CORNELL UNIVERSITY LIBRARY FROM Cornell University Library QH 307.E17 The living organism; an introduction to t 3 1924 003 030 818 Cornell University Library The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003030818 THE LIVING ORGANISM Ai THE LIVING OEGANISM AN INTEODUCTION TO THE PROBLEMS OF BIOLOGY BY ALFEED EAEL, M.A. LATE SCHOLAR OF OHBIST'S COLLEGE, CAMBKIDOE OF THE INNER TEMPLE, BARRISTER-AT-LAW Eontron MACMILLAN AND CO., Limited NEW YOKE : THE MACMILLAN COMPANY 1898 Lo A II rights reserved PREFACE Among the many branches of that organised pursuit of knowledge which has attained in this age its most marked development, there is none which has so profoundly influenced current thought as Biology. The conceptions derived from biological research have proved not only an intellectual gain of remarkable value in their proper sphere ; but they have had, so dominant are they in character, far-reaching results in other directions. The great tide of new ideas has been too strong to be contained within its own channel. The neighbouring fields of philo- sophy have been affected. The human outlook on Nature has been changed. But just as new ideas colour those which have been previously acquired, so does the loss of a single conception involve the disturbance of many. And, therefore, if Biology is to be a sub- VI THE LIVING ORGANISM ject of education as well as of research, there are urgent reasons why aU who aid in its progress should help to make its foundations stronger, more self-contained, and steadier. Without dwelling on this point, it may at least be observed that inaccurate conclusions and un- sound speculation have more serious issues in the case of Biology than in any other of the Natural Sciences. Security against these results must come about through care in the instruction of rudi- ments. As far as the intellectual difficulties of the rudiments will permit, a change in the pre- valent attitude of the student towards them seems desirable. Too much is taken for granted. The problems and generalisations of the science of living objects are regarded too complacently by the beginner. He is too easily contented with description and narrative ; and it may be mentioned that practical work in the laboratory is often little more than an aid in remembering description. That which is a mere statement or a collection of terms in a text-book does not become a course of reasoning because it is followed concretely in the laboratory. The dis- section of typical organisms is not necessarily an intellectual exercise. PREFACE vii Moreover, since Biology as the science of living things deals with phenomena of which we air have some kind of knowledge, its ideas lend themselves very readily to popular discussion. It has provided new terms and phrases for a public interested in novelty but impatient of study. Yet the common occurrence of such terms as Heredity and Natural Selection does not imply a widespread extension of scientific research. The respect shown for any generalisa- tion of a chemical or physical nature affords a striking contrast to the confidence with which biological subjects are discussed. It would appear that the problems of inanimate Nature, the qualities and changes of matter, are to be left in the hands of experts who approach them after a rigorous training, while untrained judg- ment may exercise itself over the mystery of life. Nevertheless it is with great diffidence that I have ventured on this essay to deal with some of the difficulties of the subject, and to sketch in outline a course of thought which may serve as an introduction to more special study. Detail has been sacrificed in it to breadth of view. Practical illustration is to be found in many excellent text-books, and by the side of those Vlii THE LIVING ORGANISM more solid achievements this effort must play a supplementary and subordinate part. The object of the book will be attained if it succeeds, although it may be chiefly by negative criticism, in directing attention to the important truth, that though chemical and physical changes enter largely into the composition of vital activity, there is much in the living organism that is outside the range of these operations. CONTENTS CHAPTER I INTEODUCTOEY STATEMENTS The exercise and end of perception — The nature of knowledge — The nature of observation — Variety of forms in the world — Systematic knowledge needed — Biology deals with living things Pages 1-10 CHAPTEE II SOME CONDITIONS OP ACQUIRING KNOWLEDGE OF LIVING THINGS Subject and Object — Perception a part of life — The various sciences overlap — Biology deals with feelings as well as appearances ....... 11-18 CHAPTER III AN OUTLINE OF THE SCHEME OF BIOLOGY Explanatory remarks — Elementary ideas of Biology belong to two classes — Common forma and changes of life to be described in general terms — Details not to obscure gener- THE LIVING ORGANISM alities — Generalisations simplify description — Changes of matter common to all forms — Description of the scheme of Biology Pages 19-29 CHAPTEK IV THE STRUCTUEES ACCESSORY TO ALIMENTATION IN MAN General description — The organ concerned in exchange of gaseous material — The organ occupied in disfrihution and excretion — Mechanical analogies are misleading — The general results of circulation .... 30-42 CHAPTER V A DESCRIPTION OP OTHER FORMS WITH REGARD TO ALIMENTATION Vertebrates — Molluscs — Arthropods — Echinoderms — Simpler animals — Plants — Summary and amplification . 43-55 CHAPTER VI THE OBJECT OF CLASSIFICATION Need of an order for living objects — Simple description inade- quate — The process of classification — Difficulty in applying the process to living objects — Dual aspect of the organism as possessing form and as presenting change — Classification simplified by regarding both form and function — Idea of development in classification — Conception of types — Influ- ence of authority — Communication of knowledge increases its exactness — Opinions of others to be recognised — Summary 56-79 CONTENTS CHAPTER VII CERTAIN GENERAL STATEMENTS CONCERNING 0E9ANISMS AS INDIVIDUALS Explanatory — Life continuous, Forms intermittent — Form dis- turbed in reproduction, but life persists — Death the sequel to reproduction — Further discussion of growth — Assimila- tion the reality underlying growth — Eeproduction con- nected with the process of growth — Permanence of the form — Summary Pages 80-96 CHAPTER VIII A GENERAL DESCRIPTION OF THE ORGANISM AS RELATED TO ITS SURROUNDINGS Relation of Subject and Object — Our difference from other organ- isms in relation to surroundings — One part of life engaged in observing other parts — Natural Science chiefly describes phenomena — Organism both Subject and Object — Organism and surroundings inseparable in some respects — Thought based on sensation, but implying something more — The same world of Objects giving impressions to innumerable individuals — Meaning of "Self" — Perceptions and ideas — Province of Biology — No disparity between organism and environment — A contrast necessary — Link between organ- ism and environment 97-117 CHAPTER IX THE MATERIAL BASIS OF LIFE Introductory — Living changes few in number and forming a constant group — Matter concerned in the changes to be THE LIVING ORGANISM considered — Difficulty in perceiving the substance as common — Degrees iu resemblance of material — Similarity of substance and similarity of behaviour — Process of generalising — Observation needs control and definition — Limitation of chemical methods — Application of chemical nomenclature — Complementary relation of plants and animals — Chemical names given to certain constant phenomena . .... Pages 118-136 CHAPTEE X THE OEGANISM AS A CHEMICAL AGGEEaATB Description of chemical changes — The organism as an aggregate of certain kinds of matter — Chemical description not dis- tinctive — ^Description of matter in general terms — Reality of sensations — Perception of sameness in material objects is exact — All knowledge of Nature based upon the percep- tion of similarity in quantity or quality — Test of sameness applied to living matter — Primary restriction of observa- tion — Protoplasm more than a chemical compound — Con- stant features of living matter do not preclude variety of form — Difficulty iii localising attributes . . 137-158 CHAPTER XI THE ORGANISM AS A CENTRE POR THE TRANSFORMATION OF ENERGY Physical methods and results applicable on certain conditions — Classes of change to which applicable — Conception of energy — Energy of animals derived from plants — The organism not an ordinary conservative system — Resemblance of organic activity to that of other systems — Distinctive fea- tures of organic activity 159-174 CONTENTS xiii CHAPTER XII CERTAIN ASPECTS OF TORM AND DEVELOPMENT Need of guidance— Meaning of degree in these matters— Ex- ternals of life dealt with in form— Structure and material to be considered — Value of analysis — Structure demon- strates composite nature of activity — Organism together with environment form a system — External changes affect- ing the organism — Reaction of the organism — Danger of pseudo-explanations — Cell-division incidental to growth and reproduction — Idea of cell to be used with reservation — Products of cell-division not necessarily alike — Prejudice ia matters of form and change — Environment assists com- prehension of development — Extension of idea of develop- ment and environment — Two main paths of development — ^Hypotheses useful in co-ordinating facts — Ideas of cell- arrangement more useful than ideas of cell — Cell-arrange- ment less signiiicant than combination of function — Nerve - development connected with highest function — Equilibrium checked by the Organism — Summary Pages 175-228 CHAPTER XIII THE MEANING OF SENSATION Introduction — Illustration of ordinary mutual action — Addi- tional results when one object alive — Effects of external things belong to two classes — Character of sensation — Im- plication of mechanism in consciousness — The sentient subject 229-249 CHAPTER XIV SOME OF THE PROBLEMS PRESENTED BY THE ORGrANISM Recapitulatory — Species — Variation and Adaptation — The Cell as Agent — The unity of the Organism . . 250-266 CHAPTEE I INTEODUCTOEY STATEMENTS The introduction to a fresh study in some cases is a definite event in personal history. It is possibly an occurrence marked by some circum- stance of time or place. Certain ideas may be suggested for the first time or, it may be, facts first come witliin our ken under conditions which render the occurrence memorable. But this is rare. The acquisition of any portion of knowledge is, in reality, seldom a sudden operation. It is more usually an insensible drifting through a multitude of mental states, and one idea may be the result of many preliminary efforts. It is difficult to claim for any portion of knowledge that it is absolutely new, and difficult to assign to it an origin or moment of inception. A little reflection makes it clear that most of our thoughts grow gradually out of those which previously existed. The more recent mental B 2 THE LIVING ORGANISM chap. conditious, so far as they are progressive, are built up of simpler and earlier states. A gradual progress in thought may often be traced through many stages from an origin which is distant and obscure, though great care and skill are necessary for success in this performance. This statement, if it can be realised for a single idea, or even for any given class of thoughts, holds still more true of such a vast body of knowledge as is denoted in speaking of Natural Science. There is no absolute and marked beginning of such a subject, as there can be no end, in minds which have ever been active in its acquisition. We shall learn hereafter that minds must be so occupied as long as they exist. Activity of this kind is a condition of their existence. We are always learning, though not always are we learn- ing with method or with advantage. We perceive Objects and Changes It is unnecessary to speak of the variety or the number of objects which come within our perception, and the instances of change are innumerable. A complex world of endless objects and changes appears before us, and our attempts to understand it have created Natural Science. I INTRODUCTORY STATEMENTS 3 The Act of Perception is the Beginning of Knowledge The objects and the changes in those objects, which together constitute our world, give rise to successive acts of perception. It may be said that perception is exercised on objects (or things), and on changes (or events); and each individual perceives within certain limits, and not beyond. Our science or knowledge is based upon, and begins with, the perception of our surroundings. The Amount of Knowledge depends partly upon the Extent of Perception This statement must be true, if knowledge be a result of perception. The wider the region surveyed, in other words, the greater the number of objects and changes perceived, and the more accurate the perception, the greater will be the amount of knowledge. The value of knowledge, however, is estimated by very different means. The worth is not likely to be confused with the amount. The Bange of Perception for the Individual is limited The individual can explore but a limited region of the world. A few alone of its innumer- 4 THE LIVING ORGANISM chap. able objects and changes can come ■within the compass of his mea,ns of perception. The experi- ence of other individuals may assist him to widen the circle of his own knowledge. Information gained from others may add to his personal store. It is the aim of education to put the learner in touch with accumulated knowledge, as well as to render successive additions to knowledge possible. The capacity to perceive may be greatly extended by a careful training which has these ends in view. The Exercise of Perception needs to be assisted and directed The mere accumulation of facts, as gained from repeated acts of perception on one's own part, or from statements of perception on the part of others, is not the only end towards which the student of science is directed. Unassisted efforts would probably lead to this result in the main, and then little intellectual progress would be made. Guidance and direction are always needed by the learner, and in almost all stages of civilisation the younger generation has been found to rely upon the older. The Extent of Knowledge is not so important as its Nature We do not necessarily know more, because we I INTRODUCTORY STATEMENTS 5 have come into touch with a larger number of facts or statements. Knowledge, or science, does not begin until facts are perceived to be connected in some way or other. The facts to be known are without limit. On the other hand, the capacity of the individual to perceive when facts are connected is limited very narrowly. It is important, then, that the working of our perception should take the right direction. The meaning of right, however, remains to be defined. To observe is to perceive intelligently It has been stated that ordinary perception, even when the action frequently repeats itself, does not necessarily lead to knowledge. For comprehension of what is perceived, it is essential that the percipient individual should be able to refer the things or events which are before him to that permanent record of past experience which he speaks of as his mind. Perception may be intelligent, or it may be without meaning and without use. When it is directed to a certain end, and when it is con- sciously performed for definite purposes, it is usual to describe it as an act of observation. Exact Knowledge begins with accurate Observation There is no doubt that accuracy in personal 6 THE LIVING ORGANISM chap. observation is essential to progress. Without some training in the special modes of observation which are needed in the branch of knowledge to be undertaken by the student, he cannot expect to be able to interpret rightly the records of previous observers. Their work will not be understood, nor wiU their descriptions convey the right meaning to him. The methods of acquiring exact knowledge and of gaining a faculty for correctly interpreting recorded facts of observation, based as they are primarily upon accurate personal observation, cannot be given in a few propositions. The following pages describe a few conditions which have a special bearing on Biology. An Experiment is a special Kind of Observation When the events to be observed are very complex, it is usual to resort to an experiment, whereby acquaintance may be made with a single aspect or a single component of a given change at a time. All observation partakes more or less of the character of an experiment, in so far as it has ulterior aims. The Number of different Substances in the World is limited, though the Number of different Forms is indefinite There is no doubt that the number of different objects even within our own compass is inde- I INTRODUCTORY STATEMENTS 7 finitely large, and within the known world there is no imaginable limit to the variety of distinct things. Yet the many objects coming under our observation are not unlike in all respects. In some of their properties they are frequently alike. Their distinctness or separateness is none the less true because they possess some degree of sameness. The substance or material of two distinct objects may be alike, while the form,, shape, size, situation, or state may differ. Herein lies the main boundary between the province of Chemistry and that of Biology. Chemistry deals with the composition of bodies, and does not regard their form. It is concerned, too, with the nature of the changes which may occur when different objects are brought together, but it pays no attention to the form or to the identity of those objects. We may say, then, that Chemistry is confined to substance, while Biology deals with the substance and also with the form and identity of certain objects. The term Form may be used to denote Condition or State, as well as Shape and Size For^n is that which is occupied or filled, that which contains, as distinct from what is con- tained. And so we come to use the word form as the sign for the mode or state in which an 8 THE LIVING ORGANISM chap. object appears to us. The form is opposed to the substance of an object. The matter or substance may be similar in different objects, while great variety of substance may be presented under the same form. Then, as we iind expressed in the science of Chemistry, matter exhibits great variation, inde- pendently of difference of form. With what is denoted by the narrower meaning of the term form Chemistry does not often concern itself The investigation of states' of matter, on the other hand, does form part of chemical research, though it is, speaking strictly, the subject of Physics. The Acquisition of systematic Knowledge is the End in view The propositions which have now been laid down form a suitable introduction to our subject. They have no special reference to any particular branch of natural science, but they apply to all knowledge derived directly or in- directly from observation. In connection with Biology, however, they are apt to be forgotten. In that science it is more than usually important to start in the right direction, and, indeed, to maintain through- out a correct attitude with regard to the foundations of our knowledge of Nature. For this reason, after recapitulating the gist of what I INTEODUCTORY STATEMENTS 9 has been already stated, we shall proceed in the following chapter to extend our list of preliminary- statements. We derive our knowledge of Nature from the exercise of observation, an act which has two component parts — the normal activity of the senses on the one hand, and the direct control of the intelligence on the other. The mere perception of the objects and changes among which we live is not enough for reasoning beings. It is not enough to receive impressions of nature as a series of separate and distinct phenomena, nor to receive them as a crowd of confused images. The acquisition of systematic knowledge exacts much more than a passive submission to external influences. It is a process evidently controlled and directed to a large extent by the experience accumulated in the past and made accessible through records. One's own observa- tion does not bring to light the connections between phenomena and the orders among events, until it is aided by the experience of others and shaped by reflection. Indeed any course of study is only to be distinguished from the daily round of ordinary watchfulness and reflection by the fact that these activities, which are evoked in some degree from every individual by his surroundings, are therein directed and controlled to a definite purpose. 10 THE LIVING ORGANISM chap, i And with such a purpose do we undertake the study of Biology. Biology is the Science which treats of living Things Such a statement as this will scarcely satisfy the inquirer, for it does not tell him enough. As to what is meant by a living thing, there is indeed a general, though indefinite, consent, and it is sufficient for the ordinary pursuits and thoughts of most people. Animals oi plants as examples of living things are easily recognised. Mistakes are made, it is true ; but, as a rule, the thoughts we have about animals and plants are precise enough for ordinary purposes. To be more precise or more definite, our ideas would need an amplification which must be the result of guidance and training. Although it may be useful at this stage to make a more exact statement of the nature of our subject, it will not be till the end of our course, in default of some previous training, that the meaning of the statement can be compre- hended more definitely. It suffices now to say, that the science of Biology is a certain body of connected knowledge, which is derived from the observation of living objects and from reflections based on that observation. CHAPTEE II SOME CONDITIONS OF ACQUIRING KNOWLEDGE OF LIVING THINGS The special Difficulties of the Subject are great The material of study may be named, and even the end, but we must be content to give to the mental processes which are concerned in the acquisition of all exact knowledge, whether biological or not, nothing but the shortest of descriptions. Mental changes are difficult to follow. We cannot, for example, understand what is meant by a generalisation or an abstract thought, till our minds have learnt how to generalise, and we have been conscious of many an abstract thought. To attempt to give a definition of a thought so abstract as that represented by the word life would be useless. Too wide a range of experi- ence would be needed to grasp the full meaning of such a word. The forms which exhibit life, and the activities 12 THE LIVING ORGANISM chap. which represent it, must be first observed and pondered over, both separately and collectively, before we can gain an adequate conception of life as a whole. That our ideas about life are limited will be apparent at an early period, and there will be no stage at which our mental activities are not confined at some points by barriers which cannot be passed. But it is not so much the boundaries set to our thoughts that prove the first impediment to progress. It is rather the vagueness of the thoughts themselves. The more familiar examples of living things may be, it is true, the subject of certain propositions more or less valuable. But how is it possible that all the varied forms and events which come before us can be covered by the single word life ? It is not merely the innumerable individuals nor the almost innumerable kinds of individuals which bring about our perplexity. We are troubled by the difficulty of incorporating the multitudinous forms and the varied changes in some comprehensive statement, the difficulty, in fact, of finding anything which applies to all cases and may be expressed of all alike. There is in some instances indeed little to be perceived, save an indistinct manifestation of an unusual movement or an organic shape. When any part of living nature confronts us, it needs no little skill in unravelling our thoughts II ACQUIRING KNOWLEDGE OF LIVING THINGS 13 and no little patience in observation, to gain con- sistent ideas ; and, still more evidently, the best powers of the intellect will be needed before any order or arrangement can be given to the total sum of living things. The attainment of an order out of the apparent confusion has been the result of many generations of thought. Among the products of that achievement are the following elementary ideas. Perception implies the Existence of a Ferceiver These words convey a truism, which hardly seems to need expression. Yet it is given in order to emphasise the fact that perception is to be regarded as an event which has two compon- ents. The thing perceived and the person who perceives stand in apposition to one another. There is a 'physical universe on one side, and a heing sensitive to it on the other side. The Thing perceived is the Object. That which perceives is the Subject This is but a repetition in other words of the previous statement. A name is now given to each aspect of the act of perception. The subject perceives ; the object is perceived. It is advisable to be content with this statement for the present, without attempting to grasp all that it may suggest. Further consideration would be interesting, but it would lead us away from Biology. 14 THE LIVING ORGANISM ohap. Perception implies Life The ability to perceive or to receive impres- sions is clearly a character which belongs to some living objects. It cannot be said with certainty that the character is one which always distinguishes living from inanimate things, until we have decided what things are alive and have learnt more about perception itself from our own practical experience. It should be noticed, however, that the term subject has, so far, only been used with reference to an animal, and a rational animal. Whether all forms of life can exhibit the same relation to external nature as is implied in the use of the complementary terms, subject and object, remains a question for later consideration. The various Sciences encroach on one another, and in Biological Investigations the Elements of several Sciences are involved The full discussion of the matter on which we have entered involves the study of other sciences. Psychology, for example, is one which specially deals with mental processes, resolving them into their elements and tracing out definite stages in the operation of thinking. It is a science which is occupied wholly with those facts of life which are described as subjective, namely, Consciousness and Thoright ; and even a slight acquaintance with II ACQUIKING KNOWLEDGE OF LIVING THINGS 15 such facts, with their origin and their analysis, will prevent many disastrous blunders in our biological conceptions. It is hoped that certain ideas, which belong strictly to Psychology rather than Biology, will be conveyed in these pages to the advantage of the student of the latter science. The Sources of Error are much the same in all Branches of Science But difficulties and errors are not confined to any one branch of study. They are common to all, and in all they are chiefly due to the same causes. Preconceptions and erroneous judgments are foremost in retarding progress, and with these, as a rule, beginners in Biology are plentifully endowed. The thoughts which are aroused in their minds by a given term do not always agree with the thoughts which are truly represented by that term. From such faults incorrect interpretations of description arise ; the record of a fact fails to recall the fact where such defects exist. By a constant reference to definitions, probable errors of judgment and imperfect generalisations may be avoided in many cases. But the form in which this subject is introduced, and the length of our preliminary discussions, are dictated by consideration of the exceptional difficulty in avoiding hasty generalisations and unwarranted assumptions in dealing with life. 16 THE LIVING ORGANISM chap. The Study of Life should include Feelings as well as Appearances Finally, we may assert that the acquisition of knowledge varies very little in its methods. The mental faculties which are employed in Biology are called into use in other branches of science. It is evident from our previous state- ments that some attention must be given to thoughts and ideas, as well as to objects and changes. That which we ourselves think about the world, and perceive in it, must be part of our study. And it is best to realise this at the be- ginning, before trying to form judgments even about the simplest appearances of life. It would lead, more certainly in the case of Biology than in most branches of science, to incomplete, if not to erroneous conclusions, to ignore the relation of the observer to the thing observed. Yet the full meaning of that relation can be but imperfectly understood, even at the end of our course. There are, then, two classes of things which must be admitted to exist beyond doubt, namely. Feelings and Objects. No exercise of thought ought to lead to a confusion of these two classes. They are esteemed by universal consent to be separate and distinct in our consciousness. We accept as the primary facts of our life the exist- ence of a manifold world of feelings and thoughts, forming what we call Mind, together with that of II ACQUIRING KNOWLEDGE OF LIVING THINGS 17 a complex world of objects beyond and external to that mind. Feelings have always to be referred, directly or indirectly, to a world of objects, and yet they must be regarded as having an existence apart from those objects. Consciousness takes this form most readily. Whether the judgment im- plied by the distinction is a final one depends upon the individual. Por most people it is final. But it may be asked, What has Biology to do with this fundamental generalisation, that there is a Self, or perceiving mind, and a Not-Self, which is the world of objects distinct from the perceiv- ing self? It will be the aim of the following pages to show that reflections which arise from a , consideration of the relation of Self and Not-Self, ) {y or, as it may be termed more fittingly, the Subject and Object, are essential to an adequate grasp of biological questions. Further, we may say that the world, which is apparent to us as external, everywhere presents itself as a diversified substance in incessant change. At the same time, it is evident that without some permanence of substance, or con- stancy of form, we should be unable to detect change of any kind. Our conception of life is necessarily associated with the image of a certain permanent form of matter undergoing certain modes of change. Our conception of life is limited, in other words, c 18 THE LIVING ORGANISM ohap. ii no less and no more than the rest of our very conditional and relative knowledge. Lastly, it may be repeated, we can observe life in others and also feel it ourselves ; but though the life of others appears to us as definite changes taking place in diverse forms, it is meaningless to speak of feeling or observing the feelings of other living objects. ■ CHAPTEE III AN OUTLINE OF THE SCHEME OF BIOLOGY Explanatory Bemarks The statements to be subsequently made about the organism will be found simpler in kind than most of those already encountered. They de- scribe the more prominent appearances, or what are commonly called the more striking facts of life. These appearances are presented to all of us in the same fashion. The mode of presenta- tion — why this or that thought should he aroused iy a given object — is a question not touched upon in this chapter. Yet the resemblance of ourselves, the observers, to the objects we are observing must not be for- gotten. So much in common exists, that there is a danger of considering everything to be alike. It is advisable on many grounds to give atten- tion to this tendency, and there is no doubt that it is an influence in many of our judgments con- cerning the nature of life. Ideas derived from 20 THE LIVING ORGANISM chap. our own experience of life are too readily trans- ferred to other forms of life. The resemblances are apt, indeed, to disguise the differences. As already stated, the mode of treatment employed in these pages has taken its shape from these considerations. It has mainly originated in the effort to separate assumptions from truths, and to show that the thought which is a part of our own life is occupied in forming conceptions about life as a whole. Hence it is that mankind is only in appearance occupying the first place in this essay. It is necessary to deal with some of the con- ditions of hitman consciousness at the beginning, lest our incomplete conceptions should rank as truths and many difficulties he ov&rlooked. The elementary Ideas of Biology belong to two Classes Our earliest observations and our earliest in- formation in this science will give rise to impres- sions which fall naturally into two groups. ■ There are, standing in marked contrast, two main categories in which the ideas of Biology may be placed. It will seldom happen that there is any apprehension of physical life which does not come under the heading either of " Thoughts about Form," or " Thoughts about Changes." In other words, the material of Biology suggests a clear separation of the facts of form from those of change. Yet it must not be supposed that the two Ill OUTLINE OF SCHEME OF BIOLOGY 21 classes are unrelated. Hereafter it may be im- portant to treat the two classes of facts together, while at the present stage it is a great conveni- ence to distinguish them in our minds. It is an advantage to place on one side the impressions derived from a multitude of living and material objects of very varied shape and structure, and to keep them as far as possible in the background, when ideas of the changes associated with life are occupying our attention. During the progress of observation and in the course of description, forms and changes necessarily come together. It is in the process of reflection and during considera- tion that they need to be separated. The common Forms and Changes of Life must be first described in general Terms The forms of life are beyond enumeration, and the illustrations given below are a few in a multitude. The changes, however, which living forms exhibit are quite limited in kind. The most prominent are changes of position, the most universal are those connected with feeding, and these two classes of change will be the first to be described in outline. It is in connection with such events that some description of the forms of life is most fittingly introduced. The Animal Kingdom, as it is called, is made up o'f individuals which are in most cases capable of locomotion. The Vegetable Kingdom, so 22 THE LIVING ORGANISM chap. called, is distinguished by immobility.^ All members of both divisions are alike in their dependence upon certain external matter, which we call food. The act of feeding is a necessity for every living object. But it is a very short step towards an arrangement of these living objects to divide them into animals and plants. Sub-division after sub-division has yet to be made. The dwellers in the sea or air differ from those which live on land, and the differences are connected with the habits which are imposed on them by the nature of their surroundings. We may, or may not, perceive organs, limbs, and symmetry of outline; for, indeed, a definite shape cannot always be predicated of the organism. On the other hand, we may note in many cases a rigid symmetry, and for those of the same class an undeviating sameness of outline. Yet these points, if we be inclined to deal with them by themselves, are not significant enough, nor of sufficient interest, to occupy our whole attention. Details must not be allowed to obscure Greneralities We are almost compelled, by force of numbers and heterogeneity, to examine a few specimens of living forms rather than attempt a review of a larger number. Yet our comprehension of the object of study depends as much upon our capacity ' A useful, though not a strictly accurate distinction. Ill OUTLINE OF SCHEME OF BIOLOGY 23 to generalise as upon our skill in dissection or analysis. The knowledge of details of structure, and of the countless variations of structure, does not become coherent or edifying, unless it he acquired as part of a wider scheme of perception, — unless, indeed, it he conceived as suhordinate to larger principles. With the object of learning to generalise, we shall proceed to the description of certain facts of common observation. All leasts, birds, reptiles, fish, and the' innumer- able invertebrates, together with every kind of plant or tree, yield, each in their own way, some quality or property apparent to our sense of sight, which permits not only a ready distinction of species from species, but also the grouping together of numerous individuals in the same class. But where are we to begin ? Of the many appear- ances presented to us in the web of life, which will best serve for purposes of classification, or which will give us the best or the widest information ? To enumerate all the appearances or properties of .an inanimate object takes time. To give an approximately complete account of all that is to be observed in a living object is a task of much greater difficulty. Even the first attempt to carry this out will show that a bare enumeration of properties is, in itself, not enough. The various modes in which properties are connected, and the association of groups of properties, will be 24 THE LIVING ORGANISM chap. found to be more significant and more fruitful in information. If we do not limit our activity of observation by considerations of this kind, and do not learn to combine reflection with perception, we shall certainly not attain to much knowledge of our subject. Greneralisations relate to Aggregates and simplify Description In the ordinary exercise of perception very similar results are frequently obtained. Im- pressions made upon the percipient subject are often alike in all circumstances but that of time ; and the external objects, to which these similar impressions are referred, may be, in that case, mentally grouped together. When occasion arises, they may be denoted simultaneously by a single name. Such a name or sign of a number of objects is spoken of as a common name. The mental activities which result in a common name or a common idea being called into existence constitjite the process of generalisa- tion. To generalise, therefore, is to create- or receive an idea, either simple or complex, which may be a-pplied to a number of objects with equal fitness, when once it has come into existence. The fitness of the application will depend upon the accuracy with which the general idea has been formed, whether or not it has been based upon adequate observation. Ill OUTLINE OF SCHEME OF BIOLOGY 25 The aggregate of objects forms a class, and since it is thought of as a whole, by reason of all members of the aggregate possessing some property or quality in common, we are able to abridge our descriptions in using the name of the class. We no longer need to specify this and every individual in recording our observations, but our common name or general statement embraces an indefinite number of instances in a general proposition or generalisation. Description is shortened by this means wherever resemblances occur, and the range of thought is extended by economy in expression. In the following outline of some of the prominent facts in the ordinary aspect of life, the use of generalisation is apparent. The condensation of description is evident, and the acceleration in mental processes which follows the conception of classes is illustrated. Constant Changes of Matter are common to all Forms No living object, though it preserve its identity in some respects, is able to maintain the same material composition for long. Its form, though relatively constant, has a continuous stream of material passing through it. This fact is often expressed by saying that there are two operations, waste and repair, in continuous pro- gress. But it is doubtful whether anything is 26 THE LIVING ORGANISM chap. gained by the use of these metaphors, and there is always a risk of misconception through for- getting that they are metaphors.-' The most careful and extended observation has failed to detect any exception to this general statement, and it remains as a distinctive character of life, that material changes are essential to its persistence. The process of generalisation cannot be pushed further in Biology, when once it has embraced every object included in the range of the science. But it is well to remember that the limit of certainty is never actually reached. And at the most we can only say of the pro- position before us that there is nothing in the collective experience of mankind to contradict it. The Generalisation is so universal that it ceases to be instructive The linfvit of generalisation, however, is not the sole aim of scientific inquiry. Ideas of narrower range have first to be acquired and formulated. It is really more important in the present instance to be able to discern differences, rather than resemblances, in the manner in which this change of material is carried on. In fact, our knowledge of living characters is more likely to be increased by comparing different ^ A metaphor ia a word used in a sense which is not usual, i.e. with a meaning not proper to it. Ill OUTLINE OF SCHEME OP BIOLOGY 27 instances of each distinct mode of change than by struggling after the limit of generalisation. Description of the Scheme of Biology The vague description of Biology previously given, as the science of living objects, will no longer be found exact enough for our purposes. There are a number of sciences which occupy themselves with living objects, Botany, Zoology, Physiology, Morphology, Embryology, as well as others. The chief object of Biology is to serve as an introduction to any of these branches of study. But it will not serve its proper purpose by expounding the rudiments of these subjects in succession. Something more than this is needed. From the facts and generalisations accumulated in the various sciences of life, certain principles have been abstracted, and with the exposition and the application of the principles so derived Biology is almost wholly occupied. These prin- ciples are drawn from two, or at most three, prominent conceptions, to one or other of which all the sciences of life contribute every acquisition they make. They are the conceptions of form, function, and devdopment} Every fact of life comes sooner or later under one or other of these headings. ^ Development may be omitted as being a derivative of the other two, see chap. xii. 28 THE LITING ORGANISM chap. It is, therefore, essential that the facts of life which are to enter into the composition of Biology must do so as portions of a scheme. Facts in isolation may legitimately enter into the records of other sciences, but it is only in their relation to one another that facts are useful to the biologist ; for he is attempting to learn, above all things, the fixed principles which underlie the diversity of life. He is endeavouring to discover the elements which combine to form, and through which, he can understand, the complexities of Physiology, Zoology, and Botany. To gain this end, an abstraction or general conception of the organism has to be built up, however difficult the process may be. So, too, form and function, structure and change, have to be treated in a broad manner, while the individual case is but introduced in illustration, and not for its own sake. As far as possible, the attention should be directed to those phenomena in the organism which are prominent and universal — ^that is, manifestly exhibited by all. In fact, those qualities which are not modified hy form claim our first care. But to succeed in finding out what is always present, we have to learn how to pass by much that is superficial and distracting, and how to distinguish that which is really essential from that which is merely familiar. Many grada- tions likewise exist in the importance of qualities, Ill OUTLINE OF SCHEME OF BIOLOGY 29 and many steps remain to be taken before these can be discerned. All the discipline here planned is preliminary to the stage of research into ultimate causes. WTiy the form is thus, the function or the develop- ment of this or that kind, are problems of much later date, and Biology cannot he expected to answer them with certainty. CHAPTER IV THE STKUCTUKES ACCESSOEY TO ALIMENTATION IN MAN General Description A SPECIAL structure, the alimentary canal, serves in man for the reception and conversion of food. The food is progressively altered during its pass- age through this tuhe, by coming into contact with special portions of the body which react with it. More or les^ changed by or combined with these substances, the assimilable portion of the food afterwards enters into the material constitution of that body. But the incoming material does not 'permanently reside within the boundaries which we recognise as the form of the individual. A concurrent loss of matter is always going on. Even in the case of an individual rapidly growing, there is evidence that the total quantity of food taken during any given period exceeds the increment in mass which is gained. The CHAP. IV ALIMENTATION IN MAN 31 longer the period over which observation extends, the more convincing is the evidence. In the case of the mature individual, the loss which is indicated by this fact is closely balanced by a gain, and, though undergoing minor changes periodically, he maintains a fairly constant average of mass. As far as can be observed, the contrary streams of loss and gain of matter are universally associated with living changes. They are en- countered in every form of life, whether animal or plant, large or small, simple or elaborate. But it will be observed that there exists in the structure which is organic to this end, a distinction of parts ; and it is a distinction which varies according to the kind of organism under observation. In man, at the entrance to the canal is an organ, the mouth, provided with sharp and hard teeth (fixed in a framework of bone which admits of a certain degree of movement). By aid, of this apparatus an action of cutting and tearing takes place previous to the disintegration, which is afterwards brought about by the presence of solvent liquids. Some liquid is introduced together with the solid food, but the liquids which are most active enter the canal from the various glands engaged in secreting them. Certain of the glandular structures, such as the several salivary glands, the liver and 32 THE LIVING ORGANISM ohap. pancreas, are comparatively large organs con- tributing a great quantity of active material towards the process of digestion. But liquids of various kinds and functions pass at different points into the canal, and throughout its whole length there are present small structures, evidently capable of assisting in finally bringing about a close contact of the nutriment with the living substance of the body. Now the whole of the glandular apparatus is resorptive, either directly or indirectly, as well as secretory. The stream towards the canal is at least equalled by that flowing away from it. To convey a more exact picture of the changes in alimentation, we should need to describe them as a system of circulation, into the various channels of which new material is being drawn, while other material is being expelled from them. Every portion of the glandular system, with its accessory network of blood-vessels and lymph- channels, takes its meaning from this function alone, or, as may be said, it is organic to this single end. Even the more distant glands may be regarded both structurally and functionally as part of the alimentary apparatus. External to those absorbent and active layers of the canal which are more directly concerned in the exchange of material, we find a layer of muscular bands so disposed that a contraction of successive portions of its length may take IV ALIMENTATION IN MAN 33 place. The necessary contact of the nutrient material with the lining of the canal, and with successive portions of the same, is thereby made more complete, and the expulsion of material which has not been absorbed is facilitated. The Organ concerned in the Exchange of gaseous Material Adjacent to the alimentary canal proper and closely connected with it are the Iwngs, which are truly alimentary in function, though commonly spoken of as the respiratory organs. In position, growth, and function they are allied with the alimentary canal. There is, in fact, a common purpose served by both — the interchange of external matter ivith that forming part of the organisation of the body. The lungs, however, are wholly occupied in the exchange of gaseous material ; while solid and liquid exchanges take place through the canal alone. The structure of the lungs permits a ready absorption of oxygen from the inspired air, by the agency of a fine network of capillary blood- vessels, which are distributed throughout its sponge -like substance. The air enters by the trachea through the Ironchi, and thence into the innumerable air-cells which give the lungs their peculiar texture. A thin partition alone separates the air at any point from the blood, which circulates through every portion of a crowded D 34 THE LIVING ORGANISM chap. network of vessels, and a rapid and voluminous exchange of gases is thereby rendered possible. As a final result, the blood becomes richer in oxygen, and the expired air shows an increased quantity of carbon dioxide. The Organ occupied in Distribution and Excretion The circulatory or vascular system forms the apparatus by means of which material from out- side is distributed to every part of the body, and portions of the body are rejected or excreted. Although a considerable amount of matter leaves the body by way of the alimentary canal, it must not be forgotten that every particle of matter which is truly excreted, as distinguished from that which is merely unabsorbed, has passed through some portion or other of the vascular system. The process of circulation is maintained by a central propelling organ, the heart: distribut- ing vessels, either arteries or veins, and various irregular cavities and channels ; while certain liquids, hlood and lymph, with their complex ingredients, constitute the ever-changing material in circulation. The heart, which is a localised muscular en- largement of the vascular system, acts as a pro- pelling and an exhausting organ, driving blood through the arterial system by muscular contrac- tion, and assisting its return through the veins by the relaxation of its muscles. The construction IV ALIMENTATION IN MAN 35 of the chambers of the heart and the arrangement of its valves promote this work. The flow and return of the blood, to and from all parts of the body, is necessary for the work of uniformly distributing the matter absorbed from the alimentary canal and the lungs. The branch- ing of the larger vessels into smaller and smaller channels finally ends in a minute capillary net- work, which is to be met almost everywhere in the body. But the minute vessels and spaces, which constitute the network here described, begin after a time to reunite into larger and larger vessels. An inverse process is encountered. The channels soon become larger and fewer, and finally the blood re-enters the heart by a single large vessel, and begins its course anew. The construction of the system, in brief, enables the blood to be rapidly driven through every part of the body, and, as rapidly, collected together again. This bare description, however, merely gives us information, and that of a superficial kind, of the changes preliminary to assimilation. It gives something of the plan in outline, omitting altogether the subordinate movements of the blood, and of its accessory liquids, without which the general circulation would be ineflfective. But the plan, even if complete, would include few of the serious difficulties of assimilation itself. These structures are but part of the coarser 36 THE LIVING OEGANISM chap. mechanism which is engaged in the antecedents and consequences of a more subtle act. We may state that the function of the vascular system, as a whole, lies in the prepara- tion, distribution, and subsequent dispersal of all the matter associated with the organism. The substances to be found in that vascular system, in some part or other, typify all the changes of form and composition which are connected with the continuance of life. To regard the system as simply occupied in the distribution of ingested food would be to form a judgment distinctly erroneous. Distribution is part only of its function, for that which is being distributed is meanwhile being significantly transformed. The substances contained in the vessels which leave the heart undergo a succession of varied changes. At frequent stages in its course, the blood receives additional material, and also suffers loss. The sequence in states is as im- portant as the stream of material. The structures which contribute to these changes in composition are, in the main, the lun^s, liver, kidneys, and the various glands which have been already mentioned in connection with the alimentary canal. The vascular system, then, does not simply carry and allot the matter taken from the alimentary canal. It receives it by way of the laoteals, brings it under the action of living IV ALIMENTATION IN MAN 37 products at once, and continues to submit the material to a series of operations before finally localising it. A broad survey would fix the food, which has been absorbed after a series of pre- liminary changes from the alimentary canal, at one end of a lengthy process, and the arterial blood, as it is driven from the left ventricle, at the other end. These are the limits of a series of chemical and mechanical events which form an important part of vital changes. Between these two limits that which is most remarJcahle among many occurrences is the preparation of inanimate matter for the inception of life. Mechanical Analogies are misleading ; There is much to be gained from the judicious use of analogy in attempting to describe com- plicated occurrences. An analogy is often helpful as an ideal framework, on which detached thoughts may be brought into relation with one another. In illustration of this auxiliary of information we may compare the food of an organism with the fuel of an engine. The material necessary to the life of an organism resembles in some respects the substances which originate the move- ment of machinery. But just as the life of an organism is far more complicated than any activity which can be manifested by niachinery, so the events which talje place in alimentation are far more complex than those chemical and physical 38 THE LIVING OEGANISM ohap. changes which supply the motive power of an engine. The resemblance between the two lies mainly in the dependence of each for its activity upon a continuous supply of suitable material. Here the analogy holds. But in other respects the differences are so great that the analogy is likely to be misleading. Its application would be extended if we knew of a machine which is not only able to supply its own fuel and adjust its activity to varying circumstances, but also to incorporate with its own substance the fuel which supplies this activity. The food of an organism may be looked on as its fuel, but it becomes also the machinery which is at work. That which is consumed in the case of an organism is the machinery, and food repairs the gaps left in a mechanism. To be accurate in the use of our analogy, we should compare the visible substance of the organism with the fuel rather than with the machine, for that is the substance which is being consumed. But in no case has the food itself any real parallel in the fuel of an engine. The material must be radically changed in form before it can serve as fuel. Where now do we find the machine ? What is there in the organism comparable with the combination of resistant bodies„ which we recog- nise as a machine when we perceive its parts to IV ALIMENTATION IN MAN 39 be capable of certain relative motions ? Design or adaptation is evidently common to both. But the working material of the one is characterised by constancy. The substance of the machine is always the savne, the substance of the organism is in constant change. The general Eesults of Circulation But though it may be impossible to find among the complications of art or nature an occurrence resembling alimentation in many of its aspects, we may render description more easy, if not more intelligible, by noting the most marked stages in the process. There is first a selective and absorbent surface — that of the canal, and a supply of food in its neighbourhood ; and then selective and absorbent tissues, forming the bulk of the individual, and having a supply of pre- viously prepared substances always in proximity. The absorbent tissue, together with its prepared nutriment, is to be found in every part of the body. The surface at which external matter is ahsorbed is limited. The medium which permits the necessary transfer of matter from place to place is the blood; and it is in the blood that the observable alterations in the condition of the matter take place. To bring about these changes there are temporary resting-places in the form of glands, where losses, gains, and rearrangements of material take place. 40 THE LIVING ORGANISM chap. The glands may be reasonably described as resting-places, because they aU. exhibit a structure wherein the circulating liquids may be submitted, for a comparatively long period, to the action of the living material of the glands. Blood is supplied to each gland by a network of vessels, ramifying in its substance ; and material is secreted by the gland, in quantity corresponding with the supply of blood and in nature dependent on the specific activity of the gland. A retardation of the circulation here takes place, from the narrowing of the individual vessels as they branch out and increase in number ; and a loss ensues from the process of selective diffusion through the substance of the gland itself. The matter resulting from this species of filtration is either added eventually to the general stock of matter in circulation, or it passes away from the body, as occurs by way of the lungs or kidneys. The material may be rejected — that is, excreted; or,. after passing through intermediate stages, it may again join the stream in circulation to undergo further change (sometimes even allying itself with food at its first contact with the body,^ and afterwards retracing every step that is known to exist in the course of alimentation). In such cases it is described as secretion. The main course of circulation has, therefore, minor systems of circula- tion in subordinate connection with it. ^ As occurs with saliva. IV ALIMENTATION IN MAN 41 The most general description of the changes briefly recorded above, and of the localities in which they occur, is that which will give most assistance in the attempt to understand their connection with life. Our efforts will always succeed best when they take the direction of expressing observable relations in the simplest terms to be found. Only then do we extend our comprehension. The main condition of success, it may be repeated, is to make every statement as general as possible. The description which has been given of the changes occurring in glands has taken its modified form from this motive. These changes in the form of ingested matter proceed simultaneously with life. They are en- countered nowhere but in living organisms, and the whole of the substance manifesting life is undergoing change of a special character, which is too complex for analysis at this stage. Change is in progress throughout the organism ; assimila- tion and dispersion are the material constants of life. If we attempt to fix limits to the act of life and say that it begins at this stage of change or the other, we are involved in difficulty. In the end, all we can say with certainty is that each organism is a centre at which inanimate matter is made to exhibit the attribute of life. The inception of the changes would appear, therefore, to he due to something external to the substances in which they are perceived, while the initiation of 42 THE LIVING ORGANISM ohap. iv life itself is in reality nowhere apparent.. There is no moment of time or position in space at which any of these changes may be detected except life be already there; nor, on the other hand, is there, in the series of events which every particle of living matter passes throiigh, any one to be selected as a sure sign of its entry upon life. CHAPTEE V A DESCRIPTION OF OTHEE FORMS WITH REGARD TO ALIMENTATION The illustrations which have been so far given are drawn from observations in human physiology. It remains to be seen how far the principles elucidated may be applied to other organisms, and how far the structure of the latter is conformable to the generalisations about life drawn from a single class. The characters described are not found to be confined to man. , In those animals which readily admit of examination the plainest indications are given, that ingested material undergoes changes and, in part, incorporation with the organism, as it does in man. The need of food and the presence of structures for its reception and trans- formation are, indeed, almost always evident. Vertebrates A similarity in the plan of the digestive apparatus is in itself enough to give a family 44 THE LIVING ORGANISM chap. likeness to the mammalia, a large class of animals widely divergent in many other respects ; while a still wider group of animals, which are alike in the possession of a vertebral column or backbone — mammals, birds, reptiles, amphibians, and fishes, for example — have also in common most of the organs which are noticeable in man as accessory to assimilation. All vertebrata have a distinct and specialised blood-vascular system. A chambered heart is always to be found maintaining a respiratory circulation, though it is only in some of the vertebrates that it influences the larger or systemic circulation. A portal circulation without ex- ception exists, the venous blood passing through a large gland, the liver, which brings about important modifications in that liquid. Part of the contents of the alimentary canal pass through a " lacteal " system of vessels on their way to the blood-vascular system proper. ^ Renal organs of secretion are invariably connected with the cir- culatory system, and either lungs or gills serve for the exchange of gaseous matter, of which oxygen is the important item. It is scarcely a matter of surprise that the resemblances with regard to one feature^ of organ- isation should find their counterpart in others. The striking similarity of plan to be observed in the skeleton, sense-organs, limbs, and in the disposi- tion of the nervous system, though not entering V ALIMENTATION IN OTHER FORMS 45 into the course of this argument, cannot fail to confirm the opinion that the main changes in various species have much in common, if direct experiment had not already produced that result. Yet special differences in structure, and minor differences in the corresponding functions, may be noticed, or the variation expressed in classes and orders would not be formulated. Among the most prominent distinctions it may be stated iha,t fishes and amphibians are charac- terised by the possession, during the whole or part of their lives, of gills or branchice, organs which permit of the absorption of air dissolved in water. Birds and mammals are distinguished from the latter by having four-chambered hearts to provide for the control of separate pulmonary and systemic circulations. Teleostean fishes exhibit a number of tubular appendages at the commencement of the duo- denum, called pyloric cceca, and these share in the process of digestion. Other classes of fishes are provided with an extension of the absorbent alimentary surface in the form of a spiral valve in the large intestine. The respiration of birds is remarkable for its extent. In consequence of the admission of air, not only into the lungs but also into large spaces in various parts of the body, a proportionate extension of the surface of aeration ensues, and 46 THE LIVING ORGANISM chap. the more rapid chemical change taking place in the blood is marked by a higher average tempera- ture. Molluscs It is not necessary to state that vertebrate animals are very far removed in structure from other living objects. The differences existing between a mammal and a fish are negligible in comparing either with an invertebrate animal. The MoUusca, for example, possess a long aliment- ary canal, but in them it is simpler in structure, and not enclosed in the general body-cavity. Yet salivary glands and liver are present, in their case also, to assist in the process of digestion. The vascular system is less clearly defined than in vertebrates, though a definite systemic heart is present. Definite organs of respiration may be absent, or a portion of the mantle may be adapted for aeration. Ctenidia are also of frequent occur- rence. In the fulrroonata the mantle is folded so as to provide an air chamber, into which air may pass by an aperture capable of being periodically opened and closed. Excretion takes place by kidneys or tiephridia, as well as in respiration and by the alimentary canal. The general structure of the body is wholly distinct from that of the vertebrates ; as a rule this is most clear in the absence of a skeleton and of appendages for locomotion, and likewise in V ALIMENTATION IN OTHER FORMS 47 the development of the nervous system. Yet resemblances are manifest, most prominently in the definite apparatus of digestion and in the vascular apparatus for distributing the digested material, and, less prominently, in the material of the supporting and muscular tissues. Arthropods All the segmented animals or Arthropoda — insects, crustaceans, centipedes, scorpions, ^iders, and their allies, are alike in other respects than that of segmentation. They all possess well- developed alimentary canals with similar accessory organs. Their circulatory system is also con- structed on the same plan. It is provided with a contractile heart and a fairly definite vascular system, which are placed dorsally. Eespiration may be carried on through special organs called lung-books, or by involutions of the integument called tracheae, but it is also effected in some forms by more specialised organs, the gills. EcUnoderms Among the Echinodermata we first come in contact with forms which do not possess an alimentary canal traversing the tody. All possess a canal, but in some forms there is but one open- ing. The body-cavity is filled with a watery fluid, in which float bodies resembling the white blood-corpuscles in animals of more complex 48 THE LIVING OEGANISM chap. organisation. This fluid may be regarded as the equivalent of blood. A prominent feature in their structure is the water-vascular system, the circulation in which is probably attended by respiratory and locomotory results. The development of both circulatory and alimentary systems is less marked among these forms, and is just sufficient to promote a general diffusion of material through the substance of the body. The simpler Animals In several classes of worms there are definite digestive, vascular, and excretory structures, though in the flat-worms (platyhelminthes) there is no real vascular system, and the alimentary canal has only one opening. Animals still less organised are included in the classes — ccelenterata, porifera, and protozoa. Ccfilenterata and Porifera possess a definite shape and a digestive cavity. The whole lining of this cavity ingests food without any differentiation of parts for that purpose. In some forms there are canals, affording to the organism a larger surface of contact with the water, in which it lives and from which it derives nourishment. Protozoa, on the other hand, do not always have even a constant form. They appear as very V ALIMENTATION IN OTHER FORMS 49 microscopic masses exhibiting irregular movement. The semi-fluid mass manifests some structure in the appearance known as the nucleus; and the contractile vacuole may render service in excretion. There is no cavity, but ingestion may take place at the surface, either irregularly or over a fixed area. The exchange of material appears simple and direct, there is no difference of parts to denote a division of labour, and yet this is still consistent with the existence of life. The apparent sim- plicity in form and structure does not, however, render the process of alimentation necessarily more simple, nor the problem of life more easy to solve. Plants We pass now to the other half of the organic world, the vegetable kingdom, the life of which appears to differ so much in character and in extent from that of animals, and also in its chemical and physical accompaniments. The food of animals is always in great part organic. Plants live on inorganic material, nitrates, compounds of ammonia, carbon dioxide, and similar substances, which do not support the life of animals. Hence it arises that animals are ultimately dependent for their existence upon the material continuously provided by plants. With few exceptions the food of plants is in the fluid state. It exists as gas in the air, or as E 50 THE LIVING ORGANISM chap dissolved matter in the soil. The leafy expansion of the aerial surface, and the extension of the sub -terrestrial portion of a plant by means of roots, facilitate the absorption of the diluted nutriment in sufficient quantity. In most cases, a system of vessels permits the passage of the liquids absorbed by the roots, and assists in its distribution. The porous structure of the leaves admits the important food, carbon dioxide, to their interior, and, at the same time, allows a gaseous excretion or transpiration to take place, the excreted material being chiefly water vapour and oxygen. The process of excretion is limited to this expiration of oxygen and water, together with a small proportion of carbon dioxide, and the continuance of life is therefore marked by an accumulation of material. The tree grows in bulk year by year. In structure and in appearance the animal and vegetable portions of the organic world have little in common to suggest that they are alike in the attribute of life. But though their food is so dissimilar, they are alike in their dependence upon their environment for a continuous supply of food; and, when once assimilated, the living material of organisms of either class presents little variety in chemical composition. It is therefore reasonably surmised that there is some- thing in common between the two kinds of life, different as they may be in most features. V ALIMENTATION IN OTHEE FORMS 51 A Summary and an Amplification The most patent characteristic of an animal is its movement, yet not the fact of movement alone, but the nature. The most obvious test of the life of an animal is its capability of ^on- taneous'^ movement. All animals which come under ordinary observation display at times irregular and fitful changes of position. These changes may or may not be connected with other changes external to the animal.^ But there are many other objects which are spoken of as living without exhibiting this kind of movement, and without showing any marked relation between external changes and their own activity. Vegetation, as we commonly understand the term, denotes objects which do not exhibit the kind of movement distinguishing animals. Yet we speak of a tree being alive, with evident implication that its life has something in common with the life of an animal. The change, then, which is most prominent, and is also most frequent in impressing us, is not displayed by one of the two great divisions of animate nature. Life is not so easily apprehended. Nor should we gain by an attempt to restrict the meaniiig of the word living. 'The problems would ^ Nevertheless, the exercise is conditional on a supply of energy from outside the organism. ^ This change, occurring externally in place and prior in time, is called a stimulus. 52 THE LIVING ORGANISM chap. reappear, and the restrictions would have to he withdrawn. That special kind of motion which is a marked character of animals cannot he regarded as a sign of all forms of life, since it is not shown by a moiety of living nature. As a test or sign of life in general it fails apparently. At the same time, attention may be given here to the fact that movement is never entirely absent from any living organism. Locomotion, that is, change in the position of the organism as a whole, marks the animal; while internal movements, such as may be expected in any body undergoing varied alterations, are alone apparent in plants. The circumstances of motion give more in- formation than the motion itself. We shall need to touch upon other facts of observation, and to show their range and importance, before we can begin to reconstruct from its foundations a consistent image of life. It is one of the chief difficulties of the subject we are entering upon thMt none of its elements is truly isolated. Each path of inquiry has so many issues, that the most difficult part of our task is to maintain a due regard for proportion. Each investiga- tion has its own limits and also its own special relation to other parts of a prearranged scheme, and these must be observed. Progress in the elements of a subject cannot always take place dbng a single path. It has often to proceed by V ALIMENTATION IN OTHER FORMS 53 the exercise of reflection in several directions simultaneously. In our own experience the necessity of taking food is quite as prominent a fact of life as the. possibility of spontaneous movement. The periodic satisfaction of hunger is as marked as any circumstance, if we may judge by ourselves ; and we may certainly rely upon our own feelings to tell us of the more obvious events concurrent with life. Moving and eating form part of that state, and they are special kinds of activity. All living things exhibit some modes of change. There is nothing, indeed, to bring them under observation but their special modes of change. Then what is the essence of the act of feeding ? Is it, standing by itself, a truer sign of physifial life than self- movement, or one of wider ap- plication ? All animals must take into their bodies certain kinds of matter which are spoken of as foods. This is coniirmed by universal experience. It is a fact, too, of plant life, equally certain though less prominent. There is some variety in the physical properties of this needful matter, though the differences are not so real as micy appear. And with regard to this condition, as to many others, our knowledge, that is, the practical, every-day knowledge, is incomplete. According to this, feeding applies to certain solids and liquids taken through a mouth. But the real 54 THE LIVING ORGANISM chap. act of feeding, wlien completely described, must refer to all material added to the organism, and this would include the gaseous matter forming the chief food of plants. Both animals and plants depend for their continued existence upon certain material, which is absorbed and changed in properties by contact with the living body. Here, then, we have a kind of activity which characterises all forms of life, and it is one to which attention may be paid, as bearing on the statement that living objects exhibit a specialised form of change. We must be content, however, with the bare mention of life as connected with activity or change, for the statement can be, at present, little beyond an indefinite combination of words. "We must leave on one side the details of the processes which food undergoes within the living organism, just as we must omit to review the various forms in which the process is manifested. It may, however, be mentioned that an important character of this process lies in the exercise of selection on the part of the living object. It is certain kinds of matter which are alone chosen as food, and we are unable to exclude the idea of selection even in considering the case of plants. It happens that each of the changes which we have considered so far is noticeably associated with the organism by this mark of spontaneity, V ALIMENTATION IN OTHER FORMS 55 of being exercised at will. Both locomotion and feeding are acts which appear to have as one of their constituent parts an element of choice, and it is this dement of choice which is the most distinctive feature of vital change. CHAPTEE VI THE OBJECT OF CLASSIFICATION A Review of living Objects shows the Need of an Order or Plan A REVIEW of the vast assemblage of familiar living objects, so far as this intellectual feat is possible, brings to light resemblances and differ- ences in outward form. The resemblances may he complete or incomplete, the differences great or small. But varied as form may appear when regarded superficially, a more thorough examina- tion lays bare a still more bewildering diversity. Further resemblances and differences are to be perceived in internal form or structure. The building-up, or organisation, of the animal and plant exhibits a diversity in which we may well seek for any hidden uniformity. A pro- cedure which can introduce an order, or reveal a plan amidst these phenomena, is a necessity of the first importance. Simple Description of living Forms, however accurate, is inadecLuate Up to the present, we have limited ourselves OHAP. VI OBJECT OF CLASSIFICATION 57 to mere description. The descriptions given stp,nd as records of observations, whicli do not necessitate any special skill or training on the part of the observer. The thoughts recorded have no unusual trait, and there is little that is scientific in them beyond their sequence and connection. Much of the foundation of biological knowledge is of this character, exacting little beyond accuracy of perception, such as may be demanded in any mental occupation. It is important, too, to recognise that practical work in the laboratory, the dissection and detailed examination of objects which have been aUve, does not necessarily lead to a grasp of biological principles. Such work, indeed, may end in nothing but a mrification in the concrete of unrelated facts. A description of form and structure, however accurate, is not scientific of necessity, nor does it become so when the objects described are dis- played before us. Something more is needed for our observations to be of assistance in truly enlarging our knowledge of nature, and this comes from the guidance of those who have, in the past, made observations and reflected on them. An Order or Flan is the Object of Classification It is clear, then, that description alone is insufficient for our purposes, and the practical realisation of description in the laboratory is 58 THE LIVING OEGANISM chap. likewise inadequate. To be of any value, all descriptive statements must have some reference to an orde,r or scheme previously conceived. Such schemes have their origin in work already per- formed. The thoughts and beliefs of an earlier growth must serve as our first gu^ides. Subservience to a procedure, which has been previously agreed upon, is a first condition of acquiring knowledge, though additions to know- ledge may, at a later stage, involve a contradiction of the formula by which assistance has been rendered. It is essential, indeed, to the progress of the student that he should make his observa- tions with reference to an idea already existing in the mind of others if not in his own, and in every scheme of classification such an idea has been formulated. The Process of Classificatioa The process of arranging diverse objects cannot obviously be begun by those who have but a confused conception of the objects to be submitted to the process. Yet the opportunity of placing the forms of life in classes is never entirely wanting, and the necessity for doing so has compelled our attention even from the beginning. To perceive similarity is to begin to classify. To give the same name, if only to two objects, creates a class, and in creating a class we begin VI OBJECT OF CLASSIFIOATION 59 the process called generalisation. No instrument of thought is used more frequently or applied more universally than generalisation. It is implied in every common name denoting more than one object or quality. It is more or less active, even before names can be articulated. But we need to get something more than generalisation, whether or not abstraction ac- companies it, from the effort of classification. A certain order and relation of classes must be a distinctive feature in it. It is true that the perception of similarity carries with it the separation as well as the creation of classes. Bvi the formation of classes does not necessarily simplify our outlook on nature'. To find an order among objects is the ultimate end of our inquiry. To substitute a confused multitude of classes for an indefinite variety of individuals may certainly diminish the' labour of description, but it gives little aid to the understanding. The Difficulties in applying the Process to living Objects It is not easy to bring under review all the forms which are now undergoing the changes summed up in the word life. Isolated forms are familiar in their separate existences, though the components which unite to form their manifold diversity are not so easy to discover. Nor does a collection of objects, to which the same name 60 THE LIVING ORGANISM chap. has been given merely on account of similarity of appearance, always form the kind of class to enlarge our knowledge of Nature. A process of this kind, without ulterior aims, forms part of the mental activity of every individual at every stage of experience. But a classification to he of service in Biology, or in any science, must refer to something heyond the superficial appearance at which ordinary inquiry stops short. With the actual results which have been ob- tained from classification in this science, we are, for the present, less concerned than we are with the mental creation, which precedes it and gives to it all its force. The centre of interest lies in the ideal framework which assists in the separa- tion and distinction of phenomena. In Biology, the living organism needs to become a definite conception for us. It is an abstraction which is as difficult as it is important to achieve; and any arrangement exhibiting an order of concrete examples must display this abstraction as its chief content. On the other hand, even a crude classification may give valuable assistance in the shortening of statement and the simplifying of communication hy language, and any gain in conciseness of expression cannot fail to extend the range of our thoughts. We cannot, therefore, afford to neglect such an instrument of progress at any stage of our course, however imperfectly we may be trained in its use. VI OBJECT OF CLASSIFICATION 61 If the larger aims of classification are kept in mind, the characters of biological classes should be disclosed progressively. The full meaning of such a scheme is not at once ap- parent. Our comprehension does not always move onwards by easy stages. The mind often needs to make repeated excursions from some central idea, and that not necessarily a very clear one, if it is to succeed in enlarging its circle. The organism is the conception at the centre of all biological excursions, whether they take the direction of classification, history, or ontology. The dual Aspect of the Organism as possessing Form and also as presenting Change In any arrangement of living objects it will be necessary to pay attention to the two-sidedness which they manifest. The activity of the organism must be regarded as well as the form. At the same time it must be admitted, that the form is most readily apprehended in connection with its specific activity. Or we may go below the surface, and consider the definite group of structures, which plainly constitutes that form in so many instances, as the seat of a definite group of recurrent changes jointly conferring the quality of life upon the whole substance. It is, indeed, not possible to think of the changes apart from the objects undergoing them. This is true, even of the simplest kinds of change. 62 THE LIVING OEGANISM chap. Displacement, for example, is a change in the position of a body. But there is no such thing as position without a lody to mark it. Nor again is time intelligible without material objects of some kind to define it. "With the far more involved changes of alimentation, sensation, and the like, the implied reference to an organism is obvious. Time, space, matter, and life are all relative as well as mutually dependent ideas. And this is the real meaning of the word organism — the something in which life appears, the substance which is organised for life, the body to which life must always be referred through the limitations of our knowledge. Hence an arrange- ment of all the many kinds of organisms under a coherent scheme only becomes possible when we begin to understand how activities are con- nected with, and conditioned by, the forms and structures which are organic to them. A joint Regard to Form and Function simplifies the Work of Classification Variety of form, then, is manifestly too in- definite and too meaningless to be taken by itself as a basis of classification. An arrangement of a certain value may be founded upon it, and, indeed, classes based upon observed similarities of appearance have always served for the ordinary wants of mankind. But the ordinary wants have been nothing beyond directness of denotation and VI OBJECT OF CLASSIFICATION 63 economy of description. Further wants arise with the growth of inquiry, and the effort to attain to an ampler generalisation which shall express the results of wider observation, is the beginning of a scientific system. The search for " caicses," or correspondences between facts, is a development which is logically subsequent to the desire to describe with brevity. A scientific scheme, with comprehension as its aim, takes the place of the simpler and less consistent results of generalisations, based upon appearances which are more or less detached. The results in the latter case are disconnected, or only accidentally connected, while a due regard to function brings about a systematic connection among classes. AU classes are alike with respect to certain kinds of change (though the circum- stances of the changes may vary widely), and a relationship between them is instituted as soon as the attributes in common can be clearly perceived. There is a unity underneath the diversity of form, which the intelligence must set itself to discover. It will be found in a correspondence of action or function. Now functions are limited in Jcind. They are primarily such as relate to assimilation, sensation, or reproduction. Other functions exist, it is true, but they are secondary in some degree to these fundamental activities. The function of a given structure, that is, the habitual activity which is most prominently 64 THE LIVmG ORGANISM chap. characteristic} when considered in connection with the structure or organ itself, gives rise in our minds to an image which is more easily apprehended than either function or structure by itself. Indeed, the mental isolation of the activity from the object exhibiting it is often a difficult process. This statement may he made of the organism as a whole, just as truly as of parts of the organism. Our perception seizes most readily upon some- thing undergoing change. The distinction of form from activity, that is, of Morphology as apart from Physiology, is an achievement in abstraction to which we attain at a relatively late stage in the pursuit of knowledge. The need of food, which is common to all forms, gives rise to a possible basis of classifica- tion. Since all organisms assimilate certain matter, herein is a condition of life by which all forms are brought into relationship. If it be now desired to make classes, and to compare one with the other, the variations in this common activity may serve. And it is easy to gather that variations will he most perceptible in the difference of structure which accompanies them. A difference of form marks a difference in the mode of the function. The initial and final states are approximately the same for aU. The intermediate stages exhibit variety, and give occasion for 1 See p. 98. VI OBJECT OF CLASSIFICATION 65 classification. The events contributory to as- similation, as manifested in structural variation, are crowded enough to indicate not only re- semblances and differences, but degrees of the same ; and it is the perception of distinctions in difference which renders a classification systematic, and makes it an orderly arrangement. A similar procedure may be adopted for other of the universal attributes of life, e.g. reproduc- tivity or excitability. They are properties possessed by all, but exhibited in various modes and degrees. We may place together those organisms which are alike in their relation to a coTwrnon character ; and, hy reason of distinctions in relation, we may give to our classes an order or place in a scheme. No systematic classification, however, has been based upon the facts of assimilation. Eeproduc- tion has been more serviceable, especially in the classification of plants ; while the prominent fact of excitabUity, which gains fuller meaning in the words, the relation of the organism to outer changes, has not yet been utilised.. On the other hand, a perception of all three characters, as existing in combination, has given rise to an idea called development, and this has afforded a ground of classification which has proved the most trustworthy up to the present. The Idea of Development in Classification The word development, which has a common 66 THE LIVING ORGANISM chap. usage in Biology, may denote either a process, the act of developing, or a state, the residt of a process. The present meaning is restricted to the state or condition which arises from a process of change. It is not easy to describe what is meant by a state of development. There is obviously something, which varies in degree and may reach different stages in different objects, but the something needs to be indicated. In every living object, even the simplest, there is some appearance of structure. In other words, the several parts do not present the same appearance to the observer. What the cause may be, whether the substance of one part is truly unlike that of another, are questions needing an answer. There is always some in- dication of structure and organisation in the material of life. An estimate of its complexity, that is, the extent to which a difference in parts is apparent, may be attempted by the ordinary methods of comparison. But substances which are bearing the stress of life seldom disclose their structure to the first glance, even if the difficulties of inspection be overcome, nor do they often admit of comparison. An equal degree of dissection or analysis would be required for each, and as mere size is of no consequence in qioestions of organisation or com- plexity, it is essential to be in possession of some standard before it is possible to institute a VI OBJECT OF CLASSIFICATION 67 comparison. The need of a standard for the purpose of estimating any value or vnagniivde, whatever its kind, is an axiom of science, nor is the highly composite and abstract magnitude of organ- isation exempt from this necessity. It is neither advisable nor easy to judge by appearances. The enumeration of differences is a help, the greater number corresponding with a higher degree of complexity. But this is not enough in itself. Our conception of the organism is a dual one, structure together with function beiQg the component ideas. These two aspects of the organism must be considered together. The true problem before us in estimating develop- ment is to understand how function and organ are joint factors in the degree of organisation. It may be said that structure is meaningless except as related to function, and function is inconceivable apart from the medium in which it is manifested. A separate manifestation of in- dividual functions cannot be shown except through variety of material structure ; in one sense, structure and function are the same fact. The modes of expression here differ more than the things expressed. There is one feature which stands out in marked prominence whenever we consider the correspondence between structure and function. The combinations which are possible in structure are more varied than is the case with function. 68 THE LIVING ORGANISM chap. The hinds of function, as has been previously- stated, are limited, while the modes of organisation which are contributory to them are most varied. A real correspondence is first perceived to exist when we become aware that functional processes are more numerous than functional ends. It is the variation in the mode of securing certain ends which brings about different details of structure. A fairly accurate conception of the organism, as that which displays itself by a certain mini- mum of functional changes in a complex sub- stance, may be obtained from these considerations. Divergences between organisms are manifested primarily as differences of material complexity, and only in the second place as functional differences. The development of an organism is its state mth regard to both of these complexities, and it is esti/mMed by comparison with the simplest object which is observed to manifest life. Such an object, whether real or imaginary, might serve as the standard of which the want has been described. Yet the ideas here represented are not equal to the purpose in view. A scheme based on them would not give information either correctly or adequately. The extent of development is found to be, when taken by itself, insufficient for the task of classification. The degree of divergence from a single standard form, i.e. the number of resemblances or contrasts, does not give us an order in the relations between classes VI OBJECT or CLASSIFICATION 69 which is an essential feature in systematic classi- fication. The Conception of Types If the facts of life were simpler, if life did not appear to us in every situation with such varied modifications of its known processes, and with a scope of form to match, the creation of a system would be a comparatively easy matter. The variations in complexity, whether of structure or functional processes, might have taken the form of a simple linear progress, each successive increment of complexity giving rise to a suc- cessively higher rank in the scale of organ- isation. But however important it may be to regard development as the ultimate basis of classification, we cannot perceive in the whole body of organisms any distinct signs of such a simple progression. Nor is it easy, on the other hand, when we regard a single individual, to separate, even wpproximMely, any one function completely from neighbouring events, or to succeed in accurately isolating or localising any single class of activity out of the many which combine to con- stitute its unitary existence. If living changes could be more readily contemplated in their entirety, and each be traced by itself through an undisturbed course, results could then be weighed more directly and most of our difficulties would disappear for good. 70 THE LIVING ORGANISM ohap. The mode of complexity may vary as well as the extent. In attempting to classify organisms some modification of the ordinary estimate of aggregates is obviously needed. The quantitative method fails, while a comparison with a series of distinct schemes of structure affords us the first insight into the general plan of living Nature. Hence arises the creation of certain ideal comhina- tions of characters called types, which serve as a series of separate standards of reference. A comparative review of either animals or plants shows that no single character is of use as a means of classification, nor indeed can any simple combination of characters serve that purpose. The simplest combination upon which a com- prehensive and intelligible arrangement has been founded is illustrated in botany. We find systematic botany mainly consisting of a scheme of classification of plants which is based upon the structure of flowers, the form, number, and arrange- ment of the floral whorls serving as a guide in the separation or grouping together of the objects of which they form part. On account of the prominence of the flower as a part of organisa- tion, and the importance of its function, there is much to be said for this method, and the results are of undoubted value. When the far more divergent complexity of animals is considered, a reference to types appears to be the only satisfactory means of diminishing VI OBJECT OF CLASSIFICATION 71 the confusiou of our impressions. The meanings which are assigned to the word type as used in Biology do not always agree. There will be no error in regarding a type as an ideal construction derived from a nwmber of real impressions. From observations of similar objects, or objects with more than one quality in common, we are able to create in our minds a conception of certain com- binations of qualities as existing in a number of individiuils. The type has no real existence by itself. It is a conception of a definite group of relations, presented by objects which are alike as regards the relations composing the type, though different in other respects. One group of relations enters into the composition of the mammalian type, another group into that of the echin/)derm type, and so on. By a fuU recognition of the ideal nature of types, an effective comparison of objects with one another is rendered possible. There are as many types as there are distinct groups of qualities, and as many classes as there are distinct breaks in the sequence of development. The discrimination of distinctness in this connection, it is true, may vary, but there is, at least, no question as to the gain in order resulting from this method. And though important problems arise as to the relations to be instituted between these groups of relations, the useful and orderly arrangement of living objects achieved on these lines is quite 72 THE LIVING ORGANISM chap. independent of all assumption and theory as to the origin of such relations. A classification has been eventually achieved without admitting any speculation as to the ultimate cause or origin of classes, though speculation may be quickly aroused when the abundant evidence of relationship between classes is first clearly discerned. The Influence of Authority It is an accepted fact that there can be no progress in the acquisition of knowledge, without a constant reference to the history of the subject and to contemporary opinion. Yet it is frequently found that controversy is at once aroused by any term which happens to embody a recognition of opinions already formulated. It would be difficult indeed, in any course of inquiry, to rely solely on personal observation; yet it is often assumed that there is something antagonistic to progress, and hence in contradiction to the true scientific method, in that dependence on others which is implied by the word authority. But it is not necessary to demonstrate that which is obvious, the futility of any investigation undertaken without some sort of guidance ; nor is it easy to imagine any epoch in our mental career when our thought has been quite free from external control. To be independent of past and ignorant of present achievement, to disregard the accumulated experience of all who have observed, considered. VI OBJECT OF CLASSIFICATION 73 and believed, is not a satisfactory state in which to undertake any systematic research. The unassisted intelligence is a poor tool, and the total experience of an individual is a slender fraction of the whole knowledge which mankind has amassed. Yet the larger knowledge is sealed from those who are unable to follow the methods by which it has grown to such enormous dimensions. To give a training in those methods is the chief end of education. By employing our intelligence in following the methods of others we make their knowledge our own. Any formulated thought is authoritative, in so far as it represents the collective result of observation and perception which has stood the test of time and controversy. And Biology is not a branch of science which can afford to neglect the generalisations which stand as records of past researches. The science of living things covers too large a field of survey to be successfully explored without guidance. It is in the earlier stages, however, that authority is most valuable and most appropriately relied on. Once the observation has been trained and the intelligence formed, the individual may stand alone ; and by his own efforts may hand on, in his turn, some contribution to the common stock of knowledge from which his successors may draw. There is no escape, then, from the influence of authority in scientific matters, and this must be 74 ■ THE LIVING ORGANISM chap. duly recognised. An authoritative statement expresses the highest point of positive comprehen- sion to which the intellect has hitherto attained. It shows the position which thought has taken up after controversy has rendered it exact. Knowledge grows more exact by Communication On taking the trouble to consider this quality of exactness or precision in current thought, we shall find, that so far as it exists at all, it is largely dependent upon the agency of language, by which thoughts are communicated from one person to another. The words which act as symbols of subjective states do, indeed, in their use, help to render those states more precise. A spoken or written word is a definite sign, and a feeling or a thought is frequently vague or confused. The ordinary tose of language^ tends, therefore, to increase the determinateness of thought. And this is because a given term is a sign, not of the whole confused thought, but of that in it which is capable of taking a clearer outline. It may not be going too far to say that science begins as soon as ideas are exchanged, for the exchange involves a process by which the ideas acquire more definite form. AH communicable knowledge is therefore to be looked upon as more or less exact. It would 1 And the use of diagrams or any system of signs for the purpose of description. VI OBJECT OF CLASSIFICATION 75 not be commuaicable if it were not exact, and the process of communication tends to intensify any sharpness of outline already possessed. There will be no failure, it is hoped, in perceiving that the term used in this connection is exactness and not accuracy. It is not intended to imply that any transcription of ideas into words can make them infallible. On the contrary, many exact opinions are erroneous, hut it is their quality of exactness which brings them within the scope of inquiry and discussion: Opinions of Others must be recognised The records of previous observers must serve as guides to our own work. We are not always certain of truth, though we are judges of what is inconsistent with opinions already formulated. Propositions which contradict one another, how- ever exact in expression they may be when standing alone, cannot each be true. We are, however, able to make a safe start on any inquiry when once we are furnished with some of the great generalisations which have received the sanction of many thinkers, proved useful aids to the extension of knowledge, and assumed in the progress of time clearer and likewise fuUer meaning. Herein is again apparent our dependence upon authority. But it has already been stated that a com- plete isolation of the individual worker is never 76 THE LIVING OEGANISM chap. attainable. He is never free from obligation to pre-existing opinions, upon which his own work is necessarily founded. At the outset of this inquiry, words were used which assumed the existence of mi