistry is, that all combustion depends upon 
 the energetic combination of oxygen, or matters analogous to 
 it, with certain component parts or materials of combustible 
 bodies. In no department of living nature has any causal 
 connection or natural law been established, equally definite, or 
 which can be taken in the same extended sense. "We have 
 only met with approximately similar relations among certain 
 of the phenomena, such, for example, as the dependence of 
 respiration upon a process or chain of events remotely resem- 
 bling those of combustion. 
 
THE STUDY OF NATURAL HISTORY. 51 
 
 We regard any series of natural phenomena and processes 
 as explained when we have obtained such an ' elucidation of 
 their causal connection and conformity to fixed laws as has 
 just been alluded to. Explanation in this sense means 
 nothing else than the demonstration by experiment of all the 
 co-operating conditions and agents which have produced them 
 — the demonstration why any single occurrence happens in a 
 definite manner, in fixed order. When we have cleared up 
 these hitherto obscure points, we are said, in common lan- 
 guage, to comprehend such natural phenomena and processes ; 
 just as we are able to comprehend and explain to ourselves the 
 conduct and actions of an individual, as soon as we know 
 his character and motives, and aU'the modifying and opposing 
 impulses. 
 
 But it is of the highest importance to define the exact sense 
 in which the words "explanation" or "comprehension" ought 
 to be used in every department of natural study, and to 
 restrict our acceptation of them to this sense only ; viz., that by 
 comparison and investigation we have so far explained certain 
 previously unintelligible phenomena, as to be able to deduce 
 them from one or more processes and phenomena which have 
 preceded, or accompanied them — in short, that we have shown 
 them to be the results of a certain other process or action. We 
 have, for instance, referred the fall of a body, or the motions 
 of the heavenly bodies, to the effect of gravitation ; we have 
 shown that respiration depends upon certain relations between 
 some of the component parts of the blood and the oxygen of 
 the air ; and that certain cases of paralysis are the result of an 
 extravasation of blood, of pressure upon the brain or spinal 
 marrow. The incident or phenomenon is, however, by no 
 means literally and completely explained thereby. For we do 
 not yet understand it thoroughly, any more than we are able, 
 in the case already alluded to, to comprehend or explain the 
 conduct of a man, i. e., to acquire an insight into the ultimate 
 reasons of his actions. We know, perhaps, that he was ambi- 
 tious, ardent, or amorous, and we thus explain to ourselves his 
 conduct, nay we can frequently predict it. But we do not 
 know why he was so, or why these precise qualities were in a 
 state of activity in his disposition. His conduct and actions 
 
52 METHODS OF INVESTIGATION IN 
 
 are therefore as enigmatical to us as before. To the layman a 
 disease, or a case of death, seems intelligible when he hears 
 that A had caught cold or had overloaded his stomach, or that 
 B had swallowed poison. He further understands the cure of 
 A's disease when he hears that he has had medical advice, or 
 taken some drug, or perhaps adopted a superstitious mode of 
 treatment. He is not accustomed to proceed further, in such 
 cases, in his inquiry into the causes of things, and is, there- 
 fore, not inclined to regard such occurrences as obscure or 
 incomprehensible. To the physician, however, they would only 
 be intelligible, if he knew that in A, a catarrh, an inflammation 
 of the lungs, a fit of indigestion, or a diarrhoea had been 
 produced ; or in B, narcosis, or inflammation of the stomach, &c. 
 But if he have employed certain remedies in such individuals, 
 and seen them recover, he is apt to regard their cure as 
 sufiBciently explained by the supposed efi'ects of the remedies 
 employed; for he concludes that the modifying changes and 
 conditions which produced the disease have been removed by 
 the precise efi'ect of the remedies^ and he regards the subsequent 
 recovery or improvement as a sufficient proof of their effects 
 and value. The reflecting physician — the investigator of 
 nature — would, however, be far from satisfied with this ex- 
 planation. He is not content until he has made himself 
 acquainted with every individual change in the functions and 
 tissues of the body, as well as with the manner of its occur- 
 rence, whether produced by cold, by overloading the stomach, 
 or by poison. And first he must learn the individual, chemical, 
 or physical changes and elementary processes which constitute 
 conjointly such inflammation, indigestion, or narcosis. In like 
 manner he must determine the individual influences acting 
 upon the body from without, e. g., of the atmosphere in the 
 case of catarrh ; and the particular modifying properties of the 
 substance acting from within, e. g., the poison, or the 
 remedy. We have thus, as it were, several strata of problems 
 and questions lying behind and above each other. And in 
 the attempt to explain them a greater depth is reached, just 
 in proportion to the demands of science, the technical know- 
 ledge and skill of the inquirer, and the more or less scientific 
 manner in which the attempt is made. 
 
THE STUDY OF NATURAL HISTORY. 53 
 
 We are therefore led to the conclusion that, throughout 
 nature, " explanation," in its ultimate signification, means 
 nothing but a reference of certain phenomena and processes 
 to others, or the resolving the one into the other. The latter 
 may therefore be designated as lying deeper and being more 
 general in relation to the phenomena modified by, or referred 
 to, them. We might therefore correctly call this whole pro- 
 cess of investigation and explanation {i. e. the course pursued in 
 attempting the elucidation of the causal connection of these 
 phenomena, &c., according to the inductive process), the gene- 
 ralization of a fact or incident. Thus, when we referred many 
 cases or kinds of paralysis to pressure upon the brain (either 
 from extravasation of blood, or from the presence of tumours 
 within the cranium), and deduced them from this cause ; and 
 when we referred many acute diseases, which were regarded as so 
 many forms of what was called " idiopathic fever," to inflam- 
 mation in difierent tissues, we extended the application of 
 both these conditions to a series of other phenomena and 
 processes, — i. e. we generalized them. Another instance is 
 afi'orded by what we now call " erases ;" i. e. certain changes 
 in the constitution of the blood, and in the conversion of 
 tissue, &c. ; for we now regard the most varied changes and 
 derangements, both of organs and of functions, in the living 
 body, as modified by those erases. We have not to inquire 
 here how far all this is correct, i, e. is the result of demon- 
 stration. It is sufficient for our purpose that of late certain 
 phenomena and processes have been connected together, which 
 were previously regarded as differing in character and standing 
 widely apart the one from the other; and that we have dis- 
 covered, or at least believe we have discovered, in all of them, 
 the same condition and process to be determining and essen- 
 tial. In like manner the physiologist has partly traced the 
 phenomena connected with the functions of " absorption" 
 and " secretion" to the physical processes of endosmose and 
 exosmose. He has also traced the development of the most 
 dissimilar tissues to the previous formation and further growth 
 of cells. In the former case, he generalized the processes of 
 endosmose and exosmose ; in the latter, that of cell-formation. 
 The same principle applies to the discovery of the chemist, 
 that the bleaching effect of chlorine — i. e. the destruction of 
 
54 METHODS OF INVESTIGATION IN 
 
 colouring matters, as well as its power of destroying certain 
 fetid gases, &c. — depends upon its energetic affinity for, or 
 combination with, the hydrogen and other basic substances 
 contained in those colouring matters, or fetid gases. 
 
 But sinCe, as already stated, we cannot regard any pheno- 
 menon or process as thoroughly explained because it has been 
 referred to others, or deduced from them, so we cannot be 
 content to stop here. The fact of its occurrence, and the 
 conditions under which it happens, as well as its explanation, 
 have been referred to other phenomena or processes ; i. e. to 
 those by which it is modified or to which it has been reduced, 
 ■ — in paralysis, to states of brain caused by pressure and the 
 like ; in the processes of absorption and secretion, to the prin- 
 ciples of endosmose and exosmose ; and in the destruction of 
 colours and smells, to the affinity of chlorine for hydrogen and 
 other similar elements. 
 
 The onus of the proof, to use a forensic expression, has been 
 transferred, and thrown upon those latter incidents and pro- 
 cesses which have been recognized as modifying the former. 
 Those have now to be explained which rendered the former 
 sufficiently intelligible to us ; for their own conditions and 
 causal connection are still obscure. 
 
 We are thus transferred from the consideration of one 
 mystery to that of another far less penetrable, while a new 
 mark of interrogation takes the place of the former one. Our 
 impulse to investigate, and the requirements of science, with 
 its inexorable demand for the cause of every phenomenon, or 
 occurrence, have many questions to ask in this newly-acquired 
 territory. We have, as it were, pushed our scientific outposts 
 into this region of comprehension and explanation, and fortified 
 them there. It now remains for us, in like manner, and by 
 the aid of similar processes, to conquer the unknown country 
 lying before us, and to make its subjugation subservient to the 
 advancement of science. We must seek for a new series of 
 modifying processes and circumstances which may explain 
 those just discovered, and hitherto enigmatical, in the same 
 manner as they had explained the former series. Our task, 
 therefore, is, to search for those other intermediate or deeper- 
 seated elementary agents or circumstances by whose action or 
 impulse the rest are modified. To succeed in this will be to 
 
THE STUDY OF NATURAL HISTORY. 55 
 
 discover those more general circumstances and processes which 
 present themselves with uniformity and in a certain sequence 
 in a much greater number of phenomena, and, through such 
 discoveries, to advance with certainty upon the highway of 
 generalization. 
 
 This has already been attained in the case of sciences such 
 as astronomy, physics, and chemistry, which can boast of 
 having arrived at a certain degree of exactitude. Human 
 science, working from age to age, has not only explained the 
 falling of bodies to the earth by their weight, i. e. traced it to 
 the law of gravitation, but has also referred the revolutions of 
 the moon, of the planets of our solar system, and of all the 
 other heavenly bodies, to the influence of the same cause. It 
 has proved that the common determining circumstance, as 
 applicable to all these phenomena and motions, is, that all 
 bodies mutually attract, or strive to approach each other in 
 the ratio of their weight and distance ; i. e. they are influenced 
 by the centripetal force, while this tendency is opposed by an- 
 other, viz. the centrifugal force of the heavenly bodies. In 
 other words, it has been shown that the conditions and laws 
 of all those so-called forces are essentially the same, e.ff, the 
 tendency of a given body, say of the moon, to fall upon the 
 earth, or of all the planets to fall upon the sun. Only a few 
 years ago we were accustomed to regard the electric, the gal- 
 vanic, and still more the magnetic phenomena in certain bodies, 
 as being perfectly distinct in kind, or as the manifestations of 
 essentially different and peculiar forces which, under the name 
 of imponderables, were distinguished as electricity, galvanism, 
 and magnetism. Step by step, however, it has been made 
 apparent that these mutually call forth and modify each other 
 (see Faraday, Oersted, &c.) We can now see the oneness of 
 their essential and governing laws, and trace the diversity of 
 their modes of exhibition, as phenomena, to its true source — a 
 difference in the characters of the bodies in which they occur. 
 And analogy has already hinted that the phenomena of heat 
 and light, and the laws which govern their peculiar manifesta- 
 tions, may possibly have the same origin with the so-called 
 electric and magnetic forces. Chemistry has received an 
 important aid towards generalization, or the reduction of its 
 numerous individual phenomena to one and the same circum- 
 
56 METHODS OF INVESTIGATION IN 
 
 stance, or law, in Dalton's -well-known " law of equivalents ;" 
 and we shall elsewhere have occasion to allude to several 
 nearly similar generalizations with which modern times have 
 enriched it, particularly to that of Liebig. Thus chemists have 
 now, with great probability, referred respiration and the whole 
 conversion of tissues in the living body to the higher general 
 law of the continuous oxidation, or slow combustion of its 
 oxidizable or combustible materials, more especially of its car- 
 bon. As a remote yet similar instance of this occuiTing in 
 the theory of disease, we may observe that the process of 
 inflammation, which was previously known as a common con- 
 dition, or at least as a common phenomenon in many diseases, 
 has resolved itself into another, which has been called the 
 process of exudation, and obeys the same laws ; while that 
 again has been approximately demonstrated to be dependent 
 upon certain alterations in the pressure of the column of blood, 
 or in the calibre of the blood-vessels and capillaries, or upon 
 certain changes in their contents, i. e. in the blood {e. g. in the 
 amount of blood-corpuscles, or of albumen, fibrin, or water, in 
 the plasma of the blood), which may be regarded as essential 
 and determining circumstances in relation to the process of 
 exudation. In a similar manner the common determining 
 cause of certain cases of paralysis has been shown to be either 
 an extravasation of blood in the brain, which has been reduced 
 to other more elementary and general changes or processes ; viz. 
 to ossification, or fragility, of its arteries ; or its cause has 
 been found to be a softening or analogous condition of the 
 substance of the brain itself ; or finally, an interruption of the 
 communication through the nerve fibres by certain more remote 
 changes in their substance. These modifying states again, may, 
 perhaps, be referred to deeper and more general processes, e.g. 
 to certain derangements or anomalies in the whole conversion 
 of tissues, or in the nutrition of the brain, &c. 
 
 This generalization must be carried out on a similar plan 
 throughout the whole science of natural history. It is our 
 task to show that certain series or kinds of natural pheno- 
 mena and processes, certain occurrences which have hitherto 
 been regarded as heterogeneous and modified by entirely dis- 
 similar circumstances, have, fundamentally, the same connection, 
 the same mode and regularity of origin, commencing and pro- 
 
THE STUDY OF NATURAL HISTORY. 57 
 
 ceeding in conformity to the same essential laws. We must 
 point out the essential oneness ■which underlies the accidental 
 diversity, and show how, with some comparatively subordinate 
 variation, the same thing will recur, under similar circum- 
 stances, with unchanging uniformity; and by establishing the 
 accidental, secondary, and subordinate nature of the modi- 
 fications and variations in question, we must arrive at the 
 knowledge of the higher and more comprehensive law. We 
 shall thus make our way into several consecutive or alternating 
 phases of conformity and causal connection of natural pheno- 
 mena and processes, and our comprehension of them will, at 
 the same time, advance further and deeper. While often — as 
 in the strata of our earth — whole centuries lie buried in a 
 single stratum, centuries more pass away before investigators 
 can succeed in carrying a shaft into the underlying stratum. 
 More than a century intervened between a Keppler and a 
 Newton. We can form no surmise as to how far, in the 
 various branches of natural history, this process of reduction 
 may yet be carried ; least of all in that field of vital pheno- 
 mena which has to do with the treatment of disease. We* 
 know, however, that it has its limits, and that these limits 
 must coincide with the boundaries which, the imperfection of 
 our senses imposes upon our observation of general nature, and 
 upon our investigations into it. And this will be the more 
 evident as we remember the paths by which alone, in the case 
 of any given natural phenomenon, we can arrive at the under- 
 standing of its causal connection and conditions, and thus gain 
 a competent knowledge of the laws which govern it. 
 
 This understanding has never been attained to from without ; 
 we have not derived it, so to speak, immediately from nature, 
 but rather from our own deductions from the facts which she 
 has been pleased to present to our consideration. Our know- 
 ledge of the conditions and laws which regulate the origin and 
 progress of certain phenomena has been, as it were, created 
 for ourselves. Our minds, in attempting to determine and 
 arrange these laws, have translated the enigmas which the 
 phenomena present into a language more intelligible to us, in 
 converting them into our technical formulae and familiar modes 
 of expression. And thus, as Hegel expresses himself, " external 
 phenomena have been transmitted to the internal perception." 
 
58 METHODS OF INVESTIGATION IN 
 
 When we have, by the aid of experiment, obtained some know- 
 ledge of any given series of natural processes ; when we have 
 ascertained in them a fixed mode of origin, and a simultaneous 
 or consecutive occurrence, we are justified in concluding that 
 there exists between them either a definite connection, or a 
 certain internal relation, and are warranted in calling the one 
 process or phenomenon, the condition or cause of the other. 
 But by this we can only mean that, according to our concep- 
 tion of them, the things in question bear this definite relation 
 to, and causal connection with, each other, and that we must 
 regard the phenomena and processes which we have ascertained 
 by experience to be constant in their occurrence and efiects, as 
 the real condition, or adequate cause of certain others. As it 
 is, therefore, by means of our own mental operations that-we 
 have succeeded, in the case of these phenomena and processes, 
 in ascertaining their conformity to certain laws, and in bring- 
 ing their various conditions within the scope of our intelligence, 
 we are justified in regarding all such occurrences, whether 
 standing apart or connected together, just as our experience 
 "has presented them to us. As such they have ever appeared, 
 and we may therefore conclude that they can never appear to 
 us in any other way. We thus end by recognizing ourselves, 
 i. e., our own intelligence and intuition, as the standard where- 
 by we must judge of external nature. Do these phenomena, 
 we ask, arise and recur consistently with our previously con- 
 ceived notions of them and of their natural connection, and we 
 are satisfied if we receive an answer in the affirmative ; but 
 this must not flatter us into the idea that we have penetrated 
 into the true secret of their connection, or have learnt what is 
 the real cause or nature of certain phenomena and processes, 
 or why these should call forth and modify certain others. 
 Through investigation, discovery, and the experience to which 
 they lead, we can but arrive at understanding the definite order 
 of the simultaneous or consecutive occurrence of such pheno- 
 mena and processes, and must remain as far as ever from com- 
 prehending their origin and conditions. Man, reasonable though 
 he be, is but a minute, subordinate atom in the universe, and 
 does not know whether all that exists and occurs in it, does so 
 confonflably to his reason, any more than he knows whether 
 our atmosphere, with its waters, nutritious matters, &c., is 
 
THE STUDY OF NATUBAJ. HISTORY. 59 
 
 constituted exactly in the manner most beneficial to him. By 
 the aid of his own reason, and by that alone, does he know 
 and understand external nature, i. e., all that exists and happens 
 around him, or can he render it comprehensible and available 
 to himself. It is vain, therefore, to believe or assert that we 
 have discovered the reasons, or traced the ultimate causes of 
 what occurs around us, because our limited capacity does not 
 permit us to discern, far less to penetrate into, all the various 
 events in nature. 
 
 Not even in the most certain and positive of all natural 
 sciences, physics and mechanics, are we able to inform ourselves 
 why a given substance has certain properties, or why certain 
 bodies act upon each other according to laws which may be 
 established with mathematical precision. They do not tell us, 
 for instance, why the impulse of a body in motion produces 
 motion in another body struck by it, or why a stone which 
 slips out of the hand, falls to the ground. For between the 
 stone and the ground, or between the body in motion and the 
 second body put in motion by it — e. g., a struck billiard ball — 
 we can detect no connection necessarily involving such a phe- 
 nomenon or effect. The natural philosopher has long ago 
 shown that different fluids evaporate, boil, or freeze, at very dif- 
 ferent temperatures j the fact is established, but it still remains 
 without a reason. Even the highest and most positive datum 
 which the mind of man has acquired in the comprehension of 
 nature, Newton's law of gravitation, is, in reality, only a fact, 
 and not an explanation of the fact ; i. e., it cannot give us the 
 essential and ultimate cause of the motions of the heavenly 
 bodies. Like all other so-called natural laws which we have 
 discovered, it remains in the end simply a subjective conception 
 of the human mind, a notion, explanation, or scientific hypo- 
 thesis, which we only regard as correct, or fully adequate, and 
 therefore receive as a positive law, because it is suflScient to 
 explain all hitherto known facts concerning the motions of the 
 heavenly bodies. It is possible, after all, that the heavenly 
 bodies may not attract each other, for we have never seen or 
 directly proved that they do so. It may not be from this, but 
 from some other and entirely different cause that they perform 
 their stated revolutions with their known regularity and order. 
 In a similar manner, we know of many bodies, that under cer- 
 
60 METHODS OF INVESTIGATION IN 
 
 tain circumstances they present certain phetiomena and produce 
 certain effects or phenomena in other bodies, which we speak 
 of as heat, light, and colour, or which we call electric, galvanic, 
 &c. But we do not know in what these phenomena and pro- 
 cesses essentially consist, or why a certain body (in itself) is 
 able to produce them in other bodies. 
 
 And if it is thus in even the most exact and most advanced 
 branches of natural philosophy, how can we look for anything 
 better in the science of vital phenomena, which is acknow- 
 ledged to be the most difficult and complicated of all, and 
 which must ever remain so. In reality, we do not even know 
 why we feel, see, or taste a substance ; why the volatile parti- 
 cles of a rose smell pleasantly, and those of assafoetida the 
 reverse; or why common salt has a different taste from milk 
 or butter. Much less shall we ever learn why certain bodies 
 possess vitality; i. e., present the phenomena and processes 
 which we include in the expression " life ;" why their organs 
 are developed, and converted, in a fixed order and manner, from 
 the simplest cell. Equally little can we ever hope to know of 
 the causes why, under certain circumstances, they present 
 those other phenomena and processes which we call disease; 
 or of the changes which have occurred within those bodies, to 
 produce in them phenomena and processes such as pain, heat, 
 fever, inflammation, &c., which have no existence in their 
 ordinary, or healthy condition. We shall never learn why 
 living bodies either live, or become diseased in this or that 
 respect, or why what are called diseases present themselves to 
 us under such and such conditions; neither shall we ever 
 understand the so-called essence of these phenomena, simply 
 because it is beyond the sphere of man's comprehension. 
 
 It is irrational to seek after what has once been recognized 
 as impossible, and few things have so much impeded our 
 advance in the comprehension of vital phenomena, in their 
 relation to the treatment and cure of disease, as the circum- 
 stance that we have either striven to accomplish the impossible, 
 or, seeking after the possible through impracticable processes, 
 have often failed to find it when it was near at hand. In this, 
 as in every department of natural history, the true aim is to 
 establish facts ; to determine, in any given case, under what 
 circumstances the phenomena and processes present themselves 
 
THE STUDY OF NATURAL HISTORY. 61 
 
 simultaneously or consecutively, and to reduce them to fixed 
 order and conformity, but not to trace out the ultimate and 
 specific causes of such occurrences. We have done all that is 
 humanly possible to explain the causal connection, or laws of a 
 given phenomenon or process in nature, when we have demon- 
 strated from experience, under what circumstances, and under 
 what coincidence of other phenomena and processes it con- 
 stantly occurs, and under what others it is never observed, 
 especially if we can ensure that it will always recur under the 
 circumstances which we have so determined. And having 
 done this for one series of phenomena, we are prepared to 
 demonstrate in any other series, which manifests the same kind 
 of simultaneous or consecutive occurrence, the existence of the 
 same laws; and we may now, as has been already shown, 
 extend the principle of causal connection to entirely different 
 phenomena and processes, and thus advance, step by step, in 
 the generalization and reduction of a number of things to one 
 and the same kind of conditions (Bedingtseyn). 
 
 We may speak of the cause in consequence of which certain 
 bodies or substances present certain phenomena or processes, 
 or give rise to their manifestation in others, as a " property" 
 of these bodies and substances; and may therefore imagine 
 that they produce such phenomena and processes by virtue of 
 these properties; i.e., that their capability of producing certain 
 effects, springs from these their properties and nature. 
 
 And we may further, if we are so pleased, give to these pro- 
 perties, to this capability, the name " force ;'•" and, as such, 
 briefly distinguish the whole sum or aggregate of the circum- 
 stances by which any given phenomenon or process, taken 
 singly, or in series, is wont to be modified. We thus ascend, 
 as Laplace says, from the observation of natural phenomena to 
 their laws, and mount from the consideration of laws to that of 
 forces. Our minds (Verstand) are compelled to acknowledge, 
 in nature, as many distinct properties or forces as we recognize 
 series of phenomena, or effects distinct in their conditions and 
 causal connection. Thus we are warranted in assuming a 
 force of gravitation and attraction, or of chemical affinity, an 
 electric or magnetic force, as well as a vital, or muscular and 
 nervous force. 
 
 But we must not deal arbitrarily with these forces, &c. ; 
 
62 METHODS OF INVESTIGATION IN 
 
 neither must we think that by the assumption of a force 
 we have made any advance towards the comprehension of 
 a phenomenouj or occurrence in nature, or that we have 
 thereby made it more intelligible to ourselves or others. For 
 we are unable to learn anything concerning these forces and 
 properties themselves, as such, simply because we cannot 
 immediately observe or investigate the mode of their action. 
 We have been induced to assume the existence of a " force" 
 from the necessity of accounting for certain phenomena and 
 effects, and for the regularity with which these follow each 
 other; for we have imagined that these consequences must 
 depend upon some such force. But of the force itself, as such, 
 we know and can therefore assert nothing ; neither can we hope, 
 by the aid of this abstract, hypothetical term, to understand or 
 explain more clearly than we could do without it, what is really 
 going on in nature. As we can discern nothing of the mental 
 power of the most intellectual brain unless we see certain 
 manifestations of it, so we can attain to the understanding of 
 a force, or property, and of the effects ascribed to it, by no 
 other path than the ordinary one, — i. e. the same which we 
 must have adopted without the assumption of this force, or 
 property, and which, in fact, we had adopted long before the 
 study of natural history was sufficiently advanced to bring us 
 to the abstract notion or assumption of any force or property 
 whatever. 
 
 If we further investigate those natural phenomena, the pecu- 
 liar mode of whose appearance and commencement, occurring 
 and following each other in a fixed order and sequence, first 
 excited in us the notion of their being dependent upon some 
 particular " force,'' we shall find that this fixed order and con- 
 formity is made, by a kind of mental transfer, to serve as the law 
 according to which the force acts and manifests itself. Instead 
 of saying, for instance, that the velocity with which a body falls 
 to the earth is in the direct ratio of its weight, and in the 
 inverse ratio of the squares of the distances, we now say, that 
 the cause or force by which the body falls (the force of gravity, 
 or the earth's attraction,) acts in the direct ratio of its weight, 
 and in the inverse ratio of the squares of the distances. Or, 
 in place of saying that the peculiar phenomena and processes 
 which we include in the term " life" are the result of the 
 
THE STUDY OF NATURAL HISTORY, 63 
 
 special co-operation of certain organs, &c,, in short, of the 
 combination of certain solids and fluids, and of their acting 
 with and upon each other, we give to their common cause the 
 name of " vital force." The laws which we are able to discover 
 for those processes now serve as its laws ; and all that acts upon 
 the living body and its organs and functions we now imagine, 
 primarily, to affect this vital force ; and we are thus accustomed 
 to speak of its dififerent phases and bearings, or modes of mani- 
 festation, of its increase or decrease, and of influences acting 
 upon it and the excitement produced by them. Yet through 
 this our deduction of certain phenomena from certain forces, 
 we have attained no clearer understanding of their causal 
 connection and laws than we were in possession of without its 
 aid. What we have gained through it is but the hypothetical 
 foreboding, or supposition, of an " unknown quantity," — a de- 
 termining circumstance, or influence (to which we now give 
 the name " force"), acting beneath and behind those occur- 
 rences in nature which we have been studying. To many 
 minds, this hypothesis will no doubt afford a certain relief; it 
 satisfies, in a manner, their longings after a fuller insight into 
 the causal connection and ultimate essential conditions of the 
 various natural phenomena that come under our notice. But 
 a complete misapprehension of what is necessary and possible 
 is involved in the idea that, by the mere assumption of such a 
 force, we can better understand and explain any natural occur- 
 rence whatever. For we do not arrive at that which we know 
 and are able to affirm with regard to such forces through a priori 
 assumption, but through patient a posteriori investigation and 
 deduction, — in short, through our experience. And instead 
 of all these occurrences becoming more intelligible, in respect 
 to their causal connection and laws, by the assumption of such 
 forces, these forces themselves can, on the contrary, only become 
 in some degree more comprehensible in their nature and action 
 in proportion as we become more familiar with the phenomena 
 and effects deduced from them, and acquaint ourselves with 
 their origin and with the definite mode and conformity of their 
 occurrence. 
 
 It is, therefore, little less than irrational that many, through 
 the adoption of an opposite path, have begun where they could 
 only hope, under the most favorable circumstances, to have 
 
64 METHODS OF INVESTIGATION IN 
 
 ended. Many, it appears, have entertained the hope of being 
 able to explain entirely unknown and unexplored series of 
 phenomena and processes by the operation of forces, or by 
 the laws by which such forces act, without being sufficiently 
 careful to deduce the existence of the latter from the obser- 
 vation of facts as they actually exist. For the very existence of 
 these forces must be grounded upon experiment and deduction, 
 and these have need to be of no trivial, arbitrary, or a priori 
 nature. If even the physicist, by the assumption of a force of 
 gravity, of an electric fluid, or of the materiality of heat and 
 light, has attained to no positive understanding of these forces, 
 as they exhibit themselves in their peculiar phenomena and 
 processes, how can we hope to succeed better in the field of 
 vital phenomena ? Yet many have believed that the mere 
 attributing various occurrences to the workings of a vital force 
 would enable them the better to understand their origin, and 
 the more plainly to point out their ultimate and special nature 
 and conditions. They have believed that they had compre- 
 hended the nature and essence of the processes in the healthy 
 or sick, when they had been able to describe them as the in- 
 crease or decrease of an irritability, as an excess or want of 
 stimulus, and had included -all the obscure processes which 
 induce a return to a healthy condition in the term " natural 
 healing force.'' Or they have hoped, perhaps, to explain the 
 effects and efficacy of certain remedies, by assuming, as their 
 ultimate and adequate cause, special medicinal virtues and 
 properties ; or by assigning to them a certain inherent and 
 mysterious relation to certain processes and organs in our 
 bodies. 
 
 With all this, however, no advance has been made either 
 towards the comprehension of ultimate causes, or towards an 
 insight into the effects of the remedial substances in question. 
 
 Whoever professes some insight into the things submitted 
 to our investigation, and into what is demanded of us in the 
 way of their examination, must have cleai'ly understood that it 
 is impossible by such a mode of advance, or by the employ- 
 ment of any such abstract notions, and forces by way of expla- 
 nation, to arrive at a better comprehension of the objects 
 submitted to us. He must be aware of the insufficiency, nay 
 even absurdity, of attempting thus to explain the internal 
 
THE STUDY OF NATURAL HISTORY. 65 
 
 nature and essential connection of any series of phenomena, 
 or processes in the living body, before their individual condi- 
 tions and laws have been investigated and determined. To 
 do so would be a dangerous and illogical abuse of our most 
 important and useful faculty, viz., the intellectual; and it is 
 this assumption of forces, &c., this a priori jumping at conclu- 
 sions, in short, this arbitrary taxation (Octroyiren) of the 
 human mind in the investigation of nature, which has pro- 
 duced false theories, and, perhaps, more than anything else, 
 prevented the establishment of better and more correct ones. 
 
 Such are the views which, since a more sound and positive 
 method of investigation was first introduced by Bacon, have 
 been confirmed by the ablest investigators in every department 
 of natural science — whether in the case of a Galileo, a Keppler, 
 or a Newton, a Cuvier or a Humboldt, a Berzelius or a Liebig. 
 Formerly other views obtained, and they are, even now, not 
 altogether exploded, especially from the domain of physiology 
 and medicine. Were it otherwise, how could we, even in the 
 present century, see new theories and systems not only 
 hazarded a priori, but accepted by thousands as established 
 and correct? But to force this conclusion upon us, we need 
 nothing more than the fact that such a priori attempts, and 
 the propensity to hypothetical theories, drawn from the sub- 
 jective views of the individual, are inherent in our nature, and 
 that this mode of proceeding, corresponding to a natural re- 
 quirement of the human mind, may find therein, in a certain 
 sense, its justification. 
 
 And this further leads us to consider the part which our 
 ego, i. e. our whole subjective contemplation and interference, 
 plays in the observation of natural phenomena, as shown in the 
 notions we form and the deductions we draw from what we 
 observe. We have already alluded to the influence which, 
 even in the most sober, circumspect, and a posteriori induction 
 from experience, our mental ego will obtain by way of irrepres- 
 sible co-operation. Let it here then sufB.ce to remark, that 
 we cannot proceed to the investigation of any conformity to 
 fixed laws, any causal connection of natural phenomena, with- 
 out having first formed for ourselves some notion of them ; 
 without having represented to ourselves this or that mode of 
 
 5 
 
66 METHODS OF INVESTIGATION IN 
 
 their relations as being the more probable^ and having thus 
 formed certain suppositions, certain conjectures or hypotheses 
 concerning them. Much less, without such, could we hope to 
 bring any previously unconnected and unexplained series, or 
 kinds of natural phenomena and processes, into a due and 
 more intelligible order and conformity, by means of which to 
 arrange and connect them consistently with our notions. He 
 only can hope, in the investigation of nature, to take rank as 
 a discoverer, who can form some surmise as to what he has to 
 seek for and discover, and be thus in a position to put his 
 questions so advantageously as to obtain an answer where 
 another might ask for one in vain. Thus we see that the 
 most skilled and successful investigators have arrived at their 
 best and most important discoveries by both routes, i. e. a 
 priori as well as a posteriori — e. g. a Copernicus, a Keppler, 
 or a Liebig — and we need nothing more to establish the high 
 value of scientific imaginativeness, even in the investigation of 
 the simplest natural phenomenon. The impulse, the conscious 
 foreboding of certain relations, or analogies in nature, which 
 first led a Copernicus to his discovery, induced a Harvey to 
 seek for a circulation of the blood, and finally conducted him 
 to its establishment as an ascertained fact. He himself says : 
 " Csepi egomet mecum cogitare, an motionem quandam quasi 
 in circulo haberet, quam postea veram esse reperi." These 
 men carried out by strokes of genius — apparently a priori and 
 by synthetical conception — the most comprehensive generaliza- 
 tions, and discovered the most important natural laws, without, 
 to all appearance, having to pass through the tedious, gradual, 
 and preparatory labour of systematic induction from experience, 
 i. e., a posteriori. In their hands both these modes of investi- 
 gation and discovery became one by merging in a higher pro- 
 cess peculiar to minds of their exalted calibre. 
 
 The interference of our individuality in the observation and 
 investigation of actual occurrences forms a connecting link 
 between the sober and strict process of induction from posi- 
 tively established facts — in short, from experience and a poste- 
 riori — and our whole a priori progress, or mere hypothesis 
 and speculation. In each case we advance in our investigation 
 and comprehension of nature conformably to certain innate 
 and fixed laws of our intellectual being, which are always 
 
THE STUDY OF NATURAL HISTORY. 67 
 
 fundamentally the same. The difference is only that the men 
 best qualified to take the highest rank as investigators of 
 nature, are they who are neither inclined on the one hand to 
 overestimate, nor, on the other, to undervalue this same co- 
 operation of our ego ; they have been fortunate and wise 
 enough to attach to their a 'priori conceptions and surmises 
 the precise value which these have actually possessed, using 
 them only as the first preliminary step in the whole process, 
 which aids them in testing and feeling their way towards 
 further investigation. And thus, while they have made the 
 faculty in question assist them in the discovery of an order 
 previously undemonstrated by experience, they have been on 
 their guard in not permitting such views and a priori conjec- 
 tures (however useful) to take the place of established truth. 
 They have been careful not to advance what they thought 
 possible, or probable, and the form in which they conceived it, 
 as a demonstration of the actual course of things, but rather 
 what they had proved by positive investigation, i. e., experi- 
 mentally. 
 
 A person capable of reflecting upon the things around him, 
 and of considering them in an intellectual point of view, will 
 naturally first seek to become acquainted with the object set 
 before him, and to inform himself with regard to its conditions 
 and powers of influencing other objects. But the activity of 
 this impulse naturally varies with the individual, and some 
 persons will advance far more speedily on the path to which 
 it urges than others. 
 
 Let us now place the phenomenon in question in juxtaposi- 
 tion with others which perhaps resemble it in some respect, or 
 with which we may happen to be better acquainted in their 
 causal connection ; let us compare and distinguish them, and 
 endeavour, through the process of induction already alluded to, 
 to arrive at a due understanding of them. To carry out all 
 this correctly, we must be more or less familiar with all the 
 phenomena and processes having a relation to, or connection 
 with, the phenomenon in question; we must be at home in 
 this department, perhaps also in several others. But seldom 
 have two minds been so in the same degree, and still less in 
 the same manner. To one memory and imagination will offer 
 a large number of analogous and pertinent phenomena and 
 
68 METHODS OF INVESTIGATION IN 
 
 objects, to another fewer ; to the one certain series of pheno- 
 mena will present themselves, to the other certain others ; to 
 the one all these facts will arrange themselves in a certain 
 manner, while to the other they appear very different. Then 
 ensues a necessary divergence in their attempts to explain what 
 is before them; they will, in pursuit of the same end, adopt 
 very different paths and methods, and still more, will carry 
 them out with a very different degree of consistency or perse- 
 verance. For every one is not able to place that restraint 
 upon his cravings for an explanation of the things before him 
 which another may have attained to. While one follows the 
 more certain but unfortunately more difficult path of investi- 
 gation in detail, and of strict induction from experience, a pos- 
 teriori, another omits or abridges much of this labour, 
 perhaps from a conviction that in the case in question he may 
 safely do so. His imagination and whole creative power, are, 
 perhaps, greater, the flight of his genius bolder and more com- 
 prehensive than is usual with ordinary men; or he may be 
 utterly incapable of that patient preparation of the separate 
 pieces of his structure, with which another cannot possibly, 
 dispense. Many a one, in times past, impatient of a gradual 
 advance, a slow ascent, has discovered, by a bold grasp a priori, 
 the most important laws and correct theories. Others, there- 
 fore, will make the same attempt, and place the phenomena 
 and processes in question in that connection with each other 
 which they conclude to be the most probable and correct, i. e., 
 they will explain them a priori. They now persuade them- 
 selves that the things which they observe are truly such and 
 no other than they appear to them. And thus arise those 
 rash attempts at explanation, those theoretical coups de 
 main, by means of which it has been attempted to explain 
 whole series of phenomena and processes, or even an entire 
 science, e.g., Physiology, Pathology, or Therapeutics, before 
 any of the elements and processes have been determined expe- 
 rimentally, or their causal connection demonstrated. 
 
 But it would be unjust, on the other hand, to reproach this 
 whole a priori mode of advance — whether it may have led 
 merely to individual hypotheses and combinations, or to con- 
 nected theories and entire systems — with having proceeded 
 altogether arbitrarily, from mere views and conjectures, with- 
 
THE STUDY OF NATURAL HISTORY. 69 
 
 out the support of an experimental basis. Even the most 
 precipitate and incorrect theory starts from experiments and 
 facts, and is, indeed, essentially founded upon them, because 
 they are of necessity indispensable as materials to which the 
 theorist must apply his explanations. No reasonable man 
 will pretend to demonstrate his views and conjectures by mere 
 hypotheses and opinions, or to explain by his theory things 
 which have no existence save in his own brain. Every one, 
 in short, grounds his theory upon certain facts and experiences, 
 and seeks to demonstrate it by no other aid than theirs. 
 
 The error of the less correct and successful theorist does 
 not lie in indifference to facts, but in his having ill understood 
 how to employ them. His failure or error consists in the 
 regarding as proofs what are not truly such ; in the drawing 
 of false conclusions from them, and thus arriving at an incor- 
 rect theory. On the other hand, the characteristic of the 
 correct theorist — of the successful investigator — is, that he 
 is able, from the previously unarranged and unexplained stores 
 of his observations, and of the materials gleaned from experi- 
 ence, to surmise the exact connection between them, and to 
 define and classify them in the relations they bear to each 
 other. It is he who can, from a much smaller number of 
 experiences, from more doubtful facts than are possessed by 
 the former, deduce the truth, i. e. their real connection and 
 precise laws. 
 
 But in each case it is from experiences and facts that 
 information is sought, and it is these which claim our fullest 
 attention if we would learn to understand and explain them. 
 They speak to all, but it is only men of genius, it is only the 
 chosen few, who, as of old, in the case of the]ancient Proteus 
 of Virgil's Mneid, are gifted to hear and understand them 
 aright. And for those who fail we must remember that many 
 allowances are to be made. The human mind, when confronted 
 with nature, can only advance in the path of investigation, or 
 explanation, according to its own peculiar laws ; and an exact 
 appreciation of the nature and modifications of these governing 
 laws might perhaps, could we obtain it, serve to adjust the old 
 and often troublesome schism between empirics and theorists 
 — ^between absolutism (Positivismus) and idealism, or between 
 a too objective and a too subjective science. 
 
70 METHODS OF INVESTIGATION IN 
 
 Many of these precipitate and erroneous attempts spring 
 from the natural tendency, one might almost say instinctj of 
 the human mind, to embrace within itself all the enigmatical, 
 because unexplained and divergent phenomena, or results of 
 experience. To attain, this end, it strives to show that all 
 those phenomena and occurrences are essentially of the same 
 kind and belong to the same series, and thus it seeks to reduce 
 the greatest possible number of them to the same causal con- 
 nection, or perhaps to conditions and laws with which it is 
 already in some degree familiar. The ultimate and essential 
 reason of all this seems to be, that it is natural to us to seek 
 to explain things unknown to us by the aid of things with 
 which we are better acquainted. In our haste as soon as may 
 be to satisfy our longing for the comprehension, i. e. for the 
 explanation, of the objects and mysteries before us, we begin 
 to deduce them from similar modifying circumstances and 
 processes, from the same laws which we have already estab- 
 lished for other more or less analogous phenomena and pro- 
 cesses. 
 
 Instead of investigating individual objects by the strict 
 process of induction from experience, and determining their 
 causal connection, and then advancing gradually by generaliza- 
 tion or reduction to higher or more general laws, we draw 
 conclusions — from what is already known to us in more or 
 less definite form — concerning what is still unknown to us. 
 We thus deduce from those causal connections or laws, which 
 have been demonstrated for one kind or series of natural 
 phenomena, the order and laws of an entirely different kind 
 or series ; and thus endeavour to explain their origin and 
 calculate their probable manifestation under circumstances 
 totally new, and even, perhaps, partly or entirely unknown. 
 
 We call this mode of advance the process of deduction, as 
 opposed to that of induction ; or synthesis, as opposed to 
 analysis. Thus the physicist can, from the laws which he 
 has succeeded in establishing, whether they be those of 
 gravity, of the pressure of fluids (hydrostatic laws), or of heat, 
 &c., draw conclusions concerning many other more complex 
 phenomena and processes, i. e., he can explain their origin 
 upon certain given principles, whether they occur in inanimate 
 nature or in the living body, and whether singly or in connec- 
 
THE STUDY OF NATURAL HISTORY. 71 
 
 tion with others. So can the chemist, from his laws of affinity 
 and of equivalents, often calculate with certainty what will 
 occur in untried cases, and even under different and entirely 
 new circumstances. From the results of his inquiries regarding 
 a certain number of substances and the laws of their combina- 
 tion, he draws conclusions concerning others, and predicts their 
 behaviour before he has had an opportunity of investigating or 
 becoming acquainted with them. 
 
 It is self-evident that this is the most convenient and the 
 easiest manner of arriving at the comprehension and explana- 
 tion of what is still unknown to us. Instead of investigating 
 unknown phenomena and occurrences, we have only to class 
 them along with others already known to us, if we have good 
 reason to suppose that they agree in essential points, i. e., in 
 the circumstances which modify their origin and progress. 
 And instead of the tedious process of inquiring what happens 
 in a given case, and determining the conditions and causal 
 connection of such phenomena by numerous indirect processes, 
 we can now briefly say that thdy are constituted in the same 
 manner as others already long known to us. In short, instead 
 of employing the process of a posteriori induction, we may, 
 a priori, deduce many things from the little that is with 
 certainty known to us, and from the laws which regulate 
 that little. And instead of dividing a whole group of pheno- 
 mena — e.ff., a vital function or a disease — in the case before 
 us, into its individual members or elements, and investigating 
 them singly, we may, conversely, construct and explain such a 
 group by synthesis, from the conditions or effects of the 
 elementary processes which accompany it. If we had learned 
 the causal connection and conformity to fixed laws of some even 
 of the more important processes in the living body, e. g., of 
 digestion, nutrition, conversion of tissues, or of nervous action ; 
 if we knew with certainty not only what occurs in each of 
 them, but also what modifies it, and by the constant coin- 
 cidence of what circumstances and influences it is rendered 
 possible, we could more easily thereby explain all those occur- 
 rences, and finally consistently deduce therefrom the conformity 
 of all the processes which constitute " life." The same know- 
 ledge would also sufiBciently explain the nature of disease in its 
 mechanism, origin, and cure. Every vital process, and every 
 
72 METHODS OF INVESTIGATION IN 
 
 group of vital processes, in a state of health or disease, would 
 then be au effect or a result occurring necessarily under given 
 circumstances already accurately known to us. 
 
 It follows from all this, that the desire for such a deductive 
 science is a perfectly natural and necessary one. What wonder 
 is it if we long for a state of knowledge which would give 
 us, by the aid of a few maxims and laws, an understanding of 
 all that occurs in the living body? We should then, through 
 an exact knowledge of what is taking place in our patients, be 
 enabled to deduce with certainty from a few higher principles, 
 all the individual rules for our clinical practice. When we 
 consider this want, the formation of so many theories and 
 systems to satisfy it becomes intelligible. The same circum- 
 stance has been propounded as the essential condition or cause 
 of the most dissimilar diseases : e. g., irritation or debility, 
 according to Brown; inflammation, according to Broussais; 
 so-called blood-crasis, certain derangements of the functions 
 of different parts of the nervous system, according to many of 
 the moderns. In like manner, the same essential type, the 
 same ultimate effect, has been assumed as the basis of the 
 mode of action of the most various agents and remedies : c. g., 
 debilitation or invigoration, excitation or change of tone, &c. 
 
 An entire misapprehension of the actual state of things 
 could, however, alone have induced any such attempts. While 
 these men were in reality not far from the starting point, they 
 believed themselves to be near the goal, and pretended to 
 take or give what did not yet exist. Physics, mechanics, 
 and in some degree chemistry, have gradually attained the 
 rank of deductive sciences ; not so physiology and the theory 
 of diseases. In the former sciences men have succeeded in 
 determining the similarity of several series of phenomena and 
 processes : e. g., the laws of gravitation and of hydrostatics, of 
 chemical affinity, &c. ; which are in consequence regarded as 
 effects or results which must necessarily occur under deter- 
 minate circumstances. We can, therefore, now predict what 
 effects and results will occur under certain given circumstances 
 with a definite assemblage of co-operating agents. 
 
 But, on the contrary, so long as no such natural laws have 
 been established, — as is the case in the whole theory of life, — 
 and so long as we do not know what really occurs in any vital 
 
THE STUDY OF NATURAL HISTORY. 73 
 
 process or in the course of any disease, nor by the co-operation 
 of what circumstances it occurs, any deduction in the above 
 sense is impossible. It is useless to attempt to promote the 
 comprehension of yet unknown phenomena and processes by 
 grouping them with others almost equally unknown, or to 
 attempt to explain them by adapting to them laws which 
 regulate other groups of phenomena and processes before these 
 last are themselves well understood and clearly demonstrated. 
 Even the natural philosopher is unable to calculate with cer- 
 tainty, from the laws of atmospheric pressure and gravitation, 
 and from the elasticity of gases, the distance to which a pro- 
 jectile may be thrown. Much less can he calculate from the 
 laws of action of individual agents — e. g., of heat and of the 
 process of evaporation, of the currents and electrical phenomena 
 of the atmosphere — how a given state of the weather is to be 
 brought into conformity to certain fixed laws ; and this because 
 the concomitant circumstances and influences are too compli- 
 cated, the importance and office of each individual agency not 
 sufficiently known to him. The laws of gravitation, &c., which 
 he has so cleverly discovered, do not enable him to determine 
 with certainty the behaviour of three bodies which attract or 
 gravitate towards each other; still less can he calculate with 
 certainty, a priori, the orbit of one of the heavenly bodies, but 
 must seek to discover and determine it by exact observation. 
 In like manner, no chemist can say beforehand what will occur 
 when certain complicated organic compounds are brought into 
 contact with other substances : this, in such a case, must be 
 determined by experiment. 
 
 And how shall we pretend to say that in the theory of life, 
 in which the phenomena and processes are confessedly obscure 
 above all others, we know even so much as in the cases alluded 
 to above, and that we are now in a position to venture upon a 
 method of explanation which possibly for centuries to come 
 cannot be fitly entered on ? 
 
 We have endeavoured, in the foregoing pages, to give a 
 general view of the means by which, in the department of 
 medicine, as in all the natural sciences, we must enter upon 
 the understanding of the causal connection and confortiiity of 
 certain phenomena and processes. In considering the various 
 
74 METHODS OF INVESTIGATION IN 
 
 modes in which it is possible to conduct the investigation of 
 nature, we must be careful to bring the data submitted to us 
 to the closest test; and while we contemplate the peculiar 
 circumstances and diflBculties in the objects before us, we shall 
 understand more clearly the manner in which we must apply 
 the methods of investigation, and adapt them to the peculiar 
 nature of the phenomena and processes with which we have to 
 do. Yet, after all, we shall find that the manner of tilling the 
 intellectual soil must depend entirely upon the nature of the 
 soil in question. 
 
 Our first aim, therefore, must be, as has already been fully 
 explained, to determine by the observation of the phenomena 
 and processes going on in health or disease in the living body 
 — in a word, by experience — their causal connection and the 
 conditions of their development. We have consequently to 
 discover the causes of each phenomenon and occurrence, and 
 the effects of each cause and influence, in short the special 
 conformity to fixed laws, of each incident and process in the 
 living body, &c. The most certain, and, at the same time, the 
 simplest means of doing this would evidently be to take each 
 phenomenon, each effect or occurrence separately, and to inves- 
 tigate it as much as possible apart from the others. This is, 
 however, impossible ; for since we are incapable of producing 
 life and thus establishing its peculiar processes artificially, we 
 must confine ourselves to the investigation of life as we meet 
 with it in nature and reality. There, however, no phenomenon 
 or process, and consequently no cause or effect, ever presents 
 itself for our observation in an isolated form. Further, it is 
 for the same reason impossible, in our observation of actual 
 occurrences, to bring each individual effect into connection 
 with its constant cause, or each determining circumstance, — • 
 each cause into connection with its constant effect. 
 
 At first, perhaps we think that we need not investigate 
 very deeply to find the knowledge for which we are seeking; 
 we soon, however, learn our mistake, and find that in the 
 attempt to seize what is lying before us in a state of order and 
 quiescence, we rather disarrange and displace it than render it 
 more easily understood ; for all things in nature, both without 
 and within us, are in the closest connection with each other, 
 and nothing occurs which is not in some manner connected 
 
THE STUDY OF NATURAL HISTORY. 75 
 
 with something else, and thus again with all. Every pheno- 
 menon, every occurrence, is connected by mutual relation with 
 many others ; nothing is to be imagined and contemplated by 
 itself. All here is in a state of constant change, in continuous 
 though definite progress ; what it was at one moment it ceases 
 to be with the next. In the language of Job, " it goeth by 
 me and I see it not ; it passeth on also but I perceive it not." 
 This holds good even with respect to what we call " inanimate 
 nature," which we regard as such only, because the occurrences 
 and changes in it — its life — are not contained in the limited 
 space and definite form of an organism, but are distributed in 
 boundless space, and because the occurrences and constant 
 changes do not display the sharp, distinctive features, or divi- 
 sions observable in the other part of nature which we call 
 " animated." In short — even in this relatively more simple 
 and quiescent world, nothing is in a state of rest, nothing 
 occurs in an isolated form, or has an independent existence. 
 Here also every phenomenon, every occurrence, is modified by, 
 and itself modifies, many others, i. e. is at once effect and 
 cause. 
 
 If it be difficult in inanimate nature, and even in physics, 
 to determine experimentally what phenomena and incidents 
 modify others, and by what others they themselves are modi- 
 fied — how everything occurs in a constant progression, accord- 
 ing to some fixed order and uniform plan — the difficulty is 
 infinitely greater with respect to the phenomena which it is 
 the province of the physiologist and physician to investigate. 
 In the living body all the phenomena, all the functions, are 
 intricately blended with each other, and may be compared 
 to a network of threads in which each, even the smallest, acts 
 upon the whole tissue, and in which every effect reacts upon 
 that which modifies or causes it. All these individual processes 
 and agents in the living mechanism are not only themselves in 
 a state of constant change and progress, but are incessantly 
 influenced and essentially modified by the most varying agen- 
 cies of the external world. These external agents, themselves 
 subject to continual change and modification, are also in the 
 most intimate connection with each other, and none among 
 their number can easily present itself for observation in an 
 isolated form. 
 
76 METHODS OF INVESTIGATION IN 
 
 We thus find everywhere a complexity of circumstances, an 
 oscillation between wide limits, and a mutability, not met with 
 in any other department of the study of nature ; a mutability 
 going on, not only from day to day, but from year to year, 
 and from century to century. Here also every phenomenon 
 or occurrence has doubtless its fixed causes, every modifying 
 circumstance or influence its fixed efiects, and the conformity 
 or order in which everything occurs is just as constant and as 
 necessary for the constitution of the organism as in inanimate 
 nature. But what occurs in the living body does not occur so 
 uniformly and immutably as in the physical, mechanical, or 
 chemical processes. It is not immediately and simply the 
 efiect or result of its own peculiar causes, at least it does not 
 appear so to us, because we can never observe the efiect of an 
 individual cause or agent by itself, as the physicist can observe 
 the effects of gravitation, or the chemist those of a single 
 substance. ^ With us many causes or agents affect the deve- 
 lopment and progress of the same phenomenon or process, and 
 the latter often reacts upon others, perhaps even upon those 
 which modify it. In addition to this, the whole state of a 
 living organism, i. e. the aggregate of its phenomena and pro- 
 cesses at a given moment, is modified by its preceding state, 
 and modifies that which is to follow, whence every occurrence 
 in life becomes more complicated in its conditions and deve- 
 lopment, and at the same time more variable. 
 
 Let us take, for example, an organ of our body which 
 appears to act in essential conformity to physical laws — the 
 eye. It is a physical, optical apparatus, and one of the most 
 complicated kind, but it differs in toto from those with which 
 the physicist has to deal, inasmuch as it sees instead of 
 letting another look through it, and is in connection with a 
 brain and mental eye, which see with it, and move and use it 
 at discretion. All its glasses, lenses, curtains, &c. have life, 
 are nourished and undergo changes from the first moment of 
 their formation, and they are not only more intimately con- 
 nected with each other than is the case in any mere optical 
 apparatus, but further, they are connected with the machinery 
 of the whole organism. They are thus not only under the 
 influence of light, upon which their functions essentially de- 
 pend, but under many other external and internal influences. 
 
THE STUDY OF NATURAL HISTORY. 11 
 
 From these causes the eye may become useless in a manner 
 which cannot aflfect any physical apparatus. 
 
 It is clearly indubitable that what occurs in the living body, 
 occurs to a certain extent in conformity with physical and 
 chemical laws. The material substratum of the body falls 
 more or less within their range; it commences, lives, and 
 decays under the constant influence of inanimate nature, and 
 draws from it the materials with which it builds up its struc- 
 tures. So soon, however, as these materials enter within the 
 magic circle of the living body, they do not merely combine 
 according to ordinary chemical laws, but pass into a new 
 development; and no less novel and peculiar are the pheno- 
 mena which they now offer and produce. These phenomena 
 constitute something more than the mere summing up of their 
 individual component elements. Albumen, gelatine, fat, water, 
 salts, &c. may be furnished from without, and form the proxi- 
 mate components of our mechanism, but only within this 
 mechanism are they converted into blood for the sustenance of 
 the body ; only in it do they live and unite to form muscles, 
 or become the medium of sensation, of will, and of action. 
 The living body has, so to speak, digested and converted them 
 into itself, and from this moment they begin a new and higher 
 cycle of existence and action. In like manner, in the compa- 
 ratively simpler processes — in digestion and circulation, in the 
 conversion of tissues, in respiration, or in the excretion of 
 certain substances — chemical and physico-mechanical action 
 evidently play a very important part ; but not exactly in the 
 same manner as in what we call inanimate bodies. Other 
 processes and activities, including the most intellectual, are 
 here at work, and this in conformity with entirely different 
 and peculiar laws. Thus the final effect, modified as it cannot 
 fail to be by these varying processes, is not simply a physical 
 or chemical one. The same chemico-physical processes are, 
 no doubt, going on in most diseases, e. g. in derangements of 
 digestion, nutrition, excretion, respiration, transudation, exos- 
 mosis, &c. And while, in the case of remedies, we are obliged 
 to take into consideration the many processes interweaving 
 with many others, which are again dependent upon their own 
 peculiar conditions and upon agents, acting each in its own 
 peculiar manner, and according to its own peculiar laws, we 
 
78 METHODS OF INVESTIGATION IN 
 
 must remember that the same principle in essentials, runs 
 through the laws which influence the whole external world. 
 
 We are encountered, in inanimate nature, by enough of this 
 complexity and intricacy. The physical, and still more the 
 chemical, phenomena and processes are by no means immutably 
 the same, even in our solar system. But the elements with 
 the phenomena and properties of which physics and chemistry 
 have to deal are, in a comparative sense, infinitely more simple 
 and, for a given time, more stable than the living organism. 
 They admit, therefore, of a more direct and adequate observa- 
 tion by individuals, and do not require to be observed so fre- 
 quently and under such manifold varieties of circumstances. 
 The mechanical properties or forces of these substances are 
 constant, e. g., weight, extension, elasticity, &c., and if a cer- 
 tain result or phenomenon is produced by a variety of entirely 
 different forces, or rather, if certain substances have seemed to 
 coalesce and appeared to act in different directions and accord- 
 ing to different laws, each substance has none the less acted 
 for itself, each of its effects has occurred by its own unchange- 
 able laws, and the whole result, or total effect, is only the sum 
 of the individual effects taken together. Even if, in some 
 cases, the mutual limitation or suppression of individual effects 
 has produced various modifications of the total result, or given, 
 as it were, a medium result, the physicist will be the better 
 able to comprehend their conditions and mode of occurrence, 
 from the fact of his having previously determined their indivi- 
 dual laws more or less precisely. With the chemist it is some- 
 what different, for even with respect to inorganic substances, 
 the processes he has to attend to are not only much more nu- 
 merous, complicated, and variable in themselves, but become 
 so in an especial manner, from the fact that when two or more 
 substances come together under favorable circumstances, no 
 mere addition of the one to the other, but rather a new deve- 
 lopment, with peculiar properties and effects, is produced. 
 These chemical processes bear a much closer resemblance to 
 those of the living body than do physico-mechanical processes, 
 and their determination is therefore a more difficult task. But 
 if, by the combination of oxygen with hydrogen, of an acid 
 with an alkali, or of a salt-radicle such as chlorine or iodine 
 with a so-called base, an entirely new substance is produced. 
 
THE STUDY OF NATURAL HISTORY. 79 
 
 its properties, though indeed new and peculiar, will be found to 
 be no less constant than they were in the more simple elements, 
 and, like them, may be accurately tested and determined. 
 
 "We may thus safely assume that the phenomena and processes 
 with which the physicist or chemist has to deal, are more 
 simple — that they occur under less complicated circumstances, 
 and under the influence of less numerous agents, than those of 
 the living body. They change also and oscUlate within more 
 confined limits, and even these oscillations and modifications 
 often recur with a certain regularity (e. g., the motion of the 
 heavenly bodies, the hours and seasons, the weather, &c.) whence 
 it is easier to determine these oscillations and variations, both 
 as to their order and their extent, by antecedent or simulta- 
 neous circumstances. It must also not be forgotten that both 
 the chemist and the physicist are able to produce artificially, 
 and at will, by far the greater number of their phenomena and 
 processes, and thus to place them in the circumstances most 
 favorable for the investigation of their conditions or efifects. 
 The physician, and especially the pathologist, must confine 
 himself to the investigation of life as it is presented to him. 
 The physiologist, on the other hand, is more favorably situated, 
 inasmuch as the phenomena and processes with which he has 
 to deal, are less complicated, numerous, and variable, and are 
 thus better adapted for investigation. Above all, he can ad- 
 vance more directly by the aid of experiment, and though he 
 cannot indeed produce life, he can, in some degree, vary its 
 conditions. 
 
 The particular disadvantage, however, under which both 
 labour, is the circumstance that they are not able, like the 
 physicist and chemist, so to isolate the manifold phenomena, 
 processes, and functions of the living body, as to remove any 
 one of them from the magic circle of the whole, without de- 
 ranging or arresting the entire machinery. We are unable, 
 for example, to place the lungs, the alimentary canal, the liver, 
 the brain, the process of respiration or digestion, the circula- 
 tion, &c., so as to observe the several occurrences in them singly, 
 nor can we submit them to such changes and influences as may 
 enable us to determine the conditions of their development and 
 action, and to observe in what manner their whole series of 
 occurrences conform to each other. Both physiologists and 
 
80 METHODS OF INVESTIGATION IN 
 
 pathologists, but especially the latter, are thus forced to em- 
 brace the living organism as a whole in their observation, and 
 when an experiment is made upon it by the former, the changes 
 in phenomena or processes which occur — the effects produced 
 — follow the same order, and are in essential agreement with 
 the same laws of the vital phenomena which are the subject of 
 our inquiry. In every experiment we must include most, if 
 not all the vital processes, and we must therefore take into 
 account a complicated whole in its possible variations resulting 
 from certain influences. It is therefore difBcult to ascertain 
 and precisely appreciate either the mechanism of an individual 
 process, or the changes produced in it by the different external 
 and internal circumstances which affect it. Equally difficult 
 is it to withdraw the living body for any considerable period of 
 time from the action of these other influences for the purpose 
 of investigating separately their mode of action upon each of 
 its different processes because, as in the case of the air, tempe- 
 rature, light, aliment, (and this holds good also of certain re- 
 medies), it can only exist by the co-operation of them all. 
 
 We thus see how rarely, in our branch of science, it happens 
 that an individual influence or cause, or still more, an indivi- 
 dual effect, presents itself for observation in an isolated form, 
 in such a manner as enables us to view the cause in imme- 
 diate connection with its effects for the time being, or the effect 
 with its causes. 
 
 A more comprehensive sketch of the field of study on which 
 we have entered, and its peculiarities, can only be given in con- 
 nection with the necessary methods of investigation. What 
 has been already said, may be enough to show that while the 
 investigator of what we call inanimate nature may be said to 
 be comparatively master of his field, in ours we may rather be 
 regarded as slaves, necessitated, for the most part, to struggle 
 on as best we may, along the course of the ever-moving and 
 almost unfathomable stream of life. The physicist and chemist 
 can dive more easily into the depths of the great stream of 
 their inquiry — they may even divide it into smaller streams — 
 they can put tKeir questions in a more definite form, and ex- 
 tract, by observation or experiment, clearer answers from each 
 separate fact which they have already seized. And where they 
 
THE STUDY OF NATURAL HISTORY. 81 
 
 have been least able to effect this as, for instance, in meteoro- 
 logical and many chemical processes, or throughout the whole 
 field of climatology and geognosy, or in the study of heat and 
 of the electric and magnetic phenomena, they have been unable 
 to demonstrate any constant connection between causes and 
 effects, any positive regularity or so-called laws. Yet even in 
 this field of study they have advanced to the permanent occu- 
 pation of positions of importance from whence they may safely 
 advance further. 
 
 The department of medicine rather approaches that of the 
 psychologist, the moralist, the teacher, the historian, or the 
 statesman, who, like us, have to deal with the most complica- 
 ted phenomena and processes, with an aggregate of causes 
 and effects, without being able to produce these phenomena, 
 artificially, or to take to pieces and manipulate what they meet 
 with in nature and reality. And thus these inquirers have, 
 like ourselves, been unable taarrive at a clear insight into the 
 causal connection of the phenomena before them, or at the es- 
 tablishment of any fixed laws, though they have adopted many 
 views, hypotheses, and theories, concerning which, like ourselves, 
 they are daily at issue. 
 
 Like ourselves too, they are liable to be led astray in their 
 artificial processes and rules, both by calculation and by con- 
 jecture, because their whole system of observation and investi- 
 gation contains, like our own, but too many sources of error. 
 
SECTION III. 
 
 ON THE PROCESS OF INDUCTION PROPERLY SO CALLED, OR THE 
 SEARCH, BY IMMEDIATE OBSERVATION, INTO THE CAUSAL 
 CONNECTION AND LAWS OF THE PHENOMENA AND PROCESSES 
 WITH WHICH WE HAVE TO DO. AN INQUIRY INTO THE SIMPLE 
 METHOD OF EXPERIMENT AND INTO THE INDIVIDUAL STEPS 
 AND MEANS BY WHICH IT MAY BE FACILITATED. 
 
 In the foregoing section we Lave considered in their more 
 general aspect the possibilities and difficulties of investigation 
 and the claims of the facts with which it has to deal. Our 
 present object is a far more important one, viz., to examine in 
 detail the several aids to investigation, more particularly those 
 which offer themselves as it were spontaneously, and which, 
 since their claims to attention received so powerful an impulse 
 from Bacon, have generally been first employed in the investi- 
 gation of nature. 
 
 Our scientific task consists, as has been already stated, in 
 endeavouring, as the physicist and the chemist have done in 
 their peculiar departments, to demonstrate the causal connec- 
 tion, or the conditions and conformity to fixed laws, of every- 
 thing which occurs in the living body, whether in a state of 
 health or disease. It is incumbent on us not only to seek to 
 determine everj'thing which occurs in' the functions and pro- 
 cesses of the body, and to show ■<vherein these processes consist, 
 hut also to discover their mutual affinities and relations to each 
 other and to the various external influences, and to ascertain how 
 far such known relations bear us out in regarding certain of them 
 as dependent upon certain others. It is evident, however, that 
 we must here confine ourselves to what we are able to learn 
 through exact observation and examination of things as they 
 really exist; an existence and reality which must, whether it 
 be in the case of the liviug body, or in the external world, (in 
 which, and by the co-operation of which, the body lives), alike 
 be established by experiment. 
 
INDUCTIVE PROCESS. 83 
 
 We have already learnt enough to know that we can only 
 attain our ohject — 
 
 I. By confining ourselves to individual phenomena and 
 groups of phenomena in the living body, i. e., to its functions 
 in health and disease, and — 
 
 II. By observing all those phenomena and circumstances 
 of the external world with which the processes in question, in 
 our body, are in constant natural relation, and under the in- 
 fluence of which we observe them to occur. 
 
 III. It must also be our aim to determine by observation 
 which of these phenomena and processes in the living body 
 constantly occur simultaneously or consecutively, and in what 
 constant order — in short, under what external and internal in- 
 fluences and circumstances a given occurrence or phenomenon 
 invariably presents itself to our observation. Having once 
 succeeded in the latter attempt, we might, under favorable 
 circumstances, and with the reservation of certain precau- 
 tionary measures, regard what had been demonstrated as the 
 invariable forerunner or concomitant of the phenomenon or 
 process in question, as its condition or cause. 
 
 And through this discovery of the causal connection and 
 conformity of these phenomena and processes we might look 
 upon our problem as solved. Yet if we proceed to the obser- 
 vation of those phenomena, &c., with this intention we shall 
 soon find that we cannot possibly hope to attain our object by 
 such means alone. We find before us a chaos of all possible 
 kinds of phenomena, all presenting themselves simultaneously, 
 and ofl'ering, at the outset, an inextricable confusion. Every 
 one who observes a sick person for the first time, feels confused 
 by the mass of phenomena, of so-called symptoms of disease, 
 which offer themselves to his observation simultaneously and, 
 apparently at least, without order and internal connection, 
 sometimes in one form, sometimes in another. Every attempt 
 to arrive by simple observation at a correct and methodical 
 conception of all those phenomena, and still more at a know- 
 ledge of their relations to each other, or to understand 
 which of them are to be classed together, and which con- 
 stantly occur together, appears vain. To prepare the way for 
 such an insight we must, first of all, group, and be able to 
 place side by side those which belong to a certain series — to 
 
84 PROBLEMS AND PERFORMANCE 
 
 bring them into connection with each other — in short, to efifect 
 a certain regularity in this apparent confusion. Fortunately, 
 nature herself renders us this first service, for we actually find 
 in this stream of phenomena and events, a certain arrangement 
 which we are able to recognize without much difficulty. Many 
 of them are connected with each other, and always occur si- 
 multaneously because they aid, and in fact are necessary to, 
 each other in producing some process or event which could 
 not be developed without their co-operation. 
 
 They thus present a certain ensemble, or assemblage of phe- 
 nomena, always — with comparatively slight deviations — to be 
 met with, each of which may be recognized and distinguished 
 from its fellows, with which, as does each individual wheel in 
 the works of a watch, it is used to work separately yet in con- 
 cert. Among such, we may place the individual functions or 
 processes of the living body, (as they result from the co-opera- 
 tion of its respective organs), such as digestion, respiration, 
 circulation, the various processes of excretion, motion, sensa- 
 tion, &c. We establish a certain order in all the phenomena 
 (symptoms) in the sick under our observations so soon as we 
 are able to refer them to these different functions, organs, &c., 
 and view them as what they really are, namely, simple change 
 'or derangements of those functions. In a similar sense, every- 
 thing which we observe in external nature, e. g., the atmos- 
 phere and the weather, heat, light, and electric phenomena, 
 earth and sea, solid and liquid food, presents certain connected 
 unities or collections of phenomena. 
 
 By keeping our attention, in the first instan'ce, steadily fixed 
 upon these, and by considering them, in their various stages, 
 just as they present themselves to view, we at once put our- 
 selves in possession of important data, and obtain materials 
 which the mind can further employ in its investigation of cause 
 and effect, and in tracing the conformity of, these phenomena 
 and influences. We should therefore observe more closely, 
 in all their details, the phenomena and processes in a given 
 function, or disease, &c., and compare them with such as we 
 recognize in other cases more or less similar; and thus seek to 
 determine the circumstances under which a given phenomenon 
 or process occurs. 
 
 Up to a certain point, all this is facilitated by the circum- 
 
OF THE INDUCTIVE PROCESS. 85 
 
 stance that many of those series of phenomena present a 
 regular and more or less constant course from beginning to 
 end, — as in the development of an organism, the formation of 
 its individual parts, as well as many acute, so-called epidemic, 
 or contagious diseases. Here, as in the former case, groups of 
 certain peculiar phenomena present themselves, in a more or 
 less striking form, to our observation, enabling us to distinguish 
 and recognize them with readiness. They also present them- 
 selves in a certain cycle, which remains essentially the same in 
 all cases of the same kind. In the same patient, the same 
 series of phenomena often recurs with regular periodicity, — 
 as, for instance, the exacerbation of continued, and, still more 
 strikingly, of intermittent, fever. We may quote, as analogous 
 facts, the recurrence of sleep or waking ; a certain state of the 
 weather in the different seasons ; the ebb and flow of the ocean ; 
 and the strictly periodical occurrence of all the meteorological 
 processes in the tropics. And since the latter have excited much 
 more attention in tropical countries than with us, so also have 
 those countries been the nursery of meteorological studies, just 
 as those fevers, and other acute diseases, have been the nursery 
 of the doctrines and theories we have arrived at concerning them. 
 But, with all this, we gain no insight into the proper causal 
 connection of these phenomena and processes, or into the con- 
 ditions of their development; in other words, we have yet to 
 understand them. Certain causal connections are, it is true, 
 so obvious, that the simplest experience may guide us to them : 
 we are not slow in learning that our respiration is dependent 
 upon atmospheric air, our nutrition upon the supply of certain 
 substances, our capability of seeing upon light, &c. In a 
 similar manner, simple experience has shown certain circum- 
 stances and influences to be the causes of many diseases, — as, 
 e. g., exposure to cold, errors of diet, miasmata, poison, the 
 virus of syphilis or smallpox, and the like. Simple experience 
 has also enabled us to assert, that certain drugs furnish the 
 conditions of numerous cures, — as, e.g., cinchona and iodine, 
 — just as we have learned to recognize the frost of winter as 
 the cause of the formation of snow and ice, the heat of summer 
 as the cause of thunderstorms, or of the development of vege- 
 table life. But we are as far as ever from being able to explain 
 the origin of these effects. Here, as elsewhere, observation 
 
86 PROBLEMS AND PERFORMANCE 
 
 only tells us that certain phenomena or processes occur 
 simultaneously with a certain event, or immediately follow 
 upon some other event or influence. 
 
 It cannot tell us how these phenomena actually occur, nor 
 yet how they are internally connected ; neither does it enable 
 us to bring all the phenomena and processes which we have 
 observed, whether as occurring simultaneously or consecutively, 
 into their exact relations to each other, and to say which of 
 them has played the part of cause, which of effect. The most 
 dissimilar things are here occurring at the same moment, even 
 in each individual function, as well as in each of the agents 
 which affect it from without, and perhaps help to modify its 
 condition. Many other influences, both from without and 
 from within, affect those processes ; which influences are con- 
 nected with, and perhaps mutually modify, each other. 
 
 Suppose we wished to investigate the process of respiration, 
 and to determine, by simple observation, what really occurs in 
 it, and what are the circumstances and influences upon which 
 it may depend. We should find that respiration is the effect, 
 or result, of numerous processes acting in concert (e. g., respira- 
 tory movements, inspiration and expiration of certain materials 
 in a gaseous form, certain changes in the blood), and, also, 
 that many other processes in the living body, being more or 
 less closely connected with these processes [e.g., circulation 
 through bodies like the lungs, the process of excretion by the 
 skin, kidneys, &c,), help to modify their general result in the 
 act of respiration. 
 
 And, among the external influences which obviously affect 
 respiration, we may remark, that the atmosphere, with its 
 composition, density, &c., is intimately connected with many 
 entirely different processes, — e.g., with the circulation, with 
 excretion by skin and kidneys, and with innervation. The 
 same truth applies to every form of disease, and to each event 
 or symptom that occurs in it, as well as to its origin and cure. 
 Phenomena and processes the most dissimilar,/ yet, at the same 
 time, connected with and modifying each other, present them- 
 selves simultaneously to our observation; and these, in their 
 turn, have been preceded by the most varied circumstances 
 and influences, which have themselves possibly helped to modify 
 the origin and cure of sucli disease. 
 
OF THE INDUCTIVE PROCESS. 87 
 
 It is thus clear, at the first glance, that we cannot hope, by 
 the simple observation of these phenomena and occurrences, of 
 these causes and effects so constantly connected with each 
 other, to obtain an insight into the actual processes in them, 
 or to ascertain which of them are modified by, and which 
 modify others. All this would be a comparatively easy 
 matter, if we could — as has been already explained — observe 
 each process in the natural course of things, separately, and 
 under various circumstances; if we were able to test each 
 phenomenon, each efi^ect, as well as each active and modifying 
 influence which more particularly interests us, in isolation from 
 the rest J to produce this or that modification in them, and then 
 to observe all the occurrences resulting from it. Thus, the 
 chemist can separate his compounds into their individual com- 
 ponent parts, and examine these as to their properties and their 
 behaviour towards other substances. He can even reconstruct 
 from these elements many of his most complicated compounds ; 
 and approach, by direct investigation, nearer to the compre- 
 hension of his processes, &c., and their conformity to fixed 
 laws, than is possible in the investigation of animated nature. 
 
 If we cannot place our phenomena and processes separately 
 before us, and examine each of them by itself; if we must (as 
 was assumed in the induction, properly so called, from our 
 observation of the natural state of things) confine ourselves to 
 the observation of these under their obvious aspect, but one 
 method remains to us for the proximate attainment of our end. 
 We must first of all picture to our mental eye those groups of 
 phenomena, Sec. as separated into their individual component 
 parts, and form a notion of the latter in an isolated state. In 
 other words, our first task consists in seeing, in the aggregate 
 of vital phenomena, &c., not so much the whole, as its indivi- 
 dual parts and elements, e. g. the individual phenomena and 
 processes which constitute a given function, or an entire 
 disease. We must further consider the individual circum- 
 stances of the great and complex agencies of the external 
 world (e. g. the atmosphere, climate, food), by which they may 
 be affected. And since these elements never present them- 
 selves to our observation under a single and individual aspect, 
 we must the more earnestly endeavour to form an abstract 
 notion of them, and represent them to our minds in a possible 
 
88 PROBLEMS AND PEEFORMANCE 
 
 and probable existence. To seek for them in earnest is to 
 demonstrate their existence from the establishment, on each 
 occasion, of their phenomena, properties, effects, &c. And 
 before we can ascertain and demonstrate certain circumstances 
 to be the determining causes of certain other processes and 
 phenomena of the living body, we must assume the fact of 
 their possible connection and mutual relationship, and then 
 proceed with our investigation in that .direction. 
 
 The true importance of hypothesis and surmise, in fact, of 
 our whole subjective position and interference, is to be found 
 in this first necessary step of investigation. We are apt to 
 err in the analysis of our phenomena, processes, and agencies, 
 and still more in our appreciation of the importance, action, or 
 conditions, of the individual elements, from our acknowledged 
 inability to isolate anything, and to submit it to direct exami- 
 nation, without the intervention of our ego. The more genius 
 and scientific speculation any one brings to this task, the 
 easier he will find this first step, and the more he is supported 
 by positive knowledge, and acquaintance with the subject, the 
 better he will succeed in it. For his surmises or views will 
 the more readily coincide with the natural state of things, and 
 he will be able to choose more consistently appropriate methods 
 of investigation, and to seize upon the points of his subject 
 best calculated to lead to the discovery of truth. 
 
 Having watched over our phenomena and processes until, 
 through surmise, observation, and analogy, we have been able to 
 gather them together, and build them up into a certain unity, 
 we have next to investigate the secret of their connection with 
 each other. The question is, therefore, how, amongst all those 
 elements and individual phenomena, or processes, our observa- 
 tion may best discover which of them depend upon, and which 
 of them modify, each other. We must seek, amongst the 
 mass of phenomena and processes, to ascertain the effects of 
 an individual determining circumstance, or the conditions and 
 causes of an individual occurrence, or effect, and then demon- 
 strate from experience this connection between them. 
 
 There are evidently two modes of proceeding in our investi- 
 gations. We may either confine ourselves to the phenomena 
 and occurrences in question as they present themselves to our 
 
OF THE INDUCTIVE PROCESS. 89 
 
 observation, as the complicated results of certain others (i. e. 
 of certain conditions and agents), and direct our investigation 
 to a so-called function, or to a disease, and to the individual 
 phenomena or processes which accompany it ; or we may seek 
 to acquire a clear comprehension of the circumstances and 
 influences which we regard as the probable conditions of a 
 certain occurrence or phenomenon. Our investigation is, 
 according to the latter method, directed to the determination 
 of the individual relations, or circumstances, by the influence 
 and co-operation of which we see a function, a disease, 
 or a cure commence and proceed. In the former case we 
 examine by what circumstances and influences a given event, 
 or process (e. g. respiration, diarrhoea, narcosis) is eficcted ; in 
 the latter, on the contrary, we examine what phenomena, 
 what effects, a given circumstance, or influence (e. g. atmos- 
 pheric air, an error in diet, poison) may produce. While, in 
 the former case, the subject is attacked as it were a posteriori, 
 in relation to effects, in the latter it is attacked a priori, in 
 relation to causes. 
 
 The former method leads us, first of all, to observe the 
 manifold circumstances under which the phenomenon, or occur- 
 rence in question, presents itself, e. g. respiratTon, or the excre- 
 tion of carbonic acid, the concomitant generation of heat, the 
 various phenomena of sensation and muscular irritability; in 
 like manner, that which we call inflammation, or its individual 
 phenomena and gvents, e. g. increase of temperature in the 
 part itself, the occurrence of exudations, or the formation of a 
 crust, &c., with their spontaneous changes in the course of 
 the disease, or after the employment of certain remedies. We 
 have further to observe these phenomena and occurrences 
 under other circumstances, to submit them to certain influ- 
 ences, and to determine the changes or modifications produced 
 by these, that we may ascertain to which of them they stand 
 in a constant dependent relation. We may thus hope to 
 ascertain, under favorable circumstances, the conditions upon 
 which we are justified in considering them dependent. 
 
 In the latter method we have to observe, first of all, the 
 phenomena and occurrences, with their possible changes, as 
 they arise during and after the operation of a certain circum- 
 stance, or influence ; we have to observe, e. g. all the occur- 
 
90 PROBLEMS AND PERFORMANCE 
 
 rences and changes produced by the inspiration of atmospheric 
 air and of various other gases in the lungs themselves, in the 
 composition and circulation of the blood, in the generation of 
 heat, or in certain excretions. We must also observe all the 
 changes or modifications which take place in vital processes 
 and phenomena through the operation of cold and heat, or 
 through the ingestion of a known aliment, or drug. We must 
 submit the various processes or functions of the living body to 
 the influence of one identical agent, under manifold circum- 
 stances, and observe the modifications produced by it. Under 
 favorable circumstances, we may now bring the incident, or 
 influence in question into causal connection with some or other 
 of those phenomena and occurrences, and may regard it, to a 
 certain extent, as the cause or condition of the latter, and 
 thus ascertain the eff'ects which it is capable of producing. 
 
 A few examples may serve to make our mode of advance by 
 either of these methods more intelligible. 
 
 It had been observed that the blood which returns from the 
 lungs to the heart has a brighter colour, and is in a diff'erent 
 state from that which passed from the heart to the lungs. It 
 was also in course of time conjectured that such change in the 
 blood must depetd upon certain processes in the lungs, espe- 
 cially upon the inspiration of oxygen. For the determination 
 of the connection between these two processes we had, first of 
 all, to ascertain in what these changes in the blood itself 
 consist. We had further to observe the dark venous blood 
 under the most varied circumstances, to submit it to the 
 operation of various gases, &c., and to test whether the changes 
 it underwent under such influences were kindred to those 
 which occur in the lungs in respiration. Should these changes 
 occur only after the action of oxygen, we might regard that 
 gas as being the most important agent in eff'ecting those 
 changes in the blood in respiration. We might, however, 
 have attained the same knowledge if, in our experiment with 
 oxygen, we had — whether by a fortunate accident, or by a 
 happy surmise, as to the peculiar conditions of those pheno- 
 mena — caused it to be inspired, or submitted venous blood, 
 drawn from the body, to its action. In like manner the fact 
 that lead may produce certain diseases, as colic, paralysis, &c., 
 might have been discovered during an investigation into the 
 
OF THE INDUCTIVE PEOCESS. 91 
 
 state of health of certain workmen in manufactories, foundries, 
 &c., or from an examination into lead compounds and their 
 action upon men or animals. 
 
 Each method would thus lead us to the same point, just as 
 the discoverer of gunpowder might have ascertained its com- 
 position and effects during an examination of the phenomena 
 of explosion and combustion, and their conditions, or during 
 experiments with certain explosive or combustible compounds. 
 In both cases the same circumstance would have enabled us 
 to recognize the conditions and necessary occurrence of a 
 certain phenomenon, or effect, namely, the circumstance that 
 we constantly saw a certain something precede or accompany 
 the latter, and that in such a manner as to justify us in 
 regarding it as its cause. And we might do this the more 
 safely as we had the earlier succeeded in observing the effect 
 o£ a given circumstance distinct from other phenomena or 
 effects, and the cause in question distinct from other modifying 
 circumstances and conditions. Our main object would thus 
 be to discover such cases in nature, or to produce them 
 artificially. 
 
 We must also admit that we have only two means of 
 ascertaining the causal connection of natural phenomena and 
 processes. 
 
 1. The observation of everything which we meet with in 
 nature, both within the living body and external to it ; with a 
 careful review of all the varying circumstances and incidents in 
 the case before us. 
 
 3. Experiment, — i. e., the artificial production of those cir- 
 cumstances under which we can best investigate the effect or 
 cause in question, in relation to their conditions, operation, and 
 causal connection. 
 
 We shall sometimes, according to circumstances, have occasion 
 to employ the one, sometimes the other, of these methods. In 
 many cases, the choice does not lie with us ; and, in all cases, 
 the two methods have practically a very unequal value, since it 
 is to experiment, almost exclusively, that we are indebted for 
 the means of observing our phenomena, — e.g., a function, or a 
 disease, — or the manifold influences which affect them, under 
 such varied and changing circumstancgs, that we can draw any 
 conclusion concerning their connection with each other, or 
 
93 PROBLEMS AND PEEFORMANCE 
 
 concerning the conditions of their development and operation. 
 We seldom, if ever, find in nature such a multiplicity of cir- 
 cumstances, or such a degree of clearness in them, and, 
 especially, such an isolation of the occurrence or influence in 
 question from others, as would enable us to draw from the 
 simple observation of the natural course of things a definite 
 conclusion concerning cause and effect. 
 
 It depends, in like manner, upon the peculiarities of a given 
 case, whether we have to proceed to the investigation of the 
 occurrence or phenomenon in question, and of its possible con- 
 ditions, or, inversely, to that of the influence or condition in 
 question, and of its possible effects. Here, also, we frequently 
 have no choice. But, since it is infinitely more simple, and 
 at the same time more safe, to ascertain the possible effects of 
 a cause, or of a given circumstance, than to proceed inversely 
 and seek for the possible conditions and causes of an occurrence, 
 or of a given effect, — especially under such complicated circum- 
 stances as we have to deal with, — we must always begin with 
 the former whenever it is possible for us to do so. 
 
 In the employment of both methods, we receive important 
 assistance in our investigations from certain auxiliary processes. 
 And difficult, or even impossible, as it may be to arrive, by the 
 observation of groups of pheaomena, as such, at a comprehension 
 of their causal connection and conformity, we may frequently, 
 however, obtain thereby certain formulae, and a knowledge of 
 certain facts; and thus, at the worst, acquire some compen- 
 sation for our failure in obtaining a more complete insight 
 into them. 
 
 These auxiliary processes in our investigations are the fol- 
 lowing : 
 
 1. The observation of the phenomena in question 
 under the greatest possible variety of circumstances 
 and relations. 
 
 Varying the circumstances. — Though we are not in a position 
 to investigate separately the processes in the living body,' and 
 the aggregate of all the influences of the external world which 
 affect them, we can yet frequently observe certain of them under 
 circumstances which afford us approximately correct information 
 concerning their causal connection. Our acquaintance with a 
 
OF THE INDUCTIVE PROCESS, 93 
 
 previously unknown phenomenon will approach the more nearly 
 to a comprehension of it, the more manifold the circumstances 
 have, in the course of time, become, under which we have been 
 able to observe such phenomenon, &c. 
 
 It is experiment, as has been already stated, which is here 
 indispensably necessary to us. 
 
 Do we wish to obtain a clearer notion of the influence of a 
 given agent of the external world upon certain processes in the 
 living body, by the aid of experiment, we can modify it in this 
 or that manner ; we can increase or decrease the intensity of 
 its action, — its quantity, — and can observe whether the corre- 
 sponding changes do or do not occur in those processes and 
 functions which we conjectured would be influenced by the 
 agent in question. If the former is constantly the case, the 
 probability of such a relation increases; and we may now 
 regard such process in the living body as dependent upon that 
 influence, — as directly or indirectly produced by it. If we 
 wish, e. g., to investigate the connection between the tempera- 
 ture of the atmosphere and that of our own bodies, or a certain 
 excretory process, or the origin of a disease, we may raise or 
 lower the temperature in a closed space, and allow it to act 
 for a longer or shorter time, and observe the possible changes 
 in the temperature of our own bodies, or in the excretions of 
 the skin, lungs, kidneys, &c. 
 
 If we are restricted, as is often the case, to the observation 
 of that which presents itself in nature, similar variations not 
 unfrequently occur in the natural course of things ; and while 
 we see what occurs under these altered circumstances^ what 
 changes, e.g., have taken place in the processes of the living 
 body, we may infer a certain connection between them. In 
 a study like ours, in which we cannot produce the individual 
 phenomena and processes, and are equally unable to isolate 
 them, or to bring them into contact with entirely distinct 
 external influences, one of the most important objects in the 
 investigation of nature is to observe them under the greatest 
 possible variety of circumstances, before we venture upon a 
 conjecture as to their causal connection. 
 
 This is facilitated by a comparative examination of the func- 
 tions in the various series of living organisms, and at diflferent 
 periods of development and age in the same organism. In 
 
94 PROBLEMS AND PERFORMANCE 
 
 like manner, the influence of the atmosphere and of its tem- 
 perature, moisture, composition, &c., will become more intelli- 
 gible in proportion as we investigate and understand better 
 the influence exerted by such agents over the human body and 
 over the vital processes connected with its well being. We 
 shall observe how these are affected by climate, situation, 
 seasons, hours of the day or night, &c. Diseases themselves 
 are but similar " variations of the circumstances" which nature 
 offers us, i. e., definite changes in the natural processes of the 
 body, occurring and arranging themselves in this or that manner 
 under certain circumstances. While we make it our study to 
 compare with each other the greatest possible number of 
 similar cases, with all the concomitant circumstances, in rela- 
 tion to the similarity of their occurrence and general appear- 
 ance; while we examine in what points they do or do not 
 agree, we acquire a certain notion of the probable conditions 
 of some or other of these phenomena. If, in doing this, we 
 discover that certain events {e,ff., a disease, or an individual 
 derangement during its course) proceed in the degree of their 
 development, intensity, or frequency, in direct progression with 
 some particular occurrence or circumstance, external or internal, 
 and observe that it guides their increase or diminution, we 
 may conclude that these stand in a certain relation to each 
 other and, if not in that of cause and effect, we may assume that 
 they are each the common effect of another deeper seated cause. 
 Simple experience has taught us that the life and health of 
 man are always, in a certain degree, regulated according to 
 the cy-cumstances of his outward condition, such as the quality 
 of his food, the scale of his comforts, and the climate and cul- 
 tivation of the country he lives in.- We have observed this in 
 the natural variation of the circumstances with which the 
 course of the world presents us, i. e., in a comparison of these 
 events under the different modes of life of certain classes 
 of men. We do not yet know, it is true, what the precise 
 cause of those effects may be and what part each individual 
 influence may play, but we know that those circumstances 
 conjointly have conduced to the development of such effects. 
 The same thing holds good with respect to the discovery of 
 the relations between structural changes in certain organs of 
 the body, or chemical changes in the blood, or between certain 
 
OF THE INDUCTIVE PROCESS. 95 
 
 excretory processes, fee, and the given disease considered as a 
 whole. 
 
 We can, however, much more positively bring certain phe- 
 nomena, occurrences, and circumstfinces, into causal connection 
 with each other, if we observe the same phenomenon, the same 
 modification of an occurrence to take place whenever a certain 
 circumstance, or a definite modification of any influence, or of 
 an external or internal agent, occurs — whenever, in short, a 
 certain sequent always follows a certain antecedent in all the 
 cases observed by us. Thus -we find coloured races only in 
 hol^, never in temperate climates, and when the inhabitants of 
 the latter migrate to the former they gradually approximate 
 more and more to the condition of the natives. We infer 
 from this, with tolerable certainty, the causal connection be- 
 tween these climates and the peculiar colour of their inhabi- 
 tants. We might make this inference with much more cer- 
 tainty, if we could prove that the influences to which the 
 inhabitants of those different climates are subjected are pre- 
 cisely similar in all other respects, and that situation and 
 temperature are the only points in which they essentially 
 differ. In a comparison of all the countries and neighbour- 
 hoods in which intermittent fever has been observed as an 
 endemic disease it has been found that, however much they 
 may differ in other respects, they all agree in the circumstance 
 that stagnant waters and marshes, or organic matter in a state 
 of conversion or fermentation, detritus of various kinds, and 
 the like, are met with in them. We are therefore justified in 
 the inference that intermittent fever and the above-named cir- 
 cumstance stand in some relation to each other. And because 
 it has been found further, that the number of persons attacked 
 by that disease, and the mortality, even in the same, neigh- 
 bourhood, correspond more or less in different seasons and 
 years, and even in different parts of the same city, (e. g., of 
 Rome), to the presence and extent of such marsh land, &c., the 
 probablity of such a relation is increased. For, so far as we 
 have been able to ascertain, these seasons, years, and different 
 parts of the same city, differ in no other essential circumstance 
 or influence from each other, except in the presence or ab- 
 sence, the greater or less extent and propinquity of such marsh 
 land, &c. 
 
96 PROBLEMS AND PERFORMANCE 
 
 This last method of observation, namely, that of " exclusion," 
 is of the greatest importance in our department of science. 
 We compare in it numerous cases, or series of cases, with each 
 other, which, being alike in other respects, differ only in this — 
 that the phenomenon, or event whose conditions we are seeking, 
 occurs in certain of them and not in the others. If we suc- 
 ceed in ascertaining the constant existence of a circumstance 
 (e. g. malaria), in one series, which is as constantly absent in 
 the other series, we may infer with certainty that this parti- 
 cular circumstance is the condition, or at least an essential 
 element amongst the conditions, of that event (e. g. of inter- 
 mittent fever). If we wished to ascertain the functions of an 
 organ such as the spleen, or liver, in the living body, the 
 simple removal of it would be a direct application of the 
 method of " exclusion." If animals recovered from the imme- 
 diate effects of the operation, and we afterwards observed 
 certain constant alterations in some of the functions, &c., we 
 might regard such changes as resulting from the absence and 
 non-action of those organs. When we see several persons 
 taken ill in the same manner, after the same meal, we justly 
 suspect some particular dish to have been the cause, so soon as 
 we hear that one of the persons affected ate of that dish only, or 
 that another person escaped who had eaten of all the dishes 
 except the one in question. In an investigation of the cir- 
 cumstances which might produce the unusual liability of the 
 inhabitants of certain neighbourhoods to bronchocele,. cretinism, 
 scrofula, &c., the large amount of earthy salts in the water of 
 some of those neighbourhoods was suspected of being the 
 essential condition of these phenomena. But since it was 
 found, upon accurate collation of evidence, that those dis- 
 eases are often absent in neighbourhoods where the water 
 contains the salts in question in the same quantity, and, also, 
 that in neighbourhoods whose water contains them, those 
 diseases are not endemic, this hypothesis was shown to be 
 false. 
 
 By the same method of " exclusion" we might elucidate the 
 influence of our remedies upon the course and cure of a disease. 
 Experience has long since taught us that persons suffering 
 from essentially the same disease, recover with the same fre- 
 quency and rapidity after the employment of the most various 
 
OF THE INDUCTIVE PROCESS. 97 
 
 remedies, which, so far as we know, do not possess the slightest 
 similarity in their properties, so that the positive influence of 
 those remedies upon the recovery of such persons may well 
 appear doubtful. But if it further appeared that, under similar 
 circumstances, they recovered just as rapidly and frequently if 
 no such remedies had been employed, the correctness of this 
 conjecture would be demonstrated. Several drugs have ob- 
 tained the reputation of substitutes for cinchona and quinine 
 in the treatment of intermittent fever, because many persons 
 have been observed to recover under the employment of them; 
 but further observation has shown that persons so affected 
 often recover with the same certainty and rapidity with no 
 other aid than that of good food and care in healthy hospitals, 
 so that the drugs in question may possibly have had no share 
 whatever in the cure. 
 
 II. Comparison of similab, phenomena, &c,, with each 
 other; employment op analogies. 
 
 Whenever we see any phenomenon, or object, and reflect 
 upon its nature, origin, &c., other more or less similar pheno- 
 mena and objects, of which we already possess some knowledge, 
 occur to our minds in connection with it. Those phenomena, 
 however, will occur to us most readily, which exhibit at the 
 first glance the greatest resemblance to those in question, 
 ■whether in their sensibly appreciable properties, or in rela- 
 tion to the circumstances of their occurrence and manner of 
 operation. When we see the effect of nitrate of silver upon 
 the skin, or narcosis produced by opium, we are, perhaps, 
 reminded, in the former case, of the effects of caustic potash, 
 sulphuric acid, or fire ; in the latter, of intoxication, or sleep. 
 If we see an individual suffering from pain in the chest, cough, 
 expectoration, other cases occur to us in which we had observed 
 essentially similar symptoms, or we recall descriptions of those 
 diseases which we had met with at some former period. We 
 now compare more minutely with each other the phenomena 
 in both series, and surmise the possibility that because they 
 correspond in certain points, they may also do so in several 
 others. This surmise will gain in probability as the points of 
 correspondence are proved to be more numerous and important, 
 and the more we are able to trace back these relations to a 
 common origin and nature, and to prove that the differences 
 
 7 
 
98 PROBLEMS AND PERFORMANCE 
 
 between them may be referred to comparatively subordinate, 
 or accidental circumstances and influences ; in short, the ana- 
 logy must gain in strength, in proportion to the constancy 
 with which the resemblances it has to deal with exhibit them- 
 selves, and will be further enhanced by such appearances being 
 strictly confined to the objects in question. 
 
 The foregoing instances will thus lead us to infer with added 
 certainty that there is a correspondence between corrosive, or 
 narcotic substances, both in their whole mode of action, and 
 in all their essential properties, so soon as we know that not 
 only the individual phenomena of their operation (in the 
 former case the visible changes in the corroded parts, in the 
 latter, stupefaction, tendency to sleep) are similar, but also that 
 the same similarity may be traced in the chemical character 
 of their components, and in the action of these on the tissues 
 and processes of the living body. The so-called anaesthetic 
 agents may now be regarded as analogous with greater fitness 
 than ever before, since it has been shown that they essentially 
 resemble each other, not only in their definite mode of action 
 upon men and animals, but also in their chemical composition. 
 For they all contain, so far as we know, carbon, and are more 
 or less complex combinations of that substance with hydrogen. 
 In like manner we might, from the analogy between so-called 
 acidity of the stomach, in many derangements of digestion, 
 and other acids, more justly infer that alkalies,. &c., which 
 neutralize the latter, would by virtue of their neutralizing 
 properties, also prove beneficial in that disease, so soon as we 
 could prove that the production of such acidity was a constant 
 and essential circumstance in those derangements, or, at least, 
 was intimately concerned in them. Something similar occurs 
 in the diagnosis of obscure diseases, e. g., of secondary syphilis ; 
 for the probability that, in a given patient, who presents, per- 
 haps, several contradictory symptoms, we have to deal precisely 
 with this, and not with any other disease, becomes greater the 
 more the number of those derangements and phenomena which 
 have been observed in other syphilitic patients increases in the 
 course of the disease. Thus, we can more readily make out 
 a writing in cypher or a difiBcult hand in proportion to the 
 number of signs or letters it may contain with which we are 
 already familiar. 
 
OF THE INDUCTIVE PROCESS. 99 
 
 The comparison of more or less analogous phenomena and 
 processes has facilitated our comprehensiou of individual fanc- 
 tions, as well as given us an insight into the nature of certain 
 diseases. Thus, we compared, in the former case, the pro- 
 cesses of respiration, of secretion or excretion by the skin, liver, 
 kidneys, &c., both with each other and with analogous processes 
 in plants ; aud acquired thereby an approximate notion, not 
 only of the actual occurrences in an individual function, but 
 also of their mutual action upon each other. In the latter 
 case, we compared with each other the phenomena and 
 certain anatomical or chemical changes in sick persons, and 
 constructed, from those which were common to certain indi- 
 viduals, the so-called forms or species of disease, and certain 
 groups of diseases, as perfectly as our existing knowledge of 
 those phenomena and processes permitted, or our idea of them 
 at the moment enabled us to do. The same thing will, in 
 the main point, hold good with respect to the employment of 
 various remedies. 
 
 Par more important is the question, how the use of such 
 analogies may be made to further our investigation into the 
 causal connection and conditions of our phenomena and pro- 
 cesses, or into the laws of the operation of various influences. 
 
 The practical value of such inquiries will be in proportion 
 to the fulness and exactness of our previous knowledge of the 
 phenomena and processes which analogy has to assist us in 
 comparing with each other. In the most unfavorable case, 
 however, even if the modes of origin and operation of those 
 things which we have placed side by side with certain others 
 are equally unknown to us with the latter, the mere act of 
 comparing them with each other may throw a light, if but in 
 the way of surmise, upon both, and enable us to pursue our 
 investigations at least in the track of probability. 
 
 In this, also, we have often in some degree succeeded. We 
 have long known, e. g., that sulphuric acid chars wood, linen, 
 &c., and corrodes the living tissues ; but since the great aflSnity 
 of sulphuric acid for water, and the formation of the latter 
 from the hydrogen and oxygen of those substances, has been 
 proved to be the essential circumstance or cause of the former 
 effect, the conclusion that its corrosive action upon organic 
 tissues depended upon the same cause lay near at hand. Early 
 
100 PROBLEMS AND PERFORMANCE 
 
 experience had shown, that, in persons who had been treated 
 with corrosive sublimate, this substance had entered, in common 
 with other preparations of mercury, deeply into the system ; 
 for the so-called constitutional, or general, effects were the 
 same j and the persons in question could even form an amalgam 
 upon the surface of gold coins, by bringing them into contact 
 with their skin. At a later period, it was found that certain 
 albuminous ingredients of the gastric juice are actively con- 
 cerned in the solution and digestion of food in the stomach ; 
 and, further, that corrosive sublimate enters into certain com- 
 binations with those albuminous matters in the stomach without 
 being decomposed by them, and that this, its combination with 
 a small quantity of albumen, is insoluble, but on the addition 
 of more albumen, becomes soluble, and finally passes into the 
 system. The observation of this fact led to the conclusion, 
 that the salts of silver, zinc, lead, &c., might behave essentially 
 in the same manner ; and this has been confirmed by investi- 
 gation. We had long known that bronchocele disappeared 
 under the employment of sponge, seaweed, wrack, and certain 
 mineral waters, before we could explain the cause. The only 
 analogy which could be discovered between such different 
 remedies was precisely this, their unexplained effect in that 
 disease. When iodine was found, at a later period, to be 
 present in sponge, &c., Coindet, in the comparison of those 
 effects, came to the conclusion, that this substance was the 
 cause common to them all ; and, from that moment, iodine 
 was employed with great success in the treatment of bron- 
 chocele. 
 
 It has already been intimated, that the comparison of several 
 series or kinds of phenomena, processes, &c., and the consequent 
 appreciation and employment of all their resemblances, forms 
 an indispensable starting-point for our whole process of 
 induction in the investigation of nature. The correct esti- 
 mation of analogies, giving rise, as it does, to surmises in 
 relation to the connection and conformity of various pheno- 
 mena and objects in certain essential points, has always been 
 a powerful stimulus to discovery. Discoveries have been 
 seldom, if ever, made in one attempt ; but it has usually 
 happened, that an occasional resemblance between previously 
 obscure and unintelligible phenomena, chancing to strike 
 
OF THE INDUCTIVE PROCESS. 101 
 
 forcibly on some individual mind, has led to a deeper and 
 more diligent investigation of such resemblance, until it has 
 become easy to trace them up to a root by which they hold in 
 common, and to show, through their various exhibitions, the 
 same essential circumstances, the same causal connection and 
 conformity. 
 
 Throughout the study of living nature, this attempt has 
 hitherto been less successful than in any other department of 
 science. Our employment of analogies may have led to a 
 certain approximate grouping together of such vital pheno- 
 mena, &c., as appear to agree in certain points, and perhaps 
 to the conjecture of a similarity in their mode of origin ; but 
 we have never obtained sure proof of their agreement in their 
 most essential circumstances and conditions, or a clear insight 
 into their causal connection. Nor could this well be other- 
 wise, because, in the application of such resemblances, or 
 analogies, to the determination of the essential agreement of 
 the things compared together, everything depends upon the 
 exact resemblance of their analogous points, and, consequently, 
 of the things themselves. We must, therefore, first of all, be 
 able to demonstrate that the circumstances, or points, which 
 are common to the phenomena compared and grouped 
 together by us, are, in fact, the essential and determining 
 ones : i. e., those upon which the other circumstances, pheno- 
 mena, or effects, of the obj'ects compared together by us 
 depend. But this pre-supposes a comprehension of the latter, 
 — at least of some of them, — which we do not, so far as con- 
 cerns the study of living nature, or of medicine, yet possess. 
 For this reason, no comparisons and analogies can, in them- 
 selves, render us any essential service in the comprehension of 
 our objects of study. 
 
 The simple confirmation, e. g., of the points in which two 
 or more phenomena and processes in a healthy or sick person 
 agree, is difficult enough where, as our actual case stands, we 
 are not in a position to observe them directly. In addition 
 to this, the things compare'd with each other by us (e. g., various 
 diseases or functions, the effects of certain hygienic influences, 
 or of remedies and poisons) never agree in all points with each 
 other. They may do so in several, and perhaps, in essential 
 points, but not in others. The correctness of our comparison 
 
102 PROBLEMS AND PERFOEMANCE 
 
 thus depends upon the relative value of the properties and phe- 
 nomena, upon which we have based it. We must have been 
 very fortunate if we have selected precisely the most important 
 and influential amongst them, and all guarantee for this is 
 generally wanting so long as the latter are themselves partly 
 or altogether unknown to us. We cannot even be certain 
 that we have observed all the phenomena, properties, effects, 
 &c., of the objects of our investigation. We are thus con- 
 stantly in danger of mistaking what is comparatively acciden- 
 tal and contingent, for what is essential and determining, and 
 vice versd. There is always a possibility that we may, from 
 the agreement of the things compared together by us in some 
 external, accessible phenomena and properties, have falsely 
 inferred their agreement generally and in essential points. 
 
 We must here further take into consideration that even our 
 notions of any given disease and of the so-called types and 
 unities of disease in general (e. g., fever, inflammation, gout, 
 rheumatism, &c.), are more or less obscure and fluctuating, 
 because they have arisen, in a great measure, from a very 
 superficial comparison of certain phenomena and processes, 
 which are themselves fluctuating and vary greatly in their 
 simultaneous or consecutive occurrence on each occasion, their 
 real connection being more or less unknown to us (e. g., cer- 
 tain phenomena in the sick, as those of temperature, circula- 
 tion, innervation, or of certain excretions, or anatomical and 
 chemical changes). The same holds good essentially of setio- 
 logical and hygienic influences and of our remedies. We 
 find these also in groups, the arrangement of which is founded, 
 not upon a comprehension of their more essential points of 
 agreement, but upon their remote and often doubtful resem- 
 blance in relation to certain phenomena or processes. The 
 comparison of a number of them with each other is, on this 
 account, little calculated to faciUtate our comprehension of 
 them. In our peculiar department of science, and in the 
 present state of our knowledge, analogy and comparison too 
 often, from their indefinite and arbitrary character, deserve 
 rather the name of allegory or simile. The very words which 
 we employ to designate our objects (e. g., fever, inflammation, 
 rheumatism, hemorrhoids, or alteratives, corroborants, purga- 
 tives, astringents, counter-irritation, &c.) appear infinitely 
 
OF THE INDUCTIVE PROCSSS. 103 
 
 better adapted to give rise to and propagate indistinct, allego- 
 rical notions, than to promote the investigation and better 
 comprehension of the objects to which they are applied. They 
 may suit the poet, but not the scientific investigator. 
 
 When we compare our objects with each other, for the pur- 
 pose of drawing conclusions concerning their general and es- 
 sential agreement in certain points, it is often much as if a 
 mineralogist were to infer the identity of his substances and 
 minerals from the similarity of their crystalline form,for, in reality, 
 very different substances may assume the same form, and the 
 same substances appear in very different forms. In like manner, 
 sweet and bitter almonds would appear essentially similar if 
 we could compare only their external characters, and had 
 learnt nothing concerning their chemical constituents, and the 
 properties and effects of these. Our comparison or classifica- 
 tion of them according to their former similarity would have 
 been, as we now know, in many respects a false one. The 
 analogy of the chemist, on the contrary, is a perfectly correct 
 one, when he associates fermentation with putrefaction, or soap 
 with plaster, and further, their mode of origin; for he has 
 demonstrated that they agree in certain essential points. The 
 chemist and the physicist can compare with each other many 
 of their objects and processes and infer their innate resem- 
 blance from their analogies in certain points. They may thus 
 attain to the comprehension of a wider field, presenting nume- 
 rous series of objects, phenomena, and processes. With us, 
 on the contrary, most of the phenomena and processes in the 
 living body have remained too obscure for us to deduce from 
 their similarity in certain points the fact of their essential 
 agreement, i. e., of the similarity or identity of their causal 
 connection, conditions, or effects. 
 
 Analogy and comparison will be most useful to us when we 
 endeavour by their aid to illustrate still obscure phenomena by 
 means of others, the causal connection, condition, and laws of 
 which we have already succeeded in determining ; for it can 
 aid us little to compare two or more partly or entirely un- 
 known phenomena, &c. And however advantageous it may 
 be to be able to draw conclusions from the actual steps and 
 established conditions of a process, concerning others which 
 are analogous in several points, it is, for the most part, equally 
 
104 PROBLEMS AND PERFORMANCE 
 
 dangerous, or at least useless to do this in those of which the 
 causal connection is doubtful. Our deduction of one from the 
 other cannot possibly further our insight into their nature, any 
 more than it would facilitate the comprehension of a savage, 
 to tell him that the mode of origin and the conditions of light- 
 ning are the same as those of the electric spark, or that Paris 
 resembles Berlin in certain points, both being equally unknown 
 to him. 
 
 It can thus assist us little, in the comparison of the doubtful 
 phenomena and processes with which we have to do, to draw 
 a parallel between the still unexplored processes of respiration 
 in the lower orders of animals, and respiration in the mam- 
 malia, or between the latter and excretion by the liver, or 
 skin ; or to compare inflammation with fever, fever with fer- 
 mentatiou or dysentery, and cholera with ague and the so- 
 called miasmatic diseases in general. It is the natural 
 consequence of our imperfect insight into the essential, and, 
 therefore, constant processes, or states in our patients, that we 
 are unable, e. g. to draw conclusions from typhus and its 
 phenomena in one country, which may hold equally good 
 concerning its nature in another, or to infer from the symp- 
 toms of intermittent fever and the efficacy of quinine in one 
 place, that the same symptoms will appear, and the same 
 thing prove efficacious in another. The frequent inference 
 that a medicine which is beneficial in one disease will be so in 
 another, even if both agree in certain circumstances, or phe- 
 nomena, is still more hazardous. We can by no means 
 infer from the fact that an astringent is useful in certain 
 external diseases, that it would be so in more or less analogous 
 internal diseases, as diarrhoea and dysentery, blenorrhoea and 
 suppuration of internal organs. We cannot even prove that 
 those astringent substances come into contact with the internal 
 tissues in the same manner as with the skin, or the surface of 
 ulcers, still less can we prove that they act in the same manner 
 upon both. The fact that the local employment of cold, mer- 
 curial ointment, &c., is often beneficial in simple cutaneous 
 inflammation, and that a certain cutaneous inflammation is 
 present in scarlet fever, led many to the conclusion that the 
 same applications might also be found useful in that disease. 
 This conclusion was, however, a very hazardous one, because 
 
OF THE INDUCTIVE PROCESS. 105 
 
 the two diseased states differ in essential points, and before 
 we could be warranted in employing remedies found useful in 
 other cases of cutaneous inflammation, we must first determine 
 the exact relation such inflammation holds to scarlet fever. 
 
 The foregoing pages have shown that in our whole field of 
 study we cannot draw from analogy and comparison alone, 
 conclusions whereon safely to ground the essential similarity 
 of our objects, or to establish their agreement, whether in 
 causal connection, conditions, or modes of operation. It is 
 otherwise in chemistry and physics, because in them the 
 causal connection and conformity of many phenomena and 
 processes have already been determined, and because it has 
 been found possible to show that many of the latter, which 
 had at first merely been grouped together on account of sup- 
 posed resemblances, were in reality similar, and essentially 
 dependent upon the same circumstance and process. By the 
 further discovery of points of analogy in certain substances, 
 phenomena, and processes, it became possible to refer new 
 series of these to the same mode of origin, or progress, and 
 thus gradually to enlarge the field of view. With us, on the 
 contrary, and with the objects with which we jjave to do, all 
 deductions from resemblances and analogies have continued 
 to be a more or less uncertain calculation of probabilities. 
 
 In spite of all this, the employment of analogies is an in- 
 dispensable auxiliary in our investigations, even more so than 
 in other departments of the study of nature, and the difiiculty 
 of their application proves nothing against the necessity of 
 their use, any more than a false application of them would 
 militate against a correct one. It is the ofiice of comparison 
 and classification to bring things hitherto widely separated 
 and isolated nearer to each other, and thus to enable us to 
 understand them all more practically. Jenner, for instance, 
 arrived by this method of analogy at his discovery of vaccina- 
 tion. If the foregoing observations have in any way attained 
 their end, they will have pointed out what we are yet in need 
 of, in order to turn this method of investigation to the fullest 
 advantage. Much, however, remains to be explained con- 
 nectedly hereafter. Our first object must ever be, to compare 
 together such series and kinds of phenomena, such effects, or 
 influences as agree with each other in essential rather than in 
 
106 PROBLEMS AND PERFORMANCE 
 
 accidental points. By associating certain functions and pro- 
 cesses in the sick, or certain effects of various influences of the 
 external world, or by seeking analogous points in various 
 remedies, or poisons, we sometimes succeed in bringing them 
 into the same point of view, and therewith demonstrating their 
 essential similarity. In our scrutiny of their discovered re- 
 semblances, we may meet with points which lead to the further 
 investigation of their causal connection. Thus we have already 
 succeeded in placing side by side the processes in digestion, 
 and in the conversion of substances within the body, with 
 other processes of conversion in organic substances ; those of 
 respiration, with other processes of excretion, and with oxida- 
 tion and combustion generally; and the employment of 
 analogies has already been successful in the accomplish- 
 ment of something similar in our theories of diseases and 
 remedies. 
 
 III. Application op the numerical method, or sta- 
 tistics. 
 
 This, as is well known, has become a most important aid 
 wherever it has been necessary to establish facts with great 
 precision. So,, also, in our department of study; for it is 
 self-evident, that our notion of any event or process will 
 always be more distinct in proportion to the number of cases 
 in which we have observed it and demonstrated its occurrence 
 in a given manner and under given circumstances. From a 
 greater number of cases, or instances, of a certain phenomenon 
 or event (e. g., a disease), we can much better draw a conclusion 
 concerning their probable general behaviour, i. e., concerning all 
 cases of the same kind, than if we had observed that event in a 
 few cases only. In short, a number of correct and careful obser- 
 vations will always possess a value nearly equivalent to that of 
 experience, which is, in fact, but a name for such observations 
 in their full result. 
 
 Statistics here deserve our especial consideration, inasmuch 
 as they may become the means of investigating the objects 
 with which we have to deal, in relation to their causal con- 
 nection and conformity. The question therefore is, whether, 
 and how far, — from the observation of a certain vital pheno- 
 menon, or disease, or of an influence of the external world upon 
 man, &c., in as great a number of cases as possible, under 
 
OF THE INDUCTIVE PROCESS. 107 
 
 certain variations of circumstances, and by the aid of care- 
 ful comparison with each other of all the cases observed by 
 us, — we can deduce the conditions and laws of such pheno- 
 mena, e. g., those of disease. We have further to ask how 
 statistics are to be employed for the most perfect attainment 
 of our end, — i. e., the determination of the causal connection 
 of certain events and effects, or of the effects of certain causes 
 and influences, in our department of science. Experience 
 teaches us, indeed, that on the one hand many important 
 results have been attained by this method, but that, on the 
 other, the exact value of it in the question at issue, — i. c, for 
 the discovery of causal connection, — has not always been cor- 
 rectly and impartially estimated. 
 
 By the observation of any phenomenon or event in numerous 
 cases, and by the comparison of them with each other, we may, 
 it is true, not only demonstrate their relative frequency, but 
 also — ^by taking strictly "into account all the concomitant 
 circumstances — the definite mode of their simultaneous or 
 consecutive occurrence, i. e., a certain connection, or series, 
 of various circumstances or events in a given number of cases. 
 We have thus shown a certain constancy of their occurrence 
 under given circumstances ; and have even been able to deter- 
 mine, by the observation of the occurrence in question under 
 a sufficient variety of circumstances, that this event, or effect, 
 has occurred only under a certain combination of circumstances 
 and influences, or has at least occurred much more frequently 
 under these than under any others. We are now, there- 
 fore, justified in assuming a certain causal connection, the 
 dependence of a given event upon certain circumstances and 
 influences, with more probability than its dependence upon 
 others. And we infer such a relation and causal connection 
 with much more right than if we had met with them in a few 
 cases only. It is precisely the large number of cases which 
 approaches to the value of a mathematical demonstration. 
 
 If we know, for instance, that under certain circumstances 
 (in a given county, neighbourhood, or town, or amongst persons 
 whose habits of life are similar), a thousand persons have been 
 attacked in a similar manner in a comparatively short time, or 
 that, in a thousand persons suffering from the same disease, 
 certain organs and processes have exhibited certain definite 
 
108 PROBLEMS AND PERFOEMANOE 
 
 changes, or that, of a thousand persons similarly affected, nine 
 hundred have recovered after a certain mode of treatment, we 
 can assume, with much greater probability, a certain causal 
 connection, than if we had observed the same event as a 
 consequence of the same influence, and under the same cir- 
 cumstances, in a small number of individuals only. 
 
 This probability becomes much greater if, in the enumera- 
 tion of cases, we also compare them with each other, more 
 especially if we duly vary the circumstances. We may have 
 found, for instance, in the above-named examples, that of a 
 thousand persons in other countries, or in different parts of a 
 town, particularly under different and varying social circum- 
 stances, much fewer, or more, fell sick and died ; that, of a 
 thousand persons similarly affected, and submitted to a certain 
 mode of treatment, a much smaller, or much greater number 
 died than in the other case ; or that the average duration of 
 the disease, if left to itself, was thirty days, while under the 
 use of one remedy it was fifteen, of another twenty days. For 
 here, as everywhere, we have better grounds for regarding a 
 certain circumstance, or influence, as the direct or indirect 
 condition of a given event, if we observe the latter to follow 
 that particular circumstance much more frequently than it 
 follows any others ; and we may do this the more safely, the 
 more constantly both occur simultaneously or consecutively. 
 
 It is certain, that by the mere collection of numerous cases 
 and examples of a similar kind, — under circumstances which 
 admit of our so doing, — we may establish certain highly im- 
 portant facts and empirical laws. Thus, we may determine, 
 for instance, the constant proportion of male and female chil- 
 dren born; the average duration of human life, in relation to 
 age, circumstances, &c. ; the relative frequency of disease and 
 mortality, in respect to age, climate, or certain internal and 
 external social conditions; the relative frequency of certain 
 derangements in the same disease, and its duration when left 
 to itself, or treated in a certain manner; the beneficial or 
 deleterious influence of certain sanitary conditions, — e.ff., of 
 a neighbourhood, or town, or of hospitals and other public 
 institutions, — upon health and the duration of life, &c. It is 
 only by the extended and methodical adoption of this statistical 
 method that we can hope to acquire, in our department, correct 
 
OF THE INDUCTIVE PROCESS. 109 
 
 numbers, and facts founded upon experience, in the place of 
 general and vague surmises. 
 
 On the other hand, we must not overrate, or falsely esti- 
 mate, as some have done, the scientific value of these numbers, 
 for they are, at best, nothing more than facts founded upon 
 experience, and can, as such, give us no certain indication of 
 their causal connection, i. e. no explanation of them. Statistics 
 tell us only that certain relations exist, that a certain number 
 of human beings have been born, have fallen sick, and recovered, 
 or died, but they do not give us the reasons. Our object 
 would be, to demonstrate with approximate certainty by this 
 method, that certain events and circumstances or influences, 
 which we have observed simultaneously, or consecutively in a 
 certain number of instances, did not coincide accidentally, but 
 really modified and produced each other. The collection of 
 the greatest possible number of cases and examples cannot, 
 however, any more than simple observation, do anything for 
 us here in the way of explanation. 
 
 If, like Louis and his disciples, we note, in hundreds of 
 persons sufl'ering from the same disease, the anatomical changes 
 in individual organs, or observe, as is now frequently done, the 
 alterations in the composition of the blood, urine, &c., we may 
 learn thereby, it is true,' the relative frequency of certain 
 events and effects under certain circumstances, and in certain 
 forms of disease, but nothing concerning the part they may 
 have played therein, or concerning their causal connection. 
 Here, as elsewhere, the mass of circumstances occurring and 
 operating at the same moment is, in reality, so great, that we 
 cannot, by the mere notation of the frequency of a certain 
 event, any more than by the observation of it generally, draw 
 any certain conclusion concerning its conditions and connec- 
 tion, or concerning the part which any individual circumstance 
 may have played in its production. 
 
 If we had seen a thousand men seized with typhus after 
 eating asparagus, &c., and recover after taking herb-tea, water, 
 sulphuret of antimony, and the like; or if we had observed 
 that a greater number of children were born at the change, 
 than at the full of the moon, we should not infer therefrom 
 any causal connection between those events and circumstances. 
 Such a conclusion would be rendered absurd, not only by the 
 
110 PROBLEMS AND PERFORMANCE 
 
 known inadequacy of such agencies to produce such efiects, 
 but by our consciousness of the operation of other influences 
 far more numerous and important. 
 
 If we learn, on the contrary, that only certain persons, who 
 had been exposed to hunger and misery, were seized with 
 typhus, or that in certain patients, after the administration of 
 opium, pain or sleeplessness had ceased, we should be scarcely 
 less disposed to infer causal connection than if we saw a local 
 evil disappear by the use of the knife or caustics. A single 
 case is also frequently sufficient, especially if we have reason 
 to believe the efficiency of those influences from our previous 
 experience and general knowledge of the subject. 
 
 Hence it follows that high numbers, taken alone, can by no 
 means conclusively establish a certain causal connection in the 
 things we may have observed. For, in the last-mentioned 
 instances, the observation of a thousand cases would teach us 
 nothing further concerning the actual mode of operation of 
 those influences, than could a constant relation between a 
 given event, or result, and a given circumstance — i. e. a causal 
 connection — be demonstrated by the greatest possible number 
 of solitary instances. Our inference of such a connection 
 cannot be implicitly trusted until it has been confirmed by fur- 
 ther experience, and by proofs of an entirely diiferent nature. 
 
 That many naturalists and physicians should have attached 
 so much value to numbers in themselves may be regarded as 
 a complete misapprehension of the value of statistics ; and as 
 a kindred error must we consider their belief that the causal 
 connection and conformity of certain things could be estab- 
 lished by the mere observation of their simultaneous or conse- 
 cutive occurrence, however great the number of cases might 
 be. Thus Boudin, for example, does not hesitate, on the 
 strength of certain computations, to bring the motion of the 
 earth about its axis, and about the sun, into a certain relation 
 to the weight and excreting processes of the human body, and 
 even to the varying numbers of births and deaths, of mental 
 diseases and crimes. This example shows clearly why statis- 
 tical calculations and results, in themselves, are little to be 
 relied upon as proofs of the dependence of a given event upon 
 a given influence, and the less in proportion to the greater 
 complexity of objects and processes, of possible causes, or 
 
OF THE INDUCTIVE PROCESS. Ill 
 
 effects, and to our own imperfect acquaintance with the essen- 
 tial conditions which govern the operation of these processes, 
 effects, and influences. For it is precisely such a study as 
 ours which leaves the greatest room for errors and arbitrary 
 modes of observation, and still more are we open to these 
 in our estimation of the value of the things which we have 
 observed, and in our conclusions concerning their causal con- 
 nection. In all our attempts under such complicated and 
 more or less strange, obscure circumstances, we run a risk 
 which statistics, taken singly, can do little to diminish. 
 
 Statistics are, indeed, an important auxiliary in our search 
 after experimental truth, but in determining their precise value 
 we must bear in mind the rules which we allowed to hold 
 good in our observation of natural occurrences. Por here, as 
 in other methods of investigation, the mode of their employ- 
 ment must be adapted to the nature of the objects, or questions 
 to be investigated ; and it will depend upon the manner in 
 which we apply them, and upon the arrangement of the ques- 
 tions which we wish to answer by their aid, whether they further 
 comprehension in our department of science, or merely bring 
 us to that goal to which statistical numbers, taken singly, can 
 so easily attain, viz. the jumping, by their help, to the 
 desired conclusion, no matter in how arbitrary a fashion. 
 
 The first requirement here is, that the events and cases col- 
 lected be of the same nature. To admit of any comparison or 
 classification, they must be similar in their main points and in 
 all the circumstances essential to the question at issue, or to 
 the event to be explained. But this is seldom the case in our 
 computations, e. ff., in most diseases (with the exception, perhaps 
 of many acute and epidemic diseases, and still more of the 
 chemico-anatomical changes which we can see and appreciate), 
 any more than in the circumstances of their origin or cure. 
 But if the objects and individual cases which we collect are 
 not clearly defined, and if they are susceptible of more than 
 one mode of interpretation, (e. g., dropsy, gout, rheumatism, 
 or even scrofula, pulmonary consumption, &c.), things may be 
 brought under the same denominator, and classified as being 
 essentially of the same kind, which have a very unequal value. 
 We are hence in danger, on the strength of our statistics, of 
 making assertions concerning them all which do not apply to 
 
112 PROBLEMS AND PERFORMANCE 
 
 all in an equal degree. Thus Louis has taken blood, almost 
 indiscriminately, from many hundreds of sick persons, and 
 inferred, from the results thus obtained, the inefficiency of 
 bleeding in general. 
 
 In the questions with which we have to do, one chief dis- 
 advantage lies in the great complexity of circumstances, and 
 in our comparative ignorance of the actual conditions and 
 causal connection of the phenomena and processes under ob- 
 servation. Until we become better acqainted with the condi- 
 tions of an individual process, and with the effects of each in- 
 dividual influence, we cannot say, in all the instances of any 
 event observed by us, how far it may have depended upon any 
 particular circumstance which preceded or accompanied it. 
 We shall not be able to form clearer notions from the collec- 
 tion of many individual cases, and, however often we may find 
 these in company, we cannot determine whether this may be 
 any other than an accidental coincidence. To make the nu- 
 merical method really useful in our investigations, our compu- 
 tations must not refer to the aggregate of such intricate com- 
 plications of phenomena, causes, and effects, as are connected 
 with the duration of life, with mortality, or with diseases and 
 their origin, or cure under complex circumstances, whose se- 
 parate influence at the moment of observation is unknown to 
 us, and which we are only then attempting to determine. It 
 must be our aim to collect cases which are as similar as possible 
 in their nature, (e. g., cases of inflammation of the lungs, or 
 of tubercular disease in persons of the same age, rank, consti- 
 tution, &c.), and even these under the most simple circum- 
 stances possible. Statistics must enable us to determine the 
 precise influence of any individual agency in the production of 
 a disease, or in a cure, before we can demonstrate anything 
 numerically, concerning the share to be attributed to such 
 agencies in the aggregate (e. g., the seasons, the weather, cli- 
 mate, or situation). And since the effect of an individual in- 
 fluence or circumstance may not only be complicated, but also 
 modified, or even cancelled, by the effects of various others, 
 while other final results, or so-called exceptions and accidental 
 effects are thereby produced, we must, first of all, determine 
 by the aid of statistics, the effects and influences of the more 
 constant and important individual agencies. 
 
OF THE INDUCTIVE PROCESS. 113 
 
 It may be regarded as the established result of experience, 
 that scrofula, rachitis, the formation of tubercles, and similar 
 affections, occur most frequently in the children of the poor. 
 Statistical indications of the same circumstance are also not 
 wanting, but our insight into its immediate or remote causes 
 is not furthered by them because they merely give us a certain 
 total result, and do not enlighten us, for instance, as to whether 
 those children fell sick from bad food and air, or from want of 
 care, from hereditary predisposition, from bodily malformations, 
 or a syphilitic taint derived from their parents. All this we may 
 hope to learn with more certainty as statistical comparison be- 
 comes more accurate and is better able to isolate some parti- 
 cular influence and determine its action upon any given case. 
 If a practical physician has, in a large number of cases of in- 
 flammation of the lungs, employed bleeding, suitable diet, rest, 
 and perhaps also tartarized antimony, nitre, and mercury, and 
 a certain percentage recover, he cannot infer anything from 
 that large number concerning the influence of the bleeding, for 
 instance, any more than from a few cases only. To render our 
 comprehension of the causal connection in such an instance more 
 clear, it would be necessary to exclude, as far as possible, all other 
 influences which affected the recovery or death of the patients, 
 and to determine, as definitely as possible, the part played by 
 each of them. This would be more easily done if but one 
 remedy had been employed, whether it might be bleeding, or 
 tartarized antimony, or diet and rest ; and we might thus, upon 
 an examination into the results of these various remedies, and 
 a consideration of the cures which each, taken separately from 
 the others, had effected, arrive at a decision as to which among 
 them most merited approval. 
 
 In like manner, we are not much wiser as to either the 
 cause or cure of any given disease by being simply told that 
 in a certain hospital, or in a certain town, so many persons 
 have fallen ill and died of the malady in question ; but we 
 come nearer our mark when we begin to compute the cases of 
 disease and death which have been met with in different parts 
 of a town, amongst the different classes of the inhabitants, 
 and the more so if these have been drawn up separately 
 with a reference to age, sex, social station, business, and mode 
 of life. 
 
 8 
 
114 PEOBLEMS AND PERFORMANCE 
 
 The influence of the individual momentum, or agent, upon 
 such diseases and deaths would be more clearly ascertained 
 by this method ; and, by carefully excluding other influences, 
 we might bring cases of a complicated nature into the category 
 of comparatively uniform and simple ones, or unities. 
 
 It is evident from these examples, that, in a study such as 
 ours, comprehension can only be furthered by statistics where 
 they are specially employed to test the simplest possible cases 
 of a similar kind, in the smallest possible field, and the same 
 kind of effects or influences, under the greatest possible variety 
 of circumstances, and, finally, to collect and compare with each 
 other, separately, the results obtained on each occasion. 
 
 Applied in this manner, statistics will help us to obtain 
 more exact and safe demonstration in our scientific medical 
 investigations, and thus assist us in tracing our phenomena 
 and processes to a causal conformity. As in all other sciences, 
 we should deduce from statistical computations this causal 
 connection and conformity with the more certainty, just as, 
 by the aid of statistical investigation in detail, we became more 
 conversant with the office and relative importance of individual 
 agencies, and with the conditions of individual effects. And 
 precisely because' the latter has so seldom been carried out 
 adequately in questions of aetiology and therapeutics, and in 
 the general departments of physiology, anthropology, and 
 hygiene, statistics have hitherto been far from effecting what 
 they can and must yet effect. 
 
 So long, however, as we remain but partially acquainted 
 with the actual causal connection and laws of our processes 
 and influences, statistics give us, at least,, the best possible 
 substitute, — viz., the established frequency of the coincidence 
 of certain effects with certain influences or circumstances ; for 
 the more frequently such coincidences occur simultaneously, or 
 consecutively, the sooner will their merely accidental character 
 be excluded. And if, in a study like ours, we can, for the 
 numerous reasons already mentioned, draw no conclusion con- 
 cerning their causal connection itself, it is still very important 
 to know that certain events have occurred a certain number of 
 times, under certain established circumstances. We have 
 thus, at least, acquired another fact, another law, based upon 
 experience. 
 
OF THE INDUCTIVE PROCESS, 115 
 
 The mean numerical values of statistics are important, not 
 only for our provisional comprehension and for future investi- 
 gation, but also for our art and practice. Up to the present 
 time, for instance, many remedies have the reputation of pre- 
 venting or curing disease ; but, if it were proved statistically, 
 that, amongst persons similarly affected, an equal per centage 
 recovered as quickly, or certainly, whether a given drug had 
 been administered or not, such proof would put us in possession 
 of a useful fact. Many medicines and processes have been 
 said, for instance, to be capable of preventing the outbreak of 
 hydrophobia in persons bitten by mad dogs ; and it is certain 
 that, after the employment of such means, the disease has in 
 many cases failed to appear. By the exact observation of 
 hundreds of dogs which had been inoculated with the poison, 
 or bitten by others which were mad, it has, however, been 
 ascertained, that even under the circumstances most favorable 
 for the production of the disease, — i. e., where no means, or 
 so-called preservatives of any kind had been employed, scarcely 
 60 to 70 per cent, of the animals became rabid. This fact has 
 necessarily gone far to lessen the positive value of such reme- 
 dial means. 
 
SECTION IV. 
 
 CHAKACTEMSTICS AND VALUE OF THE KNOWLEDGE WHICH MA'V 
 BE ACQUIUED BY THE OBSERVATION OF NATURAL lOBJECTS, 
 AND BY IMMEDIATE DEDUCTION FROM THEM. EXPERIENCE, 
 EMPIRICAL LAWS, AND THEIR SCIENTIFIC IMPORTANCE. 
 
 The last section explained the method after which, in the 
 department of medicine, we are accustomed to observe and 
 investigate phenomena as they present themselves to us ; and 
 to draw from what we have observed, certain conclusions con- 
 cerning their causal connection and conformity to fixed laws. 
 Our next step is, to ascertain more exactly, how far, by the 
 aid of experience, the inductive process is capable of bringing 
 us to sound conclusions concerning the things submitted to 
 our investigation. 
 
 The several processes and means peculiar to that method of 
 investigation, have hitherto been employed more than any 
 others, in science in general, and almost exclusively, in 
 medicine proper. The present question is very nearly syno- 
 nymous with the other, viz., what do we as yet know on the 
 general subject of life — whether healthy, or diseased — of its 
 causal connection, and of the laws by which its course is 
 regulated ? 
 
 It is not necessary here to prove that our knowledge is, 
 after all, imperfect and uncertain, and to explain why it is so, 
 for this has already been done. What we do know with cer- 
 tainty is, that so many thousand forms of living beings exist, 
 with certain conformations, and with certain combinations of 
 their integral parts; that many of them develop themselves 
 after a certain manner, and exhibit during their lives certain 
 phenomena, or functions and changes, which have all, no doubt, 
 their definite causes, and occur in accordance with their own 
 fixed laws ; but we do not know these their conditions and 
 laws, i, e., we are unable to point out the peculiar internal 
 connection and subserviency of the phenomena and processes 
 in the living body, either in a state of health, or of disease. 
 We know tolerably well, it is true, what occurs in many of 
 
SCIENTIFIC VALUE OF EXPERIENCE. 117 
 
 them (e. g,, in the more simple organic phenomena of sen- 
 sation, and of the contraction of muscles, in digestion, in the 
 circulation of the humours, in absorption, and in various pro- 
 cesses of excretion). In many cases we are familiar with the 
 results of certain processes and laws, but neither with the laws 
 themselves, nor with the internal and necessary mechanism of 
 the processes. At best, we have only learnt to conjecture 
 their nature with more or less probability. 
 
 It follows from this that we cannot, by the observation of 
 those phenomena and processes, as they actually present them- 
 selves to us in the aggregate, nor by the aid of induction, in 
 its more limited signification, attain a clear insight into their 
 causal connection, or conformity. All that we have thus dis- 
 covered, or 'can hope to discover under the most favorable 
 circumstances is, that certain things {e.g., certain phenomena 
 and processes in the performance of a function, or in the pro- 
 gress of a disease) constantly occur simultaneously, or con- 
 secutively, and have been always observed under constant, 
 definite circumstances, when certain internal and external 
 influences are found in co-operation. We are unable, however, 
 to say with certainty, whether certain processes {e.g., those 
 attendant upon a function, a disease, or a cure) are really 
 dependent upon certain influences, or circumstances, and in 
 how far they are so, and what is their peculiar mechanism. 
 Our comprehension, or positive knowledge, in no case exceeds 
 what we have been able to observe directly, and this observation 
 has seldom gone to any considerable depth below the surface. 
 
 We now know, with tolerable certainty, that in respiration 
 carbonic acid and watery vapour are excreted ; that heat is 
 generated, and that the character of the blood is changed in 
 such a manner as may enable it to perform its office in relation 
 to the processes going on in the body. In like manner, we 
 know that in persons suffering from pneumonia, the lungs, the 
 blood and circulation, the generation of heat, certain excretory 
 processes, &c., exhibit changes, which occur in a definite and 
 constant order. In neither case, however, do we know what 
 is the link which connects these phenomena and processes 
 together, or unites them with others j neither do we know 
 what are their conditions and adequate causes. If, in any 
 given disease, certain chemical changes of the blood, or urine. 
 
118 SCIENTIFIC VALUE OF 
 
 or certain anatomical changes of various organs [e.g., hepa- 
 tization of the lungs in pneumonia, certain heart affections in 
 the asthmatic, enlargement of the spleen in ague, ulcerations 
 of the intestines in typhus, &c., or sugar in diabetic urine, 
 albumen in dropsy, buffing of the blood in inflammatory 
 diseases, &c.), constantly occurred, even then, the mere fact of 
 their occurrence would teach us nothing concerning their 
 relations to the whole disease. But, in reality, they are not 
 constant, and do not always present themselves in the same 
 form, especially in the earlier periods of the disease. They 
 are, moreover, frequently present when other phenomena, 
 indicative of the disease, are absent, or the latter present them- 
 selves without the occurrence of the former. They cannot, 
 therefore, be regarded as standing to each other in the relation 
 of cause and effect, but must both be considered as the com- 
 mon effect of a third agency, yet unknown to us. 
 
 On the other hand, it certainly often appears as if some 
 individual organ or function had lost its normal character, 
 and the disease so far seems to be a local affection. If this 
 were really the primary condition, and if certain changes, or 
 derangements of other organs and functions constantly followed 
 in a fixed order, they might perhaps, under certain circum- 
 stances, be regarded as dependent upon those which had pre- 
 ceded them. We might then draw an approximate conclusion 
 concerning the part played by any individual organ, or 
 apparatus, or concerning the office of such an individual 
 function, and its signification in relation to others. Every 
 physician knows the influence upon medicine exercised by this 
 view ; e. g., in the so-called anatomical theory, or doctrine of 
 lesions ; and how local, and especially visible and sensible 
 changes became the starting-point for all attempts to interpret 
 and explain diseases in their general character. But in fact, 
 we never see a disease in its first commencement, except per- 
 haps in cases where we have ourselves produced it ; and we 
 cannot know all that occurs in it, or why it occurs. It is 
 therefore impossible even to form an opinion whether all the 
 phenomena which we observe have started from any given 
 point, or to determine what that point is ; e. g., how far an 
 apparently strictly local derangement may be the consequence 
 of other earlier derangements and processes. And if, in the 
 
EXPERIENCE OE EMPIRICAL LAWS. 119 
 
 further course of a disease, we observe entirely different pro- 
 cesses to occur, and other organs to become deranged, we have 
 no right to conclude, from the observation of such a series of 
 changes, &c., by itself, that the sequence has been real, and 
 not apparent only. Still less are we in a position to conclude 
 which among these is cause, and which effect ; i. e., whether 
 any, and which of those derangements are dependent upon 
 others, and whether they, as well as others, do not rather 
 result from those influences which first gave origin to the 
 entire disease. 
 
 We are equally in the dark concerning the influence which 
 all these circumstances exert in the production of any disease, 
 except only in the case of direct seizures, e. g., of injuries, or 
 poisons, and of the derangement or disease following immedi- 
 ately upon them. Many of these influences may have been 
 in operation years before the present attack, and may have 
 affected the body and its processes in a certain manner, by 
 virtue of which they may give the disease, just as a previous 
 disease might do, a peculiar character and tendency. The 
 same doubts must present themselves whenever we attempt to 
 judge of the actual influence of remedies from the simple 
 observation of the condition of the patient and the progress 
 of his recovery. We may observe various ailments to diminish, 
 nay, even in a number of cases, to disappear, after the employ- 
 ment of certain remedies, as constantly as we see day follow 
 night, or good weather follow bad, yet without being justified 
 in assuming that a given remedy has been the cause of such 
 improvement, or cure, any more than that night is the cause 
 of day, or bad weather the cause of good. Physicians would 
 be equally justified in drawing from the fact that all their 
 patients affected with pulmonary phthisis, or cancer, had died 
 after the employment of cod-liver oil, or iodine, &c., the infer- 
 ence that these drugs had been the cause of their death. In 
 short, even under the most favorable circumstances, i. e., when 
 we see certain phenomena, or events, and certain influences, 
 or circumstances coincide, or follow each other constantly, or 
 almost constantly — we do not even then know how far this 
 is accidental, or how far they are essentially connected together 
 — whether or not they really stand to each other in the 
 relation of cause and effect. 
 
120 SCIENTIFIC VALUE OF 
 
 It is true, that simple experience has, in several instances, 
 placed this beyond doubt. Thus it is established that certain 
 diseases arise, not only after the operation of animal poisons, 
 or of contagions, but also in consequence of this operation (e. g., 
 syphilis, smallpox, hydrophobia) ; that intermittent fevers 
 develop themselves chiefly in miasmatic neighbourhoods, and 
 by the agency of the miasm which prevails j that bronchocele, 
 or ague, not only disappear after the employment of iodine, or 
 quinine, respectively, but also as the consequence of their action. 
 Even in these cases, however, we do not understand the causal 
 connection of the several events, or the peculiar mechanism by 
 which the effects are produced. In these, as in other pheno- 
 mena and processes, we know nothing of the peculiar con- 
 ditions attendant on their origin and progress, or of their con- 
 nection with each other. We cannot say, for instance, by 
 what exact agency miasmatic, or marshy neighbourhoods pro- 
 duce intermittent fever j or why certain changes, or derange- 
 ments occur in persons thus affected. Neither can we say 
 why these changes, &c., occur in a certain definite order, nor 
 for what reason, and by what properties and modes of operation 
 quinine cures them. Hence, we seldom, if ever, know with 
 certainty, how far, in such cases, the effects and influences 
 which we see constantly occurring together, or following each 
 other, are, in reality, interdependent or have been caused by 
 each other ; in short, we cannot say whether their coincidence 
 has been other than accidental. 
 
 We might with more certainty infer their essential con- 
 nection as cause and effect, if we could, in any given case, 
 demonstrate, not only that the event adduced as an effect (e. g., 
 a disease, or cure), always occurs only with, or after the cir- 
 cumstance adduced as its cause, but also, that this circum- 
 stance is never present without the occurrence of its alleged 
 effect. But this we have never been able to demonstrate of 
 any one occurrence or influence throughout our whole depart- 
 ment of science. The very fact that we do not know, with 
 respect to any given function of the human body, in what 
 form, and under what circumstances it occurs in other animals, 
 renders this impossible ; still less, in the case of any given 
 disease, can we predicate under what circumstances it may 
 arise, or under what form it may appear in different individuals 
 
EXPERIENCE OR EMPIRICAL LAWS. 121 
 
 and nations, or what mode of treatment may prove most 
 efficacious in these varying cases. With regard to intermittent 
 fever, for instance, we are led to believe that it does not appear 
 in all seasons of the year, even in miasmatic districts, and that 
 it does appear in one year more than in another. The 
 inhabitants of those districts are not all attacked by inter- 
 mittent fever, although all may be more or less exposed to 
 malaria; and we cannot deny, on the other hand, that inter- 
 mittent fever not unfrequently occurs in places where we 
 cannot demonstrate the presence of marsh land, or miasm. 
 
 We further find, that a great number of persons suffering 
 from that disease are not cured by quinine, especially in 
 miasmatic neighbourhoods. Many recover without having 
 had recourse to it at all, or after the employment of entirely 
 different remedies ; just as we find numerous and entirely 
 different remedies employed for the cure of almost every 
 disease. We must therefore conclude that, in the production, 
 as well as in the cure of intermittent fever, circumstances and 
 influences entirely different from " malaria,'^ or " quinine," 
 play a very important, perhaps the chief part, and that thus 
 neither the one nor the other of these influences can, in 
 itself, be regarded as the adequate cause of the effect attributed 
 to it. 
 
 Even if we take it for granted that both always occur 
 together, i. e, that a disease (c. g. intermittent fever) never 
 occurs without the circumstance assumed as its cause (e. g. 
 malaria), or a cure without the employment of a certain remedy 
 (e. g. quinine), it would not even then be demonstrated with 
 certainty that these precise circumstances and influences had 
 produced those effects, For many influences and circumstances 
 have, in reality, been here in operation at the same time, — 
 differing, perhaps, entirely from those of whose existence and 
 effects we know anything — in every case influences and agents 
 enough whose possible office, or signification in the production 
 of a given effect (e. g. a certain disease, or cure) is equally 
 unknown to us with those of the others. It is, therefore, 
 always possible that, besides the circumstances which we per- 
 haps with due probability assume to be the cause of a certain 
 effect, other and entirely different influences may have had 
 their share in its production. An influence which we have 
 
132 SCIENTIFIC VALUE OF 
 
 perhaps overlooked, or undervalued, or concerning which we 
 were unable to ascertain anything satisfactory, may have 
 played the chief part. At all events, we are not able to de- 
 monstrate that such is not the case. 
 
 To obtain a further insight into the mode of operation and 
 influence of an individual circumstance, or agent, our next 
 step is to compare the cases in which the event in question 
 (e. g. a disease, or a cure) occurs, and to observe when and under 
 what circumstances it occurs, ■ when constantly, when with 
 certain variations, and when not at all. To determine, for 
 instance, the influence of quinine upon the cure of ague, we 
 may employ it in some cases and not in others, or administer 
 it under the greatest possible variety of circumstances, in 
 patients of different ages, sexes, &c., in larger or smaller doses, 
 or in combination with various dietetic precautions. We may 
 now compare all these cases and series of observations with 
 each other, and observe in what instances and under what 
 circumstances a cure has been effected most quickly and cer- 
 tainly, and where most slowly. Still it must be remembered, 
 that for the reasons assigned above, the importance of any 
 circumstance, or influence, as essential to any event, would by 
 no means be accurately defined. It could only be so, if the 
 given circumstance, or influence had come into operation 
 entirely alone, and if the effect attributed to it, i. e. the result 
 in question, were not only to follow it invariably, but also to 
 follow none other than one of this particular kind. "We never 
 have, however, in reality, the opportunity of observing the 
 effect of any influence, or agent by itself. Man is never, any 
 more than any other living being, for a moment under the 
 influence of but a few, and still less under that of one only of 
 the agencies of the external world, whether it be e. g. the 
 operation of malaria, or of a remedy. 
 
 We might hope to attain our end rather by isolating a 
 given influence, and allowing it to operate under an endless 
 variety of circumstances, i, e, by experimenting with it. 
 The former mode of proceeding is, however, almost impossible, 
 and the latter, at best, very circuitous. Those influences, for 
 instance, which we perhaps suspect to be the remote, or proxi- 
 mate causes of a disease, lOr the conditions essential to the 
 performance of a given function, and which we consequently 
 
EXPERIENCE OE EMPIRICAL LAWS. 123 
 
 wish to investigatej can seldom be brought to act separately upon 
 man, or even upon animals. With some this is indeed possi- 
 ble to a certain extent, e. g. with medicines and poisons, and 
 attempts are frequently made to investigate their so-called 
 physiological effects in this manner. But here we must allow 
 for the difference in their mode of operation upon the healthy 
 man, or animal, and upon the sick, and we may conclude from 
 the observation of their effects in the latter, that the peculiar 
 state of the patient and the spontaneous changes occurring in 
 disease have had far more influence in their production than 
 the operation of the substance itself. Thus, vomiting may 
 follow the administration of ipecacuanha, or tartarized anti- 
 mony, or of sulphate of zinc, or copper ; apoplexy may follow 
 upon exposure to great heat, or cold, or the use of spirits or 
 narcotics, each being produced by a variety of causes, just as 
 the body may be supported and nourished by very various 
 kinds of food. In the former of the two examples, the sub- 
 stances named evidently only give the first impulse, in the 
 latter they only aid those internal processes and operations in 
 the body, which then act, as at other times, according to their 
 own laws and by their own essential mechanism. Thus a 
 building is burnt down in the same manner, and in conformity 
 to the same laws, whether it has been set on fire by lightning, 
 or by combustibles. 
 
 To ascertain by experiment the causal connection and condi- 
 tions of any vital process, or of any disease and its cure, we 
 should be able to bring into operation artificially all the cir- 
 cumstances and influences which we imagine to be causes, or 
 at least important agents in the production of the phenome- 
 non ; observing what changes take place in man, or animals, 
 under their operation, and whether they agree or not with the 
 effects, or results (e. g. of a disease), as they occur in nature. 
 We should therefore vary those combinations of circumstances 
 and influences, and bring them into operation in different 
 ways, until at last this particular kind of effect (e. g. a certain 
 disease, or an individual change, or given state in the disease), 
 occurs. This would evidently be a very tedious process in 
 seeking to ascertain the unknown causes of a given effect, 
 especially amongst such complicated operations and influences 
 as those with which we have to deal. 
 
124 SCIENTIFIC VALUE OF 
 
 It seems more than doubtful whether we should attain our 
 object by such means, i. e. whether we should finally succeed 
 in ascertaining, by all possible variations of the circumstances, 
 the precise kind and combination of circumstances and influ- 
 ences which have been followed bj'^ the effect in question. 
 Thus Bacon doubts whether any one would ever have discovered 
 the composition of gun-powder, if he had taken its effects as 
 the starting-point of his investigations, e. g. the fact that rocks 
 are split and bullets thrown long distances by it. It is no 
 less doubtful whether we could ever produce by this method a 
 genuine intermittent fever, and enlargement of the spleen, or 
 an actual typhus, or tubercles in the lungs. An experimenter 
 does not make the possible causes of a given effect the first 
 object of his search, but rather the possible, still unknown 
 effects of a given cause — of some modifying circumstance or 
 influence. It therefore appears at once easier and safer to 
 limit our experiments to the investigation of the possible 
 effects, or modes of operation of those influences and agencies. 
 If we always succeeded in producing by the agencies we 
 employed, results corresponding exactly to those which occur 
 in reality (e. g. intermittent fever, typhus), we should then 
 have discovered, with tolerable certainty, the conditions upon 
 which they depend'. 
 
 If, however, our experiments are to stand the test of rigid 
 exactitude, and if we take into consideration all the requirements 
 they must fulfil before we can draw from them any conclusion 
 concerning the causal connection and the conditions of a dis- 
 ease, it will be evident how great are the uncertainty and com- 
 parative inconclusiveness of this mode of investigation. If the 
 chemist and physicist wish to bring similar points in their 
 peculiar department to the test of experiment, they set out, in 
 the present day, with a knowledge of the subject, an understand- 
 ing of its phenomena and processes, of the individual agencies at 
 work within it, and of the laws which govern their operation, 
 which we, in our branch of science, do not yet possess. They 
 know beforehand upon what substances and compounds they 
 have to act in concert with the agent to be investigated ; they 
 can, moreover, be certain that no other agents are acting upon 
 them at the same time, and, in order to ensure this certainty, it 
 is possible to determine beforehand the effect of any such 
 
EXPERIENCE OE EMPIRICAL LAWS. 125 
 
 ageuts, so as, if necessary, to exclude them from the operation, 
 and in any case to be able to appreciate them at their true 
 value. 
 
 The physiologist already understands approximately the 
 normal action of the organs and functions which he intends to 
 put to the test of further experiment. He can, therefore, the 
 better draw conclusions respecting their action and internal 
 connection from changes which he produces in these processes 
 by artificial manipulations, and he is thus the better able to 
 bring the effect observed into connection with its causes. 
 
 We, on the contrary, are not only in a great measure still 
 unacquainted with the properties and modes of operation of the 
 complicated influences and agents with which we have to deal 
 (e. g., marsh-land, weather, bad food, &c.) j but, moreover, we 
 find them working, not within a circle of processes already 
 known to us, but within the complicated mechanism of the 
 living body — a chain of processes whose conditions and laws of 
 operation are still more or less obscure. This is much the 
 same as if the chemist were to endeavour to ascertain the pro- 
 perties and efiects of a substance by experimenting upon a com- 
 plex mineral which contained, besides the substance in question, 
 many others with which he was not acquainted, and as if, in 
 his experiments, he were to employ impure preparations con- 
 taining many foreign and unknown substances. 
 
 Simple observation will guide us to determine the effects of 
 certain influences and agents with more ease and safety, if we 
 see them constantly produce such intense changes in the living 
 body that we can no longer doubt the dependence of the one 
 upon the other. This is the case with various remedies and 
 poisons, with some forms of contagions, with the effect of heat, 
 or cold, of injuries and surgical operations. In these cases the 
 connection in question can be all the more readily ascertained 
 from the isolated character of the phenomena, and from the 
 fact that their effects appear directly and rapidly, and without 
 being spread over considerable periods of time, as is the case 
 with many other influences and agencies. But the living body 
 acts and reacts in these instances, just as it does in others, in 
 obedience to its constant laws, and the changes observed in it, 
 and in its individual processes and phenomena, have occurred 
 under definite conditions which we do not yet understand, but 
 
126 SCIENTIFIC VALUE OF 
 
 which we can only produce in a fixed and definite manner. In 
 no experiment upon the living body is it possible to exclude all 
 other influences, especially those which tend to maintain life, 
 and for this reason we can seldom determine in what degree, if 
 at all, the changes produced (e. g., a disease, or a cure) depend 
 upon the agencies, or influences intentionally brought into opera- 
 tion. And even although we were to take it for granted, that 
 a certain disease, or definite changes in certain processes, or 
 functions, always followed in such cases, the mechanism of their 
 production would not thereby be rendered more intelligible to 
 us, because we have not yet arrived at an understanding of the 
 whole mechanism of life, — we do not yet see clearly all the 
 intermediate physiological links which exist between the opera- 
 tion of any given agent and the final result (e. g., an attack of 
 disease, the effect of a remedy, or the progress of recovery) . 
 
 The complexity of the phenomena and processes going on in 
 the living body is that which necessarily prevents our acquiring 
 a clear comprehension of their essential conditions, and con- 
 formity to fixed laws, by simple observation, and by direct ex- 
 periment ; — it is that intimate co-operation of so many pro- 
 cesses to produce one result, together with the mass of circum- 
 stances and influences which modify it from without — in other 
 words, that dependence of all processes upon every other which 
 we can possibly conceive. Whatever, therefore, presents itself 
 to our observation is only in appearance a homogeneous, simple 
 whole ; it is, in reality, rather the final result, or effect of very 
 many processes and influences, whose tendencies frequently 
 come into collision, and whose effects oftentimes cancel each 
 other. The physicist would find it very difficult to discover the 
 conditions and laws of the phenomena, or " forces " which he 
 investigates, from cases in which the tendency of one agency, or 
 force was constantly modified and deranged, or even cancelled 
 by another. As if, for example, he were required to ascertain 
 the laws of motion solely from bodies kept in a state of rest by 
 opposing forces ; or if, from cases in which motion results from 
 a combination offerees (e. g., steam, atmospheric pressure, horse- 
 power, &c.), he were required to calculate the products and 
 laws of operation of any one of them separately, e. g,, of 
 steam. 
 
EXPERIENCE OR EMPIRICAL LAWS. 123 
 
 If the process of induction is frequently accompanied by great 
 difficulties in the chemico-physical department of study, where 
 an individual effect, or an individual influence can so often be 
 investigated in a state of isolation — if it is often difficult even 
 there to separate the various phenomena and processes, and to 
 determine their conditions as well as their action (e. g., the 
 electric, magnetic, thermal, and chemical phenomena of the 
 same substance, or in the same process) — -it becomes a positive 
 impossibility in the study of the phenomena of life. As already 
 mentioned, the mere observation of the aggregates of effects and 
 causes in the living body, and the application of the process of 
 induction, properly so called, are insufficient to enable us to 
 ascertain the conditions of the vital phenomena, and the effects 
 of all the various influences upon them. We may, therefore, 
 after a calm and close examination, abandon all hope of attaining, 
 by this method, to a comprehension of the laws by which the 
 phenomena and processes are regulated, which are submitted to 
 us for investigation. So many circumstances of a modifying, 
 or of a modified and secondary kind, always enter into and com- 
 plicate the problem to be solved, that we cannot deduce any 
 true view of their causal connection, their fixed order, or the 
 laws by which they are regulated, from the mere observation of 
 vital phenomena and influences, whether in the healthy or in 
 the sick. 
 
 This circumstance accounts for the many obstacles and 
 discouragements which beset us in the present state of our 
 knowledge, and especially in our attempts to unravel or to 
 comprehend the objects of our investigation. Thus it is self- 
 evident that whenever an effect, or a definite result may depend 
 upon a variety of circumstances and influences, or upon the 
 co-operation of several of them at the same time, as must ever 
 be the case in medical science, it may happen that some one 
 individual condition, or circumstance amongst them has in any 
 given case a preponderating share in the production of the 
 supposed effect. This may help us to explain : 
 
 I. Why, in the living body, in a state of health, or disease, 
 the same event, or the same effect may occur in very different 
 manners, under varying and dissimilar circumstances — a fact 
 which greatly complicates the investigation of their causal 
 connection. 
 
128 SCIENTIFIC VALUE OF 
 
 Taking, for example, any one of the functions of the living 
 body, we know that in the long chain of the animal and 
 vegetable world, although their organs, so variously constructed 
 and combined, act in various media and under the manifold 
 influences of the external world, yet in all, perhaps, the func- 
 tion occurs essentially in the same manner, or at least with a 
 similar final result, e. g. respiration and other processes of 
 excretion, absorption and the circulation of fluids, nutrition 
 and conversion of tissues, &c. In like manner, the human body 
 maintains its integrity although supplied with very various 
 kinds of food, in some cases, perhaps, only with fruits and 
 milk, in others with the most abundant and compound aliments. 
 It has been ascertained by frequent observation, that a disease 
 may occur under very various circumstances, and yet shall be 
 essentially the same in all, and that it afifects sometimes one, some- 
 times another set of processes and organs, and these in a varying 
 connection and order. Experience also teaches that the same 
 disease may run the same course, and disappear with the same 
 rapidity under the most various modes of treatment and reme- 
 dies, or even in spite of them. Typhus, for instance, occurs 
 sometimes in overfilled hospitals and prisons, sometimes 
 epidemically in times of dearth, or other misery, and some- 
 times sporadically in individuals, without any evidence of the 
 presence of any of these deleterious agents. We also see 
 paralysis occurring, sometimes as the consequence of some 
 affection of the brain, sometimes as the result of chronic lead- 
 poisoning, and often without any such palpable cause ; in the 
 same way as asthmatic attacks may sometimes be traced to 
 defects in the heart, or its valves, yet they frequently occur 
 where no such defects exist. 
 
 If functions essentially similar may be performed under 
 very various circumstances ; if the same disease may arise with 
 and after the operation of the most various influences, and 
 cease frequently and rapidly under the most various modes of 
 treatment, it follows that the circumstances and influences in 
 question cannot possibly have determined the development of 
 those results, but rather that they have been chiefly brought 
 about by the vital processes, occurring in conformity to their 
 own laws. It is an error, therefore, though one of daily 
 occurrence, to regard any individual circumstance, or influence. 
 
EXPERIENCE OR EMPIRICAL LAWS. ]29 
 
 as the cause, or even as the essential condition of such an 
 event, although it may have been observed by different persons 
 to precede it, and even, apparently, to aid in its production. 
 For we have shov^fn that the same result, the same final effect, 
 may be produced under the operation of widely differing cir- 
 cumstances. In the imperfect state of medical knowledge, we 
 must allow largely for merely accidental coincidences, and as 
 such we may safely, in a great number of cases, set down 
 many of the so-called causes of and remedies for diseases. 
 
 It is further evident how much this occurrence of the same 
 event, under such various circumstances and influences, must 
 impede the discovery of its causal connection and peculiar 
 conditions. No single investigator can well hope, from his 
 observations of physiological processes, or of the changes pro- 
 duced by disease in any number of persons, to arrive at any 
 positive conclusion regarding the causal connection of even one 
 of all the functions and diseases. He may establish facts, and 
 important ones, but he will not easily explain them, because 
 he cannot ascertain, experimentally, all the processes associated 
 with the function he is examining, and all the conditions under 
 which it may possibly go on, nor will he have the opportunity 
 of observing the origin and termination of the disease, and the 
 progress of its cure, under circumstances sufficiently varied to 
 enable him to draw a conclusion even approximately correct 
 regarding its true causes, and the laws to which it is subject. 
 The field and range of his experience are too confined, and the 
 special manner in which he interprets and frames his deduc- 
 tions from what he has observed is not sufficiently compre- 
 hensive and correct, to enable him to advance general truths 
 on this important subject. It can only be accomplished by 
 the combined exertions of numerous observers and investi- 
 gators. 
 
 II. The fact that circumstances and influences so varied 
 co-operate in the development of the processes or phenomena 
 in question, will explain the further fact, " that in the living 
 body no occurrence or effect ever takes place with perfect con- 
 stancy and certainty, and always in the same manner ; aAd that 
 we cannot, for this reason, with perfect certainty predict or 
 expect any occurrence or effect whatever." 
 
 For supposing any one of those numerous influences and 
 
 9 
 
130 SCIENTIFIC VALUE OF 
 
 circumstances not to have come into its ordinary operation, to 
 have been in some degree modified, or to have been controlled 
 by some foreign influence, the result or final eflect cannot fail 
 to be different from what it would otherwise have been. This 
 will the more certainly be the case the more important the 
 part which the agent in question has played in any such 
 process ; in other words, the more the development of a pro- 
 cess, or of a disease, has depended upon it. The comparatively 
 weaker, and more dependent influence of other conditions and 
 circumstances will be so far modified and interrupted, perhaps 
 in some cases altogether cancelled, in consequence of some such 
 change having occurred, that the ordinary effect may either 
 not be produced at all, or not in the usual manner. The 
 same thing may happen in consequence of the accession of 
 some additional influence, or circumstance by which the oper- 
 ation of others has been in an unusual manner strengthened, 
 weakened, interrupted, or even altogether neutralized. And 
 this shows us how, among the mutable conditions of life, and 
 the varying circumstances which affect it, sometimes one, 
 sometimes another of its processes, will exhibit the most mani- 
 fold variations and changes. Hence it follows that the results 
 which we are able to obtain by the observation of the vital 
 processes, &c., oscillate within very wide limits, and that from 
 the causes already so frequently alluded to, they do this to a 
 much greater extent in disease than in health. 
 
 Thus, one person is attacked by typhus or inflammation of 
 the lungs, under circumstances in which another is attacked 
 by diarrhoea or a cold in the head, while a hundred others 
 escape altogether. While in one individual a disease assumes 
 a mild form and runs a particular course, in others, the same 
 disease, appearing at the same time, may be very severe and 
 run a course entirely different. In one dropsical patient the 
 urine contains a large quantity of albumen, in another, not a 
 trace of it ; in one country fever is accompanied by extensive 
 lesions of certain tissues, e. g., ulceration of the intestines, 
 while in another this is not the case. One of the most con- 
 stant 'events recorded in medicine is the fact that intermittent 
 fever occurs through the operation of some poison generated 
 in miasmatic neighbourhoods, and that it is cured by quinine. 
 We formerly alluded to this fact as an instance of the highest 
 
EXPERIENCE OR EMPIRICAL LAWS. 131 
 
 degree of certainty which can be attained by simple experience 
 in medicine. But in reality, men are attacked by intermit- 
 tent fever in situations where, besides marsh-miasmata and 
 the like, many other deleterious influences are in operation ; 
 not only those of climate and weather, but also unhealthy 
 dwellings, want of cleanliness, various kinds of exhalations, 
 imperfect tillage, insufficient food, &c. We know further that 
 after the removal of these influences, the disease has much 
 diminished in frequency and severity among the inhabitants : 
 we know, also, that in the same neighbourhood and place, all 
 the inhabitants are not attacked to the same extent, but that 
 the disease is in great measure confined to the lower and ill- 
 fed classes, to people of dissipated habits, to the inhabitants of 
 unhealthy and thickly-populated places, and to badly managed 
 hospitals, barracks, &c. We must therefore regard it as highly 
 probable that marsh-miasmata, taken alone, are not the ade- 
 quate cause of intermittent fever. 
 
 We may thus the better understand why the neighbour- 
 hoods in which intermittent fever occurs endemically (such as 
 Rome and its Campagna), are not by any means invariably 
 situated in the vicinity of marshes; and we may also learn 
 why intermittent fevers are not most frequent and severe just 
 where the greatest extent of marsh land exists ; and, finally, 
 why, in the neighbourhoods rarely visited by these fevers, we 
 are so little able to trace their exemption to any common 
 vantage ground in the way of situation. 
 
 To take another example, most of the persons suffering 
 from intermittent fever (those, for instance, who are treated 
 in our hospitals) are not only put under the influence of 
 quinine, but also of better food and care, and enjoy a compa- 
 ratively more healthy existence than they had done previously. 
 Thi's also partly explains why, among the persons cured, some 
 have recovered under quinine, and some without its having 
 been employed at all. 
 
 To this we must add the generally acknowledged impossi- 
 bility of concluding with certainty, that because a given person 
 attacked in a certain manner under certain circumstances, has 
 recovered under a. certain mode of treatment, the same thing 
 will invariably occur in other individuals. And we cannot, 
 from the physiological effects of any substance, e. g., of common 
 
132 SCIENTIFIC VALUE OF 
 
 salt, fatty matters, salts of lime, Sec, even of one with which 
 we are best acquainted, draw the conclusion that it would be 
 of use in a given disease, e. g., in indigestion, tubercular de- 
 posits, disease of bone, &c. For it is impossible to determine 
 a priori, in what degree such substances will produce similar 
 eflfects to those in health, if they are capable of doing so at all 
 under circumstances so entirely new and, as yet, so obscure in 
 their causal connection and conditions. We can only infer 
 their use in such diseases with probability, when it has been 
 confirmed by special clinical experience. 
 
 In short, in medical science, every one must feel it to be im- 
 possible to predict anything whatever with certainty, so long 
 as we remain unacquainted with all the conditions of a given 
 event, and ignorant as to how these conditions or influences 
 may act in any particular instance. It is only in cases of 
 direct injuries and of certain physico-chemical agencies and 
 absolutely indispensable vital conditions, that we can pretty 
 certainly predict the consequences of their operation on the 
 one hand, or of the interruption of it on the other. But we 
 have said enough to show how the continual fluctuations and 
 variations affecting the phenomena, effects, and influences under 
 discussion must impede that knowledge of their causal connec- 
 tion which observation and experiment would otherwise unfold. 
 
 III. "With this acknowledgment is intimately connected 
 the circumstance that such frequent allusion is made to accident 
 and exceptions, to unexpected effects and events. 
 
 Even the physiologist has frequent occasion to do so ; the 
 physician is compelled to admit it at every step. Thus a dis- 
 ease or an epidemic frequently breaks out under circumstances 
 in which we had not anticipated the probability of its develop- 
 ment, or is absent under circumstances where our previous 
 experience would have led us to expect it. In an epidemic of 
 typhus, dysentery, &c., many persons are attacked whom we had 
 regarded as more or less likely to escape, while others, apparently 
 under exactly the same circumstances, with the same habits, or 
 who seemed to be particularly exposed and threatened, are 
 not attacked at all. A disease may at any time run a course, 
 and events and complications may occur in it, or effects of 
 remedies be seen in it which the most experienced and cir- 
 cumspect physician had never thought probable. Remedies 
 
EXPERIENCE OR EMPIRICAL LAWS. 133 
 
 and modes of treatment under which, perhaps, thousands have 
 recovered, prove inefficient in a particular patient without our 
 being able to give even a remote explanation of the cause. 
 
 And yet all these events which, in common language, we 
 call accidents, must, under the given circumstances, have oc- 
 curred as much by way of necessary consequence as any other 
 event or effect whatever, and that from the co-operation of 
 various influences and conditions. We are accustomed to de- 
 signate as "accidental," every event and influence occurring 
 under circumstances in which we had not expected it. There 
 are cases of daily occurrence in which the circumstances and 
 conditions that would otherwise have sufficed for the produc- 
 tion or prevention of a given event (e. g., a disease or a cure), 
 have been modified, interrupted, or even altogether neutralized 
 in their action by the accession and operation of others. But 
 this has happened unexpectedly because we have not been suf- 
 ficiently acquainted either with all the conditions necessary to 
 it, or with all the influences and agencies which have co-ope- 
 rated to produce it, and have thus failed to take into account 
 many things for which we should have seen the necessity of 
 making allowance, in a more advanced state of knowledge. In 
 other words, such an event happened unexpectedly, and is now 
 regarded as " accidental," because the connection and laws of 
 operation of its causes were more or less unknown to us. We 
 have possessed, perhaps, a certain experience respecting it, in- 
 asmuch as we had observed it to occur a certain number of 
 times, together with, or after certain influences and circum- 
 stances, and yet we may not have recognized its causal connec- 
 tion with, and actual dependence upon them. The circumstances 
 under which we had observed any event (e. g., an attack of 
 disease, a fracture, the operation of a remedy), as well as our 
 knowledge of the influences which co-operated to produce it, 
 have been of such a kind that we could not deduce from them 
 a certainty of its occurrence under the same circumstances, or 
 conversely of its non-occurrence under certain others. We 
 are, perhaps, aware that some of the latter are likely to have 
 a material influence upon the effect in question, but are so 
 far ignorant of its general conditions as to be unable to judge 
 which among these many circumstances and influences has 
 really, in any given case, produced it ; or to predicate how far 
 
134 SCIENTIFIC VALUE OF 
 
 they would operate in another case. It is rather to be con- 
 cluded then, that this event or effect stands in no causal con- 
 nection with those influences and circumstances under which 
 we observed it to occur; it may either accompany or follow 
 them, or fail to occur at all. 
 
 It is just this kind of simultaneous and consecutive occur- 
 rence of certain circumstances and processes which we call 
 accidental, i. e. when they simply accompany, or follow each 
 other, without being, in reality, mutually dependent, or stand- 
 ing to each other in the relation of cause and effect. Their 
 mutual dependence and causal connection is indeed possible, 
 and in many cases, even highly probable, but we ought never- 
 theless to bear in mind the possibility of their occurrence being 
 merely accidental, simultaneous, or consecutive, so long as we 
 have not established their dependence upon each other, i. e. 
 their causal connection, and cannot, until this is accomplished, 
 consider the event in question as an instance of such a law. 
 Such a conformity, such a causal connection has, however, 
 scarcely anywhere been established in medical phenomena and 
 processes. Up to the present time any real knowledge of 
 them is almost entirely wanting, and it is just on this account 
 that we so often speak of accidental occurrences. 
 
 In former ages men regarded almost everything as acci- 
 dental, because, so long as they were unacquainted with the 
 conformity of natural phenomena to fixed laws, they were 
 accustomed to refer to fate, or necessity, all that we now regard 
 as resulting from the laws of nature. To physicists and che- 
 mists many things formerly appeared accidental which they 
 no longer regard as such, now that they have become better 
 acquainted with the causal connection and laws of the effects 
 and processes observed in their departments of science. But 
 in the living body, as elsewhere in nature, everything occurs 
 in accordance with laws, i. e. is the effect of fixed causes. 
 Deviations from natural laws, or events opposed to them, can 
 nowhere exist, they are either only antagonistic effects, or 
 modifications resulting from the intervention of other influ- 
 ences. It is therefore an error to say that any event or 
 effect whatever has arisen accidentally. All that we can say 
 is, that certain circumstances and events have occurred at the 
 same time, or followed each other, without our having known 
 
EXPERIENCE OR EMPIRICAL LAWS. 135 
 
 their causal connection, and, therefore, in the absence of any 
 known probability, contrary to our expectations. If, however, 
 we were familiar with all the laws and conditions to which 
 those effects and counter-effects are subject, we should be able 
 to predict what would occur under every given circumstance, 
 and our calculations would exclude the very idea of accident. 
 
 It follows from this that we ought to be careful how we 
 speak of " exceptions," simply because there are no exceptions 
 to natural laws ; for in the living body, as elsewhere, no effects, 
 or processes can occur otherwise than as the consequences of 
 their fixed causes, and in their definite order and dependence. 
 We speak of exceptions more particularly in those departments 
 of human knowledge in which we have hitherto acquired least 
 insight into this subordination, and have therefore not been 
 able to establish any general laws, or safe rules for practice. 
 What we have already said respecting accident, will explain 
 why, in medical science, so-called " exceptions" so much 
 abound. 
 
 All that simple observation and experience can determine, 
 and nearly aU that has yet been established in medical science, 
 amounts to this — that certain things occur (e. g. in a vital 
 process), in a definite manner and order. Our whole empirical 
 knowledge consists, in other words, in the fact that phenomena 
 observed by us in a function, or a disease, &c., very frequently, 
 or perhaps constantly accompany, or follow each other under 
 certain circumstances. We may, indeed, be convinced, that 
 those phenomena, &c. occur in conformity to fixed laws, and 
 that all the circumstances and processes which affect them 
 from within and from without, have acted in their definite 
 order and manner, but we have not ascertained those laws in 
 their actuality. We may, it is true, form certain hypotheses 
 concerning them ; we may even, in the case of individual 
 processes and influences, be able to predicate their probable 
 existence; but we can in no case clearly demonstrate their 
 causal connection. 
 
 We give the name " empirical law " to this simple fact, 
 learnt from experience, that certain phenomena and circum- 
 stances, certain effects and influences occur together without 
 our being able to point out clearly their actual mutual depen- 
 
136 SCIENTIFIC VALUE OF 
 
 dence, or their general causal relation to each other. This 
 means, therefore, nothing more or less than that, so far as we 
 have observed, the simultaneous, or consecutive occurrence of 
 any series of phenomena has invariably happened in the same 
 manner; it conveys no information whether, and to what 
 extent, any one of them is the precise effect of any other. 
 We cannot even be sure that we have surmised or recognized 
 all the circumstances and influences upon which a given event, 
 &c. may depend. We have no guarantee that the only pos- 
 sible mode and order of their occurrence, is that which we 
 have observed, or that some other, perhaps an entirely opposite 
 one, might not have been equally possible. We are, finally, 
 unable to determine what circumstances, or influences are 
 necessary to produce the process, or result in question (e. g. a 
 function, a disease, or a cure). At best we can only say, that 
 in all the cases, or instances in which it has been observed, or 
 in which a comparison has been made with reference to it, 
 certain circumstances, phenomena, or events have accompanied 
 or followed each other. But since we do not know with cer- 
 tainty their connection and mutual dependence, we cannot 
 deduce from this observation what would occur in other cases — 
 e. g. on the accession of other circumstances not previously 
 present — until we have observed such cases with equal care, 
 and have determined with equal precision in them, each simul- 
 taneous or consecutive occurrence. Hence we cannot safely 
 rely upon all that simple experience has led us to regard as 
 fact, or upon what are called empirical laws and axioms. They 
 furnish no conclusion concerning the whole, because they have 
 not made us acquainted with this whole ; for no one can be 
 certain that the circumstances which have been observed by 
 himself or by others to occur simultaneously, or consecutively, 
 will invariably be present, and will always bear the same rela- 
 tion to each other. For this reason empirical rules hold good 
 only for the place and time at which the event or the pheno- 
 menon in question has been observed, and only for the particular 
 combination or kind of circumstances, or influences under which 
 our experience of it has been acquired. Thus it would be 
 asserting much more than we can do with safety, to say that a 
 disease (e. g. dysentery, typhus, intermittent fever) will appear 
 again under circumstances similar to those which we had 
 
EXPERIENCE OR EMPIRICAL LAWS. 137 
 
 observed, in previous epidemics, to precede or accompany its 
 outbreak, whensoever these should arise, or that because in a 
 given place, or at a given time, a certain per centage of the 
 population, or of a regiment of soldiers, &c., was attacked by 
 a certain disease and died, the same thing would happen in 
 the following year, or in other places of a similar character. 
 Again, although a certain mode of treatment, or remedy, may 
 have been successful in ninety-nine cases of ague, or syphilis, 
 we cannot therefore conclude with certainty that they would 
 succeed in the hundredth case, notwithstanding the exact re- 
 semblance it appears to our best judgment to bear to the others. 
 In short, every physician knows from experience how little he 
 can rely upon any empirical rules. Every new case, every 
 contradictory experience, is enough to show their uncertainty, 
 and in some instances to overthrow them altogether, and that, 
 just in proportion to their generality and comprehensiveness. 
 And we cannot, from any empirical law, draw conclusions with 
 respect to an individual case, any more than with respect to 
 all cases of the same nature, because that precise case may 
 contradict the law and belong to the so-called exceptions. 
 
 The necessarily limited range of individual experience is 
 enough to explain why so many errors and illusions exist in a 
 science like ours. They will always occur the more readily, 
 just as the things observed are the more vague and fluctuating 
 in their nature, and our experience concerning them the less 
 to be depended upon, in consequence ; and just as the deduc- 
 tions which an individual has attempted to make from his 
 experience, are the more comprehensive ; e. g. in relation to 
 the constancy and causal connection of an event. It has been 
 shown that mere experience, as such, does not enable us to 
 draw correct conclusions ; our interpretation of the things 
 observed, must remain more or less uncertain and arbitrary, 
 our surmise of a connection between them, a '' mera palpatio.'' 
 A person, for instance, who had observed chlorosis only in 
 young girls, ill fed and of sedentary habits, would form a dif- 
 ferent opinion of its conditions and nature, from one who had 
 seen it rapidly developed as a consequence of fright, sorrow, 
 or love. The former would be led to seek its origin in some 
 change in the blood, or in some fault of nutrition ; the latter, 
 in a peculiar state of the mind, or of innervation, &c. ; and 
 
138 SCIENTIFIC VALUE OF 
 
 while the former would endeavour to affect the composition of 
 the bloodj the conversion of tissues, or the process of nutritioUj 
 the latter would direct his remedies against derangements of 
 the nervous system, &c. Both, however, would be equally- 
 wrong in attempting to draw from their respective experiences, 
 however correct in themselves, any general conclusions con- 
 cerning the state of chlorotic subjects, especially in relation to 
 the origin of the disease. 
 
 Of all purely empirical axioms and propositions it is true, 
 that even under the most favorable circumstances, i. e. where 
 such conclusions are valid for all the cases observed (e. g. in a 
 given place, or at a given time), they may prove, in other cases, 
 altogether false, or at least one-sided. If, for instance, any 
 one had observed during the last decennia, that in thousands 
 of cases of fever in Germany, or France, the well-known changes 
 in the alimentary canal, and in the mesenteric glands, were 
 constant, and if he knew, perhaps, that all the other physicians 
 of those couatries had made the same observation, he might be 
 justified in concluding that these are constant, and even essen- 
 tial occurrences, in that disease. And yet he would certainly 
 be wrong if he attempted, from this, to form a general law, 
 and to .say that such changes, or lesions, occur in all cases of 
 fever, and are essential to the nature of the disease. For in 
 Ireland, Livonia, and many tropical countries, they seldom if 
 ever occur in connection with it, and the same observer would, 
 perhaps, fail to meet with them in the epidemics of fever which 
 occur in campaigns, or if he were to see the disease under other 
 circumstances, at other times, and in other places. If again 
 in every case of ague which we had observed, certain and rapid 
 recovery followed any particular remedy, e. g. quinine, the 
 conclusion that this was a certain cure for the disease, would 
 be so far perfectly correct. But in true miasmatic and aguish 
 neighbourhoods, especially in hot countries, the fallacy of such 
 a conclusion, valid as it is for certain circumstances and per- 
 sons, or for a certain place, &c., would soon become evident, 
 and we should find that we had established only a simple 
 empirical law, not a positive and general one. 
 
 If what has been already said shows the uncertainty of 
 empirical formulse, and the impossibility of founding upon 
 
EXPERIENCE OR EMPIRICAL LAWS. 139 
 
 them, as such, an explanation of the phenomena and processes 
 connected with medicine, it would, on the other hand, be far 
 from reasonable to declare their importance in this science to 
 be but slight and dubious. This would be tantamount to dis- 
 trusting all human knowledge and capability, and to slighting 
 all the acquisitions hitherto made. Although we have found 
 ourselves unable, by the method of simple observation and 
 experience, to ascertain any positive laws, or the causal con- 
 nection and the conditions essential to the development of 
 these phenomena and processes, we have nevertheless reached 
 . a point much nearer to this knowledge than would have been 
 possible without the aid of experience, &c. In point of actual 
 knowledge, even a Celsus or Hippocrates, a Boerhaave or a 
 Sydenham, would be a smatterer in comparison with any prac- 
 tical physician or physiologist of the present day. And, 
 although we have, as yet, arrived at no certain or very correct 
 comprehension of the conditions essential to the development 
 of the processes to be investigated, as well in the living body 
 as in the external world, or of their conformity to fixed laws, 
 we can still, in every case, surmise them with much greater 
 probability of being correct than our predecessors. It is true 
 that we can never say, from mere experience, upon what a 
 given effect, or event, e. g., a vital process, an attack of disease, 
 or a recovery, really depends j nor can we, for this very reason, 
 be certain that the same event will inevitably happen in any 
 given case ; neither can we, by the aid of experience, propose 
 any plan of treatment with full certainty of success. With 
 sufficient experience and circumspection, however, reasons 
 enough will almost always exist, to render the occurrence of 
 one event much more probable than that of another. Little, 
 therefore, as we can rely upon mere empirical laws, they are, 
 nevertheless, as such, of the highest importance. 
 
 This is especially true with reference to the whole mode of 
 proceeding in the practical purposes of science; not only 
 because such empirical knowledge is the sole knowledge which 
 we possess, but also because it affords us what may be the most 
 weighty reasons — the firmest basis for practice. We have not, 
 it is true, learnt from it why such a comparatively large number 
 of persons fall sick and die, in various ways, in what are called 
 miasmatic districts, in miserable and dirty parts of towns, in 
 
140 SCIENTIFIC VALUE OF 
 
 over-filled hospitals^ &c. But we could no doubt save the 
 health and lives of thousands, if we could defend them from 
 all those influences which our experience has pointed out. No 
 one knows exactly what smallpox is, or in what the preser- 
 vative power of vaccination consists, yet millions have already 
 been saved by this precaution. We cannot say why mercury 
 does more good in syphilis than so many other remedies ; nor 
 can we be certain that a given patient will be cured by it, yet, 
 we are fully justified in employing it in his case, as soon as it 
 has been ascertained that in such patients, under similar cir- 
 cumstances, it almost always efi'ects a cure. Experience, . 
 indeed, teaches us that it frequently does no good, but rather 
 harm, and that this may possibly be the case with the patient 
 in question. But, on the other hand, a survey and scrutiny 
 of all the particular circumstances of the case, may show that 
 it" difiers in these respects from those in which mercury was 
 followed by bad effects, and that we may here anticipate good 
 results with great probability. In the same manner, the 
 skilful practitioner always knows how to apply his experience 
 of the effects and uses of his remedies in the most serviceable 
 manner, even when he has no exact knowledge of their nature. 
 Moreover, he would not be justified in waiting until such a 
 knowledge, tardily perhaps, followed his empirical mode of 
 proceeding. The patient in question, requires our aid, and 
 we must decide for, or against the employment of mercury, 
 and upon the manner in which to employ it. If we possess 
 sufficient experience, knowledge of the subject, and practical 
 tact, we shall no doubt be able to do all for that patient which 
 circumstances permit of. 
 
 Experience has long taught the seaman that in certain 
 states of the atmosphere and of the surface of the sea, when 
 the wind blows from a certain quarter, when the sea-gulls 
 approach the vessel, and the fishes swim in a particular 
 manner, a storm is at hand ; he is thence enabled to adopt 
 precautionary measures. He is perhaps as ignorant as is the 
 physician in his science of the exact connection between these 
 phenomena and the conditions and influences in operation, and 
 knows nothing of the laws by which such effects may have 
 been produced. But even if we were acquainted with all these 
 circumstances, our practice would scarcely be much facilitated. 
 
EXPERIENCE OR EMPIRICAL LAWS. 141 
 
 for they can never be so simple as those of a mechanical 
 apparatus, or of a physical or chemical process; on the 
 contrary, they must, in all cases, be extremely complex and 
 modified by many particular circumstances. "We should then, 
 in any particular instance, have to weigh manifold influences 
 and circumstances, and to make allowance for their reciprocal 
 effects ; and we should have to determine, by detailed investi- 
 gations, all the states and changes occurring in the patient. 
 Such a proceeding, however, would generally be impossible in 
 practice, just as it would be impossible for the seaman, in the 
 short time at his disposal, to make exact barometrical thermo- 
 metrical, or eudiometrical observations, or even to refer to his 
 tables on the subject. 
 
 What the practitioner especially needs, is the capability of 
 ascertaining the chief points for decision, and of choosing what 
 may best further his object in the case before him. It is this 
 rapid and correct coup d'ceil which is the most essential element 
 in what we call " practical tact ;" and this is not acquired by 
 mere knowledge, — it is not to be learnt in this way. Scientific 
 and erudite men are often least fitted to acquire it, partly, 
 perhaps, because they are not, when practising medicine, in a 
 position to form an opinion, or make a choice, from a clear 
 comprehension, and upon adequate grounds, such as their 
 habits and inclination, acquired in scientific investigation, 
 would lead them to demand. In practice, every one must 
 make the most of the knowledge he possesses, and strive to 
 turn it to the best account ; and, since there will always be 
 gaps enough in purely empirical knowledge, he instinctively 
 regulates his proceedings as if such gaps did not exist. The 
 simple experiences which generally serve as his guides are of 
 scarcely less value to him, even in a scientific point of view. 
 The correctness, not only of his practice, but also of his know- 
 ledge, increases with their extent ; for the greater the number 
 of cases which we have observed and compared with each other, 
 and the more varied the circumstances under which we have 
 observed a given event to occur, the more correct will be the 
 conclusions and empirical rules which we can deduce from 
 them, and the more extensive will be their apphcation. They 
 will go far, too, to establish the probable correctness of our 
 inferences respecting certain more intimate, though, perhaps, 
 
142 SCIENTIFIC VALUE OF 
 
 not precisely causal relations which we have assumed to exist 
 between certain effects and influences. 
 
 We cannot, indeed — :from the fact that we have observed a 
 function, a disease, or a recovery, to occur under certain 
 circumstances and influences — infer that the latter were the 
 essential conditions of the former. That some connection 
 exists between them appears the more probable the oftener we 
 have observed the same event under the same circumstances, 
 when it has not been limited to a given place and a particular 
 time. If it has been established, for instance, that the presence 
 of oxygen is indispensable for the performance of the function 
 of respiration in all animals possessing a respiratory apparatus, 
 the dependence of that function upon oxygen, — i. e., the 
 important part which it plays therein, — becomes highly pro- 
 bable. If experience has shown that intermittent fever 
 predominates in marshy districts, not only in the northern, 
 but also in the southern, hemisphere, or that it generally 
 ceases after the employment of quinine in both, these facts may 
 more safely be regarded as the conditions of those events than 
 if the same observation had been made in a small number of 
 places, and in a few cases only. In the same manner, the 
 scientific value, and the correctness, of our empirical rules will 
 be increased by all those auxiliary methods which were men- 
 tioned in connection with the process of induction. 
 
 Since that which experience teaches us always furnishes the 
 starting-point for our further investigations, and the first, 
 though imperfect materials for a better comprehension of the 
 phenomena we are studying, it must be regarded as au indis- 
 pensable auxiliary in true science. All our experiences, in 
 themselves, give us, it is true, no knowledge of these pheno- 
 mena, but they prepare the way for what they cannot give. 
 From the rough masses of information which experience 
 affords, some fortunate investigator, some speculative mind 
 obtains more scientific and available materials. 
 
 Our surmise of a causal connection between certain processes 
 is confirmed by the circumstance that further facts and know- 
 ledge of one kind or other come to our aid ; that we learn 
 something more concerning those processes, or phenomena, 
 than their mere occurrence under certain circumstances. This 
 is more especially the case where we know something of the 
 
EXPERIENCE OR EMPIRICAL LAWS. 143 
 
 properties and mode of operation of a given influence, or of 
 the manner in which the event in question occurs somewhere 
 else, even though it may occur under entirely different circum- 
 stances. Thus we can hetter infer the frequent and serious 
 attacks of disease, and the great mortality amongst the poorer 
 classes to he due to their had and insufficient food, and their 
 general mode of life, than to want of proper clothing or clean- 
 liness ; for we know, from other sources, that the former play 
 an infinitely more important part in the maintenance of health 
 than the latter. In like manner, when patients recover after 
 the administration of preparations of iron, or of bitters, the 
 so-called tonic medicines, in combination with nutritious food, 
 we may attribute to the latter the greater influence in effecting 
 a cure, because the materials contained in it are of infinitely 
 more importance in maintaining the integrity of the human 
 body than iron, bitter extractive matters, &c. 
 
 We have gradually succeeded in establishing at least ap- 
 proximately correct empirical laws for certain processes and 
 phenomena in the living body, though not in ascertaining 
 their causal connection, their essential conditions and laws. 
 This holds good especially with respect to many of the physical 
 and chemical processes in the body — such as digestion and 
 nutrition, the conversion of tissues, the processes of respiration 
 and excretion, and the circulation ; also with respect to the 
 so-called law of diffusion of gases and liquids, in endosmose 
 and exosmose, in absorption, &c. In the nervous system, also, 
 we have acquired some knowledge of the state of the nerve- 
 fibres which produce sensation and motion, partly in its peri- 
 pheral, partly in its central portions, and have even established 
 certain empirical laws according to which they act ; and how- 
 ever imperfect this knowledge may be, we have still gained 
 much in the way of a better comprehension of the whole 
 apparatus. We can now, better than heretofore, surmise, if 
 not explain, the origin and course of many diseases, by tracing 
 them to a deranged state of the internal mechanism j and we 
 can better ascertain the mode in which certain external agents 
 and influences act upon the various processes or functions in 
 the living body. In short, physiology, as well as physics and 
 chemistry, have already furnished us with many empirical truths, 
 by the application of which to the problems and phenomena of 
 
144 SCIENTIFIC VALUE OF EXPERIENCE. 
 
 our own department, we gain a readier insight into them, or at 
 least the prospect of acquiring such knowledge at some future 
 time. We owe much, therefore, to the other natural sciences, 
 and must continue to do so, not only because man is merely 
 a link in the whole chain of nature, but also because investiga- 
 tion pursues a more exact routine in them than in the science 
 of medicine. 
 
 Our knowledge of the intrinsic connection between the 
 vital processes, the laws to which they are subject, and the 
 influence of external agents upon them, is at present so im- 
 perfect, that it does not enable us to deduce from these cir- 
 cumstances, or to give any clear explanation of, the phenomena 
 and occurrences which daily present themselves to us. 
 Bearing in mind the fluctuating and fallacious nature of 
 empirical laws, we must always remember the possibility of 
 entirely different relations, of an entirely different causal con- 
 nection subsisting between the objects of our study, from that 
 which we had previously imagined. We may be right, or we 
 may be wrong, and thus it must be until we have penetrated 
 beyond mere experience, or empirical laws, to a true compre- 
 hension of the phenomena — to actual laws of nature. 
 
 We shall now proceed to speak of the means and processes 
 which may, more fully than simple experience and direct 
 induction, enable us to attain our end. 
 
SECTION V. 
 
 OF THE METHODS OF INVESTIGATION AND THE AUXILIARY PRO- 
 CESSES THROUGH WHICH ALONE WE CAN ATTAIN TO HIGHER 
 
 and more exact scientific knowledge. — analysis and 
 the synthetical (deductive) method. 
 
 Progressive resolution op many and complicated, into 
 fewer and more general^ laws. process of reduction 
 ok. generalization. 
 
 It is hoped that the two foregoing sections will have suffi- 
 ciently explained the impossibility of arriving at a clear 
 comprehension of the causal connection and conformity of the 
 phenomena and occurrences in medical science, whether in 
 their development, or operation ; an impossibility which, when 
 such complicated processes and influences are in question, 
 must exist in spite of both direct observation and experiment, 
 however careful. We have also stated the reasons which 
 render it impossible, either by the direct method of observation 
 or induction, to arrive at anything more certain than our so- 
 called empirical facts, or laws. It is in vain therefore to 
 attempt, by the direct observation of vital phenomena, as such, 
 to discover the actual connection and conditions of their de- 
 velopment and course — in short, their conformity to fixed laws. 
 This is no more possible than for the chemist, from simple 
 observation, whether of the atmosphere, water, or any other 
 complex compounds, to understand their real nature, and gain 
 an insight into the conformity of his chemical combinations 
 and processes. No more would the physicist, from observations 
 of the weather and its complex and variable phenomena or 
 processes, have arrived at the discovery of its causal connection 
 and the laws of its meteorological phenomena. 
 
 We cannot say what a so-called function, a disease, or its 
 cure, really is, i. e., in what it may consist and upon what it 
 may depend, unless we first know what individual phenomena 
 have produced it, and upon what these, in their turn, depend. 
 We must acquaint ourselves with the laws and learn the order 
 
 10 
 
146 SYNTHETICAL METHOD 
 
 according to which each of its elements has been developed and 
 has acted. There is therefore only one method, which has already 
 been alluded to, of attaining a clear insight into the conditions 
 and laws of our complex phenomena and processes. We must, 
 first of all, endeavour to understand all the individual occur- 
 rences, or ' elements which constitute a so-called function, a 
 given process, or a disease ; and further, we must ascertain 
 the conditions and laws which produce and govern these indi- 
 vidual elements, or occurrences. Thus, to understand the 
 mode of operation and the office of the complex external 
 influences which affect the living body, we must first endeavour 
 to ascertain the properties and action of each of the individual 
 circumstances and agents in the atmosphere, in our food, or in 
 a certain neighbourhood, with a given mode of life, &c., which 
 act upon the body in various combinations. And from the 
 laws once established by us of all these individual occurrences 
 and influences, of these individual causes and effects — at least 
 of the most important and essential of them — we must finally 
 deduce the causal connection and conformity of those compli- 
 cated occurrences, or efi'ects, in the living body, as well as the 
 laws of operation of those complicated agents of the external 
 world. 
 
 In other words, before we can explain the development of a 
 given function, a disease, a cure, or any other complicated pro- 
 cess, we must first have ascertained the conditions of each of 
 the individual elementary processes, efiects, &c., in it, and 
 traced their general conformity to fixed laws ; and we must go 
 on to deduce the conditions and laws of those aggregates from 
 the conditions and laws of these their individual elements. In 
 short, while we adopt what we are accustomed to call the 
 deductive method of investigation, and inasmuch as we seek to 
 explain a complicated whole from the laws and conditions of 
 its iadividual elements, we may also term our method the 
 constructive, or synthetical. Since it has been shown to be 
 impossible to ascertain the conformity and connection of effects 
 and influences under the aggregates in which they appear to 
 us in nature, we must in some degree understand the con- 
 nections of each individual effect and occurrence, before we are 
 able to determine its precise influence and mode of working ; 
 and having once estabUshed laws, both for the individual occur- 
 
AND DEDUCTION. 147 
 
 rences and effects in question and for the determining influences 
 which afiect them, we might, under favorable circumstances, 
 find ourselves in a position to deduce the laws, that is to say, 
 the development or operation of these very aggregates, and 
 thus be able to explain them from the former. Instead of 
 taking the complicated whole and attempting thus to under- 
 stand and to explain its nature and occurrences, we must 
 rather hope to understand and explain it from the separate 
 consideration of its component parts and elements. Thus the 
 anatomist, in order to comprehend the complicated organs 
 submitted to his investigation, must first isolate and recognize 
 their individual integral tissues. The direct experimental 
 method of investigation, or induction, as it was described in 
 Section III, would thus be replaced by the constructive, or 
 synthetical method, i. e., by deduction. 
 
 Thus the chemist is first obliged to isolate the individual 
 elements of the compounds which he meets with in nature, 
 whether in the atmosphere, water, minerals, or certain organic 
 substances. He must first study separately the peculiar pro- 
 perties of those elements, and observe the changes which they 
 exhibit when they come into contact with others, and the laws 
 which regulate their operation, before he can deduce, with more 
 or less certainty, the conformity in the formation and operation, 
 and the behaviour of those complex combinations from those 
 of their component parts and elements. Modern animal 
 chemistry especially has no longer been content to observe the 
 ingesta and egesta in the living body merely as a whole, but 
 has separated them into their individual ■parts, or constituents, 
 and examined each of them severally and in detail. And 
 while it has become more intimately acquainted with the be- 
 haviour of the various constituents of our food, while it knows 
 more than it ever did before of the nature of the air we breathe, 
 more about the blood, the organs and products of excretion, 
 and the constitution of the fluids necessary to digestion, it can, 
 of course, better than ever before, surmise in what manner, 
 and according to what laws, the chemical processes in the body 
 are likely to occur. Just so has the natural philosopher been 
 able better to ascertain the conformity of his complicated phe- 
 nomena and processes (e. g., of the air-currents, the weather, 
 &c.), from having become better acquainted with the laws of 
 
148 SYNTHETICAL METHOD 
 
 operation of the individual agents upon which they depend 
 (e. g., of gravitation and atmospheric pressure, of temperature, 
 moisture in the air, &c.), and with the conditions of the indi- 
 vidual phenomena, or occurrences, in which those complicated 
 processes themselves consist. This method is no doubt an 
 extremely circuitous one, for instead of directly attacking the 
 objects of our investigation, — the phenomena and processes in 
 the living body, as they present themselves in nature, — we 
 must endeavour to approach them indirectly — as it were 
 a posteriori and from within. But however this may be, and 
 whether we are able and willing to carry out all these methods 
 of investigation, or not, they must, in every case, be carried out 
 before we can either understand or explain the conformity of 
 our phenomena, or construct an even approximately correct 
 theory of them. And in so doing we shall be in the less 
 danger of yielding to illusions, of exhausting our powers on 
 barren soil, of expecting to acquire knowledge from unsafe 
 auxiliaries, or of accepting fallacies for certainties. 
 
 Just because we have not recognized this as the only 
 possible method, and failed to appreciate why it is so, we have 
 not made so much progress as we might have done, whether 
 in physiology, or in the theory of diseases, and their cure. 
 
 The mere fact of observing a broad stream flowing past us 
 would not acquaint us with the place whence all the water 
 came. To discover this, we must first seek out all its tributary 
 streams, and trace each of these to its source. We cannot 
 say upon what a complicated process {e.g., a function or a 
 disease), which is compounded of a certain number of indi- 
 vidual processes, depends, and in what it consists, unless we 
 first know in what each individual process in it consists, and 
 upon what it depends. Equally little can we judge how a 
 complex influence, composed of certain individual elements 
 (e.g., weather, climate, food, mode of life, a certain mode of 
 treating a patient) may act in the living body, unless we first 
 understand the operation of each individual agent, or circum- 
 stance in it. If we once know that a given process or efliect 
 in the living body consists in certain individual processes or 
 efi'ects, we must go on to investigate these, and endeavour to 
 determine their causal connection and conditions. And if we 
 know that a given eff^ect can be produced by a certain aggre- 
 
AND DEDUCTION. 149 
 
 gate of causes or influences, we have no alternative but to 
 ascertain separately the mode of operation of each. 
 
 There need also be no question as to where we are to seek 
 for the conditions and conformity of the vital phenomena and 
 processes ; for if we ask how the allied natural sciences, which 
 have advanced so much further than our own — chemistry and 
 physics — have already ascertained, more or less precisely, the 
 laws of iheir phenomena and processes, we find that it is through 
 examination of the substances, elements, and compounds, 
 which present those phenomena and processes ; and the same 
 holds good in the case of all the influences and circumstances 
 upon which the production of the latter depends, and by which 
 they are modified in various ways. The conditions and laws 
 of the vital processes, whether in health or disease, are therefore 
 to be sought for only in the individual processes which con- 
 stitute " life" as a whole ; and the conditions and laws of the 
 latter are to be sought for only in the organs and materials of 
 which the body is composed. And since life itself is only 
 possible under the constant influence and by the constant co- 
 operation of the external world, we must consider as its ultimate 
 source, or condition, the medium in which the living body has 
 its origin and end, in connection with the aggregate of the 
 external agents and influences which are indispensable for its 
 maintenance and integrity, viz., food, warmth, light, &c. We 
 are thus in a position to understand the changes which, in the 
 case of disease, take place in the living body, and to trace out 
 their producing cause. Some change, in consequence of certain 
 external and internal circumstances and conditions, has taken 
 place in its organs, and interfered with the mechanism of their 
 operation, so that what occurs in them ceases to occur in the 
 usual normal manner ; they no longer conform to the order of 
 their healthy activity and the result of their working, therefore, 
 is not health. 
 
 The method to be adopted in this investigation may there- 
 fore be divided into the following stages. 
 
 I. We must, from what w-e observe in nature, looking at it 
 as a complex whole (e. g., a certain function, or disease, the 
 atmosphere, food, &c.), become acquainted with the individual 
 parts of which it consists, — its various elementary processes 
 
150 SYNTHETICAL METHOD 
 
 and agents, or materials, &c. We must take this whole to 
 pieces, or at least, through a process of artificial analysis, 
 imagine it to be taken to pieces (a process which has been 
 alluded to when on the subject of induction). We must first 
 of all ascertain the individual parts or elements of which these 
 complex objects are made up, and then determine the respec- 
 tive causes or conditions of each individual process or effect, 
 and the respective effects of each individual influence and de- 
 termining circumstance in them. 
 
 II. Having once become acquainted with the conditions 
 of the individual processes, or effects, and with the modes of 
 operation, or laws by which the individual influences and agents 
 act, we have now, from the consideration of all this, to deter- 
 mine what have been the causes of a given aggregate of those 
 processes, or effects, and what have been the effects of a given 
 aggregate of those influences, or agents, under given circum- 
 stances. In other words, we have to seek to deduce from the 
 special laws or theories of those elementary processes and 
 influences the theory of these aggregates, i. e., the conditions 
 of the complicated series of phenomena and processes which 
 occur in medical science, and the effects which follow upon 
 these complicated influences and causes. 
 
 Could we bring all these to the test of exact calculation, our 
 problem would be solved as completely as the great problem of 
 astronomy — the comprehension and explanation of the motions 
 of the heavenly bodies — was solved when Newton and others 
 succeeded in deducing with certainty those motions from the laws 
 of gravitation. We might, for instance, explain in a similar 
 manner what occurs in respiration, i: e., we could point out its 
 causal connection, were we able to demonstrate so clearly the 
 conditions which attend upon the excretion of carbonic acid 
 and watery vapour, and to follow the conversion of certain 
 components of the blood, and the production of heat which 
 accompany that process, as to be able to deduce from the con- 
 ditions and laws of these individual processes those of the whole 
 process of respiration. Essentially the same thing holds good 
 in the case of every disease, and of the various influences of the 
 external world. We should be able to understand all the so- 
 called functions and diseases and all the influences of the 
 external world upon them if we oulj^knew in what causal con- 
 
AND DEDUCTION. 151 
 
 nection each of their individual processes stands, and in what 
 manner each individual influence acts upon them ; for we could 
 then calculate what share each has in the production of the 
 whole, how and whj', for instance, all those individual processes 
 in a function, or in a disease, occur simultaneously or con- 
 secutively in this given order and manner, or why the compli- 
 cated agents of the external world affect them precisely in a 
 certain manner, and not otherwise. The total result or effect 
 of a whole series of influences and determining circumstances 
 amounts, in fact, to nothing more than the effects of all the 
 individual influences and circumstances taken together. 
 
 Thus experience has long since shown that persons who 
 ascend high mountains suffer from difficulty of breathing, a 
 sense of constriction, a feeling of weakness, &c., and a question 
 arose as to how these derangements were produced. While 
 some traced them to the relatively small amount of oxygen in 
 the air, others with more reason declared the rarefaction of the 
 air and diminished pressure to be the conditions of those pheno- 
 mena. This question, however, is not to be answered certainly 
 until we know exactly in what manner and degree each indi- 
 vidual agent, or circumstance concerned may act. We must, 
 to this end, enquire into the composition and temperature of the 
 air at such elevations, into diminished atmospheric pressure, and 
 consequent disturbance of the equilibrium between the external 
 pressure and the tension or counter-pressure of the fluids and 
 gases contained in the body. For had we observed and com- 
 pared these effects in the case of each individual agent by the 
 aid of an adequate variation of the circumstances, and above 
 all by the method of exclusion (e. g., the effects of diminished 
 pressure separately in the air-pump), we might, from all this, 
 calculate with certainty what would occur under given circum- 
 stances, e. ff., at a certain elevation, and explain why it so 
 occurred. We should understand a disease just in the same 
 way were we in possession of all its occurrences, and the causes 
 whence they arise. Thus, in inflammation of the lungs, we 
 should be able to determine the connection between its indi- 
 vidual phenomena and processes were we once able to ascertain 
 the conditions that affect the increased heat of the body, that 
 accelerate the pulse, that work changes in the excretory pro- 
 cesses of the lungs, in the composition of the blood, and 
 
153 SYNTHETICAL METHOD 
 
 in the general nervous system of a patient affected with 
 pneumonia. 
 
 The foregoing pages show not only the importance of this 
 so-called deductive or synthetical method, but also its difficulty, 
 and, in a relative sense, impossibility in our science ; and to 
 this subject more special allusion will be made at a later period. 
 We find, however, on a closer examination of all our theories, 
 and more especially of all the a priori constructions and hypo- 
 theses by the aid of which we have hitherto attempted to 
 explain any vital process, any disease or its cure, that this 
 method and the expedients in it have already been adopted, 
 more or less, though often almost instinctively and in a con- 
 fused manner. Yet through a careful examination even of 
 these expedients the individual steps will become more clear 
 to us which we must take in those more exact theories, or 
 attempts at explanation, but which we have not hitherto taken 
 with the necessary insight either into their requirements or 
 real signification. 
 
 Demonstbation of the causal connection of individual 
 phenomena and pkocesses, and of the laws of opera- 
 tion of individual determining circumstances and 
 influences. deduction of the causal connection of 
 the complicated processes and influences of medical 
 
 SCIENCE. 
 
 That first step — the demonstration of the conformity to 
 fixed laws of each of the individual processes and influences — 
 assumes another step as having been already taken. We 
 must, namely, first of all, have become acquainted with the 
 individual processes, agents, or influences, which are concerned 
 in the development of a function, or of a given disease. In 
 most cases, this is not very difficult. We must observe all the 
 phenomena as they occur in nature, whether in a function or 
 in a disease, either as nature presents them to us in her great 
 agents, — i. e., in the atmosphere, food, &c., — or as we have been 
 able to produce them in an artificial or modified form by the aid 
 of experiment, Above all, we must observe in what individual 
 processes, phenomena, or circumstances, those aggregates them- 
 selves consist ; and if we are unable to do this directly, by the 
 
AND DEDUCTION. 153 
 
 help of our unaided senses, we must at least endeavour to take 
 them to pieces mentally, and to ascertain of what parts or 
 elements they are composed. We must go through that 
 mental analysis of the aggregates of effects and causes pre- 
 sented to us by nature, of which mention has already been 
 made in reference to the inductive process. 
 
 Having effected such an analysis as completely as possible, 
 the next important step is, to ascertain the causes and effects 
 of each of these individual links in the chain, — e. g., the con- 
 ditions of an individual process in the living body, and its 
 ultimate action upon other processes in it; also we must 
 determine the manner in which any individual influence of the 
 external world acts upon the body. It is self-evident that, in 
 order to do this, we must observe each of those processes and 
 influences, each individual cause and effect, separately, and 
 isolated, as far as possible, from the others, and then ascertain 
 everything which may affect and modify in various ways an 
 individual process, — e. g., in respiration, in digestion, or in 
 fever. Thus, we might determine, with tolerable facility, the 
 influence and laws of operation of the seasons or the weather, 
 and observe how food acts upon the healthy, or how a given 
 mode of treatment affects our patients, could we but cause 
 each individual agent or circumstance, in those aggregates of 
 causes, to act separately, and watch, in the former case, the 
 various degrees of temperature and moisture in the atmosphere, 
 the individual materials for the maintenance of the body ; in 
 the latter, the action of any individual remedy, or the natural 
 progress of disease, apart and detached from all co-operating 
 influences. Could we once determine the circumstances and 
 influences upon which each individual process depends, and 
 what changes will inevitably follow each of those circumstances 
 and influences, we could then bring each effect and change in 
 the living body with their concomitant conditions, each influence, 
 each cause with the tendency of its operation in the living 
 body, into their real connection. Hence, also, we might 
 deduce consistently, on the one hand, the conformity and 
 causal connection of all the vital processes, and, with them, 
 the conformity and causal connection of every disease ; and, 
 on the other, the conformity of the influences they receive 
 from the complicated agencies of the external world. 
 
154 SYNTHETICAL METHOD 
 
 To proceed, however, in this direct and simple manner is, as 
 has already been explained, impossible in the case of the objects 
 with which our science has to deal. Our phenomena and pro- 
 cesses are never, as is well known, to be met with in an isolated 
 form ; they occur rather in the closest connection with many 
 others, as more or less complex aggregates of causes and effects^ 
 and we cannot, even by an artificial process, separate them 
 from each other. We cannot, for instance, as the chemist can 
 frequently do with his substances, or the physicist with many 
 of his processes and machines, arrest all the other processes in 
 the living body, for the purpose of investigating a single one, 
 without arresting the mechanism of the whole apparatus. 
 
 In seeking to ascertain, for instance, the individual processes 
 in respiration, we cannot isolate the lungs with their circulation, 
 the blood in their arteries and veins, or the absorption and 
 excretion of certain gases by them, and then examine what 
 changes the constituents of the blood always undergo under 
 the single influence of respiration, or of the absorption of 
 oxygen into the blood; nor can we determine what influence 
 the individual processes in the body itself may exert upon 
 them (e. g., the capacity of the lungs, — i. e., the quantity of 
 air inspired, the rapidity of the circulation, the pressure of the 
 column of blood, or various processes of excretion, &c.). We 
 are equally unable to investigate directly the modifications of 
 the individual processes in respiration, as they may occur in 
 consequence of the separate operation of the individual agents 
 in the atmosphere (e, g,, its pressure, composition, moisture, or 
 temperature), or how the particular mode of the conversion of 
 tissues and the changes of individual constituents of the blood 
 in respiration, may react upon the individual processes in the 
 living body (e. g,, upon the production of heat in it, upon 
 various processes of excretion, upon conversion of tissues and 
 nutrition). 
 
 In the same manner, it would be desirable for us to be able 
 to observe and separately investigate, at any rate, the more 
 important and influential of the elementary processes in a 
 disease, in their conditions and action. It is, however, 
 unnecessary to point out the impediments to such a mode of 
 proceeding. If we were called upon to investigate a given 
 derangement of the process of respiration, we should, first of 
 
AND DEDUCTION. 155 
 
 allj have to determine which of its parts had undergone a 
 change, and what the change was which might produce certain 
 alterations in the whole mechanism of respiration, with their 
 consequences for certain processes in the living body, and, 
 therewith, for certain diseases. If we assume the most 
 favorable case, viz., that we can produce a disease artificially, 
 as an inflammation of the skin, or of the parenchyma of the 
 lung, we perhaps find the organ in question gorged with blood, 
 or loaded with so-called exudations which were not present 
 before; further, perhaps we find certain changes in the com- 
 position of the blood and temperature of the body, in the 
 circulation, in certain processes of excretion and of innervation,, 
 pain, spasm, &c. But to understand in what these derange- 
 ments essentially consist, how they are connected with each 
 other, and upon what they depend, — in short, to recognize 
 their mechanism, conformity, and fixed order, — we must first 
 have learnt the causal connection, for the time being, of the 
 individual processes in such inflammation. We must also have 
 learnt the influence of the peculiar composition of the blood in 
 it, of the circulation and its various stimuli, of exosmosis and 
 the various processes of excretion, of the conversion of tissues 
 within the body, of the production of heat, and of the tendency 
 of the nervous action. We must have made ourselves ac- 
 quainted with each of these modifications separately, under 
 given circumstances, and as they are influenced, whether 
 by other processes in the living body, or by external agencies, 
 — such as temperature, composition of the atmosphere, in- 
 gesta, &c. 
 
 All this holds good in our investigation of the numerous 
 influences and agents of the external world, whether they are 
 termed hygienic influences, or remedies. To understand the part 
 which they may have played, as well in the normal course of our 
 lives, as in the development of the derangements in a disease, or 
 in the cure of that disease, we must, first of all, have studied them 
 separately, and determined the laws of their operation. Before 
 we can lay claim to even an approximately clear insight into the 
 mode of operation and influence of a given state of the weather, 
 of the climate of a certain district, or of any particular season 
 of the year as a whole, upon our body as a whole, we must first 
 have become acquainted with their individual parts, — tempera- 
 
156 SYNTHETICAL METHOD 
 
 ture, moisturCj atmospheric pressure, winds, &c., — and learnt 
 to understand their action upon the individual processes of the 
 body, — e. g., upon its temperature, upon exhalation, the circu- 
 lation, conversion of tissues, &c. We must not only be informed 
 as to how each of these acts separately, but also as to the 
 result of their various combinations with each other ; we must 
 know, further, how their effects, through mutual modifications, 
 are increased or diminished, or perhaps altogether cancelled. 
 In the same manner, we must not only determine the effects 
 of our remedies, but watch over the less direct influences 
 exerted by the individual elements of our food, by the occu- 
 pations to which the patient has been accustomed, and by other 
 hygienic agents more or less directly active. For, so long as 
 we remain ignorant of the office and effects of the individual 
 circumstances and influences, we shall also be ignorant whether, 
 or in what manner they may have conduced to the development 
 of a disease, or to its cure j and much less are we in a condition to 
 form a correct estimate of the influence exerted by whole groups 
 of such agents. It is doubtless difiicult,especially in the case of 
 man, to investigate these agencies and influences in their 
 separate operation upon the living body and its individual 
 processes; and it is certain that they have not hitherto been 
 so investigated. 
 
 Here, as elsewhere in our department of study, we are met 
 at the first step of our investigation into the laws of operation 
 of individual influences, and into the conditions of individual 
 occurrences or effects, by difficulties which have already been 
 alluded to, and which the physicist and chemist have not to 
 contend with, either in the same form or to the same extent. 
 But although they have many advantages over us in the shape 
 of a considerable certainty of a priori knowledge, and a basis 
 of many firmly established laws to rest on, they would scarcely 
 venture from these known laws to infer what, in the case of 
 certain individual processes, effects, or agents, might occur 
 under a complication of circumstances the details of which are 
 still unknown to them, or on the accession of entirely new and 
 obscure elements. We, however, are often less scrupulous, and 
 it is only the great difficulties of our subject, and the necessity 
 which the calling of a physician entails, which can in any 
 
AND DEDUCTION. 157 
 
 degree justify our ventures in tlie eyes of the allied sciences 
 more advanced than ours in the investigation of nature. 
 
 But the greatest difficulty which we meet with is, in the 
 end, the great confusion and multiplicity of the things with 
 which we have to deal, and the impossibility of submitting them 
 to a direct and separate investigation. Each individual pheno- 
 menon, each individual process in the living body, is, in conse- 
 quence of this multiplicity of causes and effects, bound within 
 a knot, the single threads of which we can scarcely trace with 
 certainty, and in the attempt to unravel which many have 
 succumbed. But we have already gained much if we have 
 acquired a clear insight into the peculiarities of the things 
 submitted to us for investigation, and a knowledge of the 
 problems which we must solve in the first instance. Here, as 
 elsewhere, this may be regarded as the first step towards the 
 understanding of our whole subject, for where the human mind 
 has once reached this point, it has always found the means of 
 attaining its end. We can now, at least, guess what food can 
 alone satisfy us, and shall either reject what is inferior, or, at 
 best, regard it but as a succedaneum. 
 
 If we cannot easily isolate our phenomena and influences, 
 and investigate them separately ; if we are obliged rather to 
 confine ourselves to those variable aggregates which nature 
 offers us, we should accustom ourselves more and more to 
 regard them as what they are, and not, as so often happens, 
 as things in themselves simple and uniform. The first step is, 
 therefore, to divide those various aggregates of effects and 
 processes, of influences and causes, into the individual processes 
 and circumstances of which they are composed; not, indeed, 
 by fire and steel, but in our minds and thoughts. The neces- 
 sity of this analysis has long been acknowledged, or at least 
 felt instinctively, and has already been carried out in certain 
 points and in many quarters. 
 
 A different state of things prevailed of old, and naturally so, 
 in consequence of the then imperfect comprehension of nature. 
 Our predecessors necessarily confined themselves to those great 
 appellatives as they presented themselves, for instance, as " life," 
 " health," " disease," " death," &c., i. e., to the abstract notions 
 which, in the first stage of their intellectual activity, they had 
 been able to form of all these things. They also imagined 
 
158 SYNTHETICAL METHOD 
 
 equally great appellatives, or collective notions, as the causes 
 of these, whether gods or God, nature or vital force, soul, or 
 mind, &c. In the course of time, however, men gradually- 
 learnt to distinguish the individual parts of things, to detect 
 them in the aggregates, and to bring them into connection 
 with their respective causes. This analysis has already acquired 
 a greater extension, which the necessity for it will continue to 
 increase. If the anatomist, on the one hand, has long suc- 
 ceeded in dividing his complicated organs more and more into 
 their finer parts, the physiologist, on the other hand, has learnt 
 to distinguish the individual parts in the aggregates of his 
 functions, or processes, and to investigate, in detail, the mani- 
 fold phenomena of which they are composed. Even as regards 
 the act of dying, men are no longer content to perceive some- 
 thing uniform and constantly identical — i. e., death — but have 
 rather learnt to distinguish those chief powers in the animal 
 economy, the suspension of which can arrest the whole process 
 of life. In like manner, men have ceased, in the investigation 
 of their complex agents and substances, to consider them merely 
 as wholes, known only through their properties or effects, but 
 have rather striven to ascertain upon which of their individual 
 elements and agents, and, again, upon which of the properties 
 and modes of operation of these very agents, their total effect 
 upon the living body depends. And the influence of this 
 necessity soon made itself felt in the theory of disease. Men 
 soon began to separate the old unities in diseases, or " Entia," 
 into the individual elements of which they are composed. Thus 
 the anatomical changes in form and texture in an entire disease 
 were distinguished and examined separately; and the same 
 method was extended to changes of composition, and to indi- 
 vidual processes and phenomena in general, so far as they 
 appeared to occur according to chemico-physical laws, and 
 according to those which regulate nervous action. 
 
 But so certainly as this division or analysis must never be 
 regarded as our final aim, but only as the first step towards it, 
 i. e., towards the comprehension of the living whole ; just as 
 certainly must our chief object now be, to determine the causal 
 connection and conformity of all these individual processes and 
 phenomena, that we may finally deduce from them the causal 
 connection and conformity of the whole, e. g., of a function, a 
 
AND DEDUCTION. 159 
 
 disease, or a cure. And here, again, we meet with precisely 
 the same impediments which have been already so often men- 
 tioned. But however complicated the processes in the living 
 body, whether in health or disease, may be, and however closely 
 they may be connected with each other, we know, at least, that 
 they arise from what takes place in all the organs and sub- 
 stances of which the body is composed — from their properties, 
 the tendencies of their operation, or their reciprocal action, 
 just as, in fact, every effect whatsoever must spring from its 
 individual causes. It appears no less certain that the com- 
 plexity and multiplicity of the phenomena which everywhere 
 present themselves to us, arise only from the great number of 
 the individual processes, effects,, and influences i. e., of the ele- 
 ments which are concerned in the development of those complex 
 phenomena. However obscure, therefore, the connection and 
 conformity of the vital processes may appear to us at present, 
 and however difficult it may be to establish the fact of their 
 connection, we know, at least, that their conditions and con- 
 formity are, in fact, only the result of the laws by which all 
 those individual constituent processes, or agents, act, where the 
 tendency of operation of the latter is not modified, or perhaps 
 cancelled by their own simultaneous occurrence. Whether, 
 therefore, those individual occurrences and processes in the 
 living body be of a chemico-physical nature, and their laws, 
 consequently, to be termed chemico-physical ; or whether thev 
 diverge in their whole character, at least in certain respects, 
 from the occurrences which have hitherto been regarded as 
 chemico-physical, and, consequently, their laws are to be termed 
 "vital" laws, is not important here. Having divided our 
 aggregates — a function, a disease, or the external influences 
 which affect them (e. ff., the atmosphere, weather, or food) — 
 into their individual processes, or agents, it remains for us to 
 investigate the causal connection, the causes and effects, in 
 short, the conformity of each of these separately. This inves- 
 tigation must be conducted in the manner already laid down 
 for the general process of induction. Our chief means are, 
 here and elsewhere, observation and experiment. 
 
 We must, however, choose the starting-point of our investi- 
 gation, according to the particular circumstances of the case in 
 question, i. e., we must first strive to ascertain the effects of a 
 
160 SYNTHETICAL METHOD 
 
 given cause, or influence, or tlie causes and individual modify- 
 ing circumstances of a given eflect, or process, as well in the 
 living body as in the external world. We shall also generally 
 have to investigate both, either together, or in close connection 
 with each other. In the former case, we must first separate 
 the great agents of the external world, e. g., the atmosphere, 
 climate, food, occupation, and mode of life, &c., into their 
 individual elements, and examine them singly in relation to 
 their effects upon the living body. The same holds good as 
 regards the manifold agencies of our remedies. Our aim must 
 then be to ascertain and determine the mode in which each 
 active element works upon the individual processes in the living 
 body under the various modifications which their eflects undergo, 
 whether by age, sex, and other peculiarities in individuals. 
 In the latter case, on the contrary, we confine ourselves to the 
 investigation of efifects and processes in the living body itself, 
 whether in health or disease. Having, as far as possible, 
 isolated and divided these aggregates into their elements (e. g., 
 into the individual processes in digestion, respiration, the cir- 
 culation, certain processes of excretion, the conversion of tissues, 
 or innervation), we shall then have to investigate what occurs 
 in these individual processes j which of them appear changed 
 in a given disease, and in what manner, and according to what 
 order and constant sequence. We must further seek to ascertain 
 in what manner these individual processes are changed under 
 the most various internal and external influences, under what cir- 
 cumstances these their various changes occur, and how, in conse- 
 quence of such changes, they may reciprocally affect each other. 
 
 Just as it is infinitely more simple and more safe to seek 
 for the possible effects of a given cause, or influence, than for 
 the possible conditions of a process, or effect, which is still 
 obscure, especially under such complex circumstances as those 
 with which we have to deal, it is always better, if we have the 
 choice, to begin with the former than with the latter. We 
 shall, consequently, have first to direct our investigations to 
 hygienic agencies and influences, and to the possible causes of 
 the diseases with which we have to do, and then to pass on to 
 our numerous remedies, and their mode of operation. 
 
 A few examples may serve to render the mode of our advance 
 more intelligible. 
 
AND DEDUCTION. 161 
 
 If, for instance, the problem to be solved were the final 
 determination of the influence which a marshy district exerts 
 upon its inhabitants (e. g., upon their liability to intermittent 
 fever), we must first endeavour to ascertain all the individual 
 circumstances, or agents, which play any part therein, we must 
 consider the composition and other peculiar characteristics of 
 the soil and atmosphere, the temperature and its oscillations at 
 different periods of the day or year, the composition of the 
 water which those people drink, &c., and it will then be 
 necessary to determine the precise effects of these various 
 agents upon the living body. We must, therefore, study the 
 changes which the individual processes in the living body, such 
 as its nutrition and the composition of the blood, the various 
 processes of excretion by the skin, kidneys, lungs, &c., its tem- 
 perature, the circulation of the fluids, and the conversion of 
 tissues within it, and the various modifications of innervation, 
 undergo by the operation of each of these agents, and to this 
 end we must acquire a more exact knowledge of the influence, 
 in each case, of these external agents upon the vital processes, 
 by a fitting variation of the circumstances, by observations and 
 experiments of various kinds, especially, by the aid of the 
 " method of exclusion," and by comparison with the more or 
 less analogous effects of other influences — in short, by all the 
 auxiliary methods of investigation already alluded to. Under 
 favorable circumstances, we should now, from the considera- 
 tion of these established effects, or laws, in so far as they have 
 been proved to be actively concerned in the result in question, 
 be able to deduce the effect of marshy districts, and bring it 
 into conformity with fixed laws ; and now we should also 
 understand, and, consequently, be able to explain, the develop- 
 ment of intermittent fever, the so-called miasmatic cachexia, 
 the enlargement of the spleen, &c. We should no longer be 
 compelled, as heretofore, to include all the active determining 
 circumstances, or agents of those diseases, in the abstract 
 notion of a miasmatic poison, or malaria, by which, after all, 
 everything and nothing is explained. Even if, in the most 
 unfavorable, and, unfortunately, most probable case, all those 
 investigations in detail should fail to bring us to our precise 
 object, and we should remain unable to determine, with cer- 
 tainty, the conditions of that miasmatic influence, and of those 
 
 11 
 
162 SYNTHETICAL METHOD 
 
 diseases, we should none the less surely have gained much 
 important information, which might essentially facilitate our 
 comprehension not only of this, hut of many additional points. 
 This would be the case even if we had obtained comparatively 
 negative results only from all these toilsome investigations, if, 
 e.g., we could demonstrate, as is very possible, that neither 
 gases, the water, nor poisonous matter of any kind, any more 
 than the considerable reduction of temperature of the body, 
 and the like, were essentially concerned therein. And we 
 should now find ourselves justified in drawing the conclusion 
 which was, a priori, the most probable one, that in the inha- 
 bitants of those marshy districts, the material substratum of 
 their bodies, and certain of the processes in them, experience, 
 equally with the soil itself, or some of its component parts, 
 certain peculiar changes ; and that they do not fall sick in 
 consequence of these peculiar states of the soil, but rather 
 only concomitantly with them. 
 
 Again, let us suppose that experience has shown a definite 
 state of health, whether good or bad, or an unusual frequency and 
 malignancy of certain diseases, to exist among certain classes 
 of the population, in individuals whose occupations and mode 
 of life we know. Here, also, we are unable to form any 
 precise notion of the part which any individual agent may 
 play therein, e.g., their work, and the exertion necessary for it, 
 unless we also know whether, and in what manner, the other 
 agents or influences act, and what is the tendency of their 
 operation, e. g., the state of their dwellings and workshops, 
 cleanliness, temperature, and degree of moisture of the atmo- 
 sphere, and, still more, the quality and quantity of their food. 
 To acquire any comprehension of such liability to disease, and 
 its external causes, we must, first of all, seek to isolate as 
 completely as possible, and to establish the mode of operation 
 and the importance of each of those individual influences. 
 
 The same thing holds good as regards remedies, whose real 
 importance lies in the ends for which we employ them. Every 
 reflecting physician will confess that we know very little, for 
 instance, of the peculiar mode of operation of what are called 
 sudorifics and diuretics, or tonics, not even in the healthy, 
 much less in the sick. To gain more knowledge on this sub- 
 ject, we must no longer confine ourselves to the investigation of 
 
AND DEDUCTION. 163 
 
 the effect of those remedies as a whole, whether it be real, or 
 only apparent, and arbitrarily interpreted; we must no longer 
 speak superficially of their sudorific, or diuretic effects, of their 
 tonic, stimulating or depressing, solvent, alterant effects, &c. 
 We must rather first direct our investigations to all the in- 
 dividual processes and circumstances in the living body, by the 
 co-operation of which excretion by the skin and kidneys, ab- 
 sorption, nutrition, &c., are effected. We must first ascertain, 
 as precisely as possible, the internal and external circumstances 
 and influences upon which those individual processes, e. g., ex- 
 cretion by the skin, kidneys, &c., may depend, and by the 
 operation of which they undergo certain "modifications, such as 
 an increased consumption of water, variations in the composi- 
 tion of the blood (in relation to the amount of salts contained 
 in it), the consistence, circulation, and pressure of the column 
 of the blood, the relative temperature of the body, and of 
 the surrounding atmosphere, the relative inactivity of other 
 processes of excretion, &c. Or if we would acquire a clearer 
 notion of the effects of bleeding as a whole, we must first in- 
 vestigate, in a similar manner, how it may modify the individual 
 processes in the living body, e. g., how the abstraction of a 
 given quantity of blood may influence the motion and pressure 
 of the rest, the rapidity of its circulation, and perhaps its com- 
 position, &c. ; further how it may perhaps, in consequence of 
 all this, influence the processes of endosmose and exosmose, the 
 intensity of the respiration, and of other processes of excretion, 
 the generation of heat, &c. And it will always remain neces- 
 sary, in every such investigation of the changes produced in 
 an individual process in the living body by a given influence, 
 or agent, not only to exclude, as completely as possible, all other 
 important influences and agencies, but also to keep all the other 
 processes and functions, as far as possible, in their ordinary 
 equilibrium. We shall the sooner attain our present object — 
 the determination of causal connection — the better we succeed, 
 at least approximately, in causing the influence in question 
 alone to act, and this in such a manner that the particular 
 process in the living body which we wish to investigate in re- 
 lation to its conditions, e. g., to its dependence upon that in- 
 fluence, may alone undergo a change. In short we lAust, so 
 far as it is possible to do sO;, exclude everything which could 
 
164 SYNTHETICAL METHOD 
 
 render the question more complicated, and our conclusions 
 even less valid than would otherwise be the case. If, for in- 
 stance, after the long-continued use of a substance such as 
 iodine, mercury, common salt, and the like, a certain change, 
 e. g., emaciation, had been observed more or less constantly, we 
 must try to ascertain whether those substances had in them- 
 selves been positively concerned in the production of that effect, 
 and it would be impossible to decide this point with certainty 
 if the appetite had at the same time decreased, digestion been 
 deranged, or the supply of food been in any way diminished. 
 But if these, and other complicating circumstances, had been 
 sufficiently excluded, and it had been demonstrated that the 
 emaciation essentially depended upon those substances, we 
 should next have to investigate by what individual intermediate 
 operations, or physiological steps, the emaciation itself had been 
 produced, i. e., what processes in the living body had been in- 
 fluenced and changed by them in such a manner as finally to 
 produce the result in question. It would then be our office to de- 
 termine whether certain processes of excretion — in short, the 
 egestion of materials from the body — had in some manner 
 been increased, or whether the usual supply had simply been 
 diminished, or interrupted, whether it had occurred from want 
 of appetite, and from the small quantity of food taken, or in 
 consequence of some derangement of the processes of digestion, 
 assimilation, &c. 
 
 To judge whether, and how far, a disease has been removed 
 by a certain remedy, we must first ascertain by a sufficient varia- 
 tion of the circumstances, and by the method of exclusion, &c., 
 what part entirely different agents, or influences, such as diet, 
 rest, and, above all, the natural course of the disease itself, have 
 played in the cure. We must, therefore, in many series of 
 cases, have seen sometimes the one, sometimes the other of 
 these agents in operation, and have determined, by a comparison 
 of the results, under which of those circumstances the patient 
 has most frequently and rapidly been cured. In the most 
 favorable case, however, the positive value of our remedy would 
 thereby only be established empirically; the fact, namely, that 
 the disease had been cured by it, e. g., syphilis by mercury, or 
 intermittent fever by quinine. To understand further why 
 such remedies act beneflcially, we must ascertain all the modi- 
 
AND DEDUCTION. 165 
 
 fying or essential changes and processes in the disease, and the 
 way in which it is wont to be acted upon by our remedies. 
 
 Ifj on the other hand, we direct our investigations to the 
 phenomena and processes of the living body, in health or 
 disease, we must, first of all, divide them into the individual 
 agents, or elements of which they are in each case composed 
 — into their physiological links — and then investigate these 
 separately in relation to their general behaviour, conditions, 
 and mode of operation upon the other processes in the body. 
 
 Let us take one of the comparatively more simple functions 
 — the circulation. Having first distinguished its individual 
 mechanisms or agents as a whole, we must examine these 
 separately, and ascertain the circumstances upon which they 
 depend and their reciprocal action upon each other. Thus we 
 must ascertain the pressure which the heart's contraction com- 
 municates to a given column of blood, and the resistance oficred 
 to it in the bloodvessels and capillaries, &c, ; the consequent 
 rapidity of its motion in vessels of various calibre j the pressure 
 which the column of blood exerts upon the walls of the vessels, 
 and other analogous points. Having once determined the con- 
 ditions, efiects, and various modifications of the comparatively 
 simple and, for the most part, mechanical forces, or processes 
 in the circulation, we might then, with more prospect of 
 success, proceed to the investigation of their action under the 
 complex relations and influences of the living body, and to 
 the discovery of the part which its other functions and pro- 
 cesses, in operation at the same time, may play therein, e. g., 
 the respiratory movements, and the intensity, in each case, of 
 the process of respiration, and of various other processes of ex- 
 cretion, as well as certain tendencies of the nervous activity. 
 We should finally be in a position to deduce the causal con- 
 nection and conformity of the circulation as a whole, from these 
 laws of the individual agents or processes, the causes and effects 
 going on within it. 
 
 Essentially of the same kind would be our advance in the 
 investigation of a given disease. In the case of each patient, 
 we must divide the aggregate of his deviations from the normal 
 state into its individual processes or elements, into all its con- 
 necting physiological links, and endeavour to determine for 
 each its causal connection, conditions, and action. In fever, 
 
166 SYNTHETICAL METHOD 
 
 for instance, we must first observe its more constant pheno- 
 mena, its more constant and influential processes from the 
 commencement to the termination of the disease, and ascertain 
 their behaviour during its whole course, their modifications, in 
 each case by certain external and internal circumstances, and 
 their probable conditions and reciprocal action upon each 
 other. This holds good, for instance, for the increase and 
 variations of the temperature of the body ; for the circulation, 
 and the various processes of excretion by the skin, lungs, 
 kidneys, internal mucous membranes, &c. ; for the composition 
 of the excretions, and of the whole mass of the blood, and 
 finally for the varying functional states of the nervous system 
 in its different offices. If then an increase of temperature in 
 the body, an acceleration of the circulation, a certain change 
 in the composition of the blood, in the conversion of materials 
 within the body, and in the state of the nervous system had 
 been shown to be the most constant and most important 
 phenomena in a case of fever, we should next have to separate 
 each of those phenomena into its individual elements, and to 
 investigate their causal connection in the manner already 
 pointed out. We might then be able to deduce the conditions 
 and conformity of the whole process of fever, i. e., to construct 
 a theory of " fever " as a whole, so soon as we had once ascer- 
 tained the conditions and laws of its essential integral processes, 
 or changes, and the causes of the modifications in them result- 
 ing from their simultaneous or consecutive occurrence in that 
 disease. 
 
 We must always fix the starting-point of our investigations 
 in the most familiar and accessible portion of our subject, for 
 the path of perception leads from the known to the unknown, 
 from what is single and comparatively simple to what is com- 
 plex. In the investigation of a function, or of a disease, there- 
 fore, we shall more frequently have to commence with its 
 phenomena, or eff'ects, than with its causes or modifying cir- 
 cumstances. Those phenomena and processes in a given func- 
 tion, or disease, are always more familiar to us, and also 
 infinitely more accessible than their possible conditions and 
 causes. If we have once fixed upon a given circumstance, or 
 agent, as probably determining and essential in a certain func- 
 
AND DEDUCTION. 167 
 
 tion, we can then the better investigate it in its possible effects 
 upon various processes in the living body. In considering, on 
 the contrary, the agents of the external world, whether it be 
 the so-called hygienic influences, or remedies, and poisons, we 
 must commence with the investigation of their active elements, 
 and with the properties and mode of operation of these, and 
 not with those complex and variously dependent processes in 
 the living body themselves, which have either been imagined 
 to be the effects of the former, or proved to be such by experi- 
 ment. Frequently, however, it is the latter which first becomes 
 known to us; we learn the facts, that men are attacked by 
 intermittent fever in certain districts, and that they are cured 
 by quinine; that men experience dyspnoea and syncope at 
 great elevations, or that the workmen in certain manufactories 
 are attacked by colic and paralysis ; that men who have swal- 
 lowed a certain substance, or who, like the Turks, have smoked 
 opium, exhibit certain peculiar symptoms of poisoning, e. g,, 
 intoxication or narcosis. It is here from these empirically 
 established phenomena, or effects alone, that we can acquire 
 a knowledge of their causes, and ascertain their mode of 
 operation. 
 
 Whether we first direct our investigations to the effects of 
 a given influence and circumstance, or to the conditions of a 
 given process, or event, we shall always, in medical science, 
 have to deal with more or less complex and unknown objects. 
 To facilitate our investigation as much as possible, and what is 
 more important still, to render its results more trustworthy, we 
 must everywhere strive to place our problem in the simplest 
 circumstances possible. Our object, therefore, must be to ob- 
 serve the process or influence in question, under circumstances 
 (whether we may find such in nature, or be able to produce 
 them artificially) in which its character is not only sufficiently 
 distinct, but also in which it is least mixed up with and dis- 
 guised by other processes, or influences. Thus we may ascer- 
 tain what occurs in respiration ceteris paribus more easily in 
 any animal in proportion to the simplicity of its organization, 
 and of its respiratory apparatus, and especially of the process 
 of respiration in it ; in like manner, we should recognize the 
 occurrences in inflammation more easily in a simple tissue than 
 in a very complex one. So certainly as an anatomy, physiology. 
 
168 SYNTHETICAL METHOD 
 
 or chemistry of the human body pre- supposes that of the more 
 simple organisms, and even of plants, it is no less certain that 
 we shall never investigate the diseases of man with complete 
 success, or hope to arrive at a clearer comprehension of them, 
 until we have first investigated, and become familiar with the 
 more or less analogous processes, or derangements, in the 
 former, under the simplest possible circumstances. In like 
 manner the effects of a simple substance, e. g., of an alkaloid 
 such as morphia, or quinine, are more easily determined than 
 the mode of operation of their complex combinations with 
 other substances, as in opium or cinchona, unless the accessory 
 elements are absolutely inert. Our comprehension of the in- 
 fluence of a remedy upon the course, cure, or termination of 
 a disease, would also be rendered more e'asy if it only had 
 been employed in a large number of cases, than if several 
 other remedies and influences had been in operation at the 
 same time. If we judiciously selected a number of sick persons, 
 and left them entirely to nature, or at least refrained from the 
 administration of any medicines, and if it was observed that 
 those persons recovered as certainly and rapidly as after the 
 employment of those remedies, or the reverse, we should always 
 know more of their influence upon the cure than we do at 
 present. ■ 
 
 Our first attention is in all cases due to the investigation of 
 those processes, or influences, which are least dependent upon 
 others, and least variable and accidental, to those, in short, 
 which we have already recognized as the determining, or so- 
 called primary, essential, and most constant ones. Thereby 
 alone can we escape the danger of spending our time and 
 labour upon things the investigation of which is difficult on 
 account of their manifold variations, and unprofitable on ac- 
 count of the comparative insignificance of the results with 
 which they are concerned. To understand the process of 
 respiration it was, for instance, more important first to as- 
 certain the ofiice of the gases inspired, and of the interchange 
 between the blood and the air, than the possible influence of 
 the respiratory movements in themselves ; and it would be 
 more important to first determine the office of the oxygen of 
 the air than that of its watery vapour. In like manner, to 
 learn the causal connection and conformity to fixed laws in 
 
AND DEDUCTION. 169 
 
 "inflammation," we should rather investigate the phenomena 
 of increased heat, of the circulation and composition of the 
 blood, and of various processes of excretion, in relation to their 
 conditions, than those of pain or of digestion. To ascertain the 
 causal connection of the change in the composition of the blood 
 in inflammation, we should first direct our attention to one of 
 the most constant phenomena in it, viz., bufiBng. We should 
 have to investigate in what this phenomenon consists, of what 
 materials the crust is composed, and in what these materials 
 difier from the albuminous components of normal blood. We 
 must further seek for other more or less analogous changes or 
 conversions of the albuminous materials, &c., and examine the 
 circumstances comparatively under which the latter as well as 
 the buffing occur. We might thus, perhaps, succeed, not only 
 in ascertaining the conditions of the buffing itself, but also of 
 all the other more constant processes and changes in inflam- 
 mation by the co-operation of which the peculiar composition 
 of the blood, and the changes in its albuminous materials, may 
 have been produced. We might even deduce from these esta- 
 blished laws and conditions of the most essential processes in 
 inflammation those of the latter process itself, and thus explain 
 " inflammation " as a whole. The same holds good of " fever." 
 If we only knew that in fever some process, or circumstance, 
 such as increased temperature of the body, is a chief phase, 
 perhaps the condition, of many other, or even of all the pheno- 
 mena, and processes in it, we should have, first of all, to in- 
 vestigate that increase of temperature. We should have to 
 ascertain its action and variations, and the circumstances under 
 which we observe them; further their probable immediate or 
 remote dependence upon certain other processes in the body, 
 and upon various agents of the external world, and finally the 
 influence of that increased temperature itself upon the other 
 processes in fever patients. 
 
 To all this we may add that we must always commence 
 with the investigation of those individual phenomena and 
 influences, with those elements and processes in a complex 
 whole (e, g., in a function, or in a disease), which are compara- 
 tively the most simple and accessible, or with whose conditions 
 and effects we were already, perhaps, most familiar from other 
 sources. 
 
170 SYNTHETICAL METHOD 
 
 The simpler such a phenomenon or process is, and the 
 simpler and more direct may be its causes in their influence 
 and mode of joperation, the sooner are we able to draw con- 
 clusions concerning the conditions of the former from the mere 
 fact of their occurrence, and from their modifications under 
 certain circumstances. This applies to wounds, inflammation, 
 and other events resulting from mechanical injuries and similar 
 direct lesions, and to the effects of poisons. 
 
 Of infinitely more importance to us here, however, is the 
 long-established fact, that in most, indeed in all the functions 
 of the living body, certain phenomena and processes are 
 included, which commence and run their course in accordance 
 with simple physico-mechanical and chemical laws, and which 
 appear to play a more or less important part in its whole 
 mechanism. This may be observed in all the occurrences in 
 the living body and its processes which depend upon pressure 
 and gravitation, upon density or elasticity, upon adhesion, 
 capillarity, or porosity (e. g., various processes in the circula- 
 tion, imbibition or absorption, excretion of fluids and gases, 
 &c.) ; the same thing applies to the generation of ' heat and 
 electricity, and to their laws. Chemical action occurs chiefly 
 in the processes of digestion and respiration, in the develop- 
 ment of the components of the blood, and of the body in 
 general, from the materials supplied by our food, and in the 
 gradual conversion and final excretion of the converted or 
 decomposed materials of the body by the lungs, skin, kidneys, 
 liver, &c.,. — in short, in the whole process of nutrition, in the 
 whole renewal and conversion of tissues within the body. Prom 
 this it follows naturally that certain changes, certain deviations 
 of these chemico-physical processes, from the normal state, will 
 occur in all sick persons, without exception, and will exert a 
 greater or less degree of influence according to the individual 
 disease ; this is especially the case in the phenomena of fever 
 and inflammation, therefore in all acute diseases, — ^in diarrhoea, 
 indigestion, dysentery, cholera, dropsy, gout, in the formation 
 of gravel and calculus, and in all cachectic conditions. 
 
 Wherever such physico-mechanical and chemical processes, 
 or agents, are in operation, we must, first of all, apply ourselves 
 to a detailed investigation of them by the aid of experiment, 
 and according to the exact rules of natural science. Mention 
 
AND DEDUCTION. 171 
 
 has already been made of the forces which act in the circu- 
 lation. Thusj in considering the process of absorption, we 
 must ascertain the laws and conditions of simple imbibition, of 
 endosmose and exosmose, and of the motion in the absorbent 
 vessels of the materials taken up by them. If we wish to 
 investigate, for instance, all the occurrences in inflammation, 
 fever, &c., to learn in what they consist, and what may be their 
 conditions, we must not commence with their more enigmatical 
 and complicated elements, or processes, such as the phenomena 
 of innervation ; neither must we take up any given function as 
 a whole. Here, as elsewhere, we must primarily confine our- 
 selves to the investigation of the simplest processes — e. g., the 
 physico-chemical — and endeavour to determine their con- 
 formity and conditions in the case before us ; that is to say, 
 the processes and circumstances in the living body upon which 
 they depend, by which they are modified in various ways, and 
 upon which they themselves react. Having done this, we may 
 the more successfully investigate other phenomena and pro- 
 cesses — e. g., those of the nervous system. What has been 
 said will also apply to our investigation of the individual 
 external influences and agencies, to light, heat, the air, water, 
 to all the solid and fluid materials of our food, and to our 
 remedies, drugs, and poisons. We must first of all ascertain, 
 not only the properties and modes of operation of such of their 
 elements and agents as are most simple and accessible for 
 investigation, but also such of their efl'ects in the living body 
 as commence and go on in accordance with simple chemical 
 and physical laws. If we wish to ascertain, for instance, the 
 effects of morphia in the living body, and especially upon its 
 nervous system, to know in what these effects consist, and how 
 they are produced, we must not attempt to understand them 
 by way of direct investigation, but we must first ascertain 
 what changes morphia may produce in various chemical pro- 
 cesses in the body, and then trace its effects upon the circu- 
 lation, temperature of the body, and various processes of 
 excretion, &c. We may thus hope better to understand its 
 effects upon sensation and muscular contraction. 
 
 All this makes it evident that our eff'orts are insuf&cient to 
 explain either the aggregate of these efl'ects in the living body, 
 or in a function, or a disease, as a whole, because all these 
 
172 SYNTHETICAL METHOD 
 
 physico-chemical processes are, in the living body, connected 
 with many others; for the same reason, their conditions and 
 laws cannot here be so simple as in inanimate nature. If, 
 however, the conditions and laws of this species of phenomena 
 and processes in the living body were once established, we 
 should, notwithstanding what has just been said, have acquired 
 a firm starting-point and solid basis for our future compre- 
 hension of the aggregates of those functions and diseased 
 states, and of the influences of the external world upon them. 
 Were we able to test, in either case, how far certain processes 
 and elements of such aggregates can be deduced from those 
 physico-chemical processes and their laws, we should doubtless 
 acquire important information concerning those aggregates 
 themselves, and much in them, of which we have at present 
 no fixed idea, might be found capable of explanation. In 
 short, it is only by such an investigation of the minutest 
 individual phenomena and processes, and especially of such 
 among them as are simplest and most accessible, that we can 
 hope to acquire a clearer insight into the connection and con- 
 ditions of the whole. Experience has sufficiently taught us, 
 that men have for centuries gone on regarding a function, a 
 disease, or its cure, as a whole, and observing its occurrence, 
 and the modifications resulting from various special circum- 
 stances, without learning anything positive of its peculiar 
 course and mechanism, or of its conditions and conformity to 
 fixed laws. 
 
 Instead, therefore, of wearying ourselves by the investigation 
 of those great aggregates of efi^ects and influences as such — 
 i. e., as we meet with them in nature — and seeking in vain for 
 the conditions and laws of their development and action as 
 such, we must first endeavour to discover, on the one hand, 
 the conditions of each individual process, or efl'ect, and, on the 
 other, the properties and mode of operation of each individual 
 influence, or determining circumstance. Such detailed in- 
 vestigations in physiology and in the whole science of medicine 
 have an infinitely greater value than whole compendia, or the 
 most beautiful and comprehensive theories. He who has, for 
 instance, investigated the variations in the weight of the body, 
 and ascertained the amount of the excretions in a healthy or 
 sick person, or the single phenomenon of the temperature of 
 
AND DEDUCTION. 173 
 
 the body, in fever or inflammation, with all its oscillations and 
 relations to other phenomena and processes — e. g., to the cir- 
 culation, to respiration, and to various processes of excretion — 
 will doubtless have done more real service to medical science 
 than one who has brought forward the most ingenious views of 
 the aggregates of those diseases, or functions, and perhaps met 
 with a larger share of applause. And if the above method is 
 insufficient for the discovery of all the laws, still more of the 
 essential causes of the processes with which we are concerned, 
 our hopes are not disappointed, for they did not lead us so far. 
 We shall be satisfied with having discovered much that is , im- 
 portant and instructive, and our advance will, in the course of 
 time, be facilitated, where we have, perhaps, little expected it. 
 On the other hand, all our more direct attempts to fathom the 
 conditions and conformity of our processes may lead to hypo- 
 theses, but not to a clear comprehension of them. The great 
 object everywhere in the investigation of nature, and especially 
 in the medical department, is to discover, not the reasons, but 
 the mode, not the essential and ultimate causes, which lie far 
 beyond our reach, but rather the manner in which our pheno- 
 mena and processes commence and run their course, and all 
 the circumstances under which they constantly occur simul- 
 taneously and consecutively. 
 
 We have already spoken, when upon the subject of the 
 inductive process, of the assistance which is to be obtained 
 in these investigations both from observation and experiment, 
 under certain given circumstances, and from the employment 
 of analogies and statistics, and hereafter we shall have more 
 to bring forward on this subject. The mode of their Em- 
 ployment, their importance, and their services in themselves, 
 are the same in the one process as in the other. Inasmuch, 
 however, as the circumstances under which we employ them 
 here are simpler and clearer than in the investigation of 
 complicated objects upon a mere empirical basis, the results 
 obtained by us will be infinitely more certain and more con- 
 ducive to a full understanding of our subject by following 
 the deductive rather than the inductive method. 
 
 Were we to assume that the conditions and laws of all the 
 elementary processes and effects in the living body and the 
 
174 SYNTHETICAL METHOD 
 
 laws of operation of all the individual agents or influences 
 which affect them, had been demonstrated with as much exact- 
 ness as has already been attained to in chemistry, physics, 
 mechanics, and astronomy, we could then deduce, or explain 
 from them the conditions and conformity of our most complex 
 processes, and the effects of our most complex influences. This 
 construction or deduction is, in itself, so little difficult as 
 to be a matter of simple calculation. 
 
 Thus the physicist can calculate the fall of a given body 
 with mathematical precision from the known laws of gravity or 
 of the • earth's attraction, and from the laws of atmospheric 
 pressure and of the density of the atmosphere. The range of 
 a gun, and the path and velocity of a ball discharged from it, 
 can be deduced from the established expansive force of the 
 gases developed by the gunpowder, from the weight of the 
 missile, from the density and consequent resistance of the air, 
 and from the angle of elevation, &c. In like manner the 
 chemist can calculate from the known properties and laws of 
 his simple inorganic substances, the behaviour and conformity 
 of their combinations with each other — e. g., as acids, bases, 
 salts, &c. — unless, in consequence of their combination, sub- 
 stances and compounds are formed with entirely new properties 
 and with new faws of action, as is sometimes the case with 
 organic compounds. We do not aim at accomplishing any- 
 thing similar to this in the study of the vital processes, nor 
 can we attempt, with even an approximate degree of precision, 
 to deduce from the established laws of their individual agents 
 their development as a whole and the conformity of their origin 
 and course. 
 
 Had we once ascertained, for instance, the conditions and 
 laws of all the individual changes which take place in venous 
 blood, in its passage through the lungs, (e. g., the changes of 
 certain of its component parts, the egress of certain gases, and 
 the changes in its colour, temperature, density, &c.) — in short, 
 if we knew all that, on the accession of atmospheric air, occurs 
 in the lungs and in the blood contained in them, and why the com- 
 ponents of that air — e.g., the oxygen — produce those changes 
 in the venous blood, we could thence deduce with certainty the 
 conformity of respiration as a whole, and should thus be able 
 to explain the whole process. It is well known, however, 
 
AND DEDUCTION. 175 
 
 that the latter attempt has been made repeatedly before the 
 former investigations had been carried out comprehensively 
 enough and their results confirmed. 
 
 The reader is doubtless acquainted with Liebig^s ingenious 
 attempt to deduce this complex vital process and several others 
 from certain chemical processes, or agents in them, and from 
 the conditions and laws of the latter — i. e., from the conditions 
 and chemico-physiological links in the absorption of oxygen 
 into the blood, on the one hand, and in the excretion of car- 
 bonic acid from it, on the other. Liebig set out from the 
 known property of protoxide of iron to combine, when air and 
 water are present, with a larger amount of oxygen to form the 
 •hydrated red peroxide ; another fact from which he started is 
 the property of this hydrated peroxide, when in contact with 
 organic substances, to part readily with some of its oxygen, and 
 thus become reconverted into the protoxide. Many of these 
 circumstances appear to be present for the iron in the blood. 
 The oxygen inspired may combine with the iron of the dark 
 venous blood and effect a higher degree of oxidation in it, 
 whence Liebig explains the conversion of the dark venous into 
 the brighter arterial blood. The hydrated peroxide of iron, on 
 the other hand, in its further circulation through the body, 
 comes into contact, in the capillaries, with compounds and 
 substances rich in carbon, resulting from the metamorphosis 
 and conversion of tissues, and from the entrance of bile into 
 the blood, &c. It then partly yields its oxygen to these, and 
 especially to the carbon in them, and is thereby again reduced 
 to the lower degree of oxidation, while the carbon of those 
 organic substances is converted into carbonic acid by the free 
 oxygen which combines with part of the protoxide of iron in 
 the blood. In the lungs, however — where it comes into con- 
 tact with the newly absorbed oxygen and with the water of the 
 blood — it again yields up its carbonic acid, which is expired, 
 and the protoxide, thus set free, again combines with the 
 oxygen inspired, and with water, to form the hydrated peroxide. 
 
 It is also well known how Liebig sought to explain the 
 generation of animal heat by the conversion of iron, or its 
 protoxide, into the peroxide on the one hand, and on the other, 
 by the conversion of the carbon of those organic compounds in 
 the tissues and organs into carbonic acid by this process of 
 
176 SYNTHETICAL METHOD 
 
 combustion, or oxidation. It is not necessary here to examine 
 further into the basis and validity of this attempt at explana- 
 tion. It serves, in any case, as a good example of an endeavour 
 to deduce the still unknown conditions or laws of an entire 
 complex process from the conditions and laws of certain 
 simpler and better-known processes and agents — an attempt 
 ■which we shall recognize more or less in every similar theory 
 in medical science. 
 
 We are enabled further to explain by Graham^s well-known 
 law of the diffusion of gases a purely physical process^ but one 
 of the highest importance in respiration, viz., the exchange of 
 gases between the blood in the lungs and the air inspired. By 
 this law a space already filled with any gas nevertheless takes 
 up very rapidly any other gas not previously present, and this 
 occurs also where two spaces are separated by an animal mem- 
 brane. By this law we can explain the previously enigmatical 
 facts that the entrance of oxygen into the blood in the lungs 
 and the excretion of carbonic acid from it occur so rapidly 
 through the walls of the capillary vessels and cells of the lungs, 
 and in spite of them. We understand at the same time how 
 another circumstance, which appeared at first sight calculated 
 to prevent the entrance of new gases into the cells of the lungs 
 during respiration, viz., their being already full of another gas, 
 by no means produces this effect. This law of diffusion thus 
 explains to us a portion of the whole process of respiration — 
 i. e., a physical process in it, as well as certain chemical pro- 
 cesses already mentioned. We can further deduce the exchange 
 of certain fluids between the blood and the parenchyma of the 
 lungs from the known laws of imbibition, or of endosmose and 
 exosmose. Those chemical processes in respiration and their 
 established conformity to fixed laws might also aid us in ex- 
 plaining why the above-mentioned exchange of gases between 
 the blood and the atmosphere takes place in the lungs only, 
 why the oxygen inspired does not penetrate the whole body 
 with the same rapidity, and why, on the other hand, the carbonic 
 acid of the venous blood is not excreted, as well from all the 
 other organs, cavities, and parts of the body, as from the lungs. 
 We should know that it is in the lungs only that the oxygen 
 inspired, immediately upon its entrance into the venous blood 
 in them, meets with a body, viz., iron, with which it enters 
 
AND DEDUCTION. 177 
 
 into direct combination, just as, on the other hand, the carbonic 
 acid formed in the capillaries comes in contact, at the moment 
 of its development, with the protoxide of iron with which it 
 combines in the nascent state. 
 
 The above may suffice to show why we must, first of all, 
 become acquainted with the individual parts of each function, 
 or disease, in relation to their conditions, and to the conformity 
 of their development, as well as with the laws of operation of 
 all the individual influences and circumstances, by the co-ope- 
 ration of which they arise and run their course. Were we 
 once familiar with each of these individual laws of development 
 and operation, we might deduce from them the laws according 
 to which a function, as a whole, and a disease, or even life, as 
 a whole, commence and run their course. And this would 
 sufficiently explain why such is their precise nature, and why 
 they commence and go on precisely in this and in no other 
 manner. We might even determine what effects must be pro- 
 duced by a given combination of influences and agents in the 
 living body,, and be able to point out by what combination of 
 conditions and circumstances a given effect, or occurrence in 
 the living body, had been produced in the case in question. 
 We could equally predict what effects a given combination of 
 influences and circumstances would produce in a given case. 
 
 Unfortunately, however, we are not yet so far advanced in 
 medical science. We do not as yet even know all the indi- 
 vidual elements which constitute the functions and processes in 
 the living body, in health and disease, any more than the 
 individual active circumstances and agents of the influences 
 which affect them from without. Much less have we as yet 
 succeeded in demonstrating the conformity and causal connec- 
 tion of such individual occurrences, or effects, and of the indi- 
 vidual circumstances which modify them ; and this applies even 
 to those which act according to the comparatively simpler 
 chemico-physical laws. For these reasons we cannot yet 
 explain anything scientifically, and can scarcely assert anything 
 positively, while every attempt at explanation is met by doubts, 
 and allusion is made to contradictory facts or 'experiences, to 
 accident and exceptions. So long as we are unable to determine 
 the conformity of our vital processes, and of the influences 
 which affect them, we cannot speak of a scientifically correct 
 
 13 
 
178 SYNTHETICAL METHOD 
 
 physiology, or of a rational theory of disease, and of thera- 
 peutics. Such might, indeed, in many cases already exist, but 
 the true causal connection of our phenomena and processes^ 
 and the laws of operation of our influences and agents have 
 nowhere been clearly demonstrated, and our clinical practice is 
 not based upon a clear scientific comprehension, but rather 
 upon simple, more or less uncertain experience. - 
 
 Enough has already been said of the diflSculties which our 
 subject presents at every step. We have no alternative but 
 to take it as we find it ; we must not treat the problem it 
 offers us either too partially, or too narrowly, we must not 
 regard it either as too easy, or too difficult. Men must con.,- 
 tent themselyes with the knowledge of what is comprehensible 
 in nature ; and, if they do not understand all that they wish 
 to understand, they must remember that Nature, being such 
 as she is, has evidently not been designed with a view to their 
 fully understanding her. But if it is our earnest endeavour 
 to discover, amongst the mass of phenomena and circumstances, 
 of effects and causes which we observe simultanequsly or con- 
 secutively, just those which stand in a causal connection with 
 each other, we shall — if we keep our object steadily in view — 
 find more and more the means which, approximately at least, 
 will enable us to do so. Numerous as may be the effects of 
 each influence or cause, and numerous as may be the causes each 
 occurrence or effect may have, we shall, in the end, be able to 
 discover them. The main point, however, will be, not only 
 that we should observe and investigate consistently, but that 
 we should, first of all, discover and select what is most fitted 
 for investigation. This choice will, of course, vary according 
 to time and circumstances, and upon it the whole success of 
 an individual will frequently depend. 
 
 If we had already investigated nature to the full extent 
 rendered practicable by the auxiliary means which we possess, 
 we should have attained a very different status of knowledge 
 and practice to our present one. This remark applies much 
 more to the study of the vital phenomena in disease than in 
 health. Our present knowledge of diseased conditions, how- 
 ever, is but a small part of what has always been accessible 
 enough to simple experience. Thus we have ascertained, for 
 instance, next to nothing of the diseases of hot and cold cli- 
 
AND DEDUCTION. 179 
 
 mates, we know little of the various classes of animals down to 
 the simplest Mollusca and Polypes, or of the majority of the 
 analogous processes and conditions in plants, although the 
 nature and internal connection of the diseased conditions in 
 these the simplest organisms, would doubtless be much more 
 easily recognized in them than in such as are higher and more 
 complicated. Even in man these phenomena and processes 
 have not been determined to the extent attainable by the 
 simplest observation, and, least of all, in disease. We should 
 have much to do if we sought to investigate more exactly the 
 phenomena of temperature and electricity, of the circulation, of 
 imbibition, or of endosmose and exosmose, — i. e., all that which 
 could be ascertained by a more extensive employment of the 
 thermometer and scales, or of our auxiliary chemical means, in 
 the healthy and in animals, as well as in the sick. 
 
 Our whole future prospects are essentially based, as has 
 already been explained, upon the attempt to determine sepa^ 
 rately, first of all, the conditions and effects of what is most 
 simple and accessible ; we may then proceed to what is more 
 complex, and investigate it under the simplest circumstances 
 possible. We cannot, it is true, acquire by our investigations 
 any direct knowledge of the chemical processes within the living 
 body. We might, however, investigate the ingesta and egesta 
 with sufficient exactness to enable us to draw conclusions, by 
 the aid of analogies, and by comparison with other more or 
 less similar changes in organic substances, concerning the oc- 
 currences and chemical processes in the animal economy, with 
 at least much greater probability than we can do so long as we 
 have not investigated all that is accessible. Whenever any- 
 thing important is discovered in the department of physiology, 
 whether in the physico-chemical processes of our economy, or 
 in the nervous system, &c., we have long been accustomed to 
 inquire whether it may further our comprehension of the 
 origin and course of certain diseased conditions, and of their 
 cure. Here, as elsewhere, we gain, by each step that we take 
 in the analysis and investigation of the vital processes, some 
 knowledge in entirely different and often apparently uncon- 
 nected paths. With every new discovery, however remotely it 
 may be connected with the comprehensive questions of medical 
 science, we gain a wider horizon and new points of view, per- 
 
180 SYNTHETICAL METHOD 
 
 haps even clearer and mofe definite starting points. We 
 receive at once thereby an impulse to further investigation in 
 entirely new directions^ and new means of investigation are 
 afforded us such as would never have occurred to our minds 
 from the mere observation of the whole^ — i. e., of the aggregates 
 of our phenomena as such. 
 
 Thus the knowledge of those palpable changes in our 
 patients, which pathological anatomy affords us, has not, in 
 itself, essentially furthered our comprehension of the diseases 
 themselves, and of their causal connection; we have often 
 only had new questions and problems presented to us — e. g., 
 the conditions of a given lesion, of an inflammation, of exuda- 
 tions, of the processes of softening, or atrophy, &c. These 
 pathological phenomena have, nevertheless, done us infinite 
 service by affording us visible, tangible, and more definite 
 states for further investigation than our former symptomatic 
 outlines of disease — states and changes which we can frequently 
 produce at discretion. They afford us, as it were, a handle 
 by which we can grasp, and investigate more closely the dis- 
 eased processes in question. A clearer insight into the 
 chemico-physical processes of the body, in health or disease, 
 and into the part they play in its whole mechanism, would 
 render us very much the same service. It would enable us to 
 undertake the investigation of the latter in a comparatively 
 more simple and exact manner. It is not necessary here to 
 allude more explicitly to the increased knowledge of the vital 
 phenomena which we have acquired by the aid of chemistry and 
 physics, especially in the most recent times, or to the new views 
 and impulse they have communicated to further investigations. 
 
 If we are precluded from attaining our object so easily 
 and so directly as it is possible for the physicist and the 
 chemist to do in the case of at least very many of their pheno- 
 mena, no insuperable impediment exists to our progressive 
 approach to it. If we cannot comprehend directly all our 
 complex aggregates of phenomena, causes, and effects, we must 
 come at them as well as we can indirectly, whether by a more 
 extensive observation of them, as they are met with in nature, or 
 by a skilful examination of them, and an express arrangement 
 and variation of the circumstances — in short, by experiment. 
 A science whose practical object is the welfare of mankind, 
 
AND DEDUCTION. 181 
 
 and whicli can only fulfil that requirement in the ratio of its 
 own progress, must not spare this labour. Even the physicist 
 was not able to ascertain directly that our earth revolves about 
 its axis ; we even know that physicists have been sacrificed on 
 the ground of this fact being opposed to a dogma of the 
 church to which they belonged. It has only been by numerous 
 by-paths, by many indirect proofs, that this fact has been 
 established ; it was shown, for instance, that the revolution of 
 the sun, and of the whole vault of heaven, with all the heavenly 
 bodies, around the earth, is only apparent ; that the earth is 
 flattened at the poles ; and this view was confirmed by the dis- 
 covery of the laws of gravity, and of the so-called force of 
 attraction and centrifugal force. Centuries of zealoas and 
 careful investigation in astronomy and physics were required 
 for the establishment of even these indirect proofs. It is very 
 possible that with all our exertions, we shall attain nothing 
 more than an approximately clear insight into the causal con^ 
 nection and conformity of our most simple phenomena and 
 processes, and that we must content ourselves, for a long time 
 to come, with individual fragments and instalments of the whole. 
 It depends upon ourselves, however, whether other and better 
 knowledge is to follow. It will and must follow if we earnestly 
 seek it, and we shall frequently acquire further information 
 and clearer views from entirely unexpected sources, whether it 
 be from discoveries in other departments of natural science, 
 or from the successful attempts of investigators in our own.- 
 
 Yet we can scarcely hope with all this to attain to the same 
 degree of precise knowledge as has been acquired in chemistry, 
 physics, and mechanics. Such is the nature of the objects of 
 our investigation, so closely are all the phenomena and processes 
 in the living body connected with each other, and with those of 
 the external world, so varied is the order of their occurrence, 
 that we shall perhaps be always restricted to a calculation of 
 probabilities. The highest point we can hope to attain may 
 be predicted to consist in being able to give an increased degree 
 of certainty to this calculation of probabilities, by the further 
 discovery of laws, and certain constant relations of the vital 
 phenomena and processes to each other, and to external nature. 
 At present, as every one knows, any such calculation is but very 
 vague. We know but a small part of all the influences and 
 
182 SYNTHETICAL METHOD 
 
 agencies which constitute a given function, or which affect the 
 living organism in a given case of disease. And even in those 
 which are more familiar to us, we know but little of their 
 laws, and of the definite manner in which they affect certain 
 processes in the body. We may, therefore, easily form a false 
 estimate of highly important conditions and phases, or possibly 
 overlook them altogether, and, under the most favorable cir- 
 cumstances, we can acquire notions only approximately correct 
 of those most familiar to us. How then can we hope, Tvhen 
 our knowledge, even of the comparatively simplest things, con- 
 tinues confessedly so small, and our comprehension of the con- 
 ditions and connection of our individual elementary processes 
 and influences remains so imperfect, to deduce from their laws, 
 with even an approximate degree of precision, the conformity 
 of the most complicated processes and influences ? 
 
 Every theory which seeks to explain any vital function, or 
 disease, or the operation of any hygienic influence, or of any 
 remedy in the living body, or the whole cure of any disease, 
 shows that this attempt has been ventured upon at all periods, 
 and continues to be ventured upon at the present time, as well 
 as that, in a certain sense, it is perfectly justifiable. Every 
 such theory, or explanation is, in fact, a species of comprehen- 
 sive proposition, or attempt at generalization. We attempt to 
 explain by it a whole series, or aggregate of processes, effects, 
 and causes, while we do not clearly understand, and are unable 
 to explain an individual process, the production of an individual 
 effect, or the mode of operation of au individual determining 
 circumstance I From an innate feeling of necessityj instinc- 
 tively almost, every one deduces the conditions, and real or 
 supposed laws of the individual phenomena and processes with 
 which he has to deal, as well as the rules of his art, from cer- 
 tain general propositions and views. Every one, for instance, 
 who attempts to explain the conformity to fixed laws, and the 
 internal connection of a function, deduces them from his general 
 notions of life, and of the action and conditions of its individual 
 processes, whatever the amount of his knowledge of them may be. 
 The pathologist, for instance, deduces the production and condi- 
 tions of a so-called dyscrasy, or of an idiopathic affection of tlie 
 nervous system, in the former case from his notions concerning 
 the formation and composition of the blood, and its influence 
 
AND DEDUCTION. 183 
 
 upon nutrition, the processes of excretion, and the conversion of 
 tissues ; in the latter case, from his general notions with regard 
 to innervation, and from the views he may have formed concern- 
 ing the importance and mode of operation of the central organs, 
 and of the so-called centripetal and centrifugal portions of the 
 nervous system, &c. In short, we choose our remedies and rules 
 of diet, and explain their effects, according to our previous 
 views of health, or of a given disease, and according to our 
 estimate of the influence, properties, and mode of operation of 
 certain hygienic agents, or of medicines generally. 
 
 Several examples of this have already been given. A further 
 illustration of it is afforded by a disease which has long at- 
 tracted the attention, not only of the physician, but also of the 
 chemist, viz., diabetes mellitus. The numerous attempts which 
 have been made to explain all the conditions and derangements 
 in it, and especially the peculiar changes in the urine of patients 
 affected by it, in relation to its composition and quantity, are 
 also well known. Some modern theorists, Bouchardat and 
 others, have founded their explanation upon the fact that starch 
 and analogous substances are converted into sugar by the action 
 of diastase, yeast, and all the substances which belong to the 
 albuminous group. Prom this they have inferred that a simi- 
 lar conversion takes place in the stomachs of such patients in 
 an abnormal manner, and to an unusual extent, and attempted 
 to explain thereby the presence of sugar in their urine. Far- 
 ther, because alkalies and alkaline earths appeared to be of 
 service for a time in diabetic patients, — i. e,, because the sugar 
 in their urine was diminished in quantity, or perhaps disap- 
 peared for some time, they inferred that in consequence of their 
 administration, the conversion of starchy matters, &c., into 
 sugar was prevented; and that, on the other hand, their pre- 
 sence in the blood facilitated the conversion and oxidation, &c., 
 of the sugar in it. In his further observation of such patients, 
 Bouchardat remarked that the temperature of their bodies was 
 reduced 2 — 3°, and deduced from this circumstance a further 
 confirmation of his theory that the disease depended upon a 
 diminished intensity of the process of oxidation or combustion 
 within the body. To facilitate this process by artificial means, 
 he caused his patients to inspire oxygen, and asserts that he 
 observed a diminution, and even the absence of sugar in their 
 
184 SYNTHETICAL METHOD 
 
 urine. What he really observed could, howeverj at best have 
 been the diminution or disappearance of the sugar during and 
 after the employment of those means, but not in consequence 
 of their use and influence ; for neither Bouchardat nor any one 
 else has yet succeeded in demonstrating the accuracy of the 
 whole theory, and therewith the conditions and causal connec- 
 tion of the development and cure of the disease. 
 
 This example is also useful in showing us that we cannot so 
 far safely rely upon any theory, upon any single deduction, or 
 explanation in our whole science. None of them have stood 
 the test of time ; they have all yielded to our advanced know- 
 ledge, and even, in many cases, to the results of simple expe- 
 rience ; and the reasons why this could not have been othei-wise, 
 may easily be gathered from the foregoing pages. 
 
 This very disadvantage is, however, in certain respects an 
 advantage. In our dilemma as to whether or not we may 
 believe in the accuracy of any given theory, we receive a cer- 
 tain support from the very quarter in which all our attempts 
 at explanation have been frustrated, — i. e., from simple expe- 
 rience itself. It is, after all, only the observation of the 
 actual state of things — in short experience — which can afford 
 us the means of testing our various deductions and attempts 
 at explanation. Those aggregates of phenomena or processes, 
 of effects and causes, which we meet with in nature, and 
 the investigation and explanation of which present so many 
 difficulties, and destroy so many illusions, afford us in their 
 actual condition, and as they may be established by every 
 observer, the highly-important aid, of serving, to a certain 
 extent, as infallible tests of the accuracy of the boldest and 
 most ingenious theories and deductions. We always can, and 
 therefore must, by means of such observation, make a kind of 
 counter-test, and note whether, and to what extent, we have 
 calculated correctly, or falsely, in our interpretations and in our 
 deductions of the conformity and causal connection of our pro- 
 cesses. "Demoustratio longe optima est experientia," as Bacon 
 correctly observes ; and the same thing is expressed by the old 
 saying, " experience is the test of all theories ;" not, however, 
 the keystone as so many have believed. 
 
AND DEDUCTION. 185 
 
 In other words, therefore : 
 
 The laws we have deduced, i, e., all our attempts to ex- 
 plain the aggregates of our complex processes, or influences, 
 from the conditions, or laws of operation of their individual 
 agents, can only lay claim to validity and be relied upon, in 
 so far as they agree with the actual state of things, and in 
 so far as the deductions, or conclusions, to which they lead 
 us in a given case coincide with what we observe and meet 
 with in reality. 
 
 To return to the point from which we started in our inves- 
 tigations, our object is, not merely to ascertain and still less to 
 assert that certain phenomena, certain processes or circum- 
 stances may present themselves simultaneously or consecutively, 
 or that certain causes, or influences, might affect them in a 
 given manner, but rather that they in reality always present 
 themselves so and not otherwise, and exist in this constant 
 causal connection with each other. Our problem remains, to 
 test whether and how far they really so occur together, or 
 follow each other in the constant manner which accords with 
 our theories of them, and with the laws which we have advanced, 
 or inferred. Even astronomers, after having ascertained through 
 their calculations the laws by which a heavenly body moves, 
 have found themselves compelled to test the accuracy of these 
 calculations by further observation of the various positions it 
 successively assumed in the firmament. Thus Newton and 
 others have tested and ascertained, in the case of the heavenly 
 bodies, the accuracy of the laws of motion, or gravitation 
 already discovered by Keppler. In other words, it was Newton 
 and some of his contemporaries who first succeeded in de- 
 monstrating that the motions of our planets around the sun 
 could not take place in the manner in which experience has shown 
 them to do, i. e., — in an ellipse, — if they were not attracted 
 by the sun in exact accordance with Keppler's laws of gravita- 
 tion. What Keppler had calculated mathematically, Newton 
 and others have demonstrated by the aid of experience and 
 exact observation. 
 
 On the other hand, all our theories and very nearly all our 
 explanations of the causal connection and conformity of the 
 vital processes in health and disease have succumbed to the 
 test of further experience and more exact observations. They 
 
^86 SYNTHETICAL METHOD 
 
 have died out, one by one, and will continue to do so until the 
 requirements in our science, which have already so often been 
 mentioned,have been fulfilled, and what lies at least next at hand, 
 — i. e., the conformity of our individual processes, — has been 
 clearly demonstrated. Thus, neither the theory of the forma- 
 tion of sugar in diabetic patients mentioned above, nor any 
 other, has been able to withstand the test of increased expe- 
 rience and clinical and experimental investigation ; and whether 
 the same sugar had subsequently been observed to be produced 
 under circumstances, or had been found in parts, fluids, &c., 
 of the body in which, according to that theory, no sugar should 
 have been formed ; or whether no sugar had been found where 
 it ought to have been present, the theory would equally have 
 been a false one. The simple fact of the continuance of the 
 disease, and of the presence of sugar in the urine, and the 
 death of such patients proved that alkalies, earths, oxygen, &c., 
 failed to effect what, in accordance with the assumptions, or 
 postulates of that theory, they ought to have effected. No 
 less was the well-known theory of Broussais, that almost all 
 diseases depended upon an irritation, or inflammation of the 
 stomach and intestines, soon refuted by the experience that no 
 such derangement was discovered in the generality of patients, 
 at least not as a primary, or essential element of their disease, 
 and that the development, course, and cure of most diseases, 
 and the mode of operation and success of our remedies, rather 
 contradicted, than agreed with the theory. And any one who 
 has attempted to deduce, in every case, the phenomena of 
 apoplexy and the hemiplegia, &c., in it, from an extravasation 
 of blood into the brain, or from other palpable changes in that 
 organ — i. e., to explain them thereby — will no less certainly have 
 found himself contradicted by further and more exact observation. 
 It is also evident that we cannot rely upon any attempt to 
 explain either life itself, or any of its functions as a whole, or 
 depend upon any theory of the development, conditions, and 
 nature of a disease, or of the mode in which it may be acted 
 upon either by a given remedy, or by any of the various agents 
 of the external world, simply because such theories appear 
 suflSciently correct and plausible to ourselves, or others : their 
 accuracy is only to be confided in when they have been con- 
 firmed by experience, and by the determination of the exact 
 
AND DEDUCTION. 187 
 
 state of things. The fact that all theories of this kind in 
 medical science have been refuted rather than confirmed by 
 more extensive and exact experience, or that at least their 
 partial and confined character has always become evident, 
 serves to explain that distrust of them which seems rather to 
 increase than to diminish in the minds of candid investigators. 
 Hence follows the necessity, so long justly insisted upon by 
 the empirics in relation to all theory, of every where observing 
 attentively, as frequently as possible, and in all its details, the 
 obvious occurrences of nature, and the tangible results of our 
 experiments, with the mode and order of their occurrence, and 
 the circumstances under which they usually occur; and of. com- 
 paring carefully, in as many instances as possible, the cases which 
 agree in their more important points, and of observing and 
 investigating the same process, the same event, or the same 
 influence under the most various circumstances possible. In 
 other words, we must always, in our science, cleave to simple 
 experience and mere empirical facts, or laws, and must there- 
 fore, above all, seek to discover more and more of them by 
 the employment of all the auxiliary means which have already 
 been alluded to in speaking of the process of induction (see 
 Section III). 
 
 This simple empirical establishment of certain facts must, 
 however, by no means be regarded as the whole problem before 
 us ; it is not the last, but rather the first, preparatory step. 
 We must, at last, ascertain the causal connection and con- 
 formity to definite laws — in short, the theory — of the things 
 which we have established empirically, of all the phenomena, 
 processes, and circumstances which we have observed to co- 
 exist or follow each other. But since our knowledge of the 
 latter, for the reasons often mentioned already, has hitherto 
 amounted to little more than a calculation of probabilities, and 
 will doubtlessly continue, more or less, to be so, we must test, 
 as frequently as possible, whether our experience, and the actual 
 state of things agree with our conclusions, or abstractions, and 
 with the kind of conformity which we have deduced and con- 
 structed for our phenomena and processes, or whether our con- 
 clusions and attempts at explanation, our notions of their causal 
 connection, condition, or operation, have been too narrow and 
 partial, or even altogether erroneous. 
 
188 SYNTHETICAL METHOD 
 
 If in a given case, for instance, the phenomena, effects, and 
 events, which ought to have occurred according to our theory, 
 according to our views of their causes, and of the mode of 
 operation, and importance of those causes under the given cir- 
 cumstances, either fail to occur at all, or do not occur in the 
 manner to be expected, our theory — i. e., our previous deduction 
 of their causal connection and of the laws of operation of all 
 the influences which afl'ect them — can be of little or no value. 
 For although the circumstances and influences which we 
 may have regarded as the causes of the effect in question, and 
 the mode of operation and laws of which we believed ourselves 
 to have demonstrated, may possibly have existed and operated, 
 the effect or event in question (e. ff., a certain process in the 
 living body, a disease, or a cure) either does not occur at all, or 
 at least not in the precise manner and order which our theory 
 has led us to expect. We are thus obliged to confess that we 
 have not correctly enough estimated, or comprehensively enough 
 observed several, and perhaps important parts, or elements of 
 the whole process — that we have perhaps overlooked certain 
 causes of it, and the mode of operation and influence of certain 
 determining circumstances in it. To speak more concisely, we 
 have assumed certain causes, certain effects which either do 
 not exist in reality, or not in the exact form and definite con- 
 nection, and relation to each other which we have imagined. 
 
 Unfortunately, however, this correction of our theories and 
 attempts at explanation by experience is infinitely more diffi- 
 cult in medical science than in physics and chemistry, because 
 our experience and observations themselves are in a great 
 measure fluctuating, and not to be relied upon, and especially 
 because they admit of very different interpretations. A case, 
 for instance, which appears to one person to be opposed to a 
 given theory, or to demonstrate the inaccuracy of a given mode 
 of explanation, may appear to another to be a further illustra- 
 tion in its favour. At all events the latter view would be 
 justified if it could be demonstrated why, in any such case, 
 the occurrence in question, a certain effect, &c., has not taken 
 place at all, or not in the manner to be expected in accordance 
 with our theory. We should have no reason, therefore, to 
 doubt its correctness, if we had succeeded in ascertaining, and 
 clearly demonstrating, the existence of other circumstances and 
 
AND DEDUCTION. 189 
 
 influences^ by the accession and interference of which the usual 
 eifect of the causes and circumstances in question may have 
 been prevented, or in various ways modified. For we should 
 then be in a position to explain satisfactorily this apparent 
 contradiction of our theory; we could adduce valid reasons, 
 founded upon experience, why, in the case in question, and 
 under existing circumstances, the result was and must be dif- 
 ferent to the usual one. It is self-evident, however, that to 
 give such an explanation at all, and to be able to adduce reasons 
 perfectly consistent with truth, we must assume a knowledge 
 of all the active and antagonistic phases, of the whole causal 
 connection of the event in question, such as we can scarcely 
 be said to possess anywhere in our science. 
 
 However all this may be, such a counter-test, or correction 
 of our theories, or attempts at explanation, by experience, and 
 by more comprehensive and penetrating investigation into the 
 exact state of things is, as has already been explained, of the 
 highest importance. It is, in fact, altogether indispensable in 
 our science. If it does not answer, if the further ascertained 
 facts and experiences are opposed to our previous view of the 
 causal connection and conformity of certain phenomena and 
 processes, — in short, to our theory, — our attention has, at 
 least, been directed to the deficiencies in our previous observa- 
 tions and experiences, and at the same time drawn to certain 
 sources of error in our accustomed explanation and deduction 
 of those causes and laws. We are now called upon to observe 
 and more closely investigate the things in question in other 
 directions and under new relations, and to do this under the 
 greatest possible variation of circumstances, through which we 
 shall almost certainly attain a better knowledge of them, and 
 a clearer insight into their conditions and laws, than we have 
 previously possessed. The correction of our theories, &c., by 
 experience, will thus become a powerful aid to our further 
 progress, and if we only knew how to apply it correctly, we 
 need never fear that our time and labour would be thrown 
 away upon it. 
 
 After men had succeeded, for instance, as they believed, in 
 determining the rapidity with which the waves of sound 
 travelled, by exact experiments and by calculations founded 
 upon them, it appeared that the real rapidity with which sound 
 
190 SYNTHETICAL METHOD 
 
 travels did not agree exactly with the theory of its communi- 
 cation. This incongruity between reality and theoretical 
 calculation led physicists to further and more exact investiga- 
 tions, and finally to the recognition of a circumstance which 
 had previously been overlooked, viz., to the development of 
 heat in consequence of the condensation of the air, and, there- 
 fore, also by the waves of sound. It now became not only 
 possible to explain the difference between the actual velocity 
 of sound and that calculated theoretically, thus confirming the 
 accuracy of the previous theory, but a clearer insight was at 
 the same time acquired into an entirely different phenomenon, 
 — viz., into the development of heat by compression of the air, 
 under new and hitherto unknown circumstances. Just so, by 
 means of such correction by experience have many similar 
 advantages been obtained towards perfecting our theories and 
 attempts at explanation in physiology, as well as in the general 
 field of the doctrines of disease and therapeutics. They 
 have all, it is true, succumbed to this test, and possibly 
 even those which in our own time enjoy the greatest credit 
 will scarcely escape the same fate. Yet they have, none the 
 less, in their time not only satisfied certain requirements, and 
 thus been positively useful so long as their accuracy could be 
 believed in, but the deficiencies afterwards discovered in them 
 have stimulated us to further investigation, and the refutation 
 of them has, indirectly at least, furthered our more perfect 
 knowledge. 
 
 If, for instance, in the case mentioned above, all the theories 
 with regard to the formation of sugar in diabetes have failed 
 in their object ; or if we cannot, like our predecessors, deduce 
 gout, hemorrhoids, and the like, from imaginary obstructions, 
 infarction, acrimony of the humours, &c., because, in the 
 present state of our knowledge of the human body and its 
 processeSj we are aware that such cannot really occur, our 
 insight into the fallacy of those attempts at explanation has 
 led us to the further investigation of obscure diseased states, 
 and of their possible conditions, or so-called nature. If we 
 can no longer explain, as formerly, all the phenomena and 
 processes in typhus and dysentery by an inflammation and by 
 certain textural changes in the alimentary canal and in its 
 glands, &c., this improved knowledge has imparted a stimulus to 
 
AND DEDUCTION. 191 
 
 investigate entirely different processes and circumstances in 
 such patients — e.g., various processes of excretion, the com- 
 position of the blood and chemistry of the conversion of tissues, 
 certain states of the circulation, of the pressure of the column 
 of blood, of innervation, &c. And if further experience 
 shows that we have but imperfectly investigated, and falsely 
 estimated, such conditions and circumstances in those diseases ; 
 and that we can by no means yet deduce from the alleged laws 
 of their operation, all the phenomena and processes in the 
 diseases themselves, as aggregates, we shall, on that very 
 account, seek to investigate more exactly the states and 
 changes in them, and search for another causal connection. 
 
 Since experience has shown that intermittent fever and 
 other so-called miasmatic diseases do not find their adequate 
 cause in marsh-land and malaria, simply because they frequently 
 occur without these, we have begun to seek diligently for other 
 determining circumstances. Peculiar states of the temperature 
 and changes in it, the rapid cooling of the body, a peculiar 
 geognostic character of the soil, bad dwellings and imperfect 
 tillage, unsuitable food and clothing, &c., came to be recog- 
 nized as more or less probable causes. Our insight into the 
 part which so many remedies and substitutes for quinine were 
 previously supposed to play in the cure of intermittent fever, 
 was rendered much clearer by our observing that recovery 
 frequently followed without the employment of any of them, 
 by the aid of good food and nursing, in healthy dwellings, &c. 
 And if further experience should once clearly show, and 
 physicians become convinced, that the great majority of our 
 remedies have no higher value in other diseases than they have 
 in intermittent fever, that perhaps our interference in almost 
 all severe diseases can scarcely meet with any positive success, 
 we shall have more cause to seek other aid ; and the prevention 
 of those diseases will become, more and more, the special object 
 of our art. 
 
 Departments of human knowledge and practice in which, as 
 in ours, most of the facts and experiences are unexplained, and 
 for which no causal connection has been established, are pre- 
 cisely those which offer the honest investigator the widest field 
 for discovery. If he bear in mind existing deficiencies and 
 the improved mode of procedure which is so much called for, 
 
192 GENERALIZATION 
 
 he will, at every attack upon the chaotic mass before him, meet 
 with something to aid in the furtherance of his science and, in 
 the end, of his art. 
 
 Reduction of numerous apparently heterogeneous pheno- 
 mena AND PROCESSES TO ONE AND THE SAME ESSENTIAL 
 PROCESS AND CAUSAL CONNECTION. RESOLUTION OP NUME- 
 ROUS COMPLEX LAWS INTO SIMPLER, OR MORE GENERAL AND 
 HIGHER LAWS. 
 
 (Process of Generalization or Reduction.) 
 
 Special mention has been made in the foregoing pages of 
 the requirements which we must fulfil for the attainment of a 
 scientific and clearer insight into the processes and occurrences 
 which the physician meets with in nature as complex aggregates. 
 We have also endeavoured to explain by the aid of what opera- 
 tions and means this can alone be attained, viz., analysis and 
 our deductions from it. 
 
 If we have ascertained what occurs in an individual process 
 (e. g., in a given function or disease, or in a given external 
 influence), and if we have discovered, or demonstrated with 
 approximate probability, its conditions, and the laws of its 
 operation — in short, its causal connection and conformity to 
 ascertained laws — we may rest satisfied in' relation to this 
 individual case, for we have succeeded in understanding and 
 explaining it as far as we can do with regard to it individually. 
 A further scientific want is, however, by no means so easily 
 satisfied. We long to connect this individual process with 
 others; we seek to bring this individual phenomenon, or pro- 
 cess, into connection with all the others with which, as we 
 know or surmise from our experience, it stands in a certain 
 relation, or even causal connection. In the former method, we 
 had, as it were, taken to pieces and examined separately those 
 series of phenomena and processes as they were presented to 
 us in the aggregate by the living body, in health or disease, 
 and the whole mass of the influences and agents of the external 
 world. It was our office to separate into its individual ele- 
 ments, as we best might, all that which we met with in 
 nature, as a more or less complex whole, and to investigate 
 
OR REDUCTION. 193 
 
 separately its causes, or effects, before we could hope to acquire 
 any insight into its causal connection aiid conformity. 
 
 But this very process disconnects the original living whole, 
 which now lies before us in its isolated elements. We see at 
 the first glance, and almost instinctively, that we cannot thereby 
 even fully comprehend, or explain, the causal connection and 
 operation of those individual elements themselves, much less 
 their internal connection and co-operation within the living 
 body as a whole, or in external nature, nor can we trace their 
 mutual relations to each other and to the occurrences, or pro- 
 cesses in the latter. A natural impulse to comprehend this 
 whole now urges us to bring back those individual elements 
 into which we had divided it into their proper connection with 
 all the others which appear to us to be allied, or analogous. 
 But what these allied things are we usually learn from the 
 simple observation of Nature from which we started, and from 
 experience, — e. g., from the fact that we have always observed 
 them to occur simultaneously, or consecutively, and from the 
 circumstance that in the whole mass of phenomena, processes, 
 &c., certain of them exhibit greater or less similarities, certain 
 allied relations of some kind or other. Just as we recognize 
 hundreds of individual plants or animals to belong to one and 
 the same natural group, and set them down, so to speak, as 
 the individual integral links of a higher ideal organism, or 
 common type, by the resemblance in their external conforma- 
 tions, so also certain organs of the living body, and certain of 
 its tissues, appear to us to belong essentially to one and the 
 same group. For their external forms and their elementary 
 parts, and the arrangement of these, as well generally as in 
 detail, the mode of their development (e. g., from cells) and 
 their properties, &c., are found to agree in certain main points. 
 In this sense, for instance, the formation of the vertebrae is 
 repeated in the cranium of the Mammalia j and in the organs 
 of the most dissimilar animals and plants we observe the same 
 forms to recur as developments in accordance with the same 
 essential type. And as, in external nature, many individual 
 agents and processes co-operate to produce what we briefly 
 denominate weather, seasons, and climate, so we find, or at 
 least surmise, that certain functions, or processes in the living 
 body are allied and stand in a certain relation to each other. 
 
 13 
 
194 GENERALIZATION. 
 
 And the same circumstance which enabled us to recognize an 
 individual function in the aggregate of the vital phenomena in 
 a body, and to distinguish it from the others, now aids us 
 further in ascertaining which of these functions and processes 
 are allied to each other. On a closer examination of them it 
 becomes evident that certain of them are only integral mem- 
 bers or agents in one and the same process, and that they 
 assist in producing, in the end, essentially the same result ; 
 some perhaps are concerned in the nutrition of the body and 
 the maintenance of its material substratum ; others, on the 
 contrary, are connected with its finer and even intellectual 
 relations to the things that surround'it ; others, again, with the 
 propagation of the species. 
 
 In a somewhat similar manner we may recognize in many 
 states of disease such an agreement in certain essential points 
 — e. g., not only in the aggregate of their more important and 
 perhaps determining phenomena and processes, and in the 
 manner in which they run their course, but also in their 
 development and occurrence under various external circum- 
 stances, and in certain personal relations, so that nature her- 
 self might seem to have arranged them in one group. 
 
 In short, we everywhere meet with, or at least surmise, a 
 certain resemblance and agreement between various processes 
 and aggregates of functions in the living body, and the agents 
 of the external world by which they are affected. If they 
 difi"er from each other in individual points, the possibility fur- 
 nished by analogy and experience leaves it open for us to 
 suppose that any differences in these processes, &c., which we 
 have regarded as allied, any contradictions and exceptions in 
 them, may have depended upon the intervention or interference 
 of other special circumstances and phases of more or less sub- 
 ordinate importance. And we are thus justified in believing 
 that notwithstanding such differences and deviations from the 
 others, they are still very probably allied, as parts of a more 
 general, or higher whole. 
 
 We must also take into consideration a further and most 
 important circumstance to which allusion has already been 
 made, viz., that our fragmentary investigation of various parts 
 has in some degree stood in the way of our clear comprehen- 
 sion of the conditions or effects of these parts themselves in 
 
OR REDUCTION. 195 
 
 their whole extent, just because they are only fragments, or 
 individual parts of the whole. Under the most favorable 
 circumstances we may have succeeded in acquiring an ap- 
 proximately correct knowledge of any given part, say a func- 
 tion, a diseased state, or the effects of an individual external 
 influence, such as an article of food, or a remedy; in ascertain- 
 ing, with more or less exactitude, the circumstances under 
 which they occur, and iu tracing their causal connection and 
 conformity individually. But even these, when we reconsider 
 them, do not appear clear and intelligible. On examining 
 them more closely, it will appear that we cannot acquire any 
 considerable increase of knowledge concerning them, so long 
 as they remain in a state of isolation and separation from other 
 things with which they are allied, or perhaps essentially con- 
 nected. If, for instance, we had come near ascertaining what 
 occurs in the action of an external agent, such as wind or 
 rain, or in any one of the processes of the living body, such as 
 respiration, or in any individual phenomenon in a patient (e. g., 
 diarrhoea, the formation of exudations, or an abnormal excretion 
 by the skin, kidneys, &c.), and wish to learn by the co-opera- 
 tion of what circumstances it has occurred, it will soon become 
 evident that we cannot clearly understand these individual 
 occurrences, either in themselves, or in their conditions, with- 
 out a previous knowledge of many other things. 
 
 Nor can the grounds of all this long remain hidden. An 
 individual occurrence is soon seen to stand in a close mutual 
 relation to, or even causal connection with, various others ; its 
 agreement with others in certain main points soon indicates 
 the necessity of investigating and becoming acquainted with 
 these also. In the one case it was necessary to understand the 
 causal connection and conditions of various other processes in 
 the atmosphere — e. g., the formation of mist and dew, of snow 
 and hail, the conditions and laws of the variations of tempera- 
 ture at different hours of the day and seasons of the year, and 
 those of the air-currents generally, — in the other case the be- 
 haviour, conditions, and effects of other processes of ingestion 
 and excretion, of various changes in the composition of the 
 blood, of the circulation, and, lastly, of all the processes of 
 endosmose and exosmose, &c. In like manner we find in any 
 disease, taken as a whole — e. g., in scrofula, dropsy, inflamma- 
 
196 GENERALIZATION 
 
 tion, gout — that it blends with others in various ways, that it 
 is variously connected with other deranged and diseased states, 
 and that certain changes and derangements in many of these 
 diseases have, in essentials, the same ill-defined boundaries. 
 Others again agree too obviously in relation to the circum- 
 stances and conditions of their development and course, and in 
 the various phenomena they present, to admit of a doubt as 
 to a certain similarity, or even essential identity — for example, 
 the various fevers and other diseases in so-called miasmatic 
 neighbourhoods, or in those which prevail in, the tropics, or in 
 unhealthy, overfilled hospitals, and under other similar circum- 
 stances. And the same essential likeness will often be per- 
 ceived in the workings of external influences which are 
 apparently dissimilar. In many substances, some used simply 
 for food, some remedial, and others poisonous, a close observa- 
 tion of their properties and a deep investigation into their 
 effects will bring to light an agreement among them in many 
 essential particulars, in spite of the individual peculiarities in 
 which their difl'erence is apparent. 
 
 All this tends to urge us to ascertain the causal connection 
 of things which are allied and analogous, and to trace the 
 ■relations in which these more or less homogeneous phenomena 
 and processes may stand to each other. We set to work 
 accordingly to seek for a causal connection, for conditions and 
 circumstances, which are, in all of them, the basis and pro- 
 ducing cause; or in other words, we seek for a certain order 
 of things, a conformity of their development and course, to 
 which to refer all the processes and phenomena which, in 
 certain essential points, co-operate, or agree with, each other. 
 
 Success in this would lead us on to the discovery of more 
 general or higher laws — i. e., laws from which we might deduce 
 various phenomena and processes which had previously appeared 
 more or less heterogeneous, but are now found capable of being 
 explained upon kindred principles with these. It would also 
 lead us to a realization of our foreboding that these, in their 
 conditions and causal connection, in the conformity of their 
 development and course, or operation, were agreed either in 
 the main, or at least in several essential points, experience 
 having already shown us their more or less intimate connection 
 with each other, and made us aware that they all commence,j 
 
OR REDUCTION. 197 
 
 i'un their course, or operate under essentially the same, or, at 
 least, very analogous circumstances, while by this their co- 
 existence and co-operation a common result is produced. 
 
 To ascertain and demonstrate all this we must proceed as 
 we should do in the investigation of causal connection, con- 
 ditions, and laws of operation in general natural science. We 
 must form certain surmises and hypotheses concerning the 
 individual phenomena and processes, and weigh the possibility 
 of their possessing a definite kind of dependence and origin, or 
 operation. All those series of phenomena, effects, or influences, 
 which experience and our a priori notions induce us to class 
 together, must be tested and compared with each other in the 
 greatest possible number of cases and separated into their 
 individual integral elements, and the conditions, or operation 
 of these must be determined by means of the usual auxiliaries 
 to investigation. We must endeavour to discover in all of 
 them a certain activity, certain occurrences and circumstances, 
 which we may regard as their common and essential elements, 
 perhaps as the circumstances upon which they all equally de- 
 pend, or as the active agents in them all. The solution of our 
 problems, and the object of our investigation, are only to be 
 attained by ascertaining those common circumstances and 
 processes upon which those series of phenomena, effects, &c., 
 assumed by us to co-operate, or to be allied by virtue of certain 
 analogies, really depend, or by which they are essentially in- 
 fluenced. We must, therefore, in the case of all these, be able 
 to demonstrate an agreement in certain essential points and 
 even in the nature of their causal connection, conditions, and 
 operation, and we shall thus have it in our power to deduce 
 them all from essentially the same laws, or, in other words, 
 to explain them in the same manner. 
 
 Thus it has long been known that chlorine bleaches — i. e., 
 destroys colouring matters — as well as that it removes bad 
 smells, foul gases and compounds, &e. It was afterwards dis- 
 covered that it has a great aflSnity for hydrogen and so-called 
 bases in general, and^ from the great intensity or energy with 
 which it strives to enter into combination with them, it 
 was surmised that -its capability of destroying colouring matters, 
 and of removing noxioils smells, might depend upon this its 
 property and mode of operation, so that when it was proved 
 
198 GENERALIZATION 
 
 that hj'drogen and other basic, electro- negative bodies were 
 essential and constant components of those gases, &c., the 
 accuracy of such a surmise -was confirmed. The same circum- 
 stance being shown to be the essential and ultimate condition 
 of various processes, what had previously appeared to be en- 
 tirely heterogeneous effects and processes were reduced to one 
 and the same cause, and brought under the same law. 
 
 When attention was more specially directed to the digestion 
 of the individual organic elements and components of our food, 
 one of its most interesting and enigmatical circumstances was 
 noticed in the fact that coagulated albumen is gradually dis- 
 solved in the stomach and intestinal canal, and finally enters 
 the blood and general economy. It was ascertained by experi- 
 ment that neither water, nor any solution of the individual 
 salts and other materials with which the albumen comes into 
 contact in the alimentary canal, are capable of dissolving it. 
 Thus, while we failed to recognize a solvent for coagulated 
 albumen, the fact of its solution was apparent. We observe 
 the analogous phenomenon in the circumstance that certain 
 metallic salts — e.g., corrosive sublimate and nitrate of silver — 
 when employed internally or applied to blistered or suppurating 
 surfaces, are, to all appearance, precipitated by the fluids in 
 the stomach and upon the moist cutis vera when deprived of 
 its epidermis. Deposits were observed to be formed which were 
 not soluble in water, dilute acids, or other ordinary simple 
 solvents. Nevertheless persons who have taken such metallic 
 salts for a considerable time, or to whose skin they have been 
 applied, experience their general, so-called constitutional 
 effects — e. g., salivation, in the one case, and the peculiar 
 colour of the skin not unfrequently observed to follow the long- 
 continued use of preparations of silver, in the other. But since 
 we can no longer believe in purely sympathetic or dynamic 
 effects of this kind, we cannot doubt the fact that those metallic 
 compounds and deposits must in some unascertained way have 
 been dissolved and absorbed. It next appeared that these 
 metallic salts are by no means decomposed in the stomach and 
 upon suppurating surfaces, as was at first inferred from the 
 formation of those deposits, but that the latter rather consist in 
 combinations of those metallic salts, as such, with certain ele- 
 ments of the fluids in the stomach and of the pus, &c., upon 
 
OR REDUCTION. 199 
 
 tlie skin J that they are, in fact, combinations of them with 
 the albumen and chlorides of the latter. On further investi- 
 gation it has appeared that the solution of these apparently 
 insoluble substances — on the one hand the metallic compounds, 
 on the other the coagulated albumen of our food in the 
 stomach, &c. — are effected by one and the same process, or 
 circumstance, viz., by their combination with the alkaline salts 
 or chlorides and albumen of the gastric juice and other secre- 
 tions, and of the pus, &c., upon the skin, to form so-called 
 albuminates, and finally by the gradual solution of the latter 
 in the excess of albumen in those fluids. And the same pro- 
 cess, or circumstance which was thus ascertained to be the 
 common condition of these apparently different effects, is now 
 found sufficient to explain many other analogous facts and 
 effects — e. g., the solution and absorption of many other 
 metallic compounds, of many other coagulated substances in 
 the solids and fluids of our food. 
 
 Various mechanical and pharmaceutical means had long 
 been employed as topical applications for arresting hemor- 
 rhages, and partly for preventing the further development of 
 inflammation of external parts, tumours, &c., partly for dis- 
 persing, and effecting the absorption of, the latter. Thus, for 
 instance, in hemorrhage, pressure, ligatures on arteries, cold, 
 alum, substances containing tannin, &c., were employed — in 
 the case of external inflammation also cold, mechanical pressure 
 with tight bandages, &c. We have already succeeded in 
 showing, with great semblance of probability, that in all these 
 cases, means and processes, apparently very different, prove 
 beneficial by producing the same result — in hemorrhage, for 
 instance, by causing coagulation of the blood, and its albu- 
 minous constituents; in inflammation and tumours, by im-. 
 peding, or preventing, the access of blood to the] parts, and 
 perhaps further by an interruption, or a certain modification 
 of the processes of nutrition and conversion in them. Paralysis 
 of the limbs has been observed to follow upon the most dis- 
 similar influences and changes — e. g., extravasation of blood 
 into the brain, or spinal marrow, or softening of these, the 
 pressure of tumours upon these central organs, direct injuries, 
 chronic poisoning by lead, &c. We have also ascertained with 
 tolerable precision that partly certain substantive changes or 
 
200 GENERALIZATION 
 
 derangements of these central organs, or of certain portions of 
 them, partly an interruption of the normal communication 
 between them and the peripheral nerves, are the intermediate 
 link, or common condition of those phenomena. 
 
 Tt has long been known, that in the most dissimilar diseases 
 certain derangements, or affections of the stomach and intes- 
 tinal canal are constantly met with, for many phenomena in 
 chronic and acute diseases — e.g., in gastric and nervous fevers 
 — indicated this plainly enough, as did also certain appearances 
 observed in the dead body and the real, or apparent results of 
 certain remedies and modes of treatment. It is also known 
 how Broussais was first led by these facts to assume an irrita- 
 tion, or actual inflammation of the mucous membrane of the 
 stomach and intestines as the common determining and 
 essential circumstance in the most dissimilar diseases. In 
 other words, he generalized his gastro-enteritis, as others, at a 
 later period, generalized "inflammation," in whatever organs 
 and tissues it occurred, and as, in our own days, the so-called 
 Vienna school have generalized " exudations." Others again 
 have long been accustomed, in all the possible states of disease, 
 rather to seize upon functional derangements of innervation as 
 they exhibit themselves under various modifications, whether 
 in the form of pain, spasm, hallucinations, delirium, &c., or 
 as paralysis, or relaxation of individual parts of the body. 
 And when, at a later period, in consequence of discoveries in 
 the physiology of the nerves, attention was especially attracted 
 to the spinal cord, and its so-called reflex functions, many 
 pathologists endeavoured to prove that partly a functional excite- 
 ment or irritation, partly paralysis of the spinal system, or 
 rather of certain portions of it, were the ultimate common con- 
 dition and, consequently, the essential agents in those diseased 
 states. An attempt was even made to explain or deduce the 
 origin and nature of all diseases — not even excepting inflamma- 
 tion, congestion, and the like — from the same circumstance. 
 In a precisely similar manner, others, in the most recent 
 periods, have rather singled out the chemical portion of the 
 vital processes in health and disease, and the attempts to refer 
 not only inflammation and so-called " dyscrasies," but almost 
 all diseased states to " erases " of the blood, or, in other words, 
 to generalize the latter — x. e., to extend them as the common 
 
OR REDUCTION. 201 
 
 condition or essential circumstance to the greatest possible 
 number of diseases — are well known. 
 
 It is no doubt true that, like all such attempts at explana- 
 tion and generalization in our science, those just alluded to are 
 very imperfect; that great errors have been committed, and 
 the requirements of a sound logic by no means fulfilled ; for 
 we were everywhere in danger of assuming some circumstance 
 as determining and essential to various complex phenomena 
 and processes in the living body, without having first established 
 its precise importance and actual influence upon the other pro- 
 cesses individually, and, therewith, the fact of their dependence 
 upon it. Sometimes too it would be difficult to demonstrate 
 that the process or circumstance which we have assumed, in a 
 given case, as determining and essential, has even existed or 
 been in operation at all, so that its general share in the ultimate 
 result cannot but remain doubtful. Yet these attempts are 
 useful in showing us how the human mind goes to work in 
 the process of generalization or reduction. Our exertions in 
 them being directed to the deduction of a series of hitherto 
 detached, apparently unconnected, and even heterogeneous 
 phenomena, or processes, from essentially the same common 
 process or circumstance whereby they may be explained, our 
 attempts at generalization thus lead to an added value for 
 individual facts and experience, while these, on the other hand, 
 are the better understood through the synthetic connection in 
 which such attempts place them. 
 
 We cannot carry out a thorough generalization without an 
 adequate basis of established facts, while all our so-called ex- 
 perience remains, without such a generalization, a mere chaos 
 of isolated empirical facts and individual observations. We 
 do not understand them even while they stand before our eyes, 
 until we are able to view them in their internal connection 
 with each other, and with other allied and analogous things. 
 It is only by bringing them into a certain relation to each 
 other, by referring them all to the same determining process 
 or circumstance, that they acquire, as it were, vitality, and 
 are brought within the range of our perception. We can then 
 comprehend them as far as, in the present state of our know- 
 ledge, they can be comprehended. 
 
203 GENERALIZATION 
 
 It almost always happens, in such cases, that some one 
 endowed with a lively imagination and talent for combination, 
 and with an unusual amount of positive knowledge, is led by 
 certain analogies and facts to surmise some connection between 
 phenomena and processes previously regarded as isolated. 
 For the more perfect explanation of them his imagination, and 
 previous knowledge, provide him with the ways and means 
 whereby to surmise at least a certain common element as the 
 actual determining circumstance for all, and to calculate the 
 probability of this precise internal connection between them. 
 The chief point, however, is to furnish the actual demonstra- 
 tion of this, their causal connection, which may be possible and, 
 perhaps, even probable, or, on the other hand, not exist at all ; 
 and to this end it rests with him to demonstrate the depen- 
 dence of a number of processes, &c., upon one common process, 
 or circumstance. 
 
 But we know from experience that it has ever been more 
 easy to surmise than to prove the fact of such a connection 
 between the various phenomena and processes with which 
 physiology, and the theory of disease and its treatment, have 
 to do; and we may conclude that this will always be the case, 
 because it seems to lie in the very nature of the subject. For 
 a closer examination makes it evident, that the kind of demon- 
 stration which science requires is, in the end, no other than 
 the deductive process itself, — i. e., the explanation or deduc- 
 tion of certain more complex processes from the conditions 
 and laws of their more simple elementary processes. The 
 difference consists alone in our having to deal here, not only 
 with an individual complex process, or with an aggregate of 
 phenomena, but with a whole series of such, which appear to 
 us, indeed, to be allied, or to agree in all their essential points, 
 but which as certainly differ in many other respects. In both 
 cases we proceed synthetically; but in our attempts to generalize, 
 we undertake a synthesis upon much higher ground, and in a 
 much greater range than in the construction of the connection 
 and conformity of an individual process — e. g., of an individual 
 function or disease. The difficulties, therefore, the opportunities 
 for errors and false conclusions, which are considerable even in 
 the simpler attempt to deduce and explain an individual case, 
 must here be increased in a tenfold degree. Our purpose in 
 
OR REDUCTION. 203 
 
 these attempts is, to deduce numerous^ by no means entirely 
 homogeneous series of phenomena, processes, &c. — whether they 
 occur in external nature, or within the living body. — from one 
 and the same process, from the same determining circumstance, 
 or, in other words, to resolve their special conditions and laws 
 into higher and more general ones. How can we hope, however, 
 to do this with any certainty in our science, in which the 
 conditions and conformity to fixed laws of an individual 
 process, or the laws of operation of an individual determining 
 circumstance, have become so little known to us, and that only 
 with approximate probability j in which we are, therefore, 
 unable, in the series of those phenomena and processes, to 
 distinguish with certainty what is determining from what is 
 dependent, what is more essential from what is less essential, 
 or accidental and secondary? 
 
 We evidently venture, as it were, upon the second, infinitely 
 more difficult step, before we have consistently taken the first, 
 much easier and preparatory one. It is evident, however, 
 from what has already been said, that we can never take this 
 first step with complete success unless we take the second 
 along with it. Indeed, we learn from the history of medicine, 
 and of every other natural science, that this second step has 
 often been taken before the first, and that with good, though 
 perhaps only provisional, results. And in this is to be found 
 the vindication of every attempt to generalize in medical 
 science — even of those which are purely hypothetical and 
 a priori — as well as of every theory and synthetic combination. 
 The very nature of our intellectual being, and an innate impulse 
 to acquire scientific knowledge, urge us equally towards this 
 point, and nowhere more strongly than in sciences such as 
 ours, in which every step leads to phenomena and processes, 
 the conformity and causal connection of which individually, 
 and still more collectively, are but too enigmatical. And this 
 enigmatical character of the things we are concerned with is a 
 hint, at the same time, for caution in the notions we allow 
 ourselves to form with regard to cause and effect, and their 
 general connection, showing how easily we may assume the 
 merely accidental, simultaneous, and consecutive occurrence of 
 certain circumstances and events as a causal or essential and 
 constant one. Daily experience, and the observations and 
 
204 GENERALIZATION 
 
 pretended results and conclusions of the scientific investigator, 
 as well as of the practical physician, also teach us this. 
 
 This circumstance, however, far from being an absolute and 
 inevitable impediment to comprehension, may serve as the first 
 stimulus to further and more correct' investigation, and will 
 even, in many respects, be our best guide in it. What has 
 already been said of a general correction of our theories and 
 combinations by simple experience, and more comprehensive 
 and correct observations, apphes no less to these attempts at 
 generalization and theoretical deductions on a larger scale. 
 For if we examine more closely how we have been led to 
 continue our search and what has conducted us, in the end, 
 to the discovery of general laws for whole series of phenomena 
 and effects, we shall find that it has been the circumstance of 
 our a priori notions concerning them, their originating causes, 
 and the effects to which we imagined them to lead, having 
 been proved on examination to be fallacious. Circumstances, 
 processes, and influences, which we had previously regarded as 
 determining, constant, and essential, we now ascertain to be 
 more or less subordinate and accidental. More exact investi- 
 gation, more extensive experience, has taught us, that though 
 they were present when we had the opportunity of observing a 
 certain event or a certain effect, they might have been absent 
 without any change in the main result, and without interfering 
 with the occurrence of the event, or effect, in question. We 
 observe a function, for instance, to be performed, a certain 
 disease to commence, or a cure to be effected, without the 
 circumstances and agents assumed by us as essential (e. g., in 
 the former case a certain process, in the latter a supposed 
 cause of disease, or a certain remedy), having contributed 
 anything towards them, because, as they did not exist at all 
 in the case in question, they could not have exercised any 
 influence upon it. 
 
 Under favorable circumstances, on the other hand, a fortunate 
 generalization, or reduction, has been successful in discovering, 
 for the processes and effects in question collectively, a certain 
 other process, or circumstance, not only as constantly present, 
 but also as the determining influence for them all — upon 
 which, therefore, the circumstances or agents themselves. 
 
OR REDUCTION. 205 
 
 which had previously been regarded as determining and 
 essential, are proved to be dependent, and which must now, on 
 that account, be regarded as the essential, real, and immediate 
 condition of the others. 
 
 Thus, in the instance alluded to above of bleaching, &c., by 
 chlorine, we can no longer speak of its properties of destroying 
 colouring matters, removing noxious smells, &c., as being, in 
 themselves, the causes of such effects, after having ascertained 
 the chemical affinity of chlorine for hydrogen and allied sub- 
 stances, and its energetic combination with them, to be the 
 immediate and essential condition of its bleaching property. 
 According to an old notion, a halo round the moon indicated 
 rain;, it was afterwards ascertained that the production of the 
 halo depended upon watery vapour in the atmosphere, resulting 
 from the accession of a greater quantity of such vapour than 
 the atmosphere could take up in the gaseous form, — e. g., from 
 a rapid decrease of temperature. This comparative excess of 
 watery vapour was thus ascertained to be the immediate cause 
 both of the rain and of the halo, while no influence in the 
 production of the rain could be ascribed to the latter in itself; 
 and it became necessary to investigate the conditions of such 
 excess of watery vapour in the atmosphere, — i. e., the laws of 
 temperature, of the process of evaporation, and of the air- 
 currents, &c., for the better understanding the production of 
 the rain. 
 
 Thus, it was formerly believed that the atmospheric air, as such, 
 was the essential condition of respiration and of life in general; or 
 that the contact of the finger with any body was the cause of our 
 feeling the latter. In the course of time, however, it has been 
 shown that the presence of one only of the constituents of the 
 atmosphere, viz., oxygen, is the essential condition of respira- 
 tion ; that not the inspiration and expiration of oxygen, in 
 themselves, but its absorption, and the giving off of carbonic 
 acid from the dark venous blood (the exchange of these gases 
 generally), and the concomitant changes thereby produced in 
 the blood, are the most essential processes in respiration, and 
 in determining the continuance of life itself. And since it 
 was further asked, what were the sources of this carbonic acid 
 and of the carbon in the blood, and what was the action of the 
 oxygen inspired, Liebig was led to his theory of the blood- 
 
206 GENERALIZATION 
 
 corpuscles mentioned above, and of the iron contained in 
 them, as well as of the part which the latter plays in the 
 process of respiration. In like manner, it has been ascertained, 
 with regard to sensation, that it is not produced by the mere 
 contact of a body with the finger, but rather by the influence 
 the two surfaces coming into contact exert upon certain nerves 
 of sensation in the finger and, through these, upon the brain, 
 or so-called sensorium ; and, in the end, the uninterrupted 
 communication between the latter and those nerves in the 
 finger was ascertained to be the immediate and essential 
 condition of the sensation. 
 
 It was believed, not long ago, that the peculiar change in 
 the intestinal canal (the ulcers, &c., in it in typhus), was to 
 be regarded as an essential circumstance, and frequently even 
 as the condition, of entirely different phenomena and derange- 
 ments in that disease — e. g., not only of the diarrhoea and 
 pains in the abdomen experienced by such patients, but also 
 of the fever and debility, and even of the stupor, delirium, 
 &c. When simple experience taught us, however, that essen- 
 tially the same phenomena and derangements may occur 
 notwithstanding the absence of all those palpable changes in 
 the intestinal canal — e. g., in the so-called exanthematous 
 typhus — and when our comprehension of the concomitant 
 processes was increased, we could no longer regard them as 
 essentially dependent upon those anatomical lesions. It thus 
 became necessary to seek for other modifying processes, or 
 derangements, which are more constantly present, both in the 
 so-called exanthematous and in the abdominal typhus; and 
 attention was now directed to certain changes in the com- 
 position of the blood, in the process of respiration, and in the 
 generation of heat ; in various processes of excretion, and in 
 the conversion of tissues within the body, &c. Could these, 
 in their turn, be proved to be the essential and determining 
 processes in those diseases, all those various phenomena and 
 derangements in typhus would be reduced to the same causal 
 connection, and the common condition of all the known forms 
 of typhus, and perhaps of many allied states of disease, ascer- 
 tained. For similar reasons, the theory of the formation of 
 so-called exudations took, not long ago, the place of the 
 previous theory of inflammation; for it was not only ascer- 
 
OR REDUCTION. 207 
 
 tained that the process of exudation (this formation of so-called 
 exudations), was the most constant and essential phenomenon 
 amongst the local symptoms and changes in inflammation 
 itself, but that similar exudations were observed in many 
 cases which did not correspond to the more ancient notion of 
 inflammation. In a similar manner, the action of nitrate of 
 silver upon the skin and surface of ulcers, and their corrosion 
 by it, were at first observed as something altogether peculiar. 
 It was ascertained, at a later period, that this salt of silver is 
 also capable of producing the same efiects upon mucous mem- 
 branes in the stomach and intestinal canal ; and, finally, that 
 in both cases it comes into contact with the same substances 
 — i. e., with certain salts and chlorides, with albumen, &c. — 
 and that its combination with those substances, according to 
 ordinary chemical laws, is everywhere the condition upon 
 which its local effects depend. Still more recently, the more 
 or less analogous mode of operation of various other substances 
 — e.g., of certain salts of mercury, copper, and lead — has 
 been referred to essentially the same process or circumstance. 
 
 In all these cases, further investigation has shown a pre- 
 viously unknown process, or circumstance, to be the inter- 
 mediate link in causation, the proximate condition upon which 
 certain other phenomena, processes, &c., which had before been 
 regarded as the essential cause of the event or eff'ects in 
 question, themselves more or less directly, if not entirely 
 depend. The latter can, therefore, no longer be regarded as 
 the cause of the event or effects in question, but only as their 
 more remote conditions, as causes of a secondary and subordinate 
 kind j for the cause of the circumstance previously regarded 
 as their essential condition and adequate cause, has itself, as 
 it were, been ascertained. Thereby, however, we have solved 
 our problem of generalization already alluded to — i. e., we 
 have ascertained one and the same causal connection for 
 numerous phenomena and effects, a connection and conformity 
 of a higher and more comprehensive kind j or, in other words, 
 a higher and more general law than the first. We have 
 succeeded in demonstrating for a whole series of eff'ects or 
 processes, which we had previously deduced from their own 
 special influences and conditions, one and the same circum- 
 stance, or process, as that upon which they all depend, and 
 
208 GENERALIZATION 
 
 consequently, as we are accustomed to express it, to generalize 
 the latter. Phenomena and occurrences, each of which pre- 
 viously appeared to commence and run its course in its own 
 peculiar manner, according to its own conformity to fixed laws, 
 are now seen to commence and run their course in one common 
 manner, and in conformity to one common law. 
 
 This causal connection, this newly-discovered more general 
 law, is also much more constant and trustworthy than those 
 first surmised, simply because the operation of a more immediate 
 cause, or essential circumstance, cannot so easily be interrupted, 
 or even cancelled, by other intervening influences or circum- 
 stances, as the operation of a more remote and subordinate 
 condition, of a comparatively accidental influence and circum- 
 stance. The events and efifects which we had previously 
 deduced from the latter, depend, as is now evident, not 
 precisely, or at least not immediately, upon such influence or 
 circumstance in itself, but upon something intermediate and 
 nearer ; and when we have been made aware that this may 
 exist and act, not only under those circumstances, in coinci- 
 dence with the process or influence falsely regarded as cause, 
 but equally under other circumstances, many things will 
 become intelligible which had previously been obscure and 
 perplexing. Thus the circumstance or influence which we 
 had been accustomed to regard as the peculiar and adequate 
 cause of a certain event, could, in general, only be followed by 
 this effect on the supposition of different circumstances, more 
 proximate and powerful influences, being present and in opera- 
 tion. And, on account of the very presence of these latter 
 circumstances, the effect which we had expected to arise from 
 the former one might, in some cases, fail to be produced ; or, 
 conversely, the event or process which we had previously 
 regarded as its effect, might be observed without the presence 
 or operation of the very cause, influence, or circumstance, upon 
 which we had imagined it to depend. 
 
 But now that we have become better acquainted with the 
 causal connection, and have ascertained the proximate causes, 
 the actual determining circumstance or process, for the event 
 in question, the result is far otherwise. Its influence and 
 mode of operation remain essentially the same, notwithstanding 
 the variations in those comparatively subordinate, accidental. 
 
OR REDUCTION. 309 
 
 and only secondarily modifying, or co-operating circumstances. 
 Its effects will, therefore, be more or less constant, and should 
 they chance to be absent — e.g., in consequence of the inter- 
 vention or interference of other influences, we shall find our- 
 selves better able to understand the cause of such absence. 
 Thus, the bleaching effect, or destruction of colouring matters 
 by chlorine, may frequently not be produced, because, for in- 
 stance, hydrogen, and similar electro-negative elements are not 
 present in them, or are protected from the action of chlorine 
 by the presence of other substances. It is, at the same time, 
 more intelligible why entirely different substances are capable 
 of producing the same bleaching effect as chlorine — e. g., iodine, 
 bromine, acids, &c. — since we know that they possess an analo- 
 gous affinity for certain constituents of many colouring matters. 
 
 Since we have learnt that the atmosphere, in itself, is not 
 the immediate, essential condition of respiration, and of all the 
 processes connected with it, we also understand why, for in- 
 stance, some animals can breathe and live in the water equally 
 well with others in the air, and why others die notwithstanding 
 the free access of air in respiration. 
 
 Since more extensive experience has taught us that malaria, 
 in itself, is not the adequate cause of intermittent fever and 
 other miasmatic diseases, we more easily understand why men 
 may be attacked by them in districts where no marshes exist, 
 as well as in fenny districts, and on the flat and muddy banks 
 of rivers, &c. And so long as we imagined that we saw in 
 various remedies, which had been employed in many different 
 diseases, the essential and almost adequate cause of recovery, 
 it was difficult to explain why, in many cases, recovery failed 
 to follow the employment of those remedies : why recovery 
 frequently occurred where no such remedies had been em- 
 ployed; and why the same disease may be cured equally 
 quickly and certainly under the employment of the most 
 various remedies. All this, however, is easily understood 
 when we have ascertained an entirely different circumstance 
 to be the constant and essential condition of such cure, and 
 have once become convinced that the natural progress of all 
 the vital processes, the so-called spontaneous tendency to 
 recovery is, under favorable circumstances, its especial and 
 immediate condition in most patients. 
 
 14 
 
210 GENERALIZATION 
 
 If we take it for granted that we have^ in the above-men- 
 tioned manner, demonstrated a certain common process or 
 circumstance to be the special determining one for a series of 
 phenomena and processes, which simple experience has enabled 
 us to recognize as allied or analogous — if we have succeeded 
 in proving a conformity in their origin and course — the mind 
 of man will not, in the end, be satisfied even with this. The 
 same motives, the same innate reasons which led him to this 
 first step in his generalizations, will, in combination with 
 subsequent experience and discoveries, lead him further on in 
 the same path. For, in spite of our previous attempts at 
 explanation and reduction, we still meet with many appa- 
 rently entirely heterogeneous series, or groups of natural 
 phenomena and processes. We have, perhaps, succeeded in 
 demonstrating their causal connection and the conformity of 
 their origin and course singly, in each individual series and 
 species, but they still remain isolated and without any mutual 
 relation to each other. They rather appear to be widely 
 separated, and this the more, inasmuch as we have hitherto 
 discovered only differences, and a more or less general hete- 
 rogeneity in their external appearance, in their characters, in 
 the circumstances and conditions of their occurrence, and in 
 their laws — in short, in their whole nature. On the other 
 hand, we had, perhaps, scarcely ascertained a single point 
 of resemblance and agreement in them which could lead U8 
 to surmise a relation between them, still less the essential 
 similarity of their origin and course. 
 
 We now suddenly find ourselves taking this great step in 
 advance. We find that such series of phenomena and pro- 
 cesses in external nature, or in the living body, as we had 
 previously regarded as altogether peculiar and heterogeneous, 
 because they appeared to commence and run their course 
 in their own particular manner and order — for which we had, 
 therefore, assumed causes and laws entirely peculiar, as well 
 as adopted peculiar names — agree, little as we had suspected 
 it, in all their main points. Continued observations, and 
 the general extension of our knowledge, have led to the 
 discovery that the circumstances under which they occur, or 
 act, the manner and order in which they run their course, 
 agree in their essential points, and that their conditions and 
 
OR REDUCTION. 211 
 
 causes, their effects and results, are, notwithstanding all their 
 apparent differences, the same in all. 
 
 Whenever we succeed in demonstrating this — i. e., in dis- 
 covering one and the same causal connection, the same kind 
 of conformity for such various series of phenomena and pro- 
 cesses — we have also discovered a " natural law of the most 
 general, or highest kind," for we have succeeded in redu- 
 cing the special laws of several hitherto widely separated phe- 
 nomena, or processes, to one and essentially the same law, and 
 have thereby perhaps approached as near as it is possible for 
 us to do to the attainable limits of explanation and generaliza- 
 tion in the study of nature. 
 
 This has already been frequently effectied in physics and 
 chemistry. While the electrical phenomena, properly so called 
 (frictional electricity), which were the first discovered, were 
 long regarded as something entirely difi'erent from the more 
 recently discovered electricity of the galvanic battery, their 
 essential resemblance did not, in the end, fail to be recog- 
 nized. It was found that they manifest themselves in essen- 
 tially the same manner, and are produced in accordance with 
 the same laws — in short, that common electricity and galvanism 
 are identical. And when it was further observed that elec- 
 trical phenomena are produced by the magnet, and, conversely, 
 magnetic phenomena by electricity and galvanism ; when the 
 laws of this so-called induced electricity became more and 
 more known, it was necessarily concluded that magnetism and 
 electricity must agree in their essential points. The same 
 thing has, also, within a certain range, become more and more 
 probable for the phenomena of light and heat, so that all the 
 phenomena which had previously been regarded as peculiar 
 agents and forces, as so-called imponderables, appear to be, for 
 the most part, nothing else than the various modes and ten- 
 dencies in which the constant relation of the sun to our planet 
 manifests itself (Humboldt). A similar generalization, was 
 carried out by Dalton, when he demonstrated that the most 
 dissimilar bodies combine with each other, and replace each 
 other in decompositions, &c., in definite and constant propor- 
 tions, or weight-relations (called the theory of chemical atoms 
 and equivalents) . But the most brilliant example of a similar 
 discovery is the reduction of the laws which regulate the 
 
212 GENEEALIZATION 
 
 motion of our earth and of all the planets of the solar 
 system to one and the same law of weight (Newton's law of 
 gravitation) ; or, in other words, the proof that the motions of 
 all the heavenly bodies, and the fall of any given body towards 
 our earth, depend upon the mutual attraction of bodies in the 
 ratio of their mass, distance, &c. 
 
 Nothing similar has yet been effected by us in the general 
 field of organic nature, and its peculiar processes and occur- 
 rences ; at all events, we have ascertained nothing with equal 
 certainty, least of all in relation to the phenomena and pro- 
 cesses peculiar to the living body ; for, to be able to carry out 
 such generalizations in any science, or to demonstrate one and 
 the same kind of conformity in the origin and course of a 
 whole series of phenomena and effects — to bring them into a 
 correct causal relation to each other — we must first have 
 ascertained the causal connection and conformity of each indi- 
 vidual phenomenon, or process separately. After all, it is of 
 little moment how we set to work to seek and find them — 
 whether by the strict but tedious method of analysis and 
 deduction, or by that of synthetic combination — but discovered 
 they must be, and no genius will in this case compensate for 
 the knowledge of simple, or individual facts. It has already 
 been mentioned, that we have not even demonstrated the con- 
 formity in accordance with which the individual vital processes 
 and functions are performed, nor are we aware of all the con- 
 ditions and laws which govern their development, and the 
 influence which they exercise upon each other. It also follows 
 from this, that we cainnot, with even approximate certainty, 
 reduce the latter to more general and higher laws, or demon- 
 strate the same causal connection, the same kind of dependence 
 and occurrence for a number of them. We do not yet possess 
 the individual pieces, wherewith, by arrangement and accurate 
 joining, to construct a more perfect edifice. And perhaps 
 the reason why we have not yet ascertained any such higher 
 and more general laws, is partly that we have sought for these 
 too soon, without first determining those which are more simple 
 and elementary. Even a Newton stood in need of the dis- 
 coveries of numerous predecessors, who had observed the indi- 
 vidual phenomena in question, and established their laws, 
 before he could bring their separate elements into their exact 
 
OR REDUCTION. 213 
 
 relation to each other ; and a Liebig would probably not have 
 been able to connect mentally so many previously isolated and 
 obscure processes in the living body, in a chemical point of 
 view, if its individual component parts and their connections 
 with each other, as well as the materials introduced and affect- 
 ing it from without, and the various products of excretion, 
 had not previously been more or less known to him. All the 
 powers of the human mind, imagination, and a priori synthesis, 
 however bold, can be of little avail in the present state of our 
 knowledge of the vital processes in health and disease. Bacon's 
 warning, "Itaque hominum intellectui non plumse addendse, 
 sed plumbum potius et pondera, ut cohibeant omnem saltum 
 et volatum," is even more applicable to our science than to 
 any other. 
 
 Yet history, up to the present time, teaches us that, in spite 
 of all existing difficulties, such generalizations on a large scale, 
 even in our department of science, have not only been under- 
 taken, but also frequently carried out with more or less success. 
 The attempt of Liebig and his school to deduce the processes of 
 the fermentation and putrefaction of organic substances, as well 
 as the most important chemical processes in the living body, in 
 health and disease (e. g., respiration, digestion, the processes of 
 excretion, the generation of heat), from the same determining 
 circumstance, or, in other words, to reduce them all to one 
 and the same process — i. e., to the conversion of organic 
 substances by oxygen, and to their combinations with it — 
 must be regarded as the grandest instance of this kind. A 
 kind of continuous process of oxidation, or, as it were, of slow 
 combustion in various forms (depending immediately, in the 
 living body, upon the oxygen introduced in respiration), was 
 thus discovered to be the common and essential condition of 
 all these changes in the composition of organic substances both 
 within, and external to, the living body. The latter were thus 
 shown to be under the influence of processes analogous to 
 those of combustion in the common signification of the term, 
 and the act of combustion, or oxidation, was thereby generalized 
 — i. e., extended to many apparently very dissimilar processes. 
 
 This holds good, also, for those processes in the body in 
 disease, as well as in health. From an increase, or decrease, in 
 the intensity of that process of oxidation, it has been sought, 
 
214 GENERALIZATION 
 
 for instance, to deduce the origin of many dyscrasic diseases 
 and products of disease, from fever and inflammation to gout, 
 lithiasis, &c. ; also to account for emaciation and loss of weight 
 (e. g., in phthisis) from an increased conversion and excretion 
 of organic constituents in consequence of an abnormal com- 
 bination of them with oxygen; by which the increased tem- 
 perature of the body in that disease is also explained. The 
 same theory also seemed suflBcient to establish an analogy 
 between fermentation and putrefaction, and the mode of 
 origm and operation of certain organic poisons, such as con- 
 tagions and miasmata. As poisonous substances or compounds 
 maybe formed during fermentation and putrefaction (e. ^., the 
 poison sometimes formed in sausages), their deleterious action 
 in the living body was explained by a contact-action of those 
 putrefying substances, analogous to that of yeast, upon certain 
 constituents (albumen, &c.) of the living body. These enter 
 into a similar state of chemical movement, into a similar 
 process of conversion with the albuminous substances in the 
 sausage-meat itself, or with the true ferment (Kleber) in yeast. 
 The further analogy of these processes to the general action of 
 organic substances, when in a certain state of conversion or 
 putrefaction under entirely different circumstances, was next 
 observed. The origin of many diseases was thus explained — e. g., 
 the ill health of many inhabitants of towns, from the use of water 
 containing such organic substances ; the origin of so-called mias- 
 matic.epidemic, and endemic diseases, fevers, &c. — from theputre- 
 faction of large quantities of organic matters in moist, marshy 
 districts, or after inundations ; lastly, the outbreak of epidemic 
 typhus, puerperal fevers, &c., in crowded, badly- ventilated spaces, 
 in which, consequently, an unusual amount of organic and 
 animal matters exists in a state of conversion and putrefaction. 
 It will easily be understood that all this, to some extent, 
 affected our general line of conduct. The same idea, the 
 same experience, led to the building of roomy hospitals, to 
 better ventilation, and to the adoption of certain dietetic, 
 hygienic, and prophylactic measures, both on a large and 
 small scale. The advantage of the filtration of water through 
 the ground and sand is explained by the oxidation and con- 
 version of the organic matters contained in it ; further, the 
 necessity and advantage of establishing a greater fall of water 
 
OR REDUCTION. 215 
 
 by drains, &c., because its stagnation, and the consequent 
 oxidation and conversion, or putrefaction, of the organic 
 matters in it, are prevented. 
 
 It can scarcely be doubted, that in all these cases there is 
 much which is hypothetical, and possibly altogether erroneous ; 
 but every one who can understand that, by attempts of this 
 kind alone, processes hitherto isolated and widely separated 
 from each other are to be brought into an intimate mutual 
 relation, must acknowledge the value of such generalizations. 
 If their causal connection, in the precise manner assumed, is 
 by no means established, we have, at any rate> come infinitely 
 nearer than before to an understanding of it. Thus, for 
 instance, we first learnt from simple experience that dysentery 
 prevails iu the latter part of summer ; and, because about that 
 time the heat is greatest, and the fruit ripe, the occurrence of 
 that disease was referred either to the heat, in itself, or to the 
 consumption of fruit. Further experience, in other places, 
 however, and more exact statistic data — especially the circum- 
 stance that many other diseases are most frequent and fatal 
 about the same time (e. g., intermitting and remitting fevers, 
 plague, jaundice, cholera, typhus, the so-called apoplectic fevers 
 in the tropics ; and ^ here, the generality of the diseases of 
 acclimatization) — soon cast a doubt upon the correctness of 
 deducing dysentery from the above-named causes. The dis- 
 tricts and places in which dysentery and all the other diseases 
 just mentioned were observed to occur with the greatest con- 
 stancy and intensity were compared with each other, and it 
 was found that such diseases were most frequent in marshy 
 neighbourhoods, in the vicinity of stagnant water, in wide 
 tracts of untilled land, in narrow and badly-ventilated streets, 
 and houses with deficient attention to cleanliness, drainage, 
 &c. The presence of a quantity of organic substances, the 
 conversion and putrefaction of which are essentially promoted 
 by the summer or tropical heat, was finally recognized as the 
 circumstance common to them all. Instead of the heat, in 
 itself, or the consumption of fruit, narrow streets, &c., another 
 common condition could now be surmised with infinitely 
 greater probability — i. e., the development of deleterious 
 gases and so-called miasmata, and their action upon the 
 human body. And perhaps this circumstance may, at some 
 
216 GENERALIZATION 
 
 future time, be ascertained to be itself remote aud secondary, 
 and the peculiar changes in the human body and in certain of 
 its processes — e. g., an increase of its temperature (i. e., of the 
 processes of oxidation from which it results), a consequently 
 more rapid, or abnormal, conversion of certain of its constituents, 
 or of the blood, &c. — be shown to be the more immediate, or 
 direct cause. 
 
 Nor are there wanting, in the theory of other diseases, 
 empirical hints concerning their essential uniformity of origin, 
 course, and termination, and conformity as to the general 
 character of their laws. So-called inflammatory diseases, 
 accompanied by fever, and other affections which, run a rapid 
 course, were long ago classed together; cachectic, dyscrasic, 
 or nervous diseases, were also grouped together ; because 
 processes or changes essentially the same were believed to 
 occur in whole series of them : in the former class, we 
 found the point of union in local changes, such as accumula- 
 tions of blood, or the formation of certain exudations ; in more 
 general changes — such as a certain alteration in the circulation 
 and composition of the blood, in various processes of excretion, 
 in nutrition, in the generation of heat, &c. — in the latter class, 
 it was discovered in certain derangements of innervation in 
 various parts. Thus, we know that in the same individual, 
 diseased conditions which, from the mode of their occurrence 
 and from their course, we regard as dissimilar, are apt to 
 occur in a certain constant order : in one case, simple derange- 
 ments of digestion will lead to hemorrhoids, gout, lithiasis ; in 
 the other case, simple excitements of the mind and nervous 
 system will pass on to actual neuralgia, disordered intellect, 
 apoplexy, paralysis, &c. Ricord's theory, that secondary 
 syphilis in the parents may produce scrofula, rickets, and 
 other allied diseases in later generations, is also well known. 
 We have long known from experience, that it is amongst the 
 poorer classes, from deficient food and clothing, &c., that 
 diseases are everywhere most frequent and severe ; not only 
 such as are epidemic and endemic, but also atrophy, scrofula, 
 rickets, convulsions in children, the formation of tubercles, 
 phthisis, marasmus, dropsy, &c. Instead of regarding age 
 and sex, occupation and mode of life, or certain errors in 
 diet, as the essential conditions of these diseases, as was so 
 
OR REDUCTION. 217 
 
 frequently done formerly, we have now recognized one cir- 
 cumstance common to them all, as their constant and most 
 essential cause, viz., poverty — or rather its attendant had food, 
 unhealthy dwellings, and general want of attention to cleanli- 
 ness and proper clothing. It has, further, heen established 
 that the manner in which diseases arise is not essentially 
 modified by difference of climate, any more than by the 
 diflference of race or sex, but that the influence of these only 
 extends to certain variations in diseases in relation to their 
 degree, course, malignancy, and frequency. 
 
 Could we but once succeed in separating the numerous 
 forms of disease into their individual elements and in ascer- 
 taining their causal connection, we might then go on to observe 
 which of those elements are common to the occurrence of many 
 diseases, and under what circumstances they group them- 
 selves together in various ways to form the types of disease 
 assumed empirically. It would doubtless become evident that 
 the latter, in spite of all their individual dissimilarities, are by 
 no means so essentially heterogeneous as they appear to be, 
 but that they are rather to be regarded as oscillations and 
 modifications within tolerably narrow limits, in comparatively 
 subordinate and secondary points; and, finally, that they 
 exhibit those dissimilarities externally because various processes 
 of a secondary nature in them are, in many respects, modified 
 by a number of accessory circumstances. And if we could 
 once succeed in determining the changes which those individual 
 processes undergo in the healthy, or diseased, in consequence 
 of the operation of various agents of the external world and 
 under the influence of our remedies, the essential similarity of 
 their efi"ects in the living body would, in whole series of 
 diseases, become evident. If, for instance, it could be ascer- 
 tained that the abstraction of blood in plethora, inflammation, 
 fever, &c., was not beneficial on account of the quantity of 
 blood in the body being thereby lessened, but because the 
 hydrostatic pressure of the column of blood and especially the 
 oxidation and conversion of the albuminous and other consti- 
 tuents of the body, the generation of heat and a certain 
 excitement of the nervous system, &c., were thereby diminished ; 
 and if it could be further ascertained that a diminution of the 
 vital heat is here the immediate determining circumstance, we 
 
218 GENERALIZATION 
 
 should be better able to explain why coldj spare diet, and 
 cooling drinks, rest, dark rooms — in short, every thing which 
 tends to diminish the vital heat, as nauseating medicines, 
 acids, neutral salts — have similar good effects in such diseases. 
 We should have succeeded in reducing the mode of operation 
 of all those remedies to essentially the same circumstance, 
 and should better understand, not only why the same remedy, 
 the same mode of treatment, may be beneficial in diseases 
 apparently altogether dissimilar, but also why apparently 
 altogether dissimilar remedies and modes of treatment have, in 
 the end, the same result in the same disease. This process of 
 reduction, or generalization, will thus probably, or indeed 
 certainly, gain ground gradually in our special department, 
 and the mass of different diseases, as well as of our remedies 
 and modes of treatment, be necessarily reduced to a much 
 smaller number. In the former, the ancient ^gritudo will 
 again more or less take the place of the innumerable diseases 
 of our systems ; in the latter, precedence will be given to the 
 natural course of the vital processes in conformity to internal 
 constant laws, which we, under the most favorable circumstances 
 can only assist by our co-operation, and that, though by ways 
 and means the most various, in essentially the same manner. 
 
 This may suffice to show why, in the study of life in a state 
 of health and disease, as well as in the study of natural phe- 
 nomena in general, the final object of our scientific efforts 
 must be placed in deducing the greatest possible number of 
 effects from the smallest possible number of causes ; or, in 
 other words, to resolve the conditions, dependence, and con- 
 formity of the greatest possible number of apparently hetero- 
 geneous phenomena and processes into the smallest possible 
 number of hypotheses, or assumptions of laws, and in so doing 
 to bring them under the widest and most general laws. It 
 cannot be said where, in the progress of our intellectual powers 
 in this direction, the pillars of Hercules, beyond which we 
 cannot pass, stand. Much, however, already tends to show 
 that the phenomena and processes which we call " life" agree 
 in certain and even important points with those of light, heat, 
 and electricity; and perhaps, in accordance with this idea, we 
 might be justified in assuming aa the final object of our inves- 
 
OR llEDUCTION. 219 
 
 tigations and generalizations in the study of life^ the progressive 
 connection of this "life" of certain peculiarly constituted and 
 peculiarly arranged materials, with the phenomena and pro- 
 cesses of the material world in general, and the reduction of 
 the laws of both to essentially similar, or analogous ones, and 
 in every case to the smallest possible number. The advance 
 of our knowledge may not only reduce all the vital phenomena 
 and processes to a small number of elementary processes, and 
 bring these into conformity with each other, but the same pro- 
 cess may in time be extended to everything which exists and 
 occurs upon our earth. As all things had their origin simul- 
 taneously, successively, and out of each other, so are all things 
 more or less intimately connected as constituent parts only of 
 one great organism. 
 
 For the present these are, it is true, mere hypotheses, or, at 
 best, probable possibilities, and it would be sinning greatly 
 against all the principles laid down for the investigation of 
 nature to steer at once for that great final goal, or even begin 
 to fofm surmises concerning it. We must, if we would reach 
 it, begin by being convinced that we cannot yet ascertain those 
 most general and ultimate laws. We do not, at present, 
 clearly understand the causal connection of any individual 
 process in the living body ; still less are we aware how the 
 more complex functions and processes are connected with each 
 other and in conformity to what laws they occur. We must, 
 therefore, first of all, as has already so often been mentioned, 
 endeavour to determine these laws and the circumstances 
 under which many hitherto unconnected series of phenomena 
 and processes correspond in their mode of origin and course. 
 We shall thence be enabled to demonstrate experimentally 
 that the same conditions and causal connection exist in other 
 series of vital processes, and thus have it in our power to 
 reduce them to one and the same law. 
 
 On the other hand, however, it is precisely a science such as 
 ours, in which all the phenomena and processes are highly 
 complex in themselves and dependent upon the most various 
 and, consequently, fluctuating influences, that gives the greatest 
 stimulus to the hope of discovering such general laws. The 
 very complexity and multiplicity of causes and effects, and the 
 consequent oscillation and instability of the final result, are the 
 
220 GENERALIZATION 
 
 best proofs that no definite conformity has hitherto been ascer- 
 tained for them, but yet, when viewed under another aspect, 
 the best guarantee that such may and must be found. If we 
 consider the constant and uniform course of organic develop- 
 ment in relation to form and materials, as well as to its vital 
 phenomena ; if we consider the unvarying order and conformity 
 in which all the different tissues, the whole complex structure 
 of plants and animals develop themselves in the impregnated 
 germ, from the cell to the perfect organism, and, parallel with 
 these, the multiform phenomena or manifestations of activity 
 from the first moment of life to its cessation, it may be re- 
 garded as more than a surmise that, in all these cases, no 
 great number of heterogeneous agents, or causes, are in ope- 
 ration. It appears to be something more than a mere 
 hypothesis that these laws and the definite order in which they 
 act may, in the end, be reduced to a very small number. The 
 numerous malformations which may and do occur in the living 
 body, and, in a certain respect, the numerous forms of disease 
 to which it is liable, have, notwithstanding all their variations 
 and changes, only confirmed that supposition. Thus essentially 
 the same plasma, or exudation, may perhaps develop itself in 
 one case into tubercles, or cancer, and in another into the mere 
 induration or thickening of a tissue ; and many of these special 
 forms of development appear, in the end, to obtain only 
 because that which has assumed the one form cannot assume 
 the other. 
 
 The manifold and varying character of those vital processes 
 is probably dependent only upon the complex combination of 
 the organs and tissues in which they occur, upon the multi- 
 plicity and constant variations of the internal and external 
 agents and materials which co-operate to produce them, and 
 upon the variously operating properties of those agents and 
 materials themselves — in other words, upon the complex and 
 changeable nature of the circumstances and influences which 
 jointly effect one and the same result. The mode and confor- 
 mity in which the latter act, and in which those phenomena 
 or processes in the living body occur, are probably less varied 
 in their nature. Such complexity is rather apparent than 
 real, and it arises from the many different kinds and series of 
 vital phenomena, i, e. from the manifold modes and directions 
 
OB REDUCTION. 221 
 
 in which the substrata or materials of the body manifest 
 activity or vitality; just as the multiplicity of the chemical 
 processes rather depends upon the different nature of the 
 substances and their combinations with each other, than upon 
 any differences in the laws themselves, by which those sub- 
 stances and combinations qf substances are accustomed to act 
 upon each other. 
 
 Even now we may surmise that all these processes and 
 actions in the living body occur in conformity to a few simple 
 and essentially analogous laws, and, for this very reason, we 
 may anticipate the eventual reduction of those vital processes 
 to a small number of laws, and look for the consequent advance 
 of our generalizations in the science of life. At present, it is 
 true, we can only hope to carry out such generalizations 
 approximately, and thus it may remain for a long time to 
 come J but with the advance of the general investigation of 
 nature, especially in a physico-chemical point of view, we shall 
 doubtless come nearer to ascertaining more definite laws, and 
 to gaining a greater number of indefinite links for the causal 
 connection of our phenomena and processes, and thus gradually 
 advance to the knowledge of more general laws. If we have 
 hitherto succeeded in ascertaining but few of these, we must 
 the more diligently, in every fresh discovery that takes place 
 in the various departments of nature, examine the different 
 series of phenomena so enigmatical to us, and endeavour to 
 ascertain upon which of them such a discovery may possibly 
 throw more light, or what general advantage is to be reaped 
 from it in the way of our practical progress. 
 
 The wider our horizon becomes, the better shall we be able 
 to connect together many things that have hitherto been 
 unexplained, obscure, and isolated, and by linking these with 
 other better known occurrences, with which their dissimilarity 
 is proved to be only apparent, bring the more and the less 
 familiar into connection, and thus extend our knowledge of 
 the latter. And though this knowledge may fluctuate accord- 
 ing to the degree and development of our general knowledge 
 and views, and vary also with the varying mental tendency 
 and judgment of individuals, a vast ultimate gain in the way 
 of a clearer perception and a more comprehensive generaliza- 
 tion will none the less have been realized. 
 
SECTION VI. 
 
 ON CERTAIN AUXILIARY OPERATIONS AND PROCESSES. 
 
 OBSEBVATION AND EXPERIMENT. — HYPOTHESES, COMPARISON OR 
 ANALOGIES, AND THE CALCULATION OF PROBABILITIES IN 
 GENERAL. — TECHNICOLOGY, TERMINOLOGY AND DEFINITION, 
 DESCRIPTION.— GROUPING OB CLASSIFICATION. 
 
 Having endeavoured, in the above, to represent in a con- 
 nected form, and as clearly as possible, the objects of investi- 
 gation, and the modes by which it must be pursued, it now 
 seems desirable to explain their several and technical details, 
 and the expedients and operations to be adopted in such in- 
 vestigation. 
 
 We have already endeavoured to explain how our search 
 after experimental truth tends to connect these various opera- 
 tions with itself and with each other, by bringing the objects 
 with which we have to do under a conformity to general laws, 
 and by assigning to each of our mental processes its due place 
 in the mechanism of investigation. We have now to test, one 
 by one, some of the more important levers and springs of 
 inquiry, and trace their appointed share in the general process 
 of investigation, with the clearness indispensable to their correct 
 and appropriate employment. And this is necessarily of the 
 highest interest, as upon it depends the degree of certainty 
 with which we are justified in relying upon the results to be 
 obtained by its assistance. 
 
 In all cases the observation of things in their actual condi- 
 tion is the first step towards their further investigation, as an 
 insight into their nature is only to be obtained through the 
 contemplation of their existing conditions. We shall, there- 
 fore, first speak of observation, and its attendant, scientific 
 experiment. This observation, these experiments themselves, 
 involve, however, a certain co-operation on our part — involve, 
 in short, our ego — which constitutes the transition to further 
 mental operations, to hypothetical conjecture, to comparisons 
 
OBSERVATION AND EXPERIMENT. 223 
 
 and a priori combinations, with whose aid we cannot possibly 
 dispense in the investigation of causal connection, and of the 
 conformity of general phenomena and processes. Hence 
 springs the necessity of duly estimating the value of observa- 
 tion. We shall speak finally of certain comparatively subor- 
 dinate and more formal auxiliary operations, no less to be 
 dispensed with, and exerting the greatest influence upon our 
 methods of investigating and observing, and even upon our 
 very opinions and conceptions, such as language, nomenclature, 
 description, definition, and classification, as these are connected 
 with the theory and practice of medicine. 
 
 I. OBSERVATION AND EXPERIMENT. 
 
 Our final aim in all investigations of natural phenomena 
 and processes — and, among such, of those of medical science 
 — is the understanding of their causal connection and con- 
 formity to fixed laws, and the ability to establish them by 
 experimental demonstration. This demonstration consists, as 
 we have seen above, in the establishment of all the conditions 
 under which the phenomenon, or the occurrence in question 
 takes place. We must, therefore, in the first place, have ob- 
 served these phenomena and processes, and their conditions in 
 many single cases ; we must be able to infer that the things 
 which we have met with in a certain number of instances as 
 actually present, as really occurring in this or that manner, as 
 constantly happening together or in a certain order, and qua- 
 lifying each other, would exist equally and exert the same 
 influence in all cases of a similar kind. In other words, as it 
 is from these observations and established facts that we deduce 
 the causal connection and laws of the phenomena and processes 
 in question, we must be able to extend what we have found in 
 a certain number of single instances, to all phenomena of the 
 same kind, or of the same series, and thus generalize the 
 results of our observations. 
 
 To arrive at a clear comprehension of phenomena and pro- 
 cesses, we must first have observed them in a greater or less 
 number of single cases or examples, we must have become 
 acquainted with them in all their sentiently appreciable qua- 
 lities, as well as in all their relations to each other, and hence 
 
224 OBSEEVATION 
 
 the necessity of thoroughly correct, i. e., minute and complete 
 observation, becomes self-evident. 
 
 It is not, indeed, the exact province of logic to teach the 
 art of observing, and still less has it the power to form apt 
 and expert observers. All this can only be effected in each 
 particular department by education, practice, and training. The 
 true province of logic, as we have already pointed out in its 
 application to medical science, is to teach us the means and 
 processes through which we may attain to a knowledge of the 
 phenomena and incidents with which we are concerned, and 
 gain an insight into their causal connection and conformity to 
 fixed laws. And, since observation occupies so important a 
 position among these, it becomes our object to test how, by 
 its aid, we may best attain our final aim. If logic is not 
 meant to teach us how to observe, and can give us no rules to 
 guide us in this respect in any given case, it can teach us 
 something no less necessary, namely, how to estimate what 
 we have observed, and to subject the results of our observa- 
 tions to an appropriate examination. It can show us what 
 conditions each observation must fulfil before we may venture 
 to accept its results as true, and rely upon them as being 
 altogether conclusive. 
 
 These conditions, these demands upon our observation, 
 must be self-evident. All the phenomena, with their con- 
 comitants in each separate case, whether occurring in nature, 
 or under circumstances which we have ourselves induced — i. e., 
 by experiment — must have been observed correctly and inves- 
 tigated amply. We must, in all cases, observe things as they 
 really exist; we must always be convinced, and be able to 
 prove, with regard to what has once come under our percep- 
 tion, that it occupied exactly this and no other position. Our 
 observation must be in itself thoroughly exact and conformable 
 to nature and truth, and also, in an especial manner, objective 
 enough — that is, mixed as little as may be with any views, 
 deductions, or interpretations of our own framing — as all 
 these may possibly be false, and are, probably, narrow and 
 defective. 
 
 This looks, at first sight, a comparatively easy matter, as all 
 that is required for such observation appears to be but the 
 due discipline of the senses, as each department of study 
 
AND EXPERIMENT. 225 
 
 teaches us to use and apply them, assisted, in some circum- 
 stances, by the correct employment of certain auxiliaries to 
 observation — e. g., the microscope, the thermometer, the 
 stethoscope, &c. It is evident that, were the operation of our 
 senses altogether free from the possibility of error and delu- 
 sion, everything with which those senses could make us 
 acquainted would be clear, and in conformity with truth and 
 nature. Our observations, in this case, could never contradict 
 each other, and a. difference of opinion upon the subjects with 
 which they were concerned would be simply an impossibility. 
 
 But experience has, with regard to observation, a far 
 different lesson to teach us, and particularly in our special 
 province. Too frequently, as we all know, our observations, 
 in a greater or less degree, contradict each other ; and almost 
 daily is this a source of dispute and discussion. What one 
 man looks upon as an established fact — because he believes 
 that he has observed certain things as thus existing, and in 
 this peculiar relation to each other — another has failed to find 
 in a similar case, and under circumstances precisely similar. 
 In a patient, for instance, in whom A has perhaps observed 
 inflammation of an internal organ — as the brain or intestinal 
 canal, or a catarrh of the mucous membrane of the latter — 
 B has been unable to find any of thesis, but perhaps has 
 noticed something entirely different — e. g., typhus or simple 
 disturbance of the nervous function, a so-called spinal or 
 cerebral irritation, or, it may be, indigestion only. In the 
 same manner, A has perhaps traced a certain disease to certain 
 causes, and been able to cure it by certain remedies; while B 
 has been unable to see anything of the kind, and would 
 possibly have found the same remedies ineffectual in the case 
 of the same patient. 
 
 Contradictious of this kind plainly indicate that the mode 
 of observation must have been defective or erroneous some- 
 where and in some direction, and betray that what has been 
 observed has not been the simple and truthful fact or observa- 
 tion which it has been taken for. The fault may often be 
 traced to haste and carelessness in observing, to prejudice, 
 ignorance, partial views, or other defects, on the part of the 
 individual observer. It is unnecessary here to take these 
 errors into consideration, as they are, in a certain degree, 
 
 15 
 
226 OBSERVATION 
 
 inseparable from all human speculation, and are only to be 
 avoided by care or diligence. It is more important to our 
 object to point out another source of delusion, frequently 
 recurring, because it is connected less with the individual 
 observer than with the nature of observation itself. 
 
 We are apt, namely, in the process of observation, to 
 confound, almost instinctively, two things which are entirely 
 different, and to mix up with what has been actually observed, 
 the impression it has made upon our minds and judgment, 
 thus confusing perception with the deductions to be drawn 
 from it. What we think we have really observed, what we 
 believe our senses have actually detected, we concisely describe 
 as observation ; yet it contains not only what we have really 
 observed and learnt through our five senses, but includes, at 
 the same time, something entirely different — that is, our 
 interpretation and explanation of what we have sentiently 
 observed and adopted. 
 
 Thus, we say that we have seen erysipelas of the face, or an 
 ulcer of typhus in the intestinal canal ; that we have heard a 
 certain valvular bruit in the heart ; that we have felt schirrous 
 tumours in the abdomen of a sick person ; or parts of the 
 foetus in that of a pregnant woman. In reality, however, it 
 is not erysipelas we have seen, but a red, tense, shining surface 
 in the face ; on the mucous membrane of the alimentary canal, 
 perhaps, an excavation with a certain ground and border, but 
 no ulcer of typhus. In the cardiac region, we may have 
 heard, instead of the normal sounds, an abnormal, but not a 
 valvular bruit ,- in the abdomen, we may have felt bodies with 
 certain contours, of a certain consistence and mobility, &c., 
 but no schirrous tumours, no foetal limbs. But upon the 
 ground of former experience, whether our own or that of 
 other men, we are agreed to call the groups of phenomena 
 thus sentiently recognized, erysipelas, ulcer of typhus, valvular 
 bruit, &c. Even in the moment of observing them, we have 
 unconsciously, and almost instinctively, compared what we 
 have recognized in the present case with what, in similar cases, 
 we have ourselves already witnessed, or have in other ways 
 known or heard about them, and are thus ready to pronounce 
 upon their nature from their coincidence with these already- 
 noted phenomena. 
 
AND EXPERIMENT. 227 
 
 Much in this way, on first sight of a distant city, we should 
 say, perhaps, from observation, that it lies so many miles from 
 us. But we do not see this distance itself, any more than we 
 see an erysipelas or an ulcer of typhus, all that we truly see 
 being an indistinct assemblage of houses and other objects, 
 through whose apparent size, as contrasted with what we know 
 of their real magnitude, we are able to infer rightly of the 
 distance that separates us from them. Just so, when any 
 one asserts that he has seen an individual affected with fever, 
 typhus, or scrofula, he has, in reality, never seen either the 
 fever, typhus, or scrofula in question. For not only do these 
 diseases not present any condition so defined and appreciable 
 by the senses as a local inflammation, an ulcer, a bruit, or a 
 tumour, but we should be unable to recognize sentiently the 
 latter diseased conditions, as such, even if some of these were 
 present. 
 
 In all these cases, we must first consider the possibility, or 
 probability, that all the phenomena we have been able to 
 observe in the case before us correspond, completely and 
 essentially, to such and such others already observed by us in 
 similar cases. We compare the former with the idea or 
 picture of the latter already existing in our minds — often, 
 also, of many others (as, for instance, in the so-called differential 
 diagnosis of our patients) — and by this means are able to judge 
 of their resemblance or identity with these, and of their 
 difference from certain others. What we have, therefore, 
 denominated observation, and been accustomed to consider 
 the direct result of the evidence of our senses, is, for the most 
 part, a deduction — even if an unconscious one — from our 
 former experience and the notions of certain things resulting 
 from it, as — e. g., of phenomena and processes in the healthy, 
 in a so-called vital function, or of a disease, as erysipelas, 
 fever, typhus, &c. 
 
 These notions, conceptions, ideas, and images, whether cor- 
 rect or incorrect, whether formed in consequence of our own 
 former experience, or in consequence of the communications 
 and instructions of others, have existed and slumbered, as it 
 were, in our consciousness. We have abstracted some picture, 
 some particular conception of certain things and phenomena, 
 which thus, in a certain sense, has existed within our consci- 
 
228 OBSERVATION 
 
 ousness. and not external to us, and we are now reminded of 
 this picture, and of our notions concerning it, by what we have 
 observed in the case before us. "With them we involuntarily 
 compare all the phenomena or things formerly recognized 
 through our senses ; and, if we find that the latter coincide 
 with our picture and conception in all their chief points, we 
 now declare them to be indentical, and give them the same 
 name. Our former picture or notion serves us here as a means 
 of comparison and type for all similar cases. 
 
 In all cases, it lies in our very nature to be able to see and 
 recognize nothing through our senses, without, at the same 
 time, drawing from it a conclusion concerning the postulates 
 — i. e., concerning that which might have occasioned these 
 our perceptions — and forming for ourselves some notion of 
 them. For of these, our senses, of themselves, could never 
 teach us any thing. What by their aid we are able to re- 
 cognize calls forth our reflections and judgment, our combina- 
 tions or notions concerning them. And only by the creations 
 and efl'ects of these, in short, by our own co-operation in the 
 manner pointed out, can we observe, whether correctly or 
 falsely, anything whatever. We should, therefore, in a given 
 number of cases, endeavour to comprehend, as we best may, the 
 phenomena which are common, constant, and essential to such 
 cases ; we should next abstract, from numerous observations, 
 the idea — e. g., of a certain function or disease, and, finally, of 
 life or disease in general, and thus create for ourselves, by our 
 own exertions, some conception of the particular phenomena 
 which we have recognized through our senses. All that we 
 can observe of any object, or process, is only concerned with 
 the properties and states which we are able to recognize in it 
 — i. e., the impressions which our senses receive from it. On 
 the other hand, our notions and assertions concerning it — 
 which we class together under the head of observations — refer 
 not only to these our sentient impressions and perceptions in 
 themselves, but also to the object itself — i. e., to the total result 
 of these sentient impressions and the notions we form from 
 them. From those individual phenomena, and from our 
 sentient impressions in general, we unconsciously draw con- 
 clusions concerning the object itself, and its whole nature ; 
 and the notions and conceptions with which we compare a 
 
AND EXPERIMENT. 229 
 
 new case, and the phenomena observed in it, appear to have 
 arisen in the same way. 
 
 We need not here ask how and when these previous notions 
 have been acquired. It is sufficient to know that they exist, 
 and that we must everywhere, if we would obtain a clearer 
 idea of what we briefly term " observation," bear in mind the 
 fact of their existence, co-operation, and connection with all 
 that we become aware of through the senses. It foUows from 
 this, that such kind of observation not only includes what we 
 have actually observed — i. e., what we have ascertained by the 
 aid of the senses, but also the notions we have formed of what 
 we have observed, and influences our notions, not only of the 
 phenomena or properties that have come under our observation, 
 but also those which we form with regard to the object or 
 objects which may have exhibited them. We never express 
 simply what we have really seen or felt — in short, observed 
 — neither can we do so, however earnestly we may wish it. 
 What we express is our own explanation of what we have ob- 
 served, compared, and grouped with many other things ; we 
 describe it, in short, as it appears to us. For this very reason 
 however our ego, our whole previous knowledge and experience, 
 our notions and views at the moment, acquire a much greater 
 influence over the mass of our observations than we are for the 
 most part conscious of. However exact and objective our ob- 
 servations may be, there is always much of what is subjective, 
 much of our ego involved, and in most cases, especially in the 
 case of what the physician meets with at the bedside, our con- 
 clusions, notions, and views of what we actually recognize, 
 form a much larger part of our observations than the latter in 
 itself. 
 
 It. naturally follows from this that we must strive, in our 
 observations, to distinguish what we do really observe, from 
 what we do not observe ; to recognize what, in the phenomena 
 and objects observed by us, may reach our consciousness 
 directly through the senses, and what, on the contrary, is 
 merely the product of our conclusions from it ; we must be 
 aware, for instance, how, in our interpretation of what we 
 have observed, we have compared it with other things, and 
 have brought it into some relation to our previous notions. 
 And it is the office of logic to direct our attention to this 
 
230 OBSERVATION 
 
 necessity, because the circumstance of confounding these two 
 so heterogeneous elements in our observations, is a fertile 
 source of error. 
 
 Thus, in the investigation of a vital phenomenon, or of a 
 state of disease, everything which we have recognized by the 
 aid of the senses may be perfectly correct — i. e., may agree 
 exactly with the natural state of things — yet the observation as 
 a whole, and the manner in which we express it, may be 
 incorrect in consequence of the interpretation we put upon 
 what we have observed. We may have observed certain phe- 
 nomena and changes in a patient with sufficient accuracy, but 
 the opinion we express — i. e,, our assertion that we have observed 
 a certain disease in that patient — may be none the less erro- 
 neous, so soon as it leads us to infer the existence of a given 
 disease from the phenomena which we have recognized, and to 
 regard the latter as symptoms or proofs of a state which may, 
 in reality, have no existence. This species of error in our 
 observations is as possible as in the case of a hysterical female, 
 who may really experience the sensation of a ball in the throat, 
 or of another individual, who may see sparks or hear various 
 noises, although, in the case of the former, no such ball exists, 
 nor, in that of the latter, any external cause to produce such 
 effects. In both cases perception, sensation, sight, hearing, 
 have been doubtless, in themselves, correct; the error lies in 
 the interpretation of them, and in inferring from them the 
 actual existence of a compressing, shining, or sounding body, 
 or, in other words, in inferring the existence of any causes or 
 circumstances capable of occasioning those sentient perceptions. 
 In all such cases we have attributed what has been actually 
 observed by us, to influences and circumstances which have 
 not, in reality, produced it. 
 
 These examples serve to show how much, in our interpre- 
 tation of what we have observed and in the notions we form 
 concerning it, depends upon our previous knowledge and upon 
 the nature and extent of our previous experience. If any one, 
 whom experience has rendered more familiar with such hallu- 
 cinations, no longer allows himself to be deceived by them and 
 led, for instance, to assume falsely the actual existence of 
 bodies producing such sentient perceptions, equally little will 
 the experienced and circumspect physician be led into any 
 
AND EXPERIMENT. 231 
 
 erroneous and unfounded interpretation of the phenomena and 
 conditions observed in a patient — i. e., into the assumption of 
 a diseased state which has no real existence ; and he will be 
 the less exposed to this danger in proportion to the extent of 
 his previous knowledge and experience of the particular phe- 
 nomena which each case presents. 
 
 Since we are compelled to interpret what we observe in any 
 given casBj without delay, and to form for ourselves some notion 
 concerning it, and since this our interpretation of it depends 
 essentially upon the notions and views we entertain at the 
 moment with regard to similar phenomena, as well as with 
 regard to many other collateral things, the importance of these 
 notions and views, in even the simplest observation, becomes 
 evident. If our previous notions are correct, they will facilitate 
 our interpretation of what we observe in any given case, and 
 r.ender the conclusions we draw from it more trustworthy ; 
 while, on the other hand, the incorrect, or partial and obscure 
 character of our previous notions will essentially interfere with 
 our correct observation of the things before us. 
 
 One of the most important requirements for the formation 
 of such clear and correct notions will therefore be the habit of 
 accurate observation, which includes attention and exactness, 
 arid demands that we draw no conclusions from the phenomena 
 observed beyond what they safely tend to. It is also necessary 
 that we should be able, in any given case, to render a true 
 account of all its details, and to reason them out with clearness. 
 But the possibility of such a kind of observation presupposes 
 many other things — not only knowledge of the subject, practice, 
 the capability and habit of taking in all the points of a given 
 case clearly and comprehensively, but also a good memory, by 
 the aid of which we may recall, at the right moment, the results 
 of our previous experience, so that we may be able to compare 
 with them what is new in the case before us. It follows from 
 this that the kind of observation we have shown to be indis- 
 pensable must be infinitely less attainable in the study of vital 
 phenomena, and especially .of those which it is the province of 
 the physician to investigate, than in the physico-chemical or 
 anatomical department — in the simply descriptive natural 
 sciences. It is easy to understand how an observer may much 
 more easily deceive himself or overlook various important things 
 
232 OBSEKVATION 
 
 in the former than in the latter, from the absence of clear and 
 correct a priffri notions of life, disease, &c., and of the assistance 
 which such would render. The same special circumstances, 
 the very difficulties in the nature of our subject, which so 
 much, in any given case, impede observation, and so easily 
 give it the stamp of incompleteness, obscurity, and one-sided- 
 ness,, have exerted a similarly adverse influence upon our pre- 
 decessors, as upon us. 
 
 The observer at the bedside in particular has always been 
 compelled to form his notions of a disease and of its origin 
 and conditions, as well as of its cure, and of the effects of his 
 remedies in it, from a more or less incomplete examination of 
 phenomena and incidents ; and it will be long before our 
 followers are, in this respect, much more advanced than our- 
 selves. 
 
 The physician, and especially the practical physician, cannot 
 possibly gain any clearer notions of a disease, or sufficiently 
 correct ideas of the state of the patient before him, not only 
 because this is simply impossible in the present state of our 
 knowledge, but because he has seldom, if ever, felt called upon 
 to give to others a clearer and more distinct account of his ob- 
 servations, still less of his conclusions from them. Many 
 scarcely ever make any serious attempt to do so ; but if any 
 one does make it, whether in an earnest, scientific spirit, or from 
 a mere disposition to theorize, it soon becomes evident that he 
 has no certain knowledge, no correct and clear notions and 
 data upon which to rest. He rather finds himself involved in 
 a complication of hypotheses, of mere possibilities, with which, 
 if he possess any knowledge of himself and of his subject, he 
 cannot possibly rest content. And in this respect he shares 
 the lot of the statesman, the historian, and the moral teacher. 
 
 On the other hand, however, the able physician and expe- 
 rienced practitioner are by no means incapable of observing the 
 state of their patients as rapidly and distinctly as is necessary 
 for the purposes of treatment — i. e., of concluding from what 
 they recognize in their patients, and from all the peculiar cir- 
 cumstances of a given case, what is imperatively called for and 
 how they may best cure or relieve. They will, it is true, be 
 unable to give, either to themselves or others, the precise 
 grounds upon which they found their opinions of the case, or 
 
AND EXPERIMENT. 233 
 
 their treatment of it ; and it is with these only — i. e., with the 
 demonstration of the accuracy of their views, that logic has to 
 do. But they cannot furnish any adequate grounds for their 
 viewSj because they have been able to obtain only imperfect 
 hints and notions from their previous observations — in short, 
 from their experience. They may indeed have formed, though 
 perhaps unconsciously, such views and conclusions as have 
 enabled them to adopt beneficial measures in a given case, but 
 not such clear and correct notions of the state of the patient as 
 to put them in a position to deduce from them all their grounds 
 for those measures, and to thoroughly explain the reasons for 
 their adoption of that particular mode of treatment. 
 
 It then becomes evident from what has just been said how 
 much our conception and interpretation of what we have seen — 
 i. e., our observation as a whole, must depend upon our ego, 
 upon our previous knowledge and views, and upon our mental 
 capacity — in short, upon the general tendency and development 
 of our intellectual being. We draw our conclusions concerning 
 the nature, properties, and relations or causal connection of the 
 phenomena and objects before us, less from our immediate ob- 
 servations by the senses than from our previous experience, 
 knowledge, or views of similar things, and from what we regard 
 as most probable in the case before us. They depend therefore 
 upon the capability of our minds to receive impressions from 
 what we see, and upon the nature of such impressions ; also 
 upon the trains of thought, the feelings, interests, and impulses 
 called forth in the individual observer, and upon the direction 
 these may take. This explains why observation will always 
 vary in accordance with the special character of the individual, 
 and why it has always varied and will continue to do so according 
 to time and place. It was not without cause that Rousseau 
 complained that " it is a melancholy fact that so much philo- 
 sophy is required for the observation of what we see every day." 
 Thus the ancient Romans, with all their cultivation, saw, when 
 passing through Switzerland, nothing of the beauties which are 
 objects of admiration to us.^ They complained only of the 
 bad roads ; and even a Julius Caesar employed the time during 
 the passage of the Alps in writing a grammatical treatise " de 
 analogic." In a similar manner, it was long before painters 
 ' Compare A. von Humbold, ' Kosmos,' vol, ii, 25. 
 
234 OBSERVATION 
 
 knew how to draw buildings and many other objects precisely 
 as they saw them — i. e., in perspective — not as they are in 
 reality. In short, man is and remains, in a certain sense, an 
 egotistj even in the investigation that may seem most candid, 
 and in the simplest and most circumspect observation. It is 
 through a necessity of our nature that we are accustomed to 
 observe and conceive a given phenomenon or object only in so 
 far as we are able to form some notion of it. Whenever, there- 
 fore, a phenomenon or object is not of so simple a nature as 
 to be appreciated by the senses, and taken in by them at once, 
 in its whole extent — which is obviously impossible in the case 
 of any natural phenomenon, and most of aU in those connected 
 with our peculiar department — we shall be inclined, on that 
 account, to conceive and judge of it in accordance with our 
 own a priori notions. The manner in which an individual 
 observer judges of a given case will thus always depend more 
 or less upon his general train of thought. In the observation 
 of each individual case, much will depend, therefore, upon the 
 amount of our previous knowledge, upon our general mode of 
 judging and drawing conclusions, and upon the path, so to speak, 
 by which we approach a given phenomenon, or a scientific ques- 
 tion or investigation. Of the innumerable things which nature 
 offers to our view we select those only which happen to attract 
 our attention. We often take a childish pleasure in empty 
 shells and fragments, and persuade ourselves that we have 
 found the kernel or essential part, simply because we choose to 
 regard it as such. The interest we feel in our own notions 
 and views of various things is often infinitely greater than that 
 which we take in the things themselves as they actually exist, 
 and our reason, as Kant remarks, recognizes only that which it 
 has created after its own design. 
 
 These truths, as applied to observation in general, make 
 themselves doubly felt in such a study as ours, and upon us, 
 in an especial manner, it is incumbent at all times to bear in 
 mind the exact state of things. For, in medical practice, not 
 only do the most manifold and complex phenomena and 
 occurrences present themselves simultaneously to the observer, 
 without his being able to isolate and fix them, but he cannot 
 even recognize directly all the functions and organs, from 
 whose varying phenomena and changes conclusions might be 
 
AND EXPERIMENT. 235 
 
 drawn concerning the processes and occurrences at work in 
 them. We have always been necessitated to observe the phe- 
 nomena and processes which are the objects of our investigation, 
 superficially and from without, and to draw conclusions, from 
 the individual phenomena which we are able to recognize, con- 
 cerning the other, infinitely more important ones, which occur 
 within the body. It lies, therefore, in the very nature of our 
 subject, that in our case, observation and comprehension must 
 depend much more upon the mental peculiarities of the indi- 
 vidual, than they do in that of the physicist and chemist ; for 
 in our branch of science previous views and habits of judging 
 are much more intimately concerned than in theirs; and our 
 observation, as a whole, will always possess more of a subjective 
 than of an objective character. 
 
 We easily persuade ourselves that we proceed to an obser- 
 vation candidly and without prejudice, perhaps because we are 
 conscious that we do not seek to demonstrate or refute anything 
 arbitrarily and a priori. We rely upon our fixed and honest 
 intention to see and judge of all the phenomena presented to 
 us precisely as they are, and not as we might wish to find 
 them,- and because an individual may feel no interest in the 
 result of his observation in a given case ; because it may appear 
 to be indifferent to him whether it confirm or refute his personal 
 views, he, perhaps, considers himself protected from all these 
 dangers. Yet this very feeling of security, which appears to 
 him to be so well grounded, may endanger the accuracy of his 
 whole observation. In a certain sense, it is almost absurd to 
 suppose that any one can free himself entirely from prejudice, 
 and proceed to an observation without being influenced by his 
 previous views, notions, or peculiar mental tendency. This is 
 pretty much as if any one were to take out his eyes for the 
 purpose of ascertaining how he could see without them. Bacon 
 understood this much better when he said " intellectus humanus 
 luminis sicci non est; sed recipit infusionem a voluntate et 
 affectibus. Quod enim mavult homo verum esse, id potius 
 credit."! 
 
 Even the apparently unprejudiced and impartial observer 
 strives, like every one else, to attain some end, for some pur- 
 pose or other lies doubtless beneath his observation. We must 
 ' De interpietatione Naturs, lib. i, aphor. 47. 
 
336 OBSERVATION 
 
 seek to answer some question, to determine the presence or 
 absence of certain phenomena, &c., for without such motive 
 we should never undertake any observation or investigation 
 whatever. It follows, in fact, from the very attempt at inves- 
 tigation, that we desire not only simply to observe and recognize 
 certain phenomena, but also to understand them, and to this 
 end we must strive to ascertain their causal connection, condi- 
 tions, and laws. Thus the physician endeavours, from the aggre- 
 gate of the phenomena which he observes in a patient, to deter- 
 mine his actual state, and the nature of his disease — in other 
 words, the conditions and causal connection of all those phe- 
 nomena. He endeavours to ascertain the part played by certain 
 occurrences and circumstances, and to acquire a certain under- 
 standing of the effects of deleterious influences and habits of 
 life, as well as of the remedies to be employed, and the mode 
 of treatment to be adopted. The same thing holds good, in 
 essentials, for the observations of the physiologist. It is pre- 
 cisely because we have some special object in view, that our 
 investigation acquires the requisite exactitude, and that our 
 attention is directed to, and fixed upon, various phenomena 
 and things which, perhaps, from want of interest on our part, 
 might have escaped us altogether. This pursuit of a definite 
 object involves little or no danger to the accuracy and impar- 
 tiality of an observation, if the things to be observed are 
 sufficiently clear and simple not to admit of very difi'erent 
 modes of conception or interpretation; if they have become 
 more or less known to us in their conditions and effects, and 
 in their relations to other things ; or if, perhaps, in a given 
 case, only one new phenomenon or occurrence, only one enig- 
 matical circumstance presents itself among others already long 
 familiar to us. But this is never the case in medical science, 
 because all the phenomena and processes which come under 
 our observation are not only, in themselves, in the highest 
 degree complex and fluctuating, but have all remained more 
 or less obscure in relation to their conditions and effects, in 
 short, to their causal connection and conformity to fixed laws. 
 Instead of being able to acquire a clear understanding of the 
 latter, we have always, even under the most favorable circum- 
 stances, attained only to more or less probable conjectures, to 
 certain hypotheses and views. The beginner has always been 
 
AND EXPERIMENT. 237 
 
 compelled to content himself with explanations of this kind, 
 or, perhaps, with mere words which say all and nothing, because 
 his teachers had nothing better to offer. 
 
 Whether our views and notions of various things be correct 
 or not, they will not fail more or less to influence our concep- 
 tion and interpretation of all which we recognize by the aid of 
 the senses ; and so long as our knowledge of the vital pheno- 
 mena and processes remains so uncertain and, at the best, so 
 imperfect as at present, everything which we observe in a 
 given case will, on that very account, admit of various inter- 
 pretations. Our attention will easily, perhaps without our 
 being conscious of it, be directed only to that which we are 
 willing to see, or at least to that with which we are most 
 familiar; in both cases the result is much the same. We 
 shall further arrange and judge of what we observe, just as it 
 may correspond with our experience and previous views, in 
 short, with the precise stage of our mental development. The 
 practical man, with his peculiar interests and tendencies, will 
 take a different view of everything from the theorist, while 
 that taken by the latter will depend upon the particular school 
 to which he belongs, upon his general train of thought, and 
 upon his personal intentions and wishes. But this we are far 
 from regarding as prejudice, because it appears to us to be the 
 only correct and possible view ; neither can we believe in any 
 one-sidedness or partiality in our observations, because we feel 
 conscious of having honestly investigated all the points of the 
 phenomena and occurrences before us, in so far as they are 
 accessible to us, or rather in so far as they appear to us to 
 have a real existence and importance. The physiologist, and 
 with him the physician, occupy much the same position as 
 the historian and the statesman, who are, perhaps, even less 
 familiar with the phenomena and with the causes and laws of 
 the occurrences with which they have to deal than ourselves. 
 In politics, one man takes an entirely different view of the 
 same things from another, because it happens to correspond 
 better to his wishes, and to the interests of his party; he 
 easily persuades himself that he sees much which has no real 
 existence, while he overlooks, or sees imperfectly, all that is 
 opposed to his views and tendencies. 
 
 That the accuracy of observation in medical science is daily 
 
238 OBSERVATION 
 
 exposed to these dangers is a well-known fact. If we regard 
 a certain portion of a complex whole (e. g., of a function, or 
 disease), or certain of its elements, or certain circumstances 
 and influences which affect it, as important and determining, 
 and if we seek to investigate and demonstrate the operation of 
 the latter, we are but too apt to observe only what attracts 
 our special attention. And this all the more readily, because 
 everything which offers itself for our investigation is, in itself, 
 multiform and complex, and because the things with which we 
 have to deal may, in the absence of ascertained conditions and 
 laws, be classified and interpreted, with almost equal probability, 
 in various ways. The phenomena and occurrences to be 
 observed and investigated are, therefore, brought into mutual 
 relation in accordance with the views of the individual. We 
 assume such an internal relation and causal connection between 
 them as we had previously regarded to be real, or at least 
 most probable, and which we have, perhaps, sought, in a given 
 case, to ascertain and demonstrate. Our conclusion, if it 
 deserve to be so called, will thus almost inevitably depend, in 
 a great measure, upon our previous views and notions — i. e. 
 upon our experience and upon our interpretation of facts 
 already known to us. This our previous mode of interpretation 
 and explanation may, as has already been stated, be correct, 
 or erroneous and deficient; in every case it is never strictly 
 correct in relation to any vital phenomenon, because it is no- 
 where based upon a clear insight into the actual state of things. 
 On that very account, its application to a given case, though 
 more or less correct, can never be completely so, a fact con- 
 firmed by the result of every theory and attempt at explana- 
 tion. 
 
 If we bring to the bedside of the same patient a disciple of 
 Brown or of Broussais, an empiric of the old, or one of the 
 modern stamp, an adherent of the so-called Vienna anatomical, 
 or of the Giessen chemical school, a nerve-pathologist or a 
 blood-pathologist, each will recognize a different state of things. 
 The opinion which each forms of fever, for instance, and similar 
 aggregates of symptoms, of their causal connection and depend- 
 ence upon various local or general changes and conditions, and 
 of these in their relations to each other, will be different from 
 that of the others. Each of them, if he reflects upon it at all. 
 
AND EXPERIMENT. 239 
 
 will form a diflferent notion of all that he has been able to 
 observe ; he will arrange and combine the various phenomena 
 in the patient after his own manner — i. e., in accordance with 
 his own point of view; and^if the same remedy be administered 
 in a given case, the assertions and opinions of each concerning 
 its effects will equally differ. For each has expected from it 
 different services and modes of operation in accordance to his 
 previously formed theory ; he will, therefore, interpret what he 
 has observed in the manner which best corresponds to his own 
 views, and in the remedy employed will acknowledge only such 
 effects as it has been his aim to produce. 
 
 So long as Brown's system prevailed many believed that 
 digitalis produced an excitement of the heart and circulation. 
 According to their view the pulse was first accelerated and 
 rendered fuller before it could become weaker and slower, and 
 they asserted that the subsequent depression depended upon 
 the previous excitement (Saunders, Hutchinson, and others). 
 If another, a disciple of Broussais, for instance, had observed 
 exactly the same thing, his interpretation of it would have 
 been entirely different, because he would not attach the same 
 signification, or an equal importance to such excitement of the 
 circulation, &c. In like manner, at the period when the 
 simple, non-mercurial treatment of syphilis prevailed, patients 
 were believed to be injured by mercury in a degree never ob- 
 served before or since. A homceopathist of the old school, and 
 a modern disciple of Rademacher, will equally claim for them- 
 selves, and for the influence and mode of operation of their 
 remedies, credit for much which the impartial, and, perhaps, 
 correctly reasoning physician, regards simply as dependent 
 upon the natural course of the disease. The ordinary prac- 
 titioner will scarcely hesitate to assert that he has obviated 
 various diseases or abnormal conditions by means of some 
 remedy or mode of treatment. He willingly regards the 
 changes which take place in the state of his patients after the 
 employment of them, as their effects when those changes are 
 favorable — i. e., as the results of his practice, while, if the 
 changes are unfavorable, he attributes them to the natural 
 cotirse of the disease, or to various other influences and circum- 
 stances. He will further interpret the effects of his remedies 
 in exact accordance with his own theories and views. Because, 
 
240 OBSERVATION 
 
 for instance, in persons submitted to the influence of anaesthetic 
 agents, intelligence and consciousness, in the first place, then 
 sensation, motioii, and respiration, are successively suspended, 
 ether and chloroform are said to aj;t first upon the cerebrum, 
 then upon the cerebellum, next upon the posterior, and, lastly, 
 upon the anterior pyramids of the spinal cord and their nerves. 
 And when their action is extended to the medulla oblongata 
 life is said to hang by a single thread. A Flourens, a 
 Baudens, and others, take this view of their mode of operation 
 because it happens to correspond to their theories of the 
 functions of those portions of the nervous system. 
 
 In relation to the accuracy and scientific value of our con- 
 clusions, there is scarcely any difference to be found between 
 the ordinary practitioner, or even the homoeopath or disciple 
 of Rademacher, and the modern physiological physician ; for 
 the endeavour of the latter towards a more scientific advance 
 and judgment is still far from complete, and seldom to any 
 great extent feasible. His interpretation of what he observes, 
 though it may approacli nearer to the actual state of things 
 than theirs does, will not be less uncertain and arbitrary. Just 
 so will the physicist interpret the same phenomena and pro- 
 cesses in the living body, and even in the inorganic world — 
 e. g., in the air, water, or the soil, with their action upon each 
 other, upon vegetation, man, and animals — very differently from 
 the chemist, and both again differently from the professed 
 physiologist or ordinary practitioner. 
 
 In all that has been already advanced many may doubtless, 
 if they are so inclined, find sufficient grounds of discourage- 
 ment, and feel justified in mistrusting even the first and most 
 indispensable methods of comprehension in medical science. 
 Yet to perceive diflSculties does not necessitate that we should 
 allow them to overcome us, and in the case of observation, 
 especially in such a science as medicine, it has already been 
 shown that it is by no means such a simple and intelligible 
 thing as might be at first believed, and that Pontenelle was 
 quite right when he said "Tart d' observer, qui n^est que 
 le fondement de la science, est lui-meme une tres-grande 
 science." 
 
 If we compare, for instance, our present methods of ob- 
 
AND EXPERIMENT. 241 
 
 servation and investigation in the whole field of vital 
 phenomena, and even at the bedside, with those employed 
 but a few decennia ago, we cannot fail to recognize a great 
 improvement in them. Not only have we acquired, by the 
 recognition of various anatomical relations and chemico-physical 
 processes, better starting points for our observations, but, by 
 the employment of such aids, the general value of our observa- 
 tions is advanced far beyond that of earlier periods. In 
 illustration of this it may be sufficient here to mention the 
 more frequent and efi&cient employment of various auxiliary 
 means, such as the thermometer, scales, &c. 
 
 On the other hand, it is equally certain that, until we 
 become better acquainted than we are at present with the 
 internal connection and peculiar conditions and lawa of the 
 objects of our observation, our interpretation of them must 
 always be more or less obscure and arbitrary. Por, in the 
 present state of our knowledge, no one, however earnestly he 
 may strive to do so, can entirely avoid the danger of regarding 
 phenomena and circumstances as determining and essential 
 which are not truly so, and of drawing from this first error a 
 second one, in the conclusion that certain other phenomena 
 occurrences are the effects of these. Thus it remains, at pre- 
 sent, always more or less at the option of the individual to explain 
 what he observes in various ways, and to refer it to various 
 causes. And this fact brings us back to the point from which 
 we first started — viz., to the final object of all our observa- 
 tions. This, as we have already seen, by no means consists 
 in simply looking at, and recognizing by the aid of the senses, 
 various phenomena, but rather in approaching, by investiga- 
 tion, nearer to their due comprehension, and to a certain 
 insight into their causal connection and laws. Our aim, 
 therefore, becomes, to observe the phenomena and occurrences 
 with which we have to deal, in the manner best adapted to 
 the attainment of this end; and in doing this, less depends 
 upon the number of cases observed than upon the mode in 
 which we observe and draw conclusions concerning them, 
 although, under some circumstances, the number also is 
 important — e. g., for the establishment of simple empirical facts 
 and laws. A single observation may thus be infinitely more 
 valuable than a hundred others of a different kind, whether it 
 
 16 
 
242 OBSERVATION 
 
 be that something entirely new and important has been 
 discovered^ a new feature brought to light in some object 
 which has long been under observation, or attention directed 
 to a circumstance previously overlooked. The acumen of a 
 Galileo enabled him to deduce the laws of the pendulum and 
 its oscillations from the sight of a lamp swinging in a church. 
 
 The main point must always be to recognize, in a given 
 case, not only the individual phenomena, features, or fragments, 
 that go to make up the whole, but rather that whole itself, 
 with everything of which it is composed. All its phenomena 
 and circumstances must be correctly appreciated as they 
 actually exist, not only in all points, but also without 
 prejudice or onesidedness. Such, at least, are the hints 
 daily given to the observer; but, unfortunately, through the 
 peculiarities of his mental constitution, man is incapable of 
 fulfilling all these requirements to their fullest extent. In 
 the general study of vital phenomena, at least, it is absolutely 
 impossible; and thus, even those who have demanded such 
 things of others have themselves never been able to accomplish 
 them. Every process in the living body, every occurrence in 
 external nature, is so complex, and made up of so many others, 
 themselves dependent upon, or at least modified by, many 
 additional ones, that at present, and doubtless for a long time 
 to come, the most acute and best informed observer cannot 
 hope, in any given case, even to recognize them all, much 
 less to submit them all to due investigation. Remaining 
 unaware of the existence and operation of numerous circum- 
 stances and influences, he cannot observe directly by far the 
 greater number of the phenomena and processes in the living 
 body, especially the most important, but must rather arrive, 
 by various by-paths, at conclusions concerning their reality 
 and course. 
 
 On this account, those best acquainted with their subject 
 will the least give way to bitter and dangerous self-delusions ; 
 and it is precisely the younger and more enthusiastic observer 
 who has been, perhaps under the character of an innovator or 
 advocate of exact investigation, in our, and in every day, the 
 most given up to them. In practice at the bedside, for 
 instance, such men deceive themselves by imagining that they 
 have been the first to observe objectively and completely. 
 
AND EXPERIMENT. 243 
 
 One of them (Reveille-Parise) has said " On ne dit plus, 
 je crois, je pense, mais j'ai vu," but heaven knows how little 
 it must be, even if it were true or possible ! We daily speak, 
 for instance, of having observed fever, dropsy, diarrhoea, or 
 other aggregates of symptoms, while, in reality, we have only 
 observed various phenomena and changes which accompany 
 those diseases, and noticed, superficially enough, certain modi- 
 fications of the circulation, of the temperature and external 
 condition of the body and its individual parts, and of various 
 excretions, &c. At the same time, we have, perhaps, not 
 endeavoured to determine sufficiently exactly and compre- 
 hensively the more constant and often determining phenomena 
 — e. g., the increase or decrease of the temperature of the body 
 by the thermometer, the state of the excretions by the scales 
 and other physico-chemical auxiliary means. For this reason, 
 such observations scarcely deserve the name, for they add 
 nothing to our knowledge, and their results are not to be 
 relied upon. 
 
 No one who has compared the older with the more recent 
 methods of investigation, will doubt that medical observation, 
 as connected with bedside practice, has gained much in accu- 
 racy and in an objective point of view ; that, as regards the 
 physiological investigation of the body, in health and disease, 
 we have learnt to observe a much greater number of pheno- 
 mena and processes, and to do so much more exactly and 
 comprehensively than was attained to by our predecessors. 
 And if it is denied to us to fulfil the requirement already 
 alluded to — viz., to observe all the features of a given case 
 quite correctly — we must the more strive to accomplish all 
 that is acknowledged to be possible. It will thus always be 
 a main point in our observations, to ascertain as exactly as 
 possible, both in the healthy and in the sick, not only indi- 
 vidual fragments of the whole, individual phenomena and 
 occurrences, but rather everything which is in any way 
 accessible to us. It will, therefore, always be more advan- 
 tageous to determine the temperature of the body by means 
 of the thermometer, and to weigh and test chemically the 
 urine, stools, and other excretions, than, by a superficial 
 examination, to obtain only approximately correct results. 
 Bacon has said, in reference to this point, that we must not 
 
244 OBSERVATION 
 
 fear any bad smells, any " res viles et turpes. Omnia enim 
 munda mundis ; et si lucrum ex lotio boni odoris sit, multo 
 magis lumen et informatio ex re quMibet.^" 
 
 To attain this object, however, and to observe all the pheno- 
 mena and occurrences with sufficient accuracy, every distinct 
 series or kind of them, every separate branch of science, 
 requires a particular training of the senses, and, above all, 
 under an able teacher. Only by frequent and correct obser- 
 vation do we gradually acquire an eye, as it were, for every- 
 thing which is to be seen and observed, and that experience 
 and knowledge of the subject which can alone render a clear 
 and rapid survey and a correct judgment possible. And this 
 holds good alike for the physician at the bedside, the naturalist 
 or physiologist, the moral teacher, psychologist, or statesman ; 
 and is true of all whose vocation leads them to observe special 
 series or kinds of phenomena and occurrences. As the prac- 
 tised musician is capable of distinguishing, in a full orchestra, 
 the tones of each individual instrument, while the untrained 
 ear merely recognizes them as a whole, so the practised 
 stethpscopist alone can recognize the finest modulations of his 
 sounds so as to found a correct opinion and diagnosis upon 
 them. If the seaman, from certain changes in the colour of 
 the water, can foretell the coming storm, and if the geologist 
 can, from the examination of a single stone, tell the place 
 from which it was taken and the nature of the strata both 
 above and beneath it, so can the microscopist and experienced 
 physician see things for which another and less experienced 
 eye would look in vain. The professed chemist and physicist 
 will observe the chemical or physical elements of the pheno- 
 mena and processes in the living body far more correctly than 
 the physiologist and physician with their, for the most part, 
 inferior knowledge of the same things. It is seldom given to 
 an individual to be familiar with all the collateral points of his 
 objects of investigation j and if he ventures into a department 
 only half known to him, the danger of errors in his observa- 
 tions must increase in proportion to his ignorance. 
 
 All this has, however, no direct relation to medical logic and 
 lies altogether beyond its limits, for it would be a serious mistake 
 to look for the chief office, or most essential attribute of a suc- 
 ' Parasceve ad liistoriam naturalem et expeiimentalem, Aphor. 6. 
 
AND EXPERIMENT. 245 
 
 cessful observer and proficient naturalist in such technical 
 expertness and practice, in themselves. If our object can be 
 none other than the understanding of what we observe, and 
 the attainment of an insight into the conditions and laws of 
 certain phenomena and processes, the mere observation of them, 
 however correct and exact it may be, can by no means, as so 
 many have believed and as the old " medicina tota in observa- 
 tione" expresses it, be regarded as the main point. 
 
 It is infinitely more important to observe and examine the 
 things presented to us so as to draw from them the safest pos- 
 sible conclusions concerning their causal connection and the 
 mode and conformity of their development and action. We 
 must seek to distinguish, amongst the phenomena and processes 
 in the living body and in external , nature, just those which 
 stand in a constant and even essential, or causal relation to 
 each other ; and since only aggregates of phenomena and pro- 
 cesses present themselves to us, in complex forms, the observer 
 must be capable of representing them to himself mentally, as 
 isolated one from the other and standing in a certain relation to 
 various others, and this without forming any notion of them, or 
 assuming any relations for them, not strictly consistent with 
 the actual state of things. Even the phenomenon which may 
 present itself to us under the comparatively most simple aspect, 
 is so made up of many others, is so dependent upon them, and 
 is itself, in many cases, so determining for them, that we have 
 no alternative but to take it to pieces as completely as possible. 
 It is not he who simply sees the things before him, but he who 
 observes them with his mental eye and recognizes the individual 
 elements and parts of which they consist, clearly distinguishing 
 them in the general stream of phenomena and occurrences, who 
 is to be regarded as a good observer. This, as has already 
 been explained in detail, is the first, indispensable condition of 
 all progress in the investigation of the causal connection and 
 conformity of the phenomena and processes with which we 
 have to deal. 
 
 In observing them, therefore, it is especially important that 
 we should employ our five senses in the right direction, and 
 turn our attention to what is determining and essential, which 
 must then be made the starting-point for further investigation. 
 But the essential points differ with every kind and series of 
 
246 OBSERVATION 
 
 phenomena and processes in nature; those of the simple 
 chemical and physical phenomena, for instance, from those of 
 innervation, or the more complex processes of nutrition, con- 
 version of tissues, and excretion in the living body. 
 
 Our views, also, as to what really constitutes these essential 
 points have always varied and will continue to do so with the 
 stage of development of our knowledge in each branch of 
 science. What appeared to the observer and investigator of a 
 century ago to be determining and essential in the things with 
 which they had to deal, no longer appears so at the present 
 day, and a Paracelsus might well regard many things in a light 
 which would now justly procure for any one the reputation of 
 an obscure and fantastic thinker. 
 
 Neither will the exercise and correct employment of the 
 senses, in themselves, though aided by all the auxiliary means 
 possible and by the best and most accurate instruments, enable 
 us to discover, amongst the mass of phenomena and occurrences 
 before us, what is strictly essential. Our best aid here must 
 be sought in an adequate knowledge of our subject and an ac- 
 quaintance with all its collateral points and questions, and in a 
 faculty of combination derived from natural tact, to be improved 
 by practice. Our task is, to discover, in the aggregate of phe- 
 nomena before us, just those which stand in a constant and 
 essential relation to each other, and to ascertain, amongst all 
 the individual processes, the particular parts of them upon 
 which certain others depend. And yet, as they present them- 
 selves to us in nature, they give the observer no indication 
 which of them, among many others, may be the essential and 
 determining ones. We are, therefore, reduced to the necessity 
 of forming conjectures so as to gain a more or less clear idea 
 as to the probability of certain mutual relations of the pheno- 
 mena and processes which we are about to investigate, — and we 
 must, at least, be able to form an approximate notion of what 
 is essential in a given case, and where it is to be looked for. 
 Just as any one who is seeking for an object which has been 
 lost would naturally think of all the places in which it can 
 possibly be, and search, first of all, in those in which it is most 
 probably to be found ; and by this means would avoid many 
 fruitless attempts. 
 
 Scientific discovery thus demands something far removed 
 
AND EXPERIMENT. 247 
 
 • 
 from mere good luck and accidentj something also far beyond 
 the keen and practised employment of the senses ; it asks for 
 mindj a clear and unfettered survey, and an almost poetically 
 creative imagination or capability of construction. The dis- 
 coverer and successful finder must already, to a certain extent, 
 be aware of a connection between the things he desires to in- 
 vestigate j he must have acquired, whether by simple observation, 
 or by the aid of experiment, some previous notion, or at least 
 foreboding of their nature, before he can advantageously seek 
 for and, in the end, find them. For this reason a blind Newton, 
 Dupuytren, Rokitansky, or Liebig, would doubtless have seen 
 and discovered more than a hundred ordinary observers in fall 
 possession of their eyesight ; just as Huber, notwithstanding 
 his blindness, penetrated the mystery of the difi^erence of sex 
 and mode of propagation in bees, which others, with all their 
 eyes, had failed to do. Thus we have not owed the most im- 
 portant discoveries which have been made in astronomy, in the 
 living body, and in other objects of research, in all cases to 
 those who have possessed the most complete apparatus for the 
 purpose. The unfortunate Keppler, though persecuted almost 
 to the death by bigots and others, made many of his most 
 important observations upon the Prague bridge during the 
 period of his heavy affliction, and Olbers discovered two new 
 planets from the balcony of his house. 
 
 On a closer examination of the method by which men have 
 arrived at their discoveries, we find that, having first come to 
 regard various things as possible, or even probable, which had 
 not attracted the attention of any one else before them, they 
 have then pursued their investigationsin the particular direction 
 to which they may have been led by a more comprehensive 
 _and penetrating contemplation of the phenomena and processes 
 in question than others had attained to. From this they have 
 passed to the examination of new features, to which, in com- 
 paring them with other phenomena and objects, their attention 
 may have been so drawn as to render them alive to the im- 
 portance of previously unrecognized analogies. But this, the 
 chief element of successful and productive observation, is most 
 unfortunately neither to be learnt nor taught. Like every 
 other talent, it is innate, and like every other it may be exer- 
 cised and developed, both by constant and appropriate employ- 
 
248 OBSERVATION 
 
 ment in the right direction, and by the example of able teachers 
 in each department of science. To the physician in particular 
 the individual observations of a Cruveilhier, an Andral or a 
 StoU, may render more service in this respect than the most 
 complete compendium of nosology ; and the post-mortem dis- 
 coveries in individual subjects, taken up and elucidated by a 
 Rokitansky, may do infinitely more towards enabling him to 
 recognize and appreciate anatomical changes correctly than the 
 ' Handbook' of the same physician, excellent as it is. 
 
 And it is precisely the interweaving of our previous know- 
 ledge and surmises, of our personal views or notions, with the 
 investigation of the actual state of things, which forms a 
 connecting link between the whole process of induction 
 a posteriori and hypothetical deduction a priori ; between the 
 simplest and most sober investigation, by the aid of observation 
 and experiment, and mere speculation. However dissimilar 
 these methods may appear to be, and however much they are 
 really opposed to each other in certain respects, there is, 
 nevertheless, an internal connection between them as much 
 as between the general activities and tendencies of the human 
 mind which are the least apparently similar. The special 
 active element — viz., the intellectual nature proper to man — 
 is essentially the same in them all. The career of all 
 successful and eminently intellectual investigators has been 
 but an illustration of the intrinsic oneness of the various 
 methods by which investigation is pursued. 
 
 The man who is best able to recognize new and important 
 features in the things known or assumed before his time will 
 always be the one to make the greatest number of discoveries, 
 to throw the most light upon departments previously obscure, 
 and to ascertain entirely new and more correct relations 
 between the phenomena, &c., with which he has to deal. 
 For all this presupposes that the various doubts and questions 
 connected with the subject must have been present in his 
 mind ; that he has weighed within himself the sufficiency of 
 the things which others have been content to take for granted, 
 and adopted among them only such as, after the ordeal of 
 profound reflection and exact investigation, he found answered 
 by a secure affirmation. 
 
 Newton, when asked how he had arrived at the discovery of 
 
AND EXPERIMENT. 249 
 
 the laws of motion of the planetary system, could give no 
 other answer than that " he had meditated constantly upon 
 the subject;" and when Bentley admiringly and politely 
 remarked, that " Newton had killed all the game, and left 
 nothing tnore to discover," the latter said, with more reason, 
 that " there was game enough in every bush, if one only knew 
 how to start it." 
 
 Experiment has, in the course of time, become the most 
 efficient means of starting and running down this " game ;" 
 but since such direct attempts are, fundamentally, nothing 
 more than a particular kind or method of observation, all that 
 has been said upon that subject may safely be applied to 
 experiment also. The boundaries between them are still 
 further effaced by the circumstance, that, in certain respects, 
 transitions, or intermediate steps, exist between experiment 
 and simple observation. If we place a living being — say a 
 man — in certain new, unusual circumstances, for the purpose 
 of maintaining or restoring his health, which is but another 
 way of expressing that we have placed him under the influence 
 of some remedy, we already perform a kind of experiment ; 
 for, in all such cases, we no longer observe the natural, undis- 
 turbed course of things, but various modifications of it, result- 
 ing from our own interference. We experiment, to a certain 
 extent, upon the patient, as the physiologist does upon animals, 
 but do not use the term " experiment," because, in this case, 
 we have no scientific object, but rather a purely practical one, 
 in view, and because we do not employ these means for the 
 furtherance of knowledge, but to promote the health or cure 
 of a fellow-being. 
 
 The peculiarity in which experiment differs most essentially 
 from simple observation is, that in the former we are not 
 called upon to observe certain phenomena and occurrences 
 simply as they present themselves to us in the ordinary course 
 of things, but under circumstances which we have ourselves 
 produced artificially for the purpose of better investigating and 
 becoming acquainted with those phenomena, &c. We produce 
 certain changes in them ; we bring the phenomenon or occur- 
 rence in question into various new relations, and cause the 
 circumstance or influence we wish to investigate to act in 
 
250 OBSERVATION 
 
 various ways ; we combine or isolate them, for the purpose of 
 arriving at a better understanding of their conditions in the 
 one case, and of their effects in the other. Man takes the 
 initiative, as it were, of nature ; and, by placing himself in a 
 more favorable position, extracts from her clearer and more 
 definite answers. Thus, Bacon was correct when he termed 
 experimentation a " vexatio naturae ;" for in it we bring 
 various phenomena and things, various occurrences and cir- 
 cumstances, to the tribunal of our judgment, as witnesses or 
 proofs, which would never have come of themselves, and stiU 
 more certainly would have given no evidence, at least not of 
 such a character as to enable us to arrive at an insight into 
 the real course of things. What was previously dumb is made 
 to speak and to answer to our questions, and we are enabled, 
 in a certain sense, to endow even stones with language. 
 
 But if experiment has become one of the most important, 
 and even the determining method of arriving at a knowledge 
 of nature, it was far otherwise before a powerful impulse had 
 been given, in particular by Bacon, to this method of investi- 
 gation. It lay in the very nature of things, that the mind of 
 man could only arrive gradually at the employment of this 
 method. It was necessary that he should already, by simple 
 experience and observation, have acquired a certain knowledge 
 of nature ; that he should first have directed his special atten- 
 tion to various things, and learnt to take a more lively interest 
 in them, before he could proceed to this artificial mode of 
 interrogating her. It is well known to how great an extent 
 these natural difficulties were enhanced by superstition and by 
 religious and philosophical tendencies in general, even in the 
 17th and 18th centuries. It was necessary that a Bacon 
 should endeavour to prove that the majesty of the human 
 mind is not degraded by this sober and exact investigation of 
 nature, and that man is neither too dull to attempt it, nor 
 incapable of carrying it out. Even to the present day, we 
 have not learnt to employ experiment in the investigation of 
 disease, with reference to the development, course, and internal 
 connection of its peculiar conditions, either much better or 
 much more productively than the alchemists, for instance, did 
 with reference to chemical processes. 
 
 But here, also, as was proved with reference to simple 
 
AND EXPERIMENT. 251 
 
 observation, it does not fall within the province of logic either 
 to lay down rules for our path, or to direct us how to proceed 
 in it. This belongs to the respective branches and depart- 
 ments of natural science ; and all that can be of interest or 
 benefit on this subject has already been laid down when 
 speaking of the process of induction. The work of logic 
 here is that of dealing with the correct appreciation of results, 
 and of the inferences to be drawn from them. Its office is, 
 therefore, to give certain principles and aids for the arrange- 
 ment of our artificial attempts, so that we may be able to 
 draw from them, when fairly carried into practice, safe con- 
 clusions concerning the question at issue. 
 
 Here the same rules hold good, and the same points are to be 
 kept in view, as in the case of simple observation. Experiment 
 must, above all, be carried out in the manner, and under the 
 circumstances, which may best enable us to attain our object 
 — i. e., the elucidation of the question at issue, and the better 
 understanding of the objects it is concerned with. But the 
 phenomena and occurrences themselves, which we thus give 
 rise to artificially, or which we have, in various ways, changed, 
 modified, and placed in various peculiar circumstances — in 
 short, all the things which occur during our experiments and 
 all that takes place in connection with them, must be observed 
 and interpreted as carefully and objectively as any other 
 phenomena in the ordinary course of things. It is also 
 certain that the rules for observation and progress in this 
 method of investigation will always undergo certain important 
 modifications in consequence of the peculiar nature of experi- 
 ment, and of the method in which it is brought to bear upon 
 the particular objects it may have in view. On a closer 
 examination, it will become evident, namely, that if, in many 
 respects, experiment possesses essential advantages over the 
 simple observation of phenomena — i. e., as they present them- 
 selves to us in nature, it has, on the other hand, its especial 
 dangers and difficulties. 
 
 The chief superiority of experiment, as an aid to investiga- 
 tion, must always consist in the circumstance of its being the 
 sole engine by which we can ascertain, at least approximately, 
 what are, in any given case, the effects of the individual 
 agencies of the external world and of the various influences 
 
252 OBSERVATION 
 
 which affect the living body, and what is to be laid to the 
 account of the action of the individual processes in the latter 
 and of their dependence upon each other and upon things 
 external to it. We are thus able to place them, one by one, 
 on a fixed and artificial plan, in various circumstances; to 
 bring them into such relations, and to observe them in such 
 junctures as will enable us to draw more certain conclusions 
 concerning conditions in the one case, and effects in the other. 
 For, as has already so often been insisted on, everything which 
 we meet with in nature is much too complex for us to hope to 
 discover from it, as such, what is determining and what is 
 dependent, or to decide upon what may be the causal connec- 
 tion and laws of operation of those individual agencies and 
 influences, or the conditions and internal conformity of any 
 individual process in the living body. If, therefore, we are 
 ever to acquire clearer notions on these points than we possess 
 at present, we shall evidently be indebted for them almost 
 exclusively to experiment, which affords us the above-mentioned 
 advantages in investigation, and which we may in vain look 
 for from the simple observation of nature. 
 
 Experiment places it in our power to produce the particular 
 kind of circumstances under which the given effects of an 
 influence, the given conditions of an occurrence or effect, 
 manifest themselves most clearly, and allows us to arrange 
 everything for observation, just as is requisite for the discovery 
 of the causal connection and conformity to fixed laws of the 
 phenomena which we are seeking to investigate. It is only 
 by artificial attempts that we can isolate an individual pheno- 
 menon, an individual agent or influence, for the purposes of 
 observation, without at the same time being compelled to 
 include so many other elements as always present themselves 
 , in the natural course of things. We change, to a certain 
 extent, the order of nature, and create a something for our- 
 selves which we can better bring within the scope of our com- 
 prehension. We make things which, taken in themselves, are 
 intricate and obscure, in consequence of the endless variety 
 and complexity of their collateral circumstances, more clear 
 and simple ; we bring to light, and render more accessible to 
 the investigation of our mental eye, what nature has, so to 
 speak, concealed. In one case, we free nature from her bonds 
 
AND EXPERIMENT. 253 
 
 and coverings^ that she may speak to us more clearly and 
 openly ; in another, as the case may be, we confine, change, 
 or take her to pieces, that we may hear the tones, and observe 
 the phenomena which our object requires that we should 
 recognize, disguised as little as possible by others. 
 
 In short, if we have, as simple observers of nature, been 
 more or less her slaves, experiment makes us, in a certain 
 sense, her masters ; and if this, for reasons already mentioned, 
 occurs much less frequently in our special department of 
 science than in those of the physicist and chemist, investiga- 
 tion, if in a less high degree, still obtains for us the advantage 
 of less obscure answers to our more definite questions, 
 
 A further advantage, which nature would seldom if ever 
 afibrd us, consists in our being able to renew our attempts as 
 often as appears necessary in each individual case, and, in this 
 way, ascertain more easily than we could otherwise do, the 
 conditions of a given process or occurrence, and the mode and 
 laws of operation of a given influence or determining circum- 
 stance. And we shall the better succeed in this the more we 
 are able to vary the circumstances in which we choose to place 
 the occurrence or influence in question, and to observe its 
 bearing under them. We may thus, in the end, ascertain in 
 the one case all the essential and determining circumstances 
 required for the development and manifestation of a given 
 eff'ect or phenomenon, and in the other, the varied modes by 
 which a given circiimstance or influence acts, and learn how 
 it bears upon other phenomena and occurrences. Every one 
 knows how much our knowledge of many vital processes has 
 been increased by the repetition and variation of experiments, 
 and how much more familiar we have thus become with the 
 phenomena of light, heat, and electricity, with the laws of 
 gravitation and hydrostatics, in short, with all the chemical 
 and physical processes, and their conformity to fixed laws, not 
 only in external nature, but also in the living body itself. 
 
 It follows from all this, that experiment facilitates our 
 investigations and struggles for knowledge much more than 
 simple observation, because it afl'ords us more convenient and 
 infinitely more direct and certain means of attaining our end, 
 and because we can adapt it to our particular object in each 
 case, and can observe the things to be investigated as fre- 
 
354 OBSEEVATION 
 
 quently as is necessary under the precise circumstances which 
 appear most likely to further our knowledge of them. 
 
 But experience has shown that it is from this very quarter 
 that the accuracy of experiment, and the whole reliability of 
 its results, is most endangered. We incur a greater risk 
 here, in certain respects, than can be laid to the account of 
 want of skill in our attempts, or want of care in making them. 
 The latter evils are always to be avoided, if we will, but the 
 facility with which we may be deceived and led astray in 
 every artificial attempt, by our personal aims and tendencies, 
 lies in the very nature of such attempts, as well as in that of 
 the subject and of man himself. 
 
 If, for instance, in simple observation, we are apt to con- 
 found our own interpretation and explanation of what we 
 have seen, with what we have really seen and observed, or to 
 throw the two into one, the danger which, in the case of 
 experiment, is entailed upon the accuracy of our conclusions, 
 must be doubly great. For here our ego intervenes, and our 
 notions and arbitrary views play a much more important part 
 in opposition to nature and the actual state of things, than 
 in the simple observation of the latter. Our intention to seek 
 a certain something, and to see and find it, and not anything 
 else, stands out much more prominently in the one method 
 than in the other, and has often indeed been our only induce- 
 ment to make the attempt. Here, therefore, more than in 
 any case of mere observation, we incur the risk of conceiving 
 and judging of what we have recognized by the senses, and 
 which really exists and occurs, precisely as best corresponds 
 to our views and notions, to our intentions or wishes. In 
 short, nowhere so easily as in experimentation, can the ob- 
 jectivity and accuracy of observation be obscured or rendered 
 altogether illusory by the subjective intervention of the in- 
 dividual observer. Whether it be that we are led away by 
 interest, a too lively imagination, or actual prejudice, or that, 
 from indolence or too great eagerness to find what we are 
 seeking for, we strive to obtain a maximum of demonstration 
 with but a minimum of observation, the fact remains clear 
 that we are apt to see things which have no real existence, 
 and to overlook or misinterpret others which are actually 
 present. And in our appreciation of the results of our expe- 
 
AND EXPERIMENT. 255 
 
 rimentation, kindred dangers will beset us, just as the aggre- 
 gate and variations of phenomena with which our subject 
 presents us, may happen to be numerous and complex, dubious 
 and enigmatical, in any given case. For under such circum- 
 stances, the very nature of the thing itself gives much more 
 scope for an arbitrary selection, and, consequently, for sub- 
 jective assumptions and explanations, while, on the other hand, 
 there is a greater or less deficiency of fixed points upon which 
 the mind may rest, of firmly established and generally acknow- 
 ledged facts and laws, by which every one must perforce abide 
 in his attempts at explanation. 
 
 We can easily understand from all this why the facilities 
 for error are nowhere so great as in our peculiar department 
 of science, and the history of medicine up to the present day 
 furnishes sufficient proof of thi^. Yet even physicists and 
 chemists are frequently led into error by their experiments, 
 especially when these are undertaken for the direct demonstra- 
 tion of their hypotheses and views at the time. Here also 
 they may easily err in such of their conclusions as refer to the 
 more enigmatical and complex, or less firmly established phe- 
 nomena and occurrences in their respective sciences. The 
 chemist, for instance, in reference to organic combinations in 
 the living body, and to the chemical processes at work in it, 
 and in his whole calculation of probabilities concerning them ; 
 the physicist, in reference to the electric, magnetic, and mete- 
 orological phenomena, and to those of light and heat, &c. 
 Any one who has passed a considerable portion of his- life in 
 experimenting upon the electricity of the atmosphere, and has 
 directed his attention to that especial subject, will not, it is 
 true, easily assume its presence erroneously, and still less will 
 he be likely to overlook it where it is really present and in 
 operation. But he may be easily led into the error of ascrib- 
 ing to it a greater amount of influence than it really exerts ; 
 in relation, for instance, to the more complex processes in the 
 atmosphere, such as storms, whirlwinds, and the like. He 
 will not always be able to resist the temptation of regarding 
 electricity as the determining cause of various phenomena and 
 occurrences, which are, indeed, observed simultaneously, but 
 of which the conditions and causal connection may be entirely 
 diflferent, and in which electricity itself is perhaps but a de- 
 pendent and secondary phenomenon. 
 
256 OBSERVATION 
 
 That more or less similar impulses frequently lessen the 
 reliability of physiological experiments, and interfere with the 
 correct appreciation of their results, is well known. But this 
 is the case in a much higher degree when a certain personal 
 interest on the part of the experimenter comes into play, his 
 eagerness, for instance, to demonstrate and defend some view, 
 or conversely to refute it ; still more when the results of a 
 given experiment admit of a practical application in life, and 
 the experiment has, perhaps, been made solely for the further- 
 ance of practical objects, such as the diagnosis or cure of a 
 disease, the demonstration of the benefit or injury resulting 
 from the adoption of certain hygienic measures, or influences, 
 or from the administration of certain drugs. It is true that 
 perhaps no attempts are more important and useful than such 
 as these, but in none, on th.e other hand, are errors in the 
 interpretation of their results, or false conclusions drawn from 
 them, more dangerous. Thus it was, perhaps, perfectly legiti- 
 mate to endeavour to render the diagnosis of gonorrhoeal and 
 syphilitic affections as exact as possible, even by inoculating 
 the persons affected with their own virus (Eicord). It is now 
 known, however, how much mischief may be done by these 
 means, while the discoverer of them has represented them as 
 perfectly harmless, and is still convinced that such is the case, 
 because he interprets certain changes and deteriorations in his 
 patients in a different manner to his opponents, and cannot 
 see in them the effects of the inoculation. It is also well 
 known that we form conflicting and therefore erroneous opinions 
 with regard to the effects of our drugs upon the healthy and 
 sick, and upon animal life in general. These have their origin 
 partly in the personal interests of the observer, partly in the 
 neglect of indispensable precautionary measures in the arrange- 
 ment of our experiments, and still more in a faulty appreciation 
 of their results, and of the conclusions to be drawn from them. 
 Thus it happens that, in the case of almost all the conclusions 
 of medical science, there is left, as in the results of simple 
 observation at the bed-side, an opening for doubt and contra- 
 diction. 
 
 All this tends to confirm the general requirement of logic, 
 that we should never rely fully upon any single direct experi- 
 ment, in itself, and still less regard any hypothesis or previous 
 
AND EXPERIMENT. 257 
 
 view as proved by our direct experimentsj unless we have 
 obtained such clear and definite results as will not leave any 
 other interpretation than the one put upon them possible. 
 The greater, therefore, may be the interest we take in the 
 results of any experiment, the more caution must we exercise 
 in the explanation given of it, and in the conclusions drawn 
 from it. We must not he over-hasty in deducing anything 
 from individual experiments, because it happens to correspond 
 to our expectations and wishes, but should, for this very reason, 
 examine the more carefully into the possibility of a deception. 
 Bacon, therefore, had good reason for wishing that his " expe- 
 rimenta lucifera" should rather be undertaken as " experimenta 
 fructifera," or, in other words, he greatly preferred experiments 
 which further our general knowledge, to those which afford 
 the prospect of an immediate application of their results to 
 any particular practical purpose, whether it might be to com- 
 merce, to the arts, or, as in the present case, to therapeutics. 
 And if the results of any series of experiments are of such a 
 nature that only doubtful conclusions can be drawn from them, 
 sound logic requires that this fact should be clearly recognized, 
 so that we may not represent them to ourselves as anything 
 better, or more trustworthy than they really are. 
 
 The whole reliability and conclusiveness of an individual 
 experiment and its results must vary according to the com- 
 plexity and general character of the phenomena and things 
 experimented upon, and according to the question which is 
 sought to be answered, or, at least, rendered less obscure by 
 them — in short, according to the nature of all the points con- 
 nected with the problem. The simpler may be the circum- 
 stances under which we perform an experiment; the less 
 complicated are the relations in which its object stands to other 
 objects; and the less fluctuating are the modifications it is in 
 consequence exposed to, the more exact will be the conclusions 
 we are likely to draw from it. 
 
 Thus a single experiment, correctly performed and observed, 
 may serve to answer a given question with a degree of cer- 
 tainty which could not, in the case of many other questions, 
 be attained by hundreds of experiments performed under the 
 most varied circumstances, and this because we have been 
 able, in this one case, as not in the others, to test and confirm 
 
 17 
 
258 OBSERVATION 
 
 our observations by the direct and easy aid of the outward 
 senses. 
 
 A small number of experiments, in some cases one only, 
 has sufficed to show that water and other fluids will strive to 
 enter vessels exhausted of air ; that quicksilver and other metals 
 expand by heat; and that prussic acid, chloroform, carbonic 
 acid, &c., in large quantities, are fatal to men and animals. 
 And if, on any single occasion, powdered charcoal, after having 
 been swallowed by an animal, had been found in its blood, or 
 in the interior of its organs, in short, in places where experi- 
 ence had taught us that carbon in this form is never found, 
 the fact of its ingress into those parts of the body would be 
 proved with certainty. 
 
 In a similar manner a small number of experiments have 
 been enough to show the effects produced on the living body 
 by various mechanical injuries, such as the division of the spinal 
 cord, or pneumogastric nerves, or the extirpation of an organ, 
 or in the administration of various drugs or poisons. A few 
 experiments would, under certain circumstances, sufficiently 
 establish the fact that opium, chloroform, and morphia produce 
 stupefaction or insensibility; that they alleviate or entirely 
 remove pain, neuralgia, &c. ; that ague may be cured by qui- 
 nine, and bronchocele by iodine; so soon as we had learnt by 
 experience that the pain, the ague, or the bronchocele would 
 otherwise, if left to themselves, have continued a certain time, 
 whereas, after the employment of these agents, they usually 
 cease very rapidly. But if, in all these cases, we should wish to 
 become acquainted with the details of these effects, or even to 
 ascertain experimentally the mechanism and causal connection 
 of the phenomena we have recognized through the senses, an 
 entirely different series of experiments, with manifold variations 
 of the circumstances, will become requisite. By such means 
 only can we arrive at the clear understanding of what we have 
 previously known merely as facts established by simple expe- 
 rience. To be able, for instance, to judge of the effects pro- 
 duced by the division of the pneumogastric nerves, we must 
 first observe the changes which take place, the processes and 
 functions which become deranged, such as contractility and 
 secretion in the stomach and intestinal canal, the solution and 
 digestion of individual articles of food, various processes in 
 
AND EXPERIMENT. 259 
 
 respiration and excretion, the generation of heat, &c., and 
 investigate each of these separately. 
 
 Thus fresh demands for the arrangement and performance 
 of our experiments constantly present themselves according to 
 the particular kind of objects, phenomena, and processes to be 
 investigated, and according to the precise nature of the questions 
 to be answered. They will differ when the question refers to 
 simple physical and chemical processes, and when it has to do 
 with those in the living body ; and also vary in the simple 
 establishment of various facts, and in the investigation into their 
 causal connection, conditions, and laws. It is the province of 
 the respective branches of science to explain all these various 
 requirements clearly in their several order, but the discovery of 
 the causal connection and conformity to fixed laws of certain 
 phenomena and processes will always, in a scientific point of 
 view, continue to be the main object of our experiments. We 
 cannot content ourselves with mere curious discoveries, while, 
 for various practical purposes, our need of scientifically correct 
 deductions remains so great. 
 
 To obtain more definite explanations on these points by the 
 aid of experiment, the questions to be answered must, in the 
 first place, be put as simply and clearly as the existing state of 
 our knowledge at the time renders it possible. We must also 
 be able to judge which of the various phenomena, effects, &c., 
 occurring in the course of our experiments, is to be ascribed to 
 the circumstances and changes produced by us, and which, on 
 the contrary, may have had its source in circumstances and 
 influences entirely different in their nature, though operating 
 at the same time. That the opinion we form of them may be 
 rendered as easy and correct as possible, and that the pheno- 
 mena, changes, &c., which we observe in them, may not admit 
 of different or even erroneous interpretations, the latter must 
 be as little complicated by others as possible, and least of all by 
 any whose conditions and laws are unknown to us. Our ex- 
 periments must, therefore, always be undertaken under the 
 simplest possible circumstances. All the collateral circum- 
 stances and influences which may exert a modifying influence 
 upon a given occurrence, or affect the result of a given experif 
 ment, must be excluded as completely as is practicable, or, where 
 
260 OBSERVATION 
 
 exclusion is not feasible, their presence and efFects must be 
 recognized and controlled. 
 
 In all these respects, however, medicine, for obvious reasons, 
 is less favorably situated than other sciences. "VVe labour, in 
 comparison with the physicist or the chemist, under an especial 
 disadvantage, inasmuch as we are unable to produce vital phe- 
 nomena and processes at will, or even to experiment separately 
 upon those which occur in the living body, in isolation from 
 the various influences which affect them. For if we seek to 
 experiment upon the living body under circumstances so complex 
 as those met with in nature ; if, for instance, we try to produce 
 artificially the aggregate of phenomena existing in any actual 
 disease, or to bring a complicated amount of influences to 
 work, as they do in nature, upon the human body, we are not, 
 with all this, any nearer the explanation of their conditions or 
 laws of operation, in short, are as far as ever from the secret 
 of their causal connection ; as far, that is to say, as the simple 
 observation of the occurrences in nature left us. Our experi- 
 ments would only teach us that certain phenomena, events, and 
 effects are wont to manifest themselves, and to follow each other 
 in a certain manner, but we should not be any nearer ascer- 
 taining their internal mechanism, or the conditions or laws of 
 their development and course. 
 
 If we were able, for instance, to produce artificially all 
 diseases as they may present themselves in man [e.g., gout and 
 lithiasis, scurvy, ague, typhus,&c.), we should not, by this means, 
 advance much further in our knowledge of them — i. e., not 
 beyond the post hoc propter hoc — any more than a physiologist 
 who attempted to produce a living body artificially. For it 
 may be foreseen that causes and effects would everywhere be 
 complicated to such an extent that we could never, from the 
 occurrence of the latter in themselves, acquire an insight into 
 their conditions and causal connection. We have not suc- 
 ceeded in doing so, for instance, in reference to small-pox, 
 syphilis, or glanders, although we have long been able to pro- 
 duce these diseases by inoculation ; for we have never succeeded 
 in ascertaining what part each of the specific poisons plays in 
 these " contagions," or the internal mechanism by which the 
 diseases they produce are developed. And although millions 
 have been vaccinated for the purpose of protecting them from 
 
AND EXPEEIMENT. 261 
 
 the contagion of small-pox, many even now regard the reality 
 of such protection as by no means demonstrated. Essentially 
 the same thing holds good of our experiments with drugs, espe- 
 cially in the sick, because the circumstances are too complex 
 and fluctuating, and because too many other things, concern- 
 ing the influence of which we are at present unable to form any 
 clear notion, modify the result, whether this be a cure or the 
 reverse. Even in experiments upon animals, it often remains 
 doubtful what part of the changes produced — i, e., of the sup- 
 posed eff'ects of our drugs — is attributable to the circumstances 
 and influences brought into operation (e. ff., a remedy, a poison, 
 or a mechanical lesion), and not rather to entirely difl'erent 
 concomitant circumstances and influences (e. ff., changes in the 
 atmosphere, in nutrition, or in the habits of life during con- 
 finement). This applies more particularly to experiments 
 extending over a considerable period of time, in which no means 
 which act so rapidly and directly as strong poisons or the 
 knife, are adopted, but where we rather seek to ascertain the 
 manner in which certain drugs, aliments, or variations of tem- 
 perature act upon the human frame. 
 
 But however seriously the attempt may have been made, the 
 human mind has not always succeeded in overcoming such 
 natural obstacles, or in arriving at its ends in spite of them. 
 As in the perception of the physiological relations in the healthy 
 living body, so also in the perception of diseased conditions 
 and of their development and cure, we shall always receive the 
 more aid from experiments the better we are able to adapt them 
 to the particular questions to be answered. 
 
 The nature of these requirements in the carrying out of our 
 experiments follows from what has been advanced in Section V 
 concerning the analytical or deductive method. We must, 
 first of all, seek to ascertain the individual processes in the 
 living body, with their conditions and separate action, by the 
 aid of artificial means, and next trace the laws of operation of 
 the individual influences which affect them, whether they be 
 hygienic or therapeutical. Just so we must commence with 
 those parts or elements which are comparatively the most 
 simple and accessible to experiment ; first of all, therefore, 
 with the individual physical and chemical processes in the living 
 body, and in external nature which surrounds and affects it. 
 
262 OBSERVATION 
 
 And for the attainment of the main object of our experiment, 
 viz., the exact determination of the causal connection and con- 
 formity to fixed laws of the occurrence or influence in question, 
 it must be placed artificially in the most varied circumstances 
 possible, and its behaviour in each case, with the modifications 
 it undergoes, carefully observed. Hence follows the further 
 requirement, of investigating separately, by the aid of appro- 
 priate experiments, the action of all the modifying influences 
 and circumstances which may happen to be in operation at the 
 time, and which may easily render the result obscure, so that 
 we may be better able to recognize them as essential or the 
 contrary, and, if it be necessary, to exclude them with some 
 degree of certainty. 
 
 Until this has been done, all the other circumstances con- 
 nected with our experiments must remain exactly alike, and 
 all the so-called accidental influences, in short, everything 
 which may, in various ways, affect and modify the results, 
 must be excluded as far as possible. Thus, if we wish to 
 investigate experimentally the influence and mode of opera- 
 tion of a given substance, or of a certain degree of tempera- 
 ture, upon men or animals, we must, first of all, take care 
 that the latter are themselves alike — e. g., of the same age, and 
 in the same state of health ; and the same conformity must 
 extend to their food, mode of life, &c. This precaution must 
 especially never be neglected where, in consequence of such 
 differences, any variation or modification of the general result 
 might be expected to occur ; where, therefore, a doubt might 
 arise whether, and how far, the result is to be attributed 
 solely to the circumstance brought into operation intentionally 
 in the experiment, or perhaps to those other collateral circum- 
 stances and influences. 
 
 Experiment, to accomplish all this thoroughly, presupposes 
 a sound knowledge of the subject, and a definite plan, based 
 upon this knowledge, which must be carried out consistently 
 and circumspectly in the whole investigation. And this is 
 nowhere more necessary than in reference to the problems 
 and experiments of the physiologist and the physician, if they 
 would arrive at conclusions in any degree accurate. In other 
 respects, the same rules hold good here, as for observation in 
 general. 
 
AND EXPERIMENT. 263 
 
 Experiment will always afford the most important and 
 genuine discoveries to those who not only confine themselves 
 to a single question or object of investigation, but also select 
 such as are most clearly defined in their outlines, and exa- 
 mine them as thoroughly as possible in all their relations. 
 Instead of selecting for experimentation vague and ill-defined 
 phenomena and objects, and for that very reason investigating 
 them in a more or less superficial or onesided manner, we 
 must select simpler ones, such as we can investigate as com- 
 prehensively as possible under a great variety of circumstances. 
 It is always more profitable to advance from the simple to the 
 more complex and difficult, than to adopt the contrary method. 
 And just because this simplest and most natural of all the 
 rules of logic has seldom been observed in medical science, 
 above all in Germany, where the attempt has so frequently 
 been made to arrive at an immediate understanding of the 
 most complex processes by the aid of experiment, as well as by 
 simple observation, scarcely any clear insight has yet been 
 acquired into the nature of those which are comparatively 
 most simple. 
 
 By commencing with what is most simple, we constantly, in 
 the course of our investigations and experiments, discover new 
 features, new relations of the object before us to numerous 
 others, relations the existence of which we had perhaps pre- 
 viously never suspected. In the investigation of the latter we 
 also obtain infinitely more certain and definite results, because 
 we are able to connect what is new, and still obscure, with 
 what is already more familiar, and to deduce the complex 
 from the more simple — i. e., from the laws of its individual 
 elements. And since the science of medicine may safely be 
 regarded as the most intricate and obscure of all sciences, we 
 should not seek to attain our final object — i. e,, the compre- 
 hension and explanation of processes and circumstances still 
 enigmatical — directly by the aid of experiment, but must 
 rather content ourselves with mere preparatory and approxi- 
 mate results. We shall approach the nearer to this object 
 the more we succeed in imitating the methods of experimenta- 
 tion adopted in those other branches of natural science which 
 have so far outstripped our own. For as, by the results 
 obtained and by the principles inculcated in them, a new 
 
264 OBSERVATION 
 
 light has been thrown upon many obscure points in the vital 
 processes, and a new and more productive direction given to 
 our own investigations, so the technical arrangement, and the 
 accuracy of experiment can, doubtless, only gain by the 
 imitation of the methods of investigation which they have 
 adopted. 
 
 For the solution of the problems of medicine proper — 
 i. e., of the theory of diseases and their cure — experiment 
 has, on the whole, been rarely employed, and that only in a 
 very deficient manner. We have advanced but little from the 
 stage of the simple observation of our phenomena, &c. (which 
 goes but a short way in helping us to the full understanding 
 of them), towards that of intentional experiment artificially 
 carried out ; or, at most, we have but ventured upon the first 
 uncertain steps in this direction. And this is the more to be 
 deplored, because it is only through experiment that we can 
 expect to be enlightened as to the conditions by which diseases 
 act and develop themselves; in no otber way can we learn 
 the internal mechanism of their ind.ividual processes, or, 
 acquainting ourselves with their conformity to- fixed laws, 
 form a probable conjecture as to the efi"ect of our remedies in 
 bringing back a healthy and normal state. 
 
 In relation to the employment of the experimental method, 
 we stand much upon the same point as that upon which 
 chemical experiment stood in the times of phlogiston, or 
 even of alchemy > and as there the phogiston hypotheses so 
 long stood in the way of every more exact investigation, so 
 our attempts have been impeded by the old hypotheses of an 
 " archseus" or a " pneuma," and by the more modern ones, of 
 a vital force, a typical or natural healing force, and lastly, by 
 the so-called ontological conception of diseases as special 
 entities, no less than by the belief in mystical medicinal 
 forces. But as, in chemistry, weights and numbers, and the 
 more accurate methods of investigation, and consequent scien- 
 tific comprehension, made their way in spite of all opposition; 
 so in our department of science, a similar state of things must 
 evidently gain ground in the end. In relation to mechanico- 
 physical and chemical phenomena and processes, at least, a 
 good beginning has already been made. Surgery, however, 
 with its mechanical lesions and their cure, and toxicology with 
 
AND EXPERIMENT. 265 
 
 its poisons, have left therapeutics and the theory of diseases 
 far behind. 
 
 The latter branch of science has not even been able, with 
 all its experimental investigation of the external world and its 
 individual influences or agents, to seize upon the precise points 
 and features which are most important for the physician j for, 
 with few exceptions, we have not yet clearly ascertained, by 
 the aid of experiment, how and why, in consequence of their 
 action, certain diseased conditions, or certain elements of 
 disease, or more simple derangements of certain processes in 
 the living body, are accustomed to arise. With reference, 
 also, to our drugs and curative agencies, we have scarcely 
 begun to investigate, experimentally, in what manner, and to 
 what extent, it is practicable to induce the retrogression of 
 various derangements of the vital processes, and to promote a 
 consequent return to a healthy condition, and this, because we 
 know, as yet, next to nothing of their actual operation in our 
 patients, or of the manner in which they may possibly affect 
 the internal mechanism of diseases — i. e., those individual 
 processes or occurrences in the living body which have 
 deviated, in various ways, from the normal condition. 
 
 We everywhere stand in need, therefore, not only of experi- 
 ments generally, but of such as are of an entirely peculiar 
 kind — i. e., such as are carried out according to other more 
 strict and productive methods. But as in aU. medical inquiry, 
 so, also, in experimental investigation, it is that of the simplest 
 elements of a disease, and of its individual producing causes, 
 which is most important. Instead of contenting ourselves 
 with what appears to be nearest at hand, and is, perhaps, most 
 requisite for certain practical purposes (e. g., for diagnosis and 
 the simple empirical treatment of our patients), and not even, 
 as so frequently happens, carrying out this intention with 
 certainty, we must first seek to acquire, by the aid of experi- 
 ment, a certain knowledge of the things with which we have 
 to deal — i. e., to determine, more and more exactly, their 
 causal connection, and the laws of their development and 
 action. 
 
 The so-called disciple of Hippocrates, or the empiric of our 
 own times, can no longer smile at these efforts as vain, ignore 
 them as the offspring of theoretical and dogmatical aspirations, 
 
266 HYPOTHESES, ANALOGIES, 
 
 or pass them by without any lively interest. With all his 
 so-called experience, he has not, in reality, learnt to under- 
 stand anything, nor will he ever do so by the means which he 
 adopts. He can, therefore, have no just grounds for com- 
 plaint, if we declare his methods of investigation unproductive 
 for science, and incline to discard them from its service. 
 
 II. HYPOTHESES, COMPARISON OR ANALOGIES, AND THE 
 GENERAL CALCULATION OF PROBABILITIES. 
 
 Enough has already been said in the foregoing pages to 
 show why, with all our knowledge and perseverance, we must 
 at present and for a long time to come, perhaps always, be 
 restricted to more or less probable conjectures in medical 
 science. Allusion has also been made to the important ser- 
 vices which may be rendered by the adoption of experimental 
 and preliminary notions, and by the comparison of things still 
 obscure, with others which are more familiar and, perhaps, 
 analogous — in short, by an approximately correct calculation 
 of all the arguments for or against any hypothesis, or view. 
 These means must also not be regarded as merely the first pre- 
 paratory steps to further investigation, but also, in the present 
 state of things, as a temporary substitute for established truths 
 and positive knowledge in medical science, perhaps for cen- 
 turies to come. In every department of human knowledge 
 the auxiliary or compensatory means, however fluctuating and 
 unreliable, are the more important, and must the more fre- 
 quently be employed, as far as possible, in proportion as our 
 insight into the phenomena and processes in question remains 
 imperfect, and the ascertained and scientifically established 
 laws obtained for them are less numerous. 
 
 Whether we are called upon to form an opinion concerning 
 the development and conditions of any process or occurrence 
 (e. g., a disease, the effect of an agent of the external world, 
 or of a remedy), or whether we desire, as practical physicians 
 at the bedside, to exert some influence upon it, the uncertain 
 character of our notions remains essentially the same. For 
 we have everywhere only approximate, more or less vague 
 grounds for the view we take, while any resting-points, based 
 
CALCULATION OF PROBABILITIES. 267 
 
 upon positive and exact knowledge, are for the most part want- 
 ing. But if it be denied us to determine or explain anything 
 with perfect accuracy, and to base our practice upon firmly 
 established principles, we must the more earnestly strive to 
 ascertain, at least, what is most probable. Here the calculation 
 of probabilities is our best aid, which the physician will have 
 as much occasion to employ at every moment and at every 
 step as the statesman or the moral teacher in their several de- 
 partments. 
 
 Which amongst the many circumstances and influences to 
 whose operation a given patient has been exposed are precisely 
 those upon which his falling sick has depended ? How are the 
 various symptoms and derangements observed in him con- 
 nected with each other, and what changes and processes are to 
 be regarded as essential and determining, what on the con- 
 trary as comparatively accidental and subordinate ? By what 
 precautionary measures may an attack of disease be best pre- 
 vented, under given circumstances, and by which of the many 
 means at our disposal can the disease, when present, be most 
 certainly and rapidly cured ? And lastly, is it probable that 
 the patient, in his peculiar circumstances, will recover from 
 this or that particular disease, and that, too, rapidly and com- 
 pletely, or is the reverse of all this rather to be expected ? 
 These and similar questions are those which the physician is 
 called upon to answer at every moment. 
 
 For this our answer, however, we nowhere possess an ade- 
 quate amount of knowledge, but only, for the most part, a 
 doubtful and approximate insight into all the points, without a 
 correct appreciation of which that answer must be very inde- 
 finite, if not altogether impossible. We have, in reality, even 
 under the most favorable circumstances, only more or less pro- 
 bable grounds upon which to base our judgment, and it is by 
 means of the calculation of probabilities, which cannot, more- 
 over, be taken in the strict mathematical sense, that we must 
 endeavour to form the most correct possible conclusion from 
 such data, notwithstanding their uncertain character, and to 
 approach as nearly as possible to the truth. 
 
 Here again, it is not the province of logic to teach us how 
 to employ exactly, or arrange, as it were technically, the calcu- 
 lation of probabilities in any individual case. For such know- 
 
268 HYPOTHESES, ANALOGIES, 
 
 ledge depends entirely, in each branch of science, upon the 
 questions and objects of investigation, and upon the special 
 circumstances in any given case, and there only can the 
 requisite details be explained. It is more important here to 
 examine into the services which such a calculation of proba- 
 bilities may render us, and to ascertain more exactly what we 
 may hope to attain by its aid. 
 
 Our task here, as well as in simple observation, consists in 
 showing in what points of view and with what precautionary 
 measures these hypotheses and the calculation of probabilities 
 in general are to be applied, and by what proofs from entirely 
 different quarters they must be supported, that we may at least 
 rely upon their results and upon the conclusions we draw from 
 them, as far as their uncertain nature will permit. For 
 whether we avail ourselves of them for the discovery of the 
 causal connection, conditions, and laws of certain occurrences 
 in nature — ^in short, as the means of investigation and for the 
 acquirement of knowledge — or for the attainment of certain 
 practical purposes, the main point will always be, to employ 
 these auxiliary means and processes themselves as consistently 
 as possible. In other words, therefore, we must endeavour to 
 discover, amongst so many possible hypotheses and analogies 
 or comparisons, precisely those which are most correct and 
 which approach nearest to the true state of things, and, with 
 our more or less indefinite materials for calculation, to draw 
 our conclusions as correctly as possible, and to ascertain what 
 is most probable. 
 
 The misuse of hypotheses, and the many errors and delu- 
 sions to which they have led, have brought them almost 
 entirely into discredit, not only with physicians, but also with 
 other investigators in natural science. It has often been 
 thought that they could not be avoided carefully enough, 
 especially in more recent times, since the so-called more ex- 
 act methods of investigation have begun to be employed even 
 in medicine. Nearly the same thing applies to the employ- 
 ment of simple comparisons and analogies, for here also men 
 have not scrupled to group together, superficially and arbi- 
 trarily, things which, in reality, offered scarcely any points for 
 comparison, or of which the one was still as little understood 
 
CALCULATION OF PHOBABILITIES. 269 
 
 as the other. For that reason the comparison of them with 
 each other, under existing circumstances, could only be uncer- 
 tain and arbitrary, and our knowledge of them, at best, but 
 little increased. 
 
 In spite of all this, hypotheses, uncertain comparisons and 
 analogies, and the conclusions drawn from them, hare always been 
 avoided nominally only, nor could this be otherwise, simply 
 because they are indispensable. For, as we have already had 
 occasion to observe, we could not, without them, form any 
 notion of a single phenomenon or process in the living body, 
 or of the state of a patient, any more than of the mode of ope- 
 ration of an external influence, or of the beneficial or deleterious 
 effects of our therapeutical interference in any disease. Equally 
 little could we hope more closely to investigate, still less to ex- 
 plain all these things without hypotheses or conjectures. 
 
 Fortunately, however, such hypotheses or conjectures are not 
 naturally and necessarily so dangerous and useless j still less 
 does the value or worthlessness of them depend upon their 
 mere name, but rather upon their nature and upon the pur- 
 poses for which we propose to employ them. It depends upon 
 our own capability of forming consistent, and as it were legiti- 
 mate, hypotheses and conjectures — i. e., such as may impart a 
 certain real knowledge of things previously enigmatical and 
 unexplained, or at least lead us on to further investigation, and 
 in the end, perhaps, to the discovery of the real state of things. 
 It also especially depends upon whether we accept them only 
 as what they are in reality and not as anything more, perhaps 
 as facts and perfect explanations ; it further depends upon 
 whether we are willing to test their validity by the method of 
 strict investigation, and to demonstrate it by the results of 
 sound experience, or whether we seek, on the contrary, to base 
 them only upon other, perhaps arbitrary and a priori conjec- 
 tures and hypotheses, and thus to give them a certain sem- 
 blance of truth. 
 
 A natural and indeed perfectly legitimate and necessary im- 
 pulse, a want felt by the scientific investigator as well as by 
 the practical physician, makes us desire to understand all that 
 we observe to occur in nature — i. e., to ascertain its conditions, 
 laws, and internal connection. Men are wont to take an in- 
 terest in all these things, however, only in so far as they are 
 
270 HYPOTHESES, ANALOGIES, 
 
 themselves concerned — i. e., only in so far as they can under- 
 stand them, or perhaps employ them for their own advantage 
 or that of others. But nature everywhere offers us in her 
 complex phenomena and processes only enigmas and questions, 
 without affording any clue to the understanding of them. 
 For us they have, as such, scarcely any real existence : we 
 must first of all be able to form some notion concerning them, 
 and this we endeavour to do as well as we can. 
 
 What we ascertain concerning them through the senses is in- 
 deed, in itself, clear and positive enough, but the manner in 
 which we must represent to our minds the internal connection, 
 the relations of cause and effect in it, is not equally plain. 
 For that which we do not understand, and therefore cannot 
 yet explain, we assume some causal connection, some kind of 
 principle, either secondary or primary, as possible or probable ; 
 in other words, we form some hypothesis as well as the present 
 state of our knowledge enables us to do. It cannot indeed be 
 denied that such hypotheses must always be regarded as ven- 
 turesome and doubtful, and, in a certain sense, as premature 
 and arbitrary, but we have no alternative, at least in medical 
 science. And if nothing remains for us but to form more or 
 less probable conjectures concerning the causal relations and 
 internal connection of the things with which we have to deal, 
 it must be our object to shield ourselves as far as possible from 
 mistakes in the interpretation of them, and to avoid drawing 
 from them arbitrary conclusions. 
 
 A false hypothesis, an entirely groundless theory is, how- 
 ever, often better than none at all for more correct knowledge 
 in future, as well as for our practical wants at the bedside; 
 for it is only by venturing upon some such conjecture, however 
 false, concerning the conditions and laws of phenomena and 
 processes previously altogether unexplained, that we can hope, 
 in the end, to ascertain them and to bring the phenomena, &c., 
 themselves more within the scope of our comprehension. Thus 
 doubtless Columbus would never have discovered America 
 unless certain probable grounds for assuming the existence of 
 that continent had previously been made known, and unless, 
 having skilfully put together and correctly appreciated those 
 grounds, he had put to sea in reliance upon them. 
 
 Such hypotheses, however, seldom present themselves to our 
 
CALCULATION OF PROBABILITIES. 271 
 
 minds during the separate consideration of any individual 
 phenomenon or occurrence ; still less could we venture to 
 assume for itj without strong grounds, any special and new 
 mode of development — i. e., any kind of dependence and 
 causal connection in it, diifering from those already known. 
 Other phenomena and things occur to us immediately, and as 
 it were instinctively, of which we are reminded by certain 
 resemblances : and here we call to mind especially such as 
 present the most striking analogies, in certain points, to the 
 particular phenomena before us, and concerning the causes 
 and connection of which we have perhaps previously acquired 
 some definite knowledge. Lastly, we go on to assume that all 
 these phenomena may in the end commence in essentially the 
 same manner and depend upon the same circumstances and 
 causes. In short, we consider the probability that they may 
 all have one and the same causal connection, and that, conse- 
 quently, phenomena and processes still obscure and new may 
 be referred to the causes or laws of those others whose resem- 
 blance to them in certain points struck us at first. 
 
 Whether this hypothetical conclusion has been at least 
 approximately correct, or false, must depend entirely upon the 
 degree of similarity and accordance which existed between all 
 the things which we had compared with each other. Every- 
 thing depends, therefore, upon the correctness and clearness of 
 our conceptions, upon the extent of our field of view generally, 
 and especially upon our previous insight into the conditions or 
 laws of some at least of those phenomena and circumstances. 
 In short, hypotheses and comparisons of this kind can only be 
 rendered admissible by bringing the phenomenon or process in 
 question into juxtaposition with others which are really analo- 
 gous in certain main points ; and it is equally certain that this 
 comparison of things still unknown and unexplained with 
 others, can only facilitate the comprehension of them if we are 
 already more familiar with the latter than with the former, 
 especially as regards their conditions or laws. If we succeed, 
 by these our hypotheses and comparisons, in coming as near 
 as possible to the discovery of the real nature of the things 
 with which we have to deal, a most powerful aid has evidently 
 thereby been given to the investigation into their causal con- 
 nection and to the comprehension of them generally. Allusion 
 
272 HYPOTHESES, ANALOGIES, 
 
 has already been made, in connection with other auxiliary 
 means, to the important services rendered by hypotheses and 
 comparisons as links in the process of induction. 
 
 But since it has already been shewn that in the employment 
 of such comparisons and hypothetical conclusions everything in 
 the end depends upon their correctness in each individual case, 
 or, in other words, upon the question whether the precise 
 points and circumstances which led us to assume the essential 
 similarity of certain things and occurrences, and of their causal 
 connection, are in reality determining and essential, or not, the 
 uncertainty and frequently the uselessness of these comparisons 
 and hypotheses in medical science is evident enough. For, as 
 has been explained on a former occasion, we have remained to 
 the present time more or less ignorant as to what really is 
 determining and essential in all the phenomena and processes 
 with which we have to deal ; and on that account our conclu- 
 sions from the comparison of them with each other, and from 
 various analogies between them, must at present be regarded 
 as uncertain and often as entirely fruitless. 
 
 Thus, for centuries past, various vital processes and various 
 diseases have been grouped together on the strength of certain 
 analogous points in them, without any notable addition to our 
 real knowledge of them, and that for the simple reason that 
 those of one group were as little understood as those of the 
 other. " Fever," and " inflammation," especially, have always 
 been regarded in medicine as belonging to the most important 
 aggregates of symptoms, and numerous theories concerning 
 them — i. e., hypothetical attempts to explain the phenomena 
 and processes in them, have never been wanting. Every period 
 and every school up to the present day has made the attempt, 
 as well as the existing state of knowledge permitted, and in 
 the manner which accorded best with its own particular views. 
 But they have all remained mere hypotheses— i. e., the condi- 
 tions, conformity to fixed laws, and causal connection of those 
 phenomena and processes have never yet been clearly demon- 
 strated ; indeed, we have not even become as familiar with all the 
 phenomena in persons so affected as simple observation alone 
 would have enabled us to become. Thus, for instance, the changes 
 in the temperature of the body, in its electricity, in the pro- 
 cesses of evaporation and excretion by the skin, kidneys, 
 
CALCULATION OF PROBABILITIES. 273 
 
 mucous membranes, &c., the variations in weight, and the 
 modifications resulting from particular external and internal 
 circumstances have, to a slight extent onlj', been made the 
 objects of exact scientific observation. Equally little have we, 
 as yet, succeeded in ascertaining the circumstances, with their 
 influence and mode of operation, in consequence of which those 
 various changes and derangements commence and cease ; neither 
 have we by any means determined with certainty whether, and 
 how far, the return to a healthy condition may, or may not, 
 have been essentially facilitated by our artificial measures, 
 and which of these have been more successful than others. 
 Numerous views, however, obtain on the subject, and the 
 most various attempts at explanation have frequently been 
 made. 
 
 However valuable, therefore, hypotheses, comparisons, and 
 analogies, and our deductions from them, may be as the first 
 step and the stimulus to further investigation, they are worth- 
 less in many respects as a determinate conclusion. An incorrect 
 hypothesis, a comparison, however rash and vague, will often 
 indeed render us greater services than the entire neglect of 
 such means, so soon as they lead us to further investigation 
 into the conditions and laws gf things still enigmatical, but it 
 is equally certain that the best and most ingenious hypothesis 
 or comparison is highly dangerous if we accept it as an actual 
 explanation of them. Every attempt, even the most imperfect, 
 to seek at least for such an explanation by positive investigation 
 will possess a higher value than the most ingenious conjectures or 
 hypotheses, although the multitude often judge otherwise, and 
 easily accept the latter while they ignore the former. 13 ut the 
 multitude — especially in medicine — have dififerent wishes and 
 requirements from science itself, and may, consequently, con- 
 tent themselves with things which the latter must reject. 
 Experience seems to show, at least, that in the department of 
 physiology, and still more in that of therapeutics, some one or 
 other is constantly striving to appear as a kind of Newton or 
 Keppler, in fact every one who has ventured to propound a com- 
 prehensive theory or entire system : and the others who, like the 
 Israelites, are constantly expecting their Messiah, for the most 
 part willingly believe what he asserts. They greet him with 
 acclamations so that he perhaps himself believes in the truth 
 
 18 
 
274 HYPOTHESES, ANALOGIES, 
 
 of his doctrines, until the false prophet is recognized and 
 crucified. 
 
 It may, therefore, be regarded as a certain step forwards if 
 we give out our views and hypotheses as worth no more than 
 they really are; if we do not deal with them as with esta- 
 blished truths and facts ; and if we do not seek to render the 
 latter subordinate to them, but rather endeavour, by further 
 conscientious investigation of the actual state of things, to 
 furnish the confirmation or refutation of them. And precisely 
 because this has happened more rarely perhaps in medicine 
 than anywhere else; because hypotheses have, on the whole, been 
 less used than abused ; and because they have more frequently 
 tended to produce confusion and bitter delusions than to increase 
 our knowledge, they have fallen into disrepute with many. 
 
 In reality, however, hypotheses vary greatly iu their nature 
 and in respect to the services which they are capable of ren- 
 dering, and it would be both unreasonable and illogical to 
 estimate them all according to the same standard. A distinc- 
 tion must, therefore, be made between rational hypotheses and 
 such as are visionary and more or less absurd; between such 
 as are productive of results and such as are useless. In the 
 case of the former, we may (though led on at first, perhaps, 
 by our purely a priori surmises and conjectures) succeed iu the 
 end in discovering the actual state, the conditions and connec- 
 tion of things previously obscure, and in demonstrating more 
 or less clearly, by direct investigation, the accuracy of our 
 hypotheses. In the case of the latter, on the contrary, we 
 remain in our hypothetical position, and allow our conjectures 
 and subjective views to take the place of laws established by 
 experience. In the former case our hypotheses, comparisons, 
 and analogies have led us to further exact observation, perhaps 
 to investigations by means of experiment ; indeed they may 
 even, from having approached sufiiciently near to the real 
 nature of the things in question, have first rendered such 
 investigations and their successful results possible. In the 
 latter case, the exact opposite of this occurs, and from the very 
 nature of the hypotheses themselves they can, at best, only be 
 maintained by the exercise of much ingenuity, and by forcing 
 nature, as it were, to suit the particular views adopted. 
 
 It can scarcely be doubted, in fact, that the most talented 
 
CALCULATION OF PROBABILITIES. 275 
 
 and successful investigators have often first arrived at their 
 most important discoveries, and highest and most comprehen- 
 sive generalizationSj by mere hypotheses, or certain a priori 
 views. One was perhaps shrewd or fortunate enough to select 
 and examine what others had overlooked or rejected. Another 
 had perhaps surmised, and subsequently discovered, certain 
 analogies, certain internal relations or laws, where no one 
 before him had suspected their existence. To both the idea 
 occurred that it might be, that it was so, and their merit or 
 success consists only in their having hit upon the right point 
 — i. e., an innate relation, or causal connection between things 
 which it thereby became possible further to investigate and 
 prove. In the generality of cases, some striking phenomena 
 and facts led to investigation in a certain direction. Other 
 somewhat similar facts, which were afterwards met with, perhaps 
 confirmed the probability of a given conjecture, until further 
 search led at last to the discovery of a causal connection 
 between certain things previously unexplained and apparently 
 unconnected — in short, of a new law. 
 
 Thus, in the generalization of the process of oxidation already 
 alluded to — i. e., of the action of oxygen in the living body — 
 Liebig and others perhaps started chiefly from the fact that 
 notwithstanding the large quantity of oxygen consumed in 
 respiration — several hundredweight in the course of the year 
 — no increase in the weight of the body occurred, such as' 
 might have been expected from that circumstance. It was 
 evident, therefore, that the oxygen taken in could not possibly 
 remain in the body, but must escape, in combination with the 
 hydrogen and carbon of the latter, in the form of water and 
 carbonic acid, or eventually be excreted, in combination with 
 certain nitrogenous and other components of the body, in the 
 form of uric acid and urea : and because it was observed, in 
 reference to men and animals, that in the last-mentioned 
 products of excretion, and in the bile, urine, &c., and their 
 salts, more oxygen exists than in the blood from which they 
 originate; and because, on the other hand, it was found that 
 in peas and the like less oxygen exists than in pea-straw, a 
 continuous process of oxidation or combustion was assumed to 
 be going on in the former, while the reverse was supposed to 
 occur in plants (Rose). 
 
276 HYPOTHESES, ANALOGIES, 
 
 The more or less successful result of such hypotheses, or 
 rather of the investigation based upon them, combined with a 
 certain innate impulse, perhaps with a consciousness of their 
 own mental power, may frequently have induced .others to risk 
 something similar in their department of science — e. g., in 
 medicine. But theirs were no master-minds, and were in- 
 capable of following out their conceptions with the same 
 success, because, in the present state of our knowledge, 
 this is next to impossible for the physician, and even for 
 the physiologist. Here, as well as in jurisprudence, " ignoratio 
 nocet." 
 
 Every one, it is true, is at liberty to form various notions 
 concerning the enigmatical and unexplained questions or 
 objects with which he has to deal — i. e., concerning their 
 internal connection with each other and their mutual depend- 
 ence and action ; and nowhere, perhaps, has greater use been 
 made of this freedom than in medicine. It rarely happens, 
 however, that any one has better grounds for his views and 
 explanations here than the arbitrary conjectures of the moment. 
 Any given thing appears to him in a certain light because he 
 happens to view it in that light. Thus one man sees the true 
 source and starting point of nearly all diseases in the nervous 
 system, in the brain or spinal cord, or in the ganglia and their 
 derangements; another, perhaps, assumes a so-called blood- 
 crasis as the essential and determining cause of every disease. 
 Again, nearly all diseases and the effects of miasmata and the 
 like, as well as fermentation, putrefaction, and all the processes 
 of conversion in organic matters, might be regarded as essen- 
 tially dependent upon the formation and presence of fungi, 
 sporules, infusoria, &c., because some of these have, perhaps, 
 everywhere been observed to be present. One man, as expe- 
 rience has shown, may attribute the occurrence of cholera and 
 all other possible diseases to the drinking of bad water, to the 
 exhalations from stagnant pools and morasses ; another, on the 
 other hand, to an excess or deficiency of electricity in the atmo- 
 sphere ; or he may refer the diseases of towns to the carbonic 
 acid in the air which its inhabitants breathe, or to the sulphu- 
 retted hydrogen in the water which they drink. With almost 
 as much reason might any one attempt to explain the com- 
 paratively healthy condition and small mortality amongst the 
 
CALCULATION OF PROBABILITIES. 277 
 
 richer and better-fed classes of the population, when contrasted 
 with the poorer, to the fineness of the cloth which they wear, or 
 of the carpets upon which they tread. And whoever is inclined 
 to do so may not only attribute the cure of his fever patients 
 to the employment of calomel, chlorine, opium, or even simple 
 water, but he may adopt the most various views concerning the 
 mode of action of these remedies in each case. It. also lies in 
 the very nature of the subject itself, and is therefore unde- 
 serving of the least blame, that every one should attempt to 
 explain as best he may the more or less unfamiliar phenomena 
 and occurrences with which he meets, and employ sometimes 
 one, sometimes another of the hypotheses and comparisons with 
 which his knowledge furnishes him, or which appear most 
 correct according to his views. 
 
 The very existence of such hypotheses and the large number 
 of them is a testimonium paupertatis for each individual 
 investigator and still more, almost, for his whole department 
 of science. Unfavorable indeed is the status of a science in 
 which each labourer enjoys such a freedom, which might almost 
 be termed a fool's freedom ; in which we are compelled to form 
 such an estimate of the value and importance of our hypo- 
 theses; and — what is worst of all — in which such vague 
 assertions still find belief with some. 
 
 The chief danger of all our hypotheses and comparisons con- 
 sists less in the circumstance that they are employed to suit the 
 imagination or caprice of individuals than that they too often 
 pass for something better — i. e,, for the explanation of things 
 previously obscure, — and are not only given out, but also 
 accepted, as established truths. It is overlooked that all these 
 hypotheses and comparisons possess a value for science only in 
 so far as they actually suffice to explain occurrences previously 
 inexplicable — i. e., in so far as they enable us to deduce them 
 from laws already known, or from others recently discovered 
 and established. It is overlooked too that we can only rely 
 upon them when the accuracy, or at least probability, of such 
 deductions and explanations is strengthened by reasons which 
 are worthy of belief because they agree with our experience 
 and with the actual state of things — in short, with all the 
 facts and results of actual investigation. 
 
 Those investigators of nature, who have known how to 
 
278 HYPOTHESES, ANALOGIES, 
 
 employ hypotheses with the greatest success, and who have 
 thus brought them into a certain repute, are the very men who 
 have, at the same time, been least satisfied with them, as such. 
 They have all doubtless been willing to attach a higher value 
 to them only when they fulfilled the requirements alluded to 
 above, and when their probability or accuracy could be con- 
 firmed by further investigations and by a conscientious exami- 
 nation of facts. It was not the mere construction of hypo- 
 theses, not a priori surmises and conjectures, in themselves, 
 which could lead them to actual discoveries, but rather the 
 circumstance that they had hit upon such as were correct, and 
 that this correctness eventually admitted of demonstration. 
 Thereby alone did they succeed in converting their hypotheses 
 into a law, into truth. Their comprehensive and penetrating 
 glance had perhaps already been able to detect certain essential 
 relations or resemblances between various phenomena and 
 occurrences, which had escaped the eye of ordinary observers. 
 And because all these things suddenly admitted of being brought 
 into the true and only possible relation to each other, they 
 were better able to explain them than others who had gone 
 before. They discovered for them a particular kind of depend- 
 ence or action, in short, of causal connection — new laws, there- 
 fore — or referred them to others already known. But it was 
 not possible to do this by the aid of their hypotheses, in them- 
 selves, but only through the subsequent demonstration of their 
 accuracy. Their success and their merit consisted only in this, 
 that their hypotheses were precisely of such a kind as to admit 
 of demonstration, and were confirmed in the end, by all the 
 known facts. It was necessary that all the conclusions to 
 which their hypotheses naturally led should first be shown to 
 be true — i. e., to agree exactly with the actual state of things, 
 and suffice for the perfect explanation of them, — before the 
 hypotheses themselves could be accepted as correct. 
 
 This presupposes, before all, a department of science, a 
 branch of knowledge in which such demonstrations by indi- 
 viduals are possible. Various series of phenomena and occur- 
 rences, though isolated perhaps, must already have become 
 known, at least approximately, not only in relation to their 
 mere existence, but also to their causal relations, conditions, 
 and laws. Further, the questions at issue — t. e,, all the points 
 
CALCULATION OF PROBABILITIES. 279 
 
 to be determined by those demonstrations, as well as the 
 methods and processes for their investigation or solution — must 
 be of such a nature that we may be able to ascertain some- 
 thing certain and positive concerning them. 
 
 Thus it was necessary that much should already have been 
 ascertained concerning the magnitude and distance, the rela- 
 tive position and motions of the heavenly bodies; the labours 
 and observations of astronomers for many centuries were re- 
 quired before a Keppler or a Newton could arrive at his bril- 
 liant deductions. It is well known, also, how astronomers 
 continued to take observations over half the earth, according to 
 the strictest and most exact methods, with the best instru- 
 ments and other auxiliary means, in order to prepare the way 
 for the solution of similar questions. In like manner, chemistry 
 had to collect numerous, though perhaps isolated facts and 
 proofs. The conformity to fixed laws of various phenomena 
 and processes had to be determined before a Liebig, for 
 instance, could advance further by their aid, and carry out his 
 calculation of probabilities with a certain amount of likeli- 
 hood. 
 
 Physicians and physiologists, on the contrary, have scarcely 
 ever penetrated beyond the surface in their department of 
 science. They have succeeded, it is true, in establishing the 
 actual existence of certain series of phenomena and processes 
 in the living body, together with the mode of their manifesta- 
 tion and sequence. But we have nowhere ascertained exactly 
 what takes place in them ; we know next to nothing of the 
 conditions and laws of their occurrence, and the physiologist, 
 in reality, is little more enlightened than the pathologist. Our 
 methods of observation and investigation have only begun to 
 prepare the way for knowledge of this kind in the future — i. e., 
 we have only just begun to employ them in such a manner and 
 in such a direction that we may hope, in the course of time, to 
 ascertain something positive concerning the real nature of the 
 things with which we have to deal. 
 
 In the present state of our knowledge, therefore, it appears 
 altogether impossible that hypotheses and comparisons should 
 meet all the demands which may be made even upon such of 
 them as are sound and consistent; still less can any individual 
 hope to furnish proof that those which he employs exactly 
 
280 HYPOTHESES, ANALOGIES, 
 
 fulfil all the requirements which may possibly arise. The con- 
 ditions and laws of all the vital processes are so little known to 
 us that we are unable, as yet, to construct any hypotheses 
 concerning them with even an approximation to certainty ; 
 and, if we should accidentally succeed in doing so, we could 
 not, in the present state of our knowledge, and with our 
 present methods of investigation, prove the truth of our own 
 assertions. Equally little can we proceed with certainty in 
 comparing with each other the precise processes in the living 
 body, or the influences which act upon them, even though they 
 may agree in their essential points, and that for the simple 
 reason that these latter are themselves still too little known to 
 us. 
 
 All this also serves to explain why hypotheses and the 
 employment of analogies not only do little to increase our 
 knowledge of the things we are seeking to investigate — infi- 
 nitely less, for instance, than in physics and chemistry — but 
 why they even more frequently perhaps impede the acquisition 
 of it ; and the more comprehensive our hypotheses and com- 
 parisons may have been, the more frequently will this result 
 follow. 
 
 For the present, therefore, it seems more advisable to seek 
 to become better acquainted with the circumstances and laws 
 of each individual occurrence, and with the mode of action of 
 each individual agent or influence in it, instead of venturing 
 upon numerous hypotheses and conjectures concerning entire 
 aggregates of such, or even, perhaps, concerning them all. 
 Each positive demonstration of even the most insignificant new 
 circumstance or occurrence would usually possess more real 
 value than the most ingenious conjectures concerning all those 
 which might possibly arise. We should also be the more able 
 to rely upon our hypotheses and comparisons, and they would 
 the more tend to add to our real knowledge, the more we had, 
 in the course of time, become acquainted with the causal 
 connection and laws of at least individual phenomena and 
 processes. 
 
 Thus, even if we have formed a certain hypothesis, or drawn 
 a certain comparison, we can never venture to rely upon it; 
 and if this holds good for every department of natural science, 
 it applies especially to medicine. In it, least of all, can we be 
 
CALCULATION OF PROBABILITIES. 281 
 
 satisfied with our conclusions from any hypothesis, or analogy, 
 and we must strive, more and more, to replace them by others 
 more trustworthy, drawn from facts and direct investigations. 
 Since the former, under the most favorable circumstances, 
 can only be regarded as conjectures, or as a calculation of 
 probabilities, in which we have perhaps reasoned with toler- 
 able accuracy, perhaps altogether falsely, we must always 
 retire upon the only sound basis of our knowledge — i. e., 
 upon the actual state of things. We must endeavour, by 
 repeated and close examination of the latter, to apply a kind 
 of counter-test to our previous views and deductions. We 
 must examine, therefore, whether any new case, any new phe- 
 nomenon or occurrence, or perhaps the same phenomena and 
 occurrences under different circumstances, are opposed to our 
 hypotheses, to our previous conjectures and deductions. If 
 we meet with such a contradiction we must examine further 
 in what the sources of error may have consisted, or upon what 
 the differences in the results obtained at different times may 
 have depended. We must endeavour to ascertain what cir- 
 cumstance or influence has varied in each case, or what new 
 one has been superadded, so as to produce those variations or 
 modifications in the general process or result, with which we 
 have already become acquainted. 
 
 These further tests and examinations, which are a simple 
 duty in our search after truth — our highest aim — also lead 
 not unfrequently to entirely new discoveries, and to unhoped 
 for elucidations of the questions at issue ; and this again is the 
 highest reward of his labours, for which the true and con- 
 scientious investigator can anywhere look. 
 
 An infinitely more important and certain auxiliary in the 
 calculation of probabilities in medical science than hypotheses 
 and analogies has been more and more recognized in the colla- 
 tion of cases and observations of the most homogeneous nature 
 possible — in short, in statistics or the numerical method — and 
 in a certain sense, and to a certain extent, this recognition has 
 been most justly made. Allusion has already been made, in 
 speaking of the inductive process, to the employment of this 
 method as an aid to investigation. We there endeavoured to 
 explain the reasons why no exact conclusion can be drawn fron? 
 
283 HYPOTHESES, ANALOGIES, 
 
 such statistical computations, in themselves, concerning the 
 conditions and causal connection of certain phenomena and 
 occurrences, or concerning the mode of operation and ofiBce of 
 various influences in them. It is self-evident, also, that 
 for essentially the same reasons the safe employment of such 
 numbers in our calculation of probabilities must, for the pre- 
 sent at least, be very difficult, if not altogether impossible. 
 For all the products and results of statistics, important as they 
 may be in other respects, cannot, in themselves, afford us any 
 safe points of support for the elucidation of an individual case, 
 any more than for the discovery of the causal connection of 
 our phenomena, &c. The complication of circumstances, the 
 number of co-operating and modifying influences and con- 
 ditions are everywhere too great, and on the other hand our 
 knowledge of their effects or laws individually is too slight, 
 and the results of statistics are at present of too general and 
 uncertain a nature to enable us to draw any precise conclusions 
 from them. 
 
 In many instances we learn from statistics, indeed, that, of 
 many existing and operating circumstances or influences, some 
 one has more probably determined a given effect, — e. g., a 
 disease, a cure, or a death — than any of the others ; also that, 
 of many efi'ects or consequence — e.g., an attack of a certain 
 disease, its cure, death, or a certain duration of life — one will 
 occur more frequently under given circumstances than another. 
 In the latter case we may thus, by the aid of our computations, 
 rather anticipate a certain event than some other perhaps oppo- 
 site one ; in the former case we shall be able to deduce a cer- 
 tain event and its development with much greater probability 
 from one giveu circumstance than from another. All this, 
 however, for reasons which are evident enough, admits of no 
 direct application to an individual given case, nor can it lead 
 us to any even remotely safe conclusion concerning its nature. 
 So many special circumstances and influences come into play 
 in each individual case, and complicate the question and calcu- 
 lation to such an extent, that the latter, notwithstanding all 
 the numbers and results of statistics, cannot possibly be a safe 
 one, even if it were much more exact, and the office and influence 
 of all those modifying circumstances much better known to us 
 than they really are. This also explains why, in no given 
 
CALCULATION OF PROBABILITIES. 283 
 
 case, precisely that will occur which our statistical coruputa- 
 tions might lead us to expect, or, in other words, why each 
 individual case has its own special result, which could not 
 possibly have been calculated with certainty from those 
 general products of statistics, and does not agree exactly with 
 them. 
 
 If, for instance, it appeared from statistics that of 1000 in- 
 habitants of a given country or place, who are in their 20th 
 year, at least 800 live from 10 to 15 years longer, no one will 
 attempt to infer therefrom that the duration of life in any given 
 individual amongst them will be precisely the same. On the 
 contrary, the probability is infinitely greater that such individual 
 will either live beyond the age of 30 to 35, or die before he 
 attains it. Again, if we know that, of all the persons attacked 
 by Asiatic cholera in a given town, 50 per cent, die, and an equal 
 number recover, we cannot on that account assume for an 
 individual cholera patient that the probability of his dying is 
 precisely as great as that of his recovery. Such probability 
 will rather be greater or less than the one established statis- 
 tically, according to his particular circumstances — e. g., his 
 age, rank, and constitution — or according to the severity of the 
 attack. And if it had been observed in all the hospitals and 
 similar institutions of a country that of 100 persons attacked 
 by inflammation of the lungs; 80 had constantly recovered, and 
 20 died after the employment of certain remedies — e. g., bleed- 
 ing — no certain conclusion could be drawn therefrom concerning 
 the case of an individual patient. His disease and general 
 condition will always be of such a nature, that the probability 
 of his death or recovery will be either much above or much 
 below the statistical average ; and in no case will the proba- 
 bility of his death stand to that of his recovery in the exact 
 proportion of one to four. 
 
 These results of our statistical calculations have, therefore, 
 only a general and, as it were, superficial value. It follows 
 from the very manner in which such general results have been 
 obtained, that they are applicable only to a whole series or 
 class of cases and instances essentially similar to each other, 
 but not to any individual given case. For here again, nume- 
 rous special circumstances and influences are in operation — in 
 cases of disease, for instance, age, sex, constitution, mode of 
 
284 HYPOTHESES, ANALOGIES, 
 
 life, season of the year, climate, neighbourhood, &c. — in 
 accordance with which the state of things in a given case will 
 always vary, and the general result of statistics consequently 
 undergo a certain modification. 
 
 In addition to this, all these results of our statistical calcu- 
 lations — e. ff., of duration of life, of mortality, of disease and 
 its fatality, of remedies and their eifects — hold good only for 
 the particular kind or combination of circumstances under which 
 they have themselves been observed and collected. They also, 
 equally with our experiences and simple empirical data, have a 
 certain value only for a given place, a given time, or a given 
 class of men, &c. 
 
 For this reason the probability of a long life, or of good 
 or bad health, in the case of A or B, will vary greatly with 
 the circumstance of his living in Germany or France, in the 
 Delta of the Ganges or on the banks of the Mississippi; just 
 as a wealthy man has a very different prospect of health and 
 long life from an indigent inhabitant of the same place. Thus, 
 when an individual is attacked by intermittent fever, typhus, 
 or Asiatic cholera, the probability of his recovery, even under 
 precisely the same personal circumstances, will vary greatly if 
 the attack occur in Berlin, Vienna, Bengal, or New Orleans. 
 Essentially the same thing holds good of all our statistical cal- 
 culations concerning the part played by various causes of 
 disease, and concerning the influence of iudividual social cir- 
 cumstances or hygienic agents upon health and duration of 
 life, or of the various modes of treating a disease upon its 
 events. 
 
 In all these cases, therefore, we cannot speak of a calcula- 
 tion of probabilities in the strict sense of the term ; for the 
 great complexity and constant variation of all the circum- 
 stances render the safe application of general statistical results 
 to an individual case impossible, and thus make every attempt 
 to submit the latter to exact computation a mere illusion. 
 And since, in all these cases, nothing can be calculated with 
 certainty, the attempt to do so, and too great a reliance upon 
 the results of such calculations, often bring with them the 
 same dangers as when others — e. g., physicians of the old 
 school — rely upon their so-called experience. In one case, as 
 in the other, we shall equally be investing ourselves and our 
 
CALCULATION OF PEOBABILITIES. 285 
 
 assertions with a semblance of certainty to which we can lay 
 no claim whatever. 
 
 It is true that we are daily compelled to make a kind of 
 calculation of probabilities concerning the question at issue, 
 and to carry it out as well as we can in an individual given 
 case. Here, however, we fortunately possess means very dif- 
 ferent from, and more certain than, statistical numbers in 
 themselves. We shall attain our end with infinitely greater 
 certainty, namely, by seeking to estimate and determine, as 
 exactly as possible, all the circumstances which may be im- 
 portant and influential in the case before us, for the purpose of 
 drawing a probable conclusion from them. It makes no dif- 
 ference in the main point whether the question be about the 
 appreciation of various processes in the living body, or of the 
 calculation of the probable influence of various social circum- 
 stances, of the event of a disease, or of the best mode of pro- 
 ceeding in the treatment of it. A close scrutiny of the indi- 
 vidual case before us, in all its details, will aid us much more 
 in judging of its nature, and in forming a probable calculation 
 of what will occur in it, than the employment of mathematical 
 forraulse, or statistical numbers, in themselves. 
 
 In our calculation of probabilities, also, our success will 
 depend chiefly upon our knowledge of the subject, and upon 
 the extent and solidity of our experience in the particular 
 branch of science. The accuracy of such calculations will 
 thus only gradually increase in proportion as we are more and 
 more ahle to clear up the obscurity and uncertainty respecting 
 all the questions and objects which are presented to us, by 
 means of positive and exact investigation, whether it be by 
 the simple observation of the actual state of things, or by the 
 aid of experiment. And precisely because statistics are in 
 this respect also among the best of our auxiliaries, their results 
 will always retain their important position in our calculation of 
 probabilities. If we do not acquire, by their aid, any insight 
 into the conditions, causal connection, and conformity to fixed 
 laws of the processes which we are seeking to investigate, they 
 afford, at least, a sufficiency of important facts and empirical 
 laws from which we may judge more certainly of each indi- 
 vidual case, and predict with more probability what will or will 
 not occur. If, for instance, statistics have once clearly shown 
 
286 HYPOTHESES, ANALOGIES, 
 
 that not less than 60 per cent, of those attacked by Asiatic 
 cholera in a given place always die, the death of A or B, so 
 affected, will always appear more probable than if the mortality, 
 in the same place, and under the same circumstances, never 
 exceeded 20 per cent. We cannot, it is true, make any 
 definite prognosis for A and B, but the general probability of 
 their death in the one case will stand to that in the other in 
 the proportion of three to one. 
 
 Nothwithstanding all this, our calculation will ever remain 
 very uncertain, and one by no means to be relied upon, unless 
 we can call to our aid further knowledge, and other auxiliaries, 
 from the quarter already alluded to. The more extensive and 
 exact our knowledge of at least individual occurrences and 
 their laws becomes, in the course of time, the sooner shall we 
 be able, not only to draw conclusions from them concerning 
 the nature of many others, and concerning their conditions 
 and effects, but also to predict with much greater probability 
 what will occur in the cases which come under our observation. 
 For, with that clearer insight into the actual state of things, 
 and with the increase of our general knowledge, we shall 
 acquire more and better grounds for assuming one condition of 
 things to be more probable than another. 
 
 Essentially the same advantage accrues for our judgment of 
 each individual case. If we once succeed, for instance, in dis- 
 covering, in a given case, the existence of some particular more 
 important circumstance, the action of some one more or less 
 essential and determining influence, previously unknown to us, 
 not only will the development and occurrence of a given effect 
 or event become much more intelligible, but we may, in other 
 cases also, with more probability than before, look for, and 
 therefore predict, the occurrence, or non-occurrence, of this 
 particular effect or event. 
 
 If, for instance, we knew nothing more concerning a sick 
 person than that he was out of health, we could form no 
 opinion concerning the probable duration of his disease, or 
 concerning the probability of his recovery or death. So soon, 
 however, as we ascertain that he is attacked by Asiatic cholera, 
 for instance, our opinion on those points will at once become 
 more definite, and will differ greatly from the one we should 
 form if we ascertained that his disease was a simple diarrhoea, or 
 
CALCULATION OF PROBABILITIES. 387 
 
 common continued fever. So long as we know nothing more con- 
 cerning a patient than that he has much cough and expectora- 
 tion, and suffers from fever and pain in the chest, our view of 
 the danger of his state, and of the probability of his recovery, 
 will be infinitely less clear than if we had succeeded in ascer- 
 taining that he was suffering from simple bronchitis, from in- 
 flammation of both lungs, or from acute tuberculosis. And 
 since it has been discovered that, in persons affected with con- 
 tinued fever, various deeper-seated changes in the alimentary 
 canal, ulcers, &c., frequently occur, with which the diarrhoea in 
 that disease stands in some intimate connection, the prospect 
 of checking this diarrhoea by our remedies will differ greatly 
 from what it was formerly when we had no knowledge of the 
 existence of those changes in the alimentary canal. 
 
 If we are told only that a certain European is living in a 
 tropical country, we are unable to conjecture and assert any- 
 thing with certainty concerning the probability of his con- 
 tinuing in a state of health, or of his falling sick and dying. 
 If we once know, however, that, in the place where he lives, 
 yellow fever, dysentery, cholera, and the like, yearly occur 
 epidemically, we shall be able to form a prognosis for him, and 
 that a more unfavorable one than if such were not the case. 
 This prognosis will also depend very much upon various other 
 circumstances — e. g., that the European in question has lived 
 there some weeks only, or many years ; that he is temperate 
 and robust, or dissipated and weakly ; or that he is a merchant 
 or traveller in good circumstances, or forced to labour hard, 
 with bad food, in an unhealthy dwelling or neighbourhood. 
 We cannot, it is true, form a probable calculation whether an 
 individual who has been condemned to ten years' imprisonment 
 will continue healthy and leave his prison alive ; but this will 
 be much more possible if we find, on examining him, that he 
 is scrofulous, phthisical, or dropsical; or if statistics have 
 shown that, of 100 persons confined in that prison, at least 
 20 to 30 have died annually. 
 
 What has already been said may suffice to show why our 
 calculation of probabilities, equally with our hypotheses and 
 conjectures, will gain in certainty the clearer our perception 
 of the occurrences and circumstances with which we have to 
 deal becomes. So long, however, as we have advanced no 
 
288 LANGUAGE, TERMINOLOGY AND 
 
 further in this respect than at present ; so long as the essential 
 elements in a given case, the causal connection and laws of 
 individual phenomena and occurrences in it, continue to be 
 more or less unknown to us, we shall also be unable to deter- 
 mine whether and how far all the things which we have 
 observed in the case before us stand merely in an accidental, 
 or in an essential and causal relation to each other. For the 
 same reason we shall not be able to judge, or to calculate with 
 certainty, whether, under given circumstances, a given effect 
 or event will or will not occur. 
 
 III. LANGUAGE, TERMINOLOGY AND DEFINITION, DESCRIPTION. 
 
 No attempt can be made in this work to explain in detail 
 the infinite importance of language generally, as well as of 
 individual words and forms of expression, for our judgment, 
 our investigations, and, in the end, for our comprehension and 
 knowledge as a whole. Such an attempt would far surpass 
 both the powers of its author and the limits of his task. 
 
 All that it is necessary to bear in mind here is, that we 
 everywhere not only think, judge, and draw conclusions for 
 ourselves in words, but that we have generally no other means 
 at our command of expressing and communicating to others 
 our observations, deductions, or abstractions, our general notions 
 and views, or of becoming acquainted with those of others, 
 except by words — i. e., by the aid of language. All that we 
 assert concerning any phenomenon or occurrence, or that we 
 learn concerning it from others, whether it be correct or false, 
 is conveyed by words ; and since this has been the case from 
 childhood upwards, our whole knowledge, our whole world of 
 notions and views is, as it were, laid up in words. Language 
 is thus most intimately blended, and has become almost identical 
 with our intellectual ego. It has its birth and grows as the 
 latter develops itself and grows ; it has its origin in our views 
 and notions, in our conceptions of various things ,• it is, as it 
 were, only the expression or mirror of them, and reacts cease- 
 lessly upon them. The ancient Greeks even employed one 
 and the same word (Xoyoc) for reason and speech. 
 
 In short, language, as every one knows, is the indispensable 
 
DEFINITION, DESCRIPTION. 289 
 
 organ, or instrument of our whole intellectual life, whether for 
 ourselves, or for our intercourse with others. It is not, how- 
 ever, a mere passive instrument but rather one which exercises 
 the most important influence upon us and upon our whole 
 mode of thinking and judging. Locke, in his celebrated 
 ' Essay on the Human Understanding,' has rated the importance 
 of language for the mind, and the dependence of the latter 
 upon it, so high, that he may rather be said to have written a 
 treatise upon the origin and development of language and 
 forms of expression than upon the influence of these on our 
 notions and views. There exists, in reality, so close a con- 
 nection, or mutual reaction between both; language, words, 
 and the world of our ideas can so little be separated from 
 each other; that we are unable to judge of the latter, or to 
 assert anything concerning it, without having first carefully 
 weighed the former and become acquainted with their influence 
 upon our mode of thinking. Words and expressions stand, to 
 a certain extent, in the same relation to thoughts and ideas 
 as the skin does to the body (Herder). 
 
 On a closer examination it becomes evident that we cannot 
 express anything in words unless we have some conception of 
 it, nor can we utter or hear any word without its immediately 
 aiFecting our conceptions. Every word, when once uttered, 
 comes into further operation by calling forth some kind or 
 series of thoughts and notions ; it therefore, in the end, exerts 
 a much greater influence upon our judgment than the word in 
 itself — i. e., the mere sound, would exert. With every word, 
 or expression, such, for instance, as innervation, miasm, irrita- 
 tion, or inflammation, we connect certain previous notions and 
 views which our knowledge and experience bring with them. 
 Such expressions are, in fact, only short symbols of those 
 notions or views, which, whenever we employ or hear them, 
 awaken in our minds the same thoughts or ideas as we had 
 formerly connected with them, and which we had, perhaps, pre- 
 viously acquired on similar occasions and from similar obser- 
 vations. Our interpretation of the case before us will also, 
 without our being conscious of it, be influenced more or less, 
 according to circumstances, by this intervention of our previous 
 notions, this definite kind of association of ideas. 
 
 Thus, if the notions we have always been accustomed- to 
 
 19 
 
390 LANGUAGE, TERMINOLOGY AND 
 
 associate with a certain expression, or, in other words, the 
 general signification of the expression itself, have been confused 
 and indistinct, those which it now awakens in us will have the 
 same character. And whenever, on the other hand, our know- 
 ledge of anything is vague and deficient, we shall be unable to 
 express it otherwise than vaguely and deficiently in words. 
 
 These few remarks may suffice to show the necessity of closely 
 examining into the relation in which language stands to our 
 questions and problems. The ofiice of logic in the investigation 
 of nature in general, and in our department of natural science 
 in particular, is, to make us acquainted with all the ways and 
 means which may aid us in the discovery of truth and of the 
 exact state of things. And if words and language are an in- 
 dispensable instrument for the expression of what we have seen 
 and observed in our investigations, and further, for the forma- 
 tion of all the views and conclusions we draw from them, it 
 must also be the office of logic to teach us the proper use of 
 this instrument. For it will be of the highest importance that 
 we should know how to make the best use of this auxiliary in 
 the process of induction. We clothe our observations and 
 descriptions in words, or become acquainted with those of others 
 through words, and no less are our conclusions and whole train 
 of thought an operation which is performed essentially in words, 
 and indeed, as we have seen above, under the constant influence 
 of them and of the impression which they exert upon us and 
 upon our conceptions. 
 
 In addition to this, the observer, the investigator, and the 
 physician, each finds himself at every moment necessitated to 
 draw some conclusion or other; for each is compelled to form 
 some opinion of what he has recognized and observed. Their 
 conclusions, however, consist of certain phrases and assertions, 
 these again of words, and words are the expression of our 
 ideas or thoughts. If the latter be vague and erroneous, so 
 will our -words be also, and conversely, vague expressions will 
 render our mode of judging more or less vague and erroneous. 
 Hence it follows that while a clear and pertinent language and 
 mode of expression will essentially facilitate our conceptions, 
 the reverse of this will result from the use of inadequate lan- 
 guage. And every one who does not know exactly how to 
 employ language, and is not thoroughly conscious how far he 
 
DEFINITION, DESCRIPTION. 291 
 
 is influenced by it in drawing his conclusions, will easily fall 
 into error at every step in his observations, and still more in 
 the interpretation of what he has observed, and in his inferences 
 from it. He will easily incur the risk of setting a value upon 
 his notions of a thing rather than upon the thing itself, and 
 of believing that he is speaking and judging of the latter while 
 he is, for the most part, describing only his own views. It is 
 the office of logic, however, to call attention to these and 
 similar dangers, which may arise from the nature of our lan- 
 guage and modes of expression. It is further of the highest 
 importance here to examine generally how we have arrived at 
 our ideas in natural science, and especially in medicine, and 
 why these have so often been obscure and erroneous. What 
 has already been said might suflBce to explain why language 
 plays no inconsiderable part therein, and proofs enough of this 
 will be furnished in what follows. 
 
 However this may be, language has ever been the medium 
 for the communication of all knowledge and experience from 
 the earliest times to the present day, as well in medicine as 
 elsewhere. On this account it is an indispensable auxiliary, 
 an essential means for the acquisition of knowledge. To 
 attain our end, which is the discovery and determination of 
 the actual state of things, and of the laws of the phenomena 
 and occurrences which present themselves to us, that we may 
 be able to advance sound propositions concerning them — e.g., 
 concerning a disease, or the mode of operation of a given 
 influence or remedy — we must first have acquainted ourselves 
 with all the co-operating circumstances, and have, observed 
 carefully all the cases of this kind. It will easily be understood, 
 however, that it is never possible for any individual observer 
 to do this to the necessary extent ; he is necessitated to call 
 to his aid the experience of others, and to have recourse to the 
 stores of information laid up in his department of science. In 
 short, like others, the physiologist or the physician, who seeks 
 to acquire any knowledge of the things with which he has to 
 do, or perhaps to investigate them himself, has need, at every 
 step, of the experience of others for the development aad com- 
 pletion of his own ideas, and for the guidance of his judgment. 
 How much of all his scientific knowledge would, in the end, 
 be left to an individual, if all that he has gleaned from others 
 
293 LANGUAGE, TERMINOLOGY AND 
 
 could be taken fTOm him ? But all that others can teach him 
 they give him essentially only in words, and no less is our own 
 individual experience, with the ideas and inferences we draw 
 from it, laid up in the memory in words only, to be brought 
 forward again in words when occasion may require. 
 
 Thus it is that language is the great repository or store-house 
 of everything which has been observed, investigated, imagined, 
 and discovered to the present day. In it our predecessors 
 and contemporaries have recorded their achievements, and for 
 that reason language is, to a certain extent, the sacred property 
 of each science. For that very reason, again, language is not 
 only an indispensable instrument for the education of the indi- 
 vidual, but, at the same time, also the sole link by which he 
 can connect his own experiences and achievements with the 
 general stock of knowledge in his science and art. Language 
 thus forms the intellectual bond between all men who understand 
 and employ the same tongue, as well as the technical medium 
 of communication between investigators in each science and art. 
 
 That the language of science, in particular, may render the 
 important services just alluded to, it must first of all, like, lan- 
 guage in general, fulfil certain requirements. It must, above 
 all, furnish words and expressions for everything which we 
 observe and discover, for everything concerning which we form 
 notions, and which we wish to express and communicate to 
 others : in short, wherever we are in need of special words and 
 expressionSj these ought to be at our disposal. We require, 
 therefore, a terminology — i. e., an expression for every pheno- 
 menon which we recognize through the senses, and for every 
 object, with each of the properties and modes of manifestation 
 which we meet with in the observation of it, and in the com- 
 parison of it with others. In like manner we require special 
 expressions for each individual series of such objects and phe- 
 nomena as agree, or at least appear to agree, in certain properties 
 or essential points — i. e., which are of the same kind and belong 
 to one and the same group or class. In short, we require a 
 special and complete nomenclature as it exists in the greatest 
 perfection in botany, chemistry, and other descriptive natural 
 sciences, and approximately in pharmacy and even in pathology. 
 
 It is, perhaps, more essential still, that each of these words 
 
DEFINITION, DESCRIPTION. 293 
 
 or expressions should convey exactly what we wish to assert 
 concerning the things designated by them, and that they should 
 render perfectly clear to others, what we intend to express. 
 Each individual and definite expression must, therefore, point 
 out a definite object, or phenomenon, or a certain property in 
 it ; every word must have its exact meaning, its precise and 
 definite value. No expression ought to be obscure, or admit 
 of being taken in more senses than one. 
 
 It is, therefore, in the end, not of so much importance to 
 possess a language generally, — i. e., to be able to communicate 
 in words all that we wish to express, as to do so correctly and 
 consistently. Our language must, therefore, not only be com- 
 plete, but also clear and definite enough. In fact, this preci- 
 sion may be regarded as the most important requirement, for 
 upon it depend especially the clearness and certainty of our 
 ideas and judgment, and the correctness of our inferences. 
 And this again is the first condition, the indispensable means 
 for the attainment of our final aim — i. e., the discovery and de- 
 termination of the true state of things. 
 
 All this, however, as is well known, does not hold good of 
 our technical language as it exists at present ; and the reasons 
 why this is so are intelligible enough, for they lie entirely in 
 the nature of the subject itself. 
 
 We must especially take into consideration here, that the 
 technical language of medical science, like that of any other 
 science, has not been constructed with a full consciousness of 
 the requirements it ought to fulfil, or with an adequate know- 
 ledge of the ways and means which can best lead to that end. 
 Like the whole science of medicine, it has rather arisen as the 
 offspring of necessity, almost unconsciously and instinctively, 
 and has reached us much in the same form. It sprang out 
 of the practical wants of the moment, not out of an even 
 approximately correct understanding of all the things it was 
 intended to express. Men sought to propound something by 
 its aid, not only concerning the existence and occurrence of 
 various things, but also concerning their conditions and effects, 
 their connection and essential nature, and were thus necessi- 
 tated to form a language as best they could, long before they 
 had become really acquainted with the things themselves. 
 
 Our predecessors in medical science especially, who were 
 
394 LANGUAGE, TEEMINOLOGY AND 
 
 compelled to use this language because they saw and had to 
 treat the sick, were far from being scientifically educated — i. e., 
 from possessing a knowledge of the things they observed and 
 wished to designate. They were priests, or shepherds — quacks 
 — and their observations and traditions have formed the first 
 groundwork of medicine and its language. They could not be 
 conscious what phenomena and properties, what things and 
 processes they gave names to, because they had no real know- 
 ledge of the things themselves, and were unable to form other 
 than very deficient notions of life and nature, of diseases and 
 their causes, of remedies and their effects, &c. This was as 
 impossible for them as it would be for an inexperienced child to 
 describe anything consistently and correctly, or to give it a 
 fitting name. 
 
 The earliest physicians were unable, and did not attempt, 
 by their language and expressions, to do more than make 
 certain superficial assertions concerning various diseases, inju- 
 ries, remedies, &c., as they appeared to them. And if they 
 afterwards met with anything which seemed to agree in certain 
 points with what they had previously observed, they gave it 
 the same name, without knowing whether and how far the 
 agreement was real, or only apparent. In like manner they 
 instituted comparisons between such things and certain other 
 natural phenomena, but of necessity also in a rough and general 
 way, without any real knowledge either of the one or the other. 
 They further formed from what they had observed, certain 
 general notions of the causal connection, conditions, and effects 
 of those phenomena, and even advanced general propositions 
 concerning their ultimate causes, laws, and intrinsic nature. 
 But since, in all these cases, they were compelled to confine 
 themselves to the observation of various phenomena, circum- 
 stances, and occurrences, or to what happened to make the 
 most powerful impression upon their minds, and appeared to 
 them most important and interesting, and to observe all these 
 things just as they presented themselves, without having, in 
 reality, ascertained anything definite about them, it is easily to 
 be understood why their success should not have been greater 
 than it actually was. It is also intelligible enough why their 
 language should be so full of crude and vague conceits, of 
 general and obscure allegories, for their whole world of notions 
 
DEFINITION, DESCRIPTION. 295 
 
 and views itself, bore essentially the same character, and we 
 find that this is more or less the case in the language of every 
 science. 
 
 The words and forms of expression employed by our prede- 
 cessors have, however, been transmitted to us. We have been 
 necessitated to accept their language as it stood, with all its 
 deficiencies and errors. Like other relics of earlier times, the 
 expressions once formed and taken into use have remained, 
 and with them lie dormant, stratum upon stratum, whole series 
 of views and theories, which had gradually sprung up and 
 partly died away again. These have, however, continued 
 partly active, and still exert more or less influence upon our 
 language and modes of expression, and consequently upon our 
 notions and views. For since they have ever been the symbols 
 or expression of the doctrines of a science, they have been, as 
 it were, identified and incorporated with it, and with it have 
 come down to us. 
 
 If every language is, in a certain sense, rather figurative and 
 symbolical than substantive and objective j if words express 
 our notions a.nd views of a phenomenon or object rather than 
 the latter, in itself — i. e., than what we may have been able to 
 recognize in it by means of the senses — this applies especially 
 to the technical language of medical science. Instead of the 
 things actually observed and their properties, it gives us, for the 
 most part, only symbols and the crude allegorical comparisons 
 of our predecessors, such as corresponded to their imperfect 
 notions of the things themselves. Almost every term or word 
 in medical language shows this : for example, " inflammation," 
 " fever" (ferveo), " hypochondriasis," " obstructions," " hemor- 
 rhoids," " consumption," or " irritation," " reaction,^' " anta- 
 gonism," and "sympathy." 
 
 It is, however, easy to understand that expressions of this 
 kind convey no clear meaning, nor could any such be con- 
 nected with them, simply because none existed. Moreover, 
 every attempt to eflect this is rendered more difficult by the 
 circumstance that those observations and descriptions, those 
 notions and views of earlier times, have not been transmitted 
 to us in our own, but in foreign languages, and not only in 
 foreign, but, for the most part in dead languages — viz., in 
 Latin and ancient Greek. All those expressions were adopted 
 
296 LANGUAGE, TERMINOLOGY AND 
 
 and came into use under the title of learned or technical 
 language ; and, valuable as they maybe in a scientific point of 
 view, it is no less certain that a large number of traditional 
 expressions have thus come down to us, whose foreign cha- 
 racter, in itself, renders them more obscure and inexpressive 
 than they naturally are. 
 
 The well-known half-Latin jargon, with a mixture of Greek, 
 &c., was thus, from a certain innate necessity, adopted in 
 medicine; and this was favoured by the further circumstance 
 that the man of science was better able, by such means, to 
 seclude himself from the mass of the people and their lan- 
 guage, and felt himself greater and more secure in his technical 
 wisdom. And while Gothe says, "that every schoolmaster, 
 when speaking Latin, appears to himself more distinguished," 
 similar notions have exerted more or less influence down to our 
 own times, and perpetuated the use of such a form of lan- 
 guage. With German physicians, for instance, it has continued 
 to be employed in spite of everything, although the German 
 language in particular, from its richness in root-words, is better 
 adapted than any other to the formation of technical terms. 
 Nevertheless, even in our own days, we see teachers in certain 
 countries necessitated to convey their doctrines in medical science 
 in Latin — the best means, doubtless, for the concealment of their 
 own want of knowledge, and for preventing the acquirement of 
 it by their hearers. 
 
 Those expressions of earlier times have further lost in clear- 
 ness of signification as our own notions of the things they were 
 meant to designate have, in the course of time, become changed. 
 But it has been less from our inattention to their original 
 signification than from the increase of our experience and 
 knowledge, and from the contributions of entirely different 
 sciences to the latter, that the primary meaning has become partly 
 lost to us. And this happened the more easily because those 
 expressions were from the first, and in themselves, fluctuating 
 and indefinite, and admitted of various interpretations. We 
 can thus understand how their original signification might not 
 only become changed, but even lost altogether. 
 
 Notwithstanding all this, we continue to employ them, just 
 as many potentates still bear the titles of countries and dig- 
 nities they have long ceased to possess. It is also self-evident 
 
DEFINITION, DESCRIPTION. 397 
 
 to how great an extent the daily employment of words, whose 
 proper signification had become gradually changed, or more or 
 less lost, could not fail to interfere with the clearness of our no- 
 tions and views — in short, of our whole knowledge. How could 
 empty formulse, for the most part without meaning, act much 
 otherwise? But the intellectual elements which first called 
 them into life, and imparted to them their meaning and useful- 
 ness, have, in the course of time, almost entirely disappeared. 
 The notions and views, of which they were the product and the 
 expression, have made way for entirely different ones; and, 
 whether we are fully conscious of it or not, we no longer 
 cherish or partake of them ; but the words and forms of ex- 
 pression have remained, without root in our scientific conscious- 
 ness and knowledge, and hence, again, without any real value 
 for these, but rather impeding than promoting them. They 
 are opposed to each other because our knowledge and views 
 stand in a similar opposition to those of our predecessors, who 
 first brought them into use and employed them in a sense 
 which it has become impossible for us to adopt. 
 
 It thus happens that we give names to most of the things 
 with which we have to do — diseases, the efi^ects of the influences 
 of the external world, remedies, &c. — whose primary significa- 
 tion dififers entirely from that now attached to them. By 
 these names we attribute to them certain properties, relations, 
 or causes — a certain behaviour — which we are now convinced 
 do not belong to them. In short, we no longer mean to 
 assert what the words we use convey ; their literal signification 
 involves a meaning which we no longer regard as the true and 
 correct one. 
 
 Thus, in the case of such words as inflammation, fever, 
 rheumatism, melancholy, or absorption, resolution, and many 
 others, we cannot possibly entertain the same views as those 
 who employed them some centuries, or even twenty years ago. 
 Here, therefore, as in almost every other instance, we are 
 constantly necessitated to change and modify the original signi- 
 fication of the terms we employ. With those terms we never- 
 theless often assert one thing or other concerning the properties, 
 conditions, or mode of operation of the objects we are seeking 
 to investigate, which we neither intended, nor could with truth 
 assert. And, even under the most favorable circumstances. 
 
298 LANGUAGE, TERMINOLOGY AND 
 
 our terms express only vaguely and superficially the notions 
 we form, and the assertions we are able and anxious to make. 
 We are often told, indeed, that we must not adhere to 
 words in themselves, but to their present more correct mean- 
 ing ; not to the shell, but to the intellectua,l kernel. But to 
 carry out this exceeds, in many respects, the powers of man ; 
 it is requiring of him things more or less opposed to his whole 
 intellectual nature ; for, in spite of everything, it follows from 
 the employment of such words, that their former signification 
 mixes itself as a vague reminiscence with our perhaps more cor- 
 rect notions of the phenomena and occurrences designated by 
 them. Whenever we think, utter, hear, or read such words, 
 their former signification is always, as it were, re-echoed with 
 them. For this reason, also, the continued employment of 
 such half-allegorical, figurative, or even meaningless or false 
 expressions, often exerts a much more dangerous and disturb- 
 ing influence upon our notions and views than we are willing 
 to believe. Moreover, our own insight into the processes going 
 on in the living body, and all the other things which we have 
 occasion to express in words, are so imperfect, and the views 
 and notions of physiologists, and yet more of physicians, con- 
 cerning them, still show, in many respects, so little harmony, 
 that on this account, also, the meaning of these terms must be 
 more or less fluctuating and indefinite. Not only has it 
 undergone constant changes with the advance of our know- 
 ledge, but it varies also according to the peculiar views of the 
 individual. Dissimilar ideas are often called forth in difierent 
 minds by the same word or expression, or the latter are, at 
 least, employed arbitrarily, and have various meanings attached 
 to them. It may suffice here to instance the varied and fluc- 
 tuating signification of such words as irritation, excitement, 
 crasis, poison, and many others. 
 
 Some remedy for these evils might, doubtless, be obtained 
 by the employment of such words or expressious only as desig- 
 nate things simply as they are, or rather as we observe them 
 in nature, and not as we represent them to ourselves. But 
 this is impossible, especially in our department of science, 
 because, with the exception of outward forms, we can recognize 
 next to nothing directly through the senses, least of all the 
 occurrences and processes going on, as well in the living body 
 
DEFINITION, DESCRIPTION. 399 
 
 itself, as in external nature around it. And, while our obser- 
 vation and knowledge of these are essentially rendered more 
 difficult by that circumstance, the whole precarious and fluc- 
 tuating condition of our technical language is intimately 
 connected therewith. It expresses, well or iU, the generally 
 obscure notions we entertain at the moment concerning those 
 occurrences and processes rather than the latter themselves. 
 
 These considerations are, perhaps, sufficient to show how 
 far our technical language is from fulfilling the requirements 
 above mentioned. Not only, indeed, does the confused and 
 doubtful sense of the majority of its expressions disturb, in a 
 greater or less degree, our comprehension of the objects thereby 
 denoted, e, g., diseases, &c. — and still more, the description 
 and communication of them to others, — but, on the other 
 hand, the clearness and correctness of our ideas, of our own 
 inward conceptions, and consequently our whole intelligence, is 
 thereby impaired in an equal degree. 
 
 For this reason, also, our language must be regarded, not 
 only as a somewhat inconvenient, but as a decidedly faulty 
 means of expressing our thoughts, conceptions, &c. Many 
 persons, perhaps, imagine that our right use of language 
 depends essentially upon ourselves; that, in short, it rests 
 entirely with us to use it correctly or not. And thus we 
 easily arrive at the conclusion that we rule our language, and 
 forget that, on the contrary, we — that is our conceptions, and 
 therefore, our judgment — are generally more or less ruled by 
 it. Too little stress is, perhaps, laid on the fact that by the 
 constant use and reception of certain words from our earliest 
 youth, a mass of disturbing and indistinct images has gradually 
 infused itself into our ideal world. 
 
 From this state of things, we may clearly see how it is that, 
 not only in every day life and conversational language, but 
 likewise in medicine, we rarely know what we exactly mean 
 and wish to express by the use of such and such words. But 
 the cause of this deficiency is not solely or exactly that these 
 words do not in themselves express the precise meaning which 
 we wish to convey, or that, being originally derived from in- 
 distinct, if not erroneous views, they can only excite ideas of 
 a similar nature, but rather that, in the actual state of our 
 
300 LANGUAGE, TERMINOLOGY AND 
 
 knowledge, it is impossible to attach to these words a clear 
 and definite meaning. For to this day we are very far from 
 knowing enough of the objects of our science — such for 
 example as functions, diseases, or the action of any influence 
 or remedy on the living body — to enable us to say clearly and 
 distinctly what we mean by the expressions used respecting 
 them, or what, in fact, is the exact import of our words. We 
 may, in fact, almost literally apply to ourselves the observation 
 of Seume, " that we ourselves seldom know our own real 
 meaning." 
 
 Or can any one say clearly, what he exactly understands by 
 respiration, conversion of tissues, and nutrition, or by sensa- 
 tion, innervation, mind, and similar expressions ? Is any 
 physician able to define positively what he pictures to himself 
 by the terms fever, inflammation, congestion and stasis, rheu- 
 matism, hemorrhoids, dropsy, or by rheumatico-inflammatory 
 complication, and scrofulous diathesis ? Or again, what mean- 
 ing he attaches to such general expressions as irritation, crasis 
 and dyscrasis, plethora, spasms, tone, excitement, and erethism, 
 or to words like miasma, contagion, taking cold, errors in diet, 
 and the like ? We daily hear our remedies spoken of as alte- 
 rative, solvent and deobstruent, tonic, sedative or antispas- 
 modic, and certain general conditions of the body designated 
 by the terms excitement and re-action, sthenia or asthenia, 
 weakness, constitutional tendency, disposition to disease, &c. 
 And vet no one can say what images these expressions actually 
 call up in his mind, or what peculiar meaning he attaches to 
 them. 
 
 But if no one is in a position to say so much as this with 
 regard to the words he uses, it is clear that the things denoted 
 by those words cannot be exactly known, — that our under- 
 standing of them cannot be regarded as even approximately 
 correct. Every one who uses these words is, perhaps, impressed 
 with the idea that he wishes to express such and such a meaning 
 by them, and that, consequently, he uses them in a deter- 
 minate sense. And such, indeed, may generally be the case. 
 But it is a sense void of reality, i. e., of clearness and pre- 
 cision, and cannot at present be otherwise. For the sense or 
 conception attached to such words has itself arisen in a con- 
 fused and indistinct manner, and is founded on complicated 
 
DEFINITION, DESCRIPTION. 301 
 
 and exceedingly defectivCj if not altogether erroneous, views. 
 For it is ultimately the offspring of all that we have heard, 
 read, or thought of from our earliest years, but whose correct- 
 ness neither we nor any one else have yet been able to demon- 
 strate. Continually do we see ourselves reduced to the neces- 
 sity of observing, comparing, judging, and finally of denoting 
 by words, various phenomena and processes which we under- 
 stood but partially or not at all; concerning which, there- 
 fore, we do not know whether they really take place in the 
 manner in which we represent them to ourselves, and whether 
 we are justified in saying with regard to them, that which our 
 words are intended to express. Nearly all the expressions 
 which we use in medicine are, therefore, rather to be con- 
 sidered as short descriptions, or pictorial representations, of 
 our existing and always defective and indistinct conceptions 
 of this or that matter, than as a real and truthful delineation 
 of the things themselves. 
 
 It may, indeed, be safely asserted that our technical lan- 
 guage is but, as it were, a reflection of the imperfect state of 
 our knowledge; that, in short, we have no true scientific 
 language at our disposal, simply because we have no science ; 
 that we wander about in words and phrases, just as astro- 
 logy and alchemy did some centuries ago, because we are at 
 present at about the same degree of advancement as those 
 sciences then were. Should we accord to chemistry and 
 physics the rank of sciences if they designated their pheno- 
 mena and processes as we designate ours? 
 
 But our language, instead of contributing anything to the 
 advancement of medicine to the rank of a science, and at least 
 opening the way to clearer conceptions by providing definite 
 expressions for our thoughts, does, in fact, produce an effect 
 almost contrary to this. So far, indeed, from expressing by it 
 the real nature of the objects to which its words are applied, 
 it does not even enable us to say with correctness and pre- 
 cision what we ourselves — in default of a better understanding 
 of those objects — think and imagine respecting them. To 
 expect our language to express all the objects of medical 
 science correctly and absolutely, as they exist in reality, would, 
 according to the preceding remarks, amount to exacting impos- 
 sibilities from it. For that which is beyond ourselves, that 
 
302 LANGUAGE, TEEMINOLOGY AND 
 
 which is not present to our own ideas, or contained within the 
 circle of our knowledge, can certainly not be expressed in 
 words. But so much at least may we expect from our lan- 
 guage, that it shall represent, without obscurity or distortion, 
 that which we think and know respecting those objects ; that 
 it shall not supply us with words which, for the most part, do 
 not even say what we wish to express, and consequently intro- 
 duce a meaning quite different from that which we intend, or 
 which, according to the actual state of our kuowledge, have no 
 meaning at all. Or if they have a meaning (such as the 
 expressions for anatomical, chemical, and physiological objects), 
 this meaning is nevertheless seldom sufficiently fixed and 
 definite, but rather admits of extension and contraction accord- 
 ing to individual fancy; and the greater number of our ex- 
 pressions are exactly for this reason calculated to favour obscu- 
 rity rather than understanding, or perhaps to afford the 
 means of rambling in all directions, and to arm us in our con- 
 troversies with a weapon adapted equally well for attack or 
 defence. 
 
 A language like ours always holds out the temptation of 
 supplying, in a certain degree, the want of insight and know- 
 ledge of facts, by a free and unconstrained, if not reckless use 
 of words, and by expressions and phrases which mean any- 
 thing or nothing. And this state of things is especially pro- 
 moted by the use of foreign words so frequent in German 
 science. These words, indeed, more than any others, afford 
 a hiding place and cloak for our ignorance or defective know- 
 ledge, whereas by the mere use of the corresponding words in 
 the mother tongue, the unmeaning and often absurd character 
 of our foreign words would at once be brought glaringly before 
 our eyes. Thus, like all technical terms, they expose us to 
 the danger of imagining that we understand any matter much 
 more clearly than we do in reality, and thereby stand in the 
 way of the improvement of our knowledge, indirectly at least, 
 and again in a much more direct manner, inasmuch as, with 
 such a language, we can never attain to such improved know- 
 ledge. Let any one read the first work on diseases and their 
 remedies that comes to hand, provided it does not give merely 
 the appearances actually observed, but attempts also to explain 
 them, and he will soon discover that nearly every word is a 
 
DEFINITION, DESCRIPTION. 303 
 
 mystery, an allegorical picture, perhaps a bold comparison or 
 hypothesis, or perhaps, again, totally devoid of meaning. 
 
 It is true that most writers, — ^iatro-anatomists and physio- 
 logists, for example, as well as the iatro-chemists — now clothe 
 their language more and more in the garb of a certain exact- 
 ness or scientific precision. But it is merely the shell, the 
 form, and not the kernel of a scientific language, and cannot 
 indeed be otherwise, so long as we are destitute of science and 
 sound knowledge. With all our stases and erases, and -cemias, 
 indeed, we have not gained anything very satisfactory. 
 
 Nevertheless, in the actual state of things, we can do no 
 more than accept our language as it is. It is not, indeed, in 
 the power of men to change their language altogether, and 
 still less is it allowable for individuals to introduce into our 
 technical language words which difi'er from those in general 
 use, even though they may be much more correct. More- 
 over, it is tolerably certain that we shall always have a 
 number of more or less indefinite and ambiguous words, 
 without clear and well-established meaning, because this un- 
 certainty lies, to a considerable extent, in the very essence of 
 the matter; because, in fact, the things denoted by these 
 words are themselves sufficiently ambiguous, doubtful, and 
 variable, and therefore our knowledge of, and ideas respecting 
 them, cannot easily assume a more determinate character. 
 
 AU that our logic can do under these circumstances is to 
 teach us to use even this instrument, with all its errors and 
 imperfections, as correctly and as consistently with facts as 
 possible. Its province is, in general, to show how these words 
 have come into use, how they have gradually acquired their 
 actual signification, and no other, and in what sense they must 
 be used at the present time. Only so far as all this is clear 
 and distinct to any individual, will he be able to make a right 
 use of his language, in spite of all its defects, to think clearly 
 and correctly in its words and phrases, and to express his 
 thoughts and conceptions by means of it, with the highest 
 attainable degree of perfection. And to facilitate this end as 
 much as possible, logic must further point out wherein these 
 defects, ambiguities, and obscurities in our language especially 
 consist, how they have arisen in course of time, and how they 
 may in future change their character. With equal dis- 
 
304. LANGUAGE, TERMINOLOGY AND 
 
 tinctness, too, must it warn us against every application of its 
 expressions in an erroneous sense, and thereby remove, as far 
 as possible, every tendency to error on this side, and in 
 general, every danger to which our understanding is liable 
 from the use of our language. 
 
 These considerations confer peculiar importance on certain 
 words and phrases, which aim at expressing more than others, 
 which have a more general and comprehensive meaning, a 
 higher current value in the language, and whose more particular 
 examination possesses, therefore, a twofold interest for our 
 understanding. 
 
 The words in question are those which are called collective 
 words : they play an important part in our technical lan- 
 guage, as well as in all others. Thus, for example, the names 
 and expressions for the different functions of the body (such as 
 respiration, digestion, diuresis, organization) ; or for our several 
 maladies and their causes (e. g., typhus, fever, scrofula, or 
 cold, contagion, poison, malaria,) ; or the words by which we 
 usually express the mode of action of many of our remedies 
 (e. g., tonic, solvent, astringent, caustic, &c.) 
 
 Such expressions have always been necessarily used, because 
 both observation and the deduction or formation of our ideas 
 and conceptions therefrom, as well as the practical necessity of 
 expressing them in words, equally led to their employment. 
 Moreover, certain species or series of phenomena, processes, 
 actions, and other things have been designated by the same 
 name, because they seemed to agree more or less in certain 
 essential qualities or circumstances — as, for example, the 
 several diseases, influences, remedial or poisonous actions, &c. 
 The observation of these phenomena in a certain number of 
 particular cases, and the more exact comparison of them one 
 with another, have led to the conviction that, by virtue of this 
 agreement, they are in several, perhaps in all points, regarded 
 as essentia], either perfectly similar, or, at all events, allied and 
 analogous to one another. 
 
 Whether and how far this conclusion is correct in individual 
 cases, may for the present be regarded as indifferent. It is 
 sufficient to know that the observation and comparison of these 
 phenomena has led to their being regarded as essentially and 
 
DEFINITION, DESCRIPTION. 305 
 
 completely identical, or as nearly related and similar, or gene- 
 rally as connected together. Phenomena thus related have 
 been designated by the same name, and thus have arisen the 
 collective terms of medicine and physiology, as well as in 
 ordinary language — e. g., the words "weather, vegetables, 
 fruit, corn ■" or " noble, aristocrat, gentleman, citizen ;" or 
 " intelligence, virtue^ vice," &c. By a process essentially 
 similar, also, the descriptive natural sciences^ such as botany, 
 zoology, and others, have arrived at their names of species and 
 orders; and chemistry at such expressions as metal, alkali, 
 base, acid, salt, &c. 
 
 In thus designating certain series and instances of pheno- 
 mena or objects with one and the same name, we at the same 
 time express our conviction that they are more or less of the 
 same kind, or even perfectly identical. For in our ideas, in 
 our mode of representing these phenomena to ourselves, and 
 thinking about them, they are actually regarded as such. At 
 the same time we give a sort of provisional definition of them, 
 and establish a kind of grouping or classification of the things 
 themselves ; or at all events, we make the first step towards it. 
 We do, in fact, declare respecting them, that they are related, 
 and perhaps identical, and that, on account of this resemblance 
 or identity, we denote them by the same name. 
 
 Moreover, this use of collective words is perfectly correct 
 and well founded, provided always that the objects thus desig- 
 nated be really, as we suppose them to be, similar, and related 
 to each other, which is certainly the case with the species and 
 genera of the zoologist, the botanist, or of the chemist, as ex- 
 emplified in the words vegetables, fruit, food, &c. ; more or 
 less, also, in the names of certain diseases — e. g., syphilis, 
 small-pox, intermittent fever, &c. The correctness of collective 
 words of this kind requires, therefore, that such things only 
 shall be classed together, and designated by the same name, as 
 actually agree together in all, or at least in certain essential 
 points. And, on the other hand, all those must be excluded 
 which differ in these particulars, and, perhaps, on account of 
 their properties, or their internal relations, or from any grounds 
 whatever, belong altogether to another species. 
 
 But it is precisely this most essential requirement that, in 
 the present state of our knowledge, as formerly remarked in 
 
 20 
 
306 LANGUAGE, TERMINOLOGY AND 
 
 speaking of comparisons and analogies, we are, comparatively, 
 but rarely able to satisfy ; so soon, at least, as we have not to 
 deal with objects, processes, &c., which are exactly of the same 
 kind — e. g., with one and the same function, disease, or external 
 influence, or, in general, with things which are united by 
 nature in a group or ensemble, and precisely for that reason 
 may be recognized as such by an ordinary observer. And if 
 this proof of the actual agreement of things which we classify 
 together is seldom enough possible, even at the present day, it 
 is easy to understand that such proof must have been still more 
 difficult to obtain at the time when these collective words and 
 names first came into use. Those, indeed, who originally em- 
 ployed them, far from being acquainted with all the points, 
 qualities, and circumstances, which the objects included in the 
 collective name or idea might possess in common, and conse- 
 quently designating those objects by a common name by reason 
 of such knowledge, were guided rather by a confused and 
 uncertain imagination and supposition of their resemblances, 
 or by an arbitrary a priori assumption of them. Such suppo- 
 sition or assumption might indeed be right, but it might just 
 as well be wrong, and completely opposed to the actual state of 
 the matter. For, inasmuch as we can never attain to a correct 
 understanding of the equality or similarity of our objects, pro- 
 cesses, &c., from any a priori considerations, but solely by 
 fixing their common points from observation and experience, it 
 is clear that, when this experience was wanting, there could be 
 no solid foundation for any theory or classification : at all 
 events, no actual proof could be given, and so, indeed, the 
 matter has essentially remained up to the present day. 
 
 Such, for example, is the case when we designate certain 
 classes of morbid states or attacks by the same word, such as 
 scrofulous, rheumatic, gouty, &c. ; or as epilepsy, inflamma- 
 tion, leprosy, plague, dyspepsia, hemorrhoids, and the like. 
 For in thus giving the same name to states and disturbances of 
 various kinds, we likewise attach to them one and the same 
 predicate ; we declare, in fact, that in certain essential points, 
 especially in their mode of production, their conditions, and 
 their internal organization, they exhibit a general agreement. 
 And yet our understanding does not readily supply us with the 
 proofs required to establish this agreement ; indeed, we rather 
 
DEFINITION, DESCRIPTION. 307 
 
 arrive at our idea of their similarity or identity by certain re- 
 semblances of external appearances and symptoms, or of their 
 origin, progress, and the lilce. In like manner have our names 
 for the similar or analogous modes of action of our remedies on 
 patients been formed j such, for example, as " antiphlogistic, 
 alterative, solvent, tonic or strengthening, stimulating, purga- 
 tive," &c. It has always been imagined that the favorable 
 alterations and gradual cures, in inflammation, tumours, indu- 
 rations, &c., or in various states of weakness, &c., were more 
 or less brought about by the different remedies as they succes- 
 sively came into use. For that reason they were called anti- 
 phlogistics, antispasmodics, tonics, &c. 
 
 These words, however, could not be the symbols of any 
 clear, definite notions, because they had not been arrived at by 
 the road of sure experience ; because, in fact, it had not even 
 been demonstrated that those remedies would generally act in 
 the manner assigned to them, and still less that the mode of 
 action in certain essential points would be the same in all, or 
 in many of them. It was rather imagined that their mode of 
 action was of such and such a character, because they were 
 found to cure certain diseases ; and as this conclusion rested 
 on no other grounds, it became, as it were, necessary to 
 regard the mode of action of these remedies in such a manner, 
 and to make such suppositions respecting it as were most con- 
 sistent with the actual views entertained regarding the cause 
 and so-called essence of the disorder which they were used to 
 cure. And as, in the course of time, the views upon these 
 latter points changed, so likewise did the theories entertained 
 regarding the action of the remedies change, for better or for 
 worse, with them. 
 
 So one, for example, who regards hemorrhoids as essentially 
 produced by obstructions, and the like, in the hepatic circula- 
 tion, by infarctus, &c., the action of remedies employed against 
 that malady will appear in quite a different light to that in 
 which it will be regarded by another, who looks for the origin 
 of the disorder in a disturbance of the nervous system or of 
 the digestion. For, while the former ascribes to them a " dis- 
 solving purgative" action, the other thinks, perhaps, on their 
 favorable action on this or that province of the nervous system, 
 on the process of digestion, &c. The former would perhaps 
 
308 LANGUAGE, TERMINOLOGY AND 
 
 describe his remedies as " resolving ;" the latter as " antispas- 
 modicj" sedative, or strengthening. 
 
 Thus the followers of Hippocrates and the Arabs entertained 
 quite different notions upon all these matters to those of the 
 Galenians, for example, and consequently used totally different 
 names and expressions ; and, in a similar manner, a disciple of 
 Broussais differs from a pathologist of the present time ; a 
 so-called nerve-pathologist, again, from a humoral patholo- 
 gist ; and a modern chemico-physiologist talks, perhaps, of the 
 antiseptic, anti-fermenting, or oxidation-stimulating action of his 
 remedies. But that our remedies act exactly thus and not 
 otherwise, and that they have therefore an exclusive right to 
 this or that predicate, this or that name, has not yet been 
 demonstrated by the moderns any more than by their prede- 
 cessors. 
 
 It is otherwise with the action of many substances on 
 healthy persons, provided these actions take place with suffi- 
 cient distinctness and constancy ; as, for example, in the case 
 of laxatives and emetics, or of caustic, acrid, or narcotic sub- 
 stances, and the like. Such substances form definitely bounded 
 groups or species of essentially the same action; they possess, 
 therefore, essentially equal or similar properties, and are rightly 
 called by the same name. 
 
 If, now, our knowledge is to be furthered by the use of such 
 words and phrases, we must, in the first place, be able to say, 
 from positive experience of the groups or kinds of phenomena, 
 actions, or objects thereby denoted, that they do actually agree 
 in all the points and qualities which their collective name 
 expresses or involves. This, however, according to what pre- 
 cedes, we are seldom able to do completely. Experience 
 rather shows that we often enough regard totally different 
 morbid states, actions, &c., as essentially the same, taking 
 them for a kind of unity, and accordingly denoting them by 
 the same word, merely because, at the first view, and from a 
 superficial or inexact observation and comparison of their 
 symptoms, progress, and so forth, they appear to agree more or 
 less in certain properties and circumstances. Moreover, we 
 have habitually laid the greatest stress on such of their pro- 
 perties, and on such points and relations as appeared to us to 
 be the most important, and best capable of affording a standard. 
 
DEFINITION, DESCRIPTION. 309 
 
 in short, as the most essential. But we have scai'cely ever 
 been able to give any proof of this — that is to say, whether 
 and how far the qualities and relations so selected were in 
 reality such as we supposed, and whether and how far, there- 
 fore, the objects themselves were rightly classed together and 
 denoted by the same name. And because in this, as elsewhere, 
 there has always been a want of a sufficiently sure basis for 
 our notions and judgments, and of a well established under- 
 standing, and consequently, also, of fixed principles for the 
 union or separation of our objects, each one has gone his own 
 way, according to his own preference and inclination. 
 
 That our collective words must from this cause suffer much 
 greater loss of clearness and precision than any of our other 
 expressions is perfectly evident, and the confusion of our ideas 
 of the things thereby denoted is likely to be increased in an 
 equal degree. Names of diseases, such as nervous fever, 
 plague, consumption, dropsy, rheumatism, epilepsy, are used 
 sometimes in one sense, sometimes in another, and conse- 
 quently the same states are denoted with this word by one 
 person, with that by another, so that no one knows exactly 
 what he has before his mind, and wishes to designate, and why 
 he designates it by a certain expression and no other. Simi- 
 larly we daily use such words as " strengthening, tonic, solvent, 
 purgative, astringent, stimulating, exciting, &c., in the most 
 various ways. Almost every one accepts them with peculiar 
 limits and in a peculiar sense ; and even one and the same 
 expression is used, according to circumstances, in anything but 
 a uniform sense. Thus one may say of good wine, of cold 
 bathing, or fresh air, that it exerts a strengthening action, and 
 the same may be said of nutritious diet, of cinchona-bark, and 
 various bitter substances. They may, indeed, all and severally, 
 in a certain sense, exert an action of this kind ; but it is equally 
 certain that in each one of these means and influences, the 
 action must be of a peculiar kind, distinct from that of others. 
 We use then the same word in different senses, as applied to 
 wine, to fresh air, to cinchona, and to roast meat. And the 
 same may be asserted more or less of all collective words of 
 this kind used in medicine. 
 
 To this it must be added, that these words, in consequence 
 of their wider and less defined sense, are much more liable than 
 
310 LANGUAGE, TERMINOLOGY AND 
 
 others to change in course of time. Their meaning has been 
 sometimes extended, sometimes restricted, according to the 
 increasing experience and insight, or to the theories and 
 caprices of individuals. Thus we now apply the terms tubercle, 
 inflammation, typhus, paralysis, cancer, or narcotization, tonic 
 treatment, &c. — in the former case to morbid conditions, in 
 the latter to certain modes of action which were formerly not 
 referred to the same classes, and therefore not denoted by those 
 words, possibly because they were not then sufficiently well 
 known, or that the views entertained respecting them were 
 totally different from those of the present day. And, on the 
 other hand, we now no longer apply to many diseases such 
 terms as nervous fever, epilepsy, paralysis, and other so-called 
 idiopathic nervous affections, but rather call them pneumonia, 
 phlebitis, tuberculosis, or softenings, pressure, &c., upon the 
 brain or spinal marrow, because we have become acquainted 
 with certain anatomical changes connected with those diseases, 
 and these changes are regarded as the essential conditions of 
 the diseases in question. In like manner, many substances 
 and remedies which were formerly spoken of as tonic, astrin- 
 gent, diffusive, &c., are now no longer designated by such 
 terms, because further experience has shown that their action is 
 of a different character. 
 
 But the chief misfortune connected with these and other 
 expressions of technical language is, that they have long been 
 used in a certain, though obscure and ambiguous sense. And, 
 however ill-adapted, or even faulty and confusing they may 
 afterwards be found, it is very difficult to alter them, or even 
 to get rid of their signification — i. e., of the images and notions 
 formerly connected with them. 
 
 But here, again, arises further opportunity for their confu- 
 sion and obscurity, there being frequently a direct contradiction 
 between what we mean and wish to express, and that which the 
 words we use actually convey. 
 
 Par more important, however, is another consequence to 
 which these collective words and their use have led almost of 
 necessity — viz., to a kind of materialization or embodiment of 
 the ideas and images therewith connected, making them into an 
 actually existing thing (Ontology, Realism). 
 
DEFINITION, DESCRIPTION. 311 
 
 Thus from all the appearances manifested by patients suflfer- 
 ing under the same disease, a certain homogeneous picture of 
 this disease has been put together ; or, in other words, the idea 
 of typhus, intermittent fever, scrofula, &c., has been abstracted 
 from these appearances. In like manner, from the actual or 
 so-regarded efifects of all sudorific, diuretic, or antiphlogistic 
 remedies, the idea of diaphoresis, diuresis, antiphologosis, &c., 
 has been constructed and embodied. Thus, on the one hand, 
 in place of the individual concrete, patients exhibiting such and 
 such phenomena ; and, on the other hand, in place of the indi • 
 vidual actions of certain remedies, a certain idea and abstract 
 image, applicable to all, has been substituted — a kind of self- 
 existent thing or being (Ens) with its particular name. For, 
 in our imagination, we have gradually accustomed ourselves to 
 regard this idea as in a manner separated from the phenomena 
 exhibited by certain patients, which phenomena originally led 
 us to that idea and its construction. 
 
 A precisely similar series of changes has been exhibited by 
 the formation of our language and ideas with respect to other 
 matters, in ordinary life, as well as in other technical lan- 
 guages, because, in fact, it is necessitated by the nature of 
 things, and more especially of our intellectual capacity. For 
 example, just as we have arrived at the ideas and names of 
 Beauty, Virtue, Conscience, Honour or State, Law and Oppo- 
 sition, the physicist has also arrived at his abstract conceptions 
 and names of Galvanism, Magnetism, Electricity, Light, Heat, 
 Cold, Wind, Storm, &c. 
 
 In this, as in every case, partly for the sake of convenience 
 and brevity, partly in consequence of a certain carelessness, we 
 do not think clearly enough how we have arrived at these ideas 
 and modes of expression. To the names themselves (e. g., 
 typhus, diuresis) we now attach certain qualities or predicates, 
 which belong, in reality, not to them, but rather to the pheno- 
 mena, processes, or actions, from which these ideas have been 
 derived : of the latter, in fact, we predicate that which should 
 really be said of the former. Thus, we speak of a typhus, an 
 inflammation, tuberculosis, or epilepsy of a patient, and not of 
 a patient sufiering under certain disturbances comprised in 
 those ideas and words. We now speak of symptoms and qua- 
 lities, of certain peculiarities of the disease, not of the patient ; 
 
312 LANGUAGE, TERMINOLOGY AND 
 
 of certain properties and actions, of antiphlogosis, diaphoresis, or 
 tonic treatment, and not of the substances or means which have 
 been used and observed. In like manner the physicist speaks 
 of electricity, heat, wind, and weather, and ascribes to them 
 certain properties and effects, just as, in ordinary discourse, we 
 speak of virtue, conscience, honour, or of art and science, law, 
 and state, as something actually existing, and of what the one 
 commands, the other forbids, &c. Thus, instead of saying that 
 a heated or cooled body behaves in such and such a manner 
 
 e. g., expands or contracts — we say, it is a property of heat 
 to expand bodies, and of cold to contract them. 
 
 Here, as in the former case, a certain ideal picture, an 
 abstract conception, of heat, for example, in the one science, 
 or of typhus, &c., in the other, is formed and perfected, and 
 this image we then represent to ourselves as clothed with the 
 attributes which, under certain circumstances, have been ob- 
 served in a substance or in a patient. In our thoughts and 
 imagination, the two have become so united and amalgamated, 
 that we now attribute to our abstract conception, all that in 
 reality belongs only to the substances, men, &c., wherein these 
 phenomena, processes or properties are exhibited. And just 
 as the physiologist, for example, says of respiration, digestion, 
 &c., that it goes on in such and such a way, is abundant and 
 in order, or scanty and disturbed, so likewise does the physi- 
 cian speak of the origin of a disorder, of its first appearance, 
 character, progress, &c., that they exhibit certain peculiarities. 
 In short, he treats his idea of the disorder as if it were an 
 actually existing thing, instead of being the creature of his 
 own imagination and mode of thinking upon it. He makes 
 his disease increase and decrease, become complicated, change, 
 exhibit periods, and intermissions, &c. Thus it is said to be a 
 property or peculiarity of " inflammation" to arise and progress 
 with fever, to have or to produce the so-called buflfy blood, to 
 form such and such exudations and products, to be malignant 
 or non-malignant, to come to a crisis, or continue long uncer- 
 tain ; perhaps even to become nervous or gangrenous. And 
 if a patient has become ill from any action, direct or indirect, 
 of patients of the same kind, if, for instance, he has contracted 
 itch, syphilis, plague, or small-pox, then the disease itself is 
 said to be of contagious character, and we speak, moreover, of 
 
DEFINITION, DESCRIPTION. 313 
 
 a certain something or principle that originates it — i. e. of its 
 " contagium." Similarly again, we speak of the treatment of 
 a disorder — for instance, of measures directed against inflam- 
 mation of the lungs, typhus, &c., and how this or that remedy 
 is required or "indicated" by them. The remedies are, in 
 fact, supposed to act upon the disorder, not upon the patient, 
 and we speak of specifics against syphilis, gout, intermittent 
 fever, &c. 
 
 In short, the idea which we have formed from the observa- 
 tion of certain phenomena, actions or processes, and from our 
 conclusions and theories respecting them, identifies itself to a 
 certain extent in our imagination with the observed phenomena 
 and objects themselves ; we confound the two from habit, and 
 because we do not clearly enough remember or consider the 
 actual relation of the matter. And this due consideration, 
 again, we generally omit, because the very names and forms of 
 expression which we apply to those phenomena, &c., entice us 
 to such omission, — especially our substantive-words (such as 
 typhus, electricity, heat, or astringency, antiphlogosis, diapho- 
 resis, &c.), in which our ideas have been, as it were, clothed 
 and embodied. The idea once separated and embodied — that 
 of a disease or a remedy, for example — we can no longer 
 imagine it without certain properties, without such and such 
 kind and peculiarity of appearance or action, &c,, any more 
 than we can make such abstraction with regard to any other 
 object which we actually perceive, or of whose existence we 
 have otherwise any knowledge. For our knowledge and idea 
 of an actual object is likewise arrived at by the perception of 
 a certain kind of appearance and relation, and of certain pro- 
 perties belonging to it. A botanist, for example, cannot think 
 of a rose or a pink, a zoologist of a raven or a monkey, or a 
 chemist of an acid, metal, or salt, without ascribing to it cer- 
 tain properties, such as form and structure in one case, com- 
 position in another, &c. And just in the same manner a 
 physician cannot think of typhus, diaphoresis, and the like, or 
 a physicist of heat, light, or electricity, without connecting 
 with them certain qualities or attributes. 
 
 There is, however, this essential difference, that the objects 
 with which- the botanist, chemist, &c. has to deal, are actual 
 bodies, certain really existing, and definite forms or substances, 
 
314 LANGUAGE, TERMINOLOGY AND 
 
 which is not the case with those into which the physician has 
 to inquire. And because states of disease, such as typhus, 
 and scrofula, or modes of action, such as diaphoresis, anti- 
 phlogosis, &c., never actually exist as such, -and because the 
 very phenomena and properties which lead to the idea of those 
 conditions, effects, &c., cannot even be directly observed, and 
 moreover, are anything but constant, it is not possible that 
 the words above mentioned should denote a uniform, homo- 
 geneous object. For the same reason, it has hitherto been 
 impossible to connect with the word " typhus," &c., any clear, 
 definite, and constant meaning. For the abstract idea of 
 typhus, &c., has itself been arrived at in an indistinct and 
 generally uncertain way, and by a kind of confusion or ignoring 
 of the real state of the case. 
 
 It is true that in the daily use of these words and ideas, 
 the uncertainty in question is easily overlooked, and we use 
 them as if their meaning were always the same. We think, 
 perhaps, that we always use them in the same sense, whereas, 
 in reality, different persons use them in different senses. Thus, 
 accordingly as one man has seen, read, or heard of this 
 typhus-patient, another of that, each will thence have deduced 
 his own particular idea of typhus, and therefore each will use 
 the word in a different sense from the other. Many an attack 
 of disease may be regarded as typhus by the one, while the 
 other may apply to it quite a different name. And one 
 who, with respect to inflammation, lays the greatest stress on 
 certain symptoms, such as fever, pain, or a certain state of the 
 blood, — an increase of fibrin, for example, — or on the forma- 
 tion of certain exudations, &c., will deny the applicability of 
 the term inflammation to many states of disease in which 
 these symptoms are wanting, whereas another may consider it 
 fully applicable. 
 
 Moreover, our experience and knowledge with regard to 
 such diseases, and the effects of various influences, medica- 
 ments, &c., are constantly progressing, and consequently our 
 views thereupon must undergo continual variation. For ex- 
 ample, in typhus-patients, in inflammation, certain processes 
 and peculiarities {i. e. anatomical, physico-chemical, and micros- 
 copical) have been made out, which formerly were unknown. 
 And, on the other hand, it has been ascertained that many 
 
DEFINITION, DESCRIPTION. 315 
 
 phenonlena and processes, which were regarded by our prede- 
 cessors as characteristic, essential, and determining, are rather 
 of accidental and subordinate character, or at least, that they 
 occur in the same manner in patients of a totally different 
 class (e. g. fever, certain disturbances of the nervous system, 
 the formation of certain exudations, &c.). 
 
 Just as likely is a case to arise in which this or that ap- 
 pearance and property, which we had hitherto regarded as 
 constant and characteristic, is altogether wanting. In our 
 imagination we have always regarded these characters as essen- 
 tial members and indications of a disorder such as typhus, for 
 example, and now all at once we miss what we have been ac- 
 customed or had expected to see. We are thereby thrown into 
 perplexity and doubt, as to whether these anomalous cases should 
 or should not be designated by the same name as the rest. 
 
 Any one, for example, who from previous experience has 
 been led to believe that in typhus-patients, diarrhoea and in- 
 testinal ulcerations, or a certain exanthema, violent headache, 
 and delirium, &c., are constant, and even essential phenomena, 
 would not know exactly whether to include in the same class, 
 other patients, who, in many respects, exhibit the same symp- 
 toms, but without the diarrhoea, ulcerations, or exanthema 
 observed in the former. The same difficulty would occur to 
 the physician on meeting with a scrofulous patient without 
 swollen glands in the throat, &c., a patient attacked by some 
 inflammation without fever, pain, the so-called buffy blood, &c., 
 or in general with patients without those peculiar symptoms 
 and changes to which he had previously attached the greatest 
 importance, and without which he had not been accustomed 
 to suppose the particular malady to exist. In the same manner, 
 a zoologist, previously acquainted only with black-feathered 
 ravens, having a peculiar form of the beak, toes, &c., might, 
 on seeing other ravens with grey feathers, or a somewhat 
 different beak, be in doubt whether to include them in the 
 species " Raven" or not. 
 
 If, however, it should appear, on further examination, that 
 even these latter patients, in spite of such and such deviations, 
 agree, nevertheless, with other typhous, scrofulous patients, &c., 
 in many other and perhaps essential points, they must, not- 
 withstanding all those contradictions, be designated by the 
 
316 LANGUAGE, TERMINOLOGY AND 
 
 same name. For we have but one word for such patients. 
 When, however, we apply the same words also to patients ex- 
 hibiting the anomalies just noticed, we feel that we are not 
 using it in the same sense as before, because, in fact, the 
 picture presented to us by such patients contradicts, in many 
 respects, our former and accustomed notions. And just as 
 the zoologist, botanist, &c., under similar circumstances, forms 
 his species together with varieties and sub-species, so likewise 
 does the pathologist establish many sub-species and transi- 
 tional forms of his diseases. He speaks, for example, of exan- 
 thematous, contagious, and abdominal typhus, of scrofulous, 
 rheumatic, gouty inflammation, of catarrhal or typhoid pneu- 
 monia, of syphilitic and scrofulous eruptions on the skin, of 
 nervous and pituitous consumption, &c. 
 
 But in course of time the variously modified and variable 
 sets of phenomena exhibited by such patients become amalga- 
 mated, and grow, as it were, in our imagination, into one 
 picture. We abstract or form to ourselves, out of all these 
 varying and manifold forms and accidents, a more general and 
 comprehensive idea — e. g., of typhus, inflammation, &c., just 
 as the zoologist or botanist forms the idea of a genus. 
 
 Since, however, this general idea, still more than that of an 
 individual disorder, is developed in an undefined, if not con- 
 fused manner, from all the varying appearances, changes, &c., 
 exhibited by those patients, taken together — from all, in fact, 
 that has successively been seen, heard, or read concerning 
 patients suffering from typhus, scrofula, &c. — our conception of 
 it must be more or less confused and variable. Moreover it 
 is seldom, if ever, possible to make our observations on all the 
 patients designated as typhous, gouty, scrofulous, epileptic, &c., 
 or to examine and compare their several conditions in such a 
 manner and to such an extent as to discover that which is 
 constant and common to them all, much less that which is 
 actually characteristic and determining. On this account, we 
 are often unable to form a positive judgment as to whether 
 and how far such and such phenomena, changes, &c., regarded 
 as constant and essential, occur in all these patients, whether 
 such phenomena arise or may be determined in the same way 
 in all, and possibly have the same signification for the whole 
 course of their disease. 
 
DEFINITION, DESCRIPTION. 317 
 
 For this reason, every one must, for better or for worse, 
 confine himself to those appearances and circumstances whereby 
 he himself has been led, according to his own experience or 
 theoretical views, to designate these attacks of illness as typhus, 
 scrofula, &c. But these phenomena and circumstances them- 
 selves are, as already observed, of exceedingly variable and 
 uncertain nature, may sometimes be present, sometimes not, 
 or may exhibit themselves under the most various modifications 
 and combinations. And yet, in our ignorance of the particular 
 conditions, of the internal connection or conformity of those 
 states of disease, our observation and comparison, and therefore 
 our judgment, can rest only upon their external appearance, 
 or, as it were, on their upper and exterior surface, e. g., on 
 certain symptoms of general or local character and their progress, 
 on certain anatomical or chemical changes, on the constitution 
 and general character of the patients, &c. Hence it follows 
 that no one has a comprehensive, clear, and exact notion of 
 those maladies — i. e., such a notion as would have been derived 
 from actual understanding of them. And just as little, as 
 above noticed, can any such expressions as typhus, inflammation, 
 scrofula, &c., be used by all in one and the same sense, or 
 excite in all the same image, the same idea, because almost 
 every one has his own ideas on the matter, according to his 
 particular experiences and views. 
 
 Unless, therefore, the case is perfectly distinct and well 
 characterised, two physicians will scarcely agree in their 
 diagnosis and consequently in their denomination of it, and in 
 the several points relating to it. Even the same physician may 
 at different times arrive at different conclusions respecting it", 
 according to his further experience, his age, and the theories 
 and points of view which he successively adopts. 
 
 The same is true, indeed, with respect to all the influences 
 which act on man, as with respect to the action of our remedies 
 and their denomination, so long as we are deficient in a sound 
 understanding of them ; in fact, our ideas, interpretation, and 
 judgment of them, must vary continually with our knowledge 
 and experience. 
 
 It is, as already observed, scarcely possible to make any 
 radical improvement or alteration in the form and manner of 
 
318 LANGUAGE, TERMINOLOGY AND 
 
 our expressions, and their use. They are bound up with the 
 very nature of the matter, and ultimately with the entire con- 
 formation of our intellectual nature, and especially with the 
 origin and derivation of our ideas, as much as with the defec- 
 tive state of our knowledge. 
 
 Hence, also, we may understand how it is that many oppo- 
 nents and sharp critics of these modes of expression and repre- 
 sentation nevertheless make use of them, and thus, in spite of 
 all their criticism, ultimately fall into the very error which they 
 condemn. All that an individual can do under existing circum- 
 stances is, to make out clearly the real meaning of his expres- 
 sions, how he has arrived at them, and, finally, how he is to 
 use them in their true sense, and in a proper manner. 
 
 But, on the other hand, it follows from the very nature of 
 the thing, that general terms and ideas, such as ours, the exact 
 meaning of which no one is able to determine, cannot possibly 
 admit of precise or rational definition. We can say, indeed, 
 what view we take of the things to which we apply those 
 terms, and in what sense we employ them and wish them to be 
 employed by others ; but we are unable to say whether and how 
 far we are right, so long as we are deficient in a clear and defi- 
 nite understanding of the things themselves. 
 
 Nevertheless, neither science and its language, nor any in- 
 dividual for himself, can avoid making an attempt at such 
 limitation ; and this attempt at a more exact fixation and 
 limitation of the sense of our words constitutes definition. We 
 thereby state, in few words, our theory, our confession of 
 faith, on the objects and phenomena thus designated — e.g., on 
 a disease, on the properties and effects of a medicament, &c. 
 Very many words, indeed, contain a kind of definition within 
 themselves, — e. g., " disease, poison, malaria, food, remedy ;" 
 also "intermittent and nervous fever, melancholy, tonic, as- 
 tringent," &c. It is likewise self-evident that the possibility 
 of such a definition implies a previous examination and com- 
 parison, a certain knowledge, in fact, of all the objects denoted 
 by the same word. We must first determine their more im- 
 portant and characteristic qualities, and all the more essential 
 circumstances relating to them, before we can define them in 
 such a manner as to say what they are, and wherein they 
 consist. 
 
DEFINITION, DESCRIPTION. 319 
 
 This end is most easily attained in the descriptive natural 
 sciences, such as botany, zoology, anatomy, &c. ; for all that 
 these sciences require for the definition of their objects they 
 are able to observe more or less directly and comprehensively. 
 With nearly the same certainty, and partly for the same 
 reasons, the physicist and chemist may form their definitions ; 
 partly, also, because they are more or less acquainted with the 
 causal connection and order of succession of many of their 
 objects and phenomena. Thus they can state in a few words 
 what they mean by heat, light, electricity, gravitation, or by 
 oxygen, carbon, alkali, acid, or by oxidation, combustion, fer- 
 mentation, and the like, and are therefore able to define these 
 words with more or less clearness and certainty. 
 
 But it is quite otherwise with our science, because we can 
 give no correct and admissible definition of things which we 
 know but inexactly and, as it were, from without. For this 
 reason, indeed, we can scarcely flatter ourselves that we are 
 able to give a precise definition of any process in nature, but 
 least of all is this possible with regard to the phenomena and 
 processes of the living body. For we have never been able to 
 observe these things either in healthy or in diseased subjects, 
 directly and in their whole extent, but have rather been com- 
 pelled, from the little that we have observed, to draw conclu- 
 sions respecting the rest, and, in fact, the greater part. Hence 
 our definition, like our knowledge, can only relate to and rest 
 upon so much of a function, disease, medicament, &c., as is 
 known to us, or as may appear, in the imperfect state of our 
 knowledge, to be the most constant or determining and essen- 
 tial. But whether, and to what extent, this is true, we know 
 not, and we are unable to prove. 
 
 We are, therefore, not in a position to give a perfectly correct 
 and admissible definition of anything in the whole circuit of 
 life, either a function, a disease, or any individual process, or of 
 the effects of any external influence on the living body, or of 
 any medicament upon a diseased person. In the one case, as 
 in the other, we know far too little of their conditions and 
 laws of origin, or action, to enable us to extract therefrom any 
 exact definition. 
 
 For example, we have as yet no precise knowledge of all the 
 phenomena and conditions, or processes, which a patient must 
 
320 LANGUAGE, TERMINOLOGY AND 
 
 exhibit to justify us in designating him as typhous, scrofulous, 
 arthritic, epileptic, &c. And still less can we state with cer- 
 tainty in what essential points all the patients or disorders 
 agree, which we have denoted by the same word, typhus, 
 scrofula, gout, epilepsy, &c. We do not know with certainty 
 what kind of conditions, what peculiar processes are present in 
 them all, or whereby, and according to what laws, they have 
 been produced and have progressed. Our idea of them is 
 based rather upon a sort of general and more or less super- 
 ficial impression of resemblances in these several patients, on 
 their agreement in certain points and symptoms which appear 
 to us as the most important and essential, and perhaps are really 
 so, more or less, but cannot with certainty be established as 
 such. And if, in our diagnosis, we would designate a new 
 case by such and such a name, there is nothing left for us but 
 to fix the attention on those resemblances, to follow out the 
 appearances exhibited by the patient before us as well as we 
 can, to compare, and lastly, to make out in what points he 
 may agree with this or that earlier conception and picture of 
 a disease. We then include him under that one among them 
 which he appears most nearly to resemble, especially in those 
 points which we regard as most important, and give him a 
 name accordingly. But with actual understanding of the 
 matter, and consequently with characteristic definition, we are 
 here not much concerned. 
 
 The preceding observations likewise point out and explain 
 why we are less able to give satisfactory definitions in propor- 
 tion as the objects, or our ideas of them, which we wish to 
 define, are more complicated and less distinct. Least of all 
 can we attain to any rational and correct limitation of ideas 
 respecting those collective words whereby we are accustomed 
 to include entire and manifold series of phenomena, processes, 
 actions, influences, &c., — e.^., a definition of typhus and anti- 
 phlogosis, or of organism and organization, of life and disease, 
 cure, medicament, or of contagion, miasma, malaria, constitu- 
 tion, and the like. We are as yet acquainted only with sepa- 
 rate elements and parts, with particular sides of this vast group 
 of effects or causes ; we know but fragments of them, and 
 these by no means perfectly. It is therefore impossible for 
 us to determine anything with certainty and perfect correct- 
 
DEFINITION, DESCRIPTION. 331 
 
 ness ; what, for example, is true with regard to all the pro- 
 cesses going on in and peculiar to the living body, that is to 
 say, with regard to life generally and in itself j or, again, with 
 regard to all diseases, medicaments, and their properties, &c. 
 We can, indeed, predicate this or that universal or common 
 property respecting them, and perhaps, under the most favor- 
 able circumstances, may make some degree of approximation 
 to the truth. But we cannot give a definition of them founded 
 on a comprehension of their laws and all essential circum- 
 stances relating to them, and therefore worthy to be regarded 
 as convincing and satisfactory, and to remain for ever un- 
 doubted and uncontested. 
 
 Such a result may perhaps be attained, at least approxi- 
 mately, in the purely descriptive natural sciences, and even in 
 physics and chemistry, but certainly not in medicine. Instead 
 of actually defining our several varieties and series of aggre- 
 gates of effect or cause — e.g., of all vital processes, diseases, 
 &c., and thereby predicating something respecting the laws 
 which they possess in common, we find, on making the attempt, 
 that we can define or describe the former only in short words. 
 We must not, therefore, think of an exact fixation or state- 
 ment of our ideas respecting them, but only of a more or less 
 correct but limited description of what we have observed in 
 connection with them, that is to say, of those phenomena, 
 effects, and circumstances, so far as they may be known to us, 
 and regarded as the most constant and essential. 
 
 But, on the other hand, we find it impossible to renounce 
 altogether this wish to define the objects of our investigation. 
 The requirements of our intellectual existence, as well as of 
 language and communication, lead every one to this as well as to 
 a general wish to understand the operations of nature. And 
 accordingly we make out our definitions in the best way we can. 
 As in other cases, we thereby express shortly and plainly our 
 confession of faith, our theory respecting a disease, function, 
 morbid influence, action of a remedy, &c., and accordingly 
 rest our definition on all the points and circumstances con- 
 nected with it which appear to us to be the most constant and 
 essential, in short, as the pith of the matter. 
 
 But our view of these circumstances changes continually 
 with the point of view from which the objects themselves are 
 
 21 
 
833 LANGUAGE, TERMINOLOGY AND 
 
 regarded by us. It changes, therefore, according to the par- 
 ticular end, the particular science that we have in view. Thus, 
 to the zoologist and botanist, and even to the anatomist, the 
 parts and aspects of a living body, of an organism, which ap- 
 pear the most important, are different from those in which the 
 physiologist, chemist, or physician is chiefly interested. While 
 the former, in his own special capacity, is concerned only with 
 the recognition and description of external form and proper- 
 ties, structure, &c., the attention of the latter is directed to 
 totally different objects — viz., to the study of the apparatus or 
 organs, the fluids and solids of which the living body is ulti- 
 mately composed, and still more of the mode of action of each 
 upon the other, and their perpetual changes and indications of 
 activity; in short, of all the occurrences and processes in the 
 living body itself. For a similar reason, also, the point of 
 view taken by the latter in forming their definitions will differ 
 altogether from that selected by the former; and to the physio- 
 logist or physician, again, it will be different from what it is to 
 the chemist ; and consequently the several definitions thus 
 arrived at will exhibit corresponding differences of expression. 
 
 Moreover, the expression of a definition will of necessity 
 vary continually with the progress and development of the 
 particular profession, or science itself, of physiology or noso- 
 logy, for example, as of medicine in general. And because 
 those most constant and essential points, the laws which regu- 
 late the phenomena and processes of life, are precisely those 
 about which our knowledge is the least satisfactory ; and be- 
 cause our views respecting them must constantly change with 
 our knowledge and with the progress of our intelligence, the 
 definitions in our science must also, even more than in others, 
 be subject to continual variation. Older definitions are con- 
 stantly being recognized as more or less incorrect, narrow, and 
 one-sided, and are therefore overthrown and abandoned to give 
 place to others more exact. And the same fate attends our 
 present definitions, and must necessarily do so till we shall have 
 attained in our science to a sure and reliable understanding, 
 and to well-established laws of vital processes, diseases, &c. 
 
 Thus, for example, the terms disease and remedy were for- 
 merly understood and therefore defined quite differently to what 
 they are now ; so, likewise, are the meanings and definitions of 
 
DEFINITION, DESCRIPTION. 333 
 
 inflammation, pneumonia, typhus, gout, lithiasis, &c., different 
 from those which were attached to them thirty years ago, now 
 that we have become acquainted with certain alterations of the 
 organs and their texture, composition, &c. And whereas, in 
 fever-patients, for example, the ancient Greeks and Arabs re- 
 garded the increase of bodily heat as the most essential cir- 
 cumstance, and therefore restricted their appellation of the 
 disorder (n-up, Trvperog, Trwpe^tc), as well as their definition, to 
 this particular symptom, Boerhaave also looked upon cold, 
 horripilatio, and the pulsus velox, as constant and essential 
 disturbances, or as causa proxima of the disease, and therefore 
 included them in his definition of fever. We, on our part, 
 have advanced somewhat further, we have discovered that those 
 phenomena themselves depend upon certain other processes 
 and circumstances — e.g., upon certain alterations and pro- 
 cesses in the circulation of the blood, in the process of re- 
 spiration and internal oxidation or conversion of tissues, in 
 innervation, &c. And as these latter are now included in 
 our definition of " fever," the symptoms above-mentioned, 
 viz., the increase of heat, the pulse, &c., have come to be re- 
 garded as conditional, variable, or accidental, and, as such, ex- 
 cluded from the idea of " fever." 
 
 Essentially the same change, and from the same causes, 
 has, in course of time, affected all our definitions of diseases, 
 of the manifold influences and agencies of the external world, 
 and of our medicaments and their effects. And these changes 
 have been farther accelerated by the fact, that the objects of 
 our definitions have themselves, within certain limits, gradually 
 become different from what they were; men and nations, for 
 example, and their diseases, as well as the whole relations of 
 their lives. And since, from this cause, from century to cen- 
 tury, new phenomena and new objects have constantly been 
 presented to our notice, their import, and our judgment and 
 ideas of them must in like manner have undergone progres- 
 sive change. Thus men and nations — at least in civilized 
 countries- — are, in their bodily and hygienic condition, as well 
 as in their intellectual and moral nature, no more what they 
 were in the middle ages, or even 100 years ago ; and the same 
 is true with regard to their disorders, such as leprosy, venereal 
 disease, typhus, small-pox, and the like, and for this reason 
 
324 LANGUAGE, TERMINOLOGY AND 
 
 our present definitions are by no means applicable to those 
 diseases as they formerly existed, neither will those of our 
 predecessors apply to the diseases of our time. 
 
 However disturbing, if not melancholy, these external changes 
 may be in many points of view, showing as they do the variable 
 and unsatisfactory state of our knowledge, they are nevertheless 
 encouraging as proofs of our progress. For, after all, our defi- 
 nitions vary and alter solely because the old ones no longer 
 agree with the improved state of our knowledge. The more 
 defective these old definitions are, and the more clearly we see 
 their deficiencies, the sooner shall we feel ourselves impelled 
 to correct them by farther investigation, and substitute better 
 ones in their place. We must, however, as appears from the 
 preceding, beware of falling into the illusion that we can give 
 a perfectly correct and satisfactory definition of an object, pro- 
 cess, &c., in our science, as regards either the healthy or the 
 diseased body, before we have attained to thoroughly accurate 
 and satisfactory ideas respecting it — that is to say, before we 
 have become acquainted with its actual and peculiar laws. 
 
 Till then — therefore doubtless for centuries to come — we 
 shall have to content ourselves, as we may, with instalments 
 and approximate definitions, and shall not be entitled to believe 
 that (Mr definitions will have much greater permanence than 
 those of our predecessors. And, even if it were so, the case 
 would in many respects be so much the worse, — it would 
 indeed afford a proof of intellectual laziness and impotence on 
 the part of our successors. But as long as investigators and 
 thinking heads are to be found in the field of nature and of 
 life, we need never apprehend for our definitions so unlikely a 
 fate as stability. 
 
 The very constitution of the mind of man and the whole 
 course of his thinking and investigation cause him to direct 
 his attention sometimes one way, sometimes another, and to 
 occupy himself, in succeeding times and generations, continually 
 with new objects, and with new aspects and portions of his 
 great question. This direction varies also even with each indi- 
 vidual inquirer, not only according to the speciality of his 
 profession, objects, and position, but likewise according to his 
 temperament, age, and experience. 
 'It follows, therefore, as a necessary consequence, that new 
 
DEFINITION, DESCRIPTION. 325 
 
 knowledge and new ideas of our objects, and especially of their 
 laws and so-called essence, will continually arise — therewith, 
 also, new definitions of those objects ; and, in consequence of 
 the intimate mutual relation between thought and language, 
 new expressions for them. The meaning conveyed to us by 
 these expressions is indeed continually changing, just as the 
 word " love" has one meaning in the mouth of a young girl, 
 another in that of a matron, and is understood in difi^erent 
 ways by a child, a youth, and an old man. While one part 
 of our knowledge rises, and the sum of our intellectual acqui- 
 sitions on the whole increases, another portion rather perhaps 
 sinks into oblivion ; while one side, one direction becomes 
 prominent for awhile and occupies the minds of inquirers, 
 another retires into the back-ground. Thus, for example, in 
 medicine, till recently, the old controversies between the 
 humoralists and the solidists, and about juices, blood, and 
 nervous system, were constantly shifting about, hke Whigs and 
 Tories in England ; and in our own time, since investigations 
 relating to the living body, both in health and in disease, have 
 been directed chiefly to the chemical point of view, the ana- 
 tomical and microscopical have excited less attention. As 
 now the one and now the other portion of our variegated field 
 of inquiry presses on the scale, the other scale, in which nothing 
 new is laid, at the same time becomes lighter, and is neglected, 
 till a revolution takes place in the entire direction of the 
 intellect. 
 
 Other minds now, perhaps, become all at once aware of the 
 one-sidedness, the extravagances of their time, and on the other 
 hand, perhaps, perceive, more clearly than their contemporaries, 
 the portion of truth contained in many older though forgotten 
 facts and modes of representation. They become convinced 
 that by following the path hitherto traversed, the whole, the 
 nucleus of the great enigma can by no means be solved, and 
 still less has the solution been actually obtained. They there- 
 fore dig and search the more in other directions, in other 
 shafts and galleries, which have perhaps remained for years 
 covered up and neglected, and, if successful, discover new 
 answers to questions old as well as new. Moreover, in all 
 such inquiries, the human mind generally proceeds in two 
 opposite directions, — the one tending to the universal, to .far- 
 
336 LANGUAGE, TERMINOLOGY AND 
 
 reaching comprehension of resemblances, agreement, and 
 inward relations of the greatest possible number of things, and 
 to their collation and generalization, — the other more adapted 
 to the comprehension of particulars, and therefore tending 
 towards specialization, and chiefly occupied with predicating 
 this particular, more limited matter by itself, in its own rela- 
 tions, and according to its own laws. 
 
 But as these simultaneous or alternating currents and 
 counter-currents of our modes of thinking and investigation 
 produce a continual oscillation of our understanding, ideas, and 
 representations, they must necessarily be equally reflected in 
 our expressions — ^that is to say, in the sense which we attach 
 to them. But this sense is likewise subject to continual varia- 
 tion, even the meaning of our words being thus liable to be 
 altogether lost and again recovered — as is the case, for example, 
 with such expressions as nervous fever, gout, miasma, poison, 
 oxidation, and the like — and, similarly, in common life with 
 words like virtue, honour, religion, law, state, &c. And 
 whereas in course of time certain expressions become used in 
 a continually wider and wider sense, and increase in compre- 
 hensiveness (e. g., salt, alkali, oxidation, inflammation, exuda- 
 tion) ; others, on the contrary, may become more limited in 
 meaning and lose more and more of their original comprehen- 
 siveness. Thus, for example, the old term " consumption" 
 has gradually been reduced to pulmonary tuberculosis ; the old 
 " fever" to nervous fever, typhus, &c. ; the old " bark" to 
 cinchona bark, &c. 
 
 For this reason, also, there have always been found persons 
 who busy themselves, in spite of all dif&culties, with continual 
 attempts to give greater clearness and stability to our con- 
 ceptions. In other words, their endeavour is to give more 
 correct definitions of the several objects of our inquiries, per- 
 haps to substitute, in place of confused, limited, if not erroneous 
 ideas, their own more exact notions, and thereby at the same 
 time to give to certain expressions which are undefined, ambi- 
 guous, and perhaps have become almost meaningless in daily 
 use, a well-defined, exact sense, at least according to their 
 own opinion. 
 
 So far as such attacks upon the deficiences or errors of our 
 conceptions are limited to the field of science itself, and greater 
 
DEFINITION, DESCRIPTION. 327 
 
 clearness is sought by means of positive investigation, and 
 above all by conscientious personal labour, the attempt is 
 doubtless praiseworthy enough. In fact, there can never be 
 too much of such increase and illumination of our under- 
 standing by the continual addition of new matter, by new and 
 more trustworthy facts and discoveries. 
 
 But such endeavours become faulty and even dangerous, as 
 soon as they are directed solely or principally to the formation 
 of more exact definitions for their own sake, or to a mere puri- 
 fication of our forms of expression, and a fixation of their 
 particular meaning. For all such attempts at definition and 
 explanation add nothing to our knowledge, do not make our 
 ideas in the least degree more exact or more stable, and so far 
 contribute nothing essential to the matter itself. Many an 
 inquirer or " savant," who busies himself in this way, thinks, 
 perhaps, that he can thereby add something positive to our 
 knowledge, and possibly, also, under certain circumstances, 
 defend his own views and pretensions better. But all his 
 definitions and explanations, in themselves, bring us no en- 
 lightenment, unless they give greater width or steadiness to 
 our view of the disputed matters. And inasmuch as such 
 definitions and explanations are ultimately nothing but words, 
 they can, as Bacon observes, call forth nothing but words, 
 similar attempts at explanation, and further dissertations on 
 the part of others, and the result in most cases is a mere war 
 of words. 
 
 Moreover, no individual has a right to use our words and 
 phrases according to his own pleasure, and to attach to them 
 only that meaning which, rightly or wrongly, may appear to 
 him to be the only correct, one. Our medical language, like 
 every other, is the property of all and of the science, not of 
 any individual. Nearly every one of our technical terms has, 
 in course of time, acquired a certain if not definite sense, and 
 has been used, sometimes in one way, sometimes in another, 
 by all members of the profession; and to these uses they 
 adhere, and for the sake of their own understanding and the 
 intelligibility of their communications to others, must adhere. 
 And if any one thinks proper to use such an expression merely 
 in his own particular sense, according to his own peculiar 
 opinion, even though he may have the most valid reasons for 
 
328 LANGUAGE, TERMINOLOGY AND 
 
 so doing, he thereby attaches to it a much more definite — that 
 is to say, a narrower and more confined sense, which no longer 
 predicates and includes all that was formerly understood by 
 that expression. He takes from it part of its significance, part 
 of the sense which others are accustomed to attach to it. For 
 these reasons, there is but little utility in attempting, by sub- 
 sequent definition, to give greater clearness and fixity to the sense 
 of long established, though perhaps defective words; but still 
 greater confusion would certainly arise if individuals were at 
 once to use old words in a new sense or to invent new words 
 for old objects and ideas. For the words as well as the ideas 
 exist, as it were, with a certain sense, with a certain signification 
 in the minds of thousands, and, by such transformation, would 
 lose more or less of their capability of serving as carriers or 
 communicators of the existing amount of experience and know- 
 ledge. To an equal extent, also, does the use of certain - 
 modern technical words not only for the most part fail to add 
 anything to the clearness of our insight, but rather clouds it, 
 and introduces confusion into our ideas. Thus to speak of 
 " Hypersemia" instead of congestion, or of " Stasis" instead of 
 inflammation, is to say something very difi'erent from that 
 which was formerly understood by congestion and inflammation. 
 The two by no means agree, — as little indeed as pulmonary 
 tuberculosis agrees with consumption, Bright^s kidney-disease 
 or albuminuria with dropsy, abdominal typhus with nervous 
 fever, &c. 
 
 The tendency to such attempts at explanation and purifica- 
 tion, and even a certain justification of them, is certainly greater, 
 in proportion as the usual forms of expression are more am- 
 biguous and variable, more widely diffused and more altered 
 and modified by use. In like manner it is greater, as our 
 insight into the objects thereby denoted is less perfect, and the 
 more our knowledge has changed in course of time, and is 
 even now, perhaps, changing from year to year. And if these 
 causes conspire in any science, they certainly do in our own. 
 But, on the other hand, it follows from the same considerations 
 that in a branch of knowledge so enigmatical as ours, in the 
 midst of objects and processes so many-sided, ambiguous, and 
 complicated as those with which medical science has to deal, 
 no individual can be in a position to investigate, even a single 
 
DEFINITION, DESCRIPTION. 829 
 
 question on all sides and in its whole extent. He will not 
 readily succeed in determining any single process in the living 
 body in all its conditions, effects, or laws, with sufficient cer- 
 tainty to enable him to understand it thoroughly, and therefore 
 to define it with perfect precision, and in a manner which shall 
 hold good for all time. He will never be able to show that 
 his view of the matter is perfectly correct, or even superior to 
 that of others antecedent to or contemporary with him. And 
 even if he is convinced of this, he will, in the most favorable 
 case, scarcely avoid the danger of taking a part or a side for 
 the whole, and much that is subordinate and secondary for the 
 principal part. 
 
 It is evident, also, from the preceding considerations, that 
 great mischief will in most cases ensue if, in such attempts at 
 definition and explanation, greater importance is attached to a 
 clear and determinate, than to a sufficiently complete and com- 
 prehensive understanding of the objects and questions before 
 us. For however useful and valuable the former may be for 
 the understanding of the individual, its value is but doubtful 
 and transient when considered with reference to the whole 
 science and to all its cultivators. In a field like ours, clearness 
 can in general be purchased only at the expense of completeness 
 and therefore of truth. To an individual, a mode of repre- 
 sentation, an idea or expression in this confined and narrower 
 sense may be clear enough, and therefore of a certain value. 
 But to the understanding of others and still more to the whole 
 science, the gain thence accruing is but small, at least for a 
 continuance. 
 
 Every one is therefore at liberty to follow out our questions 
 and enigmas as much and as well as he can, and by his inves- 
 tigation and his newly-discovered facts to throw as much light 
 on them as possible — the more the better. Moreover, this 
 end can nowhere be attained more directly or more use- 
 fully for the science than precisely among those objects, the 
 idea and name or denomination of which appear to the in- 
 quirer, as well as to others, doubtful, or unsuitable, if not 
 entirely false. Here, even more than elsewhere, is there need 
 of further elucidation and active research. But in the names 
 and expressions themselves, provided they are to a certain 
 extent endurable and derived from the mother-tongue, there 
 
330 LANGUAGE, TERMINOLOGY AND 
 
 should be as little as possible of attempts at alteration, sub- 
 sequent explanation, or improvement, — less, indeed, in propor- 
 tion as they have been in longer and more general use ; for, 
 after all, no one has the right to make such alterations, and 
 still less, the power — that is to say, the requisite knowledge of 
 things. 
 
 And since, for all the reasons above adduced, our language 
 and forms of expression scarcely admit of any further fixation, 
 explanation, or definition, without risk of greater danger and 
 confusion than utility, it appears more advisable to give a clear, 
 searching history of each of these expressions — e. g., of fever, 
 inflammation — of the names of the several disorders, and the 
 like. In this way, our ideas of these matters might be most 
 thoroughly fixed and elucidated, by showing how these expres- 
 sions were first arrived at, how their original sense had altered 
 in course of time, and why they must now be received in a 
 sense different from that which was originally attached to them, 
 and why in this sense and no other. 
 
 The above remarks leave little to be said concerning Desceip- 
 TioN in our science, and the conditions which it must fulfil. 
 
 Like language itself, description is to us an indispensable 
 medium for the representation and communication of all that 
 cannot be otherwise presented, exhibited, and brought to the 
 knowledge of others. Such, however, is the case with almost 
 everything with which our science has to do. For we have to 
 deal with phenomena, processes, and objects which, for the 
 most part, cannot be directly perceived, much less laid hold of 
 and exhibited J as, for example, is the case with anatomical 
 preparations, animals, and plants, or the substances with which 
 the chemist has to do. Description is therefore the only help 
 that remains to us, and the best description must be that by 
 which, according to an Arabic phrase, " the ear of the auditor 
 (reader) is converted into an eye." 
 
 The requirements or conditions which we have to satisfy 
 in our descriptions are simple enough. Every description 
 should, in short, set forth and reproduce what we have ob- 
 served, or, in general, the things to be described, just as they 
 really exist. We must therefore know how to find for each of 
 our phenomena, for everything that we observe in our pro- 
 
DEFINITION, DESCRIPTION. 331 
 
 cesses and objects, the expression which is most exact and 
 best adapted to it, so that others may receive therefrom the 
 best and most complete explanation of which the matter admits. 
 The images and conceptions to which they are led by our de- 
 scription should correspond exactly with the real state of the 
 matter, as we ourselves have observed, and now wish to repre- 
 sent it. And this representation itself should convey to others 
 only that sense, and excite in them only those ideas which we 
 wish and ought to excite. 
 
 Every such description, therefore, presupposes, in addition to 
 a correct observation and apprehension of our phenomena, &c., 
 a suitable language and terminology, especially, also, the power 
 of handling it in the most appropriate manner, so as to avoid 
 all unmeaning or ambiguous and obscure expressions. 
 
 To satisfy all these requirements, however, is, as experience 
 shows, a very difficult matter. That it should be so will not 
 excite much surprise if we consider how, in every description, 
 those difficulties of our language, which we have above endea- 
 voured to depict, are raised to a much higher degree, because 
 the difficulties of our observation in general, and the defects of 
 the individual observer, together with all the dangers thence 
 arising, tend to increase them. In short, if we require all that 
 such a description in our science ought generally to furnish, 
 and all that it is within our power to furnish, and if we examine 
 more closely the peculiar circumstances and difficulties sur- 
 rounding the objects to which our description applies, we shall 
 readily understand why we are here opposed by greater 
 obstacles and more formidable rocks than in any other departs 
 ment of nature. 
 
 For the same reason, it is clear enough why good descrip. 
 tions are so rare, and good describers even much rarer than 
 good observers. But it is rarest of all to find a man who 
 is both at once, at least in an equal degree, because, in a cer- 
 tain sense, description and observation require totally different 
 qualities and dispositions. If observation especially requires 
 knowledge of facts, together with circumspection and a cool and 
 unbiassed, as well as searching and comprehensive grasp of 
 all the phenomena and circumstances, description, on the other 
 hand requires in addition, not only knowledge of language, 
 and the requisite practice and facility in its use^ but more 
 
332 LANGUAGE, TERMINOLOGY AND 
 
 especially the power of representing the observed phenomena 
 in a suflBciently clear and, as it were, plastic manner, and yet 
 with perfect accuracy. But to fulfil these conditions there 
 must also be fancy, a certain almost poetical or pictorial talent, 
 such as is rarely found in good observers, but rather appears to 
 be at variance with the peculiar disposition required for cor- 
 rect observation. And if the description of the one appear too 
 short and dry, if not obscure and diflScult to understand, that 
 of the other is apt to be too wordy, broad, often, indeed, in- 
 exact, and soinewhat too fantastic or poetical. If the former, 
 in a certain sense, confines himself somewhat too closely to the 
 given details and objective view of the observed phenomena, 
 the latter, on the other hand, often allows his subjectivity, his 
 personality, to play too conspicuous a part. 
 
 In all cases, however, the truth and credibility of our de- 
 scription are most endangered by our ready disposition to express 
 our own personal apprehension and combination of the thing 
 observed, rather than to present it plainly and clearly, neither 
 more nor less, nor different in any respect from that which it 
 really is. Here, also, our nature and intellectual constitution 
 lead us only too easily to give to our views and temporary 
 theories greater scope than they deserve. In a certain sense, 
 indeed, it may be asserted that such a thing as a pure and 
 thoroughly objective description, without any admixture of our 
 own subjectivity, is for the most part not even possible, just as 
 our observations are never strictly confined to that which we 
 perceive by our senses. We rather express by our description 
 more than we have actually observed, and thereby present, not 
 merely the objective, the pure matter of fact, but necessarily, 
 also, something more — namely, our own interpretation and 
 judgment of the matter. For good or evil, then, we must, in 
 every attempt at description, no less than in our observations, 
 express more than the thing actually observed — if only for 
 this reason, that we cannot otherwise present it in a manner 
 which shall be clear and intelligible to others, and convey to 
 them a distinct impression. Our actual observation, indeed, 
 is made only on certain individual phenomena, whereas in our 
 description, if it is to be intelligible, these phenomena must, 
 as it were, represent something, they must make their appear- 
 ance grouped and combined, with a meaning previously 
 
DEFINITION, DESCRIPTION. 333 
 
 attached to them by ourselves, and explained in one way or 
 another. 
 
 Exactly, therefore, as (for reasons given under the head of 
 " Observation") we never actually see a typhus patient, a 
 typhoid ulcer, a scrofulous gland, or inflammation of the eye, 
 &c. ; so, likewise, are we unable to give of any such objects a 
 purely objective and thoroughly matter-of-fact description ; for 
 in the very act of representing them and declaring them to be 
 such (e. ff., typhoid, scrofulous, &c.) we say of them that they 
 belong precisely to this species or series of phenomena, dis- 
 eases, &c,, and to no other. But, to be able to do this, we 
 must previously have interpreted or judged them — that is to 
 say, we must, by comparison with similar objects, have con- 
 nected them with these, and so far reduced and classified them 
 in a certain manner, and finally pronounced them to be of 
 such and such a character. This, indeed, is the case to a cer- 
 tain extent, even when, in our description, we speak of such a 
 thing as a "hot, dry skin," a "red or furred tongue," a 
 " smooth or tumefied edge of a sore," a " rattling noise or 
 percussion-tone in the chest," &c. For, in either case, we 
 have already, even at the moment of observation, consciously 
 or unconsciously, compared that which we actually perceive by 
 our senses in these phenomena, states, &c., with others which 
 resemble them, and recognized their similarity or complete 
 identity therewith. And the discovery thus made, the result 
 of that almost instinctive interpretation and comparison, — in 
 short, our deductions from what our senses perceive and our 
 conception of it, — must likewise be transferred to our descrip- 
 tion. This description, if it is to be intelUgible, must there- 
 fore contain these results of deduction and comparison in 
 addition to that which is actually observed. 
 
 Every description, then, even the best and most unadorned, 
 contains a sufficient quantity of our own additions, of our own 
 subjectivity ; and only in that way can it be rendered appro- 
 priate and intelligible. To avoid, indeed, even to a limited 
 extent, this interference and addition on our own part, we 
 should be obliged to make an enormous circuit in endeavour- 
 ing to describe each individual phenomenon, and all the 
 properties and constitutions of our objects, each by itself. The 
 result would be a description which no one could listen to, 
 
334 LANGUAGE, TERMINOLOGY AND 
 
 read, or understand. It must be remembered, however, that 
 this unavoidable addition, this subjective element, may play 
 much too conspicuous a part in our description, and easily 
 obtain the preponderance over its objectivity, as well as in the 
 observation itself. To us, moreover, this danger is much 
 more imminent than to others, because we can observe directly 
 only a very small part of our objects and phenomena; and 
 therefore, also, are seldom or never able to describe simply 
 that which we have actually seen and observed. 
 
 From this, and all that has been previously adduced, we may 
 readily see how it is that descriptions are, on the whole, so 
 seldom perfectly correct and admissible; and therefore, also, 
 seldom really useful or appropriate, and nowhere more rarely 
 than in our science. This, also, for reasons already given 
 when speaking of language, will in general, under otherwise 
 similar circumstances, be still less the case as the description 
 itself — i. e., its date, is more remote from our time. Appre- 
 hension and ideas, as well as the modes of expressing them, 
 were in former times more or less dififerent from what they are 
 now ; and moreover, in the descriptions of our predecessors, 
 the subjective element predominated in a much greater degree 
 than in later times ; so that, in fact, they often gave views, 
 arbitrary assumptions, and theories, rather than actual obser- 
 vations. The first- mentioned circumstance was, in itself, quite 
 sufiBcient to render their descriptions for the most part doubt- 
 ful, if not unintelligible, and but too frequently adapted to 
 excite incorrect images in us, rather than such as are really 
 accurate and true to nature. 
 
 In spite of all this, however, there has never been a dearth 
 of good describers or of good observers, and from the commu- 
 nications of a Hippocrates and a Celsus, as well as of a 
 Sydenham, Boerhaave, Van Swieten, StoU, and others, we 
 may, within certain limits, even, at the present day, extract a 
 sufficient amount of instructive matter. In fact, even one- 
 sided and fragmentary descriptions, whether of ancient or of 
 modern date, are often of great value, if only they contain 
 something that is true and in accordance with fact. For in 
 truth such descriptions are often our only sources of informa- 
 tion respecting many new, rare, or important matters. And 
 if the information thus obtained respecting these matters is 
 
DEFINITION, DESCRIPTION. 335 
 
 but approximate, at all events our attention is directed to 
 them; their description renders them a possession of the 
 science, and the gaps may be afterwards filled up by further 
 observation and description. 
 
 But we ourselves shall, in general, be able to avail ourselves 
 of such and of all foreign descriptions with greater security 
 and better effect upon our understanding and our independent 
 investigations, the more we have previously learnt and under- 
 stood concerning the things described. For we cannot other- 
 wise be in a position to judge whether and how far a description 
 is accurate and complete, or, on the other hand, faulty, or 
 perhaps utterly false, and therefore to be regarded as worthless, 
 or at least as improbable and doubtful. Hence we may 
 plainly see the absolute necessity of a certain scientific culti- 
 vation and insight, of a certain knowledge of facts and ripeness 
 of judgment, not only for our own observations) but likewise 
 for making use of the experience and observations of others as 
 they are communicated to us. It is only in this way that we 
 can successfully avoid the numerous deceptions and errors to 
 which others may expose us by the defective or erroneous 
 character of their descriptions. On the other hand, the 
 smaller the amount of cultivation and knowledge that a man 
 possesses, the more readily will he believe all he hears, even 
 though it may be utterly unworthy of belief; or, on the other 
 hand, he will doubt, and perhaps altogether reject what he 
 ought to believe. The one or the other he will do without valid 
 grounds, and without clear and sound judgment, because with- 
 out knowledge and experience; and whether he believes or 
 doubts, he is always in danger of doing so in the wrong place. 
 But inasmuch as such sufficient knowledge and judgment is to 
 us, from the almost entire want of sound understanding of our 
 objects and questions, nearly impossible, or at least is rarely 
 found, we may understand why even educated physicians, phy- 
 siologists, and others, are often beset by the dangers just 
 mentioned. Examples of this are to be found in abundance 
 both in ancient and modern times, and nowhere more fre- 
 quently than in the field of our setiology of diseases, and in 
 therapeutics properly so-called, especially when bias and interest, 
 or prejudice, party views, and similar personal motives like- 
 wise come into play. 
 
336 CLASSIFICATION. 
 
 Finally, there must be added a circumstance which does not 
 always receive the attention it deserves. Every foreign repre- 
 sentation or description may make very unequal impressions 
 upon others, according to their several experiences, ideas, and 
 tendencies, or according to their temperament, intellectual 
 constitution, and education. Descriptions, no less than any 
 other sentient impressions, or the vox viva of an orator, may 
 perhaps awaken in every one, even in a cultivated, impartial, 
 and circumspect person, different conceptions and associations 
 of ideas, according as they agree with his mode of conception 
 and judgment, his previous views, his habits, wishes, and 
 aims ; just as, for example, the description of a pretty girl may 
 produce different impressions upon a youth and an old man, or 
 that of a " beautiful" case of disease on the physician and a 
 non-medical person, or the representation of a battle on a 
 soldier and on a woman. 
 
 If, for example, a person has conceived this or that notion of 
 an object or a question, or if he is already engaged in its 
 investigation, he will have quite a different and a sharper eye 
 for all that relates to it, for all even half-concordant descriptions 
 given by others, than one who is interested not in this particular 
 point so much as in another, perhaps even in the very oppo- 
 site ; while the former perceives even the remotest and obscurest 
 analogies, the most ambiguous allusions and hints of others, be- 
 cause he can make use of them — the other, perhaps, receives 
 no impression from them, and consequently overlooks them. 
 
 In this, however, both may go wrong, and make an unjus- 
 tifiable use of the description of another. And precisely for 
 this reason is the circumstance just noticed worthy of the 
 attention of every investigator or physician, and especially of 
 the younger and less experienced. 
 
 IV. CLASSIFICATION. 
 
 By an almost instinctive impulse, similar to that which leads 
 to the use of language, we are induced to collate or group 
 together the things which we observe — that is to say, to classify 
 them. Our intellectual nature and requirements compel us, 
 in fact, not merely to observe the objects and phenomena with 
 
CLASSIFICATION. 337 
 
 which we have to do, and designate them by this or that name, 
 but also to imagine them combined or grouped in a certain 
 order — at least if we wish to take a complete survey of them. 
 Accordingly, every science and art has endeavoured to classify 
 as completely as possible the things belonging to it j hence, in 
 our field of inquiry, the objects classified are the phenomena 
 and processes of the living body, diseases, remedies, the 
 hundred influences and agencies of external nature, &c. 
 
 Even when we observe any object or phenomenon, and cer- 
 tain properties belonging to it, and declare it with our words 
 to be this or that (e. g., red or hard, a cutaneous or pulmonary 
 inflammation), we have already compared it with all objects, 
 phenomena, &c., of the same kind that are known to us, and 
 thereby recognized it as of such and such a kind — that is to 
 say, we have already, in a certain sense, grouped or classified 
 it. But in this case it is only, as it were, an accidental or 
 unconscious, or at all events an unpremeditated classification 
 that we make ; whereas, in classification properly so-called, the 
 objects and phenomena are, with a clear understanding of the 
 matter in hand, united into groups and classes, according to 
 their more essential properties, or reduced to a certain system. 
 
 The grand problem, the true end of our classification, there- 
 fore, is by no means to arrange objects and phenomena in such 
 groups, well or ill, in any way whatever, but rather, by this 
 assemblage of certain things in one and the same class, to place 
 ourselves in a condition to regard the objects thus united as 
 actually belonging to one another, and therefore as essentially 
 of the same kind, or at least as nearly related and analogous. 
 That which we, by our classification, declare to be so — i. e,, 
 that which, by being placed together in one and the same 
 class, is presented to us as a more or less homogeneous, and 
 essentially concordant assemblage of objects, might likewise 
 be so in reality ; for herein consists altogether the benefit 
 which classification can and ought to confer upon our under- 
 standing. 
 
 It is a consequence of our very nature that we cannot 
 observe anything — in the living body, for example, or in a 
 patient — and cannot pursue our reflections upon any observed 
 phenomenon, without a whole train of other phenomena and 
 objects occurring to us, which, from previous observation, 
 
 22 
 
338 CLASSIFICATION. 
 
 appear to be analogous or essentially similar to the one in 
 question. In order, therefore, that our judgment respecting 
 the latter may be facilitated by this comparison, it is essential 
 that the objects thus presenting themselves be really similar or 
 identical with the one under examination. Equally dependent 
 upon this condition, also, is the result of our reflection on 
 the matter, and of our inquiry into its conditions and its 
 causal connection, for a correct comparison of objects consti- 
 tutes the first step of our whole inductive process. This 
 presupposes that all the series of individual objects comprised 
 within our province are already present to our consciousness, 
 slumbering therein, as it were, in due order and connection. 
 For we cannot well form a distinct conception of any one of 
 those objects or of any individual case (of a disease, for 
 example), unless the other objects and cases belonging to the 
 same class are also present to our minds. Neither can we 
 form a correct notion of any separate series or group of such 
 objects (e. g., phenomena or things of the same species, genus, 
 or class) without comparing it with the other groups or series, 
 and therefore without having these others present to our con- 
 sciousness, to our ideal world. And it is only when our 
 conceptions on these points are as accurate as possible — that 
 is to say, when those groups are formed of things really similar 
 and connected together — that we obtain a clear and correct 
 survey of all the individual objects which together make up 
 the contents of our province (e. g., physiology, nosology, or 
 therapeutics). Far more important is it, however, that we be 
 thereby, as it were, placed in a position to apprehend and 
 judge more correctly that which we observe in any particular 
 case : for example, in any process taking place in the living 
 body, or in any action on the same in a patient ; for we can 
 then assign to this case, or rather to that which we observe in 
 it, its proper place in the entire mass of objects and phe- 
 nomena ; inasmuch as we collate it with precisely that group 
 or series of phenomena which are of the same kind, which 
 agree with it in such and such principal points. 
 
 This may sufSce to show that every classification is of the 
 utmost significance to our understanding, to our entire method 
 of comprehending and judging every individual case that falls 
 under our notice, and likewise to our further inquiry into its 
 
CLASSIFICATION. 339 
 
 causal connection and laws. And as this end is essentially 
 facilitated by a good and rational classification, so, on the other 
 hand, may it be impeded by defects and errors therein. To 
 obtain, then, all these important advantages, it is plainly 
 necessary that every classification be of such a kind — that is 
 to say, that the objects in question (e. g., vital processes, 
 diseases, remedies) be arranged in such groups or series and 
 classes, — or generally in such order, — that we may be thereby 
 immediately reminded of their more important or essential 
 properties, of their peculiar nature and relations to others. 
 For, by such a classification, not only would our ideas and 
 views respecting the individual objects thus connected be 
 placed in order, but in a correct order, — in an order adapted 
 to assist as far as possible our judgment and understanding of 
 those objects. Moreover, it is self-evident that this deside- 
 ratum is of two-fold utility in our province, and especially for 
 the theory of diseases and remedies, — for our so-called aetiology 
 and hygiene. In this even more than in other fields of inquiry, 
 we have to deal with the most varied and complicated mixture 
 of phenomena, processes, or influences ; and at each step, at each 
 individual observation (of a patient, for example), all possible 
 analogies and comparisons with various others come into our 
 minds, and with these we perhaps unconsciously connect the 
 new case. How much, therefore, must our judgment, our 
 understanding of this latter be assisted, if at this time we are 
 reminded precisely of those objects which actually agree with 
 those before us in all essential points, and the classification, 
 therefore, supports us in this first important step ! The 
 chemist derives this assistance from the grouping of his sub- 
 stances — e. g., into alkalies, acids, or into organic and inorganic 
 substances — the physicist from the grouping of his phenomena 
 into those of electricity, heat, gravitation, light, &c. And in 
 a still higher degree is this true of the descriptive natural 
 sciences, in which the union of certain sets of phenomena or 
 characters, perceptible by the senses, and established once for 
 all, serves for the formation of genera, groups, and classes, and 
 the division of all animals, for example, into the great sections 
 of vertebrate and invertebrate, or of vegetables into mono- 
 cotyledons and dicotyledons, of vascular and cellular plants, 
 &c. 
 
340 CLASSIFICATION. 
 
 It is then the especial business of each branch of science to 
 classify the things belonging to it {e.g., the vital processes and 
 influences, all diseases, remedies, &c.), according to their 
 essential or distinguishing qualities and characters, and, more- 
 over, according to those particular characters which are of 
 the greatest importance with reference to this branch of science 
 and its points of view or interests. This arrangement and our 
 classification-titles should also be such as to induce and enable 
 us to think exactly of those things which really agree, in certain 
 decisive and important points, with that which we observe or 
 would speak about in the case before us, or, at least, resemble 
 it as closely as possible ; — such allied or similar objects 
 should alone, therefore, be included in the same class or series. 
 It is true that we can, in a certain sense, select as the basis of 
 our classification any aggregate of properties, and ultimately 
 even any single property which we observe in the objects under 
 examination. And so far, our power of forming groups and 
 classes is almost unlimited — that is to say, the number of 
 them that we can form is equal to that of the properties which 
 we observe in our objects and phenomena, belonging to one 
 and not to the others, so long, therefore, as we discover dif- 
 ferences, which may serve as the basis of their division or 
 classification into so many species, genera, groups, or classes. 
 It appears, however, from the preceding considerations, that 
 those several properties and diflerences are far from being 
 equally advantageous for our classification, and that conse- 
 quently our main object — the understanding and clear survey 
 of all the objects under examination — cannot possibly be pro- 
 moted in an equal degree by them all. 
 
 Least of all is this the case in the older attempts at classi- 
 fication, and in our department of science as little as in any. 
 For here especially it follows from the nature of the matter, 
 that in the beginning, in the infancy of science, those objects 
 or combinations of phenomena can only be distinguished and 
 grouped according to those particular properties, circumstances, 
 &c., which present themselves at once to the ordinary observer, 
 and can generally be recognized with but little trouble. We 
 find this, for instance, in the older classifications of plants and 
 animals just as well as in those of diseases, remedies, &c. 
 In both cases, the existing knowledge of all the objects which 
 
Classification. 341 
 
 it was desirable and necessary to classify, was much too small 
 to admit of any other method of classification. Well or ill, 
 therefore, one and the same group was then made to include 
 phenomena, influences, and events (e. g., diseases and remedies), 
 which resembled one another only in comparatively external 
 and subordinate, perhaps altogether accidental, points and 
 circumstances. At all events, the characteristic and more 
 important properties or circumstances were then far from being 
 sufficiently established, and the objects included in the same 
 class were, for the most part, far too little known to render it 
 possible to predicate anything of a general character respecting 
 them with truth and certainty. Hence, also, it is evident that 
 such a classification could by no means promote the knowledge 
 of the things classified, but, on the contrary, must often have 
 impeded and disturbed it, and consequently that the above- 
 mentioned conditions of a good classification were far from 
 being fulfilled thereby. 
 
 To attain this end as completely as possible, we must obviously 
 rather form classes or groups respecting which we know 
 and can predicate the greatest number of general properties — 
 that is to say, the greatest number common to all the united 
 objects, and, as it were, available for them all, and at the same 
 time the most important, or determining and essential. We 
 must, therefore, be in a position not only to indicate the 
 points and circumstances in which, especially, the assembled 
 objects agree with one another, at all events more than those 
 included in other classes, but these points and circumstances 
 must be as numerous as possible, and, more especially, as im- 
 portant and essential as possible. In so far, then, as our 
 peculiar and principal object may be regarded as the compre- 
 hension of our phenomena and processes, and therefore the 
 insight into their causal connection or laws, we must, as far as 
 possible, know how to select those moments and circum- 
 stances which especially relate thereto. Thus, instead of 
 classifying diseases according to variable and accidental symp- 
 toms, or the so-called locally attacked structures and anatomical 
 lesions, &c., we should rather base our classification on their 
 necessary conditions, and on the manner of their origin, pro- 
 gress, and result ; in like manner, with respect to the agencies 
 of the external world and to remedies, we should look to the 
 
343 CLASSIFICATION. 
 
 conditions and laws of their action in general ; and again, in 
 the living body, and especially in man, to the properties on 
 which those actions depend, &c. In making such classification, 
 also, the greatest stress must be laid on those properties and 
 attributes of the things to be classified, on those circumstances 
 of their origin or action on which the others more or less 
 depend, or, at least, are only their external manifestation (as, 
 for example, the so-called morbid or remedial symptoms are 
 the manifestations of the process going on within, of the con- 
 tinual changes and conditions of the human body). Those 
 properties or circumstances which determine and serve as 
 measures of a number of others are generally called, for short- 
 ness, the essential properties. 
 
 In favorable cases we might then succeed in uniting into 
 one group or class exactly those series of phenomena, events, 
 or objects, whose common and general examination would, on 
 the other hand, throw the greatest light on each individual 
 among them, and would necessarily lead us to the observation, 
 of its most important relations — i. e., of its conditions and 
 laws, and the manner of its origin, progress, or action. So 
 far, also, a classification of this kind would be best adapted, 
 not only to afford us a certain insight into the whole of these 
 groups, and therefore into aU the objects of research in our 
 science, with respect to their essential points, but also to pro- 
 mote and facilitate the investigation. For this very classifi- 
 cation would support us in our judgment and understanding of 
 the individual case, and would likewise point out the roads 
 which would soonest lead to a further investigation and a 
 better understanding of our processes. 
 
 In short, a division according to causal connection and the in- 
 ternal relations and laws of things, is, perhaps, the best adapted 
 to the further progress, at least, of all those sciences and 
 branches of knowledge which are not merely occupied with the 
 observation, description, and enumeration of their objects, but 
 likewise aim at a thorough insight into them. But, on the 
 other hand, it is evident that in our science we are far from 
 being in a position to carry out such a classification with cer- 
 tainty. A classification, according to those considerations, 
 presupposes a comparative knowledge of vital processes, diseases, 
 and their laws, and of all external influences and remedies. 
 
CLASSIFICATION. 343 
 
 and of their eflFects, which we are at present, and shall be for 
 some time to come, very far from possessing. 
 
 For good or evil, therefore, we confine our attention to 
 certain external phenomena, properties, or effects, which we 
 find most easy to apprehend, and use them as our principle of 
 classification. If, now, by such a method, objects are grouped 
 according to the whole of their resemblances or diflferences in 
 external appearance, form, progress, &c. ; the classifications 
 and systems thus formed are called natural. On the other 
 hand, they are called artificiai, when only one or a limited 
 number of properties and characters is taken as the basis of 
 the distribution (as, for example, in Linnseus's system of the 
 organs of fructification), and more or less arbitrarily, accordingly 
 as one or another character is regarded as the most important 
 and convenient. 
 
 Prom another point of view, also, all attempts at classification 
 in general, and in our science in particular, may be divided 
 into those which rest merely on known and given external 
 indications {e.g., on phenomena or symptoms of diseases, on 
 the manner of their progress, or on the form, composition, and 
 similar properties of our medicaments), and those on the 
 other hand, in which rather the internal — that is to say, the 
 laws and mode of origin or action, in short, the more essential 
 characters, are adopted as the principle of the distribution. 
 The former are certainly, at present, the possible, or, at all 
 events, the easiest; but unfortunately they are of little use 
 excepting in the purely descriptive natural sciences — such as 
 botany, zoology, &c. — which aim, not at a thorough compre- 
 hension, but merely at the external characters — such as the 
 form and structure of the objects with which they are concerned. 
 The others, on the contrary, are, for the present, impossible j 
 but it should be our constant endeavour, for all the reasons 
 above adduced, to render them possible and available. 
 
 Every classification, however, presupposes, in the first place, 
 a fixation and limitation of the individual objects which are to 
 be classified. For every class or group comprehends a certain 
 number of such individual things and unities, which, with 
 reference to this their class or series, are called species. The 
 first step towards their classification must therefore be a certain 
 knowledge of them. Before we can think of rightly comparing 
 
344 CLASSIFICATION. 
 
 or distinguishing these species or elements — that is to say, 
 of classifying them — we must make ourselves acquainted with 
 them, each by itself, in all their more important properties and 
 relations. Now all the sciences and branches of inquiry 
 which have been more successful in this respect than ours, 
 have fortunately had to do with well-defined objects or pheno- 
 mena which present themselves to the observer as something 
 complete each in itself, well defined and isolated, or at least 
 admitting of being circumscribed and isolated with facility. 
 Thus every species, every element with which the chemist has 
 to do, whether simple or complex, has a certain number of 
 peculiar properties; each individual is a kind of unit, with its 
 peculiar mode of manifestation or of action, of combining with 
 others and being altered by them. The botanist, zoologist, or 
 comparative anatomist, when he proceeds to classify the objects 
 of his research, finds them already presented to him by nature 
 as distinct and circumscribed unities. They are, in fact, indi- 
 viduals with determinate properties or characters, which, more- 
 over, are produced according to types peculiar' to themselves, 
 and as such, develop, reproduce themselves, and pass away. 
 He has merely to observe and compare them, and make to 
 himself an abstraction of the type of each species or genus, 
 and he is immediately in a position to arrange them in groups 
 and classes according to the characters which they possess in 
 common. 
 
 But it is quite otherwise in our field of research, inasmuch 
 as neither in the processes and functions of the healthy body, 
 nor in its diseases, can there be any approach to the formation 
 of species and genera in a similar sense. The physician in 
 particular has to deal with events, — i. e., with changes in the 
 so-called normal or physiological existence and state of our 
 body, which intersect each other, modify, develop, and unite 
 themselves in a variety of ways, and this in a different manner 
 in almost every case. All his species and genera of diseases, 
 so far, indeed, as they can be said to exist, are therefore no- 
 thing but ideas or pictures deduced and constructed by him- 
 self. They are more or less arbitrary abstractions formed by 
 our intellect from that which we have observed in individual 
 cases, in order to bring their unlimited variety into something 
 like order, to obtain a more convenient survey of the objects 
 
CLASSIFICATION, 345 
 
 actually before us, and, lastly, to be able to predicate certain 
 common properties respecting them. 
 
 It is true that there are states of disease in which a certain 
 kind of unity may be supposed to exist, particularly in acute 
 and so-called specific maladies, such as scarlet fever, small- 
 pox, syphilis, cholera, and intermittent fever ; and in a great 
 number of skin diseases forms are presented to the eye which 
 might perhaps lead to the assumption of peculiar species or 
 genera, although neither in this nor in the other case do such 
 species and genera, in the strict sense of the words, exist. Be 
 this as it may, it has led to the mistake of classifying in a 
 similar manner diseases of a totally difi'erent character, without 
 the determinate ensemble of phenomena and processes ex- 
 hibited by the former, and without the same definite origin, 
 progress, &c. Nosology now includes not only such dis- 
 orders as inflammation of the lungs and typhus, but likewise 
 dyspepsia, gout, scrofula, epilepsy, and the like, as units in 
 its classification, regarding each of them, therefore, as a uni- 
 form essentially identical essence, whereas, in reality, almost 
 every particular case of the same species differs from the rest. 
 To the abstract idea of the disease, then, there is no individual 
 disease actually corresponding ; and so far the supposed noso- 
 logical unity has and can have no existence, because it relates, 
 not to any essentially uniform essence, but to mere pheno- 
 mena and their accidental and varying forms. But these 
 phenomena themselves are continually changing, because they 
 originate merely as effects or results, as secondary products, as 
 it were, from other and more deeply seated processes. For 
 similar reasons, also, every attempt at classifying diseases ac- 
 cording to their so-called " seat " in this or that organ, &c., 
 resting, therefore, on an anatomical basis, or according to cer- 
 tain changes of composition, and, therefore, based on chemical 
 grounds, cannot lead to a much better result. For, inde- 
 pendently of the consideration that separate elements or frag- 
 ments of the disorder are thereby erroneously regarded as the 
 whole, these anatomical or chemical species and units of 
 disease are not in themselves more reliable, and generally pos- 
 sess no higher value than the old symptomatic species. For 
 these material alterations, " lesions," &c., as well as other 
 phenomena or symptoms, are, after all, merely results or 
 
346 CLASSIFICATION. 
 
 members of the entire process of disease, andj under certain 
 circumstances, a portion of its necessary conditions. It is 
 often said that such and such diseases had at least the same 
 seat in an organ or texture in other cases, and that this is a 
 decisive characteristic circumstance. But, in reality, we can- 
 not speak of the seat of a disease ; we may perhaps speak of 
 the seat of a so-called morbid product, of an alteration of 
 texture, after-formation, and the like, but not of the seat of 
 a process which travels to different parts of the living body. 
 We cannot even make use of the alterations of individual 
 functions or processes in diseased persons as our ground of 
 classification, because we rarely, if ever, know which of them 
 are first, or chiefly disturbed, still less in what manner and 
 why. In so far, then, as, in these anatomical and chemical 
 changes, their causal connection and relations to other 
 changes or states in the same patient, and to the whole of his 
 disease, are far from being satisfactorily known, our scien- 
 tific knowledge of them, and therefore their applicability 
 to classification, are very slight. For, so long as we are 
 more or less unacquainted with the essential character, that 
 is to say, with the causes and connection of these changes, 
 we shall be constantly in danger of regarding comparatively 
 subordinate, dependent, or accidental disturbances, as cha- 
 racteristic and essential, and consequently of placing together 
 diseases which differ in essential characters, and, on the other 
 hand, of separating others which are essentially similar or re- 
 lated. Exactly the same is true with respect to the action of 
 the external world, and of our remedies, on the human body. 
 
 Moreover, as already observed, a comparison of all the sepa- 
 rate objects — i. e., of our so-called species and unities one 
 with another, is indispensable, when we wish to combine or 
 separate them according to their resemblances or differences ; 
 that is, to classify them. We require, therefore, for this 
 comparison a certain type or model, a single species (of 
 disease, for example), which, by exhibiting the impression of 
 all the more important properties of this series of objects, is 
 peculiarly adapted to serve as a type of comparison with others 
 of the same species and series. Such types readily present 
 themselves to the zoologist, comparative anatomist, botanist, 
 &c., but not to us ; because, for example, the several vital 
 
CLASSIFICATION. 347 
 
 processes, diseases, and actions of remedies, so far as we 
 know them, are too variable, too dissimilar in kind, and al- 
 together more or less unknown in their more essential points. 
 Finally, in classification, no single group or class can be 
 rightly formed or circumscribed by itself, but must rather be 
 viewed in relation to all the rest — i. e., as a member of the 
 whole collection of groups and classes. We ought, therefore, 
 for reasons above detailed, always to be in a position to 
 compare the things assembled in one group with those of 
 all other groups. But up to the present time we are not 
 acquainted with all the diseases to which man is subject, 
 even so far as is possible by ordinary observation; of his 
 diseases over four-fifths of the earth's surface we know very 
 little, and stiU less of those of the lower animals, and of 
 plants. 
 
 On the whole, then, it appears that it would be equally 
 vain and unsuitable to endeavour to proceed in our classi- 
 fication on the same principles as in the descriptive natural 
 sciences, or in chemistry. Nevertheless, such attempts were 
 formerly made, and are even repeated at the present day, 
 perhaps because the completeness and excellence of the classi- 
 fication in those sciences entice us to make them. We sufier 
 ourselves, in fact, to be misled by this false analogy, so far as 
 not only to discover and make out the existence of species and 
 genera of disease, but even to augment the number of such 
 species and genera as much as possible — and merely because 
 this division has its value in botany, zoology, and chemistry, 
 though in our science it has no value whatever. It is just as 
 if a meteorologist should endeavour to divide into so many 
 hundred species, and further into actual groups or classes, all 
 his phenomena and states of the weather, which are continually 
 varving and passing one into the other, according to season, 
 situation, and climate, and even on the same day ! In making 
 these attempts, it has been forgotten that the final aim of our 
 classification is by no means comparable with that of the purely 
 descriptive natural sciences, because the chief interest of the 
 physiologist and nosologist is directed to the understanding of 
 the vital processes and their laws and internal relations, and 
 not, as in the sciences just mentioned, to a mere acquaintance 
 with external appearances, form, &c. It has been forgotten 
 
348 CLASSIFICATION. 
 
 that our end, as well as our fame, can only be promoted by 
 searching for the laws and relations just mentioned, and thus, 
 by the discovery of the causal connection and more essential 
 characters of our diseases, medicinal actions, &c. continually 
 reducing the number of those species and genera, rather than 
 seeking to establish new and more extended ones. And if we 
 are not at present in a position to assist our understanding and 
 insight by our classification, in the manner already indicated, 
 that classification at least should not render the matter more 
 diflScult, or introduce additional confusion into our notions, 
 already so doubtful and indistinct, respecting those diseases, &c. 
 All our attempts at classification, however, ultimately agree, as 
 experience shows, in this respect only, that they either arrange 
 diseases, remedies, &c., according to phenomena, or properties, 
 and circumstances, which for our purpose are destitute of 
 positive value; or that they represent properties, causes, and 
 effects as actually present, which are far from being demon- 
 strated ; in some instances, not even investigated or probable, 
 but are rather hypothetically assumed, and then used for the 
 purposes of classification. 
 
 It is true that the latter state of things cannot be avoided, 
 if we wish to form such a classification according to hitherto 
 received principles, and in the ordinary manner. For, in fact, 
 our knowledge of all vital processes, diseases, remedial actions, 
 &c., is far from being sufficient to enable us to judge in 
 what principal points many of these agree, and in what they 
 differ ; and for this reason, all the higher or universal, and at 
 the same time more reliable, principles are wanting to our 
 classification. In other words, we are not at present, and 
 probably shall not be for some time to come, in a position to 
 form large groups or classes with certainty, and in accordance 
 with the actual state of things, or to predicate anything that 
 can rightly be considered as applicable to them all. And so 
 long as we are unable to do this, there is nothing left but to 
 form SMALL GROUPS of those objects (e. g., diseases and 
 remedies), which agree in all their more important properties, 
 and in the more essential points and circumstances, so far as 
 they are known to us. But our view of these more essential 
 and characteristic properties changes with the progress of our 
 knowledge, and with each period of its development, and to an 
 
CLASSIFICATION. 349 
 
 equal extent, as already observed, according to the particular 
 department of inquiry in view, and its peculiar interests. For 
 example, those properties of a substance or of a remedy, which 
 perhaps appear the most important to the chemist and natu- 
 ralist, are not so to the therapeutist and physician. The 
 latter, in his professional capacity, is interested in those quali- 
 ties only by virtue of which substances act upon and do 
 good to a patient ; and a classification according to these effects 
 — i. e., according to the changes induced by those agents 
 and substances in the state of his patients, would be the 
 best adapted to his wants. The hygeist and toxicologist, on 
 the contrary, would attach the greatest importance to those 
 properties and modes of action of the same influences or 
 substances by virtue of which they keep man in a healthy 
 state, or are capable of hurting him. In the study of diseases 
 themselves, the physician will regard, as the most important, 
 those aspects and circumstances which relate to their causal 
 connection, and to the manner of their origin, progress, and cure. 
 Hence, also, it appears that anatomical changes can have 
 but little value as a principle of classification of diseases, 
 because, in any division founded thereon, little or no atten- 
 tion would be paid to the very points which to the physician 
 are the most important, because in fact, the classification-titles 
 could not teach or suggest anything respecting those points. 
 Is it indeed to be expected, when we place together the 
 diseases of the same organ — (e. g., of the brain or stomach, 
 commencing with simple irritation, congestion, inflammation, 
 and proceeding to extravasation of blood, softening, cancer, 
 &c.), that much that is common and applicable to them all 
 can be predicated respecting them ? The same remarks may 
 be applied to attempts at classifying diseases according to 
 purely physiological or chemical principles, because the noso- 
 logist, if he would be true to his own interests, must not look 
 to foreign sources for the principles and points of view of his 
 classification. The scientific problem of the physician, as such, 
 is solely, as already observed, to attain to a knowledge of his 
 morbid processes, remedial actions, and their laws and causal 
 connection ; and for this reason, the phenomena and processes 
 in patients which bear directly thereupon, are alone adapted to 
 form the basis of his classification. 
 
350 CLASSIFICATION. 
 
 In such a classification, therefore, we must place together 
 those diseases, remedies, &c., which exhibit such phenomena, 
 processes, or states in common — that is to say, those which are 
 to us the most essential and characteristic. We must there- 
 fore endeavour to discover those which probably possess these 
 characters, and seek in the long list of our diseases, remedies, 
 &c., for those which most nearly agree with each other in these 
 respects. We must, in the first place, examine the cases and 
 circumstances in which these phenomena, effects, or processes, 
 stand out in the strongest relief, exhibit the highest development, 
 are least complicated by the presence of others, and therefore 
 present themselves to our notice with the greatest clearness. 
 Supposing, for example, that we had recognized the increase of 
 bodily temperature as such a characteristic phenomenon of a 
 series of morbid states, its relation, origin, and progress, &c., 
 would perhaps in the next place have to be more precisely 
 established by observations on patients sufiering from fever 
 and inflammation, because in such patients the observations 
 would be most easily made ; and those diseases in which this 
 (together with other characteristic phenomena) exhibited itself 
 most strongly and consistently, would then be placed together 
 in a group. Thus much having been established, we must 
 then look for the same phenomenon or element of disease in 
 its less distinct and prominent development, under circum- 
 stances and in patients in whom it exhibits itself in a lower 
 degree, is more complicated, masked and impeded by others, 
 and perhaps has undergone certain modifications. And if, in 
 course of time, we succeed in discovering the laws, the deter- 
 mining conditions of this series of phenomena, and in showing 
 that the same process or circumstance is characteristic of a 
 whole series of diseases, we shall then have made a nearer 
 approximation to another object of our science — the progres- 
 sive generalization or reduction of our processes of disease. 
 We shall then be more and more in a position to refer differ- 
 ences in them, which are apparently qualitative, and regarded 
 as essential, to mere quantitative differences. Lastly, it is 
 self-evident that neither in such cases, nor anywhere in nature, 
 can we safely use any single character — e. g., any single phe- 
 nomenon or process — as a ground of division in the formation 
 of our groups, but must rather avail ourselves of the greatest 
 
CLASSIFICATION. 351 
 
 possible number of characteristic and essential circumstances 
 — that .is to say, if we wish our groups to be natural, in 
 accordance with the actual state of things, and at the same 
 time instructive. 
 
 In the present state of our knowledge, these small groups 
 will at first, as above observed, include only a few diseases, 
 remedies, &c. : it is possible, even, that a group may in some 
 cases be made up of not more than a single disease. At 
 all events, we should hear no more of such classes as febrile 
 and inflammatory diseases, neuroses, dyscrasias, and the like, 
 or of a division of maladies into acute and chronic. It would 
 rather be necessary at first to divide such classes into small 
 groups, and put together typhus, plague, and cholera, dysen- 
 tery, acute exanthematous and syphilitic diseases, &c., in their 
 several forms, each in a group by itself. And in the theory 
 of remedies, instead of forming classes, such as organic and 
 inorganic substances, or diuretic, exciting, tonic, and astrin- 
 gent medicines, resolvents, alteratives, &c., we should rather, 
 perhaps, form groups containing only mineral and vegetable 
 acids, alkaUes and their salts, certain metals, narcotic sub- 
 stances, &c. On the other hand, the farther our knowledge 
 extends in various directions, the sooner shall we be able gra- 
 dually to enlarge these groups, or cautiously to unite with 
 them other groups agreeing with them in certain essential 
 points, and thereby to form more general and comprehensive 
 groups or higher classes. Moreover, the formation of these 
 classes would be further promoted by previously arranging 
 these small individual groups amongst themselves in our system, 
 according to their degree of relationship or analogy. We must 
 therefore seek to arrange them in such a manner, that those 
 groups which agree with or resemble each other in the most 
 numerous and important properties, processes, and circum- 
 stances, may be placed nearest to each other ; and those which 
 present but few and subordinate points of resemblance, the far- 
 thest. This mode of classification in natural groups, and accord- 
 ing to the degree of relationship or agreement, has perhaps been 
 carried to the highest pitch of technical perfection in compa- 
 rative anatomy and physiology. The mode of classification 
 adopted in these sciences exhibits to us, thus far, the most 
 complete example for our own, and we shall therefor^ do well 
 
352 CLASSIFICATION. 
 
 to proceed in our field of inquiry according to their prin- 
 ciples, but self-reliant, and with due regard to our own interests 
 and points of view. 
 
 It is not, however, the province of our Logic to enter fur- 
 ther into the mode of carrying out such a classification, or 
 into its technical details. Its task is sufficiently accomplished 
 in setting forth the universal principles of classification, and 
 the conditions which every classification must fulfil if it would 
 satisfy the requirements of our science, and therefere, also, of 
 its Logic. 
 
SECTION VII. 
 
 ON FALLACIES, THEIR DIFFERENT SPECIES, SOURCES, AND 
 IMPORTANCE. 
 
 Experience shows us, that errors and false conclusions are of 
 constant occurrence in our department of science, and, indeed, 
 are more particularly frequent in medicine, strictly speaking, 
 than perhaps in any other sphere of human knowledge and in- 
 vestigation. We are hence led to infer that some circumstances 
 must exercise so preponderating an influence as to cause us to 
 observe and interpret the same thing in many different ways, 
 whence deductions are drawn opposed to truth and fact. And, 
 again, many things are by this means made to appear correct and 
 proved without such being really the case. Upon these chances 
 of error, offering themselves at every step of an investigation, we 
 have sufficiently dilated on a former occasion. That we should be 
 constantly misled in observing and attempting to explain phe- 
 nomena and agencies, whose internal conformity and order have 
 as yet been so insufficiently defined, can by no means be re- 
 garded as wonderful. One may comprehend how even the 
 most gifted and highly talented men have been induced, under 
 such circumstances, and excusably so, to examine attentively 
 some very complicated matter, — perhaps even to attempt to 
 unravel and explain it, — before they have learnt to understand 
 its separate portions, or are in a position to answer with cer- 
 tainty even the most simple question concerning it. As in 
 every branch of human knowledge where there is a want of 
 solid foundations and of fixed principles, so in ours, only too 
 much depends upon the peculiar views and conceptions, upon 
 the tact and, so to say, instinct of the individual; and since 
 every one is free and unrestrained in his faith, doubt, or rejec- 
 tion, — in short, perfectly uncontrolled in his whole proceed- 
 ings, — he is the more prone to error in this particular branch 
 than in any other. However precious, therefore, liberty may 
 be in other matters, so as " to make up half the value of man's 
 existence," as Homer expresses it, yet in science it is the re- 
 
 23 
 
354 ON FALLACIES. 
 
 verse. Being then so circumstanced that we are all liable to 
 error, and doubtless have already erred scores of times, the 
 necessity of first learning thoroughly to understand and care- 
 fully to watch over ourselves, — that is, our mental processes, 
 — the creation and addition of our ego in connection with our 
 every observation and experiment, and more particularly with 
 our conclusions, is obvious. But since this is the peculiar 
 province of logic, we shall enter into its consideration with 
 more minuteness. It would be of small avail to dismiss the 
 subject with some commonplace phrases or trivial advice, as 
 for instance, that one ought to guard against all error, that 
 one ought to observe correctly and prove everything, and that 
 experiments should result only in such conclusions as really 
 follow, free from all prejudice, and so forth. How much more 
 useful to prove in detail that everybody, even the most acute 
 and sober-minded among us, may be deceived, at the same 
 time stating the causes and reasons ! Thus will he not only be 
 convinced that he himself, together with others his predecessors 
 and contemporaries, is exposed to the danger of error at every 
 step, but he will the sooner learn how that danger is to be 
 avoided. Although, from a knowledge of the rocks which 
 threaten him, his own feeling of security might be diminished, 
 still he would derive an advantage in estimating his own 
 achievements and the faults of others with due modesty and 
 precaution. 
 
 Instead of enumerating the various errors, and the apparent 
 show of reason by which they are supported, it will be far more 
 important for us thoroughly to examine into the cicumstances by 
 which we are misled, and how we are in consequence erroneously 
 induced to consider observations to be correct, facts to be proved, 
 and deductions to be true. Without some foundation in reason, 
 no one could conceive even the most erroneous views, neither 
 could he have drawn his conclusions, however false j his error 
 must have lain in his estimation of the convincing power of those 
 reasons, and of the reliance to be placed upon certain experiences 
 and assumed facts. But even if ready access to the comprehen- 
 sion of our subject be denied, we ought, at all events, to possess 
 a sufficient knowledge of it to prevent our believing that we 
 understand a thing when we really do not ; we should, at least, 
 have made such progress as not to accept a doubtful thing as a 
 
ON FALLACIES. 355 
 
 decided fact, or downright error as truth. And since it appeared 
 that physicians were even less upon their guard against this delu- 
 sion than investigators in other departments of science, especially 
 in aetiological and therapeutical questions, an explanation of the 
 circumstances likely to lead to errors on either side was deemed 
 the more indispensable. 
 
 In short, though the chapter of fallacies — the pathological 
 part of our logic, as it were — be bitter enough in many re- 
 spects, it is nevertheless a very useful one. Even correct 
 observations and accurate modes of investigation will be bene- 
 fitted by this knowledge of their reverse, just as the laws of the 
 formation of tissues, and the functions of the body in a state 
 of health, are better understood by observing their deviations in 
 disease. Thus, had our faults and errors been applied to their 
 proper use, they would frequently have shown themselves to be 
 the first defective edition of the truth, or at least its preface. 
 For alas ! it is only in the old myth that Minerva bounds at once 
 out of the head of Jupiter, whilst in reality severe and pro- 
 tracted labour-pains are generally required. Error, itself, how- 
 ever, has in nearly every instance paved the way to a better 
 understanding : " Ex errore citius emergit Veritas quam ex 
 confusione," says Bacon. 
 
 It is probable that in every case it is through our judgment 
 that, in the end, we err. Thus something appears to us as 
 real or proved, at least as very probable, without being either 
 the one or the other; or, on the other hand, we doubt or 
 wholly reject correct and real facts, or perhaps consider a thing 
 as erroneous which, nevertheless, is in perfect conformity to 
 truth. The sources of these errors of judgment, the causes 
 and circumstances which have induced them, are most nume- 
 rous and complicated, sometimes being only of a remotely 
 disposing, at others more nearly of a determining character. 
 On a former occasion mention was made of these, in so far as 
 they depend upon the special nature of our department — that 
 is, upon the peculiar difficulties which, for instance, the ex- 
 ternal world, as well as vital phenomena, diseases, &c., oppose 
 to our observation and interpretation, and to the formation of 
 correct opinions. These may even be looked upon as compar 
 ratively extrinsic circumstances, and are essentially always the 
 
356 ON FALLACIES. 
 
 same ; they are, moreover, unavoidable in a certain sense, inas- 
 much as the means at our command for their more perfect 
 exploration and correct comprehension, often appear insufficient. 
 Of far more importance for us at present, is the consideration 
 of such sources and motives of fallacies as lie within ourselves, 
 whether they be owing to imperfect comprehension or wrong 
 points of view, or to desires and aspirations resulting frora our 
 peculiar individual tendencies. They are all mutually and most 
 intimately connected with each other, and possess a higher 
 degree of interest here, since they may be avoided more or less, 
 or, at all events, more so than in the former ; for, in the end, 
 we and our ego — that is, our manner of contemplation, and 
 the relation in which we stand to nature in general, and to the 
 objects of our investigation especially — are more at fault than 
 the latter per se. The fact, likewise, of our knowledge and 
 powers, in regard to the grand problems of our subject, being 
 necessarily defective, is of less significance to us in this case 
 than the circumstance that we do not even know how to com- 
 prehend, in a correct and clear manner, things which ought by 
 no means to be beyond the horizon of our faculties. And the 
 precise circumstances or causes which impede, if not altogether 
 prevent the attainment of what is possible for us, and lead us 
 into error where we might have found truth if we had sought 
 for it more skilfully or more earnestly, require to be specially 
 considered here. 
 
 That a powerful influence is exercised by the susceptibility 
 and moral condition of the individual upon observation and 
 judgment, and that hence an abundant source of error arises, 
 requires no proof. Everything which makes a very vivid im- 
 pression upon our feelings, particularly if it captivate our 
 imagination, which keeps our interest in suspense, which rouses 
 our will and energy, or excites our fears in an unusual degree, 
 influences our whole intellectual being, and at the same time 
 clouds our perceptions or warps our judgment. In this state 
 we are less fitted for a calm and circumspect investigation 
 and correct judgment ; and whatever has in this manner once 
 taken hold upon our minds may be compared to a pair of spec- 
 tacles improperly adapted to our vision. The one is of neces- 
 sity almost as certainly allied to the other, as that a person 
 under the influence of wine or passion observes, examines, and 
 
ON FALLACIES. 357 
 
 judges quite differently from what he would in a sober and 
 calm condition. 
 
 The relation in which the observer is accustomed to be 
 placed in regard to the object of his research — that is, to 
 nature and reality — continually favours the operation of this 
 cause of error, and this in proportion to the influence of the 
 former upon himself or his intellectual being ; whilst it is only 
 by the slow road of research that we can obtain an insight into 
 nature, into vital phenomena, disease, &c., and, above all, by 
 the help of the cool and sober operations of our reason : on the 
 other hand, much of that which is submitted to our observa- 
 tion acts less upon our reason and judgment than upon our 
 feelings, imagination, and vague recollections, and more upon 
 these than upon the exercise of our will. Everybody has perhaps 
 experienced the excitement produced by a new discovery, 
 or a new and striking idea, whether his own or another's ; and 
 the judgment and approbation of the bulk of mankind are more 
 prone to be influenced by that which acts upon their feelings 
 and imagination than by that which merely appeals to their 
 understanding. It is, in short, exactly that part of our nature 
 which is influenced by external circumstances, and attuned to 
 vibrate to their touch, and in the naturalist or physician not 
 less than in others. Our feelings thus wrought upon, we are 
 no longer what we were, and what we ought to be for a calm 
 investigation. Now, whether the stimulus be no more than an 
 ardent zeal to find out, prove, or accomplish anything, slightly 
 tinctured, perhaps, with ambition, vanity, or rivalship; or 
 whether it be fear, excited by supernatural events or religious 
 belief; or lastly, whether it be the apprehension of pain and 
 disease, or anxiety to alleviate it in others, after all, in sub- 
 stance, it remains the same. For all these are but gradations 
 of passionate excitement ; and let them, as we advance, mani- 
 fest themselves in different directions, still their influence upon 
 our observation, conception, and judgment, after all, will only 
 prove different in degree and not in kind. No sooner do 
 certain feelings or tendencies preponderate, than we cease to 
 preserve that calmness of examination which we may possess in 
 reference to other matters, and which is so essential in our 
 observations and researches. 
 
 This effect is the more likely to be produced the greater the 
 
358 ON FALLACIES. 
 
 natural vivacity of the individual, the more confined the extent 
 and solidity of his knowledge, the lower his horizon, the more 
 limited his education, perhaps, and lastly, the more he is defi- 
 cient in an intimate knowledge of his subject, and in discrimi- 
 nation and clearness of judgment. The earnest desire, too, of 
 finding something corresponding to our own views and expec- 
 tations permits of our seeing such correspondence where it does 
 not exist ; or this may happen from our being under the do- 
 minion of some authority. In the former case we overlook 
 the arguments on the opposite side because we do not wish to 
 see them, because they are not consonant with our own notions, 
 wishes, and tendencies — or, at least, we do not view and judge 
 of the matter according to the actual state of things. 
 
 In both cases our state-of excitement and mental tendency, 
 ■whether we be conscious of it or not, our interest and narrow- 
 mindedness have blinded us to the defects of our whole argu- 
 ment. In the one case we do not ask for the same strict 
 proofs in accepting a thing as true and evident, no more, for 
 example, than does a partial, although perhaps a just judge, or 
 a favorably disposed jury ; we are satisfied with half-evidence, 
 or with such as is false, whilst in the other case we may, 
 perhaps, be blind to the most clear and valid reasons. In the 
 one case we perhaps merely notice that small part of the whole 
 which may be correct and proved, or at least probable enough, 
 because it just happens to answer to our ideas and wishes, and 
 overlook that which is wanting in the evidence, or which would 
 require quite a different interpretation. In the other case it is 
 just the reverse, although we may not be aware of it, perhaps 
 because we really have no hidden intention, or because we be- 
 lieve ourselves to be free from all peculiar tendencies, narrow- 
 mindedness, or partiality. The history of all times furnishes 
 us with examples of these sources of error ; and if we justly 
 wonder at the errors and blindness and great superstition of 
 our ancestors — for instance at their alchemy and astrology, 
 their philosopher's stone, or their faith in so-called signatures, 
 witchcraft, &c. — our successors will probably have little diffi- 
 culty in discovering similar aberrations and fallacies in us. 
 
 But the above further shows how, in the end, it is our judg- 
 ment and reason — that is, our interpretation and examination 
 of the things we observe, and especially the conclusions we draw 
 
ON FALLACIES. 359 
 
 from them — by which we err, even in the case of such fallacies as 
 are wont, proximately and especially, to have their origin in our 
 sentient and moral being. It is always from one or other of 
 these causes that seeming arguments appear to us to be real, 
 and false conclusions to be correct. We shall fall into such an 
 error much more easily and directly if its remoter sources, and 
 the circumstances which dispose us to it at the moment, are on 
 the side of our reason and judgment. For faults and defects 
 in this quarter naturally exercise an immediate influence upon 
 our whole mode of proceeding, especially in respect to what is 
 most important here — namely, the general character of our 
 arguments and conclusions, so that they likewise may become 
 defective, if not utterly wrong. But as soon as our judgment 
 has once become influenced in this manner from any quarter, 
 so that the freedom of its action has become disturbed, and 
 that in future it can only be looked upon as an erroneous con- 
 clusion pro or contra, it becomes a prejudice, and in so far 
 one of the chief sources of all our errors. But the manner in 
 which we arrive at it, and the remote motives intrinsically 
 connected with our prejudice, may also be manifold. 
 
 The influence of our ego — i. e., the great and inevitable part 
 which it plays in all our researches, observations, and conclu- 
 sions — must be regarded as the most determining and impor- 
 tant cause of such prejudices, because, lying essentially in the 
 whole nature of man, it manifests itself, more or less, in all of 
 us. This, also, has been sufficiently alluded to on a former 
 occasion. All things external to us, — nature, with all her 
 phenomena and processes, whether they be called animate or 
 inanimate, — only exist for us in so far as we have some concep- 
 tion or idea of them. It is not so much the things in them- 
 selves which have become intelligible to us by all our observa- 
 tions and researches, as rather our own conception and views 
 of them, as these have arisen in one way or another from those 
 observations and the deductions drawn from them. Those 
 phenomena and things exist, as it were, for us only in so far as 
 we have formed some conception of them ; and on that account 
 we are so easily induced to believe that they can only exist in 
 reality, precisely as we happen to conceive of them. More- 
 over, we are wont to take an interest in them, or occupy our 
 minds with them, only in so far as they correspond to our 
 
360 ON FALLACIES. 
 
 own ideas and views of them ; and whatever we observe, hear, 
 or otherwise ascertain concerning them at a later period, must, 
 as it were, adapt itself to our former ideas or views upon the 
 subject before it can appear correct to us. Here, as every- 
 where else, we have, as investigators, hardly any other alterna- 
 tive than to try to bring things into such relations to each 
 other as we regard as the most probable ones ; but these will 
 most frequently be such as best correspond to our former con- 
 ceptions and views. In natural science every explanation and 
 hypothesis is readily accepted as the correct one, provided it 
 only harmonizes with our previous ideas and notions. 
 
 Prom this we may likewise understand how it is not easily 
 given to any one, and least of all in a department of science 
 like ours, to adhere strictly to what is considered the first con- 
 dition of every observation and research — namely, to be entirely 
 unbiassed, and to take, in every case, a free and impartial view 
 of the subject. But as these preconceived ideas and views of 
 ours may be false, and especially as they are, at best, but 
 narrow, defective, and vague, our judgment, at any later mo- 
 ment, will almost necessarily contain more or less of prejudice. 
 At all events, it would be above the nature and powers of man 
 to guard against all errors from that quarter, and no illusion is 
 more ridiculous, none more dangerous, than to imagine that it 
 is nevertheless possible to avoid them. 
 
 For even the honest investigator, the most sober thinker, 
 cannot so far emancipate himself from that influence, and from 
 the consequent obscuration of his views and judgment, as would 
 be requisite, or as he himself may wish or believe. Whilst he 
 cherishes the belief that he confines himself to what is objec- 
 tive, and to facts, he easily overlooks the circumstance that it 
 is never his senses which observe and discover, or combine and 
 explain anything, but rather his mind and its interference 
 which, as it were, render those facts what they are. And it is 
 precisely this his mode of conception, which renders it impos- 
 sible to free himself from the influence of his intellectual being, 
 his whole train of thought and feeling at the moment. But 
 these, again, are most intimately connected with the whole 
 world of experiences, ideas, and notions which he has gained in 
 the course of time. Whether we may wish and approve of it 
 or not, there have long existed in us a certain knowledge and 
 
ON FALLACIES. 361 
 
 manner of viewing the things around us, and a certain way of 
 conceiving and representing them in one relation or another, as 
 well to each other as to ourselves. 
 
 And all this, however correct or incorrect it may he, exerts 
 a constant influence upon us all, and becomes, more or less, a 
 measure of our judgment — an authority. We can neither 
 render it ineffective, nor do away with it, any more, for in- 
 stance, than we can strip off our skin (D'Alembert). But if 
 this happens in the solution of ordinary problems, of which, 
 among others, the well-known tale of Homer and his fishermen 
 affords a striking instance, it will take place in a much higher 
 degree in the case of the problems of nature and our efforts to 
 solve them. 
 
 Moreover, our whole world of ideas, our habitual manner of 
 thinking, conceiving, and judging of all the things around 
 us, is continually taking new shapes, according to the mental 
 constitution of the individual, his peculiar abilities and ten- 
 dencies, the extent and clearness of his horizon, the degree of 
 intellectual development he has attained, and the nation he 
 belongs to. 
 
 Everybody, for instance, is aware of the difference which 
 exists in this respect between the Germans and the English or 
 French, between the North and the South ; and how, in natural 
 science, as well in medicine as in other branches, the propen- 
 sity of the former for a no less grand than vague and obscure 
 mode of conception and generalization, for premature and 
 groundless, because too comprehensive and profound systema- 
 tizing and theorizing is regarded as characteristic. Our mode 
 of reasoning and judging of a given case will further vary con- 
 tinually with the society around us, and with the circumstances 
 and times in which we live. And as we are always influenced 
 by the remembrance of what we experienced and thought' on 
 former occasions, and by the manner in which we have pre- 
 viously been wont to observe and reason, the importance of 
 another circumstance becomes evident at the same time — 
 namely, of the period at which we first became acquainted with 
 certain things. 
 
 Much depends, also, upon the point of view from which we 
 first learnt to observe various things — e. g., the problems and 
 phenomena in our department of science — and upon the 
 
362 ON FALLACIES. 
 
 methods which we adopted in our observations. For all this 
 cannot fail to exercise a powerful influence upon the views that 
 we may take of all our future experiences and observations 
 during our whole lives, as well as upon the conclusions we draw 
 from them. Thus each of us may find, upon a more minute 
 examination, that he has arrived, perhaps unconsciously, at one 
 inference or another, and consequently at certain general ideas 
 or notions, by things which he observed or experienced on some 
 former occasion. Perhaps we have never given utterance to 
 them, nor even arrived at a clear perception of them ourselves ; 
 but they may, nevertheless, influence our judgment on a future 
 occasion, as readily, for instance, as the likeness of one person 
 to another, long ago become repugnant or endeared to us, will 
 more or less determine our opinions, our sympathies, or anti- 
 pathies in regard to the former. 
 
 But all this gives a certain embarrassment and partiality to 
 our judgment, by which we now may be led just as readily to 
 a rash, perhaps totally wrong belief in the truth of certain 
 things or views, as to unbelief or rejection of others. This 
 danger threatens us because, if we observe, in a given case, 
 anything which agrees with our former views and expectations, 
 we are not wont to seek, with anything like the same zeal, for 
 further causes and proofs, as when it is contradictory to them. 
 In the latter case we are apt to be too critical and sceptical, 
 and even ask for proofs which cannot be furnished to such an 
 extent, and with such accuracy and strictness, in a department 
 like ours ; while in the former case we are too credulous, and 
 are satisfied, perhaps, with the most equivocal arguments or 
 facts. If, for instance, we once assume some condition or 
 causal connection as the true or most probable one, in a given 
 function or disease, we continue to observe, search, and reason 
 on in the same track, without taking other and quite diffe- 
 rent possibilities sufficiently into consideration. We treat our 
 view and conception of it at the moment as a fact about which 
 there can be no further doubt, and which now only requires to 
 be explained, or employed for the explanation of other things. 
 From these our general ideas or principles we now form our 
 opinions or explanations of individual phenomena and pro- 
 cesses. If any one, for instance, has assumed some anatomical 
 lesion of the lungs, the brain, or one of the valves of the heart. 
 
ON FALLACIES. 363 
 
 or some peculiar " crasis" of the blood, as the essential and 
 determining condition of a given disease, he looks upon every- 
 thing else — all the other phenomena and processes which may 
 be present — as the eflfect of the same cause. He explains and 
 arranges everything to his own satisfaction, just as it appears 
 to him as alone possible or probable, according to his anato- 
 mical or chemical point of view. If the belief has once pos- 
 sessed him that he has cured a patient by a given remedy, 
 nothing remains for him to do but to inquire or to explain in 
 what manner this result may have been effected. 
 
 And he who assumes the atmosphere of marshes, or " mias- 
 mata,'' to be the essential cause of intermittent fever, will not 
 hesitate to consider and explain all the other concomitant cir- 
 cumstances, relations, and influences — e. g., the higher tempe- 
 rature of summer, of the tropics, &c. — in exact accordance 
 with this point of view — that is to say, as promoting the for- 
 mation and intensity of action of those marsh-miasms, and, 
 consequently, the development of intermittent fever. He 
 perhaps takes too little into consideration various other co- 
 operating circumstances, which may be modified in different 
 ways, and act more or less according to the season of the year, 
 the temperature and climate, the quality and culture of the 
 soil, &c. 
 
 In short, here as little as anywhere else, can we consider 
 ourselves guarded against the danger of such errors of judg- 
 ment. On a more calm examination, it becomes sufficiently 
 obvious to every observer and investigator, especially in our 
 department of science, that in the study of natural phenomena 
 we are little better off than children, and that in this im- 
 measurable labyrinth we wander about well nigh as strangers. 
 We therefore necessarily look about for some support, and for 
 a certain guidance ; and what first naturally presents itself to 
 us is exactly what we formerly knew, thought, and remember, 
 concerning various things, or certain views, ideas, or theories, 
 which are the prevalent ones among our contemporaries or 
 with ourselves. We constantly reason, and form combinations 
 and conclusions, under the influence of some authority or other. 
 And we shall be governed by this authority the more, the less 
 we possess a clear and self-acquired knowledge of our own and 
 a thorough comprehension of our subject, and the greater is the 
 
364 ON FALLACIES. 
 
 general uncertainty of knowledge in the particular department 
 of science — as, forinstance, in ours. For the feeling of our own 
 uncertainty, and the want of a trustworthy basis for our judg- 
 ment, of firm ground beneath our feet, make us submit the 
 more readily to every foreign authority, whether it be such as 
 is old, or such as is novel and in vogue at the time. 
 
 In a science such as ours, in which the objects to be in- 
 vestigated are so manifold and complicated, and at the same 
 time so little understood, we may arrange everything nearly to 
 our own liking, as well, for instance, as in politics. We may 
 bring whole series of phenomena and processes, or influences, 
 into certain new relations to each other, and thus explain them 
 in a manner which is novel and peculiar to ourselves ; we may 
 turn our attention in different directions, and to different 
 things, which, perhaps, had not been noticed previously, or at 
 least not in this light. And if we possess not only acuteness 
 of mind, with a certain amount of knowledge and faculty of 
 combination, but likewise sufiicient eloquence and reputation, 
 we shall find many who believe us, and many who do not. 
 They will have faith in anything novel the more readily, if it 
 agrees more or less with their own former notions and points 
 of view, and if they believe that it furnishes further confirma- 
 tion of them, whilst, in the reverse case, they reject it. Even 
 in every day life we are easily influenced by the words and 
 opinions of others, provided they correspond to our own, or 
 perhaps even confirm them ; while, in the opposite case, we 
 doubt or reject them. For some everything which is novel, 
 striking, or piquant, has a much more irresistible charm than 
 for others; they view nearly everything in the exact light 
 which the new doctrine and fashionable theory of the day 
 throw upon it. 
 
 Thus, in the end, it will depend entirely upon concomitant 
 circumstances and upon the peculiarities of individuals, how 
 far we are accessible to the influence of any authority, of 
 novelty, or fashion — i. e. whether we believe in it, perhaps are 
 enthusiastic about it, or reject it altogether. In many respects, 
 indeed, every new point of view, everything which draws 
 us away from our old fashioned, perhaps narrow and false 
 views, and shows us things in a new light, may, for that very 
 reason, further our knowledge, or at least prepare the way for 
 
ON FALLACIES. 365 
 
 its acquisition, and ought, therefore, to be welcome to us. 
 But, in reality, such new views more rarely influence us in 
 this way than we ourselves are perhaps aware of. For, as we 
 have shown already, we do not easily, at a later period, relin- 
 quish the notions and views which we have once adopted, and 
 incorporated, as it were, with our whole intellectual being and 
 consciousness, either in any essential points, or for any length 
 of time. Perhaps we could hardly do otherwise, however 
 earnestly we may desire to do so, any more than we can feel 
 quite at home in a foreign country. We are all young but 
 once, we can only once go through the whole cycle of experi- 
 ences and all the processes which have brought our inward 
 being into connection with nature and men, as well as with 
 the facts and doctrines of our science; and indeed into the 
 exact kind of connection which has now become our own, or, 
 in other words, which forms our whole world of ideas, and 
 peculiar mode of thinking and judging of everything around 
 us. How rarely, upon the whole, this happens, is proved by 
 the circumstance that the world is wont to wonder at every 
 really novel mode of viewing things, and at every discovery or 
 original idea in individuals, and to attack or do homage to 
 them according to circumstances. And at the same time it 
 shows how rarely we are able to free ourselves from common 
 and predominant notions, and from the influence of what we 
 have learnt ourselves, or of traditional knowledge and opinions. 
 Thus, for instance, the so-called mediocrity even amongst 
 the learned and men of science, will not easily give up 
 such traditional opinions; their intellectual horizon, and the 
 influence of the views already adopted, as well as interests of 
 an entirely difi'erent nature, perhaps, are opposed to this. 
 From this it also follows, that in no science can the views 
 •and the approval of contemporaries be looked upon as a proof 
 of the correctness of a theory, or an opinion, any more than 
 their condemnation can be regarded as a proof of the contrary. 
 " Anticipationes," says Bacon, " satis firmae sunt ad consen- 
 sum. Quandoquidem si homines etiam insanirent ad unum 
 modum et conformiter, illi satis bene inter se congruere possent." 
 Without ever seeing with their own eyes, or standing upon 
 and walking with their own legs, they remain throughout 
 their whole lives subject to a foreign authority, and it is only 
 
366 ON FALLACIES. 
 
 this latter which changes, whilst they perhaps believe that 
 they have sufficiently emancipated themselves from it. 
 
 Others, again, are prejudiced against all that is novel, and 
 confirmed in their dislike of it from other causes. The more 
 experienced and cooler thinking man is perhaps' aware, from 
 his own experience, how difficult it was even to arrive at his 
 present state of knowledge, and how easily it may happen that 
 by one false step in advance or sideways, he may lose more 
 than he can gain. But especially in a department of science, 
 which, like medicine, is at the same time a practical one, this 
 is a point of double importance : and not without cause may 
 he now reject everytRing novel, which threatens to disturb, if 
 not to destroy this comparative accuracy of his knowledge and 
 practice ; especially as he does not know how much, perhaps 
 even of what is good, may be lost at the same time. But 
 setting aside these and other reasons, which may be in them- 
 selves legitimate, his opposition to all that is new may spring 
 from prejudice, narrowmindedness, or total error, and may 
 thus extend so far as to degenerate into the well-known 
 plodding spirit of the multitude. If one party, the empirics 
 of the old school, for instance, doubt much that is novel 
 chiefly because it does not correspond to their views, its 
 advocates, on the other hand, are frequently not less mistaken, 
 and that in consequence of their predilections, and partiality 
 for their own prevailing view or conception of the subject. 
 This, for instance, applies just as well to the representatives 
 and followers of our so-called modern exact medicine, to 
 pathological anatomists, microscopists, and chemists, as to the 
 physicians of the old school. For what the former cannot see 
 nor lay hold of, is said, according to many, not to exist at all ; 
 and if others hold a different opinion upon any subject, it is 
 pronounced to be erroneous or obsolete, if not wholly absurd.' 
 And, on the other hand, all novel views and explanations, - 
 even the most correct experiences and facts, may be doubted, 
 ignored, or attacked by the latter, only because they happen 
 to be contradictory to the notions which have become habitual 
 to them. If, for instance, some stubbornly adhere to the 
 ancient routine, and perhaps boast, as empirics, of an experi- 
 ence which they do not and cannot possess, others build 
 theory upon theory, which, in a department like ours, so 
 
ON FALLACIES. 367 
 
 frequently may have the appearance, but cannot bear the 
 real character, of scientific explanations. Both parties are 
 confirmed in their mode of viewing things by the circumstance, 
 that hardly in any other department of science is it so rare, 
 upon the whole, as in medicine, to find a more universal 
 education, a certain philosophical and clear insight into the 
 sources of our knowledge, and into the origin as well as the 
 nature of our notions and their connection with each other. 
 This may also serve to explain, why, in medical science, so 
 much may be believed, and, on the other hand, so much 
 doubted, without there being adequate reasons for the one or 
 for the other. 
 
 Many may be of opinion that a discovery or assertion of A. 
 cannot possibly be correct, or else certainly many others must 
 have found it out previously. In this they overlook what is 
 peculiar to genius, namely, to have a preconception of one 
 thing or another, to make combinations of various kinds, and 
 now, under favorable circumstances, to find out and to 
 demonstrate what others did not surmise and therefore did not 
 look for. With s^me, this doubt of everything new and un- 
 accustomed, of everything which does not agree with their 
 own ideas or views, grows to a perfect spirit of contradiction. 
 And great minds are, in the end, no less exposed to errors of 
 this kind than mediocre ones, and in the case of both it 
 frequently enough happens that some motive of a personal 
 or moral kind is added to those which are strictly scientific. 
 Thus in a case in which we perhaps reject the most certain 
 facts and established truths, because we do not understand 
 them, or because we are too much attached to our previous 
 notions, it not unfrequently happens that some private interest, 
 some rivalship or other, or at least the desire to uphold former 
 views and assertions in spite of everything, is the inducing cause. 
 And certainly every one who, for instance, has written a 
 comprehensive and complete work on any experimental science, 
 on any subjects or problems of natural history, whether on 
 physiology in general, or on diseases and their cure in par- 
 ticular, has been necessitated to state and maintain many 
 things without having had sufficient and absolutely valid 
 proofs at his disposal. He has, perhaps, assumed things as 
 probable tvhich were only remotely possible, or accepted as 
 
368 ON FALLACIES. 
 
 established truths, what ought, at most, to have aj)peared 
 probable to him, and has, indeed, to a certain extent, been 
 justified in so doing. For he himself, equally with his 
 readers, frequently had no other alternative than to accept 
 much in good faith, were it only because they themselves were 
 not able previously to investigate and to examine everything 
 accurately. And consequently future corrections, doubts, and 
 contradictions will never be wanting, because there is never 
 any lack of hazardous and partial views and assertions, and 
 even of decided deceptions in a science like medicine. But 
 he who is once possessed by the spirit of contradiction, and of 
 stubbornness of opinion, will try to maintain his former views, 
 even in spite of the most valid reasons and refutations, and 
 often will rather doubt the most evident truth, than their 
 correctness. And thus it happens, in the end, that any one 
 may so easily, almost from a certain innate necessity, con. 
 tinue to be deceived and mistaken so soon as he has once 
 fallen into error ; and this nowhere more readily than in refer- 
 ence to matters and questions, our knowledge of which is still 
 so fluctuating and obscure, and our mode .of conceiving and 
 judging of them so arbitrary, as in medical science. 
 
 Moreover, the very nature of man induces him^ to a certain 
 extent, to advance the most rash and premature opinions con- 
 cerning the precise things which he understands least of all, 
 and to which he has given the least amount of mature and 
 calm thought. For here, least of all, is he acquainted with all 
 the details of a given question, with all its conditions or com- 
 plications, and because his knowledge and experience do not 
 give him any certain grounds for one view or another, he now 
 the more readily draws an arbitrary conclusion suitable to his 
 own wishes. And again it can hardly be doubted that errors 
 from this source occur more frequently in medical science than 
 in any other. For even to explain, in some measure, the most 
 simple phenomena in the living body, or the most frequent 
 occurrences in our patients, we should require an amount of 
 knowledge which we are far from possessing, and still less does 
 our knowledge suflSce for the construction of comprehensive 
 and correct theories. And yet, on the other hand, we almost 
 daily find ourselves induced, and even compelled, in our 
 capacity as teachers and writers, to give some explanation of 
 
ON FALLACIES. 369 
 
 various things, and we do this, as well as we are able, in 
 accordance with our views at the moment. No one can well 
 be blind to all these gaps and defects, and misapprehend or 
 ignore them altogether ; and the wish to see them filled up will 
 become the more ardent, and our love of science, as well as our 
 necessities, induce us to help to effect this, the more fully we are 
 conscious of their existence. We attempt it as well as we can, 
 and, in doing so, are easily led out of our depth. We strive, 
 by hypotheses or arbitrary conjectures, by calculation and 
 imagination, to supply what is wanting in sound and positive 
 knowledge. We attempt to gain, by a bold coup-de-main, 
 what could only be taken by a regular and protracted cam- 
 paign, and frequently fail altogether. But if, in departments 
 of science which have been least illuminated by the torch of 
 research, the wish to see and find one state of things rather 
 than any other be superadded, there will be no end of a priori 
 combinations, of arbitrary, even paradoxical assertions and 
 attempts at explanation. And as these now fall into the hands 
 of men of essentially the same class, and of not much greater 
 knowledge, their fate, that is the approval or opposition they 
 meet with, will depend less upon their correctness and real 
 merit, than upon their agreeing with, or being opposed to, the 
 views or tendencies of the majority, and especially to the opinions 
 of the highest contemporary authorities. Moreover, a danger 
 is wont to arise from such an unrestrained use of hypotheses 
 and conjectures, from such arbitrary and hazardous attempts 
 at explanation, a danger which is the greater, as they not only 
 chiefly affect that part of our being which is most accessible, 
 namely the imagination, but likewise because by these means 
 two wants or wishes of the great mass or perhaps of every 
 individual are more or less satisfied, at all events more so, than 
 by a logical, sober, and deliberate research and judgment. 
 These are, firstly, the desire of understanding and becoming 
 acquainted with as much as possible in the most easy and 
 convenient manner; and, secondly, of obtaining something 
 comprehensive, and complete for their science, and rules and 
 points of support as certain and fixed as possible for their art 
 and practice ; and the great majority are not wont to inquire 
 closely whether all this has been done in a more or less 
 arbitrary and uncertain or even false manner. That which is 
 
 24 
 
370 ON FALLACIES. 
 
 held out to them is sufiGicient to satisfy thenij at least for some 
 time, and this the more, the better it suits their own ideas and 
 wishes, and the less of the latter they see themselves compelled 
 by it to relinquish. We eagerly accept, almost without exa- 
 mination, the often too confident assistance which is proffered 
 us against so many doubts and misgivings of our own, whether 
 it be in regard to our science, or to our art, very much, for 
 instance, as the beggar takes what is offered to him. 
 
 Now it is evident that in a science such as medicine there 
 is a double opportunity for errors of every description from all 
 those quarters which we have been considering, whether it be 
 in consequence of our doubtful, fluctuating, and unreliable 
 knowledge, or owing to our private interests and efforts. And 
 yet one of the most important possessions of man, his health, 
 is at stake. The dread of danger and the instinctive impulse 
 to guard against disease and pain, or to see ourselves delivered 
 from those which have once befallen us, equally oome into 
 consideration, as well as the efforts of the physician to satisfy 
 this desire as far as possible, For this is what his profession 
 and his conscience demand, and not the less upon its fulfilment 
 do his own advantage and profits, as well as his reputation 
 depend. And thus, lastly, it happens, that numerous induce- 
 ments and sources of error offer themselves to us at every step. 
 
 But if such errors frequently remain within the limits of 
 harmless illusion, so that we merely find and see exactly what 
 we are so fond of seeing — in short, if we frequently err from 
 mere credulity and self-deception — they may, in others, in- 
 crease to actual superstition or mysticism, the part played by 
 which, in medicine and even in some physiological matters, 
 needs no further explanation here. Men deeply skilled in 
 human nature pretend to have found out that certain tendencies 
 to error are to be found in every, even the most enlightened, 
 individual. But experience teaches, how these germs are first 
 brought to full development by an imperfect, if not decidedly 
 wrong observance of the laws which regulate our thoughts and 
 judgment, whether it be in consequence of a deficiency of 
 education, and of insight generally, or in our particular de- 
 partment of science, or in consequence of religious points of 
 view, favoured, perhaps, by peculiar experiences and so forth. 
 
ON FALLACIES. 371 
 
 But in order to laake this entire mechanism or process of 
 erring, which arises from all those different peculiarities of dis- 
 position, more clearly understood, and to bring it before us 
 according to the actual state of things. Logic must proceed 
 with a certain knowledge of the subject and of human nature 
 in general. The individual investigator must not only be well 
 acquainted with his department, but must likewise have suffi- 
 cient knowledge of mankind in general ; and the old proverb, 
 " Learn to know thyself," is especially applicable to the natural 
 philosopher and to the physician. For only by this means can 
 he hope to arrive at a better understanding of the mental pro- 
 cesses going on in others, -and at a better distinction of the 
 subjective from the objective, of the additions made by indi- 
 vidual observers and investigators from the actual state of 
 things and from that which is really perceivable by the senses. 
 It ought to be generally known that the natural philosopher 
 is in the same position and proceeds in the same manner 
 as others in regard to his observations and explanations, his 
 opinions and conclusions — i. e,, not only as a man in general, 
 but also as a man of a peculiar disposition and character, ac- 
 cording as his mode of viewing things happens to be at the 
 time; that even in his researches he can never divest him- 
 self of this, but that, on the contrary, he will view, compre- 
 hend, and judge everything differently according to his whole 
 train of feeling and reasoning ; for, in the end, it is of little 
 use to ascribe those aberrations in an off-handed manner to 
 onesidedness, prejudice, superstition, or mysticism, and the like. 
 For these are not, in themselves, defined causes and levers, but 
 are most intimately connected with the whole intellectual cha- 
 racter, with the whole mode of conception in individuals, and 
 subject, moreover, to the most manifold transitions into each 
 other. Everything will here rather depend upon a more 
 delicate psychical analysis, and our recognition of those errors 
 in our science will only become sufficiently clear by, our know- 
 ing how to trace in detail their so complicated and ever-vary- 
 ing sources, and the manifold combinations of cause and effect 
 in them. Of especial interest to us in this place are such 
 errors as spring, more or less directly, from our defective or 
 otherwise faulty understanding and judgment. For in so far 
 as they are wont to arise from the adoption of erroneous or 
 
372 ON FALLACIES. 
 
 bad methods of investigation, in themselves, and from false 
 inferences drawn from their results, and consequently consist 
 essentially in a wrong or defective application of logical rules, 
 they fall more within the province of our Logic than others. 
 
 If, for example, any one arrives at a false view in regard to 
 the mode of origin and intrinsic connection of a disease because 
 he still believes in supernatural agencies, in spells and witches, 
 and ascribes the falling ill of some person to these, this error 
 does not come under our consideration nearly as much as if 
 he has erred in his judgment about it, because he has made 
 use of defective or erroneous methods and expedients in his 
 observations, or because he has drawn wrong conclusions from 
 them in consequence of ignorance, onesidedness, and such like. 
 In the same manner it is of greater interest to us here that a 
 physician should believe himself capable of understanding the 
 whole of a disease and its causal connection by the pulse only, 
 or by similar symptoms, by the use of the stethoscope or per- 
 cussion, or perhaps by an analysis of the blood, or a post- 
 mortem examination, than that a quack pretends to find it out 
 from the urine which has been sent to him. And if any one 
 persuade himself that he can cure diseases, such as typhus, gout, 
 tubercular disease of the lungs, mania, &c., by his remedies, 
 because he desires to serve his patient as well as himself by 
 this belief. Logic has likewise less to do with this than if he 
 had arrived at the same error in consequence of imperfect 
 observation at the bed-side or at his experimenting-table, and 
 at wrong conclusions drawn therefrom. In the following part, 
 therefore, more especial mention will be made of these sources 
 or motives of error, that is to say, in so far as it arises essen- 
 tially from a faulty application of the common rules and laws 
 for the observation and establishment of facts, and for cor- 
 rectly appreciating and drawing conclusions from them. 
 
 But even among errors of this kind by no means all are of 
 the same interest to us, as some much more than others have 
 their source in the nature of man, as well as in the peculiar 
 species and character of our objects of investigation, and on that 
 account are more difficult to avoid than certain others. In 
 the end, indeed, we are all but unskilful horsemen on our own 
 ground, and " whichever way God and our horse wishes" ap- 
 plies more or less to all of us. And yet the one rides his 
 
ON FALLACIES. 373 
 
 horse not only with more grace, but likewise with better suc- 
 cess, than the other, because there exists a great difference 
 between knowing a thing and knowing it well, and still more 
 between knowledge and understanding and the power of exe- 
 cuting, between the will and the deed. We daily see natural 
 philosophers and physicians mistaken in questions and matters 
 where others did not err ; where, therefore, it was likewise more 
 or less in the povi^er of the former to have guarded against 
 error, provided they had better understood and more earnestly 
 sought to do so. The chief sources of such errors are there- 
 fore essentially of a subjective, or personal character, whether 
 it be a want of knowledge of the subject, and of practice, 
 levity, a rash disposition, or prejudice and superstition, perhaps 
 even the belief that certain opinions and views require no de- 
 monstration. All these motives of our errors, whether they be 
 remote or near at hand, may be avoided by any one if he will 
 but adhere to the common rules of logic, and apply them to 
 his department of science ; and since these have been explained 
 connectedly on a former occasion, they require no further 
 mention in this place. 
 
 It is otherwise with errors which arise from faulty or at 
 least onesided and obscure general points of view in our science, 
 in short, from faults and defects in the science itself, as well as 
 from certain faulty methods of investigation in it. And pre- 
 cisely these causes of error are more frequent, and at all events 
 far more serious than the former, for they depend essentially 
 upon the doubtful and unexplained nature of our whole sub- 
 ject. If the mere comprehension and distinction of the indi- 
 vidual vital processes or influences often appear difiBcult enough 
 to us, much greater difficulties in regard to our judging them 
 arise from the circumstance, that hitherto we have become 
 acquainted, and that very deficiently, with a small part only of 
 their extent, importance, and character, and of their relations 
 to each other. It is impossible, therefore, that we can already 
 have any clear and correct conceptions of them j and it is not 
 given to everyone to reason clearly upon anything in such a 
 doubtful and obscure department of science, or to give even to 
 himself a satisfactory account of what he means or wishes to 
 say. It may, perhaps, rather be assumed that it is, in general, 
 impossible for the human mind to undertake any investigation. 
 
374 ON FALLACIES. 
 
 and especially any interpretation or appreciation of what it has 
 observed, without being influenced by partiality or prejudice. 
 For in all cases, and especially in the theory of disease's, and 
 of their causes and cure, well nigh all positive and secure 
 points of support, and bases for the investigation of them, are 
 hitherto wanting. We are especially in want of that criticism 
 of the improbable, or barely probable and possible, by our 
 science itself, and by parts and doctrines of it which are reliable 
 and once for all fixed, as it exists in physics and chemistry, 
 and partly too in physiology. No sooner, therefore, do we 
 attempt to go beyond simple experience and facts — beyond 
 that, which we are taught by our senses — than, whether we wish 
 it or not, our ego, our subjective opinions and intervention 
 must play a preponderating part. But by this very means the 
 way is opened for our falling into error, in consequence of 
 wrong starting-points, one-sided conceptions, or preconceived 
 notions. 
 
 Oui" task then is, to bring these errors before our readers, 
 and, for the sake of a better view, to do so, as far as possible, 
 in a certain order. 
 
 All research and explanation in matters belonging to medi- 
 cine as well as to nature, in general, consist, in the end, in our 
 drawing a conclusion from the behaviour of certain phenomena 
 and processes in individual cases, ascertained by observation 
 and experience, as to the behaviour of all phenomena, &c. of 
 the same kind, and more especially as to their causal connec- 
 tion — i. e., as to the laws of their origin and development, or of 
 their action. By observation, and by the discovery of the 
 general state of things, we have to prove the correctness of 
 this conclusion — i. e. the existence of the causes or effects which 
 we have deduced or assumed. In the end, therefore, all our 
 errors and faults can only consist in the circumstance, that in 
 some place or other, a link, an element, and even, in most 
 cases, several are wanting in our investigation and demonstra- 
 tion. We draw a false conclusion from the things observed 
 by us, whether it may be owing to our having observed them 
 in an imperfect and wrong manner, or to our having inter- 
 preted them falsely and brought them into a causal connection 
 which does not correspond to the actual state of things. 
 
ON FALLACIES. 375 
 
 We shall now successively treat of our errors in the indivi- 
 dual steps or parts of investigation and demonstration. But in 
 this no strict classification can be thought of, because those 
 errors themselves are most intimately interwoven, and because 
 it is less our object to give a special description of them than 
 to show their intrinsic connection. If, for instance, there is a 
 deficiency of observation and determination of the true state 
 of things, there will usually be a much greater want of compa- 
 rison of them with others, of correct interpretation of what has 
 been observed, and of conclusions as to the exact connection of 
 cause and effect. And if we happen previously to have had 
 some incorrect, or at least obscure notions in regard to the 
 latter, if our whole point of view has been in any way imper- 
 fect, or if we had a special interest to find some particular 
 state of things and not another, the observation itself will 
 very rarely prove quite correct. It has, therefore, appeared 
 suitable, first of all, to give a more close consideration to cer- 
 tain complicated errors — namely, to those in which the whole 
 mode of conception, the general starting points and manner of 
 investigation and interpretation have been wrong, or at least 
 onesided and confused, which naturally could not remain 
 without influence, as well upon the observation and establish- 
 ment of facts, as upon their interpretation, and upon the whole 
 method of demonstration in individual cases. In so far, such 
 errors may be termed " Collective- or universal- errors," in 
 comparison with others which we shall consider afterwards. 
 
 I. ERROKS IN THE WHOLE MODE OF CONTEMPLATION, OR 
 CONCEPTION AND JUDGMENT. 
 
 (Collective or universal errors.) 
 
 History shows us how long it took the human mind, how 
 many circuitous paths and indirect and erroneous methods it 
 had to adopt, ere it advanced so far as to occupy that objective 
 sober position in regard to nature and reality which now, at 
 least, appears the only correct and possible one. 
 
 This lies, indeed, entirely in the nature of the subject itself. 
 All that which we are accustomed to include in the term 
 nature," and of this, again, especially the " animate" part, is 
 
376 ON FALLACIES. 
 
 of such a kind, that we can only arrive by successive steps at 
 a more correct and profound understanding of it. Here the 
 human mind cannot accomplish or discover anything by itself, 
 and at once, as it has in its power to do in the sphere of ima- 
 gination and art. For this, not only able heads and faculties, 
 which always have been, and always will be, rare, are required, 
 but likewise time, a certain solid advance of understanding, — 
 and this, again, not only in every individual department of 
 natural science in particular, but rather in all of them together. 
 With all this, however, our whole conception of nature and life 
 must, in the course of time, become a different one ; further, 
 the view we take of our relations to everything which exists 
 and takes place externally to our bodies, as well as of its rela- 
 tions within itself; and finally, no less our opinion as to the 
 mode by which we may acquire an insight into these relations, 
 and into the so-called " laws of nature." 
 
 On that account, also, every individual has always been 
 more or less dependent, in his views of nature and life, as well 
 as of all other things, upon the degree of civilisation and 
 knowledge attained by his nation, and even by mankind gene- 
 rally, at the period in which he lived, — the sincerely religious 
 man of old times, as well as the sceptic and materialist of our 
 own day. Everyone is and remains a child of his time, and 
 however much an individual genius may be in advance of it, 
 he will be so in a far higher degree by his grand and free con- 
 ception, by his correct surmises of the mutual relations of 
 various things, than by his penetrating investigation of them, 
 and consequent sufficiently comprehensive and correct demon- 
 stration of the accuracy of his views. Many a one, indeed, dis- 
 covers single important facts ; but rarely or never will it be given 
 to one man to bring them into their proper connection with all 
 the things bound up with them, or even to determine with suffi- 
 cient accuracy the conditions of their origin, mutual relations, 
 and laws. This necessarily shows that even the greatest minds 
 of all times will essentially remain within the limits of the 
 general position which their period holds, and more or less 
 under its influence. And this position, these general views 
 and conceptions, have, as we have already observed, continually 
 been changing, and fortunately, by degrees, always become 
 more correct ones. 
 
ON FALLACIES. 377 
 
 Thus it is well known thatj even as late as during the middle 
 ages, superstition of every description — e. g., the belief in a 
 direct agency and mediation of the devil and his adjutants^ 
 male as well as female, in the power of witches and sorcerers 
 — prevailed universally. Now, at that time, the ascribing 
 of all sorts of things, — for instance, of the causes of tem- 
 pests, storms, earthquakes, and such like events in nature, 
 as likewise of diseases and their cure, — to the devil and witch- 
 craft, or perhaps, in deficiency of something better, to the 
 Jews, may have been just as natural as our present disbelief of, 
 and even aversion to, every explanation of this kind. And, 
 even in the present day, the uneducated man, the obscure 
 thinker and mystic, for instance, takes quite a diflferent view of 
 the subject from the natural philosopher or physician. We 
 are likewise well acquainted with the part which that belief in 
 supernatural agencies and processes, in the power of magic, 
 and such like, has played in the whole field of natural science 
 — in physics and chemistry, for instance, in astronomy and 
 meteorology, as well as in medicine — and how it has been 
 continued even to our times, especially in the latter science. 
 In those times, as well as in our own, it was found more con- 
 venient, and, in a certain sense, even more natural, for man to 
 speculate upon diseases and their cure, upon phenomena and 
 processes in nature generally, and to attribute them to various 
 hypothetical influences or powers, just as he happened to form 
 a notion of them, than to examine carefully and laboriously 
 into their intrinsic relations. Here, still more readily than 
 elsewhere, men took their ego as the starting point for their 
 conclusions, and easily believed, not only that all the radii of 
 the world must necessarily meet in a person of so much im- 
 portance as man, but likewise that he could and might explain 
 everything out of himself by his views and ideas. The mental 
 tendency and degree of civilisation of those times could, indeed, 
 only lead to such hypotheses and notions about those things as 
 can now be considered no better than superstition. At the 
 same time this superstition, whatever form it might take, was, 
 in the end, based upon the natural want or desire of man to 
 interpret everything within and around him, and in all these 
 cases to give to himself and his ideas a point from which he might 
 start, or to which he might hold fast as well as he could. 
 
378 ON FALLACIES. 
 
 Men only erred in regard to the appreciation of their know- 
 ledge and resources ; and having once committed an error in 
 their judgment of that which alone can afford us the insight so 
 much longed for, they likewise erred in the selection of their 
 methods of investigation, as well as in the manner of carrying 
 them out. Even in the present day no one, and least of all in 
 our department of science, can free himself from a certain 
 degree of superstition, taking the word in its more extended 
 sense, inasmuch as he is compelled to believe in many things 
 without sufficient proof, and without a clear comprehension of 
 what he does believe, and of his reasons for so doing. Al- 
 though he admits the various inexplicable phenomena conti- 
 nually going on around and within him to be mysterious or 
 extraordinary and surprising, still he is anxious for some solu- 
 tion, and in this condition is readily impressed by any inter- 
 pretation, and assents to anything which may facilitate an 
 explanation, or affords some compensation for a better under- 
 standing. It is from this condition of things that superstition 
 derives its chief support, in whatever shape it may present 
 itself, and in whatever direction it may offer its assistance. 
 However wrong it may be, man always believes that he can, by 
 its aid, satisfy some want of his nature. Superstition flatters 
 him with the fulfilment of his dearest wishes, and not only 
 holds out the prospect of understanding that which he has not 
 yet learnt to comprehend, but likewise of accomplishing that 
 for which he has been longing, whether this be gold and for- 
 tune, health and long life, or a foreknowledge of that which is 
 to come. Now whether he anticipates such results and ser- 
 vices from supernatural agencies, from the moon, stars, amulets, 
 philtres, and elixirs of life, or from miraculous pictures of saints, 
 from so-called sympathetic means, from impossible remedial or 
 curative powers, &c., makes no difference in the main. It is 
 likewise sufficiently well known that to this longing and want 
 of man, even in our times, is to be traced his judgment of 
 nature and its reciprocal relations to him, his opinion of the 
 origin of many diseases, and also his belief in certain re- 
 medies and their modus operandi. And further, the transition 
 from common superstition to modern mysticism may be thus 
 demonstrated, and at the same time an explanation found for 
 the contradiction which always exists between the true investi- 
 
ON FALLACIES. 379 
 
 gation of nature and such superstition^ -whether it present 
 itself in its usual form or not. 
 
 A further kind of deviation from the right path, of not less 
 extent and influence, has heen termed " teleological," which, 
 originating in man's nature like genuine superstition, arises from 
 the limited character of our comprehension, and from a certain 
 subtle selfishness almost without a motive. For since man, 
 like every other created being, is depend^t upon surrounding 
 nature, he must learn to understand her for the furtherance 
 of his own interests ; and this is not to be accomplished from 
 nature's own advancements and by her unveiling herself to 
 him, but by his own endeavours, and the exercise of his mental 
 faculties in exploring her. Everything existing and occurring 
 external to him has only such an existence for him as is per- 
 mitted by his consciousness ; all those innumerable threads 
 which bring him into connection with nature and the external 
 world begin at his consciousness and ego, and at his notions 
 concerning them, and terminate there also. Hence he is 
 readily brought to look upon himself — i. e., upon his ego, which 
 alone has procured him such conceptions — as a sort of centre, 
 and is led to identify all external things with it aad his inte- 
 rests. Just as princes and their courts have believed that land 
 and people existed for them alone, so may he at last be simple 
 enough to imagine that nature and the world have been created 
 solely for his sake, to supply his wants alone, and have been 
 arranged and regulated merely to suit his understanding; 
 that even the moon and stars were ordained to stand in 
 a special relation to a being like man, to govern his fates, 
 to rule over his prosperity, his sickness, and recovery, and 
 lastly, to regulate the atmospheric phenomena and climate of 
 his earth. 
 
 To the same source, in the end, may be traced the further 
 error, that everything in nature not only exists and occurs for 
 a certain purpose, but also for just such purposes as may 
 "happen to appear to us the best and most suitable. It was 
 thought that nature must, so to say, go to work with design 
 and judgment, and with such design and according to such 
 laws and principles as we just happened to be acquainted 
 with. Now a twofold temptation to an error of this kind 
 existed at the first origin of medicine, more especially as an 
 
380 ON FALLACIES. 
 
 art. Led on and animated by the desire of curing diseases, 
 &c., the practitioner was from the very first induced to bring 
 everything existing and taking place in nature, into a one- 
 sided, teleological relation to the welfare and prosperity of 
 man, to his falling ill and still more to his recovery, and 
 to observe and judge of it from this point of view alone. 
 Thus, instead of looking upon the life and well-being of man 
 simply as the necesgary consequence of the processes in his 
 body, acting in unison, according to fixed and never changing 
 laws, and also as the consequence of the influences and 
 agencies of the external world acting here as elsewhere accord- 
 ing to their own laws, all this was thought to take place with 
 the very purpose and object that man should prosper and 
 continue healthy. And again, in the case of his falling sick, 
 instead of looking upon it as a thing taking place and pro- 
 ceeding in his organism according to its fixed and never- 
 changing laws, only under circumstances and conditions differ- 
 ing from the usual and normal ones, and consequently with 
 other results than the usual one of health, every disease was 
 thought to be a violation or contradiction of the above laws of 
 our organism and life, or a deviation from its purpose. Thus 
 diseases are said to have peculiar hostile intentions, or a desire 
 of occasioning some mischievous disturbance, and one talks of 
 the tendency of inflammation .to dissolve and destroy the parts 
 affected by it, of a disposition or tendency of articular rheu- 
 matism to affect the heart, and of scarlatina to affect the 
 brain, &c. On the other hand, the healing tendency is attri- 
 buted to those processes which, by an innate necessity, lead to 
 cure and recovery. So, for instance, absorption and resolution, 
 or the conversion of so-called products of disease, are said to 
 take place for the sole purpose of removing the noxious matter 
 and re-establishing the normal state. 
 
 Up to the present day medicine has taken an interest in the 
 atmosphere and the weather, in food, in the properties, modes 
 of action, &c., of drugs, only in so far as they bear upon the 
 maintenance of health, the occurrence of disease, and the 
 process of cure in mankind. And although, in a certain sense, 
 with a perfect right of so doing, still we can neither com- 
 prehend and judge of this correctly, nor can we make use of 
 those influences in the proper and most useful manner, unless 
 
ON FALLACIES. 381 
 
 we have previously acquired a sufficiently comprehensive know- 
 ledge of their peculiarities and effects. 
 
 The fault of attributing one's own views or ideas, and 
 one's own desires or tendencies, to nature, lies at the bottom 
 of the whole teleological error — in other words, just what one 
 happens to think, and how one does so, is actually thought to 
 exist and take place in nature. And since one is thus far on 
 the high road towards playing the dictator — the arbitrary in- 
 terpreter of nature's laws — by looking upon one's subjective 
 conceptions as objective and possessing a real existence, there 
 needed but one short step to the so called " ontological" mode 
 of contemplation, and even to downright mysticism — errors and 
 confusions, whose character has made itself well enough known 
 in our department of science. These errors, however, rest 
 essentially upon the same basis as the preceding, inasmuch as 
 we set to work in an a priori and arbitrary manner, sub- 
 mitting ourselves to our own disposition and prevailing ideas, 
 and interpreting and arranging nature's proceedings for the 
 convenience of explanation or conception. 
 
 Now what is usually denominated "Ontology" consists 
 essentially in this, that by abstracting all the determining 
 circumstances and conditions of a certain event (for example, 
 of life, of some natural phenomenon, or of a disease) and com- 
 prising them in one's mind as a something — as an object — 
 a real existence is conferred upon it in one's thoughts, and it 
 is transformed into a peculiar principle, existing and acting for 
 itself. Whether one now conceives it to be a "force," or 
 personifies it in a more palpable and allegorical manner, as 
 possessing a body and substance, or even, like the ancients, as a 
 species of god, and similar metaphors, makes but little differ- 
 ence in the essential motive and character of this mode of 
 contemplation — man is induced to do this by his natural, 
 almost instinctive desire to render things intelligible and to 
 conceive of them in his own way and in a manner as con- 
 venient and easy as possible, and therefore corresponding to 
 his own ideas and position; and thus it is that we see this 
 error creeping in in every day life. From inattention, for 
 the sake of convenience or brevity, and for similar reasons, we 
 put in the place of the real state of things, our abstract idea of 
 a thing or " being," even if it is only by bestowing upon it 
 
383 ON FALLACIES. 
 
 a substantive appellation. When speaking of technical terms, 
 we had occasion to show how we are the more readily led into 
 this error by our customary words and names, and especially by 
 the number of substantives in the Latin language j since we 
 easily believe that to every such particular name or word, and 
 to the ideas which we connect with them, a certain something 
 must correspond. Just as we say, for instance, " history men- 
 tions," or "the law, the state demands this and that," whilst 
 it is individual men who mention it, or who have found the 
 law suitable, so we likewise speak of memory, reason, will, or 
 of heat, light, tempest, and their peculiarities, conditions, 
 effects, and laws (as existing) in and by themselves. And if 
 the savage attributes peculiar causes to all he sees or feels, and 
 further personifies these as gods, demons, fairies, and the like, 
 so the physicist, who has seen the electric spark, abstracts 
 therefrom his idea of the electric fluid, and from the solar 
 light and its phenomena and mode of manifesting itself, 
 abstracts the notion of a light-material, beam of light, &c., 
 and similarly the physiologist his nervous fluid, &c. In one 
 case as well as in the other the real state and cause of things 
 was assumed to correspond to the distinctions of all these 
 phenomena, effects, and causes, as we just happen to conceive 
 and arrange them. Thus we speak of electricity, heat, mag- 
 netism, and other imponderables, whether we imagine them as 
 an ens, a something in itself, or as a mere " force" and so 
 forth, instead of conflning ourselves to the bodies and sub- 
 stances themselves, in which we have observed the phenomena 
 or properties denominated warm, cold, luminous, electric, &c., , 
 we rather confine ourselves to the causes of them, which we 
 have ourselves abstracted and more or less personified, and 
 now speak of qualities, effects, &c. (e. g. of light, heat, elec- 
 tricity), as peculiar matters or forces in themselves. We pro- 
 ceed in exactly the same manner in respect to the vital force 
 when we sum up the aggregate of all the circumstances and 
 influences which may lie at the bottom of the whole process of 
 life, as something existing by itself, as a unity. We now 
 readily look upon this abstract em as a kind of self-acting 
 executive power, as an active and effective thing in itself, 
 which is even endowed with a power of creating for itself a 
 substratum, the living body ; we speak of its rise and fall, its 
 
ON FALLACIES. 383 
 
 action in one direction or another, perhaps even with peculiar 
 beneficial tendencies and motives : for the sick, for instance, 
 we imagine this vital force to be disturbed and changed in 
 various directions or ways; remedies and drugs are supposed 
 to aflfect it by means of peculiar curative or medicinal powers 
 of their own. But in itself already, this vital force — as an 
 offspring of the kindly purposes of nature — has been endowed 
 with a disposition to react against such disturbances of its 
 regular action, as encroachments upon its legitimate executive 
 power, just as an able statesman or general would do, and thus 
 it has manifested itself as the natural healing force. Thus it 
 was assumed that it was this force which led to curative efforts, 
 to favorable crises, and finally to preservation and cure. 
 
 By the same method of abstraction, and of the personifica- 
 tion of the abstract notions formed, what took place and was 
 observed in patients, came to be regarded as a thing existing 
 per se — i. e., as " disease." Now whether we form a certain 
 number of species of disease from the latter, or whether we 
 speak of peculiar acrimonious matters, or poisons (for instance, 
 the poison of gout), and such like, per se, or whether we 
 attempt, even somewhat more palpably, to represent those 
 diseases as a kind of organism and parasitical being, also 
 makes little difference in the main point. In the one case, as 
 in the other, we have combined together, as a unity in itself, 
 that which we observed in a certain number of patients 
 similarly affected ; from single cases of a " disease" we ab- 
 stracted the picture, the notion of this disease, as, for instance, 
 we abstracted the notion of the colour " red" from all red 
 things, or that of warmth, hardness, from what we observed in 
 all warm and hard bodies. And as we now speak of the pro- 
 perties, effects, and laws, for instance, of a red colour, or of 
 warmth, as of a thing in itself, we in a like manner speak of 
 those of a disease. < Thus one disease is said to increase the 
 heat of the body, to weaken the person attacked by it, to 
 spoil his appetite, or digestion ; it is said to grow, ripen, and 
 cease; to be capable of travelling and wandering, of being 
 benign or malignant ; to demean itself in a friendly or hostile 
 manner towards colleagues, that is, towards other diseases ; to 
 change, be hereditary, or generate a poison, a contagion, by 
 which it infects others and propagates itself. The physician. 
 
384 ON FALLACIES. 
 
 however, is said happily to have the wish and power of guiding 
 it, driving it here and there, or expelling it entirely, or at least 
 of fixing, neutralizing it, &c. 
 
 A further criticism of these ontological views would be 
 superfluous in this place. We have here to treat only of their 
 actual existence, as they happen, in various ways, to develop 
 themselves in us from early youth, and to grow together with 
 our notions, so that they now usually become more or less 
 determining for our whole mode of conceiving and judging 
 throughout life. It has likewise been shown, on a former occa- 
 sion, how this species of Ontology lies, in a manner, in the 
 nature of the case itself, being not only the nearest at hand 
 and most convenient for our conception of all those natural 
 phenomena, processes, &c., but likewise for explaining and im- 
 parting a knowledge of them to others. For exactly this faci- 
 litates a concise, and still more a comprehensive, as it were, 
 plastic representation of them, on which account it is very 
 much in favour, especially with teachers, orators, and writers. 
 But that, nevertheless, a certain confusion, and even a decided 
 error lie at the bottom of this whole manner of contemplation, 
 representation, and expression, requires no proof here. We 
 attribute a real existence to the views and conceptions of any 
 phenomenon or object, which we have adopted for the sake of 
 greater convenience, or for other reasons, and now proceed as 
 if everything were exactly so as we have imagined it to be. 
 
 From this point also a natural transition takes place to that 
 host of errors, which we are wont to comprise as purely arbi- 
 trary, a priori dicta and hypotheses, as random assertions and 
 attempts at explanation, or speculations. For, in the end, the 
 same circumstance is to be found at the bottom of these also, 
 namely, that we take it for granted that certain things must 
 necessarily be so, and stand exactly in that relation to each 
 other which we have assumed for them, without, however, 
 having ascertained the real state of things, and therefore with- 
 out furnishing any positive proof of the accuracy of those our 
 conceptions, attempts at explanation, and theories. But that 
 this kind of self-deception and error has always been the bane 
 of all sciences, and especially of medicine, is sufficiently well 
 known ; and it is to be foreseen, that such will continue to be 
 the case so long as we attempt to give an explanation, or even 
 
ON FALLACIES. 385 
 
 a coherent theory of things, our knowledge of which is, at best, 
 but fragmentary. On that account we Hkewise find such an 
 a priori mode of proceeding, and similar errors, no less in cer- 
 tain branches of physics and chemistry, than in physiology and 
 medicine. In all these sciences we frequently draw conclusions 
 concerning individual cases and their laws, from certain general 
 theories and views, the correctness of which is problematical — 
 at all events not proved by experience — instead of ascending 
 to those general theories through a previous discovery of the 
 former. 
 
 But, on the other hand, this whole a priori mode of pro- 
 ceeding lies in the nature of our subject itself, and in our legi- 
 timate longing for knowledge. We know also that we should 
 hardly ever discover anything, unless we had previously thought 
 of its possibility, and that even the most able and sober inves- 
 tigator is wont to pass from his original, frequently hypothetical 
 notions about certain things to the investigation of their real 
 state, therefore from his ego to the thing itself, to reality. 
 He now readily proceeds a step further, and takes that as 
 proved, as a fact, which, after all, is so only according to his 
 views. 
 
 Yet some persons have always been led into this error more 
 than others, because their whole nature urges them to it. And 
 if they err by overrating the importance and character of their 
 subjective opinion, in itself, there are others again opposed to 
 them, by whom these a priori views and mode of proceeding 
 are regarded as entirely worthless, who erroneously believe 
 that they have done all that is necessary by the simple observa- 
 tion of various things, because their capability and horizon find 
 their limits here. For the former, the investigation of all the 
 questions and details cannot proceed quickly enough, and they 
 give too much scope to their ego ; they mostly see and find too 
 much, and build their theories and explanations upon a basis 
 for which their experience furnishes no guarantee. The latter, 
 on the contrary, adhere to individual and isolated points, and 
 are incapable of putting to themselves higher and more pro- 
 ductive problems in their investigations ; they now see and find 
 little enough, because they did not understand what and where 
 they were to seek. They readily, however, doubt everything 
 which has been found and asserted by the former, more so, in 
 
 25 
 
386 ON FALLACIES. 
 
 fact, than is right — i. e., they even doubt what may be correct 
 in their discoveries, or theories. They even despair of the pos- 
 sibility of any discovery or certainty in general, perhaps because 
 it would not succeed in their hands, and could not, in conse- 
 quence of the peculiar constitution of their minds. These, as 
 well as the others, in a certain sense, confound their ego with 
 reality, in giving themselves up to the mistake, that their sub- 
 jective views and notions of the matter must necessarily be the 
 only correct ones. 
 
 The spirit of doubt or scepticism, in general, is, therefore, 
 no less a species of a priori error, inasmuch as it leads us to 
 interpret the real state of things in some way, and to form 
 some, though perhaps only a negative opinion about it, without 
 having previously become acquainted with it in a sufficiently 
 clear and comprehensive manner. We perhaps seek, by this 
 means, to guard against arbitrary a priori abstractions, without 
 considering, that " doubt is a good beginning, but a bad end." 
 We ignore or deny what we are unable to explain, and reject 
 an unexplained fact altogether rather than confess, openly and 
 honestly, that we cannot account for it, or that it appears sur- 
 prising to us, perhaps even disagreeable, because it is opposed 
 to our former views. 
 
 Thus it appears, in the end, that all the errors which have 
 been alluded to above are, in fact, nearly of one and the same 
 kind. In this long series — from a priori conjecture to the 
 ontological and teleological, or even theological mode of con- 
 templation, and finally to downright mysticism or superstition 
 — no distinct boundary can be drawn, because their principle, 
 their fundamental source is, in the end, of the same kind, i. e., 
 because they differ from each other in degree only, or in their 
 prevailing direction. No well-educated man, indeed, will now- 
 a-days believe fully in a devil and his associates, but many a 
 one does believe, more or less, in some personified "forces" 
 and the like (for instance, in a sort of materiality of a disease, 
 in itself), and perhaps hardly ventures to admit to himself his 
 doubts as to others. The well-educated physician of our days 
 may smile at the superstition of his ancestors, who looked upon 
 gold and pearls as sovereign remedies, or expected great things 
 from yellow substances in jaundice, and from red ones in 
 hemorrhages. But if he would only examine more closely 
 
ON FALLACIES. 387 
 
 why it is that he himself believes in the positive services of a 
 great number of his remedies, he would find no essential differ- 
 ence between his own reasons and proofs, and those of his 
 predecessors. What was then looked upon as most important 
 and determining was assumed to be so in reality ; and if certain 
 changes, or perhaps the most remarkable recoveries were ob- 
 served in a patient, physicians did not long hesitate to look 
 upon them as brought about by their remedies, because they 
 had previously relied upon their having such effects and pro- 
 perties. 
 
 Like our predecessors, we proceed to our observations with 
 certain ideas, with previously fixed views, and because we 
 happen to be convinced of the correctness of these, the result, 
 or rather our judgment of it, is such as corresponds to our 
 previous ideas and expectations. Certain phenomena and 
 events, certain agents and influences, which we have perhaps 
 constantly observed to accompany or follow each other, which 
 we have, therefore, always considered as allied, and standing in 
 a causal relation to each other, are now believed to occur simul- 
 taneously in all cases, and even to bear the relation to each 
 other of cause and effect. Because we are accustomed to ima- 
 gine a certain state of things and particular kind of causal 
 connection, and now, perhaps, are not capable of conceiving 
 the possibility of any other, we take these for granted. Our 
 error everywhere consists in our unhesitatingly attributing a 
 real existence to our subjective views and conceptions, whether 
 we further look upon them as active forces and influences, as 
 laws, or personify them as real bodies and entities. Things, 
 therefore, which, so to say, are facts only through and for us 
 — i. e., according to our notions — we in all cases look upon as 
 real, objective facts. And, instead of previously deriving these 
 our ideas and inferences from an adequate determination of the 
 true state of things, and making them subordinate to the latter, 
 we do exactly the reverse. "We now judge of and explain 
 the positive according to our notions concerning it ; we arrange 
 and deal with it just as our point of view, and perhaps our 
 tendencies and wishes, require. 
 
 A thinking man, however, would hardly fall so easily into 
 this error if there were not an entirely different error in the 
 background — namely, the opinion and conviction that those 
 
388 ON FALLACIES. 
 
 views or notions respecting various things were in reality cor- 
 rect, and even the only possible ones ; that they were, in short, 
 self-evident truths, and therefore did not require to be further 
 investigated and determined by appropriate research and expe- 
 rience, &c. From the very beginning we regard them as esta- 
 blished truths or facts, just as much, for instance, as our 
 feelings, sentient perceptions, propensities, passions, &c. The 
 error, therefore, consists, in the end, in our confounding certain 
 things, with which we can only become better acquainted by 
 an examination into their relations, and by positive experience 
 concerning them, more or less with such notions or things as 
 are of themselves intelligible to us, because they are in a 
 manner only originated by and for ourselves. But as such a 
 notion, in regard to all the things at an understanding of which 
 we can only arrive by the way of experience and research, is 
 an erroneous one, we commit the greatest breach of all the 
 rules of logic — i. e., we regard such a demonstration of the 
 accuracy of our views as wholly, or at least nearly superfluous. 
 We neglect it altogether, or, even if it be attempted, it is 
 necessarily insufficient and defective, because we neglect to 
 furnish, and, indeed, cannot furnish, the exact proofs which 
 alone could demonstrate anything — namely, the proofs taken 
 from established facts, and from trustworthy experience. 
 Nevertheless, we are satisfied with such, whether it be that we 
 have, in general, no clear notion of that which, in the question 
 before us, would be requisite for the proof; or whether it be 
 that, from whatever reason — for instance, from prejudice, in 
 consequence of peculiar tendencies, &c. — we are satisfied with 
 half-proofs, or even with such as are altogether inadequate. 
 
 II. ERRORS IN THE DISCOVERT OF THE STATE OF THINGS. 
 
 It has been pointed out on a former occasion why, in 
 this place, no further mention can be made of such errors 
 and mistakes in our observations as have their source in certain 
 defects of our senses or artificial instruments themselves, any 
 more than of those which, in the end, can only be looked upon 
 as consequences of awkwardness, negligence, and the incapacity 
 of individuals. The former are always more or less unavoid- 
 
ON FALLACIES. 389 
 
 able sources of error, and not so much the fault of the indi- 
 vidual observer, as of the objects which he is called upon to 
 observe, or of the auxiliary means which are at his disposal. 
 The latter however, are too easily to be avoided to require any 
 further explanation here ; and, moreover, the necessary instruc- 
 tions in regard to them can only be furnished by each indivi- 
 dual branch of science, not by logic. 
 
 Of greater importance to us, however, are such errors as 
 spring from entirely different faults in our observations, espe- 
 cially those which consist in a false interpretation of the things 
 observed, whence errors in our whole judgment and apprecia- 
 tion of the state of things necessarily result. Now in this we 
 may err, either by observing things wrongly — i. e., by believing 
 that we have recognized a state of things, in a given case, 
 which is not the real one — or by entirely overlooking certain 
 things or circumstances in our observation. In reality, in- 
 deed, both these kinds of error frequently enough occur simul- 
 taneously; but the interest attached to the comprehension of 
 them requires separate consideration in this place. 
 
 Now if we examine more closely, how it happens that we 
 make the first mistake, and how we are led to take certain 
 things, which were accessible to our observation, for some- 
 thing which they are not in reality, a circumstance presents 
 itself as the most important and final cause, which has already 
 been alluded to on a former occasion. We mix up what 
 we have recognized through the senses with our view and 
 interpretation of it ; we confound or identify, as it were, our 
 conclusions and conceptions of it with what we have really 
 observed. We regard not only the latter, but likewise the 
 former, as real and direct perceptions through the senses, and 
 now record them as such. 
 
 A confounding and throwing together of these two elements 
 in our observations is the more easy, as both everywhere occur 
 together, and must naturally do so. Thus, we are never con- 
 tented with merely seeing or feeling a phenomenon or object, 
 but we wish and are obliged to form some notion of it, and 
 this again only becomes possible through some further expla- 
 nation or interpretation of what we have observed. The error, 
 therefore, merely consists in our not having been acquainted 
 with, or at least not having noticed, the true state of things. 
 
390 ON FALLACIES. 
 
 and in our believing and asserting that something has really 
 been observed by us — i. e., recognized through the senses, 
 which is rather only our interpretation or explanation of what 
 we have observed. 
 
 Even expert observers are exposed far more frequently than 
 they are aware of to mistakes in consequence of this confound- 
 ing of different things, because they are not always suSiciently 
 conscious of everything which takes place in an " observation," 
 or of their whole mode of proceeding in it. 
 
 We the more readily neglect to make a distinction between 
 these two elements in our observations, because what we re- 
 cognize through the senses is, in itself, without further inte- 
 rest to us as observers and investigators, but rather only in 
 so far, as we may draw a further conclusion from it concerning 
 the things themselves which we have observed — i. e., concerning 
 their real existence and bearing, their properties, and so forth. 
 It has, in a manner, become a habit with us, to proceed almost 
 instinctively, and without a clear consciousness, directly from 
 our perceptions through the senses to the interpretation of the 
 things observed, and, as it were, to melt down both into one 
 act. But this interpretation may now be an incorrect one, 
 even if the observation, in itself, have been completely cor- 
 rect. We know, for instance, how long it took to produce 
 the conviction that it is not the sun which day after day moves 
 through the sky above us. Everybody could see it with his own 
 eyes rising in one quarter and setting in the other, and nothing, 
 therefore, was more natural than the conclusion involved in 
 this perception through the senses, that the sun moves round 
 our earth from east to west. And it is well known that many 
 circuitous paths and protracted researches were required to 
 show that this conclusion was incorrect. No physician hesi- 
 tates to assert, for instance, that he has seen an ophthalmia, 
 a schirrous ulcer, or even a typhus, a dysentery, a critical sweat, 
 or a sediment in the urine, in his patients. And yet this, as 
 we have shown on a former occasion, is utterly impossible in 
 the strict sense of the term, and in so far this assertion itself 
 is a mistake, i. e., a confounding of that which really took 
 place with our judgment or interpretation of it, however cor- 
 rect the latter may have been. But that such a mistake still 
 more easily and more frequently takes place in everyday life, 
 
ON FALLACIES. 391 
 
 and especially among less educated or careful persons^ is suffi- 
 ciently well known. Every physician may become aware of 
 this, for example, from the reports of his nurses or midwives ; 
 every natural philosopher or physiologist from those of his 
 assistants. It rarely enough happens that such persons are 
 able to describe and report, for instance, what they have ob- 
 served in a patient, simply as they have noticed it. They do 
 not say only or exactly what they have seen, heard, &c., but 
 at the same time, and especially, what they have concluded from 
 it, and how they interpret it. In this manner every assertion 
 perhaps contains a whole chain of conclusions and notions, if 
 not entire explanations or theories. 
 
 But here, as well as in the case of the motion of the sun, 
 this throwing together of observation and interpretation affords 
 the most ample opportunity for error. And it is only a 
 thorough knowledge in each branch of science, and practice 
 in observation, which can protect us against it, and still more a 
 constant attention to this point, namely, the accustoming our- 
 selves to keep these two processes (observation and interpreta- 
 tion) sufficiently separate, and especially to distinguish them in 
 our appreciation of that which we have observed, and in its 
 application to further conclusions and attempts at explanation. 
 But precisely in this point even physicians and natural philo- 
 sophers fail much more frequently than they are themselves 
 aware of, whence many of their errors may be explained. Thus 
 it had long been observed that patients suffering from dysen- 
 tery frequently pass no urine, or at least only a very small 
 quantity, and that equally little bile or pigment of bile is to be 
 found in their stools. And thus far this may pass as a fact 
 established by our senses. But we are further wont to speak 
 of a retention of urine or bile as having been observed, and 
 now proceed to assume a spasm of the bladder, &c., as its 
 cause. For, as physicians are accustomed to interpret a state 
 in which no urine is passed as a retention of urine, they now 
 assert that they have observed it in a given case, whilst pro- 
 bably, in most cases, it did not exist at all, but rather there 
 simply happened to be very little or no urine in the bladder at 
 the time, and consequently none could be voided. In a similar 
 manner it has long been customary to speak of a caking 
 together of the hair in plica polonica by a viscous fluid, which 
 
393 ON FALLACIES. 
 
 was said to be secreted by the scalp, though the fact itself had 
 never been demonstrated. What really had been observed was 
 nothing more than that the hair is entangled with dust, scales 
 of epidermis and such like into one dense mass, and from this 
 an inference was drawn as to its cause — i. e., the presence and 
 action of that viscous fluid. 
 
 But it is evident that we may still more easily fall into error 
 in our observations, and that in a more dangerous manner, if 
 a want of knowledge, actual prejudice, peculiar tendencies, or 
 even superstition on our part, are present. An individual in a 
 state of so-called nervous excitement, or delirium, may regard 
 his visions and sensations as objective, another his nightmares 
 or hallucinations — i. e., may attribute a real existence to them, 
 external to his consciousness and whole world of sensations. 
 He has, from infancy, been accustomed to this kind of connec- 
 tion, this dependence of his sentient perceptions upon external 
 and actually existing objects. In the case of nervous excite- 
 ment, or delirium, also, his sentient perception has, in itself, 
 been so far quite correct that he has, perhaps, really seen 
 frightful animals, persons who have long been dead, or even 
 the devil in person, or has heard their voices, and it is only his 
 conclusion as to their real existence, externally to his inward 
 world of sensation and his imagination, which is false. Essen- 
 tially in the same manner might even those errors of supersti- 
 tious and visionary persons and demoniacs find an explanation, 
 who perhaps assert in good earnest that they have seen ghosts, 
 saints, the Madonna, or God himself, appear in person, and 
 even have held formal conversations with them, and that, too, 
 without any intention to deceive. Their mistake, doubtless, 
 consisted only in their assuming a material object as existing 
 externally to them, in the place of what they perceived merely 
 subjectively, and now being sufficiently superstitious, stupid, 
 or exalted, to take their conclusion, and their interpretation of 
 it, for an actual perception. 
 
 Still more numerous are the circumstances and causes 
 which may lead us into the other chief error in our observa- 
 tions, viz., that of entirely overlooking certain other phenomena 
 and things which really exist and are present. Yet such an 
 error is facilitated, not only by the great complexity of all 
 our phenomena, but also and still more by our being able to 
 
ON FALLACIES. 393 
 
 recognise directly only the smallest part of what is submitted 
 to us for observation. From this cause we easily overlook one 
 thing or the other, and perhaps even judge of what we have 
 really noticed or observed, in a one-sided and imperfect, if not 
 utterly wrong manner. Setting aside, here, negligence, want 
 of knowledge of the subject, and other deficiencies on the part 
 of individual observers, a certain prejudice, and the necessarily 
 limited capabilities of the human mind in a study like that of 
 medicine, may be regarded as the chief causes of our imperfect 
 recognition of various points. Even in the observation of the 
 simplest and most accessible things, we often see our compre- 
 hension of them impeded to an extent which will scarcely 
 appear possible to future generations. Hippocrates was so far 
 correct when he said that observers must be free from all pre- 
 judice and superstition. But where there is a want of compre- 
 hension and conviction, founded upon sure knowledge and 
 upon positively adequate proofs, as is the" case in medical 
 science, it is difficult, if not impossible to remain free from all 
 prejudice and superstition. And by attributing such errors of 
 the observer simply to embarrassment, prejudice and the like, 
 we do not gain nearly as much as we should do by a closer 
 examination into the ways and circumstances, which may lead 
 us iiito them. 
 
 But we are led into errors, not merely by the peculiar diffi- 
 culties of our subject, but also and still more by certain direc- 
 tions and tendencies of our intellectual being, the more subtle 
 motives and threads of which cannot always be traced with 
 sufficient clearness. Some of these have been spoken of already 
 in the preceding chapter. One of the most important causes, 
 however, of our overlooking various things so easily, consists in 
 this, that what we have really observed and noticed makes 
 too strong an impression upon us and attracts our attention 
 too much, to allow us, at the same time, to notice and give 
 their due importance to many other things' connected with it, 
 or at least to have the will to do so. The more remote 
 motives or circumstances, however, which lead us to this, may 
 again be of very different kinds, and sometimes are more on 
 the part of our understanding and judgment, sometimes more 
 upon that of our impulses and volition, or absence of the 
 latter. 
 
394. ON FALLACIES. 
 
 It lies in the very nature of our subject that everything 
 which we ourselves perceive in a direct manner, everything 
 which makes a vivid impression upon our senses, and, by this 
 means, upon our minds and consciousness, not only remains 
 more strongly imprinted in our memory, but likewise more 
 immediately, and, therefore, more forcibly influences our 
 notions and judgment, than other things. We now, in general, 
 readily, even during our observations, lay the greatest stress 
 upon this — more, perhaps, than it deserves — and at the same 
 time overlook many other things, because we happen to attach 
 more importance to the first, and confide in its being of a 
 more important character and decisive influence, — whether it 
 be, for example, the moon and stars, storms and lightning, a 
 superstitious remedy, images of saints, or, perhaps, some pre- 
 tended specific. In every case it is something which is capable 
 of acting directly upon our senses, whilst we are not able im- 
 mediately to perceive others which, in the case at issue,, are 
 perhaps of at least equal importance. So, for instance, we see 
 the patient himself attribute the greatest value in his cure to 
 such medicines as he sees, tastes, smells, and swallows ; and he 
 is not always so wise as that old Greek, who, in the temple, 
 inquired also after those who had been drowned in spite of 
 their offerings. And, in the end, the natural philosopher is as 
 little able to free himself from the influence of this law of our 
 nature as the physician. All those things, however, which 
 have once made a deep impression upon us, whether it be by 
 their appearance and appreciable properties and peculiarities, 
 or by their being novel and surprising, appear to us from the 
 first, to be of especial importance, and, on that account 
 already, we easily regard them as the essential causes of 
 certain effects and events. Thus anatomical lesions, which are 
 visible and palpable, and certain chemical changes and pro- 
 ducts, which we observe in patients or corpses, make a far 
 deeper impression upon our senses than many other things, 
 and it can hardly be doubted that all this does not remain 
 without influence also upon our opinion as to their importance 
 and the part they take in the aggregate of a disease. Exactly 
 the same thing probably applies to all those phenomena and 
 states which are perceptible to our senses in a direct manner, 
 by the aid of auscultation or percussion, the speculum, the 
 
ON FALLACIES. 895 
 
 thermometer, or the scales, &c. But for the sake of what we 
 have found out by these means we the more easily overlook 
 and undervalue everything else, because that which we have 
 perceived by our senses, and which alone, perhaps, is accessible 
 to us, on that account, also, frequently appears to us to be 
 most essential and determining. A further source of error, 
 which is in many respects connected with the preceding one, 
 is to be sought in the circumstance that, in general, all that is 
 positive and affirmative makes a much deeper impression upon 
 us than anything else, especially what is simply negative, and 
 that for this reason alone the former more easily remains in 
 our memory, and finally influences our judgment, than the 
 latter. Every one will remember, both more easily and more 
 willingly, such experiences and cases, for example, as speak for 
 his opinion, and which are considered by him as further con- 
 firmations of it, than those which are contradictory to it ; and 
 just as, for this very reason, every one in his successes only 
 too easily overlooks that which is unsuccessful, so the phy- 
 sician is often led by the favorable cases, which he has cured 
 by his treatment, to overlook those in which he has failed to 
 efi^ect a cure. And if a physician has used any remedy 
 throughout a long series of cases, and has seen every one of 
 them recover, he will involuntarily regard it as an efficacious 
 one, at all events more than another, who has not effected 
 with it so many cures. The positive — i. e. the fact of the 
 recovery or cure of his patients — makes its impression upon the 
 former as usual, and, on that account, he will be predisposed 
 to attribute an active part to his remedy, whether it may 
 have played such a part in those cases or not. 
 
 It must here also be taken into consideration, that anything 
 for which we happen to interest ourselves, from one cause or 
 other, or which we are striving or wishing for, likewise appears 
 to us as the most important; or else we should not have 
 sought nor striven for it. But as this now especially, if not 
 wholly attracts our attention to itself — e. g. some aspect of a 
 function or disease — we only too easily overlook, for its sake, 
 everything else, and perhaps, in the one point, see too much, 
 see something everywhere because we have the desire of seeing 
 it. And if personal interests or desires come into full play ; 
 if, for instance, we have an interest in seeing one thing and 
 
396 ON FALLACIES. 
 
 not another; if, by our observations, we wish to prove former 
 opinions and assertions, or to oppose those of others, there is 
 no end of errors, especially in a science such as medicine. 
 If, in the present day, a Piorry finds large spleens where 
 nobody else discovers them, and where, perhaps, none such are 
 present, it is well known that during the middle ages, and long 
 before the discovery of America, many always believed that 
 they could see land to the west from the Canary Islands, 
 merely because they wished to do so, and that without ever 
 being really able to see it, simply because none existed there. 
 To errors from this quarter, however, every one will succumb 
 most easily, if he has to act at the same time, (as, for example, 
 the physician at the bed side), and if, upon his judgment, and 
 still more upon the judgment of others as to his services, well 
 nigh his whole existence as well as his reputation depend. 
 The physician is here much in the same position with regard 
 to his judgment of his own measures and remedies as the 
 teacher with regard to his method of education, and the 
 statesman with regard to his regulations and laws. All of 
 them frequently see and find precisely what they wish to see 
 and find. They perhaps compare themselves to such technical 
 men, for example, as operate upon inanimate and passive 
 objects only, and overlook that they have to deal with entirely 
 different things, with processes which are self-acting, and pro- 
 ceed according to their own peculiar laws. But as physicians 
 so frequently wish to demonstrate the positive services of their 
 remedies, the most abundant opportunity for error is furnished 
 by the circumstance that their observation, and still more 
 their interpretation of the state of things, only too easily 
 become one-sided, if not entirely incorrect. And this is like- 
 wise essentially furthered by the denominations of our reme- 
 dial agents. Remedies, for instance, which from the beginning 
 have been placed before us and praised as antiphlogistics, 
 astringents, &c., we are now accustomed to imagine as acting 
 just in this way and in no other. We are now not only dis- 
 posed to regard something to which we had previously attached 
 the greatest importance — e. g. a given remedy — as the really 
 determining one among all the circumstances and influences 
 which precede or accompany a cure, but we likewise interpret 
 all the changes taking place in the state of a patient in the 
 
ON FALLAClEvS. 397 
 
 precise manner which best corresponds to our expectations and 
 views of the effect of that remedy. We now, perhaps, even 
 perceive so-called antiphlogistic, astringent, or solvent effects 
 from them, where none such occur, where they perhaps have 
 acted quite otherwise, or where such changes or curative 
 effects were owing to entirely different circumstances. In 
 short — in this, as in other things — if we once are upon a false 
 track in our interpretations and conclusions, we proceed 
 further and further upon it, and everything is now made to 
 serve as an additional confirmation of our views, even if, in 
 reality, it should prove something quite different, perhaps the 
 exact contrary. 
 
 Those obscurations which our observation and perception 
 may suffer frqra everything novel, and from the prevailing 
 tendency or fashion, are too well known for it to be necessary 
 to enter into them more deeply in this place. And the 
 liability to them in every science, and above all in medicine, 
 where that which is already given to us seldom, in the end, 
 makes us feel perfectly satisfied, and where we now expect 
 from new directions, doctrines, and remedies, what the old 
 ones were not able to accomplish, lies near enough at hand. 
 
 Those portions of the external world, of life, or of diseases, 
 to which at the time the attention, perhaps the whole bent of 
 the mind is directed, will now exercise a preponderating 
 influence upon our mode of observation, — whether it be the 
 so called imponderables, electricity, nervous force, certain 
 anatomical and chemical points, or pure dynamism in these. 
 Every one hopes and believes that he will best be able to solve 
 the grand problem ; and the discoverer is wont, even more than 
 others, to attach importance to what he advances, and must 
 do so frequently, if it be only for the purpose of attracting so 
 much attention to it as it deserves. And history likewise 
 teaches us how, in this point, one view, one theory followed 
 upon the other, just as in medicine one " infallible" remedy 
 upon the other; and every one of them was more or less 
 believed in and followed, in its time, because it appeared to 
 correspond to facts and experience. They appeared so, how- 
 ever, because the observer looked upon and interpreted things 
 exactly as his belief or the prevailing views warranted. For 
 instance, after the Emperor Augustus had been cured by his 
 
398 ON FALLACIES. 
 
 physician, Antonius Musa, by means of cold baths, everybody, 
 and especially the higher classes, used cold baths, and believed 
 that they experienced the most excellent effects from them ; 
 even a Seneca praises his baths and swimming exercises in the 
 Calends of January. In the same manner, St. John's sti- 
 mulating liniment was, in its time, considered as excellent a 
 remedy for consumption as cod-liver oil, for instance, is at 
 present ; and although St. John himself died of that disease, 
 his admirers nevertheless erected a monument to his memory. 
 A similar kind of embarrassment and confusion is daily seen 
 to arise from the circumstance that the observer is not able to 
 keep himself free from the influence of antiquated notions and 
 views, perhaps of actual prejudices, to the extent which would 
 be requisite for the freedom and perfect correctness of his 
 conception. In each case he does not stand upon an entirely 
 objective ground, but under an authority, whether it be that 
 of the ancient or the novel, and now finds everything exactly 
 as this authority represents it. 
 
 He may now overlook the most accessible and apparently 
 intelligible things and simplest relations, because he does not 
 at all think of their possibility or probability, and this, 
 because he has always imagined them quite otherwise, and 
 never doubted the existence of certain other relations between 
 them. Thus, for instance, the worthy Sir Thomas Brown, 
 who, animated by the zeal for truth, himself wrote about 
 Common Errors in the year 1646, was yet so thoroughly per- 
 suaded that the sun moved round our earth, that he could 
 never hear the contrary opinion without attempting to render 
 it ridiculous. No less was the belief of many chemists in 
 phlogiston so firmly rooted, that it could only with difficulty 
 be overthrown by a Lavoisier, a Berzelius, and their scales, so 
 long as it was preferred to attribute the circumstance of burnt 
 bodies becoming heavier to some mysterious property of 
 phlogiston of making bodies lighter. That many errors in 
 observation in our department of science have arisen from the 
 same cause, and continue to do so daily, needs no proof here. 
 These are essentially favoured, not only by the natural diffi- 
 culty and obscurity of all our problems and objects, but also 
 by the circumstance, that a man must be a specialist in order 
 to be able to observe anything in a sufficiently accurate and 
 
ON FALLACIES. 399 
 
 correct manner. But specialists, again, readily conceive things 
 in a one-sidedj or, at least, not in a sufficiently unbiassed and 
 independent manner; they easily overlook many things be- 
 cause they frequently, for the sake of views and theories once 
 adopted, look only in one direction, to one quarter. Even our 
 expressions and denominations, as has been explained already, 
 exert the same influence, the same authority. We do not 
 readily adopt new views concerning remedies, for instance, 
 which have long been considered as antiphlogistics, tonics, &c. 
 Thus, we assume that we have subdued an inflammation by 
 some remedy or other, because it is said to act antiphlogisti- 
 cally, and it is said to act antiphlogistically because it happens 
 to be considered an " antiphlogistic." 
 
 HI. ERRORS IN THE COMPARISON AND DEDUCTION OF GE- 
 NERAL PRINCIPLES, ESPECIALLY IN RELATION TO THE 
 CAUSAL CONNECTION OE CERTAIN THINGS. 
 
 These errors even much more than the others, are, in the 
 end, connected with each other ; and since, at the same 
 time, their name is legion, an allusion to the most important 
 of them, and especially to their sources, may suffice in this 
 place. 
 
 If we inquire, however, how it is that we may so readily 
 fall into such errors nearly at every instant, one circumstance 
 shows itself as the chief source in all cases, which lies in our 
 whole nature, and in a certain instinctive impulse and require- 
 ment of man. For all of us are apparently more or less in- 
 clined — frequently even compelled — to pronounce a judgment, 
 perhaps to make some general assertion in regard to one thing 
 or another, which we understand but half, or not at all, and 
 consequently to conclude, explain, or assert by far more than 
 we can correctly do — i. e., than our experience or our know- 
 ledge warrants. Unfortunately, also, the temptation to such a 
 venture appears nowhere greater than precisely where the 
 greatest dangeir exists^ — namely, where our knowledge least 
 enables us to declare anything with certainty as to the causes 
 and connection of various things. Now, whether it be a justi- 
 fiable thirst for knowledge, the exigency of the moment, or 
 
400 ON FALLACIES. 
 
 pure vanity and thoughtless zeal, &c., which urges us to do so, 
 our imagination and arbitrary combination always lead us fur- 
 ther than our insight or proofs will reach, and we overleap 
 what we cannot accomplish. 
 
 But opportunity for such errors is, of necessity, hourly 
 afforded by the manner in which we arrive at an opinion in 
 general, at a judgment of things which are only half known, 
 or entirely problematical. For here nothing remains for us, 
 at present, but to draw conclusions as to their conditions and 
 the whole state of things in them, from those of others of which 
 we already possess more knowledge or experience. What we 
 have thus found to be more or less true in individual cases (for 
 instance, in regard to a disease, or in experimenting upon the 
 mode of action of some influence, or upon the processes going 
 on in a function), we not only extend to all cases, processes, 
 &c., of the same kind, but likewise to such series and species 
 of things as appear to us to agree more or less with the former 
 in certain essential points. In other words, we generalize 
 that which we have found in the former, and which, with 
 regard to them only, is proved with more or less certainty. 
 But so soon as the latter, which we have placed under the 
 same category, and assumed to be essentially the same as cer- 
 tain others, have been, as so frequently happens, only partially 
 known to us, we extend those general principles and assertions 
 much further than we are justified in doing. For we compare 
 things with each other, and even declare them to be essen- 
 tially the same, without by any means having become suffi- 
 ciently acquainted with them, and without, perhaps, having 
 compared, much less determined, all the points and circum- 
 stances connected with them which ought to be carefully con- 
 sidered. It is manifest, however, that in a department of 
 science like ours, in which so little has been clearly and com- 
 prehensively investigated and become known, especially in 
 relation to causal connection, hardly anything of the above 
 description can be asserted positively. On the contrary, we 
 are always in danger of extending that which we have ascer- 
 tained in regard to certain cases, and which is but imperfectly 
 determined even for these, to others, to which perhaps it does 
 not apply at all, or where it is at least doubtful whether and 
 to what extent it may be applicable. Not even statistics, one 
 
ON FALLACIES. 401 
 
 of our best auxiliaries in this respect, can protect us against 
 such errors, because here, also, cases and things are so readily 
 and frequently brought under the same denomination, as being 
 of essentially the same kind, as unities, which, on account of 
 their differences, are not at all adapted to being classed with 
 each other. This applies, also, to analyses of the blood and 
 urine, even in patients suffering from the same disease, so soon as 
 they are made by different chemists ; and much more to obser- 
 vations or cases of a given disease, to histories of cures, &c., 
 because in these, least of all, can we assume their agreement 
 in all the essential points, especially in those with which we 
 are still unacquainted. In all these cases the possibility exists 
 that our classifications or comparisons are only partly and ap- 
 proximately correct, or perhaps even totally wrong. 
 
 But this likewise shows that by far the greater number of 
 general assertions and theories in our department of science 
 may, at least, be wrong ; that even, at best, they can only be 
 regarded as more or less probable, and far more frequently as 
 half true or premature, whether it be that we assert anything 
 positively by them, or whether we deny anything generally, 
 and perhaps unhesitatingly declare it to be impossible. For 
 so soon as we make any assertions of this kind concerning 
 things, processes, &c., which we have, at best, become but par- 
 tially acquainted with, and the internal connection and laws 
 of "which have remained more or less obscure, our general 
 assertions in regard to them are always premature, and more 
 likely to be erroneous, in one way or another, than perfectly 
 correct. 
 
 It may, indeed, already be advanced that many of them 
 niust be wrong — namely, whenever anything is asserted which 
 never can be demonstrated from experience, because the things 
 in regard to which those assertions are made are beyond the 
 reach of all observation and of all certain proofs. Neverthe- 
 less, such assertions are daily made, not only in common life, 
 but even by men of science ; for instance, if it were said that 
 a given individual had never, during his whole life, uttered 
 anything but the truth, had never been afraid, or never 
 dreamt, &c., this would be to assert more than can ever be 
 proved, if it were only because even the person concerned 
 cannot, in after-life, remember everything with perfect accu- 
 
 26 
 
402 ON FALLACIES. 
 
 racy which happened to him when he was a child or a boy. It 
 is much the same if we say that everything occurs in the living 
 body according to laws altogether peculiar and different from 
 those of so-called inanimate nature, or, as we frequently ex- 
 press it, that entirely different forces are in operation in the 
 one case and in the other. For we have not yet even become 
 perfectly familiar with the phenomena and processes in inani- 
 mate nature — e. g., in the atmosphere, the soil, &c. — much less 
 with all their conditions and laws. And even if our know- 
 ledge of them should become greatly increased in future, it 
 may yet be foreseen that it will never be sufficient to enable 
 us to say that we know and understand them all, so that, even 
 under the most favorable circumstances, we shall never be even 
 in a position to demonstrate the existence of such forces, &c. 
 The same would be the case if we should declare anything in 
 nature, whether animate or inanimate, of which we can only 
 acquire a knowledge from experience, to be absolutely impos- 
 sible, merely because we had never observed it ; or if, for the 
 same reason, we were to assert that it could never take place 
 in a given manner, even under entirely different and novel 
 circumstances, for we can never be assured that conditions and 
 circumstances may not come into action somewhere or some- 
 how which may bring about a result never observed before. 
 And just because no proposition merely founded upon experi- 
 ence, no empirical law, in itself, can be considered as an actual 
 law of nature or causation, we easily fall into error in all 
 general assertions of the above kind. 
 
 It is likewise evident that this will apply to everything going 
 on in living bodies, whether healthy or diseased, which is an 
 object of our observation or research in general, and finally of 
 our assertions, so soon as it does not simply relate to space, 
 weight, number, &c. We do not yet know nearly enough 
 of the peculiar conditions and internal mechanism of all those 
 processes, to be able to venture upon such a generalization 
 with even approximate certainty. 
 
 Although such a venture always presupposes an illogical 
 over-estimation of our knowledge, it is precisely those the 
 horizon of whose knowledge is the most confined who are wont 
 to express themselves most decidedly. Aristotle says : " Qui 
 respiciunt ad pauca, de facili pronunciant." We daily, for 
 
ON FALLACIES. 403 
 
 instance, hear physicians affirm that a certain state of things 
 always obtains, and that certain symptoms are always present 
 in persons suffering from a given disease ; that a given disease 
 absolutely indicates a particular kind of treatment ; that certain 
 remedies have always rendered the most positive services in it, 
 and other similar general assertions. But alas ! our know- 
 ledge of all the points thus pronounced upon isj in reality, 
 much too slight to enable us to make any assertions of this 
 kind. With most physiologists, it is an axiom that nothing 
 can pass, except in a state of solution, from the intestinal canal 
 into the blood ; and yet they have made scarcely any experi- 
 ments on the subject up to the present day, but rather conclude 
 that it is so from certain analogies and probable reasons, which 
 for the present, and as such, do not prove anything with cer- 
 tainty. Here, as in the case of any other phenomenon or 
 process in the living body, the conditions and conformity to 
 fixed laws are not yet sufficiently established to enable us to 
 say that any other state of things but the one assumed by us 
 is absolutely impossible. We are apt to regard simple obser- 
 vations, isolated facts, or so-called empirical laws, as scientific 
 explanations and real laws ; and the mere knowledge of the 
 fact that certain things perhaps always occur at the same time 
 or successively is now considered as an understanding of their 
 causal connection and peculiar conditions. 
 
 Another circumstance intimately connected with the above 
 is, that we easily fall into error whenever we seek, for instance, 
 to form a conclusion from the state of one function, or of one 
 patient, as to that of other processes or states of disease, which 
 perhaps resemble these in one way or another, or even as to their 
 state under circumstances almost entirely unknown to us. 
 But, in reality, the individual observer only too readily arrives 
 at the belief that what has been observed and experienced by 
 him must always take place precisely in the same manner, and 
 hold good for all times and circumstances. But since all that 
 which the physiologist or the physician knows concerning the 
 occurrences and processes which he is seeking to investigate, 
 for the present consists rather in a knowledge of their occur- 
 ring together or in succession, and manifesting themselves in a 
 certain manner, than of an insight into their proper conditions 
 and laws, the individual observer can infer nothing more from 
 
404 ON FALLACIES. 
 
 all his observations and investigations than that, under given 
 circumstances, he has seen certain things always occurring 
 simultaneously or in succession, and running a certain course. 
 He is liable to error, therefore, whenever he extends his expe- 
 rience to things (such, for instance, as organisms, functions, 
 cases of disease, effects of medicine) which have neither been 
 observed and investigated directly by himself nor others. 
 Everybody, for instance, is aware how erroneous it would be 
 for an individual to conclude, from the mere circumstance of 
 his having observed ulcerations of the intestines in all the cases 
 of typhus fever which he met with, that they are present in all 
 cases of that disease, at all periods, and in all countries ; or 
 that, because a hundred years ago a certain per-centage of the 
 inhabitants of a given town, country, or hospital, died yearly, 
 an equal number must likewise die in the present day. And 
 it would be no less erroneous to assert that the state of lepers 
 and plague-stricken persons could not have been such as the 
 ancients have described, merely because we see it to be quite 
 different now ; or to conclude that, because cases of intermittent 
 fever, for example, are generally speedily and safely cured in 
 G-ermany by bark, the same would be the case in the Campagna 
 of Rome, or in New Orleans, &c. But everyone may be taught 
 by his own experience how prone we are to make such general, 
 and on that very account hazardous, if not erroneous, asser- 
 tions ; how easily the insignificant " I" is converted into the 
 abstract " one" and " it ■" for instance, instead of saying, " I 
 have observed a certain thing, I believe it to be true, I take 
 this or that view of it," we are wont to say, " It is a matter 
 of experience, it has always been observed, it is the object, 
 the indication, &c." 
 
 In the present state of our knowledge we run the same 
 risk, even in the most simple comparisons and analogies, of 
 shooting beyond the mark, and, under the most favorable 
 circumstances, can add but little to our knowledge by such 
 means — at least nothing certain. Nothing prevents us, it is 
 true, from comparing various things with each other ; neither 
 could we, as has been shown already, free ourselves from 
 this necessity even if we wished. The reasons which, for 
 the present, render it difficult, if not impossible, for us to 
 ascertain anything positive by such means, have likewise 
 
ON FALLACIES. 405 
 
 been explained. Prom the circumstance of certain things or 
 processes (for example, some function, disease, effect of me- 
 dicines) being similar, perhaps even identical, in one or more 
 points, in certain properties, &c., we conclude that they must 
 likewise agree in other points and properties, and this, too, 
 precisely in the essential ones, which, at the utmost, we 
 have only discovered in some of them, not in all. The 
 proof of this, however, we are not able to give, because our 
 knowledge, for the present, rarely or never enables us to 
 form a certain judgment whether those properties or points 
 which we have observed in the things compared together by 
 us stand in such an essential connection with their other 
 properties, &c., that the existence of the latter can be in- 
 ferred from that of the former. In short, as matters happen 
 to stand, our analogies and comparisons rather deserve the 
 name of uncertain allegories, pictures, or metaphors ; and often 
 enough we do not fare much better than Captain Fluellen, 
 in Shakespeare's Henry V, who insisted upon comparing 
 his Harry with Alexander of Macedonia. And if we are not 
 even able to compare together with some, degree of accuracy 
 various functions, diseases, effects of medicines, &c., in regard 
 to their external appearances or symptoms, we are much less 
 able to draw any safe conclusion from their agreement in 
 certain points, as to the identity of their causal connection, 
 conditions, and laws of action. 
 
 All this, however, suffices to explain the uncertainty, if not 
 utter incorrectness, of all our comparisons. If, for instance, 
 we unhesitatingly compare the processes and laws of respira- 
 tion with those of combustion, or the functions of the nerves, 
 and their laws, with those of electricity ; or if, from the simi- 
 larity alone of certain anatomical lesions in several diseases, 
 we conclude their essential identity, it is just the same thing 
 as if any one were to conclude that gentian, from the fact of 
 its tasting bitter, like cinchona, must likewise contain certain 
 alkaloids, or cure intermittent fever with equal certainty. We 
 meet with comparisons of such calibre and tenor at every step, 
 especially in medicine ; for instance, from certain processes in 
 wounds and fractures which are more or less analogous to 
 inflammation, implying a favorable result in regard to their 
 cure, some have inferred the usefulness or curative tendency 
 
406 ON FALLACIES. 
 
 of inflammation in general. Because astringent substances 
 containing tannin had an astringent taste, and may really be 
 of use in external hemorrhages, suppurations, &c., by coagu- 
 lating albumen, they were likewise thought to be of use in 
 cases of internal hemorrhages, hsemoptysis, and of purulent 
 expectoration, as well as in diarrhoea and diaphoresis. And 
 because the iodide of potassium dissolves certain combinations 
 of quicksilver or lead with albumen in the test-tube, it is 
 likewise said to dissolve similar combinations of these metals 
 with the albuminous principles of the body, and so to effect 
 perfect cures in cachexia induced by either of them (Dor- 
 vault). 
 
 These examples already prove how an erroneous employment 
 of comparisons and analogies, especially in our department of 
 science, almost necessarily follows so soon as we endeavour to 
 explain a series of phenomena, processes, or effects, or to build 
 up connected theories and systems. For in this way we are 
 compelled to compare all these series of things according to 
 certain analogous points, and to infer their essential similarity, 
 or even identity (in regard to their connection), from their 
 conformity in the few points which we can appreciate, whilst 
 we are by no means in possession of any certain judgment 
 whether and to what extent the points or circumstances in 
 which they agree are in reality the essential ones or not. 
 
 This shows the intimate concatenation in which these errors 
 and defects in comparison and judgment generally stand in 
 regard to our classification and its peculiar imperfections and 
 faults — for instance, in the department of pathology and materia 
 medica. And as such a defective classification is itself the 
 inevitable consequence of our imperfect discernment in regard 
 to the things to be classified, so their defective, or wrong clas- 
 sification necessarily reacts in a troublesome manner upon our 
 whole discernment, our judgment of the objects which have 
 been grouped together, and thereby likewise upon their com- 
 parison, as well as upon all our assertions about them. It has 
 been adverted to already upon a former occasion, how things 
 are classed together under one and the same head, the exact 
 agreement of which in the more essential points is frequently 
 very doubtful and at all events rarely proved, because all of 
 them are more or less problematic to us in their intrinsic con- 
 
ON FALLACIES. 407 
 
 formity, conditions and effects. And yet the mere fact that 
 certain diseases, remedies, &c., have been brought in one way 
 or other under the same head of classification, naturally gives 
 rise to the idea, that they will likewise agree in all their 
 more essential points. We are therefore further tempted, at 
 every instant, to make different general assertions at different 
 times about them, which, for the above reasons, however, are 
 for the most part highly arbitrary and uncertain, if not 
 decidedly erroneous. A single glance at any attempt at clas- 
 sification in our department will prove this. 
 
 Such errors are no less essentially promoted by our technical 
 language, and terminology, by its abundance of mere figures 
 and metaphors, and of terms either ambiguous or nearly 
 meaningless and decidedly false. It is said often, indeed, " in 
 verbis simus leves ;" yet the history of medicine, in particular, 
 shows how dangerous and injurious the daily employment of 
 words without a meaning, at least without a clear and definite 
 one, may become. It is likewise suf&ciently well known what 
 frequent opportunities for a thousand errors are afforded by such 
 terms, for instance, as irritation, excitation, antagonism, me- 
 tastasis, tone, reaction, &c., and how, from our ontological names 
 of diseases, the real state of things may easily be overlooked, 
 and the clear and correct understanding of the states thus 
 denominated disturbed. Similar errors are wont to arise from 
 the double meaning, the ambiguity of so many of our terms 
 (for example, consumption, nervous fever, plethora, stagnation 
 or stasis, lymphatic, or to strengthen, to astringe, to dissolve, 
 &c.), because we are so easily led to conclude, that what is 
 applicable in one case — i. e., taking a term in a peculiar mean- 
 ing — would likewise be applicable in another, in which the 
 same term is applied in an entirely different sense. 
 
 All this shows that the most important element in all our 
 errors of the above kind (in our comparisons, &c.) is, that we 
 compare certain processes, influences, and other things, with 
 each other, of which the more essential points and parts are 
 more or less unknown to us. And the common cause of the 
 comparisons or classifications proving uncertain, if not decidedly 
 false is, in the end, that we look upon certain properties and 
 circumstances, which appertain equally to both, as essential or 
 determining ones without their being so, or at least without 
 
408 ON FALLACIES. 
 
 their being proved to be such. But since our endeavours are 
 directed to the explanation of all those processes, effects, &c., 
 and to giving ourselves and others a certain account of them, 
 we lay stress upon some single ones out of the whole aggregate 
 of simultaneous or successive phenomena and circumstances as 
 being the essential and determining ones. And because the 
 latter have rarely or never become accurately known to us, 
 because in our judgment about them we necessarily proceed 
 in a more or less abitrary and a priori manner, we easily fall 
 into error, and perhaps look upon subordinate, secondary cir- 
 cumstances as determining or essential ones, and still more 
 frequently regard individual fragments or parts as the whole. 
 Comparisons and general assertions of the above kind always, 
 therefore, involve the erroneous notion, that we have already 
 become acquainted with the real conditions of the process or 
 event in question, and with the laws of action of the influences 
 which affect it, and that we are thus capable of forming a 
 judgment about it, whilst in reality we frequently do not even 
 know all the modifying and co-operating circumstances, much 
 less their real influence and mode of action. All we know 
 rather consists merely in this, that certain circumstances, 
 influences, and effects, certain events and phenomena, always 
 occur simultaneously or successively. 
 
 Upon the same circumstance depends the well-known kind 
 of error in our judgment or conclusion, which has long been 
 expressed by post {cum) hoc propter hoc. For here the defect 
 consists in our not being able to assign any other cause for our 
 conclusion and assertion that certain circumstances are the 
 real conditions of certain events or effects, than that those 
 circumstances had preceded the event or effect in question — 
 had been observed before, or at the moment of its occurrence. 
 But there can hardly be any attempt made, at present, to 
 explain a single process in the field of life, whether in health 
 or disease, i. e., to show its causes, without this error occurring 
 more or less. For every one who undertakes this, asserts, in 
 the end, that a given agent or element, (for example of a 
 function, disease, cure, , &c.,) was the really determining and 
 essential one, without for the present being able to give better 
 reasons for his assertion than the fact, that those agents or 
 circumstances had always been observed in connection with 
 
ON FALLACIES. 409 
 
 the event or process in question. Perhaps too, in the most 
 favorable case, certain other grounds of probability might 
 speak for such an influence of the circumstances in question. 
 The physiologist, for instance, falls into the above-mentioned 
 error if he summarily ascribes to the bile an essential part in 
 digestion, or if he assumes the higher oxidation of certain 
 parts of the blood during respiration to be the essential con- 
 dition of the latter; if he declares the atmospheric air to be 
 the only indispensable agent of all respiration, or the heart 
 that of all circulation, or looks upon the formation of infusoria, 
 fungi, and such like, as the cause of all processes of putrefaction 
 and fermentation, and even of many diseases, (especially such 
 as are contagious and miasmatic). But that pathology and 
 therapeutics, in particular, well nigh in all their attempts at 
 explanation, fall into an error of this kind, is evident at the 
 first glance, whether such an attempt may belong to the 
 department of aetiology and pathogeny, or of the treatment of 
 disease. Nearly every day brings forth explanations, such for 
 example, as that cretinism, scrofulosis, and other endemic 
 diseases are caused by the water which is drunk and the lime 
 it contains, or by the deficiency of light in a valley, or by its 
 marshy soil, by certain winds, perhaps even by some article of 
 food. In the same manner, some select from the whole ag- 
 gregate of circumstances and influences which have, in many 
 cases, preceded the occurrence of pulmonary consumption, 
 scrofulosis, and the like, the single fact, that the parents and 
 relations likewise suffered from the same disease, and the 
 affection is now attributed to an inheritance of pulmonary 
 consumption, scrofulosis, &c., and, under certain circum- 
 stances, even to infection by it. And if any one should attri- 
 bute the nostalgia of the Swiss to the denser and heavier air 
 of the plains, or scurvy to the use of salt food, it is much the 
 same as if one national economist were to attribute the com- 
 merce and industry of Great Britain to its abundance of coals, 
 another to its insular position, and a third to the circumstance 
 of its having a rich aristocracy. And those who at one time 
 regard some disturbance of the functions of the nervous system, 
 at another some " crasis" of the blood, or certain other 
 anatomical changes and conditions, not only as what they are,' 
 namely as single elements or parts of the whole disease, but as 
 
410 ON FALLACIES. 
 
 the essential and properly determining points of it, fall, essen- 
 tially, into the same error. If even the father of pathological 
 anatomy, Morgagni, has given his work the title " de sedibus 
 et causis morborum," others, who see, for example, in the 
 whole of a disease only certain appearances or processes in 
 various organs, or even in single tissues, who judge of its 
 course and danger well nigh only according to the local lesions 
 attending it, and declare that one person died of the ulcera- 
 tions he had in his intestines or lungs, another of disease of 
 the heart or softening of the brain, err in a similar manner. 
 That we do this, however, nearly in every conclusion regarding 
 the cure of our patients by medicines and other remedial mea- 
 sures has already been complained of by Zimmermann. We 
 conclude, for instance, that the breaking out of an illness has 
 been prevented by prophylactic measures, or that a disease has 
 been cured by certain remedies, simply because these have been 
 employed. But whenever we have no other more valid reasons 
 for this conclusion, than the fact of their employment and of 
 the consequent recovery of a certain number of patients, it is 
 a mere conclusion by post {cum) hoc propter hoc, unless it had 
 previously been shown that such patients, under other circum- 
 stances, and left to themselves, are not wont to recover with 
 equal rapidity and frequency. This also explains why the 
 faith in so many remedies is giving way more and more, and 
 why so many of them are now thought totally ineffective, to 
 which the best cures were formerly attributed ; not so much 
 because our scepticism, in itself, has become greater, but rather 
 because our manner of observing and forming conclusions has 
 become more circumspect, and because it has been proved 
 that most patients recover just as well without any of those 
 remedies. Essentially the same kind of error is likewise at 
 the bottom of the well-known doctrines of a so-called an- 
 tagonism of certain diseases, of erases of the blood, dyscrasias, 
 &c. Leaving out of the question that the ontological alle- 
 gorical conception of diseases as something self acting and 
 having an independent existence is perhaps carried further 
 than is compatible with our present notions and knowledge, 
 the assertion that the mere presence, or previous existence, of 
 a certain disease, or disposition to a disease, &c., has prevented 
 the development of certain other diseases — e. g., that a cancer- 
 
ON FALLACIES. 411 
 
 cachexia or intermittent fever has prevented the development of 
 tubercles and pulmonary consumption — must be regarded as a 
 premature and even false conclusion. For at all events a number 
 of other circumstances and influences have constantly and in all 
 cases been in operation which likewise might have had a share 
 in determining the result in question, the influence of which, 
 however, has hitherto remained just as little known. In the 
 end, therefore, nothing more certain is known, than that people 
 who are attacked by cancer and die of it, do not likewise fall 
 ill and die of pulmonary consumption, and vice versa. And 
 in so far this manner of forming a conclusion does not essen- 
 tially differ from the homoeopathic doctrine of antagonism, 
 according to which a disease is said to be cured by a more or 
 less similar one having been artificially established by some 
 remedy or other. The substance of this doctrine, however, 
 was sufficiently well known to the sorcerers and witches of the 
 middle ages. If, for instance, an antagonist, an enemy, was to 
 be tortured, poisoned, or entirely done away with, they formed 
 an image of him in wax, clay, &c., and treated this with poison, 
 the dagger, or fire. Yea in the old Germanic law the case was 
 provided against that in this manner a witch might swallow a 
 free man with skin, hair, and all, and disgorge him again. 
 
 From all the foregoing it might be inferred, that every con- 
 clusion which we seek to draw in our department in regard to 
 the causal connection of any process or event, and especially 
 every assertion in regard to the conditions and actual develop- 
 ment of a function, a disease, or its cure, will suffer more or 
 less from the common error of this post {cum) hoc propter hoc. 
 Proofs for all these conclusions, such as science must demand, 
 we are for the present incapable of furnishing, and in so far 
 they must be considered as more or less hasty and uncertain, 
 if not as decidedly erroneous. Therefore we may always doubt 
 and attack them again, and even, as our history and the expe- 
 rience of every day teach us, may assert the exact contrary, 
 and, to a certain extent or in a certain sense, be justified in so 
 doing. 
 
 It is not necessary to explain further, in this place, by what 
 means alone a conclusion of the above kind, which is perhaps 
 erroneous, or at least very doubtful, may be made to gain in 
 
412 ON FALLACIES. 
 
 credibility and truth. This would evidently be the case only 
 if we should succeed, upon entirely different grounds, by fur- 
 ther and special observation, in furnishing the proof, that those 
 circumstances and influences, which have been assumed as 
 determining or effective, really possess the capability of pro- 
 ducing the effects attributed to them. And so long as this has 
 not been determined, every conclusion in regard to their causal 
 connection will be a doubtful one, even in the most fortunate 
 case, because it is only based upon the simple empirical fact of 
 the simultaneous or successive occurrence of certain circum- 
 stances and effects. We may already, for instance, conclude 
 or assert with certainty, that if a person, • after partaking of 
 food with which a poison, such as arsenic, copper, &c., has been 
 mixed, is taken ill in a certain manner, the poison and not the 
 food must be considered as the cause of his illness. And if we 
 once know that the property of rendering arsenic ineffective 
 belongs to a certain combination of iron only, and that no one 
 who is poisoned by it will die, provided that preparation of 
 iron be employed in the proper manner and early enough, we 
 may safely attribute the cure of the person poisoned by arsenic 
 to that preparation of iron, even if, at the same time, entirely 
 different remedies or circumstances were acting upon him. In 
 the same manner, for instance, we justly regard cinchona 
 (quinine) as a remedy for intermittent fever, quicksilver for 
 syphilis, iodine for bronchocele, opium for pain, &c., because 
 special experiences have shown, that such patients, left to them- 
 selves, or treated with other remedies, do not recover by far so 
 frequently or speedily. In short, it is only by such special 
 proof of the mode of action and influence of the individual agents 
 6v circumstances in the given case, whether it be furnished by 
 experience or scientific research, that our fallacious manner of 
 concluding cum or post hoc can be converted into the alone 
 correct one of propter hoc. So long as this has not been done, 
 everyone is in a manner free to consider sometimes one thing 
 and sometimes another as the cause of the event in question, 
 for instance of a disease or cure — and this, as may be foreseen, 
 will frequently lead to error. The theorist will find the greatest 
 room for this error in the setiological chapter of our pathology, 
 as well as in medicine itself. Whilst, for instance, the patho- 
 logist at one time selects for himself the functions of the 
 
ON FALLACIES, 413 
 
 nerves, at another the blood and its changes, or local anatomical 
 changes, as the starting point and essence of all diseases, the 
 therapeutist may, if he chooses, with equal right ascribe the 
 cure of thousands of his patients to innocent drugs, to homceo- 
 pathic or even sympathetic remedies. Thus we are in danger 
 of confounding cause and effect together if we assert that grief 
 may give rise to disease of the stomach and even to cancer of 
 that organ ; that the habit of sleeping after dinner, the siesta, 
 causes obesity, congestion of the brain, and apoplexy ; or that 
 cancer of the uterus is produced by the cessation of the menses 
 in the climateric years. 
 
 And since, as has been explained on a former occasion, it is 
 not always quite clear to us, what it is exactly that we wish to 
 prove, and that must be proved, and still less, in what manner 
 alone it might be proved, a further source of an entire series 
 of errors in our conclusions and assertions, as well as in our 
 attempts at explanation in general, exists, which we are wont 
 to comprise under the name of tautologies, arguments in a 
 circle, and petitiones principii. Whilst, in the one case, we give 
 a mere indirect description of the occurrence to be explained, 
 and which we believe ourselves to have explained thereby, (for 
 instance a disease, or the effect of some remedy,) whereas we 
 are only describing it with other words, in the other case, we 
 accept something as a proof of the course and connection of 
 what is going on in a function, a disease, or a cure, which would 
 itself first require an explanation. 
 
 However gross such an error may appear, and however easy 
 it may seem to avoid it, the latter, at least, is not the case, and 
 in our department of science everything, from the imperfection 
 of our knowledge to the defects and want of precision of our 
 terminology, coincides to favour such errors. 
 
 An old well-known example of this is furnished by the doc- 
 trine that " opium acts narcotically and hypnotically, because 
 it possesses a narcotic and hypnotic power" (Moliere), and 
 everybody must be aware that many attempts at explanation — 
 e. g., in regard to a disease, or the effects of a remedy — are, in 
 the end, no better. Many a one, for instance, believes that he 
 has given a sufficiently satisfactory explanation of the origin of 
 intermittent fever and miasmatic diseases by assuming that, in 
 certain localities, " marsh miasmata" or " malaria" are evolved. 
 
414 ON FALLACIES. 
 
 and that miasmatic diseases are now generated because the 
 people have been poisoned by a malaria. Thus we likewise 
 very rarely have a better reason for assuming the so-called 
 strengthening, tonic, or solvent effects of certain remedies upon 
 our patients, than the circumstance that those remedies have 
 the name of tonics, or solvents, and are considered as such. 
 Errors of this kind, however, are very likely to occur so soon 
 as we see ourselves compelled, not to deduce the causal con- 
 nection and conditions of an event (for instance of a function, 
 a disease, or a cure), from the determined laws of action of all 
 the circumstances and influences acting upon it, but rather to 
 infer them casually and superficially from other more or less 
 uncertain conclusions, perhaps even from purely hypothetical 
 notions on the subject. There is, however, no other more 
 correct mode of proceeding at the disposal of one who wishes 
 to explain anything in medical science, or who attempts to 
 give his categorical judgment about the influence of any agent, 
 whether deleterious or beneficial, upon the living body, or 
 about any process in the latter. For he at once sees himself 
 compelled to draw together his contingent of reasons from all 
 quarters, without always examining into their trustworthiness 
 in such a manner as would be necessary ; and now he is easily 
 induced to take the most doubtful conclusions as proofs of 
 others, and in this manner to explain one unknown quantity 
 by another, as, for instance, in the above case of the effect of 
 opium. If we once assume as correct, what has been asserted 
 at the end of the sentence (for instance, that opium has a 
 narcotic effect) we are now easily led to infer or explain the 
 anterior part of the sentence from it (for instance, that opium 
 produces sleep), and now again conclude that the end of the 
 sentence itself must be correct, because that which had been 
 explained and inferred from it, or which had been expressed 
 in the anterior part of the sentence, was an undoubted fact. 
 
 As, in our inability to furnish positive demonstrations, we 
 are so fond of flattering ourselves with the notion, or rather of 
 cheating ourselves into the belief, that we had already dis- 
 covered a causal connection for various things, we now infer 
 from it what ought, first of all, to have been proved before we 
 could be justified in accepting it as the cause or proof of what 
 is asserted in the anterior part of the sentence. Thus, for 
 
ON FALLACIES. 415 
 
 instance, we conclude that a so-called antiphlogistic, resolvent 
 remedy must certainly act antiphlogistically or resolvently be- 
 cause it is an antiphlogistic, resolvent remedy. Intermittent 
 fever and other miasmatic diseases are assumed to be generated 
 by marsh-miasmata, &c., because in marshy districts, the 
 noxious influence of which is undoubted, miasmata and malaria 
 are evolved, which have such an injurious effect upon men. In 
 patients affected with typhus fever or dysenteric disease, or 
 siaffering from pneumonia, &c., the entire disease, its course, 
 malignity, and result, are assumed to depend essentially upon 
 the local lesions — in the former of the intestinal canal, in the 
 latter of the lungs — for these are regarded as the seat, the 
 starting-point, and the properly determining or essential part 
 of the whole disease. 
 
 Exactly the same error, in the end, underlies every attempt 
 to deduce or to explain the mode of action of our remedies in 
 a disease from the causes or the nature of the latter, in short, 
 from the general state of things and from the intrinsic connec- 
 tion of the disease itself, which are likewise unknown to us. 
 It is inferred, for instance, that venesection, nitre, quicksilver, 
 &c., are beneficial in pneumonia, or steel in chlorosis, from 
 their causing some change in the blood and its composition, 
 and bringing it back to its normal state ; an abnormal compo- 
 sition of the blood, in one way or other, being assumed as the 
 determining and essential cause of the diseases in question. 
 Iodine, salts, &c., are said to act upon the " lymphatic system" 
 in scrofulous patients, because it is the seat and essence of 
 scrofulous disease. But it is even more erroneous and rash to 
 form a conclusion from the real or imagined success of a 
 remedy, or mode of treatment in a disease, as to the intrinsic 
 nature of the latter itself, as for instance the old doctrine of 
 Hippocrates — " Naturam morborum ostendit curatio,^' recom- 
 mends. In this manner, perhaps, A. infers the catarrhal nature 
 of hooping cough from the services which he has derived, or 
 at least thinks he has derived from hydrochlorate of ammonia, 
 emetics, and such likej B. its spasmodic nature, or a neurosis 
 of the pneumogastric nerves, from the beneficial effects of 
 valerian or musk. And his hypothesis, that these or other 
 diseases are no more than metastases of scabies, another per- 
 haps endeavours to uphold by the precipitate conclusion that 
 
416 ON FALLACIES. 
 
 certain remedies (for instance tartar-emetic ointment, vapour- 
 baths, &c.) are only of use in those diseases by re-establishing 
 a kind of eruption upon the skin resembling scabies. But 
 what opinion should we have of the logic of a physicist, who, 
 after evolving certain gases, or mere watery vapour, or heating 
 his furnace, not only believed that he had exercised a positive 
 influence upon the weather or other processes in the atmo- 
 sphere, but also attempted to explain the causal connection 
 and laws of these from the only half-understood properties and 
 modes of action of those his gases, &c. 
 
 We are the more likely to be tempted into such an error in 
 our conclusions if a certain explanation of a process, (for 
 instance of a disease, or a cure), or our conjecture in regard to 
 a certain causal connection in it, happens to be correct, or at 
 least sufficiently probable for certain cases. For that which is 
 applicable to these, we now with so much the more confidence 
 extend to other cases, for instance to certain other series of 
 diseased conditions, cures, &c., which appear to us to agree 
 with the former in the main points; and so soon as the latter 
 does not prove to be the case, we assume that our previous con- 
 clusion is a false one. Thus, after the sudden disappearance of 
 scabies, certain affections, such as palpitation of the heart, 
 dyspnoea, neuralgia, &c., may have arisen, which we might, if 
 we pleased, interpret as so-called " metastases of scabies." But 
 if we once take such cases as proved metastases of scabies, we 
 are easily led so far as to extend the connection which, in the 
 former, was perhaps assumed with some probability, to entirely 
 different diseases, likewise occurring in patients who had pre- 
 viously been suffering from scabies and had been cured of it, 
 for example, even to cancer, medullary sarcoma, tumor alhus, 
 &c. What might possibly be applicable in the one case is 
 likewise believed to be so here, where this kind of causal con- 
 nection is infinitely more doubtful, i. e., where it has not even 
 been proved, whether scabies and its cure might have had any 
 part whatever in the origin of those diseases ; and thus a com- 
 plete scabies-group might be constructed, as, for instance, the 
 well-known one of Autenrieth. 
 
 Connected with this is the fact, that in our judgment and 
 conclusions in a given case we often readily start from certain 
 general doctrines or abstract truisms, or even from common- 
 
ON FALLACIES. 417 
 
 place notions, and take them as proofs for those conclusions of 
 oursj without having previously determined whether they are 
 exactly^ applicable to the case at issue. Our error, therefore, 
 consists in our regarding something as absolutely and always 
 true or valid, whilst it, perhaps, merely applies to certain cases 
 and to a certain ensemble of circumstances, which, in the case 
 in question, are not all present, and where, therefore, our con- 
 clusion from it must become a false one. And how frequently 
 conclusions of this kind are drawn in practice, is suflSciently 
 well known. Thus it is said that cold is an agent hostile to 
 life, and that it must, therefore, act injuriously upon various 
 persons. And he who is once persuaded of the absolutely 
 injurious effects of quicksilver in syphilitic patients, will easily 
 attribute all casualties which may happen to such patients to 
 this remedy ; while he who, on the contrary, looks upon it 
 as the only remedy for syphilis, will likewise believe it to be 
 indicated, even where it may be injurious. In both cases, how- 
 ever, the conclusion is not more correct than if any one were 
 to infer from the fact, that only a given per centage out of a 
 thousand births arrive at a certain age, that a certain A. or B. 
 would likewise attain this age, and neither die sooner nor later. 
 A further circumstance by which this kind of error is essen- 
 tially promoted, is to be found in the obscure and especially in 
 the ontological mode of contemplation in medical science, as 
 well as in the ambiguity of our technical language and its Latin 
 phraseology. For it is precisely behind learned expressions of 
 this kind that defects, if not decided errors of our understanding 
 and of our whole train of reasoning, are hidden. The inter- 
 pretation of a given case is now perhaps expressed by a general 
 abstract term or sentence, which is by no means an explanation, 
 but merely a kind of indirect description of the case in ques- 
 tion, therefore by words and expressions, which, in the end, 
 only state in another form the fact of this event and the 
 existence of the things to be explained. We readily, however, 
 accept them as a kind of interpretation, because we are misled 
 by the tenor of the words themselves. If, for example, diseases, 
 such as dysentery, cholera, typhus, make their appearance as 
 epidemics, the physician naturally wishes to explain their oc- 
 currence, though he is, indeed, for the most part unable to do 
 so. But instead of expressing his error, his reasoning in a 
 
 27 
 
418 ON FALLACIES. 
 
 circle, in clear words, and of saying, for instance, that those 
 diseases appear epidemically because it happens to be their 
 character and nature to do so, he perhaps says that they 
 prevail epidemically at present, because the epidemic genius 
 morborum, the epidemic constitution of this year, or of this 
 district, happen to be of this kind. In a similar manner the 
 fact, that children of scrofulous, or syphilitic parents are like- 
 wise frequently scrofulous and sj'philitic, is sought to be ex- 
 plained by saying that a hereditary disposition to those dis- 
 eases was innate in them. And if various influences or reme- 
 dies aff'ect certain persons in a peculiar manner, this is held to 
 be dependent upon their constitution, temperament, &c. In 
 the same manner it is said, that certain functions, certain 
 excretory processes, are connected with each other, because 
 they stand in sympathetic relation to each other ; that cantha- 
 rides act irritatingly upon the urinary organs, and that quick- 
 silver acts upon the salivary glands, because they stand in a 
 specific relation to those organs. Again it is asserted that con- 
 sumptive patients do not suffer from cancer, and that pul- 
 monary consumption and tubercular disease in general are very 
 rare, or entirely absent, in miasmatic districts, because an 
 antagonism exists between those diseases. 
 
 Finally, daily experience teaches how we are most easily led 
 into the gravest of these errors in our reasoning and attempts 
 at explanation, if we follow any decided tendency therein, or 
 if we seek to demonstrate the correctness of a previously- con- 
 ceived notion, and this especially during a contest with oppo- 
 nents — perhaps pressed by their cogent objections. Into this 
 difficulty all of us, in the end, are thrown easily enough, even 
 the most calm and clear thinkers, because we all believe so 
 many things without having real and valid reasons for doing 
 so, frequently even without knowing, or at least without re- 
 membering, how we acquired this belief, these conceptions 
 and notions. In the beginning we perhaps yielded to the 
 natural desire of looking upon those circumstances and points, 
 under which we just happened to have observed the event or 
 effect in question, (for instance, a disease or a cure,) as being 
 also the causes of these. We have perhaps arranged and ex- 
 plained everything according to this our point of view, and 
 have leisurely formed further combinations, built up further 
 
ON FALLACIES. 419 
 
 conclusions upon previous hypotheses, without clearly enough 
 recognizing their prematureness or one-sidedness. It is only, 
 perhaps, during a contest with an opponent or in the pre- 
 sence of an opposite opinion that we find ourselves induced to 
 look round for real reasons and more valid proofs for our asser- 
 tions and previous attempts at explanation. But as we have 
 brought forward the latter without having previously examined 
 into the real state of things more accurately, aud still more 
 without having become acquainted with it in a sufficiently 
 comprehensive and correct manner, we, in the end, commit 
 one logical error after the other in our reasoning. 
 
 Proofs enough of this are furnished by every controversy 
 and polemic treatise, and nowhere to such an extent as in 
 medicine — with the exception, perhaps, of politics and the daily 
 press. 
 
CONCLUSION. 
 
 As it is the province of scientific history to trace up the 
 growth and expansion of thought, and to track, step by step, 
 the course through which our knowledge of natural subjects 
 has attained to its present development, so it is the task of 
 logic to decide upon the final establishment of truth, through 
 the accurate adjustment and balancing of the particulars which 
 history furnishes. 
 
 Now in bringing our labours in this particular department 
 to a close, a few questions such as these suggest themselves. 
 To what point have the increased resources and superior 
 enlightenment of the present day brought us ; to what further 
 acquisitions may our hopes and endeavours reasonably tend ; 
 and by what means may we most speedily and safely press 
 forward upon the path of progress ? 
 
 It has been explained already how the art of healing, pass- 
 ing from the simple empiricism of its first attempts to alleviate 
 human suffering, became mixed up with the superstitious 
 practices and mystical ceremonies of the existing age and 
 nation. And the stamp of this its origin and infancy has, to 
 some extent, remained impressed upon it even to the present 
 day, in an adherence to traditionary maxims, a proneness to 
 indulge in rash hypotheses, and a deficiency in an accurate 
 knowledge of the subjects with which, as a science and an art, 
 it is concerned. How often, even in the present day, do we 
 see medicine in the dark both as to the object it would achieve 
 and as to the means by which it would achieve it. As an 
 art, it too seldom attains to a clear insight into the processes 
 required for the accomplishment of its proposed objects, and 
 failing this, we see it attempting to carry them out through 
 a series of arbitrary and self-imposed rules. It now acts upon 
 the results of simple experience, relying solely upon the indi- 
 
CONCLUSION. 421 
 
 cation a juvantibus et noceniibus, without any clear discern- 
 ment of the processes and conditions upon which the fulfil- 
 ment of its task of prevention or of cure depends, and with as 
 little real understanding of the means and appliances whereby 
 this desired end is to be attained. 
 
 By this we do not mean to imply that medicine has attained, 
 so far, to nothing more definite than a collection of single 
 facts or cases, histories of diseases and cures, which time and 
 observation have gathered together. The human mind has, 
 in this respect, proved itself both willing and able to reflect 
 upon that which it has observed, to arrange its complicated 
 materials, and to discriminate which among them is best fitted 
 to assist it in its proposed efforts. From the very beginning 
 the observer has sought for an explanation of the phenomena 
 and processes in the living body, its ailments, and their cure; 
 and in this manner one system has followed upon the other. 
 Each of them, probably, as it arose, gave rise to expectations 
 of which advanced experience, in its turn, demonstrated the 
 fallacy, and one generation after another questioned, doubted, 
 or abolished what the preceding one had looked upon as 
 established certainties,, perhaps without being able to replace 
 them by anything more stable and reliable. For nearly all 
 medical interpretations or theories were of such a nature that 
 a single new case, an individual novel fact, was perhaps 
 suflBcient to shake the conclusions we had built upon them, or 
 even to prove them utterly false. And nearly every hitherto 
 praised remedy and medical treatment is in equal danger of 
 being abandoned on the appearance of a new one ; while only 
 simply empirical facts — whether in science or in art — have 
 enjoyed a real stability. 
 
 Bacon looked upon the source and origin, as well as the 
 results and progress of a science, as the sign or criterium of its 
 trustworthiness and healthy state ; and attached weight to the 
 circumstance of the most able specialists and writers of a 
 period being agreed upon its main doctrines and views, or not. 
 Kant asserts the same thing when he says — " We may easily 
 judge by the results of our labours whether we are pursuing 
 the cultivation of knowledge by the sure and enlightened path 
 of a science. If, after many preparations and provisions, it . 
 begins to flag as soon as an object is attained, or, in order to 
 
423 CONCLUSION. 
 
 attain it, has frequently to go back and set out upon a fresh 
 course; also, if it finds a difficulty in making its different 
 plans and combinations work harmoniously together towards 
 the attainment of the end they are jointly concerned with, we 
 may feel certain that our study has not yet entered into the sure 
 path of a science, but is so far merely seeking about for it." 
 
 If we judge of our medical acquisitions by this standard, the 
 result may not prove particularly flattering in regard to medi- 
 cine as a science. But it is of little use to close our eyes, and 
 to pay compliments to ourselves and to each other upon a pro- 
 gress and upon acquisitions whose nature and extent, after all, 
 remain undefined. For we have not yet advanced from em- 
 piricism to science, using this latter word in its full meaning, 
 and the rules or principles according to which the physician 
 as well as any other artist acts, are not safely to be trusted so 
 long as he is not able to deduce them from an adequate un- 
 derstanding of the objects with which his attention is con- 
 cerned ; so long as the practical observation of every indi- 
 vidual case, and every additional circumstance connected with 
 it, demand his special attention, calculation, and consideration. 
 
 And here the physician is almost necessarily wont to con- 
 tent himself with a mode of observing and judging which 
 other arts and sciences have long ago abolished, on account 
 of the instability and uncertainty attached to them. Few 
 among us, even now, see clearly, and fewer still will openly 
 confess, how little all our bed-side experiences are in reality 
 able to prove and establish, from the abundant and inevi- 
 table sources of error connected with our observation of 
 disease and cure, and from the uncertainty to which we are 
 liable in seeking to trace out these in their conditions 
 and true causal connection ; an uncertainty which is increased 
 by our being yet far from possessing a just knowledge of their 
 common laws, as shown in the unchanging conformity or 
 order of their actions, influences and processes. In every 
 individual case, therefore, we are left to a doubtful calculation 
 of probabihties in regard to the total effect or final result, 
 (e. g. of a disease or cure,) as a whole, in our endeavour to 
 ascend to their possible, and, in the precise case at issue, 
 perhaps more probable conditions. Even diseases which phy- 
 
CONCLUSION, 423 
 
 sicians have been observing daily for centuries — from the 
 simple furuncle; catarrh, or spasm, to inflammation of the 
 lungs, typhus, or epilepsy — offer us too many problems to 
 allow us to boast of having possessed ourselves of the essential 
 processes and intrinsic concatenation of circumstances byvrhich 
 they are attended. We have only become better acquainted 
 with a few of their individual phenomena and effects, and 
 therefore, in spite of ourselves, we are compelled to allow our 
 judgment in the case of an individual patient to be directed 
 by conjectures more or less uncertain concerning the con- 
 ditions and nature of his disease, and by comparisons more or 
 less adventurous with other patients, similar states, &c. And 
 after all we must endeavour to remove symptoms and phe- 
 nomena of disease whose peculiar nature, cause, and import- 
 ance we have not yet been able to recognize with certainty. 
 Again, the physician must form a conclusion as to the pro- 
 bable benefit of his measures and remedies by taking the 
 particular circumstances of each individual case into due con- 
 sideration, and this because the treatment and measures he 
 adopts are seldom based upon a knowledge of the mode in 
 which they act upon the disease in question, but are generally 
 simply empirical, and have probably been discovered by mere 
 chance. Aristotle said " ubi desinit physicus, ibi incipit medi- 
 cus," and so, in essentials, it has remained to the present day. 
 All this brings us to the question why our knowledge has, 
 after all, remained so stationary? And to this our previous 
 remarks on medical logic will furnish the best answer. Its 
 chief cause — in addition to the many inevitable difficulties of 
 our department of science — may be traced to an opinion 
 which, especially since the time of Bacon, has gained a certain 
 footing among us, viz., that in general the experimental know- 
 ledge of all that takes place during the natural course of 
 events, as they are connected with patients and their cure, 
 was the main point by means of which we might, singly and 
 unaided, arrive at an understanding of the nature and con- 
 ditions of the disease. This is expressed, for instance, by 
 Baglivi's "ars medica tota in observationibus," and so it 
 came to pass that we learnt to be contented with the observa- 
 tion and collation of simply empirical facts, and, to a great 
 extent, have remained so even to the present day. But in 
 
434 CONCLUSION. 
 
 the general investigation of nature, our aim and our task 
 must consist in the discernment of the connection and con- 
 formity of its various processes, as well in health as in disease ; 
 and the want of fully understanding this has led to an undue 
 neglect of the only ways and means by which the end in 
 question, had it but been more clearly placed before us, 
 might have been attained. Knowledge, it is true, can only 
 arise from experience, but we must not, under circumstances 
 so complicated and difficult as those with which we are con- 
 cerned, rely, for understanding them, upon experiences alone. 
 Some, so-called empirics, little able to judge how the matter 
 really stands, are accustomed to condemn all desire for deeper 
 and more penetrating research as being vain, theoretical, and 
 valueless. In this they pit experience against scientific 
 knowledge, or practice against theory, observation against 
 penetrating inquiry, in a manner which, while it betrays the 
 confusion of their own ideas, must also work badly for the 
 very carrying out of those practical requirements to which 
 they attach themselves so exclusively. Empiricism has always 
 advanced its claims with a presumption exactly proportioned 
 to its inability to establish them. Instead of modestly doubt- 
 ing the trustworthiness of its insight and the actual value of the 
 conclusions it leads to, it is satisfied with the little it has, or 
 rather believes itself to have, and perhaps does not even 
 recognize the facts by which the one as well as the other are 
 daily rendered questionable. It holds fast by authority and 
 prescription, for want of considering that such were established 
 at a time when science was but in its infancy, and that, if we 
 justly accord faith to the age and experience of an individual, 
 so ought we, on kindred grounds, to yield it to the science of 
 our days, in right of the more mature and experienced age it 
 has attained to. Others, on the contrary, incline to believe 
 that the bold and perhaps ingenious achievements of an indi- 
 vidual may at once attain to results which the most circum- 
 spect investigation of centuries has been aiming at, and it is 
 well known that false prophets, pretending to be able to fulfil 
 such requirements, have never been wanting. 
 
 To this we may add that every science, in proportion to its 
 inability to plant its inferences upon a solid experimental basis, 
 becomes more dependent upon all other sciences, just as a weak 
 
CONCLUSION. 435 
 
 power becomes dependent upon its mightier neighbours. All 
 our so-called auxiliary sciences — anatomy and physiology, as 
 well as chemistry and physics — have thus successively acted 
 upon the ill-joined materials of medical science ; so also has it 
 been influenced by the changing systems of philosophy, just as 
 its development happened at the time to be connected with the 
 various discoveries these have made, and the various points 
 they have established. Never has there been a want of heads 
 to apply these detached hints to the purposes of medical science, 
 or a lack of hands to work up these scattered crumbs falling 
 from the master^s table ; only it has proved that the elevation 
 so gained has, at the same time, afforded a standing-point from 
 which to view the desert that surrounds our improved edifice. 
 And, instead of setting about the diligent cultivation of this 
 waste, we have too often become bewildered and blinded by the 
 sirocco of crude hypotheses and arbitrary a priori attempts at 
 explanation which was unceasingly wafted across it. We found 
 ourselves able, perhaps, to cast various things into the new 
 form, but their kernel, their intrinsic value, remained the same. 
 Yet we have seen many physicians attach weight to the opinions 
 of men of general scientific enlightenment, who have at the 
 same time, held no position in regard to their medical attain- 
 ments. We have allowed the auxiliary sciences to play the 
 dictator over us in succession, instead of endeavouring ourselves 
 to solve our own problems after the methods they have sug- 
 gested. We have expected to arrive by their aid at knowledge 
 which can never be attained except through our own exertions ; 
 and with this are connected an over-estimation of novel acqui- 
 sitions, and that fallacious semblance of positivism or exactness 
 which has crept into medicine in the train of microscopico- 
 anatomical and chemical methods of investigation. Instead of 
 inciting the physician to scientifically circumspect and sober 
 investigation in his own department, they have rather tended 
 to lull him into a fresh kind of delusion, and to entice him into 
 hazardous hypotheses and theories without ground and founda- 
 tion. He who perhaps understands pretty well how to explain 
 the appearances in a post-mortem dissection, and to auscultate 
 and percuss the chest of a patient, has often thereby become 
 an authority in medicine — the celebrity of the day ; and so it 
 has been with many microscopists and chemists, who, perhaps, 
 
426 CONCLUSION. 
 
 have furnished us with a number of hypotheses and one-sided 
 arbitrary explanationSj but rarely with facts and proofs. And 
 if the wood at one time prevented us from seeing the single 
 trees, we are now prevented by the number of single trees from 
 seeing the wood. 
 
 It wouldj on the other hand, be not only unjust, but even 
 quite absurd, to doubt that important progress has been made 
 in the field of general knowledge in our science. The scien- 
 tific horizon of the student of our day is an infinitely wider 
 one than that which the most able physician enjoyed even a 
 century ago ; and views, notions, and theories which flourished 
 a few decennia ago, are now seen in their true light of impos- 
 sibilities. And if doubts must remain as to the certainty of 
 our bed-side practice, it is no less certain that every patient, 
 attended by an able physician, receives from him the maximum 
 of assistance which his case makes obtainable. It is easy, in 
 all cases, for the sceptic to confound mere uncertainty with 
 impotence, and to class difficulties and impediments with im- 
 possibilities ; and Bacon justly calls it a calumniation of the 
 human mind, as well as of nature, to declare that to be impos- 
 sible which happens to surpass our present powers, and to lie 
 beyond the limits of our actual mental horizon. Here, too, 
 the words of Humboldt are sufificiently encouraging to us, in 
 which he says, " it is a certain test that much may yet be ex- 
 pected of a science when the facts and discoveries connected with 
 it still stand unconnected, and nearly without relation to each 
 other — yea, even if they appear to be contradictory." For it 
 is well known that no science furnishes more opportunities of 
 making discoveries, and of reconciling apparent contradictions 
 of all kinds, than does that of medicine. We must still regret 
 that physicians and investigators of nature, from their imperfect 
 acquaintance with causal conditions, are apt to deceive them- 
 selves as to the extent and certainty of their knowledge and 
 power, so that, by striving for things which, under the given 
 circumstances, are impossible, they overlook and leave undone 
 that which is sufficiently capable of accomplishment. For no 
 cause can more impede the fitting choice of the ways and means 
 which can alone lead to our desired end, than the want of a 
 clear and discerning knowledge of causes and the efi'ects attached 
 to them. And on this deficiency the chief stress has been laid 
 
CONCLUSION. 427 
 
 during the whole course of our argument. We have no longer^ 
 as in former days, to contend with the spirit of superstition, 
 still less to complain of the want of aids and resources. Our 
 chief impediment lies in ourselves; in the want of discerning 
 what are our nearest and most important tasks ; in the employ- 
 ment of unproductive, if not of wrong, methods of investigation ; 
 and in the imperfect and scanty employment of such as are 
 good and fertile in improvement. 
 
 It may, perhaps, appear presuming, and forgetful of the 
 principles already laid down, if I venture to add some intima- 
 tions as to how the inquiries connected with medical science 
 may proceed, so as to most surely tend to the attainment of 
 the object with which we are so deeply, both as regards theory 
 and practice, concerned. Yet I feel that I cannot more fitly 
 take leave of my reader than by pointing out a few of the ways 
 and means by which the physician may arrive at a clearer 
 knowledge of his objects, and be able to carry them into more 
 efficient practical working. 
 
 If we look upon the course which other branches of 
 human knowledge have pursued in their development, we shall 
 recognize an analogy pervading them all. A. Comte has ob- 
 served that all knowledge, more especially such as regards 
 nature, runs through three stages : that of fiction and poesy, 
 of simple faith, and dogmatic opinion (Comte calls it the theo- 
 logical state) ; which is succeeded by that of arbitrary hypo- 
 theses, a priori abstraction, combination, or speculation (which 
 he describes as the metaphysical state) ; while, last of all, 
 arrives the stage of sober but positive science, based upon a clear 
 understanding of what it has to deal with. The first is the 
 necessary starting-point, the last the requisite aim and only 
 legitimate conclusion, just as the individual who, during child- 
 hood, takes his belief upon trust, resting its grounds on the 
 authority of others, becomes in youth a speculative metaphy- 
 sician, and concludes, at a more mature age, with a clear 
 insight and rational discernment which, at the same time, 
 permit him to doubt of much that was formerly believed in 
 implicitly. 
 
 During each of these epochs of our knowledge and judg- 
 ment, the human mind must proceed in whatever pursuits and 
 
428 CONCLUSION. 
 
 researches it enters into just as the state of its existing know- 
 ledge permits it. First of all, we seek to comprehend and discern 
 that which a higher degree of knowledge would teach us it was 
 in vain to aspire to — I mean the understanding of the intrinsic 
 nature or essence^ the ultimate cause, as well as the true pur- 
 pose, of all the things round about us. But the nearest, 
 because the most convenient, substitute for this is found in 
 referring these unknown causes to some arbitrary arrangement, 
 effected during the first stage by the intervention of a super- 
 natural agency, which man can only imagine as personified. 
 For everything he sees he has, as G. Forster says,'^ " but one 
 cause, and this he calls God. For him a God thunders in 
 the clouds, and leads him over the sea; to him there exists 
 a God in the green oak and in the fragrant flower.^' At a 
 later period, during the speculative metaphysical stage, this is 
 replaced by similar but less distinctly personified abstractions 
 and a •priori conceptions — i. e., so-called " forces," which are 
 imagined as acting self-efficient entities which dwell in matter, 
 and can of themselves call forth all the phenomena and pro- 
 cesses which we observe to occur in it. Now it matters little, 
 in regard to the main point, whether they are called force of 
 gravity, or vital force, whether nervous or electric fluid, or 
 principle of heat or light. In the last stage of science and 
 positive investigation of nature, man learns to give up the in- 
 quiry into, and desire of understanding, the peculiar essence 
 and ultimate causes of the things which surround him. All 
 he wants is to determine, by sober positive investigation, 
 the way and manner, the order and conformity to fixed laws, 
 according to which certain phenomena and processes in nature 
 really take place. Law, and a firm and intrinsically necessary 
 order, step, in all things, into the place which has, on one side, 
 been left vacant for chance to fill, and, on the other, been 
 filled up by allegorical and arbitrarily erected aggregates of 
 causes. 
 
 Upon this last stage we have long since seen natural philo- 
 sophy and chemistry fairly enter ; and as the investigation of 
 the physiologist, and even of the pathologist, have already 
 passed its threshold, we may expect to see the whole body of 
 medical science follow in their train. 
 
 ' Opera Omnia, vol. vi, p. 176; Leipzig, 1843. 
 
CONCLUSION. 439 
 
 First of all, as regards observation^ medicine seems at last 
 to have aimed at a sober view of its objects ; to understand, if 
 not yet thoroughly, the nature of the tasks and problems set 
 before it ; and to have become aware of the extent of the capa- 
 bilities it can bring to bear upon them. But we have yet to 
 emulate and copy more closely the methods by which our sister 
 sciences have attained to such solid and brilliant acquisitions. 
 And in all cases we must begin with that which lies the nearest 
 and is the most easy — i. e., with the expansion and determi- 
 nation of our simple experience of natural objects, or with the 
 comprehensive yet exact confirmation of everything which, in 
 the field of life, with the outward influences that bear upon it 
 — in health as well as in disease — is already accessible to our 
 observation. We must not be satisfied with a merely super- 
 ficial observation of phenomena, but must seek after their elu- 
 cidation with all possible accuracy as regards all their bearings, 
 making use of all mechanical aids to this end, — such as weights 
 and measures, retorts, and other similar expedients. Just as 
 the phlogiston-theyry was overthrown by the sole help of the 
 scales, and by this the path was formed towards a better under- 
 standing of chemical processes, so may we also expect from 
 stricter methods of observation to gain for the future a more 
 certain knowledge. At present, with regard to the living 
 human body, not even the smallest part of that is accurately 
 determined which might be ascertained by mere simple obser- 
 vation — least so of all in the case of the sick, with regard to 
 whom a more accurate system of investigation has only taken 
 root in this century. Just as far are we from even an empi- 
 rical acquaintance with the various diseases of the different 
 zones and nations of the world, and remain even more in the 
 dark with regard to the analogous conditions in plants and 
 animals, especially in those of the lower orders. We are, there- 
 fore, in a great measure deficient in that comparative knowledge 
 which the anatomist, the botanist, and the zoologist have at 
 their disposal. And yet we shall hardly arrive at any specific 
 knowledge of the diseases of our temperate zone without having 
 become acquainted with those which prevail in the others, any 
 more than we should be in a position to form a clear idea of 
 mankind in general, before we had become acquainted with 
 the human race as it exists under climates and aspects the 
 
430 CONCLUSION. 
 
 most varying. It is with us, here^ as in meteorology-j where we 
 have such need of reliable observations with regard to the state 
 of the atmosphere and climate in the tropical and polar zones, 
 that we cannot yet attain to such an insight into its processes 
 as would justify us in speaking of meteorology as a whole. 
 
 But as our chief aim — i. e., knowledge — can never be 
 attained by the mere observation of the natural course of 
 things in itself; as we do not, for instance, learn to under- 
 stand a disease solely by the determination of the phenomena 
 (symptoms) in the patient in question, but seek to trace out 
 and bring to light the circumstances and changes by which 
 these phenomena themselves may be caused, here, as in all 
 cases, our chief task must be to determine their causal con- 
 nection and conformity to fixed laws. We have endeavoured, 
 on a former occasion, to explain the manner in which we 
 should proceed for this purpose. Before all things, we must 
 begin with the most simple and, comparatively speaking, most 
 accessible relations and circumstances. Instead, for instance, 
 of adhering, in our so-called setiology, to 'miasmata, marshy 
 atmospheres, or even to epidemic constitution, disposition to 
 disease, and such like terms and aggregates, all the properties 
 and laws of action of the individual agents, or influences, 
 ought first to be investigated separately. Diseases themselves 
 must not be looked upon as anomalous isolated processes and 
 conditions, but rather as a series of simple modifications, or 
 peculiar forms of various processes in the living body, difi'er- 
 ing only in the gradations or transitions of their physiological 
 conditions or modes of action. The physician can never hope 
 to attain to an accurate understanding of the diseases he has 
 to deal with until he has learnt to connect together, as a 
 whole, what has, in the course of time, become disjoined in 
 physiology and pathology. We should likewise previously en- 
 deavour to ascertain the conformity and intrinsic connection 
 of the individual processes or elements of a disease, instead of 
 seeking in the first place to explain the whole, and to pro- 
 nounce upon its proper ultimate causes. It is by this kind 
 of resignation and wise self-restriction that other natural 
 sciences have been able to attain that which we, up to this 
 day, so painfully miss, and have yet to look for. We have, 
 perhaps, laid these words of Descartes too little to our hearts ; 
 
CONCLUSION. 431 
 
 " Nous devons preferer la connaissance de quelque peu de verite, 
 h, la vanite de paraitre n'ignorer rien." Everybody must know 
 that the conquest of medical science is not to be achieved by a 
 coup-de-main, nor even by a number of these in succession, let 
 them be ever so well aimed and skilfully combined, but that 
 it must be attained to by a regular and methodically conse- 
 quential research. The " anticipatio mentis et naturse" is 
 quite a different thing from the circumspect and slowly, but 
 surely, progressing " interpretatio naturae" and " recte Veritas 
 temporis filia dicitur, non auctoritatis." (Bacon.) 
 
 But for this it is obvious that we need a concurrence in the va- 
 rious branches of our investigation, as well as that, from as 
 many sides and under as varying aspects as possible, they should 
 meet and co-operate to one given end. In this track phy- 
 sicists and astronomers have long ago preceded, us, and only by 
 numerous observations, bearing upon one end, yet taken from 
 many points of the globe, and carried on through a long series 
 of years, have they been able to attain to a better under- 
 standing of such phenomena, for instance, as those connected 
 with the magnetism of the earth and the relations of weather 
 and climate, as well as such as relate to the movements of the 
 celestial bodies. We should learn more and more, in regard 
 to medical problems, to effect the same distribution and combi- 
 nation of labour. And as men of science, in separate countries, 
 have already formed themselves into societies for the advance- 
 ment of their general aims, they may the more easily, to this 
 end, join hands over the whole civilized globe. 
 
 It does not rest with us to prove, here, that the whole prac- 
 tice of the physician, with the success and certainty attached 
 to it, must depend upon the advance of true scientific know- 
 ledge, for Bacon, in the superscription of his second book, has 
 taken the interpretatio naturae to be synonymous with regnum 
 hominis. 
 
 Far from there existing any discrepancy between the know- 
 ledge of a thing and the power of doing it, between understand- 
 ing and performing, it is obvious that the two things are 
 inseparably linked together. Such a difference, it is true, may 
 exist between the capabilities and talents of the individual phy- 
 sician and investigator, because one and the same mind is not 
 
432 CONCLUSION. 
 
 often found capable of following up comprehensive scientific 
 principles, and of at the same time so applying his results as 
 to make the best practical use of them. It is left (generally 
 speaking) to some men to discover and furnish scientific rules, 
 ideas, and truths, while others have best understood how to apply 
 and render them useful. Our art depends, in a much higher 
 degree than any other, upon those sciences which are con- 
 cerned with the investigation of the living body, and with that 
 of general nature and its processes. And in medicine we 
 can only speak of fixed principles, and of a consciousness of 
 security in our practice, in proportion as those sciences them- 
 selves have attained to established truths. Every artist is com- 
 pelled to aim at a certain result (with us, for instance, the cure of 
 a patient), and seeks by one or other proceeding or interference 
 on his part to produce an efi'ect, the success of which entirely 
 depends upon the coinciding of certain conditions and circum- 
 stances. Every physician, therefore, as well as every other 
 artist, should be in possession of an amount of knowledge at 
 least sufficient to make him capable of judging by what pro- 
 ceedings and means he may best be able to accomplish the 
 result he has in view — for instance, the fulfilment of an " indi- 
 cation", at the bedside, or the cure of a patient. He should 
 be able to assure himself as to the circumstances and properties 
 from which the effects of the remedies and mode of treatment 
 he has adopted have arisen ; he must know what has influenced 
 and modified them, or perhaps directly opposed them, and, in 
 the latter case, must strive to ascertain whether such opposition 
 arises in the body he is acting upon, or is worked by the agent 
 he is employing. And it is evident that the principles and 
 rules of his art will (fnly be useful to him in so far as they are 
 based upon an understanding of and accordance with, what has 
 here been stated. But his mere art, as such, will never put 
 him in possession of this knowledge, &c. It is science alone 
 which so instructs him as to the efficiency of his art as to enable 
 him to judge of the means and measures by which he may most 
 safely attain to the ends it is concerned with. Then only 
 would it be the province of his art to furnish him, by the aid 
 of such knowledge, with appropriate and fixed rules for the most 
 complete possible performance of his task. 
 
 We know, however, that in medicine we have not yet. 
 
CONCLUSION. 433 
 
 either in knowledge or in skill, attained to this point, In no 
 art can knowledge be converted into tolerably certain precepts 
 or rules for the practitioner so long as that knowledge itself is 
 so fragmentary and incomplete as ours. For our rules of art 
 are not (and this of necessity) derived from an understanding 
 of the processes or conditions on which we are called upon to 
 act, or from a knowledge of the remedies by means of which 
 we expect to act upon them, but are drawn solely from our 
 experience at the bed-side, taken in connection with an 
 empirical knowledge of a more or less uncertain character. 
 We have not yet even ascertained so much by simple observa- 
 tion as to know whether certain diseases may not perhaps be 
 cured by the course of nature, undisturbed by any interference 
 of art. And yet this step would appear to be indispensable to 
 the formation of any judgment with regard to the adoption of 
 such interference in the majority of cases. We can only 
 attribute a value to our empirical rules in those ordinary and 
 average cases, from the observation of which they have been 
 derived as the final result of a certain number of individual 
 expei-iences. Even in the most favorable case, therefore, they 
 can only be looked upon as a general guidance, the observance 
 of which, in the individual case at issue, must again require a 
 special consideration of all the concomitant circumstances, and 
 an appropriate modification of our proceedings in accordance 
 with these. Thus it is less important to know that such and 
 such results are, in general, to be obtained by certain mea- 
 sures or remedies, than to be able to ji^dge whether and how 
 far these will prove available in a given case, and what modi- 
 fication our treatment will have to undergo on account of the 
 peculiar circ"umstauces of the latter. But the possibility of 
 arriving at this judgment — the most important element in our 
 practical proceeding — is the result, as is clearly evident, of our 
 previously acquired insight and knowledge. 
 
 Now, if the present state of our knowledge scarcely enables 
 us to calculate or predict anything with certainty, least of all 
 shall we be able to do so with regard to the results of our art. 
 Not as if the processes and occurrences in our patients were 
 deficient in a certain conformity of their own ; nor as if effects 
 could here take place without their adequate causes, or could 
 fail to take place in spite of the action of their adequate 
 
 28 
 
434 CONCLUSION. 
 
 causes, but because a number of causes and circumstances are 
 here at all times in operation, the influence or laws of which 
 have remained for the most part, if not entirely, unknown to 
 us. In all cases, therefore, we can only attain to a kind of 
 supposition of probabilities, and not to a demonstration of 
 certainties ; and even the probability of the former will, in a 
 great measure, depend upon the discernment and circum- 
 spection of the individual, To this must be added that we 
 physicians never are, nor shall be, masters of all the cir- 
 cumstances and influences under which, or against which, we 
 have to act : we can do as little in this respect as the navigator 
 or the statesman. If, then, there is any established certainty 
 in medicine, we must not place it in the result of our curative 
 attempts, but in the due understanding of what the preserva- 
 tion of health, or the completion of the cure, renders necessary. 
 Our security consists, therefore, in the recognition of the 
 indications at the bed-side, but not in their fulfilment. This 
 makes it apparent that medicine might be infinitely more 
 powerless and inefficient, as an art, than it is in reality, even 
 if, as a science, it already held a high and secure position. 
 
 That the patient should expect his physician to fulfil all that 
 which the interest of his health requires lies in the nature of 
 the case, even if in this, as so frequently happens, he is asking 
 for what is impossible. Unprofessional people are not aware 
 of the limits which are placed alike to our knowledge of our 
 art and its application. It is more to be wondered at that 
 physicians should themselves further this error, by thinking 
 proper to surround themselves with a halo of power which they 
 do not possess, renouncing that to which their art truly en- 
 titles them, and may, in future, do so in a yet higher degree, 
 as shall be presently shown. Nobody thinks of blaming or 
 deriding the natural philosopher or meteorologist because he 
 has not the power of averting tempests and storms, or of 
 converting bad into fine weather ; nor does he ever propose to 
 deceive himself or others by the assumption of such an attri- 
 bute of Divinity. Yet in our department of science, decep- 
 tions, at least self-deceptions, of this kind are not rare, although 
 we have also to deal with processes and events which, equally 
 with those of the natural philosopher or meteorologist, take 
 place and proceed according to their fixed, unchangeable laws. 
 
CONCLUSION. 435 
 
 And whatever the physician is capable of changing, modifying, 
 and effecting in his peculiar province, he can only accomplish 
 through his knowledge of these laws, and through his respect 
 for their operations. 
 
 We are far from wishing to quarrel with physicians who see 
 the highest destination of medicine in its practical activity, as 
 exerted for the health and bodily welfare of their fellow-creatures. 
 Not without good reason may they be proud of this their voca- 
 tion, for a nobler or more important one does not exist. But 
 if they really are as desirous of affording relief as they aver 
 themselves to be, and if they feel the whole responsibility which 
 they have taken upon themselves with their calling, it will be 
 their endeavour to adopt those measures and ways of succour 
 which are most surely conducive to their noble end in the relief 
 of suffering humanity, and to render their duty a more and 
 more attainable thing. What our ancestors were wont to look 
 upon as the only, or at least the most efficacious, means towards 
 such an end can no longer be considered such by us. What a 
 Paracelsus, or even a Sydenham, was warranted in believing, 
 the physician of the present day neither can nor dare believe, 
 any more than that the earth is a disc, or that there is no such 
 thing as the circulation of the blood. If we look over the long 
 series of our remedies and modes of treatment, we see them, 
 with few exceptions, one after the other, condemned as ineffi- 
 cient, and sinking into oblivion; and it is only our ignorance, 
 and consequent vague, if not erroneous, appreciation of their 
 actual efficiency and services which have always remained the 
 same. It is the most experienced physicians, best able to form 
 a judgment in the matter, who have always been the first to 
 perceive that when disease, more especially if its character 
 be virulent, is once generated, medical skill can afford little help 
 of a positive nature, even by the use of those measures upon 
 which we have been accustomed to place the greatest reliance. 
 J. Primerosius has said in his Preface,^ " Recte scripsit Hippo- 
 crates, medicinam omnium artium esse prsestantissimam .... 
 verum addit : propter ignorantiam eorum qui eam exercent, et 
 eorum qui temere de illis judicant, reliquis artibus inferiorem 
 videri." And essentially the same thought is expressed in the 
 
 ' ' De vulgi erroiibus in Medicina,' lib. iv ; Amsterdam, 1641. 
 
436 CONCLUSION. 
 
 complaint of Reveille Parise •^ " La medecine est la plus noble 
 des professions, et le plus triste des metiers." 
 
 Fortunately, however, medicine is not so utterly destitute of 
 expedients as our fears would lead us to imagine, only we must 
 not look for them in our medicine-chests, but rather in Nature 
 herself, and in her laws. We must learn how to satisfy the 
 exigencies of the sound as well as of the diseased human body, 
 and we must unlearn, little palatable as such a process may 
 be, much that we have heretofore rested on as certain. We 
 must renounce faith that has held dominion over us for cen- 
 turies ; and if the physician would remain, or, to speak more 
 justly, would become, what his loftiest aims point to — the friend 
 and counsellor of his suffering fellow-creatures — he will find 
 himself compelled to adopt other ways and means than he has 
 hitherto been contented with. " Be truthful if you would be 
 believed and trusted" is here an applicable maxim. Man, 
 even now, in all civilised countries, enjoys a better state of 
 health than he has done in any former period ; for many deadly 
 plagues and epidemic diseases have, in a great measure, disap- 
 peared. But we have not become more free from them through 
 learning to cure them better than our ancestors were able to 
 do, but simply because the general habits of mankind have 
 become, through an advanced civilization, more favorable to 
 the maintenance of health. From this the physician may de- 
 rive a valuable hint ; and, forsaking the attempt to accomplish 
 impossible ends by impossible means, he will the more endea- 
 vour to achieve that which lies evidently within the limits of 
 possibility, and will learn, first of all, to look upon the preven- 
 tion of disease as his primary and most sacred duty. When 
 disease has already obtained ground, he will accustom himself 
 to lay less stress upon his remedies than upon supplying his 
 patient with all the necessaries of life. The more fully he 
 becomes aware how much, even under his best endeavours, lies 
 altogether beyond the compass of his powers, so much more 
 earnestly will he strive, by means of such expedients as are 
 attainable, to preserve and promote health, alike in the indivi- 
 dual and in the state. 
 
 In short, it is probable that the therapeutics of the old school 
 will have to give place more and more to prophylaxis, a change 
 
 ' 'Gazette Medicale de Paris,' No. 29, 1851. 
 
CONCLUSION. 437 
 
 which has already beeu effected to some extent in practical 
 North America (Massachusetts). By this, not only will the 
 natural alliance between medicine and hygiene be re-established, 
 but a more intimate bond than hitherto will be formed between 
 these and all other natural sciences. And this will the more 
 certainly take place the more physicians become clearly con- 
 scious that they must learn to look upon man only as a part 
 of entire nature, in regard to his existence and requirements, 
 his health, sickness, and recovery. A truly scientific and prac- 
 tical education, combined with the positive activity such an 
 education implies, will place the physician in a far higher and 
 more secure position in the public credit than he gained from 
 the nimbus former times drew around him, or than he won 
 from the privileges with which the state and its laws are wont 
 to endow him. 
 
 To many it will perhaps appear melancholy to reflect that 
 the utmost our science can accomplish is, to render itself super- 
 fluous through the success of its endeavours to preserve man- 
 kind in health. However, it is the greatest glory of the 
 physician to relinquish such aims as are merely personal and 
 selfish, in favour of the general benefit of mankind : but, after 
 all, the danger of seeing medicine and its services rendered 
 superfluous does not threaten us very closely. 
 
 But this will the sooner take place the more physicians 
 become penetrated by the spirit of true scientific re- 
 search in all things wherewith their practice connects them. 
 And to further this enlightened investigation as far as in us 
 lay, was one of the highest and most significant tasks we placed 
 before us in our " Medical Logic." 
 
 J. E. ADLABP, PBINTEB, BARTHOLOMEW CLOSE.