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 Outlines of physiolojoical psychology: a 
 
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OUTLII^ES 
 
 OF 
 
 PHYSIOLOGICAL PSYCHOLOGY 
 
PROFESSOR LADD'S WORKS. 
 
 INTRODUCTION TO PHILOSOPHY. An Inquiry 
 after a Progressive Rational System of the Principles of the 
 Particular Sciences in their Relation to Ultimate Reality. 
 I vol., Svo, S3.00. 
 
 ELEMENTS OF PHYSIOLOGICAL PSYCHOLOGY. 
 A Treatise of the Activities and Nature of the Mind, from 
 the Physical and Experimental Point of View. With nu- 
 merous illustrations. $4.50. 
 
 WHAT IS THE, BIBLE? An Inquiry of the Origin and 
 Nature of the Old and New Testaments in the Light of 
 Modern Biblical Study. i2mo. $2.00. 
 
 THE DOCTRINE OF SACRED SCRIPTURE. A 
 
 Critical, Historical, and Dogmatic Inquiry into the Origin 
 and Nature of the Old and New Testaments. 2 vols., 
 Svo, $7.00. 
 
 THE PRINCIPLES OF CHURCH POLITY. Crown 
 
 Svo, $2.50. 
 
OUTLINES 
 
 PHYSIOLOGICAL PSYCHOLOGY 
 
 A TEXT-BOOK OF MENTAL SCIENCE 
 
 ACADEMIES AND COLLEGES 
 
 BY 
 
 GEORGE TRUMBULL LADD 
 
 Professob or Philosofbt in Yale Unitebsitt 
 
 NEW YOKK 
 
 CHAELES SCEIBNEE'S SONS 
 
 1891 
 

 COPTBIGHT, 1890 
 
 Bt CHARLES SCRIBNER'S SONS 
 
PREFACE. 
 
 In the early part of 1887 I published the results of sev- 
 eral years of research, in a book entitled " Elements of 
 Physiological Psychology." The very gratifying reception 
 almost immediately given to this work showed an extended 
 and profound interest in the experimental and physiological 
 study of mental phenomena. The signs of this interest 
 have continued unabated until the present time ; and the 
 book has been widely adopted, both in this country and 
 abroad, for private reading and for the instruction of 
 classes. 
 
 Although the "Elements, etc." did not enter into the 
 detailed history of discoveries and discussion of theories in 
 the field of physiological psychology, it was necessarily 
 somewhat voluminous and technical. For it aimed to give 
 a summary of the entire field ; and thus to render accessible 
 the data and conclusions to be found, separated, only in 
 scores or hundreds of larger and smaller monographs. 
 
 Almost immediately the demand arose for a smaller and 
 less technical book, which should be adapted to aid the 
 teacher with classes less mature, or able to afford less time 
 to the subject. The present volume has been written for 
 the express purpose of meeting this demand. It is not, 
 however, a mere abridgment or revision of the larger work. 
 While it, like the larger work, surveys the entire field, it 
 omits all details, discussions, and references, which — how- 
 ever valuable for the purposes of more thorough mastery 
 
vi PKBPACB. 
 
 — are likely to embarrass beginners of more limited 
 patience and ability. The Parts (I. and III.) which 
 treated of the nervoxis mechanism and of the nature of 
 mind as related to the body, have been in this volume 
 relatively much abbreviated ; while the Part (II.) which 
 treated of the phenomenal relations existing between the 
 excited organs and mental phenomena, has been relatively 
 somewhat expanded. Here considerable new material — 
 especially in the chapter on " Consciousness, Memory, and 
 Will " — has been added. I have thus aimed to furnish 
 a complete and yet compact text-booh for the briefer study 
 of mental phenomena from the experimental and physio- 
 logical point of view. 
 
 In carrying out the general aim of this manual, both 
 pupil and teacher have been kept in view. The material 
 has been arranged so as to adapt it for learning with the 
 least imnecessary expenditure of strength and time. It is 
 my hope also to have succeeded in providing those who 
 give instruction with a book which can be successfully 
 taught. 
 
 Some equipment of apparatus is desirable, if not abso- 
 lutely indispensable, for the most effective instruction in 
 physiological psychology. This equipment need not, how- 
 ever, be large or expensive. A set of models of the brain 
 (I recommend the Bock-Steger), a few charts, a judicious 
 selection of histological preparations, a machine for mixing 
 color-sensations, etc., are of great assistance. 
 
 For the use of teachers, of more advanced or mature 
 pupils, and of such readers, generally, as can command 
 the patience and the time, the " Elements of Physiological 
 Psychology " is still to be preferred. For most teachers 
 who adopt the present, smaller treatise as a text-book in 
 the class-room, the larger work will be found indispensable 
 for their private use. The latter is still, in most of the sub- 
 ordinate topics, well abreast of the very latest researches. 
 
PREFACE. Vli 
 
 And if its material is constantly supplemented by those 
 notices of new discoveries for which one must look to 
 periodical literature {e.g. the American Journal of Psy- 
 chology^, it will serve to keep even the teacher who is not 
 a specialist in the lines of physiology and psycho-physics, 
 in advance of his classes. 
 
 Having been for some years a teacher of this subject, I 
 am well aware what are the difficulties of presenting it. 
 But I have also learned that the rewards which follow the 
 overcoming of those difficulties are correspondingly great. 
 It will be a matter of great interest to me, therefore, to 
 receive suggestions and encouragement from those of my 
 fellow-teachers who may avail themselves of this book. 
 
 GEORGE TRUMBULL LADD. 
 
 Yaie University, Nbw Haven, 
 Nov., 1890. 
 
TABLE OF CONTENTS. 
 
 PASES 
 
 Introduction. Nature of Phtsiological Psychology 1-10 
 
 CHAPTEK I. 
 Substance of the Nervous Substance 11-30 
 
 CHAPTER n. 
 Structure of the Spinal Cord and Brain .... 31-73 
 
 CHAPTER III. 
 Structure of the Organs of Sense and Motion . . 74-102 
 
 CHAPTER IV. 
 Development of the Nervous System 103-115 
 
 CHAPTER V. 
 General Physiology of the Nerves 116-134 
 
 CHAPTER VI. 
 Reflex and Automatic Nervous Functions .... 135-157 
 
 CHAPTER Vn. 
 
 Mechanical Theory of the Nervous System . . . 158-176 
 
 ix 
 
X TABLE OF CONTENTS. 
 
 CHAPTER Vni. 
 
 Sensory and Motor Functions of the Cerebral paobs 
 Hemispheres 177-195 
 
 CHAPTER IX. 
 
 Sensory and Motor Functions of the Cerebral 
 
 Hemispheres — Continued 196-227 
 
 CHAPTER X. 
 The Quality of Sensations 228-253 
 
 CHAPTER XI. 
 The Quality op Sensations— Continued 254-270 
 
 CHAPTER XII. 
 The Quantity of Sensations 271-289 
 
 CHAPTER Xni. 
 Perception by the Senses 290-321 
 
 CHAPTER XIV. 
 Perception by the Senses — Continued 322-860 
 
 CHAPTER XV. 
 Time-relations op Mental Phenomena 361-380 
 
 CHAPTER XVI. 
 Feelings, Emotions, and Movements 381-413 
 
TABLE OF CONTENTS. XI 
 
 CHAPTER XVII. 
 
 PAOEa 
 
 Consciousness, Memory, and Will 414-444 
 
 CHAPTER XVm. 
 Age, Sex, and Temperament 445-461 
 
 CHAPTER XIX. 
 Connection of Body and Mind 462-477 
 
 CHAPTER XX. 
 The Nature of Mind 478-499 
 
 INDEX 501-505 
 
PHYSIOLOGICAL PSYCHOLOGY. 
 
 INTKODUCTION. 
 
 NATURE OF PHYSIOLOGICAL PSYCHOLOGY. 
 
 The satisfactory definition of any science is often one of 
 the latest and most diflficult achievements of that science. 
 Our definition of the particular science which we intend 
 to consider must, therefore, be understood as preliminary. 
 It involves positions upon various disputed questions which 
 the beginner is quite unable to comprehend ; and it must 
 be allowed, in a measure, to rely upon the course of the 
 following investigation for its explanation and defence. 
 Everything cannot be said at once. Terms must be freely 
 used, the meaning of which will be made clear only by 
 their use; and answers to later inquiries will sometimes 
 be implied in what is said upon inquiries that are earliest 
 raised. 
 
 It is plain that a correct conception of Physiological 
 Psychology involves some special knowledge of those two 
 sciences whose names are combined in the term itself. 
 These are, of course, Psychology and Physiology. It is 
 also plain that a peculiar relation is assumed to exist 
 between certain of the results obtained by the study of 
 these two sciences ; otherwise they could not properly be 
 combined in one term. It is furthermore suggested by 
 this compound name, that the science which furnishes the 
 noun — namely, psychology — defines the end which we 
 desire to reach; while the science which furnishes the 
 
2 PHYSIOLOGICAL PSYCHOLOGY. 
 
 adjective — namely, physiology — prescribes the means 
 which we are to employ. This suggestion we shall find 
 to be confirmed by our subsequent investigations. 
 
 Deflnition of Pysohology. — It was for a long time custo- 
 mary to define psychology as " the science of the human 
 soul." Sometimes the definition went so far as to add that 
 the soul, " as the real foundation of the spiritual life," or 
 as "the subjective spirit," is the "subject-matter of psy- 
 chology." Of late, however, serious objections have been 
 raised against every such definition. It has been com- 
 plained that the word " soul," although its German equiv- 
 alent is freely employed in biological and physiological 
 treatises, cannot be sufficiently kept free, for scientific pur- 
 poses, from theological and other prejudices. The word 
 "mind," which had originally a much narrower signifi- 
 cance, has therefore been substituted in the greater number 
 of English works on psychology. Thus Mr. Sully defines 
 psychology as "our general knowledge of mind reduced 
 to an accurate and systematic form." 
 
 Other objections to the customary definition of psychol- 
 ogy are not met, however, by exchanging the word " soul " 
 for the word "mind." Thus it is said that both words are 
 often used so as to conceal the unproved assumption that 
 mind or soul is an independent entity ; whereas it is the 
 business of the science of psychology to prove, if it can, 
 the existence of such an entity. Biology, which aims to 
 extend its researches so as to include mental as well as 
 other vital phenomena, sometimes asserts that it wishes the 
 opportunity to explain what occurs in consciousness without 
 making use of any assumptions. Some writers, then, have 
 gone so far as to advocate " psychology without a soul." 
 Others, on the contrary, have thought they found proof, 
 in the complex phenomena of human life, of both an " ani- 
 mal " and a " rational " soul. 
 
 In order to the intelligent pursuit of physiological psy- 
 
NATURE OF PHYSIOLOGICAL PSYCHOLOGY. 3 
 
 chology, it is necessary to notice the foregoing objections 
 only very briefly. Our view of the best preliminary de- 
 scription of the nature of psychology is as follows : It is 
 expedient, as far as possible, to avoid all controversy at 
 the beginning of our scientific investigation. We should 
 therefore be willing, where this can be done, to dispense with 
 controverted words in forming our fundamental concep- 
 tions. It is also more satisfactory, from the purely scien- 
 tific point of view, to have the definition include only a 
 description of that particular group of phenomena which 
 it is the business of the science itself to explore. In this 
 way, then, we define psychology with reference to its primary 
 problem, which is, the description and explanation of the 
 states of human consciousness, as such. 
 
 If the term " sentience " seems preferable to conscious- 
 ness, it must be understood as equivalent to consciousness 
 in the broader sense of the latter word. We may then say 
 that psychology is the science which describes and explains 
 the phenomena of the sentient life of man. 
 
 This definition plainly implies an acquaintance, already 
 gained, with a certain class of phenomena. These are the 
 phenomena of consciousness. What it is " to be conscious," 
 and what is that peculiar character which belongs to all 
 phenomena of consciousness, as such, can never be defined. 
 
 It would be inconvenient and unnecessary — not to say 
 impossible — to refuse to speak of the " soul " or " mind " 
 simply through fear of unscientifically making the assump- 
 tion that some such entity really exists. In all languages, 
 and in the every-day use of them all, men in expressing 
 their states of consciousness, as well as in addressing their 
 fellows, employ such terms as " I " or " me," and " thou" 
 and " he," or " it." But all these words imply some kind 
 of reference to a subject of the phenomena of conscious- 
 ness ; they also imply a contrast between this subject and 
 other subjects to which other phenomena are attributed. 
 
4 PHYSIOLOGICAL PSYCHOLOGY. 
 
 In all the earlier part of our inYestigation, whenever we 
 use the word "mind" or "soul," we wish to imply no 
 more than all- men inevitably mean whenever they say 
 " I " see, or think, or feel, or purpose, this or that. It is 
 the seeing, tliinking, feeling, and purposing, etc., as states 
 of consciousness, with this possible reference to a subject 
 of them all {states of consciousness as subjective'), which 
 constitute the field to be explored by psychology. 
 
 Definition of Physiology. — The science which is -to be 
 combined with psychology in our investigations is human 
 physiology. This is the science of the functions of the 
 human physical organism. Its modern study implies an 
 acquaintance with several other sciences with which it 
 is closely allied, or upon which it is dependent. These 
 'are molecular physics and chemistry, as related to the 
 structure and changes of the tissues of plants and ani- 
 mals ; biology, including the allied phenomena of plant life ; 
 embryology and the general theory of development ; and 
 gross and special microscopic anatomy, or histology. It 
 is only, however, with a small part of this vast domain that 
 physiological psychology has directly to deal. Its chief 
 concern is with the structure and functions of the human 
 nervous system. 
 
 Definition of Physiological Psychology. — It has already 
 been implied that our conception of this science is depend- 
 ent upon the way in which we understand the two sciences 
 to be combined in its pursuit. But the science of psychol- 
 ogy fui'nishes the end or final purpose of our researches. 
 In other words, we aim to describe and explain the states 
 of human consciousness, as such. On the other hand, 
 physiology furnishes the peculiar means to be employed, 
 — the point of view held in our description, and the 
 method and source of our explanation. We study the 
 subject-matter indicated by the noun ; but we study it by 
 use of the somewhat peculiar means and ways of approach 
 
NATURE OF PHYSIOLOGICAL PSYCHOLOGY. 5 
 
 indicated by the adjective. "We may, then, define physi- 
 ological psychology as the science of the phenomena of 
 human consciousness in their relations to the structure and 
 functions of the nervous system. It is psychology, because 
 it is the science of the human mind, or soul ; it is phys- 
 iological psychology, because it regards the mind as stand- 
 ing in peculiar relations to the bodily mechanism. 
 
 method of Physiological Psychology. — In its method this 
 compound science necessarily partakes of the character- 
 istics of the two sciences which enter into it. But these 
 two sciences dififer somewhat widely in respect to their 
 long-established methods. They also difEer in their very 
 nature in such a way as to make necessary a difference of 
 method in their pursuit. It has always been held by a 
 great majority of its students that the method of psy- 
 chology is necessarily what is known as " introspective." 
 But there can be no doubt that the method of physiology 
 is one of external observation and experiment; since 
 physiology is a physical science and has to determine 
 external facts of the structure, development, and functions 
 of a physical mechanism. It is not strange, therefore, that 
 doubts and even disputes have arisen as to the possibility 
 of combining these two methods, and as to the proper way 
 of making the combination, in case it is to be made at all. 
 These doubts and disputes are, however, for the most part, 
 unimportant. 
 
 The method to which psychology has, from time almost 
 immemorial, appealed is, as has been said, introspection, or 
 self-consciousness. The exhortation given to the student 
 of mental phenomena is, accordingly, made to run as fol- 
 lows : " Would you know what it is to see, to hear, to 
 think, to feel, to desire, to will? Then look within your- 
 self and fimd the answer there." To answer such ques- 
 tions, inspect within (mfro-spect) ; to know what is the 
 meaning of consciousness, in any of its varied forms, be 
 
6 PHYSIOLOGICAL PSYCHOLOGY. 
 
 seZ/-conscioiis, or aware of the states of consciousness as 
 immediately known to be your own. But like the defini- 
 tion of psychology, this conception of its method has of 
 late been much called in question, and its lack of scientific 
 character as well as its general unfruitfulness have been 
 exposed. 
 
 What view, then, shall we take of the use of introspec- 
 tion in psychology, and more particularly, in physiological 
 psychology ? Now there should be no mystery or arrogant 
 assumption about such words as " science " and " scientific 
 method." Science is knowledge — real, verifiable, syste- 
 matic. Scientific method is nothing but the way of arriv- 
 ing at such knowledge. In physiological psychology, as a 
 science, any way of arriving at genuine knowledge is jus- 
 tifiable ; all ways of arriving at such knowledge should be 
 diligently and skilfully employed. But the phenomena 
 which we must somehow know, in order to describe and 
 explain them, are states of consciousness ; and states of 
 consciousness, as primary facts, can be ascertained in no 
 other way than in and by consciousness itself. This way 
 of ascertaining these facts is introspection. Introspection 
 is, therefore, not only a legitimate but it is an indispen- 
 sable method of physiological psychology. To object to 
 it, so far forth, is not only inexpedient and useless, but is 
 even absurd. 
 
 Psychology as a science, however, requires not only that 
 we should ascertain by introspection what the states of 
 consciousness, as primary facts, actually are, but also that 
 we should explain these facts and their relations to one 
 another in the life of the mind. Such explanation requires 
 at least two things : these are, the analysis of the states 
 into their simplest factors, and the discovery of the laws 
 under which the states are related to each other and to all 
 the conditions on which they depend. Our adult states 
 of consciousness furnish the problems to psychology ; they 
 
NATTJBE OF PHYSIOLOGICAL PSyCHOLOGY. 7 
 
 are its primary facts, the admitted data from which it 
 takes its start. But they are all, as states, exceedingly 
 complex, and involve numerous factors. Self-consciousness 
 can no more discover all the factors which have united to 
 form these states than simple external observation can 
 analyze a portion of water into its constituent oxygen and 
 hydrogen gases. Especially is it true that few of the 
 antecedent and accompanying conditions of these complex 
 states of consciousness can be discovered by introspection. 
 Introspection, therefore, can never serve as the sole method 
 for establishing a science of psychology. 
 
 Moreover, those antecedent or accompanying conditions 
 of the states of consciousness, which physiological psy- 
 chology particularly endeavors to discover, are the struc- 
 ture and functions of the nervous system. About these 
 matters introspection can, as a rule, tell us nothing 
 whatever. The physical science of physiology, with its 
 method of external observation and experiment, must 
 be relied upon to describe such conditions of mental phe- 
 nomena. 
 
 It is obvious, then, how physiological psychology must 
 combine the two methods which belong to the two sciences 
 on which it depends. Introspective psychology must fur- 
 nish us with the description of those complex states of con- 
 sciousness, as such, which it is desired to explain. These 
 furnish the problems to be solved. Physiology, on the 
 other hand, must be relied upon for a description of the 
 living and active nervous system, regarded as giving con- 
 ditions to the origin and character of the states of con- 
 sciousness. Physiological psychology, therefore, attempts 
 to bring the two orders of phenomena, those called mental 
 and those belonging to the nervous system, face to face. 
 It considers them as mutually related ; it endeavors, as far 
 as possible, to unite them in terms of a uniform character, 
 under law. Its method is to explain the phenomena of 
 
8 PHYSIOLOGICAL PSYCHOLOGT. 
 
 man's sentient life as correlated with the life and growth 
 and action, under stimuli, of his nervous system. 
 
 Divisions of the Subject. — The different chapters of this 
 book fall under three main divisions. We shall first con- 
 sider the structure and functions of the nervous system 
 from the modern mechanical point of view. In these ear- 
 lier chapters we must rely upon the method of external 
 observation and experiment as employed by the modern 
 science of psychology. Our object will be to give a clear 
 picture in outlines of what the nervous system of man is, 
 and of how it acts in response to the different forms of 
 stimuli which excite or irritate it. This work requires 
 little reference to states of consciousness or to the nature 
 of the mind. We shall, in the main, consider the nervous 
 system as a purely physical mechanism. Yet even in these 
 chapters certain important considerations bearing upon the 
 nature of the mind and its relations to its bodily basis will 
 indirectly come into view. 
 
 The next eleven chapters (VIII.-XVIII.) may be con- 
 sidered as constituting the second or main division of the 
 book. In these chapters the various relations which the 
 science of physiological psychology has discovered between 
 the states of conscious mind and the conditions of the 
 excited nervous system, are presented in order. Such 
 relations may conveniently be considered under three gen- 
 eral groups or classes. The first group comprises the 
 relations which can be established between the condition 
 and activity of the higher nervous centres and the phe- 
 nomena of conscious sensation and motion. The principal 
 question raised under this head concerns the so-called 
 " localization of function " in the hemispheres of the brain. 
 The second group of relations includes the phenomena 
 with which psycho-physics (in the more precise use of the 
 term) attempts to deal. Such are the relations which 
 exist between the quality, quantity, combination, and time- 
 
NATUKE OJ? PHYSIOLOGICAL PSYCHOLOGY. 9 
 
 order of the various stimuli which irritate the nervous 
 system, and the kind, amount, composite result, and time- 
 relations of the mental phenomena. A third class of 
 relations considers mind and body as dependent upon dif- 
 ferences of age, sex, race, etc. 
 
 At the close of the more strictly scientific discussions 
 of the book, we shall be in position to verify certain con- 
 clusions as to the nature of the human mind, and as to its 
 general connection with the bodily organism. Some of 
 the considerations introduced at this point will be of the 
 kind ordinarily known as " metaphysical." "We consider 
 it scientific to postpone these questions, as well as all 
 assumptions bearing upon them, until we have candidly 
 and thoroughly discussed the related phenomena and the 
 laws (or uniform ways) of their relation. But we also 
 hold that psychology, even when it employs the physi- 
 ological method, has the right, and is under obligation, to 
 suggest and defend true conclusions as to the nature of 
 the mind. 
 
 Benefits of the Study. — It has been shown that physiolog- 
 ical psychology can scarcely claim to be an independent 
 science, or even a separate and definite branch of general 
 psychology. It is, nevertheless, a most interesting, sug- 
 gestive, and productive way of studying mental phe- 
 nomena. For a long time the so-called " old psychology," 
 as pursued by the introspective and metaphysical methods, 
 made little or no advance. In a single generation, as pur- 
 sued by the experimental and physiological methods, the 
 science of psychology has been largely reconstructed. 
 
 The modern science of man emphasizes the necessity of 
 studying his nature and development as that of a living 
 unity. Man is known as the head of a series of physical 
 and psychical existences. Only by considering him in this 
 way can we have a trustworthy and adequate picture of his 
 mental life and mental evolution. Such a consideration 
 
10 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the psychology -which relies solely upon introspection and 
 metaphysical speculation is unable to furnish. The actual 
 achievements of the new science of physiological psychol- 
 ogy — though, of course, still including many uncertain- 
 ties and leaving many gaps to be filled — are a sufficient 
 justification of its demands upon all students of the human 
 mind. Further proof of the benefits of its study we con- 
 fidently leave to the test of the student's experience. 
 
CHAPTER I. 
 
 SUBSTANCE OF THE NERVOUS SYSTEM. 
 
 Chemistry and the microscope have succeeded fairly 
 well in analyzing the substance of the human nervous 
 system. For this purpose it is safe, within certain limits, 
 to dii'ect our observation and experiment upon the lower 
 animals, and to draw inferences from them which will 
 apply to the case of man. The chemical constituents and 
 minute structure of the elements which compose all ner- 
 vous substance are largely the same. In describing these 
 matters, it is not, then, so necessary to pay strict attention 
 to the specific animal form from which the substance is 
 derived. It is the way in which the elements are com- 
 bined into organs, and the development and elaboration 
 of function as dependent upon these organs, which con- 
 stitute the marked differences between the nervous sys- 
 tem of man and that of the lower animals. 
 
 The elements which enter into the nervous substance 
 require to be considered in three ways: (1) as respects 
 their chemical constitution ; (2) as respects their form or 
 structure ; (3) as respects their general physiological func- 
 tion. For purposes of convenience and orderly arrange- 
 ment we reserve the third consideration for another 
 chapter. 
 
 CHEMISTRY OF THE NERVOUS SUBSTANCE. 
 
 There are few perfectly certain facts which can be 
 obtained from the science of physiological chemistry, 
 respecting the constitution of nervous matter. These facts 
 
 11 
 
12 PHYSIOLOGICAL PSYCHOLOGY. 
 
 are suggestive and valuable, though their bearing on a 
 theory of nerve-function is not always clear. The neces- 
 sary chemical analysis is encompassed with many special 
 difficulties. Nervous substance is a product of life, and liv- 
 ing tissue cannot be at the same time preserved in normal 
 condition and subjected to the treatment of the laboratory. 
 Even when we succeed in determining the constituents 
 which compose it, their constitution — their normal chemical 
 arrangement and behavior — cannot easily be preserved. 
 It is impossible, for example, to determine the specific 
 gravity of uncoagulated blood, " except by operating with 
 extreme expedition, and at temperatures below 0° C." 
 
 Kinds of Nervous Matter. — There are two kinds of ner- 
 vous matter, — white, or fibrous, and gray, or vesicular. 
 These differ in color, microscopic structure, specific gravity, 
 and chemical constitution. The specific gravity of the 
 gray matter in man is given as 1.029-1.038; that of 
 the white matter, as 1.036-1.043. The lighter weight of 
 the gray nervous substance is due to the fact that it 
 contains relatively more of water and less of solids. The 
 percentage of water and of solids may be approximately 
 given as follows : of the gray, 81.60 and 18.40 ; of the 
 white, 68.35 and 31.65. The amount of water in both 
 kinds of nervous substance differs with age, sex, and in 
 different regions of the spinal cord and brain. It is larger 
 in the young animal than in the adult, larger in the brain 
 than in the spinal cord. These facts are doubtless con- 
 nected with the degree of susceptibility to new impres- 
 sions, and with the ease with which changes in habits are 
 effected, both in the nervous substances, and, as connected 
 with it, in the mind. 
 
 Non-phospliorized Bodies. — Of the solids composing the 
 nervous substance, more than one-half in the gray and 
 about one-quarter in the white consist of certain proteid 
 or albuminous bodies. Such bodies are the only ones 
 
StJBSTANCE OJ? THE NERVOUS SYSTEM. 13 
 
 never absent from the active living cells; they exist in 
 all vegetable and animal organisms. Very little is known 
 of the peculiar chemical constitution which these proteid 
 bodies take in the nerve-centres. They may be said to 
 represent there the presence of that general matter of life 
 which is the physical substratum of all vital phenomena. 
 
 Three other non-phosphorized bodies are found in the 
 nervous tissues ; these are called Cholesterin, Neurokera- 
 tin, and, more doubtfully, Cerebrin. Oholesterin is abun- 
 dant, especially as a constituent of the white matter of 
 the cerebro-spinal axis and of the nerves. It is supposed 
 to exist, preformed, in the brain. It is described as a 
 " monad alcohol," crystallizing in beautiful white crystals. 
 Its formula has been given as CseH^O-f-HjO. Neurokera- 
 tin may be derived from the medullated nerve-fibres and 
 the gray matter of the nervous centres; it is not found 
 in the non-meduUated nerve-fibres. It contains nitrogen 
 and a small percentage of sulphur. Oerehrin was an- 
 nounced by Miiller, in 1858, as a nitrogenous body to be 
 obtained from a precipitate of the brain. The existence 
 of this substance preformed in the brain has, however, 
 been disputed, although some of the chemists who dis- 
 pute its existence admit the existence of a body "for 
 which we may retain the name of ' cerebrin.' " The sig- 
 nificance of these bodies for the mental life is not appar- 
 ent, except so far as the fact is suggestive that they are 
 aU of a very highly complex chemical character. Of the 
 meaning of this fact we shall speak further on. 
 
 The Phosphorized Fats. — The most significant constitu- 
 ents of the substance of the nerve-centres, from the point 
 of view both of chemistry and of physiological psychology, 
 are certain complex phosphorized fats. These bodies are 
 highly characteristic of the centres of the nervous system. 
 They are therefore of special interest to the student of 
 physiological psychology. There are in particular three 
 
14 PHYSIOLOGICAL PSYCHOLOGY. 
 
 substances about the chemical constitution of which much 
 dispute has arisen, but which belong in this class. They 
 are called Protagon, Lecithin, and (more doubtfully again) 
 Cerebrin. Protagon was discovered in 1864, and announced 
 as a new proximate principle that -can be separated from 
 the brain, in a paper read in 1865 (by Dr. Oscar Lieb- 
 reich). Its name signifies that he considered it to "lead 
 the van." It is a very elaborate compound. Its formula 
 has been given as Cii6H24i]Sr4022P ; or, more recently, as 
 C160H308N5PO33. In spite of denials and disputes, subse- 
 quent very careful researches seem to make good the 
 claim of protagon to be the best established " phosphorized 
 proximate principle of the brain." In calling it a "proxi- 
 mate principle," it is of course assumed that it exists pre- 
 formed in the brain, and is not the result of the somewhat 
 elaborate process which is necessary to obtain it. 
 
 Lecithin is an organic compound which exists in large 
 quantities in ova, spermatozoa, etc., as well as in the ner- 
 vous tissues. It is supposed by some to be only one of a 
 similar group of bodies which possess a higher percentage 
 of phosphorus than protagon, and is, perhaps, formed from 
 protagon by the addition of the needed phosphorus. We 
 might then speak of " the lecithins " as a class of highly 
 phosphorized compounds. 
 
 If we regard — and this seems most probable — prota- 
 gon as the definite proximate principle among the phos- 
 phorized fats of the brain, cerebrin becomes one of those 
 bodies that are of ill-defined properties, and doubtful claim 
 to existence as proximate principles. 
 
 It is not necessary to speak in particular of other prod- 
 ucts which are found by laboratory treatment of the ner- 
 vous substance, and which are perhaps to be regarded as 
 products of the decomposition of protagon and lecithin. 
 
 Extractive and Inorganic Matters, — Certain extractive 
 matters, such as creatin, xanthin, and lactic acids, which 
 
SUBSTANCE OP THE NERVOUS SYSTEM. 15 
 
 are found especially in the muscles, are also found spar- 
 ingly in the brain. A very small amount — varying from 
 0.1 to 1 per cent. — of inorganic matters, such as alkaline 
 phosphates and sulphates, chalk, magnesia, oxide of iron, 
 etc., also exists in the brain. 
 
 Specific Chemistry of the Elements. — The more minute 
 chemistry of the nerve-cells tells us simply that they are in 
 the main protoplasmic and therefore rich in albuminous 
 bodies. Since the gray matter is much poorer in complex 
 phosphorized constituents, we conclude that the cells, 
 which enter into this matter, are also poor in the same 
 constituents. The different parts in the structure of the 
 nerve-fibres seem to differ in chemical constitution. Their 
 membranous envelope, like that of the muscles, yields 
 gelatin on being boiled. The axis-cylinder is a mixture 
 of albuminous and complex fat-like bodies. The chemical 
 constitution of the nervous elements of the retina of the 
 eye is very closely related to the phenomena of sight ; 
 for this sense is thought to be dependent upon the pro- 
 duction, by the stimulus, of photo-chemical changes in 
 these elements. The retina seems, accordingly, to contain 
 the same bodies as the central nervous system. Even the 
 two segments into which the rods and cones of the retina 
 break up exhibit marked differences in their chemical, as 
 well as optical characteristics. 
 
 Chemistry of the Functions of the Nerve-Elements. — Like 
 every other natural material structure, the nervous system 
 is obviously adapted to a peculiar kind of work. Chem- 
 ically considered, it has two very important characteris- 
 tics : its constitution is extremely complex, and the 
 compounds that enter into it are highly unstable. It is 
 evident, then, that it contains, stored, a large amount of 
 disposable energy ; and, also, that it readily yields this 
 energy, whenever the equilibrium of its molecules is even 
 slightly disturbed. But a more remarkable thing about 
 
16 PHYSIOLOGICAL PSYCHOLOGY. 
 
 it is, that — as we shall see later on — it explodes, as it 
 were, with increasing surrender of its energy as the num- 
 ber and intensity of the demands upon it are increased. 
 Within certain limits, it behaves very much as would a 
 conyenient kind of gun, which should be so arranged as 
 to go off with greater energy, as the pressure of one's 
 finger on the trigger were repeated or increased. 
 
 More wonderful still, — the nervous substance may be 
 said to make its own powder as fast (within certain limits) 
 as it is burned. It is itself the seat of a chemical synthe- 
 sis, which results in constructing the peculiar bodies just 
 described, from the material furnished by the blood. 
 Such bodies have a high value as combustibles ; for — as 
 has been said — they hold in store a large amount of 
 easily disposable energy. Yet further, the nerves, as 
 distinguished from the nerve-centres and the end-organs 
 of sense, can act repeatedly in quick succession with 
 undiminished force. It would seem, then, that they must 
 have the power of recombining immediately the molecules 
 which have been thrown down from their condition of a 
 highly complex compound having an unstable equilibrium. 
 Nerves appear to be so constituted chemically, that they can 
 serve as laboratories to retain the constituents of their own 
 substance and to reform them as fast as they are dissolved. 
 
 It is therefore impossible not to regard the substance 
 of the nervous system as especially fitted by its chemical 
 constitution to serve the purpose which it actually per- 
 forms. It is so constituted as to be in a high degree 
 susceptible to the slightest attacks from various kinds of 
 stimuli. It acts and recovers, and propagates the changes 
 set up in any part of it, with a high degree of rapidity. 
 It stores in compact form a large amount of easily dis- 
 posable energy. It is precisely such a system of physical 
 bodies as this, which is fitted to be especially correlated 
 with the phenomena of conscious sensation and motion. 
 
SUBSTANCE OF THE NERVOUS SYSTEM. 17 
 
 STRUCTURE OF THE NERVOUS ELEMENTS. 
 
 From the science of chemistry we now turn to the 
 science of microscopic anatomy or histology, and inquire 
 what it can tell us with respect to the structural form of 
 the nervous elements. If we analyze with a microscope 
 a section of the nervous matter of the central organs, its 
 apparently homogeneous character breaks up into three 
 or four kinds of substances. Of these one at least is not 
 generally considered to have a nervous character. 
 
 Nenroglia. — A diffuse, finely granular substance, called 
 "neuroglia " or " nerve-cement " exists in quantities large 
 enough to form an essential part of some localities of the 
 brain and spinal cord. It appears on examination to be 
 a delicate net-work, in which certain small cells (called 
 "neuroglia cells"), supposed to belong to the sustentac- 
 ular tissue, and other more conspicuous cells, usually of a 
 stellate shape, are found. It is not always clear to what 
 its appearance of granular or molecular matter is due. 
 The office of the neuroglia is supposed to be — as the 
 name signifies — the holding in place of the true nerve- 
 elements by filling in the gaps between them. It is 
 therefore classed with the connective, or sustentacular, 
 rather than the nervous tissue ; although it forms a con- 
 stituent of the nervous substance in the great nerve- 
 centres. 
 
 Nerve-corpuscles. — Very minute bodies, scarcely more 
 than from arlnr to rrnnr of an inch in diameter, and con- 
 sisting either of naked nuclei or of nuclei with only a 
 small amount of surrounding protoplasm, are found abun- 
 dantly in the gray matter of certain of the nervous centres. 
 Some of them, like the typical nerve-cells, give off proc- 
 esses. They vary much in shape, — are multipolar, 
 bipolar, or unipolar. Some of them so closely resemble 
 the more highly developed nerve-cells called " ganglionic " 
 
18 PHYSIOLOGICAL PSYCHOLOGY. 
 
 that they have been described as " nuclei invested by only 
 a small quantity of cell-substance." It is probably not 
 possible to draw any fixed line through this class of 
 minute bodies, or to separate the more highly developed 
 members of the class from the larger and more elaborate 
 bodies to which the name of "nerve-cells" is unhesi- 
 tatingly given. They may therefore be regarded as nerve- 
 corpuscles in various stages of development, from mere 
 granules to ganglionic cells. 
 
 The undoubtedly nervous elements of the substance of 
 the nervous system are of two kinds, as respects their 
 structural form: these are nerve-fibres and nerve-cells. 
 The white matter of the peripheral nerves and of the 
 nerve-centres is composed of nerve-fibres. The gray mat- 
 ter of the nerve-centres contains, besides the nerve-fibres, 
 numerous nerve-cells. Both these elements require then 
 a more detailed description. 
 
 NERVES, NERVE-FIBRES AND THEIR FIBRILS. 
 
 Nerves. — What is ordinarily called a " nerve " appears 
 to the naked eye as a cord of a whitish or grayish color 
 and uniform structure. On examination, however, we 
 find that it consists of several bundles (or " fascicles "), of 
 various sizes, bound together by connective tissue. When 
 followed toward the surface of the body, it divides and 
 subdivides, until its subdivisions consist of a single nervous 
 element called a nerve-fibre. The bundles of the nerve are 
 enclosed in a special sheath (called neurilemma or peri- 
 neurium'). As the nerve-fibres run toward the central 
 organs they are, as has been indicated, bound together to 
 form a nerve-fascicle. A small amount of connective tissue 
 appears between the several fibres within the same sheath. 
 The character of the sheath itself is changed and it 
 becomes attached to surrounding structures by a layer of 
 connective tissue. 
 
SUBSTANCE OF THE NBEVOTJS SYSTEM. 
 
 19 
 
 Kinds of Nerve-fibres. — The nerve-fibres which compose 
 those nerves that run from the central organs to the pe- 
 ripheral parts of vertebrate animals, are divided into two 
 classes. These are called medullated nerve-fibres, or nerve- 
 tubes, and non-meduUated nerve-fibres, or fibres of Bemak, 
 
 ,. yjTL 
 
 ■—It, 
 
 Fie. 1. — Cross-section of the Sciatic Nerve of Man. */,• C-^fter Key and Retzius.) 
 The left lower half is schematic. ?i, n. Bundles of nerve-nbres, surrounded by pn, pn^ 
 the periDeurium ; between them appears the connective tissue, epineurium (ep, ep), and 
 adipose substance (a<Z). 
 
 The former belong particulai'ly to the brain and spinal 
 cord; they are found only in vertebrate animals. The 
 latter belong particularly to the sympathetic system. This 
 distinction, which is easy to make for the peripheral nerves, 
 becomes difficult or impossible when we attempt to carry 
 it out within the more complex nerve-matter of the central 
 organs. 
 
 Within the nerve-centres of the brain and spinal cord 
 there appears, at first sight, to be a considerable variety of 
 nerve-fibres. Here we find very fine nerve-threads which 
 
20 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 require an enlargement of five hundred or more diameters 
 to make them even visible. Certain very delicate trans- 
 parent lines, differing from the fore- 
 going by their larger size and fibrillar 
 structure, also appear. These are 
 the so-called "naked axis-cylinders." 
 Both of these may be invested with 
 a medullary sheath and so converted 
 into meduUated nerve-fibres. Or, in 
 the peripheral nerves, they may be 
 found without such a sheath. And 
 whether meduUated or not, they may 
 become invested with a delicate cov- 
 ering membrane (called " sheath of 
 Schwann"). 
 
 It will be noticed, however, that it 
 is the presence or absence of the 
 medullary sheath which constitutes 
 the one important difference between 
 the different classes of nerve-fibres. 
 It is therefore customary to distin- 
 guish only two kinds of nerve-fibres, 
 according as they have, or have not, 
 this covering of medullary substance. 
 Fibres of Hemak. — These nerve- 
 fibres are distinguished chiefly by the 
 absence of the medullary sheath. 
 They are grayish and translucent, 
 with flattened nuclei lying at frequent 
 Fig. 2. -Pib.es of Remak intervals aloug their surface. When 
 Dor"«A."(RSo"Nu' gathered into bundles, within the 
 t^f'^-pZt^htTi. sheath of neurilemma, they are not 
 '°^ ° " ^' placed side by side. They are rather, 
 
 as it were, formed within the interior of the nerve, where 
 they unite and divide so as to form an intricate net-work 
 
SUBSTANCE OF THE NERVOUS SYSTEM. 
 
 21 
 
 of fibres. When grouped into still larger bundles, of 
 nerves, they are sometimes alone, but are more frequently 
 connected with the medullated fibres. 
 
 Medullated Nerve-fibres. — By carefully teasing a nerve 
 with fine needles we may separate its fibres for micro- 
 scopic examination. While still fresh, certain of the fibres 
 appear with a central part and a border 
 on each side, like a translucent liquid 
 in a tube of translucent walls. 
 
 By using different staining solutions, 
 which act differently upon the different 
 parts of its structure, the three-fold 
 character of the medullated nerve-fibre 
 is demonstrated. We thus distinguish : 
 (1) An outer membrane, extremely thin, 
 pellucid, and having nuclei, called the 
 "sheath of Schwann"; (2) an interior 
 layer of dimly granular, white, and highly 
 refracting substance, semi-liquid during 
 life, and called the " medullary sheath " ; 
 and (3) a cylindrical band of transparent 
 albuminous material, called the "axis- 
 cylinder." 
 
 Since many nerve-fibres, although they 
 are only naked axis-cylinders, perform truly nervous func- 
 tions, we conclude that this interior portion of the nerve- 
 tube is alone essential to its nervous character. The 
 sheaths may then be regarded as insulators. 
 
 Besides its three-fold longitudinal character, modifi- 
 cations ill the structure of the nerve-fibre occur along its 
 length. Of these, two are most important. Places of 
 constriction appear at certain points, situated beneath the 
 outer sheath ; these constrictions are made at the expense 
 of the medullary sheath. They are called annular con- 
 strictions, or nodes of Ranvier. The portion of the nerve- 
 
 FiQ. 3. — KeduUated 
 Nerve-fibres, withdouble 
 aud irregular contour 
 showing. (Schwalbe.) 
 
Or" 
 
 Fig. 4. — A, Medullated Nerve-fibres from 
 the Sciatic of a Rabbit, stained with osmic 
 acid, and diasociated in water. (Ranvier.) 
 
 B, Single "Fibre Enlarged ^"o/j, a, a, An- 
 nular constriction B, or nodes of Ranvier, 
 nearly midway between which is Ji, the 
 nucleus, with protoplasm, p, surrounding it; 
 ca, axis-cylinder. 
 
 Fig. 5. —Medullated ITer^'e - iibrcs. 
 (Scbwalbe.) a. Axis-cylinder; s, sheath 
 of Schwann; n, nucleus; p, p, granular 
 substance at the poles of the nucleus; 
 r, r, Ranvler*8 nodes, where the me- 
 dullary sheath ia interrupted and the 
 axis-cylinder appears; i, i, incisures of 
 Schmidt. 
 
SUBSTAKCE OP THE NERVOUS SYSTEM. 
 
 23 
 
 fibre included between two of them is called an "inter- 
 annular segment." 
 
 Each segment of a nerve-fibre has a flattened elliptical 
 nucleus, generally about half-way between the two nodes 
 which bound the segment. This nucleus sometimes com- 
 prises within it a still smaller nucleus (nucleolus). Be- 
 tween the nucleus and the medullary 
 substance there exists a minute mass of 
 protoplasm. 
 
 Other small irregularities of structure, 
 which the medullated nerve-tubes exhibit 
 under the higher powers of the micro- 
 scope, it is not necessary to describe (see, 
 however, Fig. 5). 
 
 Fibrils of the Axis-cylinder. — A discus- 
 sion has been going on for .some forty or 
 fifty years as to the meaning of certain 
 yet more minute divisions which appear, 
 under the very highest powers of the 
 microscope, in the structure of the axis- 
 cylinder of medullated nerve-fibres. Some 
 investigators claim that fibrils can be dis- 
 tinctly traced (as see Fig. 6) in living 
 nerve-fibres, where they are in process 
 of forming and are still naked, or where 
 they are seen just issuing from nerve-cells. 
 These fibrils they regard as the ultimate ap^a^'rancronh" a^s^- 
 
 j. ,, . • J J cylindei-a of Medullated 
 
 " nerve-lmes — swimming or suspended. Nerve - fibres. (Hans 
 
 . n • 1 T 1 Schultze.) 
 
 as it were, in a semi-nuid medium — along 
 which the nerve-processes run. But others regard the 
 substance, in which these "primitive" fibrils appear sus- 
 pended, as the real nervous substance; and they describe 
 it as diffused in the cavities of a sponge-like network. 
 
 Whichever of the foregoing views is taken, it would 
 seem that the structure of even the axis-cylinder is not 
 
 m. 
 
24 PHYSIOLOGICAL PSYCHOLOGY. 
 
 homogeneous ; but that it contains provision for parallel 
 or interlacing lines of nerve-action, running along within 
 the delicate covering of cells which forms its limit. So 
 marvellously minute and complicated are even the so-called 
 elements of this nervous mechanism ! 
 
 Size of ITerve-fibres. — As a rule, the non-meduUated 
 nerve-fibres are smaller than the meduUated, — the former 
 being from irinnr to x^tj o^ ^^ inch in diameter, and the lat- 
 ter from x^tnr to Tinnr- But this rule is not always followed. 
 In the white matter of the spinal cord the meduUated 
 fibres vary in size from yxinr to ^^ao of an inch ; but near 
 the gray matter of the cord, they are sometimes not more 
 than Ym^ oi an inch. The fibres are much finer in the 
 gray matter of the cord and brain (tttbtt to Tiwns of an inch 
 in diameter) ; they are finest of all in the superficial layers 
 of the brain, or in the nerves, of special sense. In some 
 instances the axis-cylinder may be not more than lo^ooo of 
 an inch in diameter. 
 
 GANGLIONIC NERYE-OELLS. 
 
 The undoubtedly nervous cells vary greatly in size and 
 shape, but when subjected to the microscope they all ex- 
 hibit certain common characteristics. 
 
 Ganglion-cells. — These nerve-corpuscles may be de- 
 scribed as irregular masses of protoplasm, finely granular 
 and delicately striated, with a large nucleus which is well 
 defined and vesicular in appearance, and usually contains a 
 shining nucleolus. They send off one or more processes. 
 In shape, some are nearly round ; others are egg-shaped, 
 caudate, stellate, or like a flask or the blade of a paddle ; 
 still others resemble the foot of an animal with claws. In 
 size they vary from about -^ to ^Vr of an inch. 
 
 To a certain extent, the shape and size of the nerve-cells 
 are characteristic of the part of the central nervous system 
 where they are found. For example, large cells of irreg- 
 
SUBSTANCE OP THE NEKVOtTS SYSTEM. 
 
 25 
 
 ular shape with branching processes are found in the 
 " motor " regions of the spinal cord. Cells very similar to 
 these seem also to be present in certain " motor " regions 
 of the brain. Pyramidal cells are char- 
 acteristic of the cortex, or gray rind, 
 of the brain; and a peculiar layer of 
 irregular globular cells is found just at 
 the inner edge of the gray matter of 
 the cerebellum. The most recent re- 
 searches indicate the possibility of dis- 
 tinguishing the sensory from the motor 
 cells in the cortex of the brain. The 
 former are thought by some observers to 
 be smaller in size, flask-shaped or bal- 
 loon-shaped, and less susceptible to 
 staining. In the same regions the 
 motor type is thought to be pyramidal. 
 The Ganglionic Globe. — The higher 
 powers of the microscope reveal the 
 bewildering complexity of the structure 
 of the fully developed nerve-cell. But 
 regarding its details there is still uncer- 
 tainty and dispute. The bipolar gan- 
 glion-cell of the fish has usually been 
 considered as a common type. This cell 
 has two parts : (1) A covering, which is 
 described as " fibrillary " ; and (2) a 
 
 - , IP -I 1 . Fig. 7. — Nerve-cell from 
 
 sflobe composed oi granular substance the spinai Ganglion of the 
 
 ° , . . . » Kay. 3iio/j. (Ranvier.) mp, 
 
 and COntammg near its surface a nu- Medullary sbeath of nerve- 
 
 . 1 T A fi^i^^i enclosing ca, the 
 
 cleUS with one or more nucleoli. A axls-cylmder, the fibrils 
 
 of which (f) separate and 
 
 recent description from this point of mn over the ganglionic 
 
 ^ '■ . globe, m; n, nucleus. 
 
 view makes the nerve-cell consist, not 
 only of a nucleus, but also of a " dense tangle " of ex- 
 tremely minute fibrils with an irregularly granular material 
 filling the spaces between them. 
 
26 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Others regard the " fibrillary " or " striated " appearance 
 of the cell as indicating that the exceedingly, small (" primi- 
 tive ") nerve-tubules, of which it mainly consists, are sus- 
 pended, as it were, in a spongy network within the cell- 
 body. 
 
 Processes of the Ganglion-cells. — It is generally agreed 
 that two kinds of processes are given out by certain of the 
 nerve-cells ; but the character and fate of these processes 
 are still in dispute. Deiters and others describe the case 
 — and their account has until recently been the accepted 
 one — in the following way : Ordinarily, only one of the 
 processes of the nerve-cell becomes continuous with the 
 axis-cylinder of a nerve-fibre. This process is therefore 
 called the " axis-cylinder process." It can often be dis- 
 tinctly. seen to be fibrillated; its fibrils are continuous with 
 those of the axis-cylinder of the nerve-fibre. The other 
 processes, also, have fibrils, but they are not continuous 
 with those of any nerve-fibre. These latter processes are 
 sometimes called " branching," since their fibrils ramify, 
 separate, and unite again, and finally become lost in an 
 intricate network of extremely minute nervous filaments. 
 
 Others, whose investigations are more recent (Golgi, 
 Forel, KoUiker), maintain that the axis-cylinder process 
 is always found to be branched. In some cases the axis- 
 cylinder maintains its identity, but gives off many fine 
 lateral branches. In others, the branching is more profuse 
 and rapid, and the axis-cylinder soon loses its identity. 
 These investigators also deny that the so-called " branch- 
 ing processes," which do not become continuous with axis- 
 cylinders, communicate with each other; they do not 
 " anastomose." 
 
 CONNECTION OF THE NERVE-FIBRES AND NERVE-CELLS. 
 
 Few subjects of microscopic anatomy are more baffling, 
 and at the same time more interesting and important, than 
 
SUBSTANCE OF THE NERVOUS SYSTEM. 27 
 
 the exact determination of the physical connection between 
 the two principal elements of the nervous substance. 
 On the one hand, it has been held that no connection 
 between nerve-cells and nerve-fibres can ever certainly be 
 made out, and that even its existence is doubtful (e.g. by 
 Wyman, in 1852). Next, a direct connection is thought to 
 be made out in certain instances and assumed to hold good 
 as a rule (e.g. by Vulpian, in 1866). Then we have the defi- 
 nite theory, said to be " established," that for every nerve- 
 cell there is a corresponding nerve-fibre which is continuous 
 with its one " axis-cylinder process." Thus the ganglionic 
 nerve-cell is assumed to be "the one perfectly definite type " 
 of all the seemingly different nerve-elements. Nervcrfibres 
 are, accordingly, described as nerve-cells drawn out into a 
 long process which serves to connect them with other sim- 
 ilar cells and fibres, or perhaps with the muscular fibres 
 which the nervous substance commands. On the other 
 hand, the more careful recent researches seem to indicate 
 that the relations between the separate elements of the 
 nervous substance are much more intricate and often indi- 
 rect than this captivating theory would lead us to suppose. 
 In the midst of such contradictory evidence from the 
 experts themselves, we may content ourselves with stating 
 the views of the more recent investigators. For in the 
 use of the higher powers of the microscope only what is 
 recent is of much value. The more recent views main- 
 tain that rarely, if ever, does a direct origin of the nerve- 
 tubes from the nerve-cells take place. The slender fibrils 
 of the central nervous substance come, partly, from the 
 breaking up of the processes of the nerve-cells ; they 
 come also, partly, from nerve-tubes that mn across from 
 one portion of this substance to another, or run into it 
 from the periphery of the nervous system. It is in this 
 " fibrillar mass," which must be regarded as interposed 
 between them and the nerve-cells, that the nerve-tubes 
 
28 PHYSIOLOGICAL PSYCHOLOGY. 
 
 have their origin. In other words, the connection between 
 nerve-cells and nerve-fibres of the peripheral nerves is ordi- 
 narily indirect. 
 
 The attempt has been made to procure additional evi- 
 dence on this subject by counting the nervous elements 
 of both kinds in the ganglia and roots of the same sections 
 of the spinal cord. But tliis method gives conflicting 
 results. One investigator (E. A. Birge) finds that his 
 count makes the number of fibres and cells so nearly alike 
 (e.^. in ten motor roots 5734 fibres and 5777 cells) as 
 to give countenance to the theory, that each fibre has a 
 special direct connection with a single cell. Other inves- 
 tigators, however, find their count favoring the view that, 
 in the roots of the spinal cord, two cells, as a rule, unite 
 their processes to make up the axis-cylinder of a single 
 nerve-fibre. Some observers claim to have seen through 
 the microscope cases of such a union. 
 
 It must be admitted, therefore, that the exact manner 
 of the connection between the nerve-cells and the nerve- 
 fibres is not, as yet, determined. The evidence goes to 
 show, however, that it is very largely indirect. But 
 possibly both kinds of connection — namely, the direct 
 and the indirect — may be at some time est9,blished to the 
 satisfaction of all parties. It may then, also, be possible 
 to tell what is the meaning, as respects the function of 
 the nervous elements, of these two kinds of connection. 
 And, indeed, some very careful observers have already 
 advanced the theory, that the connection is direct in the 
 case of the motor nerve-tubes, ahd indirect in the case of 
 the sensory nerve-tubes. But this theory has at present 
 no sufficient evidence. 
 
SUBSTANCE OF THE NEEVOUS SYSTEM. 29 
 
 CONCLUSIONS FROM THE STRUCTURE OF THE NERVE- 
 ELEMENTS. 
 
 In spite of all doubts respecting many and important 
 details of the structural character of the nervous sub- 
 stance, the general bearing of what is known is evident 
 enough. The entire nervous system of man is compounded 
 of a very few kinds of nerve-elements, put together into 
 a great variety of organs, whose structure and functions 
 the subsequent chapters will explain. Here then is a 
 wonderful unity composed of an almost infinite covuplex- 
 ity. The nerve-elements are essentially the same in all 
 the organs of man's nervous system. The same kind of 
 molecular disturbance, called " nerve-commotion " or ner- 
 vous "impulse," may be supposed to be producible and 
 capable of propagation in them all. But even these 
 elements are so indescribably fine in their structure, and 
 are probably connected to form the system in such an 
 infinite number of slightly different ways, that this nerve- 
 commotion can be indefinitely varied as to its shading, 
 intensity, and extent and paths of distribution. 
 
 Especially do we notice that the elements of the ner- 
 vous system are fitted to form " tracts " along which the 
 nerve-commotion may run. Every nerve-fibre constitutes 
 one such tract, — capable, it would seem, of subdividing 
 at either end into a considerable number of fibrils or sub- 
 ordinate tracts. The nerve-cells, too, seem fitted to serve 
 as tracts for the propagation, and perhaps also as centres 
 for the distribution and modification (" shunting places " 
 they have sometimes been called) of the same nerve- 
 commotion. The processes which they give off — whether 
 directly or only indirectly, or both, does not concern our 
 present purpose to determine — serve to bring them into 
 connection with other nerve-elements of the same kind; 
 and through the peripheral nerves, with the muscles and 
 
30 PHYSIOLOGICAL PSYCHOLOGY. 
 
 special organs of sense. Both kinds of nerve-elements 
 are certainly adapted to serve the purpose of " conduc- 
 tivity " in an exceedingly complex system of interrelated 
 organs. 
 
 Among the organs of the nervous system, moreover, 
 we shall find prominent the so-called "end-organs of 
 sense." Of course, the importance of these organs for 
 the life of the mind needs no defence. But the organs 
 of sense, in so far as they are nervous in character and so 
 capable of serving the purposes of a life of conscious sen- 
 sation, are constructed by combining the same two nerve- 
 elements, — namely, the nerve-fibres and the modified nerve- 
 cells. The " irritability " of the nerve-elements is therefore 
 an indispensable thing. As a matter of function, it is 
 provided for in their very structure. They are so made, 
 so delicate and so sensitive, that the slightest amount of 
 the appropriate kind of stimulus, furnished by external 
 nature, stirs them to nervous action. 
 
 In a still more wonderful manner do we find that these 
 elements, when combined into the central organs of the 
 brain, are irritable in correlation with all the changing 
 phases of the mind. For this reason, among others, we 
 may be inclined to maintain, that no other mechanism in 
 nature is so surprisingly fitted for the most important 
 relations as that which is made by combining the nervous 
 elements. As a system, this mechanism depends, for what 
 it is and for what it can do, upon the structure, chemical 
 and microscopic, of the nerve-corpuscles and nerve-fibres of 
 which it is composed. 
 
CHAPTER II. 
 
 STRUCTURE OF THE SPINAL CORD AND BRAIN. 
 
 The nervous elements, whose chemical constitution and 
 formal structure were described in the last chapter, are 
 combined into a great variety of "organs"; and these 
 organs are systematically arranged, in relation to each 
 other, for the accomplishment of a common work. This 
 arrangement of organs, all of which are made by com- 
 bining the nerve-fibres and nerve-corpuscles in their " bed- 
 ding" of connective tissue, is called — significantly — the 
 " Nervous System." It is the mutual condition and recip- 
 rocal action of the elements which give its peculiarities 
 to this mechanism. 
 
 It will greatly assist our understanding of the nervous 
 system if we, from the first, regard it in the light of an 
 appropriate idea. Such an idea is secured when we con- 
 sider the whole as a natural development in response, as it 
 were, to a problem requiring a mechanical solution. This 
 idea may be presented more clearly by considering how a 
 similar but much simpler problem is solved by an amoeba. 
 The amoeba, under the microscope, appears wholly, or 
 almost wholly, structureless. But it is, of course, com- 
 posed of a great number of molecular elements which are 
 undergoing constant change. It is alive ; its substance is 
 therefore (1) metabolic, (2) respiratory, (3) reproductive. 
 But more important still for our purpose is the fact that 
 the amoeba is (4) irritable and (5) automatic. When it is 
 acted on by stimuli from without, it suffers an explosion of 
 energy which generally results in its changing its form and 
 
 31 
 
32 PHYSIOLOGICAL PSYCHOLOGY. 
 
 place. Some of its movements seem rather due to unknown 
 internal changes, and are therefore called "automatic." 
 Thus does the amcsba solve its problem of adjusting itself 
 to its changing environment. 
 
 Let now the problem become much more complicated, 
 and the mechanism employed for its solution correspond- 
 ingly complex. The metabolic, respiratory, and repro- 
 ductive functions of the animal will each have separate 
 systems of organs assigned to their use. A system of 
 muscles will be formed which will possess in an eminent 
 degree the " amoeboid contractility." But the property of 
 being irritable and automatic will become the special endow- 
 ment of the nervous system. 
 
 A greater differentiation of organs and functions of 
 organs must take place as the problem of the life of the 
 animal becomes more complex. Certain groups of cells 
 must become more eminently irritable or susceptible to 
 external stimuli ; certain others more eminently automatic 
 or susceptible to internal stimuli. But if all the groups of 
 cells are to be connected into one system, strands of irritable 
 protoplasm must be stretched between them, — thus binding 
 them together into a community of action. Still further: 
 it is obviously necessary that the muscular system, upon 
 which the separate movement of the different masses of the 
 animal's body, or of its whole body at once, depends, shall 
 be connected with both the external and the internal groups 
 of cells. Only in this way can the various forces of nature 
 reflexly influence its movements, designed — as they are 
 — to keep it adjusted to its changing environment ; only 
 in this way also can the animal exercise any " will of its 
 own." 
 
 The most highly developed nervous system will, then, 
 consist of the following necessary parts : (^) End-organs 
 of Sense, like the skin, the eye, the ear, etc. ; (J.') End- 
 organs of Motion, like the attachments which the nerves 
 
STRUCTURE OF THE SPINAL, COED AND BRAIN. 33 
 
 have to the muscles ; (5) Central Organs, like the periph- 
 eral ganglia, the spinal cord and the brain, — in which may 
 comie to exist (6) certain regions more distinctively motor, 
 and (b'y others more distinctively sensory, and (6") perhaps 
 still others more particularly intellectual ; and finally, ( C) 
 Conducting Nerves, which will be either (c) afferent and 
 sensory, or (c') efferent and motor. 
 
 Now the nerve-elements in man are actually combined 
 into these various classes of organs — namely, end-organs 
 of sense and motion, central organs, and conducting 
 nerves — to make a nervous system. To accomplish this, 
 the nerve-fibres are bound into bundles, called " nerves," 
 in the manner already described (p. 18). The nerve-cells 
 are grouped into masses of nervous matter, called ganglia, 
 or gathered into larger bodies ; and these are intersected 
 with minute ramifications of the nerves, and interspersed 
 with the finely granular substance called neuroglia. Of 
 these masses or larger bodies, together with the nerve- 
 cords which connect them, two so-called systems are 
 formed. These are called the " Sympathetic System " and 
 the " Cerebro-spinal System." 
 
 THE SYMPATHETIC NERVOUS SYSTEM. 
 
 A pair of nervous cords, situated one on each side of 
 the spinal column, three main " plexuses " in the cavity of 
 the thorax and abdomen, and a large number of smaller 
 ganglia widely distributed over the body, especially in 
 connection with the veins and arteries, constitute the 
 Sympathetic Nervous System. Each of these nervous cords 
 consists of a number of ganglia united by intermediate 
 nerves. In the other regions of the spinal column the 
 number of these ganglia equals that of the number of 
 vertebrae (see Fig. 8) ; but in the region of the neck there 
 are only three ganglia. The three main plexuses are col- 
 
34 PHYSIOLOGICAL PSYCHOLOGY. 
 
 lections of nerve-cells and a dense plexiform arrangement 
 of nerve-fibres. One is situated at the base of the heart ; 
 another in the upper part of the abdominal cavity; and 
 the third in front of the last lumbar vertebra. 
 
 From the gangliated cord, just described, a communi- 
 cating and a distributing series of nerve-branches are de- 
 rived. By the former the sympathetic system is brought 
 into close anatomical and physiological connection with the 
 cerebro-spinal nervous system. The distributory branches 
 of nerves connect the gangliated cord with the viscera and 
 blood-vessels of the body. A recent view (Gaskell, in a 
 paper read May 24, 1888) considers the so-called " sympa^ 
 thetic ganglia," not as representatives of an independent 
 nervous system, but as belonging to the spinal system as 
 truly as do the ganglia of the posterior roots (see Fig. 10). 
 But the former differ from the latter in being efferent 
 rather than afferent; and in that the fibres enter them 
 as meduUated but emerge as non-meduUated. 
 
 The interest which the sympathetic nervous system has 
 for the study of physiological psychology is largely indi- 
 rect. This fact is partly due to our comparative lack of 
 knowledge respecting its more specific functions. It seems 
 to form a bond between the sensations, emotions, and 
 ideas, which have their physical basis in the cerebro-spinal 
 system, and those organs in the chest and abdomen whose 
 condition is so closely related to such psychical states. 
 The causes of many vague sensations and feelings, and of 
 the coloring of the "background," as it were, of our life 
 in the body, undoubtedly lie, partly, in the stimulation of 
 the nerves of this system by the thoracic and visceral 
 organs. The effect of certain emotions upon digestion, 
 circulation, and other functions of these organs, is too well 
 known to require detailed statement. 
 
STKUCTtrKE OF THE SPINAL COED AND BRAIN. 35 
 
 THE CEREBROSPINAL NERVOUS SYSTEM. 
 
 The spinal cord and brain are the great centres of the 
 Cerebro-spinal System. These masses of nervous matter 
 are situated in the bony cavity of the spinal column and 
 the skull. 
 
 Membranes of the Spinal Cord and Brain. — The cerebro- 
 spinal nervous substance has three coverings or mem- 
 branes. These are the dura mater, the arachnoid, and the 
 pia mater. 
 
 (1) The membrane lying next to the wall of the bony 
 cavity of the cerebro-spinal axis is called " dura mater." 
 It is white, tough, fibrous. In the skull it becomes identi- 
 cal with the inner lining of the bones. On passing into the 
 spinal column it somewhat changes its character. It puts 
 forth three processes which divide — although only incom- 
 pletely — the cavity of the skull into two symmetrical 
 halves, and into an upper and a lower space. These pro- 
 cesses are (a) the falx cerebri, sickle-shaped, and extending 
 between the two halves of the large brain ; (6) the falx 
 eerehelli, a similar process between the two lateral lobes of 
 the cerebellum ; and (c) the tentorium eerehelli, an arch 
 over the cerebellum. 
 
 (2) The "arachnoid" membrane is transparent, com- 
 posed of delicate connective tissue. Toward the dura 
 mater it presents a smooth, firm surface. It is reflected 
 on to the roots of the spinal and cranial nerves. The 
 space below this surface is called "subarachnoid"; it is 
 divided into smaller spaces by bundles of delicate tissue, 
 and its inter-communicating areas are filled by an alkaline 
 fluid. 
 
 (3) The " pia mater " is a vascular membrane, — a net- 
 work of fine branches of arteries and veins, held together 
 by delicate connective tissue. It closely invests the ner- 
 vous substance of both spinal cord and brain; it sends 
 
36 PHYSIOLOGICAL PSYCHOLOGY. 
 
 prolongations into the fissures and columns of the cord, 
 and dips into the fissures between the convolutions of the 
 brain. In this way the minute blood-vessels are brought 
 into the interior of the nervous substance. 
 
 These three membranes are not themselves possessed of 
 nervous functions; but by them the nervous masses of 
 the cerebro-spinal axis are protected, held together, " cush- 
 ioned," and nourished with blood. 
 
 Cranial and Spinal Nerves. — The cerebro-spinal axis, or 
 great central nervous mechanism, is connected with the 
 end-organs of motion and of sense by forty-three pairs of 
 nerves. Of these, thirty-one pairs are "spinal nerves," 
 and twelve pairs are " cranial " or " encephalic." 
 
 The thirty-one pairs of spinal nerves originate in the 
 substance of the spinal cord and pass out of the spinal 
 canal through openings called " intervertebral foramina." 
 Of these, counting from above, the first eight pairs are 
 " cervical," the next twelve " thoracic " or " dorsal " ; 
 then five " lumbar," five " sacral," one " coccygeal." Each 
 nerve arises from the side of the cord by two roots, an 
 anterior and a posterior. The former is composed of 
 motor nerve-fibres. The latter is composed of sensory 
 nerve-fibres, and has a swelling or ganglion upon it (see 
 Fig. 10). Immediately beyond the ganglion the two roots 
 unite. The united nerve soon after separates into two 
 divisions, each of -which contains both sensory and motor 
 fibres, that are distributed, one upon the back and the 
 other upon the front and sides, to all parts of the trunk 
 and limbs. 
 
 The cranial nerves are divided by Continental authori- 
 ties into twelve pairs, and by British authorities into nine. 
 These may be arranged in three groups : (1) the exclu- 
 sively sensory nerves ; (2) the exclusively motor nerves ; 
 and (3) the mixed nerves. To the first group belong the 
 olfactory, the optic, and the auditory. To the second 
 
Fis. 8. — View of the Cerebro-spiual 
 Axis. (After Bourgery.) Vs- The right 
 half of the craDium and trunk has been 
 removed, and the roots of the spinal nerves 
 dissected out and laid on their several 
 vertebrse. F, T, O, cerebrum; C, cere- 
 bellum; P, pons Varolii; mo, medulla 
 oblongata; Jtis, ms, upper and lower ex- 
 tremities of the spinal marrow. CI. to 
 CVULL. are cervical nerves; DI. to DXII., 
 dorsal; LI. to LV., lumbar; SI. to SV., 
 sacral; Col., coccygeal. 
 
38 PHYSIOLOGICAL PSYCHOLOGY. 
 
 group belong the nerves that supply the principal muscles 
 of the eyeball, the muscles of facial expression and of the 
 tongue, and the so-called spinal accessory nerve. To the 
 third group belong the three nerves which are distributed 
 so widely over the mucous membranes and muscles of the 
 face, tongue, pharynx, and internal organs, namely, the 
 trigeminus, the glossopharyngeal, and the pneumogastric 
 or vagus (see Figs. 15 and 18). 
 
 By these pairs of peripheral nerves the sensory areas of 
 the body have the impulses originating in them conducted 
 to the central nervous mass, while the motor areas are con- 
 trolled from the same central mass. Thus sensation and per- 
 ception, which are dependent upon the excited condition 
 of the end-organs of sense, are made possible. And by 
 reflex and automatic action of the cerebro-spinal axis both 
 involuntary and voluntary movements of the trunk and 
 limbs are accomplished through the conducting nerves. 
 
 STRUCTURE OF THE SPINAL CORD. 
 
 The Spinal Cord extends in the spinal canal from the 
 aperture (foramen magnum'), through which it connects 
 with the brain, downward to opposite the body of the first 
 lumbar vertebra. Here it tapers off into a slender thread 
 of gray nervous substance (filum terminale). Its length 
 is, in the adult, from fifteen to eighteen inches. It is 
 nearly cylindrical in shape, its front and back surfaces 
 being somewhat flattened. It has two considerable enlarge- 
 ments of its girth, an upper (cervicaV), from which arise 
 the nerves that supply the upper limbs, and a lower Qum- 
 har} which supplies the lower limbs with nerves. 
 
 Fissures and Commissures of the Cord. — The spinal cord 
 is almost completely divided for its entire length into 
 right and left halves by two " median " Fissures ; a some- 
 what broader one in front (anterior), and a somewhat 
 deeper but narrower one behind (posterior). Two bands 
 
A 
 
 B 
 
 6-| 
 9- 
 
 40 ] 
 
 
 Fig. 9. — A, Anterior, and B, Posterior, View 
 of tbe Spinal Cord and Medulla Oblongata. B', 
 the Filum terminale, which has been cut off from 
 A and B. 1, Pyramids of tbe medulla, and 1', 
 their decussation. 2, olives; 3, lateral strands 
 of the medulla; 4', calamus scriptorius; 5, the 
 funiculus gracilis; and 6, the funiculus cuneatus; 
 7, the anterior, and 9, the posterior, fissures; S, 
 the antero-lateral depression ; 10, postero-lateral 
 groove. C, the cervical, and L, the lumbar, 
 enlargements of tbe cord. 
 
 10- 
 
 fli 
 
40 
 
 PHYSIOLOGICAL PSYCHOLOGy. 
 
 of nervous matter, called Commissures, unite its halves 
 and prevent the fissures from dividing it completely. The 
 front one, at the bottom of the anterior fissure, is the white 
 commissure ; the one behind, at the bottom of the posterior 
 fissure, is the gray commissure. The latter is larger than 
 the former, except at the cervical and lumbar enlarge- 
 ments of the cord. Along its entire length the gray com- 
 missure encloses a minute canal (^central canaT). 
 
 Coluinns and Horns of the Cord, — Each half of the cord 
 is subdivided by the entrance of the nerve-roots into three 
 
 Columns. These 
 are (a) the ante- 
 rior, which lies 
 between the ante- 
 rior median fissure 
 and the anterior 
 roots ; (6) the pos- 
 terior, which lies 
 between the pos- 
 terior median fis- 
 sure and the pos- 
 terior roots ; and 
 (c) the lateral, 
 which lies at the 
 side of the cord 
 between the other 
 two columns. 
 Transverse sec- 
 cord 
 
 Fio. 10.- 
 
 , Anterior, and B, Lateral, View of a Portion 
 of the Cord from the Cervical Region. Yj. (Sohwalbe.) 
 1, Anterior median, and 2, posterior median, fissures. At 
 3, IB the autero-lateral depression, over which spread the tlOUS of the 
 anterior roots (5). The posterior roots (6), with their 
 ganglion C6 ) arise from the postero-lateral groove, and shoW that itS Sub- 
 unitmg with the anterior roots form the compound nei-ve (7) 
 
 Stance, like all 
 nervous substance, consists of both white and gray ner- 
 vous matter. The former is external and composes the 
 columns of the cord; the latter is internal and is sur- 
 rounded by the white matter. The relative amount of the 
 
STRUCTURE OP THE SPINAL CORD AND BRAIN. 41 
 
 two varies in different portions of the cord. At the lower 
 end of the cord scarcely any white matter is found ; the 
 amount of such matter increases from below upwards, and 
 is largest in the cervical region. The amount of gray 
 matter is greatest in the two enlargements of the cord. 
 
 The gray columns and their commissures form a figure 
 somewhat like a Roman H or a large X, or a pair of 
 butterfly's wings. But the lateral masses of these crescent- 
 shaped bodies are narrower in the thoracic region, and 
 broader at the cervical and lumbar enlargements. The 
 limbs of the figure thus formed are called Morns ; of these 
 horns each side has therefore two, a rounded anterior and 
 a longer and narrower posterior horn. The division into 
 columns, fairly well marked on the surface, is lost as we 
 pass into the central gray matter. The anterior horn 
 has here an appearance of " spongy substance " ; the pos- 
 terior, of a kernel of such substance surrounded by " gelat- 
 inous substance." 
 
 White Substance of the Cord. — The external or white 
 matter of the spinal cord, besides connective tissue and 
 lymph- and blood-vessels, is composed of nerve-fibres. The 
 essential part of these fibres is the axis-cylinder ; although, 
 when fully developed, they have also the medullary sheath. 
 They vary in size, the thickest being found in the outer 
 portions of the anterior columns (x^Vff to -^ivs of an inch). 
 In the lateral columns the finer ones lie near the gray 
 matter; but in the posterior columns they increase in 
 thickness as they approach the posterior gray commissure. 
 
 The direction of the nerve-fibres in the white substance 
 of the cord is either vertical, or horizontal, or oblique. 
 The vertical fibres are most abundant and are united into 
 fascicles which ascend toward the brain. The horizontal 
 fibres are either commissural or fibres of the roots. The 
 fibres of the white commissure run horizontally along the 
 median border of the gray matter of the horns, and become 
 
42 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 interwoven with the vertical bundles of the anterior horns. 
 Most of them pass from the substance of the anterior horn 
 of one side across to the anterior column of the other side. 
 Fibres of the Roots. — Much interest is attached to the 
 determination of the exact course, in the spinal cord, of 
 the fibres from its anterior and posterior roots. Its inti- 
 mate structure, as fitted for those reflex functions which 
 are its peculiar property as an organ, is thus understood. 
 The details are given differently, however, by different 
 observers with the microscope. Nor is this strange, since 
 the fibres of the posterior root, especially, divide into 
 bundles so minute and so intricately interwoven with the 
 vertical fibres of the posterior column that their course is 
 extremely difficult to trace. 
 
 CO.I, 
 
 Fig. 11. — Section of the Spinal Cord at the Level of the Eight Pair of Dorsal Nerves. 
 Vi. (Schematic, from Sohwalbe.) s. a., anterior fissure; s.p., posterior septum (or fis- 
 sure); CO., anterior, and c.;)., posterior, commissures; c.c, central canal; co. a., anterior 
 horn ; co.l., lateral horn ; co.p., posterior horn ; a, anterior lateral, and 6, anterior 
 median, cells; c, cells of the lateral horn; d, columns of Clarke; e, solitary cells of the 
 posterior horn; r.a., the anterior, and r.p., the posterior, roots; /, bundle of fibres of 
 the posterior horn; and ,/", bundle of the posterior column; /", longitudinal fibres of 
 the posterior horn; s.g.R., gelatinous substance of Kolando; /.a., anterior, f.l., lateral, 
 andyi^., posterior, columns. 
 
STBUCTUEB OW THE SPINAL COED AND BEAIN. 43 
 
 Most recent authorities recognize two main diyisions of 
 the fibres of the posterior root on their entrance into the 
 spinal cord. Of these, one, said to be the earliest devel- 
 oped, enters immediately the " gelatinous substance " of 
 the posterior horns and becomes lost in it, or passes through 
 it to form a connection with the cells of the " columns of 
 Clarke " (see Fig. 11). The other portion of the fibres of 
 the posterior roots, said to be developed later, passes for 
 a little way outside of the gray matter along the back part 
 of the lateral column, and then, after running upward a 
 variable distance, buries itself in the gray substance of the 
 posterior horn. 
 
 The fibres of the anterior roots traverse obliquely the 
 white substance of the cord, and either enter the gray matter 
 , of the anterior horns on the same side, or pass by the an- 
 terior commissure to the other side of the cord, or pass into 
 the lateral columns and the posterior horns. 
 
 Gray Substance of the Cord. — The nerve-fibres which 
 form the principal mass of the gray substance of the 
 spinal cord are generally non-meduUated, and frequently 
 divide and subdivide to form extremely minute plexuses. 
 Besides these elements, this substance contains large num- 
 bers of ganglion-cells. These cells are described as multi- 
 polar and as regularly giving off the two kinds of processes 
 already spoken of (see p. 26). Gerlach thought he could 
 trace the very finest ramifications of the so-called " branch- 
 ing " process of the nerve-cells of the cord until they par- 
 ticipated in those plexuses of nerve-fibres which he regards 
 as an essential constituent of its gray substance. Others 
 consider the fate of these processes to be still unknown. 
 
 Many of the nerve-cells of the posterior horns are exceed- 
 ingly small, and are distributed through the above-men- 
 tioned plexuses of minute nerve-threads. Indeed, some of 
 the most recent investigations have concluded that the 
 nuclei of the motor nerves in the cord often run into each 
 
44 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 other, and cannot be distinctly circumscribed. Character- 
 istic groups of ganglion-cells of different sizes also occur at 
 various places in the gray matter of the cord. In the 
 anterior horns of the cervical and lumbar regions there 
 
 are three such groups 
 of large cells. One 
 other important group 
 is situated at the inner 
 angle of the base of 
 the posterior horn ; 
 and, in its extent up 
 and down the cord, 
 it forms the so-called 
 " column of Clarke " 
 (see Fig. 11). 
 
 Tracts in the Spinal 
 Cord. — It is evidently 
 of the greatest impor- 
 tance to trace out 
 those paths of ner- 
 vous substance along 
 
 Fio. 12. — Section of Dorsal Part of the Spinal which the nCrVOUS 
 Cord, showing the Gray Matter of the Horns. ™^]. 
 
 (Henle.) Ca, anterior white, and Cg., gray commis- impulsCS may paSS in 
 sure; Co, central canal; V, vesicular column; 8, spongy ^ . 
 
 substanceof the posterior horn, surrounded by g,gelat- \^q Spinal COrd. 
 
 inous substance; Pr, reticular process ; Ti, inter- ^ 
 
 median lateral tract. Neither the micrO- 
 
 scope nor physiological experiment, however, finds it 
 easy to unravel these paths. Two other methods of 
 their determination are most effective ; and when the 
 evidence of both coincides, it may be regarded as fairly 
 conclusive. These methods are the embryological and 
 the pathological. The former makes use of the fact that, 
 in the development of the spinal cord, the medullary 
 substance of the nerve-fibres in different tracts is consti- 
 tuted at different times, so as to render them distinguish- 
 able when viewed in cross-section. The pathological 
 
STEtrCTUKE OF THE SPINAL COED AND BEAIN. 45 
 
 metliod attempts to reach the same result by tracing the 
 lines along which degeneration takes place when the nerve- 
 fibres have been separated from their 
 place of origin and nourishment. 
 
 By the methods just described, two 
 principal tracts, which extend along 
 the greater part of the cord, have been 
 made out. From their upper con- 
 nections they have been named the 
 " pyramidal " and the " lateral cerebel- 
 lar." The pyramidal tract is trace- 
 able down from the anterior pyramid 
 of the medulla oblongata. It divides, 
 on entering the upper portion of the 
 spinal cord, into two tracts. Most 
 of its fibres cross over, well up in the 
 cord, and pass down in the back part 
 of the lateral column as a compact 
 bundle. This crossed (or lateral) part 
 of the pyramidal tract can be traced 
 as far down as the third or fourth 
 pair of sacral nerves. Some of the 
 fibres, however, do not cross in the 
 upper part of the cord. These form 
 the uncrossed (or anterior) part of the 
 pyramidal tract; on passing down- 
 ward they gradually diminish, and 
 cease in the dorsal region of the cord. ,. ^»-.^3.- sections through 
 
 o the epinal Cord at aifierent 
 
 The direct lateral cerebellar tract lies ft^^eBui^nJ^" L^e^l 
 between the lateral pyramidal tract ™^°e°.°^2ir of the°\^^"! 
 
 III., of the 'sixth; and IV., 
 of the twelfth, dorsal nerves ; 
 and v., of the fourth lumbar 
 nerves ; pv, uncrossed (Or 
 
 and the outer surface of the cord. 
 It disappears in the lumbar region. 
 
 In the posterior white column a l^^^J^ irSl^^l^f'^^i^m. 
 tract can be traced as far downward l.e?eb*enar' tract; '^f tract ™f 
 as the middle of the dorsal region 
 of the cord ; it is called the " tract (or column) of GoU." 
 
46 PHYSIOLOGICAL PSYCHOLOSY. 
 
 Meclianism of the Spinal Cord. — This brief description of 
 the structure of that nervous mass which lies withiii the 
 bony cavity of the spinal column shows plainly its adapta- 
 tion to the general purpose of conducting nerve-commotions 
 up and down, and of acting as a series of reflex and, 
 possibly, automatic centres. Its substance consists largely 
 of ascending and descending tracts of nervous elements. 
 It is also a pile of nerve-centres, each one of which may 
 have its own peculiar functions, but all of which are bound 
 together — up and down, right and left, and obliquely — 
 so as to act unitedly under control of the central organs 
 lying above. It has special local mechanisms; yet, as a 
 whole, it is connected with the general mechanism of the 
 cerebro-spinal axis. It is adapted to do a great variety of 
 work, as it were, by itself ; and yet it can be made to do 
 service under the command of the brain. It is also at 
 various levels — thirty-one in number — bound by the con- 
 necting nerve-cords to the end-organs of sense and motion. 
 
 STBUCTURE OF THE ENCEPHALOHT. 
 
 The Encephalon, or Brain in the most extended sense of 
 the word, includes all that mass which is contained within 
 
 Cb 
 
 Mo 
 
 Fio. 14. — View of the Brain in Profile. %. (Henle.) CT, cerebrum; CTJ, 
 cerebellum; Jfo, medulla oblongata; P, pons Varolii. 
 
STKUCXUEE OF THE SPINAL CORD AND BKAIN. 47 
 
 the cavity of the skull. On removing it from this bony- 
 cavity four divisions are apparent to any observer. Imme- 
 diately above the section by which it has been separated 
 from the spinal cord, and appearing as an enlarged prolon- 
 gation of the cord, is (J) the Medulla Oblongata. Cov- 
 ering the upper back part of this organ, and extending 
 beyond it on both sides, is (//) the Cerebellum, or Little 
 or Hinder Brain. Swelling out, and in front of the 
 medulla, is (Illy the Pons 
 Varolii, or so-called "bridge" 
 of the brain. While above 
 both pons and cerebellum, 
 and filling by far the larger 
 part of the cranial cavity, 
 when the entire mass is in 
 its place, is (/F) the Cere- 
 brum, or Large Brain, — the 
 Brain proper. 
 
 External Appearance of the 
 Medulla Oblongata. — This 
 organ is somewhat pyramidal 
 in form, about one and one- 
 fourth inches in length, 
 
 .-, J. , -I , • -I Fig. 15. — Diagrammatic diaaectlon of the 
 
 tnree-IOUrtnS to one men medulla oblongata and pons to show the 
 
 - , . . -1 . _i J course of the fibres, a, superficial, a', deep 
 
 broad in its widest part, and. transverse fibres of the pons; 6, 6, anterior 
 
 _ , -I jt ' 1 Tx pyramids ascending at 6 through the pons ; 
 
 one-halt inch thick. Its Citir c,c,olivary bodies; c', olivary fasciculus in 
 
 the pons ; d, d, anterior columns of cord ; e, 
 
 tenor pyramids appear con- inner part of the right column joining the 
 
 ■*'' . anterior pyramid ;/, the outer part going to 
 
 tinUOUS with the anterior the ollvary fasciculus; ^.lateral column of 
 
 cord ; h, the part which decussates at k^ the 
 
 columns of the cord : its decussation of the pyramids ; I, the part 
 
 which joins the restiform body ; i», that which 
 
 lateral area shows upon its forms the fasciculus teres ;«,arciform fibres 
 
 ^ 1 and 2, sensory and motor roots of fifth 
 
 upper end an elevation nerve; S.sixthnerve; 4,portlodura; 5,por- 
 
 xrir tio mtermedia; 6, portio mollis of seventh 
 
 called the " olivarv bodv " ; °'"'^'^! 7,glosso-pharyngeal; 8, pneumo-gas- 
 l/dlieu. Wie uxiva,i_y uuu._y , j^..^. ^^ ^^^^^^ accessory of eighth nerve; 
 
 its posterior tracts appear lo, hypo-giossai nerve. 
 
 continuous with the posterior columns of the cord. Just 
 
 outside the upper part of each posterior tract there 
 
48 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ascends to the cerebellum a strong tract named the 
 " restiform body." A part of the posterior tract is marked 
 off from the rest by a septum of the pia mater ; this part 
 is called funiculus gracilis, which, further upward, broad- 
 ens out into the clava. The back part of the lateral area 
 also broadens out into a wedge-shaped body, known as the 
 cuneate funiculus. (Fot further details, see Fig. 15.) 
 
 Internal Structure of the Medulla. — An important re-dis- 
 tribution of the nervous substance, both white and gray, 
 takes place in the medulla oblongata. The arrangement 
 of the nerve-elements thus becomes much more complex 
 than that of the spinal cord. To understand this we must 
 note chiefly the following particulars : (1) The external 
 portions of white substance on the back part of the organ 
 (the posterior tracts and restiform bodies) diverge and 
 become thinner ; thus the central gray mass is opened up 
 and allowed to come to the surface between the sides of 
 the surrotmding white matter. (2) The great vertical 
 tracts of nerve-fibres from the spinal cord change their 
 course greatly, and other new tracts from the cerebrum and 
 cerebellum are gathered up within this organ, for trans- 
 mission downward. (3) In this way the central gray mass 
 of the horns becomes much broken, and its distribution 
 changed. A number of large nuclei are also added to 
 the nervous mass in this organ. 
 
 The attempt to trace the various tracts of nerve-fibres as 
 they ascend through the medulla from the columns of the 
 cord leads us to notice : — 
 
 The Decussation of the Pyramids. — The external white 
 matter of the medulla oblongata is only to a small extent 
 a direct continuation of the columns of the spinal cord. 
 A large bundle of nerve-fibres, which in the cord lies in the 
 back part of the lateral column, pushes its way obliquely 
 through the gray matter of the anterior horn, and passes in 
 front of the central canal to the pyramid of the opposite 
 
STRtrCTTJRE OP THE SPIKAL COED AND BEAIN. 49 
 
 side. The abrupt passage of so many fibres through it 
 breaks up the anterior horn, separates part of it from the 
 rest, and pushes' this separated part over to one side, and 
 close to a part of the posterior horn. The posterior horn 
 also is shifted sidewise by the increased size of the pos- 
 
 Fis. 16. — SectioD showing the Decussation of the Pyramids at the point where the Spinal 
 Cord passes into the Medulla Oblongata. %. (Schwalbe.) f.l.a., longitudinal anterior 
 fissure, through which the bundles of pyramidal fibres (py^py*) are crossing over at 
 d; V, anterior, and 5, lateral pyramids; Co., anterior horn with groups of ganglion- 
 cells, a and ft; cc, central canal; /.r., formatio reticularis; ce, the neck, and ^, the head, 
 of the posterior horn; n.c., nucleus of the funiculus cuneatus; and n.g., of the funi- 
 culus gracilis; H\ funiculus gracilis; H^, funiculus cuneatus; x, group of gangUon- 
 cells. 
 
 terior tracts ; it comes to lie almost at right angles to the 
 posterior median fissure ; its head enlarges and approaches 
 to the surface, which it pushes out into a projection (funi- 
 culus of Rolando) and higher up, into a distinct swelling 
 (tuhercle of Rolando'). 
 
 Tracing the principal bundles of fibres from the spinal 
 cord through the medulla gives the following result : The 
 posterior column of the cord forms the substance of the 
 
50 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 three posterior strands of the medulla; namely, gracilis, 
 cuneatus, and funiculus of Rolando. A great part of the 
 lateral column (the lateral pyramidal tract) passes into 
 the opposite pyramid of the medulla, and ascends toward 
 the cerebrum. Another part (the direct lateral cerebellar 
 tract) passes by the middle of the organ, obliquely back- 
 ward to the restiform body ; but the remainder of it dips 
 under the olives and continues upward. Most of the an- 
 terior column of the cord dips under the pyramid of the 
 j^ medulla and passes up- 
 
 "■ -^— ■' ■ /'■<'• . wardtowardthecerebrum; 
 
 but part of it continues 
 into the pyramid of the 
 same side (see Fig. 15). 
 
 Formatio Reticularis and 
 ITuclei of the Medulla, — 
 By the " decussation of 
 the pyramids" the sub- 
 stance of the anterior 
 horns of the medulla is 
 broken up into a coarse 
 network (^formatio reticu- 
 laris), containing nerve- 
 cells intersected by bun- 
 
 FiG.17. — Section showing Q-ray Matter of the ,, p _oi -ri • i 
 
 Medulla Oblongata, in the region of the upper dieS 01 IlbreS. r OllT SpCCial 
 crOBSingof the Pyramids, */i. (Schwalbe.)/.?.a., ,, . „ i ,. 
 
 anterior, and s.l.p., posterior, lissures ; n.XI. nUCiCl, 01 gClatinOUS ap- 
 nnd n.XIL, nuclei of the vagus accessorius and . , 
 
 hypoglossal nerves ; d.a., so-called upper cross- pearaUCC, and Containing 
 ing of the pyramids ; py, anterior pyramid in ■"■ ^ ° 
 
 which is n.txr, the nucleus arciformis ; o, begin- multipolar nerVC-Cells, are 
 ning of the olivary nucleus ; o^, accessory oil- ^ 
 
 vary nucleus; J-.r., formatio reticularis ; g, to be UOted in Cach half 
 substantia gelatinosa ; f.a., f.a^,f.a?, arciform 
 
 fi''"*- of the medulla ; these 
 
 are the nucleus arciformis, the nucleus olivaris or " dentate 
 body," the nucleus olivaris accessorius, and the nucleus pyra- 
 midalis," sometimes called " inner accessory nucleus " 
 (see Fig. 17). Other nuclei consist of those groups of 
 multipolar cells to which the " roots of origin " of certain 
 
STKUCTUEE OP THE SPINAL COKD AND BRAIN. 61 
 
 cranial nerves are traced. These nerve-nuclei receive their 
 names from the nerves whose fibres are supposed to origi- 
 nate in them. 
 
 External Appearance of the Gerebelliim. — In the Cere- 
 bellum the general arrangement of the two kinds of ner- 
 vous matter is the reverse of that of the spinal cord and 
 the medulla ; the gray matter is outside, the white within. 
 This organ may be described as a white or medullary mass, 
 composed of three pairs of large stalks of nerve-fibres, en- 
 veloped in a wrinkled covering of gray nervous substance. 
 These three stalks are called the " peduncles " or " crirra " 
 of the cerebellum; they serve to connect it with three 
 other organs, with parts of which they are continuous. 
 They are called (1) the inferior peduncle, which is identical 
 with the restiform fascicle as it ascends from the meduUa 
 to the cerebellum ; (2) the superior peduncle, which con- 
 nects the cerebellum forward (with the tegmentum of the 
 cms) ; and (3) the middle peduncle, which passes down 
 on the side into the pons (see Figs. 18 and 19). 
 
 The surface of the cerebellum shows two hemispheres 
 
 k.6 
 
 Fig. 18.— Lower Surface of Cerebellum. Va- (After Sappey.) 1 inferior vermiform 
 procesB ; 2, 2, vallecula ; 5, flocculus ; 6, pons Varolii ; 8, middle peduncle of the Cere- 
 bellum • 9 medulla oblongata. Various pairs of nerves are seen thus : 12 and 13, roots 
 of fifth pair ; 14, sixth pair ; 15, facial nerve ; 17, auditory ; 18, glossopharyngeal ; 19, 
 pnenmogastric ; 20, spinal accessory ; 21, hypoglossal. 
 
52 PHYSIOLOGICAL PSYCHOLOGY. 
 
 or lateral lobes, united by a central lobe called the vermi- 
 form process. The central lobe, on its upper surface, is 
 a mere elevation ; but on its lower surface, where it lies 
 at the bottom of a deep depression (vallecula'), its " ver- 
 miform " character is well defined. The surfaces of the 
 cerebellum are divided by fissures into smaller lobes or 
 lobules. 
 
 Internal Structure of the Cerebellum. — The interior rela- 
 tions of the nerve-fibres of the peduncles of this organ 
 are extremely intricate, and are not known in much detail. 
 United in a white core, they form a rather uniform mass 
 which is interrupted, however, by certain nuclei of a 
 gelatinous appearance. Several bodies of gray matter are 
 found in this core ; of these the more important is dis- 
 closed by cutting through a little to the outside of the 
 central lobe. This body (the corpus dentatum of the cere- 
 bellum) is arranged like the dentate body of the medulla. 
 
 The gray matter of the cortex, or rind, of the cerebellum 
 is constructed in a peculiar manner. It consists of thin 
 plates (lamellce) of gray substance, which are penetrated 
 by prolongations of the white matter of the core. The 
 branches of the white matter within the plates of gray sub- 
 stance impart to it an arborescent appearance, and lead to 
 the name of " arbor vitse " (see Fig. 19). In the cortex 
 itself three distinct layers may be distinguished: (1) an 
 external "molecular layer" having, in a framework of 
 connective tissue, a few roundish cells and minute fibres ; 
 (2) an internal layer, which merges gradually into the 
 substance of the core, and contains multitudes of granules 
 whose nature is in doubt; and (3) a middle layer com- 
 posed of a single irregular row of large ganglion-cells, 
 called '' cells or corpuscles of Purkinje." Comparatively 
 large processes from these cells appear to ramify within 
 the outer layer. 
 
 Structure of the Pons Varolii. — The Pons, or " Bridge of 
 
STRUCTURE OP THE SPINAL CORD AND BRAIN. 53 
 
 the Brain," is a thickening of the yentral wall of the fourth 
 ventricle, composed of the middle peduncles of the cere- 
 bellum encircling and blending with the continuation 
 upward of the medulla. The general direction of its 
 
 rtt" 
 
 Fio. 19. — Median Section through the Stem of the Brain. (After Reicbert.) M, me- 
 dnlla oblongata ; of which Pa are the pyramids, decussating at pd; c, central canal ; 
 _pp, restiform body ; Pv, pons Varolii ; F4, fourth ventricle ; av, arbor vitae of the cere- 
 bellum : p, pyramid ; u, uvula ; to, nodule ; as, aqueduct of Sylvius ; Cr, crus cerebri ; 
 Q, corpora quadrigemina ; P, pineal gland ; Th, optic thalamus. Commissures : ca, the 
 anterior ; cm, the mollis : and cp, the posterior, F3, the third ventricle ; A, corpus 
 albicans ; tc, tuber cinereum ; i, infundibulum. 
 
 superficial fibres is transverse, though the lower ones 
 ascend slightly and the superior ones descend somewhat 
 obliquely. On removing these superficial fibres the pro- 
 longed fibres of the pyramids are exposed to view ; these, 
 as they ascend through the pons, are intersected by trans- 
 verse fibres. 
 
 Nuclei of gray matter are found everywhere between 
 the fibres of the ventral part of the pons. The back part 
 of the organ is chiefly constituted by a continuation up- 
 ward of the formatio reticularis, and of the gray matter of 
 the medulla. Several important collections of nerve-cells 
 lie embedded in this reticular formation; the principal of 
 
64 PHYSIOLOGICAL PSYCHOLOGY. 
 
 these is the " superior olivary nucleus." Other nuclei in 
 this region give origin to the seventh or facial nerve, and 
 to portions of the fifth nerve. 
 
 Structural Significance of the Lower Farts of the Brain. — 
 The very formation of the organs which have just been 
 described is indicative of their service in the mechanism 
 of the cerebro-spinal axis. This service may be said to be 
 of three kinds. They constitute the paths over which the 
 nerve-commotions are to run between the upper brain and 
 the spinal cord. They also serve as organs in which the 
 roots of origin of important pairs of cranial nerves may be 
 planted. And closely connected with these functions is 
 their peculiar adaptability to act as central organs. They 
 are arranged more elaborately than the spinal cord, and in 
 more immediate connection with the brain and the higher 
 organs of sense — so as to perform various reflex and auto- 
 matic functions. But while they share in these general 
 characteristics of structure, they have peculiarities belong- 
 ing to each. 
 
 The medulla oblongata is obviously an organ of con- 
 duction between the spinal cord below and the parts of 
 the brain lying above itself. Its peculiarities in dis- 
 charging this office are twofold. The nerve-tracts from 
 above are greatly compacted, are gathered together — as 
 it were — into shape to be further compressed vrithin the 
 spinal cord. The nerve-tracts from below, on the other 
 hand, are broken up and distributed to the side into the 
 cerebellum and into the principal parts of the crura cerebri. 
 Moreover, a great amount of crossing of the nerve-tracts 
 takes place in this organ. This is significant of the 
 important fact that certain functions belonging to the 
 trunk and limbs of the body are to be connected with 
 the opposite side of the higher central organs. It indicates 
 that "right-handed" man is "left-brained." But the 
 enlarged and varied bodies of gray nervous substance 
 
STRTTCTtTBE OF THE SPINAL COED AND BRAIN. 65 
 
 which the medulla contains show that it is " packed," as 
 it were, with centres for the discharge of reflex and auto- 
 matic functions of the lower sort. Some of these would 
 appear to he under the immediate control of the brain 
 above, and others not. 
 
 The cerebellum is certainly an organ of very striking 
 structure. It has, in its white core and three pairs of 
 peduncles, the mechanism of a conducting organ. But its 
 many masses of internal gray substance and its gray cortical 
 matter plainly show that it is a great central organ as well. 
 In the aspect of an organ for conduction, its peculiarity is 
 that it is so much to one side of the cerebro-spinal axis. 
 It lies — Hke an immense system of Y-tracks — out of the 
 course of the direct lines, and yet bound by nervous con- 
 nections with all the other organs of the encephalon. As 
 a central organ it resembles, far more closely than any of 
 its neighbors, that crowning nervous mechanism, which is 
 called pre-eminently the Brain. 
 
 The pons Varolii appears to be chiefly an organ for con- 
 densing and re-distributing the nerve-tracts which it con- 
 ducts. But its structure is that of a central mechanism 
 as well. 
 
 MORE DETAILED DESCRIPTION OF THE CEREBRAL ORGANS. 
 
 That portion of the encephalic contents which is called 
 the Cerebrum or Large Brain much exceeds in size all of 
 the rest. Besides the convoluted surface, it contains 
 within its base certain great ganglia ; and a number of 
 other nervous masses also appear here. It is of general 
 ovoid shape, and is divided — above, in front, and behind 
 — into two halves or "hemispheres," by a deep longitudi- 
 nal fissure. If these hemispheres are drawn asunder, they 
 are seen to be connected by a broad white band of nervous 
 matter (the corpus callosurn). The processes of the dura 
 mater which separate the two halves (^falx cerebri'), and 
 
56 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 which separate them both from the cerebellum (tentorium), 
 have already been described (p. 35). 
 
 Under Surface of the Cerebrum. — From the front of the 
 
 Fio. 20. — Under Aspect of the Brain. (Henle.) B, basis of the crura cerebri ; Coa, cor- 
 pora albicantia; P, olfactory bulb; II*, optic tract; Tc, tuber cinereum; Lpp, posterior 
 perforated space; Ccl, corpus callosum; Let, lamina cinerea terrainalis; Spa, anterior 
 perforated space; T, tegmentum: The, thalamus opticus; P, pons; Mo, medulla oblon> 
 gata; I. to VIII., first to eighth pair of cranial nerves. 
 
 pons very large white nerve-cords are seen passing upward 
 and forward to the cerebrum from the organs lying below 
 ("cerebral peduncles" or crura cerebri'). Around each of 
 these cords winds a flat band, the optic tract; these tracts 
 
STKUCTUKE OF THE SPINAL COBD AND BEAIN. 57 
 
 come together in front to form tlie optic commissure, from 
 which the two optic nerves arise. On each side of the 
 deep longitudinal fissure stretches the olfactory tract, end- 
 ing in its bulb. The intercranial part of this nerve is 
 really a projecting portion of the brain. (For the other 
 bodies on this surface, see Fig. 20.) 
 
 Upper Surface of the Cerebrum. — On top, the cerebral 
 hemispheres present the appearance of gray nervous 
 matter arranged in folds, called " convolutions " or gyri. 
 These are separated by " fissures " or sulci, of varying 
 depth. A considerable difference exists in the develop- 
 ment of the different convolutions, and in the strength with 
 which the different fissures are marked. The details of 
 this aspect of the brain vary in each individual, and even 
 in the two hemispheres of the same brain. Some sulci 
 and their corresponding gyri appear with a marked 
 regularity in the more fundamental stages of the foetal 
 brain. They have been divided therefore into primary, 
 secondary, and even tertiary, classes. 
 
 Lobes of the Cerebrum. — By means of the primary sulci 
 the hemispheres of the brain have been " mapped out " into 
 five territories, called Lobes. These are the (1) Frontal, (2) 
 Parietal, (3) Temporal or Sphenoidal, or Tempero-sphe- 
 noidal, (4) Occipital, and (5) Central or Insula, or Island 
 of Ren. The frontal lobe is divided from the parietal, on 
 its upper and lateral surface, by the Fissure of Rolando 
 (sulcus centralis') ; and on its lower surface from the tem- 
 poral lobe by the horizontal branch of the Fissure of 
 Sylvius. The parietal lobe is divided from the temporal, 
 for the greater part, by the Fissure of Sylvius, and from 
 the occipital lobe, on its median sui-face completely, and 
 on its upper surface only very incompletely, by the parieto- 
 occipital fissure. The temporal lobe is separated from the 
 frontal and parietal as already described; but the boun- 
 dary between it and the occipital lobe is very ni-defined. 
 
58 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Fia. 22. 
 
 sphenoidal convolutions- 10 sunerim- ii I'w'^Ti ■ ^ ,o ■■ f"? ^' '■ ^' "nfenor temporo- 
 ., P, V, a, four arectent convolutions.' ' ' ^^' '°^'™'' °°°'P"*' convolutions; 
 
STRTJCTUKE OF THE SPINAL COKD AND BEAIN. 59 
 
 The Island of Meil lies concealed beneath the frontal, pari- 
 etal and temporal lobes ; it consists of a few short convolu- 
 tions which may be disclosed by drawing aside the margin 
 of the Fissure of Sylvius. In describing the other lobes 
 the boundaries of the occipital lobe have been sufficiently 
 defined. 
 
 Snlei and Gyri of the Upper Surface. — The frontal, tem- 
 poral, and occipital lobes all have three principal con- 
 volutions arranged in nearly parallel tiers (superior, 
 middle, and inferior). On each side of the Fissure of 
 Rolando are the two central convolutions, sometimes 
 called "ascending frontal" and "ascending parietal." 
 Among the sulci, the Fissure of Sylvius is much the most 
 important. It exists in the foetal brain at the third month, 
 and is made by folding the entire hemisphere into an 
 arch. The Fissure of Rolando is also always present in 
 the human brain, and is rarely or never bridged over by a 
 secondary gyrus. It appears in the foetus as eariy as the 
 end of the fifth month. (For further details, see Fig. 22.) 
 
 Median Aspect of the Cerebrum. — On this aspect of each 
 hemisphere appears an important convolution which arches 
 around the corpus callosum, and is separated from the first 
 
 Fig. 23. — Convolutions of the Inner and Tentorial Surfaces of the Left Hemisphere, 
 i, t, 1, calloso-marginal fissure; Z, Z, calcarine fissure; m, m, hippocampal fissure; n,n, 
 collateral fissure; PO, parieto-oooipital fissure; 17, 17, marginal convolution; 18, 18, 
 gyrus fomicatus; 18', quadrilateral lobule; 19, hippocampal gyrus; 19', its recurved 
 end ; 25, occipital lobule ; 9, 9, inferior temporo-spbenoidal convolution. 
 
60 PHYSIOLOGICAL PSYCHOLOGY. 
 
 frontal convolution by a deep and constant fissure (the 
 sulcus calloso-marginalis') ; it is called from its shape, gyrus 
 fornicatus. Its back end curves downward and forward 
 under the name of gyrus hippocampi, to the inner tip of 
 the temporal lobe. The passage without break of one of 
 these convolutions into the other is considered by Ecker 
 to be a most important difference between the hemispheres 
 of the brain of man and those of the ape. (For further 
 details, see Fig. 23.) 
 
 Spaces and Bodies within the Cerebral Mass. — By cutting 
 off successive slices of the cerebral hemispheres their 
 general internal structure may be exposed. Beneath the 
 corpus callosum, and roofed over by it, is a space in the 
 interior of each hemisphere. These cavities are called 
 lateral ventricles. They are separated by a thin trans- 
 parent wall (the septum lucidum'), and are moistened by a 
 serous fluid. The roof of another cavity, the third ventri- 
 cle, is formed by an expanded fold of the pia mater (velum 
 interpositum'). Each lateral ventricle has a central space 
 and three curved prolongations, or cornua, (the anterior, 
 the posterioi;, and the descending,) which extend into the 
 cerebral mass. 
 
 On the floor of each lateral ventricle the exposed por- 
 tions of the great "basal ganglia" of the cerebrum are 
 visible. Two large pear-shaped bodies of gray color are 
 here seen, with their broad extremities directed forward 
 into the anterior cornua of the ventricle, and their narrow 
 ends outward and backward. They are called, from their 
 striped appearance when cut open, "striate bodies" or 
 corpora striata. Between the diverging portions of these 
 bodies are certain ovoid masses called "optic thalami." 
 Each thalamus rests upon one of the crura cerebri ; on its 
 outer and back part are two small elevations (corpora 
 genioulata, internum and externum). Along the floor of the 
 descending cornu of the ventricle, the inner surface of the 
 
STBUCTUEB OP THE SPINAL COED AND BKAIN. 61 
 
 gyrus fornicatus, doubled upon itself like a horn, appears 
 as a white eminence (^hippocampus major or "horn of 
 
 Fio. 24. — Baaal Oanglia of the Cerebrum seen from above. (Henle.) Ccl, genu of the 
 corpus caJloBum; Ce, corpus striatum ; Vsl, ventricle of the septum lucidum; Cf, column 
 of the fornix; St, stria terminalis; Tbo, optic thalamus; and Ts, its anterior tubercle ; 
 Com, middle commissure between the thalami and over the third ventricle; Fv, pulvinar; 
 Cn, conarium or pineal gland ; Cop, corpus quadrigeminum. 
 
 Ammon "). An arch-shaped band of nerve-fibres, called 
 the " fornix," is situated beneath the corpus callosum. It 
 consists of two lateral halves which, in front, form two pil- 
 
62 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 lars that descend to the base of the cerebrum and become 
 the corpora albieantia. Behind and between the optic 
 thalami, and resting on the back sm-face of the crura 
 
 Fig. 25. — A Deeper Dissection of the Lateral Ventricle, and of the Velum Interposi- 
 tum. a, under surface of corpus callosum, turned back; 6, &, posterior pillars of the 
 fornix, turned back; c, c, anterior pillars of the fornix; d, velum interpositum and veins 
 of G-alen; e, fifth ventricle; /,/, corpus striatum; ^, ^, taenia semicircularis; A, A, optic 
 thalamus; ^, choroid plexus; £, taenia hippocampi ; m, hippocampus major in descending 
 coruu; 7t, bippocampuB minor; o, eminentia collateralis. 
 
 cerebri, are four eminences in two pairs, called corpora 
 quadrigemina ; the front pair are the nates; the back pair, 
 testes. 
 
 The structure of some of the bodies already referred to 
 requires a yet more detailed description, in order to even 
 an elementary knowledge of the superior cerebro-spinal 
 mechanism. 
 
STEUCTUEB OF THE SPINAL COED AND BEAIN. 63 
 
 The Cmra Cerebri. — These strong peduncles of the 
 brain ascend from the pons to the optic thalami and the 
 striate bodies. The fibres which constitute them are 
 arranged in two groups, separated by the gray matter of 
 the substantia nigra. The front j 
 
 portion is called crusta. Of its /'^^'""^ 
 
 fibres an important part is contin- /^ f^' \ 
 
 uous -with the longitudinal fibres *x^ * i \. 
 
 from the pyramids of the medulla ; f \v^ j >^ A 
 it receives other fibres from the \^'' J/\ J 
 substantia nigra. Many of the fig. 26. -tecUon through 
 fibres of the crusta run to the 'Z,^£roi^t^Zftl\ 
 nuclei of the striate bodies and ^?''te°'c™B'"LUri^- "tl^ 
 terminate there; but some radiate "^ntum of the cru^ cerebri. 
 
 upward through the internal capsule directly to the cere- 
 bral cortex. 
 
 The back portion of the crus is called tegmentum. Some 
 of its fibres come from the anterior column of the cord 
 and radiate upward to the optic thalami. These fibres are 
 diffused. Others are collected into more well-defined 
 tracts, — especially a tract coming from the superior pe- 
 duncle of the cerebellum, and passing forward over the 
 anterior end of the fourth ventricle (see Fig. 19). 
 
 The formatio reticularis is continued into the tegmen- 
 tum, and some fibres appear to arise in its cells. 
 
 The Striate Bodies. — Each corf us striatum consists of 
 two masses, the upper one of which (nucleus caudatus') 
 projects into the lateral ventricle ; the lower one (nucleus 
 lenticularis') is embedded in the white substance of the 
 hemisphere, and constitutes the principal part of the body. 
 These two are separated by an important layer of white 
 matter called the " internal capsule." 
 
 The details of the structure of the striate bodies are 
 insufficiently made out. The nucleus caudatus receives 
 from the capsule, on the side turned toward it, several 
 
64 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 bundles of fibres. All parts of the nucleus lenticularis 
 are pervaded with bundles of white fibres. Some bundles 
 pass into it from the adjacent parts of the capsule ; some 
 connect it with the caudate nucleus; some radiate from 
 it toward the cerebral cortex. The gray matter of this 
 organ has free nerve-nuclei distributed through it. 
 
 The striate bodies have apparently a special connection 
 
 with the frontal and parietal 
 lobes, but also with some con- 
 volutions of the temporal lobe 
 and the Island of Reil. 
 
 The Optic Thalami. — The 
 gray matter of this organ is 
 subdivided into several parts, 
 
 Cap- 
 
 »"''• t int. 
 
 Clatiatrtini 
 
 Thalam. opt- 
 
 eorp: eallasi 
 
 Hinlerer 
 
 Thail del 
 jfucteu» 
 eaiidattcfi 
 
 Comu 
 posteriua 
 
 Fig. 27. 
 
 Fig. 28. 
 
 These and the following two Figures show the arrangement of the white and gray 
 suhBtance in the interior of the cerebrum. (All four are from Q-egenbaur.) 
 
 Fig. 27. — Horizontal Section through the Right Hemisphere. 
 
 Fig. 28. — Frontal Section through the Cerebrum in front of the Fornix. Posterior 
 surface of the section displayed. 
 
 SO that two or more nuclei are distinguished by different 
 authorities. This subdivision is only partial, however; the 
 organ is therefore, perhaps, best described as a mass of gray 
 nervous substance, with multipolar and fusiform cells, and 
 everywhere traversed by nerve-fibres. Its external and 
 
STEUCTaKE OP THE SPINAL CORD AND BRAIN. 66 
 
 under surfaces are not free, but are united with other parts 
 of the brain. 
 
 On the outer surface of the optic thalami is the white 
 matter of the internal capsule, composed of fibres diverg- 
 ing from the crusta into the hemispheres. With these 
 fibres mingle those which radiate from the interior of the 
 organ itself. According to a recent authority, the thala- 
 mus is the primary centre of the optic nerve. 
 
 Fio. 29. Pis. 30. 
 
 Vie. 29. — Frontal Section througb the Bight Hemisphere of the Cerebrum in front of 
 the Commissura Mollis. Posterior surface of section displayed. 
 
 Fig. 30. — Frontal Section through the Cerebrum back of the Commissura KoUis. 
 Front surface of section displayed. 
 
 The Corpora Qnadrigemina. — In the interior of the front 
 pair the most characteristic portion of this organ is 
 found; it is a layer of fine nerve-fibres running longitu- 
 dinally, between which are small, scattered nerve-cells. In 
 the external strata of these bodies multipolar cells are 
 abundant ; in the interior, at the sides of the Sylvian 
 aqueduct, is a collection of gray matter which is continu- 
 ous with the lining of the third ventricle. The third and 
 fourth nerves originate in the nervous substance which 
 lies along this " Aqueduct " (see Fig. 20). 
 
 Layers of the Cerebral Cortex. — The general arrangement 
 of gray nervous substance upon the surface, and of white 
 
66 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 matter within, is adhered to in all parts of the cerebral 
 cortex. But the form and distribution of the nerve-cells 
 
 
 Fio, 31. — Section through the Cerebval Cortex of Man, prepared with Osmic Acid. *Vi- 
 (Sohwalbe) . /, principal external, and II, internal, layer ; x, layer lying as a limit between 
 the two; m, medullary Buhstance sending out bundles of nerve-fibres into //; I, layer 
 poor in cells, but with an external plexus of nerve-fibres (la) ; 2, layer of small, and 3, 
 of large, pyramidal cells; 4, inner layer of small nerve-cells. 
 
 are different in different regions and in different layers of 
 the same region. As a rule the cortex has five layers or 
 lamince. The entire thickness is, in the adult, from -^ to 
 ^ inch. The first layer shows delicate nerve-fibrils run- 
 
STRUCTURE OF THE SPINAL CORD AND BRAIN. 67 
 
 ning parallel to the surface and interlacing with a few 
 small branching nerve-cells. The second and third layers 
 contain a large number of pyramidal or spindle-shaped 
 cells. In the second layer the cells are about ^ruv i'lch in 
 diameter, and are closely pressed together. In the third 
 are fewer cells, but they increase in size to perhaps xwir 
 or ^-^ inch, and have their long axes perpendicular to 
 the surface. The fourth layer contains large numbers of 
 small, globular, and branching cells ; the fifth, spindle- 
 shaped bodies with long tapering processes, and smaller 
 irregular cells, very compactly accumulated. 
 
 The number of nerve-cells in the cortex is enormous. 
 In a bit of its substance, 1 millimeter square and ^ milli- 
 meter thick, 100 to 120 have, on an average, been counted. 
 
 Modifications of the arrangement just described are 
 found in certain regions of the cerebral cortex. In the 
 occipital lobe, for example, the number of layers is increased, 
 by intercalating granule layers, to seven or eight. In cer- 
 tain layers, called "motor," large cells (named by Betz 
 " giant-cells " ) resembling those in the anterior horns of 
 the spinal cord, are found. Conjecture and research are at 
 work with the question, whether certain of these layers, 
 and the cells they contain, are not more distinctively sen- 
 sory, and certain others more distinctively motor. This 
 subject is very important in its relations to our entire 
 conception of the nature and fimctions of the cerebral 
 mechanism. But as yet histology, even when aided by 
 physiological experiment, has determined nothing definite. 
 
 Systems of Cerebral Nerve-fibres. — The nerve-fibres of the 
 white substance of the brain are of three classes, according 
 to the destination of the fascicles into which the fibres are 
 gathered. There are the (1) downgoing or peduncular, 
 (2) the commissural, and (3) the arcuate (^fibrae propriae). 
 The peduncular system of nerve-fibres connects the cere- 
 brum with the lower parts of the encephalon. This system 
 
68 PHYSIOLOGICAL PSYCHOLOGy. 
 
 is called the corona radiata; it is the "blossoming out" 
 of the nerve-fibres on their way between the hemispheres 
 and the lower ganglia. Looked at from above, this system 
 represents the contracting of the downgoing nerve-tracts 
 as they are narrowed into the internal capsule and then 
 taken on to the crura cerebri. (See Fig. 27.) A con- 
 siderable portion of this system, however, terminates in 
 the optic thalami and the striate bodies. 
 
 The principal tract of the commissural system of cerebral 
 fibres is formed in the corpus callosum. This system con- 
 nects the two hemispheres of the brain. That the fibres 
 of the corpus callosum are not wholly commissural, follows 
 from the fact that, since this commissure lies above the 
 plane of the corona radiata, the peduncular system, on its 
 way to the hemispheres, here intersects with the commissu- 
 ral. A smaller commissure (the anterior^ passes below the 
 lenticular nuclei of the striate bodies and connects the con- 
 volutions around the Sylvian fissure. 
 
 The system of arcuate fibres of the cerebrum connects 
 the gray matter of more or less distant convolutions of the 
 same hemisphere. These fibres may often be described as 
 a " garland-like interweaving " of two convolutions around 
 the sulcus between them. In certain localities, where the 
 fascicles into which the fibres are gathered are strongly 
 marked, they have received special names ; such are the 
 fasciculus uncinatus, which crosses the bottom of the 
 Sylvian fissure, the fillet of the gyrus fomicatus, extending 
 longitudinally in that convolution, etc. The function 
 of the arcuate fibres is plainly that of joining into a 
 diversified unity the different portions of each cerebral 
 hemisphere. 
 
STKUCTUEE OF THE SPINAL COBD AND BKAIN. 
 
 PATHS OF NERVOUS IMPULSES IN THE SPINAL COED AND 
 
 BRAIN. 
 
 The foregoing brief description of the cerebro-spinal 
 nervous system shows that it is a mechanism constructed 
 so as to afford " Tracts " or " Paths," to a greater or less 
 degree distinct, for the transmission of nervous impulses. 
 It is, however, only to a very limited degree that histology 
 alone, or even when helped by embryology and pathology, 
 can make out precisely where these paths lie. (Several of 
 those belonging _to the spinal cord, that are more distinctly 
 traceable by the histological method — for example, the 
 pyramidal tract, both crossed and uncrossed, the direct 
 lateral cerebellar tract, the paths of the anterior and of the 
 posterior nerve-roots, etc. — have already been described.) 
 In the brain also it is thought by eminent authorities that 
 certain chains of nervous organs, in which the gray masses 
 are successively connected by nerve-cords between, can be 
 pointed out. With this in view, three collections of nervous 
 matter (the locus niger, and the two nuclei of the striate 
 bodies), with the bundles of nerve-fibres which bind them 
 together, have been called "ganglia of the crusta" by 
 Meynert. Another chain, consisting of the tegmentum, 
 the red nucleus (a collection of large pigmented cells near 
 the Sylvian Aqueduct), the corpora geniculata, and the 
 optic thalami, has been proposed by the same authority. 
 
 It is only, however, when the aid of physiology (patho- 
 logical and experimental) is summoned, that much prog- 
 ress toward certainty can be made in determining paths 
 of nervous impulse within the cerebro-spinal axis. Even 
 with this aid, there is still room for conjecture and uncer- 
 tainty. Anticipating additional evidence which will sub- 
 sequently be more fully described, we now indicate the 
 probabilities concerning certain of these paths. 
 
 Paths in the Roots of the Spinal Cord. — The honor of the 
 
70 PHYSIOLOGICAL PSYCHOLOGY. 
 
 truly " epoch-making " discovery, that the anterior roots of 
 the spinal cord are motor and the posterior, sensory, must 
 be divided between Sir Charles Bell and Magendie. This 
 discovery may be said to have opened the door to modern 
 experimental physiology. The demonstration of the fact 
 is performed by dividing these roots, respectively, and then 
 observing the physiological results. When a posterior root 
 is divided, all the structures supplied by the divided nerve 
 lose their sensibility; while the muscles supplied by the 
 corresponding anterior root continue to be thrown into 
 action by the will and by reflex stimulation. In this case 
 also, stimulation of the central end of the divided root 
 produces sensory effects ; but stimulation of the peripheral 
 end produces no motion. When an anterior root is divided, 
 on the contrary, the muscles supplied by the nerves of this 
 root cannot be made to act by will ; but no sensory paraly- 
 sis is produced. Moreover, stimulation of the peripheral 
 end of the nerve will now throw the muscles into contrac- 
 tion ; but stimulation of the central end will produce no 
 effects. Thus far, then, the paths in the spinal cord may 
 be said to be distinctly traceable. 
 
 Paths in the Anterior Columns of the Cord. — The general 
 arrangement of the motor paths in the anterior part of the 
 spinal cord is maintained throughout. Histology has 
 shown us, however (p. 40), that the two halves of the 
 cord are bound together by the commissures ; this fact sug- 
 gests a crossing, at least partial, from one side to the other, 
 of the nervous impulses. Experiment upon the lower 
 animals seems to show that a partial crossing of the motor 
 paths takes place in the cord. In man's case, most if 
 not all of this crossing from side to side, so far as the 
 paths of voluntary motion are concerned, occurs very high 
 up, if at all, in the spinal cord. But the structure of this 
 organ is such as plainly to provide for an intermingling 
 of the paths of the sensory and the motor roots at about 
 
STRUCTURE OP THE SPINAL CORD AND BRAIN. 71 
 
 the same level. Thus its character as a pile of centres is 
 maintained. 
 
 Paths in the Posterior Columns of the Cord. — In the 
 posterior parts of the spinal cord are the paths by which 
 the sensory impulses chiefly run from the posterior roots 
 up to the brain. These paths also seem to undergo a par- 
 tial crossing from one side to the other in the cord. In 
 the lower animals, according to the evidence of experiment, 
 the sense of feeling is retained after the cord has been cut 
 entirely through from the front to the posterior columns. 
 Stimulation of these columns produces signs of pain and 
 other sensory effects. Some investigators would confine 
 the paths, by which sensory impulses of touch pass along 
 the cord, to the posterior columns ; they would assign 
 to the gray matter of the cord, the paths for impulses giving 
 rise to sensations of pain. Others consider that these 
 columns conduct sensory impulses only so far as the nerves 
 from the sensory roots pass through them ; it is then the 
 gray substance which carries these impulses upward. The 
 conclusions by which some experimenters locate motor, and 
 even voluntary motor, paths in the posterior columns, are 
 extremely doubtful. 
 
 Paths in the Lateral Columns of the Cord. — In these por- 
 tions of the spinal cord both the paths of motor and those 
 of sensory impulses are found. As to the former there is 
 little or no dispute. As to the existence of sensory paths 
 in the lateral portions of the cord, the evidence of experi- 
 ment is somewhat conflicting: but, on the whole, it seems 
 to favor an affirmative conclusion. This conclusion accords 
 well with histology. 
 
 It must be remembered that, when we speak of " paths 
 in the spinal cord," we are not to think of a perfectly fixed 
 and rigid course like that of the iron rails upon which a 
 locomotive runs. No nerve-commotion, when started in any 
 portion of the cord, is necessarily and under all circum- 
 
72 PHYSIOLOGICAL PSYCHOLOGY. 
 
 stances compelled to take one, and only one, path to its 
 destination. Secondary paths, besides the primary and 
 more ordinary paths, exist in abundance. A considerable 
 work of substitution, especially as regards the tracts along 
 which the sensory impulses move, may then take place. 
 Even in the case of the voluntary motor tracts in man, 
 although such a work of " substitution " apparently does 
 not take place, a certain latitude of movement from a 
 straightforward course undoubtedly exists. 
 
 Paths in the Brain. — The evidence already presented 
 from histology indicates that certain tracts, probably motor, 
 pass from the crusta through the internal capsule, without 
 entering the basal ganglia, into the frontal and parietal 
 convolutions. Other tracts, which are probably sensory, 
 run through the tegmentum, enter the thalamus and sub- 
 thalamic region ; then, after being redistributed, emerge to 
 find their way to the temporal and occipital lobes. How 
 well physiological experiment agrees with this general 
 conclusion, we shall see subsequently. 
 
 The paths by which the sensory impulses travel in the 
 brain must be exceedingly intricate ; for the phenomena 
 connected with all sensory disturbances are very compli- 
 cated and often conflicting. For example, if a sensory 
 cranial nerve is severed, the different functions of feeling 
 pain, of pressure, and of temperature, and the power of 
 localization, in the region supplied by that nerve, are all 
 lost. But disease of the cerebro-spinal axis may impair 
 one or more of these functions, and leave the other intact. 
 Again, loss of the sense of temperature and of the mus- 
 cular sense rarely occur separately; but muscular sense 
 frequently disappears and the sensitiveness of the skin to 
 pressure is retained. 
 
 The paths both of motor and of sensory impulses, cross 
 in the region of the pons Varolii and medulla obloiagata. 
 All the paths of both kinds lie very close to each other in 
 
STRUCTURE OF THE SPINAL CORD AND BRAIN. 73 
 
 the white nervous substance surrounding the basal gan- 
 glia. There is considerable recent evidence ^ to show that 
 the tracts followed by impulses of muscular sensation pass 
 through the posterior columns or cornua of the spinal 
 cord, and are gathered into more or less distinct bundles, 
 at the back part of the internal capsule, before they diverge 
 to enter the hemispheres. 
 
 The confidence with which M. Luys, in his work on the 
 " Brain and its Functions," has localized the paths of 
 motor impulses wholly in the striate bodies, and those of 
 the different sensory impulses, olfactory, visual, tactual, 
 auditory, in those four centres of the optic thalami which 
 he distinguishes, cannot be maintained. The tendency of 
 modern investigation is to place more emphasis upon the 
 fibrous nerve-matter surrounding these organs as furnish- 
 ing paths for the conduction of both kinds of impulses. 
 
 Substantially, in its more obvious outlines, as we have 
 described it, but with an infinite and indescribable com- 
 plexity of details, is constructed this marvellous mechan- 
 ism of the nervous system. Some of the more particular 
 functions of its parts will be investigated in other con- 
 nections. But even this description shows its fitness to 
 serve as a physical basis for the equally indefinite and 
 indescribable complexity of the mental life. How many 
 variations of fundamental types do the organs of the phys- 
 ical mechanism display ! And of how many kinds, shades, 
 degrees of intensity, and modes of local coloring, are our 
 sensations and their representative images susceptible ! 
 The immense variety and essential unity of this physical 
 basis suggest a corresponding variety in unity of the 
 psychical life. 
 
 1 Bastian, in Brain, April, 1887, p. 69 f. 
 
CHAPTER III. 
 
 STRUCTURE OF THE ORGANS OF SENSE AND 
 MOTION. 
 
 In the general division of labor among the organs of 
 the nervous system, certain groups of cells at the surface 
 of the body become especially sensitive to external stimuli. 
 These cells accordingly acquire the special function of 
 receiving and modifying the action of such stimuli, and 
 thus of setting up in the conducting nerves a neural pro- 
 cess which is propagated to the central organs. Every 
 " end-organ," therefore, looks both inward and outward. 
 
 Significance and Kinds of End-organs. — The en'd-organs 
 are divided into two classes: first, end-organs of sense, 
 and second, end-organs of motion. The former are in 
 general made up of cells, which, posteriorly, pass into 
 nerve-threads that are gathered into the nerve of special 
 sense ; and which, anteriorly, develop conical or fusiform 
 processes. The simplest type is, then, a hair-like process 
 extending outward and connected by a sensitive cell with 
 a nervous filament extending inward. Only a small part, 
 however, of what are called "the organs of the special 
 senses " belongs to the nervous system. The greater part 
 (as, for example, of the ear, the eye, the skin) consists 
 of mechanical contrivances designed to modify the exter- 
 nal stimulus, while conducting it to the truly nervous 
 mechanism. 
 
 End-organs of Smell. — That portion of the mucous mem- 
 brane of the nose which clothes the upper region of the 
 nasal cavity, and is called regio olfactoria, contains the 
 74 
 
OE6AKS OF SENSE AND MOTION. 
 
 75 
 
 
 end-organs of smell. Two different kinds of cells are 
 here discovered. By Max Schultze and most 
 other investigators, one of these is consid- 
 ered non-nervous and epithelial, the other 
 nervous and olfactory. The epithelial cells 
 are the larger, have an oval nucleus of consid- 
 erable size, and extend through the whole epi- 
 thelial layer. The olfactory cells are spindle- 
 shaped, with a round nucleus, and very fine 
 long processes. Other investigators believe 
 that this difference is not a fixed distinction 
 of kinds, but is rather indicative of different 
 stages of development. The exact relation of 
 the fibrils of the olfactory nerve (which is the 
 specific nerve of smell, and really, in part, a 
 lobe of the brain) to the epithelium of this 
 region is not made out. It seems probable, 
 however, 'that they do not pass directly into factory ceiu and 
 
 ^ J r J EpUheliiil Cells 
 
 the processes of the end-organ cells, but are from the Mucous 
 
 ■*■ o Membrane or the 
 
 lost in a network whose interstices are filled f°^-J",('-- i^^- 
 
 ter Schultze.) 
 
 up with nerve-granules. 
 
 The contrivance for bringing the stimulus to the end- 
 organs of smell is comparatively simple. It is necessary 
 only that a current of air, in which the stimulating parti- 
 cles float, should be drawn over the mucous membrane of 
 the region. Since in expiration the current is carried past 
 th^ sensory parts without striking them, smelling is almost 
 entirely confined to inspiration. When "snuffing," we 
 increase the amount and force of the air drawn into this 
 region, by first creating a partial vacuum in its cavity. 
 
 End-organs of Taste. — On the upper surface of the root, 
 and on the borders and apex of the tongue, and in some 
 cases, on the anterior portion of the soft palate, are found 
 certain papillae. Of those papillae which contain the end- 
 organs of taste two kinds are distinguished ; the circumval- 
 
76 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Fig. 33. — Transverse Section through a Pap- 
 illa Oircumvallata of a Calf. Showing the ar- 
 rangement and distribution of the gustatory bulb. 
 ">/,. (Engelmann.) 
 
 latce and the fungiformes. The circumvallate papillae are 
 composed of connective tissue invested by epithelium 
 arranged in plates (lamince). At the sides where the 
 epithelial layer is thinner, the end-organs of taste form 
 
 a zone which extends up- 
 ward to the level where 
 the papillae are no longer 
 protected by the lateral 
 wall. In the fungiform 
 papillae these organs ap- 
 pear in the epithelium 
 which covers their upper 
 surface, and in the sur- 
 faces of the sides. 
 The Gustatory Flasks. — These structures, sometimes 
 called " gustatory knobs " or " bulbs " occupy flask-shaped 
 cavities in the papillae, which they completely fill. Their 
 lower part rests on connective tissue; their upper part or 
 neck has an opening or pore, of from -^^^ to twi^ inch in 
 diameter. Each flask consists of from fifteen to thirty 
 
 long, thin cells, ar- 
 ranged like the leaves 
 of a bud around its 
 axis. The margin of 
 the pore is formed by 
 bringing several cells 
 together. 
 
 The gustatory flasks 
 also are composed of 
 two kinds of cells, one 
 epithelial, the other ^ms- 
 tatory. The epithelial or " investing " cells are long, nar- 
 row, bent, spindle-shaped, with a nucleus well marked. 
 The outward end is pointed, the central end branching. 
 The gustatory cells are thin, long, and highly refractive of 
 
 Fig. 34. — Gustatory Bulbs from the Lateral Qua 
 tatory Organ of the Babbit, 'v/-^, (Engelmann.) 
 
ORGANS OF SENSE AND MOTION. 
 
 77 
 
 Fig. 35. — a, Isolsited Gustatory Cells, from the Lat- 
 eral Organ of tbe Kabbic; &, an Investing and Two Gus- 
 tatory Cells, isolated but still in connection, '^'^/i. (En- 
 gelmann.) 
 
 light, with nearly the whole body occupied by an elliptical 
 nucleus. The body of the cell is elongated into two pro- 
 cesses ; the upper one of which is broad, but bears a short, 
 fine point, like a stiff 
 hair. This point lies ,» 
 in a canal and rarely 
 projects from the 
 pore of the flask. 
 
 The glosso-pha- 
 ryngeal nerve is the 
 principal nerve of 
 taste ; but the lingual 
 branch of the trige- 
 minus is thought by 
 some to take part in sensations of this sense. The nerve 
 is distributed to the back of the tongue, then enters 
 the papillae where it forms a 
 minute plexus interspersed with 
 nerve-granules. Its connection 
 with the nerve-cells of sense is 
 probably indirect, through this 
 plexus and its granules. 
 
 End-organs of Touch. — The 
 sensory nerves distributed to 
 the skin, the organ of touch in 
 the larger sense of the word, 
 terminate either in free end- 
 fibrils or in special structures 
 called "tactile corpuscles" or 
 " end-bulbs." These special 
 structures have been named 
 after different investigators. 
 The three or four different kinds 
 may, however, be considered 
 as modifications of one type. The first of these structures 
 
 Fig. 36. — Corpuscle of Pacini (or 
 Vater) from the Mesentery of the Cat. 
 (After Frey.) a, nerve with its sheaths; 
 h, system of tunics constituting tbe 
 capsule of the corpuscle ; c, axial canal, 
 in which the nerve-fibre ends. 
 
78 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 to be discovered (more than a htindred and fifty years 
 since, by Vater) was the so-called " Corpuscle of Pacini " 
 (or Vater). These bodies consist of 
 layers of connective tissue, arranged 
 ^ 4ffik l%= concentrically, and most closely 
 packed near the centre. The layers 
 i- J) ""^^ MK surround a cavity containing a soft, 
 nucleated material into which the 
 nerve penetrates. The axis-cylinder 
 of the nerve-fibre which enters the 
 
 The bulb 
 In 
 
 FiQ. 37.— Bnd-bulbs from 
 
 Eje'"'iA^r^mk^Tf, ^^^^ ^® finely fibrillated. 
 
 form'r^coirwHh'n'fhetnd' cousists of granular substance. 
 
 The 'nfr've^fibre of"5 ends ^an these bodies abound in the palms 
 
 within in the form of a knot. ^f ^j^g j^^j^^ ^^^ ^^^ ^^^^^ ^f ^^ie fcct ; 
 
 but especially in the palmar surfaces of the fingers and 
 toes. In some places they are visible to the naked eye 
 
 as a minute grain ^ to ■!■ inch 
 in diameter. 
 
 The "End-bulbs of Krause" 
 are similar to the foregoing 
 structures. They are small 
 capsules of connective tissue 
 in which nuclei can be de- 
 tected, and in which the nerve- 
 fibrils seem to terminate in a 
 coiled mass or bulbous ex- 
 tremity. 
 
 The " Corpuscles of Wag- 
 ner" (or Meissner) are oval- 
 shaped bodies bearing some 
 resemblance to a miniature fir- 
 cone. The nerve-fibres appear 
 like " creeping roots," to wind 
 beneath the papillse of the skin and, interpenetrating 
 them here and there, to terminate in the corpuscles. Within 
 
 Fig. 38. — Corpusclesof Touch. (Af- 
 ter Frey.) a, from the soft skin of the 
 duck's hill ; b and c, from the papillse of 
 the tongue of the same animal. 
 
ORGANS OF SENSE AND MOTION. 79 
 
 the corpuscles, the fibrils are described as forming two or 
 three coils and joining together in loops. Of 400 papillae 
 counted in ^ inch square, on the third phalanx of the 
 index finger, these corpuscles were discovered in 108. 
 They are from -g^y; to Yhs inch long. 
 
 Since the surface of the skin is everywhere sensitive to 
 pressure and to temperature, but these special structures 
 are not found everywhere, it follows that they cannot be 
 the sole organs of touch. As has already been said, the 
 free nerve-fibrils must act as the end-organs of those sen- 
 sations which belong to the whole surface of the body. 
 Research and conjecture have not yet succeeded in assign- 
 ing special functions to any of the varieties of the end- 
 organs of touch. 
 
 STRUCTURE OF THE EYE. 
 
 With the exception of the ear, the end-organ for the 
 sensations of light and color is by far the most elaborate 
 and complicated. It is obviously adapted to be the instru- 
 ment of an intellectual and "geometrical" sense. Con- 
 sidered as a whole, its plan may be stated in one sentence 
 as follows: The Eye is an optical instrument of the 
 nature of a water camera obscura, with a self-adjusting 
 lens, and a concave sensitive membrane of nervous matter, 
 on which an image is formed. Its structure affords a 
 practical solution of several problems. Among these the 
 first is of a purely mechanical sort, and may be called " the 
 problem of protection." 
 
 Coats or Tunics of the Eyeball. — Three coverings sur- 
 round the eye, one of which, in part, acts also as a refract- 
 ing medium. (1) The external coat consists of two parts, 
 (a) the Sclerotic (or " white of the eye ") a firm, fibrous 
 membrane of connective tissue intermingled with elastic 
 fibres ; and (6) the Oornea, or translucent front one-sixth 
 part, which rises and bulges in the middle like a watch- 
 
80 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 glass, and which is covered with conjunctival epithelium. 
 (2) The second coat also consists of two parts, (a) the 
 Choroid, which is of a dark brown color, due to the pres- 
 
 Fig. 39. — Horizontal Section through the Left Eye. Vi- (Schematic, from Gegenbaur.) 
 
 ence of pigment cells ; and (6) the Iris, a circular, disk- 
 shaped diaphragm, in the form of a lens, which is bathed 
 with aqueous humor and has in its centre a circular aper- 
 ture (the "pupil"). The anterior border around the iris 
 consists of the ciliary muscle and the ciliary processes. 
 
ORGANS OF SENSE AND MOTION. 81 
 
 (3) The Retina is the third, or inner coat of the eye. It 
 is a delicate membrane, consisting of nine or ten layers, 
 of exquisite transparency and almost perfect optical homo- 
 geneity. Its inner surface is moulded on the vitreous 
 body, and it extends from the entrance of the optic nerve 
 nearly as far forward as the ciliary processes. 
 
 Befracting Media of the Eye. — The eye has four translu- 
 cent refracting media. These are (1) the Cornea, already 
 spoken of as the anterior one-sixth of the outer tunic of 
 the eye. (2) The Aqueous Humor fills the space back of 
 the cornea and is divided by the iris into two chambers, of 
 which the front one is the larger. It is limpid and watery, 
 but holds certain salts in solution. (3) The Crystalline 
 Lens is situated between the iris and the vitreous body. It 
 is transparent, biconvex, with its antero-posterior diameter 
 about one-third less than the transverse diameter. It con- 
 sists of a capsule and an enclosed body, is of "buttery 
 consistency " and made up, like an onion, ef concentric 
 layers. (4) The Vitreous Humor consists of a number of 
 firm sheets, between which fluid is contained, built into a 
 body that is, optically considered, transparent and nearly 
 homogeneous. It is a gelatinous form of connective tis- 
 sue. Though it occupies most of the bulk of the eyeball, 
 it has comparatively little physiological significance. 
 
 Appendages of the Eyeball. — Of the accessory parts of 
 the eye, — eyebrows, eyelids, lachrymal glands, etc., — only 
 the muscles have any interest to physiological psychology. 
 Of these there are six which are attached to the eyeball, 
 somewhat like a bridle to a horse's head. Four of these 
 muscles spring from the bony wall near the point where 
 the optic nerve enters, extend through the length of the 
 socket, and pass directly to the eyeball, where they are 
 attached to it, — one above, one below, one on the outer, 
 and one on the inner side (the recti ; internal and external, 
 superior and inferior'). The other two muscles of the eye 
 
82 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 are called oblique. The superior internal oblique, instead 
 of running directly to connect with the eyeball, passes 
 through a ring, then turns round, and is attached obliquely 
 
 Fig. 40. — MuBclesof the Left Human Fig. 41. — Muscles of the Left Human Bye, 
 
 Eye, seen from above, rs, rectus supe- seen from the outside, ir, Zevoior of the upper 
 
 rior; re, rectus ezternus ; and H^, rectus eyelid, which covers the rectus superior, rs; 
 
 internus; 08^ superior oblique, with its re, os, as in the preceding figure; ri/", rectus 
 
 tendon i, which runs through the mem- inferior; oi, inferior oblique, 
 branous pulley u, at the inner wall of 
 the cavity of the eyeball. 
 
 to the upper surface. The other oblique muscle begins at 
 the inner wall in the socket, passes under the eyeball, and 
 is attached to it opposite to the superior oblique muscle. 
 
 Formation of the Retinal Image. — The problem which is 
 to be solved by the end-organ of vision, in its most general 
 form, may be stated as follows : A mosaic of localized sen- 
 sations of light and color must he so constructed that changes 
 in the quantity, quality, local coloring, and sequence of these 
 sensations shall be interpreted as the size, shape, locality, and 
 motion of external visible objects. The most important part 
 of the solution of this general problem falls upon the 
 retina. And the most important problem, subordinate to 
 the general problem, is the " formation of an image " upon 
 the retina. But this problem is an optical one. It is solved 
 by the translucent refracting media of the eye. 
 
 The four media of the eye constitute a system of refract- 
 
ORGANS OF SENSE AND MOTION. 83 
 
 ing surfaces, each of which is separated from the one adjoin- 
 ing by a circular cut, as it were, in the whole refracting 
 substance. Thus the "image" of the first refracting sur- 
 face of this system of surfaces becomes an " object," as it 
 were, for the second refracting surface ; the second " image " 
 an " object " for the third surface, and so on. In tracing 
 the coui'se of the rays through these media two things 
 must chiefly be taken into the account. They are (1) the 
 indices of the refraction of the refracting media, and (2) 
 the geometrical form and position of all the limiting 
 surfaces. 
 
 Our knowledge of the indices of the refracting media 
 of the eye is derived by taking the average result of an 
 examination of a number of eyes supposed to be normal. 
 In this calculation the lens is, of course, much the most 
 important of all the media. But the structure of the lens 
 is such (see Fig. 42) that the index of refraction is not 
 
 Fio. 42. — Median Section through the Axis of the Lens of the Eye. (Schematic, after 
 Babuchin.) 
 
 homogeneous throughout. Each layer has its own index, 
 and the amount of the index of each layer increases toward 
 the kernel of the lens. By this contrivance the entire 
 work of refraction done by the lens is made greater than 
 the work which could be done by a homogeneous lens with 
 an index of refraction equal to that of its most highly 
 
84 PHYSIOLOGICAL PSYCHOLOGY. 
 
 refracting part. The mean index for tlie lens of the 
 normal eye may be given = 1.4545. The mean index of 
 refraction for the cornea is given at about 1.3507 ; of the 
 aqueous humor at 1.3365-1.3420; of the vitreous body 
 at 1.3382-1.3485. 
 
 The position and form of the surfaces of the refracting 
 media can be only approximately determined. Three of 
 these surfaces are most important, — namely, the anterior of 
 the cornea and the two surfaces of the lens. The convexity 
 of the anterior surface of the cornea is greater toward its 
 edge than at its vertex, where it resembles a section of an 
 ellipsoid. The images formed when the pupil is expanded 
 are thus made sharper. No observable refraction takes 
 place at the back surface of the cornea. 
 
 Accommodation of the Eye. — The ability to alter the re- 
 fracting conditions of the eye for varjdng distances of the 
 object is called its "power of accommodation." This 
 adjustment obviously cannot take place like that of the 
 photographer's camera obscura, where a considerable change 
 can be made in the distance of the lens from the screen on 
 which the image is formed. It is, in fact, effected by 
 changing the convexity of the lens, — principally, if not 
 wholly, at its anterior surface. This may be demonstrated by 
 several methods of experiment. Indeed, when accommo- 
 dation is taking place, the pupil may be seen to contract 
 and to draw its edge forward. Helmholtz calculated the 
 amount of this movement at j-^ to -^ of an inch. 
 
 The mechanism for accommodation of the eye to varying 
 distances of the objects must be in control of the brain, for 
 the accommodation is voluntary ; it must also consist of 
 muscles that lie within the eyeball. The most generally 
 accepted hypothesis of its action has hitherto been that 
 proposed by Helmholtz. It is assumed that the lens, when 
 at rest, is in a state of tension by its own elastic power. 
 It is kept flattened by the radial tension of the suspensory 
 
ORGANS OF SENSE AND MOTION. 
 
 85 
 
 ligament (sometimes called the zonula, — a structureless 
 membranous body, interposed between the ciliary part of 
 the retina and the vitreous humor, and radiating outward). 
 The mechanism for withdrawing the tension consists of the 
 
 Conjunctiva 
 cgrneac 
 
 Proc. ciliarix 
 
 roAiarer circulixrcr 
 
 Cilianwslcel 
 
 Fie. 43. Sectional View of tbe ConnectionB of the Cornea, Ciliary Muscle, Ciliary 
 FroceBsea, etc. '%. (Gegenbaur.) 
 
 ciliary muscle, the fibres of which are fixed at one end, at 
 the edge of the cornea. When this muscle contracts, the 
 other ends of the fibres are drawn toward its fixed ends ; 
 they thus relax the tension of the suspensory ligament by 
 p ullin g in the opposite direction to this tension, and the 
 lens is allowed to bulge out by its own elastic forces. 
 
 More recent researches, however, seem to emphasize the 
 elasticity of the vitreous body as an important factor in 
 accommodation. For near distances, the contraction of the 
 circular fibres of the ciliary body increases the pressure in 
 the vitreous body, driving it into the spaces at the side 
 of the lens, and bringing the suspensory ligament into a 
 stronger convexity. 
 
 It is the oculo-motor nerve which furnishes in the poste- 
 rior strands of its roots, the fibres that serve the ciliary 
 muscle. Their place of origin is in the back part of the 
 
86 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 floor of tlie third ventricle. This place lies very close to 
 that where stimulation produces contraction of the inter- 
 nal rectus muscle, the use of which is connected with 
 adjustment for near distances. Thus all the mechanism of 
 accommodation is made to work together for the production 
 of the image on the retina. [It is assumed that the laws of 
 optics under which the formation of the image takes place 
 are known, or are to be acquired, from the proper sources. J 
 
 Outer surface. 
 
 ft> — Layer of pigment cells. 
 
 ■ Layer of rods and cones. 
 
 .Membrana limitans externa. 
 
 .Outer nuclear layer. 
 
 — Outer molecular layer. 
 
 y — Inner nuclear -layer. 
 
 . luner molecular layer. 
 
 J ... Layer of nerve-cells. 
 
 ' — Layer of nerve-fibres. 
 
 . .Membrana limitans interna. 
 Inner surface. 
 Fio. 41. — Diagrammatic Section of the Human Eetina. (Schultze.) 
 
ORGANS OF SENSE AND jMOTION. 
 
 87 
 
 i 
 
 H 
 
 Given the formation of the image 
 upon the retina, it is further re- 
 quired, in order to vision, that 
 the proper physiological processes 
 should be set up within this organ. 
 For it is the Retina which contains 
 the nervous elements by whose ac- 
 tion the system of refracted rays 
 is changed into a mosaic of nerve- 
 commotions. We require then a 
 detailed description of the struc- 
 ture of this wonderful organ. 
 
 Layers of the Retina. — The ner- 
 vous and other elements of the 
 / retina are arranged in ten layers, 
 — counting from within outward 
 and backward, — the names and 
 order of which are given in the 
 accompanying schematic represen- 
 tation (see Fig. 44). By no means 
 
 L- all the retinal substance is nervous. 
 Numerous radial fibres, which pene- 
 tra'te its entire thickness, are of 
 connective tissue, in the gaps of 
 which the true nervous elements 
 lie embedded. These gaps are 
 ,, particularly large in the second, 
 U~- third, fifth, and seventh layers. 
 
 Figure 45 shows (diagrammati- 
 cally) the connections of the 
 true nervous elements as they 
 
 (^ extend through the retinal layers. 
 ^ We notice here (a) the retinal 
 fibres of the optic nerve, lying 
 parallel to the surface. They are 
 
 Fio 45 — Diagrammatic representation of the Connections of the Nerve-flbres in the 
 Retina.' (Scbnltze.) The niimbers have the same reference as in rig. 44, 
 
88 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 non-meduUated, extremely fine, arranged in ray-like bun- 
 dles, radiating on all sides from the place of entrance of 
 
 the nerve. Next (6) come 
 the ganglion-cells, resembling 
 the multipolar nerve-corpus- 
 cles of the rest of the cerebro- 
 spinal system, which form the 
 principal part of layer No. 3. 
 These cells at ■^ j| v _|{;/^ Vw^^-rv 
 the " yellow 
 spot" are eight 
 or ten deep, but 
 diminish in 
 number toward 
 
 Fio. 46. — Diagrammatic Section of t^^ Ora ServatU. 
 
 the Posterior Part of the Ketina of a Pig. ^ n 'P'Kq vic^t. 
 
 «»«/,. (Schultze.) 7, part of outer nu- Kyj -l-ne uei- 
 
 clear layer; 8, membrana limitans ex- ._r__,„ cAa-rv^a-ni-o 
 
 terna; 9, rods and cones. Each of the VOUb eiCmenuS 
 
 cones, which are in very close apposition, -.i: i „ "vr a 
 
 contains in its inner segment a highly re- 01 layer 1>I 0. tt 
 fractile body, the function of which is i i -i 
 
 unknown. probably con- 
 
 sist of extremely fine filaments connected 
 with the processes of the ganglion-cells. 
 (d) Each nucleus-like body in No. 5 is 
 thought to be connected by fibres, both in- 
 ward and outward, (e) In the outer molec- 
 ular layer (No. 6) are numerous filaments 
 of nervous character, while its star-shaped 
 cells are probably not nervous. (/) In 
 layer No. 7 are many nucleus-like bodies 
 connected by radial fibres with the nervous 
 elements of the rod-and-cone layer. Accord- 
 ing to their connection they are called rod- |Ss' of^thl surfacl 
 granules and cowe-granules, respectively. ?e°^gths"lff th^tate"- 
 Rods and Cones of the Retina. — The struc- (Scruu™';) T^e 
 ture of layer No. 9 is particularly interesi> °„"r fsTroken 'into 
 ing. It consists of a multitude of elongated ^^b/ren?.'"" "' '"" 
 
 Fig. 47. — Rod and 
 Cone from the Hu- 
 man Ketina, pre- 
 served in perosmic 
 
OEGANS OP SENSE AND MOTION. 
 
 bodies arranged side by side, like rows of palisades. 
 These bodies are of two kinds, — one cylindrical, extend- 
 ing the entire thickness of the layer (^^ inch long), 
 and called "rods"; the other, flask-shaped, shorter, and 
 called " cones." The inner ends of both bodies are 
 supposed to be continuous with the fibres of the outer 
 nuclear layer. Each rod, or cone, is composed of an inner 
 and an outer segment or limb. The inner limb appears 
 under the microscope protoplasmic, and feebly refractile. 
 The outer limb is highly refractile. It has been thought 
 that an extremely minute nerve-filament is drawn through 
 the axis of these bodies. It is assumed that they are con- 
 nected with the fibrils of the optic nerve by means of the 
 retinal nerve-cells and radial fibres. 
 
 In close connection with the rods and cones stand the 
 flat six-fiided cells of the pigment-epithelium. In the cen- 
 tre of the eye only cones appear, which are here of more 
 slender form and increased length ; so that not less than 
 1,000,000 are set in ^ inch square. Not far from the 
 centre each cone is surrounded by a crown-shaped border 
 of rods. Toward the ora 
 serrata the cones become 
 rarer. 
 
 The Yellow-spot and th( 
 Blind-spot. — The place oi 
 clearest vision, and the 
 physiological centre of tht 
 eye, is the "yellow-spot' 
 (macula luted) ; it is of 
 oval shape, about ^ inch 
 long, with a depression in 
 the centre (Jovea centralis). 
 About \ of an inch interior 
 from the middle of this 
 spot is the place where the 
 
 ,S Ch 
 
 Fig. 48. — Bguatorial Section of the Right 
 Eye, BhowiDg the Papilla of the O^tic Nerve, 
 the Blood-vessels radiatiog from it, and the 
 Macula Lutea. y,. (Henle.) B, eclerotlc; Ob, 
 choroid ; and B, retina. 
 
90 PHYSIOLOGICAL PSYCHOLOGY. 
 
 optic nerve breaks into the retina. This place is called 
 the " blind-spot," because it can be shown to be inoper- 
 ative in vision. Its size varies considerably for different 
 eyes (-j-V to -^ inch long). It is wanting in all the ner- 
 vous elements. 
 
 Photo-chemical Processes in Vision. — The physiological or 
 nervous process concerned in vision can be shown to 
 begin in the rods and cones at the back part of the retina. 
 Indeed, by throwing a strong light through the cornea, 
 and causing it to be reflected within the eyeball before it 
 reaches the nervous elements of the retina (an experiment 
 devised by Purkinje), it is possible to perceive the arbores- 
 cent figure formed by the shadow of the blood-vessels 
 expanded on the front part of our own retina. Yet the 
 rods and cones are not directly irritable by light, so as to 
 produce visual sensation, — at least, not unless the inten- 
 sity of the stimulus be so great as to be injurious to the 
 nervous substance itself. How, then, can we see the 
 feeblest rays of the moon as reflected from white paper? 
 A photo-chemical process has accordingly been assumed 
 to result from the direct action of the light ; and this 
 process it is which acts as the immediate stimulus of the 
 nervous elements. 
 
 Yet after many careful experiments, especially by Kiihne 
 and his pupils, it is difficult to establish the nature of the 
 photo-chemical process concerned in vision, or of the par- 
 ticular pigments upon effecting changes in which the pro- 
 cess is dependent. Any theory involves, chiefly, these two 
 things : fiist, the decomposition by the light of some sub- 
 stance found in the epithelial elements of the retina ; and, 
 second, the action of the decomposition-products thus 
 gained upon the protoplasm of the nervous end-organs. 
 There seem to be decisive objections against making the 
 pigmentum nigrum, or the "visual purple," or any other 
 known pigment, the only substance whose decomposition 
 
ORGANS OF SENSE AND MOTION. 91 
 
 by the light is necessary to vision. And as to the nature 
 of the changes produced in the rods and cones by the 
 decomposition-products of any pigment, we are really igno- 
 rant. A photo-chemical theory of vision seems, therefore, 
 to be a desideratum rather than a scientifically established 
 and definite fact. 
 
 The most patent thing revealed by the structure of the 
 eye is its adaptation to serve as the organ of a highly differ- 
 entiated system of intellectual and " geometrical " sensory 
 impressions. The fuller significance of this truth cannot be 
 understood until we have made a detailed study of those 
 series of sensations — infinitely varied, delicately shaded, 
 quickly successive, and speedily and firmly fusing together, 
 as it were — which result from the activity of this organ 
 of sense. 
 
 STRUCTURE OF THE EAR. 
 
 The End-organ of Hearing, like that of vision, so far as 
 the principal part of its bulk is concerned, consists of 
 mechanical contrivances for applying the stimulus to the 
 genuine nervous elements of the special sense. The true 
 end-organ is the mechanism of epithelial and nervous cells 
 which is connected with the terminal fibrils of the special 
 nerve of this sense. A brief description of the non-nervous 
 structure is, however, desirable for our purpose. 
 
 The entire Ear consists of three parts, or ears; these 
 are the external ear, the middle ear, or tympanum, and 
 the inner ear, or " labyrinth," as its complicated structiire 
 causes it to be named. 
 
 I. The External Ear. — Exclusive of the plate of carti- 
 lage which projects from the side of the head, the external 
 ear consists of two parts. These are the concha and the 
 external meatus. (1) The concha is a rather deep hollow 
 of a shell-like shape. It is probably of little or no use in 
 sharpening our acoustic perceptions ; although it appears 
 
92 PHYSIOLOGICAL PSYCHOLOGY. 
 
 to be of some service in discerning the direction of sound. 
 (2) The external meatus is a curved passage leading from 
 the bottom of the hollow of the concha to the drum of the 
 ear. Its most obvious office is the protection of the ear- 
 drum ; though it may also modify certain tones by its own 
 resonant action, — strengthening the high ones and dead- 
 ening the low, in some degree. 
 
 If we place a resounding body iu contact with the teeth, 
 the intensity of the sensation of sound is much increased. 
 This appears to us to be due to direct conduction through 
 the cranial bones ; but it is more probable that the 
 principal path of conduction is indirect, through the ear- 
 drum and small bones of the middle ear to the fenestra 
 ovahs. 
 
 II. The Middle Ear, or Tympanum. — This part of the or- 
 gan of hearing is an irregular cuboidal chamber, situated 
 in the temporal bone, between the bottom of the meatus 
 and the inner ear. Its outer wall is the membrana tympani 
 
 or " drum " of the ear. In the 
 
 inner wall, which separates it 
 
 from the labyrinth, are two 
 
 1 openings called "windows" 
 
 — the fenestra ovalis and the 
 fenestra rotunda. Near its 
 anterior part it opens into 
 the Eustachian tube. And 
 an irregular chain of bones 
 
 — called auditory hones — 
 
 Fie.49.-Drumof the Right Ear with S*^^**'^^^ ^''^OSS the Cavity 
 
 fH^Se7™?;Sda*ty4aniftBu:6: ^^^^^ ^^s outcr to its inner 
 
 chian tube; *, tendon of the tensor tym- Tvall 
 
 pani muscle out off close to its insertion ; 
 
 ma, anterior ligament of the malleus ; Mcp, rri,- TVTo-mlirQTiQ TTrm-nani ai- 
 
 its head; and Ml, its long process. Stp, ■'■^^ memorana lympaiU, OP 
 
 Spir^ tympanica posterior. jj^,^ ^^ ^^^ jjg^j. _ rpj^-g ^^^_ 
 
 brane consists of three layers, — an external, and internal 
 mucous, and the intermediate membrana propria. The 
 
ORGANS OF SENSE AND MOTION. 93 
 
 last is the true vibrating membrane, and is composed of 
 unyielding fibres arranged both radially and circularly. 
 
 A flat membrane, evenly stretched, whose mass is small 
 in proportion to the size of its surface, is easily thrown 
 into vibration by acoustic waves striking against one of its 
 surfaces. It responds readily to tones which approach its 
 own fundamental tone, but is scarcely at all affected by 
 divergent tones. Such a membrane, therefore, cannot 
 repeat a motion which consists of a series of harmonious 
 partial tones. In order to perform such a service, a mem- 
 brane must be so arranged and connected as to have no 
 preponderating tone of its own. For this the ear-drum is 
 prepared by two devices : (1) It is drawn inward into a 
 funnel-shaped form by being attached to one of the auditory 
 bones (the handle of the malleus) ; and (2) it is loaded 
 with a chain of bones so as to have no trace of a tone of its 
 own (see Fig. 60). Thus is secured for it the property of 
 taking up the vibrations of a large scale of tones. 
 
 Moreover, since the apex of its funnel bulges inward, 
 the ear-drum serves to concentrate the force of the vibra- 
 tions from all sides. Loading it with the auditory bones 
 serves also to dampen its vibrations and prevent them from 
 continuing too long. This gives speed to the rate at which 
 definite auditory sensations can be repeated. 
 
 The Eustachian Tube. — This opening from the middle 
 ear into the mouth is of indirect but important physiolog- 
 ical service to auditory sensations. In its normal position 
 the tube is neither closely shut nor wide open. When we 
 swallow, it opens and thus effects a renewal of air in the 
 middle ear, maintains an equilibrium of pressure on both 
 sides the drum, and conveys away the fluids that collect 
 in its cavity. But if it remained constantly wide open, we 
 should be likely to hear our own voices as a roaring sound, 
 and the passage of the air in and out during respiration 
 would effect the tension of the drum. 
 
94 PHYSIOLOGICAL PSYCHOLOGY. 
 
 The Auditory Bones. — The chain of bones which stretches 
 across the tympanic cavity consists of three members, — the 
 Malleus ("hammer"), the Incus ("anyil"), and the Stapes 
 (" stirrup "). The malleus has a head separated by a con- 
 stricted neck from an elongated handle. The latter is 
 attached to the centre of the membrana tympani. The 
 incus has a body and two processes. On the front surface 
 of its body is a saddle-shaped hollow. Its short process is 
 bound by a ligament to the posterior wall of the tym- 
 panum. Its long process ends in a rounded projection (^os 
 orbicular e). The stapes has a head and neck, a base and 
 two crura. These are put together so as to give it the 
 stirrup-shape, which its name implies. The manner in 
 
 which these bones articulate 
 may be fairly well seen by 
 the accompanying - figure 
 (No. 50). 
 
 The auditory bones are 
 moved on each other at their 
 joints by two or three mus- 
 cles, — especially by the ten- 
 sor tympani. This muscle is 
 inserted into the malleus, 
 Y ' near the root, and serves to 
 
 FIG. 60. -Bol. of the Ear, as seen m ^^g^^^^ the tympanic mcm- 
 i'STanv;?r/o7wSir?b-iyVhfslt;! brane by drawing the malleus 
 
 and II the long, process ; c, Us body, and irrnrnrrl TVip npmietif" TriVirn. 
 
 pi. the process for articulation with the mwaru. ±ne aCOUStlC VlDra- 
 
 Bi&pes (processus orbicularis). M, Mai- fi„„(, imnnrtprl >nr +Tio Tnom 
 
 leus (hammer), of which Mc is the neck; llOUS, impariea Dy tUC mCm- 
 
 Mep, the head; Ml, the long process; and 1,^5,^,0 tn tVip«p hnnps nrp Tint 
 
 Mm, the manubrium; S, stapes (stirrup), UiaUBLU uneht! UUntJh, die UOl 
 
 with its capituium,cp. longitudinal but transverse. 
 
 They do not, however, resemble the vibrations of a stretched 
 cord or a fixed pin. The bones vibrate as a system of light, 
 small levers, with a simultaneous motion around a common 
 axis. The vibrations are sympathetic, and vary greatly 
 for tones of different pitch and similar intensity. 
 
OEGANS OP SENSE AND MOTION. 
 
 95 
 
 General Office of the Middle Ear. — By this part of the 
 organ of hearing the acoustic waves are transmitted to the 
 inner ear, while their character is greatly modified. Mod- 
 ification is necessary to prepare the stimulus for the organ- 
 ism of the inner ear. The waves in the air, when they 
 reach, the ear-drum, have a large amplitude but a compara- 
 tively small intensity. Their motion must be changed 
 into one of diminished amplitude and increased intensity. 
 But the transmitting, vibrating media must also have the 
 power of answering to the different tones of any pitch 
 perceptible by the ear. 
 
 m. The Internal Ear, or Labyrinth. — It is in this mar- 
 vellously complex organ that the terminal fibrils of the 
 auditory nerves are distributed and the end-organs of hear- 
 ing are placed. It consists of three parts — the Vestibule, 
 the Semicircular Canals, and the Cochlea. Each of these 
 parts is, as it were, made twice over — once in the form of 
 channels cut in the petrous bone (the osseous vestibule, 
 etc.), and again in the form of a membrane (the membra- 
 nous vestibule, etc.) suspended in the bony cavity, but only 
 partly filling it. 
 
 No. 3. 
 
 ■vpj 
 
 Fio. 51. — No. 1, OsaeouB Labyrinth of the Left Ear, from below; No. 2, of the 
 Bight Ear, from the ioside ; No. 3, of the Left Ear, from above. (Henle.) Av, aque- 
 duct of vestibule ; Fc, fossa of the cochlea ; Fee, its fenestra (rotunda) ; Fv, fenestra 
 of the vestibule (ovalis); ha, external ampulla; h, external semicircular canal; Tsf, 
 tractus spiralis forammosus ; vaa, ampulla of the superior semicircular canal; vc, pos- 
 terior semicircular canal ; and vpa, its ampulla. 
 
 (A) The Vestibule of the Ear. — The central cavity of 
 the inner ear, called -the "vestibule," is the earliest 
 
96 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 and most constant part of the labyrinth. In its outer wall 
 is the fenestra ovalis ; its anterior wall communicates with 
 the scala vestihuli of the cochlea. The membranous vesti- 
 bule is composed of two sac-like dilatations — the upper 
 and larger called utriculus, the lower saoculus. 
 
 (B) The Semicircular Canals. — These curved channels 
 open into the utriculus. They are three in number, 
 about one inch in length and ^V iiich in diameter. They 
 have a regular relative position — their planes being at 
 right angles to each other — as indicated by their names 
 — superior, posterior or vertical, and external or horizon- 
 tal (see Fig. 51). Near the vestibule they dilate into the 
 so-called ampullce. 
 
 Both the osseous vestibule and the osseous canals contain 
 a fluid (^perilymph') in which the corresponding membra- 
 nous parts — themselves 
 distended with a fluid (ew- 
 dolympK) — are suspended. 
 The oifice of this fluid is 
 very important in the trans- 
 mission and further modi- 
 fication of the acoustic 
 waves. 
 
 ((7) The Cochlea. — This 
 wonderful organ is shaped 
 like the shell of a common 
 snail, about \ inch long. 
 It, too, consists of a mem- 
 branous sac in an osseous 
 cavity. The whole passage 
 is imperfectly divided into 
 two canals by a partition- 
 wall of bone (the lamina 
 spiralis'), which winds 2^ 
 times around an axis (the modiolus'), like a spiral staircase* 
 
 Fee 
 
 Fis. 52. — OsBeouo Cochlea of the Right 
 Ear, exposed from in front. Vi- (Henle.) 
 t, section of the division-wall of the cochlea; 
 tt» upper end of the same; Fee, fenestra; 
 H, hamulus; Md, modiolus; Ls, lamina spira- 
 lis. 
 
ORGANS OP SENSE AND MOTION. 
 
 97 
 
 Uj/amenttiiii 
 spiratt 
 
 Stria 
 vascularis 
 
 Lamina 
 iaailarii 
 
 Of these canals, the one which faces the base is called scala 
 tympani; the other, which opens into the vestibule is the 
 scala vestihuli. At 
 the apex they com- 
 municate through 
 a small hole (the 
 helicotremdy. From 
 the free edge of 
 the spiral lamina 
 to the outer wall 
 the interval is 
 bridged over by 
 the basilar mem- 
 brane. Still another 
 
 membrane (memr Fio. 53. — section through one of the Colls of the 
 
 brane of Reissner-) *""'"'''■ "^^ (s^'-^'-' "- ^egenbaur.) 
 arises from a crest attached to the same lamina and ex- 
 tends to the outer wall, so as to make a minute canal 
 between itself and the basilar membrane. In this canal 
 — called scala intermedia, or ductus cochlearis, or " canal 
 of the cochlea " — the nervous end-organs of the cochlea 
 are found. 
 
 The Organ of Corti. — On that surface of the basilar mem- 
 brane which is directed toward the small canal of the 
 cochlea is placed a structure which consists of a wonder- 
 ful arrangement of cells. Some of these cells are curved, 
 elongated, and placed in two groups — an inner and an 
 outer (rods, ot fibres of Corti). The two are arranged (as 
 shown by Fig. 54) so as to make a bow or arch over an 
 exceedingly minute canal (canal of Corti) between them 
 and the basilar membrane. These rods of Corti increase 
 in length from the base to the apex of the cochlea. Each 
 rod rests upon one or two of the transverse fibres of the 
 basilar membrane. The Organ of Corti is separated from 
 the endolymph of the, ductus cochlearis by the so-called 
 
98 
 
 PHYSIOLOGICAX, PSYCHOLOGY. 
 
 membrana tectoria. (For the shape and position of the 
 "hair-cells," inner and outer, the supporting cells, etc., 
 see the accompanying diagrammatic representation.) 
 
 Fio. 54. — Organ of Corti in the Dog. ^^/x. (Waldeyer.) 6 — c, homogeneous layer 
 of the basilar membrane; u, its vestibular layer; v, its tympanal layer; d, blood-vessel; 
 /, nerves in spiral lamina ; g^ epithelium of spiral groove ; A, nerve-hbres passing toward 
 inner hair-cells z, X;; Z, auditory hairlets on inner hair-cells; I — Zj lamina reticularis; m, 
 heads of the rods of Corti jointed together; the iuner rod seen in its whole length; the 
 outer one broken off; n, cell at base of inner rod; p, q, r, outer hair-cells; s, a cuticular 
 process probably belonging to a cell of Belters ; i, lower ends of hair-cells, two being 
 attached by cuticular processes to the basilar membrane; w, a nerve-fibril passing into an 
 outer hair-cell; z, a sustentacular cell of Belters. 
 
 Distribution of the Auditory Nerve. — The auditory nerve, 
 on approaching the labyrinth, divides into several portions. 
 In the vestibule, branches are distributed to the utriculus, 
 the sacculus, and each of the three ampullae. In a ridge in 
 the wall of each of these dilatations (the crista acoustica) 
 columnar and fusiform cells are found, with processes from 
 the latter of which the fibrils of the auditory nerve are 
 brought into connection, — probably by means of that 
 minute network of fibrils with which we have already 
 become familiar in the other end-organs of sense. The 
 so-called " auditory hairs " are found by recent observers 
 to be connected with the columnar cells ; they form, on the 
 inner surface of the epithelium of the ridge a " thick-set 
 
ORGANS OF SENSE AND MOTION. 
 
 wood." Calcareous particles exist (the otoliths or "ear- 
 stones ") in both saccule and utricle, lying embedded in 
 contact with the nerve-epithelium. 
 
 The cochlean 
 branch of the audi- 
 tory nerve pierces 
 the modiolus and 
 gives off lateral 
 branches which pass 
 into channels in the 
 osseousspirallamina. 
 Here the fibres radi- 
 ate to the membra- 
 nous lamina and are 
 connected with a 
 ganglion of cells. 
 Beyond this gangli- 
 on they lose their me- 
 dullary sheath, and 
 become extremely 
 fine axis-cylinders, 
 the delicate fibrils 
 of which are proba- 
 bly connected with 
 the nerve-plexus of 
 the fibrils from the cone-cells of the organ. 
 
 Special Office of the Labyrinth. — The greater bulk of the 
 inner ear, like the whole of the other principal parts, is 
 used to transmit and modify the acoustic waves. We have 
 seen that the membranous labyrinth is filled with, and sus- 
 pended in, a fluid medium. Molecular oscillations of this 
 fluid can scarcely, however, serve as the direct stimulus of 
 the nerve-elements. Its dimensions are so very small in 
 comparison with the length of the acoustic waves as trans- 
 mitted by the shocks of the stirrup at the fenestra ovalis, 
 
 pulla 
 
 Fio. 55. — Scheme of the N'erve-endiQgs in the Am- 
 illse. (After Budinger.) 1, membranous wall of the 
 ampullae, with a Btructureless border 2, through which 
 the nerve-fibre 3, sends its axis-cylinder 4; 5, plexiform 
 connection of the nerve-fibres; 6, auditory cells; 7, sup- 
 porting cells; 8, auditory hairs. 
 
100 PHYSIOLOGICAL PSYCHOLOGY. 
 
 or the pulsations of air at the fenestra rotunda, that the 
 movement of the entire fluid mass would be practically 
 instantaneous. Several places may be pointed out, how- 
 ever, into which the waves of the fluid could retreat, by 
 the membranes yielding, or by itself running into pores and 
 through the passages connecting the various parts. The 
 friction of these movements back and forth, especially when 
 increased by the action of the otoliths, might thus irritate 
 the nerve-elements. The basilar membrane would undoubt- 
 edly be thrown into vibration by the unequal pressure of 
 the fluid, and thus the nervous structures situated upon it 
 might be irritated. In all this, however, much is still a 
 matter of doubtful conjecture. 
 
 A still more difficult question to answer is this : How 
 does the ear manage to analyze the acoustic influences? 
 This organ plainly is not contrived so as to reproduce 
 changes in the form of acoustic oscillations in such manner 
 that these changes can be made apparent to the eye or to 
 touch. But our experience with " clangs," or the musical 
 notes of ordinary kind, seems to require that we should 
 find in the ear some sympathetic vibratory apparatus. 
 Such apparatus must suffice for all kinds of noises, and for 
 all musical tones, and for simultaneous hearing of several 
 tones as harmony, and for so rapid a succession of different 
 sensations as occurs when we hear a melody, or even the 
 crackling of an electric spark at intervals of 0.002 sec. 
 
 It has been for some time commonly assumed that the 
 vestibule and semicircular canals are the organs for hear- 
 ing noises, and the cochlea for hearing musical sounds. 
 This differentiation of function is certainly suggested by 
 the marked differences in the structure of their parts. 
 The otoliths and hairs of the former do not seem adapted 
 for regular sympathetic vibrations. The rods of Corti and 
 radii of the basilar membrane suggest that here is the 
 apparatus needed for acoustic analysis. 
 
ORGANS OF SENSE AND MOTION. 101 
 
 Recent investigations, however, tend to show that the 
 physiological distinction between noises and sounds will 
 not hold with sufficient rigor. The two seem to pass into 
 each other by insensible gradations. It has been found 
 possible to make a series of sharp noises, like a watchman's 
 rattle, as often as 600 times per second, without producing 
 a musical tone, if all extra accompanying sounds are com- 
 pletely dampened. On such grounds it has been concluded 
 that we hear noises and tones with the same organ. 
 
 It was first argued by Helmholtz that the fibres of Corti 
 — some 3000 in number and arranged in rows on the 
 basilar membrane like the keys of a piano-forte — are 
 just suitable for the required sympathetic vibrations. 
 But these rods are stiff and not easily vibratory, and their 
 office seems to be that of supporting the hair-cells. Birds, 
 moreover, can appreciate musical notes but have no rods of 
 Corti. It has therefore been proposed by Hensen and others 
 to regard the radii of the basilar membrane as themselves 
 graded to pitch. These radii, by moving up and down, 
 might excite the conical hair-cells, whose number is sup- 
 posed to be about sufficient to satisfy the demands of 
 musical analysis. More recently still, it has been conjec- 
 tured that, since the arches of Corti at the base of the 
 cochlea are small and little spread, and those at the upper 
 end are larger ajid much spread, the size and the shape of 
 these structures may approximately compensate each other ; 
 this would make it possible for all of the arches to vibrate 
 to each of the fibres of the basilar membrane (like the 
 sounding-board of a piano). 
 
 We are obliged to confess that our knowledge of the 
 minutest structure of the ear, and especially of the manner 
 in which it performs its functions, is exceedingly frag- 
 mentary. As one principal investigator remarks: "It 
 is possible that the working of this apparatus may be 
 altogether different from any of our present conjectures." 
 
102 PHYSIOLOGICAL PSYCHOLOGY. 
 
 END-ORGANS OF MOTION. 
 
 The motor nerves of animals have their peripheral con- 
 nection with either electrical organs, or secretory glands, 
 or muscular fibre. A very brief consideration of the last 
 case, only, will suf&ce for our present purpose. 
 
 After a motor nerve has entered the substance of the 
 so-called voluntary or striated muscle it breaks up into 
 nerve-twigs between the muscular fibres. The axis-cyl- 
 inders of the nerve-twigs lose their medullary sheath, and 
 subdivide into fibrils, which form a flat branching mass 
 within certain disk-shaped bodies inside the sheath of the 
 muscle-fibre (the sarcolemma). These bodies are the so-called 
 " motor end-plates." In the non-striated (or non-voluntary) 
 muscles, the nerves subdivide into very minute plexuses 
 of nerve-fibres, which are distributed in the connective 
 tissue that separates the muscular fibres. 
 
 The shape and structure of the motor end-plates are 
 different for different animals, and even for different mus- 
 cles of the same animal. The mode of the termination of 
 the nerve in the muscle is thought to be somewhat dis- 
 tinctive of the different parts of the muscular structure. 
 Sometimes the axis-cylinders are enlarged, with granular 
 corpuscles attached or adjacent. Sometimes a granular 
 mass, with its nuclei, forms a kind of floor for the terminal 
 nerve-fibres ; and this eminence may be either elongated, 
 elliptical, or circular. 
 
CHAPTER IV. 
 DEVELOPMENT OF THE NERVOUS SYSTEM. 
 
 In that living germ, in which the life of the indi\ddual 
 human being originates, there is no apparent distinction of 
 bodily organs, or of physical and psychical activities. To 
 scientific observation this germ seems " undifferentiated." 
 But it undergoes a development, and before it can be sub- 
 jected to ordinary observation it has unfolded itself into 
 an elaborate organism. The course of this development 
 . can be traced, in man's case, only very imperfectly by even 
 the most patient embryological investigation. 
 
 Fortunately, however, the very first things in the life of 
 the other mammals, and even of the chick (the most con- 
 venient subject of study for embryology) are in most 
 important respects similar to those of man's earliest devel- 
 opment. This knowledge, indirectly derived, is constantly 
 being more and more supplemented by direct microscopic 
 inspection of the human embryo, at various stages in its 
 life. Thus a sketch of the principal outlines of man's 
 pre-natal evolution is made possible. A few points selected 
 from such a sketch, and having reference especially to the 
 nervous system, furnish helpful suggestions with regard to 
 certain questions in physiological psychology. 
 
 EARLIEST DEVELOPMENT OF THE BODILY LIFE. 
 
 The following brief description of the earliest develop- 
 ment of the animal body is chiefly taken from the detailed 
 embryology of the common fowl.^ 
 
 1 For further study of this subject, Foster and Balfour's Elements of 
 Embryology, London, will probably be found most accessible and ser- 
 viceable. 
 
 103 
 
104 PHYSIOLOGICAL PSYCHOLOGY. 
 
 The Ovarian Ovum. — The immature egg (ovarian ovum) 
 of any animal presents the characters of a simple cell. It 
 appears as a naked protoplasmic body containing in its 
 interior a nucleus (^germinal vesicle^, and within this a 
 nucleolus (the germinal spof). It is enclosed in a capsule 
 of epithelium called the " follicular membrane." The 
 principal difference between the ovum of a mammal and 
 that of a bird consists in the amount and distribution of 
 the food-yolk. The human ovarian ovum is only -j-sr to 
 j-5-5^ inch in diameter, because it contains so little food- 
 yolk ; but this small supply is uniformly distributed. 
 
 As the ovum matures, its body grows in size, and gran- 
 ules appear in the interior. As these -earliest granules 
 enlarge, others appear at the periphery. The germinal 
 vesicle travels toward the surface, and accessory germinal 
 spots make their appearance. The cells of the follicular 
 membrane — at first a single row — now become two or 
 three deep. The superficial layer of the ovum is converted 
 into a striated membrane. Between this and the cells of 
 the follicular membrane another membrane (the vitelline) 
 afterward appears. The striated membrane disappearing, 
 the vitelline remains alone. But the essential constituent 
 of the body of the ovum is an active, living protoplasm. 
 
 Impregnation and Segmentation. — The spermatozoon, or 
 male fecundating element, may itself be considered as a 
 cell, the nucleus of which is its head. Impregnation 
 takes place by the entrance of a spermatozoon into the 
 ovum, followed by the fusion of the two. On entering, 
 the substance of the tail of the spermatozoon mingles with 
 the protoplasm of the ovum, while the head enlarges and 
 also fuses with a portion of the ovum, thus constituting 
 the nucleus of the impregnated egg. In this actual fusion 
 of substance derived from both parents, provision is made 
 that the offspring shall partake of the physical and psy- 
 chical characteristics of the two. 
 
DEVELOPMENT OF THE NERVOUS SYSTEM. 105 
 
 Segmentation, or " yolk-cleavage," follows fecundation of 
 the ovum. This process consists in dividing the ovum 
 into a number of cells from which all the cells of the full- 
 grown animal are the lineal descendants. The germinal 
 disk of the ovum is thus broken up into a large number of 
 rounded segments of protoplasm, called the blastoderm. 
 The upper segments being smaller than those beneath, the 
 beginning of two layers is thus made. This distinction 
 is then made more obvious by the segments of the upper 
 layer arranging themselves side by side into a membrane 
 of columnar, nucleated cells; but the segments of the 
 lower layer continue granular, and form a close, irregular 
 network of cells. 
 
 As the process of segmentation goes on, the differences 
 among the ova of different species of animals become more 
 clearly marked. The mechanical explanation of this is, in 
 part at least, the difference in the amount and distribution 
 of the food-yolk. 
 
 The Blastodermic Vesicle. — A narrow cavity now appears 
 between the two layers of the ovum, which soon extends 
 so as to separate them completely, except in the region 
 near a small circular area. In this area the inner mass of the 
 ovum has remained longer than elsewhere exposed, before 
 the outer cells closed over it. The enlargement of the 
 ovum, and of the cavity between the layers, gives the 
 whole structure the appearance of a vesicle vdth a thin 
 wall. It is therefore now called the blastodermic vesicle. 
 Its walls are for the most part composed of a single row of 
 outer flattened cells ; while an inner lens-shaped mass of 
 cells appears attached to a portion of the inner side of the 
 outer layer. As the vesicle grows rapidly, this inner 
 mass becomes, on the whole, flattened so as to spread out 
 on the inner side of the outer layer. But its central part 
 remains thick, and forms an opaque spot, which is the 
 beginning of the area where the embryo is to form (the 
 embrt/onic area"). 
 
106 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Fig. 56. — Vascular Area and Embryonic Area of the Embryo of a Babbit, seven days 
 old. ^/i. (KSlliker.) 0, o, the vascular or opaque area; ag, embryonic area; pr, 
 primitive Streak and groove; rf, medullary groove. 
 
 The Three Layers of the Embryo. — In tlie area just 
 described there are first formed two distinct strata. Of 
 these, the upper one consists of rounded cells, which lie 
 close to, and become fused with, the flattened outer layer ; 
 it is then called epiblast. The lower one consists of 
 flattened cells, and is called hypoblast. We have thus a 
 double-walled sac (the gastruld). Between these two 
 strata, or layers, a third soon makes its appearance ; from 
 its position it is called mesoblast. 
 
 These three layers are found in the embryo of all ver- 
 tebrate, and of most invertebrate, animals ; and from them 
 all the different parts of the animal organism are developed. 
 The history of the life of every animal, thus constituted, 
 is in its earlier stages a history of the evolution of these 
 layers. The hypoblast is the secretory layer ; and from it 
 almost all the epithelial lining of the alimentary tract, and 
 
DEVELOPMENT OF THE NERVOUS SYSTEM. 107 
 
 of its glands, is derived. From the mesoblast come the 
 skeletal, muscular, and vascular systems, and the connec- 
 tive tissue of all parts of the body. But it is the develop- 
 ment of the epiblast which most concerns us. For from 
 it is evolved the central and peripheral nervous system, 
 the epidermis, and the most important parts of the organs 
 of sense. 
 
 From the beginning, then, the skin in which the end-organs 
 of touch and of the other sensations are situated, as well as 
 all the organs of special sense, constitute, with the brain and 
 spinal cord, one interconnected mechanism. 
 
 DEVELOPMENT OF THE NERVOUS SYSTEM. 
 
 The process of differentiating the layers of the blasto- 
 derm is intimately connected with another, in which the 
 foundations, as it were, of the nervous structure are laid. 
 This is — 
 
 The Formation of the Medullary Groove. — A short sickle- 
 like thickening, due to a forward propagation ("linear 
 
 Pf ,_ Pt 
 
 s 
 
 s 
 
 Fie. 97. — Primitive Streak of tbe Embryo of a Babbit, eight days and nine hours old. 
 2™/i. (Kolliker.) No medullary groove has yet been formed, ax, primitive streak ; pr, 
 primitive groove; pf, primitive fold; ect, ectoderm (or epiblast); mes, mesoderm (or 
 mesoblast); en<, entoderm (Aj^oMosO. 
 
 proliferation ") of epiblastic cells in a straight line, occurs 
 near the junction between the pellucid and the opaque 
 areas, and stretches inward upon the embryonic area. It 
 is called the primitive streak. Its middle line then shows 
 
108 PHYSIOLOGICAL PSYCHOLOGY. 
 
 a shallow furrow called the primitive groove (see Fig. 57). 
 In the embryonic area, to the front of the primitive streak, 
 the axial part of the epiblast thickens; two folds arise 
 along the boundaries of a shallow groove ; the folds meet 
 in front but diverge behind, enclosing between them the 
 front part of the streak. These are the medullary folds, — 
 the first definite features of the embryo. 
 
 The part enclosed between the medullary folds is called 
 the " medullary plate " ; it is the portion of the epiblast 
 which gives rise to the central nervous system. 
 
 The Notochord and the Neural Canal. — Meanwhile an 
 important change has taken place in the hypoblast, in 
 front of the primitive streak. An opaque line has ap- 
 peared, running forward from the front end of the streak, 
 and stopping short at a semicircular fold near the front part 
 of the pellucid area. This opaque line is a concentration 
 of cells in the form of a cord, — the so-called Notochord. 
 Changes in it are to give rise to the distinctively vertebral 
 structure of the animal. The fold is the future head-fold. 
 
 And now a portion of the blastoderm in the pellucid 
 area, heretofore nearly flat, is " tucked in," with the form 
 of a crescent. Looked at from above, this tuck appears as 
 a curved line along the margin of the medullary groove. 
 Thus the blastoderm becomes at this spot folded in the 
 form of the reversed letter 2 (the "head-fold" already 
 referred to). The upper limb of the fold grows forward, 
 the lower backward. As the fold enlarges, the crescentic 
 groove deepens and its overhanging margin rises above the 
 level of the blastoderm. . 
 
 Meanwhile the medullary folds increase in height and 
 lean over toward the middle line. They soon come into 
 contact in the brain-region, although they do not at once 
 coalesce. They thus form a tubular canal, called the 
 Neural (or medullary) canal. By the closing of the folds 
 in the head-region, the open medullary groove has now 
 
DEVELOPMENT OP THE NERVOUS SYSTEM. 
 
 109 
 
 The front end of the 
 
 ■A bl 
 
 become converted into a tube, which is closed in front but 
 remains open behind. 
 
 Formation of the Cerebral Vesicles, 
 neural canal has a more rapid 
 growth than the rest. It 
 swells into a small bulb or 
 vesicle, whose cavity is con- 
 tinuous with the neural canal, 
 while its walls are formed of 
 the epiblast. This bulb is the 
 first "brain-bud," or cerebral 
 vesicle. From its sides the 
 processes of the optic vesicles 
 soon grow out. Behind the 
 first vesicle a second, and 
 behind the second a third, 
 is soon formed. Thus there 
 come to be three brain-buds, 
 or germinal brains. From 
 them are to develop the fore- 
 brain, the mid-brain, and the 
 hind-brain. 
 
 Flexure of the Neural Canal. 
 — The fore-brain vesicle, or 
 front part of the neural canal, 
 becomes bent downward 
 through inequalities of 
 growth. By increase of this 
 flexure the front portion is 
 folded down so that the second vesicle, or mid-brain, pro- 
 jects in front of it. 
 
 AU the subsequent development of the nervous system 
 is connected with the growth of the three cerebral vesicles 
 and the flexure of the neural or medullary canal. 
 
 Development of the Cerebral Vesicles. — From the front 
 
 Fio. 58. — Foi-e-part of an Embryo-chick 
 at the end of the second day, viewed from 
 the Dorsal Side. y,,,. (Kolliker.) Vh, fore- 
 brain; Ablj ocular vesicles; Mk, mid- 
 brain ; HJi, hind-brain ; JT, part of the heart 
 seen bulging to the right side; Fom, vitel- 
 line veins; Mr, medullary canal, spinal 
 part; Mr', medullary wall of the mid-brain ; 
 Uw, proto-vertebral somites. 
 
110 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 part of the fore-brain the vesicles of the cerebral hemi- 
 spheres swell out. Each of these lateral brain-buds has a 
 cavity which is continuous with the cavity of the fore- 
 brain. The cavities on either side become the lateral 
 
 Mid-brain 
 
 Foramen 
 ^onroi 
 
 N. opt. 
 
 Infundi- 
 
 N. trig. 
 
 Fig. 59. — A, Brain of an Embryo of the Rabbit. B, Brain of an Embryo of the Ox. 
 In both cases the side-wall of the left beinisphere is removed. (After Mlhalkovics.) 
 
 ventricles of the brain. The original vesicle of the fore- 
 brain, having ceased to occupy its front position, develops 
 into the parts around the third ventricle. The front 
 portion of the third cerebral vesicle is now marked off by 
 a constriction ; thus the hind-brain is separated into two 
 parts, — the rudimentary cerebellum with the pons in 
 front, and the rudimentary medulla oblongata. 
 
 The following table — taken from the ninth edition of 
 Quain's Anatomy, exhibits the relation in which the de- 
 veloped parts of the brain stand to its fundamental rudi- 
 ments : — 
 
DEVELOPMENT OP THE NEEVOUS SYSTEM. Ill 
 
 I. 
 Anterior Pri- 
 mary Vesi- 
 cle. 
 
 II. 
 Middle Pri- 
 mary Vesi- 
 cle. 
 
 ni. 
 
 Posterior Pri- 
 mary Vesi- 
 cle. 
 
 1. Prosencephalon, 
 Fore-brain, 
 
 Thalamen-cephalon, 
 2. Inter-brain, 
 
 Mesencephalon, 
 3. Mid-brain, 
 
 '4. Epencephalon, 
 Hind-brain. 
 
 Metencephalon, 
 5. After-brain. 
 
 Cerebral Hemispheres, Corpora 
 Striata, Corpus Callosuiu, 
 Fornix, Lateral Ventricles, 
 Olfactory Bulbe. 
 
 Thalami Optici, Pineal Gland, 
 Pituitary Body, Third Ven- 
 tricle, Optic Nerve (prima- 
 rily). 
 
 (Corpora Quadrigemina, Crura 
 Cerebri, Aqueduct of Sylvius, 
 Optic Nerve (secondarily). 
 
 (Cerebellum, Pons Varolii, an- 
 terior part of the Fourth 
 Ventricle. 
 
 fMedulla Oblongata, Fourth 
 I Ventricle, Auditory Nerve. 
 
 The Cranial and Spinal Nerves. — Along the cerebro-spi- 
 nal cavity — formed as described above — various changes 
 in the lining of the epiblast take place. This lining is 
 thickened at the side so that the cavity comes to resemble 
 a narrow vertical slit. The sides and floor of the canal of 
 the cerebral hemispheres are also much thickened. But 
 in the region of the third and fourth ventricles the roof of 
 the canal becomes very thin. 
 
 The cranial nerves spring out of a band, composed of two 
 plates, which connects the dorsal edges of the neural canal 
 with the external epiblast. The fusing of the two plates 
 makes the band into a crest on the roof of the brain. As 
 the roots of the cranial nerves grow centrifugally and 
 become established, the connecting crest is partially obliter- 
 ated. In its earliest stages a cross-section of the brain-tube 
 is essentially like the spinal cord in its internal structure. 
 The region of the medulla leads the others in the develop- 
 ment of the nerve-paths. 
 
112 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 In the spinal cord, the posterior roots of the nerves 
 appear as out-growths of a series of naedian cell-processes 
 i on the back side of the 
 
 cord. Recent discoveries 
 indicate that the motor- 
 nerves of the cord, as 
 well as of the brain, arise 
 from the fundamental 
 plate. 
 
 Development of the An- 
 terior Fortionsof theBrain. 
 — Further details con- 
 cerning the later changes 
 in thehind-brainandmid- 
 brain may be omitted. 
 But the fate of the an- 
 terior portion of the cere- 
 bro-spinal substance re- 
 quires a brief further 
 description. Of its two divisions (see the Table, p. Ill), 
 the posterior (thalamen-cephalon), is at first a simple vesicle, 
 
 formed of spin- 
 dle-shaped cells 
 with walls of 
 nearly uniform 
 thickness. Its 
 floor gives rise 
 to the optic 
 chiasm and the 
 optic nerves ; its 
 sides become 
 thickened into 
 the optic thala- 
 mi ; its roof gives 
 rise to the pineal gland and surrounding structures. 
 
 Fig. 60. — Head of the Embryo of a Sbeep, cut 
 through the middle. Vi* (Kolliker.) «, under 
 jaw; z, tongue; s, septum narium; occipitale 
 oasilare; th, thalamus opticus; vt, roof of the 
 third ventricle; cp, posterior commissure; mft, 
 mid-brain divided by a fold into two parts ; /, falx 
 cerebri; ff, terminal plate of the fore-brain. At 
 the prolongation of the line of fm is the foramen 
 of Monro, t, tentorium cerebelli ; cl, cerebellum ; 
 p2, plexus of the fourth ventricle. 
 
 occipitalis 
 
 Fio. 61. — Brain of a Six-months Human Embryo. Natu- 
 ral size. (Kolliker.) ol, olfactory bulb ; fs, fissure of Syl- 
 vius; c, cerebellum; p, pons Varolii; /, flocculus; o, olive. 
 
DEVELOPMENT OF THE NERVOUS SYSTEM. 113 
 
 The larger portion of the development from the anterior 
 primary vesicle constitutes the rudiments of the cerebral 
 hemispheres. Here a floor and a roof must be distin- 
 guished. The former develops into the striate bodies by 
 the thickening of its walls. The latter forms the hemi- 
 spheres proper. 
 
 One principal characteristic of the mammals is the early 
 enlargement of the cerebral hemispheres. In the human 
 embryo they are even by the tenth week much larger than 
 all the rest of the brain. They grow from before back- 
 ward and thus cover up, one after the other, the optic 
 thalami, corpora quadrigemina, and cerebellum. This 
 physical evolution is indicative of the future intellectual 
 superiority and intellectual growth of the human being. 
 We have already seen how early and significant is the 
 formation of the most important convolutions and fissures. 
 By the end of the seventh, month of embryonic life, the 
 principal features of the cerebral hemispheres are already 
 definitely fixed. 
 
 Development of the Eye. — Lateral growths of the brain- 
 buds, called the "optic 
 
 vesicles" (see p. 109), ^ j ^ j 
 
 give rise to the ner- 
 vous parts of the eye. ' 
 These vesicles are 
 
 c 
 
 originally connected 
 
 with the sides of the ^^^ 62. — Longitudinal Sections of the Eye of an 
 
 a „. 1 1 „„„4„i„ Embryo, in three stages. (Erom Remak.) 1, com- 
 
 nrSt cerebral vesicle mencement of the formation of the lens I, by depres- 
 
 i_ T_ _j. J -J Bion of a part of ft, the corneous layer; «, r, the prim- 
 
 by snort ana Wiae jUve ocular vesicle is doubled back on itself by the 
 
 T, , •, .1 depression of the commencing lens. 2, the depression 
 
 StalKS ; tney tnen for the lensls now enclosed, with the lens beginning 
 
 ,- T . 1 . to be formed on the inner side; the optic vesicle is 
 
 stand at nearly right more folded tack. S, a tUrd stage, in which the sec- 
 
 , ondary optic vesicle g I begins to be formed. 
 
 angles to the embryo. 
 
 The stalks become narrow and form the rudiments of the 
 optic nerves. At the same time the rudiments of the 
 retina are formed from the vesicles themselves. 
 
114 PHYSIOLOGICAL PSYCHOLOGY. 
 
 The bulb of the optic vesicle is then made into a cup by- 
 doubling it upon itself. The lens of the eye is formed by 
 thickening some of the superficial epiblast and involuting 
 it inward over the front of the optic cup (see Fig. 62). 
 This involution has at first the form of a pit ; then of a 
 closed sac with thick walls ; then of a solid mass. The 
 subsequent development of the eye depends upon the fact 
 that the walls of the optic cup grow more rapidly than 
 does the lens, and that their growth does not take place 
 equally in all portions of the cup. 
 
 The different layers of the retina are formed by differen- 
 tiations of the anterior wall of the" hind portions of the 
 optic cup. Here the cells multiply rapidly, and undergo 
 important changes while the wall is thickening. In its 
 early development this wall resembles the brain in its 
 structure. It may, indeed, be considered as a part of that 
 organ. 
 
 Development of the Ear. — The organ of hearing originally 
 appears on either side of the hind-brain as an involution 
 of the external epiblast, sunk in a mass of mesoblast. It 
 is then shaped as a shallow pit with a wide-open mouth. 
 As the mouth closes up, the pit becomes a vesicle, the otic 
 vesicle. The walls thicken, and the cavity enlarges. Its 
 shape becomes triangular, with the apex of the triangle 
 directed inward and downward. This apex is elongated 
 into the cochlear canal. Part of the vesicle is stretched 
 out into a long narrow process (recessus vestibuW), and 
 from the wall of the main body protuberances grow which 
 become the vertical semicircular canals. Other protu- 
 berances are stretched out and curved into other parts of 
 the organ. 
 
 The ^ cochlear canal is further elongated and curved. 
 When it has reached two and a half coils, the thickened 
 epithelium of its lower surface forms a double ridge, from 
 which the Organ of Corti is developed. 
 
 Histogenetio Development of the Nervous System. — All 
 
DEVELOPMENT OF THE NERVOUS SYSTEM. 115 
 
 the coarser differentiations of structure which have been 
 described are but the expression, as it were, of secret and 
 exceedingly minute changes, called " histogenetic." Deli- 
 cate threads of nervous tissue have been laid down, and 
 nerve-cells have been propagated (^proliferated') along defi- 
 nite lines. The white matter of the spinal cord first appears 
 in four patches at the front and back of either half. The 
 individual fibres appear like small dots in these patches. 
 The gray matter is formed by differentiation of the principal 
 mass of- the walls of the medullary canal. The outer cells 
 lose their epithelial character, and become converted into 
 true nerve-cells, with nerve-fibres as prolongations. The 
 nerve-fibres remain for a considerable time without the 
 medullary sheath. 
 
 The early histogenetic development of the brain back 
 of the cerebral hemispheres is very like that of the spinal 
 cord. In the floor a superficial layer of delicate nerve- 
 threads is early formed. In the fore-brain the walls of the 
 hemispheres become divided into two layers, the inner of 
 which unites with the fibres of the crura cerebri to give 
 rise to most of the white matter of the hemispheres. The 
 outer layer of rounded cells becomes further differentiated, 
 the deeper part, with its multiplication of numerous cells, 
 forming the principal mass of the gray matter of the 
 cortex. 
 
 Thus does the impregnated ovum, by a process of evolu- 
 tion, become developed into that wonderful complexity of 
 organs which constitutes the body of the human child. Of 
 the correlated psychical development of the embryo little 
 or nothing of a scientific character can be known. But the 
 physical process by which the nervous mechanism comes 
 into being is, nevertheless, suggestive for the student of 
 physiological psychology. To some of the conjectures 
 and speculations which legitimately follow from our still 
 meagre knowledge of human embryology, we shall return 
 at another time. 
 
CHAPTER V. 
 
 GENERAL PHYSIOLOGY OF THE NERVES. 
 
 The question, What can Nervous Substance do? natu- 
 rally follows the consideration of its chemical and formal 
 constitution. An answer to this question, however, can- 
 not he gained by inference from our knowledge of the 
 anatomy and histology of the nervous system. It is only by 
 indirect processes of observation and experiment, combined 
 with no little conjecture, that even the beginnings of a 
 clear scientific conception of the functions of this system 
 can be found. The attainments of science on this subject 
 may conveniently be stated under two heads, preceded 
 by a brief introduction. We consider then, first, certain 
 modes of activity belonging to all nervous matter as such ; 
 and, second, — with more of detail, — the "Nerves as 
 Conductors," and the "Automatic and Reflex Functions 
 of the Central Organs." 
 
 Functions of the Nervous Elements, — Nerves and nerve- 
 cells have certain properties in common; within certain 
 limits both can do the same things. These properties may 
 perhaps be summed up in the two words Excitability (or 
 "irritability") and Conductivity. Both are capable of 
 becoming, under the action of stimuli, the subjects of a 
 specific kind of molecular motion called " neural." When 
 stimulated or irritated, they originate, as a unique func- 
 tion, the process which may be called " nerve-commotion." 
 But both nerve-fibres and nerve-cells can also propagate 
 this peculiar kind of molecular agitation from point to 
 point ; they can conduct nerve-commotion. 
 116 
 
GENERAL PHYSIOLOGY OF THE NERVES. 117 
 
 Nerve-commotion is never, of course, an uncaused event. 
 The causes that excite or irritate the nervous elements 
 to exercise their peculiar function are called '■^stimuli." 
 Stimuli are of two kinds, external and internal. The 
 former comprise all such modes of energy as excite nerve- 
 commotion by acting on the peripheral parts of the ner- 
 vous system, — the terminal nerve-fibrils or end-organs of 
 sense. Internal stimuli act directly upon the substance 
 (nerve-cells) of the central organ ; they consist in general 
 of changes in the blood-supply, — increased or decreased 
 oxygen, presence of drugs, etc. 
 
 General Office of the Nervous System. — In all forms of 
 animal life, except the lowest, the action of the nervous 
 system constitutes a chief characteristic of their difference 
 from all forms of plant life. Plants as well as animals 
 have contractile tissue ; but the former never have nervous 
 tissue, not to say, a nervous system. The unique functions 
 of this system, as possessed by all the higher animals, can 
 perhaps best be summed up in the one word, "concate- 
 nation." The linking, or chaining together — as it were — 
 of distant and different physical organs and systems, and 
 of the action of the other parts of the body with the 
 phenomena of psychical life, is the unique function of the 
 nervous mechanism. 
 
 In the plant, for example, every part acts directly and 
 slowly upon contiguous parts only, for the effecting of 
 those changes upon which its life and growth depend. 
 But in the case of the animal, by the mediation of the 
 nervous system, an effect produced in one part of the 
 body may make itself quickly felt in every other part. 
 A draught of cold air, for example, strikes some portion 
 of the surface of the body. Immediately, the heart and 
 lungs modify their action ; the muscles contract ; the secre- 
 tions are distm-bed; a shudder runs through the body; 
 and perhaps the mind is seized with a vague feeling of 
 
118 PHYSIOLOGICAL PSYCHOLOGY. 
 
 fear. Thus changes which involve the tissues and func- 
 tions of almost all the organs of the body are accomplished 
 by the mediation of the nervous system. 
 
 MORE PARTICULAR FUNCTIONS OF ALL NERVES. 
 
 We have already seen (p. 32 f.) that the plan on vrhich 
 the nervous system develops leads to a threefold economy 
 of organs. In this threefold economy, the office of con- 
 ducting the nerve-commotion between the end-organs and 
 the central organs has been assigned especially to the nerves. 
 The function of conducting neural molecular agitations 
 belongs, indeed, as an essential function, to all nervous 
 substance. But the nerve-fibres, as bound together into 
 nerves, possess, in all normal conditions of the nervous 
 system, this office pre-eminently. Moreover, it is only as 
 exercised by the nerves that the laws of neural conduction 
 can be at all satisfactorily examined by direct experiment. 
 
 Physiological Distinctioiis in the Nerves. — If we considered 
 only the different effects produced by conducting nervous 
 processes along the different nerves, we should be com- 
 pelled to divide the nerves into a variety of classes. In 
 this way it has been proposed to distinguish " nerves of 
 motion," " nerves of inhibition " (or check upon the action 
 of other nerves), " nerves of secretion," " nerves of nutri- 
 tion" (trophic nerves), "centripetal nerves that have no 
 sensory function," and " sensory nerves," whose irritation 
 may result in conscious sensation. 
 
 The question arises at once, however, whether the differ- 
 ent obvious results which follow irritating all these nerves 
 are due to real differences in the functions of the nerves 
 themselves, or to differences in the structures and connec- 
 tions where the nerves terminate. We do not consider the 
 electrical current which passes along different wires essen- 
 tially different, because it may be used to write a message, 
 light a jet, ring a bell, or cause the legs of a frog to twitch. 
 
GENERAL PHYSIOLOGY OF THE NERVES. 119 
 
 For reasons which need not be mentioned, it has been 
 customary to reduce all possible classes of nerves to two, 
 according to the direction in which they perform the ser- 
 vice of conduction. Those nerves which conduct nerve- 
 commotion outward from the nervous centres are called 
 "efferent," or "centrifugal," or "motor." Those nerves 
 which conduct nerve-commotion inward toward the ner- 
 vous centres are called " afferent," or " centripetal," or 
 "sensory." 
 
 Afferent and Efferent Nerves. — The attempt has further 
 been made to reduce the two foregoing kinds of nerves to 
 one class. It is properly claimed that a difference in direc- 
 tion does not necessarily prove an essential difference in 
 function. In favor of such a difference, however, it has 
 been urged that heat is a stimulus of afferent but not of 
 efferent nerves ; and that a constant current passing along 
 an efferent nerve, so long as there are no sudden changes 
 in its strength, does not make the attached muscle con- 
 tract, while such a current does seem to excite impulses in 
 a sensory nerve. 
 
 On the other hand, the rate of conduction in both kinds 
 of nerves seems to be about the same ; and, indeed, most 
 of the laws, to which we are about to call attention, apply, 
 essentially unchanged, to both. It may further be urged 
 that even more marked differences than those referred to 
 above can be accounted for by the differences in the sources 
 of the stimulation. A molecular disturbance, which would 
 be quite powerless to stir the sluggish muscle-fibres when 
 transmitted to them by a motor-nerve, might occasion pro- 
 found changes in the sensitive ganglion-cells of the central 
 organ when transmitted to this organ by a sensory nerve. 
 
 Various attempts have been made, more or less success- 
 fully, to demonstrate by experiment that motor and sen- 
 sory nerves can be made to discharge each other's functions. 
 Some experimenters have succeeded in uniting the central 
 
120 PHYSIOLOGICAL PSYCHOLOGY. 
 
 end of the sensory nerve of the dog's tongue with the 
 peripheral end of the motor nerve, on the same side. 
 Others have reversed the course of the nerve-fibres in the 
 tail of a rat, by bending this appendage over, and planting 
 its end in the back. If these experiments are not quite 
 satisfactory, those of Kiihne may fairly be said to be con- 
 clusive. He showed that if we divide the broad end of the 
 sartorius muscle of the frog into a forked shape, the same 
 stimulation will ascend the fibrils of one tine of the divided 
 muscle, and descend the fibrils of the other tine. 
 
 No good reason appears, then, why we should not con- 
 sider all nerves as essentially alike in their powers of 
 conduction. It is upon this assumption that the science of 
 so-called " General Nerve-Physiology " is built up exper- 
 imentally. In building up this science, the efferent nerves 
 of frogs have been chiefly used for purposes of experiment. 
 A preparation of such a nerve with a muscle attached is 
 the subject whose behavior is investigated. 
 
 The Nerve-Muscle Preparation. — The most convenient 
 form of machine for experiment in "general nerve-phys- 
 iology " requires a freshly dissected (gastrocnemius or other) 
 muscle of a frog with the attached (sciatic or other) nerve. 
 Such a preparation can be kept alive for some time in a 
 cool moist chamber. By the simple contrivance of connect- 
 ing the end of the muscle with a lever, arming the lever 
 with some means of making a mark (pen, bristle, or needle), 
 and bringing its point to bear on a travelling surface (plain 
 or smoked paper, or glass), the time and amount of the 
 contractions of the muscle maybe recorded. Stimulation 
 may be accomplished with any kind of irritant, but for 
 obvious reasons the electrical current is preferable as a 
 rule. It may be applied under the greatest variety of 
 conditions, and to any point in the nerve, and with any 
 degree of intensity. 
 
 The line traced by the armed end of the lever, as it rises 
 
GENERAL PHYSIOLOGY OE THE NERVES. 121 
 
 and falls with the contractions of the muscle, is called the 
 " muscle-curve." This curve is a measure of the observ- 
 able effect produced by irritating the nerve. If the elec- 
 trical current flows with the course of the nerve toward 
 the muscle, it is called " descending," or direct ; if it flows 
 in the opposite direction, it is "ascending," or inverse. 
 The movement of the muscle which follows closing of the 
 current is called the "making contraction," or "closing 
 contraction " ; that which follows its opening is called the 
 " breaking contraction," or " opening contraction." When 
 the single stimulations are repeated with sufBcient rapidity, 
 the spasms fuse into one prolonged effort of the muscle, 
 known as "tetanus," or "tetanic contraction." The nerve 
 may then be said, with the muscle, to be " tetanized." 
 
 CONDITIONS OF THE FUNCTIONS OF NERVES. 
 
 Of the conditions under which alone the nerves are 
 capable of exercising their functions the most important 
 are the following three : — 
 
 (1) Vitality of the Nerves. — ■ A nerve cannot act as the 
 conductor of a nerve-commotion unless it is alive. The 
 process of conduction is not therefore merely mechanical, 
 like that of electricity along a wire, but is physiological 
 and vital. The death of the nerve is not, however, simul- 
 taneous with that of the body from which it is taken, or of 
 the muscle to which it is attached. On the contrary, by 
 careful treatment, it may be preserved alive for some time 
 after excision. Since the nerve, unlike the muscle, has no 
 death-rigor, it is difficult to say precisely when it is dead. 
 The existence of electrical phenomena in the nerve for 
 some time after it has ceased to excite the muscle is 
 thought by some authorities to show its continued vitality. 
 
 Nerves, when dying, exhibit two marked changes of 
 excitability. Immediately after being cut, the excitability 
 of the nerve increases, and afterward sinks to zero by sue- 
 
122 PHYSIOLOGICAL PSYCHOLOGY. 
 
 cessive stages of diminution. The course of these changes 
 is different for different portions of its length. Again, the 
 lower portion of the cut nerve seems to preserve a given 
 degree of vitality for the longest time. Hence "Valli's 
 principle: Nerves die from the centre to the periphery. 
 
 Closely allied to the foregoing changes are those which 
 take place when the cut nerve remains in its place in the 
 living animal organization (in situ'). For such a nerve 
 the law of increased irritability immediately after section 
 seems, in most cases, to hold good ; the application can be 
 tested, however, only in the case of motor nerves. Nerves, 
 cut in situ, lose their vitality after a time — in warm- 
 blooded animals, of three or four days, but in cold-blooded, 
 of a week or more. A fatty or granular degeneration 
 (discovered by Waller in 1850) takes place in nerve-fibres 
 that are severed from the central organ ; and this degener- 
 ation proceeds from the place of section to the extreme 
 peripheral portion of the fibre. A cut nerve remaining in 
 situ may be regenerated by the axis-cylinders growing out 
 of the central portion and running into, and between, the 
 sheaths of Schwann of the peripheral portion. According 
 to some authorities the conductivity of the nerve is then 
 regained earlier than its power of local irritability. 
 
 (2) JJse of Oxygen by the Nerves. — As compared with 
 the end-organs and the central organs, or even with the 
 muscles, the nerves are relatively independent of the pres- 
 ence of oxygen for the exercise of their physiological func- 
 tion. The irritability of the nerves continues almost as 
 long in a moist vacuum, or in indifferent gases, as in the 
 air. It may be argued, however, from the marked depend- 
 ence of nervous tissue, in general, upon a supply of arte- 
 rial blood, as well as from the general mechanical theory 
 of the nervous system, that some oxygen is an essential 
 condition of the activity of the nerves. 
 
 (3) Recovery from Exhaustion. — The nerves, when " ex- 
 
6ENEBAL PHYSIOLOGY OF THE NEEVES. 123 
 
 hausted " — as it is said — cannot perform their physiologi- 
 cal functions. But exhaustion of the nerves is difficult to 
 distinguish from exhaustion of the central organs or of the 
 end-organs. In the case of the nerve-muscle machine 
 Bernstein thinks he has shown that by far the greater part 
 of the effects of prolonged and severe stimulation is due 
 to the mwscZe-element in the machine; and that exhaus- 
 tion in the nerve comes on much more slowly than in the 
 muscle. Indeed, some have gone so far as to hold that the 
 nerve is not exhausted at all, but resembles in this regard 
 a metallic wire. But more recent researches seem to 
 show — as indeed we should expect on grounds of general 
 theory — that a prolonged tetanizing current may fatigue 
 the nerve, even when the end-apparatus continues able to 
 perform its functions. Ordinarily, however, when we are 
 tired nervously, it is the central organs, or end-organs, 
 rather than the conducting nerves, that are tired. 
 
 PHYSICAL PROPERTIES OF THE NERVES. 
 
 The phenomena called forth by irritating a nerve depend 
 upon the character, amount, and method and place of 
 application, of the stimuli employed. This dependence 
 suggests certain truths as to the physical properties of the 
 nerves as conductors. 
 
 Mechanical Properties of the Nerves. — The elasticity, 
 ductility, cohesion, etc., of nerves are of little interest to 
 the student of physiological psychology. More pertinent 
 is the fact that all kinds of mechanical attacks upon the 
 nerves excite them, and are followed by pain in case of 
 the sensory nerves, and by contraction in the case of motor 
 nerves. Tetanus may be produced with a toothed wheel 
 or hammer. A certain suddenness of the shock seems 
 necessary to excite the nerve. Pressure on a nerve may 
 be gradually increased until its power of conductivity is 
 lost, without exciting it. Slight pressure or traction 
 
124 PHYSIOLOGICAL PSYCHOLOGY. 
 
 seems to increase the irritability and speed in conduction 
 of the nerve. Yet nerves may be cut so suddenly as not 
 to excite them. 
 
 Thermic Properties of the Nerves. — Little is known as to 
 the specific heat of nerves, or as to their power to conduct 
 heat. But the effect of heat on the function of these organs 
 is very marked. The results of experiment differ as to the 
 degree of heat which will act as a stimulus upon the 
 nerves. Considerable changes in the medium temperatures 
 appear to have no effect. One investigator found that 
 suddenly warming a nerve to about 35°- 40° C. occasioned 
 a spasm in the attached muscle ; and warming to a higher 
 degree produced tetanic convulsions. Long ago that noted 
 authority, E. H. Weber, showed that heat and cold do not 
 produce sensations when applied directly to the sensory 
 nerve-trunks in man. For this peculiar sensory effect the 
 intervention of end-organs seems necessary. 
 
 Four periods have recently ^ been distinguished in the 
 effects produced by heat upon the irritability of the motor 
 nerve. These are thus described: (^) Gradual increase 
 to a maximum of irritability, — viz. 32.75°-39.25° C. ; 
 (^) then gradual diminution of irritability to its total loss ; 
 (C) condition of no irritability, a period coming at any 
 point within 5° above the temperature of maximum con- 
 traction ; and finally (i)) development of heat-rigor. 
 
 Warmth increases the immediate expenditure of energy 
 in an excised nerve, and so hastens its death ; cold delays 
 this expenditure and so conserves the nerve. 
 
 Chemical Properties of the Nerves. — The effect of most 
 chemical agents on the nerve is to destroy without exciting 
 it. Changes of the amount of water in the substance of 
 the nerve affect its functional activity. A slight drying 
 raises its irritability; and drying also produces contrac- 
 
 1 By Charles L. Edwards, in Johns Hopkins Studies from the Bio- 
 logical Laboratory, June, 1887. 
 
GENERAL PHYSIOLOGY OP THE NEKVES. 125 
 
 tions ending in tetanus. Swelling the nerve decreases its 
 irritability to the point of entire loss. Certain acid and 
 alkaline solutions also affect the nerve very much like 
 drying it. Some organic substances, like \irea, sugar, and 
 glycerine, irritate the nerve. The principle seems to be, 
 that all chemical stimulation of the nerves is closely con- 
 nected with the destruction of the nervous tissue. 
 
 Electrical Properties of the Nerves. — The resistance of 
 living nerves to the electrical current is probably about 
 the same as that of the muscles ; it has been given at 
 50,000,000 times that of copper wire. The conductivity 
 of the nerve has also been given as, on the average, 14.86 
 times that of distilled water. 
 
 The excitatory effect of the constant current upon the 
 nerves follows the principle stated by that great explorer, 
 du Bois-Reymond, in 1845. This effect, as measured by 
 the contraction-curve of the muscle, does not correspond 
 to the absolute value of the intensity of the current at each 
 moment, but to the change in this value from moment to 
 moment ; and the effect is greater the less the time in 
 which changes of the same magnitude in the current 
 occur, or the greater their magnitude in the same length 
 of time. The essential fact is that constant currents, 
 while they remain constant, do not irritate the nerve; 
 variations in theSe currents do irritate it. 
 
 Even upon the sensory nerves it is not certain that the 
 constant current itself, apart from changes in its strength, 
 can have much excitatory effect. The sensory experiences 
 which follow such a current are chiefly due to changes 
 induced in the end-organs and central organs. 
 
 Excitatory Effect of the Constant Current. — If we experi- 
 ment with the electrical current upon a nerve we find that 
 its excitatory effect is dependent upon the direction in 
 which the current flows. The following table, by Pfliiger, 
 gives the results reached by a large number of observers : — 
 
126 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Strength or 
 
 Ascending Cukkent, 
 
 Descending Cubkent. 
 
 COBRBNT. 
 
 Making. 
 
 Breaking. 
 
 Making. 
 
 Breaking. 
 
 Weak .... 
 Medium. . . 
 Strong. . . . 
 
 Contraction 
 Contraction 
 Rest 
 
 Rest 
 
 Contraction 
 
 Contraction 
 
 Contraction 
 Contraction 
 Contraction 
 
 Rest. 
 
 Contraction. 
 Rest or weak 
 Contraction. 
 
 The most important point in this table is more clearly 
 brought out by the following recent summary ^ of results : 
 " Up to a certain strength of current a stimulus will give 
 contraction when the cathode lies next to the muscle (i.e. 
 the current is descending), which will give no contraction 
 when the anode is in that position (current ascending). 
 Above this strength the reverse holds, and a stimulus 
 which is followed by contraction when the excitation has 
 to pass the anode, evokes no response when it has to pass 
 the cathode." 
 
 The excitatory effect of the electrical ctirrent upon the 
 nerve is also dependent upon the strength of the current. 
 It increases with the strength, from the lowest observable 
 point, until it soon reaches a maximum ; after this, further 
 increase of the effect of the current is to be recognized 
 only by the expanding of this condition of higher irrita- 
 bility — called " electrotonus " — over the extra-polar parts 
 of the nerve. 
 
 The effect of the current upon the nerve also depends 
 upon the length of nerve excited, and upon the angle at 
 which the stimulus is applied. Up to a certain limit — 
 fixed by different investigators at from t^ to I- inch — the 
 excitatory effect increases with the length of the nerve 
 through which the current flows. The electrical current 
 
 1 An Article by 6. N. Stewart, in Journal of Physiology, Oct., 1889. 
 
GENERAL PHYSIOLOGY OF THE NERVES. 127 
 
 apparently does not excite the nerve at all when it flows 
 through it precisely at right angles to the nerve's axis. 
 
 The duration of the current also influences its effect as 
 a stimulus. It would appear that the current must act 
 upon the nerve for at least about 0.001|- of a second in 
 order to excite it. By cooling the nerve this " sluggish " 
 period may be increased to nearly 0.02 of a second. In 
 ordinary circumstances, however, it is thought that the 
 action of the stimulus for 0.017-0.018 second will cause 
 the muscles to contract as much as the same strength of 
 current when constantly applied. 
 
 Electrotonus of the Nerves. — When the nerve of a nerve- 
 muscle machine is under the influence of a constant cur- 
 rent of electricity, very important changes in its condition 
 are observed, as respects both its excitability and its con- 
 ductivity. The general fact that such changes are pro- 
 duced as the effect of applying the constant current is 
 undoubted. But the precise nature of some of these 
 changes is disputed ; while no theory has as yet been de- 
 vised which will satisfactorily account for them all. We 
 shall confine our account at present to the briefest possible 
 statement of the more important alleged facts ; any refer- 
 ence to theory which seems desirable at all, will be made 
 in another connection. 
 
 The changed condition of a nerve, as respects its phys- 
 iological function, which is produced in it by a constant 
 electrical current, is called "Electrotonus." "Pfliiger's 
 law," so-called, states the case, in general, as follows : The 
 excitability of a nerve under the action of the constant cur- 
 rent is increased in the catelectrotonized region (that is, on 
 both sides of the cathode, or negative electrode, — the 
 point where the current leaves the nerve), and diminished 
 in the anelectrotonized region (that is, on both sides of the 
 anode, or positive electrode, — the point where the current 
 enters the nerve). This law is said, by a chief modern 
 
128 PHYSIOLOGICAL PSYCHOLOGY. 
 
 authority, to hold good of all kinds of stimulus, and in 
 all cases. 
 
 The electrotonic effect of the constant current upon the 
 nerve, like its direct excitatory effect, is influenced by the 
 strength of the current, by its direction, its making and 
 breaking, and by the length of the nerve through which 
 the current flows. The changes called " electrotonic " 
 occur in the region of the negative pole (cathode) imme- 
 diately upon making the current; they then quickly but 
 slightly increase and afterwards fall off more slowly again. 
 In the region of the positive pole (anode) the changed 
 condition develops more slowly until it reaches a maxi- 
 mum, and then gradually diminishes. 
 
 Recent researches have led some investigators to hold 
 that the conductivity of the nerve is changed by the con- 
 stant current in a different manner from its excitability. 
 In its electrotonic condition — that is to say — the conduc- 
 tivity of the nerve is found to be less around the cath- 
 ode than around the anode. From this the conclusion is 
 drawn that the origin of the process of excitation of the 
 nerve is not like its propagation. Into the refinements of 
 this change, when the stimulus of the electrical current is 
 applied to different parts of the nerve outside, or within, 
 the poles (inter-polar and extra-polar) we cannot enter. 
 
 PROCESSES EVOKED IN CONNEOTIOHr WITH THE FUNCTION 
 OF NERVES. 
 
 When the nerve is excited certain processes connected 
 with its physiological action are indicated, in a more or 
 less obvious way. 
 
 Mechanical Processes in Excited Nerves. — No appreciable 
 mechanical changes, like the contraction of the muscle- 
 fibre, can be detected in excited nerves. Whatever changes 
 occur are invisible and impalpable. In the nerve-cells, 
 however, mechanical changes can be detected as the result 
 
GENERAL PHYSIOLOGY OF THE NERVES. 129 
 
 of excitation. Repeated and prolonged excitation of the 
 ganglion-cells of the posterior root results in shrinkage 
 of their nucleus and of the cell-protoplasm 5 and in chang- 
 ing the nucleus from a smooth and regular to a jagged 
 and irregular outline. The large cells show most of this 
 effect of being obliged to do work; the small cells little or 
 none at all. The average shrinkage of the large cells is 
 found to be measurable as — in some cases — from 24 to 
 36 per cent.^ 
 
 Thermic Processes in Excited Nerves. — If any rise of tem- 
 perature is produced in a nerve by irritating it, the amount 
 is exceedingly small. Helmholtz concluded that his means 
 of detecting heat to within a few thousandths of a degree 
 showed no such change in excited nerves. On the other 
 hand, nervous excitation appears to produce a perceptible 
 change of temperature in the centres of the brain; and 
 this change can scarcely be due wholly to increased flow 
 of arterial blood. But to this subject we shall return in 
 another connection. 
 
 Chemical Processes in Excited Nerves. — The most obvious 
 indications that chemical processes are concerned in the 
 physiological functions of excited nerves are certain 
 changes in "reaction," or in taking stains, which some 
 observers claim to have found. It has been asserted that, 
 after extreme exertion caused by cramping in cases of 
 strychnine-poisoning, the nerves have an acid reaction. 
 Very recently two observers, on comparing two frogs, one 
 of which was killed after resting and the other after having 
 the eighth nerve stimulated for an, hour, found several per 
 cent, more nuclei staining red in the stimulated than in 
 the rested pair of nerves. Evidences of marked chemical 
 changes in the nervous centres, due to work done there, 
 are of course not wanting. But the direct experimental 
 evidence for the same thing in the nerves is still incomplete. 
 
 1 See the American Journal of Psychology, May, 1888, pp. 479 ft. 
 
130 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Electrical Processes in Excited Nerves. — In 1843 du Bois- 
 Reymond found what he considered direct experimental 
 proof of the existence of electrical currents in the nerves. 
 It had, of course, been previously conjectured that nerve- 
 commotion is a phase of electricity. But this experi- 
 menter discovered that, if we cut a nerve and then apply 
 an electrometer to it, the cross-section is negative toward 
 the longitudinal surface of the nerve. The current, which 
 is thus shown to be flowing in the nerve, from the cut end 
 to the equator, is called " natural nerve-current," or " current 
 of rest." Its electro-motive force is greater, the larger and 
 thicker the nerve. In the sciatic nerve of a frog it is given 
 at from 0.022 to 0.046 of a Daniell's cell. It continues for 
 some time after the irritability of the nerve is lost. 
 
 The same investigator found that the " current of rest " is 
 diminished in energy by tetanizing the nerve. This swing 
 of the needle which measures the " current of rest," back- 
 ward toward zero when the nerve is repeatedly irritated by 
 passing through it an interrupted current, is called " nega- 
 tive variation." It shows that the electro-motive force of 
 the nerve is diminished by the nerve being excited. 
 
 The bearing of these phenomena also upon a general 
 mechanical theory of the nervous system will be referred 
 to in other connections. 
 
 LAWS OF CONDUCTION IN THE NERVES. 
 
 Only a very few statements can be made, with respect 
 to the physiological function of the nerves as conductors, 
 which are properly entitled to the dignity of being called 
 " laws. " And these laws are determined almost wholly by 
 experiments with the motor nerves of frogs. There is evi- 
 dence, however, in respect to certain of the more simple 
 forms of activity, that all nerves conduct nerve-commotions 
 in essentially the same way. 
 
 Relations of Magnitude between Stimulus and Besult. — On 
 
GENERAL PHYSIOLOGY OF THE NERVES. 131 
 
 attempting accurately to compare the amount of the stim- 
 ulus applied to the nerves with the amount of resulting 
 nervous impulse, great difficulties are encountered. There 
 is indeed no absolute measure for either of the values which 
 it is desired to compare. Electricity is the only stimulus 
 of the nerves that admits of a fairly approximate measure- 
 ment by objective standards. The effect produced by 
 stimulation is almost wholly manifested in organs with 
 which the nerve is connected, rather than in the nerve 
 itself. It does not, therefore, admit of easy direct 
 measurement. 
 
 Measuring the result of the stimulus in the nerve by the 
 amoimt of contraction produced in the connected muscle, 
 we find it to be (as has already been indicated, see p. 126) 
 within certain limits, directly proportional to the amount 
 of the stimulus. Two remarkable apparent exceptions to 
 this law are noted : (1) On increasing the amount of the 
 stimulus beyond the point necessary to produce the first 
 maximum contraction, another stage is reached in which 
 the effect further increases, in proportion to the stimulus, 
 until a second maximum is gained. (2) In some circum- 
 stances, after reaching the first maximum, the effect dimin- 
 ishes with the increase of the stimulus, then rises on further 
 increase until the second maximum is reached. 
 
 The excitability of the different nerves is different, and 
 of different localities of the same nerve under different 
 circumstances. It is usually greater in winter than in 
 summer. In the cut nerve it is greater near the cross- 
 section. The reflex effects of stimulating a sensory nerve 
 are said to be greater the nearer the central organ the 
 stimulus is applied. The lower part of a nerve is found 
 more excitable under the ascending, the upper under the 
 descending, induction-current. 
 
 Stmunation of Stimulations in the Nerves. — In order to 
 keep the successive waves of nerve-commotion apart, an 
 
132 PHYSIOLOGICAL PSYCHOLOGY. 
 
 interval of about j^ second must elapse between the re- 
 peated stimulations. Otherwise they fuse, and tetanus 
 results. If tliis interval is observed, the combined effects 
 of the different stimulations may be piled, or " summed " 
 up, in the nerve. They may then be seen in superimposed 
 contractions of the muscle. This law is also important for 
 a mechanical theory of the nervous system. 
 
 Speed of Nervous Impulses. — In 1844 the great physiolo- 
 gist Miiller declared it forever, impossible to know the 
 speed of the nervous impulses. In 1850 Helmholtz an- 
 nounced the speed as from 26.4 meters (86.6 feet) to 
 27.25 meters in motor nerves. Subsequent researches 
 have, in the main, confirmed the conclusion of Helmholtz. 
 The rate of nervous impulses varies greatly, however, 
 under different circumstances. By changes in temperature 
 results can be obtained in the motor nerves of man, varying 
 from 98 feet to 295 feet per second. The general conclu- 
 sions for the sensory nerves favor numbers lying between 
 98 and 131 feet per second. As soon as the strength of 
 the stimulus rises above a certain limit, the speed of the 
 resulting impulses appears to increase with the strength 
 of the stimulus. 
 
 In the spinal cord and in the brain the speed of the ner- 
 vous impulses is, in general, much slower than in the 
 peripheral nerves. This is due to the far greater com- 
 plexity of these organs, and to the accompanying possibility 
 of the impulses spreading into side tracts, as it were : in 
 brief, the greater variety and amount of the work that 
 must be done. Exner calculated the speed of motor 
 impulses in the cord at 11 to 15 meters (about 36 to 49 
 feet). The sensory impulses of the cord, he thought, 
 travel at the average rate of about 8 meters (about 26^ 
 feet). Sensations of touch arise, as we all know by expe- 
 rience, later than sensations of pain, when we are struck 
 with a missile, or burned with a brand. Some have main- 
 
GENERAL PHYSIOLOGY OF THE NERVES. 133 
 
 tained, therefore, that the speed of the former is to that of 
 the latter as from 27 to 50 meters compared with 8 to 14. 
 The argument is not conclusive, however, since we do not 
 know the length of the paths by which the impulses that 
 produce the two kinds of feeling travel, or the kind and 
 amount of cerebral action which they respectively involve. 
 
 Integrity of the Nerves Necessary. — The slightest separa- 
 tion of the parts of a nerve, even if its cut ends are left 
 in the closest mechanical contact, destroys its power to 
 conduct nervous impulses. Nerve-commotion, unlike the 
 electrical current, cannot jump the smallest gap in the ner- 
 vous structure. The ancients knew that tying a nerve 
 prevents its action. They explained the fact by saying 
 that the flow of nervous fluid was thus hindered. So also 
 does the fineness of the localization which belongs to the 
 organs of motion, and especially to the organs of special 
 senses, like the skin and eye, indicate the physiological 
 isolation of the nerve-fibre during its course between the 
 end-organs and the central organs. It would further seem 
 that the law of the " specific energy " of each nervous ele- 
 ment is connected with the assumption necessary to explain 
 the phenomena attendant upon the starting and propagat- 
 ing of nervous impulses in the conducting nerves. But 
 to this subject of the " specific energy " of the nervous 
 elements we shall recur at another time. 
 
 When speaking of conduction in the nervous substance 
 of the spinal cord or of the brain, we are not to think of the 
 nerve-commotion as moving along one fixed path, after the 
 exact analogy of the far simpler case of the nerve-muscle 
 machine. The spinal cord does not act as a "perfectly 
 isomorphic medium " for the transmission of nervous 
 impulses. Its extremely complex structure has shown us 
 that it is not adapted to act as such a medium. The case 
 of the brain in this regard is even more complicated. 
 After all the thousands of experiments which have been 
 
134 PHYSIOLOGICAL PSYCHOLOGY. 
 
 performed in what is called "nerve-physiology," we are 
 not yet in a position even to indicate with scientific exacts 
 ness a complete mechanical theory of those molecular 
 wave-like disturbances which the application of stimuli 
 produces in a single nerve attached to a muscle. How 
 much less then do we know of the molecular science of 
 the nerve-commotions in the cord and in the brain? Yet 
 that the nerve-commotions are molecular wave-like changes 
 there can be no doubt. And these changes are connected 
 with, but are not identical with, those mechanical, ther- 
 mic, chemical, and above all, electrical processes, which 
 have just been described. 
 
CHAPTER VI. 
 
 REFLEX AND AUTOMATIC NERVOUS FUNCTIONS. 
 
 When a physiological function is occasioned in some 
 peripheral nerve, independently of a so-called act of will, 
 by the stimulation of some other peripheral nerve, this 
 function is said to be "reflex." In other words, reflex 
 action is the result of the secondary stimulation of one 
 nerve, through a central organ, by the primary stimulation 
 of some other nerve. On the other hand, all excitations 
 of the nervous system which originate in the nervous 
 centres themselves are called "automatic." Doubtless 
 this term must often be used to conceal our ignorance of 
 the real origin of a neural process ; doubtless also, many 
 processes, which a't first sight appear to be automatic, are 
 afterwards discovered to originate reflexly. Notwith- 
 standing this, nervous impulses which result in the move- 
 ments of the muscles, or in the inhibition of such move- 
 ments, apparently originate in the central organs under 
 the action of internal stimuli. But such automatic activi- 
 ties belong distinctively to the central ganglia of the 
 brain. 
 
 Kinds of Reflex Action. — Theoretically, various kinds of 
 reflex nervous action are supposable in the nervous system. 
 Thus two motor nerves might be combined through a 
 central organ (" co-motor reflexes ") ; or an excitation 
 arising in a motor nerve might, without an act of will, be 
 transferred to one or more sensory paths ("reflex-sen- 
 sory"). As to the existence of "co-sensory reflexes" — or 
 cases where the excitation of one peripheral sensory nerve, 
 
 135 
 
136 PHYSIOLOGICAL PSYCHOLOGY. 
 
 through the central organ, occasions the excitation of 
 another locally different, peripheral, and sensory nerve — 
 there can be little doubt. The nose, for example, may be 
 made to tickle by looking at the sun ; and strong rubbing 
 or squeezing of one muscle may sometimes occasion pain 
 in muscles located far away on the surface of the body. 
 But only one kind of reflex functions of the nervous system 
 seems hitherto to have been made available for purposes 
 of scientific experiment. These are the so-called "reflex- 
 motor," or "sensory-motor." Such terms are given to reflex 
 action when a motor nerve is stimulated in a secondary 
 way, through a central organ, by applying stimulus to 
 sensory nerve-endings. 
 
 We must carefully guard ourselves, however, from the 
 misconception that lurks in the word "reflex." The effect 
 of the central organ is never that of simply turning back, 
 or reflecting, a nerve-commotion from one path to another. 
 On the contrary, the passage of a nerve-commotion through 
 a central organ profoundly modifies both the condition of 
 the organ and the character and distribution of the nerve- 
 commotion itself. 
 
 THE SPINAL CORD AS A CENTRE OF REFLEX 
 MOTOR ACTIVITIES. 
 
 Our previous survey of the structure of the spinal cord 
 suggests the truth that it is specially adapted to act as a 
 central organ in the exercise of a variety of reflex-motor 
 functions. The older investigators assumed a great variety 
 of special mechanisms, consisting of distinct systems of 
 sensory and motor nerve-fibres, with connecting cells, appro- 
 priated for the sole purpose of executing the various kinds 
 of reflexes. Modern investigation tends rather toward the 
 view that there are no special elements of the cord appro- 
 priated merely to reflex-motor functions. The whole 
 structure of the organ is such as to adapt it in all its parts, 
 for this as well as for other nervous activities. 
 
KEFLEX AND AUTOMATIC NEKVOUS FUNCTIONS. 137 
 
 The Eeflex-Hotor Machine. — The most convenient piece 
 of mechanism for experimenting to discover the laws 
 of spinal reflexes is the so-called " brainless frog." This 
 preparation consists of the spinal cord, still alive, but sep- 
 arated from the brain by section below the medulla oblon- 
 gata. If the flank of such a frog be touched, a slight 
 twitching of the muscles, which lie immediately below the 
 spot of the skin thus stimulated, will result as a reflex 
 motion. If a hind leg be stretched out and pinched it will 
 respond in a purposeful way to withdraw itself from the 
 irritation. Increasing the strength of the stimulus will 
 elicit reflex motions involving the fore leg of the same 
 side ; then both legs of the other side ; and perhaps, finally, 
 all the muscles of the body. If when one leg of a brain- 
 less frog is irritated it is at the same time prevented from 
 movement, the cord of the preparation will sometimes use 
 the other leg to accomplish the purpose of removing the 
 irritation. 
 
 Phenomena, similar to those obtained from the brainless 
 frog, may be obtained from other brainless animals. A 
 decapitated salamander, when the skin of one of its sides 
 is pinched, will bend that side into a concave shape. 
 
 It was for some time supposed impossible to obtain simi- 
 lar phenomena from the spinal cord of mammals. And, 
 indeed, the spinal reflexes in the case of a mammal whose 
 cord has been disconnected from his brain, are, immedi- 
 ately after section, comparatively weak and purposeless. 
 But if such an animal be kept alive for some time, then 
 strong, varied, and purposeful movements will follow 
 sensory stimulation of the skin of the parts below the 
 place of section. After some weeks or months, reactions 
 resembling those described in the case of the frog begin to 
 appear. Moreover — a very significant fact ! — it is found 
 that the breed, sex, age, and training of the animal deter- 
 mine the character of these reflex brainless movements. 
 
138 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Strength and Suddenness of Spinal Eeflexes. — Continuous 
 irritation of the skin of a brainless animal, if slowly ivr 
 creased, does not give rise to reflex movements. But a 
 much smaller degree of stimulus, if suddenly applied, will 
 call forth such movements. Repetition of the shocks with 
 the electrical current is much more effective than is the 
 constant current, in starting spinal reflexes. And here 
 we are reminded again of the law already announced, as 
 holding good in " general nerve-physiology " (see p. 125). 
 A decapitated frog may be placed in water, and the water 
 slowly heated until its life is destroyed, without its show- 
 ing any reflex activity. Even normal frogs — though with 
 much more difficulty — can be heated, either locally, vnth 
 one leg in the water, or all over, while sitting on a cork 
 in a cylinder of water, without causing motion, if the 
 increase of temperature be gradual enough. 
 
 Speed of Spinal Reflexes. — It has already been said 
 (p. 132) that the process of conduction suffers a delay while 
 passing along the spinal cord. The time of " cross-con- 
 duction" in the cord also seems to depend upon the 
 strength of the stimulus. By increasing its strength — 
 it has been calculated — the time consumed by the spe- 
 cifically central processes may be diminished from 0.055 to 
 0.047 of a second. With very strong stimulus the time 
 occupied by the central processes becomes almost too brief 
 to detect. 
 
 Condition of the Spinal Cord. — The character of the 
 resulting reflex movement is very largely determined by 
 the condition of the cord when the sensory impulses enter 
 it. Lesion increases the excitability of the part below the 
 lesion. Some drugs heighten and some depress its excit- 
 ability. When the cord is poisoned with strychnine, for 
 example, the slightest stimulation will cause such an 
 explosion in it, and such a diffusion of energy along 
 unaccustomed paths, that convulsive cramping is occa- 
 
KEFLEX AND AUTOMATIC NERVOUS FUNCTIONS. 139 
 
 sioned over the entire body. Changes of temperature also 
 seem to affect the reflex-motor activities called forth by 
 stimulating the spinal cord. 
 
 Effect of Locality. — The extent and character of the 
 spinal reflexes depend, in a remarkable way, upon the 
 locality to which the stimulus is applied. The most 
 remarkable difference is perhaps that evoked by irritating 
 some spot on the skin of the brainless animal, and then 
 comparing the result with that obtained by applying the 
 stimulus directly to the trunk of the sensory nerve. A 
 slight irritation of the skin may result in the extended 
 movement of many muscles, combined in a purposeful 
 way. The direct stimulation of the trunk calls forth 
 irregular movements in a few muscles only. What par- 
 ticular reflex actions follow stimulation, depends upon the 
 particular locality of the skin to which the stimulus is 
 applied. 
 
 Laws of Spinal Reflexes. — The most general rule of the 
 reflex-motor activities of the spinal cord may be stated in 
 terms like the following : The irritation of a sensory nerve 
 with a small degree of stimulus gives rise to reflex move- 
 ments which originate in the cord on the same side, at 
 about the same altitude as that at which the sensory 
 impulses enter the cord; increased stimulus gives rise, 
 also, to movements that arise on the other side of the cord, 
 at about the same altitude ; a still greater increase, to those 
 that originate on both sides of the cord, with the prefer- 
 ence, however, to the same side. 
 
 It would seem, then, that the nerve-commotion which 
 enters the cord is dispersed, first, along the network of 
 cells and fibres near the point of entrance on the same 
 side ; then, across, at the same altitude, to the other 
 side; then, up and down on both sides of the cord. 
 Excitation, started anywhere in the cord, tends to radiate 
 in all directions, but with the preference for certain paths 
 
140 PHYSIOLOGICAL PSYCHOLOGY. 
 
 marked out by the structure and habits of the cord. 
 Hence the spinal cord has been called " the organ for the 
 dispersion of irritation." 
 
 Alleged Automatic Functions of the Spinal Cord. — This 
 organ is not capable of " irregular automatism," — that is, 
 of such spontaneous excitation as takes place in the higher 
 centres of the brain, on volition. It does, however, dis- 
 charge certain functions that are less certainly reflex than 
 those which have already been considered. What is called 
 the "tonic action" of the cord upon the muscles is a 
 marked instance of such functions. The fact that this 
 action does not simultaneously contract all the muscles 
 connected with the cord, or any one set of them with the 
 same energy as any other, throws some suspicion on its 
 automatic character. Moreover, we can often ascribe the 
 " tone " of the muscles of the brainless animal to the action 
 of subtle influences, such as movements of the air, etc., 
 upon the surface of the skin. If a brainless frog be hung 
 up, after having the sciatic plexus cut on one side, the 
 muscles of the leg on the other side have the better " tone." 
 But the same flaccid condition of the muscles on the cut 
 side exists when only the sensory roots of this plexus are 
 cut. 
 
 The circulation of the blood in a brainless animal seems 
 to be in a measure dependent upon the condition of the 
 spinal cord. Hence it is claimed that so-called " vaso- 
 motor centres " exist in the cord. Circulation may 
 continue with regularity in a decapitated frog ; but the 
 removal of any considerable part of the cord aff<ects it. 
 This result appears to arise through the loss of tone thus 
 occasioned in the blood-vessels; and the mechanisms for 
 expanding and contracting these vessels are apparently 
 interlaced with those for contracting the skeletal muscles, 
 in all parts of the cord. Hence the possibility that part, 
 at least, of the result may be reflex rather than automatic. 
 
KEFLEX AND AUTOMATIC NBKVOUS FUNCTIONS. 141 
 
 Centres in the Spinal Cord. — The mechanism of this 
 central organ is so constituted as to connect the motor 
 with the sensory tracts, more favorably in some regions than 
 others. Such regions are called " reflex centres " of the 
 spinal cord. A considerable and indefinite number of such 
 centres exist; and some of them have been located. It 
 has, indeed, been laid down as a general principle that 
 "the spinal cord is the proximate centre, the proximate 
 physiological hearth of excitation, for all the nerves that 
 originate from it." Since the very influential experiments 
 of the German investigator, Groltz, upon the spinal cord of 
 dogs, many functions formerly ascribed to the brain have 
 been shown to have their proximate centres in the cord. 
 
 The spinal reflex centres of different animals differ ac- 
 cording to their structure and habits. With frogs, stimu- 
 lation of any portion of the skin induces reflex movements 
 in all of the muscles. With rabbits, however, a reflex 
 action of a hind leg can be caused by sensory stimulation 
 of a fore leg, only in case one-third or more of the medulla 
 oblongata is left attached to the cord. " Trotting reflexes " 
 — that is, movements of the diagonal opposite extremities 
 by stimulation of one limb — can be obtained only in ani- 
 mals with which such movement is natural. According to 
 the researches of Ferrier and Yeo, the stimulation of each 
 motor root of the nerve-plexuses of monkeys calls forth 
 combined movements involving the co-operation of nu- 
 merous muscles widely separated anatomically. But all 
 the resulting movements are such as are seen associated 
 togetber in the ordinary activity of the animal. 
 
 The spinal cord of every animal seems, then, to be an em- 
 bodiment of the specific functions and of the habits of the 
 species to which the animal belongs ; as well as of the indi- 
 vidual peculiarities acquired by the animal in the previous 
 use of the cord. 
 
 ISTothing more than a reference is necessary to the vari- 
 
142 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ous centres which experiment discovers in the spinal cord, 
 — such as the vaso-motor, those for micturition, defecation, 
 parturition, etc. 
 
 Excitability of the Cord as a Whole. — The question has 
 been much debated whether the spinal cord as a whole is 
 excitable or not. Some have held that the movements 
 obtained by applying a strong stimulus directly to the cord 
 arise only reflexly, — in so far, that is, as the stimulus 
 involves the sensory roots. The cord, therefore, is held to 
 contain no motor elements that are directly excitable 
 except the central paths of the nerve-roots. Others have 
 held that, while the gray matter is absolutely inexcitable 
 and the posterior columns very excitable, the anterior 
 columns possess only a moderate degree of excitability. 
 The evidence is therefore conflicting. It is scarcely pos- 
 sible to be more precise than to affirm that certain longi- 
 tudinal parts of the cord are susceptible to direct irrita- 
 tion, — without saying what, exclusively, these parts are. 
 
 Inhibitory Effect of the Brain. — If the legs of a frog are 
 allowed to dip into dilute acid, the interval between 
 contact with the acid and the withdrawal of the cord is 
 considerably lengthened when the spinal cord remains undi- 
 vided below the medulla oblongata. The cord alone with- 
 draws the leg quicker than the cord as influencedTjy the 
 brain. Moreover, the cord alone can be depended upon to 
 respond with great regularity, in the form of definite reflex 
 movements, to a given amount of irritation applied to a 
 particular spot. But connection with the brain disturbs 
 this regularity. The cord is thus said to be inhibited by 
 the brain. We cannot, accordingly, so well calculate 
 what the cord, when under the influence of the brain, will 
 do. 
 
 We do not enter upon the disputed question whether a 
 special inhibitory apparatus belongs to the brain in its 
 connection with the spinal cord. There are no sufficient 
 
REFLEX AND AUTOMATIC NERVOUS FUNCTIONS. 143 
 
 grounds for assuming the existence of such a mechanism ; 
 but then, as Dr. Ferrier has said : " The nature of the inhibi- 
 tory mechanism is exceedingly obscure." The important 
 thing to notice, however, is that the cord, while having a cer- 
 tain independent power of functioning in various ways, is 
 controlled hy the higher centres of the hrain. Were this not 
 so, we could not, on the one hand, commit to it the task of 
 doing reflexly so many things for us ; and, on the other 
 hand, malce it carry out our desires by acting, or refraining 
 _ from acting, according to our will. In standing, walking, 
 running, playing upon musical instruments, writing, using 
 tools, etc., the activities requisite are exceedingly complex. 
 They involve a complicated and rapid interchange of the 
 following three processes : (1) spinal reflexes ; (2) reflex- 
 motor impulses that imply the trained inhibitory and 
 controlling action of the centres of the brain in con- 
 nection with the special organs of sense ; and (3) special 
 and more definite motor innervations that are due to con- 
 scious acts of volition. For all the life of habit in its 
 control over the movements of the trunk and limbs, and 
 for the possible inhibition, breaking, or changing of such 
 habit, the functions of the cord in their relations to the 
 functions of the higher parts of the cerebro-spinal axis, 
 are indispensable. 
 
 REFLEX AND AUTOMATIC FUNCTIONS OF THE LOWER BRAIN- 
 CENTRES. 
 
 On passing from the spinal cord into the brain, the diffi- 
 culty of determining the special functions of the different 
 nervous centres becomes greatly increased. The phe- 
 nomena become much more complicated ; and the parts are 
 less easily reached for purposes of observation and experi- 
 ment. 
 
 Methods of Observation and Argpument. — The methods of 
 research into the functions of the central organs of the 
 
144 PHYSIOLOGICAL PSYCHOLOGY. 
 
 brain are chiefly these two, — stimulation and extirpation. 
 Both, of course, can be in general applied only to the 
 lower animals. In the first method, some form of stimulus 
 is used to irritate a definite locality in the brain, and the 
 results of such irritation are carefully noted. To use this 
 method the organs must be exposed. With the skill and 
 safeguards of modern surgery this can be done for a con- 
 siderable portion of the brain, without permanent injury 
 to other organs or death of the animal. Those organs that 
 lie deepest cannot be treated by this method with the same 
 success. The stimulus of the electrical curi'ent is by far 
 the most convenient for experiment; but care must be 
 taken to circumscribe the effects of its diffusion through 
 the surrounding substance. 
 
 With the method of extirpation, the difficulties and the 
 need of caution are even greater. The " secondary " effects 
 of the lesion of any part of the brain of an animal are often- 
 times greater than those which can be justly ascribed to 
 the injury of the organ primarily affected. On the whole, 
 then, it is very difficult to arrive at a consistent view of 
 the facts. The phenomena observed are often confusing 
 and even apparently self-contradictory. 
 
 The argument from such data of facts can scarcely be 
 expected to yield a perfect demonstration. Valid objec- 
 tions may be raised to the very nature of the inferences made 
 by many observers. It is a doubtful assumption, for ex- 
 ample, that the activities which remain, when some of the 
 organs of the brain of an animal are extirpated, belong 
 wholly to the organs that remain, while the activities that 
 have disappeared belong wholly to the organs that have 
 disappeared. In such an exceedingly complicated mechan- 
 ism as the brain, with its extremely complex and close 
 interrelation of parts, the distinct marking off of " organs," 
 and " areas," and " centres," does not command our perfect 
 confidence. Specific differences belonging to different 
 
REFLEX AND AUTOMATIC NERVOUS FUNCTIONS. 146 
 
 kinds of animals, and individual differences between the 
 different members of the same species (in the case of the 
 higher animals), must certainly be much more taken into 
 account than they have heretofore been. It is difficult to 
 credit the inference that a particular portion or area of the 
 brain's substance is the (only) organ for particular func- 
 tions, so long as instances may be brought forward where 
 the function has been discharged in the absence, or after 
 the destruction, of such alleged " organ." 
 
 The difficulties of investigation of this subject are great- 
 est in the case of man. For man, of all the animals, has the 
 most complicated brain, and the most complex system of 
 functions connected with this organ. Moreover, he is of 
 all animals apparently — in his developed and adult life — 
 least dependent for his higher psychical activities upon the 
 condition of any small circumscribed portions of the brain. 
 Nor can he be experimented with as can the lower animals. 
 Inferences from them to him need to be guarded with 
 special care, so much does he differ from them both in 
 brain and in mind. The testimony of pathology is, gener- 
 ally, far from satisfactory. For when disease destroys the 
 substance of his brain, it does not nicely limit or definitely 
 announce the stage and spreading of the lesion it produces. 
 
 In spite of all difficulties, however, the localization of 
 reflex and automatic functions in the brain of the higher 
 animals, including man, has made great progress within 
 the last twenty years. Indeed, it is within this time that 
 the science of " cerebral localization " may be said to have 
 been established. It is even at present worth, for man, far 
 more than it has cost, whether of scientific painstaking on 
 his part, or of pain-bearing on the part of the lower an- 
 imals. It promises for the future a great extension of our 
 knowledge of the relations of man's body to his mind; 
 and — what is even more important — the ameliorating or 
 cure of some of the most distressing of human ailments. 
 
146 PHYSIOLOGICAIi PSYCHOLOGY. 
 
 PARTICULAR FUNCTIONS OF THE MEDULLA OBLONGATA. 
 
 Above the spinal cord the medulla is the organ about 
 whose functions we have the most precise information. In 
 general it may be said to be the organ of the " vegetative " 
 and also of the lowest animal life. 
 
 Reflex-Motor Functions of the Medulla. — These are more 
 intricate and of a higher order than those belonging pri- 
 marily to the spinal cord. They are particularly such as 
 stand related to the vital functions of the heart and blood- 
 vessels ; to respiration and its allied movements in cough- 
 ing, sneezing, etc. ; to muscular movement in swallowing, 
 vomiting, etc. ; and to the mimetic movements of laughing 
 and weeping. Some of these functions are purely reflex, 
 some only partially so. Thus one cannot swallow except 
 through action of the medulla ; but the lungs and heart con- 
 tinue to move after the paths between them and this organ 
 are destroyed. Sensory stimulation of the medulla may 
 occasion reflex movements along a large number of motor 
 tracts. Thus irritation of the throat will occasion simul- 
 taneously, swallowing, coughing, shedding tears, contortion 
 of the countenance, and changes of respiration and heart- 
 movement. 
 
 Automatic Functions of the Medulla. — The chief auto- 
 matic centres of this organ are those connected with breath- 
 ing, the movements of the heart, and the innervation of the 
 blood-vessels. The excitation in these cases must be sup- 
 posed to originate as a neural process within the organ ; 
 and the stimulus causing it is doubtless to be found in the 
 changing blood-supply. The medulla seems peculiarly sus- 
 ceptible to the condition of the blood. It is probably due 
 to the periodic reoxidation of the blood by the rhythmic 
 action of the lungs that the medulla sends out rhythmic 
 impulses from its respiratory centre to the lungs. 
 
 Centres in the Medulla. — This small piece of nervous 
 
KEFLEX AND AUTOMATIC NERVOUS FUNCTIONS. 147 
 
 matter may be said to be packed, full of important vital 
 centres. Among tbese the respiratory centre was first 
 located by the French physiologist Flourens in the V- 
 shaped apex of the fourth ventricle, or beak of the Calamus 
 scriptorius. Since the smallest injury here causes complete 
 cessation of respiration, he called it the " vital knot " (noeud 
 vital). Later investigators have located this centre 
 somewhat higher up. With it the various modifications of 
 respiration — such as sighing, sobbing, yawning, crying, 
 laughing, coughing, sneezing, hiccoughing — are connected. 
 
 A vaso-motor centre exists near the middle part of the 
 medulla. It is probably both automatic and reflex. The 
 removal of the parts in front of the medulla causes no per- 
 ceptible influence on the blood-pressure; we therefore 
 conclude that this organ itself contains the principal vaso- 
 motor centres of the brain. Through it very complex 
 muscTilar movements connected with changes in the circu- 
 lation can be called forth, as witness the effect of a draught 
 of air. In the same organ is a so-called cardio-inhihitory 
 centre ; it is through this centre, probably, that the heart 
 is stopped by impulses originating in the brain, when severe 
 pain or sudden and great emotion overpowers us. 
 
 The centre of deglutition lies still higher up. Destruction 
 of this organ makes swallowing impossible. Centres con- 
 nected with the secretion of spittle, sweat, tears, etc., have 
 been located in the same region, — namely, the floor of the 
 fourth ventricle. But we need not enter upon further 
 details in this matter. 
 
 Co-ordination of Movements by the Medulla. — If this cen- 
 tral organ be left connected with the spinal cord, but 
 severed from the organs lying above it, the frog thus pre- 
 pared becomes a more complex mechanism than is a simple 
 spinal cord. Such a preparation will execute movements 
 which the cord alone cannot execute. It will not, indeed, 
 move spontaneously ; but when irritated, by being placed 
 
148 PHYSIOLOGICAL PSYCHOLOGY. 
 
 in unnatural or uncomfortable positions, it will behave in 
 a highly purposeful way. Laid on its back it will make 
 efforts — generally unsuccessful — to turn over. Placed 
 in the water it will swim, — with movements less perfect 
 than those of the normal frog, but much more complex 
 than those possible for the cord alone. 
 
 The medulla oblongata of mammals seems capable of 
 executing very varied purposeful co-ordinated movements 
 of the muscles. A young rat, with its higher central 
 organs severed from the medulla, will cry when its toes are 
 pinched, will swallow, and perform complex movements of 
 the limbs. Infants, born with the centres above this 
 organ undeveloped, perform the associated movements of 
 sucking when put to the breast. Moreover, injury to this 
 organ seems to have a marked effect on the co-ordination 
 of the muscles. The most recent investigations connect 
 the upper part of the medulla Avith the gray matter of the 
 third ventricle, and with the semi-circular canals, in bal- 
 ancing the animal and otherwise co-ordinating its mus- 
 cular movements, in response to impressions of touch. 
 
 Associations among the Centres of the medulla. — The dif- 
 ferent small areas of this organ are very curiously related 
 in regard to their physiological functions. Some of them 
 are more excitable than others. Some of them can be 
 voluntarily excited; but others cannot. Some of them 
 are regularly associated together in their functions ; some, 
 seldom; some, never. We can voluntarily control the 
 movements of the lungs, within certain limits ; but cannot 
 stop, or quicken, by a volition, the movements of the heart. 
 We can at will make the medulla execute a cough, but 
 not a sneeze. We can call the swallowing centre into 
 operation without involving any other centres. In general, 
 the things which the medulla does for us, without taking 
 account of the condition of consciousness, are much more 
 important than the things we can make it do, by volitional 
 impulses sent from the cerebral hemispheres. 
 
REFLEX AND AUTOMATIC NERVOTJS EITNCTIONS. 149 
 
 BEHAVIOR OF THE ANIMAL DEPRirED OF ITS CEREBRAL 
 HEMISPHERES. 
 
 An animal which possesses all the nervous substance of 
 the brain except the cerebral hemispheres, is capable of 
 executing movements that differ greatly from those already 
 described as belonging to the spinal cord and the medulla 
 oblongata. Few of these movements, indeed, appear per- 
 fectly spontaneous or highly intelligent. And such move- 
 ments as have this appearance may generally be explained 
 as resulting from the complicated mechanical interaction of 
 the parts remaining, — cord, medulla, pons, crura cerebri, 
 cerebellum, corpora quadrigemina (or optic lobes), and 
 basal ganglia, — in response to a variety of connected 
 sensory impulses to which the parts are pecuharly sus- 
 ceptible. 
 
 The two animals, by experiment upon which most data 
 for forming a conclusion respecting these organs are 
 derived, are the frog and the pigeon. They are certainly 
 far enough removed from man in their nervous structure 
 and mental life. But of late, considerable success has 
 been obtained in keeping alive the higher mammals 
 after loss of large portions of their cerebral hemispheres. 
 By supplementing such observations with those of human 
 pathological cases, and by arguing upon general grounds 
 of comparative anatomy and physiology, a tolerably clear 
 view may be obtained of the most general uses of all those 
 parts of the brain that lie between -the medulla and the 
 cerebral hemispheres. 
 
 A frog from which the cerebral lobes alone have been 
 removed will, when appropriately stimulated, move about 
 almost as perfectly as a normal frog. It can swim well, 
 can leap and crawl. It can turn over easily when laid on 
 its back, and can balance itself on a tilting board. Sub- 
 merge it in water, and it will rise to the surface for air. 
 
150 PHYSIOLOGICAL PSYCHOLOGY. 
 
 It will avoid objects by guidance of the light. On the 
 other hand, it seems stupid, pays no attention to flies 
 placed near it, and will remain motionless, if kept from 
 irritation, for hours. 
 
 • The case of the pigeon from which the cerebral hemi- 
 spheres have been removed has been frequently investi- 
 gated. Certain details respecting its behavior have, 
 however, never been satisfactorily settled. The most 
 recent careful and extended observations describe the 
 phenomena about as follows : For a few days after los- 
 ing their hemispheres pigeons execute no spontaneous 
 movements. Soon, however, the time spent by them in 
 a slumberous condition becomes shorter, and they begin to 
 wander around the room without weariness. Their move- 
 ments are guided by sight from the first. Toward the 
 end of the first week they will clamber over a wall 12 
 centimeters high ; a few days later they will mount in the 
 corners of an enclosure 17 centimeters high. Their move- 
 ments seem perfectly regulated by impressions of touch. 
 They balance themselves on the hand or the edge, of the 
 table. But noises do not appear greatly to influence their 
 movements. 
 
 But do the actions of pigeons thus deprived of their 
 cerebral hemispheres show spontaneity and striving for a 
 goal ? This question is difficult to answer in a perfectly 
 conclusive way. Such birds will move around by day in 
 a very lively fashion, and sleep fast at night. Many of 
 their movements seem to have their origin in vegetative 
 functions ; but some of them also in complex impressions 
 of the special senses. When dislodged from the hand, or 
 from a stick, by turning it, they will aim their flight toward 
 a definite object; they exhibit a preference for one object 
 rather than others, as a place for alighting. They do not 
 appreciate the color or smell of food, and will eat it when 
 soaked in salty and other infusions; but even normal 
 
REFLEX AND AUTOMATIC NERVOUS FUNCTIONS. 161 
 
 pigeons have scarcely any higher perception of the differ- 
 ence between grain and stones than that which is based 
 on difference in size and weight. They do not feed them- 
 selves, — even when the grain is put into the front part of 
 their bUls. It is doubtful whether this is due wholly to 
 lack of perceptive power or also to a lack of power for 
 making the necessary co-ordinations. 
 
 On the whole the conclusion seems warranted that the 
 bird which has lost only its cerebral hemispheres moves in 
 a world of bodies whose situation, magnitude, and form 
 determine its movements, but whose apperceived relations 
 to the bird have ceased to influence it. It literally "mrnds" 
 nothing. It exhibits no fear of particular objects; no 
 recognition and no preference — of a sexual or other kind. 
 
 The phenomena which occur in the case of the higher 
 mammals, on partial or total loss of the cerebral hemi- 
 spheres, tend to confirm the same conclusion. The maimed 
 rabbit or rat will co-ordinate its muscular movements in 
 response to sensory impulses from the organs of touch, 
 hearing, and sight. But the definitely psychical qualities 
 seem largely or wholly to have departed from the actions 
 of the animal. The case of the more intelligent of these 
 mammals will be further considered in a subsequent 
 chapter. 
 
 The organs of the brain which lie between the medulla 
 oblongata and the cerebral hemispheres are all very inti- 
 mately related in their functions. To a certain extent 
 they act independently; within certain limits they can 
 assume each other's functions. They have largely the same 
 connections with the peripheral organs of sense and motion. 
 In general, they may be said to constitute that portion of 
 the nervous mechanism which serves as the central organ 
 for the complex co-ordination of impulses of the special 
 senses with the control of the motor apparatus. They 
 mediate a large part of that incessant and complicated 
 
152 PHYSIOLOGICAL PSYCHOLOGY. 
 
 readjustment of the animal's body which responds to the 
 effect of the environment on the peripheral organs of sense. 
 "We do not in this connection consider to what extent their 
 function necessitates or involves " sensations," in the only- 
 correct, psychical meaning of the word. 
 
 PARTICULAR FUNCTIONS OF THE CEREBELLUM AND BASAL 
 
 GANGLIA. 
 
 It is very difficult to assign the particular place which 
 belongs to each of the organs that lie between the medulla 
 oblongata and the cerebral hemispheres, under their general 
 function as already stated. 
 
 Functions of the Cerebellum. — Testimony as to the effect 
 of the extirpation or lesion of the cerebellum of mammals 
 is very conflicting. Almost the entire length and breadth 
 of its surface, both gray and white matter, may be removed 
 with little or no observable result. On approaching the 
 strands connected with the middle peduncles, disturbances 
 of motion begin and increase rapidly in proportion to the 
 amount of substance removed. Many of these disturb- 
 ances, however, are only temporary; permanent disturb- 
 ances occur, as a rule, only when the injuries affect the 
 lower third of the organ. 
 
 One-sided lesions of the cerebellum seem to have a much 
 greater effect upon the co-ordination of motion than that 
 obtained from symmetrical lesions. The former — espe- 
 cially when sudden — occasion, at least temporarily, pecu- 
 liar rolling movements of the eyes, suggestive of vertigo. 
 The entire body of the animal also rolls around its own 
 axis, — generally, though not invariably, toward the in- 
 jured side. In all cases of lesion, the places of the union 
 of the cerebellum with the medulla and with the crura 
 cerebri seem most important. 
 
 The evidence of pathology respecting the functions of 
 the cerebellum is, in the case of man, even more conflict- 
 
REFLEX AND AtTTOMATIC NERVOUS FUNCTIONS. 153 
 
 ing than the evidence of experiment with the lower 
 animals. Several well-known instances have occurred 
 where the cerebellum was either entirely wanting or had 
 become almost totally destroyed by disease. In most, if 
 not all of these instances, the balancing power of the 
 patient was imperfect. Some investigators have regarded 
 cerebellar ataxy as an almost unfailing result of the dis- 
 ease of the 'vermis of this organ ; but others have pointed 
 out numerous cases where this result did not follow, even 
 when the disease involved the entire vermis. During 
 twenty-four years ending 1887, Dr. Allen Starr found 160 
 cases of cerebellar disease reported in American medical 
 literature, in 40 of which symptoms and autopsies were 
 somewhat carefully described. Of these 40 cases there was 
 — headache in 26; insubordination of the limbs in 25; 
 vertigo in 20 ; vomiting in 18 ; blindness in 14. The 
 same year a German authority reported that, of 364 cases 
 of cerebellar disease, 260, or 71 per cent., had headache ; 49 
 per cent., nausea ; 33 per cent., affections of the eyesight. 
 
 It must be admitted that the entire evidence makes it 
 difficult to place much confidence in any induction respect- 
 ing the particular functions of the cerebellum in man. 
 But on the whole, it indicates that this organ is concerned 
 in securing precision of adjustment and balance of the two 
 sides of the body, in response to impressions of sense 
 (especially perhaps of sight and touch in the most general 
 meaning of the latter word). In discharging this office, 
 the cerebellum seems to be connected with the semicircu- 
 lar canals. 
 
 It need scarcely be added that modern physiology gives 
 no support whatever to the hypothesis of Gall, who con- 
 nected sexual feeling with the cerebellum. Nor is there 
 any good evidence to show that it is the particular organ 
 of any emotion, instinct, or form of intelligence. 
 
 Functions of the Corpora Quadrigemina. — Experiments 
 
154 PHYSIOLOGICAL PSYCHOLOGY. 
 
 upon these organs are difficult on account of their small 
 size and deep situation in the brain. The evidence from 
 lesions produced upon the lower animals has for a con- 
 siderable time tended to connect the corpora quadrigemina 
 with sensory impulses, not to say sensations, of sight. 
 Extirpation on one side appears to cause blindness of the 
 opposite eye ; and the amount of blindness is different in 
 different animals, as the decussation of the fibres in the 
 optic chiasm is more or less complete in different animals. 
 Moreover, when the brain is removed in front of these 
 organs, and they are themselves left intact, the animal can 
 still guide and co-ordinate its motions in response to visual 
 impulses. The reason for all this is not quite clear. It 
 may be that destruction of the nervous substance in this 
 region abolishes those movements of the muscles, in 
 response to the stimulation of light, which involve com- 
 plicated co-ordinations with other excitations of sense, or 
 with earlier established experience. We agree with the 
 remark of Eckhard, that much of the functions commonly 
 attributed to these bodies should be ascribed rather to the 
 region in which they lie. 
 
 Certain disturbances of motion and impairment of the 
 power of co-ordination of the muscles controlling the face, 
 eyes, trunk, and limbs, follow injury or extirpation of the 
 corpora quadrigemina. But this effect also is probably 
 largely due to the irritation and lesion of the surrounding 
 nerve-tracts. While, then, these organs are connected 
 with the cerebellum, pons, and medulla, in securing equi- 
 poise and precision of movement, it is scarcely safe to 
 attempt a more precise localization of their motor 
 functions. 
 
 Functions of the Optic Thalami. — Some special relation 
 of the optic thalami to impressions of sight is generally 
 admitted. The fact that animals deprived of their cerebral 
 hemispheres alone are capable of adjusting their movements, 
 
IlEFLEX ANi) AUT^OMATIC NEKVOUS FUNCTIONS. 155 
 
 in a complicated way, to visual impulses, seems to indi- 
 cate that the mechanism of these organs is associated 
 with the corpora quadrigemina in performing this function. 
 Disturbances of vision, sometimes amounting to complete 
 blindness, have been observed in human patients as the 
 apparent result of disease of these organs. Some observ- 
 ers, as Dr. Ferrier, and even Wundt, have connected the 
 optic thalami with the regulation of the muscles in response 
 to sensations of touch. The evidence on which this con- 
 clusion is based is, however, very doubtful. And, indeed, 
 the part which they appear to play in the reflex-motor and 
 automatic mechanism of sight may be rather due to secon- 
 dary effects on the surrounding nerve-tracts. It is even 
 now not wholly out of place to quote the remark, made 
 some years ago by the French authority, Vulpian, " We 
 know nothing of the special functions of the optic thalami." 
 
 Functions of the Striate Bodies. — The special motor sig- 
 nificance of the corpora striata is undoubted. As Dr. 
 Ferrier has maintained, the rule is, that stimulation or de- 
 struction of these organs in man and in the monkey causes 
 results almost exactly like those obtained by the same 
 treatment of the motor centres of the cerebral hemispheres. 
 Lesions of the striate bodies, in the case of the animals, 
 are usually followed by laming of the limbs of the opposite 
 side. This result does not, however, always occur. In 
 man, paralysis of the arms and legs of the opposite side 
 follows disease of one of these organs. And yet a case 
 has recently been reported ^ where destruction of the ante- 
 rior and irmer parts of the striate bodies on both sides was 
 followed by no paralysis of the limbs. 
 
 While, then, there is much evidence for the view of 
 Wundt, who considers these ganglia to be organs pre- 
 eminently for the co-ordination of those motor impulses 
 which are derived from the cerebellum and the cerebrum, 
 1 In Brain, July, 1887. 
 
156 PHYSIOLOGICAL PSYCHOLOGY. 
 
 we cannot affirm, without qualification, that the striate 
 bodies are exclusively motor and the optic thalami exclu- 
 sively sensory. 
 
 In 1884 J. Ott pointed out that cutting the corpora 
 striata is speedily followed by a marked rise of tempera- 
 ture. Other experimenters also have discovered proofs 
 that these bodies are in some special sense " fever-centres," 
 cerebral areas in special connection with the vaso-motor 
 system. 
 
 Gray Matter of the Third Ventricle. — Important central 
 functions appear to belong to the nervous substance which 
 lines the floor and walls of the third ventricle. One ex- 
 perimenter (Bechterew) finds evidence, as he thinks, that 
 this substance operates in connection with the olivary 
 bodies for the co-ordination of motor impulses with sen- 
 sory impulses of touch, and with the semi-circular canals in 
 response to sensory impulses of sound. There seems no 
 doubt that the matter around the third ventricle is of 
 importance in co-ordinating movements necessary to the 
 equipoise of the body through impulses derived from 
 changes in the axial direction of the eyes. 
 
 It thus appears — to repeat from our advanced point of 
 view what has already been indicated — that all the cen- 
 tral organs lying between the cerebral hemispheres and the 
 medulla oblongata are engaged in the general function of 
 co-ordinating, in a highly complicated way, the movements 
 of the muscles with the sensory impulses of the special organs 
 of sense. In the normal condition this function is under 
 the control of the hemispheres of the brain. The separate 
 organs form a complex interrelated system, corresponding 
 to the complex psychical life of motion in response to sen- 
 sation. In general, even in the case of the lower animals, 
 the functions of these organs, when bereft of the cerebral 
 hemispheres, shows a lack of psychical quality, of conscious, 
 and especially of intelligent, feeling, desire, and planning. 
 
KEFLEX AND ATJTOMATIC NEKVOCfS F0NCTIONS. 157 
 
 It is quite purely " automatic " (in the narrow sense of the 
 word), — the reaction, without intelligence, upon internal 
 and external stimuli of a highly complicated physical 
 mechanism. 
 
CHAPTER VII. 
 MECHANICAL THEORY OF THE NERVOUS SYSTEM. 
 
 That much of the human body exhibits the struct- 
 ure and movements of familiar machines, there can be 
 no doubt. Its members support and act on each other 
 according to those laws of the lever, pulley, baU-and-socket 
 joint, etc., with which the science of mechanics has to 
 deal. These laws do not need special modification when 
 applied to the case of the body. Less obvious, but equally 
 undoubted, is the machine-like character of certain muscu- 
 lar and epithelial structures. The heart, for example, is a 
 pump with chambers and valves ; and the flow of the blood 
 through the arteries resembles that of a fluid pumped 
 through conduits of unequal and changeable sizes. The 
 lungs maj' be compared to a bellows which alternately 
 sucks in and expels the surrounding atmosphere. So also 
 is the pull of the tendons on the bones like that of a cord 
 or chain attached to a mass, for its movement. 
 
 But the contraction of the muscular fibre is a very dif- 
 ferent affair from any of the movements to which reference 
 has thus far been made. It is a vital motion brought 
 about in the molecules of the muscular substance by the 
 stimulus of the nervous discharge into it. Yet the living 
 muscle may be looked upon as a molecular mechanism. 
 [We choose the word " mechanism " as preferable to 
 machine, because it does not imply the action of one rigid 
 mass, as a mass, on another, under the known laws of 
 mechanics.] It is a system of minute particles of matter 
 which act upon each other at indefinitely small distances. 
 158 
 
THEORY OP THE NERVOUS SYSTEM. 159 
 
 When any motion is set up in one part of the system, such 
 motion is propagated according to laws that are determined 
 by the constitution and arrangement of the particles them- 
 selves. 
 
 The basis for a mechanical theory of the nervous system 
 has been laid in the considerations of the previous chap- 
 ters. These considerations have all hitherto been such as 
 dispose us favorably toward some mechanical theory. In 
 the largest meaning of the word "mechanism," physical 
 science knows of no other way to consider any system of 
 interacting masses, or molecules, like those of the nervous 
 system. And yet the considerations of the previous chap- 
 ters have also prepared us for the statement that every 
 mechanical theory of the nervous system must be very 
 incomplete, and almost wholly of a tentative character. 
 The behavior of even a small piece of nerve attached to a 
 muscle (the so-called " muscle-nerve machine ") baffles the 
 explanations of all the students of physical science. How 
 much more, then, an organism of the nervous sort, so 
 infinitely complicated as the cerebro-spinal axis of man ! 
 
 Our survey of physiological psychology would, however, 
 be inexcusably incomplete, did we not set forth the more 
 essential features of every mechanical theory of the ner- 
 vous system. And the point we have now reached seems 
 the proper one for dealing with this subject. 
 
 Chemical Theory of the Ifervous System. — Little can be 
 added to what has already been said (see pp. 15 ff.) con- 
 cerning the exact chemical processes which take place in 
 the formation of the nerve-fibres and nerve-cells, or during 
 their functional activity. In the nervous substance, itself, 
 however, we find the same chemical elements which exist 
 everywhere in nature ; these are, especially, the four ele- 
 ments, oxygen, hydrogen, nitrogen, and carbon. We have 
 no reason to believe that the essential laws of the combi- 
 nation and dissolution of these elements are different in 
 
160 PHYSIOLOGICAL PSYCHOLOGY. 
 
 this substance from those known to have control elsewhere. 
 The fact that the combinations are not precisely the same 
 is to be traced back to the original constitution and devel- 
 opment of the substance itself. 
 
 Nucleated granules in the very chemical constituents 
 which give conditions to all the subsequent activity of the 
 molecules, are revealed by microscopic examination of those 
 cells from which the whole body springs. In the original 
 living germ, with which the body begun, and in all its 
 subsequent development, every chemical change in the 
 nervous substance may be regarded as a movement of the 
 physical molecules, — under conditions furnished by their 
 constitution and previous arrangement. 
 
 All the energy expended in the movement of the body 
 as a whole, or of any of its larger masses, originates in 
 minute molecular changes. These changes stand, of 
 course, in direct relation to the chemical constitution of 
 the tissues in which they occur. As we have already 
 seen, nervous substance holds in store a large amount of 
 easily disposable energy. This energy is yielded freely 
 and rapidly, if anything occurs to start the process within 
 the system of molecules of which the substance is com- 
 posed. When the molecules break up and recombine their 
 elements in simpler but more staple forms, they render 
 kinetic a great amount of energy which was formerly 
 latent. 
 
 On the other hand, the chemical constitution and envi- 
 ronment of the nervous substance are such as to place 
 certain checks upon the process of breaking up; and to 
 elicit and enhance the reverse process of building the sub- 
 stance up again into the more complex but unstable com- 
 binations. Thus kinetic energy again becomes stored for 
 future use ; and expenditure is kept within the limits of a 
 wise and safe economy. That one and the same stimulus 
 may facilitate both these processes involves a view of the 
 
THEORY OF THE NERVOUS SYSTEM. 161 
 
 nervoiis mechanism, under the general terms of a mechani- 
 cal theory, to which we shall recur again. 
 
 Mechanical Theory of the Structural Forms. — No devel- 
 oped mechanical theory of the significance of the different 
 forms, whether of elements or of organs of the nervous sys- 
 tem, is as yet possible. Our mental picture of the nerve- 
 commotions that pass from one nervous element to another 
 (nerve-fibres or nerve-cells) does not admit of details of 
 differentiation dependent upon minute differences of struc- 
 ture. In general, however, we note the relatively large 
 size of the motor nerve-cells. Glimpses of possible pecu- 
 liarities belonging to sensory as distinguished from motor 
 layers or areas of nervous substance, are beginning to be 
 obtained by histological science. 
 
 In general, the arrangement of the nervous elements 
 into a system answers to the demands of a mechanical 
 theory. The problem is one of concatenating the different 
 physical systems of the body, and of adjusting the relations 
 of the whole to changes in the environment. This prob- 
 lem demands a threefold exercise of function. The 
 mechanism answers the problem with three sets of organs 
 — namely, the end-organs, the more strictly conducting 
 organs, and the central organs. The end-organs — as, for 
 example and most strikingly, the eye or ear — are mechani- 
 cal contrivances for receiving and modifying some of the 
 forms of movement which take place outside of the body ; 
 and then for applying these modified forms of move- 
 ment to peculiarly differentiated nervous cells .and fibres. 
 It is the oflfice of the great mass of the eye to transmit 
 and refract the light; of the greater part of the ear to 
 transmit and condense the acoustic waves. But the ner- 
 vous elements of the retina, and of the organ of Corti, 
 change these physical processes into physiological proc- 
 esses. This change, too, they effect as properly constructed 
 molecular mechanisms. 
 
162 PHYSIOLOGICAL PSTOHOLOGY. 
 
 The nerves also are mechanisms, consisting of minute 
 particles, whose structure fits them to take up an agitation 
 started at any point, and transmit it from molecule to 
 molecule, in accordance with the constitution and laws of 
 the molecular system which they constitute. 
 
 The solution of the problems in mechanism, which fall 
 to the lot of the central organs, involves yet more compli- 
 cated structures and functions. Among those problems 
 are the following : Incoming molecular disturbances must 
 be so modified and distributed as to occasion other disturb- 
 ances outgoing along a number of definite tracts so that 
 co-ordinated groups of muscles may contract, simultane- 
 ously or in the right sequence, in a highly complicated 
 way. Moreover, the movements that control respiration, 
 secretion, digestion, and the circulation of the blood and 
 other fluids, must be united so as to work to a common end ; 
 they must also be modified as the changes in the environ- 
 ment require. Still further, all the natural processes must, 
 in the central organs, be correlated with the processes of 
 the mind. Only in this way can sensations and perceptions 
 arise, through the action on the body of external stimuli ; 
 only in this way can perceptions, and their accompanying 
 desires, emotions, and volitions, get expression in the 
 physical realm, and induce changes in external things. 
 
 This indefinite and general view of the mechanical 
 structure and functions of the nervous system obviously 
 needs to be somewhat further expanded. 
 
 General Mechanical Of&ce of the Nervous System. — The 
 development of a rich and varied life, both animal and 
 intellectual, requires a great variety of related sensations 
 and motions. The sensations are primarily designed to 
 give notice to the animal of changes in his environment to 
 which his condition must be adapted by changes of his 
 bodily parts. "Within certain wide limits, the same office 
 is performed by sensory impulses which do not give rise to 
 
THEORY OF THE NERVOUS SYSTEM. 163 
 
 sensations, — in the only true meaning of that word, as 
 psychical states. But sensations, as primary psychical 
 states, form the basis of intellectual attainment and 
 development. 
 
 The forces of external nature continually irritate the 
 peripheral parts of an animal's body. These forces are the 
 stimuli of sensory impulses, only when they are converted, 
 within the tissues of the body, into molecular motions of a 
 physiological kind. The mechanism of the nervous system 
 accomplishes this work of conversion; it then propagates 
 the molecular disturbances to the proper central organs, 
 and through them again to the external and muscular 
 tissues of the body. Thus the play of the energies of 
 external nature, instead of being injurious or destructive, 
 becomes useful in maintaining the equilibrium on which 
 life depends. It also becomes educative, — not only of a 
 wise use of the bodily organs, but also of the higher life 
 of the mind. 
 
 Now it is plain that all this requires a constant equili- 
 hrating of the interaction of different and distant parts of the 
 body. How shall this general important office of " equi- 
 librating" be performed? Only by a highly elaborate 
 arrangement of an indefinitely great number of very com- 
 plex molecules. Such a molecular mechanism is the nervous 
 system. The various forms of physical energy — such as 
 light, heat, sound, chemical change, etc. — set into molecu- 
 lar agitation cei-tain nicely adapted parts of this mechanism. 
 This agitation is propagated from place to place, along the 
 tracks prepared, and accompanied by other physical changes 
 of a chemical, thermic, and electrical kind. These func- 
 tions of the nervous system are nothing but the movements 
 of physical elements, whose constitution and changes, when 
 performing their work, it is indeed very difficult to discover, 
 but which Tindoubtedly have a physical constitution and 
 which change their relations in space under laws resembling 
 
164 PHYSIOLOaiCAL PSYCHOLOGY. 
 
 those familiar to general molecular science. But this is 
 precisely what science understands by a "molecular 
 mechanism." 
 
 On the other hand, it cannot be denied that such a de- 
 scription as the foregoing is not full and exact enough to 
 satisfy the demands of scientific research. It is confessedly 
 based upon conjecture ; it is full of gaps and assumptions. 
 A complete and satisfactory mechanical theory of the 
 nervous system would have to answer a number' of ex- 
 tremely difficult special problems, the very beginning of an 
 answer to which has scarcely, as yet, been attained. 
 
 What, for example, is the precise nature of those chem- 
 ical changes which — we have every reason to believe — 
 go on in every nerve when it is irritated ? If the process 
 of excitement consists in the explosive decomposition suc- 
 cessively of the elements of the nerve, what checks the 
 process of explosion ? Why is not all the energy expended 
 by the excited nerve ? How does it manage to repair itself 
 so as to answer, within certain limits, all the demands which 
 it is possible to make upon it ? So, too, if we attempt to bring 
 the nervous mechanism under the terms of a general elec- 
 trical theory, we find a number of difficult and hitherto 
 unanswerable problems awaiting us. How shall the phe- 
 nomena of electrotonus in nerves be explained in terms of 
 any known electrical theory? How shall we regard the 
 so-called "natural current," etc.? 
 
 These immense and perhaps, in some instances, insuper- 
 able difiiculties do not, however, excuse us from the obli- 
 gation to hold firmly by the proposal to regard the nervous 
 system under the terms of a mechanical theory. Molec- 
 ular science in general — in all its different branches of 
 heat, electricity, magnetism, etc. — encounters many and 
 great difficulties. But it knows no other way, in fidelity 
 to principles established by all scientific experience and by 
 all the past development of physical science, than to face 
 
THEOBY OF THE NERVOUS SYSTEM. 166 
 
 the difficulties with successive attempts to overcome them, 
 and thus satisfy all the phenomena in terms of a meehanieal 
 theory. In the nervous system of man, molecular science 
 finds its most complicated and baffling problems. These 
 problems, too, it must continue to regard in fidelity to its 
 most general established principles. 
 
 It only remains for us briefly to sketch several of the 
 forms which have been taken by the attempt to frame a 
 precise theory of the functions of the nervous mechanism. 
 
 Wave-Theory of Nervous Action. — That the molecular 
 disturbances caused in the nervous substance by tha action 
 of stimuli move from place to place, after the analogy of 
 waves, is shown by all the phenomena with which so-called 
 " general nerve-physiology " attempts to deal. In par- 
 ticular have we seen (p. 130 f .) that the effect of several 
 excitations of a nerve is compounded, in some sort, in the 
 movement of the attached muscle. Those excitations 
 which are simultaneous, or which follow each other with 
 the right degree of rapidity, are "summed up" in the 
 nerve, like waves of nerve-commotion piled upon one 
 another. Besides cases of " summation," those of "inter- 
 ference " seem also to exist. Moreover, the effect of one 
 excitation, in certain instarujes, especially within the cen- 
 tral organs, appears to " facilitate " the subsequent passage 
 of other excitations along the same path. 
 
 Elaborate experiments have been made to determine the 
 laws which control the " summation," " interference," and 
 "facilitation" of the waves of nerve-commotion within 
 the nervous mechanism. Let the interferences be called 
 " positive " when the currents are moving in the same 
 direction, and " negative " when they are moving in oppo- 
 site directions. Certain interferences may also be noted 
 which have a "heightening" effect; for the result actually 
 produced in the muscle appears to be greater than the 
 sum of the two single effects gained by the partial exci- 
 
166 PHYSIOLOGICAL PSYCHOLOGY. 
 
 tations if uncompounded. When, on tlie contrary, the 
 result is less than the sum of the separate partial excita- 
 tions, the effect is said to be " depressing." When, in the 
 third place, the result is reduced to zero, the effect is 
 "inhibitory." All the foregoing kinds of result may be 
 obtained by compounding the nerve-commotions. But so 
 complicated are the phenomena derived by the various 
 forms of compounding as to forbid our regarding the 
 organs themselves as simple and substantially homoge- 
 neous structures. The effects produced hy wave-like '■'•in- 
 terferences " in a nerve depend upon the original molecular 
 constitution of the nerve excited. Moreover, in general, the 
 results of interference conform to the same rules after 
 decapitation or poisoning as before. The interferences 
 that occur in reflex action also follow the same course as 
 those which occur by direct stimulation of the motor 
 nerves. 
 
 In brief, — even in the case of the simple nerve-muscle 
 machine, — it is the molecular constitution of the sub- 
 stance, which acts as a mechanism, that determines all 
 the many variable elements resulting from the molecular 
 disturbance of this substance. 
 
 The phenomena which the central organs exhibit when 
 excited are, of course, far more complex and difficult to 
 bring under known laws of molecular wave-like impulses, 
 than are the phenomena of the comparatively simple nerve- 
 muscle machine. In general, the motor excitation of any 
 extremity of an animal, from the brain, " facilitates " the 
 subsequent passage of reflex stimulus affecting the same 
 extremity; and, conversely, reflex stimulation of any ex- 
 tremity " facilitates " the passage of a subsequent motor 
 excitation from the proper area of the brain to that ex- 
 tremity. For example, stimulating the toes of the fore- 
 leg of a rabbit produces a greater reflex movement of the 
 same leg, with the same amount of stimulus, if the cerebral 
 
THEORY OF THE NERVOUS SYSTEM. 167 
 
 motor-centre for that leg has just been directly stimulated. 
 Different reflex excitations may also be made to " assist " 
 each other in a similar way. But by this method of ex- 
 periment, also, certain results of compounding excitations 
 are attained which seem incompatible with any known 
 theory of the summation or interference of molecular 
 wave-like disturbances. 
 
 Strictly speaking, we cannot represent, without qualifi- 
 cation, the behavior of a single nerve under stimulation 
 from two currents of electricity acting upon it in combi- 
 nation, as though it were an affair of the " addition " or 
 "subtraction" of their separate effects. It is possible that 
 a stimulation equal in amount to a + J may not excite the 
 nerve, although one equal to h alone will excite it, in case 
 a current equal to a has just previously been acting in the 
 nerve. Excitations already existing in a nerve, when 
 further stimulation is applied, are then not simpl)'- added 
 to or guhtracted from the latter. They rather tend to pro- 
 duce obscure molecular changes in the nerve itself, and 
 these changes show themselves, in the nerve, in a very 
 variable and baffling way, as places and phases of exalted 
 or depressed excitability. Let a represent the strength of 
 current required to excite a nerve in its normal condition. 
 When the nerve itself is in the condition of exalted excita- 
 bility, a current weaker than a will excite it ; but when it 
 is in the condition of depressed excitability, a current 
 stronger than a will not excite it. 
 
 How obscure and complicated are the molecular con- 
 ditions connected with the excitement of a nerve, is 
 further shown by observing the effect of cross-section 
 upon its behavior. For example, for some minutes after 
 cross-section, binding the nerve produces a large increase 
 of its excitability in the injured place. This is true for 
 all kinds of stimuli, including the electrical current in 
 both directions. Five to ten minutes subsequently, how- 
 
168 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ever, the making of the current in the opposite direction 
 to the current induced by cross-section frequently has a 
 diminished rather than an increased effect. 
 
 Electrical Theory of Nervous Action. — - A leading authority 
 has declared that the two most important principles which 
 must enter into any theory that undertakes to explain the 
 behavior of the nerves in relation to electricity are these : 
 (1) the principle of electrical excitation, and (2) the 
 principle of the so-called " current of action." 
 
 We have already seen (p. 127 f .), that the passage of an 
 electrical current through a nerve produces a changed 
 condition of excitability called electrotonus. It has also 
 been shown that this condition varies in different parts 
 of the nerve, with the distance of each part from the elec- 
 trodes, and with the strength of the polarizing current. 
 The condition is in general one of increased excitability 
 (and perhaps decreased conductivity) around the cathode, 
 and of diminished excitability around the anode. The 
 time required for the development of this condition is not 
 perceptibly later than the electrical current which occa- 
 sions it. The condition seems also to spread itself over 
 the nerve with a speed equal to that of the process of 
 excitation. 
 
 Another important fact already noted (see p. 130), is that, 
 with the nerve as with the muscle, the galvanometer shows 
 the passage of a current when one of the electrodes is 
 placed at its cut end and the other at its equator. This 
 so-called " natural current " is diminished by stimulating 
 the nerve, as is shown by the return of the needle toward 
 the zero-point ("negative variation"). 
 
 How now shall these two cardinal groups of facts be ex- 
 plained in terms of a defensible electrical theory? The 
 question cannot, at present, be answered with all the accu- 
 racy and detail which physical science requires. Consider- 
 able progress has, however, been made toward a probable 
 answer to several of the particular inquiries involved. 
 
THEORY OP THE NEBVOtfS SYSTEM. 169 
 
 Theory of the so-called " Natural Current." — Two ways of 
 regarding the phenomena referred to above as the " natural 
 nerve-current," or " current of rest," have been proposed. 
 An intelligent choice in favor of one of them now seems 
 possible. The first of these theories (that of du Bois- 
 Reymond) holds that a true natural current exists in the 
 nerves, previous to their excitement or injury by cross- 
 section. This current is made obvious by the deflection 
 of the needle of the attached galvanometer. It is then to 
 be regarded as the resultant of the innumerable unobserved 
 currents belonging to the separate molecules of the nerve. 
 To account for the latter, an elaborate theory is proposed, 
 which regards every molecule of the nerve as a minute 
 battery with positive and negative poles. It is the pres- 
 ence of these molecules which gives rise to currents in 
 the medium that surrounds them. 
 
 In order to account for the fact that such " natural " 
 currents are exceedingly small or wholly wanting, when 
 the structure is uninjured, this theory is obliged to resort 
 to very complicated and artificial hypotheses. Under this 
 weight it may be said utterly to break down. 
 
 The rival theory (advocated especially by Hermann) 
 denies the existence of any true " current of rest " in un- 
 injured nerves. It regards the starting of the current as 
 due to the injury inflicted by cross-section. For, whenever 
 a nerve is cut or any of its fibres injured, the molecules at 
 once begin to die. But this implies chemical and other 
 changes. These changes, in which the death of the mole- 
 cules consists, develop the electrical currents. The mole- 
 cules, disturbed by the injury, become negative toward the 
 uninjured parts. 
 
 Instead, then, of seeking an elaborate special explanation 
 for the phenomena of " negative variation," we may hold 
 that they are precisely what we should expect in view of 
 our knowledge of general electrical theory. So-called 
 
170 PHYSIOLOGICAL PSYCHOLOGY. 
 
 "negative variation" is not due to the diminution of a 
 current previously existing. It is simply a manifestation 
 of the electro-motive forces which come into action at the 
 moment and at the seat of excitation. As this wave passes 
 along the nerve, each minute portion of the nerve becomes, 
 first, negative, and then positive, toward the adjoining por- 
 tions. The resultant of these small local currents is an 
 excess of those from the cut end over those to the cut end, 
 — that is, the so-called negative variation. 
 
 Thus the phenomena of the "natural current" and 
 " negative variation," so called, are all to be Ibrought 
 under the one general principle. AH excitable protoplasm, 
 when dying or irritated, becomes negative towards its own 
 uninjured and unirritated parts. 
 
 Theory of the Electrotonus of Nerves. — It has been said 
 that any electrical theory of the action of the nervous sub- 
 stance must be prepared to explain the phenomena of 
 changed excitability produced by the constant current in 
 the nerve. The point of starting for that form of theory, 
 which has most claims to credence, may be taken from a 
 discovery made some years ago by Matteucci. In 1863 
 this truly great investigator noticed phenomena, similar to 
 those of the nerve in the electrotonic condition, occurring 
 in over-spun wires when moistened with a conducting fluid. 
 If an electrical current be applied to the moist covering 
 of such a wire, every part of the wire will develop a cur- 
 rent flowing in the same direction with the primary current, 
 but with its strength diminishing as the distance increases 
 from the points where the primary current is applied. No 
 such current arises, however, if the wire is made of amal- 
 gamated zinc, and its covering is moistened with a solution 
 of sulphate of zinc. It appears, then, that the changed 
 electrical condition of the wire depends upon the limiting 
 surfaces of its metal centre and its moistened covering 
 being polarizable. That is to say, as has been more re- 
 
THEORY OF THE NERVOUS SYSTEM. 171 
 
 cently maintained,^ a conductor consisting of a centre and 
 a conducting covering, with polarizable limiting surfaces, 
 as soon as a momentary electrical current is sent through 
 any portion of it, begins successively to exhibit a current 
 of the same kind at every other place in it. 
 
 Can a nerve be regarded as having the properties of the 
 over-spun wire, with its polarizable limittag surfaces ? 
 Every nerve-fibre may certainly be said to consist of a 
 centre and a covering substance. The needed limiting 
 surfaces may, perhaps, be found between the axis-cylinder 
 and the medullary sheath. An inner polarization, such as 
 takes place between the wire and its moistened covering, 
 may then take place between this core of the nerve and 
 one of its sheaths. The electrotonic current may, there- 
 fore, be due to an escape of this polarizing current. Such 
 a current is wanting in dead nerves, because the requisite 
 inner polarization cannot take place in dead nerves. 
 
 Various objections have been brought against an electri- 
 cal theory of the nerve as formed after the analogy of 
 the over-spun polarizable wire. Some of these objections 
 are based upon very complicated results which are gained 
 by stimulating the nerve under a variety of conditions, 
 and with the exciting current applied to different parts of 
 the nerve, — intra-polar as well as extra-polar. To explain 
 these results it seems necessary to suppose that a number 
 of " secondary action-currents " are evoked by the stimu- 
 lus; and that these currents are superimposed upon one 
 another, and upon the electrotonic variations due to the 
 polarizing cun-ent — all in a bewildering complexity of 
 combinations. But — with the condition of the Ptolemaic 
 system just previous to the discovery of Copernicus in 
 mind — we feel obliged for the present to stop and await 
 conjectures warranted by further researches. 
 
 It is perfectly obvious that " the platinum wire, with its 
 1 By Hermann, in Pfluger'a Archiv, 1885, xxxv., p. 23 f. 
 
172 PHYSIOLOGICAL PSYCHOLOGY. 
 
 moist sheaths, is no (complete) model of the irritable 
 nerve." A single nerve-muscle preparation, taken from 
 the leg of a frog, behaves in such a way as to show that it 
 is, even as regards its electrical properties, a much more 
 complicated mechanism than is any such wire. We must 
 confess, then, that we have no adequate theory for explain- 
 ing the behavior of this comparatively simple nervous 
 apparatus. How far, then, are we from a complete mechani- 
 cal theory of the human nervous system ! Any statement 
 of an intelligent and judicious attempt to form such a 
 theory possesses, however, a certain interest and value. 
 
 Mechanical Theory of Wundt. — In the attempt to con- 
 sider the nervous system as a molecular mechanism we are 
 obliged to reason, for the most part, deductively. We 
 cannot successfully investigate directly the chemical and 
 physical constitution of the nervous elements, and the 
 changes which they undergo in the discharge of their 
 functions. By assuming certain general principles of 
 molecular physics, and especially the law of the conserva- 
 tion of energy, we can speculatively show how living 
 beings may be brought under the control of these princi- 
 ples. This is the mode of procedure adopted by the Ger- 
 man authority. Professor Wundt. 
 
 All living beings take a noteworthy part in that process 
 of interchanging potential and kinetic (inner and external) 
 energy, which goes on everywhere in nature. In all ani- 
 mals which have a nervous system, it is this system which 
 controls the process. The process itself is a species of 
 combustion. The source of the peculiar activities of the 
 nervous system in controlling this process lies in the 
 nature of the chemical combinations found in its substance. 
 
 The nervous system, regarded as unaffected by stimuli, 
 may be theoretically compared to a fluid in a condition of 
 equilibrium. In fact, however, the nervous system never 
 is in a condition of perfect equilibrium. Not only is there 
 
THEORY OF THE NERVOUS SYSTEM. 173 
 
 a ceaseless play of energy internal to the system, in which 
 the atoms separate from their old combinations as nervous 
 substance and reunite, in new combinations, to form the 
 same kind of substance ; but also a continuous process 
 goes on by which the molecules of the nervous substance 
 are broken up to form less complex but more stable non- 
 nervous compounds. The reverse of this last process is 
 also constantly going on in the body ; the nervous system 
 is being nourished, or built up, by the more stable com- 
 pounds of other substance being broken up and their 
 atoms used to form the nervous substance. 
 
 Here, then, are two processes of change constantly going 
 on. One represents the passing of the atoms from the less 
 stable to the more stable combinations, the destruction of 
 the nervous substance, and the setting free of stored or 
 potential energy. The energy thus made apparent Wundt 
 calls "positive." The other process represents the passing 
 of the atoms from the more stable to the more highly com- 
 plex but less stable combinations, the repair of the nervous 
 tissue, the storing of energy and the vanishing of kinetic 
 energy. The energy stored up, when the more stable 
 combination vanishes, is called " negative." The positive 
 molecular energy of the nervous system is recognized as 
 heat set free, as contraction of the muscles, etc. ; its nega- 
 tive molecular energy exists in the form of heat becoming 
 latent, or of inhibitory action upon the course of the exci- 
 tation of the nerves, etc. 
 
 Wundt would explain the process of excitation and con- 
 duction in the nerves, in accordance with the foregoing 
 theory of positive and negative molecular energy. In all 
 cases, when a nerve is excited, two classes of opposed 
 effects are set up in its substance. One is directed toward 
 the production of external energy, — such as secretion, 
 stimulation of ganglion-cells, movement of the muscles, 
 etc. The other is directed toward the control of the 
 
174 PHYSIOLOGICAL PSYCHOLOGY. 
 
 energy thus set free. The general law Is, that hy the 
 application of stimulus both of these opposed effects are 
 augmented in the nervous substance. That is to say, irri- 
 tating the nervous substance accelerates both the recom- 
 bination of the atoms of its highly complex molecules in 
 less complex but more stable forms ; and also the escape 
 of the atoms from these forms and their return to the more 
 complex and less stable combinations. The work which 
 the nerve does external to itself depends upon the former 
 process. It is a species of combustion, in which the com- 
 plex molecules break up and their atoms pass into more 
 stable and simple combinations. It involves, of course, 
 the exhaustion of the nerve. It implies that the positive 
 molecular energy is more accelerated than the negative, by 
 the irritation of the stimulus. The entire sum of energy 
 thus set free to do external work is distributed in three 
 principal directions : in the continuous excitation of the 
 nerve ; in producing heat ; in producing the reverse pro- 
 cess of negative molecular energy. 
 
 Wundt's theory becomes more complicated when he 
 attempts to apply it to the central organs of the nervous 
 system. Here the chief thing of which account must be 
 taken is the observed fact that a greater amount of stimu- 
 lus is needed to move a muscle through a collection of 
 ganglion-cells. The nervous substance of the central 
 organs offers a greater resistance to the progress of a nerve- 
 commotion than is offered by the nerves. On the other 
 hand, this substance has stored within it a vast amount of 
 energy ; it is, therefore, in a condition to answer a demand 
 made upon it by developing a far greater amount of work. 
 Wundt finds proofs for this view in the phenomena of 
 " reflex poisons," of " summation," of " inhibition " (see p. 
 165 f.) , etc. He concludes that when summation takes place, 
 the several sensory excitations have been conducted in the 
 brain to different sensory regions, and have then passed 
 
THEORY OP THE NERVOUS SYSTEM. 175 
 
 simultaneously from them into the corresponding motor 
 elements of the central organ. But when inhibition takes 
 place, the excitations have been conducted so as to come 
 together and counteract each other in the same sensory 
 central region. 
 
 Excitation of the central organs, like irritation of the 
 nerves, increases both their positive and their negative ner- 
 vous energy. But the positive molecular energy of the 
 central organs is but slightly increased by a momentary exci- 
 tation. Prolonged excitation, however, causes the positive 
 condition — i.e. the condition of doing work external to the 
 system — to predominate over a wide area. In the nerve, 
 as a rule, the nervous substance is used up, and the pro- 
 cess of restoring it and storing energy goes on, compara- 
 tively slowly. An excited ganglion-cell is in a condition 
 analogous to that of the nerve at the anode when the con- 
 stant current is passing through it. In the cells, as a rule, 
 the production of the complex molecules in which energy 
 is stored predominates. 
 
 The fundamental properties of nervous matter con- 
 sidered from the mechanical point of view are, according 
 to Wundt, these two, (1) to receive external impressions, 
 in order by them to be determined in its own molecular 
 condition ; and (2) to transform the potential energy of 
 the body into kinetic, partly under the immediate, and 
 partly under the progressive, influence of these impressions. 
 
 Wundt proposes an elaborate and highly speculative 
 view of the molecular constitution and functions of the 
 ganglion-cells. But we refrain from entering upon a sub- 
 ject so largely conjectural. 
 
 In conclusion, we return to the general truth that the 
 entire nervous system may undoubtedly be regarded as a 
 vastly complicated molecular mechanism. Its chemical con- 
 stitution is highly complex and correspondingly unstable. 
 It performs, as a mechanism, the general work of bringing 
 
176 PHYSIOLOGICAL PSYCHOLOGY. 
 
 together into unity the functions of the other systems of 
 the body. It performs this work under the laws of molecu- 
 lar physics. But what it does by way of function depends 
 upon what it is in respect to molecular constitution. And 
 so complicated is the application to it of the general theory 
 of molecular physics that, thus far, all the resources of 
 that science have been quite insufficient to afford detailed 
 explanations. 
 
CHAPTER VIII. 
 
 SENSORY AND MOTOR FUNCTIONS OF THE CERE- 
 BRAL HEMISPHERES. 
 
 Ordinary observation does not make known to us the 
 great significance of the nervous system for the life of 
 conscious sensation and motion. It is only accident or the 
 dissecting-knife which exposes the peripheral nerves to 
 our sight. In the case of the central organs, and espec- 
 ially in the case of the contents of the skull, there is little 
 in our daily experience which leads to the suspicion of 
 their significance or even of their existence. That mech- 
 anism of nerve-fibres and nerve-cells, on whose activity all 
 our knowledge of things, including our own bodies, is 
 dependent, does not convey any direct knowledge of itself. 
 
 It is not so strange, then, as might appear at first sight, 
 that the ancients, as a rule, attached little importance to 
 the brain. The physician Alcmseon is, indeed, reported by 
 later writers to have regarded it as the meeting-place of 
 the senses. A similar view is ascribed to the celebrated 
 Hippocrates, and was accepted by Plato. But Aristotle, 
 the greatest of all inductive philosophers in antiquity, 
 although he was the son of a physician, and was for his 
 time exceedingly well acquainted with the dissection of 
 animals, made little account of the brain. He seems to 
 have regarded it as quite unfit to be the seat of the 
 sensus communis, — a lump of cold substance chiefly use- 
 ful as a source of fluid for lubricating the eyes ! 
 
 Nor can the great significance which modern science 
 attributes to the brain be held to have its origin largely 
 
 177 
 
178 PHYSIOLOGICAL PSYCHOLOGY. 
 
 in direct feelings connected with the exercise of its 
 functions. 
 
 To be sure, we localize in the head certain phenomena 
 of consciousness connected closely with processes of thought. 
 The act of attention, for example, results in feelings of 
 strain in the muscles of the eye, or over the skin of the 
 forehead and its adjacent parts. Sensations of hearing, 
 smelling, and tasting originate in the head, and some- 
 times seem to penetrate its interior. After-images, or 
 spectra, appear with the eyes closed as seated in the upper 
 front part of the face. We " talk, to ourselves " within the 
 head, as it were. Eager and concentrated observation, or 
 concentrated reflection, may develop painful feelings in 
 the cerebral region. Men lean the head on the hand in 
 support of meditation ; or rub it vigorously to awaken the 
 powers of memory or reasoning. In this highly " nervous " 
 age, the attention of multitudes is undoubtedly directed 
 to the existence of sensations localized on the surface, of, 
 or within, the skull, which were scarcely noticed by the 
 ancients. It was the effect of strong passion and desire on 
 the visceral organs which attracted the attention of the 
 latter, as all their language shows. The brain, in the popu- 
 lar estimate as a matter of seemingly direct knowledge, is 
 a modern organ. 
 
 The phenomena of self-consciousness are confirmed in a 
 general way by observation of what happens to others. A 
 blow upon the head, or the shutting off of the blood-supply 
 by pressure at the neck, disturbs or suspends conscious- 
 ness. Several of the principal organs of sense, regarded as 
 avenues for sensory impulses, are so related to the contents 
 of the cranial cavity as to suggest that it may serve as 
 their common place of meeting. It was this obvious fact, 
 naively interpreted, which led certain ancient anatomists, 
 like Galen and Herophilus, to locate the soul in the brain. 
 
 Modern science is, of course, not satisfied with the vague 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 179 
 
 results derived from feeling and ordinary observation of 
 others. It attempts to establish definitely and experimen- 
 tally the function of the contents of the cranial cavity in 
 the life of consciousness. In this attempt it considers, 
 first, certain general facts which connect the entire brain 
 of man, and especially the cerebral hemispheres, with his 
 psychical life. It then tries to assign the more particular 
 functions, connected with the varieties of this psychical 
 life, to particular parts of the hemispheres. This investi- 
 gation leads to " the localization of cerebral functions." 
 
 GENERAL SIGNIFICANCE OF THE BRAIN FOB THE 
 PSYCHICAL LIFE. 
 
 A multitude of physical considerations place beyond 
 doubt the supreme influence of the human brain upon the 
 phenomena of consciousness. 
 
 Consciousness and the Cranial Blood-supply. — The free cir- 
 culation of arterial blood, with its supply of oxygen, is 
 necessary to the central organs for the proper fulfilment of 
 their functions. It has been calculated that, while the 
 weight of the entire encephalon is about one forty-fifth of 
 the body, the supply of blood used up in the encephalon is 
 about one-eighth or one-ninth of that required by the 
 whole body. The presence of impui-ities in the blood, 
 derived from drugs or otherwise, quickly and profoundly 
 makes itself felt in modifying the phenomena of con- 
 sciousness. The quickening of the circulation by alcohol 
 or quinine is productive of an increased speed of the train 
 of thought and imagination. 
 
 Consciousness and the Temperature of the Brain. — It has 
 been known for some time that a rise and fall of tempera- 
 ture in the substance of the brain is connected with changes 
 of the psychical states. Experiments upon the lower ani- 
 mals lead one observer to conclude that, in the case of any 
 animal which enjoys integrity of the nervous centres, all 
 
180 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the sensory impressions which arrive at the hemispheres 
 produce a rise of temperature by their very transmission. 
 But, furthermore, psychical activity, independently of the 
 sensory impressions, develops a certain degree of heat in 
 addition to that developed by the impressions themselves. 
 
 More recent experiments seem to show that strong im- 
 pressions do not, as a rule, result in a simple rise of tem- 
 perature in the cerebral areas, but rather in an alternation of 
 rising and falling. This alternation occurs over the entire 
 area of the hemispheres, but with different speed and 
 degrees of augmentation in the different local areas. The 
 elevation is greatest in the occipital protuberance ; and it is 
 greater and more rapid for emotional disturbance than for 
 sensation or intellectual work. A variation, but of a con- 
 siderably less degree, takes place in the temperature of 
 the brain-substance even in states of cerebral repose. 
 
 The conclusion seems warranted that these changes of 
 cerebral temperature are not due simply to changes in the 
 arterial circulation. They appear independent of the 
 rhythm of respiration, but dependent on the rhythm of 
 metabolic activity. They show — that is — that work is 
 being done in the nervous substance in connection with the 
 increased psychical activity. 
 
 Consciousness and the Waste of Brain-substance. — An in- 
 crease in the gross waste of tissue can be shown to be the 
 accompaniment and physical correlate of mental work. 
 This waste is indicative of brain-work. It shows that 
 potential energy of the nervous substance has become 
 kinetic. The quantity of sulphates and phosphates excreted, 
 in comparison with the quantity carefully estimated as 
 entering into the diet, is noticeably increased by increasing 
 the mental work. To yield these sulphates and phosphates, 
 the highly complex compounds of the phosphorized con- 
 stituents of the brain have been disorganized. 
 
 Size of Brain in Different Animals. — A comparison of the 
 
SENSOBY AND MOTOR BBAEN FtTNCTIONS. 
 
 181 
 
 s this relati 
 Finch . . 
 
 3n: — 
 
 231 
 
 Eagle . . 
 
 
 160 
 
 Pigeon . . 
 
 
 104 
 
 Rat . . . 
 
 
 82 
 
 Gibbon 
 
 
 48 
 
 Young Cat 
 
 
 39 
 
 Sai-Ape 
 
 
 25 
 
 brains of different animals shows a certain general agree- 
 ment between their size and structure and the mental 
 development of the same animals. A rough relation 
 between the size of an animal's brain, relative to the weight 
 of his entire body, and the animal's place in the scale of 
 general intelligence, may then be claimed. The following 
 table — compiled by Exner on the basis of the works of 
 Carus and J. Miiller — exhil 
 
 Tunny-fish .... 1:87,440 
 
 Land Tortoise . . . 1 : 2,240 
 
 Shad 1: 1,837 
 
 Tadpole 1: 720 
 
 Elephant 1 : 500 
 
 Salamander .... 1 : 380 
 
 Sheep '.1: 351 
 
 Fault may, indeed, be found with the estimates of this 
 table ; and, even if they are accepted, they show several 
 marked exceptions to the rule they are intended to estab- 
 lish. For example, no one would think of placing the 
 elephant, in intelligence, behind the salamander and the 
 sheep. The rule itself holds only in a loose and indefinite 
 way. 
 
 Growth of the Brain. — The brain grows with great 
 rapidity for the first few years of the infant's life. At birth 
 its weight, as compared with the rest of the body, is, in the 
 male about 1 to 5.85, in the female about 1 to 6.50. The 
 increase in the weight of the rest of the body is relatively 
 so much greater that by the end of the second year, the 
 brain is about 1 : 14 of the body's weight ; by the end of the 
 third year 1 : 18. It increases in absolute weight until 
 well on into middle life ; but after middle life it diminishes 
 at about the average rate of 1 oz. in ten years. It is only 
 in a general and indefinite way that we can claim that the 
 growth' of the brain in size corresponds with the develop- 
 ment of the psychical life. 
 
182 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Weight of the Brains of Individual Men. — The average 
 vreight of the brain of the adult European is, for the male, 
 from 46 to 52 oz. ; for the female, 42 to 46 oz. Many 
 human brains rise above the upper average ' ranges, and 
 some fall below the lower average ranges, without marked 
 mental peculiarities being connected with these variations. 
 Numerous instances of large excess of the average weight 
 of brain on the part of men of unusual intelligence have 
 been recorded. For example, the brain of Byron was 
 scarcely under 79 oz. ; Cromwell, 78.8 oz. ; Cuvier, 64.5 oz.; 
 Webster, 53.6 oz. On the other hand, persons of unusual 
 intelligence have occasionally been found to have brains 
 of size below the lower average just mentioned. And 
 numerous men with big heads and no corresponding 
 growth of mental capacity are to be noted by any observer. 
 
 The brains of the insane are not, on the average, below 
 those of the sane in weight. Idiots, on the contrary, as a 
 rule, have brains far below the average weight ; and, con- 
 versely, a brain of only 30 oz., or under, in an adult, indi- 
 cates decided lack of mental capacity, if not complete 
 idiocy. Most of such unfortunates are cases of arrested 
 cerebral and, therefore, mental development. It may be 
 said, then, that a certain size or development of brain- 
 mass is necessary to average intelligence; and that an 
 unusual but healthy development of the brain's size is 
 favorable, but not necessary, to unusual mental activity. 
 
 Brains of Different Races. — Many data have been gath- 
 ered to show that the average weight of the brains of the 
 different races is indicative of their place in the scale of 
 human intelligence. Most of these data are lacking in the 
 requisite scientific exactness. The calculations have been 
 made for the most part from the size of the cranial cavity 
 as ascertained by measuring a large number of skulls. In 
 this way it is inferred that the average weight of brain in 
 the African, Australian, and Oceanic races falls from 1 oz. 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 183 
 
 to 4 oz. below that of the more highly civilized European. 
 The weight of brain among the Chinese, however, has been 
 calculated to be about that of the Caucasian race in 
 Europe. The low weight of the brain of the Hindus is a 
 function of their smaller bulk of body. Among savage 
 races there seems to be a great lack of cases rising up to 
 or above the higher ranges of the weight of the brain as 
 found in European races. On this evidence, also, our con- 
 clusions must remain only general and tentative. 
 
 Belative Development of the Hemispheres in Man. — On 
 comparing the brains of different animals the conviction 
 becomes irresistible that the development of the expanded 
 and convoluted cerebral hemispheres forms a certain meas- 
 ure of the quantity and quality of the animal's psychical 
 life. This development, in size, number, and depth, of the 
 cerebral convolutions, is the most distinctive feature of 
 the human brain. In fishes, generally, both cerebrum and 
 cerebellum are small ; but there is relatively an enormous 
 development of the ganglia connected with the organs of 
 sense. In amphibia the cerebral hemispheres are relatively 
 enlarged; in reptiles they are pushed still farther back- 
 ward ; while in birds the vesicles of the mid-brain are par- 
 tially hidden by the development of the hemispheres. In 
 the lower mammals this process of development is con- 
 tinued; but it is only in the higher mammals that the 
 occipital lobe enlarges backward so as to cover mid-brain, 
 cerebellum, and medulla oblongata ; and that the fore-brain 
 so enlarges and pushes forward as to constitute a true 
 forehead. 
 
 Moreover, the forms of brain found permanently in the 
 lower animals are extremely similar to those shown in suc- 
 cession by the development of the embryo of the higher 
 mammals, and especially of man. This higher evolution 
 of the brain-mantle, as it appears in man, is not attained 
 without many breaks in the animal series. But through 
 
184 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the process of its evolution the position and structure of 
 the ganglia of the trunk remain in general the same, 
 though decreasing in relative importance with the increase 
 in the size of the mantle. Thus does comparative anat- 
 omy display the supreme significance for the psychical life 
 of the cerebral hemispheres. 
 
 We shoixld not be true to all the facts, however, if we 
 did not admit that, in each great group of animals, varia- 
 tions occur in the degree of cerebral convolution, such 
 that it cannot be said accurately to measure every ascend- 
 ing degree of intelligence. The ruminants, for example, 
 although rather dull, have numerous and deep convolu- 
 tions. The marmoset shows a relatively smooth and non- 
 convoluted surface when compared with other monkeys no 
 more intelligent. 
 
 Individual Differences of the Cerebral Convolutions. — The 
 attempt has been made to show that the brains of less 
 highly intellectual races, or individuals, among men are 
 relatively poor in cerebral convolutions. The attempt 
 indicates perhaps a probable truth ; but it has not as yet 
 succeeded in giving us a scientific certainty. The brains 
 of idiots (or cases of arrested development) are, no doubt, 
 often poor in convolutions. We have already seen that 
 an almost infinite variety exists in the minutiae of the 
 arrangement of the gyri and sulci of the human brain. 
 But marked anomalies in the shape of the head, and in the 
 cerebral convolutions — especially upon the left hemi- 
 sphere — are said to be more frequent among the mentally 
 disordered. 
 
 Into other more elaborate attempts to fix standards for 
 a scale of brain development that shall measure psychical 
 activity and development, we do not think it wise to enter. 
 
SEliSOEY AND iVIOTOK BEAIN FUNCTIONS. 185 
 
 SPECIAL SIGKIFICANGE OF THE CEREBRAL HEMISPHERES 
 
 IN MAN. 
 
 The facts and conclusions to which reference has just 
 been made show that the general significance of the brain 
 for the psychical life of man, in common with all the ani- 
 mals, cannot be doubted. They also indicate that, in 
 man's case, the cerebral hemispheres have a special sig- 
 nificance. The evidence of comparative anatomy and of 
 general physiology points to that convoluted rind of gray 
 matter, which is the mantle of the human brain, as the 
 physical crown of man, in comparison with all the other 
 animals; as the physical basis, in a special way, of his 
 superior psychical hfe. This indication is amply confirmed 
 by other facts of physiology, especially of the experimental 
 kind. 
 
 The simple spinal cord of a frog, acting as a molecular 
 mechanism, will perform a few wonderful feats (see p. 137). 
 Joined with the medulla oblongata, optic lobes, and other 
 lower parts of the brain, it will show largely increased 
 signs of a complex psychical life. But there is great 
 doubt as to how we are to interpret these signs ; whether, 
 indeed, they are to be understood as signs of a psychical 
 life at all. The purposeful movements of the cord of a 
 decapitated frog or salamander have led some physiologists 
 to argue that consciousness must have its seat in the cord 
 of these animals. Plainly here, however, the argument is 
 scarcely stronger than that which could be made to show 
 that a conscious life has its seat in the molecules of the 
 climbing plant, or of those living corpuscles which float in 
 the blood, or of the cilia that move in the intestines. 
 
 A large portion of the purposeful activity of the human 
 body is not definitely correlated with any conscious mental 
 activity; for example, breathing, swallowing, winking, 
 changing the posture of the body in sleep or in states of 
 
186 PHYSIOLOGICAL PSYCHOLOGy. 
 
 profound meditation, and even the highly complex opera- 
 tions involved in walking, singing, playing on musical 
 instruments, or handling tools. In these and similar cases, 
 the intricate purposeful play of the physical mechanism is 
 by no means necessarily connected with a corresponding 
 series of conscious sensations and volitions. 
 
 In proportion as the hemispheres of an animal's brain 
 become relatively developed, not only their absolute but 
 also their relative significance is increased. Their in- 
 'fluence upon the movements of the animal is greater, the 
 higher it stands in the scale of cerebral development and of 
 intelligence. A frog or a pigeon, deprived of its hemi- 
 spheres, can do what it is quite impossible for a dog or an 
 ape to do in similar condition. Yet the most marked result 
 of the loss of these parts of an animal's brain is the sudden 
 and great departure of intelligence, of truly psychical or 
 '^ mind " quality, from its life. This result is, moreover, 
 the more marked the higher the animal stands in the scale 
 of intelligence, whether as an individual among its own 
 species or as a species among other kinds of animals. The 
 more mind an animal has to lose, the more it actually seems 
 to lose, when its cerebral hemispheres are destroyed. 
 
 On these grounds and others which have previously been 
 considered (see Chapter VI.), we are inclined to hold that 
 the functions connected with man's conscious psychical life 
 are limited, almost wholly if not exclusively, to the cere- 
 bral hemisplseres. Only in them is the physical basis laid, 
 so to speak, for the life of conscious sensation and volition. 
 Unless changes in the peripheral parts of the nervous sys- 
 tem, and even in the lower portions of the brain, find 
 expression in changes within the cerebral cortex, no effect 
 in consciousness results. Conversely, all motor changes 
 produced by changes in states of consciousness reach the 
 lower portions of the cerebro-spinal axis, and the peripheral 
 parts of the nervous system, through effects first realized 
 
SENSOBY AND MOTOR BRAIN FUNCTIONS. 187 
 
 in the cerebral cortex. The physical basis of human 
 consciousness is certainly pre-eminently, and — we believe 
 — exclusively, the convoluted cortex of the cerebrum. 
 
 But the cerebral cortex is an exceedingly complex organ ; 
 the rather is it a system of complex organs. It is not a 
 homogeneous mass. Its different areas are not homogene- 
 ously constructed ; they have a variety of connections and 
 relations to the incoming sensory tracts and to the out- 
 going motor tracts. The question therefore arises : Have 
 the different members of this complex system of organs 
 different relations to definite motor activities in the periph- 
 eral regions, and to the various phenomena of conscious 
 mental life ? In other words : Have the different areas of 
 the cerebral hemispheres all the same office and value in 
 relation to the life of sensation and volition ? This is the 
 question of " the localization of cerebral function." 
 
 History of Discoveries in Cerebral Localization. — Notwith- 
 standing the strong presumption in favor of a division of 
 function among the areas of the cerebral cortex, the 
 experimental science of cerebral localization dates back 
 only twenty years. After the doctrines of the older school 
 of phrenologists (Gall, Spurzheim, etc.) had fallen into 
 disfavor, the great experimental physiologists pronounced 
 against the localization of cerebral function. The French 
 authorities, Longet and Flourens, for example, declared 
 that they had irritated the cortical substance with a variety 
 of stimuli applied to various localities, and had extirpated 
 portions of it selected from different places, without obtain- 
 ing any marked results upon the muscular movements. 
 Meynert, indeed, put forth the opinion that the anatomical 
 connections show the anterior portion of the cerebrum to 
 be used for motor, and the posterior for sensory functions. 
 Broca held to a special connection between a convolution 
 of the frontal lobe and the use of articulate language. 
 And in 1864 Dr. Hughlings Jackson suggested that certain 
 
188 PHYSIOLOGICAL PSYCHOLOGY. 
 
 convolutions superintend those delicate movements of the 
 hands which are under the control of the mind. 
 
 It was not until 1870, however, that the doctrine of cere- 
 bral localization began to be placed upon a firm experimen- 
 tal basis. E. Hitzig had noticed that certain movements 
 of the eyes and of other muscles followed application of 
 the faradic current to the head of his patients. In com- 
 pany with G. Fritsch he begun to experiment by applying 
 electricity to minute areas of the cerebral cortex of dogs, 
 and watching the results. The notable fact was thus dis- 
 covered that some areas respond to stimulation by co- 
 ordinated contractions of the muscles of the opposite half 
 of the body, while others do not ; and that the motor parts 
 lie in general to the front, the non-motor to the rear, of the 
 convexity of the cortex. In their first announcement they 
 indicated five so-called " motor centres." 
 
 Since the " epoch-making discovery " of Fritsch and 
 Hitzig, many diligent and skilful investigators have been 
 constantly at work; and the results, not only in their 
 scientific but also in their practical bearings, — as says 
 a recent writer, — " with the achievements of antiseptic 
 surgery, constitute the grandest triumphs that adorn the 
 history of the noble science and art of medicine." 
 
 Kinds of Evidence for Cerebral Localization. — Three chief 
 lines of evidence, leading from three great groups of facts, 
 must be considered. These are experimentation, pathology, 
 and comparative anatomy. Each of these has its peculiar 
 advantages and peculiar value ; each has also its peculiar 
 difficulties and dangers. The physical and chemical pro- 
 cesses of the cerebral substance are exceedingly difficult 
 of determination. Its nervous tracts can be only slowly 
 marked out, and that at cost of immense and painstaking 
 labors. Its parts are so situated as to be removed from 
 easy observation or experiment. Disease begins and pro- 
 gresses here unnoticed, or is only indicated by symptoms 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 189 
 
 which requii'e the analysis of an expert. Argument from 
 the lower animals to man can be onlj' cautiously applied, 
 for the likeness of the physical structures of the two is far 
 from perfect; and as to the mental life of the other ani- 
 mals, we are, at the best, much in the dark. It is, then, 
 only by the most persistent, candid, and cautious use of 
 all three of the available kinds of evidence that a conclu- 
 sion can be reached. 
 
 Evidence from Stimulation. — In the localization of cerebral 
 function two kinds of experimentation may be employed. 
 These are stimulation and extirpation. The immediate 
 object of experiment by stimulation is, of course, to dis- 
 cover what groups of muscles can be contracted by apply- 
 ing irritation to definite areas of the cortex. It is assumed, 
 then, that such areas are, either directly or indirectly, con- 
 nected in some special way with the contracting groups 
 of muscles. The most efficient and manageable stimulus 
 is the electrical current, but mechanical and chemical 
 irritation may be employed in certain cases. 
 
 The fact that the same intensity of the electrical current, 
 which will call into movement definite groups of muscles, 
 when applied to certain more or less extended areas of the 
 cerebral cortex of man and of the other higher animals, 
 will not excite the same movements if applied only a frac- 
 tion of an inch distant from these areas, is now established 
 beyond doubt. The interpretation of this fact, and the 
 right to speak of these areas as " motor " areas, have, how- 
 ever, been disputed. It was claimed, immediately after 
 the experiments of 1870, that the effects of the stimulus 
 were due to extrarpolar conduction of the electricity in the 
 substance of the brain. This organ, it was said, would 
 diffuse the electricity like any other practically homoge- 
 neous substance. It was, moreover, soon found that, if a 
 motor area be separated from the underlying substance by 
 a circular cut, it is excitable with only a small increase in 
 
190 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the strength of the stimulus. Or if the gray surface be 
 wholly removed, and the stimulus applied to the blood 
 in the cavity, the customary result follows. From these 
 and other facts it has been argued that these areas are not 
 true cortical " motor centres." 
 
 In answer to objections like the foregoing the following, 
 among other similar arguments, are urged. When the 
 animal is deeply etherized, the excitability of the cortical 
 regions is wholly or partly lost. This could scarcely hap- 
 pen if the substance of these regions acted only as a homo- 
 geneous conducting medium for the electrical current. It 
 is also found by most observers that a stronger stimulus is 
 necessary to move the muscles from these centres, after 
 the gray substance of the surface has been removed. The 
 electrical current seems also to be retarded in passing 
 through this superficial matter; it is a fair assumption, 
 then, that the interval is spent in evolving the particular 
 nervous function which belongs to this matter. Indeed, 
 that the evidence from stimulation connects certain por- 
 tions of the gray surface of the brain with the movements 
 of certain groups of muscles, in a peculiar way, is now 
 scarcely to be denied by any one acquainted with the 
 nature and extent of the phenomena. 
 
 Evidence from Extirpation. — It is natural to argue that 
 those areas of the cerebral cortex, whose loss is followed by 
 the loss or disturbance of motion in definite groups of mus- 
 cles, or by the loss or disturbance of any class of sensory 
 impressions, are functionally related in some peculiar way 
 to such muscles or organs of sense. The argument, how- 
 ever, needs caution in application. For in the first place, it 
 is impossible at each stage of the experiment to know what 
 is the precise condition of the brain. Local and extensive 
 inflammations, secondary lesions and degenerations of the 
 nerve-tracts, cannot easily be followed by the experimenter 
 in detail. It is generally found that the effects of extir- 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 191 
 
 pating any so-called " sensory " or " motor " area change 
 from time to time. Not infrequently they appear to be 
 almost wholly temporary. Among those effects that seem 
 to be permanent, some are obviously so ; but others are so 
 delicate as almost wholly to escape observation. It is, of 
 course, peculiarly difficult to tell just what is the nature 
 of an animal's sensory activities ; and how much of intel- 
 lectual or "psychical" quality is lacking to its hearing, 
 smelling, tasting, feeling, or seeing. 
 
 Evidence from Pathology. — It is pathology which gives 
 us the most direct evidence for the localization of cerebral 
 function in the case of man. We cannot burn or cut away 
 portions of the human brain merely for purposes of experi- 
 ment. Yet accident and disease destroy the different 
 areas of its cortical substance. Such lesions, however, are 
 rarely circumscribed nicely like those which can be made 
 in the brain of an animal by the knife or corroding acid of 
 the operator. They are usually accompanied by lesions in 
 the sensory and motor tracts below the cortical substance ; 
 and this may vitiate the conclusion otherwise to be derived 
 from them. It is only by post-mortem, as a rule, that the 
 last state of the case can be exactly known. And the 
 reports of post-mortem cases have hitherto — owing to the 
 ignorance and carelessness about such matters of the aver- 
 age physician — been so lacking in precision as greatly to 
 embarrass the progress of science. 
 
 The evidence from pathology has thus far been exceed- 
 ingly conflicting. Gradually, however, clearer light from 
 this source has been shed upon the important question of 
 cerebral localization. Physicians and surgeons are, in 
 general, becoming better acquainted with the more impor- 
 tant facts. Even now it is possible for the skilful prac- 
 titioner to relieve or cure certain diseases by surgical means 
 directed in accordance with the newly discovered truths 
 of cerebral localization. The investigator in physiology is. 
 
192 PHYSIOLOGICAL PSYCHOLOGY. 
 
 meantime, accumulating material for more extended and 
 accurate inductions. 
 
 Evidence from Comparative Anatomy and Histology. — 
 
 The comparative study of animal structure, combined 
 with experiment by electrical irritation, shows that, on the 
 whole, the " excito-motor areas " which may be discovered 
 on the hemispheres of the brain increase in number and 
 definiteness with the increase in elaborateness of structure 
 and in general intelligence. Only traces of such areas 
 can be found in the case of frog or pigeon; only a few 
 areas can be doubtfully pointed out in the case of rat or 
 guinea-pig. But the convolutions of the brains of dogs 
 and, particularly, of the man-like apes, are much more 
 specialized in respect to function. While then we cannot 
 approve of the argument which transfers the map of so- 
 called " centres " indicated for these higher animals to the 
 cerebral hemispheres of man, we admit the principle that 
 the probability of a correspondence in the localization of 
 cerebral function increases with their anatomical likeness 
 to man. Hence the superior value of experiment with the 
 brains of monkeys. 
 
 As histology succeeds in tracing the connections of the 
 different areas of the hemispheres with one another, and 
 with the nerve-tracts of the lower parts of the brain and 
 of the spinal cord, it affords evidence confirmatory or cor- 
 rective of the evidence from experimentation and pathol- 
 ogy- 
 
 Use of all the Evidence. — The detailed study of the 
 problem of the localization of cerebral function is one of 
 the most stimulating and instructive instances of the use 
 of inductive methods to disentangle the truth from a con- 
 fused mass of seemingly conflicting phenomena. The 
 proof of the truth must combine satisfactorily the evidence 
 from all the sources. In making the necessary induction 
 the following course is, in our judgment, most effective. 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 193 
 
 The indications of experiment upon the cerebral hemi- 
 spheres of the animals — chiefly, of course, those most 
 closely allied to man in their cerebral structure — must 
 first be gathered and carefully weighed. The two forms 
 of experimentation — stimulation and extirpation — should 
 confirm each other, in order to give the surer indications. 
 Guided by these indications we must then seek light from 
 human pathology. All accessible pathological cases must 
 be sifted and those only selected for use which have the 
 definite and trustworthy character necessary to fit them for 
 the purposes of induction. Especially must care be taken 
 that our theory do not neglect the consideration of negative 
 cases ; and even of those cases which (in themselves con- 
 sidered) furnish indications contradictory of the great body 
 of collected cases. The corrective or confirmatory evi- 
 dence of anatomy and histology may then be applied to 
 our conclusions. Only when all the lines of evidence 
 unite with a large and substantial agreement, if not with 
 an absolute uniformity, can we feel the highest attainable 
 confidence in our results. 
 
 The Argument from ITegative Cases. — The first general 
 principle, to be admitted in all attempts at a theory of the 
 localization of cerebral function, is of a negative character. 
 Considerable areas of the cortical substance, when stimu- 
 lated, do nx>t occasion any movements in the muscles of 
 the body. Considerable portions of this substance may be 
 destroyed and no appreciable loss or disturbance of any 
 motor, sensory, or intellectual activities result. The early 
 researches of Fritsch and Hitzig pointed out only five 
 spots — each one of a small fraction of an inch in diameter 
 (2-3 mm., as a rule) — that could be definitely related to 
 the movement of certain groups of muscles. Between and 
 around these areas lay the much larger areas of negative 
 result. Though the number of irritable spots on the hemi- 
 spheres of the brains of the higher animals has since been 
 
194 PHYSIOLOGICAL PSYCHOLOGY. 
 
 considerably increased, the non-irritable portions still re- 
 main greatly in the predominance. 
 
 Large portions of the cortical substance from the brain 
 of an animal may be removed without the operation being 
 followed by the permanent and complete loss of any func- 
 tion, motor or sensory. Indeed, a few eminent observers 
 still maintain that the nature and extent of the psychical 
 disturbance are largely or wholly independent of the local- 
 ity from which the brain substance is taken. 
 
 The negative evidence from certain cases in human 
 pathology is even more remarkable. There are recorded 
 many instances of large lesions in the cerebral hemispheres 
 of man with little or no resulting mental disturbance. 
 One authority tells of a young man who had a foreign 
 body of four fingers' breadth square buried in his brain, 
 and yet lived for a long time afterward in the enjoyment 
 of all his faculties. Another communicates the case of an 
 Italian laborer whose skull was crushed, in the right 
 parietal region, by a stone. This patient subsequently lost 
 so much of the substance of the brain that it was calcu- 
 lated the lesion must extend down to the corpus callosum. 
 He, too, lived without mental impairment; but with a 
 laming of the limbs on the left side. 
 
 Other remarkable cases of lesion of the brain, followed 
 by little or no loss of psychical functions, are such as this : 
 A man whose skull was crushed with a stone, and whose 
 entire left hemisphere (on his death twenty days later) 
 was found to be a disorganized mass, continued in appar- 
 ently full possession of his powers of motion, sensation, 
 and intelligence. Instances of defective brains are also on 
 record. In one such case, the place of the right hemi- 
 sphere was discovered to have been filled with a serous 
 fluid. No peculiarities of this person's mental life were 
 noticed ; but there had been from birth lameness of the left 
 side of the body. 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 195 
 
 Extensive lesions without marked disturbance of the 
 motor or sensory functions are especially frequent in the 
 frontal lobes. They occur, however, not very infrequently 
 in the occipital and temporo-sphenoidal lobes. A case is 
 recorded of an officer shot through the middle of the fron- 
 tal lobes, who till death showed no signs of any kind of 
 paralysis. The work of M. Pitres contains a large collec- 
 tion of cases in which' these lobes have been the seat of 
 extensive disease, without any symptoms of lunacy or of 
 psychical disturbance. The so-called " American crowbar 
 case " is well known. An iron bar, 3 feet 7 inches in 
 length and 1^ inches in diameter, passed entirely through 
 the top of a man's head, near the sagittal suture in the 
 frontal region. But the patient recovered in a few min- 
 utes so as to ascend a flight of stairs and give to the sur- 
 geon an intelligible account of his injury. He lived 
 twelve and a half years afterward, with no noticeable 
 impairment of his sensory or motor powers. 
 
 In the words of a distinguished physiologist, it must be 
 confessed that the understanding of cases like those just 
 mentioned " is made more difficult rather than easier by 
 recent researches." The evidence of these negative cases 
 is, indeed, quite too much neglected by those who make 
 haste to erect on insufficient data a plausible theory. 
 Indeed, the general fault of writers on the localization of 
 cerebral functions is that they consider, as a rule, only the 
 cases which suggest or confirm their theory ; while they 
 neglect those even more important negative cases which 
 tend to refute, correct, or modify the theory. 
 
 And yet, a large amount of concurrent testimony from 
 all these main sources of evidence warrants us in announc- 
 ing certain positive results. A science of the localization 
 of cerebral functions, in some justifiable meaning of these 
 words, may be said to be fairly defined. 
 
CHAPTER IX. 
 
 SENSORY AND MOTOR FUNCTIONS OF THE CERE- 
 BRAL HEMISPHERES. — Continued. 
 
 The region of the brain whicli is especially concerned 
 with the motor functions lies about the great central fis- 
 sure, or Fissure of Rolando. More precisely, it embraces 
 the ascending frontal convolution (^gyrus centralis ante- 
 rior), the ascending parietal (the gyrus centralis posterior), 
 and the prolongation of the two on the median surface of 
 the brain (in the lobulus paracentralis). 
 
 LOCALIZATION OF THE MOTOR CENTRES ON THE 
 CEREBRAL CORTEX. 
 
 Areas excitable by Stimulation. — The original experi- 
 ments of Fritsch and Hitzig located five areas on the cere- 
 
 FiG. 63. — Hitzig's Motor Areas on the Cortex of the Dog. The left hemisphere 
 belongs to one animal, the right to another; a, the sulcus cruciatus, around which the 
 gyrus sigmoideus bends; 0000, area for the face. The other symbols are explained in 
 
 the text. 
 
 196 
 
SENSOKY AND MOTOE BRAIN FUNCTIONS. 197 
 
 bral hemispheres of the dog, which responded to irritation 
 with the movement of definite groups of muscles. They 
 were (1) the centre for the muscles of the neck (A in the 
 Fig.) ; (2) the centre for the extensor and adductor of the 
 fore-limb (+) ; (3) the centre for the bending and rota- 
 tion of the same limb (-I-) ; (4) the centre for the hind- 
 limb (q^) ; and (5) the facial centre (© — ©). These 
 investigators also obtained contractions of the muscles of 
 the back, tail, and abdomen by stimulating interlying 
 points, but failed definitely to circumscribe areas for these 
 muscles. 
 
 The accompanying figure (No. 64) shows the numerous 
 " centres of electrical irriration," which Dr. Ferrier 
 
 Tie. 64. — Areas on the Left Hemisphere of the Monkey, by stimulating which Ferrier 
 obtains motion in definite groups of muscles. 
 
 claimed, some six years later, to have discovered on the 
 cerebral hemispheres of the monkeys with which he has 
 experimented. It will be noticed that these centres, like 
 those discovered in dogs by the two German explorers, lie 
 around the great central fissure, known in the human 
 brain as the Fissure of Rolando. 
 
 Recent experiments in the attempt to establish motor 
 centres by electrical stimulation tend to confirm the gen- 
 eral conclusion. Some, however, have claimed that 
 
198 PHYSIOLOGICAL PSYCHOLOGY. 
 
 changes in tlie excitability of these minute areas take 
 place ; that certain ones, at first excitable, after a time 
 cease to be so, and that others, at first not excitable, after- 
 ward become excitable. Very suggestive is the further 
 alleged discovery that a number of minute areas for each one 
 of several different groups of muscles exist in the larger 
 " excitable zone " of the cortex. The fibres whose func- 
 tion it is to contract these groups of muscles would seem 
 then to proceed directly from a number of cerebral spots 
 belonging to each group. These minute areas for the 
 different muscles of the extremities are said to be limited 
 with great sharpness ; they do not wholly cover each 
 other; and those for any particular muscle are of small 
 extent in comparison with the field or zone which may be 
 looked upon as common to all the extremities. 
 
 The Extirpation of " Motor Centres." — As a rule, the de- 
 struction of those areas of the cerebral hemispheres, from 
 which co-ordinated movement of definite groups of muscles 
 can be excited by stimulation, causes a temporary or per- 
 manent impairment in the use of the same muscles. Thus 
 the evidence of extirpation confirms, in a general way, the 
 evidence from stimulation. The pioneer investigators, 
 Fritsch and Hitzig, removed from two dogs the substance 
 of . the centre which they had fixed upon as that for the 
 " right fore extremity." They observed that these animals 
 afterward used the right fore-leg unskilfully. Since that 
 time many observers have refined and multiplied this class 
 of experiments in the localizing of the motor functions of 
 the hemispheres. We now refer to some of the results 
 thus obtained. 
 
 Experiments of Munk.— This investigator experimented, 
 at first, by removing clean-cut circular bits about f of an 
 inch in diameter and -^ of an inch thick from the convex 
 surfaces of the parietal, occipital, and temporal lobes of 
 dogs. His general conclusion was as follows : If a line be 
 
SBNSOBY AND MOTOK BRAIN FUNCTIONS. 
 
 199 
 
 drawn from the terminal point of the Fissure of Sylvius 
 vertically toward the falx cerebri, it will approximately 
 mark out the limits of an anterior motor and a posterior 
 sensory sphere. 
 
 FlQ, 65, — Areas on the Brain of the Dog. (According to Munis.) A, centre of the 
 Eye; B, of the Ear; C, of tbe seneations of the hind-leg; D, of the fore-leg; E, of 
 the Head; F, of the Apparatus for protecting the Eye; G, of the Begion of the Ear; 
 H, of the ISeck ; J, of the Kump. 
 
 Munk's attempts at more precise localization are indi- 
 cated in the accompanying figure (No. 65). It will be 
 noticed that three of these centres — Q, i>, and E — 
 correspond fairly well with those fixed upon by the first 
 experimenters in stimulation. In the regions indicated on 
 the chart, Munk claimed to find that small and definitely 
 
200 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 circumscribed extirpations are regularly followed by defi- 
 nitely localized disturbances of motion. 
 
 For example, let the region D be removed from tbe left 
 hemisphere of the brain of a dog. Then if any other of the 
 animal's limbs be ever so lightly touched, he will heed it ; but 
 hard pressure, pinching, and sticking of the right fore-leg is 
 either followed by no result, or by Avhat seems to be only 
 the reflex withdrawal of the leg, without attention. More- 
 over, the dog will suffer this limb to be placed in awkward 
 and uncomfortable positions. He no longer handles his 
 food with the right foot, and does not give this limb to his 
 master on call. In running he slips on this foot. These 
 and other phenomena led this investigator to hold that the 
 animal had lost the " cerebral " or intelligent quality from 
 the management of this limb, and perhaps had no mental 
 picture of it in mind. 
 
 Experiments of Horsley and Sehafer. — The value of ex- 
 
 FiG. 66. — Lateral Surface of Brain of Monkey. (Taken from " Brain.") 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 
 
 201 
 
 periments by way of stimulation and extirpation upon the 
 cerebral hemispheres of the monkey is, on account of the 
 resemblance of this animal's brain to that of man, undoubt- 
 edly very great. Among the latest physiological researches 
 bearing on the localization of motor centres in the cere- 
 brum, perhaps none are more important than those of the 
 two investigators whose names head this paragraph. Their 
 conclusions are represented in the accompanying diagrams 
 (Figs. 66 and 67). It must be understood, however, that all 
 
 Fig. 67. — Median Surface of Brain of Monkey. (Talsen from " Brain.") 
 
 the so-called " motor centres " marked on these diagrams 
 have not the same evidence in their favor. Some of them 
 await further experimental evidence. A warning must 
 also be uttered against attempting to copy this provisional 
 chart off, unchanged, upon the map of the human brain. 
 
 Interpretation of the Phenomena. — The meaning of the 
 apparent loss of the animal's functions through extirpation 
 
202 PHYSIOLOGICAL PSYCHOLOGY-. 
 
 of the so-called " motor centres " is not perfectly clear. 
 It will always be difficult to designate precisely what fac- 
 tors in the complex sensory-motor activities of a dog or a 
 monkey drop out as the result of removing a certain area 
 of its cortical substance. Several explanations of such 
 phenomena of motor disturbance are possible. It may be 
 held, in the first place, that the extirpated centres are 
 exclusively motor ; they are, that is, the areas in which 
 alone can originate the different efferent impulses to the 
 groups of muscles that move the limbs. The only impair- 
 ment of functions is, then, the loss of connection between 
 the "projection-fibres" and the cerebral substance which 
 controls them. 
 
 But others hold that the real loss of function in these 
 cases is sensory rather than motor. The disturbance or 
 loss of motion is, then, only the expression of a loss of the 
 sense of touch in the parts to be moved. In other words, 
 it is "tactile ansesthesia." In proof of this conclusion, 
 attention is called to the fact that an animal thus operated 
 upon will allow parasites to gather on that surface of the 
 skin whose cortical area has been removed. The inability 
 of the animal to use its extremities as hands may also be 
 assigned to a loss of those finer sensibilities which guide 
 such movements. 
 
 Or, again, the impairment of function may be regarded 
 as largely due to the loss of power to hold before the mind 
 a picture of the limbs, and of the movements which it is 
 desirable to excite. This would seem to indicate injury to 
 the animal's general psychical quality, and might involve 
 both the sensory and the motor factors. The importance 
 of the " association-fibres " in these cortical centres is 
 beyond doubt. For if the centres be carefully cut round 
 so as to sever these fibres, but not the " projection-fibres," 
 their loss of function is almost, if not quite, as great. In 
 fact, all the disturbances — whether sensory or motor — ap- 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 208 
 
 pear to be of the kind which indicates loss of cerebral, and 
 so of psychical quality in the handling of the extremities, 
 rather than the laming of any particular group of muscles. 
 Indeed, one principal authority (Goltz) still insists that 
 the general impairment of intelligence which results from 
 removing any considerable amount of brain-substance, 
 from whatever area it is taken, constitutes the most 
 marked feature of all these cases, ile finds that, although 
 impairment of both tactile and muscular sense may tem- 
 porarily occur, yet the animal by giving " increased atten- 
 tion " is able to feel the slightest touch on any area of the 
 skin. 
 
 In view of all the evidence, our provisional conclusion 
 may be expressed as follows : Certain areas of the brains 
 of the lower animals, especially of the dog and monkey, 
 have a special value and use in the control of the muscles 
 of the body. These areas are situated in that reg'io-n of 
 the cortex which corresponds, in man, to the convolutions 
 on either side of the Fissure of Rolando, and to the adja- 
 cent lobule (lohulus paracentralis) on the median surface of 
 the brain. The loss or disturbance of motor function which 
 follows injury to these areas is often due to complex men- 
 tal disturbances. These are partly sensory, — impairment 
 of the nicely shaded tactile and muscular sensations by 
 which the animal guides its limbs ; partly motor, — impair- 
 ment of power to execute the volition, or realize in actual 
 movement the mental picture of the movement and the 
 desire to move ; partly more purely psychical, — impairment 
 of power to form complex mental images of the specific 
 sort required, and of mental ability to take an interest in 
 or to comprehend complex objects and situations. 
 
 In the case of the higher animals (and especially of the 
 monkey), a further discrimination of these areas may be 
 attempted with some success. Localization of the con- 
 nected sensory and motor factors in these complex activi- 
 
204 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ties places the former more to the rear, and the latter more 
 to the front, of this general area. What is true of the gen- 
 eral area is perhaps true of the particular areas into which 
 the general area may be divided. The broader outlines of the 
 diagrams prepared by Horsley and Schafer (see p. 200 f .) 
 may be taken as indicating to human pathology its partic- 
 ular problems. 
 
 Our reliance must now be placed upon Human Pathology. 
 And although much has been done by others in the nearly 
 ten years since Exner's work appeared,^ the thoroughness 
 and carefulness of his induction entitles it to be still con- 
 sidered as representative of the most trustworthy conclu- 
 sions. 
 
 Exner's Induction of the Motor Areas in Man. — The con- 
 clusions of this authority were based upon researches into 
 several thousand cases of cerebral disease which had been 
 followed by post-mortem examination. From this large 
 number, 169 "test-cases " were selected. In all these cases 
 the record was trustworthy, full, and unambiguous; and 
 no other lesions than the one in some particular cortical 
 area had occurred to complicate the inferences. The test- 
 cases were tabulated on three sets ef maps, according to 
 three methods of induction : (1) Method of negative cases ; 
 (2) method of percentage; (3) method of positive cases. 
 Thus the first map showed what areas of the cerebral cor- 
 tex, if any, are not necessarily connected with motor or 
 sensory functions. The second map showed the amount 
 of prohahility that a given small area will be the seat of 
 disease, in case this disease has been followed by a given 
 kind of sensory or motor disturbance. [For this purpose 
 the map was divided into 367 small quadrilateral sections.] 
 The third map simply tabulated the cases of lesions aetu- 
 
 1 Investigation into the Localization of Function in the Cerebral Hemi- 
 spheres of Man. Vienna, 1881, 
 
SENSOKY AND MOTOR BRAIN FUNCTIONS. 
 
 205 
 
 ally connected with observed disturbances of function, in 
 the spots on the cortex where they occurred. 
 
 Pis. 68. — Lateral View of the Human Brain. (Schematic, Ecker.) F, frontal, 
 P, parietal, O, occipital, and T, terpporo-sphenoidal lobes. S, iissure of Sylvius, with 
 B', the horizontal, and S", the ascending ramus; C, sulcus centralis; A, anterior, and 
 B, posterior, central convolutions; Fl, F2, F3, superior, middle, and inferior frontal con- 
 volutions; fl, superior, f2, inferior frontal sulci; f3, sulcus praeceutralis; PI, superior, 
 and P2, inferior parietal lobule; the latter, the gyrus supra-marginalis, and P2', the 
 gyrus angularis ; ip, sulcus interparietalis; cm, end of ealloso-marginal fissure; 01,02, 
 03, occipital convolutions; po, parieto-occipital fissure; o, transverse, and o2, inferior 
 longitudinal sulcus; Tl, T2, T3, temporo-spbenoldal convolutions; and tl, t2, temptsro- 
 sphenoidal fisauren. 
 
 Field of Latent Lesions. — In Exner's collection of cases, 
 20 were found in each hemisphere which had been followed 
 by no disturbances whatever, whether of motion or of sen- 
 sation. But since the collection comprised 101 lesions of 
 the left hemisphere, and only 67 of the right, it will be 
 seen that the chances of a lesion being latent (i.e. resulting 
 
206 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 in no disturbance of function) are much greater for the 
 right than for the left hemisphere. On the right hemi- 
 sphere the entire surface, with the exception of the two cen- 
 tral convolutions, the paracentral lobule, and small portions 
 of the convex and inferior surfaces of the occipital lobe, is 
 
 ..-P 
 
 Fig. 69. — View of the Human Brain from Above. (Scbematic, Ecker.) The letters 
 have the same reference as in the preceding figure. 
 
 latent. On the left hemisphere the latent field is much 
 less extensive. This result of the induction restates the 
 well-known fact that extensive lesions frequently occur 
 in the frontal, temporal, and occipital lobes, without occa- 
 sioning any noticeable motor or sensory disturbance. 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 
 
 207 
 
 The regions not latent Exner divided into "absolute 
 fields " (or areas within which no lesion occurred without 
 the expected result) and "relative fields" (or areas in 
 which more than fifty per cent, of the cases of lesion 
 resulted in a disturbance of function). 
 
 Fields of the TTpper Extremities. — Exner's induction from 
 the test-cases seemed to show that the "absolute field" 
 for the upper extremity on the right hemisphere (i.e. field 
 for the left arm) includes the paracentral lobule, the ante- 
 rior central convolution (with the exception of a small 
 
 Fio. 70 . —Median Aspect of the Right Hemisphere. (Schematic, Eoker.) 00, cor- 
 pus callosum. Gyrl : Gf, fornicatus; H, hippocampi (with its sulcus h), and U, uncin*. 
 tus- PI', prsBCuneus; Oz, cuncus; oc, oalcarine fissure, with its two rami oo and oc". 
 D, gyrus descendens; T4, the lateral, and T5, the medial, gyrus occipito-temporalis. 
 
 part of its lower end), and the upper half of the posterior 
 central convolution. The "relative field" for the same 
 extremity extends further, and includes the back part of 
 the three frontal convolutions, the front part of the parietal 
 lobe, and a considerable part of the neighboring median 
 
 surface. 
 
 On the left hemisphere the fields for the upper extrem- 
 
208 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ity (i.e. the right arm) are more extended. Here the 
 " absolute field " extends over the greater part of the upper 
 parietal lobe; and perhaps over portions of the median 
 surface of the occipital lobe. The " relative field " com- 
 prises a yet larger area of this general region of the brain. 
 All this corresponds to the fact that, in the great majority 
 of men, the right hand and arm are more employed for the 
 discharge of delicate and highly intelligent functions, and 
 therefore require a larger cerebral assistance and control. 
 
 Fields of the Lower Extremities. — Exner's induction 
 points out, as the " absolute field " on the right hemisphere 
 for the lower extremity (i.e. the left leg), the paracentral 
 lobule, the upper third of the anterior central convolution, 
 parts of the corresponding third of the posterior central, 
 and some small areas, behind and below, on the lohulus 
 quadratus. The " relative field " of the same limit is, of 
 course, larger. On the left hemisphere the "absolute 
 field" includes also most of the upper portion of the 
 parietal lobe. 
 
 The lower extremities can scarcely have the functions 
 of their different parts localized with the same degree of 
 precision and amount of differentiation which belong to the 
 upper extremities. This fact corresponds to the relatively 
 low cerebral and psychical character of their sensations 
 and motions. More of the brain and mind is required for 
 the control of the arms than of the legs. 
 
 General Motor Eegion in Man. — The "exquisitely mo- 
 tor " region of the human cerebral cortex lies, then, around 
 the Fissure of Rolando and in the paracentral lobule. It 
 reaches over, in a somewhat indefinite way, into the adja- 
 cent parts of the frontal and parietal lobes. Besides the 
 " mstor areas " of the extremities, those for the muscles of 
 the eyeball, tongue, head, and neck are in this same gen- 
 eral region. For example, in nine cases of Exner's collec- 
 tion, in which the muscles of head and neck were affected. 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 209 
 
 the lesions were all situated in one of the two central con- 
 volutions. 
 
 There can be no reasonable doubt, therefore, that the 
 general indications, which were said to be derived from 
 experiments with the dog and the monkey, are confirmed 
 by human pathology. As two celebrated investigators 
 (Charcot and Pitres) have summed up the evidence : 
 " The cortex of the cerebral hemispheres in man may be 
 divided, functionally, into two parts, motor and non- 
 motor, according as destructive lesions do or do not cause 
 permanent paralysis on the opposite side of the body. 
 . . . The motor zone includes only the ascending frontal 
 and ascending parietal convolutions and the paracentral 
 lobule." 
 
 Further Specialization of Motor Areas. — More specific 
 statements as to the localization of functions for small 
 parts of the extremities, or even for particular groups of 
 muscles, cannot be made with the same confidence. Clin- 
 ical and surgical evidence is accumulating, however. For 
 example, a case is reported, definitely connecting spasms 
 beginning in the right lower, and extending to the right 
 upper, limb and to the face, with a lesion in the upper 
 third of the ascending frontal convolution on the left side ; 
 and another case, connecting cramps in the left thumb and 
 fore-finger, spreading up the arm, with a tumor situated at 
 the line of the junction of the lower and middle thirds of 
 the ascending frontal and parietal convolutions. 
 
 One authority (Horsley) divides the " arm area " as 
 follows : for the shoulder, in the upper part ; the elbow, 
 next below and behind; the wrist, next below and in 
 front; the thumb, lowest and behind. In the area just 
 above the superior frontal sulcus, he thinks that the move- 
 ments of the lower and upper limbs are blended. Another 
 authority (Dr. Mills) thinks that " instead of dividing the 
 central or Rolandic Fissure into thirds, it is better, perhaps. 
 
210 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 to divide it into fourths, placing the area of representation 
 for the lower extremity in the fii'st fourth ; that of the 
 face in the lower fourth ; and the area for the upper 
 extremity includes the second and third fourths." 
 
 Fio. 71. — Areas of the Mesial Aspects of the Cerebrum. (Taken from " Brain.*') 
 
 The accompanying diagrams (71 and 72) may be said 
 to represent the most advanced views in the localization 
 of cerebral motor functions in man. For this very reason, 
 and because they are based only upon "positive cases," 
 instead of upon an induction taking also the "negative 
 cases ■' into the account, they should be received in a cau- 
 tious and tentative way. 
 
 localization of Sensations of the Skin and Muscles. — There 
 is considerable evidence to show that the regions called 
 "motor" are also the principal seats of those lesions of 
 the cerebral cortex which result in loss of the sensations of 
 touch (tactile aneesthesia,) and of muscular sensations. 
 
SENSORY AND MOTOR feRAiN FUNCTIONS. 
 
 211 
 
 This has led some to hold that the so-called "motor" areas 
 are the central representatives of the sensory impulses 
 which originate in the skin and muscles of the same limb 
 
 FiQ. 72. — Areas of tbe Lateral Aspect of the Cerebrum, and Sub-diTlsiona of the 
 Motor Area. (Taken from " Brain.") 
 
 which is moved from these areas. For the conception of 
 "sensory and motor centres," therefore, one authority 
 would substitute the conception of excitable cortical areas 
 reacting after the manner of sensitive peripheral surfaces : 
 the true motor centres lie below. We have already seen 
 (p. 67) that histology has attempted to distinguish motor 
 and sensory cells in the same layer, or motor and sensory 
 layers in the same area, of the cortical substance. The 
 distinctiou is not, however, as yet established. 
 
212 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Human pathology has not yet succeeded in assigning an 
 "absolute field" for tactile sensations. There is no portion 
 of the cerebral cortex where lesions are invariably and 
 necessarily followed by disturbances of these sensations. 
 Exner's induction included 22 cases of marked disturbance 
 of tactile sensations. Of these 16 were located wholly in 
 the two central convolutions, and 3 others partly in the 
 same convolutions. The percentage of such cases arising 
 from injury to the right hemisphere is about twice as 
 large as that of the left. This has led some to conclude 
 that sensibility is the predominating function of the right 
 hemisphere, as motion is of the left. 
 
 The psychical relations between disturbances of motor 
 function and disturbances of tactile and muscular sensation 
 are undoubtedly very complex. Physiology has not yet 
 unravelled the corresponding cerebral relations. Perhaps 
 we cannot do better than to conclude with one writer: 
 There is probably a general region for sensations of touch, 
 pain, temperature, pressure, etc., of the peripheral parts, 
 and this region is divisible into minuter areas ; these areas 
 have close anatomical and morphological relations with the 
 corresponding motor areas, but are probably not always 
 wholly identical with them. So far as the two regions are 
 not coincident, that mainly appropriated to sensory func- 
 tions lies further back. It perhaps includes the gyrus 
 fornicatus, the hippocampal convolution, the pre-cuneus, 
 and the postero-parietal convolutions. 
 
 LOCALIZATION OF THE SENSORY CENTRES OF THE CERE- 
 BRAL CORTEX. 
 
 It requires no argument to show that experiment upon 
 the lower animals is relatively of little value in determin- 
 ing the cerebral sensory centres in man. Localization of 
 " sensory centres " so-called is in general more difficult on 
 account, partly, of the greater complexity of the psychical 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 213 
 
 phenomena and of the physical apparatus concerned. In 
 particular, it is almost impossible to tell with confidence 
 what are the psychical experiences, the sensory states of 
 consciousness, of an injured dog or monkey. Yet by com- 
 bining with experimentation the carefully sifted evidence 
 of human pathology, the areas of the brain-cortex con- 
 cerned in vision have been localized with approximate 
 accuracy. 
 
 Centre of Sight according to Farrier. — In the earlier edi- 
 tion of his work on the "Functions of the Brain" this 
 investigator claimed that destruction of the gyrus angularis 
 (see Fig. 68) produces loss of sight in the opposite eye ; 
 while stimulation of the same region produces movements 
 of the eye. In a subsequent edition Dr. Ferrier has ad- 
 mitted his error in localizing the visual centres in this 
 convolution to the exclusion of the occipital lobes. And 
 further investigation seems to have shown that the gyrus 
 angularis can be removed without any permanent effect 
 whatever upon the sense of sight. 
 
 Centre of Sight according to Munk. — This investigator 
 details the following among other phenomena which result 
 from extirpation of the region marked Al, (see Fig. 65,) 
 from the brain of a dog. The animal may, in general, be 
 said to exhibit marked symptoms of " psychical blindness." 
 By this term it is meant to say that the dog cannot form 
 the visual images or ideas which give meaning to the visual 
 impressions. It will guide itself by sight, even under 
 difficult circumstances. But it does not recognize the dish 
 from which it has been accustomed to take food, the man 
 who has been its keeper, the threatening whip or coal of 
 fire. If only a small area of the brain's substance is re- 
 moved, it recovers psychical sight by again learning the 
 meaning of its visual impressions. Extirpation, however, 
 of the cortical surface somewhat widely around Al, in 
 connection with this concentrated centre itself, results 
 
214 PHYSIOLOGICAL PSYCHOLOGY. 
 
 (when both hemispheres are involved) in complete and 
 permanent " psychical blindness." Similar phenomena are 
 obtained by Munk through experimenting upon monkeys. 
 He concludes, therefore, that a large part of the convex 
 surface of the occipital lobes is the seat of perceptions (?) 
 of sight ; but the visual memory-images are especially con- 
 nected with the sight-centre Al. 
 
 Further Extension of Sight-centres. — Other investigators 
 have thoroughly traversed the ground covered by tlie 
 experiments and conclusions of Munk. They find that no 
 blindness of the clear spot of vision is produced in the 
 opposite eye by extirpating his centre Al, in the case of 
 dogs. It is even claimed that the most extensive lesion 
 of Munk's entire visual area does not necessarily result in 
 the loss of the animal's vision. Moreover, it is found that 
 disturbances of sight may follow lesions in the other lobes, 
 especially in the frontal lobes. Some years since it was 
 maintained that the cuneus is especially concerned, with 
 the occipital lobes, in the functions of vision. Regions 
 adjacent to the cuneus are also, on the authority of some 
 experimenters, declared to be connected with the same 
 functions. 
 
 The more recent experiments with stimulation by the 
 electrical current seem to show that movements of the 
 eyes can be obtained by irritating various areas in and 
 around the occipital lobes. Three zones are mentioned by 
 one authority (Schafer) : (1) the parts about the parieto- 
 occipital fissure, connected with movement of the eyes 
 downward; (2) the lower surface of the lobe and of the 
 adjacent convex and mesial surfaces, connected with move- 
 ments of the eyes upwards ; (3) area between the two, 
 connected with lateral movements. 
 
 The evidence from experiment with the lower animals 
 does not, therefore, clearly and definitely indicate where 
 pathology is to inquire for the visual areas in the case of 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 215 
 
 man. The convex surface of the occipital lobes is certainly 
 indicated in a general way. The adjacent convolutions 
 on the same lobe and in the cuneus, etc., are less clearly 
 indicated. Indeed, the most recent investigations (Lanne- 
 grace, 1889) on dogs and monkeys find hemiopia after 
 injuries in almost any part of the cortex, and ambliopia 
 after injuries to limited areas in the parietal and frontal 
 lobes. How wide and somewhat scattered are the areas 
 of the cortical surfaces which are more or less definitely 
 concerned in all the complex phenomena of vision, even 
 among the highest of the animals, is accordingly apparent. 
 How much more, then, may we expect to find the same 
 complexity of phenomena, and variety of localities in- 
 volved, in the case of man ! 
 
 Exner on Visual Centres in Man. — The answer of pathol- 
 ogy to the question. What areas of the human cerebral 
 cortex are chiefly concerned in visual sensations and per- 
 ceptions? is ambiguous. The method of "negative cases," 
 according to Exner, yields no assured results. The induc- 
 tion does not point out any "absolute field" of vision. 
 But the methods of " percentage " and of " positive cases " 
 point clearly to the occipital lobe, and especially to the 
 upper end of the first occipital convolution (01 in the 
 chart, p. 205) as its most intensive portion. The region 
 of less intensity extends over the other occipital convolu- 
 tions, the cuneus, and the adjacent parts of the lohulus 
 quadratus. 
 
 Additional Evidence from Pathology. — An increasing num- 
 ber of positive cases indicate that the induction just stated 
 is substantially correct. But it still remains true that we 
 cannot say no other areas than those mentioned above have 
 particular connection with the phenomena of intelligent 
 vision. One chief authority (Wilbrand) has been led to 
 the following conclusions respecting what he calls " psychi- 
 cal blindness." If the impressions be cut off in their 
 
216 PHYSIOLOGICAL PSYCHOLOGY. 
 
 course along the optical tract, blindness, in the more ordi- 
 nary sense of the word, results ; but visual hallucinations, 
 dream-Yisions, and subjective light-sensations are still pos- 
 sible. If, however, the perceptive centre (that pointed out 
 by Munk, see p. 199 f.) be destroyed on one hemisphere, then 
 complete cortical blindness takes place in the opposite half 
 of the field of vision. If this centre be destroyed in both 
 hemispheres, subjective visions, hallucinations, etc., are 
 impossible. If the visual " memory-areas " (see p. 213 f.) be 
 also thoroughly destroyed, then all impressions of form 
 and color lose their psychical and intellectual character. 
 They become unmeaning or unfamiliar impressions. We 
 cannot vouch for the full accuracy of these distinctions. 
 They await further confirmation. 
 
 Kinds of " Psychical Blindness." — Disturbances and loss of 
 intelligent and appreciative sight may be due to a variety 
 of causes, occurring either singly or combined. This fact is 
 the expression of the variety of the cortical areas that are 
 concerned in some part of the very complex activities of 
 such vision as man enjoys. Thus, to adopt provisionally 
 the classification of one writer, " psychical blindness " may 
 be due (1) to disturbance of the organism for associating 
 the perception of the visual object with other ideas (with- 
 out disturbance of the perception itself) ; or (2) to dis- 
 turbance of both the perceptive and the associative activity; 
 or (3) to disturbance of the perception exclusively. Cor- 
 responding to these necessary factors in all intelligent and 
 appreciative vision are the various cortical areas and tracts 
 of " projection " and " association " fibres. Thus the whole 
 apparatus of vision involves not only those areas which have 
 been shown to be especially concerned, but also other less 
 intensive associated areas in the parietal, temporal, and 
 even frontal lobes. 
 
 Division of the Visual Field. — Persistent and skilful 
 attempts have been made to divide the general field of 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 217 
 
 vision, and to assign to the divisions distinct sub-areas in 
 the general cortical region concerned in visual perception. 
 The investigations of histology seem clearly to indicate 
 that in the higher animals, and especially in man, the optic 
 nerve contains one system of fibres which crosses over to 
 the opposite side (either in the optic chiasm or beyond), 
 and one system which remains uncrossed. The retina of 
 each eye appears, then,, in marCs case, to he rep7'esented on 
 the cortical surface of both hemispheres of the brain. Patho- 
 logical cases confirm this conclusion from histology. 
 
 The assumed state of the case is then described by one 
 writer in the following terms : " If we imagine the visual 
 areas of the two cerebral hemispheres to be united in the 
 middle line, we may conceive each retina, as projected in 
 its normal position over the united area. It will then at 
 once appear that the upper and lower parts of both retinas 
 will fall upon the corresponding parts of the united area ; 
 that the outer part of the left retina and the inner part of 
 the right will fall on the outer portion of the left side of 
 the united area, and vice versa ; and that a vertical line 
 bisecting each retina will fall along the line of union of 
 the two cerebral areas." 
 
 Cortical Centres of Smell and Taste. — Nothing definite has 
 yet been determined as to those areas of the human brain 
 which are connected with sensations and perceptions of < 
 smell and taste. Both centres are located by Dr. Ferrier 
 close together in the subiculum (see Fig. 68) and neigh- 
 boring parts of the convolutions of the temporal lobe. 
 Munk, however, would localize smell in the gyrus hippo- 
 campi. A recent writer (Dr. Mills), while admitting that 
 the localization of the cortical centre of smell is still un- 
 certain, thinks that the evidence points toward the region 
 of the uncinate convolution and its vicinity. 
 
 The Centre of Hearing. — The upper convolution in the 
 temporal lobe has been assigned by Dr. Ferrier to the 
 
218 PHYSIOLOGICAL PSYCHOLOGY. 
 
 auditory sensations. But this auditory centre is localized 
 by Munk in the region marked £1 (see Fig., p. 199), for 
 its greatest intensity ; and with less intensity in the ad- 
 jacent regions marked B. Recent investigations seem to 
 indicate that the upper temporal convolution can be com- 
 pletely extirpated without disturbing permanently the 
 sense of hearing. With considerable probability does one 
 authority extend the so-called " auditory sphere " over the 
 whole surface of the temporal lobe, and probably also the 
 "horn of Ammon." 
 
 Centres Concerned in Articulate Speech. — To speak of a 
 cortical centre for human speech seems in itself to involve 
 an absurdity. All the processes of the mind are deeply 
 and complexly involved in the use of language ; if, then, 
 we are to be faithful to the theory of localization itself, we 
 are compelled to admit that a considerable part of the 
 entire brain, including a variety of centres so-called, must 
 exercise their functions in connection with these mental 
 processes. 
 
 In treatises of the years 1861-1865, Broca announced 
 the discovery that the lower convolution of the frontal 
 lobe is "the seat of the faculty of articulate language." 
 This way of stating the case involves the absurdity to 
 which reference has just been made. But the discovery 
 in physiology thus announced was of the highest impor- 
 tance and, properly stated, has maintained its place among 
 the truths of cerebral science. 
 
 Phenomena of Aphasia. — Any permanent disturbance or 
 loss of the power to apprehend, or to express one's self in, 
 articulate language, if it is due to lesions of the cerebral 
 cortex, is called " aphasia." The phenomena of this dis- 
 ease are exceedingly varied, and very interesting. They 
 range all the way from those resembling the results of 
 inattention in normal persons Qe.g. such as that of the 
 German professor who certified in writing, "A. B. has 
 
SENSOKY AND MOTOR BEAIN PUNCTIOKS. 219 
 
 attended my remarkable lectures in chemistry with inor- 
 ganic assiduity.") to the utter loss of intelligent speech, 
 in cases of progressive paralysis with dementia. 
 
 Sometimes the aphasic patient is entirely speechless, but 
 understands what is said to him, and can express himself 
 in writing. Sometimes he can pronounce words of one 
 syllable only ; sometimes only a few senseless or extraor- 
 dinary syllables or words. Not infrequently the ability to 
 render certain words or sounds is joined with the inability 
 to render other closely similar words or sounds, in a most 
 surprising way. One patient, thus afflicted, could say 
 " Bon jour," but could not say " bonbon." In another 
 celebrated case the entire vocabulary of the aphasic person 
 was limited to the five words, oui, non, tois (for trois), 
 toujours, and Le Lo (instead of Le Long, the man's name). 
 Four of these words were used with a substantially correct 
 meaning ; but " toujours " was the word employed when- 
 ever the patient could not express his meaning by gestures 
 or by the rest of his stock of words. 
 
 Kinds of Aphasia. — The variety of phenomena connected 
 with this form of cerebral disease is such as to provoke 
 investigators to a more careful classification of the cases. 
 Thus various subdivisions have been made. The word 
 agraphia has been employed for the inability to express 
 thought in written language, — an inability which may be 
 incomplete or absolute. In some cases, highly cultivated 
 persons become unable to produce a single letter with the 
 pen. Others write long rows of letters arranged in mean- 
 ingless fashion, or with a genuine word occurring here 
 and there. 
 
 In certain cases of aphasia it is " word-deafness " which 
 is the prominent factor in the disease. Persons thus af- 
 flicted hear words as confused murmurings, with no mean- 
 ing in them ; at the same time the sense of hearing for the 
 tick of a watch may be very, acute. In other cases, the 
 
220 PHYSIOLOGICAL PSYCHOLOGY. 
 
 patient can hear and articulate, but the " acoustic image " 
 of the word as a symbol of the idea has perished. 
 
 In many cases of aphasia the phenomenon of what is 
 called " word-blindness " is the most prominent factor. 
 The connection of tliis disease with disturbances of the 
 visual centres has been noticed by many observers. Some 
 have held that " optical aphasia " is a distinct kind. Of 
 seven reported cases of cerebral defect of vision, five of 
 which had " psychical blindness " and could not read, six 
 cases showed extensive lesions, generally in the occipital 
 and temporo-occipital regions. Hence we may argue that 
 the sight-centres in the occipital lobes are connected by 
 association-fibres with the centres for uttering language in 
 the temporal and frontal lobes. 
 
 Novel affections have also been noticed in which the 
 patients can read a few lines, but apparently get no sense 
 from it, and give up the attempt in despair. The name of 
 " dyslexia " has been given to such cases ; and in some of 
 them post-mortem examination has shown lesions interfer- 
 ing with the tracts between the visual areas and the con- 
 volution in which Broca located articulate speech. 
 
 Dr. Starr suggests a name (" apraxia ") for a wider class 
 of cases, of which " word-deafness " and " word-blindness " 
 are the best known examples. The significant feature of 
 such cases is the inability to recognize the use or import of 
 an object. Of this inability there may be as many kinds 
 as there are kinds of sensations. The cerebral disease con- 
 sists in the lesion of the connections which are normally 
 maintained among the "residua" of the various groups of 
 sense-impressions. 
 
 Cerebral Areas of Lesion in Aphasia. — In Exner's collec- 
 tion of cases, all but one of the 31 lesions resulting in 
 aphasia were on the left hemisphere of the brain. Dr. 
 Seguin, out of 260 cases, calculated the proportion of 
 aphasias due to lesion on the left side as compared with 
 
SENSORY AND MOTOE BKAIN FUNCTIONS. 221 
 
 the. right, to be as 243 : 17 or 14.3 : 1. It appears then 
 that, so far at least as the motor functions are con- 
 cerned, speech is left-brained. In this (the left) hemi- 
 sphere, the anterior central convolution and the adjacent 
 convolutions of the frontal lobe, but especially the bacJc 
 part of the loiver frontal convolution, have much the high- 
 est intensity as seats of aphasic lesions. Of 53 cases care- 
 fully collected by one authority, t50 were in the left hemi- 
 sphere, 24 in the lower frontal convolution, 34 in this 
 convolution and adjacent parts, 19 either in the Island of 
 Reil alone or in it and adjacent parts. Yet the same 
 authority gives 2 cases of aphasia following lesions in the 
 front part of the frontal lobe, 3 in the parietal, 4 in the 
 occipital. 
 
 Further 4)istiiictions in Areas of Speech. — Attempts have 
 been made, with more or less of probability, to localize 
 the lesions which occasion the different kinds, or are 
 connected with the different factors and phases, of aphasia. 
 Thus Exner is inclined to assign " motor aphasia " to the 
 third frontal convolution, " word-deafness " to the middle 
 temporal convolution, and "agraphia" to the lower and 
 front part of the parietal lobe. In partial but substantial 
 agreement with him, another authority would locate "hear- 
 ing language " in the first and part of the middle temporal 
 convolutions ; " seeing words " in the lower parietal ; 
 " writing " at -the foot of the left middle frontal ; and 
 " speaking words " at the foot of the left lower frontal 
 convolution. Each centre is thus situated amidst larger 
 related areas, — the motor, in the wider field of arm, tongue, 
 and jaw ; and the sensory, in the general fields of hearing 
 and sight. Each centre is, therefore, the focus of certain 
 kinds of memory-images. 
 
 The foregoing delineations are rather more definite than 
 it is wise at present to attempt to be. "We cannot do better 
 than to close this branch of the discussion with the remark 
 
222 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of Kussmaul, " It is, a priori, probable that an enormous 
 association tract in the cortex has been assigned to speech, 
 even though the key-board of sound may be confined to 
 the anterior cortical regions." With reference to the last 
 clause, however, it is to be noticed that the loss of power 
 to sing and to understand melodies, or to use and under- 
 stand numbers, is not necessarily connected with the loss 
 of articulate speech. 
 
 Evidence from Histology and Anatomy. — The general dis- 
 tribution of motor and sensory areas which has been made 
 above is confirmed — or at least it is not disturbed — by 
 researches in comparative histology and anatomy. That 
 the motor tracts from below run to the frontal and front 
 parietal and temporal regions of the brain, while the sen- 
 sory lie, on the whole, in the direction toward the hinder 
 cerebral parts, can scarcely be doubted (compare p. 72 f.). 
 It is perhaps more doubtful, and yet, on the whole, prob- 
 able : — as says Dr. Starr — • that " the third set of fibres of 
 the projection system includes those which lie just posterior 
 to the motor tract, and fill up to a considerable extent the 
 space between it and the radiation of the visual tract, 
 towards the occipital lobe." This set of fibres, he thinks, 
 convey the sensory impulses of touch, pain, temperature, 
 and the muscular sense. They lie around, and to a certain 
 extent coincide with, and interpenetrate, the motor areas. 
 
 RELATION OF THE CEJREBRAL AREAS TO "GENERAL 
 INTELLIGENCE." 
 
 The more ardent advocates of the theory of the local- 
 ization of cerebral functions find it difficult to refrain from 
 assigning some portion of the cerebral cortex to the for- 
 mation of concepts, and to the mental activities sometimes 
 spoken of as " general intelligence." Of course, for this 
 purpose the frontal regions offer themselves as peculiarly 
 tempting. General considerations of comparative anatomy 
 
SENSORY AND MOTOR BEAIN f'UNCTIONS. 223 
 
 might be said to favor this view. For it is with respect to 
 the development of these regions, as one most significant 
 feature, that the human brain surpasses that of all the 
 other animals. Experimental evidence might also be 
 appealed to, — such as that which finds the mentality of 
 birds, for example, whose fore-brains have been removed 
 without injury to remaining portions, reduced to a con- 
 dition resembling idiocy. 
 
 On the other hand, there are perhaps no other portions 
 of the human brain where so extensive lesions may occur 
 with little or no impairment of any bodily or mental func- 
 tions, as the frontal regions. Small lesions in other regions 
 are not infrequently productive of much more serious 
 mental disturbance. 
 
 It should also be noticed that the words " general intel- 
 ligence " are somewhat ambiguous, and may be really 
 misleading. Strictly speaking, there is no such thing as 
 general intelligence. Especially in the earlier stages of 
 development, and with the lower animals, any impaii-ment 
 of the sensory or motor functions occasions a certain dis- 
 turbance or loss of " intelligence." In a case like that of 
 aphasia, in man, how shall we separate between the def- 
 inite and concrete loss of functions which we designate by 
 "psychical deafness,'" or "psychical blindness," and the 
 disturbance and loss of general mental power ? All intel- 
 ligence is intelligence about something or other, and resting 
 upon a -basis of sensations and volitions. 
 
 Moreover, the phenomena to which the veteran opponent 
 (Goltz) of the theory of localization constantly appeals, 
 show that, in the lower animals, the descent toward idiocy 
 is, in a general way, proportioned to the amount of cere- 
 bral substance which has been functionally disturbed or 
 extirpated. Even temporary functional impairment of the 
 cerebral centres tends to pull any one down toward idiocy. 
 Such impairment occasions a diminution of mental vigor 
 
224 PHYSIOLOGICAL PSYCHOLOGY. 
 
 which shows itself in more or less specific ways, according 
 to circumstances. Goltz describes a dog which lived for 
 fifteen months after having lost one entire hemisphere, 
 basal ganglia included. Both motion and sensibility were 
 impaired on the side opposite the lesion ; but there was 
 complete loss of no sensory or motor function. The 
 animal was a simpleton, without fear or sportiveness, and 
 with impaired hearing and sight. But the removal of one 
 frontal lobe from an animal is found to occasion little or 
 no severe disturbance of mental functions. With both 
 frontal lobes gone, however, the animal cannot eat unaided, 
 nor use his paws as hands. The removal of the occipital 
 lobes occasions, Goltz believes, far more profound changes 
 than loss of both eyes ; the animal then loses psychical fear 
 and interest, and is mentally degenerate. 
 
 In man's case we can localize with considerable success 
 the functions on which the psychical quality of sensory 
 impressions is dependent; and we can point out the tracts 
 which must be traversed if memory-images are to be 
 aroused, and the impressions attain a meaning and connec- 
 tion with the past mental life. But as to cortical areas 
 which may serve as a physical basis for the mental activi- 
 ties that are " logical " or " intellectual," — in the higher 
 sense of these words, — we are quite in the dark as to 
 where to look for them, or as to the use to which we should 
 put them in case they could be found. 
 
 Summary of Principles. — Three principles seem to sum 
 up the results obtained by discussion of the evidence ad- 
 duced in the two preceding chapters. 
 
 1. The Principle of Use and the Law of Hahit. The 
 different elementary parts of the nervous system become 
 capable of performing their specific functions, only when 
 brought into proper connections and exercised in the 
 performance of those functions. No elements or groups of 
 
SENSORY AND MOTOR BRAIN FUNCTIONS. 225 
 
 elements act in isolation; what they do, and can do, 
 depends upon their connection with other elements. This 
 is especially true of the different minuter or larger areas 
 of the cerebral cortex. Their functions are dependent 
 upon their relations to one another and to the inferior 
 regions of the brain, as joined together by " association- 
 fibres " and " projection-fibres." 
 
 Moreover, the repeated action of the nervous elements, 
 in the connections in which they are placed, develops in 
 them a special fitness for performing specific functions. 
 The areas of the cortex improve by exercise. By repeated 
 activity, in their appropriate connections, they gain in 
 facility and value with respect to their specific functions. 
 
 2. The Principle of a Local Specialization of Function. 
 In the cerebral cortex, as elsewhere through the entire 
 nervous system, certain parts have, in all normal and 
 ordinaiy circumstances, certain specific functions to per- 
 form. In the spinal cord we found particular areas, either 
 as located by a cross-section at each altitude, or as so-called 
 " centres " placed above and below each other in the length 
 of the cord, to have specific functions assigned to them. 
 In the lower parts of the brain the principle of the local- 
 ization of function appears to be also carried out. The 
 evidence adduced in the last two chapters establishes 
 beyond reasonable doubt the existence of the same prin- 
 ciple as applied to different parts of the cortex of man's 
 brain. And, indeed, it is just here that we should expect 
 to find the most definite and perfect application of the 
 principle. 
 
 So-called " centres," or " areas," or " fields," of the sur- 
 face of man's brain are in no case, however, to be regarded 
 as portions of its nervous substance that mark the limits 
 within which specific functions are always" rigidly confined. 
 Such " centres " are not to be thought of as mathematical 
 
226 PHYSIOLOGICAL PSYCHOLOGY. 
 
 points or as definitely circumscribed collections of cells. 
 They do not appear to be perfectly isolated localities. 
 They are not necessarily the same in their exact outlines 
 for individuals of the same species, or for the same indi- 
 vidual at all times. They widen when a heightened energy 
 is demanded of th6m. They obviously overlap and inter- 
 penetrate in certain cases. Especially is this true of the 
 regions in which the motor and sensory functions are con- 
 nected for the control of the same parts of the body. 
 They are intimately interconnected and associated in 
 function ; so that one of them cannot, as a rule, be cut out 
 without injury to others ; or its function greatly impaired 
 without disturbing the function of other associated cen- 
 tres. 
 
 3. The Principle of Substitution. Furthermore, the 
 performance of the functions allotted, as it were, to these 
 so-called centres, is not necessarily, under all circum- 
 stances, confined to them. If such areas become absolutely 
 or relatively unfitted to perform their normal functions, it 
 is possible, within certain limitations, for other areas to 
 assume these functions. The areas, however, which can 
 be substituted must have the proper connections. It is 
 due, in large part, to the working of this principle of sub- 
 stitution, that animals subjected to experiments in extirpa- 
 tion, as a rule, recover the powers of sensation and motion 
 which they have temporarily lost. A certain large elas- 
 ticity, as it were, of the nervous system is implied in the 
 very laws of reflex or sensory-motor activity as applied to 
 the spinal cord (see p. 139 f.). This principle does not 
 operate arbitrarily ; it will not meet all possiHe demands 
 made upon it. 
 
 The portions of the same hemisphere of the brain that 
 are just adjacent to the so-called " centres " (the larger 
 areas surrounding or continuous to the smaller), and, on 
 account of its bilateral structure, the corresponding por- 
 
SENSOKY AND MOTOR BRAIN FUNCTIONS. 227 
 
 tions of the other hemisphere, are best capable of exercising 
 their substitutive functions. The assumed functions also 
 fall, of course, under the law of habit. Perhaps these 
 statements cover all that it will finally be found necessary 
 to admit. 
 
CHAPTER X. 
 
 THE QUALITY OF SENSATIONS. 
 
 The variety of our sensations seems, on first reflection, 
 bewilderingly great. But the popular way of viewing 
 them has reduced them all to five classes, according to the 
 organs of the body through which the sensations are known 
 to be received. Hence the five kinds of senses — smell, 
 taste, hearing, sight, and touch — which everybody recog- 
 nizes. The inadequacy and, in some respects, inaccuracy 
 of this popular classification are readily made apparent. 
 But it is not seen, without careful and detailed scientific 
 research, what classification ought to take its place. The 
 various and uncertain uses of the word ^'■feeling " are cal- 
 culated to emphasize our doubts and difficulties on this 
 point. 
 
 Simple Sensations. — Strictly speaking, there are no ex- 
 periences of which we are- conscious that can be called 
 simple — or absolutely uncompounded — sensations. In- 
 deed, in all our adult life we have no experience even of 
 pure but complex sensations, as such, — that is, of sensa- 
 tions regarded as states of consciousness disconnected from 
 images of memory and imagination, and unrelated to 
 things, perceived or imagined, as their so-called "quali- 
 ' ties." Moreover, the simplest sensation which we can 
 detect in connection with our perceptions or memories of 
 things is no more absolutely simple to psychology, in its 
 nature, than is the drop of water to chemistry. 
 
 The " simple sensation " is then a fiction of psycho-physi- 
 cal science. It is not realizable as a state of consciousness 
 228 
 
QUALITY OP SENSATIONS. 229 
 
 in experience. It is a theoretical factor into which science 
 breaks up those complexes of consciousness which have 
 the predominating characteristics of all sense-experience. 
 
 Quality distinguished from Quantity. — Consciousness en- 
 ables us to distinguish between the quality and the quan- 
 tity, or intensity, of our sensations. We are immediately 
 aware both of the hind of the mental affection which arises 
 through excitation of the organs of sense, and also of 
 variations in its amount. Thus a distinction is possible 
 between " the how " and the " how much " of the resulting 
 state. That the quality and the quantity of sensations 
 are closely related, our experience makes perfectly clear. 
 Intense smells and tastes are different from weak ones, in 
 their characteristic quality, even when they are excited by 
 the same object. Very intense sensations of every kind 
 tend to pass over into sensations of pain. Sensations of 
 light touch differ in kind from those produced by heavier 
 pressure of the same object on the same locality of the 
 organ. Yet the distinction between quality and quantity 
 is clearly made by the consciousness of every one. 
 
 ftuestions relating to the Determination of Quality. — The 
 inquiries which physiological psychology raises concerning 
 the quality of sensation are, chiefly, these four : (1) What 
 is the precise locality of the organism where the specific 
 excitation which occasions each kind of sensation origi- 
 nates ? (2) What is the character of the stimulus, and 
 the nature of its action upon the organism, in producing 
 the specific excitation ? (3) What are the various kinds 
 of sensations which appear in consciousness and the various 
 corresponding kinds of stimuli on which the sensations 
 are dependent? (4) What are the laws by which the 
 quality of the sensations is related to the several kinds of 
 stimuli? None of these questions can be answered com- 
 pletely by modern experimental psychology. But some- 
 thing of a strictly scientific character can be said in reply 
 
230 PHYSIOLOGICAL PSYCHOLOGY. 
 
 to eacli; and none of them can be properly neglected 
 in our considerations. We shall not, however, think it 
 necessary always to keep their consideration separate. 
 
 SENSATIONS OF SMELL AND TASTE QUALITATIVELY 
 CONSIDERED. 
 
 In beginning with these sensations we are considering 
 those, first, which are least intellectual in quality, and at 
 the same time most indefinite and difficult to reduce to 
 terms of scientific statement. 
 
 Excitable Region for Sensations of Smell. — It has already 
 been shown (p. 74 f.) that the part of the mucous membrane 
 of the nasal passages known as the regio olfactoria contains 
 the end-organs of smell. Here the nerve of smell {olfac- 
 torius) is spread out. It must be reached by the stimulus 
 being, in all ordinary circumstances at least, borne thither 
 by the current of air in the act (usually, if not always) of 
 inspiration. 
 
 Stimulus of Sensations of Smell. — The excitation of the 
 end-organs of this sense seems to require that the stimulus 
 should act upon them in gaseous form. Thus objects like 
 arsenic, which at ordinary temperatures are inodorous, 
 when vaporized by heat, excite intense sensations of smell. 
 Fluid bodies which give off an odorous reek, when brought 
 in their fluid form into contact with the organs, as a rule, 
 have no smell. Most observers have followed the opinion 
 of Weber, who held that no fluid, not even eau de cologne, 
 when poured into the nostrils and remaining against the 
 organs, can excite olfactory sensations. The reason for 
 this has been attributed to the temporary impairment of 
 the organs by being soaked, or to the mechanical barrier 
 which the fluid makes between the odorous particles and 
 the apparatus of smell. 
 
 The conclusion of Weber has more recently been con- 
 tested. It has been considered that fish have true sensa- 
 
QUALITY OP SENSATIONS. 231 
 
 tions of smell. And some observers report that, by using 
 a ± tube and introducing into the nostrils solutions of 
 camphor, clove oil, cologne, etc., they have succeeded in 
 exciting the specific smells of these substances. 
 
 Mechanical and Electrical Excitation of Smell. — Some 
 physiologists have asserted that they could obtain sensa- 
 tions of smell by different forms of mechanical irritation, 
 such as vibration of the nostrils, violent sneezing, etc. 
 Nearly a century ago Ritter experimented by using bits of 
 graphite and zinc thrust into the nostrils, and thought he 
 thus excited genuine sensations of smell. He described 
 the positive pole as effecting a trace of smell like that of 
 " ammonia " ; the negative pole produced a kind of " sour " 
 smell. It is by no means certain that these sensations 
 were not sensations of touch and taste rather than specific 
 sensations of smell. And although some modern experi- 
 menters claim to have a distinct sense of smell, for ex- 
 ample, with the cathode in the nose on opening the 
 current, and with the anode on making the current, the 
 electrical stimulation of specific sensations of this sense 
 can scarcely be said to be experimentally established. 
 There is no proof that thermic stimulation will excite the 
 sense of smell. 
 
 Subjective Sensations of Smell. — Experiments to prove 
 that the sense of smell may be excited in animals by 
 injecting odorous substances into their veins are very 
 uncertain. Human pathological cases show that com- 
 pression of the olfactory nerve by tumors may produce 
 sensations. There is no doubt that disturbances of the 
 central organs, such as accompany insanity, may cause 
 subjective smells. Indeed, to be thus afHicted is some- 
 times symptomatic of disease of the brain. And we know 
 how powerfully the brains of some persons are affected, so 
 that nausea and giddiness result, by even very weak odors 
 from some substances. 
 
232 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Properties of Odorous Bodies. — There seems to be no one 
 characteristic which a body must possess in order to excite 
 the specific kind of sensation which we distinguish as that 
 of smell. Some plants are odorous by day alone, others by 
 night alone. Some have a smell when dry; others give 
 off only a weak odor when dry, but a stronger one when 
 moistened. In general, the effect of any odorous sub- 
 stance depends upon the ease with which it may be vapor- 
 ized, and the speed and extent of its diffusion through the 
 atmosphere. 
 
 In 1756 it was discovered (by Romieu) that small bits 
 of camphor on water exhibit a peculiar rotary motion. It 
 was afterwards shown that other odorous bodies have a 
 similar motion on the surface of water ; and that a thin 
 layer of water on a perfectly clean plate will withdraw 
 itself as soon as pulverized camphor is spread upon it. 
 Similar phenomena have been noticed in the cases of some 
 two hundred odorous substances of either vegetable or 
 animal structure. From such data the conclusion is drawn 
 that all odorous substances have the power, especially when 
 in contact with moisture, to set up such a motion of their 
 outside particles as distributes them through the surround- 
 ing atmosphere. Beyond the general theory, that the 
 power to give off those peculiar " effluvia " which excite 
 the end-organs of the olfactory nerve is characteristic of 
 all odorous bodies, it cannot be said that much is known. 
 
 Classification of Smells. — The specific sensation of smell 
 must, first of all, be distinguished from other forms of sen- 
 sation with which it is combined and ordinarily confounded. 
 Many so-called sensations of taste (as that of the onion, 
 etc.) are really sensations of smell. Substances like am- 
 monia and acetic acid excite sensations of so-called " com- 
 mon feeling" through their action on the tvigeminus as 
 well as the olfactory nerve. 
 
 But after these distinctions are carefully made, all 
 
QUALITY OF SENSATIONS. 233 
 
 attempts to classify sensations of smell, as such, remain 
 unavailing. The division into pleasant and unpleasant 
 depends upon the changing whims of individuals. To 
 some persons the smell of assafoetida, of burning feathers, 
 of rank cheese, is pleasant. A classification according to 
 the objects which yield the odor '(" smell of a rose," etc.) 
 is not a classification of sensations of smell at all. A clas- 
 sification on chemical grounds is unsatisfactory ; chemists 
 differ much concerning the smell of the same substances. 
 Nor have the attempts to distinguish various olfactory 
 fibres, or systems of fibres, as appropriated to specific sen- 
 sations, been successful. 
 
 We are obliged then to say that no known principle will 
 bring order out of this bewildering confusion. There is 
 no classification of the sensations of smell, as such. To 
 quote from a prominent authority : Sensations of smell 
 form "a discrete manifoldness which has an unknown 
 arrangement." 
 
 Our knowledge respecting Sensations of Taste and their 
 excitement and laws is only a little more advanced than 
 that respecting sensations of smell. 
 
 Excitable Eegious for Sensations of Taste. — The question 
 whether a tastable substance excites specifically the same 
 sensations, when applied to all places of the organ of taste, 
 is somewhat difficult to answer experimentally. Descrip- 
 tions which speak of tastes as " prickly," " piquant," " cool- 
 ing," etc., confound other sensations with those of this 
 sense. The more general conclusion seems to be, that 
 sweet and sour are tasted chiefly with the tip of the tongue, 
 bitter and alkaline with its roots. In 1888, in the laboratory 
 of Johns Hopkins, it was discovered that a certain deriva- 
 tive of saccharine would produce sensations of bitter when 
 applied to the back part of the tongue, and of sweet when 
 applied to the tip and borders of the anterior half. It 
 should be said, however, that another observer reports the 
 
234 PHYSIOLOGICAL PSYCHOLOGY. 
 
 sensibility of the root of the tongue for sweet greatest in 
 nine cases out of ten, with which he experimented, and of 
 the edges of the tongue for sour, in seven cases out of ten. 
 The same observer, however, found that the root retains 
 best its taste for bitter, and worst its taste for sour. 
 
 In all such experiments considerable allowance must be 
 made for the idiosyncrasies of individuals. It must also be 
 remembered that it is difficult carefully to circumscribe the 
 application of stimulus to the end-organs of taste. More- 
 over, in some cases the sensibility to excitement extends 
 outside of the tongue more widely than is common ; it 
 may be found in the soft palate and the contiguous arch. 
 Indeed, the record of one patient is given who, when the 
 entire tongue had been removed, retained some taste 
 caused by touching the back of the throat or the mucous 
 membrane of the stump. 
 
 Stinmlus of Sensations of Taste. — Only fluid bodies, or 
 such as are soluble in a fluid or menstruum, excite sensa- 
 tions of taste. Absolutely insoluble bodies are, without 
 exception, tasteless. Not all soluble substances, however, 
 excite sensations of taste ; and no known law regulates the 
 relation between the two. It has been claimed by some 
 experimenters that certain gases, when made to act upon 
 the organs of taste, excite in them the specific sensations 
 of this sense. It is difficult, however, to prove that the 
 tongue has been so thoroughly dried in any case, as to 
 prevent the absorption of these gases by its moist capillary 
 layer. 
 
 Meclianical and Electrical Excitation of Taste. — It is doubt- 
 ful whether the sensation of taste can be excited by 
 mechanical means. Certain authorities of high rank de- 
 scribe such sensations as mingled with the feelings that 
 follow rubbing or pressing the tongue. The debate over 
 the question whether electrical stimulation excites sensa- 
 tions of this sense continued for a hundred years. It was 
 
QUALITY OF SENSATIONS. 235 
 
 finally shown that, when a chain of four persons is arranged 
 in such a manner as to send a current of electricity through 
 the tongue of one, the eyeball of another, and the muscles 
 of a frog-preparation, held by two of the four, the same 
 excitation causes, simultaneously, an acid taste in the 
 mouth of one observer, a flash of light in the eye of 
 another observer, and a movement of the muscles of the 
 frog. Other experiments confirm the view that electricity 
 is an excitant of the sensations of taste. 
 
 Subjective Sensations of Taste. — The attempts made to 
 prove that animals may be affected with sensations of this 
 sense by injecting tastable substances into their blood, 
 have led to no residt. Most of the alleged instances of 
 subjective sensations of taste are probably due to substances 
 really brought to the tongue in the saliva. It is note- 
 worthy that we rarely or never dream in terms of this sense. 
 
 Properties of Tastable Substances. — As to what it is in 
 certain substances which fits them to excite the end-organs 
 of the tongue and soft palate, we are much in the dark. 
 Experiments lie in the line of discovering some relation 
 between the chemical constitution and action of these sub- 
 stances and the different kinds of taste. This relation has 
 been thought to be of the simplest sort with the acids ; a 
 great variety of which, when we exclude the sense of smell, 
 are found to have the same taste. Many of the carbon com- 
 pounds have a distinct sour taste. Moreover, all the solu- 
 ble chlorides are found to be salt (like table salt) ; only 
 with the highest members in the series of compounds the 
 taste becomes more saline and develops into a bitter. 
 Many sweet substances are alcoholic bodies, and contain the 
 radical CH^OH. 
 
 On data such as the foregoing it has been claimed ^ that 
 tastable bodies are surrounded by vibrating matter which 
 acts on the sensitive surfaces of the organ ; and that the 
 1 For example, by J. B. Haycraft, in Brain, July, 1887. 
 
236 PHYSIOLOGICAL PSYCHOLOGY. 
 
 quality of the sensation is dependent upon the character 
 of the vibrating matter. Just as a certain class of salts of 
 allied physical and chemical properties vibrate in a certain 
 way, and stimulating the eye, produce the same color-sensa- 
 tions ; just so do similar sapid compounds, which contain 
 elements of the same compound radical, vibrate in similar 
 way and produce the same taste. Apparent exceptions to 
 the simpler laws may be due to the fact that the tongue, 
 like the eye, has no power of analysis. The same taste 
 may then be produced by a simple vibration, or by a com- 
 pound of simple vibrations. 
 
 Classification of Tastes. — Sensations of this sense are, in 
 ordinary experience, combined with those of smell, touch, 
 temperature, common feeling, and the muscular sense. It 
 has been customary to distinguish at least four specifically 
 different sensations of taste, — namely, sour, sweet, salt, 
 and bitter. To them "Wundt would add the alkaline and 
 the metallic. All other so-called tastes are then supposed 
 to be compounds of these specific, simple sensations of taste 
 with one another, and with the other kinds of sensations 
 mentioned above . It seems very doubtful, however, whether 
 this classification will satisfy all the experiences we have 
 under this sensation. In consciousness, the sensations of 
 this sense, like those of color and light, are not analyzable 
 into so few simple elements. The sensations, as such — 
 that is to say — are not exhaustively classified. Moreover, 
 the similarity of our sensations of taste to those of smell, 
 in respect of their bewildering variety, is quite too marked 
 to make us satisfied with any of the existing schemes of 
 classification. 
 
 SENSATIONS OF THE SKIN, MUSCLES, JOINTS, ETC., 
 QUALITATIVELY CONSIDERED. 
 
 At least two specifically different sensations — namely, 
 Pressure and Temperature — have generally been admitted 
 
QUALITY OF SENSATIONS. 
 
 237 
 
 to have their organ in the skin. It is only recently, how- 
 ever, that the sensations arising by irritation of this organ 
 have been discriminated and discussed, in a thorough man- 
 ner, by experimental means of investigation. In general, 
 it should be said that many of the sensations which we 
 localize in the skin are really of cerebral origin, and result 
 from the compounding of a variety of sensory impulses, 
 in the appropriate way, within the cerebral centres. 
 
 Excitable Begions for Sensations of Pressure. — The so- 
 called " feelings," or more properly sensations of pressure, 
 are dependent upon the excitation of the sensory nerves of 
 the skin through their end-organs. The excitation of the 
 trunk of these nerves produces sensations of pain, but not 
 those definite sensations of touching and being touched, 
 which we are able so definitely to localize. 
 
 c 
 
 T 
 
 
 Fie. 73. — Arraogement of Pressure-spots (Goldscheider). A, dorsal and radial sur- 
 face of the first phalanx of the index finger; B, membrane between thumb and index 
 finger; 0, dorsal surface of fore-arm; D, back; E, inner surface of fore-arm; F, back of 
 hand. 
 
 It is a comparatively recent discovery that the definite 
 pressure-sensations are aroused only by exciting minute 
 areas of the skin called " pressure-spots." These spots are 
 
238 PHYSIOLOGICAL PSYCHOLOGY. 
 
 arranged in a manner somewhat like that of the " tempera- 
 ture-spots" (to be explained subsequently). They are 
 placed in chains, as it were, sometimes more and some- 
 times less thickly set. These chains ordinarily radiate 
 from a kind of central point, and run so as to form circu- 
 lar, or pyramidal, or longitudinal figures. They are most 
 numerous in the areas of the skin most sensitive to pres- 
 sure. The different spots differ in regard to sensitiveness ; 
 some are much more easily excited than others. 
 
 Distinctions in Pressure-sensations. — The investigations 
 of Goldscheider lead him to distinguish two specifically 
 different sensations which enter into what is ordinarily 
 called the "feeling of pressure." If a very fine point of 
 metal, wood, or cork, be touched lightly to the skin, it will 
 be found to awaken a definite sensation only at certain 
 minute spots. This sensation, when the pressure is light, 
 is very lively and delicate, and is often accompanied by 
 the feeling of being tickled. On increasing the pressure, 
 however, the sensations change their character; the feel- 
 ing becomes as though a small hard kernel were pressed 
 against the skin. Between these spots it is not possible 
 by pressure to excite the same characteristic sensations. 
 Stimulation of the spaces between the pressure-spots pro- 
 duces a dull, indefinable, " contentless " sensation ; and, if 
 the pressure is increased, a feeling of being pricked or 
 stuck. 
 
 In respect to quality, pure and simple, sensations of 
 pressure scarcely admit of further classification. We 
 localize them in the general field of touch ; but we do not 
 recognize kinds of them, as we do in the case of sensations 
 of smell and taste. The distinction between " light touch " 
 and "sensations of weight" is one of degrees of compound 
 sensations involving the muscles and joints, etc., as well as 
 the skin. As simple sensations, they differ in intensity 
 rather than in quality strictly so-called. 
 
QtlALITY OF SENSATIONS. 239 
 
 The attempt has sometimes been made to identify sen- 
 sations of light touch with sensations of temperature. 
 Weber held that cold bodies resting on the skin appear 
 heavier than they are, and warm bodies lighter. One sil- 
 ver dollar of the temperature of 25°-19|-° F. appeared 
 as heavy as two dollars of 98^°-100^°. The same conclu- 
 sion has been drawn from the observation that it is difficult 
 to distinguish, in certain parts of the skin when irritated 
 through a square opening in a piece of paper, whether the 
 cause of the irritation is a light brush from cotton or the 
 approach of a slightly heated surface. But small wooden 
 disks, when heated to 122° F., were found by another 
 observer to feel heavier than really larger ones when not 
 warmed. And even if the same stimuli could be used to 
 excite either one of these two classes of sensations, the 
 qualitative distinctness of the sensations themselves would 
 not be impaired. Moreover, cases have been reported where 
 areas of the skin suffering from a complete loss of sensi- 
 tiveness to light pressure have been more highly sensitive 
 than was normal to sensations of temperature. 
 
 Excitable Eegions for Temperature-sensations. — Certain 
 minute areas, and these only, are susceptible to irrita- 
 tions of a kind to result in sensations of heat and cold. 
 Such spots are insensible to pain and probably also to pres- 
 sure. Moreover, some of these minute areas are sensitive 
 to cold only (" cold-spots ") ; others of them to heat only 
 ("heat-spots"). When the topography of the skin is 
 carefully mapped out, these two kinds of temperature-spots 
 appear not to be superimposed. They are not located 
 alike on the symmetrical parts of the two sides of the 
 same individual, nor on the corresponding parts of differ- 
 ent individuals. In general, they occur in lines that radi- 
 ate from centres coincident with the roots of the hairs. 
 These lines often cross each other and form figures of vari- 
 ous shapes. Heat-spots are, on the whole, less numerous 
 
240 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 than cold-spots ; but in parts of the body -where the skin 
 is most sensitive to either temperature, the corresponding 
 kind of spots is most numerous. " Temperature-spots " 
 have been divided into first class and second class, accord- 
 
 FiG. 74. — Arrangement of Temperature-spote. A, beat-spots; and B, cold-spots — 
 from the palm of the left band (Ooldscheidei') , 
 
 ing to the degree of strength with which they react on 
 moderate stimulation. Some of them are irritated only by 
 excessive temperatures. The same temperature may seem 
 ice-cold to one spot and only cool to another. 
 
 Stimulus of Temperature-sensations. — Whatever form of 
 energy excites the nerves of the skin at the " heat-spots " 
 or " cold^pots " calls forth the specific sensations corre- 
 sponding to these spots. Thus, the electrical current, or 
 puncturing the skin with a point, may be felt as either 
 cold or hot, respectively. Among the inducements to 
 sensations of heat, the following have been mentioned by 
 Hering as the more ordinary : All checking of the radia- 
 tion of heat when the blood-supply remains unaltered ; all 
 contact with a medium or an object of higher temperature ; 
 all increase to the heat of the skin coming from the interior 
 of the body. On the contrary, different areas of the skin 
 feel cold, when the convection of the heat from the skin 
 increases while the blood-supply remains unchanged ; when 
 there is contact with objects that have the same tempera- 
 ture as the air, but convey the heat more rapidly than it ; 
 on contact or proximity to objects colder than the skin ; 
 and on lessening, in any way, the interior warmth of the 
 body. 
 
QUALITY OF SENSATIONS. 241 
 
 Laws of Excitation for Temperature-sensations. — It is 
 
 difficult to bring the recent discoveries in physiological 
 psychology, regarding the origin and nature of tempera- 
 ture-sensations, into any relation with the physics of objec- 
 tive heat as a mode of motion. It will be seen (when we 
 come to consider the perceptions that arise through these 
 sensations in part) that psycho-physical principles — such 
 as those of contrast, relativity, exhaustion, etc. — have a 
 large share in determining the character of this class of 
 our particular experiences. 
 
 Sensations of temperature seem also to have a certain 
 dependence on the temperature of the thermic apparatus 
 itself. This law has thus been stated by its leading expo- 
 nent: " As often as the thermic apparatus at any point in the 
 skin has a temperature which lies above its own zero-point 
 we have a sensation of heat ; in the contrary case, a sen- 
 sation of cold. Either sensation is so much the more 
 marked or stronger, the more the temperature of the ther- 
 mic apparatus at the time varies from the temperature of 
 its own zero-point." [By the " zero-point " of any part of 
 the skin is meant the exact objective temperature which at 
 that part will produce no sensation of either heat or cold.] 
 According to this principle it is proposed to explain all 
 our ordinary sensations of temperature. 
 
 The earliest great observer in this field (E. H. Weber) 
 thought, however, that all rising of the temperature of the 
 skin is felt as heat, and its sinking as cold. Thus, if we 
 hold one hand in moderately cold water, and dip the other 
 repeatedly in the same water, the sensation of cold is 
 stronger in the latter, although the temperature of the 
 hand held constantly in the water is the lower. Yet the 
 most important recent observer (Goldscheider) calls atten- 
 tion to an experiment which shows that, if one hand be 
 left for ten seconds in water of the temperature of 104° F., 
 
242 PHYSIOLOaiCAL PSYCHOLOGY. 
 
 and then both hands immersed in cold water, the warmed 
 hand will feel the cold less distinctly than the other. 
 
 Our perception of the absolute degree of temperature, 
 and of minute variations in temperature, is most acute for 
 places in the scale lying close to the normal temperature 
 of the skin. It must be confessed that the exact manner 
 in which changes of objective temperature act upon the 
 thermic apparatus to excite it is unknown. Possibly the 
 immediate stimulus of this apparatus consists of some form 
 of chemical or electrical energy developed by the increase 
 and decrease of that molecular motion which physics calls 
 « heat." 
 
 The question whether qualitatively distinct sensations 
 arise in the mind through irritation of sensory nerves 
 seated in the muscular fibre has been much debated. In 
 our judgment, however, valid reasons may be given for 
 maintaining the existence of Muscular Sensations. Most 
 of the evidence in proof of this position properly belongs 
 in connection with the development of complex percep- 
 tions of the position and movement of the eye, the limbs, 
 etc. 
 
 Existence of Sensations of the Muscular Sense. — For some 
 time it was disputed whether the muscular fibres are di- 
 rectly connected with sensory nerve-fibrils. In 1874 Sachs 
 apparently demonstrated the afiirmative of this disputed 
 question. The psychological evidence for muscular sen- 
 sations is partly immediate, and based upon the testimony 
 of consciousness, and partly indirect and experimental. 
 
 It can scarcely be doubted that we localize certain mas- 
 sive sensation-complexes in the muscles of the different 
 parts of the body. This impression is peculiarly fresh 
 and strong when, attending carefully to our sensations, 
 we lift weights, or take positions, which call into action 
 unused muscles of the limbs or trunk. In itself con- 
 sidered, little stress might be laid upon this appeal to the 
 
QUALITY OP SENSATIONS. 243 
 
 immediate testimony of consciousness on a psycho-physical 
 question. But it will become apparent by our subsequent 
 study of perception that the theoretical need of muscular 
 sensations, in order to account for the knowledge of the 
 developed mind, confirms the testimony of consciousness. 
 
 Moreover, experiment and observation of the more care- 
 ful scientific sort, on the whole, favor the assumption of a 
 muscular sense, whose sensations vary in the quality which 
 they assume in the conscious life of the mind. For in- 
 stance, there seems to be no regular parallelism between 
 the loss of the other modes of sensibility and the loss of 
 muscular sense-impressions. In rare cases, in what is 
 called " locomotor ataxy," there may be little loss of ordi- 
 nary sensibility and yet a marked deprivation of muscular 
 sense. On the other hand, sensibility of the skin may be 
 impaired or destroyed without impairing the ability to dis- 
 criminate weights when the muscles are moved. 
 
 A recent experimenter found that, after temporary 
 destruction with cocain, of the sensibility of the larynx 
 and vocal cords, a singer could sing almost (if not quite) 
 as accurately, as respects pitch, as before. With what did 
 this singer guide his voice, if not with the muscular sen- 
 sations and their memory-images? Another observer 
 reports the case of a patient who had lost an area of skin, 
 10x12 cejitimeters, without any influence on the muscular 
 sensibility of the subjacent contractile bodies. 
 
 Nature and Kinds of Muscular Sensations. — The precise 
 manner in which the muscular sensations are originated, 
 by excitation of the sensory nerve-fibrils lying within the 
 muscles, is unknown. The stimulus immediately acting on 
 these end-organs might be conceived of as either mechani- 
 cal or chemical, or electrical. It can scarcely consist 
 in the mere irritation caused by the molecular changes 
 that accompany the contraction, tension, and relaxation of 
 the muscles. We do not see, however, that our ignorance 
 
244 PHYSIOLOGICAL PSyOHOLOGY. 
 
 of the manner in which degrees of pressure act to produce, 
 through the end-apparatus of sense, different qualities of 
 sensation, is much more profound in the case of the 
 muscles than in the case of the skin. 
 
 It must also be confessed that muscular sensations are 
 very difficult of analysis by the method of self-conscious- 
 ness. In consciousness they exist as complexes, entangled 
 with sensations that arise through irritation of the " pres- 
 sure-spots " and " temperature-spots " of the skin, and in 
 the joints, etc. Moreover, muscular sensations, of them- 
 selves, seem to differ chiefly in " extensity," and quantity, 
 or intensity, rather than in quality. It is only as already 
 localized, and combined with sensation-complexes of other 
 kinds, that the muscular sensations admit of being dis- 
 tinguished as respects quality. 
 
 To this very difficult subject we shall return in other 
 connections. 
 
 Sensations of the Joints, Tendons, etc. — Experimental evi- 
 dence has tended to show that certain kinds of sensations, 
 of value in our perceptions of the positions and motions of 
 the body, originate in the joints. Goldscheider experi- 
 mented by resting the hand, palm upward, in a plaster cast, 
 bending the index finger back by changing the pressure of 
 a small weight, and then measuring the least angle of bend- 
 ing which could be perceived at the first joint. By a 
 faradic current complete insensibility of the joint was then 
 produced. It was now found that the finger must be bent 
 farther than before in order to have its flexure perceived. 
 Sensations produced by irritating the nerves of the joint 
 would appear, then, to enter into the perception of the 
 movements of the finger. It has also been discovered that 
 ataxic persons can recognize slow movements of the limbs 
 with short excursions, if accompanied by pressure on the 
 joints ; otherwise not. 
 
 Various Unclassified Sensations. — Experiments with a 
 
QUALITY OF SENSATIONS. 245 
 
 travelling metallic point, carrying the stimulus of a cur- 
 rent of electricity over the skin, reveal an astonishing 
 diversity of sensations awakened at different points of the 
 surface. "Thrill-points," "tickle-points," and points of 
 cutting pain, are all thus distinguished through irritation 
 of the same stimulus. Places occur where the rate of 
 motion seems suddenly to increase without any objective 
 increase of its rate (" acceleration-points ") ; other places 
 occur where, although continuing to move with uniform 
 velocity, the travelling point seems to stop (" blind-spots " 
 of the skin). Strange tangles of sensation, from which 
 unaccustomed sensations can be partially disentangled, 
 spring up in consciousness. 
 
 " Sensations of motion " are sometimes spoken of as 
 though they formed a distinct kind. This we believe to be 
 incorrect. "Without a succession of qualitatively different 
 sensation-complexes arising in consciousness, no perception 
 of motion can occur. This perception is, however, pecul- 
 iarly fundamental and instinctive, as it were. 
 
 THE QUALITY OF SENSATIONS OF SOUND. 
 
 There are two kinds of sounds — tones, or musical sounds, 
 and noises. The latter are those sounds which are wanting 
 in periodic regularity of stimulation and in the peculiar, 
 pleasant modification of consciousness which tones have. 
 Tones and noises are actually blended in nearly or quite 
 all sounds. Noises may be compounded out of musical 
 sounds, as, for example, by striking at once all the notes of 
 an octave upon a piano-forte. Noises are not easily class- 
 ifiable and are of little interest either to physical or to 
 psychological science. Hensen has, however, distinguished 
 three " categories of unmixed noises " ; these are the " beats " 
 (or pulsations which disturb the purity of some musical 
 tone), the crackle, crack or crash, and the hissing noises. 
 
 Nature of the Musical " Clang." — The tones of ordinary 
 
246 PHYSIOLOGICAL PSYCHOLOGY. 
 
 experience are complex sensations. They result from the 
 blending of several simple tones into one compound tone. 
 This blending is not so complete, however, that a trained 
 ear cannot analyze it. For the complex musical sounds 
 of ordinary experience we borrow from the German usage 
 the word " clang." The quality of tones considered as 
 simple sensations is their pitch, which is spoken of as 
 "high" or "low," according to the place which we assign 
 to our acoustic sensations as immediately apprehended, and 
 compared together, in consciousness. The quality of the 
 complex tones, or " clangs," is the so-called timbre, or 
 " tone-color." 
 
 The Pitch of Simple Tones. — It has been said that the 
 quality of simple musical sounds is their "pitch." Sub- 
 jectively considered, this quality is immediately determined 
 by the place we assign the tone in a musical scale. In this 
 scale — for reasons to which reference will subsequently 
 be made — we fix all notes as higher or lower, on comparison 
 of their characteristic quality. Objectively considered, the 
 pitch of tones depends upon the rapidity of the periodic 
 vibrations (the number in a given unit of time, usually 
 one second) which occasions them, or, what is the same 
 thing, it depends upon the length of the sound-waves. 
 
 The pitch of tones is theoretically determined by meas- 
 uring the number of vibrations found necessary to produce 
 some characteristic musical sound which it is convenient 
 to delect as a fixed point in the musical scale. The place 
 of the other tones may then be fixed with relation to this 
 tone selected as a point of starting, according to those 
 simple numerical relations between the tones with which 
 physics has made us familiar. Thus, in the German scale 
 the tone of the pitch called a^ is fixed at 440 vibrations in 
 a second. The French scale fixes the same tone at 435 
 vibrations, and the theoretical pitch in England gives 512 
 vibrations for A 
 
QUALITY' OF SENSATIONS. 247 
 
 Limits of Pitch. — Sensations of musical sound have both 
 an upper and a lower limit ; that is to say, vibrations either 
 below or above a certain number, per second produce no 
 sensations of musical sound at all. The difficulties of 
 determining these limits are great, and considerable allow- 
 ance must be made for individual peculiarities. Some 
 persons can discern tones of a pitch below or above those 
 tones audible to others. Helmholtz thought that the tone 
 (or musical quality) of the sound begins to fade out when 
 the vibrations are fewer than 34 per second. Tuning-forks, 
 vibrating 28 times in a second, have been heard as a weak 
 drone. Preyer, however, considered that 16 vibrations 
 enabled him to hear a tone. For most ears vibrations 
 slower than 28 to 32 per second make only a buzzing or 
 groaning noise. 
 
 The majority reach the upper limit of pitch when list- 
 ening to tones produced by 20,000 to 22,000 per second. 
 Some persons can, however, hear musical sounds produced 
 by 30,000 or 40,000 vibrations in a unit of time. Perhaps 
 in certain very sensitive ears the upper limit may be placed 
 as high as 50,000. More acute tones than these are 
 unpleasant noises, and finally become inaudible. 
 
 The range of the average human ear is rather more than 
 nine octaves of pitch, — reaching from about A^ of the sub- 
 contra octave (27^ vibrations, German scale) to above c' of 
 the seven-times-marked octave (16,896). 
 
 Sensitiveness to Differences of Pitch. — Preyer found that 
 unpractised persons, experimenting with the octaves lying 
 in the naiddle of the musical scale (from c to e^), distinguish 
 a difference in pitch corresponding to from 8 to 16 vibra- 
 tions per second. A few are, however, so " deaf " to pitch 
 that an interval of less than a musical " third," or even, in 
 the higher and lower parts of the scale, a "seventh," is 
 indistinguishable. If a person is insensitive to differences 
 of less than a tone or a semi-tone, he may be said " not to 
 
248 PHYSIOLOGICAL PSYCHOLOGY. 
 
 know one note from anotlier." In a trained musical ear 
 the sensitiveness may be mucli greater tlian that men- 
 tioned above. Thus, in the range most easily covered by 
 the human voice (e^ to c^) successive notes can be distin- 
 guished, as respects pitch, when they differ by not more 
 than i, or even ^ and |, of a single vibration. Thus, where 
 the piano gives 24 notes, the ear can perhaps distinguish 
 3000. But in the upper limits of the scale (e.g. above c^) 
 well-trained ears may identify notes that differ by 100, or 
 even by 1000, vibrations per second. 
 
 Distinctions in Purity of Interval. — Individuals differ 
 greatly in their ability to tell when two notes of different 
 pitch have just the right amount of interval. This ability 
 varies in all persons for different intervals. Thus, if the 
 sensitiveness of the trained ear for the purity of the inter- 
 val of an octave were denoted by 5000, that for the purity 
 of the interval called " the fifth " would be 822 ; for " the 
 fourth," 211 ; for the " major third," 198 ; for the " minor 
 third," 117 ; etc. 
 
 Judgments of Absolute Tone. — ■ We have already said that 
 discernment of difference in the pitch of tones is immediate ; 
 and that an appeal to consciousness indicates the place to 
 which each note, in comparison with other notes, shall be 
 assigned in the musical scale. But discernment of the 
 absolute pitch of a musical sound is a very complex and 
 difficult operation, dependent upon natural "good ear" 
 and upon training. One observer (Stumpf) found, by 
 experimenting upon four persons, all musicians, that only 
 one of them seemed even to approach infallibility. 
 
 Means for Discernment of Pitch. — The trained musician 
 can put several hundred tones, distinguished in pitch by 
 the ear, between the notes sounded by two white keys of 
 a piano, at the most favorable parts of the scale. But 
 Jenny Lind scarcely succeeded in singing in quarter-tones. 
 It would seem then that the muscular sensations connected 
 
QUALITY OF SENSATIOIfS. 249 
 
 with forming or apprehending the quality of musical 
 sounds do not furnish our sole means for discriminating 
 differences of quahty. This power seems to be an imme- 
 diate comparison of the tones, as heard, in our conscious- 
 ness. 
 
 Formation of the Scale of Pitch. — The arrangement of 
 musical sounds in a series called a " scale " depends upon 
 an immediate power of the mind to discern the difference 
 in characteristic quality between any two notes when com- 
 pared. This arrangement is conveniently symbolized by a 
 series of different positions assigned along a straight line. 
 Of any three, unlike tones, one must be, and only one can 
 be, arranged as respects pitch between the other two. 
 Whenever any two tones, as, for example, m and n, are 
 given, another " sliding " tone which begins with m and 
 onds with n is possible. In this respect the scale of musi- 
 cal sound is — as we shall see — different from that of the 
 varying shades of color. There are two ways of going 
 from yellow to blue (i.e. through green and blue-green, or 
 through violet, red, and orange) ; but there is only one 
 way of getting from a} to c^ (viz. through h\ c^, d?, etc.). 
 The series of tones is therefore spoken of as a continuous 
 and infinite series. 
 
 The terms which we apply to the relations as respects 
 quality, of the musical sounds in the scale — "high," 
 "low," "intervals," etc. — are taken from the complex 
 tactual, muscular, and visual sensations which accompany 
 and fuse with the acoustic. In sounding the so-called 
 " lower " tones, the vocal organs are depressed ; in sound- 
 ing the " higher," they are elevated. Low notes make in 
 consciousness the impressions of breadth and gravity which 
 correspond to the foundations of a spatial structure. In 
 reading the musical scale by sight, we look up for notes of 
 the higher pitch, down for those of the lower pitch. In 
 playing on stringed instruments, the hands are correspond- 
 
250 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ingly moved. Properly speaking, however, differences of 
 pitch are not representable as relations of space. In other 
 words, the terms applied to such differences all result from 
 associated mental impressions. 
 
 The Timbre of "Clangs." — When any single note is 
 sounded on a musical instrument, or by the voice, the 
 result is a " clang," or composite musical sound. This 
 clang may be objectively regarded as the summing-up of 
 the waves of a fundamental tone (the simple tone of the 
 note sounded) and the waves of certain partial tones 
 belonging to the fundamental tone. The stimulus which 
 occasions the complex sensation is, then, a complex sound- 
 wave. The composite quality of each "clang" depends 
 upon the character of this complex sound-wave. 
 
 We have seen that each sensation among the ordinary 
 musical " tones " is composed in consciousness of several 
 absolute qualities of simple tones. Every "clang" may 
 be subjectively regarded as the fusion, more or less 
 complete, in consciousness, of the simple and qualitatively 
 unlike tones corresponding to the composite acoustic 
 waves. These partial tones, or " over-tones," are the 
 " harmonics " of the clang, or single compound tone. 
 This composite quality or " coloring " of the note thus 
 produced, and which is different for different instruments 
 and voices, is called its "timbre." It is dependent upon 
 the number, pitch, and relative strength of the simple 
 tones which are compounded into the " clang." 
 
 Those simple tones, whose vibrations stand in simple 
 mathematical relations when combined into a " clang," 
 produce in consciousness a peculiar, pleasant sensation; 
 those whose vibrations stand in complex mathematical 
 relations, when combined, produce an unpleasant sensation. 
 Thus the eight different notes of every octave stand in the 
 following relations to each other : — 
 
QUALITY OP SENSATIONS. 251 
 
 C:D:E: F : G : A : B : C^ 
 
 8 : 9 : 10 : lOf : 12 : 131. : 15 : 16 
 
 That is to say, while the tone C makes one vibration, the 
 tone I) makes f, and E makes |, etc. ; or while Q makes 
 8 vibrations, B makes 9, E makes 10, etc. 
 
 Consonance and Dissonance. — When two or more "clangs" 
 are sounded together, the result is a highly complex sen- 
 sation, with a characteristic pleasant or unpleasant feeling 
 attached. If the feeling is pleasant, the resulting complex 
 of fused sensations is called a " consonance " or " chord " ; 
 if the feeling is unpleasant, it is a " dissonance " or " dis- 
 cord." Thus c and e^ struck together make a pleasant 
 combination of " clangs " ; c and c?, or c and c sharp, or c 
 and its seventh, h above, make an unpleasant and discordant 
 combination. 
 
 Consonance and dissonance differ from the cases of com- 
 bination, already considered as belonging to every " clang," 
 with respect to the relative strength of the partial tones 
 when compared with the fundamental tones. In the 
 clang the over-tones are weak in comparison with the 
 fundamental tone ; in the chord, or discord, the fundamental 
 tones of the other clangs are strong and stand in powerful 
 relations of consonance or dissonance toward the funda- 
 mental tone of the lowest clang among them. 
 
 There are degrees of consonance and dissonance which 
 depend upon the amount of coincidence or disagreement 
 belonging to the acoustic waves of the different tones 
 which are combined. With the relation of "the Third" 
 we come upon the borders of a dissonance ; indeed, the 
 ancient Greeks and Romans regarded the Third as a dis- 
 sonance. The major Third and the major Sixth are 
 called "medial consonances" by Helmholtz; the minor 
 Third and minor Sixth are called " imperfect consonances." 
 The following table represents these differences : — 
 
252 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Octave (1:2) fc^^W^^. 
 
 Twelfth (1:3) | c\c' 9'c^ e^ g'h'c^f 
 
 Fifth (2: 3) {" Y '["",/ "l - 
 
 Fourth (3:4) fcld gi c^ 6^ g^ 
 
 Major Third (4: 5) {" H' / f"" 
 
 It is difficult to give a satisfactory psycho-physical cause 
 for the characteristic feelings of pleasure and pain which ac- 
 company those sensation-complexes that are called "chords" 
 and " discords." The cause assigned by Helmholtz is the 
 absence or presence of " beats." It is found that the feel- 
 ing of dissonance is much increased when the difference in 
 pitch of two tones that lie near together is progressively 
 diminished. This feeling is due to the successive shocks, 
 called " beats," that occur as the pitch of the tones becomes 
 more nearly the same. It reaches its height when the 
 number of the beats is about 30 per second. For example, 
 if h^ (495 vibrations, in German scale) and c^ (528 vibra- 
 tions) are struck together, the number of beats is 33 
 (528 — 495 = 33), and the dissonance is strongly marked. 
 The feeling of consonance Helmholtz considers to be due 
 to the absence of beats. This reason is, however, only a 
 negative one. 
 
 It has been proposed to supplement the negative reason 
 given above by a positive one. The pleasure of conso- 
 nance is thus allied to that which follows all — even dim 
 and half-conscious — recognition of relations. The so- 
 called " tonicity " — or property of being recognized as a 
 constituent of a single fundamental tone — of consonances 
 is thought to afford the reason for the pleasant feeling con- 
 sonances excite. To this is added the so-called " phonicity " 
 
QUALITY OP SENSATIONS. 253 
 
 of the consonances; and by this is meant the property 
 which consists in the possession of certain partial tones 
 that are common to all tones. 
 
 It may well be doubted whether these explanations really 
 explain. Indeed, in the present condition of our knowl- 
 edge, we are obliged to consider the peculiar and charac- 
 teristic pleasant quality of consonances, and the opposite 
 quality of dissonances, as fundamental and inexplicable 
 facts of our primary experience. 
 
CHAPTER XI. 
 
 THE QUALITY OF SENSATIONS. — Continued. 
 
 The analysis of the qualities of Sensations of Sight is 
 much more intricate than that of any of the other senses. 
 They may all be divided, however, into sensations of color 
 and sensations of light. But as we shall soon see, in form- 
 ing "perceptions" of sight various other classes of sensa- 
 tions are closely blended with those of color and light. 
 
 Conditions of Experimenting. — In order to detei-mine 
 under what conditions the quality of visual sensations 
 varies, no little care is required. Changes in quality are 
 found to be dependent upon a variety of causes which, as 
 a rule, act together, but cannot be discriminated by self- 
 consciousness. Quality of sensations — color, for example — 
 depends upon the amount of white light which is mixed 
 with any particular " spectral " color. Only the " color- 
 tones " derived by spectral analysis are found to be " pure " 
 or " saturated." (Probably, as we shall see subsequently, 
 even these are not perfectly so.) The size of the colored 
 object, and the resulting extensity, or breadth, of the sen- 
 sation, affects its quality; so does the intensity of the 
 stimulus, and the time during which it acts. The same 
 stimulus also produces different sensations when it falls 
 upon different areas of the same retina. The quality of 
 the sensation further depends upon the previous condition 
 of the retina. 
 
 VISUAL SENSATIONS CONSIDERED AS RESPECTS QUALITY. 
 The question before us may then be stated in the follow- 
 ing somewhat complex form : What sensations result from 
 
 254 
 
QUALITY OF SENSATIONS. 
 
 255 
 
 the stimulation of a sufficiently small, but not too small, area 
 of the most central part of a normal retina, for a given 
 time, when it is not fatigued, and the eye is at rest, and 
 with neither too great nor too small intensity of a given 
 kind of light? 
 
 Excitable Areas for Visual Sensations. — Sensations of light 
 and color are, so far as their peripheral origin is concerned, 
 occasioned by irritation of the rod- and cone-layer of the 
 retina. Probably each element of this structure may be 
 regarded as an isolated sensitive spot, which corresponds, 
 on the one side, to definite excitations from appropriate 
 stimuli ; and, on the other side, to the smallest distinct 
 sensations of light and color. In order that two visual 
 sensations may be seen as separate, and lying side by side, 
 two neighboring retinal elements must be excited by the 
 stimulus. 
 
 This view is confirmed by the degree of accuracy of 
 which the trained eye is capable. Few observers, for exam- 
 ple, can distinguish two stars 
 as two, unless they are apart 
 from 60" to 70", —the num- 
 ber differing for different 
 eyes. The angle thus covered - 
 corresponds very closely to 
 the size of a retinal element, 
 — namely, from 0.00438 mm. 
 to 0.00526 mm. Moreover, 
 if white lines be drawn on a 
 black ground so closely to- 
 gether as to approximate this limit of vision, they will 
 appear, not straight, but knotted and nicked (see Fig. 75). 
 This fact is due to the action of the stimulus on the rods 
 and cones. 
 
 Stimulus of Visual Sensations. — The ordinary form of 
 stimulus which is understood to act directly on the end- 
 
 FiG. 75. — A Bhows the appearance of 
 lines drawn very closely together, which is 
 supposed to be dne to their falling upon the 
 nervous elements of the retina iu the man- 
 ner shown hy B. 
 
256 PHYSIOLOGICAL PSYCHOLOGY. 
 
 organs of vision is liglit, — or certain exceedingly rapid 
 oscillations of so-called luminiferous ether. The actual 
 immediate excitant of the rods and cones we have seen, 
 however, to be — it is probable — certain photo-chemical 
 changes of an unknown character. But these changes, 
 and so the sensations of color and light, may be occasioned 
 by other forms of stimulus than light. 
 
 Mechanical stimulus of the eyeball by pressure upon it 
 with the fuiger or a blunted stick results in the production 
 of so-called phosphenes, — disks of light with darkly col- 
 ored edges. A blow on the head, or an electrical current, 
 may cause optical sensations. The quality of the sensa- 
 tions aroused by the electrical stimulation seems to change 
 with the direction (ascending or descending) of the cur- 
 rent. The retina has also a "light of its own" QJSiffen- 
 lichf) ; for its nervous elements are rarely or never inactive, 
 but have a continuous tonic excitation. This " own-light " 
 is very changeable and seems to have a rhythmic move- 
 ment. It is probably due to the photo-chemical changes 
 produced by the changing character and amount of the 
 blood-supply. 
 
 In this connection, we may note the remarkable phe- 
 nomena of so-called "color-audition." In rare cases, the 
 hearing of a sound is spontaneously accompanied by the 
 seeing of a color, which varies with the sound heard. A 
 case in France has recently been reported — hereditary in 
 father, and in son and daughter — where the vowels, open 
 or mute, when pronounced, provoked definite color-sensa- 
 tions. Thus, a, a' and d, excited the sensation of red or 
 salmon color ; e, e\ or 6, of white ; «', of black, etc. Certain 
 obscure cerebral peculiarities seem to be implied in idio- 
 syncrasies of sight like this. 
 
 The Various Color-tones. — It has already been said that 
 only by use of the spectrum can we obtain "pure" or 
 " saturated " color-tones. This instrument, on account of 
 
QUALITY OF SENSATIONS. 
 
 257 
 
 the different refrangibility of the different colored rays 
 which compose the compound ray of white light, is able 
 to analyze the color-tones. It is thus discovered that the 
 compound sensation produced by sunlight is made up of 
 simple components corresponding to oscillations ranging 
 all the way from about 370 billions to about 900 billions 
 per second. The quality of the simple color-sensations 
 discovered by this analysis varies characteristically — as 
 the following table will help to illustrate — according to 
 the changes in number of the oscillations. 
 
 NAME OP FKAUNHOrEB'S LINK. 
 
 NTJMBBB or VIBRA- 
 TIONS PER SECOND. 
 
 ■WATB-LBNQTHB IN THE AIB. 
 
 
 Billious. 
 
 Millimeters. 
 
 B 
 
 450 
 
 0.000 6878 
 
 C 
 
 472 
 
 0.000 6564 
 
 D 
 
 526 
 
 0.000 5888 
 
 E 
 
 589 
 
 0.000 5260 
 
 F 
 
 640 
 
 0.000 4843 
 
 G 
 
 722 
 
 0.000 4291 
 
 H 
 
 790 
 
 0.000 3928 
 
 The table shows that rays of light which have a number 
 of oscillations less than 450 billions per second, so far as 
 they affect the retina at all, occasion the sensation of red. 
 This sensation does not change quality greatly as the 
 number of oscillations rises from 450 to 470 billions. 
 Beyond this limit (C), however, the quality of the color- 
 sensation changes rapidly, takes on a yellowish tone 
 (orange), and finally at 526 billions (D) corresponds to a 
 decided yellow. This sensation then becomes greenish, as 
 the number of oscillations increases, until they reach about 
 589 billions per second, when green (^) appears. The 
 green then becomes bluish, and at 640 billions blue (.P) 
 begins to arisfe. From this on to about 722 billions (F- (?) 
 
258 PHYSIOLOGICAl, PSYCHOLOGY. 
 
 the colors lie between tlie blue and the violet until the 
 decided violet comes to view. 
 
 The spectrum has no sharply defined limit at either end. 
 At both ends it passes gradually into black, but more 
 gradually at the violet than at the red end. 
 
 Brightness of Color-tones. — - The impression made by the 
 colors lying immediately about D (D-^) is stronger than 
 elsewhere. Or, as we should say, the colors are naturally 
 " brighter " here (about the green-yellow of the spectrum) 
 than the other colors. This difference cannot be due to 
 the objective energy of the rays of light, whether as 
 measured by their chemical or their calorific effect. It 
 must be due, then, to the structure of the retina, and its 
 peculiar sensitiveness to stimulations by the color-rays of 
 this region of the spectrum. Crimson light requires many 
 times more energy than green in order to be strong enough 
 to read by it. 
 
 Least Perceptible Variations of Colors. — The sensitiveness 
 of the retina to slight variations in quality of the color- 
 tones is also different at different portions of the spectrum. 
 In general, it is greatest in the blue and blue-green regions 
 (I> and F). The precise ratios which express this differ- 
 ence of sensitiveness to slight variations at different por- 
 tions of the spectrum are given somewhat differently by 
 different observers. 
 
 The Composite Nature of Colors. — Our ordinary color- 
 sensations, Kke those of musical sounds, are not pure and 
 simple, but complex. For the analysis of these sensations, 
 however, unlike that of musical sounds, the method of 
 conscious discrimination is of no avail. Sensations of color 
 cannot be mentally analyzed into their constituent elements. 
 They persistently maintain, in consciousness, that single 
 and uncompounded quality which has resulted from the 
 fusion of the different elements supplied by the rays of 
 different color-tone. 
 
QUALITY OF SENSATIONS. 259 
 
 When the wave-lengths of the two colors that are mixed 
 vary but slightly from each other (a few billion osoillr^tions 
 per second), the result of their mixture may be recognized 
 as a "shade" of one of the same two colors. Thus many 
 shades of so-called " orange " would readily be recognized 
 as mixtures of yellow and red. That certain blues are 
 greenish, or greens bluish, is manifest to everybody. 
 
 The color-impressions formed by mixture are not all 
 different from each other. So that if we were to mix color- 
 tones that lie apart at all possible distances along the 
 spectrum, the number of resulting compounds would not 
 be unlimited. In fact, the number of the resulting sensa- 
 tions would be much less than the number of the compound 
 physical processes which stimulate the retina. The quality 
 of these colors formed by mixture depends upon the place 
 in the spectrum from which the simple color-tones are 
 selected, and upon their intensity. Moreover, we may 
 discover two ways of advancing, by this process of mixing 
 color-tones, to any of the composite colors. We may pass, 
 for example, from yellow to blue, either through green- 
 yellow, green, and blue-green, or through orange, red, 
 purple, and violet. 
 
 Number of Colors Distinguishable. — Newton formed a sort 
 of octave of fundamental colors, consisting of the seven 
 members, — red, orange, yellow, green, blue, indigo, and 
 violet. But there is really no basis for this classification, 
 either in science or in ordinary experience and usage. 
 Indigo, as a kind of semi-tone between blue and violet, has 
 no more right to a place in this scale than have many other 
 intermediate tones ; the same is substantially true of orange. 
 The purples, which lie on the scale between the blues and 
 the reds, are entirely overlooked in this classification ; the 
 browns, too, find no place anywhere. 
 
 Before raising the question as to how few in number are 
 the colors which may be called " fundamental," we may fitly 
 
260 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 notice that the number of color-tones actually discernible 
 by the human eye is very great. One authority places it, 
 in oil-colors, at 100 ; but in the spectrum another authority 
 thinks it possible to discover 230 distinct tints. Herschel 
 considered that the workers on the mosaics at Rome must 
 have distinguished 30,000 different color-tones. If we 
 allow for differences of brightness and purity of tone, the 
 actual number of sensations possible with this sense, may 
 well reach into the hundreds of thousands. 
 
 Complementary Colors. — If certain color-tones, having a 
 given intensity, are united on the retina, the result is a 
 sensation wholly unlike either of the two thus united. 
 This sensation we call " white " ; and the two colors which 
 produce it by their admixture are called " complementary." 
 Such a mixture may be obtained in various ways, — e.g. by 
 superimposing two spectral rays, by blending the reflected 
 images of two colored wafers, or the visual impressions of 
 colored surfaces on a revolving top or wheel, etc. 
 
 Following is Helmholtz's table of complementary colors : 
 
 
 
 COMPLEMENTARY 
 
 
 BELATION OF 
 
 COLOR. 
 
 "WATE-LENGTH, 
 
 COLOK. 
 
 WAVE-LENGTH. 
 
 WAVE-LENGTH. 
 
 Red 
 
 2,425 
 
 Green-blue 
 
 1,818 
 
 1,334 
 
 Orange 
 
 2,244 
 
 Blue 
 
 1,809 
 
 1,240 
 
 Gold-yellow 
 
 2,162 
 
 Blue 
 
 1,793 
 
 1,206 
 
 Gold-yellow 
 
 2,120 
 
 Blue 
 
 1,781 
 
 1,190 
 
 YeUow 
 
 2,095 
 
 ludig'o-blue 
 
 1,716 
 
 1,221 
 
 Yellow 
 
 2,085 
 
 Indigo-blue 
 
 1,706 
 
 1,222 
 
 Green-yellow 
 
 2,082 
 
 Violet 
 
 1,600 
 
 1,301 
 
 The complementary colors for different persons are not 
 always precisely the same ; indeed, they may differ for the 
 two eyes of the same person. 
 
 ftnality as related to Intensity. — When the intensity of. 
 the light approaches either a maximum or a minimum, 
 
QUALITY OF SENSATIONS. 261 
 
 important changes in the quality of the resulting sensar 
 tion occur which are independent of changes in the wave- 
 length. At the maximum intensities all distinctions of 
 color-tone cease, and even homogeneous rays appear white. 
 Before reaching this maximum, red and green pass over 
 into yellow. Near the minimum intensities every color- 
 tone, except " saturated " red, becomes colorless when seen 
 alone on a perfectly black ground. The different color- 
 tones disappear at different degrees of intensity of the 
 light, — green remaining visible in the weakest light. 
 
 ftuality as related to Time. — Changes of color-tone take 
 place when the time during which the light acts upon the 
 retina is reduced to a minimum. A certain " light-mass " 
 (considered as the product of duration by intensity') is nec- 
 essary for a sensation of light or color. Sensations of 
 saturated color can be produced by instantaneous illumi- 
 nation of the spectrum with an electric spark ; but more 
 time is needed to produce these sensations with a weaker 
 light. 
 
 On this subject a recent investigator has arrived at the 
 following conclusions : (1) As the illumination increases, 
 the rate of the waning of the sensation decreases. (2) For 
 weak illuminations and brief stimulations, the waning 
 of the sensation is nearly inversely as the square of the 
 illumination. (3) The color of the light has no effect. 
 [This point is, however, disputed by other observers.] 
 (4) Exposure of the eye to a dark room increases the sen- 
 sation. 
 
 ftuality as related to Zones of the Retina. — Important 
 changes in the quality of our sensations of light and color 
 are dependent upon the place of the retina on which the 
 stimulus falls. For purposes of experiment the entire 
 organ has sometimes been divided into three zones, — a 
 •central or polar, a middle, and an outer or peripheral. 
 These regions seem to differ as respects the distinctness, 
 
262 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the quality, and the intensity, of the sensations produced 
 by the same stimulus. In general, while an indefinite 
 number of clearly distinguishable color-tones are possible 
 when the light falls on the polar zone, this number is 
 reduced to comparatively few impressions on the middle 
 zone ; and all color-tones gradually become indistinguish- 
 able on passing through the outer zone. At a certain 
 distance from the centre, blue and yellow alone are seen ; 
 and farther away, none of the color-tones are apparent. 
 Red changes through orange and violet to blue, as we pass 
 toward the periphery of the retina. Blue and yellow 
 become paler, — apparently in proportion to the amount of 
 green in them. 
 
 The best evidence seems to show that the sensitiveness 
 of the retina to sensations of light — unlike that of color- 
 tones — increases toward the peripheral region. The 
 opposite of this view has, however, been maintained. 
 Recent and apparently careful experiments fix the maxi- 
 mum sensitiveness to light at a distance of 20°-25° hori- 
 zontal, and 12°-15° vertical, from the retinal centre. The 
 lower portion is found to be less sensitive than the upper ; 
 and possibly the temporal side is more sensitive than the 
 other side of the retinal area. The cause of this increase 
 in sensitiveness toward the periphery is unknown. It has 
 been conjectured that this is due to the highly developed 
 structure of the rods which act as mirrors to reflect the 
 light. 
 
 Phenomena of Color-blindness. — In certain cases, defects 
 of vision exist which seem to show that the entire retina of 
 some individuals resembles the middle or the outer zone 
 of the normal retina. Such individuals are said to be 
 "color-blind." Two classes of cases are distinguished. 
 In the one class, which is much the more frequent, a par- 
 tial or complete insensitiveness to red rays exists; the 
 spectrum may then be said to be shortened at the red end. 
 
QUALITY OF SENSATIONS. 263 
 
 In other cases this insensitiveness applies also to the green 
 or blue-green or green-yellow or " blue-violet " color-tones. 
 It has been proposed to divide all cases of color-blindness 
 into two groups, — the " red-blind " and the " green-blind." 
 
 Important modifications of the sensations of light and 
 color are due to the previous condition of the retina, or to 
 the contemporaneous condition of the parts adjoining that 
 on which the stimulus falls. Under the first head fall the 
 phenomena of "inertia" and "exhaustion"; under the 
 second, the phenomena of " contrast." In both classes of 
 cases there is some evidence to show that obscure complica- 
 tions, of a cerebral rather than a peripheral origin, have an 
 influence on the result. This should be borne in mind in 
 considering those relations of quality, and its changes, 
 which are now to be examined. 
 
 Phenomena of After-images. — If we close our eyes after 
 looking for a time intently at any bright object, an image 
 of this object remains for some time and only gradually 
 fades out of sight. Such an image is called a '■^positive 
 after-image," because its bright and dark parts correspond 
 to those of the original object. This delay in the fading 
 away of the image from the retina is said to be due to the 
 physiological " inertia " of the organ. 
 
 But if we continue to regard the after-image, we observe 
 that its parts undergo a change of color. The white 
 changes into greenish blue ; then into indigo-blue, violet, 
 and finally a deep rose color. If we look at a green sur- 
 face for some time, and then fix the eye upon a white 
 surface, the latter will become of a red color. In general, 
 the color which this class of after-images assumes is the 
 color " complementary " of the color of the object. These 
 images are therefore called " negative after-images." More- 
 over, the color-tones of the spectrum can be made to 
 appear brighter by looking at them immediately after 
 having filled the eye for some time with the complemen 
 
264 PHYSIOLOGICAL PSYCHOLOGY. 
 
 tary color. It thus appears that some spectral colors are 
 act completely "saturated." Such phenomena are said 
 to be due to the principle of "exhaustion." The end- 
 organs — and also, it is probable, the central organs — after 
 use upon one color-tone, for a time lose their sensitiveness 
 to the stimulus which produces this color-tone. 
 
 Phenomena of Contrast. — A bright object appears brighter 
 with surroundings darker than itself, and darker, with sur- 
 roundings brighter than itself. In the case of gray disks 
 on a background darker than themselves, the increase of 
 brightness is found to be closely proportional to the differ- 
 ence in brightness between the disk itself and the back- 
 ground; but it is probably independent of the absolute 
 brightness of the latter. This phenomenon is called " con- 
 trast," — the word in this instance being applied to 
 brightness of color-tone. 
 
 When colored instead of white light is used in exper- 
 imenting under this law, phenomena similar to those of 
 complementary colors are obtained. For example, a small 
 square of white on a surface of green, when covered with 
 a transparent sheet of tissue-paper, appears as red on a 
 surrounding surface of a whitish hue ; on a red ground it 
 appears as green, on a blue ground as yellow, and on a 
 yellow ground as blue. 
 
 As yet we have no full and satisfactory explanation of 
 the phenomena of contrast. Helmholtz at one time ascribed 
 it to deceptions of judgment, such as we are familiar with 
 in estimating distances. But this theory seems strained 
 and remote from the facts. A satisfactoiy partial explana- 
 tion is found in the physiological principle that stimulus 
 of any element of the retina tends to spread over contig- 
 uous elements ; and, in turn, the effect of the stimulus on 
 the elements on which it falls is modified by the condition 
 of the contiguous elements. But besides all this, we seem 
 compelled to refer to the influence of obscure cerebral 
 
QUALITY OF SENSATIONS. 265 
 
 conditions that are dependent upon the associated action 
 of the nervous elements of the cerebral centres themselves. 
 The necessity for this will be more apparent when we 
 come to consider the formation of visual perceptions. 
 
 GENERAL THEORY OF VISUAL SENSATIONS, 
 
 The complicated character of the sensations of light and 
 color, as respects their quality, renders it peculiarly diffi- 
 cult to frame any general theory which shall embrace and 
 satisfy all the phenomena. The groups of facts, which 
 chiefly need theoretical explanation, are the following: 
 
 (1) It is possible to produce all the color-tones by mixing 
 certain fundamental colors, which must be at least three 
 (and probably, better, four) in number. And the inter- 
 mediate shades lying between any two proximate color- 
 tones can be produced by mingling these color-tones. 
 
 (2) The saturation or purity of the color-tones depends 
 upon the intensity of the light; and all the color-tones 
 may be graded downward, as it were, into colorless light. 
 
 (3) Any two colors of the spectrum chosen at proper 
 intervals along its scale, when mixed, will produce white. 
 
 (4) The theory must explain the phenomena of after- 
 images, color-blindness, and contrast, either by the way in 
 which it regards the preceding classes of facts, or in some 
 secondary manner derived from, and based upon, these 
 facts. 
 
 Yoimg-Helmlioltz Theory of Visual Sensations. — Among 
 the several theories proposed for the explanation of the 
 foregoing phenomena, that brought forward by Young 
 and elaborated by Helmholtz has been most widely ac- 
 cepted. This theory takes its point of starting from the 
 fact that we can. produce all the many color-tones by mix- 
 ture of a few so-called "fundamental " colors. It assumes 
 three fundamental colors. Of these, green must be one, 
 because green has no complementary color. The other 
 
266 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 two may then be taken from the two ends of the spectrum; 
 they are red and either violet, or indigo, or blue. 
 
 It is then further assumed that, in every sensitive por- 
 tion of the retina, three kinds of nervous elements exist. 
 The excitation of each of these elements separately would 
 produce only that kind of fundamental color-tone which is 
 peculiar to the specific elements excited. We may say, 
 then, that there are in the retina elements of " green-color 
 sensation," elements of " red-color sensation," and elements 
 of " blue-color sensation." 
 
 But every actual sensation is a complex affair. Its char- 
 acter is determined by the relative intensities with which 
 the different kinds of nervous elements are combined to 
 produce it. This may be illustrated by the accompanying 
 diagram (No. 76), where the curved lines M, Gr, and B 
 
 Fig. 76. — Biagram from Fiok, illuBtrating {he Toung-Helmholtz Theory. (For ex- 
 planation, see the text.) 
 
 represent the three fundamental colors, and the curves 
 described by them show the strength of the influence exer- 
 cised by these colors in forming the complex result ; while 
 the perpendicular lines indicate the several color-tones of 
 the spectrum. 
 
 The Young-Helmholtz Theory should be gratefully rec- 
 ognized as a brilliant attempt at explaining the phenom- 
 
QUALITY OF SENSATIONS. 267 
 
 ena of sensations of light and color. It is most success- 
 ful with the facts that relate to the mixing of colors. 
 It is perhaps most unsuccessful with the phenomena of 
 color-blindness, contrast, and the dependence of color- 
 tones on time, place of the retina stimulated, etc. Those 
 who dispute it consider, and apparently with good reason, 
 that its failure on these points is decisive against it. For 
 example, it does not appear that the colors wanting in the 
 different forms of color-blindness correspond to the three 
 fundamental colors of the normal system. Red-blind per- 
 sons ought, according to this theory, to see white as green- 
 ish blue, and green-blind persons ought to see it as purple. 
 But apparently both see white as we all do. Moreover, 
 pure yellow is not displaced, in the spectrum of the color- 
 blind, in the direction of green, or pure blue in the direction 
 of violet. 
 
 It must be confessed that the more elaborate theories 
 which have been proposed to take the place of that known 
 by the name " Young-Helmholtz " are scarcely more satis- 
 factory. We shall refer, however, to one or two of them. 
 
 Bering's Theory of Visual Sensations. — This authority 
 insists that we must regard the changes of sensation 
 through which we pass when viewing the different shades 
 of gray, from white to black, as analogous to other color- 
 sensations. Moreover, he considers that six, instead of 
 three, color-tones must he assumed as fundamental, in order 
 to produce all the other color-tones by admixture of these 
 six. Hering, therefore, proposes the following pairs of 
 fundamental color-tones, — black and white, green and 
 red, blue and yellow. The first member of each pair 
 (black, green, and blue) he considers to be the result of 
 a process of " construction " of visual substance. The 
 second member of each pair (white, red, and yellow) he 
 ascribes to the " destruction " of such visual substance. 
 
 Apparently decisive objections to this theory have been 
 
268 PHYSIOLOGICAL PSYCHOLOGY. 
 
 brought forward. Among them one of the most conclusive 
 seems to be the following. A light composed of red and 
 green may be made to seem to the eye the same as a 
 light composed of yellow and blue. If, then, the eye is 
 "fatigued" to red, instead of the red-green mixture ap- 
 pearing greenish, and so distinguishable from the yellow- 
 blue mixture, they both appear the same to the fatigued 
 eye. 
 
 Wundt's Theory of Visual Sensations. — Another view em- 
 phasizes a supposed difference in the processes, rather than 
 in the kinds of retinal elements, belonging to the different 
 color-tones. A very elaborate example of such a view is 
 the theory of Wundt. We state only a few of its principal 
 features. (1) The retina may be assumed to be in a con- 
 stant state of internal excitation, to which the sensation 
 of hlack corresponds. Hence when other excitations are 
 absent, we have the sensations of more or less darkness. 
 (2) Every external excitation sets up two kinds of processes 
 in the retina, — one a color process (" chromatic "), the 
 other a colorless process (" achromatic "). These two 
 processes follow different laws. (3) The colorless (achro- 
 matic) process is of a uniform photochemical character; 
 and its intensity in uni-colored light is dependent partly 
 on the intensity of the light, and partly on the length of 
 the waves. It reaches a maximum at yellow, and falls off 
 in both directions. (4) The color (chromatic) process is 
 of a manifold photochemical character, and it changes by 
 insensible degrees with the length of the wave. (5) Each 
 process of excitation outlasts for a certain time the stim- 
 ulus which occasions it, and exhausts the sensibility of the 
 sensory substance for the stimulus. 
 
 By combining these features, Wundt thinks that all the 
 phenomena, except those of contrast, which are due to a 
 cerebral origin, may be accounted for. 
 
 Symbolism of Visual Sensations. — The foregoing laws of 
 
QUALITY OF SENSATIONS. 
 
 269 
 
 the changes in visual sensations, and the nature of the 
 theory which must be devised to account for them, have 
 been represented to the eye by various ingenious devices. 
 Among them the most common is the so-called color tri- 
 
 i'^ 
 
 ^•n^ 
 
 W 
 
 PUnPLE 
 
 ^XG 
 
 Fie. 77. — Color-triangle, from Fick. (For explanation, see text.) 
 
 angle (see Fig. 77). In this triangle the different color- 
 tones may be regarded as lying along a curved line, from 
 red to violet ; and the difference, in the scale, between any 
 two color-tones is measured by the angle made by two lines 
 drawn from the point TT through the points occupied on 
 the lines by those two color-tones. 
 
270 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Figure 78 is a scheme for showing the relations of color- 
 tones by two concentric circles, 
 each color in one circle corre- 
 sponding to its complementary 
 color in the other circle. In 
 the phenomena of contrast, if 
 the color inducing the contrast 
 be represented by a segment 
 of the inner circle, the coinci- 
 dent segments of the two cir- 
 cles represent the direction in 
 which the induced change is 
 moving. For example, the seg- 
 ments representing green and purple coincide, and so do 
 those representing red and blue-green. Green on a red 
 ground is, therefore, modified as it would be if blue-green 
 were mixed with it; and red on a green ground, as it 
 would be if purple were mixed with it. 
 
 Fig. 78. — Scheme for showing the 
 Belutious of Color-tone (Bee text). 
 
CHAPTER XII. 
 THE QUANTITY OF SENSATIONS. 
 
 By an act of mental analysis, which all can perform, the 
 amount of sensations is distinguished from their kind, the 
 intensity from the quality. The nature of this analysis 
 may be illustrated by familiar examples: such are the 
 "dying away" of the tone when a skilful player draws 
 his bow with gradually diminishing force over the string 
 of a violin ; or the increase in the noise made by a bell as 
 we approach the place where it is sounding. So, too, we 
 readily recognize changes in our sensations when more of 
 pressure or of temperature, whether hot or cold, is applied 
 to the skin. 
 
 Ordinary Experience Insufficient. — It is also obvious, how- 
 ever, that the measurement of the amount of our sensations 
 by consciousness directly, is very inexact. This is true 
 even when the sensations compared belong to the same 
 sense. We should hesitate, for example, to say whether a 
 given noise were four, or five, times as loud as one imme- 
 diately preceding. And no one would think of affirming 
 the exact fraction, in hundredths, of the amount by which 
 the brilliancy of one lamp surpasses that of another. 
 
 The inadequacy of such direct comparison of sensations 
 in consciousness becomes more apparent when we attempt 
 to place sensations of the different senses side by side. 
 We apply, indeed, terms of intensity — such as "weak," 
 "very weak," "strong," "very strong," or "moderate," 
 etc. — to all kinds of sensations. But we should consider 
 it absurd to affirm : The rose smells as sweet as the grass 
 looks green ; or, The coffee is as strong as the sky is blue. 
 
 271 
 
272 PHYSIOLOGICAL PSYCHOLOGY. 
 
 That the measurement of the quantity of our sensations 
 is complicated with changes in their characteristic quahty 
 has already been remarked. Increase in the brightness of 
 a color invariably changes its characteristic color-tone. 
 The strong smell of musk or assafoetida is not the same 
 kind of sensation as the weak smell of these objects. Only 
 in the case of musical tones are we able at the same time 
 carefully to attend to both the quantity and the quality of 
 our sensations, and so approximately determine that the 
 former is changing while the latter remains unchanged. 
 Even in the case of these acoustic sensations, any consid- 
 erable change of intensity changes also the relation of the 
 over-tones to the fundamental tone, and so the " tone-color- 
 ing " of the " clang." 
 
 Two Questions relating to Quantity. — The general inquiry 
 into the quantity of our sensations involves two subordi- 
 nate questions. These are : (1) How little, or how much, 
 respectively, of each kind of stimulus produces the least, or 
 the greatest, amount of resulting sensation, of which the 
 mind is capable ? and (2) What is the law regulating the 
 relation in which changes in the intensity of sensations, as 
 estimated in consciousness, depend upon changes in the 
 intensity of the external stimuli? The first question is 
 a question of the limits within which sensations may vary 
 in quantity and remain sensations of the same sense. The 
 second question is a question of the uniform relations (or 
 law) which are maintained, within the limits, among the 
 various sensations compared. 
 
 Difficulties of the Investigation. — The answer to both of 
 the foregoing questions is accompanied by many difBcul- 
 ties. It has just been shown that our subjective standards 
 for measuring the amounts of our sensation-experience are 
 very inadequate. The objective standards for measuring 
 the quantities of the stimuli which occasion the sensations 
 are also far from satisfactory. This is, of course, especially 
 
QUANTITY OF SENSATIONS. 273 
 
 true of the senses of taste and smell ; since we do not even 
 know what properties smellable and tastable substances 
 must possess in order to irritate the nerves of these senses. 
 So is the measurement of the stimulus which occasions 
 sensations of temperature made difficult by the fact that 
 its amount is dependent upon the zero-point of the skin 
 itself, — a matter that varies greatly and is always difficult 
 of determination. For sensations of pressure, light, and 
 sound, we can make the necessary determinations with a 
 greater approach to exactness. 
 
 The "Least Observable Difference." — There is, however, 
 one kind of measurement respecting the quantity of sen- 
 sation which can be made in consciousness with a great 
 degree of accuracy. Suppose that two sensations of the 
 same quality are produced, either in quick succession upon 
 the same area of the organ of sense, or simultaneously 
 upon corresponding areas of the organ, by amounts of 
 stimuli that are equal, or very nearly equal: then the 
 attentive mind can tell with considerable accuracy whether 
 the intensities of the two sensations are exactly equal, or 
 differ minutely. This difference of quantity in the sensa- 
 tions which marks the limits of the mind's power of dis- 
 cernment is called " the least observable difference." The 
 problem of measuring accurately the quantity of sensations 
 becomes then the problem of determining the least observable 
 difference of quantity for each kind of sensations, and for 
 every point along the scale of degrees of quantity. 
 
 [Much debate has arisen over the question : Is the least 
 observable difference of two sensations itself a constant 
 quantity ? Into the nature and merits of this debate we 
 cannot undertake to enter. In the way in which the ques- 
 tion is often discussed, the whole matter is, in our judg- 
 ment, resolved into misleading figured of speech. There 
 is no mental entity, or mental state, corresponding to this 
 term, " least observable difference." 
 
274 PHYSIOLOGICAL PSYCHOLOGY. 
 
 For example, if the additon of n to the stimulus S is 
 the smallest amount that will so change the mental state 
 X as to make it pass over into a state x\ — which latter 
 state the mind judges to be a state of increased amount 
 of sensation, — then we can recognize and accept this fact 
 as a fact. It does not follow, however, that we may argue 
 that x'—x = L, and that this A is itself entitled to be 
 called a " least observable difference," as though it were a 
 fixed quantity of mental experience. There are in con- 
 sciousness the sensations x and x' ; and we judge one to be 
 greater than the other. But A (or x' — a;) is only a fiction 
 growing out of a figurative application of mathematical 
 terms to subjects that elude all correct representation by 
 such terms.] 
 
 Methods of determining the limits. — There are two ways 
 of determining the lower limits or least amount of stimulus 
 which occasions any sensation at all. We may choose a 
 weak stimulus, that is, however, slightly stronger than is 
 necessary to produce a sensation when applied; and we 
 may then diminish it by minute gradations until the 
 exact point is reached and noted at which it ceases to 
 produce any sensation at all. Or we may choose, at first, 
 a stimulus too weak to produce any sensation, and then 
 increase it by gradual minute increments until the point is 
 reached, and noted, at which some sensation is produced. 
 By these two methods the " sensitiveness " of the different 
 areas of the different organs, under different circumstances, 
 may be tested. 
 
 In the cases of sight and sound the attempt to fix the 
 lower limits of the sensations is greatly embarrassed by 
 the fact that the organs of sensation are rarely or never 
 perfectly free from excitation beyond our control. The 
 eye has its " own-light "; the ear is never in " absolute 
 stillness," or freedom from stimulus by the movements of 
 surrounding structures of the head. 
 
QUANTITY OF SENSATIONS. 275 
 
 The upper limit, or maximum amount of stimulus which 
 results in producing sensations of each class, cannot be 
 determined experimentally. Large quantities of stimulus 
 not only fatigue and endanger the nervous structure upon 
 which they act ; but they also arouse such an amount of 
 painful feeling, and of influence from allied forms of sensa- 
 tion, as to overwhelm the particular kind of sensation 
 whose quantity it is desired to measure. Very concen- 
 trated odors or solutions, exceedingly intense lights and 
 noises, are not simply smelled, or tasted, or seen, or heard; 
 they are all painfully felt, as it were, over extended areas 
 of the body. 
 
 We may affirm in general, however, that the " capacity " 
 of each sense varies directly as the amount of stimulus 
 
 which it can receive. Let — stand for the measure of the 
 sensitiveness of the sense, and C stand for the measure of 
 
 its capacity ; then — will represent the " circuit " or range 
 
 S 
 
 of the sensations of which the sense is capable. 
 
 Methods of determining the Least Observable Difference. — 
 There are three different ways of measuring the sensitive- 
 ness of the mind to minute changes in the amount of sen- 
 sations as dependent upon changes in the intensity of the 
 stimuli. Of these the first (1) is called " the method of 
 least observable difference." Two ways of applying the 
 principle of this method are to be noticed. If we follow 
 one of these ways (sometimes called " the method of mean 
 gradations "), we first select two sensations, produced by 
 two different intensities of the stimulus, which are sepa- 
 rated by a clearly perceptible interval as respects their 
 quantity (A and 0}, and we then inquire, what intensity of 
 the stimulus is necessary to produce a sensation that seems 
 to lie exactly midway (Jf ) between these two ? In other 
 words, we try to locate the sensation M as exactly half- 
 
276 PHYSIOLOGICAL PSYCHOLOGY. 
 
 way between A and 0. We then seek to put K half-way 
 between A and M\ and so on, until a scale of graded least 
 observable differences is reached. But if we follow the 
 other way of applying this method (sometimes called " the 
 method of minimum changes "), we seek directly to judge, 
 all along the scale of intensities, what change of stimulus 
 is just enough to produce a change in the amount of the 
 resulting sensation. 
 
 (2) "The method of average error" consists in trying 
 to fix upon an amount of stimulus which will produce a 
 sensation that seems exactly equal to another sensation 
 selected as a standard of estimate. Repeated trials of this 
 sort result, of course, in a number of guesses, some of 
 which are more or less out of the way. By averaging all 
 the trials, the degree of sensitiveness for that sense, at 
 that place in the scale, is determined. 
 
 (3) In "the method of correct and mistaken cases," 
 trial is made to see how many right, and how many wrong, 
 guesses occur in the effort to detect minute additions or 
 subtractions in the amount of stimulus. Thus : let Ji = 
 the whole number of guesses, and r = the number of right 
 
 guesses; then— = the sensitiveness to minute differences, 
 r 
 
 for that particular position in the scale, and particular 
 kind of stimulation. In this way a scale can be manufac- 
 tured, — the positive value of - being kept imchanged. 
 
 T 
 
 All three of these methods are alike in that they aim at 
 constructing a scale of degrees of sensitiveness by deter- 
 mining the least observable differences, for all the senses, 
 and for the various gross amounts of stimulus, under a 
 variety of circumstances. 
 
 The Law of Weher or Fechner. — The attempt to formu- 
 late the results reached by thousands of experiments, by 
 each of the foregoing methods, has resulted in a "law" 
 
QUANTITY OF SENSATIONS. 277 
 
 known by the name of Weber, or Fecbner. The former 
 of these investigators propounded the principle of this 
 " law " ; the latter has defended and elaborated it by a 
 vast amount of research. Weber's law admits of state- 
 ment in several forms : (1) The difference between any 
 two stimuli is experienced as of equal magnitude in case 
 the mathematical relation of those stimuli remains un- 
 altered. (2) If the intensity of the sensations is to increase 
 by equal absolute magnitudes, then the relative increase of 
 the stimulus must remain constant. (3) The strength of 
 the stimulus must increase in a geometrical proportion in 
 case the strength of- the sensation is to increase in' an 
 arithmetical proportion.^ 
 
 Value of Weber's Law. — Familiar experience makes us 
 aware that the difference in the amount of our sensations 
 does not increase in direct arithmetical ratio with the 
 increase in the intensity of the stimuli which cause the sen- 
 sations. For example, the difference between the shadow 
 cast by one taper and that cast by two is readily observable 
 in a dimly lighted room, but is wholly unobservable in 
 open sunlight ; or the strength in the ticks of two dif- 
 ferent clocks can be nicely discriminated, but not the 
 
 lA simple statement of Weber's principle maybe given as follows: 
 
 Let H = the intensity of the light of one-half of a white field ; = the 
 
 smallest fraction of stimulus added to S that will produce an observable 
 increase in this intensity ; and H + -— = the intensity of the other half 
 of the same field. Then let S=the sensation produced by H, and 
 S+ s = the sensation produced hj S+ — — : s will now, of course, repre- 
 sent the so-called " least observable difference " at this point in the scale. 
 We have, then, H produces S; S+—-, or ^^ R, produces S+s; 
 
 101 ff 
 
 iUS+ ^Sq-j or Hi • iU S, produces 8+ s+s; and so on. That is to 
 
 say, it s is to be kept of the same magnitude, then M must be multiplied 
 by the same magnitude ^. 
 
278 PHYSIOLOGICAL PSYCHOLOGY. 
 
 amount of noise made by two successive discharges of a 
 cannon. 
 
 To the principle involved in this familiar experience 
 Weber's law attempts to give an exact scientific expression. 
 It has been well said^ that its value depends upon its 
 furnishing a means of comparing the sensibility of differ- 
 ent incommensurate senses. As formulated in terms of 
 the method of correct and mistaken cases, it means that 
 the standard by which the relative qualities of our sen- 
 sations are judged, is independent of the absolute magni- 
 tude of the stimuli, but depends solely on the ratio of the 
 stimuli. As formulated by the method of average error, 
 it means that the probable error will not be influenced 
 by a change in the absolute magnitude of the stimulus 
 according to which the adjustments are to be made. 
 
 After years of diligent experimenting, in countless 
 numbers of cases, the so-called law of Weber is weaker 
 rather than stronger, in its claim to be an exact expression 
 of the universal relation between changes in the intensity 
 of the stimulus and changes in the amount of the resulting 
 sensations. The most that can be said is this: The law 
 summarizes many facts reasonably well within a certain 
 range of sensations lying near the middle of the scale of 
 quantity, and for certain of the senses. 
 
 Least Observable Difference in Sensations of Pressnre. — 
 Various causes affect our sensations of pressure, as respects 
 their smallest discernible quantity. Among them are the 
 presence of muscular sensations, mingled with sensations 
 of the skin (temperature, etc.), the locality to which the 
 stimulus is applied, the interval of time allowed after 
 applying the stimulus, etc. Weber ascertained that, when 
 the interval was 15 to 20 seconds, under the most favor- 
 able circumstances, 14^ could be distinguished from 15 
 
 1 By- Professor Jastrow, in the American Journal of Psychology, 1888, 
 p. 298, 
 
QUANTITY OF SENSATIONS. 279 
 
 grammes of pressure, 14| from 15 ounces, etc. That is, 
 some persons distinguish weights which differ in the ratio 
 of 29 : 30, when laid on the volar side of the last phalanx 
 of the finger. If allowed to raise and lower the weights, 
 the niceness of the discrimination is increased so that the 
 ratio becomes 39 : 40. 
 
 More recent experiments seem to show that the quotient 
 of sensitiveness for sensations of pressure varies greatly 
 with the different absolute values of the weights employed. 
 One calculation places it at j^ for weights of 300 grammes 
 to ^ for weights of 3000 grammes. Another series of 
 experiments gave results (somewhat doubtful, however), 
 varying as the following table indicates : — 
 
 Absolnte weight. Least observable difference. Quotient of Sensitiveneea. 
 Grammes. G-rammes. 
 
 10 0.7 tV 
 
 50 1.7 3^7 
 
 100 2.4 A 
 
 200 3.6 ,V 
 
 300 4.6 ^^r 
 
 400 5.2 yV 
 
 450 6.5 i^ 
 
 500 25.5 ^V 
 
 When the weights are raised, it would appear (according 
 to the latest experiments) that we are influenced in our 
 estimate of their magnitude by the speed with which they 
 rise. Indeed, it is held by some observers that the entire 
 validity of Weber's law in such cases depends upon the 
 fact that a just observable difference in the speed of their 
 rise corresponds to a just observable difference in their 
 weight. 
 
 Lower Limits of Sensations of Pressure. — The absolute 
 sensitiveness of the different areas of the skin to sensations 
 of pressure differs exceedingly. This difference is due to 
 a variety of circumstances, — such as, the number and sen- 
 sitiveness of the nervous elements present in the skin, the 
 
280 PHYSIOLOGICAL PSYCHOLOGY. 
 
 thickness of the skin, its tension over the tinderlying 
 parts, attention, use, habit, etc. Following are the num- 
 bers which have been found to measure the lightest weight 
 which would produce a sensation on various parts of the 
 body: on the forehead, temples, and dorsal side of the 
 fore-arm and hands, 0.002 gramme ; volar side of the fore- 
 arm, 0.003 gramme ; nose, lips, chin, eyelids, and skin of 
 abdomen, 0.005 gramme ; volar side of the fingers, 0.005- 
 0.015 ; finger-nails and skin of the heel, 1 gramme. 
 
 Quantity of Temperature-sensations. — It is nearly impos- 
 sible to apply Weber's law to sensations of heat and cold. 
 We do not know exactly what to measure as constituting 
 the quantitative changes in temperature. The temperature 
 of the so-called " zero-point of the skin " is very change- 
 able. The one rule which seems most general is this: 
 The skin is most sensitive to changes which lie near its own 
 zero-point. The nicest discrimination of two temperatures 
 is attained where one lies just a little above, and the other 
 just a little below, this zero-point. Under such circum- 
 stances, changes will be read by the skin amounting to 
 onlyi°or,l^°F. 
 
 We have already seen (p. 239 f.) that the sense of tem- 
 perature depends for its fineness upon the extent and 
 locality of the surface of the skin which is excited. Since 
 the modern discovery of heat-spots and cold-spots that can 
 be located, with different degrees of intensity and in vary- 
 ing numbers, on the different areas of the body, the table 
 of sensitiveness to temperature has been greatly changed. 
 In general, it may be said that the sensitiveness of the 
 forehead to cold is intense, but to heat only moderate ; that 
 of the breast to cold moderate along the sternum, and 
 elsewhere very intense, while to heat it is only moderate, 
 except near the nipples ; that of the back everywhere very 
 intense to cold, and only moderate to heat; while in all 
 
QUANTITY OF SENSATIONS. 281 
 
 parts of the hand the intensity of sensitiveness is nearly- 
 alike for both cold and heat. 
 
 Measure of the Stimulus for Sensations of Sound. — If 
 the quantity of our sensations of sound varied in direct 
 proportion to the intensity of the stimulus, it would be 
 impossible to execute nicely shaded passages of music. 
 How exactly the law of Weber applies to musical sounds, 
 it is difficult to tell because the experiments are necessarily 
 complicated with so many conditions. We have already 
 seen that no considerable increase in the intensity of a 
 tone is possible without changing its timbre. Pitch also 
 has a great influence upon our estimates of intensity. In 
 experimenting with noises the absence or presence of so- 
 called " entotic " sounds (sounds that originate in the 
 action of physiological changes within the organs contigu- 
 ous to the inner ear) is of great influence. The order in 
 which the sounds are heard seems also to have something 
 to do with our impressions of their loudness. Of two 
 successive equal sounds the second regularly seems the 
 greater. 
 
 It is also a matter of some dispute whether the intensity 
 of the acoustic stimulus is to be measured by the product 
 of the mass of the falling body into the height from which 
 it falls (mX/i); or by the product of the mass into the 
 square root of the height (mX-y/K). The former mode 
 of measurement is probably more correct. 
 
 Weber's Law applied to Sensations of Sound. — By making 
 large allowances for relations of time, and using the method 
 of correct and mistaken cases, some of the older experi- 
 menters succeeded in establishing the law of Weber as 
 fairly accurate for sensations of noise of moderate intensity. 
 More recent researches still leave the matter in doubt, 
 however; at any rate, unexplained variations of the so- 
 called law arise at various points along the scale, and near 
 the upper and lower limits it seems to fail completely. 
 
282 PHYSIOLOGICAli PSYCHOLOGY. 
 
 The sensitiveness of the ear for minute differences in 
 the intensity of sensations of tone seems to be greater than 
 that for noise. But here the variations from Weber's law 
 are numerous. The following tables sum up the results 
 of two recent, extended sets of experiments. In the first 
 the unit of measure for the strength of the tone was taken 
 "below the threshold," and the fraction of " discriminative 
 sensibility " is given for the different places on the scale 
 marked by different multiples of this unit of intensity. 
 [The threshold value was about 1.6, as expressed in units 
 of the same intensity.] 
 
 Intensity. 
 
 Discriminative sensibility. 
 
 Intensity. 
 
 Discriminative seneibility 
 
 5 
 
 .135 
 
 106 
 
 .140 
 
 20 
 
 .108 
 
 10' 
 
 .153 
 
 10" 
 
 .112 
 
 108 
 
 .161 
 
 10» 
 
 .118 
 
 109 
 
 .178 
 
 10* 
 
 .116 
 
 10i» 
 
 .225 
 
 105 
 
 .131 
 
 10" 
 
 .850 
 
 Of course, if Weber's law held exactly the fraction in 
 the second column of the table would remain unchanged. 
 
 By using tuning-forks and the method of "just observ- 
 able difference," another observer obtained the following 
 results : — 
 
 Number of vibrations 64 128 256 512 1024 2048 
 
 Just observable difference 149 .159 .232 .251 .218 .362 
 
 Fraction demanded by Weber's law .15 .30 .60 1.20 2.40 4.80 
 
 In this table we note a wide discrepancy between the 
 fraction of just observable difference as determined by 
 actual experiment and that demanded by the law of 
 Weber. 
 
 Lower Limit of Sensations of Sound. — The least amount 
 of sound which will excite sensation depends, of course, 
 upon many circumstances. Of these the most important is 
 as nearly perfect stillness as it is possible to obtain. Under 
 the most favorable conditions an incredibly small amount 
 
QUANTITY OF SENSATIONS. 28S 
 
 of energy expended on the ear will excite sensation. One 
 observer has fixed the limit at the noise made by a cork 
 ball of 1 milligramme (about 0.0154 grain) weight falling 
 from a height of 1 millimeter (0.03937 inch). Another 
 has calculated that an amplitude in the molecules of the 
 air not more than ^ the wave-length of green light, doing 
 upon the ear-drum only about ^ of the work done upon 
 the same surface of the pupils of the eye by a single 
 candle, will evoke a sensation of sound. Yet another 
 calculation fixes the energy at the threshold, for a musical 
 tone of 440 vibrations, as about \ that for sight (e.^. of 
 the light of a star of the sixth or seventh magnitude). 
 
 Astronomers were for a long time, before the promul- 
 gation of Weber's law, aware of the fact that the magni- 
 tudes of the stars are not to be classified according to their 
 absolute brightness as determined by photometric observa- 
 tions. Sir John Herschel assumed this when he made the 
 series of magnitudes run 1:2:3:4, etc., while the series 
 according to photometric brightness run 1: ^ : ^ :yV5 ^tc. 
 Something like the same principle is required to account 
 for our ordinary experience with sensations of light. The 
 finer gradations of shade in a lithograph or photograph 
 are not lost when we take it from the open sunlight into 
 a dimly lighted room. Some principle resembling Weber's 
 law is necessary to account for this. 
 
 Measure of the Stimulus for Sensations of Sight. — The 
 accurate measurement of visual sensations is complicated 
 with the facts that the retina has a " light of its own," 
 and that the laws of change in quality operate to obscure 
 the laws of the change in quantity. Earlier experiments 
 took the form of determining the distance to which a 
 candle must be removed from an object in order that the 
 shadow produced by its light might disappear in the shadow 
 produced by another candle of like power but situated at 
 
284 PHYSIOLOGICAL PSYCHOLOGY. 
 
 a fixed near distance from the object. It was thus dis- 
 covered that marked variations occur when we diminish 
 considerably the light of the background on which the 
 shadows are cast ; and that the quotient which represent3 
 the least observable difference varies with the different 
 intensities of the light employed. 
 
 Helmholtz and other late observers have used rotating 
 disks with small black stripes upon their white surfaces 
 ( " Masson's Disks "). The grayish circles made by the 
 admixture of the color of the stripes with that of the sur- 
 faces are then compared, as a test of the eye's sensitiveness 
 to minute differences. The experiment may be varied by 
 looking at these disks through gray glasses of varying 
 intensity. In experimenting with color-tones the method 
 may be used of comparing a white surface with one in 
 which colored light has been mixed with the white. 
 
 The later experiments seem to show that the effect of 
 background is enormous ; and that the absolute strength 
 of the stimulus used is also very important. 
 
 Weber's Law applied to Sensations of Sight. — The earlier 
 experiments, conducted under the supervision of Fechner, 
 were held to show that the law of Weber applies to sensa- 
 tions of light ; and that the least observable difference, for 
 absolute values of moderate inteasity, is about y^, — this 
 being the smallest average difference in the brightness of 
 the shadows which the eye can detect. But subsequent 
 observations found the quotient to vary from ^;g for weak 
 intensities of light to t^j for stronger intensities. Helm- 
 holtz placed the medium value of the quotient of least 
 observable difference at j^-g: Aubert found a variation 
 of from 1^ to 1-57^, even when not using absolute values 
 of light above the middle of the scale of intensity. If care 
 is taken to exclude disturbances from changes in the ad- 
 justment of the eye, from retinal exhaustion, reflection of 
 the light from surrounding objects, etc., it seems probable 
 
QUANTITY OP SENSATIONS. 285 
 
 that Weber's law expresses the facts approximately well for 
 sensations of light, when the strength of the stimulus is kept 
 within the middle ranges of the scale of intensities. 
 
 The same conclusion is apparently warranted with 
 respect to sensations of color. The quotient of least 
 observable difference is found to be different, however, for 
 the different color-tones. Perfect agreement is not yet 
 secured as to the nature of this difference : thus while one 
 observer has adopted the quotients, t\ for red, -^-^ for 
 yellow, -^ for green, -rb- for blue, ^ for violet, others 
 make the sensitiveness of the eye greatest for changes in 
 green rather than violet. 
 
 Lower Limit of Sensations of Light. — The least intensity 
 of light which will produce any sensation at all was given 
 by Aubert at ^^-^ of that reflected from white paper in the 
 light of the full moon. Individual differences are here, 
 however, so potent that all such calculations are very 
 uncertain. There is, indeed, some evidence to show that 
 certain persons are so extremely sensitive as to detect the 
 presence of stimulus that lies far below the "threshold" 
 of the average consciousness. 
 
 Quantity of Sensations of Taste. — It seems quite impossi- 
 ble to test by experiment the applicability of Weber*s law 
 to sensations of taste. The conditions under which the 
 stimulus is applied, and its effect noted, are such as not to 
 admit of giving scientific exactness to such experiment. 
 The importance of individual idiosyncrasies in sensations of 
 this sense is too well known to need mention. 
 
 Many experiments designed to fix the " lower limit " of 
 the sensations of taste have yielded very interesting results. 
 They show the astonishing tenuity of some forms of stim- 
 ulus which will secure an appreciable effect in conscious- 
 ness. The following facts are interesting as bearing on 
 this point, rather than instructive as suggesting any law 
 of the nervous system or of the mind. 
 
286 PHlfSiOLOGiCAL PSifCHOLOGY. 
 
 Experiments in testing the effect of seven vegetable 
 bitters on forty persons yielded these restdts : of salicine, 
 1 part in 12,000 parts of water was detectable ; of mor- 
 phine, 1 in 14,000 ; of quinine, 1 in 76,000 (some observers 
 have claimed to detect 1 part in 1,000,000) ; of quassine, 
 1 in 9000 ; picro-toxine, 1 in 197,000 ; of aloine, 1 in 210,- 
 000 ; of strychnine, 1 in 826,000 (twelve tasters detected 
 1 part in 1,280,000). 
 
 The following table involves a comparison, with respect 
 to sensitiveness of taste, between the males and the females 
 experimented upon : — 
 
 Object tested. Male observers. Female observers. 
 
 Quinine 1 part in 392,000 456,000 
 
 Sugar (cane) 199 204 
 
 Acid (sulph.) . 2,080 3,280 
 
 Soda (bicarb.) . 98 .... . 126 
 
 Salt 2,240 1,980 
 
 In general, a smaller absolute quantity of stimulus, 
 when in a relatively concentrated solution, will suffice to 
 excite the end-organs of taste. 
 
 ftuantity of Sensation of Smell. — The sense of smell has a 
 great degree of " sharpness," or capacity for excitement by 
 small quantities of stimulus, as distinguished from " fine- 
 ness," or power to distinguish minute variations in the 
 sensations. No experimental testing of the applicability 
 of Weber's law to sensations of this sense seems practi- 
 cable. 
 
 Incredibly small quantities of some substances will 
 excite sensations of smell. One experimenter found that 
 a current of air containing nnnnnr of vapor of bromine 
 excited a strong unpleasant sensation. Atmosphere pol- 
 luted with i7ooo Tnr of sulphuretted hydrogen could be 
 detected. It was calculated that ^TnyTrnnr milligramme of 
 musk was the least perceivable amount. A recent report 
 is based upon experiments conducted by dissolving the 
 
QUANTITY OF SENSATIONS. 287 
 
 smellable substances in alcohol, sprinkling them in an 
 empty closed room with an atomizer, and mixing them 
 with the air with a fan. It was thus found that a sub- 
 stance called "mercaptan" could be detected in volu- 
 metric proportion to the air of only 1 to 60,000,000,000. 
 It was thus calculated that 4^00^0000 milligramme of this 
 substance must excite sensation. The minuteness of 
 this quantity may be faintly imagined when we remember 
 tbat 1 4ii (,(,(, milligramme of soda is about as little as can 
 be detected by the microscope. 
 
 On referring to what was said (p. 277 f.) of the value and 
 significance of Weber's law we find our statements con- 
 firmed. Among the more cautious observers the conclu- 
 sion has been forming itself as the result of years of 
 experiment, involving thousands of cases, that the facts to 
 which the law appeals can be summarized equally well in 
 several formulae ; and that none of these formulae hold 
 good without many important exceptions. These excep- 
 tions have to do, in part at least, with laws of perception 
 and judgment to which reference wiU subsequently be 
 made. 
 
 Interpretation of Weber's Law. — Previous to experiment 
 and scientific observation we should be inclined to suppose 
 that the strength of the resulting sensation would vary in 
 direct proportion to the strength of the stimulus. But we 
 have seen that this is not so. The law proposed by Weber, 
 and elaborated and defended by Fechner, holds that the 
 sensations vary in quantity in an arithmetical proportion 
 while the stimuli vary in a geometrical proportion. The 
 so-called " law " turns out to be only one formula, which 
 we may adopt in connection with others, to express the 
 facts approximately for certain classes of the sensations 
 when they have a moderate intensity, and when our esti- 
 mate of them is undisturbed by conditions extraneous to 
 their simple characteristic of quantity. How shall this 
 
288 PHYSIOLOGICAL PSYCHOLOGY. 
 
 law — or these formulse — be iuterpreted? Three forms of 
 explanation have been proposed in answer to this inquiry. 
 
 The psycho-physical explanation of Weber's law was 
 adopted by its distinguished advocate, the physicist Fech- 
 ner. This explanation insists upon making the law one 
 of the widest application and highest import, as stating 
 the relations between organic and spiritual activities. 
 Fechner made the law, indeed, a basis for far-reaching 
 philosophical speculation regarding the world of matter 
 and mind. It need scarcely be said that we find absolutely 
 no warrant for such a view. 
 
 The physiological explanation holds that the law of 
 Weber apphes to the relation between the stimulus, re- 
 garded as a mode of energy external to the body, and the 
 amount of physiological action which it occasions in the 
 nervous elements which it excites. The law may then be 
 considered as one instance of a larger " neuro-physic " 
 law which applies to all stimuli that diminish the excita- 
 bility of the organism on which they act. Of this larger 
 law the formula might run somewhat as follows : " The 
 excitation caused by a change of intensity in a stimulus 
 that diminishes excitability remains the same, if the re- 
 lation of the change of intensity to the intensity on the 
 basis of which the change is made remains the same." 
 This rule holds good, however, only under similar condi- 
 tions and within certain limits of absolute intensity of 
 the stimulus. " Outside these limits ... an increase of 
 excitation occurs with small, and a decrease with great, 
 intensity." 
 
 The psychological explanation of Weber's law resolves it 
 into a special case under the greater law of the relativity 
 of our inner states. In general, it may be said that every 
 mental state has its value determined, both as respects its 
 quality and its so-called quantity, by its relation to other 
 mental states. It is the amount of change which mental 
 
QUANTITY OP SENSATIONS. 289 
 
 apperception chiefly appreciates. Hence the important 
 influence that attention, interest, habit, contrast, natural 
 power of discrimination, etc., have upon those " estimates " 
 on which we have to rely for a formula like that called 
 Weber's law. 
 
 It seems to us undoubted that both the physiological 
 and the psychological interpretation are necessary in order 
 to understand the significance of whatever truth belongs 
 to this celebrated so-called " law " of the relation between 
 changes in the intensity of the stimulus and the resulting 
 changes in the quantity of our estimated sensations. 
 
CHAPTER XIII. 
 
 PERCEPTION BY THE SENSES. 
 
 Theke is a very wide difference between having sen- 
 sations, however intense and complex, and knowing the 
 qualities of things by use of the senses. Sensations, in 
 themselves considered, are plainly psychical states; and, 
 as such, they are devoid of a locality, or even an existence, 
 external to the mind. But things are known as so-called 
 objective or extrarmeiital existences; they are all, as we 
 are wont to say, extended and related to one another "in 
 space." Indeed, the one characteristic which things pos- 
 sess, as perceived by us, but which does not belong to the 
 simple sensations which are the factors of the perceptions, 
 is their space-form. 
 
 Now a study of the development of the mind shows 
 indisputably that the perception of things does not come 
 at once. We all have to learn to know things, — their 
 space-qualities and spatial relations. As we shall see sub- 
 sequently, it is not altogether out of the way to say that 
 we have to learn to construct things perceived, in order to 
 perceive them. The general problem which physiological 
 psychology has to solve in this field of inquiry may, then, 
 be stated as follows : On the basis of what combinations 
 of physical processes of sense do the different resulting sen- 
 sations come to be combined into perceptions of things, under 
 the new characteristic of space-form ? 
 
 In treating this branch of the subject, the method which 
 we have, in the main, followed thus far, may profitably be 
 reversed. It will make the whole of this difficult matter 
 290 
 
PERCEPTION BY THE SENSES. 291 
 
 clearer if we give, first, a sketch of the general psycho- 
 logical theory of perception, and then speak, afterward, of 
 particular forms of perception as illustrating the general 
 theory. 
 
 GENERAL THEORY OF PERCEPTION BY THE SENSES. 
 
 The fact that perception by the senses implies such a very 
 complex and long-continued evolution of the mind makes 
 its scientific analysis both more difficult and more neces- 
 sary. The ordinary operations of consciousness are wholly 
 unable to do anything adequate toward making the requi- 
 site analysis. 
 
 " Common-sense " View of Perception Erroneous. — We 
 cannot look on any complex object — for example, a land- 
 scape — without the conviction that we are immediately 
 being impressed vrith a faithful copy of what exists wholly 
 external to us, in reality. These exira-mental beings and 
 the events which happen between them are, in the judg- 
 ment of so-called " common-sense," quite enough to account 
 for our perceptions. Indeed, they form the only necessary 
 or possible explanation of these perceptions. 
 
 Scientific psychology shows that, strictly speaking, beings 
 and happenings outside of our minds and bodies, in them- 
 selves, furnish no explanation whatever for our percep- 
 tions. They are and can be nothing to us, except as they 
 affect us. They affect us only by action on the nervous 
 system, — beginning with the end-organs of sense, continu- 
 ing along the sensory nerve-tracts, and issuing in cerebral 
 changes. But such induced activities of the nervous sys- 
 tem are nothing to us, as minds, unless they are followed 
 or accompanied by psychical changes. It is, indeed, only 
 as necessary physical conditions of the psychical changes 
 that they can be said to be either the explanation or the 
 object of our perceptions. 
 
 Physiological View of Perception Inadequate. — But if the 
 
292 PHYSIOLOGICAL PSYCHOLOGY. 
 
 unscientific view of the nature of perception by the senses 
 is Ulusory, the view of physiological science alone is inad- 
 equate. Indeed, the latter may be so represented as only 
 to continue, in a more elaborate but indefensible form, the 
 illusions of the ordinary impression. This, for example, 
 is the case whenever the physical image formed on the 
 retina is considered, in itself, to account for the mental 
 perception of the visual object. The nervous processes 
 which result from that orderly arrangement in the action 
 of the stimulus upon the end-organs, which appears as a 
 retinal image to the inspection of another observer, is in- 
 deed a necessary physical condition of our clear perception 
 of the object. But the retinal image never becomes a kind 
 of inner object for our own brain or mind. The same 
 thing is true of the orderly arrangement of the excited 
 elements in the cerebral substance itself. There is no 
 brain-image, copied from the object, which the mind can 
 immediately contemplate; and, if there were, we should 
 need another eye connected with another brain to make 
 use of it. 
 
 Neither does the accurate physiological description of 
 the construction of the "peripheral areas upon which the 
 stimulus acts furnish, in itself, any reason for the percep- 
 tion of these areas as in space, or for distinguishing them 
 from other areas nearer or more remote. To regard the 
 mind as diffused through or over the surface of the skin, 
 taking note — as it were — of the condition of this organ, 
 or of the presence of the bodies with which it is in contact, 
 is exceedingly crude and erroneous. 
 
 The Factors and Processes of Perception Psychological. — A 
 true theory of the nature and growth of that knowledge of 
 things which comes through the senses must always be dis- 
 tinctively psychological. For all the factors built, as it 
 were, into the products which we call " perceptions " are 
 mental^ as we have already seen, these factors are sensa- 
 
PERCEPTION BY THE SENSES. 298 
 
 tions and sensation-complexes. The process of building, 
 whether it be accomplished, for any object, more slowly or 
 with what appears as a practical instantaneousness, is a 
 mental process. The development of the capacity for this 
 process is the result of a mental evolution. These truths 
 must be admitted, from whatever point of view our study 
 of perception is conducted. It is as necessary for physio- 
 logical psychology to admit these truths as for psychology 
 studied from the introspective point of view. 
 
 With these preliminary remarks, we enumerate the fol- 
 lowing considerations as necessary to any true theory of 
 perception by the senses. ' 
 
 (1) Synthesis of Sensations Necessary. — In order to ex- 
 plain those steps by which the mere having of sensations 
 issues in the perception of objects by the senses, we must 
 assume that a combination of two or more qualitatively 
 different series of sensation-complexes has taken place. 
 This combination is sometimes spoken of as an " associa- 
 tion " of sensations. But the word " association," on 
 account of its established use to denote relations formed 
 in time amongst different mental images, is not well suited 
 to express the combination of sensations and sensation- 
 complexes, with one another and with their memory- 
 images, to form an object of sense. Such combination is 
 rather of the nature of a chemical fusion (if we may bor- 
 row from physical processes and products a figure of 
 speech), in which the factors lose their individuality, and 
 the resulting compound product is determined by all the 
 factors, without appearing to contain them. The word 
 " synthesis " is selected to describe such a process of psy- 
 chical uniting. 
 
 (2) Spatial and Non-spatial Series of Sensations. — Series 
 of sensations which arise in the mind, on successive irrita- 
 tion of closely contiguous portions of the sense-organ, are 
 fitted to enter into the process of "psychical synthesis." 
 
294 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Series of other sensations belonging to a different class of 
 senses are not thus fitted. The former may be called 
 "spatial series ' of sensations; the latter, "non-spatial" 
 series of sensations. Senses whose excitation gives rise to 
 spatial series of sensations may be called "geometrical 
 senses '' ; those that produce only non-spatial series of sen- 
 sations may be called " non-geometrical senses." 
 
 For example : sensations of smell are obviously not fitted 
 to form a so-called spatial series ; indeed, they are incapa- 
 ble of being arranged in any series whatever. A being 
 possessed of mere sensations of smell, without any of the 
 tactile or muscular sensations which accompany those sen- 
 sations in the case of man, would have — so to speak — no 
 elements from which to construct objects of sense. The 
 sense of smell is decidedly non-geometrical. On the con- 
 trary, we shall see that sensations of the eye and of the 
 skin are of the " spatial-series " kind. These organs are 
 the leading, and we believe — Avith the sensations of the 
 muscles, joints, etc. — the only geometrical senses. By 
 use of these senses we construct a world of objects having 
 spatial qualities and set in relations of space. 
 
 (3) Need of Local Signs. — The locally different parts of 
 the organs of the geometrical senses must each have some 
 mental representative in the sensations which stimulation 
 of each calls forth. As parts of the physical organism, 
 they have no significance for the mind. Only the psychical 
 changes which their irritation causes can become factors in 
 the psychical products and processes of perception. The 
 theory of perception seems then to demand the assumption 
 that all sensation-complexes, which are to become factors 
 of perception, must have a peculiar " local stamp," or 
 shade, or mixture of quality, — dependent upon the place 
 of the organ at which the stimulus is applied. This 
 peculiar local stamp, or shade, or mixture of quality is 
 called a " local sign." It is to the philosopher Lotze that 
 
PERCEPTION BY THE SENSES. 295 
 
 we owe the first elaborate theory of " local signs " and their 
 relation to the formation of the perception of objects by 
 the senses. 
 
 (4) Stages of Perception. — To perceive objects of sense 
 is something which must be learned by every human mind. 
 This is as true of objects near as of those remote ; of the 
 organs of our own body, as seen or felt by ourselves, as of 
 the distant mountain or the fixed star. The end aimed at 
 by nature, so to speak, is the clear and accurate construc- 
 tion of a " field of vision " and a " field of touch," by the 
 two great geometrical senses. Perception is then — we 
 can scarcely repeat or emphasize the declaration too much 
 — a mental achievement. 
 
 In the one work of perception two particularly note- 
 worthy stages are to be recorded. These are the " locali- 
 zation " and the " objectifying," or " eccentric projection," 
 of the sensation-complexes. By the former we understand 
 the transferrence of these sensation-complexes from mere 
 psychical states to processes or conditions recognized as 
 belonging to more or less definitely fixed points or areas of 
 the extended body. By the latter we understand the giving 
 to these sensation-complexes an " objective " existence, as 
 qualities of objects (so-called " things "), situated within a 
 field of space and in contact with, or more or less remotely 
 distant from, the body. 
 
 (5) Characteristics of the Spatial-series. — In the process of 
 perception by the senses, some of the many different sen- 
 sation-complexes come to be localized as affections of the 
 different parts of our own bodies ; some of them also 
 become projected — so to speak — outside of our bodies 
 as qualities of things, either in contact with our bodies 
 or situated at a distance from them. But not all kinds 
 of sensation-complexes — it has been said — lend them- 
 selves to this kind of constructive treatment. Not all of 
 them organize themselves into a world of independent 
 
296 PHYSIOLOGICAL PSYCHOLOGY. 
 
 realities, spatially extended and spatially related. We 
 inquire then, What characteristics must the series of sen- 
 sation-complexes, arising through excitement of the organ 
 of sense, possess in order to lend themselves to this synthe- 
 sizing and organizing process ? 
 
 Plainly it will not do to suppose that any two sensation- 
 complexes, in order to combine in the construction of an 
 object, must originate through the excitement of elements 
 of the organ that actually lie side by side. The object 
 perceived is indeed made up of parts contiguous in space. 
 But the extension of the object perceived is never a copy 
 of the extension of that nerve-expanse of the eye or skin, 
 by irritation of whose minute parts the object is presented 
 to the mind. For example, the nervous elements, on whose 
 irritation the perception of an extended visual object 
 depends, lie in the retinas of two eyes. Each retinal 
 image is interrupted by the " blind-spot." The images have 
 no value for perception unless the results of the irritation 
 are propagated to the brain. In the brain, we know that 
 the nervous elements, whose irritation results in the per- 
 ception of the extended visual object, do not lie at all side 
 by side after the exact manner of the parts of the object 
 itself. 
 
 It is not necessary to perception that the nervous ele- 
 ments concerned in the production of the extended object 
 shall themselves sustain cei-tain spatial relations to each 
 other. What is necessary is that the series of sensation- 
 complexes which result from the irritation of these nervous 
 elements shall be capable of definitely and reciprocally 
 determining each other as series of sensations. To accom- 
 plish this, several characteristic qualities are necessary. 
 
 A. Spatial-series of sensations must include sensations of 
 similar quality that admit of easy, rapid, and frequent repe- 
 tition in varying order of arrangement. Senses which, like 
 the eye and hand, have organs capable of rapid, precise, 
 
PEftCBMlON Bt fHB SENSES. 297 
 
 and nicely graded motion, are obviously equipped with 
 that peripheral mechanism which is favorable to the pro- 
 duction of spatial series of sensations. In the use of the 
 eye, for example, there are produced various intermingling 
 simple sensations of light and color-tones, together with 
 muscular sensations of accommodation and of motion due 
 to the action of the six muscles, and sensations of tactual 
 sort as the eye rolls in its socket, etc. Moreover, these 
 series of sensations thus evoked are capable of repetition ; 
 not only forward in the order of a, /3, 7, S, . . . fi, or in 
 the reverse order of yi*, \, «, . . . /S, a, but also in an end- 
 less variety or an interlacing network of fused sensation- 
 complexes. 
 
 The same thing holds true of the series of sensations 
 of light pressure, fused with factors derived from that 
 unclassifiable crowd of other sensations located in the skin, 
 as the hand moves over some object, or as an object is 
 moved over some surface of the body. The same thing we 
 believe to be also true of the muscular sensations, — though 
 upon this point there is more reason for doubt and differ- 
 ence of view. 
 
 But obviously nothing similar can occur with the suc- 
 cessive or fusing sensation-complexes of smell, or taste. 
 Whatever series of such sensations we succeed in evoking 
 in consciousness do not admit of "easy, frequent, and 
 rapid repetition in varying order of arrangement." 
 
 The case of the ear, however, is sometimes contested. 
 The question is raised : Why, if this view of the spatial- 
 series of sensations be correct, should we not objectify the 
 different tone-colors as lying side by side in superficial ex- 
 tension, or as having the three dimensions which belong to 
 objects seen and touched ? The objection implied in this 
 question is not serious. In the first place, the ear is not, 
 like the eye and the hand, a movable organ usable at will for 
 the exploration of an object. Moreover, by far the greater 
 
298 PHYSIOLOGICAL PSYCHOLOGY. 
 
 number of the sensations it brings to us consist of sudden 
 shocks of noise which occur to interrupt, as it were, the 
 continuous flow of sensations of the eye, skin, and muscles. 
 Sensations of musical tone, arranged in serial order, are 
 relatively very rare. Few people have heard frequently 
 more than a half-score of tunes. And even such series of 
 sensations of sound do not shade into each other; or at 
 all meet the conditions of the very point we are arguing, 
 — viz., that of being adapted for easy, frequent, rapid, and 
 varied repetition. 
 
 B. Spatial series of sensations must he comparable and 
 assoeiable with each other. In the use of the eye, graded 
 series of sensations of color and light, with distinguishable 
 differences of quality and quantity, are constantly accom- 
 panied by similarly graded series of tactual and muscular 
 sensations. These different spatial series are comparable 
 and assoeiable with each other. The visual objects per- 
 ceived are dependent upon such qualities as possessed by 
 these series of sensation-complexes. So, too, the different 
 series of sensations that arise from the simultaneous irrita- 
 tion of connected areas of muscle and skin possess the 
 qualities necessary for the so-called " geometrical " senses. 
 In particular, in forming the field of touch, the fact that 
 the peripheral parts of the body so frequently come into 
 contact with each other, is of great significance. Thus, 
 two series of sensation-complexes corresponding to the 
 perceptions of "touching" and "being touched " are, as it 
 were, brought into juxtaposition in consciousness. This 
 " juxtaposition " is not itself a spatial juxtaposition ; but it 
 is the necessary precondition of our forming the perception 
 of the object as consisting of parts lying side by side. 
 
 C. Spatial series of sensations must he differentiated hy 
 the possession of '■'■local signs." It has already been said 
 that we understand by a " local sign," that peculiar mix- 
 ture or shading of quality which belongs to sensations. 
 
PERCEPTION BY THE SENSES. 299 
 
 otherwise qualitatively alike, on account of the particular 
 locality of the organ to which the stimulus is applied. 
 Lotze, the originator of the theory of local signs, con- 
 ceived of them, in the special ease of the eye, in the 
 following way. In addition to the same sensation (for 
 example, red, B^ which each color-tone produces at all 
 places of the retina, it produces also an "adjunct" or 
 " accessory " impression, a, /3, y, etc., for each of the differ- 
 ent retinal places, a, b^ e, etc. . The nature of this adjunct 
 impression for the different places of the retina he ex- 
 plained as follows : When the image of a luminous point 
 falls upon any place of the retina lying outside of the 
 " clear-spot " of vision, we instinctively rotate the eye in 
 order to bring this image upon the most sensitive spot 
 of the retina. Thus a series of changing "feelings of 
 position " have been developed, corresponding to each arc 
 through which the eye has been frequently rotated. To 
 fixate the point ^, rotation has taken place frequently 
 through arcs corresponding to PH, RE, SE, etc. To these 
 arcs of rotation correspond the " feelings of position," ire, 
 pe, (T€, etc. 
 
 Now when two or more points of the retina, lying in 
 different directions, are simultaneously stimulated, — for 
 example, P, R, S, — this calls into consciousness 'at the 
 same time all the " feelings of position " corresponding to 
 the arc of rotation of each point. 
 
 Objections may be raised to Lotze's view of the nature 
 of the so-called "local signs " of the eye. Especially does 
 the term " adjunct " or " accessory " impression seem to us 
 unfortunate. Nor are we perfectly sure that the excited 
 retinal elements do not, of themselves and irrespective of 
 previous movements of the whole eye, have a peculiar 
 value in consciousness. But the assumption, that the 
 different minutest distinguishable areas of the eye and 
 skin have attached to their action peculiar shadings in the 
 
300 PflTSlOtOGlCAL PSYCHOLOGY. 
 
 resulting qualities of the sensations evoked, seems required 
 for the construction of any intelligible theory of percep- 
 tion. Moreover — as we shall see subsequently more in 
 detail — the same assumption also seems warranted by the 
 facts. 
 
 In general, then, we conceive of the local signs in the 
 following way: The irritation of the different elements 
 of certain organs of sense gives rise to sensations which 
 differ in the shading of their quality, according to the 
 locality in the organ at which the elements are situated. 
 But, especially in our ordinary experience, the irritation of 
 none of these elements takes place singly. The simulta- 
 neous irritation of several of these elements results then 
 in a " sensation-complex " ; and this sensation-complex is 
 distinguished from all other most nearly similar sensation- 
 complexes, by a peculiar mixture of shades of quality 
 dependent upon the number and local character and rela- 
 tion of all the elements thus simultaneously irritated. 
 
 For example, the sensation-complex aroused by irritating 
 together the retinal elements a, 6, c, d, etc., differs from 
 that aroused by irritating the retinal elements h, c, d, e, 
 etc. The same thing holds true of locally related nervous 
 elements of the skin. Indeed, each of the spatial series of 
 sensations is characterized by a kind of local coloring for 
 its different sensation-complexes. 
 
 The foregoing theory is, therefore, opposed to that of 
 Bain and others of the so-called Associational School, who 
 endeavor to reduce all local signs to 'mere symbols of 
 associated differences in the muscular sense. We shall see 
 abundant reason for holding that the muscular sense has 
 by no means such an exclusive position as the theory of 
 this school would indicate. 
 
 One other important consideration remains. The local 
 signs of the different spatial series evoked in the use of a 
 very complex and active organ, like the eye or the hand, 
 
PERCEPTION BY THE SENSES. §01 
 
 must necessarily modify each other. Hence there arise 
 admixtures of sensations dependent upon the fusion of the 
 specific energies of the nervous elements simultaneously 
 excited. For example, the place where we locate a visual 
 object does not depend merely upon the place where its 
 image falls upon the retina ; but also upon the " feelings of 
 position " which indicate to us the amount and direction 
 of the turning of the eye, and even of the head, neck, and 
 trunk of the body. Thus, too, is our perception of the 
 position, size, shape, etc., of any object, when located in 
 contact with the skin, dependent upon a gross mixture of 
 many delicately variable sensation-complexes belonging to 
 various spatial series. The complication and elaborateness 
 of experience, and the niceness and variety of discrimina- 
 tions, which this theory implies, will be no obstacle to any 
 student of the mind who has carefully observed and 
 reflected upon the phenomena. 
 
 Indeed, we may observe our own sensations in a way 
 which seems to give the warrant of immediate intuition 
 to the view which regards them as infinitely varied in 
 local coloring. Let one select two portions of the body 
 whose structure and function are most nearly identical; 
 and then compare the sensation-complexes called out by 
 simultaneously irritating these portions. The correspond- 
 ing areas on the tips of the two middle fingers will fulfil 
 the necessary conditions. When we gently rub these 
 finger-tips together (but only in case neither is too widely 
 differenced from the other by some peculiarity of structure 
 or use, — e.g. by a callous spot or something similar), the 
 sensation-complexes corresponding to the terms "touch- 
 ing" and "Tseing touched" seem to fluctuate between the 
 two fingers. Either finger, accordingly, can at will be 
 regarded as touching or as being touched. Or, perhaps, 
 the whole sensuous condition evoked almost entirely loses 
 its objective reference, and seems to resemble the purely 
 
302 PHYSIOLOGICAL PSYCHOLOGY. 
 
 subjective character of smells or sensations of musical 
 tone. 
 
 Under ordinary circumstances, however, the two sets of 
 spatial series evoked by bringing two areas of our own 
 bodies into contact are so strongly characterized by the 
 local signs belonging to each, that we have no choice as 
 to which member shall be regarded as touching, and which 
 as being touched. For example, if the forehead be moved 
 against the stationary tip of a finger, the character of 
 the sensation-complexes will deceive us into attributing 
 motion to the finger rather than to the forehead. The tip 
 of a finger of normal sensitiveness in contact with the tip 
 of a callous finger is determined as the one touching some- 
 thing ; the callous finger is determined as a part of our 
 body, being touched. Pricks, hard pressure, pains, sen- 
 sations of creeping and tickling, we locate in the body. 
 Indurated spots of our own skin we regard as foreign 
 substances. In general, sensations characterized by local 
 signs which have a strong and decided tone favor the 
 process of localizing ; sensations of a toneless kind favor 
 the process of objectifying. 
 
 (6) "Empiristic" and "Nativistic" Theories. — Two rival 
 views exist as to the explanation of the nature and origin 
 of perception by the senses. They have been called 
 the " nativistic " (or intuitional) and the " empiristic " by 
 Helmholtz, and the "nativistic" and "genetic" by Wundt. 
 These different views can scarcely be spoken of as opposed 
 theories ; they are better described as the result of tenden- 
 cies which appear in the attitudes assumed by two classes 
 of observers towards two classes of facts and towards the 
 explanation of the facts. Adherents of the "nativistic" 
 view are inclined to depreciate the explanations offered by 
 the empiricists, as to how and why our perceptions come to 
 have the character they actually bear; they themselves 
 prefer to emphasize the intuitional and underived activity 
 
PERCEPTION BY THE SENSES. 303 
 
 of the mind. But adherents of the " empiristic " view, on 
 the contrary, are inclined to admit no explanations which 
 refer to the mind's native constitution or powers; they 
 prefer to fill in the gaps of knowledge with explanations 
 derived by conjecture from alleged experimental data. 
 
 "We believe that certain principles, contended for by 
 both these theories, must be admitted. The right to 
 " explain " mental phenomena, by giving the descriptive 
 history of their rise and development, and by scientific 
 statement of the relations they uniformly sustain to each 
 other and to phenomena of a physical order, is, of course, 
 beyond question. It is for this right that the " empiristic" 
 school contend. In concession to this view it must be ad- 
 mitted that the " immediateness " or intuitional character 
 of all our perceptions is illusory. This is as true of the 
 art of seeing and touching common things, as it is of the 
 art of handling a graver's tool or of playing upon a violin. 
 
 On the other hand, the "empiristic" theory can never 
 so far perfect its explanations as rightfully to withhold 
 from the mind, considered as the subject of the psychical 
 phenomena, the claim to possess all its jso-called native 
 powers. The elements of perception are psychical factors, 
 — sensations and sensation-complexes; they must, there- 
 fore, be regarded as forms of the mind's reaction on occa- 
 sion of the stimulation of the nervous centres in definite 
 ways. The laws of the synthesis and evolution of the per- 
 ception-products and perception-processes are mental laws, 
 — that is, constitutional and native modes of the behavior 
 of the subject which we call mind. Especially is it true of 
 this characteristic of " space-form," which belongs to all the 
 complex products of perception by the senses, that it is a 
 subjective and mental mode of arranging and regarding 
 the sensation-complexes. Space-form is mental form; to 
 impart it is a mental achievement which implies a native 
 character to the mind. 
 
304 PHYSIOLOGICAL PSYCHOLOGY. 
 
 In making such admissions as those immediately forego- 
 ing, it is implied that we have reached the limits of scien- 
 tific explanation by tracing the genesis and uniform rela- 
 tions of the phenomena. But such limits are met in all 
 attempts at scientific explanation. They are not, indeed, 
 to be arbitrarily set up, nor held fixed in place at points 
 beyond which scientific research has succeeded in passing. 
 But their existence is to be acknowledged in every form 
 of science. 
 
 Our general position will subsequently receive special 
 illustration in the case of the eye. It is over the theory 
 of perception by this organ that the " nativistic " and 
 the " empiristic " views are most warmly debated. Some 
 investigators conclude that perception of "extensity" in 
 three dimensions is native to the eye. Others would limit 
 this native power of the eye to the perception of extension 
 in two dimensions. Others still take tne more purely "em- 
 piristic " position and contend that the original sensation- 
 complexes of a visual order have no spatial qualities ; they 
 are to be regarded as neither " out " nor " spread-out," — 
 whether in two or three dimensions. Yet the most extreme 
 " empiristic " position cannot avoid virtually ascribing to 
 the mind the native power to have and to combine the 
 sensation-complexes, in such order and manner, that the 
 perception of objects in three space-dimensions is the actual 
 result of its activity. 
 
 The theory which we shall now illustrate involves the 
 following position on this point : Perception is an achieve- 
 ment due to extremely complex activities of the psychical 
 subject — the Mind ; it involves the synthesis of a number of 
 sense-data according to laws that are not dedueible from the 
 nature of the external objects, or of the physiological action of 
 the end-organs and central organs of sense. What are the 
 laws, or uniform modes of action, followed in the genesis 
 and development of perception by the senses, has already 
 
PERCEPTION BY THE SENSES. 305 
 
 been somewhat fully stated. The subsequent treatment of 
 the particular senses will explain and illustrate them more 
 fully. It will also add to them a number of subordinate 
 laws ; and it will indicate how far, in each case, the " em- 
 piristic" and the "nativistic" views are capable of scien- 
 tific verification. 
 
 It must constantly be borne in mind that the scientific 
 position, as psychology takes and maintains it, regards the 
 nature and evolution of perception as a subjective affair. It 
 discards, at once and for all, the so-called " common-sense " 
 point of view, from which the perceptions are regarded as 
 " copies " or "impressions " of things having a ready-made 
 and ea;*ra-mental existence. Neither is its point of view 
 the same as that of purely physical or physiological science. 
 In other words, we investigate the genesis and development 
 of perceptions, not the constitution and growth of material 
 things. But since we are considering psychology from the 
 physiological point of view, we regard this genesis and 
 development of perceptions as determined by, and con- 
 ditioned upon, the activity of the nervous system when 
 excited by external stimuli. 
 
 PEECEPTJON BT THE " NON-GEOMETBICAL" SENSES. 
 
 A certain measure of perceptive knowledge of things 
 comes to us indirectly through those senses which have 
 been called "non-geometrical." Strictly speaking, the 
 knowledge thus gained never becomes an immediate per- 
 ception of things. The rather does it always remain an 
 indirect knowledge about things ; but about things which 
 we perceive directly through the " geometrical " senses 
 so-called. 
 
 Perceptions of Smell. — The perceptions of this sense 
 differ only as respects fineness, duration, and accompany- 
 ing tone of feeling ; they have neither size nor shape, nor 
 spatial properties of any kind. They are not, as sensation- 
 
306 PHYSIOLOGICAL PSYCHOLOGY. 
 
 complexes purely of smell, directly localized. They are 
 indirectly localized, however, in the nose and surrounding 
 parts of the face, by the tactual and muscular sensations 
 which accompany them. 
 
 The exploits of some animals give .ground for the con- 
 jecture that every species, and probably every individual 
 animal, has an odor of its own. From our own experience 
 we know that different smellable objects produce character- 
 istic sensations of smell. In this indirect way we are said 
 to perceive the object in whose effluvia the irritation of our 
 end-organs originates. Its distance and direction are 
 known by the variations in intensity and quality of the 
 sensations, particularly as we turn the head, and as we 
 advance or recede in one direction or another. In case of 
 simultaneous influence from two smells, the stronger over- 
 whelms the weaker. We cannot hold these sensations side 
 by side, as it were, even by means of the tactual and 
 muscular data with which they are connected. 
 
 Perceptions of Taste. — Since the tongue is the chief 
 organ of touch, and is very mobile and sensitive to pres- 
 sure, sensations of taste are closely connected with those of 
 touch. In themselves considered they have no spatial 
 qualities, no local habitation. » 
 
 When a sour mass is laid on one half, and a bitter mass 
 on the other half, of the tongue, a conflict of sensations 
 takes place. We may determine this conflict, under cer- 
 tain circumstances, by choice ; but we cannot place the two 
 conflicting sensations side by side in consciousness. When 
 certain tastes compensate each other — as, for example, 
 when the sugar neutralizes the acid of the lemon — it is 
 probable that the compounding of the two effects takes 
 place in the brain. The sensation of bitter is particularly 
 difficult to cover or neutralize. 
 
 Perceptions of Hearing. — We know that we hear with 
 the ear, chiefly through those sensations of shock to the 
 
PERCEPTION BY THE SENSES. 307 
 
 muscles and skin of the region which are produced by loud 
 and massive or piercing sounds. Certain acoustic sensa- 
 tions called " entotic " originate through excitement within 
 or near the organ itself ; the stimuli of these sensations are 
 probably, in most cases, transmitted through the tympanum. 
 Thus a low musical tone, due to the vibration of the adjoin- 
 ing muscles, may be heard by pressing the fingers in the 
 ears and setting the teeth tightly together. Yawning may 
 produce a cackling noise ; quinine and other cerebral exci- 
 tants induce ringing or singing in the ears. The beating 
 of the heart and the whirring of the blood are often audible. 
 The localization of " entotic " sounds is always an elaborate 
 act of judgment, and is often extremely perplexing. In 
 certain pathological cases the power to distinguish between 
 them and external sounds is wholly lost. 
 
 We orientate ourselves in space, with reference to exter- 
 nal sounds, as an acquired art, differing greatly in different 
 individuals and dependent upon previous experience in the 
 use of the senses of sight and touch. The data on which 
 these judgments are founded are only partially explored. 
 It appears that the sensitiveness of the skin of the external 
 meatus and of the tympanum, as well as the position and 
 normal direction of the semi-circular canals, are involved. 
 Some patients with angesthesia of the skin, extending to 
 the meatus and tympanum, can hear perfectly well the tick 
 of a watch, but cannot tell on which side of the head to 
 place it or whether the sound is external to the head or 
 not. Recent experiments tend to show that possibly the 
 nerves of each ampulla have a specific energy in localiza- 
 tion. With normal ears, right and left are rarely confused ; 
 but positions where the angle made by the direction of the 
 sound with the plane of two canals is nearly equal are 
 easily confused. Years ago Rayleigh found that the direc- 
 tion of a tuning-fork could be much better detected, when 
 
308 PHYSIOLOGICAL PSYCHOLOGY. 
 
 held to the right or to the left of the head than when held 
 either behind or before. 
 
 Our perceptions of the absolute distance of sounding 
 objects are entirely dependent upon our knowledge of the 
 quantity and quality of the sounds ordinarily proceeding 
 from them. It may be that a change in timbre aids our 
 perception of the distance of a musical " clang." 
 
 Sensations of sound appear, therefore, not to be directly 
 localized, but to be projected, through complicated indirect 
 inferences, in a space constructed by the activity of the eye 
 and the hand. The utmost that could be claimed would 
 be that the "sensations of position" originating in the 
 semi-circular canals have become so fused with certain 
 acoustic sensations as to constitute a kind of tact which 
 has the semblance of intuitive perception. Even this 
 fusion, however, we believe to be an acquirement depend- 
 ent upon our perceptions of things by the geometrical 
 senses. Hearing, then, belongs among the non-geometrical 
 senses. 
 
 CONSTRUCTION AND USE OF THE FIELD OF TOUCH. 
 
 Every account of the process by which a Field of Touch 
 is constructed, and extended objects become known as in 
 contact with the skin at definite points or areas, must begin 
 by describing the data which the mind has for such activity. 
 
 Fineness of the Skin's Sense of Locality. — The physiolo- 
 gist E. H. Weber first established a rule for measuring 
 accurately the fineness with which different areas of the 
 skin are able to localize objects in contact with them. For 
 this purpose he made use of the two points of a compass, 
 blunted so as to prevent the sensation of being pricked. 
 The minimum distance at which these two points, when 
 applied to any area, could be felt as two localized sensations, 
 was the measure of the sensitiveness of that area. This 
 distance he found to vary from about 1 millimeter for the 
 
PEECEPTION BY THE SENSES. 
 
 309 
 
 tip of the tongue, 2 for the volar side of the last phalanx 
 of the finger, 5 for the red part of the lips, and 11 for the 
 cheek, to 31 for the back part of the hand, 40 for the fore- 
 arm, and 68 for the skin of the middle of the back, and of 
 the upper arm and leg. A recent investigation with the 
 same means for measurement has employed the " method 
 of equivalents," — that is, the compass points were placed 
 4 or more lines (1 line = 2.256 mm.) apart on the fore- 
 head; and it was then found how far apart the points 
 of a second compass must be, on the various areas of the 
 body, to give a sensation of equal aperture. The numbers 
 of the table are given in ratios of the parts compared. 
 
 o a 
 
 
 gg 
 
 21 
 
 4 
 
 2g 
 
 11. 
 911 
 
 11 
 
 o a 
 
 Is 
 
 S * i 
 
 4 lines 
 
 1.668 
 
 1.0165 
 
 0.972 
 
 
 
 0.5 
 
 1.051 
 
 8 " 
 
 1.353 
 
 0.9763 
 
 1.043 
 
 0.982 
 
 1.012 
 
 1.0 
 
 1.055 
 
 12 " 
 
 
 
 1.048 
 
 0.996 
 
 1.022 
 
 1.5 
 
 1.044 
 
 16 " 
 
 
 
 1.037 
 
 0.989 
 
 1.018 
 
 2.0 
 
 1.033 
 
 20 " 
 
 
 
 1.016 
 
 0.985 
 
 1.000 
 
 2.5 
 
 1.028 
 
 24 " 
 
 
 
 1.032 
 
 1.003 
 
 1.017 
 
 . 3.0 
 
 1.025 
 
 Character of the " Sensation-circles." — The areas on the 
 surface of the skin within which the foregoing minimum 
 distances of the points of the compass are felt as two, are 
 called " Sensation-circles." They have, as a rule, an ellip- 
 tical shape with their long axes up and down. Their 
 variation may be shown by the following experiment : 
 Separate the points of the compass just a little less than 
 is necessary for their being felt as two when applied to 
 some particular area (say the cheek) and then cause them 
 to travel slowly, without changing their aperture, over other 
 areas, — the person experimented upon being blindfolded. 
 
310 PHYSIOLOGICAL PSYCHOLOGY. 
 
 The points will appear in consciousness to separate more 
 and more as the more sensitive areas are traversed ; and they 
 will appear to come nearer together again as the less sen- 
 sitive areas are traversed. The sensitiveness of the different 
 areas is in inverse proportion to the size of the sensation- 
 circles. 
 
 The same principle holds when the entire area of the 
 sensation-circles is filled up so as to make a continuum of 
 localized sensations. Thus Weber found that the circular 
 form of a tube of 1^ Parisian line in diameter could be 
 recognized by pressure on the tip of the tongue ; while on 
 the skin of the abdomen the diameter of the tube must 
 reach 3f inch before its fonn was recognizable. The same 
 thing can be shown by laying rods on the skin. 
 
 Great differences exist between different individuals 
 with respect to the sense of locality on corresponding areas 
 of the skin. Some are not more than one-fourth as sensi- 
 tive as others. This sense is also capable of rapid culti- 
 vation. In a few hours the perceptive power of some areas 
 can be more than doubled. Such growth in power is slower 
 at first for the areas not in ordinary use ; it is more rapid 
 for those accustomed to daily use. It is a very surprising 
 discovery that practice, exclusively with a member of the 
 body on one side, will result in improving the correspond- 
 ing member of the other side. Thus Volkmann reduced 
 the minimum perceivable distance with the tip of the 
 finger on both hands — on the right from 0.85 to 0.4, and 
 on the left from 0.75 to 0.45 line — by practising exclu- 
 sively with the left finger. 
 
 The high degree of fineness for certain space-perceptions 
 attained by some blind persons is well known. With those 
 of normal vision some parts of the body, especially the tips 
 of the fingers, are capable of receiving great refinement of 
 cultivation. But one experimenter failed, even by persist- 
 
PERCEPTION BY THE SENSES. 311 
 
 ent education for an entire month, to reduce the obtuseness 
 of the skin of the back more than by about one-fourth. 
 
 Explanation of the " Sensation-circles " of the Skin. — The 
 reason for this marked difference among the different areas 
 in the general field of touch is both physiological and psy- 
 chological. The physiological reason is not, however, very 
 clear. It was natural at first to assume that each circle is 
 provided with one nerve-fibre only, whose terminal expan- 
 sion covers the entire circle. But every point within each 
 circle is itself sensitive, and the circle as a whole may be 
 diminished greatly by the effect of practice. Such an ex- 
 planation, therefore, will not hold. Weber himself thought 
 that the sensation-circles all contain a number of isolated 
 nerve-fibres ; and that, in order to have the impression of 
 two- distinct localized sensations, several unexcited fibres 
 must exist between the two excited fibres. 
 
 The psychological explanation of the sensation-circles of 
 the skin accords with the principles already laid down for 
 all perception by the senses; it therefore illustrates and 
 proves those principles. These circles represent the spatial 
 difference between the points at which stimulus must be 
 applied to the skin in order that the difference in the "local 
 coloring " of the different resulting sensations may be "just 
 observable." The " local signs " of the skin are complex 
 mixtures of sensations belonging to the different localities. 
 As such they are dependent, not only upon unchanging, 
 anatomical and physiological differences, but also upon 
 habit and upon association with each other and with other 
 spatial series of sensations belonging to the same organ. 
 
 More precise description of the causes why the sensation- 
 circles — or, what is the same thing, why the degrees of 
 the fineness of local perception — differ so greatl)' for dif- 
 ferent parts of the body's surface, would include the follow- 
 ing particulars. The skin of the different areas varies with 
 respect to richness in nerve-fibres, thinness, and so sensitive- 
 
312 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ness to light pressure, and character of the support and 
 tension it receives from the underlying parts of fat, muscle, 
 tendon, and bone, when stretched across them. The rela- 
 tive fineness of the organ's sense of locality is also a func- 
 tion of its mobility. Thus, in general, the power of locali- 
 zation belonging to the different parts of the arm, from 
 the shoulder-joint to the finger-tips, increases in some such 
 proportion as the movableness of its different parts. 
 
 The view to be taken of the nature of Weber's "sensa- 
 tion-circles " has been largely changed by the recent experi- 
 ments — already reported (see p. 237 f .) — of Goldscheider 
 and others. The fineness of discrimination possible for 
 any area of the skin depends largely upon how all the 
 points irritated stand related to the specific "pressure- 
 spots " within that area. Only when two irritating points 
 touch two pressure-spots are they felt as two. The impres- 
 sion of being doubly touched may be excited by the points 
 of the compass when lying much nearer together, if the 
 pressure-spots upon which they rest belong to two dif- 
 ferent chains than if both spots belong to the same chain. 
 The minimum distance which admits of perception is sur- 
 prisingly reduced by selecting pressure-spots which have a 
 first rate of intensity; that is, from which the chain of 
 such spots radiates, or at which it makes a sharp bend. 
 How much the table of least observable differences can be 
 reduced by careful experimenting under this rule, a com- 
 parison of the following figures with those given by Weber 
 (see p. 308 f .) will show : — 
 
 Part of the body. mm. 
 
 Back 4-6 
 
 Breast 0.8 
 
 Forehead 0.5-1.0 
 
 Cheek 0.4-0.6 
 
 Nose and chin 0.3 
 
 Upper au4 Ifiwer arm . . 0.5-1.0 
 
 Part of the body. mm. 
 
 Back of hand 0.3-0.6 
 
 1 and 2 phalanges (volar) . 0.2-0.4 
 1 and 2 phalanges (dorsal), 0.4-0.8 
 
 Upper leg 3.0 
 
 Lower leg 0-8-2.0 
 
 Back, and sole of fgot . . Q.^X.O 
 
PERCEPTION BY THE SENSES. 313 
 
 When an area of the skin is touched with any object, 
 even so small as the blunted points of the compass, a large 
 number of pressure-spots, and of other spots of specifically 
 different sensations, are simultaneously excited. The result 
 is a very tangled complex of sensations fused into a sensa- 
 tion-complex, having its own peculiar local coloring. Sen- 
 sations of pressure are primarily " punctiform " ; it is only 
 as they are massed, and fused with other sensations, that 
 perception of a tactual continuum results. 
 
 The ultimate explanation of the " sensation-circles " of 
 the skin, as regarded in the light of the most modern 
 researches, forcefully illustrates and confirms the theory 
 of perception by the senses which was stated in general 
 form at the beginning of the present chapter. 
 
 The construction of the field of touch, in the most general 
 meaning of the words, is closely connected with the rise 
 and growth of another form of perception ; we refer to — 
 
 Perception of Motion 1)7 the Skin. — Different parts of the 
 surface of the body differ greatly with respect to their 
 power of discriminating the fact, the direction, and the 
 amount of motion in contact with them. Specific " sensa- 
 tions of motion " are referred to by some writers on this 
 subject. We believe the language to be misleading. Per- 
 ception of motion depends upon the successive irritation of 
 the organ in such manner that the local coloring of the 
 resulting sensation-complexes is changed with the right 
 degree of rapidity. These sensation-complexes fade into 
 each other, as it were, after a manner analogous to that of 
 the fields of vision when we slowly turn a kaleidoscope 
 before the eye. 
 
 The discriminative sensibility of the skin for motion is 
 much greater than that for separate touch as determined 
 by Weber's experiments. It does not, however, seem too 
 great to be accounted for by changes in local coloring as 
 possible in accordance with the more recent experiments. 
 
314 PHYSIOLOGICAL PSYCHOLOGY. 
 
 G. Stanley Hall found the average distance, in millimeters, 
 whicli a metallic point could move over the skin at a rate 
 of 2 mm. per second, before a judgment of direction could 
 be securely formed, — as follows : forehead, 0.20 ; upper 
 arm, 0.40; fore-arm, 0.44; skin, 0.60; palm, 0.74; back, 
 0.86. 
 
 Motion of a point travelling over the skin can be pro- 
 duced so slowly as not to be perceived at all, even after two 
 or three inches have been actually traversed. Heavy weights 
 moving at the same rate of motion as light weights seem 
 to move faster. The heat-spots and cold-spots are probably 
 of service in judging the rate and direction of motion. 
 The same thing is true of sensations of deep pressure, when 
 called forth in combination with those of light touch. 
 
 Conclusions from the foregoing data agree admirably 
 with the several points in the general theory of perception 
 which have already been proposed. Our perception of 
 moving bodies is especially keen because the motion does 
 not simply multiply, but also diversifies our data for filling 
 up the dermal blind-spots, and so judging the nature of 
 impressions. The perception of each locality may be de- 
 scribed as based upon a " tangle " of various dermal sensa- 
 tions ; for the dermal " local signs " are complex mixtures 
 of sensations, which give to each locality a characteristic 
 local stamp. Our ability to perceive the rate and direction 
 of motion over the skin depends upon the degree, quality- 
 mixture, and rate, of the changes of these sensation-com- 
 plexes. 
 
 Localization of Temperature-Sensations. — In all our ordi- 
 nary perceptions constructive of the field of touch, sensa- 
 tions of temperature are combined with those of light 
 pressure or of motion. Eecent experiments show that the 
 minimum distance apart at which two cold-spots or heat- 
 spots can be felt as two, differs greatly for the different 
 
PERCEPTION BY THE SENSES. 
 
 315 
 
 areas of the body. The following table gives the results 
 of Goldscheider's experiments, in millimeters : — 
 
 PART OF THB BODY BXPEKIMBNTED 
 
 WITH. 
 
 COLD-SPOTS. 
 
 HEAT-SPOTS. 
 
 Forehead, cheek, and chin 
 
 Breast 
 
 0.8 
 
 2.0 
 
 1-2 
 1.5-2.0 
 1.5-2.0 
 
 2-3 
 
 0.8 
 
 2-3 
 
 3-5 
 
 4r-5 
 
 Ahdomen 
 
 4r-6 
 
 Back 
 
 Upper arm 
 
 4r-6 
 
 2-3 
 
 Lower arm 
 
 2-3 
 
 Hollow of the hand . . . 
 Back of the hand, and upper 
 
 and lower 
 
 leg. 
 
 2.0 
 3-4 
 
 It will be seen that the sense of locality connected with 
 the cold-spots is about twice as fine, as a rule, as that 
 connected with the heat-spots. Although the temperature- 
 sensations, by constituting a part of the " local mixture," 
 probably aid in the perception of spatial relations by the 
 skin, they are not well fitted in themselves to constitute 
 a so-called " spatial series." Whenever, for example, any 
 area of the skin is stimulated by both heat and cold simul- 
 taneously, and at points too near together to be discrimi- 
 nated by touch, the two sensations are not localized as 
 Ijdng side by side. The area, on the contrary, feels as 
 though it were being touched alternately with a hot and 
 a cold object; that is, a wavering of perception takes 
 place similar to that which takes place in a so-called 
 "strife of color-sensations." Moreover, if we bring to- 
 gether two large areas of the skin, that differ considerably 
 in temperature, it is difficult by strict attention to the tem- 
 perature-sensations alone, to tell which area is the warm 
 one and which the cool. 
 
316 PHYSIOLOGICAL PSrCHOLOGY. 
 
 ORIENTATION OF THE BODY IN SPACE, WITHOUT SIGHT. 
 
 How our perceptions — or " feelings," as they are some- 
 times called — of the position of our own bodies, either as 
 wholes or with respect to the relations of the different 
 members, are connected with the dermal sensations, has 
 been much debated. That the sensation-complexes Tirhich 
 have just been described, and which are localized in the 
 skin, are of great assistance in forming these perceptions, 
 there can be no doubt. Patients afflicted with anaesthesia 
 of the skin have great difficulty in telling, with the eyes 
 closed, in what positions the limbs, thus insensitive, have 
 been passively placed. For example, we are told of one 
 such patient that, " with an arm elevated by a weight and 
 pulley, and being told to touch his knee^ he felt for it 
 about his shoulders." 
 
 A survey of the entire subject, however, convinces us 
 that it is not by sensations originating in the skin alone 
 that we orientate in space our bodies, whether as wholes 
 or with respect to their separate members, excluding the 
 guidance of perceptions of sight. In such a work of 
 orientation, the perception of the position of the limbs 
 through sensations arising in the conditions of the joints, 
 undoubtedly plays an important part. Slow movements of 
 the limbs with short excursions can sometimes be recog- 
 nized by anaesthetic patients, when accompanied by pres- 
 sure on the joints ; otherwise not. Passive movements of 
 the fingers, or other members, are less easily- recognized 
 when the joints have been rendered insensitive by the 
 faradic current. 
 
 In addition to sensations of the skin and joints, two 
 other classes of sensations have much to do with the per- 
 ception of the space-relations of our bodies, — excluding 
 sight. 
 
 Perceptions of the Muscular Sense. — Three views have 
 
PEECEPTION BY THE SENSES. 317 
 
 been held as to the character and service in perception of 
 those sensations which are attributed to the muscles of the 
 body. One of these views denies that specifically muscular 
 sensations exist; the sensations that go by this name it 
 attributes to the skin as influenced by the changes of ten- 
 sion in it, when the underlying muscles are moved. An- 
 other view (that of Wundt) resolves these sensations, so 
 far as they are not tactual, into " central feelings of inner- 
 vation," which differ only in intensity, and not in specific 
 quality, and which result from changes, initiating move- 
 ment of the body and its members, that take place in the 
 brain as correlated with acts of will. The third view 
 (which we advocate for reasons already referred to in 
 part) maintains the existence of muscular sensations as 
 important factors in those " spatial series " of sensations 
 whose data are necessary .for our perception of the chang- 
 ing relations of our body and its members, to one another 
 and to other objects, in space. 
 
 It has already been said (p. 242), we may derive a cer- 
 tain support for this view from an appeal to consciousness. 
 In moving any limb, or in changing the posture of the 
 entire body, attention enables us in a measure to separate 
 from the sensation-complexes of the skin and joints, other 
 changes in sensation which we localize in the deeper parts 
 of the flesh. As the circuit of motion gone through by 
 any limb increases, or the intensity of the strain upon the 
 muscles becomes greater, the quality of the mass of result- 
 ing muscular sensations is perpetually changing. Every 
 one who has called, by unusual exercise, upon the unused 
 and more deeply lying muscles of the body, knows what 
 surprises (consisting of qualitatively new masses of sensa- 
 tions, as it were) are the resulting response of conscious- 
 ness. 
 
 Moreover, experiment and pathology tend to confirm 
 the impression derived from attention to the phenomena 
 
318 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of consciousness. They show that the power of perceiv- 
 ing the position and movement of the body and its mem- 
 bers does not vary directly and solely as the sensitiveness 
 of the skin and joints. The superior discriminating power 
 which any limb acquires, as soon as it is permitted to move 
 over the object, and to explore it with the moving limb, is 
 due to the series of muscular sensations thus evoked. 
 When, for example, we trace, with the same spot of the 
 fore-finger, and with eyes closed, the outline of an unknown 
 object, it is the direction and amount of motion of the arm, 
 as known by the series of muscular sensations, which is 
 chiefly helpful in constituting this series of perceptions. 
 In all active touch, whether over small or large areas of 
 body, however, this series of muscular sensations consti- 
 tutes, with the dermal sensations, a sort of double system 
 of local signs. Hence, as the Cixperiments of Hall and 
 others show, our judgment of the direction of motion, 
 even when the body is itself motionless, is prompter, if 
 the weight resting on the skin and moving is increased up 
 to the limit when other disturbing sensations intervene. 
 Recent experiments seem also to show that, in estimating 
 the weight of bodies lifted, when they cannot be seen, the 
 judgment is much influenced by the speed with which the 
 weight comes up. If the motor discharge, which is calcu- 
 lated to be adjusted to the raising of any particular weight, 
 meets with unexpectedly little or unexpectedly great re- 
 sistance, and the weight rises with unaccustomed velocity, 
 very singular illusions may result. Of course, our per- 
 ception of the speed with which the weight rises is com- 
 plex, and depends upon a variety of peripherally arising 
 sensations. 
 
 Perception by the Semi-circular Canals. — Recent experi- 
 ments seem to settle beyond doubt the influence of sensa- 
 tions originating in irritation of the semi-circular canals 
 upon the sense of direction, — at least, in the case of some 
 
PERCEPTION BY THE SENSES. 319 
 
 animals. All three canals have now been separately excited 
 by the electrical current, and the direction of the resulting 
 motion seems to be specific for each one of the three. It is 
 highly probable that these same organs in man are closely 
 connected with the perceptions by which he fixes the posi- 
 tion and motion of his body and of its members in space. 
 Precisely what is the character and the amount of this 
 influence physiological psychology is not as yet in a posi- 
 tion to affirm. 
 
 We cannot proceed much farther in this direction for 
 the confirmation and illustration of the general theory of 
 perception, without introducing the case of the eye. But 
 it is probable that in orientating ourselves with closed eyes, 
 whether we remain at rest or are in motion, an important 
 difference exists between what have been called the " sta- 
 tic " and the " dynamic " perceptions and illusions. When, 
 for example, the head is twisted to one side, with closed 
 eyes, the errors in our attempt to localize are such as to 
 show that '•'■static sensations of direction" come through 
 the muscles of the eyes. On the other hand, the so-called 
 dynamic sensations produced by rotating the body are 
 largely due to variations in the endolymph pressure, as 
 the head is turned around its various axes. 
 
 Indeed, the knowledge of the positions of our bodies 
 and their members, even as gained without perceptions of 
 sight, is a very complicated affair. It depends on several 
 kinds of dermal sensations, on sensations of the joints, 
 tendons, etc., on muscular sensations, and on sensations 
 of general sensibility appreciating the gravitation of fluids 
 and the relation of internal organs of the body. 
 
 In the development of this kind of knowledge, the 
 activity of the hand, as it moves over or lies upon the 
 various surfaces of the body, is especially important. It 
 constantly carries with it, as it were, the two great series 
 
320 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of combining and separating and re-combining sensation- 
 complexes of the spatial order, — namely, sensation-com- 
 plexes of the skin and those of the muscles. 
 
 The localization of certain fixed and characteristic parts 
 of the general area of the body, that have marked local 
 characteristics and frequently recur in experience, is a 
 prime achievement in the construction and use of the field 
 of touch. To these landmarks, as it were, other points or 
 areas, subsequently discovered, are referred. One hand 
 learns to know the other ; the right hand chiefly explores 
 the left arm and side and the upper right leg ; the left 
 hand, the right arm and side and upper left leg. The 
 finger-tips, especially of the right hand (and, in the infant's 
 case, the lips), have an office to perform similar to that of 
 the retina: they are the centre, or hearth, of clear per- 
 ceptions of touch. But in order to bring them to their 
 object they must be moved: through this motion fresh 
 combinations of muscular and tactual sensations result. 
 In marked contrast with these active and discriminating 
 organs of the body stand certain parts of the surface which 
 are known to us at all only as they are clumsily excited 
 to undiscriminating responses by the pressure of our cloth- 
 ing or of the burdens temporarily in contact with them. 
 
 But long before the field of touch has been constructed 
 with any considerable approach to completeness, the eye 
 has already explored those parts of the body which are 
 open to its inspection. It learns first to know the hand, 
 which nature keeps constantly in motion before it. As 
 objects excite tactual sensations by resting on the hand, 
 or muscular sensations by being handled, the eye is also 
 active in such a way as to combine these two classes of 
 sensations with visual sensation-complexes. Very early in 
 the development of the perceptive power, it comes to be 
 the leader and critic of the discriminations connected with 
 most of the tactual and muscular sensations. Its power 
 of rapid movement over the whole field, its delicate judg- 
 
PEKCEPTION BY THE SENSES. 321 
 
 ment on account of the finely shaded complex local signs, 
 which its activity calls forth, give it a marked superiority 
 as a " geometrical " sense. For this reason, one born blind 
 can never attain the same " comprehensive simultaneous- 
 ness " for his perceptions of the spatial relations and spatial 
 qualities of his own body or of other objects. 
 
 Among the interesting complex perceptions which result 
 from the habitual synthesis of dermal and muscular sensa- 
 tion-complexes, are the so-called — 
 
 " Feelings of Double Contact." — It is by means of these 
 perceptions that, exclusive of the influence of sight, skill 
 is acquired in the use of tools, weapons, and musical instru- 
 ments. In such cases, the process of eccentric projec- 
 tion (coupled with localization) goes so far that we feel 
 the object with which the implement is in contact, not so 
 much in the hand as in the implement itself, as though it 
 were actually a part of our sentient organism. The wood- 
 carver feels his chisel move through the stuff he is shaping. 
 He guides it as unerringly as the violinist guides his finger, 
 so as to lay the tool, with a given degree of pressure upon 
 a given spot. Such management is, of course, made possi- 
 ble only by delicate changes in the local coloring of the 
 tactual and muscular sensation-complexes, as the move- 
 ment of the handle of the tool, in and with the hand, is 
 variably related to the surface of the skin and underlying 
 muscles. 
 
 Perceptions of this sort are attained through a more 
 artificial and elaborate process of localization. As skill 
 grows, they become perceptions of the texture or condition 
 of a comparatively remote external object, through an 
 organ or instrument, instead of perceptions of the condi- 
 tion of our own bodily members. The relation of these 
 " feelings of double contact " to our estimate of our own 
 personality, to our pleasure in extending the sphere of the 
 mind, as it were, has been discussed by Lotze in an inter- 
 esting way. 
 
CHAPTER XIV. 
 PERCEPTION BY THE SENSES.— Continued. 
 
 The most wonderful and complex of all the organs of 
 perception is tlie human eye. Nature has equipped it with 
 superior means for furnishing to the mind a variety of data, 
 as respects both quantity and quality, for the nicest dis- 
 criminations. It reaches a very high degree of psychical 
 development very early in life. For these and other 
 reasons it is peculiarly difficult to give a complete and 
 satisfactory account of those sensation-complexes which 
 originate through its activity, and of the laws of their 
 combination and elaborating. No less than eight different 
 data, or motifs, are assigned by one authority, as used in 
 adult monocular vision for the perception of the third 
 dimension of space. In stereoscopic vision with both eyes 
 in motion, at least two other very complicated series of 
 sensations, of " spatial " character, must be added to this 
 number. 
 
 The Empiristic and the Nativistic theories of perception 
 find their principal grounds of contention over the case of 
 the eye. The questions about which they contend may be 
 essentially reduced to this : How, and at what stage in the 
 development of perception by the eye, do the visual sensa- 
 tions attain the so-called quality of " extensity " (or big- 
 ness), as distinguished from intensity and color-tone ? 
 Several of the data enumerated in the above-mentioned ten 
 classes, are of only secondary rank and value. Thus much, 
 however, seems necessary to the most elementary form of 
 visual perception : Sensations of light and color, differing in 
 322 
 
PERCEPTION BY THE SENSES. 323 
 
 intensity and quality, hut simultaneously present in con- 
 sciousness, must he systematically ordered hy the help of 
 local signs of the retina, and associated with other spatial 
 series of muscular sensations arising from accommodation of 
 the eye and from its motion. 
 
 The Two Eyes as One Organ. — The complexity of the 
 combinations arising in the case of the eye is, of course, 
 greatly increased by the fact that there are two eyes acting 
 as one organ. Thus there are two sets of certain data to 
 consider : for example, two systems of retinal signs ; two 
 images of each object; two sets of motion in accommoda- 
 tion, and in convergence and divergence of the axes. The 
 two eyes are, however, one organ of vision in such a sense 
 that, even when one eye is closed, the perceptions of the 
 open eye are irresistibly influenced by sensations originat- 
 ing in the condition and action of the closed eye. The 
 two eyes act separately in such manner that they are not 
 one organ as the two nostrils or two ears are one ; but 
 they act together in such manner that they are more truly 
 one organ than are the two hands. We shall have fre- 
 quent occasion to notice gaps or errors in certain theories 
 of perception, which are occasioned by neglecting the in- 
 fluence of one of the two members of this double organ of 
 vision. 
 
 method of Discussion to be followed. — It is not possible 
 to trace the development of visual perception by an appeal 
 to memory or imagination. Neither are the experimental 
 data sufficient to fill up all the gaps left in consciousness. 
 We can only hope to disentangle the more important ele- 
 ments from that complexity of elaboration which they have 
 attained in experience; and then try to reconstruct into a 
 consistent theory the elements thus gained by analysis. 
 In pursuing this course it is most convenient and effective 
 to follow, as far as possible, the order of nature. We thus 
 find three stages of complexity and growth, as it were. 
 
324 PHYSIOLOGICAL PSYCHOLOGY. 
 
 which need explanation. These are : (1) The retinal image 
 of the eye at rest and the sensation-complexes which enter 
 into it; (2) the single eye as moved, and the influence 
 of these movements ; (3) the conditions furnished by the 
 existence and relations of two eyes as active together. 
 
 Corresponding to the three sets of considerations just 
 mentioned we may speak of three fields of vision, in the 
 order of their relative complexity. These are: (1) The 
 retinal field of vision, (2) the field of monocular vision, 
 and (3) the field of binocular vision. By the first we 
 mean that spatial arrangement of sensations of light and 
 color, as points lying side by side, which is due to the 
 excited expanse of the nervous elements constituting the 
 retina, and acting without motion of the eye. The field 
 of monocular vision includes all that can be seen by one 
 eye, unaided and uninfluenced by the action of the other 
 eye ; while the field of binocular vision includes all that 
 can be seen by both eyes. 
 
 Experimentally, we cannot construct, in the case of one 
 who has had a developed experience of sight, any so-called 
 "field of vision " which shall be irrespective of the exist- 
 ence and motion of both eyes. We may, however, apply 
 our analysis to the supposed cases of a retinal field, and 
 also of a purely monocular field, in order to reconstruct theo- 
 retically the process by which the mind attains perception 
 with two active and experienced eyes, constituting one organ 
 of vision. 
 
 The "Retinal Field " of Vision. — Let us close or blindfold 
 both eyes, keep them as motionless as possible, and allow- 
 ing time for all the after-images to die away, await the 
 result. We shall soon perceive a mass, or " extensity," of 
 light and color sensations, projected somewhat indefinitely 
 in front of us. Some would describe this extensity of 
 visual sensations as felt rather than seen. Within the 
 entire expanse we can perhaps, strictly without the slight- 
 
I'EKCEPTIOlSr BY THE SENSES. 325 
 
 est motion of tlie eye, localize an indefinite number of 
 minute points of color and light, lying side by side. This 
 expanse of visual sensations has no fixed and well-defined 
 outline, however ; nor can we localize any of its principal 
 parts, — upper right-hand, lower left-hand, upper centre, 
 etc., — without malcing minute excursions with both eyes. 
 If we turn the face upward, the "extensity" of visual 
 sensations is now above us ; if we turn the face downward, 
 it sinks toward our feet. It has, indeed, a certain seeming 
 of depth ; its appearance is not that of a darkly colored 
 wall or curtain placed close before the eye. But this seem- 
 ing of depth is largely, if not wholly, due to the constant 
 change in the color-tone and brightness of the minute 
 portions of the field, which has an effect somewhat like 
 that we get on looking at a very dense mist of particles 
 differently colored and drifting. 
 
 It is perfectly plain that most of this perception of the 
 locality of our visual extension is the result of acquired 
 skill. Its position with reference to the entire body implies 
 familiar and complex tactual and muscular sensation-com- 
 plexes which have been accustomed to assure us of the 
 position of the body and its members. When the field 
 ascends or descends, for example, we can only make it 
 seem so by producing in the neck the necessary " feelings 
 of position." It would not be at all out of place to say 
 that we then " see " this retinal field, above or below, with 
 our necks. 
 
 Further experiment with the so-called "retinal field" 
 serves to show us how complicated its character really is ; 
 and how much of accumulated experience and skill, won 
 in the process of localizing a great variety of sensation- 
 complexes, its perception involves. For example, a " phos- 
 phene " produced in either eye changes the character of 
 the entire field. Or if one eye be opened, the "retinal 
 field " of the closed eye is at once submerged in the objects, 
 
326 PHYSIOLOGICAL PSYCHOLOGY. 
 
 whose position, magnitude, and spatial relations belong to 
 the " monocular field " of the open eye. Here again, how- 
 ever, this field of the open eye can be drowned in a shower 
 of sparks caused by producing a strong phosphene in the 
 field of the closed eye. 
 
 In general, it will be found that the extent of the retinal 
 field, and the localization of the whole, as well as of its 
 separate parts, are dependent upon the accommodation and 
 motion of both eyes. The explanation of these facts would 
 seem to necessitate the conclusion that the perception of 
 position and of localized areas, even in the two-dimensioned 
 retinal field, depends upon the revival of associated and 
 already localized tactual and muscular, as well as visual, 
 sensation-complexes. 
 
 Immediate Spatial Form of Visual Sensations. — On grounds 
 like the foregoing, the advocates of the empiristic view (for 
 example, Wundt) are led to the claim : " Our sensations 
 of light do not immediately possess spatial form." On the 
 other hand, various forms of the nativistic view insist that 
 "we have native and fixed optical space-sensations" (so 
 Professor James). In our judgment, science has as yet 
 no perfectly certain means for deciding in favor of either 
 of these claims. Experiment and observation certainly 
 show that almost all of the perceptive value, and asso- 
 ciated perceptive influence, which changes in sensations 
 possess through activity of the eye, is acquired in the 
 development of experience. We are warranted in affirm- 
 ing that the infant has no original visual intuition of the 
 space-qualities and space-relations of anything, even includ- 
 ing the members of its own body. 
 
 The ultimate question is, however, capable of statement 
 in some such form as follows : When a number of the reti- 
 nal elements are simultaneously irritated, without motion 
 of the eyes, do the resulting sensation-complexes of light 
 and color originally possess the quality of " extensity," — 
 
PERCEPTIOK BY THE SENSES. 327 
 
 whether in two or three dimensions ? The problem pro- 
 posed in this question is theoretical. No such irritation 
 probably results in sensations of light and color without 
 accompanying accommodation, and parallel or converging 
 or diverging, movements of the organ. But would the 
 resulting sensation-complexes possess this quality of exten- 
 sity, in case they were not accompanied in the earliest 
 development by tactual and muscular sensations? The 
 question, we have already said, does not as yet admit of 
 a perfectly unequivocal answer. 
 
 It should be said, however, in favor of the nativistio 
 view, to some extent at least, that the mosaic structure of 
 the retina suggests the eye's native perception of spatial 
 form. The value of this structure for the development of 
 visual perception can scarcely be understood at all, unless 
 the irritation of each minute area of the nervous elements 
 is represented by a local sign, or shading of the resulting 
 sensation-complexes, in consciousness. Moreover, the spa- 
 tial discrimination of which the eye is capable seems too 
 great to be accounted for by changes in muscular sensation 
 produced by accommodation and rotation on its axes. On 
 the contrary, the limits of discrimination possible by per- 
 ception with the eye correspond almost exactly with the 
 limits of the retinal structure (see p. 255). 
 
 For the foregoing and other reasons we are inclined to 
 hold that spatial perception, though at most in very incho- 
 ate and indeiinite form, is native to the mind as a synthesis 
 of the qualitatively different sensations which result from 
 stimulating simultaneously the retinal mosaic of nervous 
 elements. 
 
 THE CONSTRUCTION OF THE FIELD OF VISION. 
 
 The spatial form assumed by those sensations which are 
 evoked by simultaneous stimulation of many retinal ele- 
 ments is, however, only one among several factors neces- 
 
328 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 sary in the construction of a "field of vision." Vision, 
 indeed, in any sense of the word appropriate to the adult 
 organ, involves a development of experience with moving 
 eyes. The consideration of the simplest case requires that 
 we should refer to the physiology of the eye. Only one 
 small spot of the retina (the " fovea centralis ") is capable 
 of giving a clear image of an object. When we desire to 
 see an object clearly we bring its image upon this spot and 
 fixate it there. The point of the object which corresponds 
 to the point of the image falling upon this spot is called 
 the "point of regard" (sometimes "fixation-point"). In 
 ordinary vision the complete perception of the object in- 
 volves the rapid and constant change of this point of 
 regard. 
 
 Rotation of the Eye-ball. — The wandering of the point 
 of regard over an object may be considered as accomplished 
 ^ ^ by rotating the eye upon a 
 
 pivotal pomt, or centre of 
 rotation, by motions that 
 have different axes of ro- 
 tation. This point is really 
 a minute interaxial space, 
 located about 1.24-1.77 
 mm. behind the middle of 
 th-e optical axes. There 
 are three axes to be distin- 
 guished, — an antero-pos- 
 terior, a vertical, and a 
 transverse. About these 
 axes the six muscles (see 
 p. 81) variously turn the 
 eye, — one only being 
 needed for movements in- 
 ward and outward, two 
 for movements upward and downward, and three for com- 
 
 es*; ,- 
 
 r/ext. r. inf. r. int. 
 Fig. 79.— Diagram of the AttachmentB of 
 the Muscles of the Eye, and of their Axes of 
 Rotation — the latter being shown by dotted 
 lines. The axis of rotation of the rectus, ex- 
 ternuB, and internus, being perpendicular to 
 the plane of the paper, cannot be shown. 
 
PEKCEPTION BY THE SENSES. 329 
 
 billed movements of inward or outward with upward or 
 downward. 
 
 A line drawn from the centre of rotation to the point of 
 regard is called the " line of regard." Such a line may exist, 
 of course, for each eye. A plane passing through the two 
 lines of regard is called the " plane of regard." When the 
 head is erect and the line of regard directed toward the 
 horizon, the eyes are said to be in the "primary position." 
 Rotations of the eye, without torsion, may be regarded as 
 movements of the eye upon its transverse and vertical axes. 
 Rotation of the transverse axis displaces the line of regard 
 either above or below ; the angle which the displaced line 
 thus makes with the primary line of regard is called " the 
 angle of vertical displacement." The "angle of lateral 
 displacement" is formed by rotation about the vertical 
 axes. 
 
 Torsion of the Eye-ball. — By combining an apparent 
 rotation on the antero-posterior axis with lateral or vertical 
 displacements the eye is brought into a series of oblique 
 positions. Such movement is called "torsion " of the eye. 
 The angle which measures the amount of this movement is 
 called " the angle of torsion." The law which is assumed to 
 govern all of this class of movements — namely, combined 
 movements sideways and either up or down — is called 
 " Listing's law." It has been stated by Helmholtz as fol- 
 lows : " When the line of regard passes from its primary 
 position into any other position, the torsion of the eye (as 
 measured by the angle of torsion) in the second position 
 is the same as if the eye were turned about a fixed axis 
 standing perpendicular to both the first and the second 
 positions of the line of regard." 
 
 Into the details involved in the application of the law 
 that controls the rotation and torsion of the eye, we think 
 it unnecessary to enter. One principle is of the highest 
 importance ; it is illustrated by all the movements of the 
 
330 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 eye. The construction of the field of vision, whether monoc- 
 ular or binocular, is a synthetic mental achievement depend- 
 ent upon the varying sensations which result from the 
 wandering of the point of regard over the object. Starting 
 from its primary position, the eye may come round by a 
 variety of circuits to the fixation of any particular point 
 of the object. In the pursuit of these circuits it develops 
 spatial series of muscular sensations and successively com- 
 bines them with other series of sensations of light and 
 color. Thus the form of the field of vision is dependent 
 upon the wandering of the point of regard ; and its con- 
 struction involves a progressive synthesis of the mind. 
 Direct and Indirect Vision. — Let a sheet of white paper, 
 
 eh 
 
 \e 
 
 Fig. 80 (From Hering, after Hemholtz) . — Witb the eye at the distance e-e, and fixated 
 upon the centre, the hyperbolic lines which limit the blaolj and white surfaces show the 
 so-called " right lines " of the field of Tision. 
 
PEECEPTION BY THE SENSES. 331 
 
 having a black dot in its centre to serve as a point of 
 regard, be held at right angles to the line of vision with 
 the eye fixed, in the primary position, upon the point 
 of regard ; then straight, thin slits of black paper upon this 
 sheet will appear bent when lying outside of the vertical 
 and horizontal meridians. Or let the after-images, left on 
 these meridians by light falling through very narrow 
 straight slits, be studied when torsion of the eye takes 
 place, and these images will be found themselves to suffer 
 torsion. The amount and the kind of torsion suffered by 
 the after-images in the second of the above-mentioned 
 experiments, may be discovered by use of a rectangular 
 cross. The image of such a figure is itself distorted as 
 follows for the different torsions of the eye : Upward and 
 
 to the right, thus, .-^^ ; upward and to the left, "H>s ; 
 
 downward and to the right, ^T*^ ; downward and to the 
 
 left, -4" • By connecting the lines in the field of vision, 
 
 as affected by all the possible torsions of the eyes, the 
 accompanying figure is obtained (see Fig. 80) . 
 
 It follows, then, that only those objects which are seen 
 by direct vision (that is, whose images lie in the line of 
 regard when the eye is in its primary position) appear in 
 their actual place ; objects seen in indirect vision appear 
 at the place which they would assume if their retinal 
 images were transposed to the point of regard and its im- 
 mediately surrounding points. The lines of the image do 
 not correspond to the lines of the objective thing; they are 
 constructed hy a synthesis of sensation-complexes of local 
 retinal signs and muscular sensations derived from the 
 movement of the eye. 
 
 Sensations from Accommodation of the Eye. — The mus- 
 cular sensations — or, as they are sometimes called, the 
 
332 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 a'" 
 
 "feelings of effort" — which accompany changes of the 
 focus of the eye in accommodating for near distances, 
 enter into the data of visual perception. These sensations 
 have not, however, a very clear and fixed value. If we 
 regard a black thread, stretched vertically against a white 
 background, with one eye, through an aperture in a 
 shield, we shall find that we can tell little as to its abso- 
 lute distance. Yet we can discriminate changes in its 
 distance with considerable accuracy by changes in accom- 
 modation. Helmholtz found that he required a stronger 
 accommodation to see a red than a blue stripe, through a 
 tube. 
 
 Identical and Corresponding Points. — The theory of binoc- 
 ular vision, of normal developed vision with two eyes in 
 
 motion and acting as one 
 organ, introduces other im- 
 portant considerations. If 
 the two retinas were exactly 
 similar and perfectly sym- 
 metrical, they would admit 
 of being theoretically super- 
 imposed. On such retinas, 
 when the eyes were parallel, 
 every single point of an ob- 
 ject would have its image 
 formed upon two " identical " 
 points of both retinas, — upon 
 points, that is, whose position 
 would be mathematically the 
 same with reference to the centre of each retina. 
 
 No individual, however, has perfectly symmetrical or 
 similar retinas ; and the eyes of every individual are 
 chiefly active in other positions than that called primary. 
 Those points on the two retinas — ordinarily not precisely 
 identical — which do in fact act together are therefore 
 
 -Diagram to illustrate the 
 theory of correBpondlDg retinal points. 
 The images of objects at a" or & or c" 
 will fall on corresponding points of the 
 retina — a and a', b and 6', c and c' — and 
 he seen single. 
 
PEKCEPTION BY THE SENSES. 
 
 333 
 
 b 
 
 I 
 
 ;\ 
 
 called " corresponding." In other words, the points of the 
 two retinas, falling upon which the two images of a point 
 in the object are ordinarily seen as one point, are corre- 
 sponding. 
 
 In certain cases, moreover, points of the retina which 
 do not customarily act together do, as a matter of fact, 
 cover each other ; in such cases the two points are some'- 
 times called " covering " points. Indeed, experiment shows 
 that considerable reciprocal substitution takes place among 
 the different points of the two retinas. When the lines of 
 jegard lie parallel in the plane of the horizontal meridian 
 of the two retinas, the vertical meridians do not correspond. 
 Yet a vertical meridian of the left eye, with its upper end 
 inclined to the left, may be conjoined with a vertical 
 meridian of the right eye that has 
 its upper end inclined at about 
 the same angle to the right (see 
 Fig. 80). 
 
 On this point also, then, the 
 true theory of vision receives 
 further confirmation. Perception 
 involves a fusion or synthesis of 
 sensatiortrcomplexes, the nature 
 and strength of which is deter- 
 mined, not simply by the mathe- 
 matical construction of the eye, 
 but by the data and development 
 of conscious experience. 
 
 The Double Images. — If we „ ". _. . „, . . 
 
 ° FiQ. 82.— Diagram to illnstrate 
 
 hold a finger before the eyes and phenomena of double vWon. if the 
 
 E> .' image of tbe point b fall in one eye 
 
 look, not at it, but at a distant ^^nee^of thrt^'magesVen wui 
 
 wall or at the sky; or if we ZgL'r„'fau rs'anfs.'it wfiit 
 point the finger at some distant ^aTonThfief^'LV "a'tt SS^onlhe 
 object, and keep our eyes steadily '■'^'" "^^ "' *• " ^"" "pp'" '^™'"«- 
 fixed on that object ; two transparent images of the finger. 
 
334 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 instead of one solid finger, will be seen. By experimenting 
 in this way one solid object may readily be made to appear 
 to pass through another. If two objects very similar — for 
 example, the two corresponding fingers — be held a little 
 way apart, at a foot distant and against a clear sky, one 
 solid and two transparent objects may be made to appear, 
 by combining the two middle images and keeping the two 
 outside images dissociated. In the case of a regular small 
 pattern — like the pattern of some carpets, or wall-papers, 
 or the spaces of a wire-grating — the entire two systems 
 of double images may be slipped the width of the pattern 
 simultaneously to one side, and thus combined into a new 
 system of solid forms. 
 
 Now it is obvious that the relations of the two images of an 
 
 object cannot remain un- 
 changed when the eyes 
 are moved from their 
 primary position. If the 
 eyes, for example, are 
 converged on any near 
 object, only the images 
 formed on the central 
 spots of the two retinas 
 are exactly identical and 
 corresponding. These 
 points alone are abso- 
 lutely identical ; but 
 points lying very near 
 to them are also seen 
 single because they are^ 
 as it were, accustomed 
 to act together. In 
 other words, their local 
 signs for both retinas 
 are not so unlike that 
 
 Fig. 83 (from Hering).— /, /, the sash of the 
 window, and p the black spot fixated. On the left 
 line of vision I, h lies a distant object, and on the 
 right line 7% e another object. The images of & and 
 e. as well as the image of p, fall on the place of 
 direct vision, and therefore on corresponding points 
 of the two retinas. 
 
PERCEPTION BY THE SElSTSES. 335 
 
 they do not readily fuse. They have indeed been 
 accustomed to fuse, with one another. All objects, how- 
 ever, which lie nearer or more remote than the point 
 fixated by the eye are likely to be seen double ; and those 
 which lie much below or above, or to either side, of this 
 point, are also likely to be seen double; that is- to say, 
 images of these objects do not faU on corresponding points 
 of the two retinas. 
 
 Calculation of the Horopter. — The sum of all the points 
 which are seen single, while the point of regard remains 
 the same, is called the " horopter." Much ingenuity has 
 been displayed in calculation, experiment, and discussion, 
 to determine the exact nature of the horopter. It has been 
 held to be a surface (plane or curved), a circle, a line, a 
 number of connected points. It cannot be determined by 
 calculation, because the eye in action is not a strictly math- 
 ematical instrument. It cannot be determined by experi- 
 ment upon any one person, under one set of circumstances, 
 for all persons under varying circumstances. The horopter 
 is a psychological affair, and its actual determination depends 
 upon experience, habit, attention, and individual idiosyn- 
 crasies. 
 
 With this understanding of the matter we give the fol- 
 lowing conclusions of Meissner as summaried and, in most 
 respects, confirmed by Le Conte. With the eyes in the 
 primary position, the horopter is a plane perpendicular to 
 the median line of sight. [On the contrary, another obser- 
 ver, using a " very delicate method " of determining whether 
 we are seeing double or not, decides that " the horopter is 
 a circle where the fixation-point is median and nearly in 
 the primary plane."] For all nearer points in the primary 
 plane it is a line which dips toward the observer with an 
 inclination to the visual plane, increasing with the near- 
 ness of this point of regard. When the plane of vision 
 is turned upward, the inclination of the horopteric line 
 
336 PHYSIOLOGICAL PSYCHOLOGY. 
 
 increases ; when it is turned downward, it decreases until 
 it becomes zero at about 45°, and then expands into a 
 plane. 
 
 Convergence of the Axes. — In fixating the point of 
 regard for vision of a near object with both eyes, the 
 lines of vision must converge upon the object. In con- 
 vergence the eyes rotate upon the axis in opposite direc- 
 tions. In lowering the plane of vision, convergence 
 naturally takes place ; but in elevating this plane as in 
 looking upon distant objects, the lines of regard diverge 
 toward the parallel position. 
 
 Convergence may be " symmetrical " or " asymmetrical." 
 In the former case, the two lines of regard are turned 
 inward at equal angles, and the point of regard is kept in 
 the median plane of vision; in the latter, the point of 
 regard is outside of the median plane, and the two eyes 
 are either turned at unequal angles inward, or else one is 
 turned inward, and the other outward at a smaller angle. 
 
 Changes of accommodation naturally accompany changes 
 in convergence of the eyes; and the resulting sets of sen- 
 sation-complexes enter into the perceptive construction of 
 space-form given to the object. 
 
 Influence of Effort in Vision. — A direction of attention 
 and an effort to see are probably implied in convergence 
 of the eyes. The eyes of new-born children, and eyes that 
 are recently couched, as a rule, move in parallel lines. 
 Arrest of attention brings the two eyes into use as one 
 organ. In this way the sensations which arise when the 
 muscles are innervated so as to produce convergence are of 
 marked importance in the construction of the most elab- 
 orate and intelligent visual perceptions. 
 
 It is held by some authorities that the innervation of 
 both eyes is equal even when the movements of the two are 
 unequal ; for each eye is then under the influence of two 
 innervations, one of which is directed toward turning both 
 
PERCEPTION BY THE SENSES. 337 
 
 eyes right or left, and the other toward turning them 
 inward or outward. In one eye the two innervations 
 would support, and in the other eye they would oppose 
 each other. As a result they compensate each other ; and 
 the will may be regarded as guiding its pair of horses by a 
 pull upon one rein. However this may be, there can be 
 no doubt that the mental representatives of the different 
 motions and positions are important factors in that mental 
 construction, called the "field of sight." 
 
 Conditions of Stereoscopic Vision. — By the various "helps" 
 already described stereoscopic vision is made possible. 
 Without the joint activity of both eyes, it is probable that 
 such vision cannot take place. If this be true, the field of 
 monocular vision could be directly apprehended only as a 
 plane ; since all immediate perception of depth would 
 depend upon the existence, and the coupling and uncoup- 
 ling of the double images, together with the related changes 
 in muscular and tactual sensations as the two eyes move 
 upon their axes. It is certain that our immediate percep- 
 tion of the depth of objects with one eye, if such perception 
 exist at all, is exceedingly inadequate. 
 
 It is undoubtedly true that, in adult vision, we do per- 
 ceive objects to a certain extent stereoscopically with one 
 eye closed. But it is probable that such perception is 
 mediate and indirect ; that is, it is accomplished solely by 
 secondary means of vision. Among such means are the 
 varying intensities of light and color, changes in apparent 
 magnitude, etc., — all resting on the basis of associations 
 long ago made by using the two eyes and the hands. By 
 simple experiments with one's self one may be convinced 
 how easy it is, when seeing with only one eye, to reduce all 
 vision to indistinct patches of light and color on a visual 
 plane. 
 
 There is no doubt that the double images which result 
 from the use of the eye in motion afford data for the per- 
 
338 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ception of the solidity of objects. It is more diiScult to say 
 just how this service is rendered. Artificial stereoscopic 
 vision has made every one familiar vi^ith the fact that the 
 two images of every object differ as furnished by the two 
 eyes. The right eye sees the object farther around on its 
 right side, the left on its left. Every minute portion of a 
 solid object, provided such portion lies a little way out of 
 the line of regard, instead of consisting of two exactly 
 similar sets of lines that might be exactly superimposed, 
 consists of two sets of minute curves that are partial 
 images of its lines and are different for each eye. In some 
 manner the perception of solidity is substantially aided 
 by the fusion of these partial images. 
 
 Furthermore, in all ordinary stereoscopic vision the 
 motion of the eyes successively unites and separates the 
 double images of the objects seen. In viewing all objects 
 of any size we may by attention become aware of the fact 
 that we are sweeping over the field of vision with a moving 
 point of regard. Even in the apparently instantaneous 
 perception of a more minute object, the eyes are actually 
 engaged in making short and rapid excursions around the 
 primary point of regard. It has thus been found possible 
 to claim, with much plausibility, that the localization of 
 stereoscopic figures corresponds exactly with the kind and 
 degree of motion necessary to produce fusion of the double 
 images. 
 
 On the other hand, that movement of the eyes is not 
 necessary to stereoscopic vision for trained adult eyes, is 
 proved by what is known as "Dove's experiment." A 
 field of vision, composed of two stereoscopic pictures, can 
 be constructed when lighted by an electric spark; the 
 Tihrs sec. which the flash of the spark occupies is far too 
 brief a time to admit of convergence or of change in the 
 point of regard. But we probably have in this experience 
 one of those many cases where a complex product of per- 
 
PERCEPTION BY THE SENSES. 339 
 
 ception results from the fact that the sensation-complexes 
 primarily aroused by the stimulus call into consciousness, 
 as fused with them, a variety of images of other secondary 
 sensation-complexes. In other words, instantaneous binocu- 
 lar vision of solidity and depth of objects, like monocular 
 vision of solidity and depth in general, is secondary and 
 dependent upon previous experience with both eyes in motion. 
 
 Localizing of the Third Dimension. — Perception of the 
 depth and distance of objects depends primarily, therefore, 
 upon vision with two moving eyes. For such perception 
 Hering has proposed the following law : All the lines or 
 points whose images lie, with a given position of the point 
 of regard, in the vertical horopter, appear clearly defined 
 on a surface which is either plane or slightly cylindrical ; 
 and all the lines or points Ijdng this side of the vertical 
 horopter and whose images have a " crossed disparateness " 
 (that is, the left one of the double images belongs to the 
 right eye, and the right image to the left eye) appear in 
 front of this surface ; while those lying beyond the horop- 
 ter and whose images have an " uncrossed disparateness " 
 (that is, the right image belongs to the right eye, and the 
 left image to the left eye) appear behind the surface on 
 which whatever lies in the horopter is seen. 
 
 Of course, every law like the foregoing must be trans- 
 lated into terms of psychical representation in order to 
 be a real law of perception. It implies the truth of the 
 general theory, that interpretation of the images for the 
 discernment of distance with motionless eyes is an acquired 
 art, which is dependent upon previous combination of the 
 retinal signs of both eyes with muscular sensations arising 
 from the innervation and movement of the eyes. 
 
 The " old psychology " was accustomed to hold that we 
 cannot perceive the third dimension — the depth and dis- 
 tance of objects — with the eyes. Such perception, it 
 held, always results from muscular sensations of the entire 
 
340 PHYSIOLOGICAL PSYCHOLOGY. 
 
 body, or of the gross members of the body, which have 
 become associated with visual sensations. In other words, 
 a translation from sight into touch and muscular move- 
 ment was thought to be necessary in order to see the depth 
 and distance of objects. This view is undoubtedly error 
 neous. Depth and distance are immediately perceived by 
 sight; but such perception comes, primarily, only through 
 that developed vision which uses both eyes in motion, — 
 changing the convergence of the axes and coupling and 
 uncoupling the double images with a varying point of 
 regard. 
 
 VISUAL JUDGMENT AND ERRORS OF VISUAL PERCEPTION. 
 
 Most of our experience in stereoscopic vision and vision 
 of perspective of remote objects avails itself, as it were, of 
 other helps that are not indispensable, absolutely, to the 
 construction of a field of vision. These are sometimes called 
 ^^ secondary." Vision by their aid is often called "judg- 
 ment," in distinction from so-called immediate perception. 
 But judgment, in the sense of discerning and relating 
 activity of mind, is involved in all perception. The only 
 place where we can, apparently, fix any line of distinction 
 lies between those data of sensation which are necessary 
 to any normal binocular vision whatever, and those less 
 primary means of assistance in seeing (or judging) the 
 relative positions and distances of remoter objects that 
 depend upon changing aspects of these objects. The need 
 of so-called " secondary helps " is the greater because, at 
 distances farther than from twenty to forty feet, the changes 
 which accompany convergence and accommodation become 
 practically inappreciable. 
 
 Five or more classes of secondary helps for stereoscopic 
 vision, and vision of perspective for distant objects, may 
 be enumerated. Among them the following are the more 
 important. 
 
PERCEPTION BY THE SENSES. 
 
 841 
 
 Course of the Limiting Lines. — The lines which limit any 
 object, when they are constructed by the moving eye, de- 
 termine our perception of the distance and form, in depth, 
 of that object. If these lines become confused, or run in 
 directions strongly to contradict previous experience, we 
 are liable to errors in perception. Especially when the 
 bottom lines of a distant object are covered, its distance 
 and shape in the third dimension become uncertain. The 
 same arrangement of lines, when it admits of two inter- 
 pretations, can be 
 perceived in either 
 one of two ways ; for 
 example, (as in the 
 case of Fig. 84,) as 
 either a staircase or 
 a portion of an over- 
 hanging wall. In- 
 deed, in viewing 
 such an object a 
 rhythmic change 
 
 from one form of perception to the other may occur as a 
 result of a rhythmic change in the fixation of attention 
 and in accommodation (see also Fig. 85). 
 
 On the other hand, the charac- 
 ter of the limiting lines may be 
 such as to forbid more than one 
 way of perceiving the object. 
 
 Mathematical Perspective. — The 
 size of the angle of vision which is 
 covered by the object, whether 
 near or remote, is another of the 
 so-called secondary helps. In this 
 way objects of known size are seen 
 as placed at a distance necessary 
 to give them their apparent size 
 
 Fig. 84 (f rom Wundt) . — a can be made to appear 
 either nearer or further off than &. 
 
 Fia. 85. — Tiret one, then the 
 other corner of the figure may he 
 drawn forward, partly at will. 
 
 The street appears nar- 
 
342 PHYSIOLOGICAL PSYCHOLOGY. 
 
 rower and more distant, the houses lower and more remote, 
 in the upper part of its visual picture. The tracks of a 
 railroad appear to converge in the distance ; and the same 
 thing is true of the sides of the table or box near which 
 we are standing. 
 
 Aerial Perspective. — More distant objects, on account of 
 the amount of atmosphere through which the rays of light 
 reflected from them have to pass, are more dim in outline 
 and of a changed shade of color. These alterations in the 
 character of the image furnish another secondary help in 
 our vision of perspective. Accordingly, things are seen 
 nearer in an atmosphere clearer than ordinary, more dis- 
 tant in one less clear. 
 
 Size and Direction of the Shadows. — In the morning or 
 evening light, when all shadows are lengthened, the dis- 
 tance of objects is also lengthened. The arrangement of 
 the lights and shadows is by far the most important datum 
 for perceiving the character of objects like intaglios or 
 medallions. A change in this arrangement, so as to sub- 
 stitute light and shadow for each other throughout, con- 
 verts an intaglio into a medallion, and vice versa. 
 
 Number, Duration, and Intensity of the Spatial Series. — 
 When the eye is in motion, as in vision of all objects not 
 very minute and very near, the number, duration, and 
 intensity of the different spatial series of sensation-com- 
 plexes called forth by the motion are of influence in deter- 
 mining the outline-form, size, and distance of objects. The 
 greater the number of the successive sensation-complexes it 
 produces, the greater our estimate of the size of the object. 
 For this reason the same extension of a line or surface, 
 when broken up into parts by intersecting lines, seems 
 larger than when perceived as an uninterrupted whole. 
 This principle is made use of in repetitions of figures upon 
 walls, columns, etc., in arcliitecture. 
 
 The intensity/ of the sensation-complexes entering into a 
 
PEKCEfTION BY THE SENSES. 343 
 
 spatial series has also an influence on our estimate of the 
 size of the object perceived. The size of the object is 
 increased by viewing it with moving eyes when the muscles 
 are lamed or tired. In paralysis of a muscle of the eye 
 (for example, the rectus externus), objects seen by the eye 
 moving in its shortened circuit are located where they 
 would have been if the same intensity of muscular sensa- 
 tion had been necessary to bring them to this position with 
 a normal action of the muscle. On this principle the size 
 of parti-colored and mottled objects is increased. But the 
 absence of a standard of judgment may have the same 
 effect on the repetition of the standard ; thus both unusual 
 monotony and great variety may have the same effect in 
 magnifying the size of the perceived object. 
 
 The duration of time of the eye's activity in perception 
 also has a marked influence on our estimate of the size of 
 the object. The length of time occupied in mastering com- 
 plex objects may be interpreted — especially if the atten- 
 tion required is somewhat strict and painful — as extensive 
 magnitude. 
 
 Influence of Memory and Will upon Visual Perception. — In 
 all adult vision the mind takes its token, as it were, from 
 a very incomplete outline sketch of the object and "makes 
 up," of itself, the complete object, by drawing upon its 
 store of memory-images. Visual perception is, therefore, 
 not simply according to the objective character of so-called 
 "things" to be seen; it is also very largely according to 
 the mind's custom in perception. Accordingly, when the 
 mind's habit is broken up for a time, its interpretation of 
 the sensation-complexes, and its synthesis of them into 
 recognized objects of sense, may be much altered. For 
 example, the effect of the " pseudoscope," — an optical 
 instrument which by exchanging the two stereoscopic pic- 
 tures converts convex into concave, and vice versa, — when 
 applied to a complex object, like a landscape, is very bewil- 
 
344 PHYSIOLOGICAL PSYCHOLOGY. 
 
 dering. The same thing is also true of the "telestereo- 
 scope," — an optical instrument which enables us to see a 
 larger portion of a distant object than is possible with two 
 ordinary eyes, somewhat after the fashion of a pair of opti- 
 cal organs in the sides of a gigantic head. 
 
 Within certain limits we can see what we choose to see. 
 It is held by many excellent observers that, without any 
 change of focus or of convergence, we can render any 
 object in the field of vision clearer by directing attention 
 upon it. Even when the object lies far to one side of the' 
 field, this effect — though difficult to produce — may be 
 attained by trained observers. In the case of perception 
 with a moving eye we can, to a certain extent, decide the 
 area over which the point of regard shall sweep and the 
 relative attention to be given to the subdivisions of this 
 area. Furthermore, and especially in the case of geomet- 
 rical figures, it often lies in our power to decide how we 
 will interpret certain data which admit of more than one 
 interpretation. 
 
 Accuracy of "Visual Perceptions. — Our estimate of the 
 length of visual lines and of the size of visual surfaces is 
 relative, not absolute ; it falls, therefore, to some extent, 
 under the principles discussed in Weber's law. The fine- 
 ness of ocular judgment is greater for horizontal than for 
 vertical distances. It is much less accurate when the dis- 
 tances compared lie in different directions. In particular, 
 points lying at a vertical distance of 20 mm. are estimated 
 as equally far away with those lying at a horizontal dis- 
 tance of 25 mm. Estimates of direction and distance are 
 much more inaccurate when made with only one eye. 
 
 The principal data which enter into visual judgments of 
 length, etc., are probably the local signs of the retina as 
 associated with memory-images of sensations of motion, 
 and minute changes of the coloring of muscular sensations 
 as directly dependent upon movement in accommodation 
 
PBECEPTION BY THE SEKSES. 345 
 
 and convergence. Helmholtz found that a displacement of 
 the middle one of three nails, when set in an otherwise 
 straight line, corresponding to a variation of only 0.0044 mm. 
 in the position of the retinal image, could be detected. 
 And Weber showed that a distinct muscular sensation is 
 attached to a displacement of the most sensitive spot of 
 the retina of not more than -g^ of a Parisian line. 
 
 Sore Complex Estimates of Visual Magnitudes. — The real 
 and the apparent magnitude of an object are, of course, so 
 related that one is dependent upon the other. By the 
 "apparent magnitude" of an object we mean its size as 
 perceived (or judged) by the magnitude of the angle cov- 
 ered by its image, or by the extent of the external surface 
 simultaneously excited by the rays of light reflected from 
 the object. The " real magnitude " is its size as definitely 
 measured by certain fixed standards of measurement formed 
 on the basis of generalizations from the use of both eye and 
 hand. 
 
 Distance, apparent magnitude, and real magnitude may 
 therefore be connected as three factors of one problem pro- 
 posed to the perceptive power of the eye. Given both the 
 apparent and the real magnitude of an object, and we judge 
 of its distance according to our experience of how large 
 an object of the known size ought to look at an assumed 
 distance. The distance at which the object is perceived 
 may be said to be an hypothesis framed to reconcile the 
 known with the apparent magnitude. Distance and appar- 
 ent magnitude being given, real magnitude is judged as 
 that which the object would need to have in order to appear 
 so large as it does appear at the known distance. When 
 either of the two necessary data is lacking or obscured we 
 fall back, as it were, upon such secondary helps as aerial 
 perspective, etc. 
 
 Perception of Kotion by the Eye. — The data and processes 
 already described furnish the explanation of our percep- 
 
M6 jE-llysiOLOGldAL, tSYOHOLOOY. 
 
 tions of the direction, speed, and extent of the motion of 
 objects, by the eye. Here, as elsewhere, we seem to require 
 a distinction between such perceptions as are most primary, 
 and involve the fusion of the local signs into those spatial 
 series which make it impossible for consciousness to disen- 
 tangle the component factors, and those secondary percep- 
 tions where judgment is consciously exercised in estimating 
 the value of various more or less separable data. The 
 latter form of perception is more correctly described as 
 an " inference " to the motion of a body from seeing it at 
 different places in space at successive intervals ; the former 
 appears rather as elementary and immediate perception of 
 motion on the basis of just perceptible changes in the 
 requisite sensation-complexes. We may have a perception 
 of motion when the interval between the two appearances 
 of the moving body is too minute to be observed. For 
 example, two impressions 0.045 sec. apart can barely be dis- 
 tinguished as two ; but the direction of the motion of a 
 light can be perceived when the difference between the 
 beginning and the end of the motion is only 0.014 sec. 
 On the lateral portions of the retina two disks, so near as 
 not to be seen as two, can easily be seen to change place 
 on the slightest movement. 
 
 In general, our judgments in perception of motion by 
 the eye imply the existence of some point which may be 
 regarded as fixed, and the application of a standard of 
 measurement. If no one object in the field of vision is 
 recognized as stationary, such perception becomes exceed- 
 ingly vague, and the perceptible mininum of motion 
 becomes about ten times as great. When the organ is 
 in the primary position, the point of regard furnishes the 
 means for placing things in right relations to ourselves and 
 to each other. 
 
 Perception of motion may then arise in one of two ways. 
 The object may change its relative position in the field of 
 
PERCEPTION BY TSE SENSES. 34T 
 
 vision ; this involves the successive stimulation of contig- 
 uous areas of the retina with images that are sufficiently 
 alike to be regarded as one real object. But perception of 
 motion may also be produced by the successive stimulation 
 of the same area of the retina with images that are too 
 dissimilar to be regarded as one object. 
 
 In perceiving all movements of much extent, however, 
 the eyes follow the object. When both eyes move in such 
 a way that the point of regard remains fixed on the object, 
 our perceptions of the direction and amount of motion are 
 dependent upon changes in the muscular and tactual sen- 
 sations evoked by the eye's changes of position. That is 
 to say, we judge the movement of the object on a basis of 
 judgment as to the positions and movement of the eyes 
 themselves. But we may need to turn the head, or even 
 the body, in order to follow with the eye the moving 
 object. In this case the sensation-complexes originating in 
 the action of the muscles and skin of the head and neck, 
 etc., furnish indispensable data which enter into our com- 
 putation. These data must have such an established value 
 in consciousness as to indicate the successive positions of 
 the moving parts of the body, or else we cannot " see " 
 (perceive or judge) how far, and in what direction, the 
 object has moved. 
 
 Perception of objects in motion implies perception of 
 objects at rest. Objects are perceived at rest, either when, 
 our organs of vision being themselves at rest, the images 
 of the objects do not change their position in the field of 
 vision, or when the sensations of motion occasioned by 
 moving the organs are such as we know by experience 
 correspond to those changes in the position of the images 
 which are occasioned by objects actually remaining at rest. 
 
 Thus what is really moving, and what is really at rest, 
 in a complex field of vision, often becomes a very compli- 
 cated and difficult problem for the mind to solve on data 
 
348 PHYSIOLOGICAL PSYCHOLOGY. 
 
 furnished by the eye alone. Few things connected with 
 the general subject are more impressive than the errors of 
 visual perception which originate under unfavorable cir- 
 cumstances. Indeed, where we do habitually solve thq 
 problem successfully, the data on which we solve it are 
 apt to be overlooked. They are always very difficult of 
 disentanglement. Few people have noticed that, in every 
 case of the hundreds daily occurring, when we change the 
 point of regard from a very remote to a very near object, 
 the two fields of view belonging to the two eyes rotate in 
 opposite directions, while the middle visual line maintains 
 its position in the median plane. 
 
 After-images of Motion. — Those sensation-complexes 
 which the mind builds into perceptions of motion, like 
 other sense-impressions, leave an afterimage. In this way 
 very confusing results are frequently obtained. For ex- 
 ample, if a rotating disk, with a spiral drawn upon it, be 
 suddenly stopped rotating, the points previously seen to 
 move toward the centre are now seen to move in the oppo- 
 site direction. If one eye view a rotating disk directly, and 
 the other through a reversion prism, the two impressions 
 result in confused perception ; but if the disk be looked at 
 with one eye until fatigue occurs, and then that eye closed, 
 and a white surface looked at with the other eye, an after- 
 image of the disk rotating in the opposite direction will 
 appear. 
 
 General View of So-called "Errors of Sense." — The right 
 to use the term " errors of sense" has sometimes been dis- 
 puted, on the ground that sense cannot err, and that all 
 error is really of the judgment. But this attempt at dis- 
 tinction is based upon a complete misunderstanding of the 
 nature of perception. All perception involves discrimina- 
 tion and judgment ; but errors in this sphere are not by 
 any means confined to the making of distinctions which 
 can be corrected at vnll by revision of the data, as it were. 
 
PEECEPTION BY THE SENSES. 349 
 
 When one sees a square of white paper green because it 
 is on a red ground, or yellow because it is on a blue 
 ground, it is certainly correct to say that the senses are in 
 error. The remark of Lotze is not unjustifiable when he 
 affirms : " The whole of our apprehension of the world by 
 the senses is one great and prolonged deception." 
 
 We should prefer, however, to call attention to such 
 facts as the following : Clear vision is always mental inter- 
 pretation. Objects of sense are in no case exact copies of 
 ready-made things. The data., or motifs, and the laws of 
 the mind's constructive and synthetic activity, are pre- 
 cisely the same when errors of sense are committed as 
 when so-called true and exact perception takes place. 
 Errors of sense differ from hallucinations, because the 
 former result from the activity of an organism which is 
 normal in structure and function, while the latter do not. 
 
 The errors of visual perception are almost innumerable ; 
 they can be only partially classified, according as they fall 
 under some one of the foregoing principles rather than 
 others. Certain of the more important classes are the fol- 
 lowing : — 
 
 Errors Due to the Relations of the Double Images. — We 
 have already seen that near objects erroneously appear 
 double when the eye is adjusted for distant objects, and 
 distant objects appear double when the eye is adjusted 
 for near distances. Solid . objects are sometimes seen 
 through other solid objects ; one object sometimes appears 
 two, and two objects appear one ; — and all according to 
 the law of the correspondence or non-correspondence of 
 the two retinal images. 
 
 A very old psychological puzzle is proposed in the ques- 
 tion, Why is vision single, when performed with two eyes ? 
 The question implies a complete misunderstanding of the 
 whole theory of visual perception. We do not see the 
 images at all ; but — as we have learned from the facts of 
 
350 
 
 PHysiOLOGICAL PSYCHOLOGy. 
 
 stereoscopic vision — a chief condition of the single vision 
 of all solid objects is that they shall he seen with two eyes. 
 The fusion of the data belonging to the formation of the 
 two images is the psychical condition of the perception of 
 one solid object. 
 
 Errors of Mathematical Perspective. — A large class of 
 visual errors fall under laws which regulate the smallest 
 observable differences in the muscular sensations as related 
 
 I I I I I I I I I I 
 
 iii 
 
 Fio. 86. 
 
 I M I M I 
 FiQ. 87. 
 
 to the clear perception of the lines, angles, and surfaces of 
 the object perceived. The fact that vertical distances are 
 regularly perceived as larger than equally large horizontal 
 differences has already been mentioned. On trying to draw 
 a cross with limbs of equal length 
 one is apt to get the vertical dimen- 
 sions too small ; exact squares appear 
 higher than their breadth. When 
 comparing magnitudes in the upper 
 part of the field of vision with those in its lower part, 
 one is likely to overestimate the former. The upper and 
 lower half of an "S " or a figure "8" appear of nearly 
 
 Fig. 88. 
 
 Fie. 
 
 the same size ; but when they are inverted (" g " and 
 " 8 "), the difference in the size of the two halves is 
 exaggerated. 
 
PERCEPTION BY THE SI;NSES. 
 
 351 
 
 \ 
 
 Errors arising from the Number and Variety of Impressions. 
 
 — ■ We are frequently deceived in a remarkable way by the 
 manner in which the field of vision is filled up. Such 
 errors fall in part under the principles of mathematical 
 perspective, but also in 
 part under the principle 
 which converts into " ex- 
 tensity" the number and 
 intensity of our sense- 
 impressions. 
 
 If the horizontal dis- 
 tance between two points 
 be exactly half filled with 
 a line, this line will ap- 
 pear to some observers longer than the remaining empty 
 space. A square intersected by parallel horizontal lines 
 
 \ 
 
 Fig. 90. 
 
 V 
 
 ^^ 
 
 appears elongated upward, but one intersected by parallel 
 vertical lines appears elongated sideways. If one of two 
 
 Fis. Vi, 
 
352 
 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 right angles, formed by a line cli-awn perpendicular to a hori- 
 zontal line, be filled with several lines diverging from the 
 
 O^^ — ^^ :::= — ^^ — :::=' — ^ ^^ ^ '=^ — =^ ^ — "^ — ^r — =:r — — -~^ d 
 
 Fi9. 93. 
 
 point of the angle, it will appear larger than the other 
 right angle, and the perpendicular will seem bent. Many- 
 surprising visual errors 
 result from combina- 
 tions of this and the 
 foregoing principles. 
 
 Errors of Imagination 
 under the Law of Habit. 
 — If the visual data 
 will at all permit it, we 
 incline to perceive any 
 visible object as we 
 know that similar ob- 
 jects are usually per- 
 ceived. In other words, 
 the synthesis of the vari- 
 ous sensation-complexes with one another, and with the re- 
 
 Fia. 94. 
 
PERCEPTION BY THE SENSES. 353 
 
 vived and associated memory-images, falls under the law of 
 habit. This principle is constantly taken into account by 
 the pleasant illusions of art. Their success in — as we 
 say — " deceiving " us is not strange ; for this success 
 rests upon the same basis as all the normal and habitual 
 perceptive activity of the mind. 
 
 Many errors in our perception of motion by the eye are 
 to be explained on the foregoing principle. It makes no 
 difference with the result whether the data for such per- 
 ceptions are furnished by actual changes in the position 
 of external things, or by changes confined within the 
 organs of sense. We incline, for example, where two 
 objects are seen to be changing their relative position, to 
 perceive the smaller of them as in motion ; we also over- 
 estimate the speed of small bodies in motion, and under- 
 estimate that of large bodies. 
 
 Errors chiefly Due to Inter-cerebral Changes. — The attempt 
 to discover a physiological explanation for such errors as 
 belong to the class last-mentioned brings us, of course, to 
 the cerebral visual areas as their primary source. We have 
 already seen that the phenomena of the contrast of colors 
 (p. 264 f .) must depend upon certain inexplicable activities 
 of the central organs. The same thing is true of those errors 
 of sense which occur in connection with the strife and 
 prevalence of contours, and with the binocular mixing and 
 contrast of colors. 
 
 If a well-defined image of some colored contour be 
 formed on one retina, and on the corresponding area of the 
 other the image of a uniformly colored background, only 
 the former will be visible. This is called the " prevalence 
 of contours." But if the contours of the two images of 
 differently colored objects cross on the retinas, then some- 
 times one and sometimes the other of the two colors will 
 be perceived at the place of crossing. This is called " the 
 strife of contours." If four squares of paper, — otherwise 
 
354 PHYSIOLOGICAL PSYCHOLOGY. 
 
 exactly similar, — two of red paper and two of blue, have 
 their images combined, the middle one of the binocular 
 images will be sometimes redder, and sometimes bluer, 
 than either of the side-images; but in no case will it 
 exactly resemble either of them. This is called the " binoc- 
 ular mixing of colors." If a white stripe be placed upon 
 a black surface and divided into two images, the right one 
 of which is formed by looking at one half through blue 
 glass, and the left by looking through gray glass, then the 
 right image will be seen blue, but the left will be seen 
 yellow. This is called " binocular contrast of colors." 
 
 Now in aU these and similar cases of deception it is 
 plain that the physiological conditions of the mixing and 
 contrast of the contours or colors depend upon combined 
 and contrasted changes of the brain rather than of the ex- 
 ternal organs of sense. None the less, but even the more 
 obviously, however, does their psychological explanation 
 fall under the laws of that theory of visual perception 
 which we are illustrating. 
 
 The peculiar perception of luminosity which a slightly 
 ruffled sheet of water has, is due to such a struggle between 
 the two fields of vision of the two eyes as results in a rapid 
 alternation of the white and gray images. It may be pro- 
 duced by combining two stereoscopic pictures of like con- 
 tour, but one of which is black with white lines and the 
 other white with black lines. 
 
 Certain optical illusions of motion, moreover, involve 
 very obscure and complicated applications of these and 
 other physiological principles to the centres of the brain. 
 For example, in watching a fall of water for a long time, 
 the steady succession of images passing over the retina 
 sometimes ceases to be perceived as a motion at all. The 
 images of a stationary body on the same retinal region may 
 appear to be moving in the opposite direction. In certain 
 cases, even the same elements of the retina, when stimu- 
 
PERCEPTlOaS BY THE SENSES. 366 
 
 lated simultaneously, may give rise to impressions both of 
 motion and of rest. For errors of visual perception like 
 these, unknown laws of cerebral action need to be assumed. 
 The data, in the form of sensation-complexes, and revived 
 and associated memory-images, are so complicated and 
 thoroughly fused that they scarcely admit as yet of a satis- 
 factory psychological analysis. 
 
 THE DEVELOPMENT OF VISUAL PERCEPTION: 
 
 We have now seen what are the " sense-data " which the 
 mind has, as it were, at its disposal for the construction of 
 spatial perceptions by sight ; and, also, what are the more 
 important psycho-physical laws followed in the process of 
 construction. Visual space implies coherent complexes of 
 light- and color-sensations systematically arranged. The 
 arrangement involves native activities of the mind in de- 
 pendence upon the action of the bodily mechanism of sense. 
 But it also implies mental growth, development under the 
 influence of experience. Perhaps we may rather say that 
 the development of visual perception is the organization of 
 certain sensation-complexes, arising on occasion of the 
 activity of the organ of vision, into a visual experience. 
 
 It is, indeed, difiicult if not impossible to tell just where 
 the limits must be drawn between what is native and what 
 is learned. There can be no doubt, however, that seeing 
 colors (or having observed localized or wholly unlocalized 
 sensation-complexes of light and color) is a far more sim- 
 ple and primary activity than seeing colored surfaces. The 
 perception of such surfaces — of a system of light- and color- 
 sensations related to each other as side by side in space- 
 form — results in experience from the fusion or weaving 
 together of several spatial series of sensation-complexes. 
 It involves muscular and tactual sensation-complexes 
 caused by the motions of the eye for parallel turning, for 
 accommodation, and for convergence. 
 
356 PHYSIOLOGICAL PSYCHOLOGY. 
 
 But the visual perception of extended objects, as adult 
 experience possesses it, requires binocular vision with mov- 
 ing eyes. The firm spatial connection of all the parts of 
 the field of vision requires that a system of lines of direction 
 should be fixed. These prescribe the objective points at 
 which the sensations produced by exciting together the dif- 
 ferent pairs of the covering points of the two retinas must 
 appear in visual space. To establish such spatial connec- 
 tion, both eyes must move in their joint action as a single 
 organ of vision. Thus the field of binocular vision is built 
 up by an order of experience which consists in the succes- 
 sive mastery of more and more complex problems. 
 
 The visual perception of depth involves a later and more 
 complex training as the result of experience than the per- 
 ception of two-dimensioned extension. To solve the prob- 
 lem of depth, binocular vision with moving eyes — thus 
 calling forth the muscular sensations that accompany con- 
 vergence, and the resulting combination and separation of 
 the double images — is necessary. Here, too, the presence 
 and assistance of the so-called "secondary helps" are 
 extremely important. Thus a knowledge of the solidity 
 and distance of objects is developed. But this more com- 
 plex experience, when once obtained, modifies completely 
 what is really more simple and elementary. What we see 
 of solid and distant objects with one motionless eye, de- 
 pends upon what we have learned to see with both eyes in 
 varied motion and reliance also upon all the available 
 secondary helps. The apparent " immediateness," or natu- 
 ral and " intuitive " character, of the construction of the 
 field of sight in monocular vision is one of the many illu- 
 sions with which the evolution of all our experiences is 
 interpenetrated. 
 
 These general remarks apply to the following special 
 topics connected with the development of visual percep- 
 tion. 
 
PERCEPTION BY THE SENSES. 357 
 
 Vision of Things Upright and in Correct Spatial Relations. 
 
 — Among the psychological puzzles often propounded as 
 though they were of especial difficulty we may notice the 
 following : Why do we see the upper part of the object by 
 means of the lower part of the retinal image, snidLviee versa? 
 and, Why do we see the right side of the object by means 
 of the left side of the retinal image, and vice versa ? In 
 other words, why do we see the external thing with its 
 parts up and down, and right and left, exactly the reverse 
 of the parts of the image ? To such questions the right 
 theory of visual perception and its development offers a 
 ready reply. Strictly speaking, we do not see either the 
 retinal image or the ea;^ra-mental material thing. The field 
 of vision is a subjective affair, and is like neither of these 
 two. Perception is indeed dependent upon the formation 
 of the retinal image as one occurrence in a chain of physi- 
 cal changes ; and the formation of the image is, in the same 
 way, dependent upon the action of the rays of light 
 reflected from the object : but the object seen is not a copy 
 of either image or extra-mental thing. 
 
 The field of vision gains a locality in objective space 
 only as we develop our knowledge of the relations which 
 our entire body and its different parts sustain to the earth 
 and to the different things surrounding us. The use of 
 such terms of position as " up " and " down," or " right " 
 and " left," implies such knowledge. The massive feelings 
 arising from the condition of the skin, muscles, joints, and 
 fluids of the body, keep us informed of our general rela- 
 tions to the earth and to objects on its surface. The head 
 is the upper part of the body, or part farthest away from 
 the ground ; the feet are the lower parts, in contact with 
 the ground. When the eyes move downward, the lower 
 parts of the body and objects situated on the ground come 
 successively into the field of vision ; but when the eyes 
 are moved upward, these parts successively disappear from 
 
358 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the field of vision. " Right " is the direction in which the 
 eyes, on moving, find the right hand and objects on its 
 side ; and " left " is the direction in which the eyes look 
 for the left hand and for objects contiguous to it. 
 
 Joint Action of Eye and Hand. — These two organs of the 
 body, from the very beginning to the end of life, are con- 
 stantly assisting each other in the work of perception. An 
 almost continuous process of translation is taking place 
 between the two. What is true in such a high degree of 
 the eye and the hand is true in less degree of the eye and 
 all the members ot the body of whose spatial dimensions 
 and relations visual images can be correctly formed. So 
 also in our perception of external things the eye, on the 
 one hand, and the tactual and muscular organs, on the other 
 hand, aid each other in the work of localizing. 
 
 Experiments have been undertaken to show the degree 
 of accuracy which can be attained in translating percep- 
 tions between the eye and the skin and muscles. Bonders 
 made use, for this purpose, of a very small induction-spark 
 which was to be touched with the index-finger. In fifty 
 experiments, made for distances of 60 to 610 mm., along 
 the same line of regard, in perfectly dark surroundings, 
 the distance was estimated right four times, overestimated 
 34 times, underestimated 12. The greatest errors were 
 + 35 and - 34 mm. When the surroundings were visible, 
 the spark seen with open eyes, and then estimated by the 
 finger with closed eyes, the errors were reduced. Local- 
 izing in this way, with the object out of the line of regard, 
 was much more inaccurate. 
 
 Experiments have also been made to test the relative 
 accuracy with which the three perceptive organs — eye, 
 hand, and arm — will receive perceptions of distance from 
 each other and translate them into their own terms of 
 expression. Jastrow thus concluded that, when the eye 
 is both the receiving and the expressing sense, lengths less 
 
tEECEPTION BY THE SEN^SES. S69 
 
 than about 38 mm. are underestimated, and lengths greater 
 are exaggerated. But when the hand is both the receiving 
 and expressing organ, lengths less than about 50 mm. are 
 exaggerated, and lengths greater underestimated. The 
 arm, in expressing all lengths received from the eye, exag- 
 gerates them; but it underestimates all lengths received 
 from the hand. 
 
 Let us suppose a person to stand blindfold before a ver- 
 tical table and make with one hand an excursion of definite 
 length along a thread, — moving at the same time, by will, 
 and unguided by any thread, the other hand to the amount 
 supposed to represent the same length. If the unguided 
 hand starts from a point higher up than the other and 
 moves upward, it moves less than it should do ; if it moves 
 downward, it moves more than it should do. 
 
 All such results as the foregoing show plainly that the 
 interpretation, back and forth, of visual and muscular dis- 
 tance is a matter of very complex development, and is at 
 best only imperfectly attained. It is not possible to an- 
 nounce any one principle which will explain all the errors so 
 persistently committed in this kind of interpretation. We 
 believe, however, the following two principles are chiefly 
 influential. 
 
 In the first place, each sense, when expressing its esti- 
 mate of perceptions received from itself or from another 
 sense, tends to approximate the dimensions which it is 
 accustomed to judge most accurately. In the second place, 
 in all such work of translation, memory-images of visual 
 perception are the guiding and dominating factors. For 
 example, even when moving about in the dark, in a familiar 
 room, we carry a memory sight-picture of the position of 
 the objects in the room, as well as of the size and shape 
 of the room, to guide our muscular and tactual activity. 
 When we try by arm and hand to indicate the position of 
 any member of our own bodies, or of any external object. 
 
360 PHYSIOLOGICAL PSYCHOLOGY. 
 
 we are accustomed to make our estimate first in terms of 
 memory-images of sight, and then translate through the 
 medium of these images into the required "expressing" 
 sense. 
 
 In closing this subject, attention should be directed to 
 the limitations of explanation with which the science of 
 physiological psychology everywhere finds itself encom- 
 passed. One of these limitations is, of course, reached so 
 often as we are obliged, in offering our explanations, to 
 recur to the " natural " or " native " or " intuitive " opera- 
 tion of the mind. Nor will the penetrating student of 
 perceptive processes imagine that any historical or experi- 
 mental description which can be given of such processes 
 will explain the origin of so-called " space " as a mental 
 form of activity. The study of the processes emphasizes 
 the conclusion that the space-form of all perception is 
 mental; it is jiot a copy, or representative, of ready-made 
 extrorynental existences called "things." And we only 
 anticipate a conclusion warranted by our entire science 
 when we repeat : The field of vision is a subjective affair, 
 and so is the field of touch. The same psychical subject 
 which reacts upon the stimulation of the nervous elements, 
 in the form of various quantitatively and qualitatively 
 different sensation-complexes, constructs by its synthesiz- 
 ing activity, in the development of its own Hfe, all the 
 so-called " objects of sense." 
 
CHAPTER XV. 
 
 TIME-RELATIONS OF MENTAL PHENOMENA. 
 
 Since the work of Bonders in 1868, no single subject 
 in the general study of mind — with the possible exception 
 of Weber's law — has made such a large collection of sta- 
 tistical data as that known by the title " psychometry." 
 The aim of this branch of experimental psychology is to 
 determine exactly the time-relations of mental phenomena. 
 If the results are to be estimated by the number and 
 novelty of the principles established beyond doubt, they 
 must be admitted to be remarkably small. Countless trials, 
 and innumerable tables of statistics, from which already 
 familiar generalizations (if any generalizations whatever) 
 are somewhat ostentatiously derived, thus far comprise the 
 chief treasures of the science of psychometry. The amount 
 and hopefulness of the work accomplished, as well as some 
 promise of intrinsically important results, require, however, 
 that the subject should receive a brief treatment. 
 
 Method of Experiment. — The general problem in all 
 classes of trials under this head is essentially the same. 
 It is the accurate measurement of the interval which 
 elapses between peripheral stimulation of a certain organ 
 of sense and some form of resulting motion, such as sig- 
 nifies that more or less complicated physiological and 
 psychical processes have intervened. The electrical cur- 
 rent is ordinarily used to mark the precise instants when 
 this interval begins and when it terminates. The stimulus 
 may consist in the flash or crackle of an electric spark, in 
 the sounding of a bell or a falling ball or a musical note, 
 
 361 
 
362 
 
 fHYSIOLOGlCAL PSYCHOLOGY. 
 
 in the appearance of one or more colors or figures, or 
 letters or words, etc.; and the resulting motion may be 
 with the finger pressing a key, with the foot or hand 
 closing or breaking a circuit, with the vocal organs calling 
 into a tube, etc. All such experiments may be repeated 
 upon many persons, an indeiinite number of times, and 
 under every conceivable variety of conditions and circum- 
 stances. 
 
 The difficult and valuable part of ah experiments in 
 psychometry is the analysis of the complex cerebral and 
 psychical factors implied in the processes. The difficulty of 
 this analysis is due to the speed, complexity, and subtle 
 variability of the processes which are to be analyzed. The 
 value of the analysis — if it can be satisfactorily accom- 
 plished — depends upon the hope of discovering what are 
 the nature and the relations in time of our mental pro- 
 cesses, and what the nature of their dependence upon 
 processes in the nervous system. 
 
 Simple Reaction-time. — The point of starting in all ex- 
 periment to determine the time-relations of mental phenom- 
 ena is the fixing of "simple reaction-time." The entire 
 interval between the instant when the stimulation of the 
 organ of sense takes place and the instant of the resulting 
 movement of some member of the body is called " reaction- 
 time" (sometimes "physiological time"). Reaction-time 
 is simple when everything which tends to complicate the 
 processes, and so to lengthen the interval between stimu- 
 lation and motion, has been eliminated. Simple reaction- 
 time is obtained in response to a single sensation of known 
 quality, the instant of whose appearance is expected, by 
 executing a single natural and accustomed movement. 
 
 But the simplest reaction-time is, in fact, a very complex 
 affair. It involves, of necessity, not less than seven ele-. 
 ments : (1) An action of the stimulus on the end-organ of 
 sense ; (2) centripetal conduction in the nerve ; (3) the 
 
(tiME-REtiATIONS OP MENTAL PHBNOMEKA. 363- 
 
 same in the spinal cord and lower parts of the brain; 
 (4) transformation of the sensory into the motor cerebral 
 process; (5) centrifugal conduction in the lower brain 
 and cord ; (6) the same in the motor nerve ; (7) setting- 
 free of the muscular motion. 
 
 Psycho-physical Time. — Of the seven foregoing processes 
 involved in reaction-time the one numbered (4) is much 
 the most interesting to physiological psychology. It is 
 called " psycho-physical time " and, in its more elaborate 
 form, has been analyzed by Wundt into three psycho- 
 physical factors : these are, as described after an analogy 
 derived from the sense of sight, (1) entrance into the field 
 of consciousness, issuing in " perception " ; (2) entrance 
 into the point of clear vision in consciousness, issuing in 
 " apperception " (i.e. clear and attentive perception) ; and 
 (3) the excitation of the "will," which sets free in the 
 central organ the registrating movement. For each of 
 these factors time is required. Each of them is psycho- 
 physical, — that is, each comprises physiological processes 
 in the central organs and simultaneous corresponding 
 changes in consciousness. Given, as the result of a suffi- 
 cient amount of experimenting, the average simple reac- 
 tion-time, the problem becomes : to find the three factors 
 of psycho-physical time (namely, " perception-time," " ap- 
 perception-time " or discernment-time, and " will-time "), 
 for all possible conditions and degrees of complexity and 
 delay of the psycho-physical processes. 
 
 Effect of Inertia. — Since the nervous system is com- 
 posed of related material elements, we should expect that 
 some time would be absorbed in realizing the effect of stim- 
 ulation as an activity of the different organs. We should 
 also expect that, when once excited, the effects of the ex- 
 citement would continue for some time after the stimulation 
 has ceased. It is difficult, however, to demonstrate the truth 
 of our expectations in the case of the motor nerve. The 
 
364 PHYSIOLOGICAL PSYCHOLOGY. 
 
 nerve does not seem to require that period of latent excita- 
 tion (about Ym sec.) which the muscle requires for action 
 under the influence of electricity. The case of the end- 
 organs is, however, more clearly defined by experiment. 
 These organs are capable of receiving only about so many 
 separate excitations in a given unit of time. The number 
 of such separate excitations is different, however, for dif- 
 ferent senses ; it depends also upon the quantity and 
 quality of the stimulus used, upon the place of its appli- 
 cation, etc. More than a certain number of applications 
 of the stimulus to an end-organ of sense results in fusion 
 of the otherwise successive sensations. 
 
 Smallest Interval for Sensation of Touch. — The results of 
 experiment to discover the greatest promptness with which 
 the organ of touch will act — or, in other words, the small- 
 est interval possible between two separable sensations pro- 
 duced by repeated stimulation of the skin — differ very 
 greatly. One experimenter has placed the limit at 27.6- 
 36.8 nervous shocks per second ; another at 480-640 ; 
 another at about 1000. 
 
 Smallest Interval for Sensations of Sound. — The noise of 
 the electric spark, heard with one ear only, has been dis- 
 tinguished at intervals of only 0.00205 sec. By using the 
 click of a revolving toothed wheel the interval was thought 
 to be fixed at 0.016 sec. It is increased to about 0.064 
 when the sounds are heard with both ears. Of course, far 
 fewer musical sounds can be heard in the same amount of 
 time, since a considerable part of a second must be con- 
 sumed before the tone is established, as it were. The 
 number of separate sensations of sound possible under the 
 most favorable circumstances may, then, be placed at about 
 600 per second. 
 
 Smallest Interval for Sensations of Sight. — In ordinary 
 daylight, rotating disks, whose surface is part white and 
 part black, become gray (that is, the sensations fuse) when 
 
TIME-RELATIONS OF MENTAL PHENOMENA. 365 
 
 they attain a motion of about twenty-four per second. 
 With care, under favorable circumstances, the stimuli of 
 light sensations may be kept separate at only about -^ sec. 
 If one stimulus strikes the fovea centralis and the other 
 a point of the retina 6 mm. off, the smallest interval for 
 distinct perception becomes about 0.076 sec. 
 
 If the inertia of the eye for different color-sensations 
 were very different, objects would be seen of varying color 
 according to the time during which the rays from them 
 acted on the retina. But the smallest interval for the per- 
 ception of different colors is only very slightly different. 
 Recent experiments to determine the length of time, 
 expressed in 0.001 sec, which is required to distinguish 
 each color exposed from a correspondingly bright shade 
 of gray, yielded the following mean-values : Red, 1.28 ; 
 orange, 0.82 ; green, 1.42 ; blue, 1.21 ; violet, 2.32. From 
 these results the principle was generalized that " the time 
 colored light must work on the retina, in order that it 
 may be seen, increases in arithmetical progression as the 
 intensity of the light diminishes in geometrical proportion." 
 Thig time probably represents inertia of the brain and nerve- 
 tracts as well as of the retina. 
 
 For the other senses — smell and taste — the measure- 
 ment of the smallest interval is too inaccurate to admit of 
 satisfactory discussion. 
 
 Smallest Interval from One Sense to Another. — The time 
 required for discrimination of successive sensations, when 
 they belong to different senses, is even more variable. It 
 depends, of course, upon the two senses between which 
 the discrimination is made, upon the intensity of the sen- 
 sations compared, upon which of the two sensations fol- 
 lows the other, etc. For example, the average interval 
 between sight and touch (sight following) is given at 
 0.05 sec; between sight and hearing (sight following) 
 at 0.06 sec. ; between sight and touch (sight preceding) at 
 
^66 PHYSIOLOGICAL PSYCHOLOGY. 
 
 0.071 sec. ; between sight and hearing (sight preceding) 
 at 0.16. 
 
 Mean-values of Reaction-time. — As has been already seen, 
 the point of starting in all experiments in psychometry is 
 the determination oi simple reaction-time. But the value 
 of this factor varies, by smaller or larger degrees, with 
 different individuals, and with the same individual under 
 different circumstances. By repeated experiments, under 
 the most favorable conditions, the time absorbed by the 
 sensory-motor cerebral processes is reduced as nearly as 
 possible to zero. The mind is then said to act as nearly 
 as possible in a purely mechanical way under the influence 
 of training and habit. Even then the simple reaction- 
 time of different individuals is markedly different. For 
 example, from " hand to hand " (that is, one hand being 
 hit by an electrical current and the other acting to press 
 a key) the reaction-time as given by different experi- 
 menters varies from about 0.1087 sec. to about 0.1911 sec. 
 The reaction-time from eye to hand varies from about 
 0.150 to 0.225 sec. ; from ear to hand, 0.120-0.182 ; from 
 neck to hand, 0.154, etc. 
 
 According to certain authorities the reaction-time for 
 the sensation of cold is somewhat less than for heat : for 
 example, for cold, near edge of eyelid, 0.135 sec. ; upper 
 arm, 0.150 ; abdomen, 0.226 ; inner surface of thigh, 0.255 ; 
 and for heat, 0.190, 0.270, 0.620, and 0.790 respectively. 
 Experiment amply confirms the familiar experience that 
 the contact of objects is much quicker perceived than their 
 temperature. 
 
 We may conclude, then, that under the most favorable 
 possible conditions the reactionrtime can scarcely be reduced 
 to -j^ sec, while it rarely rises much above yu s^"- 
 
 Increased Intensity shortens Reaction-time. — The effect 
 upon the reaction-time, of increasing the stimulus, for sen- 
 
TIME-BELATIONS Or MENTAL PHENOMENA. 
 
 367 
 
 sations of sound has been studied by Wundt with the fol- 
 lowing result : — 
 
 Height of hammer falling. Keaction-time. 
 
 Bee. 
 
 1 millimeter 0.217 
 
 4 millimeters 0.146 
 
 8 millimeters 0.132 
 
 16 millimeters 0.135 
 
 Height of ball falling. Reaction-time, 
 
 Sec. 
 
 2 centimeters 0.161 
 
 5 centimeters 0.176 
 
 25 centimeters 0.159 
 
 55 centimeters 0.094 
 
 Another series of experiments found that the reaction- 
 time for sensations of light varied from 0.251-0.308 to 
 0.128-0.168, according to the intensity of the stimulus in 
 six degrees of strength. Reaction-time diminishes, within 
 certain limits, as the length of the electric spark perceived 
 increases. 
 
 Expectation shortens Reaction-time. — If a preceding sig- 
 nal, at a favorable interval, informs us that we are about 
 to be called upon to react, the time necessary for reacting 
 is diminished. The cerebral centres are thus put into 
 that condition of sensitiveness to stimulation which makes 
 their activity the promptest possible. Thus the interval 
 necessary for perceiving the sound caused by a ball falling 
 25 ctm., which without signal was 0.253 sec, was reduced 
 by a signal to 0.076 sec. ; and when the fall was 5 ctm., the 
 interval was reduced from 0.266 sec. to 0.175 sec. In order 
 to secure such a result, however, the signal must noj; be dis- 
 tracting ; the interval between it and the expected impres- 
 sion must be nearly constant, and not so long as to over- 
 strain attention. 
 
 When the quality of the impression to be expected is 
 known, but its intensity is unknown, the duration of reac- 
 tion-time is increased. It is also greatly lengthened when 
 the impression takes us off-guard, as it were; in such a 
 case the reaction-time may reach 0.4-0.6 sec. Of course, 
 it takes longer to react in an unnatural or unaccustomed 
 way. 
 
368 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Finding of "Discernment-time." — Donders and his pupils 
 were the first to examine the speed of the psychical pro- 
 cesses (or " psychical reflexes," as one observer calls them ; 
 i.e. "reflexes with cognition of the excitant"), with a 
 view to determine how long it requires to recognize one of 
 two or more different perceptions of sense. To solve this 
 problem they employed several methods, not aU alike of 
 unquestionable value and accuracy. All the methods 
 reduce to this one ; namely, to find the length of reaction- 
 time when discernment without choice takes place, and 
 subtract from it the simple reaction-time. This experi- 
 menter allotted to the development of a clear perception 
 of sound, in his own case, about 0.039 sec. 
 
 A particular mode of determining the amount of time 
 required for "apperception," or discernment, was proposed 
 by Baxt; it was based upon the principle of inertia as 
 applied to the senses, especially of sight. Let us suppose 
 some image, which requires discernment for its interpreta- 
 tion (e.g. the image of a particular color, of a letter or 
 word, or of a simple geometrical figure), to be thrown upon 
 the retina, and this image succeeded after a brief interval 
 by the image of a bright white disk ; then, if the interval 
 be too brief, the first image will be " quenched," as it were, 
 by the second, and " apperception " will not take place. 
 As might be expected, it was foimd in this way, that the 
 " discernment-time," or " apperception-time," depends upon 
 the complexity of the operations required. To recognize 
 three letters at once required about half the time necessary 
 to recognize five or six. With an interval of 0.0048 sec. 
 between the two excitations, the perception of the first 
 was reduced to scarcely a trace of a weak shimmer ; with 
 an interval of 0.0096 sec, letters appeared in the shimmer ; 
 one or two of which could be recognized when the interval 
 increased to 0.0144. The discernment became clearer with 
 
TIME-RELATIONS OF MENTAL PHENOMENA. 369 
 
 an interval of 0.0192 ; at 0.0336 sec. four letters could be 
 well recognized ; and at 0.0432, five letters. 
 
 The method of Baxt does not, however, enable us to fix 
 the absolute value of discernment-time, because it includes 
 as an inextricable factor the amount of time used up in 
 the peripheral nerves. Besides, we have no means of esti- 
 mating to just what stage a psycho-physical process must 
 have advanced, when it becomes impossible for a following 
 strong impression to overwhelm it. 
 
 Two other observers (von Kries and Auerbach) have 
 attempted to measure discernment-time by a method known 
 as the " Bonders' C-method." In the use of this method 
 the subject of the experiment attempts to answer the ques- 
 tion : How long time passes after the occurrence of a stim- 
 ulation before I know the precise nature of the result in 
 consciousness ? by either reacting in a prescribed way, or 
 else by refraining from reacting at all. It was assumed 
 (probably incorrectly) that " will-time " is not involved 
 in the decision to react or not to react. From the whole 
 reaction-time, as involving the answer to the forego- 
 ing question, the simple reaction-time was subtracted ; the 
 remainder was held to be the time involved in discernment. 
 By this method surprisingly small intervals were obtained : 
 for example, for discernment of the direction of light, 
 0.011-0.017 sec; for localization of sound, 0.015-0.077 
 sec. ; for discernment between two colors, 0.012-0.034 
 sec. ; etc. 
 
 The figures just given have been contested, both on 
 account of the method employed and on account of the 
 result obtained. It must be admitted that both method 
 and result can be justified only on the supposition that we 
 are trying to determine how promptly, under the influence 
 of training and habit, one may learn to connect a pre- 
 scribed movement with a particular form of sensuous 
 impression. Under such circumstances the time required 
 
370 PHYSIOLOGICAL PSYCHOLOGY. 
 
 for strictly psycho-physical processes becomes reduced to a 
 minimum, and " discernment " as a conscious process of dis- 
 crimination largely or wholly disappears. 
 
 Still another method has, therefore, been employed for 
 disentangling the elements of this complicated problem. 
 In this method the subject of the experiment is warned 
 when to expect one of two or more colors, but does not 
 know which one to expect ; he is left to his own judgment 
 to determine, and to signal just when the act of discern- 
 ment is completed. The mean discernment-time, as derived 
 from a large number of experiments with two color-sensa- 
 tions, was fixed by this method at from 0.047 to 0.086 sec. 
 
 We may affirm, then, that the average amount of the 
 interval occupied in discernment of a very simple char- 
 acter, under favorable circumstances, is not very different 
 from that given by Donders. It varies, when there is no 
 special designed complication of the conditions, from 0.03 
 sec, or even less, to nearly 0.1 sec. Recent experiments, 
 in the dark and quiet, to find the whole reaction-time, 
 including discernment, for different colors, report the fol- 
 lowing result : for red, 0.153-0.160 sec; for blue, 0.156- 
 0.164 sec; for violet, 0.161-0.168 sec. 
 
 Several Causes that affect Discernment-time. — To discrim- 
 inate the intensities of two sensations is a relatively lengthy 
 process. For example, when requested to react upon the 
 stronger only of two stimulations of the sense of touch, we 
 require more time than to tell where we are touched.y 
 When reaction follows the weaker of two such stimula- 
 tions, the discernmenWime may rise to 0.069 sec. or 0.089 
 sec. In discerning between two simple tones of different 
 pitch, reaction follows the one of higher pitch more 
 promptly. In general, discernment-time diminishes as the 
 pitch of the tone rises ; for very high tones it nearly reaches 
 the limit required for hearing the noise of the electric 
 spark. This is due to the fact that some 15-20 vibratioiis 
 
TIME-EELATIONS OF MENTAL PHENOMENA. 371 
 
 are necessary in order to define the pitch of any tone. To 
 localize a spark by indirect vision requires more time than 
 by direct vision. 
 
 An apparently true and important difference has recently 
 been detected between two equally normal methods of 
 reacting when experimenting for discernment-time. In the 
 first, the attention is concentrated upon receiving the 
 expected sensation, and every tendency " to get the motion 
 ready," as it were, is carefully avoided. In the second 
 method, one does not think of the sensation, but concen- 
 trates the attention upon getting ready to move. The 
 reaction in the extreme " motor " type is much prompter 
 than in the sensory type, — in the proportion of about the 
 following figures : 0.125, 0.137, 0.123 sec, to 0.223, 0.224, 
 0.230 sec. 
 
 Discernment-time increased by Number of Objects. — Every 
 one knows that it takes longer — other things being equal ^ 
 — clearly to apprehend several objects than only one object. 
 In trying to discern one of four colors the time of the 
 corresponding psycho-physical processes is lengthened to as 
 much as ^ or even ^ sec, and more. In apperceiving fig- 
 ures, however, it requires little longer to master three than 
 one, but considerably longer to master four than three. The 
 obvious reason for this is our habit of grasping numbers 
 in periods of three each. Moreover, the discernment-time 
 for the different letters varies somewhat remarkably ; but 
 the " legibility " or comparative accuracy of the quick dis- 
 cernment of the different letters varies still more. 
 
 rinding of " WiU-time." — If we admit the accuracy of 
 the conclusions reached as to simple reaction-time and 
 " discernment-time " so called, it becomes comparatively 
 easy to answer the following question : How long does it 
 take, under different circumstances, to set free a voluntary 
 impulse? The simple reaction-time (i2) — or time required 
 when the nature of the stimulus is known and the mode of 
 
372 PHYSIOLOGICAL PSYCHOLOaY. 
 
 reaction fixed the same for all cases — is first found. The 
 reaction-time required to discern clearly one of two or 
 more impressions, and to announce the fact in some way 
 previously determined upon {Rd'), is then found. Finally, 
 the reaction-time is found for cases where there is involved, 
 also, a choice of one of several ways of reacting, or a choice 
 between reacting and not-reacting (^Rdw'). If Rd-R gives 
 the discernment-time, Rdw-Rd will give "will-time." 
 
 Experimenting in this way, one observer found the mean 
 interval, in the case of ten persons, required for the set- 
 ting-free of definite reaction involving a choice between 
 two possible courses, varied from 0.024 to 0..155 sec. If 
 the choice were one of ten possible courses, — for example, 
 the selection of one of the ten fingers with which to react 
 on receiving the impression corresponding to that finger, — 
 then the will-time reached 0.298-0.448 sec. 
 
 Individual Differences of Will-time. — If the curve of the 
 variations in the time required for choice by different per- 
 sons, under different conditions, be plotted, very inter- 
 esting personal peculiarities manifest themselves. In gen- 
 eral, these peculiarities are increased, as the complexity of 
 the choice rises from one to five places; they are then 
 diminished as the complexity rises to nine or ten places. 
 It thus appears that men differ more in the speed with 
 which they can choose one of two to five different courses, 
 than one of nine or ten different courses. 
 
 A careful survey of the whole field of experiment and 
 statistics shows that it is not possible, as yet, to analyze 
 psycho-physical time into its elements, with a perfect confi- 
 dence in our accuracy. By practice and by arranging all 
 the conditions as favorably as possible, so-called " discern- 
 ment-time " may be reduced almost to zero. That is to say, 
 reaction-time, including what was once " discernment-time " 
 and "will-time," ma^/ be diminished so as to be little or no 
 greater than simple reaction-time. This accords with all 
 
TIME-EBLATIONS OP MENTAL PHENOMENA. 373 
 
 our experience of the rate of speed possible to acquire in 
 all movements of the body in skilled work or in the arts. 
 The violin-player, for example, can learn to execute the 
 complicated, discriminating movements of a trill, at sight, 
 with as great speed as the most simple muscular move- 
 ments excited from the cerebral centres. 
 
 Donders assigned almost precisely the same figures (0.036 
 sec.) to will-time as to discernment-time (0.039). Under 
 comparable circumstances the two elements of psycho- 
 physical time are probably about the same. But there is 
 other evidence to indicate that successive acts of discern- 
 ment may attain a much higher rate of speed than is possi- 
 ble for successive- acts of will. 
 
 Correspondence of Time Subjective and Objective. — How 
 accurately does the estimated time-rate of consciousness 
 correspond to the movement of time as measured by objec- 
 tive standards ? Some general impressions on this point 
 are derived from all our experience in psychometrical 
 experiments. Thus one observer notes that, in a series of 
 89 reactions from eye to foot which actually had a mean 
 interval of 0.184 sec, the reaction was felt to be " too 
 slow " when it reached 0.199 sec, and pronounced " very 
 good " when it fell below 0.178 sec. The mind therefore 
 appreciated the actual interval to within about 0.01 sec. 
 
 There is abundant proof, however, that the speed and 
 duration of our impressions, as estimated in consciousness, 
 do not precisely correspond to the series of stimulations 
 which act upon the organ of sense. By an ingenious de- 
 vice Wundt showed that one rarely hears a sound, for 
 example, without some "positive" (placing it later than 
 the real time) or " negative " (placing it earlier than the 
 real time) displacement of it. When expecting a sound, 
 and attempting to locate it in connection with a movement 
 measured by the eye, the displacement is most frequently 
 
374 PHYSIOLOGICAL PSYCHOLOGY. 
 
 " negative " ; that is, one believes one hears the sound too 
 soon in the scale of visual indications. 
 
 Most Favorable Interval for Discernment. — The degree of 
 accuracy attainable in estimating the length of intervals 
 varies greatly for intervals of different lengths. There is 
 one interval most favorable of all for exact estimation. 
 Under ordinary circumstances our sensitiveness to minute 
 differences of time is greatest at about 0.7-0.8 sec. (more 
 precisely 0.71-0.755 sec). This sensitiveness to minute 
 differences of time is found by most observers to fall off 
 quickly for intervals less than the most favorable, and 
 more slowly for intervals greater than it ; and this, with 
 the result that times longer than the most favorable inter- 
 val are estimated too small ; those shorter, too large. 
 
 On applying the same method of experimenting to con- 
 siderably longer intervals, very strange and somewhat con- 
 flicting results are obtained. One observer finds that the 
 maxima of accuracy occur at the intervals which are mul- 
 tiples of the most favorable interval by some odd number ; 
 and the minima of accuracy at intervals which are multi- 
 ples of the most favorable interval by some even number, 
 — up to about 11.4 sec. Another observer finds that, with 
 0.7 sec. taken as the most favorable interval, the successive 
 points of greatest accuracy are 2.8, 7.8, 9.3, 12, and 14.2 
 sec. ; while those of least accuracy are 5, 8.5, 10, 12.8, and 
 15 sec. The former of these two authorities lays down the 
 rule that minute intervals up to 0.7 sec. are exaggerated, 
 those from this point to 5 sec. underestimated, and larger 
 intervals exaggerated again. But another authority states 
 that times shorter than 2 sec. are overestimated, and fhose 
 longer than 4 sec. underestimated. It is obvious that indi- 
 vidual peculiarities are likely to be of much influence in 
 all such estimates ; and that the entire subject requires 
 further experiment with a view to place it upon a basis of 
 broader induction, 
 
TIME-EBLATIONS OF MENTAL PHENOMENA. 375 
 
 Studies in Rhythm. — The time-rate of the most rapid 
 and accurate discernment and volition may be profitably 
 studied by determining the degree of accuracy with which 
 successive sensations (like the clicks of clock-work), having 
 a constant interval, can be counted. In this way it has 
 been found that the most successful estimates cannot be 
 perfectly sure of more than 2-4 clicks, when the interval 
 between them is as brief as 0.0895 sec. ; and, if this inter- 
 val is diminished to 0.0523 sec, they cannot be sure of 
 more than two clicks. The most successful estimates of 
 45 rapidly succeeding sensations were 42 and 43, with the 
 longer interval ; with the shorter interval, the best estimate 
 was 32, the worst 17. 
 
 It appears then that, if the interval between the sensa- 
 tions counted is less than the shortest reaction-time be- 
 tween ear and tongue, some of the sensations drop out of 
 consciousness. It. appears also that the rate of sensations 
 may far exceed the rate of motor impulses. We can hear 
 much faster than we can count. And, in general, the time- 
 sense for series of mental phenomena is different for differ- 
 ent classes of these phenomena. 
 
 Reproduction of Composite Images. — In the discernment 
 of one or more letters, numbers, or geometrical forms, 
 association and the reproduction of mental images are, of 
 course, involved. In fact, no discernment is possible with- 
 out involving these mental processes. It is interesting and 
 valuable, however, to determine how the reaction-time is 
 increased by complicating these processes. This may easily 
 be done by fixing the mean reaction-time, including these 
 processes, and then subtracting the mean simple reaction- 
 time. Thus the time required for apprehending single 
 words has been fixed at from about 0.057 to about 0.177, 
 for different persons. 
 
 All our familiar experiences concerning the differences 
 among different individuals, with respect to promptness 
 
376 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of apprehension and memory, concerning the conditions 
 which lengthen or shorten these processes, etc., receive 
 illustration from this field of experiment. The following 
 numbers (which must be taken as approximate only) prove 
 this statement. 
 
 Sec. 
 
 Time needed to translate images into one's vernacular . 0.477-0.545 
 Time needed to translate images into a foreign language 0.649-0.694 
 Time needed to translate short familiar words .... 0.199-0.258 
 Time needed to translate long and less frequent words . 0.309-0.388 
 Time needed to remember a thing very well known . . 0.400-0.800 
 Time needed to remember with choice of several answers 0.222-1.042 
 Time needed to form simple and familiar associations . . 0.368^0.507 
 Time needed to form odd and unexpected associations . 1.132-1.662 
 Time needed to form a simple and familiar judgment . 0.180-1.127 
 
 Time needed to define a familiar word 0.391-2.023 
 
 Time needed to multiply two numbers 0,049-0.098 
 
 [In multiplying two numbers we, of course, call upon 
 an extremely familiar and well-fixed association gained 
 when we learned the multiplication table. In re-forming 
 this association, however, the order of the numbers is not 
 a matter of perfect indifference; reaction, as a rule, is 
 quicker and more correct when the smaller number pre- 
 cedes. It is also somewhat quicker, in most cases, when 
 the completion of the process is announced by touching a 
 key with the finger than when it is announced by uttering a 
 word — "reproduction with finger," instead of "reproduc- 
 tion with lip."] 
 
 The really astonishing thing about these statistics is the 
 very great difference which exists in different cases with 
 respect to versatility of memory and promptness of decis- 
 ion. This fact appears when, for example, the subject of 
 the experiment is called upon to name some work of a 
 well-known writer, some city in a particular country men- 
 tioned to him, etc. ("time needed to remember with choice 
 of several answers "). The same thing is illustrated when 
 
TIME-RELATIONS 01' MENTAL PHENOMENA. 377 
 
 he judges the length of a line shown to him, or defines 
 "fame" as "a form of the ascription of praise," etc. 
 
 The Circuit of Consciousness. — Our estimates of the time- 
 rate and duration of particular factors in the general field 
 of consciousness depends, in part, upon the relation which 
 they sustain to other factors in the same field, or even in 
 the field which has just faded, as it were, out of conscious- 
 ness. Thus the general principle of the relativity of every 
 state and of every factor of every complex state, of conscious- 
 ness, is amply illustrated by experiments in psychometry. 
 
 For example, when words are connected into sentences, 
 it requires only about one-half as much time for each word 
 (as 0.138 sec. to 0.484 sec), to name them, as would be 
 required for the same words when not thus connected. 
 Single letters, too, can be named more rapidly when sev- 
 eral of them are in the field of consciousness together. In 
 nearly all cases as many as three letters, and in many cases 
 even four or five, lend support, as it were, to each other. It 
 has been calculated that the second letter in view shortens 
 the time for apperception of the one in the " clear-spot " of 
 vision by about ^ sec. ; even the fifth letter affects favor- 
 ably the discernment of every other in the circuit of con- 
 sciousness, to about the amount of ^m sec. 
 
 Another application of the same principle arises in the 
 determination of the number of impressions which can be 
 comprised in one " field of consciousness." The old-fash- 
 ioned and a priori theory of the soul decided that, on 
 account of the soul's unity, it could have before it only 
 one object at the same instant of time. Strangely enough, 
 the most advanced school of associational theorists in Eng- 
 land has maintained the same view. But experiment con- 
 firms the impression of the plain man's self-consciousness. 
 He believes that he can attend — though with varying 
 degrees of attentive perception — to several objects at the 
 same time ; and he can do what he believes he can. 
 
378 PHYSIOLOGICAL PSYCHOLOGY. 
 
 To test this matter, let us suppose that the stroke of a 
 pendulum, heard at regular intervals, is employed as the 
 stimulus. Two series of successive strokes, separated by 
 an interval, are compared without counting. How many 
 impressions can such series contain and the comparison 
 attain a high degree, or even a perfection, of accuracy? 
 With the most favorable interval (0.2-0.3 sec.) between 
 the successive impressions, and with strict attention, most 
 persons can attain a high degree of accuracy with 10 or 
 12 impressions ; some can hold in one field of conscious- 
 ness no fewer than 15 or 16 impressions. If rhythmic 
 grouping is permitted, the groups become as one percep- 
 tion, and 35 to 40 impressions are apprehensible in one 
 field of consciousness. It is thought possible by some 
 experimenters to apprehend a larger even number than 
 odd number in the circuit of consciousness. 
 
 Or, again, let us try to determine the "grasp of con- 
 sciousness " by showing from 4 to 15 short perpendicular 
 lines for 0.01 sec, and then testing the accuracy of the 
 perception possible of these groups of objects. By experi- 
 menting in this way it has been ascertained that most per- 
 sons are infallible when groups containing not more than 
 4-6 lines are displayed. 
 
 Effect of Practice, Attention, and Fatigue. — Every one 
 knows that practice and attention increase, and fatigue 
 diminishes, the speed and the accuracy of our mental proc- 
 esses. Psychometry endeavors exactly to define the amount 
 of these influences on reaction-time. Thus it has been 
 found that practice reduces about one-third (0.080 sec. to 
 0.050 ; 0.098 sec. to 0.062, etc.) the " will-time " necessary 
 for choice between two motions. By practice with five 
 possible choices, the reaction-time fell, in one case, from 
 0.239 sec. to 0.083; in another case, where one of ten 
 choices was required, the time was diminished from 0.358 
 to 0.094. The effect of practice on discernment-time is 
 
TIME-RELATIONS OF MENTAL PHENOMENA. 379 
 
 different. It may fall from as much as 0.117 sec. to as 
 little as 0.021 sec. Discernment-time continues to decrease 
 by practice after all diminution of simple reaction-time 
 has ceased. Association-time is probably sensitive to prac- 
 tice in far less degree. 
 
 The effect of attention on reaction-time, and so on the 
 psycho-physical processes involved, shows itself in a marked 
 way when attention is disturbed. Thus the mean reaction- 
 time, for a weak impression of sound, was increased by a 
 disturbing noise from 0.189 to 0.313 sec. ; and, for the sight 
 of an electric spark, from 0.222 to 0.300 sec. 
 
 Fatigue and all depletion of nervous vigor tends to 
 lengthen the period of reaction-time. The enervation of a 
 hot summer's day, of a sleepless night, or following on bad 
 news, has the same effect. In cases of idiocy, imbecility, 
 and epilepsy, the length of psycho-physical time is in- 
 creased. The simple reaction-time of a decrepit man of 
 seventy-seven, taken from the almshouse, was found at 
 first to be 0.9952 sec. ; practice reduced it greatly, but not 
 below 0.1866 sec. The appearance of sprightliness does 
 not, however, always signify a speedy and accurate per- 
 formance of the psycho-physical processes involved in reac- 
 tion. Of two young men, Exner found one with a lively 
 temperament to have a mean reaction-time of 0.3311 sec. ; 
 while the other, who had not a lively temperament, showed 
 a reaction-time of only 0.1337. 
 
 Effect of Drugs, Hypnotism, etc. — The nature of the 
 influence which alcohol has upon the speed of the psycho- 
 physical processes is not quite clearly proved by experi- 
 ment. Doubtless it differs greatly in dependence upon 
 individual peculiarities, the quantity taken, and other more 
 obscure conditions. Some observers find that a small quan- 
 tity of wine slowly drunk decreases reaction-time ; but a 
 larger quantity, in several cases, increased it from 0.1904 
 to 0.2969 sec, although the subject of the experiment con- 
 
380 PHYSIOLOGICAL PSYCHOLOGY. 
 
 sidered himself to be reacting with unusual promptness. A 
 long series of recent experiments (some 8000 in all), to 
 determine the effects of alcohol, ended in disappointment. 
 They appear simply to have showed that this drug pro- 
 duces changes in reaction-time; but no constant effect 
 dependent upon either quantity or kind could be detected. 
 
 Coffee, as a rule, decreases reaction-time, beginning its 
 effect some 20-25 minutes after being taken and continuing 
 it for about two hours. Experiment thus appears to con- 
 firm the influence of this drink to assist a certain speed 
 and accuracy of psycho-physical processes; doubtless (it 
 should be added) in those cases only where it is moderately 
 used and produces no disturbance of digestion. Subcuta- 
 neous injections of morphine delay reaction-time ; but the 
 effect soon disappears unless the injection is repeated. 
 
 In summing up the results of experiment we should be 
 warned against imagining that researches in psychometry 
 explain the origin or nature of our ideas of time and of 
 time-relations. To describe the rates and orders and dura- 
 tions of the successive ideas is a very different thing from 
 explaining the idea of succession. Upon the origin and 
 nature of this idea the so-called science of psychometry 
 throws no light. Neither has it as yet succeeded in estab- 
 lishing new principles of peculiar value in psychology. 
 We shall refer to some other of its more important rela- 
 tions when we come to speak of the psycho-physical char- 
 acter of attention and " acts of will " so-called. 
 
 One important thing to notice is that the different ele- 
 ments of psycho-physical time — such as discernment-time, 
 and will-time, and time necessary to come to consciousness, 
 as it were — ordinarily overlap and blend with each other. 
 But practice and attention tend in the direction of reduc- 
 ing them all to zero ; so that the formerly complicated 
 case comes, under these influences, to assume the psycho- 
 physical character and duration of a case of simple reaction- 
 time. 
 
CHAPTER XVI. 
 
 FEELINGS, EMOTIONS, AND MOVEMENTS. 
 
 Since the beginning of serious attempts to establish, a 
 scientific psychology the consideration of the feelings and 
 emotions has been unsatisfactory. The reasons for this 
 fact, however, are partly unavoidable, for they lie in the 
 nature of the case. 
 
 GENERAL THEORY OF THE FEELINGS. 
 
 Regarded from the introspective point of view, the phe- 
 nomena of feeling are peculiarly obscure, indefinite, vari- 
 able, and multiform. The very effort to subject them to 
 a self-conscious examination immediately changes their 
 entire character or wholly dissipates them. Their physi- 
 ological conditions, also, are laid in equally obscure, rap- 
 idly and infinitely varied changes of the central organs 
 of the nervous system. These conditions cannot be sub- 
 jected to direct observation, or even — without great dif- 
 ficulty — to the more indirect methods of experimental 
 analysis. 
 
 It is not surprising, then, to find that physiological psy- 
 chology has little beyond certain more or less well-founded 
 conjectures to offer respecting this department of investi- 
 gation. 
 
 Essential Nature of Feeling. — Several fundamentally dif- 
 ferent views exist as to the essential nature of the mental 
 phenomena for which we use the term " feeling." Indeed, 
 the term itself is, as a rule, vaguely employed. Sometimes 
 it means the sensation of pressure or of teniperature local- 
 SSI 
 
382 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ized in the skin (e.g. I feel the smoothness or coolness of 
 the marble) ; sometimes it refers to sensation-complexes 
 of an obscure and mixed origin and character (I feel tired, 
 or well, or ill at ease) ; sometimes it designates what has 
 been called more definitely, but uncouthly, " the pleasure- 
 pain series " ; sometimes it is employed for states of ses- 
 thetical or religious contemplation; and sometimes for 
 that unique recognition which the mind gives to moral 
 obligation (the feeling designated by the words "I ought"), 
 etc. 
 
 In general, three theories must be recognized as to the 
 essential Nature of Feeling. One of these emphasizes the 
 underived and primary character of such states as merit 
 this name. It claims that we can no more define what it 
 is " to feel " than what it is to know. Indeed, it would 
 seem to be, of the two, more unreasonable to require a 
 definition of feeling. For to define is to use terms of 
 ideation ; but feeling, as such, is not ideation at all, and 
 therefore its character cannot be stated in terms of idea- 
 tion. The other two theories agree in regarding feeling as 
 a secondary or derived activity of the mind. But one 
 theory is physiological, and the other may be said to be 
 "ideational," in its method of explanation. We shall pass 
 these two theories briefly in review before returning to the 
 first-mentioned and — as we believe — true theory of the 
 essential nature of feeling. 
 
 Physiological Theories of Feeling. — These theories hold 
 that those mental states which we call ^'■feelings " are, 
 essentially considered, a peculiar consciousness of the condi- 
 tion of the nervous system. That many states of feeling are 
 directly dependent upon conditions which originate in the 
 activities of the nervous elements ; and that some nervous 
 conditions are followed by painful, and others by pleasur- 
 able, feeling, there can be no doubt. It is very difficult, 
 however, to bring all of the physiological conditions of 
 
PEELINGS, EMOTIONS, AND MOVEMENTS. 383 
 
 feeling under any verifiable laws. And even, should we 
 succeed in doing this, we should not define or express the 
 essential nature of feeling. 
 
 Concord between Stimulus and Vital Activity. — The phil- 
 osopher Lotze distinguished the feelings, as mental condi- 
 tions involving pain or pleasure, from sensations as indif- 
 ferent elements of our perception of things. Pleasurable 
 feelings arise from coincidence, and painful from opposi- 
 tion, between the effects of the stimulus and any of those 
 conditions to which the regular expression of the bodily or 
 spiritual life is attached. "Feeling is, in general," says 
 Lotze, "only the measure of the partial and momentary 
 concord between the effect of the stimulus and the con- 
 ditions of vital activity." It is impossible, however, to 
 vindicate this principle as applying to all cases. The 
 disagreeable character of the slightly bitter tonic, or the 
 pleasurable sweetness of the deadly acetate of lead, cannot 
 be declared, on scientific grounds, to signify even " a par- 
 tial and momentary " discord or concord between stimulus 
 and vital activity. Lotze, moreover, was far too keen a 
 psychologist to suppose that, in laying down this principle, 
 he was explaining feeling as a secondary form of conscious- 
 ness. On the contrary, he himself expressly vindicated its 
 right to be regarded as primitive. 
 
 Belation of Feeling to Quantity of Sensation, — It is a rule 
 of wide application, that sufficient intensities of all forms 
 of stimuli are productive of painful feeling. The same 
 intensities are also, in general, antagonistic to the vital 
 conditions of the organism. On the other hand, all inten- 
 sities of some sensations of smell, taste, and hearing, are 
 disagreeable to most persons. Nor can the disagreeable 
 feelings of the higher intellectual, ethical, and sesthetical 
 order be resolved into the consciousness of more stimula- 
 tion of the nervous system than is good for its vital inter- 
 ests. The excessive and injurious stimulation of this 
 
384 PHYSIOLOGICAL PSYCHOLOGY. 
 
 system may be accompanied by a large amount of positive 
 pleasure. Of course, in all these cases, attention, associa- 
 tion, habit, and voluntary control, have much to do with 
 determining the subjective state occasioned by the appli- 
 cation of the various degrees of stimulus. 
 
 The dependence of pleasurable or painful quality (or 
 tone) of feeling upon the amount of nervous excitement 
 produced by the stimulus is most apparent in the case of 
 the sensations. Sensations of moderate intfensity are 
 usually pleasurable ; by " moderate " intensity we can 
 scarcely fix anything more definitely than the actual 
 point at which the minimum of painful feeling begins to 
 follow an increase in stimulation. From this point the 
 feeling of pain rises in intensity, as the intensity of the 
 stimulus increases. But the curves which measure the in- 
 crease of feeling and the increase of sensation do not cor- 
 respond. According to Wundt, the maximum point of 
 pleasure belonging to any sensation is the point where the 
 sensation ceases to increase in simple proportion to the 
 Strength of the stimulus. 
 
 The view which regards painful feeling as the conscious- 
 ness, so to speak, of the over-stimulation of the nervous 
 organism, is compelled to deny that any sensation can be 
 painful, absolutely, or irrespective of its intensity. Such 
 denial contradicts tolerably obvious facts. As has been 
 said, all degrees of some sensations are disagreeable to 
 most persons. To point to the fact that some substances 
 whose faint odor (as musk), or taste in moderate degree 
 (as the bitter of hops) is agreeable, become intensely dis- 
 agreeable when they excite more intense sensations, is not 
 conclusive. The faint sensations are not the same sensa- 
 tions; their quality changes on increase of stimulus as 
 truly as their quantity. 
 
 View of Bain and Grant Allen. — The English psycholo- 
 gist Bain has laid down the principle : " States of pleasure 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 385 
 
 are connected with an increase, and states of pain with an 
 abatement, of some, or all, of the vital functions." This 
 principle has been criticised as "too vague" by Grant 
 Allen, who would substitute for it the following : " Pleas- 
 ure is the concomitant of the healthy action of any or all 
 of the organs or members supplied with afferent cerebro- 
 spinal nerves, to an extent not exceeding the ordinary 
 powers of reparation possessed by the system." But this 
 statement (which, in principle, is similar to that of Lotze) 
 seems to us much more vague than that which it is in- 
 tended to replace. For what satisfactory standard, besides 
 the cessation to produce the feeling of pleasure, shall 
 measure the limit referred to in the words — "to an extent 
 not exceeding the ordinary powers of reparation possessed 
 by the system." Surely it requires a large credulity to 
 believe that the powers of repair are exceeded whenever a 
 robust man experiences a slightly disagreeable taste, or 
 an unpleasant contrast of colors, or a bit of a twinge of 
 conscience. 
 
 The Herbartian Theory of Feeling. — In strong contrast to 
 all physiological theories stands the view which regards 
 the feelings as secondary conditions of mind, dependent on 
 the relations of the ideas. This view makes a sharp dis- 
 tinction between sensation and feeling. It classifies bodily 
 pain as sensation and not as feeling. Hunger, thirst, weari- 
 ness, shivering, etc., are sensations and not feelings. But 
 sympathy, love, gratitude, reverence, admiration, etc., are 
 feelings ; since their content is of a mental rather than a 
 physical order. The author of this view was the German 
 philosopher, Herbart. 
 
 Feeling is, therefore, to be defined (so this school of 
 psychologists hold) as the immediate consciousness of the 
 rising and falling of one's power of ideating, as it were. 
 It is not a primitive activity of mind ; it is secondary and 
 results from the reciprocal action of the ideas. If the 
 
386 PHYSIOLOGICAL PSYCHOLOG-T. 
 
 ideas "inhibit" each other, the becoming conscious of the 
 check or inhibition is unpleasant ; if they " further " each 
 other and readily fuse, the conscious feeling of this fact is 
 pleasant. As the most prominent recent representative of 
 this view teaches (namely, Volkmann von Volkmar) : 
 " Feeling is the immediate consciousness of the process of 
 ideation itself as distinguished from the consciousness of 
 this or that idea," and it is conditioned upon some resist- 
 ance being offered to the process. The condition of the 
 origin of a feeling is, then, the existence of two simulta- 
 neous opposed ideas ; this co-existence occasions a state of 
 " tension," and this state gives way as one idea triumphs 
 over another. 
 
 The theory just described is interesting ; it undoubtedly 
 accounts for the conditions under which a large number 
 of our pleasurable or painful feelings originate, — especially 
 those of the higher intellectual and sesthetical order. But 
 to refuse to speak of pleasurable and painful sensations 
 and emotions as belonging to the realm of "feeling" at 
 all, because they depend upon a physical basis, is to restrict 
 the term unwarrantably. The Herbartian view, as a com- 
 plete account of the nature of feeling, is disproved by all 
 the considerations brought forward by the various forms 
 of the physiological theories. 
 
 Feeling an Original and TJnderived Form of Consciousness. 
 — We return then to our former declaration. Feeling is 
 a primitive and underived mode of the operation of conscious 
 mind. It can neither be defined by, nor deduced from, 
 processes of sensation or ideation. To know what it is to 
 feel, the highest intelligence would not of itself be capable. 
 Such knowledge comes only from having felt. And feeling 
 accompanies all mental experience, both that of sensation 
 and that of the higher intellectual processes. Discrimina- 
 tion — which is an intellectual process — is, of course, 
 involved in all recognition of the distinctions in quality 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 387 
 
 of the different feelings, and of the characteristic tone of 
 pleasure or pain which they all (or, in case we admit some 
 " neutral " feelings, nearly all) possess. But the discrimi- 
 nation of quality involves the existence of quality to be 
 discriminated. The feeling of pleasure we have in smelling 
 a sweet rose, or in tasting a favorite dish, actually differs 
 in quality^ as well as in amount of pleasure characterizing 
 its place in the so-called " pleasure-pain series," from the 
 pleasure of doing a good deed ; otherwise it could not be 
 known as different. 
 
 Physical Ba^s of Feeling. — That many of our feelings 
 depend immediately upon the condition of the nervous 
 elements is beyond doubt. But are there special nervous 
 elements — whether end-organs, nerve-fibres, or portions 
 of' the central organs — which must be excited in order to 
 give rise to painful feelings ? What is the peculiar nature 
 of the excitation upon which the different feelings depend 
 for their differences of quality ? What is the characteristic 
 change in the excitation that gives rise to the two kinds of 
 "tone" which the feelings possess, — to pleasure and to 
 pain? Physiological psychology can answer none of these 
 questions with much confidence. 
 
 The prevalent view, hitherto, has probably been that the 
 same nervous apparatus throughout, which on moderate 
 excitement produces sensations of pressure or temperature, 
 produces feelings of pain when irritated with increased 
 intensity. This view would apparently be compelled to 
 hold that muscular sensations have the same physical 
 apparatus as feelings of muscular weariness or exhaustion ; 
 and that both hunger and cardialgia arise from excitation 
 of the same nerves of the stomach. 
 
 Certain reasons exist, however, for doubting the complete 
 identity of the nervous apparatus of painful and pleasura- 
 ble feeling with that of the sensations with which such feel- 
 ing is allied. Recent experiments seem to show clearly 
 
388 PHYSIOLOGICAL PSYCHOLOGY. 
 
 that the end-organs of pressure, temperature, and painful 
 sensation, are not the same (see p. 237 f .). It is probable also 
 that impulses resulting in pain travel by more or less dis- 
 tinct paths in the spinal cord (see p. 71 f.). In certain cases 
 of disease the sensibility of the skin to pain is lost, while 
 its sensibility to touch is not weakened. The reverse con- 
 dition also sometimes occurs. In some diseased conditions 
 a difference of as much as one or two seconds occurs in the 
 time at which the sensations of contact and the feelings of 
 pain (caused — for example — by the prick of a needle) 
 arise in the mind. The painful feeling of being blinded, 
 when the stimulus of light is too intense, seems to arise 
 from simultaneous irritation of the trigeminus, rather than 
 from the same irritation of the optic nerve which results in 
 sensations of light. 
 
 The tendency of recent evidence seems to be, then, 
 toward a somewhat complete separation of the nervous 
 mechanism, whose excitement produces feelings of sen- 
 suous pain or pleasure, from that whose excitement results 
 in the production of the sensations themselves. This evi- 
 dence favors, so far as physiological theory can, the view 
 of those psychologists who regard feeling as a primitive 
 and underived form of conscious life. 
 
 As to the peculiar nature of the physiological action — 
 whether in the end-organs, the nerve-tracts, or the nerve- 
 centres — which results in conscious states of feeling, we 
 have no information. Indeed, the facts just referred to 
 are very difficult to reconcile with the rule which certainly 
 covers a large number of cases, — namely, that increased 
 intensity of stimulus, beyond a certain point, results in the 
 production of painful sensations. This rule itself is un- 
 doubtedly due to inter-cerebral relations whose physical and 
 physiological description science cannot give at present. 
 
 Classification of the Feelings. — It may be doubted whether 
 the feelings, as such and strictly speaking, admit of classi- 
 
PEELINGS, EMOTIONS, AND MOVEMENTS. 389 
 
 fication. We have already shown that, in order to be sub- 
 jected to the process of discrimination in self-consciousness, 
 feelings must actually have specific or individual differ- 
 ences in consciousness. But in the attempt to use these 
 differences, of which we are conscious, for purposes of 
 classification, we are prevented in somewhat the same way 
 as that in which we are prevented when attempting the 
 classification of sensations of smell. The vague, varied, 
 and shifting character of the phenomena, and their com- 
 plete fusion with other factors of the mental life, seem to 
 render their scientific study exceedingly difficult. 
 
 It is certain that no principle of classification can be . 
 suggested which undeniably applies to all the phenomena 
 of feeling as such. If we divide the feelings into pleas- 
 urable and painful, we raise the question whether there 
 are neutral or indifferent feelings. And if this question 
 is settled negatively, and the completeness of such a two- 
 fold division is admitted, the division itself is of little 
 value, because it does not serve to describe the variations 
 among the feelings which belong to either group of the 
 two in this " pleasure-pain series." Classifications resting 
 upon anatomical and physiological differences are not, in 
 fact, classifications of the feelings. The same thing is true 
 of all divisions suggested as arising out of the relations in 
 which the different feelings stand to the train of ideas. 
 
 Moreover, the different kinds of feeling shade into each 
 other by almost imperceptible degrees. For example, the 
 sensuous feelings cannot well be separated from the aesthet- 
 ical, in such cases as the perception of the harmony of a 
 musical chord, or of two adjacent colored surfaces. Even 
 the feelings which we call moral are usually so combined 
 with feelings having an obvious bodily basis and origin — 
 especially when the resulting states of consciousness attain 
 the strength of emotions — that a strict separation of the 
 two becomes impossible. Love, for example, ordinarily 
 
390 PHYSIOLOGICAL PSYCHOLOGY. 
 
 involves elements of both a more purely sensuous and a 
 more purely sesthetical and ethical sort. 
 
 Classes of Feelings. — It would seem then that we must 
 be content to classify the feelings, not as such, but as de- 
 pendent upon their more prominent connection with other 
 classes of the mental activities. Even after adopting this 
 principle of indirect classification, we find that the results 
 are somewhat indefinite and unsatisfactory. 
 
 It follows that neither the "physiological" nor the "idea- 
 tional " theory of feeling can furnish a sufficiently broad 
 principle of division. This statement is true of Grant 
 , Allen's classification into (1) pleasures and pains of sensa- 
 tion and (2) so-called sesthetical feelings, — according as 
 the activity of the end-organs in them is, or is not, " directly 
 connected with life-serving function." It is equally true 
 of the division, jjroposed by some followers of Herbart, 
 into (1) such feelings as are dependent upon the form of 
 the course of ideas, and (2) such as are conditioned by the 
 content of the ideas. 
 
 The following division into four classes, according to 
 the " natural organic variety " in the activities of the mind 
 and the characteristic kinds and shades of feeling which 
 accompany them, is as convenient and complete as any. 
 Thus we derive (1) the sensuous feelings, or such as de- 
 pend on the different qualities of the sensations of the 
 special senses and of common feeling ; (2) the cesthetieal 
 feelings, or those agreeable and disagreeable forms of con- 
 sciousness which correspond to the mental images of per- 
 ception and imagination, regarded as beautiful or not (the 
 varieties of the feeling for beauty and its opposite) ; (3) 
 the intellectual feelings, or those which correspond to the 
 theoretic interests called out by the higher forms of think- 
 ing ; (4) the moral feelings, or those which correspond to 
 the relations of desire and will. 
 
 The development of the elementary feelings gives rise 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 391 
 
 to a great variety of complex and mixed forms. So-called 
 " higher feelings," or " feelings of feelings," unfold them- 
 selves ; these are dependent upon the complex relations of 
 society as organized in its existing forms. 
 
 In general, the different feelings are differently charac- 
 terized by variations in content, rhythm, strength, and 
 " tone " of pleasure or pain. 
 
 The Content of Feelings. — Some psychologists have 
 denied that different feelings are distinguishable at all as 
 respects their content. In other words, they hold that 
 all feelings are to be resolved into a mere quantity (more 
 or less) of pain or pleasure ; that the " pleasure-pain series " 
 is the entire characteristic of feeling, and that different feel- 
 ings have their place in this series, as different amounts 
 of the same quality of mental states. But such a view is 
 plainly contradictory of our clearest self-consciousness, and 
 renders all scientific description of the phenomena of feeling 
 impossible. It is also virtually denied by all the language 
 of feeling. We all know that, and talk as though, the feel- 
 ing excited — for example — by a minor chord differs char- 
 acteristically from that excited by a major ; the feeling of 
 a sensation of dark gray from that of a sensation of bright 
 red ; of avarice from patriotism ; of anger from moral self- 
 approbation. 
 
 The fact that those differences in quality which the feel- 
 ings undoubtedly have are dependent upon differences in 
 the conditions of the bodily organism, or upon the relations 
 of the ideas in the mental train, does not abolish, but in 
 part explains, the characteristic differences, in content, of 
 the feelings themselves. 
 
 The Bhythm of Feelings. — Like all other mental phenom- 
 ena, the feelings occur in time-form. The movement in 
 the mental life is marked by rhythm or periodicity. This 
 movement is determined rhythmically by changes occur- 
 ring in the conditions of the nervous system or in the train 
 
392 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of ideas. Sometimes the feeling seems to pass back and 
 forth, by the zero-point in the "pleasure-pain series," be- 
 tween a slightly pronounced tone of pleasure and a slightly 
 pronounced tone of pain. No very painful or very pleas- 
 ant feelings are felt as a steady tension of body and mind. 
 
 Strength of Feelings. — Different states of the same kind 
 of feeling, and different kinds of feelings, are unlike with 
 respect to the amount of consciousness which they appro- 
 priate or absorb, as it were. The strength of feelings 
 often undergoes a series of rhythmical changes. This is 
 one proof that the condition of the end-organs and central 
 organs of the nervous system determines the strength of 
 feeling. But the course of the ideas is also of influence 
 upon changes in strength. As the sensations or ideas 
 become more clear or vivid, the feelings attached to them 
 are likely to increase; as they become more obscure and 
 feeble, the attached feelings die away in consciousness. 
 
 " Tone " of Feeling. — Nearly all feelings are — it is 
 admitted by all observers — to be described as either agree- 
 able or disagreeable. They can therefore be arranged, in 
 accordance with their characteristic agreeable or disagree- 
 able "tone," in a so-called "pleasure-pain series," as more 
 or less on one side or the other of an indifference-point, or 
 zero-point, in the scale. Whether there exist states of 
 feeling that are situated at this zero-point — and, there- 
 fore, entitled to be called " neutral," — has been much dis- 
 puted. Neutral or indifferent feelings were admitted by 
 Reid, but denied by Hamilton. Recently in England a con- 
 troversy has been carried on between Bain and others on 
 this subject, — the former claiming, and the latter denying, 
 that such feelings exist. Wundt attempts to argue for 
 their existence in a somewhat a priori manner. Since we 
 can plot the " pleasure-pain series " in a curve, part of 
 which lies below, or on the pain-side, and part above, or on 
 the pleasure-side, of the neutral line, this curve must cross 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 393 
 
 the line at some point in its course. In other words, it is 
 argued that one cannot admit that painful feelings shade 
 toward pleasurable feelings, by less and less degrees of pain, 
 and pleasurable feelings shatle away from the least observ- 
 ably painful, by greater and greater degrees of pleasure, 
 without admitting also that neutral feelings exist. The 
 reply to such an argument is as follows : The actual rela- 
 tions of the qualities and quantities of states of conscious- 
 ness cannot be accurately represented by the relations of 
 the parts of material lines. The question, whether feel- 
 ings exist which have not the slightest tone of either pleas- 
 ure or pain can be answered only by a direct appeal to 
 consciousness. This appeal we believe results in a nega- 
 tive answer. 
 
 Sensuous Feelings or Feelings of Sensation, — There are 
 some feelings which are so connected and even fused with 
 the sensations as to derive from the latter their name. 
 According to the physiologist Strieker, information derived 
 from the peripheral nerves consists of either sensations or 
 feelings. But both physiologically and psychologically con- 
 sidered the two are different. In general, the stimulus 
 must affect the end-organs of sense in order to give rise to 
 a sensation ; and, as we have already seen, sensations are 
 built as factors, or elements, into the perceptions of exter- 
 nal things. The physiologixial apparatus of feeling, even 
 of the bodily sort, is probably to a considerable extent 
 different from that of sensation. It is certain that the 
 feelings have a peculiar self-reference, and a characteristic 
 tone of pleasure or pain. 
 
 The question has been raised whether every sensation 
 has some feeling, either agreeable or disagreeable, con- 
 nected or fused with it in consciousness. This question 
 must be* carefully distinguished from the question pre- 
 viously raised ; namely, as to whether every feeling 
 belongs, or not, in the pleasure-pain series. We do not 
 
894 PHtYSrOLOGICAL PSYCSOLOGY. 
 
 think it accords witli the facts to declare that every sen- 
 sation has some feeling. But that multitudes of our sen- 
 sations are characteristically agreeable or disagreeable does 
 not admit of doubt. In the case of the "geometrical 
 senses " the feelings of pleasure or pain, which are fused 
 with the sensations, are localized as the sensations them- 
 selves are localized. Indeed, we may speak of the complex 
 object of self-consciousness as a painful (or agreeable) sen- 
 sation, or as a painful (or agreeable) feeling. The burning 
 coal, or the prick of a needle, is described as either a painful 
 sensation, or a painful feeling, in the finger, — according as 
 we wish to lay emphasis on the subjective side of the 
 suffering, or on the objective side of the experience, as 
 hodily suffering. 
 
 Character of "Common Feeling." — At all times in our 
 lives an indefinite variety of nervous impulses is pouring in 
 upon the cerebral centres from every part of the periphery 
 of the body, and from the lower parts of the cerebro-spinal 
 axis. Some of these impulses result from changes in the 
 minute blood-vessels and other capjUaries about the nerve- 
 endings ; some from the condition of the internal organs 
 and the connections of the sympathetic system with the 
 cerebro-spinal. Multitudes of impulses from all the organs 
 of sense, too weak (under the existing conditions of the 
 cerebral centres and of mental occupation) to excite con- 
 sciousness, are constantly meeting and inhibiting or rein- 
 forcing each other in the brain. These all, together, result 
 in a mSlange, or obscure mixture, of bodily feelings, which 
 serves as a sort of basis or background for the more clearly 
 conscious activities of the mental life. 
 
 Sensations in themselves heterogeneous may be brought 
 into a momentary relation by the partial identity of their 
 source of excitation, and of the nervous connections within 
 the central organs. What each of them contributes to the 
 " common- feeling " depends upon this relation ; it also 
 
JBELIlifGg, EMOTIONS, AND MOVEMENTS. 395 
 
 depends upon the relation sustained to the mind's course 
 of ideas, to attention, to association, to habit, etc. For 
 example, an obscure but massive feeling of being ill at 
 ease, may, on our giving attention to it, resolve itself into 
 sensations, with painful feelings attached, that localize 
 themselves in the cramped chest or limbs, the tired organs 
 of sense, the unhealthy digestive apparatus, etc. In con- 
 ditions of .ordinary bodily health our clearly localized sen- 
 sations, perceptions, memory-images, and thoughts, are 
 always accompanied by an undercurrent of "common 
 feeling," — the "feeling of being in the body," as it is 
 sometimes called. 
 
 ^sthetieal Feelings in General. — It has already been 
 said that it is difficult always to distinguish where the 
 sensuous feelings end and those feelings which we may 
 properly call " sesthetical " begin. Characteristic mixtures 
 of feeling — many of them scarcely to be described — seem 
 to be attached inseparably to many of our sensation-com- 
 plexes. The feelings stirred by different musical chords 
 and intervals and instruments might be instanced here. 
 The feeling excited by the same tune, as played upon the 
 violin and then upon the cornet, is not the same, irrespec- 
 tive of any known influence from association. Goethe 
 called attention to the change in spiritual tone which 
 harmonizes with the sensations awakened by looking 
 through glasses of different colors. Few would deny that 
 sober feeling characterizes sensations of black and dark 
 gray, excitement goes with red, cheerfulness with light 
 green, sensuousness with purple, cool quiet with dark, 
 blue, etc. 
 
 The distinctively aesthetical character of the feeling 
 depends, however, upon our freeing ourselves from recog- 
 nition of the sensuous basis. Pains and pleasures of the 
 skin and muscles and interior organs are distinctly unses- 
 thetical ; those of smell and taste less so ; those of hearing 
 
396 PHYSIOLOGICAL PSYCHOLOGY. 
 
 and sight less so still. Genuinely sesthetical feelings arise 
 and develop in connection with perception and imagina- 
 tion ; they therefore imply an intellectual origin and law 
 of progress. They may be said to spring from the combi- 
 nation of the sensuous feelings under the ideal forms of 
 space and time. Hearing is the principal sense for the com- 
 bination of sensuous feelings so as to produce sesthetical 
 feelings under time-form, and sight (the "geometrical 
 sense ") xinder space-form. 
 
 .ffisthetical Feelings of the Ear. — Harmony and rhythm 
 are the two principal forms of the aesthetical feelings of 
 hearing. [The laws under which the sensation-complexes 
 of consonance and dissonance are produced, have already 
 been discussed (see p. 250 f.).J Harmony is colored by the 
 way in which the clangs composing the harmony are held 
 together. In the major chord all the clangs are firmly 
 bound together by the fundamental clang, and a peculiar 
 agreeable feeling of satisfaction is the result. In the 
 minor chord the coincident overtone performs the same 
 office less obviously, and the result is an sesthetical feeling 
 tinged with dissatisfaction, or longing. Great intensity 
 of the former kind of sensation-complexes may involve the 
 pain of over-excitement ; of the latter, the pain of unrest. 
 
 In musical time the periodicity of the acoustic sensation- 
 complexes, of itself, stirs the sesthetical feelings. These 
 regularly recurring impressions, which may have a differ- 
 ent content of sound, are combined into series; certain 
 members of the series are then accentuated. Thus the two 
 fundamental kinds of musical time, or rhythm, are origi- 
 nated. These are " two-time " and " three-time " ; and the 
 feelings corresponding to each are markedly different. The 
 funeral march produces the most pronounced form of the . 
 sesthetical feeling appropriate to two-time ; the feeling of 
 the waltz is the typical form produced by the musical 
 rhythm of three-time. Thus waves of different forms of 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. '397 
 
 gesthetical feeling are made by music to rise and die away 
 within the conscious soul. 
 
 .ffisthetical Feelings of the Eye. — The pleasurable or pain- 
 ful impressions which are produced and fused with the 
 visual sensation-complexes, if they are of distinctively 
 sesthetical kind, are dependent upon the manner of the 
 combination of these sensation-complexes, under the laws of 
 the mechanism of vision with both eyes in motion. Beau- 
 tiful visual form is determined largely by the course of the 
 limiting lines. These lines, in order to arouse a pleasura- 
 ble sesthetical feeling, must accommodate themselves to the 
 laws of visual perception, as respects both their direction 
 and their extent. Lines of slight curvature, and not too 
 far continued in one direction, best comply vdth this 
 requirement. But lines of very short curvature, or too far 
 prolonged in one direction, do not produce a pleasing ses- 
 thetical effect. The mechanism of vision with both eyes in 
 motion favors lines lying chiefly in the horizontal or the 
 vertical direction. Long oblique lines are scarcely toler- 
 able ; since the eye can sweep (or construct) them only 
 incompletely and with painful effort. 
 
 The sesthetical feeling for visual form is also determined 
 by the way in which the form is constructed, through repe- 
 tition and combination of similar or dissimilar shapes. In 
 the horizontal direction the general rule is, that we expect 
 symmetry in the arrangement of the simple parts; and 
 pleasurable feeling arises at finding our expectation met. 
 In the vertical direction, however, asymmetry is the right 
 rule. These rules are dependent, in part, on our habit, 
 and upon the consequent ease with which we master the 
 details of a complex field of visual perception. Certain 
 proportions between the whole and the parts, and between 
 the connected parts of the whole, are favorable to the de- 
 velopment of pleasurable sesthetical feeling. The so-called 
 "golden diameter" — or rule, that the whole of a visual 
 
398 tHYSIOLOGIOAL PSYCHOLOGY. 
 
 perception shall be to the larger part as the larger part is 
 to the smaller part (a; + 1 : a; : : a; : 1) — is claimed by some 
 writers to hold true. 
 
 Intellectual Feelings. — It has already been seen that 
 intellectual elements blend more and more with the causes 
 which determine the character of our feelings, as we pass 
 from the lower and more obviously sensuous to the higher 
 and more distinctively sesthetical. The various activities 
 of the mind, called intellectual, have their peculiar forms of 
 pleasurable or painful feeling connected with them. As 
 to the physical basis of these feelings we are much in the 
 dark. It is obvious, however, that feeling is connected, in 
 general, with all mental action. Pleasurable feeling arises 
 where the time-rate of the ideas is moderate, and the move- 
 ment of the mental train is accompanied by no severe 
 demands upon the attention ; painful feeling, where the 
 time-rate is too slow or too hurried, and the movement of 
 the mental train " tasks " (as we say) the powers of volun- 
 tary attention. 
 
 The more immediate dependence of the feelings on the 
 relations of the ideas composing the mental train is a subject 
 which has been treated with great skill and insight by 
 those psychologists whose view was previously mentioned 
 (see p. 385 f.). The discussion of this view — the view of 
 Herbart and his followers — does not fall within the prov- 
 ince of physiological psychology. What is called the 
 "inhibition" and the "furtherance " of one idea by another 
 doubtless has its physiological basis. This basis is con- 
 trolled by the same laws of exhaustion and renewal of the 
 nervous elements, and of the reciprocal dependence in 
 which these elements stand toward each other, which we 
 have seen to hold good for the entire nervous system. 
 Indeed, all such laws have their highest and fullest exem- 
 plification in the case of the cerebral centres. When, for 
 example, we are painfully trying to recall a forgotten 
 
PEELINGS, EMOTIONS, AND MOVEMENTS. 399 
 
 name or date, what the Herbartian theory refers to as 
 an " inhibition " of ideas, is perhaps, physiologically con- 
 sidered, a physical conflict between several inchoate molec- 
 ular processes that are trying to master, as it were, a 
 particular region of the brain. But science is as yet 
 unable to work out these laws in detail. 
 
 Influence of Association. — From the point of view of con- 
 sciousness, the influence of association over the character 
 of our feelings is almost too well known to require remark. 
 What physiological psychology can say as to the explana- 
 tion of the association of ideas, in general, will be referred 
 to elsewhere. It is enough at present to remark, that all 
 kinds of feelings — sensuous, sesthetical, and intellectual — 
 come, of course, under the principle of association. In 
 this way all the more complex peculiarities of individuals, 
 epochs, nationalities, etc., are best accounted for. The 
 sesthetical feelings of the Highlander when he hears a bag- 
 pipe, of the citizen of the United States when he perceives 
 a certain arrangement of red and blue colors on a back- 
 ground of white, of the Englishman when he hears the 
 words "Her majesty," etc., all belong under this principle. 
 Under the action of this principle, "feelings of feelings," 
 the complex sentiments, and mental moods, are constituted. 
 If we introduce the principle of heredity, and consider the 
 whole subject from the evolutionary point of view, we 
 shall doubtless conclude that many forms of feeling which 
 now seem most primary and instinctive have really been 
 acquired, under the laws of association and habit, in the 
 developing life of the race. But all this would carry us 
 too far from our somewhat restricted field. 
 
 THE EMOTIONS AND BODILY MOVEMENTS. 
 
 All the feelings, when their intensity as states of con- 
 sciousness is greatly increased, are accompanied by marked 
 changes in the condition and action of the bodily organs, 
 
400 PHYSIOLOGICAL PSYCHOLOGY. 
 
 These changes in the bodily basis of the feelings react 
 upon the character of the feelings themselves, and modify 
 them most profoundly. Moreover, there are some kinds 
 of feeling, whose characteristics are chiefly determined, 
 in whatever degree they are manifested, by the condition 
 and action of the bodily organs. " Affections " and " Emo- 
 tions" so-called are developed from all forms of feeling 
 when intensified to a sufficient degree. " Passions " are 
 those states of feeling in which the very character of the 
 feeling itself may be most appropriately described as the 
 feeling of a deranged and over-excited bodily organism. 
 
 Characteristics of the Affections, Emotions, and Passions. — 
 The consideration of all affectional or emotional forms of 
 feeling involves these three important particulars : (1) The 
 characteristic feeling which distinguishes each from the 
 others; (2) the relation of the feeling to the chain of 
 ideas, and the changes induced by the feeling in the move- 
 ment of the ideas ; and, especially, (3) its relations to the 
 different bodily organs, and the reflex effect of the changes 
 in these organs, both directly upon the feeling itself, and 
 indirectly upon the feeling through the disturbance of the 
 ideas. 
 
 All affections and passions may be considered, psycho- 
 logically, as having their rise in some form of blind, in- 
 stinctive impulse. Impulse becomes connected, in the 
 development of experience, with perceptions and mental 
 images of the objects that have excited or satisfied it. 
 When this connection is established between the feeling, 
 which as blind impulse takes no intellectual account of 
 the object, and appropriate perceptions or mental images, 
 the basis for an affection or emotion is laid. 
 
 Instinctive impulses are of two general classes, — those 
 of attraction or craving, and those of repulsion. The 
 natural germ of anger or hate, for example, is found in 
 that blind, instinctive impulse of resistance, with its accom- 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 401 
 
 panying feeling of painful irritation, which all sudden and 
 intense excitements of the nervous system arouse. In the 
 child, or childish adult, anger bursts out against the inani- 
 mate object which causes pain or opposes freedom of move- 
 ment. On the other hand, the affection of the child is 
 nursed by the feeling of comfort it has in the arms, or at 
 the breast, of the mother. By a growing variety of experi- 
 ences, the impulses of attraction or repulsion become diver- 
 sified into a number of affections and passions, characteristic 
 of the different manifold relations in which the mind stands 
 toward things and persons. 
 
 All emotional forms of feeling are characterized by 
 abrupt and sudden changes in the character and time- 
 course of the train of ideas. Any sudden, strong stimulus 
 — as we all know — breaks in upon and destroys the steady 
 and peaceful flow of mental life. It has sometimes been 
 said that from feeling to emotion is a " leap." The ten- 
 dency of any violent change of mental state is, then, to 
 excite an " emotional " condition of the feelings, character- 
 ized by the peculiar kind of feeling which is appropriate 
 to the particular character of the object or mental image 
 which absorbs the state. All the emotions take men " off 
 their guard." They "upset," "banish," "interrupt," the 
 train of ideation. The members of this train, thus dis- 
 turbed by the springing in upon them of emotion, become 
 hurried, disordered, crowded, confused. 
 
 But, on the other hand, the effect of so marked and 
 rapid a disturbance of the mental train reacts upon the 
 emotion itself. The mind feels the disturbance of the ideas 
 as a new emotion, or as an added characteristic of the 
 former kind of emotion. The stream of conscious ideation 
 being perturbed, the feeling of the perturbance is an emo- 
 tional condition of the entire conscious life. Without 
 doubt this mental confusion is indicative of an unusual 
 molecular agitation, of a derangement of the circulation 
 
402 PHYSIOLOGICAL PSYCHOLOGY. 
 
 and psycho-physical chemistry, in the ideo- and sensory- 
 motor centres of the cerebral hemispheres. But here again 
 we know little or nothing of the particulars. 
 
 It is the remarkable and characteristic effect which such 
 forms of feeling produce upon certain particular organs, 
 that is the most noteworthy peculiarity of all affections, 
 emotions, and passions. The influence of shame, fear, or 
 anger, upon the vaso-motor system and the circulation of 
 the blood, is well-known. But some persons grow pale, 
 and some red, when angry. In experiment upon the lower 
 animals, the curve which indicates the amount of blood- 
 pressure is altered by the cerebral disturbance attending 
 emotions of surprise, fear, or other similar excitement. 
 Care, anxiety, strong love or hate, and all the passions, 
 produce changes in the action of the capillary vessels, 
 upon the secretions, the nutrition, etc. 
 
 The effect of some of these forms of feeling is chiefly to 
 depress, and of others chiefly to over-excite, the action 
 of the vital organs. Hence the division which Kant made 
 of the affections, into "sthenic" or "asthenic." The 
 former lame or kill by apoplexy, the latter may kill by 
 laming the heart. 
 
 But this characteristic effect of the affections, emotions, 
 and passions, upon the internal and vital organs of the body, 
 reacts upon the feelings themselves. Of this effect, anger 
 is a notable example. Under the influence of this pas- 
 sion, the teeth are set, the fists are clenched, the heart- 
 beats quicken, the breathing becomes shallow, the limbs 
 are stiffened or made to tremble, the organs of the abdo- 
 men are stirred, the creeping sensations of " goose-flesh " 
 occur, the nostrils dilate. This mingling of sensations, 
 with their characteristic feelings, and of so-called common 
 feeling, forms the physical basis, as it were, of a rising 
 tide of emotion. The tide subsides, of necessity, as the 
 nervous exhaustion caused by over-excitement of the 
 
PEELINGS, EMOTIONS, AND MOVEMENTS. 403 
 
 organism comes on. Indeed, the control of the passion 
 may be indirectly undertaken by keeping down the influ- 
 ence of these sensuous feelings. Who can continue his 
 rage, — with limp muscles, dehberate and regular breath- 
 ing, relaxed jaws and fists, and a placid face ? 
 
 It has already been shown that even the feelings called 
 sesthetical or intellectual — and, we might add, ethical and 
 religious — when they are aroused by mental images to a 
 high degree of intensity, tend to assume an emotional char- 
 acter. They then partake of all the qualities which have 
 just been described. 
 
 The Mental Moods. — Few things are more well-estab- 
 lished in the popular estimate than the existence of 
 so-called " moods " of the mind. By so vague a term we 
 designate certain general differences in the average char- 
 acter of the complex states of feeling by which individuals 
 are characterized. By the same term we also designate 
 similar differences which characterize different periods, 
 longer or shorter, in the life of the same individual. 
 
 We have spoken of the "mood" as a characteristic 
 complex of feelings. This is because the influence of the 
 sensations, perceptions, and train of ideas, upon the gen- 
 eral " tone " of the mental life is to be considered as 
 expressing itself in the mixture of feelings. The principal 
 elements that determine any particular " mood " consist of 
 ill-localized sensations arising from the visceral organs, accel- 
 erated or disturbed and depressed cerebral functions con- 
 nected with the reprod action of the ideas, vague single 
 feelings of the suppressed emotional, or the aesthetical or 
 intellectual or ethical, type, etc. The passions and emo- 
 tions, distinctly as such, run their course quickly, and give 
 color to the personality chiefly by the frequency of their 
 recurrence and the vehemence of their force while they 
 last. But mental moods are slower in change and less 
 strong in tone; they are characterized by affections and 
 
404: PHYSIOLOGICAL PSYCHOLOGY. 
 
 emotions of a low and lingering character, — pale and 
 faded specimens of the type, as it were. 
 
 It will appear that mental " moods " — as respects their 
 endurance in time, their complexity (quality of being mix- 
 tures of a vast number of obscure elements), and their 
 dependence upon the constitution and functions of the 
 entire bodily mechanism — stand midway between "tem- 
 peraments" and the particular complex states of feeling 
 which characterize our changing daily experience. 
 
 Another class of mental states, whose existence and 
 nature are intimately connected with the direction of the 
 bodily movements, consist of the so-called — 
 
 Feelings of Effort, or of Innervation, — The testimony of 
 universal experience is perfectly clear to the fact that we 
 know — it would be said by most persons, instinctively 
 and immediately — the position and condition, as respects 
 tension and strain, of our bodies and their individual mem- 
 bers. But we have already seen (p. 316 f .) that this knowl- 
 edge is the result of a development. It is of the nature of 
 perception ; and it is dependent upon a variety of l ocaliz ed 
 sensation-comple xes arising from the stimulation of skin, 
 muscles, tendons, and joints. [Among these, the amount 
 of influence exerted by the "muscular sensations" has 
 been much disputed. It is not necessary, however, in this 
 connection to repeat the arguments which have led us to 
 assign to them a principal part, but not the whole, of the 
 influence in constructing our perceptions of the bodily 
 positions, strains, and movements.] 
 
 It is plain that the view previously taken assigns a 
 peripheral origin to the so-called " feelings of effort." But 
 the question arises whether their origin is wholly periph- 
 eral ; whether, in fact, it is not partly, at least, of a central 
 origin. The great physiologist Miiller considered the ner- 
 vous process which occasions the " feeling of effort " to be 
 of purely central origin, and to consist of a discharge from 
 
FEELINGS, EMOTIONS, AMD MOVEMENTS. 405 
 
 the motor centre into the motor nerves. In other words, 
 it is the feeling of the cerebral process which innervates the 
 group of muscles, on occasion of a fiat of will. Wundt 
 takes the same view, and regards this class of feelings, 
 (which, in his opinion, differ only as respects quantity and 
 not as respects quality,) as of chief importance in account- 
 ing for our experience of solid objects of sense and of 
 whatever belongs to the inertia of matter in general. 
 
 The question, whether any elements of the compound 
 " feeling of effort " are directly dependent upon the cere- 
 bral changes which immediately accompany an act of will, 
 cannot be said to be experimentally settled. On the whole, 
 however, the tendency is in our judgment to discredit the 
 alleged proofs of such a central origin to this feeling. For 
 it seems possible to account for most, if not all, of our 
 experience of the different forms of " the feeling of effort," 
 on the theory of the peripheral origin of the factors which 
 compose it. For example, it has been claimed that, if we 
 intensely make-believe to use any limb (let it be in pulling 
 with the finger the imaginary trigger of a gun), but do 
 not actually move it, we nevertheless have the conscious- 
 ness of exerting effort; In reply it has been pointed out, 
 that the feeling of effort in such cases is due to keeping 
 the glottis tightly closed, while actively contracting the 
 respiratory muscles. Let all these parts be carefully kept 
 relaxed, and we cannot even imagine ourselves to be 
 " making the effort " of using the limb. 
 
 It is further alleged, in evidence of the central origin 
 of the feeling of effort, that persons afflicted with cortical 
 paralysis can produce the consciousness of stress of will in 
 the imaginary movement of the paralyzed limb. But in 
 such a case this feeling is probably due to the condition 
 of the joints and muscles. Even where the limb is wholly 
 lamed, the feeling is actually produced, as a rule at least, 
 by a movement or condition of squeezing and straining, 
 
406 PHYSIOLOGICAL PSYCHOLOGY. 
 
 produced in some sound but closely allied part of the body. 
 Thus Vulpian noticed that his patients produced the feeling 
 of effort in the lamed fist by actually closing the sound one. 
 Another observer (Miinsterberg) can allege no little ex- 
 perimental evidence, when he contends that involuntary 
 contraction of the muscles of sight, tension of the scalp, 
 etc., may be translated into the exertion of energy localized 
 in different' and distant parts of the body. 
 
 The case of the eye, when afflicted with partial paralysis 
 of the external rectus, is almost classical. Patients having 
 this form of paralysis localize the visual object too far out, 
 on the side of the lamed eye. The argument is as follows : 
 The patient feels that he has moved his eye much farther 
 than he really has; he therefore localizes the object by 
 this exaggerated feeling of effort. Since the peripheral 
 result actually accomplished is a diminished effort, the 
 feeling of the effort cannot originate from this result, but 
 must have a central origin. In reply to this argument it 
 has been pointed out (especially by Professor James) that 
 the argument entirely neglects what goes on in the other 
 and sound eye. The sound eye, unlike the lame one, con- 
 tinues its motion until the normal limit is reached, and 
 the corresponding amount of peripheral strain produced. 
 Since the two eyes operate as one instrument, the object 
 is necessarily localized by the condition of the sound eye, 
 no less than the lamed eye. 
 
 Testimony from persons who have suffered the amputa- 
 tion of limbs is ambiguous. A considerable proportion of 
 such persons (perhaps about three quarters) report that 
 they have had, for a longer or shorter time subsequent to 
 the amputation, the feelings of position, strain, and move- 
 ment, in the lost limb. The majority of those who have 
 lost a leg or arm have the feeling in the foot or hand ; but 
 feel the parts intervening between these members and the 
 stump, less vividly or not at all. Many who have lost a 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 407 
 
 leg can " work " or " wriggle " tlieir toes at will, — feeling 
 both the effort and the movement ; but in most cases actual 
 movements in the muscles of the stump can he detected. It is 
 probable that where such movements cannot be detected, 
 the feeling of effort originates in the strain, or movement 
 of other peripheral parts. 
 
 The connection of this discussion with a theory of the 
 will, and with the dependence of acts of will upon a bodily 
 basis, is obvious. The nature of the connection will be 
 referred to in another place. It is pertinent here to con- 
 clude that, excluding what is purely "moral" (the choice 
 and what is psychologically involved in it), the so-called 
 " f eehng of effort " is probably of peripheral origin. In fact, 
 it should not be called a feeling at all. It is rather a mix- 
 ture of sensation-complexes arising from the condition of 
 the skin, muscles, tendons, and joints, and becoming local- 
 ized (often in a very imperfect and illusory way) under 
 the influence of the stronger factors in the perception, and 
 in connection with the associated mental images and the 
 accompanying " fiat of will." 
 
 How easily the true character of a complex perceptive 
 process can be misapprehended by the conscious mind, 
 when this process is dependent upon a mixture of obscure 
 and indefinite sensations, is made apparent by facts like 
 the following. A certain patient, who had complete 
 anaesthesia and was wholly unable to discover unseen active 
 or passive movements of his own bodj^ could put forth the 
 amount of effort to raise a given weight, in case he under- 
 stood by sight its nature and its size. Otherwise he could 
 not even approximately estimate or control the amount of 
 muscular contraction necessary. It would appear, then, 
 that in this patient's case, the requisite " fiat of will " was 
 estimated and controlled by memory-images of sight with- 
 out help from the so-called " feeling of effort." 
 
 Kinds of Bodily Movements. — Changes of the position of 
 
408 PHYSIOLOGICAL PSYCHOLOGY. 
 
 our bodies and their members, considered in relation to 
 the conscious mental processes, are of two kinds. These 
 are (1) movements not dependent upon states of con- 
 sciousness, and (2) movements that, for their explanation, 
 require us to take account of antecedent states of con- 
 sciousness. Of the former, again, two subdivisions may 
 be made, — the automatic and the reflex. The nature and 
 origin of both these forms of bodily movement have 
 already been suiSciently discussed (Chapter VI.). 
 
 It should be noticed in this connection that sensations, 
 ideas, and acts of will, which have to do with the move- 
 ments of the body, constantly tend, as it were, in two 
 directions, — either toward consciousness or out of it. 
 The physical correlate of this statement is doubtless as 
 follows : The nervous processes which stimulate to motion 
 the different groups of muscles, rise and fall, with varying 
 degrees of intensity, toward and away from the higher 
 cerebral centres. 
 
 In the case of reflex movements, unaccompanied by 
 those changes in consciousness that are called ideo-motor 
 or voluntary-motor, either the ^^arc" around which the 
 neural processes are completed, has its highest point below 
 the cerebral hemispheres ; or else the processes which rise 
 into these hemispheres are relatively too weak to produce 
 any sufficient effect within the centres concerned in such 
 ideo-motor and voluntary-motor control of the muscles. 
 In the case of unconscious automatic motion, the cerebral 
 excitations which originate centrally — in changes of the 
 blood-supply, etc. — do not involve, at least with sufficient 
 intensity, these ideo-motor and voluntary-motor centres. 
 
 It is by means of these processes, in the two directions 
 just described, that our learning and practice of all com- 
 plicated movements of the body takes place. Such move- 
 ments are those concerned in feats of dexterity and skill. 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 409 
 
 in learning to handle tools, to play on musical instruments, 
 etc. 
 
 Impulsive Movements. — Those changes of the position 
 of the body and its members which involve states of con- 
 sciousness may be divided into the impulsive and the vol- 
 untary. This distinction requires, however, such a variety 
 of degrees that shade into each other as to be difficult of 
 application. By an impulsive movement we understand 
 one which, without a conscious fiat of will, follows upon 
 certain states of ideation and of excited feeling. The 
 motif for such a movement may be said to lie in the " im- 
 pulse," or push, of feeling, which determines volition one 
 way, without any proper choice. 
 
 Impulsive movements form the basis of the more dis- 
 tinctively voluntary. They are particularly prominent 
 and influential in the early development of the mind. 
 The neural processes, awakened in the brain of the infant 
 by the action oi various forms of stimulus upon the end- 
 organs of sense, are themselves the stimuli, or awakeners, 
 of states of consciousness. The tone of these states of con- 
 sciousness is one of either pleasure or discomfort. By the 
 natural mechanism of the body, certain forms of move- 
 ment are connected with these states of feeling, which in 
 general tend to enhance the feeling, if pleasurable, and to 
 relieve it, if unpleasant. Thus certain bodily movements 
 become connected with certain states of conscious feeling. 
 More indirectly, the same movements become connected 
 with the ideas and perceptions associated with the feelings. 
 The reaction-time is shorter for the impulsive movements 
 than for the voluntary ; since " will-time " proper is 
 dropped out (see p. 371 f.). 
 
 It is obvious, that the line between the automatic and 
 the impulsive movements, in the earliest life of the child, 
 cannot be drawn with confidence. And, inasmuch as the 
 same thing is true of the automatic and the reflex move- 
 
410 PHYSIOLOGICAL PSYCHOLOGY. 
 
 ments, all three of these classes (reflex, automatic, and 
 impulsive) are closely allied. It is impossible to say how 
 much of the almost constant movement of an infant's limbs 
 is reflex, how much automatic. It is equally impossible to 
 decide, in all individual cases, between the reflex and the 
 impulsive explanations of the grimaces of its face, its 
 starting at sounds, etc. There is no doubt that the gen- 
 eral order of development, however, is from the reflex and 
 automatic to the impulsive. 
 
 Voluntary Movements. — Those changes of position in 
 the body and its members, which are ordinarily called 
 '■^voluntary," are so in reality only with respect to some 
 of their elements. They involve other elements which 
 are reflex, centrally co-ordinated, and impulsive. Nor must 
 we understand " voluntary," in this connection, necessarily 
 to imply conscious deliberation and choice, — an "act of 
 free-will " in the fullest meaning of the words. 
 
 Voluntary movements are the highest* class of move- 
 ments, from the psycho-physical point of view, because 
 they require for their completion the entire psycho-physi- 
 cal mechanism. They imply a development of both bodily 
 and mental powers. They involve the five following con- 
 ditions: (1) The possession of an educated reflex-motor 
 mechanism, under the control of those centres of the brain 
 that are connected with the phenomena of consciousness ; 
 (2) impulses, in the form of conscious feelings that have 
 a tone of pleasure or pain and have become associated 
 with, (3) mental images oi. movements and positions of the 
 bodily members that experience has taught us are them- 
 selves connected with these pleasurable or painful states 
 of feeling ; (4) a conscious fiat of will, or order, as it were, 
 for the realization of these mental images ; and (5) a cen- 
 tral nervous mechanism in which, as a matter of natural 
 or acquired causation, the requisite motor impulses may 
 
FKBLIN6S, EMOTIONS, AND MOVEMENTS. 411 
 
 arise, to go forth along their nerve-tracts to the groups of 
 muscles concerned. 
 
 Careful study of these five groups of very complex con- 
 ditions, both of nervous system and states of conscious 
 mind, convinces us that the science of physiological psy- 
 chology can deal in only a very fragmentary and doubtful 
 way with most of the problems involved. Of the first, 
 second, and fifth groups (Nos. (1), (2), and (5)) enough 
 has already been said. Of the possibility of a psycho- 
 physical theory of the " fiat of will " (No. 4), as connected 
 with choice, control of attention, freedom, etc., we shall 
 speak more at length in another place. A few remarks 
 may here be made concerning the "ideo-motor " character of 
 this class of bodily changes (No. 3). 
 
 To will the movement of any particular group of mus- 
 cles we must have had experience of the actual movement 
 of that group ; i.e. of the changes in the feeling of effort, 
 in the perceptions and constitution of the entire mental 
 life, which such particular movement involves. We can 
 never " will " motion in general — motion, that is, of no 
 particular member of the body, and without specific qual- 
 ity, direction, and velocity of motion. Each member, and 
 each position of each member, and each kind, direction, 
 and velocity of movement, has its own mental representa- 
 tives in the ideation-processes of the mind. It is by these 
 mental images that the particular "fiat of will" guides 
 itself in each case. We can issue the requisite fiat of will 
 by attention (whether forced or voluntary) to the appro- 
 priate ideo-motor images ; but in no other way. Otherwise, 
 the distinction between impulsive and voluntary move- 
 ments is lost, and there is no accounting for the particular 
 character of the movement which takes place. 
 
 Dependence of Perception on Movement. — Perception is 
 a knowledge of " Things " ; and all things are known to us 
 as being external and having extension in space. Indeed, 
 
412 PHYSIOLOGICAL PSYCHOLOGY. 
 
 this is as true of our bodily members as it is of the remoter 
 objects which we learn to know through them. Now it is 
 this life of motion which gives reality to all things, whether 
 they are regarded as parts of our bodies or are known as 
 separable from our bodies. "Were it not that the child is, 
 from the beginning of its life, excited to movements — 
 reflex, automatic, and impulsive — and so acquires an ex- 
 perience of feelings of effort and of mental images repre- 
 sentative of all manner of movements, it could never gain 
 a knowledge of a real world of things. 
 
 So true is this that we cannot even form the vivid men- 
 tal image of anything, or of any change in the shape or 
 position of anything, without evoking inchoate movements 
 to serve, by the sensation-complexes which they occasion, . 
 as factors in our mental image. In the effort to form such 
 an image of a chair or a table, for example, we institute a 
 series of extremely subtle and delicate motor impulses of 
 the eye or the hand, — of the senses with which we realize 
 it. The effort to image a solid object revives the appropriate 
 inchoate motor impulses that are wont to control the active 
 perception of that object. 
 
 The Expressive Movements. — A certain appropriateness, 
 or naturalness of connection, is recognized by every one as 
 existing between some classes of ideas and feelings and 
 those positions and movements of the body which express 
 them. In this field comparative psychology and anthro- 
 pology are particularly successful. 
 
 In explaining this class of movements Wundt has sum- 
 marized the phenomena under the following three prin- 
 ciples : — (1) the principle of the direct alteration of 
 innervation. Strong emotions, with vivid ideas, exercise 
 an immediate reaction on certain cerebral centres. This 
 results in exciting some groups to action or increased ten- 
 sion ; and other groups of muscles are lamed by the same 
 process of central innervation. Hence the trembling of 
 
FEELINGS, EMOTIONS, AND MOVEMENTS. 413 
 
 limbs and derangement of speech through fear; the red- 
 dening or paling which express anger, disgust, or shame, 
 etc. 
 
 (2) The principle of the association of analogous sensa- 
 tions emphasizes such facts as imply that sensations having 
 a common tone of feeling combine most readily and thus 
 strengthen each other. In this manner, both moiith and 
 nose express in company the disgust or pleasure of smells 
 and tastes ; the muscles combine with the skin to express 
 certain sensations arising through irritation of the latter, 
 etc. 
 
 (3) The principle of the relation of particular move- 
 ments to particular perceptions of the senses is, of course, 
 a principle of the broadest application. By gestures with 
 the eyes, and head, and limbs, we indicate the ideas of 
 extension and relation in space. Care, expectation, exul- 
 tation, depression, throw the members of the body into 
 expressive postures, which correspond to the perception of 
 the objects exciting those feelings. It is under this prin- 
 ciple that the psycho-physical science of the comic, of 
 physiognomy, etc., brings a great number of facts. 
 
 Recent inquiries have elicited the interesting and impor- 
 tant fact that, as a rule, the great actors actually have the 
 feelings and ideas present in their consciousness, which 
 their acting expresses with such wonderful results. Their 
 power is the power to put themselves in the appropriate 
 condition of mind, rather than the power merely to act a 
 part. 
 
CHAPTER XVII. 
 
 CONSCIOUSNESS, MEMORY, AND WILL. 
 
 Inquiry into the physical basis of those mental processes 
 which are ordinarily classed among the "higher" is, of 
 course, peculiarly interesting ; but it is, at the same time, 
 peculiarly unproductive of well assured results. The psy- 
 chology of these processes, as studied from the introspective 
 point of view, has, on the other hand, a great comparative 
 advantage. For it is these processes which best submit 
 themselves to introspection; it is they which have been 
 most carefully and successfully studied by the method of 
 introspection. But the correlated cerebral processes — 
 even if we admit without argument that such processes 
 exist — are in precisely the opposite condition. The testi- 
 mony of the most learned and cautious experts in phys- 
 iology confirms the declaration, that such a thing as a 
 definite and detailed science of the physical functions of 
 the hemispheres of the brain does not exist. 
 
 We have previously discovered (see Chapter V.) that the 
 so-called " general nerve-physiology " of the nerve-muscle 
 machine is in a very incomplete condition. We have 
 also seen that faint and doubtful guesses, conjectural 
 modifications of general laws of the molecular physics of 
 the nervous elements (the " laws " themselves being largely 
 conjectural), comprise the answer which science can at 
 present give as to the behavior of that vast complex of 
 nerve-cells and nerve-fibres which constitutes the human 
 brain. 
 
 The only course which physiological psychology can 
 414 
 
CONSCIOUSNESS, MEMORY, AND WILL. 415 
 
 adopt in attempting to deal with mental phenomena of 
 the so-called higher order is, then, the following: The 
 facts of consciousness must be accepted on the authority 
 of consciousness, as studied by the method of introspective 
 analysis ; and then we may cautiously speculate as to their 
 probable physiological correlates, by extending the conjec- 
 tures of general nerve-physiology to the cerebral hemi- 
 spheres. This course will be adopted in the present chapter. 
 If its results are not very complete and defensible through- 
 out, the fault is to be charged to the account of the subject 
 rather than its method of treatment. 
 
 Nothing which has just been said should be understood 
 as detracting from the value of experiment in testing all 
 theories proposed to account for the so-caUed "higher" 
 mental phenomena. It must not be forgotten, however, 
 that what the experiments themselves immediately give us 
 is nothing other than more, and perhaps also novel, mental 
 phenomena. The end of the thread which we securely 
 hold in our hand always consists of observed data of con- 
 sciousness. The other end, the correlated physiological 
 brain-processes, is always hidden from our observation. 
 Nay more ; the theory of what it is that constitutes the 
 peculiar nature of these processes is still in the stage of 
 uncertain conjecture. And what it is that serves to make 
 brain-processes a fit physical basis for the mental phenom- 
 ena, or makes the conjectural changes of these processes 
 fit to act as antecedents or causes of the different kinds of 
 mental phenomena, is wholly unknown. 
 
 There are three topics under this general head to which 
 our discussion, from lack of other trustworthy material, 
 must be confined. These are the phenomena ordinarily 
 called consciousness; and the special forms of conscious- 
 ness called memory and will. 
 
416 PHYSIOLOGICAL PSYCHOLOGY 
 
 PSYCHO-PHTSICAL THEORY OF CONSCIOUSNESS. 
 
 The Nature of Consciousness. — From tlie point of Tiew 
 held by introspective psychology, consciousness cannot be 
 defined. By the term " consciousness " we mean to indi- 
 cate the most general fact of the existence, in some form, 
 of sentient or mental life. But every actual expression of 
 mental life is in some particular form ; it is a " state " or 
 " act " of consciousness. In other words, every actual 
 consciousness defines itself by some content. For conscious- 
 ness never actually is consciousness in general, — an activ- 
 ity or state that might be separated from all individual 
 state or process of consciousness, without content, as it 
 were. 
 
 Inasmuch, then, as consciousness is the condition of all 
 internal experience whatever, we cannot deduce or explain 
 its essential nature from particular forms of such experi- 
 ence. 
 
 Consciousness, or the general fact of having any form of 
 sentient life in distinction from being unconscious (as in 
 a dreamless sleep or " dead " swoon), must also be distin- 
 guished from seZf-consciousness. The latter is the con- 
 scious attribution of any particular so-called " state of con- 
 sciousness " to the Ego, or subject of them all. That is, 
 self-consciousness is a form of consciousness characterized 
 chiefly by the nature of its object (the Ego), anS by the 
 peculiar feeling of interest which fuses with the apprehen- 
 sion of this object. 
 
 We have already spoken of a " circuit of consciousness " 
 (p. 377), and of the number of objects which it can con- 
 tain. Nothing is more certain or familiar in our experience 
 with ourselves than the great variations, in respect to 
 amount of energy, degrees of clearness, and — as it were 
 — height of attainment, which characterize the different 
 states of consciousness. To represent consciousness as an 
 
CONSCIOUSNESS, MEMORY, AND WILL. 417 
 
 attenuated line, with no breadth or porisible variation in 
 breadth, is most misleading ; and yet this form of represen- 
 tation has been the accepted one with a large number of 
 English psychologists. If we are to assist our imaginations 
 to a knowledge of the truth by such partially inapt figures 
 of speech, it is better to represent the " field of conscious- 
 ness " by a series of overlapping circles having a large pos- 
 sible variation in their diameters ; or by what we see of 
 change in a kaleidoscope when we turn it slowly before 
 the eye. 
 
 The Physical Basis of Consciousness. — Little can be added 
 on this point to what has already been said regarding the 
 physical basis of the different forms of consciousness. It 
 has been concluded that, in man's case, the cerebrum is 
 probably the sole, as it is certainly the chief, " organ " of 
 consciousness (see p. 179 f.). By this we can mean nothing 
 intelligible, however, except this : that the constitution 
 and molecular changes of the nervous matter of the cere- 
 brum are the only immediate antecedents or concomitants 
 of the phenomena of consciousness ; and so that, whatever 
 takes place in the body outside of the cerebrum has an effect 
 upon consciousness only in case it gets itself represented, as 
 it were, within that supreme organ. 
 
 A recent writer (Herzen) holds that the physical basis 
 of consciousness rests on the biological law which condi- 
 tions the activity of a tissue on its decomposition and 
 ensuing regeneration. The intensity of consciousness, as a 
 neural function, depends on the intensity of the decompo- 
 sition of the brain tissue ; and it is inversely as the ease 
 and rapidity with which the inner work of one nerve-ele- 
 ment is transmitted to another. This theory explains some 
 facts. It does not appear, however, that the amount of 
 the work of decomposition in the brain-tissue is a measure 
 of the breadth, height, and depth, of the field of con- 
 sciousness. 
 
418 PHYSIOLOGICAL PSYCHOLOGY. 
 
 On grounds of general theory it is yery probably true 
 that the physical basis of any consciousness whatever rests 
 upon a certain intensity, in the appropriate centres, reached 
 by that unknown neural process for which these centres 
 are, by constitution and habit, peculiarly fitted. But any 
 consciousness is always some particular form of conscious- 
 ness. Every particular form of consciousness may then 
 be said to have its basis in a certain intensity of the neural 
 processes peculiar to those centres, whose activity is cor- 
 related with that one form of consciousness. 
 
 Physical Conditions of Consciousness. — Among the known 
 conditions of all conscious mental activity is the character 
 and amount of the brain's blood-supply. To stop this 
 supply results in putting an end for the time to all con- 
 sciousnSss ; to impede or corrupt it disturbs and depresses 
 consciousness ; to alter its character changes the character 
 of consciousness. 
 
 Observation of man and the lower animals, and experi- 
 ment on the animals by decapitation and otherwise, have 
 shown that the condition of the brain is anaemic in sleep. 
 When the amount and time-rate of the conscious mental 
 processes are lowered, the amount of arterial blood drawn 
 to the higher centres, and there used up, is diminished. 
 Dr. Cappie has propounded the theory that the physical 
 condition of consciousness, as distinguished from the 
 unconsciousness of profound slumber, depends upon an 
 excess of the pressure of the arterial circulation in the 
 brain substance over the pressure of the venous circulation 
 in the pia mater. The molecular agitation of the conscious 
 mental processes draws the arterial blood through the 
 capillary vessels, like the draught created by the burning 
 of a fire. 
 
 Whatever particular theory ma}^ be held as to the pre- 
 cise nature of the physical basis and conditions of con- 
 sciousness, thus much seems undoubtedly true. That 
 
CONSCIOUSNESS, MEMORY, AND WILL. 419 
 
 peculiar kind of " work " which is known as the con- 
 jectural molecular agitation of the nervous substance of 
 the higher cerebral centres is an indispensable condition, 
 and in some way at least a rough measure, of the so-called 
 activity or intensity of consciousness. Here again, how- 
 ever, must we refer to the very indefinite and figurative 
 way in which we can use the terms " amount," " intensity," 
 " measure," as applied to states of mind. 
 
 PSYCHO-PHYSICAL THEORIES OF MEMORY. 
 
 The mental phenomena which are grouped under the 
 general term of " Memory " offer themselves, in a tempting 
 way, to explanations derived from conjectural principles in 
 "general nerve-physiology " and in the special physiology 
 of the centres of the cerebrum. These phenomena are 
 usually understood to imply three powers, or phases of one 
 power of the mind. They are (1) retention, (2) repro- 
 duction, and (3) recognition. Of the three, only the first 
 two seem to admit of even a conjectural physiological 
 explanation; and it is doubtful whether these two, con- 
 sidered as separated (were that possible) from the third, 
 are mental processes at all. " Recognition," however, is 
 essentially of consciousness ; it is mental and cannot be 
 conceived of as having any physical representative or 
 correlate. 
 
 Psychological Theories of "Retention." — We have just 
 said that the "retention," which is commonly spoken of 
 as necessary to the phenomena of memory, cannot be con- 
 sidered as a mental act. If we ask ourselves. Where is 
 the idea or the perception I once had, between the time of 
 original experience and the time of recall? — the answer 
 must be : The " idea " or the " perception " is nowhere. 
 It does not exist in any sense of the word, since the exist- 
 ence of an " idea " or " perception " consists solely in. its 
 being an act or state of conscious life. 
 
420 PHYSIOLOGICAL PSYCHOLOGY. 
 
 But if we ask ourselves, What are those changes pro- 
 duced by stimulation in the substance of the brain, which 
 constitute the physical basis of conscious acts of memory, 
 under the laws of habit and association of ideas ? — we ask 
 a question which is perfectly intelligible, although its cor- 
 rect answer may not be obtainable. Three forms of the 
 physiological theory of memory, considered as " retention," 
 are possible. These are: (1) Memory depends upon a 
 movement persisting in the brain; (2) it depends upon 
 a certain residuum, of the nature of a "scar," or fixed 
 impression, persisting in the brain ; or (3) it depends upon 
 a persistent disposition, or tendency to movement created 
 in the brain. All such terms as the foregoing are probably 
 used somewhat figuratively when applied to the brain sub- 
 stance ; precisely what they fitly represent we do not know. 
 But the third form of theory has most evidence in its favor. 
 We shall, therefore, present the arguments in its behalf. 
 
 Fading of the Primary Image. — It is difficult to draw the 
 line between the after-images of a sensory impression and 
 the memory-images (strictly speaking) of the same impres- 
 sion. The thousands of faint impressions which enter into 
 our daily life seein quickly to vanish without leaving even 
 a trace behind. But that these impressions linger for a 
 period near, or under, the "threshold of consciousness" 
 can readily be shown. If we are called upon to direct 
 attention upon them, to fixate and describe them, within 
 a few seconds of their occurrence, we find it possible to do 
 this. Some of them admit of such recall for a period of 
 several minutes after their occurrence. But if not atten- 
 tively " apperceived " within this brief time, such impres- 
 sions usually fade away beyond all recall. 
 
 Relation of Retention to Time. — Let a line of given length 
 be regarded, for a brief time, then removed, and after a 
 varying interval the effort made to recall its image so as 
 to compare it accurately with another line of nearly the 
 
CONSCIOUSNESS, MEMOKY, AND WILL. 421 
 
 same length. It will be found that the clearness of the 
 memory-image of the visual line falls off quickly at first, 
 then more slowly, and finally approximates a stationary 
 condition. Let a tone of given pitch be sounded, and then, 
 after a brief interval, a second tone of the same, or nearly 
 the same, pitch. In such a case, according to the experi- 
 ments of H. K. Wolfe, the judgment as based, in part, on 
 the memory-image of the first tone, will be most accurate 
 at an interval of about 2 seconds. For a longer period 
 than 2 seconds, the curve of memory for pitch of tones 
 falls off pretty regularly as the interval increases to be- 
 tween 10 and 20 seconds ; then it is retarded or ceases to 
 decline ; and, further beyond, it falls off still more rapidly 
 vdth increasing time. 
 
 That patient investigator, Ebbinghaus, found that the 
 process of forgetting a series of "nonsense syllables" is 
 rapid at first, and then slower afterwards. After an hour's 
 time had elapsed, i the original work must be done to 
 relearn the series ; after 8 hours, f. But after 1 day the 
 impression retained about i its original strength ; after 6 
 days, i ; after 30 days, ^. This investigator concluded that 
 the ratio of what is retained to what is forgotten is in- 
 versely as the logarithm of the time. 
 
 Persistence of Certain After-images. — In various cases of 
 strong or repeated impressions, the complete or partial 
 after-images recur persistently for a long time after the 
 impressions have ceased. Prolonged work with the micro- 
 scope causes the visual images seen in its focus to live " in 
 the fundus of the eye " ; so that, after several hours, shut- 
 ting the eyes will make them reappear with great distinct- 
 ness. Musicians, after musical seances or after giving 
 instruction, sometimes hear the sounds repeated for days. 
 After a journey on a railroad car, the rattle of the car may 
 persist in the ears for a long time, as do. the sensations 
 
422 PHYSIOLOGICAL PSYCHOLOGY. 
 
 whose impression arises in muscles, semi-circular canals, and 
 other internal organs, after a journey by sea. 
 
 The Physical Basis of Retention. — Niepce de Saint- Victor 
 has shown that luminous undulations may be " to some 
 extent garnered up in a sheet of paper," ready to be re- 
 vealed at the call of special reagents. A plate of dry 
 collodion, after being briefly exposed to the sun's rays, 
 retains for weeks in the darkness the effects of the inde- 
 scribably delicate changes which have been wrought in it. 
 The stimulation of certain reagents will revive the images 
 latent in such a plate. The well-seasoned Cremona, which 
 has been played upon by skilled hands, will reproduce the 
 tones with superior sweetness and purity, on account of 
 the secret molecular changes of which it has been made 
 the subject by previous agitations from the bow of the vio- 
 linist. These things, however, afford us only analogies 
 for the physiological explanation of memory. 
 
 It is to distinctively biological facts and principles that 
 we must look for the proper explanation of the mental 
 phenomena which imply so-called " retention." The fun- 
 damental fact seems to be that the nerve-element — at 
 least, the nerve-cell which is concerned in psychical pro- 
 cesses (sometimes called the " psychic nerve-cell ") — is 
 modified in a permanent manner as an effect of its excita- 
 tion. We have already considered many phenomena which 
 imply this general fact. Such are the progressive estab- 
 lishment of functional centres in the spinal cord and brain 
 of a young animal (for example, the new-born puppy), the 
 phenomena of substitution in the localization of cerebral 
 function, and, especially, many of the phenomena of apha- 
 sia. The same thing is implied in that acquired skill 
 which results in " learning," as we say, so as without con- 
 scious judgment and choice to perform feats of dexterity 
 and skill. Indeed, learning to walk, to talk, to sing, etc., 
 implies the same principle. All habit, acquired in the con- 
 
CONSCIOUSNESS, MEMORY, AND WILL. 423 
 
 trol of the organism, tends to become habit of purely 
 organic self-control. 
 
 Now the nervous system is a vast and complicated 
 molecular mechanism, all coming under the general bio- 
 logical law. Moreover, we have to notice that the nerve- 
 cells, modified as they are by repeated excitation, preserve 
 and perpetuate the modification under the biological laws 
 of the nutrition of living organisms. The exercise of any 
 group of nerve-cells tends to procure their enlargement by 
 appropriation of the nutriment brought to them in the 
 blood-supply. And when these cells, thus enlarged and 
 molecularly altered according to the character and amount 
 of their exercise, multiply themselves, their offspring come 
 under the general principle of heredity in its application 
 to all living mechanisms. 
 
 The precise nature of the molecular modifications, which 
 are thus perpetuated and propagated in the elements of 
 the nervous system, is unknown. To speak of them as "per- 
 sistent vibrations," that are " weaker echoes " of the nerve- 
 commotions produced by the original stimulations, seems 
 to us neither good physics nor sound physiological psychol- 
 ogy. They are, rather, a specially complicated instance of 
 the general biological principles of modified molecular con- 
 stitution, increased nutrition, and inheritance of acquired 
 characteristics. 
 
 The physical basis of memory, as retentive, is therefore 
 laid in the habit, or acquired tendency, of the elements of 
 the nervous system. This tendency has respect both to 
 the individual elements and to the association of groups of 
 these elements. Each element — speaking figuratively — 
 may be considered as a minute area intersected by an 
 indefinite number of curves of different directions and 
 orders. Thus a molecular commotion in any such area 
 may run out into the system along any one of innumerable 
 
424 PHYSIOLOGICAL PSYCHOLOGY. 
 
 curves. In every suehi small fragment " the whole curve 
 slumbers." 
 
 Physiological Theories of Reproduction. — The nature of 
 the physical basis of memory, considered as reproductive, 
 is even more purely conjectural than that of memory 
 considered as retentive. The most probable conjectures, 
 however, are those which follow along the Unes already 
 indicated. A perpetuation of persistent and similar vibra- 
 tions in the form of " weaker echoes " does not seem prob- 
 able. The term, " dynamical associations," has been chosen 
 by one writer (M. Ribot) to describe those tendencies to 
 allied and combined action which become established in 
 and between the different nerve-elements and cerebral 
 centres. 
 
 Another writer (Professor Wm. James) has expressed 
 his views as to the nature of the physical basis for the laws 
 of association as follows : " The amount of activity at any 
 given point in the brain cortex is the sum of the tendency 
 of all other points to discharge into it, — such tendencies 
 being proportionate (1) to the number of times the excite- 
 ment of each other point may have coexisted with that of 
 the point in question ; (2) to the intensity of such excite- 
 ments; and (3) to the absence of any rival locality or 
 process functionally disconnected with the first point, into 
 which the discharge might be diverted." " Every presen- 
 tation," says another writer (FouilMe), "tends to associate 
 with other presentations on account of the identity of their 
 seat in the brain. . . . Contiguity in time links things only 
 by means of a contiguity in extension of the brain. Thus 
 are established in the nerve-paths, as on the railroads, junc- 
 tions analogous to those where the switchman determines 
 the course of the trains." [Is there, then, something to be 
 said of a mental "switchman" determining the course of 
 these trains of ideas ?] But these, and all similar physio- 
 logical theories of reproduction, seem to us far too simple 
 
COiJSCIOtJSNBSS, MEMORY, AND WILL. 426 
 
 to account for the phenomena as we have real experience 
 of them, — including the control of association by attention, 
 by sesthetical and ethical and other interests, and that 
 peculiar accompanying condition of conscious memory 
 called recognition. 
 
 Reproduction involves Forgetfulness. — " To live is to 
 acquire and lose ; life consists of dissolution as well as 
 assimilation. Forgetfulness is dissolution." This is true 
 whether we consider the subject from the mental or from 
 the physiological point of view. If all the alterations of 
 the intramolecular constitution of the nerve-cells were 
 alike conserved and propagated, and if all the " dynamical 
 associations " among the groups and centres composed of 
 the cells were always alike stable, then no basis could exist 
 for specific and characteristic reproduction of the memory- 
 images. 
 
 In the phenomena of aphasia we see how temporary or 
 permanent forgetfulness of classes of images, or of definite 
 and particular images, may be due to functional or organic 
 derangement of the cerebral centres. The same thing, in 
 less degree, is shown in the loss of memory caused by dis- 
 turbances of the blood-supply of the cerebral centres. 
 Moreover, when a number of nerve-commotions, arising in 
 different associated centres, flow together and inhibit each 
 other in a certain area, loss of the memory of objects whose 
 impressions are received in this area may be the result. 
 Whatever interferes with the working of the so-called 
 " dynamical associations " leads to confusion or forgetful- 
 ness of the memory-images. On the other hand, whatever 
 quickens and mxiltiplies the working of these associations 
 results in acceleration and enlargement of the circuit of 
 conscious memory-images. 
 
 Organ of Memory. — No tenable ground exists for speak- 
 ing of a special organ or seat of memory. Every organ — 
 indeed, every cerebral area and every psychic " nerve-cell " 
 
426 PHYSIOLOGICAL PSYCHOLOGY. 
 
 — has its own memory. What Cardinal Newman once 
 said of the psychical faculty is true of the organic basis : 
 "There are a hundred memories as there are a hundred 
 virtues." Every sense and every so-called faculty, so far 
 as it comes under the biological laws applying to retention 
 and reproduction at all, does so in the particular and 
 definite associated areas where its physical basis is laid. 
 There is sound reason, then, for speaking of a "memory of 
 the ear," " memory of the eye," etc. 
 
 There is, then, no one place where alone memory is at 
 home in the brain. Yet the memory of any perception of 
 the senses, any complex state of feeling, or of ideation, 
 involves a large number, not only of contiguous nerve-ele- 
 ments, but of more or less remotely allied centres of the 
 brain. On this point again we might appeal to the phe- 
 nomena of cerebral localization, — especially of aphasia and 
 other pathological phenomena. This is true even of those 
 cases where some particular date or name seems to slip 
 away beyond the power of recall. For example, we -have 
 record of a patient who, after a fever, lost all knowledge 
 of the letter F. 
 
 Complexity of the Mental Phenomena. — The laws of repro- 
 duction, or of the so-called association of ideas, have been 
 the subject of curious and painstaking interest for hundreds 
 of years. Probably no other subject in introspective psychol- 
 ogy has received so much attention. In the attempt to 
 simplify, the claim has repeatedly been made that they could 
 all be reduced to a small number of principles, — perhaps 
 even to a single law, like the " law of contiguity " or the 
 "law of redintegration." We shall not enter this contro- 
 verted field; it lies apart from the researches special to 
 physiological psychology. In our judgment, however, the 
 allied experimental and phj'^siological researches indicate 
 that the number of principles concerned in the reprodue- 
 
CONSCIOUSNESS, MEMORY, AND WILL. 427 
 
 tion of mental images must be greatly increased rather 
 than diminished. 
 
 The researches of Ebbinghaus into the principles regu- 
 lating his own power to learn and to remember series of 
 " nonsense syllables " (see p. 421) led him to emphasize 
 two pre-eminent sources of influence over the mental train 
 of reproduced images. These were (1) changes in the con- 
 centration of attention ; and (2) unconscious influence from 
 theories and opinions. But if this be so, how immensely 
 complex and profound must be the reasons which control 
 the reproductive energy of the entire life of any individual 
 mindr All the psychical, and all the biological, history 
 of each individual expresses itself in every act of repro- 
 duction. 
 
 The great complexity of the phenomena of associated 
 reproduction of mental images may be further illustrated 
 by the answer to the following question : When a series 
 ab c d ef g has been learned, does a recall h, and b recall 
 c, and so on ; or does a recall b, and tend also to recall c, d, 
 and the rest? In other words, do the bonds of association 
 which imite the memory-images extend below conscious- 
 ness, as it were, though in a diminishing degree, to all the 
 distant members once held together in the " circuit of con- 
 sciousness " ? The researches of Ebbinghaus answer this 
 question affirmatively. Learning once a series of even 16 
 " nonsense syllables " saves time on attempting to relearn 
 this series, in whatever manner its members, when relearned, 
 are related to each other. The strength of association, as 
 measured by this saving of time in relearning, is indicated 
 by the following table : — 
 
 Per cent. 
 Saving of time on relearning is, between contiguous members . 33.3 
 Saving of time on relearning is, skipping one syllable .... 10.8 
 Saving of time on relearning is, skipping two syllables .... 7.0 
 Saving of time on relearning is, skipping three syllables ... 5.8 
 Saving of time on relearning is, skipping four syllables .... 3.3 
 
428 PHYSIOLOOICAI, PSYCHOliOGi^. 
 
 Experiment shows also that the bonds of association ex- 
 tend backward — though with an inferior degree of strength 
 — as well as forward. The same researches placed the 
 saving of time in relearning, with inversion only, at 12.4 
 per cent. ; with inversion and skipping of one syllable, at 
 5 per cent. 
 
 A reference to the fact that reaction-time is lengthened 
 by increasing the complication and unusual character of 
 the association processes, and shortened by practice and 
 attention, reinforces the same conclusion. In reviving 
 established associations of ideas the entire mental history is 
 involved. But in forming new associations, especially, as 
 well as also in reproducing the established ones, tempera- 
 ment, disposition, and conscious regard for utilitarian, 
 ethical, and sesthetical interests, are potent influences. 
 
 The complexity of the phenomena called " mental " 
 doubtless implies a somewhat corresponding complication 
 of the brain-processes concerned in the reproduction of 
 memory-images. In brief, the adult brain is a system of 
 vastly intricate and interrelated molecular mechanisms. 
 It has been, during its entire histoi'y. in the process of vital 
 organization of these intricate interrelations. The par- 
 ticular brain-processes concerned in each act of reproduc- 
 tion all fall under the laws which control the general 
 biological process of perpetual organization. The mental 
 phenomena are a series of related " circuits of conscious- 
 ness," — overlapping and fading into each other. The brain- 
 processes are a succession of related nerve-commotions in 
 centres contiguous and distant, — also overlapping and 
 fading into each other. 
 
 The Psychical Act of Conscious Recognition. — The fore- 
 going conjectures have to do with the explanation only 
 of what is sometimes called an "organic memory." But 
 so-called " organic memory " is a purely physical affair. 
 It is utterly lacking in the power to suggest an explana- 
 
CONSCIOUSNESS, MEMORY, AND WILL. 429 
 
 tion for that conscious recognition which is the peculiarity, 
 and the peculiarly baffling mystery, of memory as a truly 
 mental affair. Let us then consider what is involved when 
 / remember this or that, — as we are wont to say. 
 
 The experience of consciousness is one of a constantly 
 changing succession of states. The rise and fall of vol- 
 untary or involuntary attention, and the change in its 
 direction, are accompanied by — rather are factors in — a 
 constant shifting of the phases and circuit of conscious- 
 ness. But of these shifting mental complexes, some bear 
 a most peculiar mark. In their very nature they claim to 
 reproduce distant and past phases or circuits of conscious- 
 ness. They are, sui generis, " representative " of the past. 
 But of whose past ? for there is no circuit of consciousness, 
 regarded as previously completed, that must not be attrib- 
 uted to some Ego, some mind. And there is no memory- 
 image, claiming to represent such circuit of consciousness, 
 that does not involve the conscious recognition of that 
 particular image, as representative of its own past, by the 
 same mind. These fundamental truths are not in the least 
 affected by any actual or conceivable mistakes of memory. 
 They simply describe the actual and indisputable pecul- 
 iarity of that factor of conscious recognition which belongs, 
 sui generis, to memory as a psychical act. 
 
 This peculiar and mysterious claim of the memory- 
 image, to represent my past state (of perception, feeling, 
 thought, etc.) is not, strictly speaking, verifiable by an act 
 of comparison. Were I to attempt this, the perception of 
 the object, renewed for purposes of comparison, would be 
 a new perception, — ■ another and different mental act ; and 
 the memory-image, revived for purposes of comparison, 
 would be a new reproduction, involving the mystery of 
 memory, as conscious recognition, in the same inexplicable 
 form. 
 
 We cannot even conceive of the nature of a physiologi- 
 
430 PHYSIOLOGICAL PSYCHOLOGY. 
 
 cal process which would serve as an " explanation " in any 
 sense of the word, for this characteristic of recognition, 
 this self-appropriation as belonging to the past of the same 
 Ego, or mind, which enters into all conscious memory. 
 All that any physiological process could possibly explaiij, 
 in case we knew its nature most completely, would be why 
 I remember one thing rather than another — granted the 
 inexplicable power of the mind to remember (consciously to 
 recognize the present state as representative of its own 
 past) at all. We repeat then the declaration of several 
 years ago : " This power is a spiritual activity wholly sui 
 generis, and incapable of being conceived of as flowing out 
 of any physical condition or mode of energy whatever." 
 
 The connection of Attention, both voluntary and invol- 
 untary, with the phenomena of reproduction under the 
 law of association, is manifest. The discussion of mem- 
 ory leads us therefore to consider, — 
 
 PSYCHO-PHYSICAL THEORIES OF WILL. 
 
 Several of the topics already discussed have included 
 those phenomena in which so-called " acts of will " take 
 part as factors. This is true of " psycho-physical reac- 
 tion-time," and its lengthening or shortening according as 
 it does or does not contain a choice between methods of 
 reaction (see p. 371 f.). It is also especially true of the 
 effect of voluntary attention upon the bodily movements, 
 and upon the associated ideas which constitute the men- 
 tal train (see p. 410 f.). From the very first, the experi- 
 ments and theories of physiological psychology have been 
 turned toward the consideration of the " will." The inter- 
 est which such inquiries awaken, on account of their con- 
 nection with problems in ethical philosophy and in the 
 philosophy of religion, is too obvious to need more than a 
 mere mention. Our general purpose, however, leads us to 
 
CONSCIOUSNESS, MEMORY, AND WILL. 431 
 
 limit the discussion of the subject to those few points 
 upon which some experimental evidence, however meagre, 
 can be gathered from the department of science we are 
 exploring. 
 
 General Physical Basis of Acts of Will. — If we use the 
 general term "will" to describe all those mental phenom- 
 ena which seem to secure the conscious direction or control 
 of the bodily movements or of the mental train, we may 
 make a probable assertion respecting their general physi- 
 cal basis. This basis is, especially, that power of automa- 
 tism which is concentrated, so to speak, in the nerve-cells 
 of the central nervous system, " Automatism," or the 
 power of originating molecular changes which cannot be 
 explained wholly by reference to the transmitted influence 
 of external stimuli, belongs to all living protoplasm. It is 
 on the basis of this fact that, as it is sometimes said, an 
 amoeba has " a will of its own." 
 
 The attempt has been repeatedly and persistently made 
 to refer all the phenomena of living organisms to the order 
 known as the "sensory-motor reflexes" (see p. 135 f.). 
 Recently this attempt has been extended (particularly by 
 Miinsterberg and others) so as to include, without exception, 
 all the highest psycho-physical processes. The principal 
 justification of the thorough-going character of this attempt 
 is our ignorance, and the desire to establish a single con- 
 sistent theory for all cases of vital activity. But so long 
 as physiology utterly fails to bring even the movements of 
 a minute amoeboid speck, or the behavior of the spinal 
 cord of a decapitated frog, under any theory of " sensory- 
 motor reflexes," we shall have (a fortiori^ to acknowledge 
 that the power of automatism belongs, in a peculiar way 
 and high degree, to the cerebral centres. 
 
 No Special Organ of Will. — It has already been shown 
 that " organic memory " is not a property of any one ner- 
 vous centre, or group of centres, located in the brain. The 
 
432 PHYSIOLOGICAL PSYCHOLOGY. 
 
 same thing is true of that property of automatism in which 
 we find the physical basis of will. Every centre of the 
 nervous system which is capable of originating molecular 
 changes in response to internal stimuli may be an organ 
 of will so-called. 
 
 But an act of the will is always an act of some particular 
 kind. There can be no volition to motion in general ; but 
 only a volition defined and limited to the movement of 
 certain limbs, or of the trunk including the limbs, with a 
 certain direction and degree of motion. Thus also every 
 act of will, for the clearer "apperception" of some object 
 in the circuit of consciousness, or for the control of the 
 mental train, is necessarily limited and defined. And the 
 physical basis of each act of will is laid in the appropriate 
 physiological action of those centres of ideation, apper- 
 ception and motion, which are concerned in that particular 
 act of will. Whenever an act of will takes place, then at the 
 cerebral areas which are correlated with that particular act, 
 the appropriate molecular changes arise in the '•'psychic 
 nerve-cells.''^ 
 
 Kinds of Acts of Will. — From the point of view held by 
 the student of ethics, it may seem incorrect and even 
 absurd to deny freedom to any so-called " act of will." But 
 from the point of view taken by physiological psychology 
 the whole matter presents itself in a different light. We 
 have already spoken of involuntary movements, that are 
 not impulsive, and of forced acts of attention (see p. 408 f.). 
 Both these phenomena imply " uni-motived " acts of will ; 
 that is, acts of will where there is no consciousness of 
 acting freely or of exercising choice, but rather the 
 contrary. 
 
 On the other hand, there are acts of will which involve 
 an indefinite amount of antecedent deliberation, of weigh- 
 ing of reasons and motives, and final choice made with the 
 clearest conviction that it is our responsible and free 
 
CONSCIOUSNESS, MBMOEY, AND WILL. 433 
 
 action. And between these two extremes there are all 
 degrees of the rational and voluntary factors in different 
 so-called " acts of will." A psychology, which is true to 
 experience, is compelled to admit that what we prize as 
 freedom of will is a matter of development, with an infi- 
 nite variety of degrees. But what corresponding provision 
 shall physiology suggest as necessary for those different 
 processes that constitute the physical conditions of these 
 phenomena? Only one answer seems to us defensible. 
 It is this : a brain, developing under biological laws, and 
 standing in its peculiar relation to the unfolding of the life 
 of consciousness, with an infinite variety of ways of blending 
 reflex sensory-motor and automatic processes in its allied 
 centres. 
 
 Every so-called act of will is then the expression of the 
 combination of several kinds of physiological processes, 
 accomplished in the centres of the brain. These may 
 include (1) sensory excitations coming from one or more 
 of the end-organs of sense ; (2) reciprocal excitement of 
 allied cerebral centres in which the processes concerned in 
 the appropriate perceptions and memory-images, with their 
 accompanying tones of feeling, are taking place ; (3) ten- 
 tative and anticipatory motor impulses which mark the 
 felt tendency to innervate particular groups of muscles; 
 and, finally, (4) a certain automatic activity of particular 
 nerve-centres under influence from the mental phenomena 
 we call " choice," — a thing which physiological science is 
 wholly unable to explain but not competent to deny. 
 
 It is the resultant of these combining processes which 
 represents on the physiological side, the complex conditions 
 of the " so-called acts of will." These acts, as they appear 
 in consciousness, are characterized by corresponding psy- 
 chical characteristics. (1) They may be more or less 
 mechanically controlled or forced by the intensity of sen- 
 sation ; (2) they may comprise a larger or smaller number 
 
434 PHysiOLOGicAL psychology. 
 
 of clear or confused perceptions and memory-images witli 
 differing intensities of different kinds and tones of feel- 
 ing ; (3) they may involve inchoate and anticipatory feel- 
 ings of effort, or strain, that signify the drawing of attention, 
 the rising in consciousness of a nisus, in one or more of 
 several directions ; (4) they may culminate, as it were, in 
 a decided choice, with its accompanying and following 
 conviction that this act is, in a peculiar and even unique 
 manner, our own. 
 
 It is, of course, the factor of choice — No. (4) — which 
 we designate as pre-eminently belonging to will. Choice is 
 not, indeed, the whole of will. There can be no act of the 
 mind as will, in the highest meaning of the words, which 
 does not involve all the other above-mentioned sets of fac- 
 tors, both psychical and physiological. Choice is, how- 
 ever, the central and distinguishing factor of those acts 
 which deserve, above all others, to be ascribed to the 
 inner and independent life of the conscious mind. In 
 the popular imagination — and we believe justly — choice 
 implies a real influence of the mind over the body. 
 
 In terms of psycho-physical science : The existence of 
 those states of consciousness, which are known to the sub- 
 ject of them as his choice, determines the arising of appro- 
 priate and correlated molecular changes in the higher and 
 controlling centres of the brain. If this fact is ultimate 
 and inexplicable, it is not, on that account, to be disputed 
 as a fact. The evidence for this fact, from experimental 
 and physiological psychology, is by no means small. We 
 shall now present it — though only briefly and in part. 
 
 Dependence of Sensation and Perception on Will. — Many 
 things which we clearly perceive, or intensely feel, or 
 vividly remember or imagine, we cannot — as we say — 
 " help " attending to. The sudden flashing of a light, or 
 the passing of a bright object across the field of vision, the 
 unexpected loud noise, the smells in the atmosphere, the 
 
CONSCIOUSNESS, MEMORY, AND WILL. 435 
 
 tastes of our food, the sensations of the skin or internal 
 organs, force themselves upon attention. Such phenomena 
 tend to confirm the crude statement, recently renewed 
 with manifold assertions and imposing array of argument, 
 by Dr. Miinsterberg : " The will is only a complex of sen- 
 sations." The act of will, even in its highest form, is to 
 be explained — this authority argues — as a sensory-motor 
 process, by the ordinary presuppositions of natural science, 
 and without the help of any immaterial principle. 
 
 But there are other phenomena which defy such easy- 
 going attempts at solution of the mystery of body and 
 mind. [The diminishing of discernment-time by voluntary 
 attention has already been remarked (p. 371).] When, for 
 example, we are attending to any sensation which is peri- 
 odically repeated but very weak, fluctuations in its inten- 
 sity constantly tend to occur. Thus a black radius on a 
 white disk, when revolving, can be made to lengthen and 
 shorten alternately. So the ticking of a watch can, by 
 placing its distance aright, be made somewhat rhythmically 
 to alternate between audible and inaudible. Now if atten- 
 tion, when directed to the sensation, is left to itself, as it 
 were, it will vacillate with a regular periodicity — the 
 explanation of which is not quite clear, and the length of 
 which differs for different senses and under different cir- 
 cumstances. But voluntary and concentrated self-directed 
 attention influences this period. 
 
 By voluntary attention we can intensify a sensation, and 
 make clearer a perception or idea, in consciousness. We 
 incline, indeed, to attend to the stronger of two excitations 
 of sense ; but, within certain limits, we can attend where 
 we will. We incline to attend to objects lying in the point 
 of regard of the visual field ; but we can will to attend to 
 objects lying in the outward portion of this field. By vol- 
 untary attention we can bring into clear consciousness the 
 otherwise invisible double images. Some experimenters 
 
436 PHYSIOLOGICAL PSYCHOLOGY. 
 
 with the phenomena of " conflict of colors," when a green 
 image is formed on one eye and a red on the other, can see 
 either, or combine the two, at will. 
 
 The analysis of complex sensations or perceptions may 
 also be performed at will. Voluntary concentration of 
 attention is necessary for the musician to hear the over- 
 tones which combine with the fundamental tone to consti- 
 tute a " clang." In mastering any complex visual object, 
 the fixation and wandering of the point of regard is, to a 
 certain extent, under the control of will. On waking grad- 
 ually from sleep, our surroundings become more and more 
 clearly defined to eye, ear, and skin, as the grade of 
 voluntary attention in analysis and discernment rises. 
 Voluntary concentration of attention, not infrequently, 
 completely dispels the illusions of sense. In expectation 
 of a particular sense-impression, concentrated voluntary 
 attention may so affect the cerebral centres as to anticipate 
 the expected perception ; it may so intensify some weaker 
 similar impression as to cause it to be mistaken for the 
 expected impression. 
 
 In fact, all experience is full of similar facts. All lan- 
 guage implies them. We cannot say, with emphasis, 
 Listen ! or Look ! — instead of Did you hear or see ? — 
 without witnessing to the influence upon the organism of 
 the mental act of choosing to attend to a particular sensa- 
 tion or perception. 
 
 Closely connected with, and indeed involved in, phe- 
 nomena like the foregoing are the following facts, which 
 bear witness to the influence of Will over the cerebral 
 centres. 
 
 Dependence of Muscular Movement and Tension on Will. — 
 No one is disposed to dispute that a large portion of our 
 muscular movement, or muscular tension in the direction 
 of movement, is reflexly or impulsively originated. In 
 such cases there is no question as to the dependence of 
 
CONSCIOUSNESS, MEMORY, AND WILL. 437 
 
 the cerebral centres as regards the psychical operation 
 of conscious choice. It is undoubtedly also true that 
 the muscles cannot be voluntarily innervated unless they 
 have been previously called into action reflexly or impul- 
 sively, so as to furnish sensation-complexes and mem- 
 ory-images of such complexes, to serve as the objects 
 for voluntary attention and choice (compare p. 411). We 
 have also aiBrmed the opinion that the so-called feelings 
 of effort and strain originate at the periphery of the body, 
 in the conditions of skin, muscles, tendons, and joints. If 
 we had only such phenomena of muscular movement to 
 discuss, we might satisfy the demand for explanation by 
 denying the influence of choice upon the cerebral centres 
 and through them upon the muscles of the body. 
 
 But there is a large class of phenomena — both involved 
 in ordinary experience and elicited by experiment — which 
 plainly belong to another order. We can, within certain 
 limits, decide " at will " — as we say — the speed, energy, 
 rhythm, and magnitude of muscular contraction, and so 
 the complexity and form of the resulting movements. 
 This we do whenever we raise a weight, for example, by 
 estimating in units of whatever standard of sense the char- 
 acter and amount of innervation of the muscles required 
 to raise it. All deliberate and rational control of our 
 bodily organs — and such control enters into the entire 
 conscious life of apperception and representation — im- 
 plies, and depends upon, the use of this power. 
 
 But we have also the unique and mysterious power of 
 inhibiting the muscular movements which would otherwise 
 be called forth by external and internal stimuli. On this 
 point Gad has shown that the reflex stimulation of the 
 eyelids with vapor of ammonia can be voluntarily inhib- 
 ited; Briicke and others have demonstrated our power 
 at will, to weaken the effect of the direct stimulation of a 
 muscle by electricity ; Eichhorst has called attention to the 
 
438 PHYSIOLOGICAL PSYCHOLOGY. 
 
 . fact that the trembling of palsy can be partially suppressed, 
 if the subject choose. 
 
 The terms " unique and mysterious " have just been 
 applied to this power of inhibition at will. Recent experi- 
 ments have seemed to disprove that this power consists in 
 the innervation of muscles antagonistic to those called into 
 action by the impulses reflexly originated. For there are 
 muscles under the control of will that have no antago- 
 nistic muscles. The muscle used in accommodation of the 
 eye is a typical instance of such an " autonomous " muscle. 
 The facial nerve, which, of all the motor nerves, has the 
 most direct anatomical connection with the higher motor 
 centres, controls muscular action in the same way. What 
 a " servant of the soul," for the voluntary and involuntary 
 expression of the life of the soul, is here employed ! 
 
 Now the reaction-time of inhibition, after brief practice, 
 appears not to differ from that of direct impulse. On vary- 
 ing the tension and amplitude of the muscular excursion, 
 the change in the " inhibition-time " follows closely upon 
 the change in " impulse-time." It is a legitimate conclu- 
 sion, then, that the paths in which the physiological basis 
 of will runs, are identical for both impulsive and inhibi- 
 tory volitions. It would seem that the place where the 
 nerve-waves, which originate the inhibition, interfere with 
 the nerve-waves which would otherwise originate the reflex- 
 motor impulse, is the common "psycho-motor" centre. 
 The direct voluntary control over the muscle, to modify 
 or to diminish the amount of its contraction, is, there- 
 fore, the expression of the influence of the will over this 
 " psycho-motor " centre. 
 
 Dependence of the Memory-images upon Will. — No part of 
 our complex mental life appears to be so completely a 
 matter of mechanism, conducted before the conscious mind 
 rather than by it, as does the so-called association of ideas. 
 This fact has already been made prominent by the phe- 
 
CONSCIOUSNESS, MEMORY, AND "WXLL. 439 
 
 nomena of reaction-time (see p. 375 f.). But eren in this 
 part of mental life, the effect of voluntary attention and 
 of conscious choice is unmistakable. This effect may, 
 indeed, be so great as to impart to the memory-images the 
 vividness of perceptions, by intensifying them and defi- 
 nitely localizing them anew in the organs by which their 
 originals were formed. This fact connects this form of 
 activity, springing from will, with the voluntary influence 
 of sensation and perception. 
 
 Artists in kinds of art which involve a special suscep- 
 tibility and activity of certain of the senses, are, of course, 
 also gifted with a specialized creative and reproductive 
 energy of imagination. Some classes of mental images 
 tend to force themselves upon us all, whether we will, or 
 not. But, on the other hand, we can all seize upon par- 
 ticular mental images, at will ; and by concentrating 
 attention upon them can clarify and strengthen them. 
 The artist's weakness and his voluntary power are both 
 special in these regards. Moreover, one can surrender 
 one's self to a comparatively passive attitude before the 
 train of associated ideas, — as when, for example, one 
 indulges in reverie and day-dreaming. Or one (within 
 certain limits) can say, to these ideas : Begone from con- 
 sciousness ! and one can enforce one's will by concen- 
 trating attention on objects of perception, or by turning 
 into other lines the mental train. 
 
 Rhythm of Attention in Perception and Association. — We 
 have already seen that weak sensations tend to rise and 
 fall below the " threshold of consciousness " in a periodic 
 way; in other words, they fluctuate rhythmically in con- 
 sciousness. This period is different for different sensa- 
 tions ; for example — as given by N. Lange — it is 3.4 
 sec. for optic vacillations, and not less than 4.0 sec, for 
 acoustic. The fluctuations of sensation this observer 
 attributes to fluctuations in attention dependent upon 
 
440 PHYSIOLOGICAL PSYCHOLOGY. 
 
 exhaustion of the cerebral centres. This explanation, so 
 far as the assumption that voluntary attention directly 
 influences the cerebral centres to exhausting molecular 
 energy, we esteem correct beyond doubt. Although it has 
 been shown recently (by Miinsterberg) that peripheral 
 changes also have a great, and even a determining influ- 
 ence, over the occurrence and the periodicity of these 
 fluctuations. 
 
 During his experiments in learning and relearning 
 " nonsense syllables " Ebbinghaus found indications of a 
 remarkable rhythm in attention. There is, he thinks, a 
 periodic oscillation of the mental susceptibility to intense 
 concentration of attention, in which " the increasing fatigue 
 seems to vary about a gradually shifting middle position." 
 Thus, in 84 experiments with six 16-syllable series, the 
 mean time for learning the 1st series was 191 sec. ; for the 
 2d, 224 sec. ; for the 3d, 206 sec. ; for the 4th, 218 sec. ; 
 for the 5th, 210 sec. ; for the 6th, 213 sec. Such a result 
 can scarcely be due to anything else than a periodic 
 exhaustion and recovery of the cerebral centres under the 
 influence of attention as an act of will. 
 
 Phenomena like the foregoing are often appealed to in 
 proof of the complete dependence of the so-called free 
 choice to attend upon the condition of the nerve-centres of 
 the brain. As -to a dependence in this direction, there need 
 be no doubt. But the primary and really astonishing fact 
 is that the mind's choice to attend exhausts the cerebral 
 centres by making them do intense and concentrated work. 
 The dependence of the activity of the ^'■psycho-motor " centres 
 upon the purely psychical phenomenon of voluntary choice to 
 attend is the most important and marvellous of all psycho- 
 physical facts. 
 
 The Experiments of Miinsterberg. — This investigator has 
 already been quoted as holding that will is nothing but a 
 "complex of sensations," a "definite grouping of sensa- 
 
CONSCIOUSNESS, MEMORY, AND WILL. 441 
 
 tions," etc. Now, from the point of view of self-conscious- 
 ness nothing can well be more false and misleading than 
 such statements as these. It is precisely this which we do 
 not mean when, without having been prejudiced by so- 
 called psycho-physical science (?), we candidly state our 
 conscious experience. The words " I will," or " I choose," 
 have a perfectly definite meaning as describing an activity 
 of the mind ; and this meaning is markedly different from 
 that which we give to the words " I have this or that set 
 of feelings or sensations." 
 
 Most students of physiological psychology who deny 
 that the mind is capable of real choice, but affirm rather 
 that what appears in consciousness as its choice is really a 
 definite sensation-complex " dictated to it by the cunning 
 conjurer, the brain," attempt to base their opinions on an 
 induction from facts. This Dr. Miinsterberg attempts. 
 In our judgment — and, for the present, granting the 
 accuracy of his experimental data — the attempt fails. His 
 experiments show that the time of a free association is 
 briefer than that of a limited association (the type of the 
 latter being as follows : Given a general term, to name an 
 instance under ft). They show that a " question-answer 
 association" (e.g. On what river is Cologne ?) is also briefer 
 than that of a limited association. But these facts may 
 reasonably be held to be due to the general truth that it 
 does take time to initiate those cerebral processes which 
 are correlated with deliberate intelligent choice. 
 
 It may also be admitted that Miinsterberg's experiments 
 add strength to the opinion that, in complex associations, 
 both the mental and the cerebral processes regularly over- 
 lap. " The mind is not a point through which each process 
 must pass in turn, but is a place in which the most com- 
 plex interactions have their play." And certainly the 
 brain is very far from being a point. This admission is 
 indicative of the exceedingly subtile and complex relations 
 
442 PHYSIOLOGICAL PSYCHOLOGY. 
 
 which exist between the different cerebral centres, and 
 between these centres and the mind. 
 
 We know of no evidence from the experiments of phys- 
 iological psychology which proves anything against the 
 possibility of what consciousness testifies to, — namely, a 
 real psychical phenomenon, unique and different from all 
 mere definite content of sensation and mental images, 
 which is, in the order of nature, a determining factor for 
 the excitation of the " psycho-motor " areas of the brain. 
 
 Special Physiological Conditions of Choice. — What happens 
 in the brain when, after two or more conflicting presenta- 
 tions of sense, or conflicting ideas, and a period of delibera- 
 tion, one of them is made the object of choice ? In answer 
 to a similar question a celebrated physiologist responded 
 some years since : " We know absolutely nothing." Of the 
 physiological processes which accompany the mental prep- 
 aration of the choice, it would seem that either one of two 
 things may be true. The more intense of the conflicting 
 processes may prevail over the others and gain possession 
 
 — as it were — of the appropriate "psycho-motor centres"; 
 or the several processes may persist and interpenetrate. 
 An example of this kind of alternative may be taken from 
 the phenomena of the "conflict of colors." But, looked 
 at from the point of view of consciousness, it is obvious 
 that the will, or choice of the mind, may decide a question 
 of conflicting perceptions or ideas. What precise physio- 
 logical process corresponds to this psychical act of choice, 
 
 — the mental phenomenon of decision after deliberation ? 
 The same confession of ignorance quoted above seems to 
 exhaust the subject. 
 
 We have seen that the effect of voluntary attention is 
 most marked upon the cerebral centres. By it some of 
 them appear to have their molecular energy relatively 
 depressed; and others are relatively heightened. By it 
 the entire mechanism of the brain may be called upon for 
 
CONSCIOtrSNESS, MEMORY, AND WILL. 443 
 
 a rapid conversion into kinetic form of the stored energy 
 of its nerve-cells. Thus, under the influence of attention 
 the "entire cerebrum (and the different cerebral centres 
 with varying relative degrees) is put into a condition of 
 changed susceptibility to external and internal stimuli, as 
 well as to the discharge of "psycho-motor" energy along 
 the various efferent nerve-tracts. Concentrated voluntary 
 attention implies a large amount of work in process of 
 accomplishment, within the cerebral centres. The feelings 
 of strain and exhaustion, the profuse sweating which often 
 accompanies experiments in reaction-time, are in testimony 
 on this point. 
 
 Choice is — as every one knows — followed by a sense 
 of relief from strain ; it is apparently significant of the sub- 
 sidence of that condition of conflicting states of tension 
 and nerve-commotion which has, before the consummation 
 of choice, prevailed in certain cerebral areas. But, as has 
 already been twice said, precisely what it is that is brought 
 about by will (or the mind making a choice), physiological 
 science cannot say. Nor does such science furnish the 
 slightest valid ground for the assertion that the choice is 
 not, what it appears in consciousness as being, — a psychi- 
 cal occurrence that determines the adjustment of physical 
 relations between the parts of the bodily organs. This 
 adjustment is, however, not primarily one of the visible 
 and gross masses of this organism, but of the molecular 
 conditions and activities of those "psycho-motor" areas 
 which control these masses. 
 
 Physical Basis of the " Higher Powers." — We decline to 
 enter upon the discussion of the question : What special 
 molecular conditions and activities are correlated with the 
 mental processes called "abstraction," "generalization," 
 etc. ; or with the higher sesthetical and ethical feelings and 
 ideas ; or with those norms of all rational life which 
 philosophy has been wont to call the " intuitions " or the 
 
444 PHYSIOLOGICAL PSYCHOLOGY. 
 
 " categories " of the mind ? Upon these subjects our igno- 
 rance is not only profound, but also — it would appear — 
 hopeless. No other higher wisdom in this field is known 
 to physiological psychology than that illustrated in the fol- 
 lowing quotation from Lotze : " For all the higher spiritual 
 faculties, which consist in judgment of the relations of 
 given conceptions, we neither 'know how empirically to 
 demonstrate a definite bodily organ, nor should we know 
 how to conceive precisely what, that is of any use, such an 
 organ could contribute toward the solution of the problem 
 — that is, the pronouncing of the judgment itself. It is 
 conceivable, on. the other hand, that these higher activities 
 might presuppose the complete and clear representation 
 of the content about which the judgment is to be passed, 
 and, consequently also the undisturbed function of those 
 organs which contribute, first, to perception by the senses ; 
 then to reproduction and combination with other percep- 
 tions ; and, finally, to the appropriate attachment of feelings 
 of value to each of them." 
 
CHAPTER XVIII. 
 
 AGE, SEX, AND TEMPERAMENT. 
 
 The relations between mental states and physiological 
 conditions and activities, which have been thus far exam- 
 ined, are in general subject to sudden alterations. From 
 moment to moment of our daily life the quantity, quality, 
 time-order, and mental combination, of our sensations are 
 dependent upon the amount, kind, rate, and conjunction or 
 opposition of the stimuli. When, however, we consider the 
 psycho-physical theories of memory and will, as well as of 
 mental moods, we find more relations of a statical character 
 established between mind and body. 
 
 There are certain relations of the mental phenomena to 
 the physical basis which change their character very 
 slowly, or do not change at all. One cannot alter one's 
 sex, parentage, or race-inheritance. In the correlated 
 development of the body and' mind, as dependent upon 
 the time of life, marked changes come, for the most part, 
 only gradually. Here, however, epochs of change occur 
 in both sets of characteristics, such as emphasize the 
 dependence of the latter upon the former. A genuine 
 and clearly marked " temperament " may be combated 
 successfully ; but the fact of the struggle reveals that 
 firm possession of the seat of influence over mental life 
 which certain obscure inherited physical traits customarily 
 maintain. 
 
 It is these " statical " relations between the life of mind 
 and its bodily basis which we now propose briefly to exam- 
 ine. The examination will only include the three points, of 
 
 445 
 
446 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Age, Sex, and Temperament. On all these subjects the col- 
 lection of data inTolves an exploration of wide and uncer- 
 tain fields. The entire investigation' is, indeed, rather 
 anthropological than strictly physiological or psychological 
 in its nature. In both the physical and the psychical series 
 there are necessarily many gaps and deficiencies. The con- 
 clusions — if such they can be called — must be received 
 with this understanding, 
 
 RELATION OF MIND AND BODY DEPENDENT UPON AOE. 
 
 Prenatal Physical Development. — The growth of struc- 
 ture, and the unfolding of physiological function, in the 
 unborn human being have been, more or less success- 
 fully, investigated by embryology. Yet this biological 
 science gains most of its knowledge of the human foetus 
 from study of the lower animals. Certain large and elabo- 
 rate organs, such as the lungs, the eyes, the ears, etc., are 
 formed under morphological conditions and influences 
 with which we are imperfectly acquainted, but vidthout 
 any corresponding psychical development. 
 
 The brain and the organs of sense, several weeks after 
 birth, are apparently very little different from the same 
 structures at birth. Yet a marked change in the mental 
 life of the child has undoubtedly taken place. It is a fair 
 conjecture, based upon grounds of " general nerve-physiol- 
 ogy," that some corresponding change has taken place in 
 the cerebral areas. Doubtless the molecular alterations 
 and so-called " dynamical associations," which constitute 
 the basis of the memory as retentive and reproductive, are 
 chief factors in this cerebral change. It is certain that 
 many of the structural and physiological changes which 
 form the more intimate foundation for spiritual activities 
 are secured only indirectly in the central organs through 
 the cultivation given to these organs by the use of the 
 end-organs of sense and motion. As Soltmann and others 
 
AGE, SEX, AND TEMPEKAMENT. 447 
 
 have found, stimulation of the motor areas of the brain of 
 new-born animals does not produce the definitely localized 
 movements usually obtained from the adult animal. The 
 use of eye and hand, in their connected activity, by the 
 new-born child educates his brain greatly in the few weeks 
 just following birth. The dependence of mind and brain, 
 preceding birth as well as afterwards, is presumably indi- 
 rect and very complex. 
 
 Prenatal Psychical Development. — Concerning the psy- 
 chology of the unborn human being we can speak with 
 little confidence. Of sensations of smell, taste, hearing, 
 and sight, there can be no question raised. The end- 
 organs of these senses are developed at birth ; but up to 
 this time they have not been active so as to arouse the 
 soul to the sensations of which they supply the required 
 stimuli. Neither can those sensation-complexes, derived 
 from the irritation of the skin, muscles, tendons, and joints, 
 on which the perception of things extended and external 
 depends, become highly developed before birth. 
 
 It is perhaps a reasonable conjecture which assigns to 
 the psychical life of the unborn infant certain sensations 
 of pressure and temperature, for the most part transient 
 and disconnected, occasioned by the changing conditions 
 and positions in the mother's womb. If we are to speak 
 of prenatal experience, this low grade of consciousness can 
 as little be accurately represented by any conscious state of 
 the human adult as can the consciousness of the animals 
 to which the structure and functions of the body of the 
 foetus, in succession, bear more or less of resemblance. 
 
 Dependence of Height on Age. — It has been estimated 
 that the growth of the fcetus in length for the six months 
 preceding birth is regular; and that it averages about 
 64 mm. a month. The mean length at birth of 100 infants, 
 measured in Brussels, was found to be 0.501 m. (or about 
 19J in.) for boys, and 0.491 m. (or about 19| in.) for 
 
448 PHYSIOLOGICAL PSYCHOLOGY. 
 
 girls. For 900 adults, in age from 19 to 30, the mean 
 height was 1.6648-1.6841 m. The average height of 80 
 students at Cambridge, England, was 1.768 m. As is well 
 known, the absolute height of adult .man varies greatly in 
 different regions and races, and under different conditions 
 of climate, food, etc. 
 
 If we express the facts by the fraction of the whole 
 height previously attained which the growth of each year 
 attains, the figures are as follows : for the first year, about 
 I ; for the second, I ; for the third, ^ ; for the fourth, -^ ; 
 for the fifth, -^-g ; for the sixth, jig^, etc. From this time to 
 the age of puberty the annual increase is nearly regular 
 at about 56 mm. Shortly before or during the period of 
 puberty, a sudden rise in the curve of growth occurs ; but 
 after this period the curve falls off until about the age of 
 twenty-five, when maturity of height may be considered 
 as attained. A very slight increase continues in most 
 cases until about fifty, when a decrease — especially in old 
 age — occurs. 
 
 The psychical life of perception and will is, of course, 
 dependent to a large extent upon the height and gross 
 bulk of the body. The knowledge of magnitudes and 
 solidity of things, and the cultivation of the feelings of 
 "Self "as a causal agency, as well as that "diremption" 
 of experience which organizes all the world into " my sen- 
 tient organism " as set over opposite to other " things," are, 
 in a general way, dependent upon growth in height. The 
 same remarks also apply to the following allied develop- 
 ment. 
 
 Dependence of Weight on Age. — Like the height, the 
 weight at birth also differs greatly according to parentage, 
 prenatal conditions of nutrition, etc. The average weight 
 of new-born infants, as ascertained in Brussels and also as 
 given in the French " Dictionary of Medical Sciences," is 
 about 3.056 kilo., or 6.735 lbs. avoirdupois. One year after 
 
AGE, SEX, AND TEMPERAMENT. 449 
 
 birth the weight has, on the average, been tripled ; in six 
 years more it has been doubled again, and in thirteen years 
 quadrupled. At about nineteen the mean weight of both 
 sexes is about the same as that of old age. The maximum 
 weight of the male is attained, as a rule, about forty ; that 
 of the female, somewhat later. At sixty the average 
 weight, like the height, begins to diminish. 
 
 The psychical development is indirectly involved in the 
 weight of the body as dependent upon age. This is par- 
 ticularly true of those sensations and cognate feelings 
 which are connected with the poise and movement of the 
 body, with its slower or more rapid adjustment to the 
 changing relations of objects in space. The entire mental 
 movement of the child is, in a measure, typified by the 
 agility of its bodily movements. The "feelings of posi- 
 tion," which belong to maturity of bodily size and weight 
 have in middle life reached the culmination of precision 
 and strength combined with speed. In all these regards 
 the psychical life of old age suffers a decline which is vis- 
 ibly manifested in feebleness and slowness of bodily move- 
 ments. 
 
 More indirectly still, and yet with great force and extent 
 of application, does the same principle concern the moral 
 and sesthetical feelings. The mind, acting as so-called will, 
 is always, even in its highest forms of emotion and choice, 
 interlocked with conditions that proceed directly from the 
 conditions of the bodily basis. The tempo of life, and char- 
 acter of the strain to which its movement answers, are not 
 the same for all its phases. 
 
 Relative Proportions among the Different Organs. — The size 
 of the different bodily organs — both absolute and relative 
 — varies greatly for the different ages of life ; but their 
 relative size remains nearly the same for all persons, not 
 obviously deformed, of the same age. The most essential 
 parts are least subject to any wide departures from the 
 
450 PHYSIOLOGICAL PSYCHOLOGY. 
 
 normal type. At birth the length of the head is about 
 half that attained on complete development — or an aver- 
 age of about 111 mm. (4.37 in.). It reaches about 154 mm. 
 by the end of the first year, and 173 by the end of the sec- 
 ond. This growth of 62 mm. in two years exceeds all sub- 
 sequent growth. The developed adult head is about, oh 
 the average, 228 mm. long, or ^ to -J- of the entire length of 
 the body. 
 
 The facts just mentioned show that the increasing size 
 of the head and of its contents of nervous matter, is cor- 
 related, not so much with absolute attainments of mental 
 sort, as with mental exercise and growth in mental powers. 
 The same truth appears in such measurements of the heads 
 of those engaged in the work of students as have recently 
 been conducted by Galton and others. 
 
 The development of back and legs and muscles, in 
 the child, is relatively very different from that of the 
 head. The back has at birth only about \ its subsequent 
 length ; the arm, \ ; the leg, up to the place of its bifurca- 
 tion, only about \. The infant's foot (which will probably, 
 if it be the foot of a civilized female, never again appear 
 in its natural proportions) is about the same length as the 
 head, — about | of the body. The hand is about ^ of the 
 length of the body. Unlike the head, the limbs grow 
 rapidly after the second year. At the age of puberty 
 they are greatly lengthened at the expense of their trans- 
 verse proportions. 
 
 The following table shows the relative weight of the 
 internal organs at birth and after maturity : — 
 
AGE, SEX, AND TEMPERAMENT. 
 
 451 
 
 
 Percentage of body-weight. 
 
 Ratio of the 
 
 TWO, THE in- 
 
 
 Infant at birth. 
 
 Adult. 
 
 fant TAKEN 
 ASl. 
 
 Skeleton ... 
 
 Muscles, etc 
 
 Lungs . 
 
 Heart . . . 
 
 Skin 
 
 Eye 
 
 Brain 
 
 16.70 
 23.40 
 
 2.16 
 0.89 
 
 11.30 
 0.28 
 
 14.34 
 
 15.35 
 43.10 
 2.01 
 0.52 
 6.30 
 0.028 
 2.37 
 
 26 
 
 £8 
 
 20 
 
 15 
 
 12 
 1.7 
 3.7 
 
 Dependence of Metabolism on Age. — To make the rapid 
 growths of the first years, a great amount of food, repre- 
 senting a great amount of potential energy, must be con- 
 verted into living tissue. This more rapid metabolism 
 of the infant is partly demanded in order to keep up the 
 normal temperature of the body, which is slightly higher 
 (0.3°) than that of the adult. The infant's body also loses 
 heat much faster on account of its extremely vascular skin. 
 Most of the metabolism is directed, however, toward the 
 construction of living tissue. 
 
 The heart of the infant is much larger, in relation to 
 the entire body, than is the heart of the adult (see Table). 
 The whole circuit of the circulatory system is traversed 
 in about 12 seconds, while the time necessary in the case 
 of the adult is about 22 seconds. The heart-beat is at first 
 about 130-140 per minute, — falling off to about 110 in 
 the second year, and to about 90 in the tenth. The res- 
 piration is about 35 per minute at first, 28 in the second 
 year, and 26 in the fifth. 
 
 Everything in the infant indicates, therefore, a mobile 
 and flexible condition of the bodily organs, with a rela- 
 tively larga development already secured to the most im- 
 portant parts of the n«rvous system. A scarcity of formed 
 
452 PHYSIOLOGICAL PSYCHOLOGY. 
 
 bodily and mental habits is indicated. The lines of habit- 
 ual action of the mechanism have not as yet been marked 
 out. Habits of mental sort, as connected with established 
 dynamical associations among the nerve-elements and cen- 
 tres of the brain, are as yet unformed. 
 
 PsyoMcal Development of the Infant. — The large size and 
 advanced development of the brain and end-organs of 
 sense at birth are indicative of mental potentialities rather 
 than of the actual mental life. If we use the word 
 " mental " to designate the phenomena of consciousness, 
 it is difficult to trace the earliest mental development. 
 The eyes of the child during the first days are seldom open 
 for any length of time. Perception by sight implies asso- 
 .ciated and co-ordinated movement of the eyes, with the 
 possibility of voluntary fixation or wandering of the point 
 of regard. There appears to be considerable difference in 
 the length of time after birth which is required to estab- 
 lish these necessary conditions. But the factors required 
 in such development, as well as the stages by which it 
 advances, have already been sufficiently discussed (see 
 Chapter XIV.). 
 
 All newly born children, since there is no air in the 
 tympanum previous to respiration, are deaf. Children dif- 
 fer greatly as respects the age at which they give sure 
 tokens of having sensations of sound. The reflex excita- 
 bility of the skin of the infant, in spite of its delicate 
 character, is much inferior to that of the adult. It is only 
 under gradual cultivation that it learns to respond in the 
 maturer forms of this "geometrical sense." Taste and 
 smell, considered as sensations void of aU perceptive char- 
 acter, apparently belong to the first days of the infant's 
 life. 
 
 After full maturity has been reached, or decline of the 
 bodily powers has begun, the mental activities are less 
 aggressive and acquisitive. But the period of more imme- 
 
AGE, SEX, AND TEMPERAMENT. 453 
 
 diate dependence of these activities upon the lower sensory- 
 motor apparatus has passed. The lines of both bodily and 
 spiritual habit have become firmly drawn. Experience is 
 stored; judgment has been trained, and is less liable to 
 sudden assaults from impulse. 
 
 SELATIYE DEVELOPMENT OF THE SEXES. 
 
 While the dependence of the mental development upon 
 the condition and growth of the bodily organs, as affected 
 by age, is substantially the same for all, certain important 
 differences separate the sexes. 
 
 Relative Height and Weight Bf the Sexes. — The curve of 
 growth from birth onward runs somewhat differently for 
 the male and female child. Before maturity the height 
 of the two is about as 1 to 0.988 ; at maturity it is about 
 as 1 to 0.937 or 16 to 15. The absolute height of the 
 European adult male is 1.467-1.890 m. (about 4 ft. 11 in. 
 to 6 ft. 4 in.) ; that of the female, 1.444-1.740 m. (or 4 ft. 
 10 in. to 5 ft. 10 in.). But at the age of sixteen the growth 
 of the girl is as far advanced as that of the boy at eighteen 
 or nineteen. 
 
 The relative weight of the two sexes does not follow 
 exactly the same rule as their height. At birth the differ- 
 ence is about 0.6 lb. avoirdupois. But although the boy 
 is born heavier, at twelve the two sexes have nearly 
 the same average weight. Woman attains her maximum 
 weight several years later than man. For normally formed 
 and well-nourished men the limits are about 49.1-98.5 kilo. 
 (108-217 lbs.) ; for women, 39.8-93.8 kilo. (98-207 lbs.). 
 
 Relative Proportions of the Bodily Members of the Sexes. — 
 Even in early childhood sexual differences become observ- 
 able, as respects the proportions of the bodily parts. The 
 bony framework of the boy is more prominent and the out- 
 lines of the limbs indicate agile and strong movement. 
 Roundness of limbs and amplitude of flesh cover the girl's 
 
464 PHYSIOLOGICAL PSYCHOLOGY. 
 
 framework. The formation of the pelvis in the two is 
 unlike; and the centre of the line of length falls on a 
 different part of the body. The chest of the adult male 
 is more developed ; his breathing is lower down ; his rate 
 of pulse and respiration less rapid. The length of his 
 arms stretched out is about 1.046 of his height; of the 
 female, it is only 1.016. The relative length of the legs 
 is greater ; and the circumferences of the various parts of 
 his body are differently proportioned. His step is to hers 
 as 1.167 to 1.000. 
 
 The average physical energy of which the male is capa- 
 ble is much the greater, — whether it be measured by lift- 
 ing weights, by pressure with the hands, or other ways of 
 producing mechanical effects. Before puberty this* differ- 
 ence has been estimated as expressed by the ratio 3:2; 
 afterward by the ratio 9:5, or even greater. The average 
 boy of nine or ten years can support himself for some time 
 with his hands ; the girl cannot. The average man can 
 lift some 164 kilo. ; the woman scarcely half as much. 
 
 The metabolism of the female,,whether measured by the 
 respiratory or other excreta, is both absolutely and rela- 
 tively less than that of the male. Her blood is less in 
 quantity, of lighter specific gravity, aind contains fewer 
 red corpuscles. 
 
 More important differences concern the nervous systems 
 of the two sexes. The weight of the female's brain, as 
 compared with that of the male, is about as 1.272:1.424. 
 The embryology of the two serves to show a difference in 
 the development of the convolutions from the eighth month 
 onward. The male is said to have, not only an absolutely 
 greater cerebral surface, but also a relatively greater growth 
 of the parts lying in front of the central fissure as compared 
 with those lying behind. 
 
 Of the more definitely sexual peculiarities of organism, 
 both stationary and periodic, and of their influence on the 
 
AGE, SEX, AND TEMPERAMENT. 455 
 
 general physical and psychical development, it is unneces- 
 sary to speak. 
 
 Mental Differences of the Sexes. — It is obvious to any 
 candid and intelligent observer that the foregoing differ- 
 ences in the bodily organism of the male and female involve 
 most profound and far-reaching differences in the mental 
 life. These bodily differences chiefly and primarily concern 
 the life of sensation, emotion, and movement. But the 
 mental life affected is fundamental and gives conditions 
 to all the so-called " higher " intellectual and spiritual 
 faculties. 
 
 The superior strength of the chest, shoulders, and hips 
 of the male, and the fitness of the limbs and trunk for firm 
 and swift movement, give him a superior consciousness of 
 ease, elasticity, and security ; both of posture and in changes 
 of position. His sensations are more sharply discerned as 
 respects qualitative content, less buried under the feeling 
 with which sensation is fused. Decision, self-control, nicety 
 and definiteness of judgment, as connected with the lower 
 life of sensation and movement, undoubtedly belong to him 
 in superior degree. Even more important sexual differ- 
 ences in the kind and amount of feeling — sensuous, 
 aesthetical, and intellectual — are connected with the devel- 
 opment of the organs characteristic of sex. The female 
 is necessarily more under the control of feeling, with the 
 exception of certain of the coarse appetites and passions ; 
 she is more subject to "moods." 
 
 The differences of the sexes in circulation, respiration, 
 and metabolism, are connected with important differences 
 in sentiment, emotion, and other forms of mental life. The 
 female can better endure privation of air, food, and exer- 
 cise ; she is more patient and successful in the passive 
 bearing of pain. But the larger mass of nervous matter, 
 with its store of disposable energy, makes the male much 
 more capable of all pursuits and achievements requiring 
 
456 PHYSIOLOGICAL PSYCHOLOGY. 
 
 such, energy. And since all scientific, political, commercial, 
 and nearly all artistic, pursuits and achievements require — 
 particularly, and with increasing imperativeness in these 
 days — the use of such energy, the average female cannot 
 compete with the average male successfully upon this 
 ground. The farther we advance in these pursuits and 
 achievements, the more determinative does the constitu- 
 tional difEerence become. It is undoubtedly the chief 
 reason for the difference — now not less marked tha-n ever 
 — between the two sexes in the higher and the highest 
 circles of such endeavor open to mankind. 
 
 We shall touch lightly upon the much disputed point of 
 the spiritual characteristics of the sexes. Probably, to cite 
 ■ a few points from Lotze will sufficiently represent the true 
 state of the case. This philosopher holds that woman 
 adapts herself more easily to new conditions of life than 
 does man, — because she is a mixture of the sanguine tem- 
 perament and the sentimental stage ; while varieties of 
 education conceal more of her native qualities. It is char- 
 acteristic of masculine philosophy to analyze phenomena ; 
 but women usually hate analysis. Masculine thought 
 recognizes that what is great and beautiful in the world 
 has its fixed mechanical conditions ; masculine effort rever- 
 ences general principles. The faith of woman is that the 
 value of no principle is independent of concrete life ; she 
 is devout toward sesthetical completeness. The notions 
 of the two even as regards spatial and mathematical rela- 
 tions are markedly different; the same thing is true as to 
 their perceptions of the nature of the concrete realizations 
 of the ideas of space and time. 
 
 THE THEORY OF TEMPERAMENTS. 
 
 Few impressions are more firmly fixed than this, that 
 different individuals (at least among the more highly 
 civilized peoples) are possessed of different natural " dis- 
 
AGE, SEX, AND TEMPERAMENT. 457 
 
 positions." The term "natural" expresses the current 
 conviction that the foundation of their differences is innate 
 and inherited, rather than the result of training and envi- 
 ronment. Experience shows that a so-called " disposition " 
 generally maintains itself under great alterations in cir- 
 cumstances, and against effort, to the close of the individ- 
 ual's life. Where it appears to be greatly modified, such 
 modification is usually made at the expense of greater 
 energy than is required even to break firmly acquired 
 habits. Upon such patent facts the theory of " Tempera- 
 ments " is based. 
 
 Kinds of Temperament. — The number 4 has been chosen 
 most often to express the fundamental classes of tem- 
 peraments. It is doubtless true that this number cor- 
 responds particularly well to the facts. On the other 
 hand, no strictly scientific induction can be made, either 
 as to the classification of temperaments, or as to the physio- 
 logical basis upon which differences of temperament rest. 
 The best obtainable treatment of the subject is, therefore, 
 a mixture of keen general observation, shrewd conjecture, 
 and speculation in the uncertain realm of psycho-physical 
 theory. 
 
 A writer of nearly a half century since (Dr. Leopold 
 George) would define the four temperaments by the inte- 
 rior relation which exists between perception and the 
 affections of the mind. Thus, for example, the greater 
 the mind's wakefulness to impressions, the greater is also 
 its susceptibility to the feelings of pleasure and pain which 
 are attached to the impressions. Hence the sanguine 
 temperament, which is distinguished by peculiar strength 
 in this interior relation. This theory is extended by its 
 author so as to apply to the different periods of life and to 
 different races of men. 
 
 Modem psychology is inclined to approach the subject of 
 temperament from the physiological and biological points 
 
458 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of view. In this way it is rendered more cautious : it can 
 scarcely, however, be said to have added much to the 
 definiteness of our verifiable knowledge. 
 
 Wundt's Classification of Temperaments, — The four-fold 
 division of temperaments is adopted by this writer on the 
 ground that, in every individual, there must be a certain 
 combination of the two factors of strength and speed in 
 that change which all mental processes undergo. The 
 affections of the mind are therefore classifiable as either 
 strong and quick, or strong and slow ; or else as weak and 
 quick, or weak and slow. By crossing these two principles 
 of division the following scheme is derived : 
 
 strong. , Weak. 
 
 Quick "Choleric^' .^ .y g^'Xr^tS.-" Sanguine." 
 
 Slow "Melancholic^ ."..-T'?dr^<^j^ "phlegmatic." 
 
 The quick temperaments are directed rather toward the 
 present, the slow toward the future. The quick require 
 additional strength, the weak additional time, in order to 
 achieve the largest amount of work possible for them. 
 The choleric and phlegmatic are temperaments, with 
 respect to action ; the sanguine and melancholic are tem- 
 peraments, with respect to feeling. 
 
 Wundt adds the following practical suggestion : " One 
 should be sanguine amid the petty sufferings and joys of 
 daily life, melancholic in the more serious hours of life's 
 more important events, choleric toward impressions that 
 fetter one's profounder interests, phlegmatic in the execu- 
 tion of the resolves that have been reached." 
 
 Lotze's Classification of Temperament. — By the term " tem- 
 peraments " Lotze understands : " (1) The differences, in 
 kind and degree, of excitability for external impressions; 
 (2) the greater or less extent to which the ideas excited 
 reproduce others ; (3) the rapidity with which the ideas 
 vary ; (4) the strength with which feelings of pleasure and 
 
AGE, SEX, AND TEMPERAMENT. 459 
 
 pain are associated with the ideas; (5) finally, the ease 
 with which external actions associate with these inner 
 states themselves." This authority also adopts the four- 
 fold division of temperaments. 
 
 The sanguine temperament Lotze holds to be distin- 
 guished by great rapidity of change and lively excitability. 
 It indicates an excess of sensitiveness to all external stim- 
 uli, and of capacity for reciprocal excitement among the 
 different psychical states. For the temperament usually 
 called " melancholic " he would substitute the term sen- 
 timental. This temperament is distinguished " by special 
 receptivity for the feeling of the value of all possible rela- 
 tions " ; but is indifferent toward bare matter of fact. It 
 implies a lively appreciation of harmony and discord, great 
 variety of sesthetical feeling and imaginative activity, — 
 often with theoretical vagueness, ready yielding of the 
 sense of duty to inclination, and dislike of hard work. 
 
 The choleric temperament is marked by " one-sided recep- 
 tivity and great energy in single directions." It implies 
 diminished susceptibility to excitement, but increased force 
 and endurance in reaction when once the feeling has been 
 aroused. Its best effect is steadiness of character ; but its 
 uncomely effect may be an obstinate and narrow persever- 
 ance in a path once entered upon, even when reasons exist 
 for deviating from or abandoning it. Finally, the phleg- 
 matic temperament is distinguished by slightly varied and 
 slow, but not necessarily weak, reactions. 
 
 Physical Basis of Temperament. — Nothing definite is 
 known as to the physiological grounds on which rests 
 the distinction of temperaments. The influence of abnor- 
 mal bodily conditions, and of certain diseases, to produce 
 or alter the disposition in a manner resembling tempera- 
 ment would seem to indicate that the original constitution 
 of the brain is not the primary determining factor. The 
 susceptibility of the end-organs of sense to external stimuli, 
 
460 PHYSIOLOGICAL PSYCHOLOGY. 
 
 and the strength of the resulting reactions in the form of 
 common feeling, as well as the constitution of the visceral 
 organs and the coloring they impart to every form of feel- 
 ing, appear to be of prime importance. 
 
 Many authorities, not without a show of reasons, assign 
 the different temperaments to the four main periods of life 
 as distinctive of them, — the sanguine of childhood, the 
 sentimental of youth, the choleric of maturity, the phleg- 
 matic of old age. The fact that different periods of life 
 are apt to be characterized by a predominance of one of the 
 four temperaments is not an argument against the physi- 
 cal nature of the basis of temperament. For changes in 
 the nature, speed, and strength of the reactions derived 
 from the end-organs, and from the internal organs of the 
 trunk, necessarily accompany the early development, the 
 maturing, and the decay of the bodily powers. These 
 things cannot fail, of course, to have a great though indi- 
 rect influence upon the cerebral centres. 
 
 Characteristics of Different Races. — The theory of tem- 
 peraments has been applied to different peoples, with more 
 or less of success. For example. Dr. George would char- 
 acterize the French as sanguine, the English as melan- 
 cholic, the Spanish and Italians as choleric, the Germans 
 as phlegmatic. More generally still, the Caucasian race 
 is sanguine ; the Mongolian melancholic ; the Negro phleg- 
 matic ; the Malayan choleric. There seems little doubt 
 that temperamental characteristics are more marked among 
 the civilized races ; if, indeed, they exist at all in any true 
 sense of the word, among the savage and lower uncivilized 
 races. It must be acknowledged, moreover, that the whole 
 matter of such an application of the theory does not admit 
 of a strictly scientific discussion and presentation. 
 
 In the more obvious external characteristics the differ- 
 ent races of men vary greatly. Such characteristics are 
 influenced, to a considerable but unknown extent, by soil. 
 
AGE, SEX, AND TEMPERAMENT. 461 
 
 climate, food-supply, and prevalent manner of living ; but 
 they are developed under the general laws of heredity 
 and variability as applied to the particular case of man. 
 It is in the special features of height, weight, and relative 
 form rather than size of the organs, that these character- 
 istic differences chiefly consist. " The real differences 
 which the races present," says an authority on this subject 
 (Quetelet), " appertain to characteristics which the eye 
 seizes better than the compasses; in order to establish 
 them firmly, an appreciation of minute differences is re- 
 quired, and a tact that presupposes a long experience in 
 such researches. One can see the diiSculties with which 
 phrenologists meet in making numerical estimates of the 
 characteristics of the skull; nothing precise can be for- 
 mulated in this regard." 
 
 Upon the general subject of individual and race charac- 
 istics it remains only to add that " pure " cases of any of 
 the four or more recognized varieties of temperament are 
 comparatively rare. Here, as in other similar subjects, the 
 lines which science attempts to draw are, in nature, crossed 
 and confused. Mixed temperaments abound among the 
 individuals of any civilized people ; and no race exists 
 that does not contain all kinds of temperaments and so 
 overlap, as it were, the boundaries of all the other races 
 — even those from which its average is most widely 
 separated. 
 
CHAPTER XIX. 
 
 CONNECTION OF BODY AND MIND. 
 
 We have tlius far been studying certain groups of rela- 
 tions which exist between the structure and activity of the 
 nervous mechanism and the phenomena called " mental," 
 or phenomena of "consciousness." These relations may 
 be summarized, with a fair amount of accuracy and com- 
 pleteness, under the following five heads. 
 
 1. The quality and intensity of the sense-element in our 
 experience is related to the condition of the nervous system 
 as acted on hy its appropriate stimuli. The true state of 
 the case with respect to these relations is, indeed, never to 
 be represented by considering this sense-element as though 
 it consisted merely of passive impressions dependent upon 
 the kind and degree of the action which the stimuli exert. 
 The same element is also dependent upon the habits and 
 the present condition of the mind, at the time the stimulat- 
 ing effect of the excited sensorium is realized in conscious- 
 ness. Mental habits and mental condition are, in turn, 
 related to the " dynamical associations " and present occu- 
 pation, as it were, of the cerebral centres at the time when 
 the mental phenomena occur. 
 
 The entire sense-element — the various kinds and degrees 
 of sensations — is a f orthputting, a characteristic mode of 
 the reaction, of the mind. Moreover, many of the phenom- 
 ena which belong under this group of relations, and espe- 
 cially the marked effect of attention upon the sense-element 
 itself, prevent us from regarding the relations as simple and 
 onesided. The mental state which is apparently most 
 462 
 
CONNECTION OF BODY AND MIND. 463 
 
 simple and passive is really a complex and characteristic 
 activity of the subject of all mental states, — namely, of 
 the mind. 
 
 2. The synthesis of our conscious experiences is related to 
 the combination in the cerebral centres of the impressions, 
 made from whatever source, upon the nervous organism. 
 That the number, form, order, and time-rate of our mental 
 states depend upon the number, kind, order, and time-rate 
 of the separate excitations which are combined in the 
 centres of the brain, there can be no doubt. At the same 
 time, no mechanical mixture or fusion of these excitations, 
 within common or allied areas of nervous substance, in the 
 least degree resembles that mental synthesis which expe- 
 rience implies. An activity that combines under different 
 laws from those which govern the various nerve-commo- 
 tions, as they are excited in the brain by external and 
 internal stimuli, must take place in order that one object 
 may be cognized by one subject, — the cognizing mind. 
 
 3. Those phenomena of consciousness which we call 
 '■'■memory" and '■'■recollection" imply relations with the estab- 
 lished molecular constitution and tendencies of the cerebral 
 centres. But the peculiarly mental phenomena, which we 
 call by these terms, bear no resemblance to those which, 
 so far as we know or conjecture them, are called by such 
 terms as " organic memory," " dynamical associations," etc. 
 Especially is it true of conscious recognition, — involving, 
 as it does, the conscious appropriation of the present men- 
 tal state, as representative of another past state, to the 
 same one subject to whom, as its states, both that which 
 represents and that which is represented belong, — that 
 this is a something utterly unimaginable and inexplicable 
 in terms of revived nerve-waves or molecular agitations 
 of a nervous mass. 
 
 4. The course of the ideas, and the changing tone of feeling 
 and emotion, are related to the vital conditions of the cere- 
 
464 PHYSIOLOGICAL PSYCHOLOGY. 
 
 hral centres. But ■ here again, mingling with all these 
 changing mental phenomena, we find what is known in 
 consciousness as self-control. Self-contvol is an immediate 
 determination of the states of consciousness, and through 
 them a determination of the states of the " body," which 
 is to be attributed to the conscious mind as its origin or 
 source. To speak of this unique experience as though 
 the science of physiological psychology had disproved its 
 reality, or had shown it actually to be other than what it 
 obviously appears in consciousness as being, is absolutely 
 without any sufficient warrant. To call this unique experi- 
 ence an "illusion" is to do violence to the science of 
 psychology in behalf of conjectures attached, but not 
 belonging, as verified facts or principles, to the allied sci- 
 ence of physiology. 
 
 5. The inherited peculiarities (tribal, family, and sexual) 
 of the organism are related to the general tone or coloring of 
 all the conscious mental life. That differences of disposi- 
 tion and temperament exist, which are innate and perma- 
 nent, and that these differences are dependent upon the 
 inherited bodily constitution, there is no reasonable ground 
 to dispute. On the other hand, we cannot adopt that fan- 
 ciful philosophy which considers the mind as the builder 
 of the body — as in some direct way fashioning to its own 
 inherent constitution and uses the organs of the physical 
 mechanism. But the popular impression that the mind 
 " influences " the body, and has even, within certain limits, 
 the power of shaping it to its needs, and of profoundly 
 modifjdng its molecular structure and action, has ample 
 warrant in the facts. 
 
 In explanation and justification of the popular impres- 
 sion we shall now speak further upon this point. The 
 popular impression, as expressed in the popular language, 
 is obviously based upon the assumption that some kind of 
 reality exists which corresponds to the term " the mind." 
 
CONNECTION OF BODY AND MIND. 465 
 
 This reality stands — it is further assumed — in real con- 
 nections with a reality of another kind, — namely, with 
 the body. The nature of these connections is vaguely 
 and figuratively (always figuratively) expressed by various 
 phrases and words. Thus, the body is frequently spoken 
 of as the " seat " or " organ " of the mind. The one party, 
 in this fancied dual partnership, is said to " influence " or 
 " control " the action of the other. Sometimes, but usu- 
 ally not in the language of the people, the phenomena of 
 consciousness are regarded as "products," or "resultants," 
 or " manifestations," of the functional activity of the brain. 
 That some kind of " bond," or " tie," or " connection," 
 exists between body and mind, few are found bold enough 
 to doubt. 
 
 What that is true to the facts of physiological psychol- 
 ogy, and also defensible by that branch of philosophy 
 which concerns itself with what men call " real," is signi- 
 fied by such popular expressions as these ? 
 
 The Body as the " Seat " of the Mind. — The mind is com- 
 monly regarded as connected with the body by being in 
 the body. This general assumption that, in some sense, 
 the mind is in the body is yet more figuratively expressed 
 by saying : The body is the " seat " of the mind. It is 
 not plain at once, however, just what is meant by this 
 figure of speech. 
 
 Experience undoubtedly justifies the popular language 
 in regarding the mind as " in " the body, in the same sense 
 of the words which warrants us in also saying : it is not 
 in yonder bird, or star, or tree. Hence, certain now anti- 
 quated forms of philosophy represented perception as 
 though it were a process in which the mind streams out 
 through the avenues of sense and thus embraces the object 
 of sensuous perception. Others thought of some image 
 or etherealized copy of the object as streaming into the 
 mind through the same avenues of sense. The modern 
 
466 PHYSIOLOGICAL PSYCHOLOGY. 
 
 study of perception, on a basis of experiment and analysis, 
 has disproved these and all similar ways of regarding the 
 relations of the mind to external things. 
 
 The ancients located the soul in the heart or the lower 
 viscera, because of certain obvious relations between men- 
 tal states and the conditions of these organs. The more 
 obvious relations, however, were for the most part con- 
 fined to the emotional states of the soul. We have seen 
 that they had little suspicion of the intimate and extensive 
 dependence of the mental life upon the constitution and 
 functional activity of the contents of the skull. Modern 
 science, with a sufficient array of evidence, emphasizes the 
 dependence of mental life upon the brain. 
 
 In whatever sense, then, the mind can be said to be 
 really " in " the body, in that sense must it be said to be 
 really " in " the brain. But what that is real do we mean 
 by speaking of the mind as having its seat within the 
 brain ? 
 
 Our present physiological and anatomical knowledge of 
 the human cerebrum and its functions is unfavorable to a 
 view which would " seat " the mind in any single and 
 limited locality of this organ. Descartes, indeed, found in 
 the pineal gland the special seat of the soul. We know of 
 no special significance which this small bit of nervous sub- 
 stance possesses. The modern science of the localization 
 of cerebral function has changed our entire way of consid- 
 ering the matter. In whatever sense the mind has its 
 "seat" in any part of the body, in that same sense it has 
 various seats for its various related activities. And yet 
 the unity of the mind in consciousness — the thing which, 
 above all others, the investigations of physiological psychol- 
 ogy are powerless to explain — is not at all affected by 
 this variety of local relations between itself and the cen- 
 tres of the brain. 
 
 An analysis of the popular language, in connection with 
 
CONNECTION OF BODY AND MIND. 467 
 
 the facts and theory examined in Chapters XIII.-XIV., 
 shows us what its real meaning is. The phenomena of 
 sensation-complexes that are localized and projected as the 
 different areas of our own hody, and the phenomena that, 
 being tinged with feelings of pleasure and pain, are most 
 obviously ascribed to our own soul as it states, are con- 
 stantly interrelated in experience. But man is a meta- 
 physical being. He naturally and necessarily assumes 
 "real" existences as the subjects of these two markedly 
 different classes of occurrences. The localized and pro- 
 jected sensation-complexes are attributed to one reality, — 
 to a material body ; the experiences that have an interest, 
 because they are so suffused with feeling, are, in a pecul- 
 iar way, assigned to another real being, to a " Self " or a 
 soul. How this " diremption " of experience comes about, 
 so far as the history of the process can be traced and 
 explained, it is foreign to our present purpose further to 
 inquire. 
 
 It is then a genuine metaphysical activity of the mind 
 which is testified to, whenever the popular language speaks 
 of the body as the " seat " of the soul. And the kind of 
 experience which fosters and supports this metaphysical 
 activity is the experience of localizing and projecting, in a 
 systematic way, certain of our own sensation-complexes. 
 
 But what is meant when, in the name of modern 
 science, we limit that part of the body, in which the soul 
 has its " seat," to the higher nervous centres ? The meta- 
 physics of this process is essentially the same as that 
 expressed in the popular language. But the kind of 
 experience on which the metaphysical assumption rests is 
 much more remote from our daily life. Its observations 
 demand rare and refined instrumentalities ; its conclusions 
 rest upon complicated and often doubtful inferences. 
 
 Unless, however, we are ready to deny all reality to the 
 assumptions and afBrmations of both popular language and 
 
468 PHYSIOLOGICAL PSYCHOLOGY. 
 
 modern scientific researches, they mean essentially the 
 same thing. Neither means that an entity called " soul " 
 is suffused through another entity called " body," as 
 luminiferous ether may be supposed to interpenetrate the 
 substance of the window-pane. Neither means that an 
 entity called soul maintains a " sitting " or other sort of 
 posture, whether in the peripheral or in the cerebral areas 
 of the entity called body. But both forms of expression 
 assume the existence, in reality, of both a body and a 
 soul. Both affirm that these two existences are, for 
 certain of their activities, interdependent. 
 
 Body as the " Organ " of Mind, — Another set of relations, 
 which are customarily assumed to exist in reality between 
 the body and the mind, is expressed by such words as 
 " organ " or " instrument." These terms are intended to 
 emphasize the connection, in reality, between the ideas and 
 volitions which arise in consciousness, and the induced 
 movements of the muscular apparatus. But the term, as 
 popularly employed, is plainly figurative to a high degree. 
 An instrument, or organ, is any material medium between 
 the masses of matter, whose shape or position we wish to 
 change, and the movable parts of our own bodies. Or it 
 is a means of sharpening, defining, and multipljdng our 
 sensations and perceptions of things. Or, again, it is an 
 apparatus, by producing changes in which, we express 
 sentiments and ideas. With the instruments of spade and 
 shovel we throw up the ground; with pulley and lever 
 we raise weights. With microscope or telescope, as organs 
 added to the natural organ of the eye, we see things minute 
 and near, or larger and far remote. With that instrument, 
 whose name is " organ," we express our musical sentiments 
 and ideas. 
 
 Few persons, however, will be found so crude in concep- 
 tion as to suppose that, in reality, when a limb is moved, 
 an. entity of some kind, called "mind," is laying some sort 
 
CONNECTION OP BODY AND MIND. 469 
 
 of material clutch — present there — upon the muscular 
 fibre. Certainly no one, well inforined enough to know 
 of the existence and character of cerebral localization, 
 supposes that this same entity plays, in a physical way, 
 upon the nerve-cells and fibres of the cerebral centres. 
 
 But every form of conception, whether popular or scien- 
 tific, which leads to the use of words like " instrument " or 
 " organ " in the effort to express essential relations of body 
 and mind, implies the same experience, and sets forth the 
 same truths. There are two realities implied, — the body 
 and the mind; and these two are, in reality, interdepen- 
 dently connected. 
 
 The Word " Connection " as applied to Body and Mind. — 
 Much of the popular language undoubtedly implies that 
 some " bond " exists between the body and the mind. In 
 summing up the results of our previous researches we have 
 frequently felt ourselves obliged to use the term " connec- 
 tion." Both these terms, however, like the ones already 
 examined, are plainly of a figurative character. Of course 
 — it needs no argument to show this — no actual bond or 
 tie, such as we employ to make two material things act in 
 certain desired relations, whenever they do not "naturally " 
 so act, unites the body and the mind. But the essential 
 truth is this : In the order of nature, the body and mind 
 do naturally act under binding relations toward each other. 
 Body and mind behave with reference to each other, as 
 though baund. 
 
 Yet again, we cannot speak of any one bond or connec- 
 tion as existing between those two beings which we desig- 
 nate by the words, body and mind. No single formula can 
 express all the various natural forms of their related 
 behavior. The whole investigation of physiological psy- 
 chology aims to discover as many as possible of those 
 natural forms of relation, of those so-called " bonds " or 
 "connections," which exist between the two. It traces 
 
470 PHYSIOLOGICAL PSYCHOLOGY. 
 
 inward and backward, the obvious changes in the periphery 
 of the body, until it finds them resulting in molecular 
 changes of mysterious chemical, thermic, nutritive, and 
 distinctively nervous, orders, within the substance of the 
 brain. With these molecular changes it " connects " the 
 concurrent or subsequent mental phenomena. But such 
 connection is no physical tie or bond. By the word " con- 
 nection," we only signify the ultimate fact that the two 
 beings, which are the subjects of the two classes of changes, 
 are in the order of nature causally related. 
 
 If it should be complained that, in this way, the entire 
 investigation of physiological psychology ends in a mys- 
 tery, the truth of the complaint must be granted. The 
 fact that body and mind are thus, in a great variety of par- 
 ticular ways, causally related, is an ultimate fact ; — this, so 
 far as science, with its legitimate inferences, can go. But 
 all so-called causal relation is equally mysterious; it all 
 partakes of the nature of ultimate and inexplicable fact. 
 That one atom of oxygen should influence, or cause, 
 another to act in a certain way, is also an ultimate myste- 
 rious fact. That an atom of oxygen should cause other 
 atoms of hydrogen, carbon, nitrogen, etc., to act in a great 
 variety of different ways, involves numerous equally mys- 
 terious and ultimate " connections." 
 
 Exertion of Energy between Body and Mind. — -Modern 
 physics has established an important principle, called the 
 "conservation and correlation of energy." Closely con- 
 nected with this principle (indeed the same thing as one 
 side of this principle), is the assumption that the quantum 
 of physical energy in the universe is invariable. These 
 principles modern biology has borrowed from modern phys- 
 ics. Strictly speaking, however, it is only within com- 
 paratively narrow lines of even physical researches that 
 the principle of the conservation and correlation of energy 
 can be inductively established. And chemistry would 
 
CONNECTION OF BODY AND MIND. 471 
 
 make few indeed of its present splendid advances if it 
 were confined to deductive predictions, under this prin- 
 ciple, concerning the behavior of molecules and atoms in 
 their various relations. In spite of all its serious attempts, 
 biology, too, is far enough from the position in which it 
 can make much use of the same principle. 
 
 Few wiU question the statement that any so-called in- 
 fluence, or causal action, of body and mind upon each 
 other, is incapable of expression in ternas of the conserva- 
 tion and correlation of physical energy. Energy, whether 
 stored or kinetic, within the nerve-cells of the cerebral 
 centres cannot become stored or kinetic in the assumed 
 subject of mental phenomena. And, really, although we 
 use terms of quantity to describe mental phenomena, they 
 cannot, as mental, be correlated under this great physical 
 principle with quantities of the molecular changes that- 
 occur in the brain. No mental energy ever passes over 
 into the brain ; no nervous energy ever passes over into 
 the mind. Indeed, the very attempt to apply the concep- 
 tions and terms, so familiar to physics and so scientific 
 when dealing with the relations of physical masses and 
 movements, ends in palpable absurdities when the subject 
 of treatment becomes the relations of body and mind. 
 
 In view of these and other similar difficulties, some 
 would utterly refuse to speak of body and mind as, in any 
 true sense of the word, causally interrelated. But such a 
 refusal leaves all popular and all scientific language with- 
 out any ground in reality on which to stand. "We are 
 obliged to talk as though the mind behaves thus and so, 
 " because " of the simultaneous or previous behavior of the 
 body, to which it naturally stands in relations. With 
 equal confidence do we, in both ordinary and scientific 
 terms, assert the causal action of the mind upon the body. 
 There is as much valid reason for aU this as there is for 
 regarding any two sets of phenomena, and any two beings 
 
472 PHYSIOLOGICAL PSYCHOLOGY. 
 
 considered as the subjects of the phenomena, as standing 
 in causal relations. There is as much reason for saying 
 that my volition causes my limbs to move, and that the 
 light-waves on the retina cause in me sensations and per- 
 ceptions, as there is for sajdng that the earth causes the 
 meteor to fall to its surface, or the sun causes the plant to 
 grow by its warmth and light. 
 
 Mind and Body in Causal Relations. — We are therefore 
 warranted in maintaining that the changes of the human 
 brain and the phenomena of human consciousness stand 
 toward each other in the relation of cause and effect. The 
 general relation of cause and effect is far more profound 
 and extensive in its application than the modern physical 
 postulate of the conservation and correlation of energy. 
 The relation of cause and effect is, indeed, the ultimate 
 fact — itself inexplicable — by the various applications of 
 which we " explain " all events in the world of matter 
 and of mind. But the principle of the conservation and 
 correlation of energy is only a valid and useful working 
 hypothesis under which we may bring certain classes of 
 physical phenomena. 
 
 When, then, we attempt to consider the relation of the 
 brain and the mind without using terms of causation, we 
 find ourselves landed in unreason through the effort to 
 escape a fundamental law of all reason. But when we 
 attempt to apply the physical formula (the principle of 
 the conservation and correlation of energy) to the case 
 of brain and mind, we find ourselves landed in absurdities 
 of a practical as well as of a scientific sort. All the re- 
 searches of physiological psychology imply that changes 
 in the material organism and changing mental states are 
 causally connected. All its discoveries are designed to 
 render more precise, and to reduce to as nearly exact terms 
 as possible, the statements of these causal relations. On 
 the other hand, all its discoveries emphasize the complete 
 
CONNECTION OF BODY AND MIND. 473 
 
 impossibility of considering these causal relations in terms 
 of the conservation and correlation of physical energy. 
 
 It may be said again that, in the last analysis, the fore- 
 going conclusion makes it impossible for science to com- 
 prehend the connection of body and mind. All that we 
 call the " science " of their relations rests back upon an 
 ultimate fact. This is true — as true and mysterious — 
 of the subjects with which physiological psychology deals 
 as of those considered by other forms of science. 
 
 But what is there in the nature of the so-called " causal 
 nexus" which should prevent its being assumed to exist 
 between the body and the mind ? In reply, we might ask : 
 What do we really mean when we speak of an event, or 
 a thing, as the " cause " of another ? What do we mean 
 when we speak of " exerting influence," or of " acting 
 and being acted upon," as between two beings in the 
 world of manifold existences? Nothing that the senses 
 can discover, or the imagination depict in terms of sense. 
 Such affirmations are born of reason; they arise from a 
 postulate of the higher activity of the mind itself. They 
 express in various modifications, the ultimate, mysterious 
 fact of a relation, in reality, between those beings whose 
 states are observed to be correlated with each other under 
 uniform laws. And that this fact of causal relation 
 maintains itself with reference to body and mind, there 
 are the most abundant reasons to affirm rather than to 
 deny. 
 
 Causal Influence of the Body on the Hind. — Speaking 
 naturally and without prejudice, no one would hesitate to 
 regard the body as a " cause " of the phenomena which 
 we attribute to the subject called the mind. Who doubts 
 that a man loses his senses, as truly as he loses a portion 
 of his brain-mass, because he has been struck a blow upon 
 the head ? The stoppage of the arteries that furnish blood 
 to the higher cerebral centres, whether by outside pressure 
 
474 PHYSIOLOGICAL PSYCHOLOGY. 
 
 or by embolism, promptly causes the disturbance or cessa- 
 tion of consciousness. The character and amount of blood 
 circulating in these centres causes marked changes in the 
 character and time-rate of mental phenomena. Witness 
 the effect upon the mind of certain drugs, or of the delir- 
 ium of fever. Schroeder van der Kolk tells of a patient 
 who, when his pulse was reduced by digitalis to 50 or 60 
 beats per minute, was mentally quiet or depressed ; when 
 it was allowed to rise to 90 beats, his mind was in mani- 
 acal confusion. Cox narrates the case of a sick man who, 
 at 40 pulsations in the minute, was " half-dead " ; at 50, 
 melancholic; at 70, quite "beside himself"; at 90, "rav- 
 ing mad." Hallucinations, not infrequently, immediately 
 cease, when the person afflicted with them assumes the 
 standing posture, or has leeches applied to the head. 
 
 But there is little need to enumerate facts, at this stage 
 of our investigations, in support of the proposition just 
 made. A large part of all the conclusions of which the 
 science of physiological psychology consists, prove noth- 
 ing whatever, if they do not prove that bodily changes are 
 the "causes" of alterations in mental phenomena. The 
 chapters on the localization of cerebral function, on the 
 quality and quantity of sensation, etc., abound in facts of 
 the order required for such proof. 
 
 The affirmation of a causal action of the body — and 
 more especially of the brain — upon the mind does not, 
 however, invalidate the claims of the mind to be con- 
 sidered a real being, or to be spiritual and free. For the 
 sole account or cause of the mind's activities can, in no 
 instance, be found in the molecular condition and changes 
 of the brain. The full account of every mental state must 
 refer directly to the nature of that subject, the mind itself, 
 of which it is the state, as its cause. Even the simplest 
 sensation is not explained solely by indicating what form 
 of nerve-commotion in the cerebral cortex is its bodily 
 
COKNECTION OP BODY AND MIND. 475 
 
 cause. Every sensation must also be considered as a psy- 
 chical activity put forth by the being called mind. There 
 is no real incompatibility between these two ways of re- 
 garding every mental state. Indeed, every change of state 
 in any physical being demands this dual way of regarding 
 it. Every such change must be considered both as caused 
 by a change of states in other beings to which it is related, 
 and also as due to activity of that being to which as a 
 change of state, it belongs. 
 
 Causal Influence of the Mind upon the Body. — We have an 
 equal right, however, to affirm that mental states, changes 
 in consciousness, are a cause of changes in allied cerebral 
 centres, and, through them, in the other tissues and organs 
 of the body. Speaking naturally and without prejudice, 
 no one would hesitate to regard the mind as causally 
 influencing the condition of the body. Even the most 
 purely vegetative of the bodily processes are dependent for 
 their character upon antecedent states of the mind. It is 
 as true that melancholy causes bad digestion as it is that 
 bad digestion causes melancholy. Care, chagrin, and 
 ennui poison the blood. Excessive voluntary application 
 and over-excited feeling wear away the brain. The most 
 modern researches into the phenomena of hypnotism lend 
 evidence to the view, that " mental suggestion " accounts 
 for the abnormal condition and action of the cerebral 
 centres quite as truly as the condition of these centres 
 accounts for the strange mental phenomena which accom- 
 pany this complex state of body and mind. 
 
 The entire class of phenomena which we are entitled to 
 call "voluntary" might be appealed to in proof of the same 
 principle. Here we might instance the voluntary innerva- 
 tion of an organ by fixation of attention, the dependence 
 of reaction-time upon the will of the person reacting, the 
 abstraction of regard from the images of sense when occu- 
 pied in reflection, as well as all the more marvellous cases 
 
476 PHYSIOLOGICAL PSYCHOLOGY. 
 
 of self-control in enduring pain, triumphing over disease, 
 etc. 
 
 The elevation of the bodily activities to a most astonish- 
 ing precision, under the influence of high and strong artis- 
 tic feeling, is also a noteworthy fact of the same order. 
 
 It appears, therefore, that the human brain is a vast 
 collection of material molecules, whose constitution and 
 arrangement are such as to connect them, in a unique way, 
 with certain forms of external physical energy. But they 
 are also capable of standing in yet more surprising and 
 unique relations to a being of a different nature from their 
 own — that is, to the mind. These latter relations involve 
 a causal connection as truly as do relations of real physical 
 beings. That material molecules and a being of the kind 
 called mind can be causally connected is, indeed, a myste- 
 rious fact. But because of its mystery, it is no less to be 
 acknowledged as a fact. 
 
 Finally, then, the assumption that the mind is a real 
 being, which can be acted upon by the brain, and which can 
 act on the body through the brain, is the only one compatible 
 with all the facts of experience. 
 
 Processes involved in the Connection of Body and Mind. — 
 All intercourse between material objects and the spiritual 
 subject we call " Self " involves three processes. Of these 
 one is physical, the other physiological, the third psychical. 
 In and through these processes, external things and the 
 subject of mental states mutually condition each other. 
 
 The physical process consists in the action of the appro- 
 priate modes of physical energy upon the end-organs of 
 sense. These modes of energy are brought to bear upon 
 the nervous portions of these organs by means of mechan- 
 ical contrivances — such as, for example, the contrivances 
 for forming an image upon the retina of the eye, or for 
 conveying the modified acoustic impulses to the organ 
 of Corti in the inner ear. With this kind of processes the 
 
CONNECTION OP BODY AND MIND. 477 
 
 science of physics — but only by a great increase in the re- 
 finement of its methods — may hope to deal more success- 
 fully in the near future. 
 
 The second process consists in transmuting the physical 
 energy into a physiological process, a nerve-commotion 
 within the nervous system ; and in propagating this nerve- 
 commotion along the proper tracts and diffusing it over 
 the various areas of the brain. It belongs to the science 
 of physiology to investigate and describe this process and 
 its laws. More particularly, the science of this process is 
 called " general nerve-physiology," with its several depart- 
 ments of more highly " specialized nerve-physiology." 
 
 The third process is psychical ; it is a process which is a 
 psychical event, a forthputting of the peculiar energy of 
 the mind. It is directly correlated with the physiological 
 process only when the latter has been realized in certain 
 cerebral areas. The psychical process cannot be explained 
 wholly as a resultant of the cerebral physiological process ; 
 yet it is an activity of the mind which is conditioned upon 
 that process. When, for example, the particular mental 
 process is the perception of some " external " object, it is 
 no less truly a psychical process. The mind creates its 
 own objects ; presents itself with its own presentations of 
 sense; acts to put forth, as its own product, that which 
 it knows as " not-itself ." But it accomplishes all this as 
 dependent upon processes that take place in other beings, 
 and with the assumption of the existence of such beings, 
 to which it stands in relations of cause and effect. 
 
CHAPTER XX. 
 
 THE NATURE OF MIND. 
 
 Theee can be no doubt that the popular impression is 
 in favor of affirming the reality, unity, and spirituality (or 
 wow-materiality) of the human mind. Indeed, so long as 
 we take only the populai point of view and employ only 
 the language which is customary to it, great difficulty is 
 experienced in even expressing such inquiries as the 
 science of physiological psychology suggests. It is, how- 
 ever, the scientific study of those phenomena which show 
 a special dependence of mental states upon nervous condi- 
 tions which disturbs the popular impression. Does science, 
 then, end in destroying this impression ? Or, does it not, 
 after disturbing and modifying it, reinstate it, substan- 
 tially unchanged, upon much surer and more defensible 
 foundations ? 
 
 The ftuestion as to the Reality of Mind stated. — Although 
 the general confidence of men in the reality of their own 
 minds is without doubt, there is no more obscure and puz- 
 zling question than this : In what does this reality con- 
 sist ? In other words : What is it to be real as all men 
 believe their mental " selves " to be real ? But this is a 
 question which it belongs to the metaphysics of mind, as 
 an important department of philosophy, fully to discuss. 
 As such, it does not properly belong to even the final con- 
 siderations of physiological psychology. 
 
 There is a form, however, in which the debate over the 
 reality of the mind may properly be considered as con- 
 nected with -the subject we have been studying. This 
 478 
 
THE NATURE OF MIND. 479 
 
 form is proposed under the heads of the arguments for and 
 against what is called the " materialistic " view or hypoth- 
 esis. For the materialistic view of mental phenomena 
 denies the popular impression, ^ — namely, that such phe- 
 nomena are to be referred to the mind as the subject or 
 ground of them all. On the contrary, it affirms that the 
 material substance of the living and active nervous system 
 (especially, or wholly, of the brain) is the only reality 
 concerned in the production of these phenomena. The 
 mental phenomena, it holds, are phenomenal of, manifesta- 
 tions of, the only " real " subject, which is in its view — as 
 we have already said — not mind, but the wonderfully 
 constituted and complex system of material molecules 
 within the bony cavity of the skull. 
 
 Is this view which we have called " materialistic " justi- 
 fied by the facts and laws of physiological psychology? 
 Or is, on the contrary, that view justified which regards 
 the mental phenomena as rightly assigned to a real being 
 to be called " the mind " ; and yet regards this real being 
 as acting in causal relations with the material substance 
 of the brain ? 
 
 It will be recalled that we have already in part an- 
 swered the foregoing questions by an argument against 
 the materialistic view. This argument wiU now be re- 
 sumed and briefly continued. 
 
 Difference between Nerve-commotions and Mental Phenom- 
 ena. — It is scarcely necessary to urge the fact that states 
 of consciousness are not identical in nature with molecular 
 agitations in the higher centres of the brain. Not even 
 the most pronounced materialists would venture to affirm 
 their identity. Minute movements, or chemical and vital 
 changes, in the molecules of the cerebral mass differ totally, 
 as phenomena, from states of sensation, of perception and 
 ideation, with their accompanying tones of pleasurable or 
 painful feeling. 
 
480 PHYSIOLOGICAL PSYCHOLOGY. 
 
 Even less, perhaps, would any one think of identifying 
 the most complicated and ample nerve-commotions with 
 those trains of thought which result in solving a mathe- 
 matical problem, or with those feelings of adoration and 
 affection which some men experience on contemplating the 
 idea of God. Mental states, on the one hand, are known 
 only as states of consciousness that are mine ; but states 
 of material molecules are conjectured as changes occurring 
 in my brain. The complete " incomparability " of these 
 two classes of phenomena is denied by none. 
 
 Modern science tends to regard all physical events as 
 modes of motion — alterations in the relations of material 
 atoms or masses to each other in space. This is as true 
 of the brain of the philosopher or of the saint as it is of 
 the falling meteor or the upturned clod of the vaUey. The 
 very assumption which underlies materialism — namely, 
 that the brain is an extra-mental and material being which 
 undergoes changes independent of all mental perception 
 or conception of these changes — seems to involve most 
 unequivocally the incomparability of nerve-commotions 
 and mental phenomena. 
 
 Mental States not " Products" of the Brain. — In the effort 
 to substantiate the being of the nervous organism and, at 
 the same time, deny that of the mind, various terms may 
 be employed to express the relation between the two. 
 Among such terms the word " product " occurs. We hear 
 it said that the brain — at least the psycho-physical centres 
 — " produces " the phenomena of consciousness. It is 
 impossible, however, to give any satisfactory meaning to 
 the word "product" in a connection such as this. By 
 this word we ordinarily understand the new form into 
 which some material substance is shaped by the action 
 upon it of some piece of mechanism. We may, indeed, call 
 certain secretions of the body the " product " of the tissues 
 which secrete them, in somewhat the same way as that in 
 
THE NATUKB OP MIND. 481 
 
 whicli we speak of the product of the field or of the loom. 
 But only the coarsest and most undiscriminating material- 
 ist could regard himself as saying what is really -valid 
 when he represents states of knowledge, feeling, or volition, 
 as in this sense of the word, the "product" of the brain. 
 When, too, we are told that the brain "throws off" the 
 mental phenomena, as a kind of surplusage — so to speak — 
 of its more legitimate form of activity by way of molecular 
 motions, we listen to words to which we are absolutely 
 without power to assign any intelligible meaning. 
 
 There is another and more plausible use of the word 
 " product " to describe the connection between the cerebral 
 centres and the phenomena of consciousness. Suppose a 
 system of material molecules to be acting under relations 
 to each other which are determined by the constitution, 
 arrangement, and environment of the molecules. We 
 may then speak of the new relations which these same 
 molecules assume as the product of their previous consti- 
 tution and arrangement, together with whatever influences 
 act Aipon them from without (their environment). Thus 
 the functional activity of the cerebral centres, at each 
 moment, may be regarded as the product of the nervous 
 substance of the centres themselves. 
 
 But this use of the word would only explain each 
 momentary condition of the brain as arising out of its 
 physical constitution and previous physical condition. The 
 explanation is perfectly legitimate; it is the business of 
 the physiology of the cerebral centres to carry such an 
 explanation as far as possible. Doubtless all the nerve- 
 commotions, all the molecular changes, in the cerebral 
 centres are, at each moment, capable of being regarded as 
 "products," under a mechanical theory, of antecedent 
 changes. If, however, such a mechanical theory of the 
 behavior of the brain, regarded as a system of material 
 beings, could be perfectly adjusted to the principle of the 
 
482 PHYSIOLOGICAL PSYCHOLOGY. 
 
 conservation and correlation of energy, we do not see how 
 it would enable us to regard the behavior of the mind — 
 the phenomena of mental states — as "products" of the 
 same antecedent changes. Out of nerve-commotions, as 
 their product, other nerve-commotions come. But how 
 are the phenomena of knowing, feeling, and choosing 
 rendered any less incomparable with the molecular changes 
 of nervous matter by speaking of them, too, as products of 
 the substance of the brain ? 
 
 Nervous Chang^es as Antecedents of Mental Phenomena. — 
 But surely, it will perhaps be said, the happenings of 
 mind, the so-called states of consciousness, are dependent 
 upon the changing conditions of the brain. Precisely so : 
 but this does not alter the necessity of assuming the 
 reality of mind, as the being whose states change, though 
 in dependence on other beings of a material kind. On the 
 contrary, if this question were to be referred to meta- 
 physics we should say that, to be the subject of states 
 which change in dependence on the changing states of 
 other beings, is in part the essence of all reality. 
 
 The investigations of physiological psychology furnish 
 abundant proof, on the other hand, that mental phenomena 
 are the regular antecedents of changes in the cerebral cen- 
 tres, and through these changes, of changes in the other 
 bodily organs. Indeed, the more comprehensive, minute, 
 and profound its investigations are, the more convincing 
 does the evidence to this effect become. On the whole, 
 there is as good reason to regard the mind as a reality 
 which influences, or acts upon the body, as tp regard the 
 body as influencing, or acting upon, the mind. 
 
 To emphasize the fact that nervous changes are the 
 regular antecedents, or causes, of mental phenomena, and 
 to deny that mental phenomena are also changes of states 
 in a real being, which we call the Mind, is therefore to 
 treat the scientific data in a one-sided way. It is, indeed. 
 
THE NATURE OP MIND. 483 
 
 to treat the psychical subject of states with more disrespect 
 than physics shows to the mass or the atom. For every 
 material mass or atom is dependent upon the behavior of 
 some other similar mass or atom, for the character of its own 
 changes. But physics does not, on this account, deny its 
 reality. In its turn, by its own behavior, each mass or 
 atom also furnishes regular antecedents, as causes, for 
 other changes in the very beings on which its own 
 behavior depends. These other beings, too, are depend- 
 ent upon it for the way in which they behave. What 
 valid reason can be given, why the reality of mind should 
 be sunk wholly out of sight, in the supposed behalf of the 
 material. molecules of the cerebrum? Surely the souls we 
 know we are should receive as much consideration as the 
 elements of that pulpy mass we call our brains. 
 
 Superiority of the Mind's Claim to Eeality. — For, in truth, 
 the claim of the mind to a real and independent existence 
 is, in some respects, unique. It is far stronger than the 
 claim which can be made for any of the existences with 
 which physical science deals. The materialistic theory, 
 of course, assumes the very opposite of this. It assumes 
 that every mental phenomenon is to be accounted for 
 iolely as a manifestation of changes going on in bodily 
 reality, — in the psycho-physical centres of the brain. 
 Nothing — says the theory — can happen by way of con- 
 scious sensation, perception, aesthetic, or religious feeling 
 and belief, abstract conception, or so-called free choice, 
 which does not find its only real explanation in the equiva- 
 lent changing states of the nervous system. 
 
 Our first impression on considering the foregoing theory 
 is one of surprise at its audacity. We have had frequent 
 occasion to remark the extraordinary difiiculties which 
 accompany the effort to establish on scientific foundations 
 almost every subordinate principle of physiological psy- 
 chology. Even in those branches of its inquiries in which 
 
484 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the methods of physical science can be most successfully 
 employed (e.g. Weber's law, the phenomena of reaction- 
 time, etc.) assured results are slow of attainment. Even 
 in such branches great caution is requisite to guard 
 against too hasty generalizations. But this theory pro- 
 poses to clear all barriers with a single leap, and to estab- 
 lish on the other side of them a complete speculative 
 science of the mind on a basis of principles that are recog- 
 nized as applicable (and even then, not always without 
 hesitation and doubt) only to physical phenomena. 
 
 But the theory of materialism is not simply inadequately 
 founded. It is opposed, not only to the popular impres- 
 sion (which assumes the reality of the mind, and knows 
 nothing, except by hearsay, about the existence of the 
 brain), but also to certain conclusions of psycho-physical 
 science. 
 
 The incomparability of the two classes of phenomena 
 (molecular agitations of the brain and states of conscious- 
 ness) we have seen to be generally admitted. The causal 
 relation, or dependence under law, of the two, has been 
 shown to be a legitimate conclusion of science. But the 
 independent (in some sort) development of the mind — its 
 life and growth as a non-material entity, under forms and 
 laws of unfolding that are unique, constitutional, wholly 
 peculiar to itself — is also a legitimate conclusion of the 
 same science. In proof of this statement we may fitly 
 appeal to certain facts treated in the preceding chapters. 
 
 Non-correlated Factors of Mental Life. — All mental life 
 rests upon a basis of sensory-motor activities. The term 
 " sensory-motor," however, may be applied either to physi- 
 cal or to psychical changes. As applied to physical activ- 
 ities, the science of physiology considers the data and laws ; 
 as applied to psychical phenomena, the term designates the 
 sensation-elements, the feelings of effort and strain, etc., 
 whieh enter into all our life of the body. Between these two 
 
THE NATURE OF MIND. 485 
 
 classes of activities " correlations," in the stricter sense of 
 the word, exist. The kind, degrees, time-rate, and " local 
 coloring," of the psychical factors depend upon the kinds, 
 quantities, time-rate, and locality of the physical ante- 
 cedents. 
 
 But the life of the mind cannot be described solely in 
 terms of the production, combination, reproduction, and 
 association of sensory-motor factors. The attempt to do 
 this induces the customary alliance between materialism and 
 sensationalism ; these two are inclined to go hand in hand, 
 as theories of mental life. The latter endeavors to expel 
 from existence those forms of mental activity for which 
 the former finds it most difficult, most impossible, to 
 account. 
 
 But a thorough analysis of mental life discloses other 
 forms of activity than those properly called sensory-motor; 
 and these forms not only do not find their full explana- 
 tion in the changing states of the brain, but are not even 
 conceivable as correlated with such states. For example, 
 an increasing amount of the sensation of pressure is not 
 identical with an additional gramme of metal laid upon 
 some area of the skin ; but the changes of quantity in the 
 sensation of pressure are correlated, under psycho-physical 
 law, with the increase in the number of grammes. Into 
 my perception of the piece of metal, as a "Thing" causing 
 my sensation, however, there enter forms of purely psy- 
 chical activity that cannot even be conceived of as thus 
 correlated. 
 
 For certain fundamental assumptions, or beliefs, enter 
 into all perception by the senses. No perception is a mere 
 combination of sensation-complexes, representable in terms 
 of correlated changes of stimuli and of nerve-commotions. 
 Perception is a knowledge of " Things." No " Thing " is 
 known as a mere grouping of sensation-complexes. And 
 whatever account one may choose to give of their nature 
 
486 PHYSIOLOGICAL PSYCHOLOGY. 
 
 and origin, there can be no doubt that various assumptions 
 and beliefs are implicated in all knowledge of things. The 
 knowledge of perception, then, involves an activity of 
 the mind which is sui generis, — an activity into the per- 
 formance of which the mind develops ; and which, although 
 it always rests upon a basis of correlated physical changes, 
 is not, as such, representable as the equivalent, or corre- 
 late of physical changes. 
 
 Things are known as " real " ; they are believed to be 
 the " subjects " of attributes, to have, and not to be, the 
 attributes. They are conceived of as acting on, and as 
 being acted upon by, each other ; they extend in an empty 
 space, which is assumed to be self-existent and indepen- 
 dent of the things. All this, and much more of the same 
 sort, is implicated in those mental acts which are often 
 falsely conceived of as the mere passive reception of im- 
 pressions ; or as the combination, under terms dictated by 
 physical mechanism, of sensations and feelings of bodily 
 strain. But, in truth, all this and whatever more is of 
 the same sort, — we repeat, — implies being and action 
 that are absolutely incapable of representation in terms of 
 such mechanism. Nor can the varying degrees and time- 
 rates of the movements of this mechanism be conceived of 
 as correlates of these modes of the mind's behavior. 
 
 What is true of perception is true of all the developed 
 mental life. Indeed, the form of mental life we call per- 
 ception, implies the exercise of the so-called higher facul- 
 ties of mind. Physical changes in the ideo-motor centres 
 of the brain are, no doubt, strictly correlated with certain 
 factors in that complex form of the mind's acting to which 
 the name of " memory " is given. Here, too, a faded and 
 weakened sensation, revived as a memory-image, may be 
 regarded the psychical equivalent of a weakened similar 
 molecular agitation in the same ideo-motor centre as that 
 where the physical basis of the original sensation was laid. 
 
THE NATURE OP MIND. 487 
 
 But of what physical changes shall that conscious recogni- 
 tion, which is the spiritual essence of all acts of developed 
 memory, be regarded as the correlate ? 
 
 Serious consideration of such a question as the foregoing 
 throws us into the same state of mind as that in which we 
 find ourselves when we ask : How many foot-pounds is the 
 equivalent of a true mother's love? or. How many cubic 
 yards represent the greatness of the thoughts in Newton's 
 " Principia " ? My memory-image of the sensations, given 
 me by a certain colored object, is — to be sure — no more 
 identical with the cerebral brain-commotions on which it 
 depends, than were the original sensations identical with 
 those original brain-commotions on which they depended. 
 But the image may be said to be, as respects quantity, 
 quality, local coloring, etc., correlated with the revived 
 physical changes on which it depends. On the contrary, 
 the spiritual fact that I consciously recognize this present 
 experience called memory as representative of my past 
 experience, and that I attribute both present and past 
 state to the same self, — all this implicates modes of men- 
 tal life which cannot even be conceived of as having any 
 physical correlates. 
 
 Keality of the Brain and its Processes. — It cannot escape 
 the acute thinker that the materialistic hypothesis secretly 
 assumes the reality and causal activity of the cerebral sub- 
 stance and of the physical changes which occur in it. But 
 scepticism can readily call this assumption in question. 
 And, indeed, the history of philosophy shows that unpreju- 
 diced reflection leads much more directly and surely to 
 doubt about the reality of matter than about the reality 
 of mind. Even the science of physiological psychology — 
 at least in some of its aspects, — tends to emphasize that 
 doubt with which the record of speculation is so familiar. 
 For this science shows us how very far is the most imme- 
 
488 PHYSIOLOGICAL PSYCHOLOGY. 
 
 diate perception of the material substance called brain, 
 from being a faithful copy of any real existence. 
 
 How — to put our doubt into the form of a concrete 
 inquiry — does the holder of the materialistic hypothesis 
 know that the patient, whose mental phenomena are ab- 
 normal, has a brain to whose diseased condition he may 
 refer this departure from the correct mental standard? 
 Only by inference from a very few cases of post-mortem, it 
 may be, to a general conclusion respecting all human 
 bodies. But inference and conclusion are mental activi- 
 ties, — modes of the behavior of conscious mind. Infer- 
 ence brings us to valid conclusion, and conclusion to real 
 existence is trustworthy, only as reason puts confidence in 
 her own laws. These laws are the constitutional ways of 
 that spiritual procedure on which — in the last analysis — 
 all confidence rests. 
 
 Suppose, however, that those observations and inferences 
 in which the science of physiological psychology delights 
 were indefinitely extended. Suppose that all the sensory- 
 motor functions were definitely localized in their proper 
 cerebral areas; that the laws of the association of these 
 areas were thoroughly comprehended; that the "nerve 
 physiology " of the brain had developed in scientific exact- 
 ness so far that the movements of each molecule of its sub- 
 stance could be predicted as certainly as can now the 
 movements of the planets. In brief, let it be taken for 
 granted that the deficiencies of knowledge which we have 
 encountered everywhere in our study of this subject have 
 all been, as fully as is conceivable, supplied. 
 
 A completed science of physiological psychology, as 
 such, would not in the least degree more firmly establish 
 the real existence of any single brain and its processes. A 
 completed science would still be — what the very word 
 " science " indicates — a system of spiritual activities, to 
 be assigned to the subject. Mind. 
 
THE NATURE OF MIND. 489 
 
 Of course it must be understood that all science is based 
 upon observation — minute, painstaking, verifiable, com- 
 prehensive. But observation itself is a spiritual activity, 
 involving immensely complicated psychical factors, imply- 
 ing numerous assumptions, beliefs, and other modes of the 
 behavior of the mind, which are not capable of being 
 represented by, or strictly correlated with, those cerebral 
 changes with which physiology deals. 
 
 We have, then, far more direct and verifiable knowledge 
 of the reality which we ourselves are, as conscious minds, 
 than of that hypothetical reality which materialism gives 
 to gyrating, swinging molecules in the centres of the cere- 
 brum. If one were determined to reduce all being and 
 action, in reality, to either of those two sets of terms with 
 which physiological psychology assumes to deal, one must 
 certainly choose the psychical rather than the physical, 
 the terms represented by the noun rather than the adjec- 
 tive, in the compound title. 
 
 Eeality of Mental Development. — That the words, "devel- 
 opment of the mind," stand for a real process, there can be 
 no reasonable doubt. What is true of every developed 
 mental activity is, even more palpably and emphatically, 
 true of the entire course of mental development. It can- 
 not be adequately described as a mere series of more and 
 more complex combinations of psychical factors of the 
 sensoiy-motor type. The difference between those incon- 
 ceivably simple activities in which mental life begins and 
 the more mature and highly developed mental activities 
 is not a difference of degree alone. Newton or Kant, as a 
 mind, is far more unlike the infant than the latter is unlike 
 one of the lower animals. There is much more which is 
 companionable and mutually intelligible between a man 
 and his dog than between a man and his newly born 
 child. 
 
 The changes which lie between the first and lowest, and 
 
490 PHYSIOLOGICAL PSYCHOLO&Y. 
 
 the more mature and highest things of human mental life 
 occur according to a plan. The life of every mind is capa- 
 ble of being made the subject of a history. This history 
 has its epochs and crises; it has, as well, its periods of 
 more steady and unobtrusive growth. But, on the whole, 
 it implies the development of that real being, whose mani- 
 festation is indeed related to the growth and activity of 
 the cerebral mechanism, but whose character is unique 
 among all developments — the so-called " human Mind." 
 
 Nor does the uniqueness of the mind's development 
 consist alone in that admitted incomparability of the phe- 
 nomena of conscious sensation to all physical phenomena, 
 to which reference has already frequently been made. In 
 all developments of a physical sort, — even including those 
 with which biology deals, — the factors which take part in 
 the development are themselves really existing entities, 
 regarded by science as endowed with natures and powers 
 innumerable of their own. The development of living 
 things, including the development of the nervous system 
 itself, is, according to science, nothing but the more and 
 more complicated and planful concourse of " the atoms." 
 These atoms are really existing beings. But simple 
 sensations, and sensation-complexes, and elementary feel- 
 ings or "feelings of feelings," and memory-images, etc., 
 although they are regarded by mental science as factors in 
 mental life, are not really existing beings at all. And 
 every attempt at a system of psychology which treats them 
 after the analogy of the elements of a physical develop- 
 ment overlooks the entire nature of the problem to be 
 solved. 
 
 The life of the mind, as it manifests itself for scientific 
 study, is a succession of "fields of consciousness." None 
 of these so-called " fields of consciousness " can be con- 
 sidered as accounting for itself. All of them are forth- 
 puttings of that living being which is the subject of them 
 
THE NATURE OF MIND. 491 
 
 all. They fade into each other ; they enlarge and diminish 
 in circuit ; they succeed each other with a varying time-rate. 
 Psychological science analyzes them into their hypothet- 
 ical factors ; it tries to determine the uniform conditions 
 of their formation, and the laws according to which 
 they follow each other. It finds them aU hung together, 
 as it were, upon a single thread, — upon the metaphysical, 
 the shadowy but necessary, assumption of the existence 
 of one entity, the soul, whose states they all are. No self- 
 consciousness is so penetrating and lively as to envisage 
 this entity in its pure being, or naked simplicity, as a 
 subject of all the states. But every act of self-conscious- 
 ness is a reference of some state to this assumed subject of 
 them all. And science can do nothing with the phe- 
 nomena of mind without virtually assuming that being 
 whose life and development binds together its own suc- 
 cession of " fields of consciousness," so-called. 
 
 The attempt to regard the planful unfolding of fields of 
 consciousness, which constitutes the life of the mind, as 
 merely the resultant of a physical evolution of the nervous 
 system, involves a constant abuse of terms. It makes 
 inevitable that mistaking of figures of speech for scientific 
 truths, against which we have already protested once and 
 again. Terms which apply well enough to a biological 
 evolution, when applied to the development of the mind, 
 have no intelligible meaning at all. The word " develop- 
 ment " itself, when applied to the mind, means something 
 entirely different from the same word when applied to an 
 organic structure like the cerebro-spinal system. At every 
 step we have to check our descriptions of the growth of the 
 soul's life by asking : " Precisely what, then, is it that we 
 mean ? " 
 
 But even if we disregarded the bearing df such a process 
 of misleading substitution in the meaning of terms, we 
 should still have valid reasons for aflfirming the reality of 
 
492 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the mind's unfolding life. For the process of this unfold- 
 ing, so far as we really know in what it consists, and upon 
 what physical conditions it is dependent, does not keep 
 equal step with the evolution of the nervous system. It 
 is indeed customary for psycho-physical science to assume 
 that mind and brain develop, as it were, hand in hand ; 
 and that the dependence of the former upon the latter is 
 so strict as to make all mental growth really an expression 
 of a physical evolution. Still, on this point, we believe 
 that the popular impression emphasizes certain facts which 
 the ordinary scientific hypothesis is apt to leave out of 
 account. 
 
 For example, at the time of birth the mind appears 
 almost or quite wholly undeveloped ; although the brain 
 of the full-grown embryo is, as respects both structure and 
 functions, a highly developed affair. The human infant 
 has by far the most complexly organized and fully equipped 
 nervous system of any of the young animals. But it has, 
 properly speaking, little or no mind. It is a truly sig- 
 nificant figure of speech which regards the mind of the 
 infant as yet unawakened ; as, indeed, waiting to be aroused 
 and set to the work of combining and interpreting those 
 sensations which are called forth by the excitation of its 
 nervous system. 
 
 Nor do we know of any valid reason for disputing 
 the apparent truth that, immediately after birth, the in- 
 fant's mind develops with a more rapid step than is taken 
 by the organic evolution of the brain. That the brain 
 grows with a marked rapidity, not only in gross weight 
 but also in complexity of structure, during the first year 
 of life, is a significant fact. That the sensory-motor factors 
 of psychical growth are dependent upon, and correlated 
 with, this physical growth, we do not for a moment ques- 
 tion. We also regard as entirely plausible the view, that 
 
THE NATUKE OP MIND. 493 
 
 innumerable " dynamical associations " are rapidly forming 
 themselves in the child's cerebral hemispheres. 
 
 But, on the other hand, a comparison of the character 
 of the mental life at the close of the first year — its un- 
 folding of the powers of perception, voluntary attention 
 and abstraction, under those constitutional norms which 
 philosophy calls the " intuitions " or " categories " — with 
 the absence of all really mental life at birth, suggests another 
 view of the case. The evolution of the brain is not a 
 complete measure, much less is it a complete explanation, 
 of the growth of the life of the mind. 
 
 Similar arguments against the view which regards the 
 mental development as only an expression or resultant of 
 the organic evolution of the brain, might be derived from 
 other periods and phases of life. It should never be for- 
 gotten that when we are describing the character and 
 causes of mental development in terms of a spiritual real- 
 ity and a spiritual life, we are speaking of that which all 
 men know. Mental curiosity, control of attention, careful 
 and comprehensive judgment, sound moral purpose — 
 these words represent terms of universal and undoubted 
 experience. That the development of the mind depends 
 upon, and consists in, these things, is beyond all question. 
 That these things are only the expressions or resultants of 
 organic brain-changes, is a hypothesis which most men 
 find it difficult to comprehend; and which, in our judg- 
 ment, no man has any right to propose as a scientific 
 necessity or even as a valid scientific faith. 
 
 We regard the following statement, then, as justified : 
 The development of mind can only be explained as the pro- 
 gressive manifestation in consciousness of the life of a real 
 being, which, although taking its' start and direction from 
 the action of the pkysical elements of the body, proceeds to 
 unfold powers that are sui generis, according to laws of its 
 own. 
 
494 PHYSIOLOGICAL FSYCHOLOGV. 
 
 The mind is a "real" being in the highest sense in 
 which any finite being can be said to 'be real. Indeed, its 
 claim to be considered real is more indisputable than the 
 same claim as put forth for any material thing; it is 
 unique. The reality of mind underlies and makes possi- 
 ble all our knowledge of other real beings ; and all our 
 assumptions as to the existence of such beings. It is only 
 on condition of granting its reality, in the highest sense 
 of the word, that we can affirm the reality of other beings. 
 
 Unity of the Hind. — Among the terms by which we char- 
 acterize the peculiar nature of that being we call the mind, 
 there is none more important than the term " unity." The 
 popular impression regards every person, every soul or 
 mind, as one, in a perfectly unique way. It is not difficult 
 to make clear to the popular impression that we may speak 
 of all material existences as, at the same time, one and 
 many, — according to the point of view from which they 
 are regarded. In the study of perception it was evident 
 that the unity of any object of sense is imparted to it by a 
 constructive, synthetic action of the perceiving mind. 
 Molecular science at once proceeds to analyze the object 
 of perception into a countless, an inconceivably great, num- 
 ber of constituent elements. The elements are regarded as 
 even more truly units than is the object of perception 
 itself. 
 
 The physical unity which science thus allows every 
 object to have is gained only as its constituent elements 
 are temporarily held together by various so-called " forces," 
 according to a variety of forms called " laws." The only 
 unity, in the stricter sense which physical science recog- 
 nizes, is that said to belong to the atom ; but in what this 
 unity consists it is difficult to make clear to the mind. 
 Indeed, the trained imagination of the physicist is scarcely 
 adequate to depict the nature of this hypothetical unity. 
 
 Mental Unity not Analogous to Physical. — Whatever kind 
 
THE NATTJEE OF MIND. 495 
 
 of unity physical science may finally succeed in indicating 
 for the individual atoms, it is obvious that such atomic 
 unity furnishes no fitting analogy for the case of the mind. 
 Indeed, we ought here to reverse the entire order of pro- 
 cedure. The unity virhich the atoms are assumed to have, 
 is due to the unifying act of the mind which thus con- 
 ceives of the atoms. Whether these conceptions fitly rep- 
 resent any ea;<ra-mental realities, we do not now inquire. 
 But whether they do, or not, there can be no doubt that 
 the only atoms known are the atoms conceived of (as real, 
 or not) ; and the only being that conceives of atoms, or of 
 anything else, is the mind. 
 
 The foregoing fact does not necessarily favor that old- 
 fashioned hypothesis which regarded the unity of the 
 mind as somewhat analogous to the unity of a homo- 
 geneous and eternally unchanging material substance. 
 Indeed, modem physical science does not regard even the 
 atoms as " unit-beings," in such a meaning of the word. 
 It was the theological interest in the attempt to place the 
 immortality of mind upon a quasi-scientific basis which 
 gained favor for this uncouth view. The argument ran : 
 The immortality of the mind depends upon its natural 
 indestructibility ; that which is indiscerptible or Indivisible 
 is naturally indestructible ; and that which is indiscerptible 
 must be a unity in the strictest sense of the word. 
 
 It is impossible to see, however, why a physical being 
 which has no distinction of parts, and undergoes no 
 changes of states, is best fitted to represent the unity of 
 mind-being and mind-life. Indeed, the very opposite of this 
 is obviously true. Comparative study shows us that, as a 
 rule, the more complex and varied is the psychical life of 
 any animal, the more complex and varied is the grouping 
 of that collection of organs which constitutes its nervous 
 " system" so-called. But the highest unity of mental life 
 is that which is built upon the greatest variety and com- 
 
496 PHYSIOLOGICAL PSYCHOLOGY. 
 
 plexity of psychical activities. It is man who, among all 
 the animals, has by far the best claim to be considered a 
 " unit-being," as regarded from the psychological point of 
 view. But it is man who has also the most elaborate and 
 complicated development of material organs, — systema- 
 tized into a cerebro-spinal axis and crowned by that peer- 
 less structure, a human brain. 
 
 Nor is this cerebro-spinal nervous system, which forms 
 the physical basis of the unity in variety of man's mental 
 life, a homogeneous and unchanging mass. Far from it. 
 No other portion of the bodily substance demands such a 
 copious blood-supply ; undergoes such rapid and important 
 changes with respect to those " dynamical associations " on 
 which the psychical habits of memory depend ; and is, in 
 general, so ceaselessly active in producing inconceivably 
 complex molecular variations in its own condition and 
 constitution. Corresponding to this physical system of 
 innumerable interacting elements and parts is an almost 
 boundless variety to the sensory-motor psychical life. For, 
 as we have already seen, certain single senses are capable 
 of hundreds of thousands of sensations that can be distin- 
 guished by minute variations in quantity, quality, and 
 " local coloring." Or, more properly speaking, in re- 
 sponse to the excitation of this wonderful nervous mechan- 
 ism in a countless variety of ways, the soul puts forth a 
 corresponding variety of those forms of manifestation 
 which are peculiar to its life. 
 
 But all this is far from being incompatible with that 
 unitary nature and existence which is possessed by every 
 human soul. In spite of what we might argue as to the 
 possible or impossible in such a case, the fact remains that, 
 in the order of nature, this very being which has such an 
 inconceivable complexity of physical and psychical activi- 
 ties is a " unit-being," in the very highest sense of the 
 word. 
 
THE NATUKB OF MIND. 497 
 
 The unity which the mind possesses is undoubtedly 
 dependent upon memory and self-consciousness. It is that 
 spiritual unity which implies the power of knowing one's 
 self, — of having states not only, but also and chiefly, of 
 referring these states to the unity of Self, and of distin- 
 guishing, in consciousness, that Self as a unique consistent 
 development, from all other selves and from all things. 
 So peculiarly is this a function of the developed mind, or 
 soul, that the words, a mind, or a soul, are absolutely 
 devoid of meaning unless they are understood as implica- 
 ting this. 
 
 It is quite possible, indeed, to raise that sceptical ques- 
 tion, of which Kant makes so much in his immortal " Cri- 
 tique of Pure Eeasou." After all, — we may ask, — is the 
 mind in reality one; or does it only, when normally 
 active, seem to itself to he one? The valid reply to this 
 question is as follows : The unity of a self-conscious 
 rational life is the highest and realest of all conceivable 
 unities. In other words, to be a developing mind, with 
 memory, reason, and self-consciousness, — this is to be 
 really one. It is this unity, which the mind undoubtedly 
 has in self-consciousness, that is alone worth contending 
 for. And if the mind were really — that is, regarded as 
 out of its own consciousness of self — one, and yet two or 
 more in consciousness, it would be no better, but rather 
 the worse off. If it were really one, but could not appear 
 to itself as one, could not be aware of its own change of 
 states, and attribute them to the one Self, which is the 
 subject of them all, its unity would be of no value. 
 
 Once more: a thorough metaphysical analysis would 
 probably show us that the unity which we attribute to 
 things is never more than a pale shadow, or faded type, of 
 the unity which we know ourselves to have. PhysicS, 
 indeed, regards the atom as the only unity, in the strictest 
 sense of the word. But this so-called "strictest sense of 
 
498 PHYSIOLOGICAL PSYCHOLOGY. 
 
 the word" is itself (probably) copied from that type of all 
 reality, which is the unit-being, Mind. Only as the mind 
 of the physicist projects, into the hypothetical being of the 
 atom, the attributes of its own life, can he call the atom a 
 unit, in " the strictest sense of the word." This is done 
 with that recognition of a kinship of all beings with mind, 
 which, after all, enters into every scientific conclusion or 
 hypothesis. 
 
 Spirituality of Hind. — The question whether we are to 
 speak of the mind as " spiritual " or not, scarcely merits the 
 grave and lengthy discussion to which it has often been 
 carried. " Materiality," as predicated of any real being, is 
 only an abstract and complex term, summing up a number 
 of so-called attributes. The word " attributes " is an 
 abstract term signifying the uniform ways of the behavior, 
 as known to us, of individual things. 
 
 Now, if we understand the term " materiality " correctly, 
 we cannot think seriously of applying it to the mind. For 
 the attributes which it covers are such as extension, im- 
 penetrability, mass, etc. ; and only in a figurative way can 
 such terms as these be applied to the subject of psychical 
 states. If, on the contrary, we use the term " spirituality " 
 as an abstract term to cover those attributes which things, 
 as perceived by mind, do not possess, but which minds 
 know themselves as possessing and exercising ; why then, 
 of course, we must affirm the spirituality of mind. 
 
 As soon, however, as we attempt to conceive of the sub- 
 stance of mind after the analogy of some ethereal exten- 
 sion, some more than ordinarily subtile expression of a 
 substratum common to all beings, we lose our right both 
 to affirm the spirituality and to deny the materiality of 
 mind. Nor can we hope scientifically to vindicate for the 
 mind such " spirituality " as would be implied in its being 
 freed from all relations to things, or from dependence for 
 the modes of its being upon the material substratum of the 
 
THE KATURB OP MIND. 499 
 
 brain. How spirit, in the meaning of unembodied mind, 
 would perceive, and feel, and think, and will, is a question 
 toward the answer of which psycho-physical science enables 
 us to make no beginning at all. 
 
 The subjects which we have been considering have a cer- 
 tain legitimate bearing upon speculative inquiries into the 
 first and the last things of Mind, — its origin and destiny, 
 its mortality or corruptibility. Physiological psychology 
 cannot explain the being of mind as arising out of the 
 development of the physical germ from which the bodily 
 members unfold themselves. It shows no decisive reason 
 against the belief that such a non-material and real 
 " unit-being," as the mind is, should exist in other rela- 
 tions than those of its present admitted dependence upon 
 the structure and functions of the body. But we have 
 already, perhaps, somewhat transgressed the limits which 
 most authorities would set to legitimate conclusions from 
 this science. Questions relating to the origin and destiny 
 of that subject of all the psychical states, whose reality and 
 unity we believe capable of defence on scientific grounds, 
 must be left to Rational Psychology, to Ethics, to Meta- 
 physics, and to Theology. 
 
INDEX. 
 
 Allen, Grant, on nature of feeling, 
 
 384 f. 
 Aphasia, phenomena of, 218 f. ; kinds 
 
 of, 219 f . 
 Aqueduct of Sylvius, 53. 
 Aqueous Humor, the, 81. 
 Arachnoid, the structure of, 35 f. 
 Attention, effect of, on reaction-time, 
 
 367 f ., 378 f . ; physical hasis of, 431 f. ; 
 
 effect of, on perception and memory, 
 
 434 f. 
 Automatic Action, nature of, 135 f.; 
 
 in spinal cord, 140 f. ; and brain, 
 
 149 f. ; physical hasis of volition, 
 
 431 f. 
 
 Bain, theory of feeling, 384 f. 
 
 Bell, Sir Charles, discovery of, 70. 
 
 Betz, " giant-cells " of, 67. 
 
 Birge, E. A., on number of nervous 
 elements, 28. 
 
 Blastoderm, the, 105 f. 
 
 Blind-spot (papilla optica) , 89 f . 
 
 Body, early development of, 446 f.; 
 relative proportions in, 450 f. ; sex- 
 ual differences of, 453 f. ; general 
 relations of, to mental phenomena, 
 465 f. 
 
 Brain, chemistry of, 12 f . ; membranes 
 of, 35 f.; structure of, 46 f., 55 f.; 
 hemispheres and lobes of, 55 f . ; ven- 
 tricles of, 60 f.; ganglia of, 60 f . ; 
 cortex of, 65 f. ; inhibitory influence 
 of, 142 f., 149 f.; as central organ, 
 149 f.; temperature of, 179 f.; com- 
 parative weight of, 181 f . ; weight of 
 human, 182 f.; relation of, to mind, 
 469 f. 
 
 Broca, convolution of, 292 f . 
 
 Capsule, the internal, 63. 
 Cells, the olfactory, 75 f.; the gusta- 
 tory, 76 f.; the auditory, 98. 
 
 Central Canal, 45 f. 
 
 Cerebellar tract, 45 f. 
 
 Cerebellum, structure of, 51 f.; func- 
 tions of, 152 f. 
 
 Cerebrin, 13. 
 
 Cerebro-spinal system, axis of, 35 f. ; 
 development of, 107 f. 
 
 Cerebrum, shape of, 55 f. ; gyri and 
 sulci of, 59 f. ; layers in its cortex, 
 65 f.; fibres of, 67 f. ; nervous ele- 
 ments in, 91, 95 f.; functions of, 185 
 f.; localization in, 187 f., 196 f., 204 
 f., 212 f. 
 
 Chemistry, of nervous system, 11 f.; 
 physiological function, 15 f.; of vis- 
 ion, 90 f. 
 
 Cholesterin, 13 f. 
 
 Choroid, the, 90 f. 
 
 Clarke, columns of, 42 f. 
 
 Cochlea, the, 96 f. 
 
 Color, stimulus of, 255 f.; tones of, 
 256 f. ; brightness of, 258; comple- 
 mentary, 260 f.; dependence of, on 
 time, 261; and place of the retina, 
 261 ; blindness to, 262 f . ; contrast 
 of, 264 ; Young-Helmholtz theory of, 
 265 f.; symbolism of, 268 f. 
 
 Consciousness, the circuit of, 377 f.; 
 physical basis of, 417 f. ; psycho- 
 physical explanations of, 418 f.; 
 unity of, 494. 
 
 Cornea, structure of, 79 f. ; index of 
 refraction of, 84. 
 
 Corona Radiata, 67 f. 
 
 Corpus albicans, 61 f. 
 
 Corpus callosum, 55 ; function of, 68. 
 
 Corpus dentatum, of the medulla, 50 ; 
 of the cerebellum, 52. 
 
 Corpus geniculatum, 60. 
 
 Corpus quadrigeminum, position of, 
 62; functions of, 153 f. 
 
 Corpus striatum, 63; paths in, 72; 
 functions of, 155 f . 
 
 501 
 
502 
 
 INDEX. 
 
 Cortex of Cerebrum, structure of, 65 f. 
 Crura Cerebri, 63 ; functions of, 151. 
 Crystalline Lens, the structure of, 
 82 f. 
 
 Deiters, processes of, 26; conical 
 
 hair-cells of, 98. 
 Bonders, time of mental processes, 
 
 359 f., 373. 
 Dove, the experiment of, 338. 
 Du Bols-Eeymond, discoveries of, 125 ; 
 
 theory of nervous action, 169 f. 
 Dura Mater, structure and processes 
 
 of, 39. 
 
 Ear, 91 f. ; the external, 91 f . ; the 
 middle, 92 f.; tympanum of, 92; 
 the internal, 95 f.; vestibule and 
 canals of , 95 f. ; cochlea of, 96; nerve 
 of, 98 f. ; development of, 114 f. ; 
 sensitiveness of, 248, 282. 
 
 Ebbinghaus, on memory, 427, 440 f. 
 
 Ecker, charts of, 205 f . 
 
 Electricity, "current of rest" in 
 nerves, 125, 169; as stimulus of 
 nerves, 125 f. ; " negative variation " 
 in nerves, 168 f. 
 
 Electrotonus, Pfliiger's law of, 127 f ; 
 theory of, 168 f., 170 f. 
 
 Embryo, knowledge of, 103 f. ; of the 
 fowl, 104 f.; development of, 107 f., 
 113 f. 
 
 Encephalon, see Brain. 
 
 End-organs of Motion, place in ner- 
 vous system, 32 f. ; structure of, 102. 
 
 End-organs of Sense, place and signifi- 
 cance of, 32 f. ; end-organs of .smell, 
 74 f. ; of taste, 75 f.; of touch, 77 f. ; 
 of sight, 79 f . ; of hearing, 91 f. 
 
 Eustachian Tube, 93 f. 
 
 Exner, views of, on localization, 204 f. 
 
 Eye, structure of, 79 f . ; tunics of, 79 f . 
 refracting media of, 81 ; appendages 
 of, 81 f. ; muscles of, 81 f . ; problem 
 of, 82 f . ; adjustment of, 84 f.; pig- 
 ments of, 90 f. ; development of, 
 113 f . ; motion of, 327 f . ; meridians 
 of, 328; torsions of, 329 f.; stereo- 
 scopy of, 332 f. 
 
 Fasciculus Gracilis, 48. 
 Fechner, law of, 276 f. 
 Feeling, of innervation or effort, 404 f . ; 
 
 of "double contact," 321 f.; nature 
 of, 379 f . ; classes of, 388 f . ; Inten- 
 sity of, 392; tone of, 390 f.; of sen- 
 sation, 393 f. ; the emotions, 400 f. ; 
 the higher aesthetic and intellectual, 
 395 f. 
 
 Perrier, centres of, 197 f . 
 
 Filum terminale, 28. 
 
 Fissures, of Sylvius, 57; of Eolando, 
 57 f. 
 
 Flourens on respiratory centre, 147. 
 
 Foramen magnum, 28. 
 
 Formatio reticularis, in the medulla, 
 50 ; in the tegmentum, 53 f . 
 
 Fovea centralis, 89. 
 
 Fritsch, experiments of, 188. 
 
 Ganglia, the "basal," 60 f. 
 Ganglion-cells, see Nerve-cells. 
 George, theory of temperament, 457. 
 Gerlach, on intimate structure of the 
 
 cord, 43. 
 Goldscheider, on " pressure-spots," 
 
 237 f.; temperature-spots, 239 f. 
 GoU, column of, see Fasiculus Gracilis. 
 Goltz, experiments of, on spinal cord, 
 
 141 ; view of localization, 223. 
 Gyri (or convolutions) of the cerebrum, 
 
 59 f . ; development of, 112 f. 
 
 Hall, G. Stanley, on perception of mo- 
 tion, 314. 
 
 Hearing, end-organ of, 91 f., 114 ; sen- 
 sations of, 245 f.; perceptions of, 
 306 f. 
 
 Helmholtz, accommodation of eye, 84 
 f.; on speed of nervous processes, 
 132 ; nature of noises, 252 f. ; con- 
 sonances of tone, 253 f. ; theory of 
 color-sensations, 266 f. 
 
 Herbart, theory of feeling, 385 f. 
 
 Hering, on temperature-sensations, 240; 
 theory of color-sensations, 267 f. 
 
 Hermann, on theory of nervous action, 
 169 f. 
 
 Hitzig, experiments of, 188; centres 
 of, 196 f. 
 
 Horopter, calculation of, 335 f. 
 
 Horsley and Schafer, experiments in 
 localization, 200 f. 
 
 Inhibition, from brain on cord, 142 f. ; 
 nature of, 437 f . 
 
INDEX. 
 
 603 
 
 Iris, the, 80. 
 Island of Reil, 59. 
 
 Jackson, Hughlings, on cerebral local- 
 ization, 187 f . 
 
 James, Professor, on the feeling of 
 effort, 406 ; laws of association, 42i. 
 
 Jastrow, on comparative judgments of 
 eye and hand, 358 f. 
 
 Krause, end-bulbs of, 78. 
 
 Kiihne, on chemistry of retina, 90 f. 
 
 Kussmaul, on aphasia, 222. 
 
 Lecithin, li. 
 
 Le Conte, on nature of the horopter, 
 325. 
 
 Listing, the law of, 329 f. 
 
 Local Signs, theory of, 294, 298 f., 327. 
 
 Lotze, theory of local signs, 294 f., 
 298 f . ; errors of sense, 349 ; theory 
 of feeling, 383 f . ; differences of the 
 sexes, 456; kinds of temperament, 
 458 f. 
 
 Luys, on basal ganglia, 73. 
 
 Magendie, discovery of, 70. 
 
 Materialism, views of, 479 f. 
 
 Matteucci, on electrotonus, 170. 
 
 Mechanism, nervous system as, 7 f. ; 
 the nerve as, 120 f.; theory of the 
 nervous, 158 f. 
 
 Medulla Oblongata, structure of, 47 f . ; 
 reflex-motor functions of, 146 f. 
 
 Meissner, calculation of the horopter, 
 325. 
 
 Membranes, of the brain, 35 f.; the 
 basilar, and of Beissner, 97. 
 
 Memory, physiological study of, 419 f . ; 
 as retentive, 419 f . ; as reproductive, 
 424 f . ; physical basis of, 425 f . ; psy- 
 chological nature of, 428 f. 
 
 Mesencephalon, development of. 111. 
 
 Meynert, description of brain, 69. 
 
 Mills, on localization of cerebral func- 
 tion, 208 f., 217. 
 
 Mind, subject of phenomena, 3 f ., 479 f . ; 
 relation to the brain, 463 f., 466 f. ; 
 480 f. ; synthetic act of, in percep- 
 tion, 292 f., 302 f., 360 f.; physical 
 explanations of, 478 f., 482 f. ; as a 
 real being, 478 f.; as a unit being, 
 494 f . ; spirituality of, 498 f . 
 
 Motions, the bodily, classes of, 407 f.; 
 the impulsive, 409 f . ; the voluntary, , 
 410 f.; the expressive, 412 f. 
 
 Miiller, J., on brain as measure of 
 intelligence, 181. ' 
 
 Miinsterberg, on memory and will, 435, 
 440 f. 
 
 Munk, experiments of, 198 f. ; motor 
 areas of, 199 f.; visual areas of, 
 213 f . ; auditory area of, 218. 
 
 Nerve-cells, elements of nervous sys- 
 tem, 17 f . ; kinds of, 24 f . ; intimate 
 structure of, 25 f . ; processes of, 26 ; 
 functions of, 116. 
 
 Nerve-commotion, causes of, 116 f.; 
 conditions of, 121 f. ; nature of, 
 127 f. ; laws of, 130 f.; speed of, 132; 
 summation and facilitation of, 165 f. 
 
 Nerve-fibres, elements of nervous sys- 
 tem, 18 f. ; kinds of, 19 f.; struc- 
 ture of the meduUated, 21 f.; fibril- 
 lated axis-cylinder of, 23 f . ; size of, 
 24 ; origin of, 26 f . 
 
 Nerve-musele machine, 120 f. ; behavior 
 under electricity, 125 f. 
 
 Nerves, structure of, 18 f . ; kinds of, 
 19 f.; the cranial and spinal, 86 f.; 
 general function of, 116 f., 118 f. ; 
 exhaustion of, 121 f.; properties of, 
 123 f. ; thermic and chemical influ- 
 ences on, 124 f . 
 
 Nervous Matter, kinds of, 12 f.; spe- 
 cific gravity of, 12. 
 
 Nervous System, a mechanism, 4 f., 
 158 f . ; chemistry of, 11 f . ; elements 
 of, 17 f. ; general function of, 31 
 f., 162 f.; structure of, 31-68; the 
 sympathetic, 33 f. ; the cerebro- 
 spinal, 35 f.; development of the, 
 107 f. 
 
 Neuroglia, nature of, 17. 
 
 Neurokeratin, 13. 
 
 Nuclei of nerve-cells, 18; of the me- 
 dulla, 50; of the corpus striatum, 
 63 f . ; of the optic thalami, 64. 
 
 Olives, the, 47 f. ; functions of, 156. 
 
 Optic Thalami, position of, 60; struc- 
 ture of, 64 f.; connections of, 68; 
 development of, 111 f. ; functions of, 
 154 f. 
 
 Organ of Corti, 97 f. 
 
504 
 
 INDEX. 
 
 Organs, kinds in nervous system, 31 f . ; 
 the central, 46 f. ; functions of, 135 f. 
 Ott, on centre of temperature, 156. 
 
 Pacini, corpuscles of, 78. 
 
 PapillsB, circumvallatse and fungi- 
 formes, 75 f. 
 
 Peduncles, of the cerebellum, 51; of 
 the cerebrum, 63 f. 
 
 Perception, nature of, 290-360; nati- 
 vistic and empiristic theories of, 
 302 f.; by smell, 305 f.; taste, 306; 
 hearing, 306 f.; touch, 308 f.; of 
 motion, 313 f. ; of temperature, 
 314 f.; of sight, 322 f.; of depth, 
 330 f., 339 ; of spatial relations, 
 330 f.; development of, 340 f. 
 
 Pfiuger, law of, 127 f. 
 
 Physiological Psychology, 1 f.; method 
 of, 5 f . ; claims of, 9 f. 
 
 Physiology, relation to psychology, 1 f . 
 
 Pia Mater, structure of, 35 f. 
 
 Pons Varolii, 47 ; structure of, 52 f. 
 
 Pressure, sensations of, 237 f. ; spots 
 of, 237. 
 
 Preyer, on sensitiveness to pitch, 247. 
 
 Protagon, 14 f. 
 
 Psychology, conception of, 2 f . ; method 
 of, 5 f. 
 
 Psychometry, method of, 359 f.; ele- 
 ments of time in, 362 f. ; results of, 
 380. 
 
 Psycho-physics, method of, 272 f . ; of 
 sensations of touch, 278 f.; of sound, 
 281 f.; of light, 283 f.; of smell and 
 taste, 285 f. ; the law of, 362 f . 
 
 Purkinje, cells of, 52. 
 
 Pyramidal tract, 45. 
 
 Quetelet, on proportions of human 
 body, 461. 
 
 Ranvier, nodes of, 21 f. 
 
 Reaction-time, nature of, 361 f . ; influ- 
 ences upon, 363 f., 366 f.; complex 
 processes of, 362 f . 
 
 Reflex action, kinds of, 131 ; in spinal 
 cord, 135 f.; conditions of, 138 1. ; 
 in the brain, 146 f. 
 
 Regio oUaotoria, 74 f. 
 
 Reissner, membrane of, 97. 
 
 Remak, fibres oi', 20 f. 
 
 Retina, the, 80; problem solved by. 
 
 82 f., 87; layers of, 87 f.; nervous 
 elements of, 87 f. ; rods and cones in, 
 88 f.; own light of, 256; field of, 
 324 f.; identical and corresponding 
 points of, 332 f. 
 
 Ribot, on memory, 424. 
 
 Rolando, fissure of, 59, 197 f., 203 f. 
 
 Schwann, sheath and substance of, 21 f. 
 
 Sclerotic, the, 79. 
 
 Seguin, on cases of aphasia, 220 f. 
 
 Semi-circular canals, the, 96. 
 
 Sensations, end-organs of, 74^101; 
 quality of, 228-270; simple, 228 f.; 
 conditions of, 229 f.; of smell, 230 f.; 
 of taste, 234 f . ; of temperature, 239 
 f . ; of pressure, 238 f . ; the muscular, 
 242 f. ; of sound, 245 f . ; of sight, 
 254 f . ; quantity of, 271 f . ; measure- 
 ment of, 272 f. ; least observable 
 difference in, 273 f . ; range of, 274 f . ; 
 spatial series of, 295 f . 
 
 Senses, organs of the, 74-101 ; classifi- 
 cation of the, 228 f . ; the geometrical, 
 293 f.; errors of the, 340 f. 
 
 Sight, end-organs of, 79 f.; photo- 
 chemistry of, 90 f. ; sensations of, 
 254 f.; after-images of, 263 f.; ele- 
 ments in perception of, 322 f.; 
 motion of eye in, 329 f . ; single and 
 double images in, 333 f. ; stereoscopic 
 and perspective, 337 f . ; secondary 
 helps of, 340. 
 
 Smell, organs of, 74 f.; stimulus of, 
 75; sensations of, 230; kinds of, 
 232 f. ; measurement of, 286; per- 
 ceptions of, 305 f . 
 
 Soul, see Mind. 
 
 Sound, analysis of, 100 f. ; sensations 
 of, 245 f . ; kinds of, 245 ; nature of 
 the musical, 246 f . ; limits of, 281 f . ; 
 direction of, 306 f. 
 
 Spinal cord, membranes of, 35 f ; struc- 
 ture of, 38 f . ;. fissures of, 38 f . ; col- 
 umns and commissures of, 40 ; horns 
 of, 40 ; white substance of, 41 f . ; 
 gray substance of, 43 f . ; nervous 
 tracts in, 44 f . ; as mechanism, 46, 
 136 f.; as a central organ, 137 f. ; 
 automatism, 140 f. ; " centres " of, 
 141 f. ; excitability as a whole, 142 f . ; 
 influence of brain on, 142 f . ; devel- 
 opment of, 107 f. 
 
INDEX. 
 
 605 
 
 Starr, Dr., disease of cerebeUum, 153 ; 
 on projection fibres, 222. 
 
 Stimulus, kinds of, 117 ; heat as, 124 ; 
 electricity as, 125 f . ; of smell, 230 f . ; 
 of taste, 233 f . ; of hearing, 245 ; of 
 sight, 255 f. ; measurement of, 272 
 f.; limits of , 274 f. 
 
 Strieker, on common feeling, 393. 
 
 Substantia gelatinosa, 41- 
 
 Substantia nigra, 63. 
 
 Sulci, of the cerebrum, 57 f . ; develop- 
 ment of, 113. 
 
 Suspensory ligament, function of, 84 f. 
 
 Sympathetic System, structure of, 33 f . 
 
 Taste, end-organs of, 75 f. ; nerve of, 
 77; sensations of, 233 f.; stimulus 
 of, 234; kinds of, 236 ; measurement 
 of, 285 f . ; perceptions of, 306. 
 
 Tegmentum, see Crura Cerebri. 
 
 Temperament, theory of, 456 f.; kinds 
 of, 457 f . ; physical basis of, 459 f . 
 
 Temperature, sensations of, 239 f.; 
 measurement of, 280; after-images 
 of, 314 ; sense of locality by, 314. 
 
 Thalamen-cephalon, 111 f. 
 
 Things, distinguished from sensations, 
 290 f. ; results of mental synthesis, 
 293 f., 304. 
 
 Tones, the musical, 245; pitch of, 
 246 f. ; sensitiveness to, 247 f. ; purity 
 of, 248 ; scale of, 249 f . ; relations of, 
 250 f. 
 
 Touch, end-organs of, 77 f . ; sensations 
 of, 237 f.; perceptions of, 308 f ; the 
 field of, 308-315. 
 
 Tympanum, the, 91 f.; membranes 
 of, 92 f.; windows of, 92; ofiioe of. 
 
 Valli, principle of, 122. 
 
 Vestibule, of the ear, 95 f . 
 
 Vitreous Humor, the, 81. 
 
 Volkmann von Volkmar, on nature of 
 feeling, 386. 
 
 Von Kries and Auerbach, on reaction- 
 time, 369 f. 
 
 Vulpian, on function of optic thalami, 
 155. 
 
 Wagner, corpuscles of, 78 f. 
 
 Waller, method of, 122. 
 
 Weber, E. H., 241; law of, 276 f., 
 287 f.; perceptions of touch, 308 f.; 
 " sensation-circles " of, 309 f. 
 
 Will, physiological study of, 430 f.; 
 physical basis of, 431 f . ; effect of, on 
 bodily motions, 436 f. ; in attention, 
 439 f. 
 
 Wnndt, mechanical theory of, 172 f.; 
 theory of color-sensations, 268, 341 f. ; 
 feelings of innervation, 405 f. ; ex- 
 pressive movements, 412 f.; theory 
 of temperament, 458. 
 
 Zonula, 85. 
 
 Typography by J. S. Gushing & Co., Boston. 
 Presswork by Berwick & Smith, Boston. 
 
Prof. LADD'S LARGER WORK. 
 
 ELEMENTS OF 
 PHYSIOLOGICAL PSYCHOLOGY. 
 
 A Treatise of the Activities and 'Nature of the Mind, from 
 the Physical and Experimental Point of View. 
 
 By GEORGE T. LADD, 
 
 PROFESSOR OF PHILOSOPHY IN YALE UNIVERSITY. 
 
 CHARLES SCRIBNER'S SONS, PUBLISHERS, NEW YORK. 
 
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