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PAUL B.HOEBEl 
 
 MEDICAL BOOKS 
 
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BOOKS 
 
 BY 
 
 PERCY G. STILES 
 
 Nutritional Physiology 
 
 i2ino of 275 pages, illustrated. 
 Cloth, $1.25 net. 
 
 The Nervous System and Its 
 Conservation 
 
 i2mo of 229 pages, illustrated. 
 
 jHSl Out. 
 
THE NERVOUS SYSTEM 
 AND ITS CONSERVATION 
 
 BY 
 
 PERCY GOLDTHWAIT STILES 
 
 INSTRUCTOR IN PHYSIOLOGY IN HARVARD UNIVERSITY ; 
 INSTRUCTOR IN PHYSIOLOGY AND PERSONAL HYGIENE 
 IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY ; 
 FORMERLY ASSISTANT PROFESSOR OF PHYSIOLOGY IN 
 SIMMONS COLLEGE, BOSTON 
 
 ILLUSTRATED 
 
 I 
 
 PHILADELPHIA AND LONDON 
 
 W. B. SAUNDERS COMPANY 
 
 1914 
 
Copyright, 1914, by W. B. Saunders Company 
 
 
 
 PRINTED IN AMERICA 
 
 PRESS OF 
 
 W. B. SAUNDERS COMPANY 
 
 PHILADELPHIA 
 
TO 
 
 EDITH ARTHUR BECKLER 
 
 Co-worker and Friend: 
 
 My colleague in developing the instruction in Hygiene 
 
 in Simmons College 
 
PREFACE 
 
 There are several excellent books devoted to the anat- 
 omy of the nervous system, there are others which treat 
 of its physiology in an illuminating way, and others still 
 which deal with its hygiene. If the present volume is 
 not to be an impertinence, it must be justified by its 
 attempt to combine some elements of the three. The 
 intention has been to present no more anatomy than is 
 essential to an appreciation of the correlated physiology 
 and to subordinate the physiology, in its turn, to the 
 teaching of hygiene. 
 
 In the chapters which deal with structure and func- 
 tion the writer has tried to gather his material from 
 authoritative sources. In those occupied more largely 
 with hygiene, personal judgments have doubtless found 
 expression. But the desire has been not so much to 
 dictate in a dogmatic spirit as to open important mat- 
 ters to fuller discussion. 
 
 Many associates have contributed to the making of 
 this book. From the number it is just to mention Pro- 
 fessor Ernest G. Martin, of Harvard, whose suggestions 
 have been numerous and valuable. 
 
 P. G. S. 
 November, 1914 
 
 7 
 
TABLE OF CONTENTS 
 
 CHAPTER I 
 Introduction 
 
 CHAPTER II 
 
 The Minute Structure of the Nervous Tissues 22 
 
 CHAPTER III 
 The Elements of Nerve Physiology : . 36 
 
 Reflexes . 
 
 CHAPTER IV 
 
 49 
 
 CHAPTER V 
 
 The General Anatomy of the Nervous System 60 
 
 CHAPTER VI 
 
 The Afferent Part of the Nervous System 75 
 
 CHAPTER VII 
 
 The Neuromuscular Mechanism 85 
 
 CHAPTER VIII 
 
 The Neuromuscular System: Neuromuscular Fatigue.. 101 
 
 CHAPTER IX 
 
 The Autonomic Nervous System 114 
 
 9 
 
10 ■ TABLK OF CONTENTS 
 
 CHAPTER X 
 
 PACK 
 
 The Cerebrum l-~ 
 
 CHAPTER XI 
 The Cerebrum and Human Development 142 
 
 CHAPTER Xn 
 
 The Cerebrum and the Life of the Individual 153 
 
 CHAPTER XIII 
 Emotion. 164 
 
 CHAPTER XIV 
 Sleep •. l^"^ 
 
 CHAPTER XV 
 Dreams 184 
 
 CHAPTER XVI 
 
 Causes of Nervous Impairment 192 
 
 CHAPTER XVII 
 
 Neurasthenia 203 
 
 CHAPTER XVIII 
 Some Matters of General Hygiene 216 
 
 Index . 
 
 225 
 
THE NERVOUS SYSTEM AND ITS 
 CONSERVATION 
 
 CHAPTER I 
 INTRODUCTION 
 
 TISSUES 
 
 Before the modern microscope was available, anato- 
 mists and physiologists recognized in the make-up of the 
 human body various types of constituent substance or 
 fabric. The different kinds of material recognizable 
 were few in number and easily assigned to certain large 
 classes. Comparison of one part of the body with another 
 showed that the same forms of organized substance were 
 found over and over again. The several varieties of 
 material distinguished came to be known as tissues. 
 
 In the hand, for example, we find the skin, the muscle, 
 and the bone, representatives of kinds of tissue con- 
 trasted in function, in physical character, and in chemical 
 composition. Closer study of the hand would add other 
 members to the list. When we consider the tissues with 
 regard to the intensity of the life-processes taking place 
 in them it is clear that this is anything but a constant 
 quantity. In some cases we have to do with structures 
 which are essentially passive in their nature and which 
 might conceivably be replaced by non-living substitutes. 
 This is true of those tissues which are described as con- 
 nective. Their service is mechanical; they unite and sup- 
 port other tissues. Bone is a conspicuous example of 
 
 11 
 
12 THE NERVOUS SY8TK.M AND ITS (X)\SKKVAT10N 
 
 this class, and very much as the skeleton determines the 
 general form of the body, so each organ is to be thought 
 of as possessing a minor framework of material which 
 behaves for the most part as though it were not really 
 alive. 
 
 It is usual to place the tissues in four large groups. 
 Besides the connective, to whicli reference has just been 
 made, we speak of the epithelial, the muscular or con- 
 tractile, and the nervous. Epithelial tissues are those 
 which form surface layers, cither internal or external. 
 They are the linings and the coverings of the organs. 
 The skin, or at least its superficial portion, is an obvious 
 example. While all the epithelia answer to the descrip- 
 tion of "coverings or linings," they vary widely in other 
 respects. Under the general term are included structures 
 as unlike as the calloused sole of the foot, the exquisitely 
 clear cornea of the eye, and the excessively thin parti- 
 tions interposed between the blood and the air in the 
 lungs. Judging the epithelial tissues by their share in 
 the total of the life-processes, we may say that they have 
 both passive and active parts to perform. In some places 
 their function is merely protective; in others they have 
 well-marked chemical activity. Secretion and absorption 
 are epithelial duties, and neither the one nor the other 
 could be carricfl out in its fulness by membranes not 
 living. 
 
 Contractile tissues are those which originate the move- 
 ments of the parts of the body. Organized into large 
 masses, they form the familiar muscles. The heart is 
 mainly composed of a peculiar contractile material 
 which is responsible for its beating. The same property 
 is manifested by elements found in the walls of the ah- 
 mentary canal, the blood-vessels, the urinary bladder, 
 the uterus, and other hollow viscera. It is evident that 
 the contractile tissues are eminently "alive" — that no 
 Hfeless substances could be expected to behave as they 
 do. Three principal varieties are recognized, conveniently 
 distinguished as the skeletal, the cardiac, and the visceral 
 
INTRODUCTION 13 
 
 — names which go far to denote the region where each is 
 discovered. 
 
 The nervous tissues are far less conspicuous in an 
 anatomic sense than the three orders just enumerated. 
 Let us imagine for a moment that each of the four 
 divisions in which we have placed the tissues could be 
 presented separately to view. Four human figures would 
 appear before us. That one composed wholly of connect- 
 ive tissue would consist of the skeleton as a basis, and 
 would show, in addition, an indication of each organ in 
 outline, with an internal system of interlacing strands. 
 It would include the ligaments which join bone with bone, 
 the cartilages which also occur about the joints as well as 
 in some other localities, and the tendons uniting muscles 
 with bones. The muscles themselves would be blocked 
 out in this picture by the surface membranes which they 
 possess and by webs of non-contractile material within. 
 
 The second figure would retain the complete contour 
 of the human form, inasmuch as it would have the skin. 
 If it were transparent enough the cavities and external 
 surfaces of the viscera would be seen defined in their 
 entirety, but with spectral lightness. The alimentary 
 canal would be traceable as a winding tube of great deli- 
 cacy within another still more diaphanous. The blood 
 system would be mapped in similar fashion. The interior 
 arrangement of each gland would show a tree-like pattern 
 of bewildering intricacy. 
 
 The third figure, consisting of the contractile tissues, 
 would be fragmentary and discontinuous. To conceive 
 of this apparition as keeping its shape calls for an extra 
 stretch of the imagination. It would supply the chief 
 bulk of the muscles and a fraction, missing in the other 
 manikins, of the alimentary, circulatory, and reproductive 
 systems. In a scattering way contractile tissue occurs 
 even in the skin, where its presence makes possible the 
 "goose-flesh" reaction. Although this third figure would 
 be less coherent than the others, it would greatly exceed 
 them in weight. 
 
14 .THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 What would remain for the fourth member of this 
 uncanny series? It has been reserved for a reconstruc- 
 tion of the nervous tissues. A distant view of it woukl 
 give the impression of a ghostly form with a more sub- 
 stantial axis expanding above into a bulbous mass in the 
 head. On closer approach the axis would prove to be the 
 spinal cord, the enlargement above would be recognized 
 as the brain, and the filmy haze which completed the 
 figure would resolve itself into many nerves, branching 
 strands proceeding from both brain and cord and termin- 
 ating in a cloud of finest filaments. These filaments 
 would be found to reach almost every part of the body 
 (Fig. 1). A large proportion .would be seen to end near 
 the external surface; a great many could be followed to 
 localities previously determined to correspond with the 
 skeletal muscles; still others would be manifestly adapted 
 to make connections with blood-vessels, glands, and the 
 contractile elements of the viscera. 
 
 By way of recapitulation the following statements may 
 now be made: The human body — or the bodj^ of any 
 animal of a highl}'' organized t^'pe — owes its relative 
 constancy of form to an inactive supporting system, the 
 connective tissues. It owes its ability to move to the 
 contractile tissues. The epithelial tissues are those which 
 establish the boundaries between the organism and the 
 environment; through them exchanges of gaseous and 
 dissolved substances take place. The service of the 
 nervous tissues remains to be indicated. The task is to 
 occupy us throughout the present volume. But a con- 
 densed preliminary discussion is desirable. 
 
 If a word is sought which shall convey a general idea 
 of the work of the nervous system, it is probable that 
 the term codrdinaiion will suggest itself. The nerves 
 serve to place various parts of the body in communica- 
 tion. This statement must he followed at once with the 
 note that the communication afforded is never directly 
 from organ to organ, but always by way of the axial part 
 of the system. Thus, there is no unbroken nervous high- 
 
INTRODUCTION 
 
 15 
 
 Fig. 1. — Diagram illustrating the general arrangement of the nervous 
 system (Martin, "The Human Body")- 
 
IG THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 way from the stomach to the heart, nor from one hand 
 to the other. Yet the stomach may influence the heart, 
 the central part of the mechanism transmitting the effect. 
 The fundamental plan of the structure involved is that of 
 a tree, and just as an ant cannot pass from one of the 
 main branches to another without visiting the trunk, so 
 all physiologic reactions employ a central link. 
 
 Coordination implies order, efficiency, and timeliness 
 in the operation of a machine. These desirable qualities 
 could not be realized in the living machine if it were not 
 for the nervous system. Coordination is akin to coopera- 
 tion, and the purposeful working together of all the parts 
 for the advantage of the whole is accomplished through 
 the aid of nerves and nerve-centers. A word which is now 
 frequently heard in this connection is integratio?!. The 
 nervous system may be said to confer integrity upon the 
 organism. This is to say that the unity or oneness of the 
 animal is almost wholly dependent upon this feature. 
 It is not entirely so, for we are realizing more and more 
 that chemical products passing from organ to organ have 
 much to do with the coordinating of activities. If the 
 nervous tissues could be instantly eliminated from the 
 body of a dog without doing other injury, the life proc- 
 esses would not immediately cease, but they would be- 
 come local and partial. They could no longer be com- 
 bined to the advantage of the animal. The nervous sys- 
 tem confers upon the associated tissues the right to rank 
 as an individual. 
 
 It is scarcely possible to use the word "individual" 
 without introducing the idea of a self-conscious being. 
 One's own nervous system is, in part, demonstrated to 
 one through personal consciousness. This is the field of 
 psychology. The physiologist is more properly a student 
 of the objective than the subjective, and he is occupied 
 for the most part with observing the reactions mediated 
 by nervous systems other than his own. Yet it may be 
 claimed that there is a considerable borderland common 
 to the two branches of science within which it behooves 
 
INTRODUCTION 17 
 
 both the psychologist and the physiologist to make 
 ventures. It is fortunate, nevertheless, that a great many 
 facts can be noted and discussed without any reference to 
 supposed mental states in animals. 
 
 We can deal with all the reactions brought about 
 through the nerve-centers in the simpler animals without 
 assuming psychic accompaniments, and the same method 
 carries us very far with our attempted analysis of nerve 
 physiology in the higher forms. A man cannot regard 
 his own brain in quite the same way in which he regards 
 his liver, but when he is bent on studying the hving nervous 
 system in a frog, a cat, or even in another human being 
 his immediate concern is with what it does — not with what 
 is felt while the action is in progress. Eventually he is 
 obliged to consider sensation in connection with his other 
 problems, but it is well to defer as long as possible the 
 admission of psychologic elements. 
 
 In accordance with what has been said, an objective 
 treatment of the nervous system will be pursued for the 
 present. The nerves will be looked upon as conductors 
 of energy. The chief source of this energy will be recog- 
 nized in the external forces which are brought to bear 
 upon the organism and which are termed stimuli. The 
 destination of the currents of energy will be found in the 
 contractile and secreting tissues whose activities they 
 modify. Life that is not one's own is manifested through 
 movement, heat production, and secretion; it is very 
 rarely that we are obliged to take other responses into 
 account. Attention must be directed to the fact that 
 nervous tissues separated from others can scarcely give 
 clear evidence of their internal changes. Muscles and 
 glands are required to testify to what is passing in the 
 governing mechanism. (Except for certain electric symp- 
 toms of very slight intensity we should not be able to 
 decide whether a detached portion of a nerve-trunk were 
 living or lifeless.) 
 
IS THIO NERVOUS SYSTKM AND ITS CONSIOKVATIOX 
 
 RECEPTORS; ADJUSTORS; EFFECTORS 
 
 These three words have recentl}^ l)een used to develop 
 a most simple and helpful outline of the general work 
 of the nervous system. Whether we consider a worm, an 
 ins6ct, a reptile, or a mammal, three departments of 
 orp;anization with functions of three orders can be indi- 
 cated. The receptors, as the name implies, constitute 
 that department of the system which is subject to ex- 
 ternal influences. Receptors are wrought upon by press- 
 ure, by changes of temperature, by chemical agents in 
 solution. In the more highly developed animals they 
 include particular sense organs like the eye and the ear. 
 Such organs translate vibratory energy of the ether and 
 the air respectively into the form of energy which nerves 
 convey. 
 
 It is to be noted that receptors may be strictly part 
 of the nervous system, as where naked endings of the 
 fibers lie exposed to contacts, or they may be mechanisms 
 made of other tissues serving to transmute and apply the 
 energy of the stimulus. Where the receptor does not con- 
 stitute a part of the nervous sj^stem the path from it to 
 the central axis must be given a special name, and it is 
 spoken of as a sensory or afferent path. 
 
 The effectors upon which the nervous system plays 
 include the contractile and glandular tissues. The effec- 
 tors are always distinct from the nervous system, and the 
 fibers stretching out to them form efferent paths. The 
 third class of working units, the adjustors, are those 
 within the nervous sj^stera which mediate between the 
 receptors and the effectors, or, more accurately, between 
 afferent and efferent pathways. It is in the realm of the 
 adjustors that the utmost complexity of organization is 
 possible. The variety of reaction so typical of animals 
 which we call "high in the scale" has its physical basis here. 
 
 Parker,^ of Harvard, has written most suggestively of 
 
 1 G. H. Parker, "The Origin and Significance of the Primitive 
 Nervous System," Proceedings of the American Philosophical 
 Society, 1911, vol. 1, No. 199. 
 
INTRODUCTION 19 
 
 the probable sequence in which the three orders of elements 
 have acquired their position in relation to the nervous 
 system of standard type. According to his hypothesis 
 there may have been a certain lowly condition — possibly 
 reahzed in sponges — in which contractility was displayed 
 only in response to distinct and direct stimulation brought 
 to bear from the outside world upon tissues having the 
 power of movement. No separate and definitely nervous 
 tissue would be requisite to apply the stimuh, but if such 
 a transmitter should be evolved it would be evident that 
 an efferent element had come into existence. Parker thus 
 conjectures that the efferent is the most primitive feature 
 of the three. 
 
 In the course of development the submergence of the 
 contractile tissues below the exposed surface of the body 
 would make it necessary that a receptor should be added. 
 Its function would be to maintain relations between the 
 exterior and the hidden effector. One receptor joined with 
 one effector would form a sufficient means for bringing 
 about one, and only one, reaction. The arrangement 
 does not admit of any flexibility. It is the simplest ex- 
 ample of what is called a reflex arc. With the addition of 
 intermediate links between the receptor and the effector 
 departments the reaction becomes less and less predictable. 
 This is equivalent to saying that it becomes more and 
 more like the actions of the higher animals — subject to 
 reinforcement, suppression, or modification under the 
 influence of changing circumstances. Many illustrations 
 will be given later which will serve to clear up this matter. 
 
 Excitation and Inhibition. — The common conception 
 of the function of nerves is that they arouse activity. 
 This is essentially true of those which stretch out from 
 the central axis to the skeletal muscles, and which call 
 forth the evident movements of the limbs, the play of 
 facial expression, etc. The muscles involved in such move- 
 ments are relaxed and paralyzed when their nervous con- 
 nections are interrupted. It is because this fact is so 
 prominent that one may easily fall into the error of sup- 
 
20 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 posing that no process of contraction or secretion takes 
 place save as the nervous system initiates it. This is very 
 far from being the case. 
 
 All the branches of the nerves which enter the substance 
 of the heart may be cut, but the heart will continue to 
 beat. Hence, we cannot beheve that each beat of the 
 heart is dictated by the efferent elements of the coordinat- 
 ing system. The power to make rhj^thmic contractions 
 is resident in the organ itself; we say that it is automatic. 
 In a less striking, but still positive, way other organs dis- 
 play a tendency to activity when removed from central 
 command. This is demonstrable for the stomach, the 
 intestine, and the urinar}' bladder. The contractile tis- 
 sues which enter into the make-up of these viscera must 
 be said to have a degree of automaticity. 
 
 When an organ has this disposition to be active on its 
 own account it will be seen that the nervous sj^stem may 
 exert a twofold influence upon it. The native, local 
 process may be accelerated beyond its average rate of 
 progress, or it may be restrained more or less radically. 
 We say that tissues which possess the automatic property 
 may exhibit either excitation or inhibition when the nervous 
 system modifies their inherent tendency. It is probably 
 just to claim that both with the heart and with the alimen- 
 tary tract inhibitory effects are more frequently witnessed 
 than are those which are clearly excitatory. If one is 
 incHned to cjuestion this, on the ground that quickening 
 of the heart-beat in exercise is a daily experience, it may 
 be answered that this quickening is known to be to a 
 great extent the withdrawal of an inhibition previously 
 operative. Withdrawal of inhibition is a form of counter- 
 feit stimulation which will repeatedly call for considera- 
 tion in later paragraphs. The slowing of the heart after 
 exercise may be a more positive instance of nervous inter- 
 vention than the hastening of its action, which seems so 
 much more impressive. 
 
 As for the alimentary canal, it lias become well recog- 
 nized that its movements are actually observed to better 
 
INTRODUCTION 21 
 
 advantage when it is removed from the reach of central 
 influences than when its nervous connections are intact. 
 It is not unhkely that there are a good many human 
 beings suffering from indigestion of nervous origin who 
 would have less trouble if their stomachs and intestines 
 could be placed quite out of reach of brain and cord and 
 left to work as determined by their own intrinsic proper- 
 ties. According to this view, suspension of the motor 
 activities of the canal is a possibility easily realized. 
 Acceleration may also be effected, but cannot be held to 
 be so common and striking an occurrence. 
 
 When the first clear instance of inhibition — the case of 
 the heart — was brought to the attention of scientists in 
 the year 1845 it was received with surprise and, at first, 
 with increduhty. All sorts of explanations were offered 
 for the phenomenon, with the intention of proving that 
 it was not a true suppression of activity. In course of 
 time, however, inhibition had to be recognized as a power 
 of the nervous system fully as direct and characteristic 
 as excitation. It is now fair to say, as a concise statement 
 of all which has gone before, that the duty of the nervous 
 system is to translate the energy of external stimulation 
 into nerve-impulses, to carry these to the central axis, and 
 to apply them through the efferent paths either to arouse 
 or to restrain the action of the contractile and secreting 
 tissues. The nature of the energy which is transmitted 
 along the nerves can best be discussed after we shall have 
 obtained some insight into the microscopic organization 
 of the nervous mechanism. 
 
CHAPTER II 
 
 THE MINUTE STRUCTURE OF THE NERVOUS 
 TISSUES 
 
 Our Introduction began with references to the existence 
 of a few tj^pes of tissue in the human body. These types 
 have been famiUar to anatomists for more than a century. 
 A large share of the credit for their recognition and 
 definition belongs to Bichat, a French worker, whose 
 short life of only thirty years (1771-1801) was extra- 
 ordinary for the extent of its achievements. Forty years 
 after the death of Bichat an important step had been 
 taken toward a more comprehensive knowledge of the 
 way in which living matter is constructed. The doc- 
 trine declared at that time is known as the Cell Theory. 
 Its estabhshment was directly due to a noteworthy im- 
 provement in the lenses made for microscopes. 
 
 The Cell Theory is to the effect that all forms of life can 
 be demonstrated to exist as single or associated units of a 
 certain standard kind. These units of structure continue 
 to bear the name of cells, though the word became fixed 
 upon them at first as the result of a misconception. It 
 is not logical to use a word which properly means a cavity 
 to stand for a more or less solid mass of material, but this 
 is the actual practice. The biologic cell may be regarded 
 as having the same relation to a cell in the precise sense 
 of the term that a cast has to the mold. In short, the cell 
 is a small parcel of living matter, the smallest which can 
 continue long to have the behavior which we associate 
 with the living state. 
 
 An average cell is microscopic in size. Many of those 
 in the body would be found to measure less than j oVcr iiich 
 in diameter; the red corpuscles of the blood, for example, 
 
 22 
 
MINUTE STRUCTURE OF THE NERVOUS TISSUES 23 
 
 are only 32-V^ ^^'^^ across their circular faces. If there can 
 be said to be a standard of form for the cell, it is the 
 sphere. But this primitive form is merely the point of 
 departure for the widest variations. The units in con- 
 tractile tissues are always greatly elongated, those of epi- 
 thelia are flattened, cubic, or prismatic, those of connective 
 tissue are irregular and often quite freely branched. The 
 
 Fig. 2. — Drawings like the above are almost always made from 
 tissues which have been prepared and colored by special means to 
 make clear, minute features, a represents an ovum or egg-cell, 
 the typical cell may be assumed to tend toward this spheric form; 
 6 is a cell from a compact tissue, to show how mutual pressure pro- 
 duces a faceted or polyhedral form; c is a contractile element such 
 as occurs in the walls of the alimentary canal, it illustrates an elon- 
 gated cell; d is an epithelial or lining cell of the order found on the 
 inner surface of blood-vessels; this is an example of extreme fatten- 
 ing; e, from the nervous system, exhibits the possibility of a branch- 
 ing development. 
 
 cells in nervous tissues are most peculiar of all, and must 
 presently be described at some length (Fig. 2). 
 
 When such diversity of form is considered the student is 
 disposed to ask: What have these differing packets of 
 organized substance in common that the same name 
 should be applied to them all? It is hard to say that 
 any single feature is always to be found in them. One 
 
24 THE NERVOUS SYSTEM AXD ITS CONSERVATION 
 
 which is prominent in the great majority is the nucleus. 
 This is a body within the cell, seemingly more dense than 
 the remainder and unlike the rest in its chemical character. 
 The last fact is proved by the individual reactions of the 
 nucleus toward selected stains or dyes. When tissues 
 are treated with such solutions, the nucleus, which maj' 
 have been quite invisible in the uncolored specimen, 
 appropriates the stain and stands out in .striking contrast 
 to the pale substance which envelops it. Excepti(nially 
 there may be more than one nucleus to a cell or, again, 
 none may be discernible. Cells are said to be composed 
 of protoplasm, and the word is often used as synonymous 
 with living matter. Huxley called it the physical basis of 
 life. The particular word cytoplasm will be found useful 
 to designate the portion of the cell which is external to 
 the nucleus. 
 
 The statement that tissues are composed of cells is 
 open to some objection. Tissues are made by cells, but 
 in the course of their development they commonly come 
 to contain material of a sort which cannot be described 
 as cellular. Such material is conveniently termed "inter- 
 cellular substance" and it is probably alwaj^s lifeless. 
 Sometimes it is scarcely recognizable, while at the other 
 extreme it may be so abundant as to constitute the main 
 bulk of the tissue and to determine its physical properties 
 and its value to the animal. Thus, bone is serviceable 
 because of the intercellular lime salts which give it rigid- 
 ity. The cells have come to occupy a very inconspicuous 
 position, and though they continue to exert a needed 
 influence upon nutrition, they are not at all concerned 
 from moment to moment in the mechanical function 
 fulfilled by the bone as a part of the skeleton. All con- 
 nective tissue is distinguished by the high proportion of 
 intercellular substance contained in it. The clear, glassy 
 concrete of cartilage, the tough, white fibers in tendons 
 and ligaments, the network between the skin and the 
 muscles — these are examples of material which is not made 
 of cells, though it was made hy them. 
 
MINUTE STRUCTURE OF THE NERVOUS TISSUES 25 
 
 It has proved far more difficult to gain a satisfactory 
 knowledge of the intimate structure of the nervous system 
 than to master the minute plan of other tissues. Students 
 at the present time are by no means agreed in their inter- 
 pretation. Fortunately, even an imperfect picture of the 
 microscopic arrangement throws much light upon the 
 physiologic processes observed. From one point of view 
 it may be claimed that the chief office of the nervous 
 system is conduction. We shall do well to attend first to 
 the elements which are known to carry on this particular 
 duty. These elements are the nerve-fibers; collected in 
 bundles they make the nerves. 
 
 A nerve is usually assumed to be a strand directly or 
 indirectly connected with the central system and large 
 enough to be followed by the naked eye as the body is 
 dissected. The fiber is too small to be traced in this way. 
 Fibers bear a relation to nerves like that which wires 
 bear to cables in which they are bound up. It follows 
 that the number of the nerves is of a moderate order, while 
 that of the fibers is expressed in millions.^ Nerves are 
 often seen to subdivide, but when such branching occurs 
 the fibers are merely assorted; they do not fork where the 
 nerve does, but are found in equal numbers in the trunk 
 and in the sum of its branches. This does not mean that 
 nerve-fibers never do subdivide, for there are important 
 instances of such behavior, but subdivision is usually 
 met with either in the central axis or near terminal 
 structures rather than in the nerve-trunks (Fig. 3). 
 
 A nerve-fiber consists of a core surrounded by one or 
 two sheaths. The double covering is the more common 
 arrangement, at least outside the brain and cord. The 
 suggestion of an insulated wire is strong. Here, as in the 
 wire, it is certainly the core which is the essential con- 
 ductor; the sheaths can scarcely be regarded as insulating 
 material in the ordinary meaning of the word, but they 
 are rather calculated to support and nourish the axis- 
 
 1 Between 3,000,000 and 4,000,000 has been estimated. Donald- 
 son, "The Growth of the Brain," Scott, London, 1895, p. 196. 
 
2G THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 cijlimler or axon, as the enclosed transmitter is called. 
 Investigation bj'^ refined methods has made it probable 
 that the axon can be resolved into a number of very small 
 fil^rils. The idea that there may be conducting units 
 finer and more numerous than the fibers as usually recog- 
 nized opens interesting possibilities. 
 
 The protective sheaths are broken into segments at 
 intervals of'a millimeter or less and thus present a jointed 
 arrangement. These joints are known as the nodes of 
 Ranvier, and the fact is to be emphasized that they do not 
 interrupt the continuity of the axis-cyhnder. This goes 
 on unbroken like the thread in a necklace. Nerve-fibers 
 attain a great length; the longest are not much shorter 
 
 Fig. 3. — Two nerve-fibers shown diagrammatically especially 
 to emphasize the continuity of the axon. A detail, further enlarged, 
 to suggest tibrils in the axon. 
 
 than the entire body. They may in other eases be so 
 short as hardly to pass outside a single microscopic field. 
 We must now consider the manner of their beginnings 
 and endings. 
 
 In studying the nervous tissues without the aid of the 
 microscope anatomists long ago began to refer to two 
 types which they called respectively gray and white 
 matter. Most of the nerve-trunks can be decisively classi- 
 fied as white matter, and when we find substance of a 
 similar appearance in the cord or the brain we may con- 
 clude that its organization is much the same as that of the 
 ordinary nerves. We have already seen that nerves are 
 bundles of fibers laid closely together and having a parallel 
 direction. The microscope shows that this is equally the 
 
MINUTE STRUCTURE OF THE NERVOUS TISSUES 27 
 
 case with other white matter. It is always and exclusively 
 devoted to conduction. 
 
 Gray matter is far more intricate in structure and its 
 physiology is less easily defined. It is massed for the most 
 part in the central nervous system. Small detached col- 
 lections, the ganglia, exist in other localities. An inspec- 
 tion of typical gray matter gives, first of all, the impression 
 of looseness of texture. Nerve-fibers are seen straying 
 through the field, but never in a compact formation. 
 Attention is quickly attracted by the curious bodies which 
 
 Fig. 4. — A common type of nerve-cell (or perikaryon) giving rise 
 to the axon of a nerve-fiber. 
 
 are most characteristic of this tissue, the so-called nerve- 
 cells. These vary widely in size, but probably have, on 
 the average, about the same dimensions as other cells. 
 In each one a conspicuous nucleus can be demonstrated. 
 But the most remarkable features of most nerve-cells 
 are the numerous processes which extend from them 
 (Fig. 4). 
 
 It has been said that the cells in connective tissue some- 
 times show a highly irregular outline. The cells of the 
 nervous system, however, surpass all others in this re- 
 spect. Their protoplasm is spun out into prolongations 
 
28 THE Xi:iiV()U« SYSTEM AXD ITS CONSERVATION 
 
 which become more aiul more slender as they branch until 
 their ultimate subdivisions defy observation. Each nerve- 
 cell, as a rule, has manj'^ of these brush-like extensions, 
 and since other cells are near at hand the processes inter- 
 lace in a bewildorino; fashion. A recent writer has likened 
 the resulting situation to that prevailing in a forest where 
 the branches of each tree penetrate among those of its 
 neighbors. Looking among the foliage from a little dis- 
 tance one cannot tell to which tree individual twigs belong. 
 
 Keeping for the moment the illustration just introduced, 
 it may be said that the observer could hardly tell whether 
 the ends of the small branches ended freely or ran together. 
 His information would enable him to decide that each 
 tree is really quite without connection with any other, 
 but he might not be able to determine this by his distant 
 inspection. This represents with entire justice the diffi- 
 culties encountered by workers who have tried to inter- 
 pret the appearance of the gray matter. They have not 
 been able to agree as to whether the processes of one nerve- 
 cell are continuous with those of others or whether they 
 merely mingle closely. Fortunately, the physiologj^ of 
 the nervous tissues can be discussed without the adoption 
 of one view to the exclusion of the other. The prime fact 
 has to be accepted that effects are produced by certain 
 cells upon their neighbors. 
 
 A term which it is most important to understand is 
 synapse. A synapse is said to exist wherever the branch- 
 ing processes of a nerve-cell transmit stimulating energy 
 to the processes of a second unit. If there is no con- 
 tinuity between the two, the synapse is a place of contact 
 or of close approach. If the adjacent units of the gray 
 matter are really bound together, the sjaiapse is the region 
 of the finest subdivision of the protoplasmic bonds between 
 them. If we speak physiologically, the synapse is a 
 functional junction; it is not absolutely necessary to 
 decide whether it is an anatomic junction. One doctrine 
 implicitly held with reference to the synapse is that trans- 
 mission across it can take place in only one direction. 
 
MINUTE STRUCTURE OF THE NERVOUS TISSUES 29 
 
 The property involved has been spoken of as a "valve- 
 action" (Fig. 5). 
 
 Most of the processes which spring from nerve-cells 
 are of the branching character which has been described. 
 They are called dendrites or dendrons. But certain proc- 
 esses are found to be of an entirely different order. These 
 can be followed often for long distances from the cells 
 which give rise to them, and are presently found to 
 acquire the sheaths previously mentioned as enveloping 
 the axis-cylinders of nerve-fibers. Just here we reach 
 a most fundamental conclusion as regards the constitu- 
 tion of the nervous system: that each nerve-fiber — or, 
 
 Fig. 5. — To illustrate a synapse (S), which is the functional 
 junction between the terminal arborizations — i. e., fine branchings — 
 of the left-hand neuron and certain dendrites of the one to the right. 
 Effects are secured only in the du-ection of the arrows. 
 
 more accurately, its central core — is the outgrowth of a 
 nerve-cell. This defines the relations existing between 
 the gray and the white matter. In the gray matter are 
 the cell-bodies; in the white matter run their long proc- 
 esses, the conductors of energy in the form which we have 
 called nerve-impulses. However far nerve-fibers may 
 stretch from the situation of their presiding cells, their 
 axons are to be recognized as continuous with the proto- 
 plasm of those microscopic elements. The axon in a 
 long fiber may contain many times as much substance as 
 the cell-body in which it originates. 
 
 A question of terminology now arises. If the axis- 
 cyhnder is part and parcel of the structural unit which 
 
30 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 has it;? nucleus in the gray matter, do we do well to call 
 the portion about the nucleus the cell and to imply that 
 the core of the fiber is not to be reckoned as belonging to 
 it? It is reasona])lc to claim that the cell should he held 
 to include all its extensions, no matter how prolonoed. 
 Histologists have appreciated the force of this argument 
 and have proposed words to denote more precisely the 
 features under discussion. What we have generally called 
 the nerve-cell may better be called the perikaryon, which 
 means specifically "around the nucleus." When we 
 adopt this we find ourselves in need of a word for the 
 combination of perikaryon, dendrites, and axon (or 
 axons) — in short, for the nerve-cell in the best sense. 
 The word supplied is neuron. 
 
 The Neuron Theory. — It is now time to outline the 
 conception of tlie anatomy and physiology of the nervous 
 system which for twenty-five years has been the founda- 
 tion of most presentations of these subjects. To do this 
 will be, in part, to restate what has gone before, but we 
 shall be led also to fresh considerations. The ideas to be 
 explained are not to be received as surely demonstrated, 
 but they have probably not seriously misled students in 
 the past, however they may have to be modified in the 
 future. New views are now urged by many skilled in- 
 vestigators and we must not ignore them. Nevertheless, 
 the traditional picture of the nervous elements and their 
 relationships remains convenient for teaching and diagram- 
 matic purposes. 
 
 The neuron theory assumes that the whole system is 
 capable of resolution into highly specialized cells of the 
 nature already indicated. These neurons are said to be 
 "concatenated," which means enchained. The indi- 
 vidual neuron is commonly supposed not to be continuous 
 with any of its fellows, but it is supposed to affect and to 
 be affected by them through synapses. The valve action 
 emphasized above gives each neuron a certain regularity 
 of performance ; it can receive stimuli at certain points, but 
 it cannot communicate them at the same places. So also 
 
MINUTE STRUCTURE OF THE NERVOUS TISSUES 'SI 
 
 it can despatch impulses to other neurons, but they cannot 
 react upon it. What follows is most important : axons are 
 nearly always channels for the conveyance of impulses 
 away from the perikaryon — dendrites are receptive in 
 function. It is probably a fact that the majority of neu- 
 rons are of the type having numerous dendrites and only 
 one axon. The arrangement makes stimulation from many 
 directions a possibility, but gives a fixed course to the 
 resulting outflow of energy. Vast numbers of neurons 
 are to be found in the central gray matter which have 
 only short processes and which do not easily admit of 
 distinguishing dendrites from axons, yet the distinction 
 is assumed. 
 
 Fig. 6. — To show how in an afferent neuron the transmission is 
 from the endings subject to stimulation (i?) to a synapse (S) in the 
 central nervous system. The perikaryon has an intermediate posi- 
 tion and its functions other than that of maintenance are problem- 
 atic. 
 
 One kind of neuron stands somewhat in contrast with 
 all the other varieties, inasmuch as it has a smooth peri- 
 karyon without sign of dendrities. A single axon runs 
 for a short distance away from the perikaryon and is then 
 found to fork and to be traceable for a long waj^ in either 
 direction. This type of unit is peculiar to the afferent 
 department of the nervous system. It is marked physio- 
 logically by the fact that it is not adapted to be stimulated 
 by other neurons, but by energies acting from sources 
 external to the nervous mechanism. In such a neuron 
 the perikaryon is usually buried far from the normal 
 operation of external stimuli. If it bore the ordinary 
 short dendrites and lay open to stimulation within the 
 
32 TH1-: NERVOUS SYSTEM A.\U ITS CONSERVATION 
 
 gray matter, this could only result in confusion of 
 reaction and, in case sensations were aroused, in 
 hallucinations. This assertion can be justified later 
 (Fig. G). 
 
 Let us consider in what various ways nerve-fibers 
 may terminate. Those which serve the receptors are 
 called afferent, those which act on effectors are said to be 
 efferent. Most afferent fibers are parts of neurons like 
 those described in the paragraph above; the perikaryon 
 in each one is neither at the beginning nor at the end of 
 the course traversed by the impulses. It is most often 
 placed on what might be called a "spur-track," nearer the 
 central than the peripheral limit of the neuron. It was 
 long a question whether the passing impulses entered the 
 perikaryon or left it quite at one side as they ran inward. 
 There is some reason to think that they actually visit it. 
 By a rather arbitrary stretching of our terms we may 
 regard the section of such a neuron that lies between the 
 periphery and the perikaryon as an elongated dendrite, 
 and the portion central to the perikaryon as the axon. 
 But it is not customary to call a fully developed and 
 ensheathed nerve-fiber a dendrite, and this is the character 
 of the conductor in question. 
 
 When we think of the limits of neurons in an anatomic 
 sense it is well for us always to have their physiologic 
 action in mind. If we do so we can speak intelligibly of 
 beginnings and endings, the first being the receptive 
 processes, and the second the terminals which transmit 
 effects to other neurons or to tissues not belonging to 
 the nervous system at all. The afferent or receptor neu- 
 rons which we have been discussing hegiyi, in this sense, 
 where they lie exposed to stimulation by pressure, heat 
 or cold, or chemical agencies. They end where they 
 form synapses with other neurons in the gray matter of 
 the central axis. To refer to beginnings and endings 
 with this meaning is an entirely different thing from using 
 the same expressions with respect to origin and growth. 
 We cannot deal here with the embryologic facts. 
 
minutp: structure of the nervous tissues 33 
 
 The neurons belonging in the class of adjustors far 
 outnumber the others in any system which can be said 
 to be highly organized. Such neurons are, by the necessi- 
 ties of the case, intermediate between other neurons. 
 They are stimulated through their dendrites and they 
 are assumed to discharge through their axons. A single 
 adjustor neuron may have a long axon and thus span a 
 wide space, or it may be restricted in its reach to a micro- 
 scopic scale. When the processes are short a large number 
 of neurons in series may be concerned in carrying im- 
 pulses for a very Hmited distance. Probably this kind of 
 transference from cell to cell is measurably slower than 
 the uninterrupted flow through the white matter. 
 
 Efferent neurons receive through their dendrites 
 stimuli which may have been furnished directly from 
 receptor elements or which may have arrived by way of 
 the adjustors. The efferent fibers extend usually to a 
 considerable distance from the seat of their origin and 
 terminate by making connections with contractile or 
 secreting cells. When mention is made of efferent 
 fibers one is most apt to think of those which excite the 
 skeletal muscles — motor fibers as commonly understood. 
 Neurons serving this purpose run an unbroken course 
 from cells in the lower part of the brain to muscles in the 
 head and neck; others similarly pass from the spinal cord 
 directly to muscles in the trunk and limbs. Efferent 
 fibers of other classes are usually, if not always, arranged 
 in tandem fashion, with a synapse in their course, so that 
 two orders have to be traversed by impulses bound from 
 the brain or cord to many peripheral structures. 
 
 We have pictured the nervous elements in the way 
 which has been considered acceptable until quite recently. 
 But, as we have already hinted, the neuron theory is 
 under a fire of criticism. We must take pains to suggest 
 possible departures from the doctrine which may come 
 to be estabhshed in time. It has been said before that 
 continuity of protoplasm from neuron to neuron is 
 assumed by many. The view that a synapse is a bridge 
 
 3 
 
34 THE NERVOUS SYSTEM AND ITS COXSKKVATIUN 
 
 rather than a place of contact impairs the .supposed 
 individuaUty of the units. A more important change 
 in our conceptions may have to be adopted if the observa- 
 tions of certain students are confirmed. 
 
 The statement that the axon of a nerve-fiber may 
 contain a numl^er of fibrils, perhaps to be regarded as 
 independent carriers of impulses, will be recalled. It 
 is claimed that in some cases fibrils like these are to be 
 demonstrated within the perikarya and extending out 
 into the dendrites. The suggestion has, therefore, been 
 made that everj^thing else in the nervous sj^stem is sub- 
 ordinate in importance to a continuous network, slender 
 
 Fig. 7. — To illustrate the conception of the neuropile which 
 subordinates the cells of the nervous system to a continuous net- 
 work of fibrils sometimes within and sometimes without the cell 
 boundaries. 
 
 and intricate. This it is proposed to call the neuropile. 
 A synapse, in the light of this interpretation, is merely 
 the place where fibrils pass from the sphere of influence 
 of one perikaryon to that of another (Fig. 7). 
 
 The chief result of these recent discoveries will probabty 
 be to lessen the prominence given to the perikarj^a in 
 descriptions of nervous activity and to emphasize the part 
 played by the fibrillar conductors. One interesting func- 
 tion of the perikarya remains undisputed. This is the 
 responsibility for the maintenance of normal nutrition 
 through all the processes of the neuron. No matter how 
 far an axon may stretch from the cell-body to which it 
 
MINUTE STRUCTURE OF THE NERVOUS TISSUES 35 
 
 belongs, its most distant portion is yet dependent upon 
 the influence of the perikaryon for its preservation in good 
 condition. Cut off from its perikaryon it inevitably 
 degenerates. This is a fact which has proved most help- 
 ful to the investigators who have sought to unravel the 
 tangled fabric of the nervous system. 
 
 Regeneration. — When a nerve has been cut and de- 
 generation has taken place, regeneration remains a possi- 
 bility. This requires months for its accomplishment. 
 New axons from the old perikarya grow along the track 
 of the former set. It seems marvellous that they should 
 push through to make appropriate connections, but they 
 often do. Of course, this may be prevented by obstacles 
 in the path; if the two ends of the cut nerve were dis- 
 placed laterally instead of remaining in end-to-end con- 
 tact the outgrowth of the fresh fibers would not occur. 
 Unfortunately for the human race, the reconstruction of 
 nerve-fibers which we observe outside the cord and brain 
 does not take place in the central axis. Injuries which 
 result in degeneration within the confines of the central 
 nervous system are anatomically irreparable. Physio- 
 logically, the accompanying losses are sometimes made 
 good by the substitution of other paths for those which 
 have suffered interruption. 
 
CHAPTER III 
 THE ELEMENTS OF NERVE PHYSIOLOGY 
 
 It was impossible to discuss the structure of the iKjrvous 
 tissues without anticipating to some extent an exposition 
 of their working. We can now proceed further with this 
 subject. We have chosen the word "coordination" to 
 express the broad function of the system, and we have 
 said that the chief property of its elements is conductivity. 
 The simplest statement of the duty discharged has been 
 said to be something like this: The receptors lie exposed 
 to external stimulation, thence the effects of this stimula- 
 tion are conveyed to the adjustors in the central axis, 
 the adjustors distribute to efferent neurons, and by these 
 the responses of muscles and glands are secured. It is now 
 time to inquire into the nature of the external stimuli and 
 the transmitted energy. 
 
 Stimuli. — A stimulus is a change, physical or chemical, 
 which is capable of producing physiologic reactions. Rais- 
 ing the temperature of a selected area of the skin is a 
 means of stimulation. Lowering the temperature may 
 have equally positive results. The application of press- 
 ure at any spot whence it may be conducted to underly- 
 ing receptors is an instance of mechanical stimulation. 
 There are in the surface of the tongue receptors which 
 can be excited by various dissolved substances. Here 
 we have an example of chemical stimulation. When the 
 retina is acted on by hght and impulses flow along the 
 optic nerve to the brain there are probably two steps in 
 the process: first, the light causes a chemical change, as 
 it docs in the photographic plate; second, some product 
 
 36 
 
THE ELEMENTS OF NERVE I'HYSIOLOGY 37 
 
 of the reaction behaves as a chemical stimulant. Electric 
 currents — or, more correctly, changes in electric condi- 
 tion — are among the most valuable forms of stimuli 
 for experimental purposes, though they do not play 
 any considerable part in the natural course of events. 
 
 The power of a stimulus to ehcit responses depends 
 upon the magnitude of the change from previous condi- 
 tions. This might be confidently predicted, but another 
 equally important fact might easily be overlooked. 
 Stimuli are effective not only in proportion to their am- 
 plitude, but also in proportion to the rate at which the 
 change takes place. In other words, changes sufficiently 
 gradual may fail of stimulating effect even though they 
 are most extensive. Demonstration of this is secured most 
 conveniently when the stimuli observed are electric; it is 
 found that rapid shifting of potential is far more exciting 
 than a slower change, while the alteration may be made 
 so gradual as to lose all efficacy. 
 
 One more fact concerning stimuli deserves emphasis at 
 this point. The withdrawal of an influence which has 
 been operating upon the hving mechanism may be as 
 truly a stimulus as would the application of a new form 
 of energy. Cold, which is to the physicist a negation, 
 must be counted a positive means of physiologic stimu- 
 lation. The same may be said of sudden darkness or 
 silence. When the baby has gone to sleep the parent 
 must not break off his lullaby too abruptly. He should 
 rather employ a judicious diminuendo, when, if successful, 
 he will have illustrated more than one biologic law. At 
 sea we wake from sleep when the regular throb of the en- 
 gine ceases. 
 
 In the early speculations of philosphers respecting the 
 manner of action of nerves the picture frequently pre- 
 sented is that of tubular conduits giving direction to 
 spurts or pulses of fluid. One is reminded of the pneu- 
 matic appliances sometimes used in church organs to 
 transmit the effect of pressure upon a key to a distant 
 valve. All such comparisons are wholly faulty and we 
 
38 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 must utterly discard thcni. The nerves are not tubes, 
 but cables, and even the axons give no evidence of any 
 progressive movement of their substance. We have to 
 do with conductors in which the material is stationary; 
 this is an important limitation as we strive to conceive of 
 the propagated impulse. 
 
 If we think of instances of conduction outside the 
 nervous system we shall be attracted by the figure of a 
 fuse. The spark which runs along the train of powder is 
 the visible sign of a destructive chemical change. A 
 protoplasmic strand might be imagined through which a 
 similar chemical change should make its way, leaving 
 behind it a track barren of further possibilities in the line 
 of conduction. Of course, this does not correspond closely 
 with what we know to be true of the nerves; they are 
 adapted to carry impulse after impulse without showing 
 impairment. The extreme resistance of white matter to 
 fatigue has made it hard to believe that its axis-cylinders 
 are in any sense "burnt out" in the performance of their 
 function. We cannot think that there is any extensive 
 waste of material as the unseen impulses travel along 
 the paths laid for them. 
 
 Conductors of physical changes are not necessarily 
 altered in the least by their service. An iron wire is not 
 worn out by the passage through it of the electric current. 
 It has not contributed energy from its own stores, as has 
 the fuse, to reinforce that which ran from one end of it to 
 the other. All the energy has come from outside the 
 conductor, and when that energy is gone the wire is left 
 sensibly unaffected. In the same way the harp-string, 
 which is plucked near one end and is swept throughout 
 its length by the resulting vibrations, comes to rest un- 
 changed except for a trifling wear and tear. Here again 
 the energy came. from outside and the conductor gave up 
 none of its own. The nerve-fiber seems much more 
 like the wire that carries the current or the musical string 
 set in vibration than like the fuse consumed in doing its 
 duty. Yet we must not hastily conclude that a nerve- 
 
THE ELEMENTS OF NERVE PHYSIOLOGY 39 
 
 impulse is an electric current, nor that it can be called a 
 vibratory disturbance. We must not hastily abandon the 
 idea that it has chemical features. 
 
 A chemical change occurring in white matter need not 
 be destructive in character. It may take place in one 
 instant and be reversed in the next with the restoration 
 of the initial condition. Something like this must be 
 true of the retinal cells in which the Ught-waves are 
 momentarily causing photochemical reactions which are 
 almost, though not perfectly, neutralized by the recupera- 
 tive changes which accompany them. It may be that when 
 'a nerve-impulse passes there is a disruption of molecules 
 and an almost instantaneous recovery. It has been sug- 
 gested that upon the passage of each impulse a sHght 
 contribution is made to the axon by the enclosing sheaths 
 and that in this way the conductivity is maintained almost 
 indefinitely. If there is any consumption of substance 
 attendant on the transfer, we should expect to obtain 
 evidence of the formation of waste-products in nerve- 
 trunks which have been functioning for a long time. The 
 fact that no conclusive evidence of this sort has been 
 secured shows that the conduction process is one of extra- 
 ordinary economy of material.^ 
 
 One is constantly tempted to present the plan and 
 working of the nervous system in terms of an electric 
 plant like that of a telephone exchange. Nothing made 
 by man is so hke the nervous mechanism, with its channels 
 leading in and out, and shifting connections to mediate 
 between them. Moreover, as we have hinted, there is an 
 electric change — slight, but- definite and characteristic — 
 which betrays the passage of each nervous impulse. The 
 flying energy is, nevertheless, not to be regarded as an 
 
 ' Even while these statements stand in manuscript comes the 
 statement of the Japanese, Tashiro, that he has demonstrated an 
 augmented discharge of carbon dioxid from a nerve-trunk convey- 
 ing impulses. His method is one of remarkable delicacy (American 
 Journal of Physiology, Proceedings of the American Physiological 
 Society, 1913, xxxi, 22). 
 
40 TH1-: NERVOUS SYSTEM AND ITS CONSERVATION 
 
 ordinary electric current.' It lias no such inconceivable 
 velocity. About the middle of the last century Hehn- 
 holtz reported that he had measured the rate at which 
 the impulses pass in the nerves of frogs and that he had 
 found it to be less than 100 feet per second. Recent 
 studies have made it probable that it is considerably 
 higher in man, ]>ut it is not by any means equal to the 
 speed of sound-waves in the air. 
 
 A most important question, and one which is proving 
 difficult to answer, relates to the part played by the peri- 
 karya when impulses are passing. Do these spend their 
 own substance to reinforce the transmission? If they do 
 they are like the relay cells in telegraphic sj'^stems. Wires 
 are not worn out with carrjdng electric currents, but 
 batteries are used up in generating them. It has been 
 the common belief that the perikarya of the gray matter 
 do suffer disintegration when the neurons to which they 
 belong are active. It is usual to say that when a neuron 
 is stimulated through its dendrites there is a discharge, 
 meaning by this an evolution of fresh energy at the cost 
 of material oxidized or otherwise degraded. Assuming 
 this to be true, we shall have an outflow of energj^ greater 
 than that applied as a stimulus. 
 
 We could, perhaps, miagine a nervous organization 
 such that no energy save that originally applied by the 
 external stimulus should be observed to flow from it. 
 This would be economic to the last degree. But it seems 
 unlikety that anj^ tissue can ever become so specialized 
 as to lose all trace of its primitive tendency' to undergo 
 some decomposition as a necessary part of its activity. 
 When contractile elements are stimulated they respond 
 
 1 Two investigators, Crehore and ^^'il]iams, of New York, have 
 recently attracted much notice by their contention that nerve- 
 impulses are actually electric in their nature. By taking into account 
 the dimensions of the fibers and assigning certain physical proper- 
 ties to the sheaths they put forth an argument to prove that electric 
 disturbances should not jiuss very rapidly in nerves, but rather at 
 about the velocity found to hold for the nerve-impulses. It is too 
 soon to say whether ph3siologists will generally be won to this con- 
 ception. 
 
THE ELEMENTS OF NERVE PHYSIOLOGY 41 
 
 by a display of energy utterly out of proportion to that 
 which was brought to bear to excite them. We say that 
 the force they exert had its source in the chemical changes 
 that took place in their protoplasm, changes that must 
 have left the tissue in an altered condition and with a 
 lessened potency for further performance. 
 
 A mechanical analogy suggests itself. Consider the 
 operation of the lock of a gun. The trigger is pulled and 
 the hammer falls, but not with the slight force applied 
 to the trigger. It comes down with the power represented 
 by the previous tension of the strong coiled spring. The 
 "stimulus" released an internal store of energy. This is 
 representative of the conditions exhibited by muscles, 
 and it is probable that with the neurons there is only a 
 difference in degree, not in kind. When we think of the 
 trifling amount of those forces which often prove suffi- 
 cient to produce extensive reactions of the organism we 
 can hardly doubt that the currents which are started 
 from the receptors receive a very marked reinforcement at 
 the cost of the gray matter. 
 
 We have some definite evidence bearing upon this 
 point. If the perikarya make contributions from their 
 own stores to forward the nerve-impulses we may expect 
 them to show fatigue and structural change in connec- 
 tion with long-sustained action. Changes associated with 
 activity have been frequently described. Some years ago 
 Hodge announced that there is a clear difference between 
 the outline and internal appearance of the perikarya in the 
 gray matter of animals killed after a night's sleep and the 
 corresponding features as seen in specimens from animals 
 killed at the close of the day. He obtained his material 
 from birds whose intense life-processes might be expected 
 to make them most favorable subjects. The statements 
 of Hodge have been widely confirmed. We must discuss 
 this important matter again in connection with the topic 
 of fatigue. 
 
 We shall assume provisionally that nerve-impulses may 
 be set going in the conducting pathways either by the 
 
4,2 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 direct effect of external stimuli or by the chemical changes 
 occurring in the perikarya. The impulses that run along 
 the afferent (receptive) channels are originated in a 
 relatively direct manner by external forces. Those that 
 traverse the adjustors and run out to the effectors may be 
 thought of as the afferent currents which have continued 
 through the synapses of the central axis, but we shall 
 probably do well to regard them rather as relays, that is, 
 impulses started anew from perikarya excited to "dis- 
 charge." This view, according to which the energy of the 
 transmission is reinforced by each neuron in the series, 
 is the older doctrine and is still dominant. 
 
 Attention must now be called to the relative ease with 
 which neurons will respond to stimuK applied at different 
 points. It is most necessary for the orderly and purposeful 
 working of the nervous system that nerve-fibers shall not 
 be easily excited save at their specialized beginnings or 
 endings. It is, in fact, difficult to stimulate a nerve at 
 any intermediate point in its course. When we do use 
 sufficiently positive means to make the stimulation 
 effective the result is such as to remind us that it would 
 be undesirable to have it a common incident. A blow 
 on the cl])ow may be forcible enough to start impulses 
 in the afferent fibers of the nerve which lies near the 
 surface at that spot, and it instantly seems to the 
 subject that he has sensations pertaining to the wrist and 
 fingers. He has excited to activity the axons which have 
 habitually brought impulses from the hand, and they still 
 awaken the same associations as though they had come 
 over the whole distance. This is a very significant 
 matter and it will be wise to place further emphasis 
 upon it. 
 
 When an electric door-bell rings, the householder is 
 usually justified in the assumption that some one is out- 
 side ringing it. Yet it might happen that a short-circuit 
 at some point along the course of the wires should cause 
 the signal. The ringing of the bell when occasioned in 
 this abnormal way would have the same quahties to the 
 
THE ELEMENTS OF NERVE PHYSIOLOGY 43 
 
 ear that had previously become famiUar. So it is with our 
 sensations; we rely on the regularity of their external 
 causation, but we are always liable to be misled by an 
 experience like that of the tingle that follows the rap on 
 the elbow. Impulses started anywhere between the 
 periphery and the central stations have the same conse- 
 quences for us as though they had been initiated at the 
 remotest terminal structures. The more one reflects on 
 this fact, the more one marvels at the freedom from con- 
 fusing hallucinations which we usually enjoy. 
 
 Are nerve-impulses all alike? This is a most interesting 
 question. The first disposition will be for one to say that 
 they must vary widely in nature to produce such dis- 
 similar effects. But most of our physiologic progress has 
 been found consistent with the idea that they vary chiefly 
 in intensity and frequency and not in the more subtle 
 ways which might be conceived. The reader must be 
 reminded that two electric currents precisely alike in 
 themselves may cause utterly unlike phenomena if they 
 are led through different fixtures. The closing of one 
 circuit, for example, may ring a bell; the closing of another 
 may light a gas-jet. It is, for the most part, quite as 
 unnecessary to suppose that different nerves carry im- 
 pulses of contrasted character as to assume that the 
 electric currents are mysteriously differentiated in the 
 case cited. The clarifying view that they are essentially 
 similar throughout the whole system is one which we owe 
 primarily to the great physiologist, Johannes Miiller 
 (1801-1858). The theory encounters many difficulties, 
 but is not to be prematurely abandoned. 
 
 Teaching experience shows that students find it ex- 
 ceedingly hard to beheve that the impulses passing along 
 various nerve-trunks are of one unvarying character. The 
 instructor is at great pains to dissuade them from speaking 
 of "messages" or "sensations" in this connection. Mes- 
 sages and sensations are evolved from nerve-impulses 
 only by a process of translation; these highly colored 
 words cannot properly be applied to the energy in transit. 
 
44 THE NKUVOIS SYSTEM AND ITS COXSKHVATIOX 
 
 Psychologists have entertained and disciplim-d their i)u- 
 pils by sup;j2;csting what would be the result of diverting 
 the impulses from one sense organ so that they should 
 enter the brain over a route normally belonging to a differ- 
 ent receptor system. The favorite proposition is to demand 
 that impulses originating in the eye be switched to the 
 auditory path, and that those generated in the ear be 
 led into the brain along the fibers of the optic nerve. 
 The subject must then hear all that he used to see and 
 see all that he formerly heard. The lightning will be 
 for him a short, sharp sound, and the thunder a pro- 
 longed, flickering light. At a concert he will hear the 
 lights, the decorations, and the costumes, but he will 
 have the extraordinary privilege of seeing the progres- 
 sions of the music. We cannot anticipate at all how it 
 will look. 
 
 Unprofitable as such flights may appear, they at least 
 afford a clear recognition of the "Miillerian principle." 
 According to this the diverse effects produced by nerve- 
 impulses in various cases are due entirely to the direc- 
 tion which these impulses are made to take within the 
 nervous system, and not at all to their own variability. 
 Moreover, the effects of stimulation must be determined 
 far more by the choice of fibers to be acted upon than b}'' 
 the kind of stimulation employed. The optic fibers are 
 usually made to bear impulses which have been initiated 
 in the retina under the influence of light, but it is possible 
 to start impulses along these same fibers by other means. 
 Thus, it is recalled from the old days of surgery without 
 anesthetics that the cutting of the optic nerve — a form 
 of mechanical stimulation — was not productive of pain 
 beyond that alread}'' being endured, but of the sensation 
 of a flash of light. It is not certain that we can always 
 adhere strictly to the doctrine of the uniform character 
 of the nerve-impulses, but to do so as far as possible makes 
 for clearness. 
 
 It is well just here to refer to a phenomenon often held 
 to be mysterious, though readily explained. This is the 
 
THE ELEMENTS OF NERVE PHYSIOLOGY 45 
 
 persistence, after amputation, of sensations long associated 
 with the member that has now been lost. The experience 
 is said to be vivid and distressing. Spiritualistic theories 
 have been advanced with regard to it. But, after all, it 
 is just what we ought to expect. The stump contains 
 all the fibers that were formerly concerned in bringing 
 the impulses from the missing limb. If certain ones 
 are subjected to unusual tension or pressure in the read- 
 justment of the tissues attendant upon the heaUng process, 
 impulses may be started along the old channels. All the 
 associations of the resulting sensations will be with the 
 peripheral localities from which impulses used to arrive 
 over these routes. 
 
 Summary. — We are now in a position to sum up the 
 substance of the last few pages. The white matter of the 
 nervous system serves to conduct impulses — which can 
 usually be considered quite lacking in individuality — 
 to and from places in the gray matter. The paths in the 
 white matter are permanent. For the most part, at least, 
 they exist from infancy and are changed only by gross 
 pathologic processes. Conductivity, the course a fixed 
 one, is the distinctive property of the fibers as it is of 
 electric wires. If this is true, what shall we say of the 
 gray matter? We shall be inclined to credit it with the 
 power of reinforcement, as already pointed out, but 
 here too we must continue to emphasize the duty of con- 
 ducting. A most important difference between the con- 
 trasted kinds of nervous tissue is found in the varying 
 direction taken by impulses traversing the gray matter 
 at different times as compared with the inflexible be- 
 havior of the white. If we liken the nerve-fibers to wires, 
 as we have just done, we may find in a switch-board a 
 partial analogy to the gray matter. Wires and switch- 
 boards both serve to conduct currents, but the latter 
 permit the interruption and the resumption of the con- 
 duction and the most extensive shifting of connections 
 between channels of entrance and exit. Similarly, wc 
 are brought to recognize that an inflowing stream of im- 
 
46 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 pulses of a certain intensity may under soni,e circumstances 
 be blocked in the gray matter, while under other condi- 
 tions it may emerge to reach the effectors more or less 
 strikingly. This property of the gray matter is spoken of 
 as variable resistance. Often it is denominated synaptic 
 resistance, on the basis of the assumption that it is the 
 synapses as previously defined which so greatly change 
 their conductivitj^ from time to time. 
 
 A little reflection will convince one that resistance to 
 the passage of impulses through the graj^ matter must 
 have everything to do with the behavior of the organism. 
 If it is temporarily lowered to a certain extent, reactions 
 will be readily produced by stimuli of slight intensity. 
 If it is lowered still further, the responses will become 
 exaggerated, confused, and exhausting. Increase of re- 
 sistance, on the other hand, will render it more and more 
 difficult to evoke reactions. Life itself has been defined 
 approximately as a continued "adjustment of internal 
 to external relations," and the biologic term, "irritabihty," 
 stands for the capacitj^ to make such adjustments. Evi- 
 dently the resistance of the central nervous system must 
 be maintained between limits not too widely separated if 
 the good of the organism is to be served. 
 
 Not only does the resistance of the central gray matter 
 vary under the influence of drugs and of the drug-hke 
 products of the body's own activity, but, what is of yet 
 greater interest, it is modified by the prolonged use of the 
 structure in cpestion. In general, repeated reactions are 
 secured with more and more ease. This is a fact of the 
 utmost import; it will be foreseen that it must be the 
 starting-point for any discussion of habit formation and 
 even of education. We say that paths of easy transmis- 
 sion tend to become established in the nervous system in 
 connection with its employment in a routine. These 
 paths are the "ruts" of everyday speech. The evidence 
 that they come to exist is found in physiology rather than 
 anatomy, that is, in observed behavior rather than in 
 visible structural features of the gray matter, but we 
 
THE ELEMENTS OF NERVE PHYSIOLOGY 47 
 
 cannot doubt that there are actual material changes 
 in the tissue, though it is not Hkely that the most 
 refined microscopic technic will ever make them recog- 
 nizable. 
 
 It will now be apparent that while conductivity is the 
 most conspicuous property of all nervous systems, it has 
 associated with it, though in a varying degree, the capacity 
 to be modified by use. The power to conduct impulses 
 along fixed pathways with fixed reactions ensuing is highly 
 characteristic of those forms of life which we regard as 
 lower and simpler. The second power is obviously pro- 
 portional to the rank which we involuntarily assign to 
 animals. So far as they possess it, they have the chance 
 to profit by individual experience. This would seem to be 
 the same thing as inteUigence objectively viewed. Com- 
 plexity of action does not necessarily imply such an 
 endowment. We marvel at the community life of bees, 
 and we are inclined to endorse Darwin's assertion that 
 the brain of the ant is the most wonderful particle of 
 matter in the universe, but upon reflection we are led to 
 give cats and dogs credit for immeasurably superior 
 organization. 
 
 An old ant is probably Kttle better than a young one 
 in meeting the exigencies of its environment. Maturity 
 in the insect is a matter of size and strength rather than 
 any acquirement of profitable responses to stimulation. 
 But maturity in the dog means an acquirement of just 
 such responses and it also means that dogs have indi- 
 viduality. The inherited nervous mechanism in the one 
 case is all but rigid; in the other it is plastic in a high de- 
 gree. We cannot deny to the ant some trace of this 
 capacity for modification through experience; the ability 
 to return to the nest seems to dentonstrate it, but we do 
 not expect to find it impressive. It will be noted that the 
 plastic property is met with in those nervous systems 
 which in the beginning of the animal's life are most 
 inadequately fitted to meet the demands made upon them. 
 We might conceive of a nervous system, as well prepared 
 
48 THK ni<:rvous systp:m axd its conservation 
 
 to make the necessary adjustments as is that of the ant, 
 which should nevertheless record the unique history of 
 the sinfi;le life, but such a combination is unknown. Our 
 chief interest is in the human beinf>;, and it is self-evi- 
 dent that the nervous system of man is, at the outset, 
 the farthest from being ready to cope with the environ- 
 ment as it is the best adapted to register individual 
 contacts. 
 
CHAPTER IV 
 
 REFLEXES 
 
 We have said repeatedly, in one form and another, 
 that it is the duty of the nervous system to produce 
 timely adjustments to changing environmental condi- 
 tions. These ■ adjustments are called reflexes. The 
 statement has already been made that a receptor neuron 
 Hnked to an effector is the simplest possible "reflex arc." 
 It is now time to enlarge upon these matters. 
 
 The word ''reflex" readily suggests the word "reflec- 
 tion." The elementary conception is of an influence 
 brought to bear upon the central nervous system from 
 without and rebounding to contractile or glandular 
 structures which are aroused to activity. This is a de- 
 cidedly crude notion and must be dismissed in favor of a 
 more accurate description. Descartes, in the seventeenth 
 century, attempted to account for the familiar reactions 
 of animals to stimuh in terms like the following: "Nerves 
 are made up of fine tubular conductors connected with 
 reservoirs of a peculiar fluid in the brain. These tubes 
 contain slender threads which are attached to valves 
 controlhng the outflow of this fluid. When there is a 
 disturbance at the exposed ends of some of these con- 
 ductors the threads are pulled and the valves opened. 
 Thereupon the energizing fluid runs down the same tubes 
 and enters the substance of the muscles, which are at 
 once thrown into contraction."^ 
 
 This is not a correct exposition of the mechanism, but it 
 is a creditable effort. It can be paraphrased in such a way 
 as to lose much of its fantastic aspect. We can recognize 
 
 1 Foster, "Lectures on the History of Physiology," Cambridge 
 University Press, 1901, chap. x. 
 
 4 49 
 
50 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 here the afferent fibers conveying a form of energy from 
 the outljdng region to the central organs, the resulting 
 release of fresh energy there, and the conveyance of the 
 returning impulses to the contractile tissues. We do not 
 now believe that the incoming and outgoing energies 
 differ in any such qualitative fashion as Descartes sup- 
 posed, but wc can recognize in his description the impor- 
 tant truth that the efferent flow is much more voluminous 
 than the afferent. If we consider typical cases we shall 
 come to appreciate the striking disproportion between the 
 two. 
 
 Fig. 8. — ^The afferent neuron influences directlj^ four efferent neu- 
 
 rons. 
 
 Take, for example, the wink which is caused by the 
 contact of a minute particle with the surface of the eye. 
 The area stimulated may be so small that we can scarcely 
 think that more than a single nerve-fiber is concerned 
 in the afferent transmission which follows. Yet to pro- 
 duce the muscular response a very large number of fibers 
 must be made to bear impulses to the muscles involved. 
 Perhaps the coughing reflex will serve our purpose even 
 better. Here an irritating particle hardly larger than 
 that required to cause the wink may act upon the central 
 
REFLEXES 
 
 51 
 
 nervous system from the larynx, with the result that 
 most of the conspicuous trunk muscles are made to share 
 in the convulsive response. It is easy to account for this 
 spread of the impulses in the hght of the apparent ana- 
 tomic organization of the gray matter. 
 
 The general rule seems to be that one afferent neuron 
 makes connections with a number of efferent elements. 
 A diagram (Fig. 8) will be helpful. It is possible by an 
 
 Fig. 9. — The adjustors extend the effect to a greater number of 
 eifei-ent paths. 
 
 extension of this principle to visualize a mechanism 
 which will insure the most multifarious discharge of im- 
 pulses after a solitary afferent conductor has been ex- 
 cited. But the painstaking histologists who have done 
 most to interpret the finer structure of the gray matter 
 believe that the spread of the process is accomplished 
 largely through the interposition of neurons of a third 
 order between those which are clearly afferent and those 
 which are definitely efferent. These, according to our 
 
52 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 preliminary classification, may be called adjusters. An- 
 other diag;ram (Fig. 9) may be introduced to show the 
 relation of the adjusters to the reflex act. 
 
 There is an evident economy in this arrangement. It 
 brings large clusters of efferent neurons under the control 
 of single afferent units. ^Moreover, there is no doubt 
 that adjusters such as we have pictured are often domi- 
 nated bj' others of a still higher order. Thus we see in the 
 nervous system an organization like that of an army, in 
 which generals are placed over colonels, colonels over 
 captains, etc. In the army the number of officers holding 
 a given rank is greater than the number of their superiors, 
 but less than the number of their subordinates. In the 
 nervous sj^stem this is probably true of the units in many 
 of the particular mechanisms, but it may not hold in- 
 variably, since, quite unlike the mihtarj' condition, a 
 neuron may be under the sway of a number of others of 
 the next grade above. This statement introduces the 
 idea that now one and now another element may be 
 responsible for the activit}^ of the same inferior group. 
 It also suggests that there may, in some sense, be a strife 
 among the interlocking neurons. We shall have future 
 occasion to dwell upon the conception that inhibitor}' as 
 well as excitaton^' influences may be exerted by certain 
 neurons upon others. 
 
 The following illustration is instructive: A man had 
 clunbed out of a sixth story window which he was to clean. 
 He stood wath his toes upon a narrow ledge, holding 
 meanwhile to the upper sash. A gust of wind took off his 
 hat and both his hands went instantly to his head. At 
 once his bod}' began tilting out into space. His hands 
 fell with great speed and force upon the sash, which, 
 fortunately, had not passed out of reach. Here a simple 
 reflex, normal under most circumstances, would have 
 proved disastrous, and was overruled by another making 
 for self-pre.servation. In all probability no reasoning 
 process preceded the .second adjustment. But the train 
 of reflections that followed was sufficiently \'ivid, and the 
 
REFLEXES 53 
 
 window-washer crawled back into the room and lay for 
 a while upon the floor. 
 
 As we are constantly speaking of nerve-centers, it is 
 time to define what is meant by that expression. A center 
 is usually assumed to be a collection of perikarya mediat- 
 ing a definite action which may be either motor or secre- 
 tory. The center is a station to which impulses flow from 
 different sources at different times, but which transmits 
 impulses always to a common path. When mention is 
 made of a center one thinks naturally of a circumscribed 
 spot in the nervous system — an anatomic conception. 
 But it is necessary to bear in mind at the same time 
 that widely separated neurons may have such connec- 
 tions that they will be unified in their activities. In 
 other words, centers may have a physiologic existence 
 where there is no focal assembling of the cooperating 
 units. 
 
 When we try to draw the line between those actions 
 of the nervous system which can unhesitatingly be called 
 reflexes and others not to be called so, we fuid ourselves in 
 the midst of difficulties. In elementary presentations of 
 the subject it is usual to distinguish between reflex and 
 "voluntary" action, but the more we observe the facts, 
 the less satisfactory this attempted distinction appears. 
 It is certainly true that in most of those movements 
 which we are accustomed to call voluntary we can still 
 recognize the directing influence of external conditions. 
 This is a way of saying that such acts partake of the 
 reflex character. We find it most clearly the case in 
 monotonous serial movements hke those of walking. We 
 say that we walk because we will to do so, but we can 
 hardly claim that the formation of a conscious purpose 
 precedes the taking of each step. At another time we 
 may analyze more fully what can be baldly stated here: 
 that each position assumed by the body and Hmbs of the 
 walker establishes stresses within and contacts without of 
 such a nature as to dictate the appropriate succeeding 
 contraction. 
 
54 THE NERVOUS SYSTEM A\D ITS CONSERVATION' 
 
 In the human subject the acts which arc seen to be car- 
 ried out by the newborn are alwaj's classed as reflexes. 
 Sucking, coughino;, sneezing, hiccups, vomiting, crying, 
 clutching, drawing up of the legs, and other examples 
 will occur to the reader. The list becomes much longer 
 when we take pains to include some which are not so 
 obvious to the domestic observer: changes in the size of 
 the pupils, changes in the distribution of the l^lood, the 
 discharge of sweat and other secretions, etc. Swallowing 
 is essentiall}^ a reflex not to be executed unless there is at 
 least a little moisture to be removed from the mouth. 
 
 As to the reactions which the child acquires with ad- 
 vancing development, we find no satisfacory standard 
 which will enable us to say of orie that it is a reflex and of 
 another that it should be otherwise named. The tendency 
 is to restrict the term "reflex" to those responses to 
 external stimuli which are common to all normal indi- 
 viduals, while those which are peculiar to certain ones we 
 call habits or mannerisms. But the claim may be stronglj^ 
 defended that a habit is a personal reflex — an instance of a 
 reaction to surrounding conditions given more or less of an 
 inevitable character by the acquired structure of the 
 subject's nervous system. Nail-biting may be regarded 
 as an unfortunate reflex manifestation in which the 
 maltreated finger-tips are sending up to the central 
 axis the impulses Avhich dictate further attacks upon 
 them. 
 
 When we pass from habits to accomplishments we must 
 still recognize a degree of connection between external 
 stimuli and the performance. The act of copying a word 
 or a sketch ma}^ transcend the reflex as commonly under- 
 stood, but would seem to include its distinctive features. 
 The copy set is a source of visual stimulation and the 
 movements of the pen held in the skilled hand are -de- 
 termined by its appearance. Even the answering of a 
 question, it may be asserted, is an act brought to pass in 
 consequence of the penetration of auditory impulses 
 through the pathways of a brain prepared to react to 
 
REFLEXES 55 
 
 them. But we shall follow the usual custom and restrict 
 the term "reflex" to responses the capacity for which is 
 inborn or universally acquired, and to acts which occur 
 as surely when the attention is occupied with other 
 matters as when they are themselves under scrutiny. 
 
 Our stock illustrations of reflexes are apt to be those 
 in which brief and abrupt movements are witnessed. It 
 is well to remind ourselves that adaptive changes of this 
 kind may be gradual and sustained in character. One too 
 easily overlooks the more continuous services of the 
 nervous system. Physiologists apply the word "tonic" 
 to such actions as are mild in degree, but maintained over 
 long periods. Under normal conditions the skeletal mus- 
 cles are incompletely relaxed; we say that the nervous 
 system is subjecting them to a tonic stimulation. This 
 subdued but definite activity of the mechanism is the 
 result of the constant inflow of impulses from various 
 sources; it has the reflex character. The slightly con- 
 tracted state of the muscles is spoken of as a "reflex 
 tonus." We speak often of an "arterial tonus," a sus- 
 tained, moderate contraction of the small blood-vessels 
 for which a particular portion of the nervous system is 
 clearly responsible. We may not be warranted in saying 
 that this tonic condition is equally with the other of a 
 reflex sort, but its variations are so, and they constitute 
 an interesting chapter in physiology — that which deals 
 with the vasomotor reactions. 
 
 "Conditioned Reflexes." — Most reflexes seem highly 
 purposeful in the sense that they are such as to con- 
 tribute to the well-being of the animal. In certain cases 
 the purposeful character cannot be recognized and the 
 reflexes appear bizarre and illogical. Some hght was 
 cast on reactions of this eccentric sort by experiments 
 reported from a Russian laboratory a few years ago. 
 The investigators found it possible to j^oke a novel 
 stimulus with one which was familiar, and eventually to 
 confer on the novel stimulus much of the efficiency which 
 at first belonged only to the famihar one. The following 
 
5b THE NHRVOUS SYSTEM AND ITS CONSERVATION 
 
 is a simple example: A dog secretes saliva when shown 
 food which he likes. The reaction is what is sometimes 
 called a psycho-reflex. The trial was made many times, 
 and on each occasion a whistle was blown while the food 
 was displayed. At len^h the blowing of the whistle 
 without the exhibition of the food sufficed to cause sali- 
 vation. 
 
 The acquired capacity of the nervous system to excite 
 the salivary glands in response to a special auditory 
 stimulus was called by the first observer a "conditioned 
 reflex." Such cases afford a striking proof of the plas- 
 ticit}' of the adjustor mechanism. Yet it may also be said 
 that thej^ afford evidence of its rigidity. In support of 
 this last statement a curious fact is to be mentioned: it 
 was found that when a dog had become so sensitized that 
 he would produce saliva when the whistle was blown, his 
 system remained quite unresponsive to notes a very little 
 sharp or flat as compared with the pitch employed in the 
 course of training. It is reported further that if a chord 
 of three notes was used instead of a single one the 
 sensitized animal would secrete saliva on the produc- 
 tion of cither of the simple constituent tones, but more 
 for two sounded together, and most for the complete 
 chord. 
 
 Have we not here something direct I3' related to the 
 mj'sterious rajjport of hypnotism? It seems strange that 
 a human subject can become indifferent to all voices 
 save one and yield abject obedience to that controlling 
 voice. But it may be conceived that this is only an 
 elaborate development of the conditioned reflex. When 
 the hypnotic state was induced the nervous system be- 
 came attuned to the particular pitch and timbre of the 
 speaker's tones. It is said that these are well enough 
 reproduced by the phonograph to make it possible to 
 substitute the instrument for the hypnotist. 
 
 Probably we are all possessed of many conditioned 
 reflexes. The reactions may be hard to detect and still 
 harder to trace to their sources in past experience. Never- 
 
REFLEXES 57 
 
 theless, frank and intelligent people can often furnish 
 illustrations. The most frequent are probably connected 
 with the large intestine and the bladder. Certain condi- 
 tions which have no logical bearing upon the functions of 
 these organs will regularly arouse them to inconvenient 
 activity. A friend of the writer cannot mislay an article 
 and begin to search for it without having an immediate 
 awakening of the colon to energetic movement. On some 
 occasion in the past there was probably a coincidence of 
 the two circumstances and a cross-tie between two 
 mechanisms has remained. Such a tie has undoubtedly 
 an anatomic existence, though we do not expect to have it 
 pointed out postmortem in the mazes of the brain. Out- 
 breaks of perspiration in certain circumstances may be 
 explained in similar ways. 
 
 Summary. — The salient facts regarding reflex action 
 may now be concisely stated. Reflexes are adaptive reac- 
 tions brought about by the influence of stimuli acting 
 upon the receptors of the nervous system. For their 
 execution five conditions must be fulfilled: (1) The end- 
 organs, or receptors, must be ready to translate the 
 energy applied from without into nerve-impulses. (2) 
 There must be pathways open for the conduction of these 
 impulses to the gray matter of the central axis. (3) The 
 central gray matter must have such an organization and 
 such a degree of irritability that the arrival of the afferent 
 impulses shall determine the departure of efferent im- 
 pulses along definite paths. The fitness of the reflex to 
 the emergency, as commonly observed, is explained by the 
 physiologic linkage of certain afferent with certain efferent 
 channels in the cord and brain. (4) There must be lines 
 of effective communication between the central stations 
 and the end-organs of the efferent system, namely, 
 muscles and glands. (5) These organs must be capable of 
 modifying their activity upon the arrival of the outflow- 
 ing impulses. The change induced may be in the direc- 
 tion of increased activity or the reverse — excitation or 
 inhibition. 
 
58 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 These statements serve to characterize reflexes in a 
 positive fashion. On the negative side we should empha- 
 size their essential indcpendent'e of mental life. We 
 note the occurrence of many reflexes, but our conscious- 
 ness is a matter of observation and not of initiation. 
 The abrupt reflexes are "quicker than thought," while 
 those which are gradual in their development are usually 
 capable of passing through all their stages without our 
 attending to them. AVhen the will is enlisted at all — if 
 we may trust our own impressions — it is about as often 
 to restrain as to advance the process which we find taking 
 place. Nothing is harder for the average student than 
 to accept the view that these acts witness only to struc- 
 ture and not to present intelligence. If the scientific 
 assertion is unwelcome, it may still be claimed that past 
 intelhgence is registered in the structure which works so 
 smoothly. Holmes said that "habit is action in the 
 present from motives of the past"; the conception might 
 be broadened to cover the field of the reflexes. But it 
 will be found unexpectedly diflficult to defend even this 
 thesis. 
 
 Voluntary Reactions. — If a man presses an electric key 
 as soon as possible after hearing a sound, feeUng a contact, 
 or seeing a spark, he is said to execute a voluntary reac- 
 tion, and the time which intervenes between the stimulus 
 and the response is called the reaction-time. It is gener- 
 ally not less than 0.12 second nor more than 0.2 second. 
 The values for different avenues of stimulation are 
 somewhat characteristic; for instance, the response to 
 sound is more prompt than that to sight. The process 
 difl'ers from an ordinary reflex in requiring attention to 
 insure the movement. The path of the nerve-impulses is 
 a long one, lying partly in the cerebrum and probably 
 including many synapses. 
 
 When the lower eyelid receives an electric shock of 
 sufficient strength there is a wink which is quite involun- 
 tary. This is a reflex and it is accomplished within 0.05 
 second of the stimulus. With a somewhat weaker shock 
 
REFLEXES 59 
 
 it is often found that the delay is three times as long. 
 Such a case is a voluntary reaction: there is a sensation, 
 a purpose to wink, and then the movement. This common 
 laboratory experiment brings the two forms of response 
 into clear contrast. Consciousness is quite incidental to a 
 reflex, and, if it is involved at all, it is subsequent to the 
 act and not connected with the chain of events leading up 
 to it. 
 
CHAPTER V 
 
 THE GENERAL ANATOMY OF THE NERVOUS 
 
 SYSTEM 
 
 It has been possible to proceed to this point with only 
 the most general statement of the spatial arrangement of 
 the parts which are united to form the nervous system. 
 A certain amount of detail must now be supplied. It will 
 be helpful to make some comparisons between what is to 
 be seen in the simpler vertebrates and what is found in 
 man. No description of the invertebrate organization 
 will be undertaken; it is most interesting but peculiarly 
 difficult to bring into line with the higher type. 
 
 Let us attend to the outlines of the nervous mechanism 
 as exemplified in the frog, an animal which has been chosen 
 for very many of the cardinal researches upon this system. 
 Here, as always, we recognize an axial or central portion 
 and the nerves extencUng from it to all parts of the body. 
 The axial portion is said to consist of the brain and the 
 spinal cord. The brain is lodged in the cavity of the skull; 
 the cord extends through a canal made by the successive 
 arches of the vertebrse, the individual bones of the spinal 
 column. Those nerves which take their rise from the 
 brain are called cranial, the reference being to the cranium, 
 which is the portion of the skull bounding the brain. 
 The nerves originating from the cord are called spinal. 
 The cranial nerves issue from the skull through openings 
 which are called foramina. The spinal nerves find their 
 way through notches between adjacent vertebrae, inter- 
 vertebral foramina, as they are called. The number of 
 both the cranial and the spinal nerves is smaller in the 
 frog than in many of the higher forms, including man. 
 
 60 
 
GENERAL ANATOMY OF THE NERVOUS SYSTEM 61 
 
 The spinal nerves emerge in pairs which are sym- 
 metrically developed. A single member, right or left, in 
 one of these pairs is found to be united with the cord by 
 two roots. These are best referred to as dorsal and ventral, 
 the former being nearer the skin of the back and the 
 latter at a greater depth. The relations referred to are 
 best understood when presented in a diagram (Fig. 10). 
 
 Fig. 10. — The upper figure shows the spinal cord within the arch 
 of a vertebra. A pair of spinal nerves is shown, each nerve having a 
 dorsal and a ventral root. 
 
 In the lower figure the heavy enclosure is the dura, mater, the 
 dotted line just within is in the position of the arachnoid, and then 
 comes the space filled by the cerebrospinal fluid. The outhne of the 
 cord itself corresponds with the pia mater. 
 
 The same figure will call attention to the protective struc- 
 tures in the vicinity. Of these, the most striking is the bony 
 arch. Within this is a dense membrane, the dura mater. 
 A much thinner membrane is applied to the immediate 
 surface of the cord and is scarcely to be separated from it; 
 this is the pia mater. Between the two membranes there 
 
62 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 is an appreciable space containing a clear, limpid liquid, 
 the cerebrospinal fluid. Strictly speaking, a third mem- 
 brane, the arachnoid, intervenes between the dura and the 
 fluid, which is, therefore, said to occupy the subarachnoid 
 space. The membranes with the fluid retained by them 
 are collectively spoken of as the meninyes. 
 
 The regular fashion in which the spinal nerves part 
 into dorsal and ventral roots might well suggest a differ- 
 ence in function corresponding to the anatomic separation. 
 It has, in fact, been known for about a hundred years that 
 the dorsal roots are almost wholly composed of afferent 
 fibers and the ventral roots even more dominantl}'^ of 
 those which are efferent. The statement of this contrast 
 in function between the roots of the two sets is known as 
 Bell's law. The cranial nerves do not part in this orderly 
 way into dorsal and ventral divisions where they join the 
 substance of the brain; moreover, they are extremely 
 unequal in size. Some are found to be composed of 
 afferent fibers, some of efferent, and some of both together. 
 It will be evident that each spinal nerve, if tested beyond 
 the point of blending of its two roots, may be expected to 
 show both characters. Most nerves are mixed in the 
 sense that they contain fibers of both kinds. In the sum 
 of all the nerves it is said that the afferent fibers are dis- 
 tinctly more numerous than the efferent. In the spinal 
 nerves the difference is moderate; in the cranial, the 
 preponderance of afferent fibers is overwhelming. 
 
 A cross-section of the spinal cord brings to view several 
 features which may be described later, but at the moment 
 only one of these will be mentioned. This is the minute 
 central canal, a reminder that the central nervous system 
 is to be regarded as tubular in its fundamental organiza- 
 tion, though the walls of the primitive tube have en- 
 croached upon its cavity until the remaining space is 
 very small compared with the masses of white and gray 
 matter surrounding it. The slender central canal of the 
 cord leads forward to a much more conspicuous series of 
 chambers in the brain. We can now outline the anatomy 
 
GENERAL ANATOMY OF THE NERVOUS SYSTEM 63 
 
 of this superior portion of the system as it is seen in the 
 frog. 
 
 Following the spinal cord to the most anterior vertebra 
 we find that it is here continuous with the tapering hind 
 
 Olfactory lobes 
 
 Cerebral 
 Hemispheres 
 
 -Diencephalor) 
 
 --- hi'td-hraiT) 
 -- Cerebelhn) 
 
 -l Medulla 
 
 Fig. 11. — Above, the frog's brain is shown in its dorsal aspect 
 and, within a similar outline, its cavities. The two lateral ventricles 
 are not numbered. The cavities extending into the optic lobes are 
 not made black because they are not characteristic of higher forms. 
 
 Below is the brain of the rabbit (dorsal view), to show how the 
 midbrain is nearly concealed by the large cerebrum and cerebellum. 
 (The scale of this drawing is much smaller than that used for the 
 frog.) 
 
 end of the brain, the medulla, or bulb. The line of demarca- 
 tion between brain and cord is assumed to lie between the 
 back edge of the skull and the first vertebra; there is no 
 sudden change in the appearance of the nervous axis 
 
64 THE XKRVOUS SYSTEM AND ITS COXSEKVATION 
 
 itself at this lAncc. If the overlying bone is removed the 
 several divisions of the ])rain will appear somewhat as in 
 Fig. 11. The medulla widens from its hinder to its 
 forward limit and the eye is caught by a deep triangular 
 hollow, opening in its dorsal surface. The apex of the 
 triangle is pointed back toward the cord. This hollow is 
 one of the chaml)ers of the brain, the fourth ventricle. 
 Unlike all the other parts of the series of cavities, this 
 one breaks the surface; the others are completely sub- 
 merged and to be seen only after dissection. A thin roof 
 which partially covers the fourth ventricle in life is almost 
 invariably stripped from it in exposing the brain. The 
 central canal of the cord opens out into the fourth ven- 
 tricle at its pointed posterior extremity. 
 
 Forward of the medulla are found the two large, ovoid 
 bodies which, with the corresponding ventral structures, 
 are conveniently covered by the term midbrain. A channel 
 extends from the fourth ventricle through this region to 
 the cavities still farther forward ; it is picturesquely named 
 the aqueduct of Sylvius. We shall find the midbrain to be 
 relatively much less prominent in the higher forms than 
 in the frog. An alternative name for this region, apply- 
 ing more accurately to the dorsal eminences, is the optic 
 lobes. 
 
 In front of the midl^rain we find in the case of the frog 
 that iDy far the larger part of what remains is the cerebrum 
 or the cerebral hemispheres. We yet distinguish, however, 
 a limited portion of the brain between these paired struc- 
 tures and directly before the midbrain as the diencephalon. 
 In the diencephalon the aqueduct of Sylvius expands into 
 a space which is quite narrow when measured from right 
 to left, but more extensive dorsoventrally. This is the 
 third ventricle. Each of the cerebral hemispheres has 
 within it a cavity which is called a lateral ventricle. 
 The total count of four ventricles is arrived at by reckon- 
 ing these two lateral chambers, the third in the dien- 
 cephalon, and the fourth in the medulla. The lateral 
 ventricles communicate with the third by small passages. 
 
GENERAL ANATOMY OF THE NKKVOUS SVSTIOM ()5 
 
 At the extreme anterior end each of tlie hemispheres is 
 prolonged into a brush-Uke development of nerve-fibers 
 which comes into relation with the nasal lining on the 
 same side. These extensions are usually termed the 
 olfactory nerves and are counted as the first in the cranial 
 series. No other nerves come into direct connection with 
 the cerebrum; even the optic nerves, which are so much 
 more important in determining the reactions of the more 
 intelligent animals, join the parts just behind the hemi- 
 spheres and affect them only after the impulses have been 
 relayed or forwarded. The optic nerves are second in the 
 series as we count from before backward. Other cranial 
 nerves emerge at short intervals behind the optic. It will 
 be better not to enumerate them now, but to speak of them 
 with direct reference to the human brain a httle later. 
 
 All the divisions which have been described as having 
 places in the organization of the brain of the frog can be 
 recognized in the brains of the higher vertebrates. Their 
 proportionate development we shall find to vary widely 
 from what has been pictured. There is one region only 
 hinted at in the brain of the frog which comes to be a large 
 feature in many cases. This is the cerebellum. Its posi- 
 tion in the frog is indicated by a slight dorsal growth 
 at the anterior margin of the fourth ventricle. 
 
 We shall now find it helpful to compare with the brain 
 of the frog that of the rabbit, which will show a state of 
 things intermediate between what has been described 
 above and the human condition which must be outlined 
 presently. If we ignore differences of absolute scale 
 we shall see at a glance that the cerebral hemispheres in 
 the rabbit are more massive than in the frog. We shall see 
 also that the cerebellum has become a part of the brain 
 only less conspicuous than the hemispheres themselves. 
 We can still discover between the cerebellum and the 
 cerebrum the surface of the midbrain, but this section 
 which was so prominent in the frog has become much less 
 so. It is evident that a moderate additional increase in 
 the bulk of the cerebrum and cerebellum would bring 
 
GtJ THE NERVOUS SYSTEM AND ITS COxXSERVATION 
 
 these two in contact and conceal the midbrain from view. 
 Incidentally it may be noted that in the rabbit the dorsal 
 aspect of the midbrain is scored by a cross-fissure, so that 
 instead of the two lobes found in the frog there is a four- 
 fold arrangement. On this account the region in question 
 is known as the corpora quadrigemina. 
 
 A change in our point of view from dorsal to lateral^ 
 will make it easier to grasp the result of the progressive 
 development of the cerebrum and the cerebellum. The 
 figure will show how the midbrain is covered in the process 
 and will suggest at the same time how the cerebrum rolls 
 forward over the olfactory nerves, and how the cerebellum, 
 extending backward, overhangs more and more the 
 cavity of the fourth ventricle. In cats and dogs a stage 
 is reached at which no glimpse of the midl^rain can be 
 had without forcibly separating the overlying parts. 
 
 To understand the ordering of the various divisions in 
 the brain of man it is first of all necessary to appreciate 
 this preponderance of the cerebrum and the cerebellum 
 over the remaining portions. But there is another con- 
 dition which enters in to complicate the interpretation. 
 This is a bending of the axis upon which the brain may be 
 conceived to be built up. In the frog a line drawn from 
 the nose through the brain and back to the end of the 
 spinal cord will be nearly straight. In the rabl)it it is still 
 true that the organization can be referred to an axis which 
 is substantially straight. It is very plain that the attempt 
 to project a corresponding line from the human nose 
 through the brain and down the full length of the cord 
 will yield a curve suggestive of a fish-hook (Fig. 12). 
 
 This bending of the axis is developed in connection 
 with the carriage of the head which is appropriate to the 
 erect position. The lower animals generally travel along 
 the line of their spinal columns. Man moves in a line 
 perpendicular to his spine; that is to say, he walks and 
 gazes horizontally while his vertebral axis is kept vertical. 
 The nervous system must be accommodated to this state 
 ^ Figure 12, upper drawing. 
 
GENERAL ANATOMY OF THE NERVOUS SYSTEM (37 
 
 of things. The bend m its axis is well indicated by an 
 outline of the cavities in the human brain and cord. 
 The aqueduct of Sylvius is inclined ventrally from the 
 line of the central canal of the cord, and the lateral 
 ventricles in the cerebral hemispheres are extended 
 approximately at right angles to this canal. The olfactory 
 
 Fig. 12. — Above is the rabbit's brain from the left; below, the 
 human brain in vertical fore-and-aft section, also viewed from the 
 left. The bent axis is introduced in the lower figure. 
 
 1, Cerebrum; 2, cerebellum; 3, midbrain; 3d, corpora quad- 
 rigemina; 3v, crura cerebri; 4, pons; 5, medulla; ///, third ven- 
 tricle, which is flanked by the diencephalon; IV, foiu-th ventricle. 
 
 outgrowths are also found to be in a plane perpendicular 
 to the course of the cord. 
 
 If, now, we make allowance for the two conditions indi- 
 cated — the overwhelming growth of the cerebrmn and 
 cerebellum and the rather sharp crook in the axis — we shall 
 find it easy to see that, after all, the sequence of the 
 
08 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 divisions in man is the same as in the frofr. It is true in 
 both cases that the medulla is the prolongation of the cord 
 within the skull. In both, the fourth ventricle practically 
 breaks through the "roof" or dorsal surface of the medulla, 
 but in man it is overhung by the cerebellum. In both 
 types the aqueduct of Syhius leads through the region 
 known as the midbrain and widens into a third ventricle 
 reckoned as the cavity of the diencephalon. 
 
 In the brains of the higher animals there is a ventral 
 feature hardly indicated in the frog, but developed, 
 gencrall}' speaking, in proportion to the prominence of the 
 cerebellum. This is the pons (pons varolii), a structure 
 which presents the appearance of an outgrowth from the 
 cerebellum clasping the medulla near its anterior border. 
 Of course, this does not correctly describe the actual con- 
 nections of the region referred to, though it is true that it 
 contains many transverse fibers which pass into the 
 cerebellum. It is to be noted that the cerebellum is dis- 
 tinctly dorsal in position to the main axis of the central 
 nervous system. It may thus be said not to lie upon the 
 direct course of the ascending and descending impulses 
 which enter and leave the cranial cavity. So it is possible, 
 for experimental purposes, to remove the cerebellum and 
 leave this chief highway still open for service. 
 
 The removal of the cerebellum, with the object of ob- 
 serving the deficiencies which follow and so drawing in- 
 ferences in regard to its previous activity, is permissible. 
 But the physiologist cannot excise the midbrain or the 
 medulla for any such purpose, since he would lose not 
 only the influence of the part withdrawn, but would 
 check the passage of impulses to and from regions an- 
 terior to the seat of operation. The destruction of the 
 medulla would leave no line of communication between 
 the cerebral hemispheres and the trunk. 
 
 A few words may now be said about the distribution 
 of gray and white matter in the central nervous system. 
 In the cord the gray matter is internal and appears in a 
 cross-section in a characteristic form often called an 
 
GENERAL ANATOMY OF THE NERVOUS SYSTEM ()0 
 
 H-figure. So far as the cord consists of white matter, it 
 can be regarded without serious error as a huge nerve 
 conveying impulses to and from the brain. Its gray matter 
 serves to mediate simple reflexes. Yet it must also be 
 remembered that the gray matter may bear a part in the 
 transmission of impulses from one level to another. The 
 gray matter of the cord shows two expansions in the course 
 of its length, one between the shoulders and one close to 
 the lower end. It will readily be inferred that these ex- 
 pansions provide for the massing of cells related respec- 
 tively to the upper and lower extremities. 
 
 In the medulla, as in the cord, the gray matter is 
 practically all internal. The H-figure, however, ceases 
 to be distinguishable, and instead there are more or less 
 isolated clusters of nerve-cells which in several con- 
 spicuous cases are in connection with cranial nerves. A 
 large proportion of the substance of the medulla, includ- 
 ing about all of its superficial portion, is made up of fibers. 
 For the most part these run longitudinally, but at certain 
 places, as revealed in sections, there are many which 
 sweep from left to right, and the reverse, crossing the 
 midline. 
 
 In the restricted region which we have termed the 
 midbrain we find that the corpora quadrigemina (Fig. 
 12, 3d), the four eminences which rise upon its dorsal 
 aspect, are largely gray matter. Within, the alternation 
 of the two types is somewhat intricate, but ventrally this 
 part of the brain consists of fibers. The ventral white 
 matter of the midbrain (Fig. 12, 3v) is seen just forward 
 of the pons for a short distance, and it is referred to under 
 the name of the crura cerebri. This is translated "the 
 legs of the cerebrum," and the fact which doubtless sug- 
 gested the odd name is that we have here a paired pedestal 
 into which the larger proportion of the fibers coming from 
 and going to the cerebrum are compressed. If a crude 
 comparison may be admitted, we may liken the cerebrum 
 to a great bouquet whose stems are gathered into the 
 crura. 
 
70 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 The cerebrum itself and the cerebellum present a con- 
 trast to the other portions of the brain when studied with 
 regard to the distribution of graj- and white matter. In 
 thorn there is a surface layer of gray substance, while the in- 
 terior — and by far the larger part of tlie whole mass — 
 is made up, in the main, of multitudinous fibers. The 
 surface layer is called the cortex, the primitive meaning 
 of the word being the bark of a tree. Certain submerged 
 portions of gray matter are found in the midst of the 
 internal white matter in both the cerebrum and the 
 cerebellum. 
 
 The human cerebrum consists of two hemispheres, 
 between which there is a very deep longitudinal fissure. 
 The separation of the two halves is so marked that one 
 thinks of the walnut kernel with its comparatively slender 
 isthmus. The comparison is faulty, however, in that the 
 cerebral hemispheres have more than one bond of union. 
 Their principal tie is to be found at the bottom of the 
 longitudinal fissure, and when cut it appears in section as 
 a white arch. It is the corpus callosum, a structure to 
 which the physiologists of the seventeenth century ascribed 
 much importance. Several minor connections are ob- 
 served lower down, all adjacent to the third ventricle. 
 
 In all the higher animals the surface of the cerebrum 
 is much scored by fissures. These are called sulci, and the 
 convex ridges between them are spoken of as gyri or con- 
 volutions. Such a type of organization evidently provides 
 for a much more extensive area of cortex than would exist 
 otherwise. Since cortical development stands in some 
 relation to the intelligence and general rank of the animal 
 in the scale of being, one is disposed to look for an espe- 
 cially marked wrinkling in the case of man. The human 
 brain is, indeed, much more fissured than that of the 
 rabbit, but it is not much more so than that of the .-.cow. 
 The attempt to make a great deal of this feature yields but 
 little comfort (Fig. 13). 
 
 Regions of the surface of the cerebrum are usually 
 denoted by employing the names of those cranial bones 
 
GENERAL ANATOMY OF THE NERVOUS SYSTEM 71 
 
 which overlie them. Thus we speak of the frontal, the 
 parietal, the temporal, and the occipital regions or lobes. 
 The principle would entitle us to refer also to the sphe- 
 noidal and ethmoidal areas, but these terms are seldom 
 heard. The word "lobe," often used with reference to 
 these organs, is, perhaps, somewhat misleading. It sug- 
 gests a degree of isolation more marked than that which 
 actually obtains. The temporal portion deserves this 
 designation more clearly than do the others, since it is 
 
 Medulla 
 Oblongata 
 
 Fig. 13. — The human brain, from the left (Morrow). 
 
 quite distinct — set off by a cleft of exceptional depth, the 
 fissure of Sylvius. On first glancing at a figure of the 
 cerebrum one recognizes which direction is anterior by the 
 presence of the temporal lobe,' pointing downward and 
 forward (Fig. 13). 
 
 The Cranial Nerves (Fig. 14). — Twelve pairs of nerves 
 are united with the human brain. It has already been 
 stated that only one of these, the pair mediating the sense 
 of smell, is joined directly to the cerebrum. These bundles 
 of fibers entering the under surface of the hemispheres 
 
72- THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 constitute the shortest aiul most direct of all the paths 
 which convey afferent impulses to the central stations. 
 This fact is dwelt upon entertainingly in "The Autocrat 
 
 Fig. 14. — View, from below, of the connection of the principal 
 nerves with the brain: /', The right olfactory tract; //, the left 
 optic nerve; //', the right optic tract (the left tract is seen passing 
 back into i and c, the internal and external corpora geniculata); ///, 
 the left oculomotor nerve; IV, the trochlear; V, V, the large roots 
 of the trifacial nerves; -] — (-, the lesser roots (the + of the right 
 side is placed on the Gasserian ganglion); 1, the oi)hthalmic; S, the 
 superior maxillary; and 3, the inferior maxillary divisions; VI, the 
 left abducens nerve; VII, VIII, the facial and auditory nerves; IX- 
 XI, the glossopharyngeal, pneumogastric, and spinal accessory 
 nerves; XII, the right hypoglossal nerve; Ci, the left suboccipital 
 or first cervical nerve (De Nancrede). 
 
 of the Breakfast Table."^ Considerably farther back 
 we find the conspicuous optic nerves, the second cranial 
 pair, reaching the base of the brain and appearing to cross 
 
 ' Riverside Edition, p. 75. 
 
GENERAL ANATOMY OF THE NERVOUS SYSTEM 73 
 
 as they meet. The feature thus produced is Uke an Enghsh 
 X or the Greek letter Chi, whence it takes its name of the 
 optic chiasma. Close behind the chiasma a short stalk 
 depends from the brain and is connected with the "pitu- 
 itary body, an unpaired organ which is lodged in a hollow 
 of the sphenoid bone. 
 
 The cranial nerves are of very unequal size and func- 
 tional importance. A large one is the fifth {trigeminal), 
 which enters the pons and thus serves as a convenient 
 reminder that four pairs of the nerves are anterior and 
 seven posterior to this structure. In this trunk are con- 
 veyed a great majority of the afferent fibers from the face, 
 the front of the eye, the linings of the nose and mouth, 
 and the teeth. It is responsible for a large share of 
 human suffering. But efferent fibers are present also, 
 and the chief muscles employed in mastication are gov- 
 erned through their agency. The seventh cranial nerve, 
 springing from the medulla just behind the pons, governs 
 the small muscles which are responsible for facial expres- 
 sion. The eighth nerve, entering the central axis very 
 near the seventh, is the auditory, interesting not only as 
 the pathway on which our hearing depends, but also for the 
 part which it plays in the maintenance of equilibrium. 
 
 The tenth nerve is one to which reference must often 
 be made. It is called the vagus or 'pneumogastric. Its 
 striking peculiarity hes in the fact that it is not dis- 
 tributed so largely to structures belonging to the head 
 and neck as to the organs of the trunk both above and 
 below the diaphragm. Hence its fibers are, as a rule, 
 much longer than those of other cranial nerves. They 
 reach muscular and glandular elements in all parts of the 
 digestive system, while certain ones end in the heart and 
 are of particular interest because of the role which they 
 fulfil in the regulation of its beating. Still others come 
 into relation to the larynx. Many of the vagus fibers are 
 afferent and bring impulses from the tissue of the lungs, 
 from the heart, and from other localities. 
 
 As to the less conspicuous nerves of the cranial series, 
 
74, THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 it is to be noted that three pairs (the third, fourth, and 
 sixth in the enumeration) are concerned in the causation 
 of movements of the eyes and in bringing about the adjust- 
 ments for varying iUumination and for vision at different 
 distances. The six slender muscles which serve to turn 
 each eyeball in whatever direction we desire are probably 
 provided more liberally with motor nerve-fibers than any 
 other muscles in the bod5^ Our command over them is 
 correspontlingly perfect; we do not fall short or (n^ershoot 
 the mark in looking from one object to another. If there is 
 another instance of such precision in control of muscles it 
 is the case of those which act upon the cartilages of the 
 larjaix in the trained singer. 
 
 Reference: Lickley, "The Nervous System," Longmans, Green & 
 Co., London, 1912. 
 
CHAPTER VI 
 
 THE AFFERENT PART OF THE NERVOUS SYSTEM 
 
 The great majority of the fibers which bear impulses 
 toward the central stations have their receptive endings 
 near the surface of the body. A minority come from 
 localities deeply submerged and, therefore, subject to 
 stimulation as the result of internal rather than external 
 conditions. The function of all afferent fibers is to cooper- 
 ate in the production of reflex responses; a certain propor- 
 tion of them, in addition, carry to the gray matter the 
 impulses which determine sensation. With the shifting 
 of our attention we are continually consigning to the class 
 of reflex producers fibers which but must now furnished 
 us with the data of consciousness. Our interest in sen- 
 sation is so immediate and overwhelming that we tend 
 to underestimate the unobtrusive work of those afferent 
 elements which at any given moment are guiding sub- 
 conscious processes. 
 
 Nerve-fibers of the Skin. — The human skin has been 
 computed to have an area of about 1.7 square meters. 
 It is thus as large as a rug 3 feet wide and 5 feet long. 
 Afferent fibers in enormous numbers lead from small sub- 
 divisions of this large expanse and no point upon it is far 
 removed from nerve-terminals. Sherrington has attract- 
 ively compared the skin with its nerves to the surface 
 of a pond where many aquatic plants are growing. Their 
 branching filaments are distinct from one another, but 
 often overlapped or entwined. When a stone is thrown 
 into the pond it stirs most decisively the growth on which 
 it directly falls, but other leaves and stems will share 
 somewhat in the disturbance. Perhaps in some respects 
 the skin is even more hke a marsh in which the foot sinks, 
 
70, THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 crushing the grasses on which it is set and at the same time 
 pressing down an area much larger than that which it act- 
 ually covers. It is precisely in this way that a pencil 
 point jiresscd into the skin stimulates powerfully the nerve- 
 twigs just ])encath the selected spot, but extends its effect 
 to others within a certain radius. 
 
 The nerve-fibers of the skin take their rise in part from 
 fine ramifications among its deeper cells. Others lead 
 away from special terminal organs of one kind and an- 
 other. These microscopic end-organs (tactile corpuscles, 
 etc.) have been minutely studied and will be found de- 
 scribed in detail in works on histology. It is needless 
 here to discuss the relation of the several types of nerve 
 ending to the several forms of stimulation to which each 
 may respond. In the light of what has been said already 
 (Chapter III) we shall assume that only one result can 
 follow the stimulation of a given fiber, whatever the 
 means employed. If we are right in taking this position, 
 we must conclude that the variety of sensations which 
 can be elicited through the skin is made possible by a 
 corresponding number of afferent pathways. 
 
 We derive from the skin at least four kinds of sensa- 
 tion — pressure, warmth, cold, and pain. As we have 
 accepted, provisionally at least, the "Miillerian prin- 
 ciple," we must believe that a fiber which is once found 
 to give the sensation of pressure when it is stimulated can 
 never give any other sensation. For the impulses, how- 
 ever they ma}^ be started on their way, are of an un- 
 varying nature and take always the same direction. 
 On their arrival within the confines of the central nervous 
 system they must produce over and over the same set of 
 effects. The only qualifying statement which should be 
 made is that strong stimuli of any kind may, very prob- 
 ably, initiate impulses which shall penetrate farther than 
 those originated by less intense applications. So, accord- 
 ing to one theory, yain may be produced by a sufficiently 
 strong excitation of any afferent nerve, its occurrence being 
 the sign of an extension of the brain process beyond the 
 
THE AFFERENT PART OF THE NERVOUS SYSTEM 77 
 
 usual field. But the more generally accepted view is 
 that pain is a sensation for which a particular nervous 
 mechanism is requisite and that the nerves concerned can 
 give rise only to painful sensory phenomena. 
 
 Experimental study supports the a priori deductions 
 in regard to the multiple character of the receptor equip- 
 ment of the skin. If one applies to the arm a heated rod 
 of glass, one's first impression is that sensations of press- 
 ure and temperature — perhaps of pain also — are produced 
 by stimulation of a single spot. But if the trial is made 
 more carefully, employing a slender instrument for the 
 test and avoiding deformation of the skin, one brings to 
 light what is called the "punctiform" distribution of 
 sensibility. By this expression is meant the existence of 
 particular areas of very small size from which particular 
 sensations can be aroused, while others cannot. 
 
 It is possible to mark off a chosen region on any part of 
 the surface of the body and to determine within its 
 boundaries the points which respond appropriately to 
 four forms of stimulation by the four kinds of sensation 
 enumerated above. Four sets of points can then be indi- 
 cated in color, and if the cutaneous map is preserved for a 
 time the points are found to be permanent. They must be 
 situated just over the endings of four distinct though more 
 or less commingled sets of nerve-fibers. It is now easy to 
 see how more than one kind of sensation may seem to be 
 produced when the skin is touched. If the object which 
 makes the contact is rather blunt, it is certain to affect 
 one or more pressure-points, while it will either give or 
 take heat to such an extent as to stimulate neighboring 
 organs which are sensitive to temperature changes. 
 The skin is Hke a mosaic so finely subdivided that a close 
 examination is necessary to resolve it into its constituent 
 parts. 
 
 We must expect that stimulation of a selected ending 
 in the skin by unusual means will give no sensation but the 
 one proper to that fiber. It is, in fact, rather difficult to 
 excite a pressure-point by forms of stimulation other than 
 
78- THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 pressure, but it is not impossible to do so, and the sensory 
 result is reported to be still a sensation of pressure. A 
 better example of perverse excitation is observed when a 
 spot previously found to be affected by cold is touched with 
 a rod which is quite hot. The spot is found to respond with 
 the only sensation which can possibly result from its 
 stimulation, namely, that of cold. So wlien any area large 
 enough to include both warm and cold spots is brought 
 into contact with something hot, the sensation has a 
 mixed character and may be discovered to contain recog- 
 nizable elements of warmth and cold. Indeed, the tingle 
 which we call "cold" may be so prominent that for a 
 moment we think that the object has a low instead of a 
 high temperature. 
 
 All the afferent fibers from the skin are gathered into the 
 many small nerves which are found in all parts of the body, 
 and these in their turn unite with others until the total 
 number of the trunks is small and their average size con- 
 siderable. In these larger nerves, as has been said before, 
 efferent as well as afferent fibers are present. If we ex- 
 clude for the moment the afferent nerves of the head, we 
 shall find the remaining fibers of this description parting 
 from their efferent fellows when the cord is closely ap- 
 proached and forming the dorsal roots as they pass in 
 between the vertebrae. Upon these roots there are ob- 
 served to be enlargements, the dorsal root ganglia, and 
 microscopic study shows that these contain the peri- 
 karya connected with the fibers passing through. As 
 stated in Chapter III, these are of an oval outline, are 
 situated on side branches from their respective fibers, and 
 they are not provided with the ordinary short, branching 
 dendrites. 
 
 Before the division into dorsal and ventral roots is 
 reached the afferent fibers from the surface of the body will 
 have been joined by a smaller but still immense number 
 from deeper regions. Some attention must shortly be given 
 to fibers of this class. It is evident that the stimuli to 
 which they are subject must be chiefly internal rather 
 
THE AFFERENT PART OF THE NERVOUS SYSTEM 79 
 
 than external. Yet they are not altogether so. Strong 
 pressures acting from without produce effects not limited 
 to the skin, but extending to the underlying muscles and 
 to other tissues. Muscles, tendons, and joints return to 
 the central nervous system a host of impulses, the results 
 of which are effective chiefly in producing adaptive re- 
 flexes, but also to some extent in consciousness. 
 
 The afferent fibers, whatever their origin, enter the 
 spinal cord well around toward its dorsal fissure, and 
 then, as a rule, each divides into an ascending and a de- 
 scending branch. The descending branches are said not to 
 run far before they terminate among the cell-bodies of the 
 spinal gray matter, doubtless by synapses, through which 
 reflexes may be brought about. The ascending branches 
 may run unbroken to the medulla or they may end in the 
 gray matter of the cord. At intervals along their course 
 the branches of both orders have short lateral extensions 
 by which they establish intercourse with other neurons. 
 The arrangement has already been sketched in connection 
 with the discussion of reflexes (see page 50). 
 
 If incoming impulses are to call forth the more elabor- 
 ate reflexes, and especially, we believe, if they are to give 
 rise to sensations, they must reach the cerebrum. The 
 pathway thither is imperfectly known and not of the first 
 importance in a work like the present. It has just been 
 said that some afferent fibers actually reach the medulla; 
 those which have come from the feet and have this 
 anterior reach are the longest of all neurons. There is 
 reason to think that much of the conduction to the brain 
 is accomplished through shorter neurons in a tandem 
 arrangement rather than over these long, uninterrupted 
 channels. When the medulla is attained in either way, its 
 own cells are supposed to take up the task of transmission. 
 These are responsible for the forwarding of impulses to 
 the important intermediate stations which flank the third 
 ventricle and are known as the optic thalami. From these 
 occurs the radiation to the cortex itself. 
 
 Sensations are apparently the psychic accompani- 
 
80. THE NKRVOrS SYSTKM AM) ITS rONSKHVATION 
 
 nicnts of certain processes in the cerebral j>;ray matter. 
 We must assume that the streams of energy flashing from 
 point to point in the cortex arc very numerous, and we 
 cannot say why some are attended with corresponding 
 phenomena in our consciousness while others are not. 
 The problem of attention is suggested at once, and this 
 belongs to the psychologist. For the physiologist it is a 
 persistent mystery how the physical mechanism can be so 
 multifarious and the su])jective experience so unified. 
 
 The afferent fibers which have thus far been discussed 
 are those originating below the head. These exert direct- 
 ing influences upon the central mechanism which we are 
 not likely to overestimate, but their contribution to the 
 current of sensation is much less vivid and interesting than 
 that furnished by way of the cranial nerves. If there is a 
 partial exception to be conceded, it is in the case of the 
 fingers, with their wonderful sensory equipment. Other- 
 wise it needs no argument to prove the superior prominence 
 of the eye and the ear in guiding intelligent conduct. To 
 be without taste or smell would be a minor privation, but 
 deafness and blindness are grave calamities, and when the 
 two are conjoined we regard the victim with a pitying awe, 
 which may be displaced by reverent admiration when we 
 witness such triumphant emergences as those of Laura 
 Bridgman and Helen Keller. 
 
 Something has been said previously of the afferent 
 service of the cranial nerves. It will ))e recalled that in 
 these nerves there is no clear assorting of sensory fibers to 
 form a series of dorsal roots. In two or three cases there 
 are ganglia in which are gathered the perikarya which 
 maintain the passing fibers. The largest of these ganglia 
 and the one most frequently referred to is the Gasserian 
 ganglion on the trunk of the great fifth (trigeminal) 
 nerve. 
 
 Vision. — The immense importance of the optic impulses 
 in determining the content of the human mind and the 
 conduct of human life is faithfully indicated in the large 
 size of the optic nerves. Nearly half a million fibers are 
 
THE AFFERENT PART OF THE NERVOUS SYSTEM 81 
 
 bound up in one of these, most massive of all purely affer- 
 ent trunks. It has been stated elsewhere that the imme- 
 diate connections made by the optic fibers are with stations 
 in the midbrain or thereabouts. From these subordinate 
 centers reflexes are doubtless caused, while, at the same 
 time, impulses mount to the cortex where the processes 
 induced become the physical basis of conscious vision. 
 
 Hearing. — The number of fibers concerned in carrying 
 the impulses on which the sense of hearing depends is 
 small compared with that of the optic conductors. It 
 has been estimated that perhaps 14,000 fibers on each 
 side are provided to subserve this function. The sound- 
 waves which have come pulsing through the air to the 
 external ear communicate their motion to a succession 
 of structures in the winding cavities of the temporal bone, 
 and ultimately to cells which can transmute this mechan- 
 ical energy to the form of nerve-impulses. The result- 
 ing currents are led to gray matter within the medulla, 
 forwarded thence to the midbrain, and finally, by a third 
 relay, to the cerebral cortex. 
 
 The auditory nerve has a second part which is not sup- 
 posed to have to do with hearing. This division, the 
 vestibular nerve, brings to the brain impulses which have 
 been started by displacements of fluids or of solid particles 
 in the comparatively large portion of the internal ear 
 which is looked upon as an organ of equilibration. There 
 is reason to believe that when one sways — or, more radi- 
 cally, when one stumbles — such mechanical disturbances 
 are brought about and impulses sent to the proper centers 
 to dictate the compensating movements which are so 
 promptly observed. The service of the ear in maintain- 
 ing the balance is one which we seldom think of, and it is 
 carried on for the most part with only slight involve- 
 ment of sensation. But excessive stimulation of the in- 
 ternal ear probably has a share in developing the disagree- 
 able feeling we call vertigo. 
 
 Taste and smell are two kinds of sensation which are 
 often blended in our experience, but the nervous paths 
 6 
 
82- THE NERVOUS SYSTEM A\D ITS COXSEUVATION 
 
 concerned are widely separated, as the}^ run from the 
 receptors to the central apparatus. The olfactory fillers, 
 as we have seen before, plunge into the under surface of 
 the cerebrum itself. The fibers on which taste depends 
 are probably scattered in the trunks of two or three 
 nerves, and their arrangement is thought to be subject to 
 a good deal of individual variation, ])ut it is certain that 
 their place of entrance into the su])stance of the brain 
 is far back of that for the impulses from the organ of 
 smell. 
 
 Sensations. — We are now in a position to make some 
 general statements based on the outlines of the afferent 
 system which have been given. It is evident that chan- 
 nels to the number of millions exist by which the central 
 nervous system may be approached from without. The 
 impulses moving along these pathways may have been 
 started by changes in mechanical relations at the nerve- 
 endings (pressure, tension, vibration). In certain cases 
 they may be the result of temperature changes, either 
 elevations or depressions. In other instances, including 
 the action of the organs of taste, smell, and vision, the 
 immediate source of the impulses must be described as a 
 chemical change. However they may originate, the 
 biologic function of all these inflowing currents is to 
 determine adaptive reactions of the reflex tj^pe. 
 
 But as human beings we find the sensations which 
 are associated with the arrival of certain of these im- 
 pulses of the greatest interest. Either intensity or novelty 
 of stimulation will be likely to insure an echo in conscious- 
 ness. We are usually quite ignorant of the state of most 
 of our internal organs; this does not mean that no im- 
 pulses are ascending from them to the brain, but rather 
 that these impulses have a monotonous character. Foster 
 is responsible for the assertion that we should instantly 
 miss the sensory contribution of the viscera if it should 
 cease. To put the proposition somewhat crudely, we may 
 say that we have no sensations from the alimentary canal, 
 but we should, in all probability, realize a difference if it 
 
THE AFFERENT PART OF THE NERVOUS SYSTEM 83 
 
 were suddenly, though painlessly, removed. The back- 
 ground of consciousness would be altered; visceral sensa- 
 tion might be hkened to the mountain range on the 
 horizon, the constant presence of which would not dis- 
 tract attention from the domestic action in the foreground, 
 though its disappearance would be something uncanny 
 and appalhng. 
 
 Sensations are commonly divided into two groups — 
 the general and the special. General sensations are those 
 which are referred to the varying conditions of the body 
 itself; special, to causes external to ourselves. Normal 
 visual sensation is clearly of the special class. This is 
 true also of hearing, smell, and taste. (It should hardly 
 be necessary to say that matter in the nasal or mouth 
 cavity is not truly within the body, but only in contact 
 with a portion of its surface.) Sensations from the 
 skin, as pressure, warmth, cold, and cutaneous pain, are 
 conveniently regarded as special, on the theory that 
 something is acting from without to give rise to them. 
 Yet it may be noted that we very readily change our 
 subjective attitude toward some of these experiences. 
 We may say that we are warm or that the room is warm, 
 shifting the reference in the most facile way between the 
 external world and the body itself. 
 
 General sensations are, for the most part, disagreeable, 
 a fact which one is inclined to connect with their common 
 relation to conditions which call for correction. If hunger 
 and thirst were pleasant to experience they would not 
 impel us to take measures for their banishment. Of 
 course, this is true of pain in general, though the remedy 
 may not be so obvious. So largely do the general sensa- 
 tions belong to maladjustments that it has been suggested 
 that the measure of health is to be found in the extent 
 to which they are crowded out by the special. A man who 
 is extremely ill may have little margin for attending to 
 what he sees and hears; bodily discomfort may almost 
 completely monopolize his attention. A man who is ex- 
 ceptionally well has little occasion to dwell on sensations 
 
84 ■ THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 of the general class. A simple diagram may serve to give 
 vividness to this contrast (Fig. 1.5). 
 
 The transition from a condition in which special sensa- 
 tions fill the field of the attention to one in which they have 
 become decidedly a minor matter may be quite precipitate. 
 
 Fig. 15. — The encroachment of the general sensations upon the 
 special in transition from health to sickness. 
 
 Consider, for example, the voyager upon the deck of a 
 steamer. At one moment we see him engrossed by the 
 beauty of the sea and skj'-, the freshness of the breeze 
 against his face, and the tingle of the pure air in his 
 nostrils. After a very brief interval he may be found 
 utterly absorbed by one horrible general sensation. 
 
CHAPTER VII 
 
 THE NEUROMUSCULAR MECHANISM 
 
 The most conspicuous manifestations of the activity 
 of the nervous system are the contractions of the skeletal 
 muscles. Locomotion, balancing, movements of the arms 
 and hands, changes of facial expression, speech — all these 
 are examples. So also is breathing, a rhythmic process 
 which we are apt to regard as similar in its nature to the 
 beating of the heart, but which is fundamentally differ- 
 ent, inasmuch as every breath is the sign of an outflow of 
 nerve-impulses from the central gray matter, while the 
 heart beats as a result of its own intimate properties. 
 
 Each skeletal muscle has a supply of efferent fibers. 
 It has also afferent connections which are of much im- 
 portance, though usually overlooked. A large muscle, 
 like the biceps in the upper arm, can be recognized to 
 consist of numerous parallel bundles set apart by connect- 
 ive tissue. These bundles, in their turn, can be resolved 
 into more slender prismatic subdivisions, and the finest 
 visible ''grain" is perhaps the indication of the fibers which 
 are the working units of the mechanism. A typical 
 muscle-fiber is of hair-like proportions, being an inch or 
 two in length and, on an average, about t^-q inch in 
 diameter. Each of these fibers may be regarded as a 
 muscle in miniature and has its own nervous connection. 
 
 It must not be inferred that the number of motor fibers 
 in the nerves is equal to the number of muscle-fibers sup- 
 plied. A single nerve-fiber, as it approaches its termina- 
 tion within the muscle, branches rather freely and is thus 
 linked to a considerable number of muscle-fibers. It 
 may govern as many as one hundred or the number may 
 be much smaller. Muscles which are under the most 
 
 85 
 
80 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 precise voluntary control have an exceptionally liberal 
 apportionment of motor nerve-fibers. Such is the case 
 with the little muscles which rotate the eyeball, executing 
 movements over which we have the most complete com- 
 mand. Doubtless the small muscles which act upon the 
 vocal cords have, as already noted, a relatively large 
 number of nerve-fibers by which their eminently skilled 
 action is determined. 
 
 Each motor fiber proceeds from a perikaryon which may 
 be in the lower sections of the brain if the destination is a 
 muscle of the head, but which will be in the spinal gray 
 matter if the muscle is in the trunk or limbs (see page 33. 
 
 Fig. 16. — A "neitromusciilar unit" as defined in the text. The 
 motor perikaryon is united through its branched fiber and end- 
 plates with five muscle-fibers. The typic number would be much 
 larger. 
 
 Every perikaryon so situated is evidently in a position 
 to bring into action a moderate number of muscle-fibers 
 if it is itself stimulated. A center for a muscle, to be 
 worthy of the name, should consist of many perikarj^a so 
 enchained as to act simultaneously upon the contractile 
 units of the muscle, leaving none of them unstimulated. 
 A fact to be borne in mind is that the fibers of skeletal 
 nmscle cannot communicate the contractile process from 
 one to another. They are insulated units and their 
 coordination must be secured, if at all, by the manner 
 in which the motor perikarya of the gray matter are 
 assembled. 
 
THE NEUROMUSCULAR MECHANISM 87 
 
 The muscle-fiber has been said to be the working 
 unit of a muscle. A motor perikaryon, with its long axon 
 extending to the muscle, branching at last and joining 
 a cluster of muscle-fibers, may be looked upon as the 
 neuromuscular unit (Fig. 16). In this combination there 
 is a set of structures not yet described. The reference is 
 to the intermediate elements between the nerve-fibers 
 at their terminations and the protoplasm of the muscle. 
 These mediating structures are called motor end-plates, 
 and they have characters which differentiate them both 
 from nerve and muscle. They must be transmitters of 
 the excitatory process from the nerve-fibers to the muscle- 
 fibers, and the interest felt in them springs from the fact 
 that they conduct with very variable facility under 
 changing conditions. 
 
 The simplest conceivable reflex finding expression 
 through skeletal muscle would be realized in case a single 
 afferent fiber were stimulated and its influence concen- 
 trated upon the dendrites of a single motor neuron. 
 The resulting flutter of a few muscle-fibers buried among 
 thousands of their fellows in a muscular mass could hardly 
 be discerned. The most restricted reflex which we can 
 observe doubtless involves a fairly large number of 
 motor neurons with their dependent muscle-fibers. More- 
 over, it is supposed that adjustor or association neurons 
 almost always intervene in the directing of the impulses. 
 
 In the present chapter it is intended to advance from 
 the discussion of the simple reflex, already familiar in 
 principle, to instances of motor performance which are 
 commonly held to lie outside this class. One thinks 
 immediately of the so-called "voluntary" movements. 
 It has previously been stated that there is no clear de- 
 marcation between the two varieties. The more care- 
 fully one analyzes the conditions surrounding each, 
 the less distinction there seems to be. A reflex move- 
 ment is one occurring prompt^ and, as a rule, inevitably 
 in response to a change of external conditions. A volun- 
 tary movement is also an adjustment depending upon 
 
88 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 external conditions, though some of the factors deter- 
 mining it may He far in tlie past. It is, of course, an act 
 of which one is conscious and which one desires to see 
 taking place. It is more profitable to attempt to unravel 
 the phj^sical mechanism than to enter the metaphj''sical 
 discussion which is suggested. 
 
 Movements of the muscles which are closely associated 
 with our consciousness and, as it seems to us, directed by 
 it are brought to pass by neurons having their perikarya 
 in the cortex of the cerebrum. The fibers belonging to 
 
 Fig. 17. — Here a "neuromuscular unit" like that in Fig. 16 is 
 shown under the sway of a cortical motor cell (b). The "projection 
 fiber" from this cell crosses the midplane of the body as suggested 
 by the line rti. In reality, a typic cortical cell probably influences a 
 number of cells of the lower order. 
 
 such neurons never pursue an unbroken course to the 
 muscles which they can call into action, but run down to 
 form synapses with nerve-elements of the type already 
 mentioned, which are either near the place of origin of 
 those cranial nerves which contain motor fibers or else in 
 the spinal gray matter. The fibers which transmit im- 
 pulses from the cortex to the neurons directly presiding 
 over the muscles belong to the class called projection 
 fibers. An odd peculiarity of these is that, as they descend, 
 they generally cross the midplane of the nervous system 
 
THE NEUROMUSCULAR MECHANISM 89 
 
 and finally enter into relations with the motor apparatus 
 on the opposite side of the body (Fig. 17). 
 
 The typic relation of skeletal muscles to the nervous 
 system having been indicated, three subjects now sug- 
 gest themselves for discussion in some detail. These are 
 the gradation of responses, coordination, and neuro- 
 muscular fatigue. 
 
 Gradation of Responses. — It is a famihar but none the 
 less a wonderful thing that we so successfully adapt our 
 muscular efforts to the purposes which they are designed 
 to serve. If one raises a book from the table one does not 
 fling it upward with useless excess of energy, nor does one 
 waste much time in preliminary contractions which do not 
 suffice to move it. Unless one is deceived in his estimate 
 of the weight to be handled, there is evidence of the most 
 admirable economy in the execution of the movement. 
 Judgment may sometimes be found at fault, as when a 
 bottle of mercury resists so surprisingly the attempt to 
 lift it or, in the opposite fashion, when an empty box is 
 picked up by one who has been handling a series of boxes 
 which were heavy. 
 
 How this grading of contractions to their uses is brought 
 about is not entirely clear. In all probability, a vigorous 
 voluntary effort means a cerebral process which is com- 
 paratively widespread and intense in degree. A small 
 movement, or the sustaining of a trifling weight, may 
 mean a less intense or a more localized process, or it may 
 mean both. If intensity is what counts, we may assume 
 that whether a contraction made by a given muscle 
 is great or small, the number of projection fibers em- 
 ployed to bring it to pass is the same. On the other 
 hand, it is interesting to consider the second possibility, 
 that is, that a contraction will be large if the number of 
 neuromuscular units cooperating to produce it is large, 
 and reduced in proportion to the reduction of the number 
 of these units engaged. Keith Lucas,^ of Cambridge, 
 England, is the physiologist to whom we owe the second 
 1 Journal of Physiology, 1905, xxxiii, 125; 1909, xxxviii, 113. 
 
90 THE NERVOIS SYSTEM AND ITS COXSERVATION 
 
 conception. Though it seems at first to be rather difficult 
 to entertain, we shall find that a strong case can be made 
 for it. 
 
 If every muscle-fiber is comparable with a rcpeatino; 
 firearm in which new annnunition is rapidly i)laced in 
 position to be discharged, it is hard to see how a stimulus 
 strong enough to have any effect can do less than discharge 
 all the energy which can possibly be released at the 
 moment. If a blast is to be fired, it is immaterial whether 
 a small or a large spark is used for the purpose. This is 
 precisely the case with the heart. The form of muscular 
 tissue composing the walls of this organ is said to obey 
 the "all-or-none law," by which we mean that none but 
 full-sized contractions can be obtained from it. 
 
 It is the conception of Lucas that the isolated fiber of 
 skeletal muscle would be found to conform to the all-or- 
 none principle if we could make experiments upon it. 
 The real difference between such fibers and those of the 
 heart, he supposes, lies in the insulated character of the 
 former and the protoplasmic union of the latter. A 
 process of contraction once started in the heart will 
 usually sweep over all the })undles which make up its 
 substance. In skeletal nuiscle such a process is definitely 
 limited to the units actually reached by nerve-impulses, 
 and a maximal response cannot be secured unless the 
 stimulation can be made to affect every fiber through its 
 end-plate. A stimulation of only a certain proportion 
 of the units will result in a movement — or a tension — at 
 the tendon less than the maximum. Because the number of 
 units is large the number of possible gradations lietween 
 the least and the greatest will be correspondingly large. 
 
 The idea set forth by Lucas can be expressed in other 
 words. It makes what we call a muscle — assuming unity 
 of action for all the fibers which can act upon a common 
 tendon — a fnuscidature, that is, a sj^stem capable of more 
 or less localized action at some times and of a mutual 
 reinforcement among all its parts when all its powers are 
 called in play. When we venture to speak of a muscle 
 
THE NEUROMUSCULAR MECHANISM 91 
 
 as though it were necessarily integral in its nature, we may 
 be taking an unwarranted liberty. '^ The objection to 
 this view, that a muscle containing some active and some 
 idle elements should give evidence of the fact by its 
 general appearance, is not a weighty one. A muscle which 
 is maintained in a prolonged contraction probably pre- 
 sents an intricate picture of alternating activity among 
 its fibers. If we could distinguish what is going on we 
 might see hundreds of these shortening, while correspond- 
 ing numbers might be relaxing. The net result of rhyth- 
 mic action on the part of vast numbers of units, providing 
 that they keep "out of step," may well be to give a gross 
 impression of constant shortening. This is precisely the 
 explanation offered by Lingle^ for the continuous or "tonic" 
 contraction observed in the alimentary canal. 
 
 If we adopt the description of the muscular mechanism 
 given above, we can accept Lucas' theories entirely, and 
 shall assume that a small movement is one to produce 
 which only a small percentage of the available fibers are 
 put into simultaneous contraction, while a large one is the 
 external sign of the more general participation of the 
 fibers. The experimenter sometimes sees indications of 
 localized responses in skeletal muscle, and more attention 
 to this matter is greatly to be desired. It is certain that 
 if there is any failure of the nerve-cells to act when a muscle 
 contraction is being sustained, there will be unemployed 
 fibers in the muscle. We readily grant that the power 
 developed by physical training is partly due to increased 
 ability to make groups of muscles act together, and it does 
 not seem unhkely that there is such a thing as an intra- 
 muscular coordination which has to be secured. 
 
 Many interesting considerations follow the admission 
 that muscles may act fractionally. It becomes quite pos- 
 sible that a part of the resources represented may not be 
 within reach of our usual deliberate control. Such inac- 
 
 ^ Gertrude F. Barbour and the author in American Physical 
 Education Review, February, 1912. 
 
 2 American Journal of Physiology, 1910, xxxvi, 361. 
 
92 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 cessible units may be thrown into action in a reflex fashion 
 or when the cerebral processes are of an exceptional char- 
 acter, as in strong emotion, hypnosis, delirium, and the 
 like. These states are often occasions for the most aston- 
 ishing display of strength. This is the more surprising 
 because the subjects are not necessarily athletic or even 
 of average muscular development. Surely in the case of a 
 man wasted by fever we have no right to assume a superior 
 condition of the muscles themselves. If such a man sud- 
 denly becomes violent and masters attendants whom he 
 could not handle when in his normal condition, it is most 
 natural to infer that his peculiarity consists in a more 
 complete power to command his limited muscular re- 
 sources than is realized at other times. 
 
 Other possible explanations may, nevertheless, suggest 
 themselves. The capacity of muscles to respond to the 
 stimulation proceeding from the central nervous sj'^stem 
 depends in part upon local chemical conditions and upon 
 the amount of the blood-pressure. When we shall dis- 
 cuss the physiologic features of emotion we shall emphasize 
 the value to the muscles of the internal secretion known 
 as adrenalin. This is poured out by the adrenal bodies 
 in times of excitement and has a marked effect in the 
 direction of reinforcing contraction and postponing fatigue. 
 To adrenalin we may ascribe a share in conferring upon 
 the individual what we recognize as the "strength of 
 desperation." Such a chemical adjustment may occur 
 in delirium or under hypnosis. 
 
 In the last-named condition it is a common demon- 
 stration to extend the body of the subject from one chair 
 to another and to seat another person upon him midway 
 between the points of support. The muscles which suc- 
 cessfully meet this severe test may be untrained and 
 insignificant in appearance. Is their unexpected rigidity 
 due to chemical alterations in their make-up or to a 
 stimulation of their fibers which is much more inclusive 
 than can ordinarily be secured? May not both classes 
 of factors be present at once? 
 
THE NEUROMUSCULAR MECHANISM 93 
 
 We need not refer to unusual or pathologic examples to 
 confirm the nnpression that the degree of command ex- 
 erted by the nervous system varies very widely indeed. 
 The most energetic responses are probably those produced 
 when a number of afferent channels are simultaneously 
 used to promote movements which could be reflexly 
 evoked in connection with either one of these paths. 
 Camis^ has shown that in the lower animals it is possible 
 to secure more powerful reflex contractions by stimulating 
 two sensory nerves at once than can be caused to occur by 
 the most intense excitation of either of these paths by 
 itself. Some would interpret this result to mean that the 
 same perikarya are more strongly stimulated when the 
 approach is made through the larger number of afferent 
 fibers; others would infer that a larger number of motor 
 neurons are made accessible to the influence of the stimu- 
 lation. Possibilities hke these will receive additional dis- 
 cussion when we reach the subject of fatigue and its 
 postponement. 
 
 Coordination. — This word has already been said to be 
 so comprehensive that it can be made to express the main 
 function of the entire nervous system. It must now be 
 viewed with especial reference to the execution of muscular 
 movements. We seldom call into voluntary action a 
 single muscle quite unaffected by any other. The use of 
 solitary muscles in pure reflexes is equally rare. In the 
 vast majority of cases, though we may be able to select 
 one muscle as the chief performer, we have to recognize 
 the auxiHary part played by its fellows in carrying out 
 even what seems a simple movement. It is theoretically 
 possible to bend the elbow by contracting a single muscle, 
 the biceps humeri, but in executing the act in the habitual 
 manner we find that the other muscles of the arm are not 
 passive, but are changing their tension in such a way as to 
 give steadiness, precision, and economy of force to the 
 whole proceeding. Certain ones directly reinforce the 
 essential movement, others assist indirectly by making 
 1 Journal of Physiology, 1909, xxxix, 228. 
 
94 • THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 more stable the parts of the skeleton which must be held 
 as a fixed anchorat^e with relation to the parts in motion. 
 
 Particular attention must be directed to the inhibitory 
 phenomena which are known to accompany most move- 
 ments. Sherrington, of Liverpool, holds the foremost 
 place among those whose researches have served to reveal 
 the importance of this matter. When a muscle is selected 
 at random and its mechanical relations are observed, we 
 can usually find one or more other muscles which can be 
 recognized as adapted to pull against it. We say that 
 these muscles are the antagonists of the first. So in the 
 case of the biceps humeri, already mentioned as applying 
 its force to raise the forearm and to bend the elbow, we 
 see that the triceps, on the back of the upper arm, must 
 have the opposite effect. Technically speaking, the biceps 
 is a flexor and the triceps an extensor. 
 
 In other parts of the body we find muscles which are 
 less clearly arranged to act as antagonists, but the prin- 
 ciple is, notwithstanding, a general one. Certain muscles 
 raise, while others depress, the ribs. The analysis of such 
 effects becomes more difficult when we consider examples 
 like the bending and straightening of the back in which 
 many muscles participate. The diaphragm offers a curious 
 illustration; when its center is drawn downward by the 
 contraction of its marginal portions the viscera are 
 crowded aside and must be accommodated by the stretch- 
 ing of the muscular abdominal walls. Hence, the ab- 
 dominal muscles are collectively antagonists of the dia- 
 phragm, but the transmission of pressure is through the 
 contents of the cavity. Sometimes opposing muscles 
 are of very unequal strength. It is plain that those 
 which raise the lower jaw and set the teeth are incom- 
 parably more powerful than those which make the counter- 
 movement, and there is little occasion for a strong mechan- 
 ism in the second case. 
 
 Often we contract antagonistic muscles simultaneously 
 and with balanced force. This is done when the object is 
 to secure firmness in any part — to resist the tendency to 
 
THE NEUROMUSCULAR MECHANISM 95 
 
 move rather than to cause a movement. When a hmb 
 which was previously held firm by such means is suddenly 
 bent, it can be shown that two changes have occurred. 
 Not only have the flexors shortened, but their opponents, 
 the extensors, have been inhibited. They do not actually 
 push, but they cease, in a perfectly definite way, to resist 
 the movement which is to be brought about. Sherrington 
 showed this in the most convincing manner by an experi- 
 ment in which the rotation of the eyeball was under ob- 
 servation. He first determined conditions under which 
 he could unfailingly secure the turning of the eye in a 
 certain direction, we will say, toward the nose. The 
 responsibility would seem to lie with the internal rectus 
 muscle. By cutting the nerve of this muscle he paralyzed 
 it. Then, repeating the stimulation which had caused the 
 reaction before, he still saw the eyeball swinging in the 
 old direction, though not so far as before. 
 
 What happened, that the eye should continue to turn 
 as though drawn by a muscle now disconnected from the 
 nervous system? The movement could be explained only 
 upon the supposition that the antagonistic muscle did not 
 fully relax until the action of its governing neurons was 
 suspended at a moment when those normally presiding 
 over its opponent were stimulated. A diagram will be 
 helpful. In the leg of an animal the same type of inhibi- 
 tion has been demonstrated. If a reflex extension has been 
 secured so frequently as to be predictable and a flexor 
 muscle is then detached from the joint, but left in connec- 
 tion with its nerve, this muscle will be found to lengthen 
 whenever the reflex is executed. It is the "law of recipro- 
 cal innervation" that when the centers excite a set of 
 muscles the antagonists are inhibited. By inhibition 
 in this case is meant the cessation of a mild continuous 
 stimulation which is normally brought to bear upon all 
 muscles excepting at such times (Fig. 18). 
 
 It will now be evident that a coordinated movement 
 requires the excitation of some muscles, each in an ap- 
 propriate degree, and the abolition of the habitual residue 
 
90- THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 of contraction (tonus) in other muscles, which must 
 .vield readily that they may not hinder the movement. 
 In all ])ut the simplest instances another element comes 
 in, that of sequence or succession in the responses of indi- 
 \ddual nmscles. Most movements occur in stages and 
 many have an alternating character. When this is true 
 we must suppose that each step establishes conditions of 
 pressure or tension in the moving parts of such a nature 
 as to excite certain receptors, and that the next shift in 
 the musculature follows as a reflex. In the higher animals 
 and in man only a little of this coordinating power resides 
 
 Fig. IS. — The principle of reciprocal innervation. The cortical 
 neuron is represented as exciting the upper of the two subordinate 
 neurons, causing the contraction of one group of muscle-fibers, 
 while it inhibits the second neuron, allowing the associated muscle- 
 fibers to relax. The + sign suggests stimulation; the — sign, in- 
 hibition. Doubtless the actual arrangement is less simple than this. 
 
 in the spinal cord. Most of it is represented in the brain. 
 At this place it is convenient to speak briefly of the 
 physiology of the cerebellum. 
 
 The Cerebellum. — It will be recalled that this division 
 of the brain is a dorsal outgrowth of the nerve-axis. It is 
 connected by a rich supply of fibers with the medulla 
 behind, the ventral region known as the pons, and, less 
 directly, with the cerebrum. Its prominence in different 
 species of animals is most unequal. It is large in the fish, 
 greatly reduced in the frog, very large again in the bird, 
 and fairly large but overshadowed by the cerebrum in 
 most mammals. A moment's reflection will show that the 
 
THE NEUROMUSCULAR MECHANISM 97 
 
 size of the cerebellum can scarcely be correlated with the 
 intelligence of these types; further consideration inclines 
 one to the belief that it is in some sense linked with 
 elaborate and active neuromuscular mechanisms. 
 
 A fish gives little indication of intelhgence, but it has a 
 most multifarious muscular system corresponding with 
 its intricately developed skeleton. The bird has much 
 more intelligence, but is distinguished most clearly by its 
 powers of flight. A prominent cerebellum seems always to 
 imply capacity for locomotion and balancing. This gen- 
 eral contention is borne out by the results of experiments 
 in which this part of the brain has been partially or wholly 
 removed. When a physiologist wishes to determine the 
 service of a particular structure in the nervous system 
 he cuts it away, if this is possible, and keeps the animal 
 alive to observe the resulting deficiency. This procedure 
 is justified only when two conditions are fufilled: first, 
 no pathways between other stations than that under ob- 
 servation must be interrupted; second, the effects recorded 
 must be those due to the actual lack of the part which has 
 been sacrificed, and not to the irritation set up at the seat 
 of the operation. 
 
 The pioneer experiments upon the cerebellum were 
 made in France about one hundred years ago. The 
 investigator found that a pigeon recently deprived of this 
 part of the brain gave a distressing picture of incoordina- 
 tion. The bird could not fly nor even keep its feet. Its 
 struggles were painful to witness, and the more so because 
 there seemed to be no lessening of the normal sensitive- 
 ness and capacity for terror. In its staggering and flut- 
 tering about there was no apparent loss of the power to 
 contract individual muscles, but the most obvious loss 
 of the ability to secure the needful cooperation of the 
 groups on whose action equilibrium in rest or motion 
 depends. The doctrine based on such observations was 
 to the effect that the cerebellum is in charge of the general 
 musculature so far as this is used for equilibration and 
 perhaps for other habitual types of performance. 
 
 7 
 
98 ' THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 The work of more recent students has sliown that the 
 control formerly credited to the cerebellum was too 
 absolute and exclusive. Our belief is still that this 
 part of the brain is much concerned with subconscious 
 muscular adjustments requiring extensive coordination, 
 but we no longer regard it as the sole seat of such regula- 
 tion. It has been found that animals recover in great 
 part from the profound effects of the removal of the 
 cerebellum, and it is natural to conclude that the imme-. 
 diate results which are so striking are due largely to irrita- 
 tion at the place operated upon and not so definitely to 
 the loss of its functioning. The recovery is never com- 
 plete. A dog without a cerebellum may walk and swim 
 again, but not with the full vigor and steacUness of the 
 normal animal. Some element of reinforcement or com- 
 pensation is permanently lacking. 
 
 As regards the human nervous system, it is usually held 
 that the cerebellum is developed by practice and that it 
 comes to contain much of the synaptic machinery for 
 maintaining the balance at rest and in motion. It has 
 often been supposed to assume command of complex 
 movements which were at first guided at all stages by 
 the cerebrum. Thus, it has been imagined that a child 
 learning to walk, whose attention is plainly concentrated 
 upon the taking of each step, is dictating its uncertain 
 movements from the cerebral cortex, but that the higher 
 mechanism is in time relieved of the detail and set free 
 for new activities, the cerel^ellum taking its place, at least 
 to a considerable extent. 
 
 If this is a correct conception, it may be inferred that 
 later acquirements of the individual, such as swimming 
 or skating, may likewise call for cerebral direction until 
 they become easy and unconscious, when their govern- 
 ment may be cerebellar. According to this view, the 
 cerebellum is intimately related to all accomplishments 
 which we can speak of as "second nature." But this is 
 more certainly true of those which involve a large share 
 of the muscles than of localized actions. The use of a 
 
THE NEUROMUSCULAR MECHANISM 99 
 
 pen probably remains essentially a cerebral act, though 
 one may trace a copy with a minimum of conscious 
 attention. Disease of the cerebellum interferes chiefly 
 with movements which call for the poising and timely 
 control of the main mass of the body rather than with 
 skill of hand. 
 
 Students are slow to realize the vast importance of 
 afferent impulses in the execution of coordinated move- 
 ments. When one sees a victim of spinal disease whose 
 disorderly and badly regulated motions make him a 
 painful spectacle, it is natural to infer that there is inabil- 
 ity to command the muscles. Yet if it is a case of typic 
 locomotor ataxia the chief trouble is with the ascending 
 paths. The afflicted man suffers from the want of a guid- 
 ing sense. He cannot readily perceive the extent of the 
 movements which he is executing, nor the resistances 
 encountered. He is likely to do much better when he 
 has the use of his eyes than he can in the dark. All people 
 are assisted by the eyes in the maintenance of equilib- 
 rium, but these receptors become still more important 
 when there is a failure of the impulses from the motor 
 apparatus itself. 
 
 Breathing. — An important subdivision of the general 
 neuromuscular system is that which stands in control of 
 breathing. The muscles used are such as we can employ 
 singly or in groups for various purposes. We can also 
 modify our breathing if we choose, but only within limits. 
 It is supposed to be impossible to commit suicide by 
 holding the breath. It is increasingly difficult to continue 
 forcing the breathing beyond one's inclination. Since 
 we cannot long underbreathe, nor yet overbreathe, it is 
 natural to assume that there is some positively acting, 
 involuntary mechanism normally dictating the rate and 
 depth of the breathing movements. We have evidence 
 of very long standing that this mechanism indeed exists 
 and that its chief center is in the medulla. 
 
 Breathing is not dependent upon the cerebral cortex. 
 Complete division of the nervous axis at the level of the 
 
100" THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 pons docs not stop the respiration. If the injury is cx- 
 tondcd l)a{'kward into the nieckiUa, breathing is susi)ondcd 
 permanently when certain cell-chisters are destroyed or 
 when they are cut off from communication with the 
 spinal cord. The French workers who first demonstrated 
 the absolute dc^pendence of life upon the integrity of 
 this very limitetl region called it the "vital knot." It is 
 generally referred to as the respiratory center. It is so 
 related to the remainder of the nervous system that it is 
 involved in almost every reflex act of any magnitude. 
 Its ordinary action seems to be determined by the condi- 
 tion of the blood which is sent to it. If the dissolved 
 carbon dioxid is increased, the center is excited to cause 
 deeper and quicker breathing. If the same gas is reduced 
 to an unusualh^ low concentration in the blood, the stimu- 
 lation of the center is suspended and there is a pause in 
 the breathing (apnea). 
 
CHAPTER VIII 
 
 THE NEUROMUSCULAR SYSTEM: NEUROMUS- 
 CULAR FATIGUE 
 
 Nothing is more familiar than the fact of experience 
 that muscles used long and severely respond less and less 
 readily to our requisitions upon them. This progressive 
 flagging of efficiency, together with the subjective sense of 
 difficulty in commanding the muscles employed, we speak 
 of as fatigue. When we add the adjective "neuromuscu- 
 lar" we open the way to a discussion of the respective 
 share of muscular and nervous elements in the develop- 
 ment of this condition. In the laboratory we can devise 
 experiments such that fatigue of muscle is studied quite 
 by itself; in the living body muscles are used only when 
 their controlling nervous mechanisms are in action. 
 
 Fatigue, whether in muscular fibers or in neurons, may 
 conceivably result from either of two causes. It will be 
 inevitable if the store of energy-producing substance 
 runs low. This is a type of fatigue which approaches ex- 
 haustion as a limit. The second possibility is that by- 
 products or end-products of the chemical process which 
 is going on may so accumulate as to become a hindrance 
 to the continuance of that process. This is probably the 
 ordinary happening: muscles which refuse to work are 
 not destitute of all fuel, but are, figuratively speaking, 
 clogged by ashes and half-burned clinkers which remain 
 as relics of the combustion which has recently taken 
 place. 
 
 So far as muscular tissue is concerned, we know some- 
 thing of the products which are capable of depressing its 
 activity. Three compounds are usually mentioned as 
 bearing a part — carbon dioxid, lactic acid, and acid 
 
 101 
 
102 " THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 potassium phosphate. These are all acidic in nature, and 
 it is supposed that any other acid, introduced experi- 
 mentally, will have a similar effect. Undefined fatigue 
 substances probably exist in addition to the ones named, 
 and they may not all have an acid character. A most 
 important fact to be noted with regard to these metabolic 
 products is this: the same 'compounds which in high con- 
 centration can poison the muscle to- the point of apparent 
 paralysis, act as stimulants when they are present in small 
 amounts. In this we find one explanation of the favorable 
 effect of moderate preliminary exercise upon muscular 
 capacity. A muscle is not so efficient when it is first 
 aroused to activity after a period of rest as it is when it 
 has been used for a time.^ 
 
 The phenomenon referred to — the gain in power which 
 comes with a brief series of contractions — is spoken of as 
 the "stair-case effect," or often, using a German equivalent, 
 as the Treppe. The proof that it is due in part at least to 
 the so-called fatigue substances we owe to Lee of Colum- 
 bia. Other factors undoubtedly enter in; when one is 
 "warming up" one profits by the adaptation of the cir- 
 culatory system to the new requirements and, perhaps, 
 also by changes in the activity of the organs of internal 
 secretion. But when all allowance has been made for 
 such sources of reinforcement, we must still attribute 
 much to the favorable influence of the products of activ- 
 ity exerted before their accumulation has become excessive. 
 
 We are now in position to consider the probable seat of 
 fatigue in the neuromuscular apparatus. Recalling the 
 unit of this mechanism as previously defined, we find 
 that the possibilities are more numerous than would at 
 first be supposed. The muscle-fiber may be fatigued. 
 The junction of nerve and muscle, the motor end-plate, 
 is another structure which is subject to impairment by 
 its own use. This is, indeed, a relatively weak hnk in 
 the chain. Fatigue of the nerve-fiber may be disregarded; 
 the enduring nature of the white matter has already been 
 1 F. S. Lee, Pop. Sci. Monthly, February, 1910. 
 
THE NEUROMUSCULAR SYSTEM; FATIGUE 103 
 
 commented upon (see page 39). But fatigue of the 
 motor perikaryon is to be reckoned with, and so is fatigue 
 at the synapses through which its discharges are deter- 
 mined. It is not wise to make dogmatic assertions as to 
 the precise order in which failure of these unlike struc- 
 tures is to be anticipated when they are kept steadily at 
 work. 
 
 If a proper balance between destructive and recupera- 
 tive processes can be struck, a neuromuscular mechanism 
 need not exhibit fatigue in spite of what seems like con- 
 tinuous use. This is the case with the diaphragm, which 
 bears its part in the taking of every breath, but seems not 
 to show any weakening of response or loss of irritability 
 until it shares the general decline of old age. As the 
 diaphragm is not automatic, but contracts only in response 
 to stimulation traceable to the brain, we must suppose 
 that in the nervous as well as in the muscular portions of 
 this combination restoration normally keeps pace with 
 decomposition, and that the waste-products are not suf- 
 fered to gather at the seat of action. (The diaphragm 
 is chosen rather than the heart to exemplify this balance 
 because the beating of the heart is not dictated from 
 without.) 
 
 If we leave out of further account the muscles used in 
 breathing and their presiding neurons, we shall be ready 
 to agree that in general our neuromuscular equipment is 
 subject to daily if not more frequent fatigue, and calls for 
 rest that it may be renewed. The renewal must include 
 the washing away or perfect neutralization of the fatigue 
 substances and the introduction of fresh fuel supplies. 
 To make our discussion concrete, let us fix our attention 
 upon an imaginary pedestrian who is found toward the end 
 of the day covering the last mile of a long tramp. In what 
 respects is his system altered from its state at setting out 
 in the morning? 
 
 His leg muscles have done the heaviest work. They have 
 produced in the course of the walk a great quantity of 
 carbon dioxid. This has, presumably, been removed quite 
 
104 ■ THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 promptly and full>- through the lungs. But the other acid 
 products may now be present to an extent which suffices to 
 render the musck's less responsive to central command. The 
 same or similar compounds may have affected the motor 
 end-plates in such a way as to make difficult the trans- 
 mission of effects from nerve to muscle. If a blockade is 
 established at this point, muscular response may fail at a 
 time when there is yet plenty of potential working capac- 
 ity in the muscles themselves. It is generally held that 
 this is just what occurs: the end-plates become imper- 
 vious to stimuli, while other parts of the apparatus are 
 still in fair working order. 
 
 One is tempted to draw a comparison between the end- 
 plate and a safety-fuse, such as is used in connection with 
 an electric fixture. The fuse is intended to be destroyed 
 under conditions which might otherwise threaten damage 
 to more valuable portions of the system. It is readily 
 renewed. So we may think of the end-plate as some- 
 thing easily impaired by use, but also easy to repair. It 
 is better that wear and tear should fall upon this structure 
 rather than upon the more highly organized protoplasm 
 of nerve-cells or muscle-fibers. We may now assign as 
 one condition associated with our walker's painful prog- 
 ress the increasing difficulty of end-plate transmission. 
 
 Another condition is operative at the same time. This 
 is the persistent return from the musculature itself, the 
 joints, and the soles of the feet of afferent impulses in- 
 hibitory to continued walking. In part these impulses 
 give rise to sensations of lameness and weariness. In 
 part they may impede action without having their sign 
 manifest in consciousness. Fatigue, so far as it is due 
 to impulses of this class, may be regarded as disinclination 
 rather than incapacity. If we are ingenuous we must 
 admit that much of our fatigue has to be classified under 
 this head. Such a source of deterrent impulses as a blis- 
 tered foot has a double effect upon the sufferer. Besides 
 making him feel disposed to stop, it causes him to adopt 
 an unnatural gait in the endeavor to "favor" the injured 
 
THE NEUROMUSCULAR SYSTEM: FATIGUE 105 
 
 member, and this means that comparatively untrained 
 muscles are called upon. Endurance is thus inevitably 
 lessened. 
 
 We have now recognized two probable elements in the 
 famihar state of the tired man. These are end-plate fatigue 
 and inhibitory impulses mounting to the centers. Addi- 
 tional factors are undoubtedly concerned. Among these 
 we may include some measure of true muscular fatigue, 
 dependent on the local chemical changes in the contractile 
 material and perhaps on changes in the composition of the 
 blood and lymph. We must bear in mind that fatigue 
 substances of this class may be distributed far and wide 
 by the circulation and depress the functional activity of 
 muscles which have not themselves been much used. An 
 unfavorable effect spreading to glands and to the nerve- 
 centers is easily possible. Our pedestrian may be feehng 
 the results of such a diffuse poisoning as he plods along. 
 
 Deterioration of the motor perikarya in the cord and 
 perhaps in the brain may be one source of the observed 
 waning of power. Reference has been made some time 
 since to the demonstration of visible changes in these 
 bodies which Hodge and others have succeeded in making 
 conclusive. A new picture of the central element in general 
 fatigue we owe to the school of Sherrington, and particu- 
 larly to one recently associated with him, Alexander 
 Forbes.^ This new emphasis is placed upon the synapses 
 through which stimulation of the motor perikarya must 
 be accomplished. Each typic perikaryon has a number 
 of these possible approaches. When it takes part in a 
 simple reflex it is not excited through the same synapse as 
 though the stimulation were conveyed to it from the 
 brain. 
 
 Now, there is reason to believe that synapses, like end- 
 plates, are links of limited endurance in the neuromuscular 
 chain. If, however, a synapse becomes fatigued and in- 
 capable of efficient conduction, there is the possibility, 
 not present in the case of the end-plate, of substituting a 
 1 American Journal of Physiology, 1912, xxxi, 102. 
 
1U(J THE \p]RVOUS SYSTEM AND 'ITS CONSERVATION 
 
 new route for the application of stimuli. We have very 
 satisfactory evidence that some of these synapses do fa- 
 tigue, and that an apparent renewal of motor connnand 
 is secured when new ways of stinuilation, involving differ- 
 ent sensory paths, are devised. Let us suppose that our 
 weary traveler suddenly hears martial music. If it is his 
 nature to be moved by the strains we may expect that, 
 for a time, his pace will be ciuickened and all external 
 signs of fatigue diminished. 
 
 How shall we interpret the marked effect of the music? 
 There may be more than one opinion as to this, but we 
 
 Fig. 19. — The principle of fatigue in reflex action — Forbes' 
 conception. When the reflex obtained through r fails, the action 
 can be renewed by shifting stimulation to ri. The motor parts 
 are the same in both cases, hence the fatigue is in a route of approach 
 to the center. One must, in imagination, multiply all the elements 
 illustrated. ^ 
 
 may indicate a possible explanation along the lines of 
 Forbes' experiments. First, we must briefly describe his 
 methods. He has studied the fatigue of the reflex mech- 
 anism in cats. A nerve containing afferent fibers is chosen 
 and its central end is stimulated. Certain muscles re- 
 spond, and one of these is selected for careful observation. 
 When the stimulation is applied repeatedly the contrac- 
 tions of the muscle are progressively reduced until at 
 length none can be secured. Fatigue at some point in the 
 apparatus is to be inferred, but where? The answer is 
 forthcoming when a shift of the electrodes is made to 
 
THE NEUROMUSCULAR SYSTEM: FATIGUE 107 
 
 another afferent nerve. Such a shift is followed by 
 renewed activity on the part of the muscle to which 
 attention is directed (Fig. 19). 
 
 In this case the motor elements used in the earlier and 
 in the later part of the trial are presumably the same. 
 It is the afferent neurons which are different. Fatigue of 
 nerve-fibers is negligible, and the conclusion must be that 
 failure to conduct has occurred at the place where the 
 impulses of peripheral origin must exert their effect upon 
 the motor neurons. This is the same as saying that we 
 have here an instance of synaptic fatigue. Much poten- 
 tial capacity for action may still reside in the efferent 
 equipment, but a new line of approach must be adopted 
 to demonstrate it. Forbes has used animals in which only 
 the cord and not the brain has been intact, thus simplify- 
 ing his conditions as far as he could. It seems legitimate 
 to extend the same principle to muscular performances in 
 which the brain is concerned. This we shall now under- 
 take to do. 
 
 The neurons, which have their perikarya in the cortex 
 of the cerebrum and send their dependent projection 
 fibers down the spinal axis, are not self -stimulated. They 
 are thrown into action, like the neurons of lower rank, 
 by impulses affecting them through synapses. Now we 
 may fairly suppose that the efficiency of these cerebral 
 motor neurons is greatest when they are stimulated from 
 all sides, so to speak, rather than in a one-sided fashion. 
 Here we have a key to the invigorating influence of 
 rhythmic music upon the walker and perhaps to many 
 other phenomena of the same class. 
 
 The tired man to whom we have so often referred has 
 been kept in motion through the day by a variety of 
 external stimuli. Some of these have had a very direct 
 effect upon the lower centers, as in the case of the im- 
 pulses returning from the soles of the feet at every con- 
 tact with the ground. These, together with others from 
 the joints, the tightening tendons, and probably from 
 the muscles themselves, have been ever prompting the 
 
108 THE NEKVOUS SYSTEM AND ITS CONSERVATION 
 
 taking of an additional step to Ijc added to the lengthening 
 series. Visual impulses, varied with the ehanging scenery, 
 have been giving rise to cerebral currents which have 
 favored the holding of the muscles to their long task. But 
 now a time has come when the impulses returning from the 
 locomotor organs are deterrent rather than encouraging. 
 Inhibition at the lower centers is overridden with increas- 
 ing difficulty by the action of the higher comj^lexes. 
 
 In the brain itself the visual currents may cease to be 
 favorable. There is no longer the desire to see bej^ond the 
 
 Impulses Impulses oj 
 
 over associatioTT'^"^^ ^ _^ ^^-—^ Visual orj^l 17 
 
 patl)S. "Will." X^ "^^ 
 
 /Ctrchral \ 
 
 )r 
 
 rv 
 
 Deterrent 
 
 Impu-lses 
 
 y 
 
 [ Afo(o) 
 V Centre, /' "^^-^ Impulses of 
 
 - Motor 
 iropuises 
 
 auditory ori^i'?' 
 
 Fig. 20. — To suggest, though incompletely, the concentration of 
 certain streams of impulses upon the motor cortex in one tired by 
 prolonged exertion. To bring in play a fresh path of approach is to 
 secure some renewal of activitj\ To abate the deterrent impulses 
 has a like efTect. 
 
 next turn of the road or to gain the next ridge. What is 
 needed to rouse the flagging cortical centers is stimula- 
 tion over afferent paths that have not yet been brought 
 into use. One of these is the auditory nerve. The ear 
 has had but Httle to do with reinforcing the walker's 
 efforts up to this time. Hence the music wakes to ready 
 response a part of the nervous system which has been 
 but little fatigued by any action strictly its own, although 
 the overflow of fatigue substances formed elsewhere may 
 have injured it to some extent. The cortical motor 
 neurons are reached over paths nearly inactive until now 
 
THE NEUROMUSCULAR SYSTEM: FATIGUE 109 
 
 and by means of synapses which have not been fatigued. 
 The new application would be vain if there were not still 
 muscular resources available and possil^ilities of synaptic 
 transmission from the projection fibers of the cerebrum to 
 the motor neurons of the cord (Fig. 20). 
 
 What shall we say of the soldier who is roused from 
 what seemed to be utter fatigue by the close pursuit of 
 the enemy and the whistle of bullets? Is this a simple 
 case of setting up brain currents which arrive at the 
 motor centers by fresh routes and unimpaired synapses? 
 It may be so in part, but whenever a strong emotional 
 reaction is entailed there are likely to be chemical rein- 
 forcements of muscular capability. This is a matter which 
 may well be left for discussion in another connection. 
 The general principle has been stated in the last chapter 
 (see page 92), where the augmented production of adren- 
 alin in times of excitement was mentioned. 
 
 The remarkable postponement of fatigue in the case 
 of those who like to dance is worthy of some comment. 
 Consider the country girl, whose daily tasks are heavy 
 enough to leave her quite tired at nightfall and ready for 
 an early bedtime. On the exceptional evening when there 
 is to be a party the usual day's work may have been faith- 
 fully done, but there may be no signs of the accustomed 
 weariness. Instead, she goes to the dance and for hours 
 pursues a form of vigorous exercise in which the muscles 
 used are, in the main, the same which were called upon 
 in the domestic round. Perhaps the emotional state is 
 intense enough to warrant the belief that internal secre- 
 tions are modified to support the muscular activity. 
 Whether this is so or not, we can see that the conditions 
 favor an extensive and symmetric stimulation of the 
 cortical areas. 
 
 When the girl in question was engaged in sweeping a 
 room she was held to her dull duty by certain internal 
 stimuli of an obscure but evidently monotonous char- 
 acter. The "sense of duty" as reahzed in consciousness is 
 attended by the transmission of impulses to the motor 
 
110 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 apparatus, but the number of these impulses is far less 
 than it might be if various external conditions favoring 
 reinforcement could be added. At the dance the reinforc- 
 ing factors are present in the most efficient combination. 
 Tlicre is the music, there are the lights and the shifting 
 play of colors as the figures move, there are contacts, and 
 all the while a richness in the psychic experience totally 
 foreign to the drudgery at home. This psychic richness 
 doubtless corresponds with the physiologic fact of multi- 
 phed brain-currents. 
 
 The difference between play and work, between doing 
 what we keenly enjoy and what we feel we ought to do for 
 some remote result, may be said to be the difference be- 
 tween a motor performance in which many pathways are 
 traversed by the impulses which unite to stimulate the 
 neuromuscular mechanism and one in which the number 
 of these paths is small and not much subject to variation. 
 Titchener once surprised an audience by the declaration 
 that "all work is a waste of time"; this he elucidated as 
 meaning that the zest which we associate with play is the 
 basis of better accomphshments than can be attained when 
 only the feeling of oliligation is operative. The boy who 
 becomes very tired of chopping wood can use the same 
 muscles in a game, and his parents may twit him with the 
 fact. But while it is true that he is using the same muscles 
 and the same spinal neurons, perhaps the. same projection 
 fibers from the cerebrum, he is not using the same afferent 
 channels nor the same cortical approaches to the motor 
 centers. The adult cannot honestly lay claim to im- 
 munity from fatigue of this sort. 
 
 Elements in Training. — A great deal that has been said 
 in this and the preceding chapter may conveniently be 
 reviewed under this head. In what respects does an un- 
 trained neuromuscular system differ from one which has 
 been developed by use? We shall find as many possibili- 
 ties in this connection as we have in our attempt to 
 analyze fatigue. We shall have to pay attention to the 
 muscles, the end-plates, and the central organization. 
 
THE NEUROMUSCULAR SYSTEM: FATIGUE 111 
 
 One fact is impressed upon the mind of the man in the 
 street: that muscles grow with use. We shall not be in- 
 clined to make this the foremost consideration, but it is 
 well worth emphasizing. This is not the place to enter 
 upon any discussion of the causes underlying this well- 
 known growth. It may be due in part to improved cir- 
 culation and in part to chemical conditions arising when 
 contractions take place. It may be said to be a principle 
 of rather wide appUcation in biology that a destructive 
 process, during vigorous life, will be followed not only by a 
 process of repair, but by overcompensation. This is held 
 to be true of antitoxin production and acquired im- 
 munity to disease. It is simply illustrated in callous for- 
 mation: when friction destroys the surface layers of the 
 skin they are not merely replaced, but their number is in- 
 creased. The increase in the mass of a muscle consequent 
 on its regular use is also a reaction from a decomposition 
 process, for every contraction is executed at the cost of 
 some substance disintegrated. But the growth of the 
 muscle is not wholly analogous to the formation of a 
 callus, because in the first case it is beheved that we have 
 no multiphcation of fibers, but only an increase in volume 
 on the part of those present. 
 
 One may make proper allowance for the greater size of 
 trained, as compared with untrained, muscles, and he will 
 be convinced that the gain in power is out of all proportion 
 to the gain in bulk. Betterment of quality must certainly 
 be admitted. The service of exercise to a man may be 
 rather to give him full command of the tissue which he has 
 than to put more at his disposal. Superior quality in 
 muscle may mean an actual chemical change by which the 
 fuel is made more available or stored in larger quantity, 
 or the chief improvement may be in the efficiency of the 
 circulation. Much will depend upon this, for the supply 
 of oxygen to the muscle protoplasm is an imperative 
 requirement. 
 
 In the third place, it is conceivable that facility of 
 end-plate transmission is one of the gains. Difficulty in 
 
112 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 securing responses because of conditions existing at the 
 junction of nerve and muscle may l)e one of the charac- 
 teristics of the untrained, as it is of the fatigued, state. 
 The increased endurance demonstrated by those who have 
 put themselves upon sparing diets (Fletcher, Chittenden, 
 et al.) is most easily explained on the theory that the 
 end-plates were previously subject to a chronic impair- 
 ment owing to the presence of avoidable metabolic prod- 
 ucts. Such a situation would be equivalent to continuous 
 fatigue and would limit at all times the working capacity 
 of the muscles. Exercise may be assumed to bring about 
 a more favorable condition at this important locality in 
 the neuromuscular complex. 
 
 Still another result of training may be more extensive 
 and effective innervation. We shall make much of this 
 if we accept the Lucas doctrine of the fractional response 
 of muscles. According to this view, the muscle which has 
 not been much used contains elements which are not 
 accessible to stimulation under any ordinary state of 
 affairs. With regular use the number of these idle fibers 
 may very likely be steadily reduced and a corresponding 
 increase of force and endurance realized. The defect 
 overcome may be at the end-plates or it may be in the 
 central nervous system. If it was originally at the end- 
 plates, we may picture the perikarya which preside over 
 the untrained muscle as being all active, but unable to 
 call portions of it into contraction. If it was central, we 
 are to conceive of idle perikarya among those which are 
 at work, each unemployed neuron having a cluster of 
 dependent muscle-fibers which remain at rest. 
 
 So far we have spoken of peripheral improvements, 
 save that in the last instance we have introduced the idea 
 of a possible central factor. We have recognized the ad- 
 vantages accruing (1) from the actual growth Of the 
 muscles, (2) from improved contractile substance, (3) 
 from more reliable end-plates, and (4) from better "team 
 work" among the neurons governing single muscles. 
 Now, by a simple extension of the last-named factor, we 
 
THE NEUROMUSCULAR SYSTEM: FATIGUE 113 
 
 may include the gain through coordination. This is what 
 we mean by acquiring skill. In all Vjut the most elemen- 
 tary movements the best combinations of contractions 
 on the part of different muscles have to be secured by 
 practice. The physiologic change which makes the 
 gain possible must consist in the establishment of new 
 ties between the various groups of neurons at all levels 
 in the central nervous system. 
 
 Better coordination means better economy of force. 
 When one is riding a bicycle in the early days of the ex- 
 perience much strength is wasted. The foot which is 
 coming up resists the foot which is going down. This is a 
 type of an interference which is widespread where many 
 muscles are set to work in an unwonted form of exercise. 
 When the "knack" is attained, much less internal work 
 is done for a given external result. This has been proved 
 by measurements of the respiratory exchange in persons 
 who were performing certain tasks (climbing hills, for in- 
 stance), with and without adequate training. It is alto- 
 gether probable that in reaching the full measure of 
 economy, precision, and endurance the cooperation of 
 the cerebellum is secured. 
 
CHAPTER IX 
 
 THE AUTONOMIC NERVOUS SYSTEM 
 
 The term which is used as the title of tliis chapter is 
 employed to cover that part of the efferent system which 
 does not control the skeletal muscles. The negative de- 
 scription seems awkward, but is nevertheless accurate and 
 final. It is equivalent to the statement that the autonomic 
 system regulates the action of the heart, the glands, and 
 all structures in which there is contractile tissue of the 
 kind known as plain, smooth, or visceral muscle. This 
 variety of tissue occurs in the alimentary canal, the 
 gall-bladder, the urinary bladder and the ureters, in the 
 reproductive organs, in the blood-vessels and lymphatics, 
 and in the bronchial tubes. It is also represented, though 
 sparsely, in the skin. It forms the accommodation or 
 focusing muscle of the eye and its presence in the iris makes 
 possible the familiar changes in the size of the pupil. 
 
 The term "autonomic" is akin to the political word 
 "autonomy," and imphes "self-regulating." A contrast 
 between this di\'ision of the nervous system and that 
 which governs the skeletal muscles is suggested. It is a 
 common practice to call the skeletal muscles "voluntary," 
 and to regard the heart and all the organs equipped with 
 plain muscle as "involuntary." The distinction is as apt 
 to mislead as to be helpful and it will not be insisted upon 
 here. Of course, it is true that we often have a fore- 
 knowledge of the movements of our skeletal muscles which 
 we do not have in any such degree with respect to the other 
 motor elements in the body nor as regards the behavior of 
 the glands. But we must note that much of the activity 
 of the so-called voluntary muscles proceeds with little 
 conscious attention on our part (breathing, balancing), 
 
 114 
 
THE AUTONOMIC NERVOUS SYSTEM 
 
 115 
 
 while we shall find that there are many correspondences 
 between the states of consciousness and the reactions 
 brought about through the autonomic system. 
 
 It will not be profitable to say much about the anatomy 
 of this division of the nervous system. The details are 
 exceptionally difficult. One point, however, must not be 
 omitted: so far as we know, each path from the cord 
 or the brain to any outlying locality reached by autonomic 
 influences is a tandem arrangement of two orders of 
 neurons (see page 33). The neurons of the first order — 
 
 Fig. 21. — To contrast the path to the skeletal muscles, already 
 familiar, in which one neuron extends from the central nervous 
 system to the contractile structures with the autonomic path in 
 which two orders of neurons are employed to span the same interval. 
 Cells of visceral muscle are represented at the end of the post- 
 ganglionic fiber. In the interest of simplicity the preganglionic neu- 
 ron is made to influence only one of the lower order. It would really 
 affect several. 
 
 preganglionic, as they are called — have their perikarya 
 within the brain or the cord and extend outside to a 
 greater or less distance. They end by forming synaptic 
 connections with neurons of the second order — post- 
 ganglionic — and these complete the transmission to the 
 secreting or contractile tissues to be affected. The syn- 
 apses between neurons of the first and those of the second 
 order are usually to be found in ganglia, detached collec- 
 tions of gray matter variously situated. Two chains 
 of these ganglia are seen in the back of the body cavity, 
 one on either side of the spinal column. Preganglionic 
 
IIG THE NERVOUS SYSTEM AND ITS CONSKKVATION 
 
 fibers reach thcnii from the neighboring spinal nerves, and 
 their postganghonio fil)ers either rejoin the spinal nerves 
 to be distributed with their peripheral branches or pass 
 directly to endings in the viscera. These two chains 
 with their connections are known under the curious old 
 name of the "sj'mpathetic system." The word used 
 never had its psychologic meaning. 
 
 "Autonomic" is a more inclusive term than "sympa- 
 thetic." The sympathetic system is that part of the 
 autonomic receiving preganglionic fibers from the thoracic 
 and lumbar portions of the spinal cord. There are auto- 
 nomic pathwaj^s beginning in the brain which are not 
 reckoned in the sympathetic system, and there are others 
 at the lower end of the spinal axis which He outside its 
 anatomic limits. We shall not often have occasion to 
 refer to the sympathetic system apart from the larger 
 complex of which it is a fraction. Ganglia belonging to the 
 autonomic system, but lying outside the two sympathetic 
 chains, are found in very many localities; for example, 
 behind the eye, in the walls of the heart, and clustered 
 about the arteries which supply the digestive organs. 
 They are not to be confused with the ganglia connected 
 with afferent paths, which are found, for the most part, 
 close to the point of entrance of such paths into the central 
 nervous system. 
 
 We may now pass to a condensed statement of the 
 operations of the autonomic system upon various depart- 
 ments of the physiologic mechanism. We may well speak 
 first of its control of the circulation. This is exercised 
 partly through the cardiac and partly through the vaso- 
 motor nerves. The heart is a muscular pump, and on the 
 force and frequency of its beat depends the volume of 
 blood sent through the arteries to all regions of the body. 
 Its beating is fundamentall}^ automatic, but subject to 
 extensive regulation through the nerve-centers. Auto- 
 nomic paths to the heart-muscle can be traced from two 
 sources. Of these, the most conspicuous and the earliest 
 to be studied is represented by certain fibers in the large 
 
THE AUTONOMIC NERVOUS SYSTEM 117 
 
 nerve known as the vagus, the tenth in the cranial series 
 (see page 73). 
 
 When the vagus nerves of a dog are both cut, it is com- 
 monly observed that the rate of the heart is considerably 
 increased. This is taken to mean that a restraining or 
 inhibitory influence was previously exerted through these 
 nerves upon the heart's activity. This impression is con- 
 firmed when the peripheral end of one of the cut vagi is 
 subjected to electric stimulation. The heart may be made 
 to stand still for some seconds and the circulation is 
 stopped. This would kill the dog in a short time if it 
 could be continued, but it cannot; the heart is said to 
 "escape," that is, to resume its beating in spite of con- 
 tinued stimulation of the vagus. Still, the rate and force 
 of the beat can be kept below the original standard for an 
 indefinite time. The natural conclusion with reference 
 to the share borne by the vagi in the government of the 
 heart is that they contain fibers through which its activity 
 is generally held in check and a reserve for emergencies 
 guaranteed. The organ may be assumed to expend its 
 power unprofitably when these fibers have been cut. 
 
 The heart receives some nerve-fibers in addition to those 
 which reach it by way of the vagi. These others come 
 from the sympathetic ganglia near its own level in the 
 thorax. They are not easily picked up for stimulation 
 in the living animal, but when the experiment is success- 
 ful they are found to have an effect just opposite to that 
 which has been described. They furnish paths through 
 which impulses can be sent to quicken and make more 
 forcible the beating of the heart. The branches coming 
 to the heart from the sympathetic ganglia are called the 
 cardiac accelerators. Simultaneous stimulation of the 
 vagus and an accelerator path brings out the fact that the 
 two sets of fibers are true antagonists; the influence of 
 the one can be neutralized through the other. 
 
 This is a type of nervous organization which we find 
 again and again in the body. Antagonistic nerves are 
 almost as obvious as antagonistic muscles. Being pro- 
 
118 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 vided with such a double supply, the heart may be made 
 to beat faster through the spurring which it receives from 
 its accelerators, or a similar ciuickening of its rate may 
 represent merely a lessening of the habitual vagus inhibi- 
 tion. A slowing heart may be exhibiting the results of 
 cessation of the accelerator prodding, or the case may be 
 one of intensified inhibition. On the whole, it is held 
 that the vagus mechanism is the more important of the 
 two. 
 
 Vasomotor Control. — A prominent department of the 
 autonomic system is that devoted to the regulation of 
 local blood-flow by bringing about changes in the diameter 
 of the small arteries and veins. The blood-vessels of micro- 
 scopic size are relatively rich in muscular elements. The 
 majority of these contractile cells are placed with their 
 long axes at right angles to the course of the blood, and 
 the natural result of their contraction is to diminish the 
 bore of the vessels and to reduce the flow through them. 
 As the situation is now pictured, it is supposed that the 
 larger arteries and veins shrink and swell as the pressure 
 of the blood within falls or rises, but that the very slender 
 vessels of both classes contract and relax by virtue of 
 the living tissue contained in their walls and in response 
 to impulses sent from the central nervous system. Nerve- 
 fibers conveying impulses to the muscular coats of the 
 small blood-vessels are called vasomotor fibers. Like 
 those which end in the heart, they are of two classes. 
 
 The first kind of vasomotor fibers to be observed at 
 work were those which we now call the vasoconstrictors. 
 By this term we designate fibers by means of which a nar- 
 rowing of the vessels can be secured. They have con- 
 nections such that when they are stimulated the contrac- 
 tile elements in the walls of the arteries or veins to which 
 they extend are shortened. The "tone" of the vessels 
 in question is said to be increased. A diminished blood- 
 flow through the parts reached by the arteries or drained 
 by the veins is to be expected. Vasoconstriction is the 
 usual effect when the peripheral portion of a nerve chosen 
 
THE AUTONOMIC NERVOUS SYSTEM 119 
 
 at random is subjected to stimulation. When such a nerve 
 is cut the vessels in the field of its distribution are gener- 
 ally found to dilate; this is taken to show that a tonic 
 influence was being exerted through the vasoconstrictor 
 fibers and that this has ceased with the interruption of their 
 continuity. 
 
 We speak of a vasoconstrictor center in the medulla. 
 There is evidence that impulses are normally flowing at 
 all times from a certain region within this section of the 
 brain to hold the small blood-vessels in most parts of the 
 body in a state of contraction beyond that which is natural 
 to them. Three orders of neurons must be required to 
 accomphsh the purpose: first, those which descend from 
 the medulla to end by synapses against preganglionic 
 neurons in the cord; second, these same preganglionic 
 neurons, whose axons run to detached gangha in the sym- 
 pathetic chains or elsewhere; and third, postganghonic 
 fibers extending from the ganglia to the blood-vessels. 
 Destruction of the well-defined vasoconstrictor center in 
 the medulla results in a universal slackening of the essen- 
 tial vascular tone in the entire body. 
 
 The second variety of vasomotor fibers is not so often 
 seen 'in action. They are the vasodilators, fibers which, 
 when stimulated, cause the enlargement of the vessels and 
 so of the blood-stream in the parts to which they lead. 
 This action is an inhibition. It was first demonstrated 
 in the case of a sinall nerve known as the chorda tympani, 
 which makes a connection with one of the salivary glands. 
 Cutting the chorda tympani has little effect on the circu- 
 lation in the gland, but when the nerve is stimulated the 
 gland becomes flushed and swollen. At the same time the 
 outflow through the veins is obviously increased; it is said 
 that the blood coming away no longer shows the darkened 
 color usual to venous blood, but is as bright as the arterial. 
 The experiment has shown that in this nerve at least there 
 are fibers through which an increase of the volume of the 
 local circulation can be brought about. 
 
 There are other, though not many, examples ofvaso- 
 
120 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 dilator action on the part of particular nerves. There 
 is sufficient rcnison for the belief that in many mixed nerves 
 vasodilator fillers really accompany the vasoconstrictors, 
 but that the working of the first class is masked in our 
 ordinary laboratory trials by the greater effect of their 
 antagonists. When we stimulate a nerve we are obliged 
 to impress the stimuli upon all the fibers in it; in the Uving 
 body there is no such necessity. Under conditions spe- 
 cially devised it is possible to obtain results which lead 
 to the view that vasodilators are widely distributed and 
 bear a considerable part in the regulation of the circulation. 
 Their existence in connection with skeletal muscles, glands, 
 the skin of the face, and the tissues of the genitals is well 
 recognized. 
 
 We are, therefore, to think of the nervous sj^stem as 
 having two routes by which it can influence the beat of the 
 heart and two by which it can modify the degree of con- 
 traction of the blood-vessels. There is the possibility of 
 inhibition of the heart through the vagi and the possibil- 
 ity of inhi])iting the tone of blood-vessels through the 
 dilators. The heart can be driven to greater contractile 
 activity by means of its accelerators and the blood-vessels 
 can be contracted in a greater degree by the vasocon- 
 strictors. The correspondence is helpful, even though we 
 have to do in the one case with rhythmic, and in the other 
 with sustained, action. But it is only fair to add that in 
 the case of the heart the inhibitory mechanism appears 
 to be more important than its antagonist, while the vaso- 
 constrictors seem to have a more conspicuous influence 
 than do the vasodilators in securing the proper distribu- 
 tion of the blood. In short, the heart is most of the time 
 inhibited to some extent, while the blood-vessels are most 
 of the time definitely contracted. Their condition is such 
 that they may be contracted more, or more relaxed, as a 
 result of variations in the activity of the vasoconstrictor 
 center. 
 
 The chief value of the nervous equipment of the heart 
 must lie in making it possible to speed up the circulation 
 
THE AUTONOMIC NERVOUS SYSTEM 121 
 
 when there is a call for more oxygen and for the rapid 
 removal of wastes from the tissues. Muscular activity 
 is the occasion when this need is most urgent and when 
 the response of the heart is most striking. In a more 
 moderate degree the heart is required to maintain a more 
 active circulation after the taking of a full meal. The 
 combined effect of vigorous exercise and a recent dinner 
 probably constitutes a maximal demand upon the reserve 
 power of the heart. 
 
 Vasomotor adaptations serve to satisfy local, as con- 
 trasted with general, needs. Activity in any limited 
 portion of tissue, as in a gland or in a small group of 
 muscles, can be supported without making an appeal to 
 the heart. It is only necessary that the blood-vessels 
 leading to the active region shall be dilated so as to con- 
 duct thither a somewhat larger share than usual of the 
 total stream. This circumscribed increase in blood- 
 supply will mean a certain subtraction from the flow in 
 other directions, but if a single small gland is to be com- 
 pared with all the rest of the body we must admit that 
 the loss shared by so many organs may easily be imper- 
 ceptible in any one of them. When a relatively large 
 mass of tissue has its vessels dilated, there is often a com- 
 pensatory construction somewhere else. The foremost 
 illustration of this principle is found in the reciprocal 
 relation between the surface of the body and the deeper 
 parts. We observe that heat applied to the skin increases 
 the flow of blood through the heated area; reason and 
 experience both show that when such an increase occurs 
 the internal vessels must be less dilated than they were 
 before. 
 
 Some space may well be devoted to a discussion of the 
 effects of external temperature on the distribution of the 
 blood. When we have evidence of increased blood-content 
 in any part we say that a congestion exists. When the 
 skin is flushed as a result of being warmed, it may be said 
 to be congested, though the word is so often used of ab- 
 normal conditions that we may prefer the milder term 
 
122 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 "hyperemic." Congestions arc of two types, active and 
 passive. In both there is a local excess of blood, but in the 
 active form it is blood swiftl}' flowing through widely 
 opened vessels, while in the passive sort it is blood arrested 
 or dammed up, a state which naturally suggests a venous 
 obstruction. 
 
 The congestion produced in the skin by heat is active 
 in character. A glance at the swollen veins convinces 
 one that they are carrying a great volume of blood out of 
 the flushed region. The reaction is a serviceable one; it 
 tends to rid the body of heat, both by increasing radiation 
 and conduction from the skin and by sustaining the activ- 
 ity of the sweat-glands, which at such a time secrete much 
 water to be evaporated. If the external temperature is so 
 high that the body is cooler than its surroundings, the 
 radiation and conduction transfers may be reversed, but 
 it remains important to have an abundant circulation in 
 support of the secretion of sweat. There is at present 
 some doubt as to how far the increase of blood-flow which 
 heat produces in the skin is a reflex and how far a direct 
 effect of the high temperature. 
 
 When the skin is moderately cooled, it becomes pale, 
 the obvious sign of diminished blood-flow. This prevents 
 a wasteful loss of heat to the exterior and so conserves the 
 bodily resources. But everyone knows that more pro- 
 nounced cooling will shortly induce a reddening. How 
 does the redness produced by cold differ from that pro- 
 duced by heat? Investigation of this question is easily 
 conducted. If one hand is put into very cold water and 
 the other into water as hot as can be borne, both hands 
 will be red, but certain differences will be quickly apparent. 
 It has been said that the veins in the heated hand are 
 swollen; in the chilled hand they are small and dark. This 
 fact, taken in connection with the tendency of the cold 
 skin to become bluish, shows that the congestion produced 
 by cold is of a passive nature. Much blood is in the area, 
 but it is making only slow progress through it. The con- 
 dition is best accounted for on the theory that a marked 
 
THE AUTONOMIC NERVOUS SYSTEM 123 
 
 contraction has occurred in the microscopic veins, holding 
 back the blood in the capillaries, which accordingly swell 
 even though the arteries leading to them may be below 
 their average size at the time. (It is the amount of blood 
 in the capillaries which determines the color of the surface.) 
 
 The capacity of the vasomotor system to make appro- 
 priate responses to changes of external temperature is far 
 from equal in different subjects. What we call "vital 
 resistance" — the power to withstand exposure without 
 ill effects — must depend largely upon the extent of this 
 capacity. It is probable that the variable feature is not 
 so much in the execution of the primary reaction to weather 
 changes, as in the reliability of the secondary adjustment, 
 the promptness and vigor of the rebound to normal vaso- 
 motor conditions after a disturbance. The person who 
 quickly develops a "glow" after a cold bath is a Uving 
 demonstration of such a vasomotor resilience, and we know 
 that such a person is not likely to take cold or to be other- 
 wise upset after being caught in a shower or obliged to sit 
 in a chilly place. Still we must not fail to reckon with other 
 factors than the vasomotor when we compare susceptibili- 
 ties; there are always chemical as well as mechanical differ- 
 ences between two human bodies, and the bacteriologist 
 refers to peculiarities of chemical endowment when he 
 speaks of the superior resistance of this or that man to 
 infecting agents. It is well for us to keep both considera- 
 tions in sight. If two men fall through the ice and both 
 escape unfortunate consequences, it is entirely con- 
 ceivable that the immunity in one case may be due to 
 vasomotor reactions which guard against the persistence 
 of conditions which invite infection, and in the other to 
 specific properties of the blood. 
 
 Something should be said of the vasomotor adjustment 
 for changes in position. This is a matter often ignored 
 by the writers of physiologic text-books, but it does not 
 require much reflection to. convince one that it is of high 
 importance. The inevitable influence of gravity on the 
 blood is to add to the pressure in all vessels below the 
 
124 THE NERVOrS SYSTEM AM) ITS COXSEHVATIUN 
 
 heart and to subtract from the pressure in those above the 
 level of that organ. The actual pressui'c of the blood in 
 any vessel is the resultant of a certain quantity referable 
 to the energy of the heart-beat plus or minus a quantity 
 due to the elevation of the locality as compared with that 
 of the heart. If the body were always erect, the situation 
 might be met, one may suppose, by th(^ development of 
 thicker and less yielding walls in the vessels of the lower 
 extremities, but, in reality, there has to be provision for 
 changes from the horizontal to the upright position, and 
 even for bringing the head to occupy the lowest place. 
 
 When a man rises from his l^ed he does not normally 
 feel any distinct faintness or dizziness as he would if there 
 were a serious impairment of blood-supply to his brain. 
 Yet the tendency for the blood to forsake the higher arcs 
 of the circulation and to distend the lower ones must be a 
 very positive force. It is manifest when there is actual 
 faintness, the indi\ddual being comparatively comfortable 
 while lying down, though he may be utterly unable to sit 
 up. We have to conclude that in health the shifting of 
 the ■ blood is prevented with singular efficiency by the 
 establishment of a higher vasomotor tone in the vessels on 
 which the added pressure falls. This is one of the first 
 functions to fail when disturbing conditions arise; it is 
 the lack of this reaction which "confines one to his bed" 
 when sick. Compensation for the head-down position 
 probably never comes to be perfect. We see even in 
 acrobats of long experience the intense flushing of the 
 face when the head is hanging down, as in swinging by 
 the feet from a trapeze. 
 
 We have seen that the vasomotor system makes im- 
 portant and widespread changes in the distribution of the 
 blood under the influence of changes of the external tem- 
 perature, and that it exercises its powers to guard against 
 injurious modifications in distribution when the posture is 
 shifted. We have also stated the general principle that 
 this system dilates (or permits the relaxation of) vessels 
 at any center of unusual activity. It would be easy to 
 
THE AUTONOMIC NERVOUS SYSTEM 125 
 
 extend this discussion by including other instances of 
 vasomotor accommodation. A most interesting and sug- 
 gestive case is the reaction which accompanies sleep. 
 This and the reciprocal case of the reaction that comes 
 with fixation of attention may be left to be dealt with in 
 another chapter. 
 
 Other Autonomic Functions. — Besides regulating the 
 beat of the heart and the local blood-supply, the autonomic 
 fibers convey impulses to contractile structures not related 
 to the circulatory system. The government of the alimen- 
 tary canal is carried on by means of such paths. Here, 
 as with the heart, there is a resident automatic power in 
 the walls of the tube, and what the nervous system does 
 is to modify the intrinsic tendency to tonic, rhythmic, 
 and progressive (peristaltic) action. A long time ago, in 
 the present treatment, it was said that inhibitory rather 
 than excitatory influences are the rule in this department 
 of nervous control. It will be convenient to discuss the 
 extent of autonomic government of the digestive tract 
 when we come to the abnormalities observed in the 
 neurasthenic. Autonomic impulses to the bladder and 
 reproductive organs are apt to be excitatory, though here 
 again the double possibihty of reinforcement and inhibi- 
 tion remains. 
 
 A division of the autonomic system which is of minor 
 significance, but interesting because it is curious, is the 
 pilomotor part. Under this head we include the fibers 
 which go to the scattering development of plain muscle 
 found in the skin. The contractile elements so placed are 
 attached to hairs which may be rudimentary and scarcely 
 noticeable. When the muscle-cells contract under nervous 
 influence, either erection of the hairs or the risings of the 
 skin known as "goose-flesh" may be caused. Occasions 
 on which the hair "stands on end" are apparently rare in 
 human experience, but they are common enough in the 
 life of the cat. This animal has an excellent pilomotor 
 system. 
 
 Of more importance is glandular control. The auto- 
 
120 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 nomic system includes nerve-paths of the standard type 
 (prcsanjiUonic and postgangUonic fibers) to many organs 
 of secretion. This is conspicuously the case with the 
 sweat-glands. It is true, too, of the tear-glands, the sali- 
 vary glands, and those in the lining of the stomach. It is 
 certainly true of the adrenal bodies and probably of the 
 pancreas. There is less certainty regarding a direct 
 nervous control of the intestinal glands, the liver, and the 
 kidney's. When glands are active it is to be expected that 
 vasomotor support will be given to them through the wide 
 dilation of their blood-vessels. But the kind of nervous 
 control of which we are now speaking is believed to be 
 exerted upon the epitheUal cells forming and cUscharging 
 the product. Typic secretory activity may be promoted 
 in two waj^s by the autonomic system: by this direct 
 stimulation of the working cells of the gland and, indi- 
 rectly, by the enlisting of the vasomotors to secure a freer 
 circulation. In some glands — for example, the kidney — 
 it is the volume of the blood-fiow on which the performance 
 of the gland chiefly depends. When this is the case it be- 
 comes difficult to decide whether government of the other 
 order, that is, by true secretory fibers, surely exists. 
 
CHAPTER X 
 THE CEREBRUM 
 
 A STUDY of comparative anatomy shows that, on the 
 whole, there is a gradation in the development of the 
 cerebrum which corresponds fairly well with the degree of 
 intelligence and the variety of reaction which different 
 animals exhibit. In the brain of man this division reaches 
 its most conspicuous rank. For at least a hundred years 
 the correlation of intelligence with the cerebral evolution 
 and especially with the extent of the cortex has been 
 universally accepted. It is said that only two animals 
 have cerebral hemispheres more massive than those of 
 man. These are the elephant and the whale; in both, 
 the great size of the body removes the brain from any 
 comparison with that of man. In fact, the brain of the 
 whale is relatively small. 
 
 Starling says that in proportion as the cerebrum be- 
 comes prominent, the possibility of predicting what re- 
 sponse will follow the giving of a certain stimulus dimin- 
 ishes. The animal is less and less machine-like. This is 
 closely connected with the fact that two animals of the 
 same species can show individual traits to an extent which 
 is determined by the importance assumed by the cerebrum 
 in the reactions of that species. One rabbit does not differ 
 in very many respects from another; two cats are quite 
 unlike and may be said to have character or personality. 
 In Chapter III the point was made that the higher type 
 of nervous system is that in which individual as well as 
 racial acquisitions are stored. We may now add that 
 such storage is the particular — though perhaps not the 
 exclusive — work of the cerebrum. 
 
 If two persons could exchange their spinal cords, 
 both being in good health, it does not appear that the 
 
 X27 
 
r_*8 Till-: .NKRvurs system axd its coxservatiox 
 
 exchange would be attended by any remarkable gain or 
 loss to cither. The slight and liniit(>d spinal reflexes would 
 not be likely to be at all strange or unfamiliar to the new 
 possessors of the transferred equipnuMit. If each could 
 now take for his own the medulla of his fellow, he might 
 notice a certain strangeness in his reactions. Vasomotor 
 idiosyncrasies might be realized. The heart might alter 
 its average rate. Experience might reveal changes in the 
 capacity of the digestive system under new central 
 government. Now, if the cerebellum were also to be 
 carried over from A to B and the corresponding part 
 removed from B and given to A, the results would prob- 
 ably be much more positive. Peculiarities of gait, accom- 
 plishments or shortcomings in the line of equilibration, 
 skill in dancing or swimming — any of these might go with 
 one cerebellum to the new owner. 
 
 The paragraph above suggests what is undoubtedly 
 true of man, that some acquisitions are registered in the 
 cerebellum if not lower down in the nervous system. But 
 when all allowance has been made for this we feel sure 
 that the man who had surrendered his spinal cord, his 
 medulla, and his cerebellum to another, receiving alien 
 structures in their stead, would still be essentially him- 
 self. One almost shrinks from contemplating the imagin- 
 ary exchange of one cerebrum for another. To do this 
 must be in a most literal sense to "give one's self away." 
 So far as we can see, the stock of memories and associa- 
 tions which A regarded as exclusively his would begin to 
 determine the behavior of the organism still wearing the 
 outward appearance of B. 
 
 This fabulous presentation merely enforces the conten- 
 tion of Loeb that the cerebrum is the chief organ of asso- 
 ciative memory.^ Animals in which it is not much de- 
 veloped have little capacity to learn anything by expe- 
 rience. In proportion as it becomes dominant in the 
 nervous system, memory becomes the basis of action 
 
 * "Comparative Physiology of the Brain" (in Science Series), 
 New York, 1900. 
 
THE CEREBRUM 129 
 
 and individuality becomes inevitable. Memory is used 
 in two senses. Speaking subjectively, we use it to mean 
 conscious recollection. We can use it in a purely objec- 
 tive way to mean no more than the modification of 
 reactions resulting from individual contacts with the 
 environment. When we say that "the burnt child dreads 
 the fire" we usually mean that the child recalls with dis- 
 tress an unfortunate occurrence in its past. But the con- 
 dition can be indicated in quite another way. We may say 
 that the nervous system of the child has been so altered 
 by a past impression upon it that it will cause the child 
 to draw back from the fire. A type of action is impHed 
 which is essentially reflex. 
 
 The boy, like the moth, may be attracted by the flame 
 until the negative reaction has been established; the 
 difference between the two nervous systems compared 
 lies to a great extent in the capacity of the higher one to 
 be modified by use, the lower one persisting in its heredi- 
 tary response regardless of consequences. The burnt 
 moth probably does not "dread the fire" in either the 
 psychologic or the physiologic sense. The contrast set 
 forth is that between a system without any part closely 
 corresponding to a cerebrum and one in which this de- 
 partment is dominant. 
 
 The general conception outlined is justified by the 
 results of experiments in which animals of various kinds 
 are deprived of their cerebral hemispheres and kept alive 
 for observation. The consequences of the loss are grave 
 just in proportion to the part played by individual ex- 
 perience in the government of the organism. Most fishes 
 survive the operation with no clear sign of deficiency. 
 When this is not strictly true it is because the particular 
 fish studied has been one which was regulated in its move- 
 ments by the impulses derived from the organ of smell. 
 It must not be forgotten that this sense organ and no 
 other is detached from the remainder of the nervous 
 system when the cerebrum is destroyed. It is said that 
 sharks, which have been made "decerebrate," as the term 
 
130 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 goes, are very sluggish. But this docs not mean that they 
 were greatly dependent upon the organization of the 
 cerebrum; they can be just as seriousl}'- ai'fccted if their 
 olfactory receptors are destroyed, the cerebrum remain- 
 ing intact. 
 
 A frog is regarded as a higlier animal than a fish. A 
 decerebrate frog, however, departs so slightly from a 
 normal one as to force us to conclude that here, as in the 
 fish, the cerebrum has no important influence on the be- 
 havior of the animal under the ordinary conditions of 
 life. It is commonly stated, however, that there are real 
 points of difference between normal and decerebrate frogs. 
 The latter are entirelj^ able to swim and hop, but they 
 will not save themselves from death in a pan of water 
 when it is slowly warmed.^ 
 
 The classic instance of the profound effects following the 
 removal of the cerebrum from an animal of high grade 
 was afforded by the experiments of Flourens, in France, 
 early in the nineteenth century. He subjected pigeons 
 to the operation, which is rather a simple one to perform 
 upon the bird. The descriptions which he gave have 
 been modified by modern students to make allowance for 
 the well-marked recovery of pigeons from the immediate 
 shock of the procedure. In this case, as in that of the 
 cerebellum, it is only the lasting consequences of the loss 
 that we have a right to emphasize. Observers have not 
 been wholly agreed concerning the nature of the deficiency 
 in all its details, but it seems safe to say that a pigeon 
 without a cerebrum gives no further sign of memory or 
 feeling. 
 
 To see such a pigeon is an instructive experience, and 
 especially when the spectator takes account of his own 
 emotional reaction. He is hkely to anticipate that he 
 
 1 Burnett (American Journal of Physiology, 1912, xxx, 80) has 
 observed that decerebrate frogs definitely lack the power shown by 
 the intact animals to become "used to" certain pathways. A trace 
 of adaptation on the part of individuals to their surroundings seems, 
 therefore, to be represented in the cerebral equipment of these 
 animals. 
 
THE CEREBRUM 131 
 
 will feel pity for the mutilated animal. Instead, he cannot 
 watch it long without finding it amusing. He becomes 
 convinced that it is not a sensitive and suffering creature, 
 but an elaborate mechanical toy. It adjusts itself to 
 external conditions with great success so far as the imme- 
 diate exigency is concerned, but with no anticipation of 
 the future nor reminiscence of the past. In default of 
 stimulation it is relatively inert. It is customary to say 
 that it does nothing spontaneously. The word, however, 
 is a vague one and may well be avoided. An action is 
 called "spontaneous" when we cannot tell how it was 
 caused. Some actions of the decerebrate bird may be 
 placed in this class. 
 
 A pigeon without a cerebrum can be kept alive for 
 weeks, but only by constant care. It will not find food 
 or water for itself, though they may be placed in its cage. 
 In flying and walking it passes around obstacles, but all 
 the evidence goes to show that there is no appreciation 
 of the objects in its path. Another pigeon exists for it 
 simply as a mass of matter, with no more power to stimu- 
 late than a block of wood. The former mate or the young 
 bird appealing for food — these are treated merely as 
 things with which a coUision is to be avoided. It is 
 clear that the eyes serve well to regulate locomotion with 
 reference to the surroundings, but they are deprived of 
 the power to cause any reaction based upon the indi- 
 vidual experience of the bird. 
 
 Detailed accounts of the behavior of the decerebrate 
 pigoen may be found in larger works and they are full of 
 interest. The main points to be insisted on are (1) that 
 the muscular capabilities of the bird remain little im- 
 paired in the absence of the cerebrum, and (2) that these 
 muscular activities no longer signify that memories 
 connected with the past hfe of the pigeon are aroused. 
 It is probably fair to claim that the word ''memory" in 
 this statement can be used either in its subjective or ob- 
 jective sense. Moreover, it is not only the previous accu- 
 mulation which is destroyed, but also the possibihty of ac- 
 
132 THE NERVOUS SYSTEM AND ITS CONSIORVATION 
 
 quiring new impressions wliich can furnish grounds of 
 conduct. 
 
 The removal of tiie cerebrum from a mannnal without 
 causing the immediate death of the animal might well 
 seem an incredible feat of surgery. Nevertheless, it has 
 succeeded in a number of cases. The most celebrated 
 of these has been the one which is referred to as Goltz's 
 dog. By three carefully conducted operations the entire 
 mass of the cerebral hemispheres and, unintentionally, 
 somewhat more of the brain was broken up and washed 
 away. The dog was kept alive and narrowly observed 
 for a j^ear and a half after the final operation. It was 
 then killed and the autopsy showed the thoroughness of 
 the destruction. Its health and strength had been de- 
 clining for some time before it was sacrificed. 
 
 The decerebrate dog afforded a general confirmation of 
 the inferences drawn from the pigeon. It was idiotic, 
 but not crippled in any department of its mechanical 
 activities. A noteworthy fact was that it was restless 
 rather than sluggish. Its aimless rovings supported the 
 opinion quite widely held that an important function of 
 the cerebrum is to inhibit the action of the lower brain 
 centers. Sometimes the dog appeared to sleep, but, if 
 we are right in our interpretation, its waking was not to 
 consciousness, but only to somnambulism. It showed no 
 fear or affection. It would snap at the hand of a tor- 
 mentor, but only under the direct stimulus of provocation; 
 it would not harbor a grudge against him. 
 
 Concerning the human being, of course we do not have 
 evidence from deliberate experiment, but we have the 
 facts in a vast number of clinical cases. A surprising and 
 instructive one has been reported quite recently. Edinger 
 and Fischer^ have described the condition of a defective 
 child that died of tuberculosis when nearly four years old. 
 It had made no appreciable progress in acquiring new 
 reactions from the day of its birth. It usually lay in 
 apparent sleep, seemed to be blind, and could not be said 
 ' Archiv f. d. ges. Physiologie, 1913, clii, 535. 
 
THE CEREBKUM 133 
 
 to show any token of consciousness. The postmortem 
 examination showed entire lack of the cerebral hemi- 
 spheres. 
 
 When we compare this shocking instance with the case 
 of the dog or the pigeon, we are led to believe that the 
 human cerebrum is of such overwhelming dominance that 
 many functions which in the lower animals can be sub- 
 served by other parts of the brain have been largely trans- 
 ferred to it. In man it is probable that the subordinate 
 centers for the eyes are incapable of any extensive or 
 useful reaction when their cerebral connections are severed. 
 It is not likely that the power to balance and to walk 
 could be preserved in man as in the dog through the 
 agency of the midbrain, cerebellum, and medulla without 
 the cerebrum. To be sure, the decerebrate child had 
 never learned to walk, and it might be urged that the 
 cerebrum might be essential for the attentive act of learn- 
 ing and not for exercising the power when acquired. But 
 we have many other cases in which the ability to walk 
 was lost when only a limited part of the cerebrum had 
 suffered injury. 
 
 In apes, which approach the human type of organization, 
 the loss of a restricted region from the cerebrum is said to 
 lead to absolute blindness so far as can be determined. 
 The power to avoid obstacles, so striking in the dog and 
 the pigeon, entirely disappears. In all probabihty, a 
 decerebrate human being would be deaf, despite the fact 
 that the auditory nerve would retain its connection with 
 the medulla and so with the remainder of the nervous 
 system. Pigeons without the cerebrum respond to cer- 
 tain sounds by sluggish movements. 
 
 Granting, as we must, that the cerebrum is essential to 
 intelligence and to all action based upon individual ex- 
 perience, we are at once led to inquire wiiether it is all 
 alike or whether particular parts have particular func- 
 tions. In other words, is there cerebral localization of a 
 definite character? This question was asked by Flourens 
 long ago, and he attempted to answer it on the basis of 
 
134 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 further experiments on pigeons. He came to believe that 
 one part is like anothcM- and that the result of an injury 
 is detorniined by its extent and not by its position. Speak- 
 ing somewhat crudely, it may be said that this view made 
 the working of the brain comparable with that of the 
 Uver: all its parts were supposed to be working in the 
 same way and all its functions would suffer — quanti- 
 tatively rather than qualitatively — from a circumscribed 
 injury. 
 
 From the time of Flourens to the present scientific 
 opinion has shifted back and forth in a curious manner. 
 In his own career he found himself called upon to defend 
 his claims against a school of ingenious persons who 
 upheld the doctrine of a very precise locaUzation of 
 cerebral properties. This teaching was presentl}^ known as 
 phrenology^ and attracted much notice. In the beginning 
 the phrenologists were sincere in purpose and more or 
 less scientific in method. Their successors departed 
 widely from the early traditions of the school, and are now 
 found in the purlieus of our cities along with palmists and 
 clairvoyants. The general conception was beginning to 
 be discredited when Holmes^ wrote of it so incisively. 
 Regarding the claim that it is possible to tell what is 
 within the skull by measuring its slight convexities and 
 depressions, he well said that this was like laying one's 
 finger on the iron wall of a safe and saying: "Under this 
 spot lies a ten-dollar bill." 
 
 Francis Joseph Gall, the Austrian founder of phrenology, 
 seems to have had little interest in the l^rain as related to 
 the body, but much in its assumed correlation with men- 
 tal endowments and defects. He and his disciple's made 
 careful measurements of the contours of the head in all 
 types of men, from the most gifted to the most defective 
 and depraved. A prominence upon the surface of the 
 
 ' The article "Phrenology" in the Encj'clopedia Britannica can be 
 recommendod. 
 
 2 "The Professor at the Breakfast Table," Riverside Edition, 
 19O-200. 
 
THE CEREBRUM 135 
 
 skull was supposed to indicate an extra cerebral develop- 
 ment beneath, and if a special merit or failing coexisted 
 in the individual the notable feature of the brain was held 
 to be responsible for it. This summary statement is 
 scarcely just to the pioneers in phrenology, for they did 
 not commit themselves until they had a great mass of 
 data. They pubhshed large books, conducted periodicals, 
 and even had museums in which the comparative study of 
 human skulls was carried on. 
 
 A cursory glance at their later writings shows how dis- 
 ingenuous they became. They showed an unrivaled skill 
 in getting around difficulties. A certain protuberance 
 was held to indicate a certain propensity, but its occa- 
 sional absence from a subject in whom that propensity 
 was well marked did not cause them any trouble. In 
 such a case they said that the subdivision of the brain 
 under discussion had been worn down by excessive 
 activity. This would seem to require a plasticity of the 
 cranial bones beyond that commonly observed. When 
 external measurements were made upon the forehead it 
 was somewhat hard to allow for the variable extent of 
 the frontal sinuses, cavities which occur in that bone, 
 but they did not fret themselves about that. 
 
 Phrenology lost the respect of conscientious men of 
 science before the middle of the century. The prevalent 
 feeling was one of skepticism regarding all claims for 
 localization of function in the cerebrum. When, after an 
 interval, new ideas concerning the connection of particular 
 properties with particular regions began to be advanced, 
 it was in a totally different spirit from that of the old 
 teachings. The new localization was of the control of 
 bodily functions and only guardedly extended to the 
 problems of the mental hfe. The return to the behef 
 that the cerebrum is not all ahke may be said to date 
 from 1870. It made headway rapidly for about twenty- 
 five years and has been followed by another reaction, so 
 that present-day writing on the subject is cautious and 
 conservative. 
 
130 THK XKliVorS SYSTEM AND ITS COXSKRVATION 
 
 The perforinances of the cerebral cortex luive been 
 likened to those of an orclu^stra. The comparison would 
 have been acceptable either to an old-fashioned phrenol- 
 ogist or to a believer in the diffuse distribution of brain 
 activity. A series of solos by different instruments 
 would symbolize the phrenologic conception; a harmoni- 
 ous production of music by many or all the players would 
 represent the other interpretation. Local injury, accord- 
 ing to the first view, would be the silencing of a solo 
 instrument and would cause intervals of stillness in the 
 symphony. If the second view were found to ])e correct, 
 the local damage would not result in absolute interruption 
 of the music, but only in lessening its volume and rich- 
 ness. 
 
 It is difficult to say exactly what is meant by "cerebral 
 localization." In all probability, the term does not mean 
 the same to different people who use it. It would seem 
 that to some it has meant that definite regions of the 
 cortex are in receipt of certain impressions, and can, at a 
 later time, give rise to impulses determined by these 
 stored impressions. Descartes must have had some such 
 an idea as this when he likened the retention of memories 
 to the imprint of a seal upon wax. Quite another view 
 is possible, and, indeed, it is the preferred one at the 
 present time. This is the conception that a given func- 
 tion appears to be connected with a given area simply 
 because so many of the paths necessary to that function 
 he -within the patch of cortex in question. 
 
 To appreciate the modern interpretation of the working 
 of the cerebrum it is necessary to keep always before one 
 the reflex principle. We readily apply this principle to 
 the spinal cord. Impulses flow in and, in consequence, 
 others are sent out. It is not difficult to extend this to 
 the medulla, the midbrain, and the cerebellum; the chief 
 difference between the responses from these parts and 
 from the cord Hes in the greater length of the pathways 
 pursued by the impulses, the greater numl)er of synapses 
 crossed, and the increased capacity for variation. When 
 
THE CEREBRUM 137 
 
 we consider the cerebrum we are too apt to assume that 
 conditions there differ radically from those at lower 
 stations. We cannot ignore the relation of the cerebral 
 structures to our consciousness, but we shall escape much 
 confusion if we hold fast so far as we may to the reflex 
 arc as the fundamental fact in the organization. 
 
 Impulses enter the cerebral cortex from the afferent 
 division of the nervous system as they enter other parts 
 of the gray matter. Only here the direction which may 
 be given to these impulses is far less certain than in the 
 lower central complexes. The net of pathways has that 
 individual character which has been emphasized, and be- 
 cause of this no two cerebral cortices can react in just the 
 same manner. The great number of simultaneous proc- 
 esses going on in the cerebrum results in apparent col- 
 lisions and interferences which make it still harder to 
 predict the effect produced by a stimulus — be it sight, 
 sound, or other external influence. Finally, a most im- 
 portant fact about cerebral reaction is the indefinitely 
 long time that may elapse between the stimulus and the 
 expressed result. A condition which operated on the 
 cortex at a certain time may seem to have been wholly 
 ineffective, but it may modify the reaction to another 
 stimulus much later. A bit of information which was 
 read with indifference and apparently forgotten may 
 shape one's course of conduct in a future emergency. 
 
 It is held by some, among others by Morton Prince, that 
 nothing is ever forgotten. Diflftculties and limitations in 
 the way of recollecting must be admitted, but it remains 
 probable that every impression made upon the cortical 
 organization is a permanent one. Every stimulus modi- 
 fies the cortical structure in some degree, and it is forever 
 unlike what it would have been if that stimulus had never 
 been applied to the receptors. The psychologic corollary 
 is that we are likely to recall under particular conditions 
 anything that we have ever heard, read, or witnessed. 
 The difficulty is to control the ''conditions" referred to. 
 The images from the distant past, often of very trivial 
 
138 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 objects and situations, which arise in our dreams favor the 
 beUef of Prince. 
 
 We must now attempt to connect the view that the 
 cortical reactions are essentially reflexes, though often 
 delayed and modified by many factors, with mod(M-n 
 doctrines of localization. A brief discussion of the "motor 
 areas" will be in order. It was discovered in 1870 by 
 German investigators that electric stinmlation applied 
 to the corebral cortex of the dog at certain, definite places 
 
 Fig. 22. — The human cerpbrum is sketched from the left side. 
 The crosses are sprinkled on the area from wliicli the muscles of the 
 right half of the body appear to be governed. This area extends out 
 of sight over the top of the brain and dips into the fissure between 
 the two hemispheres. 
 
 calls into play the muscles of the body in a manner which 
 can be predicted. The muscles thrown into contraction 
 are for the most part on the opposite side of the body. 
 In the ape motor areas exist in the same sense: excitation 
 of the cortical neurons at certain spots leads regularly to 
 movements made by corresponding groups of muscles. 
 It is known that the same representation of the muscular 
 system in mosaic form can be demonstrated on the surface 
 of the cerebrum in man (Fig. 22). These areas are evi- 
 
THE CEREBRUM 139 
 
 dently unlike each other and unlike the neighboring areas 
 from which electric stimulation elicits no visible reaction. 
 They are believed to contain the perikarya, from which 
 motor projection fibers extend downward to make synaptic 
 connections with neurons which directly innervate the 
 muscles. 
 
 But in our discussion of fatigue we have insisted that 
 the perikarya at the origin of any set of projection fibers 
 cannot be regarded as the ultimate source of the impulses 
 which traverse these fibers. By losing sight of this fact 
 many writers have probably made too much of the cere- 
 bral motor areas. They have been spoken of as though 
 they were creative in function or as though they were 
 certainly the precise spots where the metaphj'sical force 
 impinged upon the material mechanism. Loeb protested 
 against such naive views and presented the alternative 
 with great clearness in his "Comparative Physiology of 
 the Brain." 
 
 Activity in the motor areas doubtless precedes most of 
 our muscular activity. But what takes place in the 
 motor areas is the result of currents arriving within their 
 boundaries from other parts of the brain. So the re- 
 responsibility is shifted to these other regions, and from 
 these again to others. The true fountain-head is not 
 found in the cerebrum at all, but in the receptors of the 
 afferent system or in the energies of the external world. 
 When this is said we merely reiterate the statement that 
 the type of nervous action is the reflex, and that we cannot 
 make an exception of those processes which are directed 
 through the cerebrum. "Through" rather than "by" 
 is the preposition, and the distinction is of the greatest 
 importance. 
 
 The central exchange of the telephone system is an 
 impressive example of intricate mechanism, but it is, after 
 all, an intermediate point, and its function is to give di- 
 rection rather than to originate communications. More 
 damage can be done to the whole system by destroying 
 the exchange than by attacking sniy other single feature, 
 
140 THE iNEKVOUS SYSTEM AND ITS COXSEUVATION 
 
 but it is eviileut tliat cuttiiifi; all the wires at various 
 places would have the same crippling etiect. This is a 
 fair analogy to help one to understand the present con- 
 ception of the cortical centers. They are not believed to 
 originate impulses, excepting as impulses come to them; 
 their peculiarity is found in the fact that in them a vast 
 number of neural arcs of correlated function are brought 
 so close together as to be readil.y subjected either to 
 stimulation or to damage. 
 
 This may be maintained as well for other areas of the 
 brain as for the motor regions. For example, certain 
 portions of the cortex at the back of the cerebrum, par- 
 ticularly where the surface of each hemisphere is infolded 
 and lies against the surface of its fellow, are held to be 
 visual centers. It is reported that injury to these fields 
 impairs the usefulness of the eyes and, if sufficiently ex- 
 tensive, causes complete loss of sight. These are regions 
 which visual impulses enter after having been relayed by 
 the midbrain structures, and they are regions from which 
 impulses are normally sent away to other parts of the 
 brain so that other actions may be modified as a result of 
 the inflow from the eyes. To destroy such areas (on both 
 sides) is to destroy useful vision, but it is really a system 
 of pathways which has been interrupted and not a reposi- 
 tory of visual impressions. 
 
 If we reduce all the activities of the cerebrum to elabo- 
 rated reflexes and, as such, demand for them external 
 causation, immediate or past, what becomes of freedom 
 of the will? This is a troublesome and unwelcome 
 question which different thinkers have answered in 
 different fashion. It may be thought to lie outside the 
 proper sphere of the physiologist, but it confronts him 
 when he becomes a teacher of hygiene. It haunts every 
 man of science, as it has haunted theologians and philos- 
 ophers of all ages. Many have been brought to the essen- 
 tial position of Jonathan Edwards, which was, in brief, 
 the view that we are free to do what we will, but not to 
 will what we shall do. Candid scientists often admit 
 
THE CEREBRUM 141 
 
 with Miinsterbergi that one must alternate between two 
 views without seeking to reconcile them; as an investigator 
 one must look for material causes, but for the sake of 
 moral power and conviction one must hold fast the behef 
 in free agency, which has always commended itself to 
 the men who have done most for the world. 
 
 Another assertion of Miinsterberg may be quoted at 
 this point. Many writers constantly refer to the "sub- 
 conscious mind" in their discussions of brain activity. 
 Is it not better, asks the psychologist, to reserve the 
 word "mind" for that which is conscious? Phyvsiologists 
 will certainly agree to this; most of the action of the ner- 
 vous system is subconscious, but nothing would seem to 
 be gained by caUing such action mental. 
 
 1 "Psychotherapy," Moffat, Yard & Co., New York, 1909, chap. iii. 
 
CHAPTER XI 
 
 THE CEREBRUM AND HUMAN DEVELOPMENT 
 
 The motor areas of the cerebral cortex were first 
 demonstrated by experiments upon the dog, and hiter 
 shown to exist in the brain of the ape. In the cerebrum 
 of man they are known to occupy a similar position and 
 to have the same properties. This is to say, that when 
 points within them are electrically excited, movements 
 result, and chiefly on the part of muscles on the opposite 
 side of the body. The subdivisions of the general motor 
 area are permanent in the sense that the same group of 
 muscles always responds when a selected spot is stimu- 
 lated. The areas are better developed in man than in 
 the ape, and better in the ape than in the dog or the cat. 
 This is in harmony with the fact that muscular move- 
 ments in the lower animals are largely governed by means 
 of reflex arcs that do not ascend into the cerebrum. It 
 follows naturally that injury to the motor regions in man 
 results in irreparable interference with muscular move- 
 ments, though we have seen that in the dog the entire 
 cerebrum may be destroyed and the power of locomotion 
 remain. 
 
 It may seem strange that the existence of motor areas 
 should have been proved for the human brain. The facts 
 are as follows: In certain types of epilepsy it was noted 
 long ago that each attack is ushered in by an invariable 
 initial movement. The closing of one fist or the drawing 
 of the lips toward one side may give a reliable warning 
 of the approaching convulsion. When it became known 
 that definite motor areas occur in the brain of the ape, 
 the surgeons conjectured that homologous areas might 
 be assumed to have their place in the brain of man, and 
 
 142 
 
THE CEREBRUM AND HUMAN DEVELOPMENT 143 
 
 that such cases of epilepsy as those referred to might be 
 due to mechanical sources of irritation acting at the 
 subcenter for that part which was first moved at each 
 seizure. In the course of time operations for the relief 
 of epilepsy were undertaken. Acting on the theory that 
 the brain of man is similar in its large features to that of 
 the ape, the surgeons plotted in advance the presumptive 
 position of the motor areas in general, and of that one in 
 particular which was thought to be subject to abnormal 
 stimulation. In very many cases the spot of cortex which 
 they proceeded to expose was found to be under obvious 
 pressure or otherwise affected by pathologic conditions. 
 A measure of relief from the epileptic symptoms followed 
 such operations, though complete cures were not usual. 
 
 When the surface of the human brain has been laid bare 
 for these operations it has been possible to apply weak 
 electric stimuli to its convolutions, and the movements 
 made by the skeletal muscles of the subject have justified 
 the belief that the organization here is, indeed, closely 
 similar to that in the ape. Microscopic study supports 
 this view. A conspicuous system of projection fibers can 
 be traced from the supposed motor regions inward through 
 the internal white matter of the cerebrum and thence 
 down the brain-stem. In the medulla the great majority 
 of these fibers cross the midline and pass down the cord on 
 the side opposite to that of their origin. They form 
 synapses with motor cells of the cord and so command 
 the muscles. 
 
 The impression prevails that a portion of the cortex just 
 posterior to the motor areas has as a distinctive property 
 the reception of afferent impulses from various parts of the 
 body. It must be remembered that . incoming impulses 
 from without the central nervous system never find an 
 uninterrupted path to this level; the original neurons do 
 not pass above the medulla, if, as a matter of fact, they 
 extend so far. It is by synaptic relays that transmission to 
 the cerebral cortex is secured. If we adopt the usual 
 conception of the cortical centers, these areas of reception 
 
144 THE NERVOUS SYSTEM AND ITS CONSKI{VATION 
 
 are significant cliiefly as they forward impulses to other 
 places. As Loel) has said, this is a dynamic rather than a 
 static form of localization. As this is true of the sensory 
 impulses from the body at large, so it is prol)ably true for 
 the more highly developed sense organs, such as the eye 
 and the ear. 
 
 In the brain of man, as in that of the monkey, the visual 
 impulses — or, rather, the impulses of visual origin — are 
 projected to the hinder part of the cortex and, chiefly, to 
 the area called the cuneus. This is a distinctly marked 
 triangle set off by fissures upon the surface of the occipital 
 lobe which confronts the corresponding area of the opposite 
 side. As the relation between the cerebrum and the skele- 
 tal muscles is so largely a crossed or contralateral one, the 
 inference might easily he drawn that the impulses from 
 the right eye would be found to arrive in the cortex of the 
 left side, but in the human organism this is not so. The 
 relationship is less simple. Approximately half of each 
 eye has efficient connections with the cerebral cortex on 
 the same side. An able teacher has Hkened the situation 
 to that of a driver with a pair of horses. His right hand 
 holds the reins which connect with the right side of ])oth 
 the bits; his left hand is joined through the reins with the 
 left side of both. Carrying this comparison over to the 
 visual apparatus, it reads like this: the right occipital 
 cortex is functionally related with the right halves of 
 both the retinae; the left cortex, with the left halves. 
 
 The general statement just made requires a quaUfica- 
 tion in view of a very interesting fact. There is in the 
 center of each retina a restricted region, the fovea, which 
 has superior visual possibiUties. (When we speak of fix- 
 ing the eye on an object we mean fixing the image of the 
 object upon the fovea.) This part of the retina is beheved 
 to have a double representation on the cortex — both 
 eyes projecting impulses to both sides of the brain. 
 Thus, no injury confined to one side of the brain can be 
 expected to destroy the use of either fovea. It can blot 
 out nearly, but not quite, half of the field of vision. The 
 
THE CEREBRUM AND HUMAN DEVELOPMENT 145 
 
 "central vision," which is of the foremost importance, is 
 bound to survive, thanks to the reduphcated projection in 
 the cortex. 
 
 The auditory path leads first to the medulla and thence, 
 by repeated relays, to the cerebrum. The best marked 
 projection of the impulses from the organ of hearing is 
 
 Fig. 23. — The upper figure represents the left hemisphere from 
 outside, that is, from the left. The lower figure shows the internal 
 or mesial aspect of the right hemisphere, that is, the right hemisphere 
 from the left side. Areas usually claimed to possess special relations 
 are marked as follows: H, hearing; V, vision; Sm, smell; Sp, speech. 
 
 upon the cortex of the temporal lobe, and damage to this 
 part has often caused deafness. The effect is to impair 
 more considerably the reactions from the opposite ear, 
 though some hmitation is imposed upon the usefulness of 
 the ear of the same side. An area for the reception of im- 
 pulses of olfactory origin is said to be well set off. It 
 
 10 
 
l4(3 THE NERVOUS SYSTKM A\D ITS CONSEin'ATION 
 
 is not far fruin tlic place of entrance of the olfactory fibers 
 into the lower surface of the cerebral mass (Fig. 23). 
 
 While these several regions of the cerebral cortex have 
 been mentioned with especial reference to man, Uttle has 
 been said so far that would not apply as well to the more 
 highly developed animals. It is a question of great 
 moment whether there are to be discovered in the brain 
 clear and well-localized signs of human eminence. As to 
 the answer to this question, there is, unhappily, a great 
 deal of disagreement. Fifteen or twenty years ago the 
 average writer would have felt warranted in more posi- 
 tive assertions than it is usual to make at the present 
 time. But in spite of conservative tendencies there 
 are some teachings which retain weight for most physiol- 
 ogists. The first and most sweeping of these is that the 
 developments in brain organization which correspond with 
 intellectual advance are one sided rather than symmetric. 
 
 Early metaphysicians, like Descartes, were troubled by 
 the dual form of the brain. So long as they emphasized 
 its connection with mind instead of body, such a double 
 character seemed unreasonable. As soon as men began 
 to view the brain in its relations with the paired muscles 
 and sense organs of the body, its division into right and 
 left halves appeared justified. But the desire to find in 
 it some basis for a unity closer than that of two equal 
 and cooperating halves was bound to rise again. Most 
 investigators think that it has been fulfilled in the prob- 
 able fact that one of the hemispheres is dominant and the 
 other subordinate, so far as truly intelligent activities are 
 concerned. 
 
 Most people are right handed. This means that the 
 motor area on the left side of the brain has a superior 
 organization. By this we now understand a superior 
 richness of connections, association tics with other regions 
 of the hemisphere. The majority of physiologists will 
 probably go so far as to say that the machinery of intel- 
 ligence lies more in the left than in the right half of the 
 cerel^rum in right-handed individuals. It is supposed that 
 
THE CEREBRUM AND HUMAN DEVELOl'MENT 147 
 
 in the left handed the balance is reversed : the right hemi- 
 sphere is the dominant one. The most interesting claims 
 made in support of such views have reference to the repre- 
 sentation of language in the human brain. 
 
 The brain of an ilUterate man is organized in such a way 
 that oral expression of thought is possible and that the 
 speech of others is comprehended. The educated man 
 has, in addition, an equipment that makes possible the 
 expression of thought in writing and its appreciation 
 through reading. The answering of a question is an act 
 of the reflex type, but one which requires for its execution 
 the fullest development of brain paths. The manner of 
 its accomplishment must depend upon innumerable past 
 events. The destruction of certain connections might be 
 expected to render it impossible to reply to the question. 
 This is a state of things quite often realized. Brain disease 
 is often signahzed by disorders in the field of language. 
 .Such disorders are not sharply distinguished one from 
 another, but the attempt is often made to classify them 
 under several heads. In general, it may be said that the 
 power to understand and to reproduce language is asso- 
 ciated with connections made through the cortex of the 
 left hemisphere excepting in left-handed subjects. 
 
 Long ago it was noted that in cases where there had been 
 loss of intelligent speech during life a certain limited area 
 in the left frontal region was often found abnormal on 
 postmortem examination. This area became known as 
 the speech center, and the interference with speech re- 
 sulting from its impairment was named motor aphasia. 
 The reputed center is probably a place within which many 
 of the arcs which are necessary for vocal expression of ideas 
 are brought close together. Motor aphasia is not an 
 actual paralysis of the muscle groups required for speech. 
 The use of the same parts for other purposes, such as 
 swallowing, coughing, and even for voice production, 
 when this is not strictly intelligent, may remain quite 
 unimpaired. 
 
 The distinction between the intelligent and the merely 
 
148 THE NERVOUS SYSTEM AxND ITS CONSERVATION 
 
 mechanical employment of the vocal organs may be illus- 
 trated b}^ one of the many curious stories told of persons 
 witii aphasia. A man who suffered from an injury to the 
 region assumed to bear this important relation to language 
 lost all command of speech save that he still swore on 
 occasions. This seriocomic state of affairs is not difficult 
 to explain. Habitual profanity is scarcely a genuine form 
 of speech; the few words used are repeated under the 
 most varied circumstances with no specific appropriate- 
 ness. They come to be little more than animal outcries. 
 As such they might be expected to survive the wreck of 
 the organization which has for its duty the rendering of 
 thought in correctly chosen words. Thoughtful cursing 
 would be an appalling performance. 
 
 Motor aphasias may differ in degree throughout all 
 grades from a mere limitation in vocabulary to absolute 
 abolition of speech. The individual characteristics of the 
 cases are often of strange interest. A number of them 
 are cited in a fascinating way by Thomson in his delight- 
 ful book, "Brain and Personality. "^ We may refer to one 
 shrewd deduction of this practitioner which seems highly 
 suggestive. In a family of his acquaintance there were 
 several children. One of them and only one showed a 
 marked preference for using the left hand in the first 
 and second years. A rather severe struggle followed, the 
 parents and attendants seeTcing to make the child right 
 handed. Its initial tendency was at length overruled 
 and it grew up like its brothers and sisters. But in one 
 respect its history was contrasted with theirs : all the others 
 talked at an early age, while this child was distinctly 
 backward. 
 
 Thomson's explanation is an attractive one. He sug- 
 gests that in the brain of the child who showed the dis- 
 position to use the left hand rather than the right the 
 organization of the right hemisphere had begun to forge 
 ahead of that of the left. If there had been no interference 
 from without, the pathways employed in the use of lan- 
 1 Dodd, Mead & Co., New York, 1907. 
 
THE CEREBRUM AND HUMAN DEVELOPMENT 149 
 
 guage would have been opened in the right hemisphere also. 
 When the left hemisphere was forced to provide the 
 nervous government for the skilled hand the mechanisms 
 related to language had likewise to be furnished by that 
 side of the cerebrum. Time was lost when the original 
 foundations in the right hemisphere were abandoned in 
 favor of new ones which had to be constructed in the left. 
 
 When the command of spoken language suffers it is 
 commonly observed that the subject shows some loss of 
 general intelHgence and of the power to read and write. 
 But there have been many cases in which one or another 
 of these specific accompHshments has been more or less 
 completely abolished without much impairment of the 
 remaining functions. So we read of the loss of the ability 
 to write consequent on damage to a region just above the 
 speech center as usually indicated. The writing center, if 
 it has as definite an existence in space as has been claimed 
 , for it, is near the motor area for the trained hand and may 
 be thought of as a special extension of that area. 
 
 Sometimes the power to read is lost, though the victim 
 is not blind. The letters are seen clearty enough, but do 
 not rouse the associations which they had previously 
 acquired. It is a set-back in education — a return to the 
 condition of the child whose eyes are keen, but who has 
 not learned to read. Since reading is a specially devel- 
 oped function of vision, it is not strange that a state like 
 this has often attended injury to the hinder part of the 
 cerebrum on the left side and outside the general visual 
 region. Destructive processes near but not covering the 
 supposed auditory area of the left temporal lobe have 
 sometimes led to a condition described as ''word deafness," 
 sounds being distinctly heard, but words no longer serving 
 to convey their old meanings. The experience is probably 
 just that of listening to an unfamiliar foreign language. 
 
 The integral existence of four centers for language, 
 that is, for vocal speech, writing, reading, and the transla- 
 tion of words spoken by others, is not so confidently 
 maintained as it was a few years ago. If the true con- 
 
150 THE XERVOrS SYSTEM AND ITS CONSEUVATIO.V 
 
 cc'ptioii of a "('('ntci" is merely tliai it is a place where a 
 large number of paths related in function He close together 
 in the cortex, we shall expect to find that none of the uses 
 of language can be cut off by local brain injury without 
 nnlucing to some extent the other powers. This has been 
 said to be observed, at least as a rule. 
 
 The attempt has been made to ascertain whether the 
 apparent superiority of the left cortex can be demon- 
 strated with the microscope. Melius, of Johns Hopkins, 
 has recently reported that sections made from the sup- 
 posed speech center in a human brain and from the corre- 
 sponding area on the opposite side have proved to be 
 markedly unlike. The cortical layer on the left side was 
 nmch thicker than that in the specimen used for com- 
 parison. The greater thickness seemed to denote a more 
 extensive development of dendritic processes in the part 
 held to have the special functions to fulfil. But these 
 facts were not presented without a word of caution. The 
 same investigator compared sections of cortex from the 
 Ijrain of a highly educated man and others from homol- 
 ogous localities in the brain of an ignorant Austrian 
 peasant. The drawings made showed a decidedly more 
 intricate organization in one case than in the other, but, 
 contrary to the expectation of every one, the more impos- 
 ing appearance was that of the uneducated brain! 
 
 No modern advocate of cerebral localization has ap- 
 proached the old phrenologic precision in denoting the 
 functions of all regions. Large portions remain without 
 designation other than that of "association areas." 
 Through them, by few or many relays, we suppose that 
 the connections are made which determine the reactions 
 which shall occur under all circumstances. Histologists 
 have made the general statement that only the areas 
 which are definitely classed as motor or sensory have 
 projection fibers mediating between them and lower 
 levels of the nervous system. Beyond the boundaries 
 cf the areas immediately concerned with the delivery 
 or the reception of impulses traveling to or from the 
 
THIC CEREBRUM AND HUMAN DEVELOPMENT 151 
 
 various parts of the body are extensive regions linked 
 with them and with each other by paths composed of 
 "association fibers." Hence the association areas seem 
 to rank above the others in the cerebral organization, 
 being one remove farther from the receptors and effectors 
 in which the nervous system begins and ends. 
 
 Presumably it is the association areas which register 
 most fully the details of the individual history, and so 
 come to be in some sense the protoplasmic record of 
 experience and of character. But the representation is 
 diffuse, and the attempt to attribute a specific share to 
 this or that fraction of the whole has not been very suc- 
 cessful. The most attractive description of the associa- 
 tion areas and the possible distribution of their work is 
 that of Flechsig.^ He has suggested that the association 
 area which lies mainly in the parietal lobe is particularly 
 engaged in correlating the impulses received in the primary 
 sensory areas around it. The great frontal area which is 
 more distinctly withdrawn from the sensory stations, 
 but which adjoins the motor Centers, may be supposed 
 to transmit impulses to the cell groups controlling move- 
 ment. The influence exerted through the frontal region is 
 assumed to be largely of an inhibitory character. 
 
 If the views advanced by Flechsig were quite correct, 
 it should be possible to find confirmatory evidence in the 
 nature of insanity when induced by local brain disease. 
 Degeneration in the parietal region might be expected to 
 cause dulness, apathy, and inaction because the power 
 to appreciate the significance of things seen, heard, and 
 felt would be impaired. On the other hand, damage 
 to the frontal convolutions might be expected to lead to 
 erratic, ill-regulated conduct, perhaps to violence or de- 
 pravity. The facts are not entirely in accord with the 
 theory, but many individual cases are so, and it is pos- 
 sible that all can be explained under its broad provi- 
 sions. 
 
 CUnical observations constantly impress upon us the 
 1 Gehirn und Seele, Leipzig, 1896. 
 
1d2 the nervous system and its conservation 
 
 danger of being too dogmatic with regard to the local 
 functions of the brain. We are reminded of this when we 
 consider the extremely unequal results of various brain 
 injuries. Sometimes profound effects follow what seems 
 quite limited destruction; sometimes extensive lesions 
 leave no noticeable deficiency. Gunshot wounds of the 
 brain are usually fatal, but they are not always so, and it 
 is to be remembered that a bullet penetrating the brain 
 substance works havoc with the structure far beyond its 
 own path, displacing the tissue and producing pressure 
 in distant places. There have been extraordinary cases 
 of immunity from serious consequences when the brain 
 has suffered gross harm. Of those carefully recorded, 
 none is more remarkable than that of Phineas Gage.^ 
 
 The accident which befell this man occurred in the 
 year 1848, when the Rutland Railroad was under con- 
 struction in southern Vermont. It happened near the 
 village of Cavendish, where a rock cut was being made. 
 Gage, who was one of the workmen, was tamping a charge 
 of blasting-powder in a deep hole which had been drilled 
 into the ledge. The explosive was ignited and the massive 
 iron bar was torn from the hands of Gage and driven 
 through his skull. It entered his left cheek and went out 
 through the top of his head, having pushed before it a 
 cjdindric body of gray and white matter from the left 
 hemisphere. The victim did not even lose conscious- 
 ness. He survived for twenty years, and it is not known 
 that he showed any abnormalities excepting blindness in 
 the left eye. This was due to the clipping of the optic 
 nerve on that side and not to any cerebral damage. 
 
 ^ See the statement of Gage's physician, Williams, in the guide- 
 book of the Rutland Railroad, "The Heart of the Green Moun- 
 tains," 1S97. 
 
CHAPTER XII 
 
 THE CEREBRUM AND THE LIFE OF THE 
 INDIVIDUAL 
 
 In some of the tissues of the body there is a constant 
 formation of new cells at every period of life. This is true 
 of the skin, and is nowhere more evident than in the case 
 of its outgrowths, the nails and the hair. In other tissues 
 there is no addition to the original number of the cellular 
 units. It has been stated in another connection (Chapter 
 VIII) that no multiplication of the units occurs in the 
 skeletal muscles, though there may be an increase in the 
 diameter of the fibers. It is a most significant fact that 
 in the nervous system the maximum number of the 
 neurons appears to be attained very early, and hence any 
 later change will mean a diminution. The great ad- 
 vances made from infancy onward to maturity are not 
 based upon any corresponding multiplication of the 
 neurons. They are accomplished in spite of a stationary 
 or even decreasing number of these elements, and must be 
 referred to the formation of new routes of communication 
 among them. 
 
 It has been said that the limited powers of the nervous 
 system in the newborn are indicative of the great individual 
 development which awaits realization. This subject may 
 now be pursued in some detail. The receptor system of the 
 infant is probably complete. On the effector side the 
 muscles, especially those of the legs, have yet to grow 
 considerably to sustain a proper proportion to the total 
 mass of the body, but they are fully provided with efferent 
 fibers from the motor cells of the lower order in the cord 
 and brain. The department of the nervous system which 
 is farthest from its future condition is the intermediate 
 
 153 
 
154 THE NERVOUS SYSTEM AXD ITS CONSi:ilVATIOx\ 
 
 portion, the adjustor or association mechanism. The tics 
 which will later determine the responses of the orj^anism to 
 all manner of stimuli have mostly to be established; only 
 a few are congenital. 
 
 The light which enters the eyes of the newborn baby 
 probably produces the same retinal processes which it 
 will always produce. The optic paths lie ready to convey 
 the resulting- impulses to the brain. The lower centers 
 in the midbrain and thereabouts may be traversed by 
 these impulses quite as they will be in adult life, and the 
 simpler eye reflexes, such as winking and contraction of 
 the pupil, can be evoked. But the radiation of the im- 
 pulses from the visual centers in the cerebral hemispheres 
 is probably insignificant. A few months later the child 
 reaches in the right direction to grasp objects which are 
 brought into the range of its vision. Physiologically 
 speaking, this means that a serviceable bond of union 
 has been established between the receiving station for the 
 visual impulses and the area from which the motor im- 
 pulses take their departure from the cerebrum. When 
 the head is turned toward the source of a sound it seems 
 reasonable to conclude that a similar connection has been 
 secured between the auditory and the motor regions. 
 
 These phj^siologic gains are undoubtedly accompanied 
 by mental advances of a parallel sort. In a passage of 
 great literary beauty George A. Gordon^ has sketched the 
 attainment of psychologic correlation between sensations 
 mediated by different paths. He points out that for the 
 baby a month old the mother is represented by a visual 
 image, a voice, and a comforting touch. The three sensa- 
 tions have nothing in common save the fact that they 
 are welcome to the infant consciousness. A momentous 
 step is taken when they are first conceived to originate 
 in the same entity^ — a "benign power," as the author cited 
 has expressed it. On the material side this revelation to 
 the mind of the child must be conditioned by the opening 
 
 ' "Ultimate Conceptions of Faith," Houghton, Mifflin & Co., 
 Boston, 1903, 102-104. 
 
CEREBRUM AND THE LIFE OF THE INDIVIDUAL 155 
 
 of new association paths in the cerebrum. When, after 
 an interval, the child finds a name for the mother we have 
 evidence of an additional evolution of such bonds. 
 
 All of education, from infancy to the fulness of develop- 
 ment, is of this same type. "Reaction to stimulation" is 
 the term which covers almost all which the organism does, 
 but the capacity to react is always quaUfied by the entire 
 past history of the individual. Every incident in the 
 course of life has left its impression. The formation of 
 habits is the symbol of the channeling which is proceeding 
 in the cortex. This fact has been alluded to in the chapter 
 on Reflexes and it may now be enlarged upon. In infancy 
 a very few repetitions of a reaction may make it a matter 
 of regular recurrence or, in other words, a habit. This is 
 partly due, we may suppose, to the plastic nature of the 
 tissue involved and partly to the absence of paths of prior 
 formation. 
 
 When the word "habit" is used, the connotation is likely 
 to be a disagreeable one. But this ought not to be so, for 
 it is the power to form habits which is the basis of human 
 progress and efficiency. If it were not possible to acquire 
 the ability to perform many acts as though they were 
 reflexes, making no demand upon the attention, we should 
 never advance far in our individual development. If the 
 task of dressing one's self remained as laborious and con- 
 tinued to require the same thoughtful planning in later 
 life as in the days of childhood, when it was first accom- 
 plished, one would lose just so much time and strength 
 which is actually available for fresh lines of thinking. As 
 each necessary act becomes, as we say, second nature, the 
 mind is released for new conquests. 
 
 The late William James^ wrote most wisely of the ad- 
 vantages and the dangers incident to our habit-forming 
 propensity. It was his suggestion that habits can be 
 placed in three classes: those which are clearly the best 
 possible, those which are plainly undesirable, and a great 
 
 1 "Psychology, Briefer Course," Henry Holt & Co., New York, 
 1892, chapter on Habit. 
 
150 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 number wliich are neither to be particularly commended 
 nor condemned. The habits of the first class are evidently 
 to be cultivated and cherished, while those of the second 
 class are to be abandoned. These statements are plati- 
 tudes, l)ut the teachino; of James regardinfi; the ha))its 
 which are neither ^ood nor bad is worthy of cai'eful con- 
 sideration. His contention is that such habits are to be 
 arbitrarily changed from time to time; not that the new 
 practices are any more hygienic or attractive than the old, 
 but that l)y such deliberate^ chang(\s one preserves the mas- 
 tery of the situation and the adaptability of the nervous 
 system to altered conditions which the future may bring. 
 
 It is easy to find opportunities to follow this suggestion. 
 One may find that a certain phrase is being used repeatedly 
 in conversation or in writing. An equivalent phrase may 
 be substituted; this is combating the tendency to form a 
 rigid habit. A certain melody may run in the head; the 
 act of cutting short its continuance and causing another 
 air to take its place or, better still, silencing the subjective 
 music for the time is attended with an agreeable sense of 
 being in command of the cerebral activities. James has 
 said in substance that one should note what one is in- 
 clined to do and then do something else. This practice 
 might conceivably be overdone, but the want of such 
 initiative and the passive acceptance of all the minor habits 
 as they make their appearance is the common defect. 
 
 It is not too much to claim that such self-discipline is a 
 postponement of old age. We have said that the charac- 
 teristic of the young nervous system is the ease with which 
 paths may be opened in it. The nervous system in 
 middle life has many well-defined paths which are em- 
 ployed with regularity in doing the daily work to which 
 the subject has been trained. Changes become con- 
 stantly more difficult and are made more reluctantly. 
 Foster has said that in old age the brain holds a record 
 of the past rather than a promise of what may be realized. 
 Monotony of environment and consequent uniformity of 
 reaction are factors which are calculated to bring on pre- 
 
CEREBRUM AND THE LIFE OF THE INDIVIDUAL 157 
 
 maturely this rigidity, which must in any event arrive at 
 last unless death anticipates it. 
 
 The hardening of the arteries in later years is an im- 
 portant and widely discussed feature of the senile decline. 
 Portending the day when " the pitcher shall be broken 
 at the fountain or the wheel broken at the cistern," it 
 is a material type of the invisible change in the constitu- 
 tion of the central gray matter which gradually limits its 
 capacity to respond to new exactions. Much as arterio- 
 sclerosis can be postponed by temperance in eating and 
 drinking and by a wise ordering of all the activities of 
 life, so the loss of plasticity in the cortical organization 
 can be delayed by the same temperate conduct with the 
 added element of a studied variety in its employment. 
 It seems to be much more within our power to do this 
 than to prevent the inevitable stiffening of the crystalline 
 lens which abolishes the accommodation for near vision 
 at about the same period for all persons with normal 
 eyes. 
 
 It will be gathered from what has been said that if the 
 young nervous system excels the older one in its capacity 
 for variation in reaction, the older one surpasses the 
 younger in its confinement of its energies to profitable 
 channels. It is the more economic of the two. This 
 is much like saying that it has the greater exercise of in- 
 hibition. In it, wasteful diversions of nerve-currents to 
 call into play effectors which serve no useful purpose have 
 become reduced to a minimum. When a child no longer 
 cries when matters are not altogether to its liking and, 
 instead, seeks compensations in each situation, it has sup- 
 pressed or inhibited a lower type of reaction in favor of a 
 higher one. The progress of education always continues 
 to be marked by such substitutions. 
 
 This inhibition of primitive reactions by others based 
 upon complex experiences is best illustrated by the human 
 being, but is not wholly wanting in the most intelligent 
 of the lower animals. The dog that endures abuse at the 
 hands of children without turning upon its tormentors 
 
158 THE NEK^■OLS SYSTEM AND ITS CONSERVATION 
 
 exhibits it impres^sivcly. We feel at once that we may ae- 
 knowledge kinsliip witli a creature in which we recognize 
 the beginnings of virtue and nobihty. Translated into 
 physiologic terms, the self-control on the part of the dog 
 stands for the existence in its brain of countercurrents 
 which sta}^ the execution of the simpler reflexes. 
 
 As men and women we find ourselves called upon not 
 only to restrain many of the elementary reactions, but also 
 to emplo}^ inhibition with reference to trains of thought. 
 The power of concentration and the power of detach- 
 ment are nearly related. It might seem that they were 
 diametrically opposed, but a little consideration shows 
 that what we call "concentration" depends on the banish- 
 ment of irrelevant ideas, and one who can do this will, as 
 a rule, have the ability to banish the central as well as the 
 competing thoughts at the proper time. Those who have 
 carried the most crushing responsibilities for long periods 
 and rendered the greatest services to mankind, have fre- 
 quently been those in whom the power of detachment 
 from their cares was most remarkable. 
 
 Lincoln furnishes an illustrious example. Those who 
 were near him were puzzled and sometimes offended by 
 the abandon with which he put aside perplexing problems 
 to enjoy humorous books or amusing plays. It was not so 
 plain to them as it appears to us now that this relaxation 
 was the physical and mental salvation of the heavy-laden 
 president. Because he could dismiss the pressing questions 
 when it was no longer profitable to dwell upon them, he 
 could return with renewed strength and clarified judgment 
 to his task a little later. Stedman saw the motive and 
 wrote sympathetically of 
 
 "... one who, longer to endure, 
 Called mirth to case his ceaseless dole, 
 Yet kept his nobler purpose sure." 
 
 The same fine attainment of mastery over the currents 
 of the mental life lias often given efficiency to those who, 
 unlike Lincoln, have had no large endowment of physical 
 
CEREBRUM AND THE LIFE OF THE INDIVIDUAL 15!) 
 
 stamina. This was doubtless the case with Darwin, who 
 could not long pursue any single interest, but had to find 
 something to contrast with it after a short period of atten- 
 tion. The quantity and the quality of the work which he 
 produced in spite of this hmitation convince us that he 
 must have had in equal measure the power to appl}^ him- 
 self in the most concentrated fashion and to relax with the 
 same degree of success. The latter achievement is probably 
 found to coexist with the ability to go quickly to sleep. 
 
 One who has cultivated the ability of turning resolutely 
 from one line of thought to another will find abundant 
 opportunity for the exercise of this power in effacing what 
 is disagreeable in favor of what is pleasant. This may be 
 true either of memories or of anticipations. The healthy 
 mind — doubtless correlated with a healthy brain — is 
 greatly aided by nature in banishing distressing recollec- 
 tions. Psychologists recognize that such an individual 
 retains in his thought much more of detail and of vivid- 
 ness when the experience reviewed is pleasant than when 
 it is the reverse. A normal person should be able to 
 reproduce with but little diminution the feelings which 
 attended joyous and uplifting moments, but he should 
 find that pains and mortifications recalled from his past 
 have atrophied to colorless abstractions. The opposite 
 condition is particularly deplorable and may characterize 
 the neurasthenic. 
 
 In the voluntary control of thoughts regarding the future 
 we must recognize a matter of inestimable importance. 
 They are happy who can systematically magnify the ap- 
 proaching good and disregard the impending ill, consider- 
 ing it only to the extent that prudence and unselfishness 
 require. There are few examples more inspiring than those 
 which we owe to women who approach terrifying surgical 
 ordeals with their attention steadfastly fixed on other con- 
 cerns. We do right to pay tribute to their self-forgetful- 
 ness, but it may fairly be added that their splendid disci- 
 pline is the best thing possible for the conservation of 
 their own resources in the crisis. 
 
1(30 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 Much is written of the injury to general health which 
 is wrought by fear. The teaching is not so familiar that 
 there are many people who need to limit the extent to 
 which certain entirely happy expectations occupy their 
 minds. Yet this may fairly be claimed when dwelling on a 
 distant happiness becomes a cause of discontent. The 
 homesick college student knows that to be forever reckon- 
 ing the daj's that remain between the present and the 
 tardily coming vacation brings more of depression than of 
 stimulation. It is better to emphasize the agreeable con- 
 ditions which can generally be discovered close at hand. 
 
 Monotony in occupation and association must be held 
 to threaten harm to the nervous system and so to the 
 general health. We see the consequences in remote 
 country districts, where each person sees but a few others, 
 and where the round of duties to be performed is narrowly 
 fixed from day to day and from year to year. Add to the 
 wearing uniformity of circumstance the anxiety over the 
 slender income and it does not seem strange that in such 
 localities the proportion of mental derangement is high. 
 In many a weather-beaten farmhouse there are taciturn, 
 desponding, and bigoted people, cherishing bitter grudges 
 against neighljors, and making no effort to maintain 
 sociability in the family circle. Every such man or 
 woman is a witness to the tragic results of life without 
 wholesome variety in contacts and interests. 
 
 A mind well stocked ought to be able to neutralize in a 
 great measure the drawbacks of such surroundings, though 
 it frequently appears that the man of ostensibly high 
 education is quite dependent upon external sources of 
 diversion. Not many college graduates could spend a 
 Avinter on a poverty-stricken farm without repining, but it 
 may be asserted that the success of an academic training 
 may be measured by the capacity of the possessor to find 
 contentment independently of novel stimuli. It is too 
 much to ask that he shall prefer such isolation; formal 
 education is naturally a preparation for further develop- 
 ment in which the environment should bear its part. 
 
CEREBRUM AND THE LIFE OF THE INDIVIDUAL 1()1 
 
 But if the exigency arises it should be possible for the 
 trained mind to meet it with equanimity. 
 
 A store of happy memories and generous affections 
 should be competent to provide a foil to the depressing 
 influence of monotonous circumstances for a time at least. 
 Few would care to be tested long. Books have been one 
 of the chief resources of those who have contended without 
 degenerating against the tedium and pettiness of their 
 lot. Memorized portions of the best literature may have 
 a share in saving intellect and character from deteriora- 
 tion. The silent or audible rehearsal of such passages 
 may be more beneficial than a concert or a play. No one 
 can estimate the steadying power that has been operative 
 in the minds of our ancestors as they have pondered the 
 words of the Bible, "the ever-open Thesaurus" of immortal 
 truth immortally phrased. 
 
 As we think of the means of avoiding a dead level of the 
 mental fife and the value in it of reserve capacity for in- 
 hibition, the topic of the Sabbath suggests itself. It is 
 easy to caricature and condemn the Sunday of the Puri- 
 tans. Many of the restraints which it imposed may ap- 
 pear arbitrary and undesirable. But certain great bless- 
 ings came from it to those who cordially acquiesced in its 
 conventions, and even in a measure to those who con- 
 formed more grudgingly. It made a radical break with 
 the routine of the other six days and it encouraged self- 
 control rather than self-indulgence. The ''Continental 
 Sunday," toward which we seem to be moving, has too 
 little of inhibition. The jaded nervous system, by a 
 property which may be called perverse, demands excite- 
 ment, when the real need is rest. We shall find in this fact 
 the key to much that we have to discuss in a later chapter. 
 
 The student who refuses to let his studies encroach 
 upon his Sunday is not likely to regret his course. He will 
 find a zest in his work when he resumes it on Monday which 
 is the direct consequence of the intermission. The relig- 
 ious prohibition of our fathers may not be well founded, 
 but the dictates of hygiene may be made to take its place. 
 11 
 
Ki'i TlIK XKKVOLS SYSTEM AND JTS ("OXSKRVATION 
 
 Those who ck'iimr a^auist the ijroscriptiun t)f religion may 
 ur^e that the assigned En<2;hsh literature or history is intrin- 
 sically finer than an}' matter likely to be substituted for it; 
 on grounds of hygiene, however, a change is to be desired. 
 Some experiments recently reported from the Harvard 
 Medical School support this claim in a very i)()sitive waj'.' 
 
 Daily trials were made upon a large number of students 
 to determine their "sensory threshold," meaning in this 
 case the least electric shock which the}' could feel. The 
 stimulation was through two fingers of the same hand. 
 When all the results were averaged, it was found that a 
 diminution of irritability was registered from day to day 
 as the week passed, until on Saturday the threshold reached 
 its highest level. That is to say, it took a stronger shock 
 to attract attention on that da}^ than on any other. On 
 Monday the threshold was down again; this is the same 
 as saying that the irritability was restored to the highest 
 pitch. There must have been some cumulative fatigue 
 from one day to the next which was not offset by the night's 
 rest. 
 
 The students in this group probably had very variable 
 programs for Sunday. But it could be said of all of them 
 that the occupation on that day afforded a contrast with 
 that which filled the rest of the week. Perhaps we may 
 find in facts like these the explanation of the uniform 
 seven-day cycle agreed upon by so many races and 
 creeds. Experience may have shown that a longer period 
 of routine leads to progressive impairment of efficiency, 
 while economic pressure has not permitted the interrui)- 
 tions to become more frequent. Surprise has been ex- 
 pressed that the subjective judgment on Monday morning 
 is apt to be that the condition is one of unusual inertia 
 rather than (jf superior capacity. It is very likely true 
 that the highest irritability does not correspond with 
 the best state of the nervous system for consecutive work. 
 The subject may be too easily distracted. Hence, it may 
 
 ' Martin, Withington, and Putnam, American Journal of Physiol- 
 ogy, 1914, xxxiv, 97. 
 
CEREBRUM AND THE LIFE OB^ THE INDIVIDUAL 163 
 
 very well be that the best working days will come later in 
 the week. Still, the important fact remains that a balance 
 must be maintained, and the seventh day, bringing change 
 if not rest, is invaluable. 
 
 A word regarding the relation of attendance on church 
 services to the health of the nervous system may not be out 
 of place. If we hold to the principle that a contrast in 
 thought and feeling is what we must seek to secure when 
 we turn from our common, necessary interests to others 
 which invite our attention, we shall find that much can 
 be said in favor of the formal exercises of rehgion. To 
 cease from our narrow calculations, our competitive 
 endeavors, the struggle to please all types of associates, 
 and to contemplate fixed and eternal realities is to alter 
 as completel}^ as possible the currents of mental life. 
 
 It may be said in this connection that the atmosphere 
 of very many churches at the present time is far less favor- 
 able to this bitterly needed substitution than it was 
 twenty-five years ago. When a church becomes a socio- 
 logic forum its power to restore the jaded individual is 
 obviously lessened. We cannot wholly regret the heroic 
 note in current preaching, the insistent call to social 
 service and political reform, but this is a function which is 
 shared with the press and the secular platform, while 
 spiritual renewal is the preeminent office of the church of 
 Christ. 
 
CHAPTER XIII 
 
 EMOTION 
 
 The fact has been emphasized that a very large propor- 
 tion of the action of the nervous system proceeds without 
 clear tokens in consciousness. On the other hand, it msiy 
 be urged that the general coloring of consciousness is 
 sjanptomatic of much that is taking place in all depart- 
 ments of the neural mechanism and, indirectl}^, of many 
 states of the outlying organs which we cannot attend to in 
 an analj'^tic fashion. Our intense feehngs we speak of as 
 emotions, and it is generally held that their development 
 depends in a great measure upon conditions outside the 
 cerebrum through which the fusion of effects is brought 
 about. 
 
 The doctrine that stirring feelings never have an ade- 
 quate force in the mind until there is a characteristic 
 inflow of afferent impulses from various sources to give 
 them positiveness is known as the James-Lange theory. 
 According to this view a person is not truly angry until 
 his muscles have assumed a certain tension, his heart 
 action a certain rhythm, and his blood-vessels a certain 
 tonic regulation. He does not realize rage until his facial 
 expression and his posture combine to denote it. His 
 emotion is interpreted to himself by the same signs which 
 make it known to others. If one who feels angry can 
 inhibit the muscular manifestations and relax his features 
 he will experience a sense of ludicrous impotence and dis- 
 satisfaction, though he may be well aware that the occa- 
 sion for his wrath retains its full validity. 
 
 So the experience of grief in its fulness requires the sen- 
 sations that accompany the muscular state of one who has 
 given way to sorrow and the tingle of shedding tears. To 
 
 164 
 
EMOTION 165 
 
 know the meaning of fear, one must blanch and cower. 
 These ideas are not readily accepted by the student who 
 considers them for the first time; they have not proved 
 convincing to all psychologists. But for our present pur- 
 pose it does not much matter whether the bodily accom- 
 paniments of emotional states precede or follow the feeling. 
 What concerns us is the plain fact that they attend it 
 closely. They are, moreover, in proportion to its intensity, 
 and it is important to realize that all emotion is exercise 
 and often of a strenuous and far-reaching kind. 
 
 People who criticize athletic sports often argue some- 
 what in this wise: Here are 20,000 people idly viewing a 
 contest in which 18 baseball players are taking part. The 
 proportion of the idle to the active is more than 1000 to 1. 
 Such a statement does but scant justice to the facts. There 
 is an unsuspected quantity of muscular activity among the 
 spectators as they watch the game, and they often find 
 that they have earned a wholesome fatigue when it is 
 ended. As they bend forward or rise in their seats, per- 
 haps giving vent to cheers or imprecations, as they flush 
 and tremble, now holding the breath and now gasping or 
 sighing in the stress of their feeling, we cannot question 
 that both the skeletal muscles and the autonomic system 
 are being strongly played upon. It is only when the game 
 is very one sided or the looker-on is very blase that the 
 hours passed in the grandstand can be classed as idle. 
 
 A previous reference has been made to the fact that in 
 times of marked excitement the adrenal bodies are aroused 
 to unusual activity and discharge their powerful product, 
 adrenalin, into the circulation at a more rapid rate than 
 normal. The demonstration and the interpretation of 
 this fact we owe to Cannon. He was able to show by a 
 delicate test that adrenalin makes its appearance in the 
 blood of a cat when the animal has been agitated by the 
 sight of a dog. Additional experiments by workers in 
 the same laboratory have shown that adrenalin is capable 
 of delaying the onset of muscular fatigue. This is accom- 
 plished partly, though not wholly, by its acting as an anti- 
 
IGO THK NKRVOrS SYSTEM AND ITS COXSKiaATlON' 
 
 dote to the fatigue substances at the end-plates. Under 
 the same concUtions which cause the discharge of adrenaUn 
 there is hkely to be a notable rise in the sugar of the blood 
 above the usual small percentage. 
 
 The rise of the sugar may be sufficiently marked to cause 
 some of it to pass into the urine. This feature of the 
 emotional state has been noticed in human ])eings. Can- 
 non found that such an escape of sugar occurred in most 
 of the members of the Harvard footl^all squad at the time 
 of the game with Yale in 1913. This was true of the sub- 
 stitutes who had merely expected to be called in as well 
 as of the active players. Moreover, the same "emotional 
 glycosuria" was found to be common among the specta- 
 tors. It is probably a rather frequent reaction; possibly 
 the excitement of being examined for life insurance may 
 sometimes suffice to cause it and to mislead the physician 
 who detects sugar in the urine. In all cases it is the glyco- 
 gen or animal starch in the liver which has been trans- 
 formed to furnish the sugar, and it is believed that the 
 change is brought about by the influence of adrenalin in 
 the blood. 
 
 Cannon has shown great insight in his explanation of 
 these phenomena of emotion. The fundamental fact is 
 that emotions are experienced b}^ the lower animals and 
 by primitive men at moments when vigorous action is to 
 follow. Rage is the prelude to conflict. Fear will be fol- 
 lowed by flight. Sexual passion will eventuate in sexual 
 aggression. Civilization compKcates the order of reaction, 
 and inhibition of the higher type represses these activities. 
 The physical accompaniments of emotion are better suited 
 to the ancestral than to the modern conditions. The 
 mobilization of sugar appears to anticipate a demand for 
 fuel on the part of the skeletal muscles. The extra adre- 
 nalin at the same time promotes endurance. 
 
 Very recently Cannon and his co-workers have demon- 
 strated another and a curious change in the blood after an 
 emotional crisis. This is a distinct reduction in the time 
 needed for coagulation. The clotting of the blood is a 
 
EMOTION 167 
 
 defensive reaction tending to check hemorrhage and, in 
 case of wounds, to increase the chance of survival. Cannon 
 suggests that emotion is experienced when wounds are 
 imminent, and so a purposive character can be discerned 
 in this physical change as in the others. 
 
 If emotion is exercise, it may be asserted that a life 
 poor in emotion is a life which lacks wholesome stirrings 
 in both the neuromuscular and the autonomic realms. 
 It is probably true that people who have had a humdrum 
 existence are apt to be wanting in endurance. The 
 country cousin on a visit to the city is utterly wearied by 
 days of sight-seeing and evenings of entertainment in 
 spite of keen enjoyment of it all. It has often been ob- 
 served that volunteers from .the city are more readily 
 made into seasoned and hardy soldiers than are the more 
 formidable looking farmers. A measure of training is 
 inseparable from irregular hours, various associates, 
 changes of boarding-place, and the more harmless dissi- 
 pations of the city. The hurry, the noise, and the glare, 
 the very things which are held to injure the nervous sys- 
 tem, harden it and adapt it to endure new forms of stimu- 
 lation if it is intrinsically strong enough to withstand 
 them. 
 
 At the same time it is easy to see that excess in emotion 
 is exhausting to all the physical resources. Most people 
 know how profound is the weariness which succeeds a 
 severe paroxysm of anger. It is not much less marked 
 after sudden joy or a thrilling spectacle. There seems to 
 be much that is common to all the major emotions, though 
 they seem well differentiated in retrospect. Cannon 
 thinks it probable that the adrenal body is similarly in- 
 volved in all of them. The feeling of weakness that comes 
 in their wake may be due in part to a subnormal produc- 
 tion of adrenalin on the part of the exhausted cells. 
 
 Long ago James wrote in his always illuminating way of 
 the use and abuse of the emotions. He made much of the 
 idea that every emotion experienced should become a 
 motive for conduct. If it cannot be so applied, its repeti- 
 
168 THE NERVOUS SYSTEM AND ITS CONSEKVATION 
 
 tion should, so far as possible, be avoided. This teaching 
 now appears to have much more biologic truth in its favor 
 than it seemed to have when first pul^lished. If the occa- 
 sions in the lives of animals when emotion is stirred are occa- 
 sions for decisive action, we must heed the moral and not 
 too radically break with our inheritance. If the primitive 
 expression is out of the question, we may still be ingenious 
 enough to find a harmless or even a profit al)le substitute. 
 
 Specialists are now laying all possible stress on the 
 connection between nervous disorders and the suppressed 
 or unsatisfied tendencies which are believed to work harm 
 during long periods of latency. The curbing of a wish, 
 when this means not only the check but the annihilation 
 of the desire, is a noble exercise of inhibition. The denial 
 of expression simultaneously with the continued enter- 
 tainment of the wish is exceedingly hurtful. The frequent 
 experience of emotions which do not secure any motor 
 outlet is also abnormal. Anger maj^ not lead to fighting, 
 nor even to scolding, but it may be turned into a motive 
 for vigorous action. Some one has shrewdly suggested 
 that the boy who is heartily vexed at being set to chopping 
 wood or weeding the garden will work all the more swiftly 
 and energetically for his irritation. If this is the actual 
 result, and not an ill-natured dallying over the task, he 
 will be much better off at the close than if he had sulked 
 and idled until excused. "Emotion" and "motion" are 
 words nearly related, and the conditions for which they 
 stand should be related as closely. 
 
 The emotion of sympathy is one which we readily 
 recognize as peculiarly exhausting to bear when it cannot 
 be translated into acts. "Let us love not in word, neither 
 in tongue, but in deed and in truth" — there is hygiene as 
 well as humanity behind the injunction. Sympathy with 
 suffering may in many cases subject the one who feels it to 
 a torture more keen than that which has occasioned it. 
 Such vicarious pain is not to be avoided altogether, but it 
 is greatly alleviated when one finds something to do for 
 the sufferer. How the useless torment of viewing dis- 
 
EMOTION 169 
 
 tress is replaced in the physician by the endeavor to relieve 
 is set forth in the exquisite story of "Rab and his Friends" 
 — ''pity, as an emotion, ending in itself or, at best, in tears 
 and a long-drawn breath, lessens, while pity as a motive 
 is quickened, and gains power and purpose." 
 
 It was with similar ideas that James taught that the 
 pleasure of the drama or the symphony concert ought to 
 find its application in the better performance of one's work 
 or the readier expression of kindness toward one's asso- 
 ciates. The same may be said of the exaltation felt in the 
 presence of beautiful natural scenes. This seems like 
 ethical preaching, but it is none the less sound hygiene. 
 In fact, the present age far more than any that has gone 
 before understands the closeness of the parallel. The 
 teaching with regard to emotion is, after all, just that of 
 pedagogics, that it is not profitable to receive without 
 giving back. Reaction is the law of the nervous system 
 from first to last. 
 
 We have attempted to make the point that all emotion 
 is exercise, and that, accordingly, emotion in moderate and 
 reasonable variety is a source of general development; in 
 short, of training. It will be well to show how women, far 
 more frequently than men, are hkely to suffer from the 
 want of such stimulation. They often work by them- 
 selves and lack the spur of companionship during a large 
 part of the day. Their friendships are seldom as warm 
 and comforting as those between men. Many do not find 
 time for the daily paper, and, with all its faults, the press 
 causes its readers to visualize and in imagination to enter 
 into the course of stirring events. The husband, who 
 profits by the diversion of his newspaper, the little journey 
 to and from his place of business, a more or less social 
 occupation, and a lively luncii party at noon, should not 
 forget how colorless by contrast has been the day of the 
 wife at home. More deliberate effort is necessary in her 
 case than in his to bring in the needed elements of enthu- 
 siasm and interest. It is peculiarly unfortunate that so 
 many women are denied the full benefit of the Sabbath 
 
170 THE XEKVOUS SYSTEM A.\D ITS CONSERVATION 
 
 through being requiretl on that day to evolve the most 
 elaborate dinner of the week. The natural consequence 
 of such restriction in scope for the emotional life is at 
 first loss of ambition and later of endurance also. 
 
 A pica may be entered here for singing. We Americans 
 are too self-conscious to enter readilj^ into this wholesome 
 pleasure. It would do us good to imitate the Germans and 
 make singing a common feature of our gatherings. Even 
 singing by one's self may be beneficial. The advantages 
 derived are parti}'' those of a general neuromuscular 
 exercise and in part connected with the very marked and 
 agreeable emotional reaction. People who sing, though 
 it may be quite badly, are apt to have attractive personal- 
 ities. A charming old minister who set the highest value 
 upon congregational singing once said that the Scripture 
 was drafted to include the least gifted individuals in the 
 injunction to "make a joyful noise unto the Lord." 
 
 Cannon has assembled many of the facts concerning 
 emotion in a novel and suggestive form.^ After enumerat- 
 ing the autonomic manifestations, so largely his own dis- 
 coveries, he points out that the regional distribution of 
 these in the topography of the nervous system is distinct 
 and curious. The outflow of impulses accompanying the 
 major emotions is concentrated in the thoracico-luml^ar or 
 so-called sympathetic division. This department contains 
 the fibers which command the dilation of the pupil, the 
 secretion of sweat, the addition of adrenalin to the blood, 
 the development of goose-flesh, acceleration of the heart, 
 reduction of blood-flow in the digestive tract, and the in- 
 hibition of its activity. We have noted that these changes 
 prepare an animal for exertion. Even those which seem 
 to have a negative character — as the anemia produced in 
 the alimentary canal — may be indirectly helpful, since 
 they reinforce the circulation in the skeletal muscles. 
 
 Now, there are autonomic paths which start from the 
 cranial region and which are, therefore, anterior to the 
 sympathetic. The responses to stimulation of these 
 ' American Journal of Psychology, 1914, xxv, 2.56. 
 
EMOTION 
 
 71 
 
 paths are not familiarly recognized in tlie display of emo- 
 tion. They include slowing of the heart, contraction of 
 the pupils, salivation, and increased activity of the alimen- 
 tary canal. They seem characteristic of periods of tran- 
 quiUity rather than of excitement. Again, posterior to the 
 sympathetic, we have the sacral autonomic. In the 
 fibers comprised in this division are those which promote 
 micturition, defecation, and sexual reactions. While the 
 bladder and the rectum may fall under the disturbmg 
 influence of emotions, their normal actions are executed 
 in the absence of agitating conditions. 
 
 Cannon's grand generalization is, accorcUngly, to the 
 effect that the thoracico-lumbar autonomic has an "emer- 
 gency function," and that it is employed in crises of rage, 
 fear, and pain to give the animal the utmost command of 
 its resources. The activities of the other autonomic 
 mechanisms have to be held in abeyance at such times, 
 and are carried on only. when there is no external cause of 
 distraction. It is urged that the autonomic accompani- 
 ments of all the major emotions are too nearly identical 
 to differentiate them, and that this fact restricts and 
 weakens the James-Lange theory. No condensed state- 
 ment can do justice to the article referred to, which should 
 be consulted. 
 
 A manifestation of emotion which is of minor impor- 
 tance, but which has attracted popular attention because 
 of its picturesque aspects, is found in certain disturbances 
 of ihe electric equihbrium of the body.^ It is probably 
 fair to claim that all physiologic processes are attended by 
 quick shiftings of potential. These changes have been 
 extensively studied in nerves, in muscles (including the 
 heart), and in glands. They are of small magnitude and 
 must be registered by delicate instruments. If the two 
 hands are plunged into cups of salt solution which are 
 connected through a sufficiently sensitive galvanometer, 
 there will be evidence of electric instability. The rhythm 
 
 1 Wells and Forbes, Archives of Psychology, New York, March, 
 1911. 
 
172 THE NERVOUS SYSTEM AND ITS C'ONSEIIVATION 
 
 of the heart-heat will he reproduced hy osciUatioiis of the 
 indicator, ^\)h^ltary muscle contractions will displace it. 
 Now, if a series of words is spoken in the presence of the 
 man whose hands are in circuit with the galvanometer, it 
 is likely that at least a small excursion will follow each 
 word. But some words will have much more power than 
 others to give direction to his thoughts and to arouse his 
 feelings. The swing of the galvanometer will faithfully 
 demonstrate the degree of the emotional response. Thus, 
 if names of girls are repeated, the suljject of the inquisi- 
 torial experiment may react to each stimulus b}^ an appre- 
 ciable sign, but he will pay tribute to the name of his 
 fiancee by a striking movement of the recorder. These 
 electric disturbances are not surely localized, but they 
 testify to the involvement of contractile or secreting 
 structures — perhaps of both — in the phenomena of emo- 
 tion. 
 
CHAPTER XIV 
 SLEEP 
 
 About one-third of an average human Hfe is passed in 
 the familiar and yet mysterious state which we call sleep. 
 From one point of view this seems a large inroad upon the 
 period in which our consciousness has its exercise: a sub- 
 traction of twenty-five years from the life of one who 
 fives to be seventy-five. Yet we know that the efficiency 
 and comfort of the individual demand the surrender of all 
 this precious time. It has often been said that sleep is a 
 more imperative necessity than food, and the claim seems 
 to be well founded. 
 
 The writer once asked a psychologist how he would 
 define sleep, and received the answer, "Why, it is nothing 
 at ah." It has been simply described as inattention. 
 Both these characterizations turn upon the idea that sleep 
 is a suspension of consciousness and ignore its physiologic 
 features. Our own judgment as to whether we have been 
 asleep or not is evidently based upon the same concep- 
 tion. If this is the whole story, no animal can be said to 
 sleep unless we grant that it is conscious at other times. 
 We readily recognize that sleep is more clearly a part of the 
 lives of the higher animals than of those below them in the 
 scale, but it is hard to set fimits to its occurrence. All 
 mammals and birds are assumed to sleep; probably the 
 reptiles do, but we do not feel so sure about the frog or the 
 fish. 
 
 It might be more rational to reverse the order of inquiry 
 and, instead of asking how far down in the scale there is 
 sleep, we might ask, at what level as we ascend the scale, 
 do we find animals awake? Is not all life, below a certain 
 stratum, somnambulistic? An idea much hke this has 
 
 173 
 
174 TIIK XKUVOUS SYSTEM AND ITS C'OXSKKVATIOX 
 
 been expressed by Thomson. It is, briefly, as follows: 
 Sleep becomes necessary at the same stage in develop- 
 ment where there is the earliest entertainment of consciovis 
 purposes. Animals which are never actuated by such pur- 
 poses will not overdo. Their metabolism, their Avaste, 
 and repair will go on in a fairly even manner, each output 
 of energy being followed by a prompt subsidence of 
 activity to permit recuperation. But as soon as there is 
 any germ of will, any interest in the pursuit of an object, 
 the organism will be spurred on until the compensatory 
 change has to be of a profound and long-continued kind, 
 and, moreover, has to abolish the entertainment of the 
 conscious purpose while it is in progress. 
 
 While we cannot help emphasizing the relation of sleep 
 to consciousness, and, therefore, on the physiologic side, 
 to the cerebrum, we are obliged to concede that other 
 parts of the nervous system are involved. This is plain 
 from the fact that decerebrate birds and mammals still 
 exhibit an alternation of two conditions which have the 
 outward aspect of sleeping and waking. The periodic 
 depression is not confined to the cortex, though a slight 
 change in the chemical condition of the cerebral gray 
 matter would seem to be sufficient to produce the purely 
 psychic experience of going to sleep. 
 
 Whatever may be the essential condition of .sleep, it is 
 favored by the cessation of external stimulation and post- 
 poned by the action of such disturbances. It is probably 
 for this reason that most animals are disposed to sleep 
 at night. This will most surely be the case with those 
 which receive a large share of their guiding impressions 
 through the eye. Normal man falls in this class. His eyes 
 are his most important receptors, but because of his com- 
 mand of artificial lighting he is not compelled to submit 
 tamely to the suggestion that he go to sleep at sundown. 
 He has developed a curious habit of being active far into 
 the night and sleeping far into the da}', at least in the 
 spring and summer of the temperate zone. This tend- 
 ency may suggest a whimsical citation of the first law 
 
SLWEP 175 
 
 of mechanics: "A body in motion continues in motion, 
 a body at rest continues at rest, unless acted on by an 
 external force." 
 
 The purpo.ses served by sleep are plain. It is a state 
 in which the local and general losses of the tissues, which 
 have not been fully met as they have taken place, can be 
 offset. Bodily rest without sleep gives an opportunity 
 for such repair in the skeletal muscles, but not neces- 
 sarily in the receptor system, and certainly not in the 
 cerebrum. Even the skeletal muscles are probably better 
 rested in sleep than they can be otherwise, for their relax- 
 ation is more complete. As to the autonomic mechan- 
 isms, it is harder to determine how far they are granted 
 a remission of activity during sleep. We have to bear in 
 mind the fact that many of the autonomic influences are 
 inhibitory in character, and the interruption of such cur- 
 rents would lead to an actual increase of activity in the 
 organs reached by the nerve-fibers. No case of this kind 
 is certainly known, but the principle helps us to under- 
 stand how there may be no interference with digestion 
 while an animal is sleeping, as it is likely to after eating 
 heavily. 
 
 Many theories have been advanced to account for the 
 passage from the waking to the sleeping state. It will be 
 helpful to consider what conditions other than sleep com- 
 monly suspend consciousness. Two suggest themselves, 
 the one mechanical and the other chemical. One is inter- 
 ference with the circulation in the brain, and the second 
 is anesthesia by drugs carried through the medium of the 
 blood. Though we may call the first a mechanical cause 
 of unconsciousness, it is, doubtless, a chemical one at bot- 
 tom, for lack of blood-supply must lead to chemical altera- 
 tions in the neurons. Fainting is an instance of this action. 
 The other type of influence may be illustrated by ether or 
 chloroform narcosis, as well as by the coma of diabetes, 
 where the acidity of the blood is the source of trouble. 
 Normal sleep has sometimes been thought of as a swooning 
 and sometimes as an anesthesia. When the former cause 
 
17() THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 is assumed, we have an anemia theon-; the alternative is 
 a theory of toxemio. 
 
 The nightly experience of falling asleep does not very 
 distinetl.y suggest fainting. But when the drowsiness is 
 unusually compelling and unwelcome, as when one nods 
 in church, the resemblance does not appear so remote. 
 The rapidity of the passage from clear consciousness to the 
 realm of dreams or to oblivion favors the belief that a 
 mechanical factor has operated to determine it. The 
 most natural assumption is that a vasomotor change 
 has taken place. Howell has pointed out that such a 
 change may be due to fatigue of the vasomotor center. 
 During our waking hours this part of the autonomic 
 system is required to respond to frequent and varying 
 demands. Some of its duties have been indicated in an 
 earlier chapter. 
 
 If the center is really subject to fatigue, we may sup- 
 pose that it eventually becomes difficult to stimulate it 
 sufficiently to maintain the normal arterial tone. If it 
 lapses from its average condition, the blood-pressure will 
 decline and the flow will proceed more slowly through 
 the widened vessels. In the brain, encased as it is in a 
 rigidly walled enclosure, the slow flow wall be in vessels 
 which cannot materially widen. Hence, the brain suppl}^ 
 will be reduced and the maintenance of its activities 
 threatened. It remains possible in an}' ordinary case to 
 spur the center to renewed action, to raise the general 
 pressure, and so to drive the blood once more with an 
 adequate velocity through the capillaries of the brain. 
 
 Drowsiness is the sul^jective sign of the slowing cir- 
 culation in the cerebrum. In fighting it off one resorts 
 instinctively to the employment of external stimulation. 
 This is the object attained by taking a slightly uncom- 
 fortable position, by raising one's eyes to the light, and 
 by moving parts of the body. The exclusion of stimuli, 
 conversely, favors the relaxation of the vascular system. 
 
 ' "Text-book of Physiology," Fifth Edition, W. B. Saunders Co., 
 Philadelphia, 1913. 
 
SLEEP 177 
 
 When we court sleep we seek quiet and darkness. By 
 lying down we reduce to a minimum the inflowing im- 
 pulses from muscles, tendons, and joints. We avoid ex- 
 tremes of temperature. We interrupt, so far as we may, 
 the more vivid trains of thought. Thus, in favorable cases, 
 we withdraw from the vasomotor center the nerve-currents 
 which prompt it to react upon the blood-vessels, and we 
 are rewarded by a welcome change in the character of our 
 consciousness, if not by its actual suspension. 
 
 The fact that one can be awakened at any time by 
 stimuli supports the theory that the immediate cause of 
 sleep is the slackening of the blood-flow through the brain. 
 A state of general poisoning could not be done away with 
 on the instant by the stimulation of afferent paths. 
 Nevertheless, the acceptance of the vasomotor hypothesis 
 leaves a place for the toxemia theories. It is the accumu- 
 lation of chemical compounds, fatigue substances, in the 
 body fluids and perhaps in the protoplasm itself that leads 
 up to the central failure. We have, therefore, to distin- 
 guish between the cause of the approach of sleep, which is 
 metabolic, and that of its onset, which is mechanical. 
 It seems to be the distribution of the fatigue substances 
 rather than their actual amount which makes sleep a 
 pressing necessity. We know that we may be very tired 
 and find sleep impossible. 
 
 When the ties between the outer world and the indi- 
 vidual consciousness are severed as one sinks to sleep 
 there is an interesting and fairly definite order in the 
 process. Muscular control is lost before sensation; there 
 is an interval of delicious relaxation of which one is 
 pleasantly aware. Shortly the cutaneous sensibility is 
 gone, while the knowledge of the position of the extremi- 
 ties lingers for a little. Under such circumstances one 
 still reahzes the posture, but not the contact with the 
 bed. Havelock Elhs^ has suggested that this apparent 
 absence of any support may be explained by the dreaming 
 consciousness as the experience of floating in space or of 
 1 "The World of Dreams," Houghton, Mifflin & Co., Boston, 1911. 
 12 
 
178 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 fallinji;, two very coininou impressions, llcai'ing is the 
 latest means of communication between the world without 
 and the isolated mind. It is likewise the first channel to 
 be reopened as one is roused or wakes gradually from 
 sleep. 
 
 The depth of sleep at different times in the course of tlu> 
 night has often been tested. In the trials most frequently 
 referred to, the measurement was based on the loudness of 
 the sound necessar}^ to awaken the sleeper. All observers 
 have agreed that the deepest sleep, as indicated by such 
 methods, comes quite earl}^ probably within the second 
 hour, if not the first. We know that if we are awakened 
 within this period the experience is one of violent subject- 
 ive and bodily disturbance. The nervous shock is such 
 as to make it hard to compose one's self again. It is a very 
 different matter to be aroused from the later and shallower 
 sleep; then the response to a call is easily obtained, but, 
 unhappily, it is correspondingly easy to sink back to 
 sleep. 
 
 After the first deep sleep there is a shoaling which is 
 about as rapid as the previous subsidence into the depths. 
 Within three hours of the beginning a condition is reached 
 in which there is marked sensitiveness to stimulation. 
 Opinions differ as regards the later behavior of the nervous 
 system. According to one set of data there is a gradual 
 and progressive reduction of the depth of sleep during the 
 three or four additional hours of its continuance. Others 
 have noted a second deepening toward morning. This 
 last description appears to fit in with a great deal of in- 
 dividual experience; a wakeful time may be passed 
 through about 5 o'clock, and it may be harder to get up 
 two hours later than it would have been at dawn. A 
 German writer, accepting the double-peaked curve as nor- 
 mal, has referred it to the impression made upon the 
 centers when the infant woke once each night to be fed. 
 Little children who no longer wake at this time are apt to 
 show a restless interval between two periods of heavy 
 slumber. 
 
SLEJiir 
 
 179 
 
 On any theory we should expect to find, as in fact we do, 
 that the greatest depth of sleep would be soon reached 
 and passed. There should be a steady gain in the direction 
 of the sweeping away of fatigue substances and a steady 
 improvement in the capacity for reaction, which is what we 
 measure when we induce waking. It does not follow that 
 
 Fig. 24. — A schematic diagram of Mosso's pletbysmograph for 
 the arms: a, The glass cyhnder for the arm, with rubber sleeve and 
 two tubulatures for filhng with warm water; s, the spiral spring 
 swinging the test-tube, t. The spring is so calibrated that the level 
 of the liquid in the test-tube above the arm remains unchanged as 
 the tube is filled and emptied. The movements of the tube are re- 
 corded on a drum by the writing point, p. (Howell.) 
 
 the time passed in shallow sleep can be much shortened 
 without detriment. The experiments cited show only 
 that certain mechanisms require less than three hours to 
 regain almost their full irritability; there are many more 
 which may need a longer exemption from the demands of 
 the waking state. 
 
 The vasomotor changes which mark the coming on of 
 
180 THE .NERVOUS SYSTEM AND ITS CONSERVATION' 
 
 sleep and its departure have been demonstrated in the 
 normal human being by an indirect, but sensitive, method. 
 Tliis is the use of the instrument known as the plethysmo- 
 graph (Fig. 24), which, in its usual form, is a glass cylinder 
 designed to accommodate the hand and forearm of the 
 subject. A tight but comfortable closure at the end 
 toward the elbow is secured and the whole is filled with 
 water. A delicate gage is connected with the interior 
 and any displacement or drawing back of water is made 
 evident. A displacement must mean an increase in the 
 volume of the arm and hand, a withdrawal must indicate 
 a shi'inkage. Such changes in volume, when they occur 
 at all rapidl}^, may be ascribed to changes in the amount 
 of blood in the part. More gradual changes might be due 
 to variations in the quantity of the lymph. 
 
 When a person schools himself to go to sleep with his 
 arm enclosed in a plethysmograph it is found that a 
 marked dilation of the member occurs at about the time 
 when the threshold is crossed. This testifies to a diminu- 
 tion of the tonic activity of the vasoconstrictor center. 
 It has already been pointed out that such a slackening 
 will result in a more sluggish cranial circulation. Hence 
 it is inferred that when the record from the plethysmo- 
 graph shows a widening of the vessels in the arm there is 
 a simultaneous flagging of the blood-supply to the brain. 
 When waking occurs there is a sharp contraction of the 
 arm. It is very significant that external stimuli applied 
 during sleep, but not sufficing to rouse the sleeper, never- 
 theless cause vasomotor responses. In the experiments 
 directed by Howell, he himself being the subject, the 
 watcher at the bedside saw that occasional noises and 
 vibrations interrupting the quiet of the night registered 
 themselves through the distinct narrowing of the vessels 
 of the arm which they called forth. The reaction might 
 be described as a threat of v/aking. 
 
 On the side of hygiene there is much to be said of sleep. 
 Questions frequently asked and not at all easy to answer 
 are: How nmch sleep is best and how far do individuals 
 
SLEEP 181 
 
 differ in their requirement? How can one know whether 
 enough sleep is taken? Is it possible to sleep too much? 
 All these are related questions and all are important, but 
 intelhgent people will be likely to answer them in very- 
 different ways. We may attempt to deal with the last one 
 first, and we will venture the assertion that it is possible 
 to sleep more than is best. The fact that it is found diffi- 
 cult to get up in the morning is by no means a sure sign 
 that more sleep should be taken. It may be only a sign of 
 laziness. It is better to be guided by the evening feeling 
 and particularly by the demand of the eyes for a release 
 from their task. 
 
 The disciples of Horace Fletcher claim that one of the 
 benefits realized when a low diet has been adopted is 
 found in the fact that the hours of sleep may be shortened 
 without making inroads upon health. The obvious sug- 
 gestion is that a part of the sleep of average men is a coma, 
 an avoidable intoxication, due to an excess of narcotizing 
 substances absorbed from the burdened intestine. Whether 
 this is a typic condition or not, it is probably exempfified 
 by some heavy eaters. The picture of the carnivorous 
 animal gorged with concentrated food and crawling away 
 for a long sleep is familiar enough. Many young men and 
 women who supposed that certain hours of sleep were 
 necessary to their efficiency, have discovered, after mar- 
 riage and the coming of children, that they are capable of 
 much more work with much less sleep than they formerly 
 believed. 
 
 With advancing age the need for sleep seems generally 
 to diminish. In the Preacher's classic description the old 
 person is said to "rise up at the voice of the bird." Many 
 readers will recall the uneasy habits of the aged, who 
 cannot lie peaceably in bed until the younger members of 
 the family consider it time to get up, but are found 
 bustling feebly about imaginary duties in the early hours 
 of the morning. The nervous system in which the decom- 
 position processes have become lessened in intensity has 
 less need of the compensatory state. 
 
1S2 TIIK MOIlVOrS SVSTlvM AM) ITS CON'SKHVATIOX 
 
 Js llu'iv any scicutilit' basis for the okl tc'ai-hin>>;, "Early 
 to bed and early to rise"? It would seem at first as 
 though sleep at one time should have as much virtue as at 
 another. Still the ancient maxim may have a certain 
 foundation. To be up early and to ^o "early to bed" 
 means that the use of artificial light will be reduced to a 
 minimum. It is not likely that any substitute for day- 
 light can be found which will not impose a severer tax 
 upon the e^'es than does their natural form of stimula- 
 tion. Whatever tires the eyes has a widespread and de- 
 pressing influence upon the whole nervous system. Again, 
 lying abed late in the morning has the disadvantage that 
 the sleeper is likely to be affected by light and noises which 
 may deprive his rest of some of its potenc}^ for good, even 
 though they do not interrupt it. 
 
 Neuron Theories of Sleep. — We have regarded sleep as 
 a state induced indirectly l^y fatigue substances acting 
 upon the system and directly by the failure of an adequate 
 cerebral circulation. Other aspects of the condition insiy 
 be selected for emphasis. All the facts of sleep might be 
 explained by the conception of varying synaptic resistance. 
 The establishing of gaps in the motor paths would remove 
 the muscles from central control. Similar gaps anywhere 
 along the paths which conduct impulses from the receptors 
 would cause sensory paralysis for the time. Thought, in 
 the absence of the means of present guidance from the 
 external world and deprived of the power to express itself 
 through the neuromuscular mechanism, must be limited 
 to a rehearsal of memories and should take on the character 
 of dreaming. We should expect that a further impairment 
 of intercourse among the various regions of the cerebruni 
 must suspend even this kind of psychic activity. 
 
 Reasoning along the lines just indicated, certain physiol- 
 ogists have pictured the passage from waking to sleeping 
 as due to the interposition of extra resistance at the 
 synapses. The idea was first expressed as a literal snapping 
 of connections between the discharging and receptive 
 processes of the neurons, but this has come to seem 
 
SLEEP 18ft 
 
 highly improbable. Still, the conception has a symbolic 
 if not a literal value. We have seen in our general discus- 
 sion of fatigue that the synapses may be regarded as links 
 of low endurance, and this makes it reasonable to give them 
 a place in our hypotheses of sleep. 
 
 It is curious to find that the idea that the junctions of 
 the neurons may, in some sense, open and close has been 
 used in two lines of speculation of a distinctly contrasted 
 character. According to the more familiar view — already 
 outlined — it is the breaking apart of the nervous units 
 which paralyzes objective and subjective activity. An- 
 other theory, originating in Italy and not widely known 
 here, makes precisely the contrary assumption, that sleep 
 is the accompaniment of an extensive commingling of 
 cell processes. The establishment of new connections 
 between the neurons might explain the confusion and 
 irrational combinations occurring in dreams. The general 
 failure of reactions and, finally, of consciousness itself 
 might be explained as due to a dissipation of the nerve- 
 currents in so many paths that there should nowhere be 
 any effective intensity. Waking, then, might be pictured 
 as the resvmption of intercourse among the neurons, or as 
 the restriction of intercourse to the usual serviceable chan- 
 nels after a period of disorderly diffusion. 
 
 A mill is usually stopped by closing the gates and inter- 
 rupting the stream that has been turning its wheels, but 
 it could be stopped by opening sluices in the dam and 
 diverting a large share of the water. The two possi- 
 bilities correspond roughly with the neuron theories of 
 sleep. Either a cessation or a scattering of impulses within 
 the brain may conceivably result in unconsciousness. 
 The second theory is better adapted to an explanation of 
 dreams, a matter to which we must now turn. 
 
CHAPTER XV 
 
 DREAMS 
 
 Most people, even though they may be much interested 
 in the achievements of science, will probably be found 
 quite skeptical concerning the idea that dreams are 
 worthy of any serious notice. In common judgment it is 
 a weakness to think or talk much about the strange scenes 
 we witness in sleep. This feeling is probably the result of 
 emancipation from the superstitious faith in the revealing 
 virtue of dreams which was once universal. Tawdry 
 books, purporting to give a basis for the interpretation of 
 dreams and attaching an occult significance to every 
 common object seen by the dreamer, are still circulated. 
 However fanciful these publications may be, their purpose 
 is not wholh^ unlike that of a rapidly increasing mass of 
 sober scientific writing. 
 
 We cannot follow this subject far, but it would be unwise 
 to omit all reference to dreaming, for it is fruitful of sug- 
 gestions concerning hygiene. One of the most obvious 
 has to do with the general content of the dream. Havelock 
 Ellis^ classifies dreams as follows: (1) There are those 
 which are determined by the bodily conditions existing 
 at the moment; these may be called somatic, presentative 
 dreams. (2) There are those which are shaped by stimuU 
 acting from without; they may be called external, presen- 
 tative dreams. Other dreams are not clearly related to 
 present circumstances, but are mosaics of memories. 
 Ellis calls such dreams ?'epresentative and su})divides 
 them into two classes, the recent and the remote. It is 
 a matter of moment whether one's memory dreams are of 
 the recent or the remote kind. 
 
 ' "The World of Dreams," Houghton, Mifflin & Co., Boston, 1911. 
 184 
 
DREAMS 185 
 
 A man who is happy and not overtired, who is meeting 
 his obhgations with reasonable ease and success, is likely, 
 when he goes to sleep, to encounter persons and scenes 
 quite other than those he has lately known. Unexpected- 
 ness is the foremost quaUty of his dreaming experiences. 
 If he is skilled in unravelling the composition when he 
 reviews it after waking, he may be able to detect many 
 of the sources and to convince himself that they belong to 
 relatively distant periods in his career. It will usually be 
 his impression that he has not been thinking at all of the 
 matters which have been brought before him in his 
 dreams. 
 
 If he is seriously tired, anxious, and overwrought, he 
 may be compelled to attend to visions of an entirely 
 different class. Such a man may continue, in dreams, to 
 pursue the interests of his daily life. The same problems 
 which he had to face when waking confront him in his 
 sleep. The chess-player who has finished a hard game 
 shortly before going to bed may find the board again set 
 before him and be forced to consider the possible results 
 of each move through a long series. When he rouses 
 himself he feels that he has not rested well. In the same 
 way one in grief or fear may still entertain these feelings 
 and ponder their causes while he sleeps. Now, all dreaming 
 is partial insomnia, but there can be no question that it is 
 better to be awake to novel and diverting thoughts than to 
 find no release from the pressing concerns of one's routine 
 existence. "Recent representative" dreams clearly consti- 
 tute an unprofitable overtime performance on the part 
 of some of the brain mechanisms. 
 
 The statement just made suggests that it may not be 
 wholly whimsical to claim that dreams of the other (re- 
 mote) order afford some of the elements of a vacation. 
 The body does not find the same wholesome change of 
 environment and exercise as though an actual outing 
 were taken, but the purely mental content may be much 
 the same. Dreams may be at least as beneficial as a mov- 
 ing-picture show, which, in fact, they greatly resemble. 
 
ISO THE XEKVOLS SYSTEM AND ITS CONSERVATION 
 
 So long as they have the unexpected character, their oc- 
 currence does not seem to indicate that there is any failure 
 to recuperate the powers of those nerve-complexes on which 
 the strain of the ensuing day must fall. It may be 
 asserted that dreamless sleep is the ideal, but we do not 
 know surely that it is ever realized. People who say they 
 never dream, more probably dream and forget. We know 
 how uncertain at best is our recollection of most dreams. 
 The impressions seem to be destroyed by the strong light 
 of day asi though they were images upon a photographic 
 plate. Much as we have to develop our negatives in 
 rooms dimly lighted by selected rays, we have to rehearse 
 our dreams in the half-waking condition at dawn if we are 
 to make them our permanent possession. This does not 
 imply want of vividness in dreams when they are first 
 experienced; Ellis is apparently justified in his striking 
 aphorism: "Dreams are real while they last; can we say 
 more of life?" 
 
 The writer once had occasion to discover how completely 
 a lapse of memory may create the impression that there 
 has been unconsciousness. Nitrous oxid had been given 
 for the extraction of two teeth. When he came to him- 
 self he told the dentist that he was much gratified by the 
 entire success of the anesthesia. He left the office with 
 the same feeUng of satisfaction. On the street a few min- 
 utes later he recalled with appalling distinctness the pain 
 of the second extraction. No impression of the first 
 operation ever returned. It is disquieting to think that 
 one may suffer severely and then report in good faith that 
 one did not, but it is the same with dreaming. 
 
 The subject matter of dreams may be of considerable 
 assistance in answering a very important question. A 
 person who wakes day after day with feelings of weariness 
 and incapacity may be either indolent or tired. It is 
 likely that the sensations are much the same in the two 
 cases, and yet it is necessary that the two conditions shall 
 be distinguished. Clearly enough, mischief will be done 
 if one who is reall}^ fatigued and in need of more rest 
 
DREAMS 187 
 
 mercilessly condemns himself for laziness and redoubles 
 his efforts to overcome the inertia. On the other hand, a 
 man who is actually lazy and failing to make the most of 
 himself may be led into habits of self-pity and self- 
 indulgence by concluding that he is seriously tired. 
 When face to face with this problem it is well to ask 
 whether the dreams have been mostly of the recent or the 
 remote type. If they have been filled with the cares of 
 the day, there is good ground for assuming that cumula- 
 tive nervous fatigue is developing. If they are recalled 
 as fantastic, varied, and curious, the conclusion may be 
 less welcome, but also less ominous. 
 
 As to dreams of the "presentative type" — those in which 
 immediate circumstances connected with the body itself 
 and sources of stimulation close at hand are concerned — 
 the most interesting facts established are those with 
 regard to symbolic depiction of the causative conditions. 
 It is quite plain that the dreaming mind usually refers 
 all its experiences to external affairs. It gives them an 
 objective existence. Suppose, for example, that a man has 
 an uncomfortably palpitating heart. When he is awake 
 he is in no doubt of the actual nature of the case, but 
 when he falls asleep and dreams, it is not to feel that his 
 heart is rapid and irregular, but to view some scene sug- 
 gestive of difficult action, it may be a horse struggling to 
 draw a load up a hill or a laborer grappling with a heavy 
 stone. The writer once lay thinking of the physiologic 
 action of the heart as sleep drew near, and when the 
 border-line was crossed he saw at once a huge pulley- 
 block. It was so good a symbol of a weight-raising device 
 that he awoke with lively gratification. 
 
 According to the same principle, the victim of indi- 
 gestion does not think while he dreams that he is suffering, 
 but he becomes a witness of some spectacle of violence or 
 horror. Dreams referable to distention of the bladder 
 symbolize the real trouble in naive and amusing ways. 
 One who was in such a case thought that he turned on a 
 faucet which did not run. The trivial dream perfectly 
 
188 THE XERVOrS SYSTEM AND ITS CONSERVATION 
 
 figurcil the neetl that existed and the desirable inhibition 
 that postponed its satisfaction, but the facts were made 
 to appear as external to the dreamer's person. Thus we 
 are constantly detaching portions of the self and treating 
 them as separate objects of attention. Ellis has discern- 
 ingh' pointed out that this tendency is not entirely absent 
 from the waking mind and that it may become a con- 
 spicuous one at times. This is particularly true when the 
 temperament verges toward the neurasthenic. 
 
 The unfortunate person who is mentally depressed is 
 prone to charge upon others the faults which are his own. 
 When he is quick tempered, he is convinced that they are 
 impatient. Precisely as the dreamer does, he fails to recog- 
 nize that the matter which offends and outrages him is 
 part of himself. If he feels better for a while, he concludes 
 that his housemates have become more thoughtful and 
 kind. It is harder for him to recognize his own respon- 
 sibility than it is for any of us to realize that the rising and 
 setting of the sun are illusions due to the movement of 
 our planet. It may be added that it is even more im- 
 portant to conquer the tendency to self-deception in the 
 first instance than in the second. The man who can 
 make the correct allowance for his own ups and downs 
 while he sits in judgment on others best deserves to be 
 considered awake. 
 
 We are told by certain writers of the present time that 
 dreams are reliable sources of information for the special- 
 ist regarding many facts of personal history and exist- 
 ing tendencies which the patient would prefer to hide. 
 Dreams form a large share of the material used for diag- 
 nosis by the psychanalysts.' It would be presumptuous 
 for a lay writer to criticize their principles, which have 
 often been justified by the success of their work. Never- 
 theless, it may be said that one who reads their exposi- 
 tions without special training is likely to conclude that 
 psychanalysis is the art of putting the worst possible 
 construction upon all that the subject thinks or dreams. 
 
 ' Brill, "Psychanaly.si.s," ^^'. B. SnuiKlers Co., Philadelphia, 1912. 
 
DREAMS 189 
 
 According to Freud and his school, sexual impulses 
 are determinative in the shaping of most dreams. In the 
 troubled consciousness of the dreamer there are present 
 at once the current of desire and the sense of the restraint 
 which is habitually imposed upon it. Both are disguised 
 almost beyond recognition, for the dreaming mind is cu- 
 riously disingenuous and indirect. The concealment is so 
 effectual that the average reader does not readily accept 
 the interpretations placed upon the dream imagery by the 
 modern successors of Joseph and Daniel. It seems as 
 though people of an introspective turn might do them- 
 selves serious injustice by applying too rigorously the 
 Freudian ideas to self-examination. 
 
 For such there are certain consoling considerations. 
 First of all, it may be stated that the relation between the 
 waking and the dreaming life of a man who is approxi- 
 mately normal is one of contrast rather than one of resem- 
 blance. Therefore, if a man seems to display a tendency 
 to cowardice, frivolity, deceit, or sensuality in his dreams, 
 it may be because these evil traits have been decisively 
 subordinated in his waking hours to their very opposites. 
 It is only when the will is in abeyance that they can be 
 brought to the fore. It is the best of us that goes to sleep 
 most soundly, and if there is a shocking deficiency in 
 generosity and renunciation in the apparent character 
 of the dreamer, it may be that the instruments of these 
 faculties are plunged into a narcosis which is the sign of 
 their continuous exercise during the day. It is reasonable 
 to suppose that in health the parts of the complex mech- 
 anism which are most employed while one is awake will be 
 most profoundly restrained from action when sleep has 
 come. 
 
 For similar reasons it is unjust to conclude from the 
 unworthy impulses of a man in delirium that his previous 
 life has been one of hypocrisy and duplicity. It may 
 well be that he has been master of the situation until his 
 fine powers have been temporarily dissipated. We must 
 bear in mind that virtue does not consist in the inability 
 
190 THE NEKVOllS SYSTEM AND ITS CONSERVATION 
 
 tg I'onceivo of misconduct, but rather in the strength to 
 refrain from it and to "overcome evil with good." This 
 is eminently true of the sexual life, and, even if the claims 
 of Freud are fully accepted, it does not follow that men 
 need lose self-r(>spect or become cynical rejiarding the 
 high principles b}' which the lives of their associates are 
 governed. 
 
 We have quoted the statement that sleep is inattention. 
 By contrast, the state of complete waking may be regarded 
 as one of attention, and, more precisely, of attention of the 
 active order. Psychologists distinguish active from passive 
 attention, the former requiring the voluntary selection of 
 its objects and the removal of their competitors by a 
 process of inhibition. Passive attention is that which is 
 involuntarily yielded to stimuli which we are unable to 
 ignore. This is clearly the case when we dream; we are 
 not able to follow up the features of the dream which in- 
 terest us, but are compelled to shift our thought to others 
 which, in turn, elude our scrutiny. Ellis has said that 
 dreams have always the character of dissolving views. 
 Objects which excite our curiosity persist in fading away 
 and becoming overlaid by new ones seemingly unrelated 
 to the first. 
 
 We have spoken chiefly of the part played in dreams by 
 memories and bodily conditions. The special sense organs 
 doubtless bear their part. This is true even of the eyes, 
 which are sources of vague sensation even when closed. 
 It is believed by many, including Bergson, that the glim- 
 mering effect which anyone may notice on shutting the 
 eyes is quite influential in suggesting the scenery of 
 dreams. It may be thought a very limited source for 
 such elal)orate phenomena, but, as Bergson points out, it 
 is our habit when awake to fill in the details of what we 
 see in scant outline. Dreams influenced by sounds are 
 rather common, and serve to raise interesting questions 
 as to whether we recall our dreams as they actually oc- 
 curred or arrange their conteiits in a new order. To use 
 an illustration from Ellis: A man dreams that heenhsts in 
 
DREAMS 191 
 
 the army, goes to the front, and is shot. He is awakened 
 by the slamming of a door. It seems probal)le that the 
 enhstment and the march to the field are theories to ac- 
 count for the report which really caused the whole train 
 of thought, though it seemed to be its latest item. 
 
 A dentist made the following experiment twice with the 
 same results: While a patient was inhaling nitrous oxid 
 the names of the stations on a local railroad line were 
 repeated to him. When consciousness returned he was 
 asked what he had dreamed. In each case the reply 
 was, "I thought that I went on a long railroad journey 
 and at last met with a terrible accident." One cannot 
 doubt that the catastrophe was the dreamer's interpreta- 
 tion of the violent extraction of a tooth. 
 
 The dreaming state is one which usually has little or no 
 motor expression. Ellis has called attention to the fact 
 that in dreams we may either think that we move with 
 extraordinary ease and speed, or we may have the sense 
 of inability to command the muscles. Of course, the 
 second state is one in which we have a more correct 
 impression of the actual situation. The author cited 
 thinks that it is always associated with shallow sleep 
 when there are sensory signs of the immobility of the 
 limbs. With deeper sleep these signs would disappear 
 and the dreamer would not be deterred from imagining 
 remarkable indulgences in locomotion and aviation. 
 
 The lack of brightness in the ocular sensations possible 
 to one with closed eyes may account for the report com- 
 monly made that dream scenery is colorless and sober. 
 This is not necessarily the case; the writer often ex- 
 periences surprise and pleasure when, after a winter day, 
 he finds that in his dream country the grass is brilliantly 
 green, the sky intensely blue, and the sunshine as golden 
 as that of a Sorolla landscape. It is generally agreed 
 that sensations of taste and smell are rarely noted in 
 dreams. 
 
CHAPTER XVI 
 
 CAUSES OF NERVOUS IMPAIRMENT 
 
 When we look into the faces of men and women as we 
 meet them on the street-cars we are painfully impressed 
 with the widespread prevalence of ill health. The aver- 
 n^c expression is not one of comfort, hope, and good-will, 
 l)ut of depression, anxiet}^, and absorption in self. The 
 exceptional face which is radiant of strength and benevo- 
 lence is conspicuous in the dreary succession. The temp- 
 tation is to pass a harsh judgment upon those who seem 
 so unhappy and unfriendly and to condemn them for not 
 being otherwise. Reflection convinces one that this is 
 unjust. They are the victims of heredity, of malnutrition, 
 of poverty, and, not seldom, of voluntary sacrifices. It 
 is not for the casual spectator to say how far they are 
 suffering from personal dereliction which should have 
 been avoided. Whatever the past facts have been, the 
 present difficulty with most of these people is imperfec- 
 tion of nervous equipment. 
 
 A considerable share of this may be charged to neurotic 
 inheritance. Every one can think of families in which 
 nervous instability is exemplified in various forms by the 
 different members. These are the families which are 
 given to quarreling and recrimination at home, but unite 
 with even greater pugnacity against the outsider who 
 has incurred their displeasure. They make themselves 
 miserable, but seem unable to help it. Where the taint 
 is graver, there is downright neurasthenia. From such 
 stock come certain individuals with marked talent, but 
 hampered by self-consciousness and excessive sensitive- 
 ness. The temperament is not a modern development, 
 as commonly assumed, but as old as the time of Plato, 
 
 192 
 
CAUSES OF NERVOUS IMTAIRMIONT 193 
 
 who is said to have described it with jj-reat precision and 
 to have declared such persons to be "undesirable citi- 
 zens" for his republic. 
 
 But the proportion of people who fall far below the 
 normal in courage and perseverence, in kindliness and 
 contentment is too large to allow us to say of every case 
 that the inheritance was much to blame. We must pass 
 on to the circumstances affecting the individual. These 
 may be divided into those which are strictly physical and 
 those which can be described as unfortunate mental 
 habits. Among the physical factors are some which are 
 bodily and some which are environmental. 
 
 We may conveniently mention first disturbances of 
 nutrition. The opinion is commonly held that many 
 powerful personahties have been perverted by dyspepsia. 
 This is said, for example, of Carlyle. Of course, it is hard 
 in such instances to say which is cause and which is effect. 
 The indigestion may be the result of the inefficiency of a 
 nervous system in which pessimism is a congenital char- 
 acteristic. This is a difficulty of interpretation which we 
 constantly encounter in all discussions of this kind. But 
 whether despondency and cynicism are primary or sec- 
 ondary, there is no reasonable doubt that when they are 
 once estabhshed they continue to impair the digestive 
 capacity, and the alimentary trouble tends to intensify 
 the nervous deficiency. Thus, we have an illustration of 
 what is known to physicians as a "vicious cycle." 
 
 The reaction of a disordered stomach and intestine 
 upon the brain is not solely by means of nerve-impulses 
 such as result in general sensation. It is now believed 
 that the influence exerted is largely due to chemical 
 products originating in abnormal fermentation processes 
 in the canal. Entering the blood, these deleterious com- 
 pounds are borne to all parts of the body, but they have 
 an especially marked effect upon the central nervous 
 system. The condition in which these poisons are circu- 
 lated and become productive of mischief is spoken of as 
 auto-intoxication. It is favored by overeating, especially 
 
 13 
 
194 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 of nitrogenous foods (meats, eggs, and legumes). But it 
 may develop also when the diet is scanty, for it has become 
 clear in recent times that underfeeding may so enfeeble 
 the reactions of the organs of digestion that they do not 
 care for tlie food so well as they would for a larger and 
 more stimulating ration. 
 
 Auto-intoxication is frequently associated with anemia, 
 and this condition — a diminution of the oxygen-carrying 
 substance in the blood — always threatens injury to the 
 nervous system. It implies limited endurance in every 
 pursuit. Just how the anemia of auto-intoxication is 
 caused is not always plain. In some cases it is probably 
 due to the continuous formation in the intestine of a 
 poison which is destructive to the red c^jrpuscles. 
 
 Among the bodil}^ sources of nervous damage we do well 
 to emphasize eye-strain. Attention has already been 
 called to the primacy of the eye among the receptors 
 through which the organism is stimulated. It follows 
 that excessive use of the eyes or their employment under 
 difficulties must be harmful in a high degree. A little 
 space may be here devoted to a comparison of the common 
 visual defects as causes of central trouble. The normal 
 eye may be abused — as by reading with poor light or in 
 situations where there is vibration (in the cars) — but it is 
 of special importance to discuss the near-sighted, the far- 
 sighted, and the astigmatic conditions. 
 
 Near-sight is a defect ordinarily referable to too great 
 depth of the eyeball. The effect upon the retinal image 
 is the same that is produced in a camera when the dis- 
 tance between the lens and the plate is made greater than 
 it should be for landscape work. The distant view be- 
 comes blurred and indistinct, while objects at short range 
 are sharply defined. So in the near-sighted eye no clear 
 picture of the distance is obtainable, but things close 
 by are seen with a minimum of effort. What is called the 
 normal eye is used without strain for observing things at a 
 distance, and applied to near work with a certain sustained 
 contraction of what is known as the accommodation 
 
CAUSES OF NE-RVOUS IMPAIRMENT 195 
 
 muscle. Moderate near-sightedness adapts one to read 
 or sew with even less fatigue than if the eyes were strictly 
 normal. Nevertheless, the condition has serious disad- 
 vantages. 
 
 If a child is at all near-sighted it may be predicted that 
 the defect will grow graver during the period of school 
 hfe. The actual nervous strain involved is shght, but the 
 indirect results may be deplorable. The boy who cannot 
 see well at a distance cuts a ludicrous figure in vigorous 
 outdoor sport, and, being subjected to ridicule, abandons 
 the attempt to take part in it. At first he is sensitive and 
 aggrieved. Later he convinces himself that athletics are 
 not worth while and he inchnes to become a bookworm, 
 with a serious lack of physical stamina. It is fortunate 
 if he is not a conceited prig in the bargain. 
 
 Far-sight, so far as its cause is concerned, is the exact 
 opposite of near-sight. The eyeball is not deep enough. 
 A simple experiment with a camera will serve to show that 
 such a relationship between lens and screen will result in a 
 failure to focus anything sharply, though the distance will 
 be better imaged than the foreground. By an effort such 
 as one with normal vision makes to see objects nearby, 
 the far-sighted person secures clear vision for distance; to 
 read or do other close work he must subject the accommo- 
 dation muscle to an additional strain. Thus, his eyes are 
 never at rest when they are being used at all. Yet he can 
 see quite well anything to which he turns his attention, 
 and it may be hard to make him accept the fact that he 
 has a visual defect calling for glasses. Headaches, indi- 
 gestion, and general nervous disturbances may result 
 from this condition. 
 
 Regular astigmatism is an imperfection of the cornea or 
 anterior surface of the eye. In the majority of cases the 
 trouble is an excess of curvature up and down as com- 
 pared with that from right to left. This has been well 
 described as spoon-shaped cornea; in geometric temis 
 this important refracting surface of the eye is ellipsoid 
 instead of spheric. The purely optical consequences 
 
19(3 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 need not be set forth; the word "astigmatism" means 
 Hterally "not pointedncss," and the reference is to the fact 
 that with such curvatures a point outside can never be 
 imaged as a point upon the retina. Vision can never be 
 satisfactory, but at a given moment certain Hnear features 
 of the scene will be clearer than others which have a dif- 
 ferent direction. The attempt to change the degree of 
 accommodation so as to have a better definition for the 
 second set of lines results in sacrificing the sharpness of the 
 first. Hence, there is a restless flutter of the accommoda- 
 tion mechanism, a perpetual attempt to gain a compre- 
 hensive view, which is destined always to be baffled. 
 
 The effects of common astigmatism ui3on health are 
 much like those of far-sight. The glasses used to correct 
 the deficiency must themselves be astigmatic, but in a 
 sense opposite to that in the eyes to which they are added. 
 They must have their least curvature in the meridian in 
 which the cornea has its greatest. The mounting of such 
 lenses is evidently a matter of importance, for there is 
 only one position in which they can fulfil their purpose. 
 
 Sound heredity, successful nutrition, and eyes free from 
 hurtful strain go far toward securing an efficient nervous 
 system, but we have yet other factors to reckon with. 
 All bodily conditions which cause discomfort must be 
 regarded as possible sources of central injury. It is prob- 
 able, moreover, that many peripheral derangements which 
 we think we can ignore or which may even have escaped 
 our recognition, may be productive of much harm. We 
 have seen that this is true of far-sight. An eminent 
 surgeon, G. W. Crile, has furnished striking evidence that 
 this may be frequently a fact. The foundation of his 
 exposition is the body of information we possess with 
 respect to anesthesia.' 
 
 When ether or chloroform is introduced into the blood 
 and carried to the brain there is an interruption of certain 
 processes in the neurons which modifies or destroys con- 
 sciousness, but we have no warrant for assuming that 
 1 Boston Medical and Surgical Jom-nal, 1910, clxiii, 892. 
 
CAUSES OF NERVOUS IMPAIRMENT 197 
 
 ordinary anesthesia suspends all the many central activi- 
 ties. In fact, we know that it does not, for it would be fatal 
 if it did. The presumption is that certain synapses arc 
 much more easily affected than others, whence it follows 
 that we can subdue cortical currents to a considerable 
 extent without paralyzing the respiratory center. Now, 
 it is the belief of Crile that when an operation is con- 
 ducted under ether or chloroform, streams of impulses 
 ascend to the brain from the seat of the cutting and 
 cauterizing. These would produce terrible pain in the 
 conscious subject and reflex struggHng of the most desper- 
 ate intensity. In the actual case the pain is avoided and 
 the reflexes are greatly reduced. But are we to suppose 
 that the afferent impulses are wholly without effect upon 
 the brain? Crile contends that they continue to work 
 injury to the central gray matter even in the absence of 
 consciousness and reflexes. 
 
 Experimental evidence has been secured by making 
 microscopic studies of the brain tissue in animals which 
 have undergone severe operations under the common 
 anesthetics. Cellular changes are described which are 
 of the same nature as those long held to denote profound 
 fatigue. Such alterations are not seen in the brains of 
 animals which have merely been etherized for a long time 
 without operation. Hence, Crile refers them to the inflow 
 of impulses from the parts that have been so powerfully 
 stimulated. 
 
 All this may seem to be a technical digression, but we 
 shall find that it opens certain considerations of the most 
 practical kind. It will be noted that the central fact in 
 Crile's thesis is this: Sensation does not constitute a 
 reliable measure of the damage done to the nervous sys- 
 tem by afferent currents. To disregard a source of such 
 impulses is not to nullify their influence. It is always 
 better to remove the cause than to seek to suppress the 
 cerebral echo. Using a text Uke this, we msiy indict 
 the principles of psychotherapy under any of its various 
 names when it seeks to treat organic disease. It under- 
 
198 THK XERVOUS SYSTK.M AND ITS CONSERVATION 
 
 takes to abolish pain, and this it may do willi surprising 
 success. But this is a species of narcosis and carries with 
 it no certain assurance that the nervous system is not to 
 suffer progressive injury from the sulx'onscious stimula- 
 tion. 
 
 This criticism should not be launched without giving 
 larger recognition to the usefulness of psychotherapeutic 
 measures, even where the trouble is an organic one. 
 Freedom from pain favors sleep and nutrition. Hence, 
 it may easily prove to be the only condition which is 
 needed to initiate a recovery. Again, the banishment of 
 pain is always beneficent when the disease is incurable. 
 But when the peripheral cause of distress can be corrected, 
 it is always better to attend to it. 
 
 One can readily think of a rather large number of 
 ph^^sical lesions which are apt to be tolerated or even for- 
 gotten which are possil^le sources of injurious stimulation. 
 Defective teeth afford an example. Many troubles asso- 
 ciated with, the feet, such as corns, broken arches, or even 
 badly fitted shoes, belong in the same class. Nasal ob- 
 structions may have the same influence. Hemorrhoids 
 and uterine displacements are more serious conditions 
 and have a like tendency, only more obviously effective. 
 Surgical operations for the relief of such conditions may 
 bring about what is little less than a regeneration of the 
 character of the individual. Among temporary causes 
 of imperfectly realized nervous strain may be mentioned 
 the wearing of orthodontia appliances. Children obliged 
 to submit to these instruments may not complain of great 
 distress, but they are likely to be made irritable and tired by 
 the constant wear and tear. An additional factor in some 
 cases is found in the loss of pleasure in eating which the 
 apparatus is likely to entail. 
 
 A word of criticism may be introduced here regarding 
 current views concerning ventilation. The simple and 
 summary doctrine prevails that air cannot be bad unless 
 it is too warm. The odors by which we usually gage the 
 success or failure of a system are lightly treated. It is 
 
CAUSES OF NERVOUS IMPAIRMENT 199 
 
 said that we soon cease to perceive them, and that, there- 
 fore, they do not signify anything of moment. Is this not 
 a dangerous assumption? An odor is the sign of a chem- 
 ical agent working upon the nervous system; we have no 
 right to say that this agent has ceased to act when we have 
 ceased to feel its immediate effects. Such a claim is equiv- 
 alent to the assertion that nothing can influence a sleeper 
 unless it wakes him. 
 
 Less attention is usually paid to the bodily sources of 
 nervous impairment such as we have been discussing than 
 to the influence of occupation, surroundings, and the 
 mental life. Nervous break-downs are most frequently 
 attributed to overwork. But according to the judgment 
 of the ablest specialists work in itself is not often the sole 
 cause of these disasters. Work may be hard and fatiguing, 
 but if it is congenial and at all successful, if it does not 
 encroach upon the hours of sleep, and if it is not a subject 
 of anxiety which the worker cannot easily dismiss, it is 
 not likely to do him harm. If, on the other hand, the 
 work involves worry and discouragement, if it so fills 
 the mind that it cannot be put aside at will, it. does become 
 a menace to the poise and efficiency of the nervous system. 
 
 If work is of an unwelcome kind and is performed in a 
 rebellious spirit, so much the worse for the subject. The 
 question may be asked: What of the mill-operatives, with 
 their monotonous and uninteresting ta.sks, are they 
 particularly subject to nervous disease? One would at 
 first say that they must be so, but there are certain fac- 
 tors which favor their protection against it.^ They are 
 not obliged to think of their work at all beyond the hours 
 assigned to it. Unless they are doing piece-work they 
 have no ambition to increase speed. Moreover — and this 
 is a very important point — they do not have at short in- 
 tervals to make choices between different duties which de- 
 mand attention. There is a restful element in having but 
 one definite thing to do and being freed from the anxiety 
 
 ^But see Goldmark, "Fatigue and Efficiency," New York Chari- 
 ties Publication Committee, 1912. 
 
200 THE XERVOIS SYSTEM AM) ITS CONSERVATION 
 
 lest some other matter should have had the precedence. 
 The sense of being pressed by numerous concerns of nearly 
 equal urgency is pro]>ably a root of much evil in the Ufe 
 of the "careful and troubled" housewife. 
 
 The clash of antipathetic i-)ersonalitics is a most serious 
 element among the causes of nerve-fag. It is one which 
 becomes steadily more potent for injury when a certain 
 measure of fatigue has arrived, for added irritability means 
 more and more grievous friction. It is a rare family in 
 which the atmosphere is not improved by temporary sepa- 
 ration of the house-mates. The entertaining of visitors 
 serves a good purpose when the guests absorb attention 
 that would otherwise be bestowed exclusively upon 
 members of the home circle and in a critical spirit. It is a 
 lamentable fact that in most families there is more restraint 
 in speech and more consideration in conduct when out- 
 siders are present; this suggests another valuable service 
 rendered by company. Neurasthenia is, in a certain sense, 
 a contagious disease: one case fully developed may give 
 rise to others, though the secondary ones are ordinarily 
 less severe. 
 
 Some one has shrewdly pointed out that one fruitful 
 source of mischief in the nervous system consists in what 
 may be succinctly described as not minchng one's own 
 business. People easily fall into the habit of fretting over 
 the beliefs and the behavior of their associates in matters 
 in which individual liberty ought to l:>e respected. Among 
 the uneducated this results in the attempt to dictate, and 
 futile contention follows. Higher in the social scale a man 
 or woman who commits this error may not be so aggressive, 
 but will brood unhappily over the principles or actions held 
 in such strong disapproval. It is nmch better not to be 
 the "brother's keeper" unless the interest is clearly philan- 
 thropic. Why should a man distress himself because a 
 fellow-being is fond of cheese, which he does not like?— 
 or goes to church, which he does not wish to do? It is 
 sound hj'giene to live and let live. The world, indeed, 
 needs reformers, but their task is one which calls for so 
 
CAUSES OF NERVOUS IMPAIRMENT 201 
 
 much personal sacrifice that they should be sure the cause 
 is worthy of the expenditure. A sense of humor is a sav- 
 ing grace for those in whom the impulse to regulate the 
 lives of others is a powerful one. 
 
 Let us summarize the conditions we have named as 
 helping to maintain the nervous system in a normal 
 state and so to keep the individual happy and efficient. 
 We have recognized that a sound inheritance goes far to 
 secure this end. Any neurotic tendency of the stock is a 
 handicap and makes it the more imperative that other 
 unfavorable influences shall be avoided. Physical defects 
 are to be corrected wherever possible, even though it may 
 seem easy to put up with them. Environmental factors, 
 such as fresh air, well-regulated illumination, and quiet for 
 the hours of sleep, must receive attention. A moderate 
 but not a harassing variety of occupation and thought is 
 to be recommended. And no responsibility which it is 
 not clearly a duty to bear — no gratuitous anxiety — is to 
 be assumed. 
 
 Sometimes people exhaust themselves in what is judged 
 to be purely unselfish and sacrificing devotion. To such 
 it may be necessary to say that future as well as present 
 usefulness must be considered. The sum total of service 
 that can be rendered to the family or other associates is 
 likely to be greater when there is some deliberate sparing 
 of one's self, some reservation of time for rest and recrea- 
 tion, than when the offering of labor and sympathy is 
 absolutely unsparing. Of course, there are exceptional 
 crises when any thought of self would be base, but, as a 
 rule, the greatest contribution can be made by those who 
 practise a wise conservation of their resources. 
 
 Reference must be made once more to the inestimable 
 value of the Seventh Day for the preservation of the ner- 
 vous system. The deepest degradation to which the 
 Sabbath can be subjected is to fill it with odd jobs left 
 over from the week's routine. The compulsions of 
 Sunday should be from within, not from without. So far 
 as possible the day should bring complete release from 
 
202 THE np:rvois system and its conservation 
 
 habitual petty cares and scope for the icleaUstic Ufe. 
 A certain parallel may be suggested between the renewing 
 function of the Sal)bath and the benefit to the eyes that 
 proceeds from relaxing the muscle of accommodation. 
 We necessarily bestow much of our attention upon objects 
 close at hand and rapidly changing. We rest our eyes by 
 looking away to the mountains with their unvarying out- 
 lines. So the nervous system, after making its swift 
 adaptive changes to meet the innumerable little exigen- 
 cies of the six days, may well be permitted on the seventh 
 to find a profoundly restful relation to "the things which 
 are not seen." 
 
CHAPTER XVII 
 NEURASTHENIA 
 
 In the previous chapter we have attempted to catalog 
 some of the factors which tend to subject the nervous sys- 
 tem to gradually deepening injury. We have now to de- 
 vote some space to the ways in which this injury is usually 
 manifested. "Nervous fatigue," ''nerve fag," "nervous 
 prostration," "nervous exhaustion" — these are expressions 
 used to denote different degrees of a condition which is 
 covered by the word "neurasthenia. "^ It is an example of 
 what is called a "functional disorder." By this term 
 physicians characterize diseases in which no structural 
 change in the tissues can be demonstrated postmortem. 
 Ordinary neurasthenia is thus brought into contrast with 
 those perversions of nervous reaction which are caused by 
 obvious abnormalities of the brain — paralyses, manias, 
 epilepsies, etc., due to hemorrhages, tumors, infections, and 
 the like. The adjective organic is the one chosen to set 
 over against the term "functional." 
 
 The distinction between functional and organic troubles 
 is often a helpful one, but it may be criticized as unscien- 
 tific. There is a medical maxim which says, "There is no 
 psychosis without a neurosis," that is, the nervous system 
 will not act in an abnormal way unless it is physically 
 abnormal. All its disorders are, therefore, organic in the 
 best sense, and a functional disease is a fiction. All that 
 can be claimed for the so-called functional disturbances is 
 that the derangement is chemical rather than structural, 
 molecular rather than molar. It follows, however, that 
 recovery is much more probable in the functional cases. 
 
 ^ The word is often restricted to cases of a certain t5T)e. It is 
 here used more inclusively, but in a way which does no violence to 
 the root meaning. 
 
 203 
 
204 THE NERVOUS SYSTKM A.\D ITS CONSKUVATION 
 
 If a layman is to enter at all upon a theme which properly 
 belongs to the practitioner, he should cite the authority 
 from which ho draws most freely. The chief source of the 
 folk)wino; account is Courtney's "The Concjuest of Nerves." ^ 
 The book can be connnended to all who seek an analj^sis 
 of neurasthenia at once scientific and sympathetic, with 
 many sane suggestions for its relief. The same author has 
 contributed the section on the nervous system in Pyle's 
 "Personal Hygiene," - where a more condensed presenta- 
 tion of similar material may be found. 
 
 The nervous system seems to suffer from fatigue of two 
 orders. First, there is that which may be called the daily 
 tj'pe, from which complete recover}^ occurs in the course 
 of a night's sleep. This has been sufficient^ discussed (see 
 Chapter XII). Another type of fatigue is that which is 
 cumulative from day to day, and which cannot be quickly 
 compensated. It results from the coexistence of some 
 or all the factors mentioned in the last chapter, and when 
 it is far enough developed it is recognized as neurasthenia. 
 There is a single principle which proves to be the key to 
 the problem: it is the fact that in nervous fatigue of the 
 central order there is a large element of hypersensitiveness 
 and consequent excessive activity. 
 
 We usually think of fatigue as a distinct depression of 
 capacity for action. This is true in a general way of the 
 neuromuscular system, though even with the simplified 
 conditions of laboratory trials it has been shown that a 
 moderate amount of contraction increases the working 
 power of muscle. Lee has interpreted this as meaning 
 that the metabolic products of the contractile process, 
 the same compounds which in larger quantities will limit 
 the performance of the mechanism, act at first as stimu- 
 lants. This seems to be much more distinctly the case 
 with the neurons of the brain and cord. 
 
 We can often observe in people tired by a day of excite- 
 ment — perhaps of sightseeing— that there is an appear- 
 
 1 Macmillan, New York, 1911. 
 
 ^ W. B. Saunders Co., Philadelphia. 
 
NEURASTHENIA 205 
 
 ance of stimulation. They are talkative and demonstra- 
 tive. They laugh easily and with abandon. Their state 
 suggests a mild intoxication. It may be that the condi- 
 tion is more like an intoxication than we should be in- 
 clined to think. We account for the garrulity of banquet- 
 ers by saying that the alcohol has acted as a narcotic, 
 selecting the inhibitory centers for its primary action and 
 so giving the outward and subjective signs of stimulation. 
 The influence of the fatigue substances upon the brain 
 may be much like this. Whether the secret of the in- 
 fluence consists in a general stimulation or in the with- 
 drawal of desirable inhibitions, the obvious result is aug- 
 mented activity. 
 
 Once before we have alluded to the fact that the tired 
 nervous system craves employment, though it needs 
 repose. Many people will appreciate the following in- 
 stance cited by J. J. Putnam: An overwrought woman 
 had appealed to an old physician for advice. He had told 
 her that she must rest. Her reply was that she did not 
 feel tired and could not bring herself to be still. ''Madam," 
 said the doctor, "you will have to lie down until you are 
 tired and then rest." A hyperexcitability like this is un- 
 happily common in children, who nowadays have less 
 training in the exercise of inhibition than fell to the lot 
 of earlier generations. We may now go on to see how con- 
 sistently the neurasthenic exemplifies this heightened 
 nervous activity in every department of his organization. 
 It is easy to recognize that a vicious cycle is involved, 
 the overaction intensifying the fatigue and yet failing to 
 bring automatic relaxation. 
 
 Guided by Courtney, we shall consider the signs of 
 neurasthenia as they appear in four realms. These are: 
 (1) The motor mechanism, (2) the sensory equipment, 
 (3) the autonomic or visceral field, and (4) the tempera- 
 ment. The connections of all these are such that dis- 
 turbances in one must be expected to overflow upon the 
 others. The reflex principle makes this inevitable. In 
 order that an organism shall be properly adjusted to 
 
200 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 its normal environment its central nervous system must 
 have a medium degree of resistance to the transmission 
 of impulses. If the resistance is raised, as by anesthesia, 
 the result is too great inertia; if the resistance is unduly 
 lowered, there are wasteful and exhausting reactions in 
 response to stimuli which might as well have failed to 
 produce any discharge of energy. 
 
 1. In the realm of the skeletal muscles nervous fatigue 
 expresses itself in the familiar form of restlessness. The 
 victim has less than his usual endurance and may be con- 
 sciously tired by his own unprofitable activity, but he 
 cannot keep still. He crosses and uncrosses his legs, 
 fum})les with his watch-chain, twirls his moustache, walks 
 about aimlessly, and tries one chair after another. Court- 
 ney has acutely noted the predilection of the neurasthenic 
 for rockers, which give an outlet to his uneasiness. In 
 some sanitariums the trouble is attacked along this fine; 
 hard and simple manual work is prescribed and pushed to 
 the point of weariness, that primitive exhaustion which 
 is pleasant by contrast with the other and which brings 
 sleep as its reward. 
 
 2. The sensory symptoms are just what we might expect 
 if the central characteristic is one of lowered resistance. 
 Stimuli which are not noticed by one in health are felt 
 unpleasantly, and sensations readily ignored by the normal 
 man become torment. This is true for the cutaneous sen- 
 sations; the neurasthenic is dissatisfied with the feeling 
 of his clothes and his bed. He is morbidly sensitive to 
 changes of temperature. When others would say merely' 
 that the room had grown a trifle warm, he says that it is 
 unbearably hot. When it is really a little cooler than is 
 ideal, he feels thoroughly chilled. He is much affected 
 by all changes of weather and may conceive an aversion 
 for certain winds, proving his keenness of judgment by 
 announcing each change. 
 
 The eyes share the general supersensitiveness. Strong 
 light is objectionable and the shrinking from it may grow 
 into photophobia. The after-images, those spots of com- 
 
NEURASTHENIA 207 
 
 plementary color which anyone may observe after looking 
 fixedly at bright objects, become persistent and dis- 
 quieting. The entoptic appearances, the shreds and spots 
 in the humors of the eye and the twinkling corpuscles in 
 the capillaries of the retina, obtrude themselves upon the 
 attention. Johannes Miiller was at one time greatly dis- 
 tressed by the loss of the power to exclude these things 
 from his consciousness. They may be seized upon as 
 symptoms of ocular or brain disease. 
 
 As it is with the eye, so it is with the ear. Sounds be- 
 come wearisome; sometimes the loud ones are particularly 
 irritating, so that the subject cannot bear to hear children 
 at play, sometimes the greatest annoyance proceeds rather 
 from sUght and repeated noises, hke the ticking of a clock 
 or the gnawing of a mouse within the bedroom wall. 
 Olfactory stimuli may have an intensified effect and the 
 detestation of certain odors may seem unreasonable. 
 The sensory relations of the neurasthenic should serve 
 to make clear to a well person how desirable it is to be pro- 
 tected against so many of these possible sources of dis- 
 comfort by the height of the normal "threshold." The 
 same external forces assail the vigorous and the weakened 
 subjects ahke, but the sufferer from nervous fatigue 
 is like a man without a cuticle — everything is felt too 
 keenly. 
 
 3. As the admission of impulses into the central fabric 
 is too free, so the outpouring that follows is too profuse. 
 We have seen how this is expressed through the neuro- 
 muscular system as unrest. We have now to turn to the 
 autonomic system. Impulses sent out over the paths of 
 this system may have either inhibitory or excitatory 
 effects. We find evidence of their action upon the heart, 
 the blood-vessels, the digestive tract, the genito-urinary 
 organs, and the sweat-glands. The list might readily be 
 extended to include still other responding elements. 
 
 Heart symptoms in the neurasthenic are common. 
 They may be due in part to the direct flow of impulses of 
 undesirable intensity from the medulla to the organ; they 
 
208 THE NERVOUS SYSTEM AXD ITS CONSERVATION 
 
 are xcvy lik(>ly to be aujijinciited by rcHox influences from 
 a disordered alinientar}^ canal. Irregularities of the 
 heart-beats are likely to be noticed and there are uneasy 
 sensations of abnormal mobility about the heart, feelings 
 "as though it turned over," etc. The acceleration during 
 muscular activity may seem greater than it should be 
 and the ^'ictim may become fearful of local organic defects. 
 Along with the cardiac misbehavior thei'e will probably be 
 vasomotor instability. It is the duty of the vasomotor 
 system to maintain a proper and nearly steady arterial 
 pressure. Failure to do this may result in feelings of 
 faintness and vertigo, perhaps, at other times, in head- 
 ache. 
 
 To the perverted action of the vasomotor system we may 
 ascribe the exaggerated judgments of warmth and cold 
 already mentioned. If the nervous mechanism is in such 
 a "hair-trigger" condition that a slight rise of the external 
 temperature causes an intense flushing of the skin, while a 
 slight depression renders it anemic, these impressions are 
 to be expected. It is to be remembered that the tempera- 
 ture which we feel is that of the skin and not that of the air. 
 The waxing and waning of the cutaneous blood-flow will 
 have as much to do with the sensation as the state of the 
 air outside. In the neurasthenic the vasomotor changes 
 which accompany emotion are excessive. Extraordinary 
 outbreaks of perspiration are frequent. 
 
 The symptoms arising from the functional derangement 
 of the alimentary canal are of especial importance. It 
 was stated in an earlier chapter that this essential system 
 has such a degree of automaticity that in many cases it 
 might work better with no intercourse with the brain and 
 cord than it is actually observed to do. Foster speaks of 
 the improvement of digestive capacity often noted in the 
 aged. As the nerve-centers become less dominant the 
 stomach and intestine do their duty in a more reliable 
 manner than they did under more constant regulation, 
 and the former dyspeptic "eats with the courage and 
 success of a boy." In view of such facts we can under- 
 
NEURASTHENIA 209 
 
 stand that the organs of digestion in the neurasthenic are 
 suffering from too much intermeddUng. 
 
 The central influence is so largely inhibitory that the 
 chief effect may be characterized as a general retardation 
 of the activities of the tract. This includes a loss of posi- 
 tiveness in movement and a withholding of secretions. 
 The stomach retains its contents longer than it should, and 
 instead of being acted upon by a strong and antiseptic 
 gastric juice, they are fermented by micro-organisms. 
 What happens in the stomach is continued with minor 
 variations in the intestine. The extensive decomposition 
 may well give rise to definitely poisonous bodies and so 
 to auto-intoxication, which is thus both a cause and an 
 effect of neurasthenia. Another annoying result of the 
 fermentation is the voluminous production of gas. This 
 feature of nervous prostration is so marked that some 
 physicians have thought that the quantity of the gas could 
 not all be due to bacterial action. They have considered 
 whether it might not come in part from an actual .secre- 
 tion of carbon dioxid from the blood into the tract. At 
 any rate, it becomes a source of discomfort, even of sharp 
 pain, while the distention is likely to occasion reflex dis- 
 turbances of heart action. The picture is a familiar one, 
 particularly in the country, where there is less thought 
 for appearances — the sallow, angular dyspeptic, with fre- 
 quent sighs and yawns and noisy belching of gas. 
 
 With deficient tone and peristalsis, constipation is to be 
 anticipated. It may be extreme and is a matter much 
 brooded over by the sufferer. He may be much given to 
 experimenting with cathartics and enemata. On the 
 other hand, constipation may actually exist and yet be 
 unrecognized, for, if there are massive accumulations in 
 the colon which the relaxed muscles fail to displace, the 
 local irritation may set up a catarrhal condition with 
 liquid discharges made urgent by the ever-present gas 
 and simulating diarrhea. There are two places in the 
 large intestine where fecal retention is likely and which 
 may become the seat of pain. One is near the spleen 
 
 14 
 
210 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 (close to the lower ribs on the left side) and the other is at 
 the sigmoid flexure lower down on the same side. Severe 
 pain is said to arise from the overloaded sigmoid and to be 
 referred to the left groin and hip-joint. 
 
 These various pains are not readily attributed by the 
 neurasthenic to their ignoble and commonplace cause. He 
 is half-anxious to find grounds for the belief that he is 
 suffering from a mortal disease, and he prefers the idea 
 of a cancer to constipation of nervous origin. Courtney 
 says incisively that his fears lead only to an anticlimax — 
 he is very likely to develop hemorrhoids. 
 
 The genito-urinary tract does not escape the influ- 
 ences of the overactive centers. The concentration of 
 the urine varies in an erratic way between extremes. 
 When it is scanty and high colored, depositing sediment 
 on standing, the subject may diagnose his case as Bright's 
 disease. If, a little later, it becomes pale and profuse, 
 he may decide that he has diabetes. There is plenty of 
 pernicious advertising matter to confirm any of his con- 
 clusions. The bladder is hkely to be irritable and micturi- 
 tion frequent. The reactions of the reproductive organs 
 come in for a share of anxious surveillance, especially in 
 the young. Here, even more than with the kidneys, the 
 insidious suggestions of quacks sent broadcast in their 
 repulsive literature may stimulate agonies of fear. 
 
 4. Many glimpses of the subjective state in neurasthenia 
 have already been afforded. It is one of egotism, disregard 
 of others, and self-pity. We have most of us reason to 
 cherish memories of men and women who have gone with 
 splendid heroism and unselfishness through seasons of 
 suffering and even to death. We know of sainted invalids. 
 But these cases which move us so deeply to reverent ad- 
 miration are the ones in which the nervous system in its 
 higher parts has been left relatively unscathed. When it 
 is disordered we can no more expect an exhibition of fine 
 and strong character than we can expect beautiful music 
 from an instrument which is altogether out of tune. The 
 neurasthenic is not his best self. 
 
NEURASTHENIA 211 
 
 When this is said, the question arises, Is there a sharp 
 hne between the temporary warping of disposition that 
 we see in the neurasthenic and the irresponsibility of def- 
 inite insanity? A recent writer has set a standard which 
 is an attractive one if we can be wise enough to apply it 
 rightly. It is this: The neurasthenic differs from the 
 psychasthenic, as we may call the graver defective, in the 
 fact that he fabricates nothing, but merely exaggerates and 
 distorts. There is some foundation for all his complaints. 
 He is not insane until he is in touch with things which 
 have no existence for other people. Fortunately, in the 
 vast majority of cases, he is destined to recover his poise 
 and not to cross the sinister boundary. 
 
 There are few things more difficult than to deal 
 humanely and yet firmly and consistently with neuras- 
 thenia. A tolerant and even mind is called forgone that 
 shall possess all the temperance and perspective which for 
 the time being are so sadly wanting in the patient. The 
 most cruel anguish which must be endured is in experien- 
 cing the enfeeblement of affection which has overtaken the 
 stricken husband or wife. Cutting words from the once 
 loyal companion, bitterness that would never be exhibited 
 to a stranger, must be borne without remonstrance. The 
 superiority of the sanitarium to the home in most cases 
 may be traced to the usual failure to live up to such exac- 
 tions. In the institution some restraint is imposed upon 
 the patient by the strangeness of his contacts, while the 
 trained attendants maintain a uniform attitude instead of 
 alternating between caresses and angry argument. 
 
 It must not be forgotten that the suffering described by 
 the neurasthenic is as real as any that life brings. It 
 merits sympathy. Yet the free expression of much 
 sympathy sinks the victim in deeper despondency and 
 encourages him to invent new theories to account for his 
 misery. It also makes his future appear darker than ever. 
 Even the most earnestly phrased sympathy will not seem 
 adequate to the pity-consuming neurasthenic. He remains 
 skeptical as to the possibility that anyone can really appre- 
 
21J THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 c'iate his woe. He is likely to wish that his friend might 
 feel just what he feels, showing in this the marked con- 
 trast between his own state and that of the sufferer with 
 rheumatism or tuberculosis, who is glatl that others are 
 well if he cannot be. 
 
 The studied withholding of sympathy from neuras- 
 thenics has often had remarkable results. It is doubtle.ss 
 practised in many sanitariums, and there is one institution 
 in particular in which it is a chief measure of treatment. 
 The broken-down business man who comes to this resort 
 does not wait long before he attempts to set forth his tale 
 of hopeless suffering, but each attendant cuts short his 
 expatiating with brusque or jocular rejoinders. The 
 spirit of the neurasthenic is deeply wounded and, at first, 
 his self-pity is intensified. Perhaps he casts himself upon 
 his bed and weeps in his desolation, turning his face to the 
 wall like the undisciplined Hebrew king. 
 
 If we bear in mind that the central fact in neurasthenia 
 is excess of nervous activity, we shall foresee that correc- 
 tion must come from inhibition. Now, one of the first 
 steps toward the attainment of self-control is taken when 
 the patient becomes assured that he cannot obtain the sym- 
 pathetic response which he so greatly craves, and begins 
 to hold his tongue. Another reaction which is sometimes 
 beneficial is the provocation of the invalid to anger. At 
 the sanitarium referred to, the harsh attitude maintained 
 by the attendants leads readily to the loss of temper on the 
 part of the sufferer. If he forgets himself so far as to lay 
 hands upon his nurse, he is vigorously handled. Insulted 
 and humiliated, he descends to the uttermost depths after 
 such a passage at arms. But if the experience is repeated 
 at intervals, the regular habits and general hygienic con- 
 duct of the institution having their effect in the mean- 
 time, the emotion of anger gradually comes to bring with 
 it a sense of power instead of impotence. The return of 
 self-reliance and self-government is said to be splendid to 
 witness. If a day comes when the convalescent demon- 
 strates that he can put his tormentor out into the corridor, 
 
NEURASTHENIA 213 
 
 he rejoices with a hvehness that he had never expected to 
 reaUze again. 
 
 Plainly, this systematic piquing of the nervous invalid to 
 restore both the capacity for inhibition and for vigorous 
 performance cannot be practised successfully upon those 
 who have organic disorders as an important element of 
 their condition. Medical or surgical treatment is appro- 
 priate in all such cases. Attractive meals and acceptable 
 forms of recreation are of great importance. Courtney 
 protests against the common error of sending neuras- 
 thenics into the country, where they find a degree of stag- 
 nation that is as distressing to them as the excess of 
 action from which it is planned to have them escape. 
 A medium condition is to be chosen, in which both the 
 sense of pressure and the sense of enforced idleness may be 
 avoided. If the patient is willing to be lazy for a while, 
 this is very fortunate, but it is more likely that he will 
 demand some variety of interests. 
 
 Exercise is a definite need of the neurasthenic, but it is 
 desirable that it shall be interesting and not merely mechan- 
 ical. Courtney recommends hunting, because it is so well 
 calculated to take one out of self and fix the attention on 
 the world outside. The more the mind can be made to con- 
 cern itself with the messages of the special sense organs, 
 the less it can dwell upon the misbehavior of the body. 
 Much may be said in favor of walking in mild or incipient 
 cases. Long tramps in the country are not quite so refresh- 
 ing as they were before the automobiles filled the roads 
 with dust and stenches and woke the echoes with their 
 raucous and insulting horns, but it is still possible to 
 choose routes over byways which are rarely invaded by 
 motor cars. The most stimulating element in a walk is 
 novelty. The country should not be well known to the 
 walker. He will then have a delightful series of surprises 
 as the unexpected landscapes open to his view, broad 
 prospects from the hill-tops and glimpses of rushing brooks 
 in shaded valleys. 
 
 A vigorous walk of a hundred miles in four days taken 
 
214 THE XEKVOUS SYSTEM AND ITS CU^■SER^■AT10X 
 
 when one has recojiiiized signs of nervous fatigue will often 
 exert a prolonged and favorable influence on one's condi- 
 tion. It is hard to find a congenial companion for such an 
 excursion, and on some accounts it is not a bad plan to go 
 alone. There can then be no clash of wishes, and it may be 
 profoundly restful not to be obliged to talk. The gentle 
 mental stirring which attends the uncertainty regarding 
 the course and ending of each stage is exceedingly whole- 
 some. Equalh^ so on the phj'^sical side is the profuse out- 
 puring of perspiration and the compensator}- water drink- 
 ing. Village hotels rather than farmhouses are to be 
 recommended as stopping-places. They do not impose 
 the obligation of sociability upon the tired wayfarer and 
 they usually offer him the luxury- of a hot bath. 
 
 Sea- voyages are often beneficial to those who lack vigor 
 for more active recreation. There is hardly another situa- 
 tion in which individual responsibility is so successfully 
 annulled and one's fortunes so absolutely committed to 
 others. But the life on shipboard does not appeal to all 
 temperaments. The scenic aspect of the ocean presents 
 abundant variety to the observer who loves it, but another 
 finds it monotonous. 
 
 We have previously maintained that intellectual inter- 
 ests ought to make for stability of nervous organization. 
 It should now be clear that what the neurasthenic most 
 lacks is sense of proportion. His own concerns are mag- 
 nified undul}^ and the present circumstances are allowed 
 too greatly to outweigh those which have obtained in the 
 past and may return in the future. It is a mark of mental 
 soundness to be able to overrule such a tendency. If a 
 man passing through temporary troubles can hve over the 
 happier events of an earlier time, and can realize the prob- 
 ability that they will again be realized, he is sustained by 
 these ties as the Alpine tourist is held safe by the other 
 members of his party. 
 
 Some knowledge of science is well calculated to fortify 
 one against egotism. It is hard to see how anyone who 
 possesses the scientist's grasp of time and space can fall 
 
NEURASTHENIA 215 
 
 into the habit of overemphasizing his own importance to 
 the universe. Yet he should not think meanly of himself. 
 The poise that springs from having a scientific perspective 
 is compounded of belief in the value of individual effort 
 and the restful conviction that when such effort flags 
 through weariness the creative currents of nature flow on 
 in other channels. 
 
 This comes very near to religion, at least to Matthew 
 Arnold's faith in "a power not ourselves that makes for 
 righteousness." This has been called the irreducible 
 minimum of religion. For the vast majority of mankind 
 the philosophic belief is not a commanding motive until 
 it is warmed with an infusion of devotion and personality. 
 But whatever the clothing of the central idea, its inesti- 
 mable power to sustain health and efficiency has been rec- 
 ognized in every age. At the present time it is familiarly 
 associated with Christian Science. 
 
 To an outsider the leadership of this cult appears 
 domineering and mercenary. The adherents seem utterly 
 inconsistent. We see them yielding to hunger, fatigue, 
 cold, and heat. They grow old, sicken, and die. Yet 
 we may not doubt that they maintain on their course 
 an exceptionally high average condition. If a touch of 
 fanaticism encourages them in the belief that the same 
 achievements are denied to those who hold other creeds, 
 we can understand that this very defect is a source of 
 positiveness and conviction. Bigotry is better for man 
 than indifference, though we may well seek to combine 
 earnestness with generosity and tolerance. 
 
CHAPTER XVIII 
 
 SOME MATTERS OF GENERAL HYGIENE 
 
 It will be well to supplement the suggestions already 
 made with some others that do not readily find their place 
 under the titles of previous chapters. Emphasis has been 
 placed on the fact that all that favors the well-being of the 
 nervous system goes to support the general health. But 
 there is danger of a one-sided view if the opposite asser- 
 tion is not admitted ; namely, that all that ministers to the 
 other systems helps to preserve the nervous mechanism. 
 
 Five heads may be suggested which shall fairly cover 
 the requirements of hygiene. These are: (1) A sound in- 
 heritance, (2) successful nutrition, (3) suitably varied 
 activity in all departments of organization, (4) rest prop- 
 erly adjusted to the foregoing, and (5) a wholesome en- 
 vironment. When we consider the last-named subject we 
 find that it covers some matters for which the individual 
 is responsible and some which rest upon the community. 
 Sufficient attention has already been bestowed upon some 
 of these topics; others may now be granted a little space. 
 
 The teachings of modern science concerning heredity 
 may have confused the thinking of some intelligent 
 readers, and it may be worth while to venture a few com- 
 ments. The widespread interest in eugenics makes people 
 who are intellectually honest anxious to be rightly in- 
 formed as to how far they can influence the physical and 
 mental estate of their children. The average man will 
 probably be found to have a very definite behef in this 
 connection. He thinks that his moral victories secure 
 stamina in the offspring, and that his lapses weaken his 
 progeny. He is likely to think that athletic training on 
 his part will endow his son with a superior musculature. 
 21Q 
 
SOME MATTERS OF GENERAL HYGIENE 217 
 
 Similarly, he may assume that scholarly achievements of 
 his own will make similar attainments easier for his 
 children. 
 
 When a man holding views like these first hears that 
 scientists generally deny "the inheritance of acquired 
 characters" he is likely to feel that his moral responsibil- 
 ity has been gravely impaired. The immediate impression 
 is that conduct is without significance in heredity, and that 
 a very strong and noble motive for self-restraint has been 
 abolished. Reflection will convince one that such im- 
 pressions are not wholly warranted. One's obUgations are 
 scarcely impaired. 
 
 In the first place, there are at least two consequences of 
 transgression which are still believed to pass on from father 
 to son. Syphihs is one of these. The other is the complex 
 of effects induced by alcoholism. Therefore, deterrents 
 from the two commonest forms of intemperance remain 
 in full force. Gonorrhea is not strictly inherited, but the 
 peril of infection at birth and the inclusion of the wife in 
 the calamity leave every possible ground for continence 
 unshaken. 
 
 It may now be pointed out that in matters less specific 
 than these the individual may still have reason to consider 
 carefully what manner of hfe he has led when he con- 
 templates parenthood. His acts may not have modified 
 the stock, but we now regard them as illustrating its 
 properties. These properties are regarded as having 
 great stability. The son resembles the father not because 
 of certain acts which the father performed, but because 
 the inheritance common to both makes them likely to behave 
 in a similar way under similar circumstances. Some one 
 has expressed the fact picturesquely by saying that "the 
 son is not a chip of the old block, but father and son are 
 both chips of the same old block"— the immemorial 
 ancestry which they share. 
 
 This being the case, a man reviewing his career and hav- 
 ing in mind the probable future of his children may reason 
 somewhat as follows: "My indulgences and my denials 
 
218 THE NERVOUS SYSTEM AND ITS CONSERVATION 
 
 have scarcely aft'ected the capacities of the stock. But 
 my mdulgences have exhibited its inherent weaknesses and 
 my self-restraint has shown its streng:th. My failures 
 are ominous and my victories reassurin"-, for the like are 
 to be expected in the life of my son." The ^rave and final 
 question is whether the stock ought, on the whole, to be 
 perpetuated. This is comphcated by the consideration 
 that the son will owe half his inheritance to the mother. 
 "He is his father's half-])rother by a different mother." 
 While it is fair to give due weight to this fact, it is hkely 
 that many men have trusted too freely to the maternal 
 stock to neutralize their shortcomings.^ 
 
 The data of eugenics are easily subjected to ridicule, 
 while, at the other extreme, too much may be expected 
 from the new science. We can already see that at least 
 one valuable service may be rendered by it. The workers 
 in this field are showing that hereditary defects are of two 
 classes, those due to lack and those due to positive features 
 of the germ plasm. A lack can be made good by proper 
 mating; a positive property will taint the offspring what- 
 ever partner may have been secured, and so can never be 
 neutralized. It is agreeable to find that the majority of 
 abnormalities are deficiencies, and theoreticalh^ can be 
 bred out of the race instead of being allowed to die out. 
 Practically, however, the strong and efficient can hardly 
 be expected to forego mating with their equals to redeem 
 the weaker stocks. 
 
 Since reference has been made above to the damage 
 done by alcohol, we may pursue the subject further and 
 say something of its individual as well as its hereditary 
 results. Two opjwsing views of the general problem are 
 maintained. Most writers assume that alcohol is a chief 
 cause of degeneracy. On the other hand, it is ingeniously 
 maintained that the indulgence is as much a sign as a 
 cause of the conditions with which it is associated. Accord- 
 ing to this conception, a drunkard is a man who would 
 
 1 Jordan, "The Heredity of Richard Roe," The American Uni- 
 tarian Association, Boston, 1911. 
 
SOME MATTKIiS OF GENERAL HYGIENE 219 
 
 have> been a worthless fellow even if he had never discov- 
 ered the consolations of liquor. This we can readily 
 grant for certain cases, but we can think of others where 
 we feel sure that nothing but alcoholic intemperance has 
 stood in the way of useful or even briUiant attainment. 
 
 One thing which we do not much like to remember is 
 that none of us are many generations removed from ances- 
 tors who were frequently intoxicated. Only the Mahome- 
 tan can claim that his case is otherwise. Reid Hunt, com- 
 paring the toxicity of grain alcohol and wood alcohol as 
 determined upon the lower animals, found that while 
 wood alcohol is more poisonous than the other the differ- 
 ence is much less than for man. His suggestion is that the 
 human race is habituated to grain alcohol by ages of drink- 
 ing. It has never gained any such tolerance for wood 
 alcohol largely because it has not often employed it as a 
 beverage. 
 
 Keeping the welfare of the nervous system in the fore- 
 ground, let us consider the action of alcohol as experienced 
 by those who take it very moderately. It is popularly 
 held to be a stimulant, and the claim has a measure of 
 scientific support. But most students emphasize its de- 
 pressant property, pointing out — what has been said 
 elsewhere — that to depress the inhibitory centers is to 
 ''take off the brakes" and to create an appearance of 
 stimulation. The most impressive articles that have been 
 written in defense of the retention of alcohol have come 
 from writers who did not recommend it as a stimulant, but 
 as a means of promoting mental relaxation and social ease. 
 It is disquieting to the advocate of total abstinence to 
 find that the great majority of the most original and, 
 on the whole, the most admirable men have valued alco- 
 hol as a social reagent. It begins to seem as though a 
 reaction were setting in, but it will evidently be a long time 
 before the representative gatherings of leaders in poUtics, 
 letters, and even in education will forego their wines 
 without complaint. 
 
 The temperamental change induced by alcohol in 
 
220 THi: xKiivors system and its coxsiohvation 
 
 moderate (luantities is hij^lily chanictcristic. It iiui}' be 
 described as intellectual myopia, a condition in which all 
 that is near at hand — the present company and the inter- 
 ests of the hour — will be found dominant, and all that is 
 remote from these will tend to be excluded. Thus, the 
 cares that weighed upon the banqueter before he came to 
 the feast and the problems he must face next morning are 
 forgotten. We have insisted that this detachment is most 
 desirable and hygienic. But the ideal is to compass it at 
 will without the employment of a chemical artifice. One 
 who can relinquish care as a voluntary act can take it up 
 again promptly and earnestly. The banishment of obliga- 
 tion by alcohol does not permit the same decisive resump- 
 tion of responsibilit3^ It is well for the man who is head 
 of a family, when he reviews some convivial occasion, to 
 ask himself whether the wife and children at home did not 
 recede farther from the forefront of his consciousness than 
 he would have chosen to have them. Perhaps the bachelor 
 need not be so exacting in his introspective judgment. 
 
 It seems wellnigh impossible to write without bias of the 
 social use of alcohol. Those who uphold it charge their 
 opponents with a want of charity and with a disposition 
 to demand needless renunciations of pleasure. They would 
 probably assert that the tj^pical moderate drinker is a 
 kindlier man than the typical abstainer and that he is 
 not less efficient. To be quite just to those who maintain 
 this position one should read the pleas of such writers as 
 Holmes, Mlinsterberg, and Heinemann.^ 
 
 If it is a difficult matter to pass judgment upon those 
 who use alcohol, what shall be said of caffein, the active 
 principle of tea and coffee? This is an agent which we 
 sometimes hear unsparinglj'- condemned, but most vigor- 
 ously by those who have substitutes to offer. Many 
 
 1 Holmes, "The Autocrat of the Breakfast Table," Riverside 
 Edition, Houghton, Mifflin & Co., Boston, p. 1S7 et seq. Miinster- 
 berg, "American Problems from the Point of View of a Psychol- 
 ogist," MofTat, Yard & Co., New York, 1910. Heinemann, "The 
 Rule of Not Too Much," Chicago, 1912. For counter-arguments, 
 see Crooker, "Shall I Drink?" The Pilgrim Press, Boston, 1914. 
 
SOME MATTERS OF GENERAL HYGIENE 221 
 
 experimental studies have consistently shown that caffein 
 is a true stimulant, actually increasing the capacity for 
 muscular and mental work. The advisabihty of resorting 
 to a stimulant must depend largely upon the extent of the 
 after-effect and upon possible cumulative injury. 
 
 A most painstaking investigation of the properties of 
 caffein was reported recently by Hollingworth.^ It was 
 conducted upon a considerable scale, a staff of 7 trained 
 workers gathering data from 16 subjects (of whom 10 were 
 men and 6 women). In all trials of this kind it is neces- 
 sary to keep the subjects in ignorance of the times at which 
 they receive the drug to be tested. HoUingworth gave 
 them at intervals gelatin capsules many of which were 
 blanks, while others contained measured doses of caffein. 
 The heaviest dose equalled the quantity in two large cups 
 of coffee. Ingenious tests were made as a matter of daily 
 routine, whether the caffein was given or not. Speed, 
 dexterity, discrimination, and mental alertness were 
 observed. 
 
 The results of the research were almost entirely favor- 
 able to caffein. Gains were recorded in all the capacities 
 investigated. The tests made with the typewriter were 
 of the most practical interest. When caffein had been 
 received by the worker the copying was accomplished 
 somewhat more rapidly and with fewer errors than at 
 other times. Moreover, when mistakes were made, they 
 were more often recognized on the instant. It is instruc- 
 tive to compare these facts with those that have been 
 secured with alcohol. Both alcohol and caffein probably 
 inspire the user with confidence in his ability to do his best. 
 But there is a divergence in the actual performance, 
 alcohol failing to give the promised reinforcement, and 
 caffein confirming the subjective impression quite deci- 
 sively. 
 
 We naturally assume that a period of stimulation will 
 be followed by one of corresponding depression, as the 
 
 ^ "Archives of Psychology," The Science Press, New York, 
 April, 1912. 
 
222 THE NERVOUS SYSTEM AND ITS CONSKKVATION 
 
 trough of a wave follows the crest. HoUingworth has 
 failed to find evidence of any such reaction. Nothing in 
 the report is more unexpected or more important if it shall 
 be sustained. If it is possible to enhance working power 
 and not entail any extra fatigue, we must conclude that the 
 part played by the stimulant may be quite innocent and 
 desirable. Several years ago a wise teacher suggested 
 that a whip is appropriate for the lazy, but not for the 
 tired, horse.^ 
 
 In spite of HoUingworth's impressive findings, it would 
 be unsafe to conclude that all people can advantageously 
 use tea and coffee. Many exceptions are apparent. Even 
 among the members of HoUingworth's squad the larger 
 doses caused some feverish conditions, headache, and 
 sleeplessness. If such reactions were markcfl and long 
 continued, there can be no doubt that the favorable effects 
 of caffein would soon be exchanged for detrimental ones. 
 Only three or four of the subjects were non-users of 
 caffein before the experimental period. It is probable 
 that there are a good many abstainers from coffee who 
 have learned b}^ disagreeable experience that they must 
 do mth'out it. 
 
 While we may not condemn in a sweeping fashion the 
 taking of caffein, nor even the guarded indulgence in 
 alcohol, there is no room for two opinions regarding the 
 dangers of more active drugs. All use of morphin, cocain, 
 and their congeners is perilous. Temperance in their 
 employment is conceivable, but seems scarcely ever to be 
 realized. The tendency to increase the dosage is almost 
 irresistible. There is hardly a spectacle so tragic as that 
 of the drug victim, steadily deteriorating in character, until 
 his moral cowardice, dishonesty, and lack of self-respect 
 are incredible to the members of his family. Some one 
 has said that "the drunkard turns night into day and the 
 morphinist turns day into night." The influence of cocain 
 seems to resemble that of alcohol rather more than that of 
 
 ' Hough and Sedgwick, "The Human Mechanism," Ginn & Co., 
 Boston, 1906, chap. xx. 
 
SOME MATTERS OP GENERAL HYGIENE 223 
 
 morphin; it leads to reckless and violent crime. There is 
 a popular impression that the habit-forming alkaloids 
 produce delightful subjective states. This seems rarely 
 to be the case after the first foolish ventures; the most that 
 the unhappy wretch reports later is that the drug relieves 
 — and often incompletely — the misery of abstinence. 
 
 A final word may be added concerning the attitude which 
 we should maintain toward medicine and the medical pro- 
 fession. Physicians were once held in high respect by all 
 civilized people. At the present time, when the attain- 
 ments and principles of the profession merit, far more than 
 ever before, popular esteem and admiration, a hostile and 
 skeptical spirit is often manifested. Several causes for this 
 are evident. The fact that drugs are less relied on to 
 remedy diseased conditions than was formerly the case 
 has encouraged the hasty conclusion that they have no 
 value at all. Errant schools, using pecuhar therapeutic 
 methods, have fiercely attacked the main body of prac- 
 titioners. Patients who have been benefited by these 
 special measures have joined heartily in denying the virtue 
 of other kinds of treatment. Psychotherapy has led to the 
 same reaction in spite of the broad views urged by its 
 ablest exponents. Certain periodicals have made inces- 
 sant, mahcious attacks upon the profession, charging 
 mercenary aims, unwarranted experimentation upon hu- 
 man subjects, and failure to effect cures. It is amusing 
 — even while it is irritating — to note that those who write 
 such articles charge the physician with being unwilHng to 
 adopt new methods, and in the next paragraph cry out 
 against his innovations. The dignified silence main- 
 tained by medical men in the face of these attacks is not 
 properly appreciated by a thoughtless public. 
 
 When it is suggested that physicians and surgeons ask 
 excessive fees there are two or three reflections that should 
 modify judgment. It is a trite saying that restoration to 
 health has a value not easily expressed in money. Second, 
 we should consider the investment of time, strength, 
 and means which has equipped the doctor for his respon- 
 
224 THE XKHVOrS 8YSTi:.M AXD ITS CONSERVATION 
 
 sible service. Third — and this is often overlooked — it is 
 the generous payments of those who can afford them which 
 make it possible for the practitioner to give his best skill 
 freely to the poor. 
 
 Too many intelligent people have failed to read of the 
 achievements of medical science. It is only when the 
 former insecurity of life is contrasted with its present 
 conservation that our indebtedness to the profession is 
 realized. The stories of the conquest of small-pox and 
 yellow fever are among the most thrilling that can be 
 found in human annals. The discovery of the chief 
 methods of anesthesia and of the way to avoid surgical 
 infection — these have almost an equal power to grip \hc 
 reader. A little acquaintance with the literature of 
 seventy-five years ago suffices to make one realize the 
 horror of epidemics, particularly of yellow fever and 
 cholera. Typhus fever, which once ravaged the steerages 
 of emigrant ships, has become a rare and curious disease. 
 Pessimists often lay stress upon the increasing prominence 
 of certain causes of death. They forget that since man is 
 mortal, the individuals who escape one malady must later 
 be counted among the victims of another. The happy 
 fact is that they have lived through longer, more vigorous, 
 and more rewarding lives. 
 
INDEX 
 
 Accelerators, cardiac, 117 
 Accomplishments, 54 
 Adjusters, 18, 33, 52 
 Adrenal bodies, 92, 109, 170-172 
 Afferent paths, 75-82, 99, 143 
 
 type of neuron, 31, 32, 78, 79 
 Age, 156, 157, 181 
 Alcohol, 217-220 
 Alimentary canal, 125, 208 
 AU-or-none law, 90 
 Amputation, 45 
 Anemia, 194 
 
 theory of sleep, 175-177 
 Anesthesia, 196 
 Anger, 168, 212 
 Animals, decerebrate, 129-133, 
 
 174 
 Ant, 47 
 
 Antagonistic muscles, 94 
 Anticipation, 159, 160 
 Aphasia, motor, 147-149 
 Association areas, 150, 151 
 
 fibers, 151 
 Associative memory, 128, 129 
 Astigmatism, 195, 196 
 Ataxia, 99 
 Auditory area, 145 
 
 nerve, 73, 81 
 Auto-intoxication, 193, 194, 209 
 Automatic property, 20 
 Autonomic system, 114-126, 175 
 in emotion, 170-172 
 in neurasthenia, 207-210 
 Axis of nervous system, 66, 67 
 Axis-cyUnder or axon, 26 
 15 
 
 Bell's law, 62 
 
 Brain, circulation in, 175 
 
 frog's, 60-65 
 
 gray matter in, 70 
 
 rabbit's, 65-67 
 
 ventricles of, 64 
 Breathing, 99, 100 
 Burnett on decerebrate frogs, 130, 
 
 note 
 
 CAFrEiN, 220-222 
 
 Camis on reflexes, 93 
 
 Cannon on emotion, 165-167, 
 170, 171 
 
 Cardiac accelerators, 117 
 nerves, 116-118 
 
 Cavities of central nervous sys- 
 tem, 62-64 
 
 CeU theory, 22 
 
 Cells, 22-24 
 
 Cerebellum, 65, 68, 96-99, 128 
 
 Cerebral hemispheres. See Cere- 
 brum. 
 
 Cerebrospinal fluid, 61 
 
 Cerebrum, 64, 70, 88, 127-155 
 lobes of, 71 
 
 Chiasma, 73 
 
 Chorda tympani, 119 
 
 Christian Science, 215 
 
 Cii'culation in brain, 175 
 
 City Ufe, 167 
 
 Cold, sensation of, 78 
 
 Concentration and detachment, 
 158 
 
 Conduction, 25, 79 
 
 225 
 
22() 
 
 INDEX 
 
 Congestion, 121, 122 
 
 Connective tissue, 11 
 
 Constipation, 209, 210 
 
 Contractile tissue, 12 
 
 Convolutions, 70 
 
 Coordination, 14, 93 
 
 Corpora quaclrigcmina, 66 
 
 Corpus callosum, 70 
 
 Cortex, 70, 136 
 
 Coughing, 50 
 
 Courtney on neurasthenia, 204- 
 
 213 
 Cranial nerves, 60, 71-74 
 Crile on unfelt injury, 196-199 
 Crura cerebri, 69 
 Cytoplasm, 24 
 
 Dancing, 109 
 
 Darwin's use of limited strength, 
 
 159 
 Decerebrate animals, 129-133, 
 174 
 
 child, 132 
 Degeneration, 35 
 Delirium, 92 
 Dendrites, 29 
 Dendrons, 29 
 Depth of sleep, 178 
 Descartes on memorj^ 136 
 
 on reflexes, 49 
 Diaphragm, 103 
 Diet, influence of, 112 
 Dreams, 184-191 
 
 classified, 184 
 
 eyes in, 190 
 
 sensations in,. 197 
 
 symbolism in, 187 
 
 visceral symbols in, 187 
 Drugs, 222 
 
 EfTcctors defined, 18 
 
 Elbow, 42 
 
 Electric i)henomena, 17, 39, 171 
 
 Ellis on dreams, 177, 184-191 
 
 Emotion, 164-172 
 
 Epilepsy, 142 
 
 Epithelial tissue, 12 
 
 EquiUbrium, 81, 97 
 
 Escape (of heart), 117 
 
 Eugenics, 216-218 
 
 Evolution of nervous system, 
 
 19 
 Eye-muscles, 74 
 Eyes in dreams, 190 
 Eye-strain, 194-19t) 
 
 Far-sight, 195 
 
 Fatigue and dreams, 185-187 
 
 general, 203-205 
 
 neuromuscular, 101-110 
 
 synaptic, 105 
 Fatigue-products, 101, 102 
 Fibers, association, 151 
 
 regeneration of, 35 
 
 secretory, 126 
 Fibrils, 26, 34 
 Fingers, 80 
 Flatulence, 209 
 
 Flechsig on association areas, 151 
 Fletcher on hours of sleep, 181 
 Flourens, pioneer experiments, 
 
 130, 133 
 Forbes on fatigue, 105-107 
 Foster on old age, 156, 208 
 Freud on dreams, 189 
 Friction, domestic, 200 
 Frog's nervous system, 60-65 
 Functional and organic disorders, 
 
 203 
 
 Early conceptions of nerve ac- i Gage, Phineas, 152 
 tion, 37 : Gall, phrenologist, 134 
 
INDEX 
 
 227 
 
 Ganglia, 27, 115, 116 
 
 of dorsal roots, 78 
 Ganglion, Gasserian, 80 
 Genito-urinary symptoms, 210 
 Glands, nervous control of, 126 
 Goltz's decerebrate dog, 132 
 Gordon on infant mind, 154 
 Gradation of muscular responses, 
 
 89-93 
 Gravity and the circulation, 123, 
 
 124 
 Gray antl white matter, 26-28 
 
 matter in brain, 70 
 in cord, 68 
 Growth of muscles with use, 111 
 Gyri, 70 
 
 Habits, 54, 155, 156 
 
 Hearing, 81 
 
 Heart, 116-118, 120, 121, 208 
 
 inhibition of, 117 
 Heredity, 192, 216-218 
 Hollingworth on caffein, 221, 222 
 Howell on sleep, 176, 180 
 Hunt on alcohol, 219 
 Hygiene, 155-163, 167-170, 180- 
 
 182, 185-187, 200-202, 213-224 
 Hypnotism, rapport of, 56 
 
 Individual, 16, 47, 127 
 
 Infancy, 153-155 
 
 Inhibition, 20, 21, 157, 209. 212 
 
 of heart, 117 
 
 withdrawal resembles stimula- 
 tion, 20, 205, 219 
 Inhibitory influence on centers, 
 
 104, 108 
 Integration, 16 
 Intelligence, 127, 146 
 Intercellular substance, 24 
 Intoxication, 205 
 
 James on emotion, 167, 168 
 
 on habits, 155, 156' 
 James-Lange theory, 164, 171 
 Jordan on heredity, 218 
 
 Language, 147-150 
 Law, all-or-none, 90 
 
 BeU's, 62 
 Lee on fatigue, 102, 204 
 Lincoln's power of detachment, 
 
 158 
 Lingle on tonus, 91 
 Lobes of cerebrum, 71 
 Localization, 133-152 
 Loeb on locahzation, 139 
 Lucas on muscular action, 89-93 
 
 Martin et al. on sensory thresh- 
 old, 162 
 Medicine, 223, 224 
 Medulla, 63, 128, 143 
 Melius on the cortex, 150 
 Memory, 137, 161, 186 
 
 associative, 128, 129 
 Meninges, 61, 62 
 Midbrain, 64 
 Monotony, 160 
 Motor aphasia, 147-149 
 
 areas, 138-143 
 
 end-plates, 87, 102, 104, 112, 166 
 
 neurons, 33, 85 
 Miiller, 43, 207 
 MiiUerian principle, 44, 76 
 Mimsterberg on free agency and 
 
 mind, 141 
 Muscle-fibers, 85 
 Muscles, antagonistic, 94 
 
 eye-, 74 
 
 Near-sight, 194, 195 
 Nerve action, early conceptions 
 of, 37 
 
228 
 
 INDEX 
 
 Nerve, auditory, 73, 81 
 
 imijulscs, 37-40, 43 
 
 olfactory, Go, 71 
 in fish, 129 
 
 optic, 65, 72 
 
 trigeminal, 73, SO 
 
 vagus, 73 
 
 vestibular, 81 
 Nerve-centers, 53 
 Nerve-fibers, 25, 26 
 Nerves, 25 
 
 cardiac, 116-118 
 
 cranial, 60, 71-74 
 
 spinal, 60 
 Neurasthenia, 188, 203-215 
 
 sensations in, 206, 207 
 Neurasthenic temperament, 188, 
 
 210 
 Neiu'omuscular fatigue, 101-110 
 
 unit, 86, 87 
 Neuron, afferent type, 31, 32, 78, 
 
 79 
 Neurons, motor, 33, 85 
 
 postganglionic, 115 
 
 preganglionic, 115 
 Neiu-opile, 34 
 Newborn, 54 
 Nodes of Kanvier, 26 
 Nucleus, 24 
 Nutritional disturbances, 193 
 
 Occupation, 199 
 Olfactory area, 145 
 
 nerve, 65, 71 
 in fish, 129 
 Optic chiasma, 73 
 
 nerve, 65, 72 
 Orthodontia, 198 
 Overwork, 199 
 
 I^AIN, 199 
 
 Paths of easy transmission, 46 
 
 Perikaryon, alteration through 
 activity, 41, 197 
 defined, 30 
 
 reinforcing function, 41 
 related to nutrition, 34 
 
 Phrenology, 134, 135 
 
 Pilomotor action, 125 
 
 Play and work, 110 
 
 Pk^tliysmograph, 179 
 
 Pons, ()S 
 
 Postganglionic nem-ons, 115 
 
 Posture, 123, 124 
 
 Preganglionic neurons, 115 
 
 Prince on memory, 137 
 
 Profanity, 148 
 
 Projection fibers, 88, 143 
 
 Protoplasm, 24 
 
 Psychanalysis, 188-190 
 
 Psychasthenia, 211 
 
 Psychology, 16, 140 
 
 Psychotherapy, 197, 198, 215 
 
 Punctiform sensibility, 77 
 
 Putnam on fatigue, 205 
 
 Rabbit's brain, 65-67 
 Ranvier, nodes of, 26 
 Rapport of hjqjnotism, 56 
 Reaction-time, 58 
 Reading area, 149 
 Receptors, 18, 76 
 Reciprocal innervation, 95, 96 
 Reflexes, 49-59, 87 
 
 conditioned, 55 
 
 type of all nervous action, 
 139 
 Regeneration of fibers, 35 
 Religion, 163, 202, 215 
 Resjjiratory center, 100 
 Restlessness, 206 
 Right-handed condition, 146 
 Roots, dorsal and ventral, 62 
 Ruts, 46, 156 
 
INDEX 
 
 229 
 
 Sabbath, 161-163, 201, 202 
 Science, 214, 215 
 Sea-voyages, 214 
 Secretory fibers, 126 
 Sensations, 44, 76-84, 104 
 
 general and special, 83, 84 
 
 in dreams, 191 
 
 in neurastlienia, 206, 207 
 Sensibility, punctiform, 77 
 Sensory threshold, 162, 207 
 Sexual life, 189, 190, 217 
 Sherrington on coordination, 94- 
 
 96 
 Singing, 170 
 Skill, 113 
 Skin, 75, 121 
 Sleep, 173-183 
 
 anemia theory of, 175-177 
 
 depth of, 178 
 
 toxemia theory of, 175-177 
 Smell, 81 
 
 Speech center, 147-150 
 Spinal cord, 60, 69, 127 
 gray matter in, 70 
 Spontaneity, 131 
 Starling on cerebrum, 127 
 Stedman on Lincoln, 158 
 Stimuli, 17, 36, 37, 82 
 Strain, eye-, 194-196 
 Sulci, 70 
 
 Symbolism in dreams, 187 
 Sympathetic system, 116, 170 
 Sympathy, 168, 211 
 
 withholding of, 212 
 Synapse, 28, 33, 88 
 
 valve action of, 29, 30 
 Synaptic fatigue, 105 
 
 resistance, 46, 182 
 
 Taste, 81 
 
 Temperature and blood-flow, 121, 
 208 
 
 Thomson on aphasia, 148 
 
 on sleep, 174 
 Tissues, 11-14 
 
 connective, 11 
 
 contractile, 12 
 
 epithelial, 12 
 
 nervous, 13 
 Tolerance, 200 
 Tonus, 55, 119 
 Toxemia theory of sleep, 175- 
 
 177 
 Training, 91, 110-113 
 Treppe, 102 
 Trigeminal nerve, 73, 80 
 
 Vagus nerve, 73 
 Valve action of synapse, 29, 30 
 Vasoconstrictors, 118 
 Vasodilators, 119, 120 
 Vasomotor reactions, 55, 118- 
 
 125, 208 
 Velocity of nerve-impulse, 40 
 Ventilation, 198, 199 
 Ventricles of brain, 64 
 Vestibular nerve, 81 
 Visceral muscle, 114 
 
 symbols in dreams, 187 
 Vision, 80 
 
 Visual areas, 140, 144 
 Vital resistance, 123 
 Voluntary action, 53, 58, 87 
 
 Walking, 53, 98, 213 
 
 Waste-products of nerve, 39 
 (and note). See Fatigue. 
 
 Wells and Forbes on electric dis- 
 turbances, 171 
 
 Wink, 50 
 
 Women, dull lives of, 169 
 
 Writing, 149 
 
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