■lihfiiS'Ui ihs ' 
 
 ■!1fU;iil!;i4nirnn'!lii;ii!!!ill!'',ltHl:i 
 
 "TO FUNDAMENTAL LAWS: 
 OF HUMAN BEHAVIOR 
 
 MAX MEYER 
 
 y 1 
 
3-35 
 
 BOUGHT WITH THE INCOME 
 FROM THE 
 
 SAGE ENDOWMENT FUND 
 
 THE GIFT OF 
 
 1891 
 
 1357 
 
4rCU 2 1 1348 ^ 
 
 ifc out 
 
 ^ee^«4e- 
 
 ^« iviflir28'54 
 
 IDHVf-4«^wfi9*4l 
 
 N 2S 
 
 Cornell University Library 
 BF335 .M61 
 
 Fundamental laws of human behavior; lect 
 
 olin 
 
 3 1924 029 038 011 
 

THE FUNDAMENTAL LAWS OF 
 
 HUMAN BEHAVIOR 
 
 Lectures on the Foundations of any 
 Mental or Social Science 
 
 hy 
 
 MAX MEYER 
 
 Professor of Experimental Psychology 
 in the University of Missouri 
 
 RICHARD G. BADGER 
 
 THE GOBHAM PRESS 
 BOSTON 
 
u 
 
 Copyright 1911, by Richard G. Badger '■^[ 12j. 
 
 All rights reserved *■ 
 
 
 The Gorham Press, Boston, U. S. A. 
 
CONTENTS 
 
 PAGE 
 
 Lecture 1 1 
 
 Being, doing, thinking. Thinking of humanity 
 in terms of thought. The subjective and the ob- 
 jective. Consciousness and nervous function. The 
 nervous system compared with a telephone system. 
 Designing a nervous system. Sensitivity, con- 
 tractility, conductivity. Differentiation of tissues. 
 An analogy of tissue conductivity. Deformation 
 of the body bringing about change of its situation. 
 Avoiding an obstacle. The story of the snail. A 
 nervous system of impossible design. 
 
 Lecture 2 16 
 
 Contraction at a point other than that of stimu- 
 lation. The moth and the light. A steady stimu- 
 lus causing a periodic motion. The need of a 
 nervous system proportional to the development 
 of special motor organs. Sensory and motor 
 points of the body. Nervous connections represen- 
 ted graphically by arches. Cells the biological 
 elements of structure. A nerve cell not a cell but 
 a part of a cell. Neuron, fiber, ganglion cell. 
 Types of neurons. Collaterals. Terminal arbor- 
 ization and dendrites. White and gray matter. 
 Relative unimportance of the ganglion cell for a 
 theory of mental life. 
 
 iii 
 
iv CONTENTS 
 
 Lectures, 30 
 
 Locomotion of the jelly-fish. Concerted action 
 of all the divisions of the body and local respon- 
 siveness. Need of a gradation of connections dif- 
 fering in resistance. Corresponding points. Re- 
 sistance dependent on length of conductors. Con- 
 nections of non-corresponding points. Impossible 
 manner of connecting the neuron arches. First 
 improvement of manner of connection: One-way 
 valves at the meeting points of neurons. Second 
 improvement: The connections between the arches 
 being themselves arches consisting of three neurons 
 each. 
 
 Lecture 4 46 
 
 Reflex arches. Their peripheral and central points. 
 Central sensory points and central motor points. 
 Central points of a lower and higher order. Let- 
 tering of diagrams explained. Central sensory and 
 central motor neurons. Reflex and instinct. In- 
 stinct a selecting and collecting agent. Overflow 
 of a strong sensori-motor discharge into the most 
 closely connected arches. The source of motor 
 power different from the signal for its expenditure. 
 What a nervous excitation can be likened to. 
 Signaling by rods and levers or by pneumatic 
 tubes. Velocity of signal very great, but not 
 infinite; not dependent on intensity. A neuron 
 likened to an electric storage element. A simple 
 picture of a nervous process needed for our imagi- 
 nation of nervous function. 
 
 Lecture 5 59 
 
 Advantage of comparing the nervous process 
 
CONTENTS V 
 
 with a process of streaming. Analogy of the jet- 
 pump. The whole nervous system permeated by 
 £Uiy nervous process, but not with uniform intensity. 
 Suction at motor points; openings made at sensory 
 points. Velocity of the relief of tension. Condi- 
 tions of the intensity of streaming at any definite 
 point of the system. Exhaustion. Resistance 
 increasing with, and even more rapidly than, the 
 flux. Overflow not identical with universal per- 
 meation. The selective function of an instinct ex- 
 plained by the principle of deflection, the collective 
 by that of overflow. 
 
 Lecture 6 69 
 
 Tension of the total muscular system not inter- 
 fering with special activities. The motor point 
 not identical with the point that is moved. Rel- 
 atively fewer reflexes, more instincts in higher 
 animals. The compounding of nervous elements 
 into groups, of these groups into larger groups, and 
 so on, into a single nervous system. The nervous 
 system of a worm. Nerve centers. Lower and 
 higher centers. The nervous system of a crayfish. 
 The brains of fish, frog, bird, and mammal. The 
 nervous -system of man. The cerebral hemi- 
 spheres of man. 
 
 Lecture 7 85 
 
 Learning. The susceptibility of nervous con- 
 ductors. Variations of the nervous path. (1) 
 Two kinds of variation of response. (2) Sensory 
 condensation. (3) Motor condensation. Grace- 
 ful motion. Inhibition. How a child comes to fear 
 the fire. 
 
vi CONTENTS 
 
 Lecture 8 98 
 
 Substitution of a direct for a devious nervous 
 path. Nervous tension inducing growth. Auto- 
 matic action. Periodic levels of learning. Two 
 meanings of forgetting. Positive and negative 
 susceptibility of neurons. The curves of learning 
 and forgetting. 
 
 Lecture 9 110 
 
 Sensory condensation in piano playing. Propor- 
 tional reduction of the resistance of higher and 
 lower centers connecting the same corresponding 
 points. The positive (and negative) susceptibility 
 of a higher center greater than that of a lower center. 
 Motor condensation in grasping. 
 
 Lecture 10 120 
 
 Order of acquisition of the first four classes of 
 habits. Control of the sense organs of the head. 
 Direction and extent of the fixation movement of 
 the eye. Improvement by experience of the fixation 
 movement of the eye. A variation of response re- 
 sulting from a close succession of nervous processes 
 just as from a deflection of one by another. Co- 
 ordination of the eyes. How an infant learns to 
 face a sounding object. Control of the hands and 
 arms. Learning to raise the arm in response to a 
 visual object above the eyes. Loose co-ordination 
 of eye and hand. 
 
 Lecture 11 138 
 
 Control of the feet. The abUity to walk equal 
 to rising plus balancing. Reflex of straightening 
 the legs. Reflex of squatting. Balancing with 
 
CONTENTS vii 
 
 hand support preceding free balancing. Balancing 
 on one leg preceded by balancing on both. Walk- 
 ing not a simple instinct, but a compound of re- 
 flexes united largely by experience. Balancing 
 sideways preceding balancing fore-and-aft. Stretch- 
 ing the foot reflexly toward a thing which impresses 
 the eye. Locomotion resulting from this reflex. 
 Creeping. Creeping on two legs preceded by 
 creeping on one. Influences of creeping on walk- 
 ing. Sitting up. Finger-sucking superseded by 
 other habits. Free standing rarely preceded by 
 walking. One-sidedness and general clumsiness of 
 first walking. Encouraging a child to stand: a 
 purely negative event. The so-called instincts of 
 construct! veness and destructiveness : rather habits. 
 
 Lecture 12 153 
 
 Repetition of motor activity characteristic of 
 learning in childhood. Variation of the order of 
 earliest accomplishments. Speech organs: whis- 
 pering and singing. First speech sounds. General 
 and specific resistances of neurons. The motor 
 outlet of a group of successive nervous processes 
 determined by the temporal order of the qualita- 
 tively different processes. The general resistance 
 as well as the specific resistance reduced by any 
 special flux; but the reduction of the specific resist- 
 ance outlasting that of the general resistance. 
 Possibility of a particular distribution of specific 
 resistances resulting from experience. 
 
 Lecture 13 168 
 
 A simple sensory excitation bringing about a 
 temporally complex response. Some, but by no 
 
viii CONTENTS 
 
 means all, temporally complex responses to a simple 
 sensory excitation explainable on the basis of 
 geometric-mechanical rivalry of motor organs. 
 Multiform variation of response. Importance of 
 kinesthetic sensory activity. Two stages in the 
 development of speech. Reflex pointing and utter- 
 ance of a dental sound. Left-handedness during 
 the first months of life. Right-handed reflex 
 pointing. Right-handedness and speech. Ac- 
 cented and gesticulating languages. 
 
 Lecture 14 181 
 
 Spatial perception. Inherited responses to 
 spatial form. Acquisition of unitary groups of 
 conductors serving all objects of the same design. 
 Mutual attraction of nervous processes of equal 
 strength. Melody and harmony. Two kinds of 
 tonal similarity. Neurons applying their specific 
 resistance in various degrees to a variety of pro-: 
 cesses. Rhythm equals subjective grouping of 
 objectively uniform excitations. Habits of per- 
 forming group motions consisting of one eflFective 
 and (one or) several preparatory movements. No 
 counting in rhythmical perception. Why all com- 
 mon rhythms are of the doublet and triplet kind. 
 
 Lecture 15 196 
 
 Imitation. Auditory and visual imitation at 
 different stages of life. Kinesthetic imitation not 
 inherited; of little importance even when acquired. 
 Emotional reactions. Either contraction or relaxa- 
 tion prevaihng in either organic or skeletal muscles. 
 Emotional reactions inherited. Emotional reac- 
 tions either of direct or of indirect value, for ex- 
 
CONTENTS ix 
 
 ample, as signals for social interaction; especially 
 in primitive man and in animals. Civilized man, 
 deriving little benefit from his emotional reactioms, 
 practically unable to control them by experience. 
 
 Lecture 16 211 
 
 The speech function serving as a generalizing 
 function. Abstraction a kind of generalization. 
 Advantages of the written language in generaliza- 
 tion for individual use and for communication. 
 Science the sum total of all those generalizations 
 which mankind has tested and collected. Written 
 symbols becoming a class of (artificial) objects to 
 which man learns to respond as formerly he learn- 
 ed to respond alone to the objects of nature. Arith- 
 metic. The generahzation "force" in mechanics: 
 a creation of man like all other generalizations. 
 Advantage of handling words rather than things. 
 Danger of speculation. 
 
 Lecture 17 ' 227 
 
 The generalizing function changing from a ner- 
 vous and muscular into a purely nervous function. 
 Relation between processes in the higher nerve 
 centers and strictly subjective experiences. Ner- 
 vous functions of generalization especially likely to 
 have also the subjective aspect. For the generaliz- 
 ing nervous function in another person's brain we 
 substitute an imaginary mental state. The ner- 
 vous correlates of sensation and imagery. Associa- 
 tions of successive and\ of simultaneous mental 
 states. Attention. Pleasantness and unpleasant- 
 ness. Insufficiency of introspective psychology. 
 
ILLUSTRATIONS 
 
 FIGURE PAGE 
 
 1 An impossible nervous system 6 
 
 2 Simplest motor response of a snail 9 
 
 3 Snail turning 11 
 
 4 SnaU avoiding a rock 11 
 
 5 Neuron arches 21 
 
 6 Growth of a neuron 23 
 
 7 Types of neurons 25 
 
 8 Collaterals 26 
 
 9 GangUon cell 27 
 
 10 Nervous system of a jelly-fish (acalepha) 31 
 
 11 Nervous system of a jelly-fish (hydromedusa) . . . 35 
 
 12 Impossible manner of connection 39 
 
 13 Imperfect manner of connection 40 
 
 14 One-way valves 41 
 
 15 Imperfect manner of connection 45 
 
 16 Nervous architecture: Neuron arches and their 
 
 possible connections 46 
 
 17 Possible modification of details in nervous archi- 
 
 tecture 46 
 
 18 Pbssible modification of details in nervous archi- 
 
 tecture ; 64 
 
 19 The bulk of the nervous system of an earth-worm 71 
 
 20 Low and high centers: Group formation in the 
 
 nervous system 73 
 
 21 Nervous system of a crayfish 78 
 
 22 Brain of a fish; double view 79 
 
 23 Brain of a frog; double view 80 
 
 24 Brain of a bird; double view 81 
 
 25 Brain of a lower mammal; double view 81 
 
 xi 
 
xii ILLUSTRATIONS 
 
 26 Nervous system of man; double view 82 
 
 27 Brain of m&tn; double view 84 
 
 28 Burnt child fears the fire 93 
 
 29 Automatic action: Short-circuiting in the ner- 
 
 vous system 102 
 
 30 Steps in acquiring skill: Periodic levels of learn- 
 
 ing 104 
 
 31 Learning dependent on time 106 
 
 32 Forgetting dependent on time 107 
 
 33 Forgetting immediately after practice 108 
 
 34 Sensory condensation explained Ill 
 
 35 Thumb and finger movement 116 
 
 36 Learning how to grasp 118 
 
 37 Fixation movement of the eye 122 
 
 38 Simultaneous innervation of antagonistic muscles 124 
 
 39 Improvmentof the fixation movement of the eye.. 126 
 
 40 Co-ordination of the two eyes or any two organs 130 
 
 41 Raising the hand 134 
 
 42 Motor response dependent on tempor'al order of 
 
 stimulation 159 
 
 43 An acquired distribution of specific resistances. . . . 165 
 
 44 Multiform variation of response 170 
 
 45 A simple stimulus calling forth a temporally com- 
 
 plex response 172 
 
 46 The simple perception of space 182 
 
 47 Sensory points serving form stimulations 183 
 
 48 Spatial stimulation with inherited response 184 
 
 49 How the habit of rhythm may be acquired 191 
 
 50 Tension of facial muscles in joy or anger 204 
 
 51 Relaxation of facial muscles in disappointment. . 209 
 
 52 Naming takes the place of handling 212 
 
 53 Handling takes the place of talking 212 
 
 54 Generalization without actual speech 
 
 55 Two directions in successive association 
 
PREFACE 
 
 THE complete dependence of all human activity 
 on the functional properties of the nervous 
 system and on the changes which these functional 
 properties undergo during life, is much empha- 
 sized in innumerable treatises written by physiologists 
 and psychologists. Yet the way in which these changes 
 come about is described in such vague, subjective terms, 
 that the changes, the "education" of the iiervous system, 
 appear to the young student as mysterious, as miraculous, 
 as unreal, almost incredible, after the reading of these 
 treatises as before. Let me quote from such a treatise 
 by a distinguished physiologist — very admirable and very 
 convincing provided one is convinced even before reading 
 it — ^the following sentences: "As a result of experience, 
 
 definite tracks are laid down in this system. The candle 
 
 flame injures the skin once when the finger is brought 
 into contact with it. The one act of injury which has 
 followed the first trial of contact suffices to inhibit any 
 subsequent repetition of the act. " Such a description of the 
 matter does not clarify it to the young student, but merely 
 substitutes for the mystery which from ancient times has 
 surrounded it, another mystery clad in modern terms. 
 "Experience" is spoken of as if it were a concrete reality, 
 a powerful agent producing changes, instead of making 
 it clear that experience is only an abstract name for the 
 very fact that these changes occur. "Injury" is said to 
 inhibit an act, but the student is left to look in vain for an 
 
 xiii 
 
xiv PREFACE 
 
 analogy among the objective realities he knows, where an 
 injury received by machinery results in the reversal of 
 its motion. A stick of dynamite placed on a rail certain- 
 ly does not cause a locomotive to stop, the next time, 
 before touching it. The mystery can be removed from 
 human activity only by offering the student concrete, al- 
 though perhaps hypothetical, images and uniting these into 
 a system no more complex than the machinery which 
 moves about him everywhere in his e very-day life. 
 
 To make clear the functional changes which occur in 
 the nervous system and which, determining the indi- 
 vidual's life activity, are of tremendous importance to the 
 individual and to society, it is necessary and customary 
 to use diagrams of the nervous system. I have used such 
 diagrams of my own design in this book too. I am pre- 
 pared for hearing from anatomists and perhaps even 
 from physiologists and psychologists the judgment 
 that my diagrams look queer, that they do not reproduce 
 what one sees in the dissecting room with and without a 
 microscope. I confess that I have committed this sin 
 with the full conscience of what I am doing. It is custo- 
 mary, in the diagrams which illustrate nervous functions, 
 to imitate the actual curving of the nerve fibers passing 
 from the spinal cord to the brain and here from lobe to lobe. 
 But I am convinced that this is not only unnecessary, but 
 even harmful. In this book the diagrams illustrating 
 function have been entirely separated from those illustrat- 
 ing anatomy, and the former have been designed exclusively 
 with a view towards making clear the fundamental laws 
 of learning. However queer they may look to the anato- 
 mist, they will be the more useful to the student of human 
 activity for whom this book is written, because they will 
 free him of the tendency to burden his mind with irrelevant 
 curves resulting from mere accidents of growth. 
 
PREFACE XV 
 
 What this book proposes to do is essentially an inves- 
 tigation into the problem contained in the following ques- 
 tion: What are the simplest assumptions, necessary and 
 sufficient, to explain hypothetically the facts of human 
 behavior as dependent on the function of the nervous 
 system? Having answered this question, it attempts 
 to illuminate the deep-rooted habit of describing human 
 behavior as dependent on subjective states, on states of 
 consciousness, — a, habit which still largely governs the 
 sciences of human society, preventing them from throwing 
 off the shackles of subjectivity. 
 
 My thanks are due to my wife for aid and advice in 
 preparing this book; and to my assistant, Mr. A. P. Weiss, 
 who drew the illustrations, for his devotion to this work. 
 
 M. M. 
 
FIRST LECTURE 
 
 Being, doing, thinking. Thinking of humanity in terms 
 of thought. The subjective and the objective. Consciousness 
 and nervous function. The nervous system compared with a 
 telephone system. Designing a nervous system. Sensitivity, 
 contractility, conductivity. Differentiation of tissues. An 
 analogy of tissue conductivity. Deformation of the body 
 bringing about change of its situation. Avoiding an ob- 
 stacle. The story of the snail. A nervous system of im- 
 possible design. 
 
 WHEN we meet one of the things which 
 surround us in nature, we ask, perhaps 
 more frequently than any others, one of 
 these three questions : What is it? What 
 doesitcio? What a.re its thoughts? We know many things 
 with respect to which the first is the only question we ask. 
 We pass through a street which is being paved. When we 
 are told that the blocks of stone put down in regular rows 
 by the workmen, are granite, we are probably entirely 
 satisfied. But when we approach a mill and see the 
 wheels turning, we are not satisfied when we know only 
 that it is a mill. We desire to know what it does, for 
 example, whether it is likely to injure us if we step nearer, 
 or whether it can do special work which we need to have 
 done. When a cow or bull crosses our path, we are again 
 not satisfied if we know only the animal's name. We are 
 much concerned with the animal's action. Will it compel 
 
 1 
 
2 HUMAN BEHAVIOR 
 
 us to change our direction, or can we safely remain where 
 we are? When, thirdly, as school children, we are with 
 our teacher in the class room, we are greatly interested, 
 not only in what he does, but still more so in what he 
 thinks. If he thinks well of us, we are glad. But let us 
 raise the question how we know whether our teacher 
 thinks well of us or not, and we must admit that we can 
 not directly know his thoughts, that is, have his thoughts any 
 more than he can have our thoughts, — that we know it only 
 through our observations of what he does in giving us 
 things, in writing what we may read, in speaking what we 
 may understand. Yet if we are asked whether we are 
 chiefly interested in our teacher 's_acts orjn his thoughts, 
 we are probably quite ready to assert that we regard his 
 thoughtSj_the existence of which we can not directly know, 
 but only assume, as of far mgrejmportance to us than his 
 acts, which we do know directly. In this apparent con- 
 tradiction lies in a nutshell the problem with which we 
 have to deal in this book^ Why do we think of humanity 
 almost exclusively in terms of thotight, although oiir 
 experience contains no other person's thought, but only 
 I his behavior? Many other examples Could be used to 
 show that a person's thoughts, which nobody can have 
 but himself, are nevertheless of the greatest concern to 
 others who can not know them, can not have them. When 
 parents send their children to school, they send them in 
 ordfer that their intellects may be trained, their characters 
 developed. Let us inquire what is meant by such words 
 as intellect and character. The dictionary tells us that 
 they refer to thought processes, not to particular activities 
 or to a person's appearance. The most important train- 
 ing, then, which every parent strives to give his child, is a 
 training of his powers of thought, of this mysterious 
 unknown, 
 
BEING, DOING, THINKING 3 
 
 Not infrequently we hear people speak of brain work 
 and of manual labor. We hear them distinguish between 
 brain workers and those who work with their hands. 
 The distinction seems quite acceptable. Of course, those 
 who use these phrases do not mean that they know much 
 about the workings of the brain. They simply mean 
 that certain persons, although they do not do much 
 which can easily be seen, are nevertheless active in that 
 they think. They work mentally, as we say. And for 
 this mysterious unknown they often receive a high salary. 
 
 Very common is this emphasizing of thinking, this 
 complete or relative disregarding of an individual's doing 
 or being, in ethical valuations. A boy has placed a plank 
 across the street car track and derailed the car. He tells 
 us that he thought that the foundations of the bridge a 
 little distance away had been washed out and that he 
 intended to stop the car and save our lives.X Whatever 
 may be the facts in the case, that is, the doing and the 
 being of the water, the bridge, the car, and the boy him- 
 self, — we probably praise him for his thoughts atid inten- 
 tions. Or, the boy tells us that he wished thus to injure 
 and punish another boy whom he saw as a passenger on 
 the approaching car. Whatever may, again, have actually 
 happened, visibly and audibly,— for the boy's thoughts 
 we hg,ve only contempt, we call them wicked. Yet the 
 boy's being and doing is the same in both cases: he looks 
 the same and he has placed the same plank in the same 
 manner across the track. It is again this mysterious 
 unknown, his thoughts, which concerns us chiefly. 
 
 The most conspicuous example, perhaps, is to be found 
 in reHgious doctrines and ideals. Not good works, but 
 faith decides the test which the Christian has to undergo, 
 according to the Apostle. Not what man does, or what he 
 is, gives him his rdligious qualification, but his faith, 
 
4 HUMAN BEHAVIOR 
 
 that is, his thoughts, again this same mysterious un- 
 known. 
 
 In none of these examples are anyone's thoughts 
 known to, that is, had by, any one other than himself. 
 Even an Inquisition, which has power over life and death, 
 is unable to find out what is thought by those whose 
 religious or irrehgious thoughts it pretends to investigate. 
 It can find only what is done by them, including, of 
 course, under doing what is written and spoken. 
 
 For more than two thousand years a science has existed 
 which has devoted itself to the mysterious unknown 
 which we have just characterized by examples. One may 
 give it the name of mental science, or, rather, mental 
 sciences, for in our modern times science is breaking up 
 into many branches, according to the diversified interests 
 of mankind and in consequence of the limitation of 
 individual mental capacity. Until quite recent years these 
 mental sciences were based upon the conscious experiences 
 of the individual who "professed" the science, upon 
 introspection. Duri ng the last few decades the convic - 
 tion bec ame general that a science of the subjective , an 
 introspectiv e science, because of its liimte3~possibility of 
 generalization, hardly deserved_the_naine of a science. 
 In order to remedy the defect which had been discovered, 
 objective methods, like those used in the physical sciences, 
 were introduced into the mental sciences, to supplement 
 the subjective method of introspection. In the following 
 pages we shall attempt to study by objective methods 
 the most fundamental objective facts which are related to 
 subjective phenomena, and as comprehensively as possible 
 to make clear this relation between objective facts of 
 being and doing and the subjective experiences of our own 
 thinking. 
 
 No other fact concerning the relation between the 
 
THE SUBJECTIVE— THE OBJECTIVE 5 
 
 subjective (the individual consciousness) and the objective 
 (the world of the natural sciences) can be more impressive, 
 •than that consciousness seems to be entirely or, at least, 
 relatively dependent on, conditioned by, the function 
 of an individual's nervous system. So generally is this 
 recognized, that even the extreme assertion that con- 
 sciousn^s is impossible without the existence and function 
 of a nervous system, would undoubtedly find a majority 
 of votes among scientists. 
 
 This will justify — if for the present such a justification 
 seems necessary — our beginning with the study of the 
 nervous system's significance for thq> being and doing of 
 those objects in nature which are known to possess a 
 nervous system. 
 
 We may compare a nervous system with the telephone 
 system of a city or even of a nation, which enables a 
 person to give orders in one place and have them received 
 and executed in another. A nervous system consists 
 essentially of an immense number of string-like structures, 
 very fine and relatively very long, just as a telephone 
 system consists essentially of a large number of conducting 
 wires. However immense the number of these strings may 
 be, they are never found as a disorderly mass, but always 
 arranged according to definite rules. For the sake of 
 understanding clearly the significance of their architectural 
 arrangement for the behavior of an animal — we know that 
 all /those things in nature which possess a nervous system, 
 aiid even many without it, are called animals — let us 
 imagine that we have the duties of a creator and that wt 
 have to furnish a given animal with a nervous system of 
 our own design. How, then, should we systematize, that 
 is, put together into a unit, all the strings which we are 
 to insert into the animal's body? The simplest plan 
 seems to be that of uniting all the strings so that one of 
 
6 
 
 HUMAN BEHAVIOR 
 
 the two ends of each string is located in a single point of 
 the body, whereas all the other ends are left unconnected 
 and are distributed among the various parts of the body, 
 like the diagram of Figure 1. Suppose we offered an 
 
 Center 
 
 Fig. 1 — An impossible nervous system. 
 
 animal which has thus far been without a nervous system, 
 a nervous system of this design. Should the animal be 
 grateful for our gift? Would this gift be helpful to the 
 animal in its struggle for life.'' 
 
 In order to answer this question, we must first gain 
 some insight into the life, the being and doing, of an 
 animal which possesses no nervous system. Let us make 
 ourselves familiar with the behavior of a simple animal 
 which we all greatly admired in our childhood days, the 
 snail. It is true, the snail does have a rudimentary kind 
 of a nervous system. But the snail is anatomically so 
 simple that it could almost equally well get along without 
 it. That snail, then, of which we shall now speak, is 
 indeed only an imaginary snail but near enough to reality 
 to serve as an example for the demonstration of certain 
 general laws of animal behavior. 
 
 We recall that among the main properties of living 
 matter are sensitivity, contractility, and conductivity. 
 
DESIGNING A NERVOUS SYSTEM 7 
 
 In the lowest forms of animal life every particle of the 
 body shows all three of these properties about equally. 
 In the higher forms of animal evolution this is quite 
 different. Our muscles, for example, have but little 
 sensitivity and conductivity. At the expense of these 
 two the third property has been so much increased that 
 the muscles may be caUed the contractile tissue of our 
 body. In such a case we speak of the differentiation of 
 tissues. Muscular tissue has become differentiated from 
 the rather uniform tissue of lower forms of life, just as 
 in modern society the individual has become differenti- 
 ated and can, for example, make excellent shoes, but no 
 clothes to cover the other parts of the body, whereas the 
 undifferentiated savage makes tolerably good clothes for 
 himself as well as shoes. 
 
 Differentiation of tissues is, of course, not restricted to 
 the one kind just mentioned. Other tissues lose most of 
 their contractiUty, but become the more capable of con- 
 ducting any process which happens to go on in one point 
 of them to aU their other points. This does not mean 
 that the velocity with which the excitation travels in 
 them becomes much greater. Analogies from physics and 
 chemistry make it fairly certain that the velocity of 
 conduction, the velocity of the current, remains about 
 the same. But the resistance of the conducting tissues 
 becomes much less. Such tissues are the nervous tissues, 
 those strings of which we spoke above and about which we 
 shall have to say much more further on. The main 
 property of nervous tissue is its conductivity, by which 
 the strings are capable of serving like telephone wires 
 conducting electric currents. It is important that, in 
 thinking of increased conductivity of tissues, we do not 
 think of increased velocity of conduction. While we need 
 not deny that the velocity of conduction may be somewhat 
 
8 HUMAN BEHAVIOR 
 
 affected by this differentiation, what we mean chiefly is 
 that the excitation is offered less resistance by the nervous 
 tissue than by any other tissue, that it travels through 
 nervous tissue, not more quickly, but certainly more 
 strongly, more effectively than through the non-conduc- 
 tive tissues. 
 
 Other tissues, again, differentiate in such a manner that 
 they obtain a highly increased sensitivity at the expense 
 of their other properties. Think of the ease with which 
 we find our way on a dark night when, during new moon, 
 only the stars aid us with their faint hght. The sensitive 
 elements on the retina, the background of our eye, respond 
 even to this faint Ught and stimulate the nerve ends 
 which, through their conductivity, enable the various 
 parts of the body to execute the proper movements. 
 These three properties, however, sensitivity, contractility, 
 and conductivity, are by no means the only properties of 
 living matter. They are merely those properties which 
 chiefly concern us in our present study. In addition, 
 there are many other properties of less importance for our 
 present purpose. If we desire to know more about them 
 and the various ways in which tissues differentiate, we 
 must consult the text-books of the sciences which are 
 devoted to these problems, namely, histology, the science 
 of tissues, and biology and physiology, the sciences of 
 the function of living matter. 
 
 We mentioned that the main property of the string- 
 Uke elements which make up the nervous system, is their 
 conductivity. Let us now apply this knowledge to our 
 problem of the acceptability or non-acceptability of the 
 gift which we offered to our imaginary, nerveless snail. 
 There is, according to our assumption, and, indeed, 
 practically in accordance with the actual facts, no differ- 
 entiated tissue in the snail's body. Each particle is 
 
TISSUE CONDUCTIVITY 9 
 
 sensitive, each particle contracts when stimulated, and 
 each particle conducts what goes on therein to the neigh- 
 boring particles, causing the same process in them. 
 
 Suppose, now, the snail, spread out over the ground 
 as when creeping, is very gently touched at the point of 
 the tail end marked in Figure 2. Owing to its sensitivity, 
 
 Fig. 2 — Simplest motor response of a snail. 
 
 the tissue touched responds. Being contractile the 
 tissue responds by contracting, so that the tail assumes 
 an unsymmetrical form like the one shown in possibly 
 exaggerated manner by the dotted line in Figure 2. The 
 excitation, first caused in the part touched, spreads in 
 consequence of the conductivity of the tissues. What this 
 conductivity means may be made clear by an example taken 
 from ordinary experience. If we drop a small quantity of 
 syrup into a glass of water, we can see how it gradually 
 spreads through the whole fluid until the chemical con- 
 stitution, different just after the drop fell, again becomes 
 uniform all through the fluid. When we speak of an 
 "excitation" caused in a tissue by a touch, this means, 
 too, that the chemical constitution of the point touched 
 has been changed and that this change tends to spread 
 wherever it can, until the constitution has again become 
 
10 HUMAN BEHAVIOR 
 
 uniform everywhere. This spreading is meant when we 
 speak of the conductivity of the tissues. The excitation, 
 then, spreads from the contracted part to all the other 
 parts of the animal's body. Wherever it reaches, con- 
 traction of the tissues occurs. But, naturally, just as the 
 syrup spreading out through the water becomes more and 
 more dilute at the starting point, so the excitation spread- 
 ing out through the body becomes weaker and weaker 
 at the starting point. Finally, perhaps after a second or 
 two, the intensity of the excitation has become quite 
 uniform all through the body, and the contraction, the 
 density of the tissues, has also become equalized all through 
 the body. Only the deformation of the body surface and 
 a weak uniform excitation and contraction of the whole 
 body remain as the effect of the touch. 
 
 Now, the chemical state which we have called excita- 
 tion, means the presence in the tissues of chemical sub- 
 stances which are not normally there. It is natural, then, 
 that the forces which are always active in living matter 
 will tend, after the external influence has ceased, to bring 
 about such spontaneous chemical changes that the normal 
 condition is restored. Gradually, therefore, the normal 
 chemical constitution of the body returns, and as it 
 returns the state of contraction disappears. The body 
 expands again. However, since the previous contraction 
 had become practically uniform in a deformed body, the 
 expanded body, having regained its normal shape, no 
 longer has its previous situation. The deformation by 
 the sudden shrinking occurred on one side; the reformation 
 of form by expansion occurred on all sides of the body. 
 Its axis has slightly turned in the direction indicated by 
 the two arrows perpendicular to the axis of Figure 3. 
 
 The application of the few and simple facts which we 
 have just learned, at once reveals their great importance. 
 
DEFORMATION OF BODY 11 
 
 We desired to gain some insight into the life of an animal 
 which possesses no nervous system, in order to answer 
 the question whether a particular nervous system with 
 
 Fig. 3 — Snail turning. Fig. 4 — Snail avoiding a rock. 
 
 which we intended to furnish the animal, would be an 
 acceptable gift to the animal or not. The most important 
 activities of an animal are plainly those of protection 
 and of nutrition. Let us see if we can comprehend the 
 behavior of our snail when it is either in search of food 
 or avoiding an injurious object. 
 
 Suppose the snail is creeping on the ground in the 
 direction of the arrow I in Figure 4. Let us take the 
 mechanics of locomotion in the forward direction for 
 granted, so that we may take up at once the more special 
 problem which concerns us here. The snail, creeping 
 forward, approaches the stone which accidentally lies in 
 its way, and the right side of the head comes into contact 
 with the stone. (For simplicity's sake we assume that 
 our imaginary snail has no tentacles.) We know now, 
 from our previous discussion, what must happen. The 
 part which has been excited by the touch of the stone. 
 
12 HUMAN BEHAVIOR 
 
 contracts. A little later, expansion of the body occurs, 
 but expansion not only of the part near the stone but of 
 all the body with practical uniformity. The result is a 
 change of position. The axis of the snail now assumes a 
 position more nearly that of the arrow II. The internal 
 conditions — ^whatever they may be — which caused the 
 original forward movement, again become effective. The 
 snail, moving forward, perhaps again comes into contact 
 with the stone. The same happens as before. The axis 
 again turns toward the left. Again the forward move- 
 ment begins and now, perhaps, is continued without 
 touching the stone; the actual path being approximately 
 that indicated by the solid line. 
 
 All this is by no means an extraordinary event in the 
 animal's life, an unusual kind of behavior. It is prac- 
 tically the complete story of the snail. The snail, in 
 order to live, must eat. Lack of food, continued for some 
 time, results in chemical changes in the body. In conse- 
 quence of structural and functional properties of the 
 body which we cannot study here, these chemical changes 
 bring about a forward movement. A rock (or any other 
 obstacle) lies in the way. If the rock could permanently 
 stop the forward movement, the snail would starve to 
 death. But, in one or several stages, a change of the 
 situation is brought about by a change of the direction 
 of the animal's axis. Now the snail creeps on. Other 
 obstacles which may be encountered are taken in the 
 same way. On its forward march the snail, by accident, 
 sometime passes over edible substances, which stimulate 
 the mouth organs and, consequently, are consumed. 
 Later, lack of food brings about locomotion again, and 
 the same things happen in the same cycle. 
 
 One may feel incKned to exclaim: An animal's life 
 cannot be so simple, so automatic as that, — dependent 
 
THE STORY OF THE SNAIL 13 
 
 on the mere accident that food substances should be in 
 its fortuitous path ! But why not ? It is true, many a snail 
 will fail to come across any food substances and die of 
 starvation. Such is life! But enough will have better 
 luck and live to propagate the species, for food adapted 
 to the needs of snails is common on earth. 
 
 Not only food is obtained in this — ^if one wishes to call 
 it by that name, mechanical — ^way; protection against 
 injury is thus made possible too. If the snail instead of 
 approaching a rock, had come near a directly injurious 
 substance, it might have changed its route even before 
 touching that substance; for the tissues of its body are 
 excited, not only by touch, but also by many other in- 
 fluences, for example by a change of temperature, or by 
 the effect of a volatile chemical substance. A piece of 
 camphor instead of a rock would have turned the snail 
 some distance before touch would have been possible. 
 Another important method of protecting itself is that of 
 completely retiring within its shell. This again requires 
 no additional mechanism. We supposed above, that 
 the touch of which we spoke was a very gentle touch. It 
 will, of course, always be gentle if it results from the 
 snail's — ^this slowly moving animal's — own motion. If 
 the touch is relatively strong, as when a child touches 
 the snail with a straw, the excitation resulting and spread- 
 ing with great force all through the tissues must cause, 
 not only the tissues at the point of contact, but also the 
 • neighboring tissues, possibly all of the body, to contract 
 vigorously. If the whole body contracts strongly, it 
 must, since a part of it is attached to the interior of the 
 shell, necessarily disappear in the shell. It is to be noted, 
 however, that one kind of behavior is impossible in this 
 kind of an animal, namely, stimulation occurring at one 
 point of the body and contraction occurring exclusively 
 
14 HUMAN BEHAVIOR 
 
 at an entirely separate point of the body. There must 
 always be what may be called a wave of both excitation 
 and contraction, spreading from the point of stimulation 
 more or less-^so little, indeed, in some cases that contrac- 
 tion may seem to be confined to the point of stimulation, 
 or so much in others that clearly the whole body is in- 
 volved. But the point of stimulation can not in any 
 case fail to be included in and to be the center and starting 
 point of the wave of contraction. Nevertheless, a snail 
 does not need a nervous system in order to live. It can 
 behave in the way in which we have described it as be- 
 having without possessing nervous tissues of any kind 
 whatsoever. 
 
 Nevertheless we may wish to appear generous and offer 
 our snail the nervous system of our design in Figure 1. 
 Although the snail can get along without a nervous sys- 
 tem, why should it not get along even better when in 
 possession of our gift, we might naively ask. Imagine 
 the snail had accepted the gift and were approaching the 
 rock in Figure 4. The moment when the contact occurs 
 one of the peripheral ends of the nervous strings is excited. 
 The strings are so differentiated that they have an im- 
 mensely greater conductivity, that is, lesser resistance, 
 than the undifferentiated tissues. The excitation, there- 
 fore, is conducted to the point where all the nervous strings 
 are connected and thence with great intensity of flux along 
 all the nervous strings, thus reaching effectively all the 
 parts of the body. Consequently, all the parts of the 
 body contract practically at the same time with great 
 force. A prompt and relatively strong contraction at 
 the point of stimulation, followed slowly by a weak and 
 uniform contraction of the whole body is no longer possible. 
 The resulting change of position is also impossible. The 
 whole body contracts and, after a while, expands again, 
 
AN IMPOSSIBLE NERVOUS SYSTEM 15 
 
 to touch, of course, the rock in exactly the same way 
 that it did the first time. In consequence of the touch, 
 the whole body contracts again. It expands again, con- 
 tracts again, expands again, contracts again, and so on 
 ad infinitum, until the animal is either exhausted or 
 starved or both. Any way of avoiding the obstacle is 
 impossible. It is clear, then, that the snail would be very 
 much worse off with this kind of a nervous system than 
 without any. Without any nervous system it can live 
 quite well, unless it happens to have exceedingly bad 
 luck. With this nervous system it can not live any more 
 than a human being could live who, whenever he saw or 
 heard anything, instead of normally responding to the 
 situation presented, would invariably have an epileptic 
 fit, a violent and entirely useless unadapted muscular 
 contraction. 
 
SECOND LECTURE 
 
 Contraction at a point other than that of stimulation. 
 The moth and the light. A steady stimulus causing a 
 periodic motion. The need of a nervous system proportional 
 to the development of special motor organs. Sensory and 
 motor points of the body. Nervous connections represented 
 graphically by arches. Cells the biological elements of 
 structure. A nerve cell not a cell but a part of a cell. Neuron, 
 fiber, ganglion cell. Types of neurons. Collaterals. Ter- 
 minal arborization and dendrites. White and gray matter. 
 Relative unimportance of the ganglion cell for a theory of 
 mental life. 
 
 LET us consider, quite apart from any special 
 problem, in what manner and for what purpose 
 strings conducting like telephone wires could 
 be serviceable in an animal's body. It is plain 
 from the foregoing that they are needed only in case the 
 contraction is to occur not at all at the point of stimula- 
 tion, but at some other point. This can be brought 
 about only by conducting away the excitation from the 
 point of stimulation by string-like tissues which cannot 
 themselves contract, but possess a greater conductivity 
 than ordinary, undifferentiated tissues. Carried to an- 
 other point, the excitation can there cause the contraction 
 desired. This kind of function is necessary in all the 
 more highly organized animals. Take an insect, a moth 
 for example. We know that the most striking behavior 
 
 16 
 
THE MOTH AND THE LIGHT 17 
 
 of a moth is its flying towards any source of light. 
 This is the result of the nervous connections between 
 the wings and the eyes. The right eye is connected 
 (if not exclusively, at least better) by nervous strings 
 with the muscles of the left wing, the left eye with the 
 muscles of the right wing. If the moth has the source 
 of light on its right side, the right eye receives more light 
 and consequently a stronger excitation than the left eye. 
 The left wing then beats the air more forcefully than the 
 right wing, and the axis of the animal is turned to the 
 right until both eyes are excited by the light with equal 
 intensity, that is, until the moth flies directly towards 
 the Kght. 
 
 We need not discuss here the question as to the value 
 of this instinct (instinct is the name given to such con- 
 nections between sense organs and motor organs) to the 
 moth. We may take this value for granted in spite of 
 the fact that millions of moths are destroyed because of 
 this instinct of flying toward the light. Sources of light 
 destructive to moths on the surface of the earth are a 
 very recent invention of mankind, for which nature 
 cannot be expected to have made provision in giving the 
 moth its biological inheritance. It is not difficult to 
 imagine that this flying in the direction of more strong- 
 ly illuminated or lighter objects rather than of darker 
 ones aids the moth in obtaining food. So much is plain 
 that it could do a moth, whose anatomy is (relatively) so 
 highly developed, no good whatsoever if an excitation 
 caused by light in the region of the head would cause a 
 contraction of the tissues located in the same place. In 
 order to be of any value to the animal it is necessary that 
 the chief sensory areas, the eyes, and the chief motor or- 
 gans, the wings, be connected with each other by different- 
 iated tissues of the conducting kind, by nerves. 
 
18 HUMAN BEHAVIOR 
 
 It may not be amiss, even at the danger of getting a little 
 side-tracked, to discuss another fact which is of great 
 significance for the behavior of animals. We said that 
 the movement of the moth's wings was caused by the 
 excitation occurring in the eye. The question may be 
 asked: How can a rhythmical movement like that of the 
 flapping wings be caused by a continuous excitation like 
 that in the moth's eye? We have no need to explain 
 this here in detail, but it is important to point out, that 
 such a transformation of something continuous into 
 something discontinuous is an exceedingly common 
 occurrence in nature. It is especially important to note 
 that it occurs in the inorganic world, the dead part of nature, 
 as frequently as in the organic world, in living nature, so 
 that we cannot be accused of having neglected the possible 
 claims for recognition of any so-called vital or mental 
 forces when we simply stated that the wings flapped 
 merely because of light falling steadily on the animal's 
 eye. Let us take from the inorganic world a few examples. 
 The wind passing steadily over the surface of the ocean 
 does not cause, by friction, simply a motion of the surface 
 water in the same direction and a compensatory move- 
 ment of lower layers of water in the opposite direction. 
 It causes, as we all know, a motion of the particles of 
 water which takes place, only to a slight extent in the 
 horizontal direction of the wind, mostly in a vertical 
 direction, up and down, causing waves which periodically 
 rise and fall a considerable height. Or, when we blow a 
 whistle steadily, the result is a rhythmical movement of 
 the particles of air enclosed in the whistle, a physical 
 sound. When water flows very slowly from the faucet 
 in our kitchen, it does not fall in a continuous and very 
 narrow stream, but in periodical drops. Air blown under 
 water through a tube, similarly rises iii periodical bubbles. 
 
PERIODIC MOTION 19 
 
 Nobody thinks that such a transformation in these cases 
 requires any hypothetical vital or mental forces. To 
 assume any such forces in the case of muscular activity 
 is equally unnecessary. What we have said about nervous 
 excitation in the eye causing rhythmical motion of the 
 wings is really all that need be said, unless we are specially 
 interested in the details of physiological science. 
 
 Let us returii to our problem as to the kind of a nervous 
 system which could be regarded as an acceptable gift by 
 our snail or any other animal. We saw that only one 
 kind of behavior is impossible to the snail without a ner- 
 vous system, namely, a contraction at one point of the 
 body in response to an excitation started at a different 
 point, without any contraction occurring at this latter 
 point, or at least, without a contraction occurring at the 
 point of stimulation with any force approaching that 
 of the contraction at the former point. For example, if 
 the tip of one of the tentacles of a snail — ^let us think of 
 a snail with tentacles — is affected by a certain stimulus, say 
 fire, it might be safer for the animal to respond by a 
 strong backward movement of its locomotor organs, 
 however far these are from the point of stimulation, than 
 to respond strongly by a contraction of the stimulated 
 tentacle and weakly by action of the locomotor organs. 
 We see at once the close connection between the existence 
 of a nervous system and of highly developed special or- 
 gans, especially of locomotor organs. Higher animals, 
 having legs, must indeed, because they have these special 
 organs, respond to stimuli occurring at certain excitable 
 points of the body by a forward movement of the legs, 
 to stimuli at other excitable points by a backward 
 movement of the legs, and by no other motor reaction. 
 The snail, which has scarcely any specialized motor 
 organs, just on this account does not absolutely need 
 
20 HUMAN BEHAVIOR 
 
 a nervous system. So much nervous tissue as the snail 
 possesses, serves minor purposes which do not much con- 
 cern us here. 
 
 On the other hand, if an animal has specialized loco- 
 motor and other motor organs, fins, wings, or legs, with 
 double sets of muscles, for forward and backward motion, 
 its nervous system must be designed according to the 
 following plan and can not be designed in any other way 
 without defeating its purpose. Certain excitable points 
 of the body must be connected by conducting strings with 
 certain contractile tissues located in definite points of the 
 body; other excitable points must be connected with 
 certain other contractile tissues of the body. If we 
 simplify our way of expressing this, we may say: Each 
 sensory (that is, excitable) point of the body must be con- 
 nected by a conducting string with a definite motor (that 
 is, contractile) point of the body. Let us remember, hpw- 
 ever, that the facts are not quite so simple as they are 
 expressed in these words. Actually, a single sensory 
 point is scarcely ever excited in isolation, and a single 
 contractile point, a single muscle fiber, never contracts 
 while all other fibers remain at rest. However, general 
 statements of fundamental facts for the purpose of re- 
 membering and reflecting upon them in the abstract, are 
 always artificially simplified. Otherwise they would be 
 of little value to our thought, which is limited in capacity. 
 All scientific laws, even the greatest and most famous of 
 them, are artificial simplifications. This justifies, then, 
 our speaking of the connection of one sensory point with 
 one motor point as if such a simple nervous connection 
 were possible. 
 
 We may represent such nervous connections graphically 
 as in Figure 5. Each sensory point S is connected with 
 a motor point Jf by a conductor, represented in the figure, 
 
SENSORY AND MOTOR POINTS 
 
 21 
 
 of course, by a line. That this line has the form of a 
 flat arch is not essential. This special form of the diagram 
 has been chosen here because of its convenience, which 
 will later become even more evident. Since there are a 
 
 Se Sd Sc Sb Sa Ma Mb Mc Hd Me 
 Fig. 5 — ^Neuron arches. 
 
 great many sensory and motor points, the diagram ought 
 to contain a great many arches. In our figure they are 
 all represented by only five. They are drawn one above 
 the other because this is the most convenient form of 
 drawing them, not because any such connections are 
 likely to be actually found in a similar parallel arrange- 
 ment. The difference in size of the arches is also a mere 
 matter of convenience, without any actual meaning. If 
 no other assumptions are made at any later time, we shall 
 always regard the arches as representing nervous con- 
 nections of the same length. 
 
 Let us at once apply this diagram. We spoke above 
 of the instinct of a moth of flying toward the light. Take 
 Sj to be the right eye and Sc the left eye. Of course, an 
 eye is not a single sensory point, but since it functions in 
 this case as a unit, there can be no objection to speaking 
 of it and representing it graphically as if it were a single 
 point. Take Mi, to be the left wing's muscles and M^ 
 
22 HUMAN BEHAVIOR 
 
 the right wing's muscles. Again we understand that the 
 muscles of a wing are not a single motor point. The 
 muscles of one wing are, indeed, two sets of muscles, so- 
 called antagonistic sets, of which one serves the upward, 
 the other the downward movement. Each of these 
 muscle sets consists of thousands of muscle fibers. One 
 fiber or a small group of these fibers may be called quite 
 correctly a motor point of the body. However, since the 
 whole double set of muscles functions together, brings 
 about the definite effect, the flapping of one wing, we may 
 speak of it here and represent it graphically as if it were a 
 single motor point. The wonderful instinct of flying 
 toward the flame is then represented graphically, simply 
 by Sj being connected with Mi but not with M„ and S^ 
 being connected with M„ but not with M^. 
 
 Having understood the all-pervading importance of 
 these conducting strings for the behavior of all more 
 highly organized animals, it is natural to seek for some 
 more detailed knowledge about their growth, their struc- 
 ture, and their function. 
 
 The smallest structural elements of which both animal 
 and vegetable organisms consist have for about a century 
 been called "cells." This means literally boxes — we 
 have a box under our house which we call a cellar. The 
 name appears less strange to us on knowing that those 
 structural elements which were first discovered by means 
 of the microscope happened to look like little boxes. 
 These were plant cells. It was, of course, soon found that 
 not all vegetable elements of structure are box-like. Some, 
 for example the long and thin flax fibers used for the 
 manufacture of linen, do not resemble a box. But the 
 name cell had already been adopted by the biologists as a 
 general name for elements of structure and was now applied 
 also to those elements to which it was not applicable in 
 
NERVE CELLS 23 
 
 its literal meaning. It was equally applied to the elements 
 of structure in the vegetable and animal kingdom, and 
 the whole living world was — and is — said by the biologists 
 to consist of cells. Accordingly the strings, which serve 
 as conductors for excitations in the bodies of higher animals, 
 ought to be called cells, — for the sake of distinguishing 
 them from other kinds of cells, perhaps nerve cells. Such, 
 however, is not the case. The term nerve cell has come 
 to mean, unfortunately, something different. We shall 
 at once see what and why. 
 
 In its most undeveloped form an individual unit of 
 nervous tissue is a small, almost spherical body (Figure 6, 
 
 Fig. 6 — Growth of a neuron. 
 
 a). As this body grows it becomes pointed in one or 
 more places and sends out a string-like prolongation, 
 which continues to increase in length (Figure 6, 6, c, and d), 
 so that it may become easily a hundred thousand times 
 as long as it is thick, reaching a total length of several 
 feet, whereas its thickness is always microscopical. The 
 original little ball from which the string grew out, con- 
 tinues then to exist as a relatively thick swelling of the 
 string. We must remember, however, that it only looks 
 thus, that it did not originate as a swelling of the string. 
 Being relatively bulky, it is not difficult to understand 
 that this thickened part of the string should have attracted 
 the interest of investigators before the exceedingly fine 
 
24 HUMAN BEHAVIOR 
 
 string. When it was first the object of biological research, 
 its belonging as a part to the long and fine fiber was over- 
 looked. It was studied as an individual thing, and the 
 name cell, generally applied to the elements of biological 
 structure, was applied, instead of to the whole fiber with 
 its swelling, to the swelling alone, which was called a 
 nerve cell. So the inconsistent use of the word cell in its 
 application to nervous tissue, referred to above, came 
 about and is still almost universal. 
 
 In more recent years a new, unambiguous terminology 
 has been adopted, which we shall use in the following. We 
 shall call the whole structure, the fiber with its swelling, a 
 neuron, the fiber without its swelling simply fiber, and the 
 swelling alone a ganglion cell. The use of the word 
 ganglion cell is explained thus: In nervous tissues gray 
 looking masses are frequent which, on microscopical 
 examination, reveal themselves as accumulations of 
 swellings with the contiguous pieces of their fibers. It 
 is as if we had a large number of ropes each having a 
 knot somewhere and had taken all these knots in one of 
 our hands. What we then have in our hand might be 
 compared with the accumulation of swellings just men- 
 tioned. Such a mass of nervous tissue has long been 
 called a ganglion. Now, it is a peculiar biological fact 
 that these swellings of neurons are not found simply here 
 and there in isolation, but that they are always found in 
 groups, sometimes not very large, sometirnes very bulky, 
 — ^these very ganglions. Since the swellings of the neurons 
 are always found in ganglions, they have been given the 
 name of ganglion cells, which we shall adopt here. 
 
 Many are the forms in which the neurons present 
 themselves. Figure 7 shows an assortment of them. 
 The swelling may be at one of the ends as in the case of 
 a and c of the figure, or away from either end as in the 
 
NEURONS 
 
 25 
 
 case of b, d, and e. The long fiber may split into two 
 fibers as in c, or even into more. The swelling may 
 happen to occur just at the point of the division of the 
 
 a 
 
 b c d e 
 
 Fig. 7 — Types of neurons. 
 
 string. In this case the neuron looks Hke d. The string 
 may in its course turn sideways, form a kind of loop, 
 and continue from the turning point in the original 
 direction. If now the swelling happens to be at the place 
 of the loop, the neuron must look like e. In all these 
 varieties of form we find the same structure, a string with 
 a swelling. Some years ago, when the interest of the 
 histologists was still in the main restricted to the ganglion 
 cell, various kinds of such cells were distinguished accord- 
 ing to the number of long fibers which they sent out, and 
 called unipolar (a), bipolar (b) and multipolar (d) cells. 
 Since the ganglion cell has ceased to be regarded as an 
 element of structure in the former sense, these distinctions 
 and names have practically lost their significance. . The 
 neuron is essentially a string capable of conducting an 
 excitation from one end to the other. AH structural and 
 functional properties are necessarily subservient to this 
 end of conduction. 
 
26 HUMAN BEHAVIOR 
 
 Certain features of the neurons, which are not shown 
 in Figure 7, should still be mentioned. We said that the 
 long fibers sometimes split into two fibers. Another 
 breaking up of the fiber may occur in a manner similar 
 
 Fig. 8 — Collaterals. 
 
 to the way in which a river takes up large tributaries. 
 Long fibers may enter the main fiber as in Figure 8. The 
 tributaries, which most commonly form with the main 
 fiber angles of approximately ninety degrees, are called 
 collaterals. But still another feature of the neurons is 
 to be mentioned. Each ending of a nervous string looks 
 somewhat like the frayed-out end of a thread. The end 
 breaks up into a large number of relatively short branches, 
 the so-called terminal arborization (Fig. 9, at a). In 
 case the swelling of the neuron happens to be located at 
 one of the ends of a neuron, these small branches must 
 naturally come out of the swelling itself. The neuron 
 then looks like Figure 9. The branches proceeding from 
 the swelling are called dendrites, which is a Greek name 
 meaning about the same as the Latin name terminal 
 arborization, namely tree-like branchings. In Figure 9 
 a neuron is represented whose main fiber is relatively 
 
STRUCTURE OF NEURONS 27 
 
 short, almost shorter than the dendrites. This shortness, 
 however, is not the rule, but rather the exception; the 
 main fiber, often also called the axis cylinder, usually 
 greatly exceeds the dendrites in length. 
 
 There is frequently a difference in coloring between 
 the parts of a neuron. The ganglion cell looks dark, the 
 
 Fig. 9 — Ganglion cell. 
 
 fibers lighter. This has given rise to the distinction of 
 white and gray matter in the brain — gray matter taking 
 its name from the presence of numerous dark ganghon 
 cells among the fibers. The popular view, however, of 
 the greater importance of the gray matter than of the 
 white matter is a superstition. 
 
 The ganglion cells have a delicate interior structure, 
 and even the fibers are not simple, but possess an interior 
 structure, so that they may be said to consist of fibrils. 
 About the functional significance of these inner divisions 
 
28 HUMAN BEHAVIOR 
 
 of a neuron too little is at present definitely known. The 
 question as to the function of the ganglion cell and the 
 fibrous parts of the neuron must be answered at present 
 in a manner very dififerent from that which was customary 
 fifty years ago. It was then often asserted that the 
 ganglion cells were the residences of ideas, each little 
 box the seat of one idea, so that the total mental capacity 
 of a person might be determined by counting the number 
 of his ganglion cells. It is now recognized that an idea 
 can not be said to have its seat anywhere. The ganglion 
 cells do not have any more direct relation to our mental 
 life than the conducting strings, On the contrary, we 
 shall see that we can fairly well understand our mental 
 life without any reference to the ganglion cells. Their 
 physiological significance is probably, in the main, only 
 of the following two-fold kind. The ganglion cell is the 
 point of vegetation, so to speak, from which all growth 
 proceeds, and it is the storehouse from which the neuron 
 in any emergency can quickly draw the means of sub- 
 sistence. We have seen that the whole string of a neuron 
 grows from a little sphere. This sphere continues to 
 exist even after the neuron with all its ramifications has 
 obtained its full development, and is then the ganglion 
 cell of the neuron. If growth is necessary later, because a 
 branch of the neuron has been cut oflF or otherwise de- 
 stroyed, new growth proceeds from that point of the string 
 which is farthest from, but still connected with the gang- 
 lion cell. On the other hand, if a conducting string is 
 continually used for hours, changes in the appearance 
 of its ganglion cell occur which probably indicate changes 
 of a chemical nature, called by the physiologists signs of 
 fatigue. It seems that the string, in order to serve con- 
 tinuously for a long time as conductor of an excitation, 
 needs to be resupplied with certain chemicals, and that 
 
SIGNIFICANCE OF GANGLION CELL 29 
 
 these chemicals are kept in store for the string within the 
 ganglion cell, which, because of its size, is less quickly 
 exhausted than the string. Whether the ganglion cell 
 has any significance in addition to those functions just 
 mentioned, seems doubtful. 
 
THIRD LECTURE 
 
 Locomotion of the jelly-fish. Concerted action of all 
 the divisions of the body and local responsiveness. Need of 
 a gradation of connections differing in resistance. Corres- 
 ponding points. Resistance dependent on length of con- 
 ductors. Connections of non-corresponding points. Im- 
 possible manner of connecting the neuron arches. First 
 improvement of manner of connection: One-way valves at 
 the meeting points of neurons. Second improvement: The 
 connections between the arches being themselves arches 
 consisting of three neurons each. 
 
 WE have stated that the fundamental 
 principle upon which the design, — ^the 
 architecture, so to speak, — of the nervous 
 system is based, is the following one. 
 Each sensory point of the body is connected by a con- 
 ducting string with a definite motor point of the body. 
 The selection of a suitable motor point for connection is 
 nature 's proper business to which she has attended during 
 a long process of evolution of the animal race. Every 
 animal is born with fully developed connections of this 
 kind, or, at least, with rudiments which by heredity are 
 predetermined to grow into such connections during the 
 individual's early life. If an animal is born without 
 them, life is impossible. 
 
 However, it is easily seen that a nervous system of this 
 extremely simple kind will need improvement as soon as 
 
CONCERTED ACTION 31 
 
 the animal race which possesses it makes progress from 
 the most primitive to a somewhat higher organization of 
 its bodily functions. Let us consider an example. A 
 jelly-fish of the kind called acalepha still has an exceed- 
 ingly low organization; yet it will make clear what we 
 wish to understand. For locomotion it has a bell-shaped 
 body, so that, on contraction of the bell, the whole body 
 moves through the water in the direction of the closed 
 end of the bell. When seen from the front the bell looks 
 like Figure 10. On the periphery of the bell there are 
 
 Fig. 10 — Nervous system of a jelly-fish (aealepha) . 
 
 eight points (one of which in the figure is marked S). 
 From each of these points conducting fibers similar to the 
 fully developed neurons in higher animals pass into the 
 neighboring tissues, but not far enough to come into 
 actual contact with the fibers radiating from any other 
 point iS. The purpose of these fibers is clear; they con- 
 duct any excitation occurring at any point of the rim 
 with but slightly diminished effectiveness to all the 
 tissues of that eighth-division, causing thus a uniform 
 response of the whole division to any stimulus applied to 
 any one of its points. In addition to these one fiber 
 seems to, pass from each S in the direction of the center 
 of the bell. For what purpose? Obviously, to make it 
 more certain that during the process of locomotion no 
 division of the bell lags behind the others in contraction. 
 
32 HUMAN BEHAVIOR 
 
 It is plain enough that no straight-way locomotion would 
 result if, for example, the tissues on one side of the rim 
 would contract when, having lagged behind, all the 
 diametrically opposite tissues are still in expansion. 
 This lagging behind, however, would frequently occur. 
 To understand it readily, let us imagine the analogous 
 case of eight leaky places on a water pipe. Suppose the 
 frequency of the dropping at each place to be about the 
 same, say, one drop a second. But even then we could 
 not expect all the drops to fall simultaneously, eight fur- 
 ther drops to fall again simultaneously after a second, and 
 so on. The eight drops would fall in a quite irregular 
 succession. Let us make the appUcation to our case. 
 The rhythmical contraction would be caused by the 
 chemical constitution of the jelly-fish at the time in 
 question, when perhaps no food has been taken for some 
 time and locomotion thus has become necessary. The 
 chemical constitution being about the same in all divisions, 
 no division wotdd have a frequency of periodic contraction 
 differing much from that of any other division of the 
 body. Nevertheless, the contractions would not occur in 
 the eight divisions simultaneously any more than the 
 falling of the eight drops spoken of above. But this 
 simultaneity could be easily insured by connecting the 
 eight divisions by conductors. Now, as soon as one of 
 the divisions spontaneously begins to contract, this con- 
 traction causes an excitation in the nervous plexus of 
 that division; This excitation is carried to all other 
 divisions and at once all other divisions begin to contract. 
 This connection of all the divisions of the body would 
 work beautifully if no other kind of locomotion were ever 
 needed than straight-way locomotion in response to an 
 internal stimulus, the chemical constitution of the body 
 at the particular time, for example, some time after the 
 
LOCAL RESPONSIVENESS 33 
 
 last taking of food. =But frequently external stimuli act 
 upon the body and require, not a straightforward loco- 
 motion, but a change of direction as response. For 
 example, the jelly-fish, while swimming, strikes a rock 
 with one side of the bell. The jelly-fish then must change 
 its direction. That division which touched the rock 
 must contract more strongly than any other, especially 
 than the diametrically opposite division, in order to bring 
 about the change of direction. Without conduction, the 
 predominance of the action of the one division touched 
 would be certain. But with perfect conduction to all 
 other divisions it would be equally certain that no such 
 predominance of a local reaction, no local responsiveness 
 to an external stimulus would be possible. Here is, 
 then, the necessity of a compromise. And this compro- 
 mise is effected by having the eight radial fibers not join 
 in the center, but stop short before reaching each other. 
 Thus undifferentiated tissues, tissues of high resistance, 
 are interposed to weaken the excitation coming from one 
 of the divisions to such an extent that only one division 
 can react strongly to the external stimulus. All others 
 react only weakly. 
 
 One must not think that for a concerted action of all 
 divisions of the bell, like the action of straightforward 
 locomotion, string-like conductors of differentiated tissue 
 are indispensable. The various divisions of the rim of 
 the bell might force each other into the same periodicity 
 and, what is still more important for our present considera- 
 tion, into the same phase of periodic contraction through 
 the ordinary conductivity of the undifferentiated tissues. 
 Whatever division is at any moment the first to contract, 
 might send its excitation by means of conduction through 
 the undifferentiated tissues to all the others and thus 
 force the whole rim to contract at the same time. This 
 
34 HUMAN BEHAVIOR 
 
 is the more possible when the periodic contraction of each 
 particle is not the result of an external stimulus but, as 
 we have seen, the result of a chemical constitution at any 
 given time practically uniform throughout the whole 
 body. The stimulus coming from one division, not 
 having to cause, but only to hasten in all the others the 
 contraction which would have occurred a little later any- 
 way, need be only weak. Nevertheless, the question 
 remains if it would not be too weak if it had to pass wholly 
 through undifferentiated tissue. Nature, therefore, must 
 make the radiating conductors just long enough to meet 
 this condition of reducing the resistance just enough for 
 concerted action; but not the least longer, for every in- 
 crease of their length is equivalent to cutting down the 
 local responsiveness without which the animal could not 
 survive. We understand thus why the radiating fibers 
 do not join in the center. 
 
 It is interesting to note that compromising, which is 
 the very foundation of all social life of animals, of all 
 social institutions of mankind, is found to be an essential 
 f u nction in the individual life of any one of the very lowest 
 animals which possess a nervous system. The unity of all J 
 organised nature, which is the fundamental concept of 
 modern biology, is exemplified by this role played in any 
 life, low or high, by compromises. Two conflictiiig con- 
 ditions seem to make life impossible. But the problem 
 would be hopeless only if a complete denial of the demands 
 of either the one or the other were insisted on. On the 
 one hand, concerted action calls for the most perfect coq- 
 duction from any division of the rim of the bell to all 
 the others. On the other hand, local responsiveness calls 
 for the interposition of high resistances between the 
 diametrically opposite divisions of the rim. The com- 
 promise must then consist in this, that all the divisions are 
 
A COMPROMISE 35 
 
 connected by conductors, but in such a way that conduc- 
 tion from one point of the rim to opposite points is by the 
 properties of the conducting medium itself more resisted 
 than conduction to neighboring points. Nature has, as 
 we saw, solved the problem by stopping the differentiated 
 radiating conductors as far short of the center as the 
 condition of local responsiveness requires, leaving in the 
 center enough undifferentiated tissue interposed to meet 
 this requirement. Another way of fulfilling the condition 
 of varying resistance is by resorting to the length of the 
 differentiated conductors without interposing any un- 
 differentiated tissue. There can be no doubt that the 
 length of a nervous conductor determines its resistance 
 as the length of telegraph and telephone wires determines 
 their resistances. The longer the conducting string, the 
 greater its resistance. Nature has solved the problem 
 in this way in another kind of jelly-fish, called hydromedu- 
 sa. Here all the points of the rim are connected by differ- 
 entiated conductors forming a ring, as shown in Figure 11. 
 
 Fig. 11 — Nervous system of a jelly-fisli (hydromedusa) . 
 
 If any division of the rim contracts, the excitation is by 
 this ring conducted to all other divisions. But the excita- 
 tion reaching opposite divisions of the rim is much weaker 
 than that which reaches neighboring ones, in accordance 
 with the varying length of the conductor. This difference 
 in the intensity of the conducted excitation does no harm 
 
36 HUMAN BEHAVIOR 
 
 in the case of ordinary, straightforward locomotion. The 
 rhythmical contraction is in this activity the result of the 
 chemical constitution of the body which, perhaps, has 
 been the result of lacking food for some time. This 
 chemical state diflPers but slightly in the various parts of 
 the body. The different divisions of the rim, therefore, 
 would contract and expand in almost the same periodicity 
 anyway. A very slight excitation conducted from else- 
 where is then sufficient to hurry up any division which 
 without this excitation would lag behind. But when a 
 stimulus acts from without on any point of the rim, only 
 those divisions are caused to respond strongly to the stimulus 
 which are in the neighborhood of the stimulus. The 
 other divisions of the rim, receiving a weaker and weaker 
 excitation the longer the piece of the rim over which the 
 excitation has to travel, are considerably affected only 
 in the neighborhood of the point of stimulation. The 
 divisions opposite this point remain practically unaffected 
 by the stimulus. 
 
 Let us glance back again at Figure 10. We said that 
 (1) the radiating fibers help to prevent the lagging behind 
 of any division in the ordinary activity of locomotion. 
 The figure makes it clear that any excitation is more 
 effectively conducted between any divisions by the help 
 of these fibers than it could be conducted through the 
 undifferentiated tissues. (2) The local responsiveness is 
 retained by the radiating fibers stopping short before 
 reaching the center of the bell. For example, if S is 
 stimulated by an external influence, the excitation is 
 carried also to a, b, and c, but more weakly to a and b 
 and very much more Weakly still to c. In order to reach 
 c the excitation has to pass from the radiating fiber S to 
 the radiating fiber c over a rather long step of undifferenti- 
 ated tissue. Undifferentiated tissue has a much higher 
 
GRADATION OF RESISTANCES 37 
 
 resistance than nervous tissue. Consequently, the ex- 
 citation reaching the points, a, b, and c, is more and more 
 weakened, and no interference with the local responsive- 
 ness at the point S can appear. If the" radiating fibres 
 did unite at the center of the bell, a, b, and c would 
 all be equally excited. The problem of universal con- 
 nection of all parts of the body by conductors of low 
 resistance, combined with undisturbed local responsive- 
 ness, can therefore be solved architecturally in more than 
 one way. Figures 10 and 11 represent two solutions of 
 the problem, both found in nature. But the solution of 
 Figure 11 is the more perfect one, because the universal 
 communication through conductors is more perfect, while 
 local responsiveness is as satisfactorily retained as in the 
 other case. 
 
 The example of the jelly-fish has taught us that one 
 kind of nervous connections within the animal body is 
 not sufficient. There must be many kinds, — or rather, 
 there must be a gradation of connections differing in the 
 resistance offered by the conductor in the various cases. 
 If it is desirable for an animal's well-being that an ex- 
 citation occurring at a certain point, say A, be followed 
 most readily by a contraction at the point a, the points 
 A and a must be connected by a conductor of small 
 resistance. Let us call those points which are thus 
 connected corresponding points, in order to have a brief 
 term by which we may refer to them. If, as in the case 
 of a jelly-fish, these corresponding points A and a are 
 practically identical, the conduction is a self-evident 
 fact even without any special conductors. If, as in the 
 case of the moth, A is an eye and a the muscles of a wing^ 
 the conduction between the corresponding points must be 
 mediated by a nervous string, or chain of nervous strings, 
 of the shortest length possible under the anatomical 
 
38 HUMAN BEHAVIOR 
 
 conditions. But all — or at least some — of the other 
 (non-corresponding) contractile points of the body must 
 also be in some way connected with the point A. Other- 
 wise, no concerted action would be possible. The jelly- 
 fish would, for example, be scarcely capable of swimming 
 straight ahead; the moth would hardly be able to alight 
 on a twig or leaf which happens to impress itself on the 
 moth's eye and towards which the moth must act, not 
 only with its wings, but also with its legs. These further 
 connections with the point A, however, in order to leave 
 the connection A-a in its proper functional order, must 
 have a higher resistance, — as we have seen, must be 
 longer than A-a. 
 
 Jn higher animals, whose tissues are all differentiated 
 to perform special functions, the nervous connections are 
 practically aU connections between sensory and motor 
 points, that is, between points of the body which are by 
 differentiation specially sensitive to particular physical 
 or chemical influences, and points which are of differenti- 
 ated contractile tissue. It is true that nerve fibers are 
 also found to end in tissues which are not contractile; in 
 glands, for example. However, these cases are the 
 minority, and may be left out of the discussion here, 
 since we are especially and directly interested in behavior 
 only, which depends, of course, on the function of con- 
 tractile tissues, of muscles. We have represented in 
 Figure 5 the short — or direct, as we may say — connections 
 between corresponding sensory and motor points in the 
 shape of arches. We must now find a way of representing 
 graphically those nervous conductors which lead from 
 each sensory point to those motor points which are not 
 corresponding. These conductors must be, as we have 
 found, longer than the conductors directly connecting 
 corresponding points. It is clear, then, that we could no< 
 
IMPOSSIBLE MANNER OF CONNECTION 39 
 
 represent the conductors connecting non-corresponding 
 points as they are represented in Figure 12. This figure 
 is shown here merely because some books, treating these 
 problems somewhat superficially, actually give figures 
 like this as an example of how nervous connections are 
 constructed. Let us agree that any straight line which 
 has no cross-connecting point between its ends, shall 
 always represent a standard length, and also, unless any- 
 thing is said expressly to the contrary, a unit of resistance 
 Such lines as S^Ml, which has a crook inserted between 
 its straight ends, are included under this definition. This 
 line is drawn so as to indicate that it is not in contact 
 with SIMI-; for this purpose the method of drawing 
 which is generally used by electrical engineers to indicate 
 crossed, but mutually insulated wiring, has been adopted. 
 A glance at the Figure 12 shows that the conductor 
 
 S'b^ ^M^ 
 
 Sb Sa Ma Mb 
 
 Fig. 12 — Impossible manner of connection. 
 
 Si^SlMlMa connecting the non-corresponding points Sj and 
 Ma has not a greater resistance than the conductor 
 SjSiMjMj, since both are made up of three standard 
 lengths, although our requirement is that it shall have a 
 greater resistance. We must look for a different kind of 
 graphic representation to suit our needs. 
 
 Neurology, that is, the anatomy and physiology of the 
 nervous system as it actually exists and functions in 
 animals and in man, teaches us an important fact which 
 we 'ought to represent in any diagram of nervous connec- 
 
40 
 
 HUMAN BEHAVIOR 
 
 tions. It has been found that the same two points (one 
 sensory and one motor) are almost generally connected 
 in several ways, by shorter and also by longer conductors. 
 For example, if pain is caused in a dog's foot and the foot 
 is withdrawn, the nervous excitation may travel from the 
 foot to the spinal cord and thence to the muscles moving 
 the foot. Or, it may travel from the spinal cord farther 
 on to the dog's brain, thence back to the spinal cord and 
 now only to the muscles. If we combine this require- 
 ment of a two- (or many-) fold connection of greater and 
 lesser length between corresponding points with our 
 previous requirement that the connections of non-cor- 
 responding points shall be longer than the (direct) con- 
 nections of corresponding points, the diagram of Figure 
 13 readily suggests itself. We draw four conducting 
 
 C 
 
 Sb Sa Ma Mb 
 
 Fig. 13 — Imperfect manner of connection. 
 
 strings from Sl, Sl, Ml, and Ml and unite them in a 
 central point which we may call C. All our requirements 
 are then fulfilled. We can travel from Sa to the corres- 
 ponding point Ma over a longer route by C (four stand- 
 ard lengths), or over a shorter route (three standard 
 lengths) avoiding C; and we can travel from Sa to the 
 non-corresponding point M^ only over a longer route 
 
IMPROVED MANNER OF CONNECTION 41 
 
 SaSlCMlMi, of four standard lengths. The same holds 
 good for starting from the sensory point Sj. 
 
 Nevertheless, this diagram of Figure 13 is not yet 
 quite satisfactory, but must be perfected in at least two 
 ways. First, an excitation starting from one sensory 
 point, for example S^ in Figure 13, can iiot only pass, over 
 various routes, as we have seen, into the conductors 
 MlMa and MIM,,, but also from C into the conductor CSj 
 and from Ml into the conductor MlSl, and then further 
 from Si, into the conductor SlSi,. Thus the excitation, 
 whose ultimate end is naturally the causation of contrac- 
 tion in contractile tissues, would be only partly used for 
 this end; a large part would be wasted by going into 
 sensory points where, in animals with highly differentiated 
 tissues, no contraction is possible. We must, therefore, 
 draw our diagram in such a manner that the passing of any 
 excitation into a sensory point is excluded. One way of 
 doing this is by drawing each conductor, each neuron, in 
 the shape of an arrow-like rod as shown in Figure 14. We 
 
 A>- 
 
 Fig. 14 — One-way valves. 
 
 can then easily agree and remember that the point of any 
 arrow shall mean that no excitation can enter here from 
 any other neuron, whereas the split end shall mean that 
 an excitation can enter here, but can not pass out. Any 
 point like the point D in Figure 14, where several neurons 
 
42 HUMAN BEHAVIOR 
 
 meet, indicates then, according to the manner of drawing, 
 that an excitation may pass from AD into either DB or 
 DC, but that no excitation can pass from either CD or 
 BD into DA. It is as if a double one-way valve located 
 at D allowed the flow of a fluid in one direction, but pre- 
 vented the flow in the opposite direction. We must ask, 
 of course, if the facts known to neurology permit the 
 assumption that the meeting point of two or more neurons 
 functions like a one-way valve. 
 
 Experiments have proved, it is true, that an excitation 
 may travel to the other end of a neuron, in whatever end 
 it is called into existence by the application of an artificial 
 stimulus. But with respect to the propagation from 
 neuron to neuron, neurological experiment and observa- 
 tion seem to agree with the view expressed in the diagram 
 of Figure 14. Everybody knows that our feet are con- 
 nected with our eyes as well as with our ears, and, of 
 course, also with other sense organs. If a strange and 
 ferocious looking animal suddenly appears to any ordinary 
 person's eye while he is sitting, he jumps up and starts 
 running. If he is sitting in the theater, and suddenly 
 the fearful cry "fire" strikes his ear, he also jumps up and 
 starts running. That is, the muscles moving his feet are 
 connected with his eye as well as with his ear. But his 
 eye and ear are connected with many other muscles too; 
 else, for example, he would not turn his head in response 
 to a friend's call or eat what is placed before him on the 
 dinner table. Now, neurologists have discovered in the 
 brain the so-called motor region of the foot. If this 
 region of the brain is artificially stimulated, the muscles 
 belonging to the foot contract and move the foot. Sup- 
 pose the excitation caused by the stimulus could proceed, 
 not only in the direction of the motor organs most closely 
 connected, but also in the direction of sense organs, for 
 
ONE-WAY VALVES 43 
 
 example, the eye and ear. The eye and the ear are 
 very closely connected with the motor region of the foot 
 in the brain; they are also very closely connected with 
 many other muscles of the body. It should then have 
 been observed that in response to the artificial stimulation 
 mentioned not only the foot, but many parts of the body 
 moved. If such were the case, the neurologists would 
 never have discovered the motor region of the foot. This 
 very discovery means that they observed an exclusive 
 reaction of the foot to stimulation of this region of the 
 brain. We are justified, then, in our assumption of a 
 one-way propagation of an excitation from neuron to 
 neuron. We need not assert, dogmatically, that no other 
 interpretation of the experimental facts is possible. But 
 the assumption of one-way conduction from neuron to 
 neuron, always away from sensory 'points and toward motor 
 points, is simple enough and does not contradict any 
 known facts. Besides, the anatomical connection be- 
 tween neurons is of such a wonderfully elaborate kind, 
 that it seems quite probable that the meeting points have 
 a peculiar function, actually perhaps much more compli- 
 cated than the siniple function of a one-way valve. The 
 neurons do not run into each other like wires soldered 
 together, but their end branches are interwoven. The 
 purpose of this method of connection is not known, but 
 it surely involves more than a mere making one out of 
 two. 
 
 We said above, with reference to Figure 13, that the 
 diagram of that figure needs additional features in order 
 to make it more perfect. First, then, we shall draw the 
 meeting point of several neurons in the manner of Figure 
 14, indicating for each neuron the direction from a sensory 
 point and the direction towards a motor point. A second 
 improvement is necessary because the diagram of Figure 
 
44 HUMAN BEHAVIOR 
 
 13 does not permit the representation of a series of motor 
 points which can all be reached from one definite sensory 
 point, but only over conductors each differing in resistance 
 from all others. These conductors, in order to have each 
 its special resistance, must all differ in length. At the 
 same time, each motor point may have its own sensory 
 point with which it is connected by a conductor of mini- 
 mum length. The whole case, then, is somewhat com- 
 parable to that of the jelly-fish in Figure 11, where all 
 contracting points can be reached from any point stimu- 
 lated, but only over paths differing in resistance. The 
 insufficiency of the diagram of Figure 13 becomes clear 
 if we enlarge it by connecting (in Figure 15) in the same 
 way not only two, but three pairs of corresponding points. 
 In Figure 15 an excitation can travel from S^ to M^ over a 
 path of three standard lengths. From S^ to Mj, an 
 excitation can travel only by C over a path of four standard 
 lengths. We have, therefore, a difference of resistance. 
 But from S^ to M^ there is again a path of four lengths, 
 so that there is no difference of resistance between the 
 path leading to Mf, and that leading to M^. In order to 
 represent a gradation of resistances we need a diagram 
 differing from that of Figure 15. Instead of a point C, we 
 have to introduce a line, as shown in the horizontal lines 
 of Figure 16, representing each a neuron of standard 
 length and resistance. In other words, the connections 
 between the arches must themselves be arches consisting 
 of three (or more) neurons each. 
 
 In Figure 16 three colors have been used in order to 
 facilitate the recognition of the direction from sensory 
 points to motor points. All green conductors in the 
 figure can be traveled only in the direction from below 
 up, all red ones only in the direction from above down, all 
 violet ones only in the direction from the left to the right. 
 
 We can travel, in Figure 16, from Sa to Ma over Sl and 
 
-a 
 o 
 S 
 
 fe 
 
ARCHES OVER ARCHES 
 
 45 
 
 Ml directly, taking a path of three lengths. From S^ to 
 Mb the shortest path is over Sl, Sli, Mli,, and Ml. 
 This path has a total length of five units, two more than 
 from Sa to Ma. 
 
 From Sa to M^ the shortest path is over Sl, S%, S^i,,;, 
 
 Mlbc, 
 units. 
 
 itf^ 
 
 i,c. Ml. This path has a total length of seven 
 At the same time the corresponding points Sj and 
 C 
 
 Sc Sb Sa Ma Mb lie 
 
 Fig. 15 — Imperfect manner of connection. 
 
 Mb are connected by a short path {S^, Sl, Ml, M^) of 
 three units, the corresponding points S^ and M^ also by a 
 short path {S„ Sj. Ml, M^) of three units. This dia- 
 gram, therefore, exactly fulfils the condition of universal 
 connection without interference with local responsiveness 
 of an animal's body./ We shall have to investigate 
 whether a nervous system like the one represented in 
 Figure 16 is sufficient for the needs of all the higher and 
 the very highest animals, — whether we have a right to 
 assume that even the nervous system of man is built 
 essentially (apart from simplification and elaboration of 
 the details) on the design of this figure. We have, of 
 course, the right to assume this, if wte can convince our- 
 selves that all the actual functions of the nervous system 
 in man's body are thus made comprehensible. 
 
FOURTH LECTURE. 
 
 Reflex arches. Their peripheral and central points. 
 Central sensory points and central motor points. Central 
 points of a lower and higher order. Lettering of diagrams 
 explained. Central sensory and central motor neurons. 
 Reflex, and instinct. Instinct a selecting and collecting agent. 
 Overflow of a strong sensori-moior discharge into the most closely 
 connected arches. The source of motor power different 
 from, the signal for its expenditure. What a nervous excita- 
 tion can be likened to. Signaling by rods and levers or by 
 pneumatic tubes. Velocity of signal very great, but not infi- 
 nite; not dependent on intensity. A neuron likened to an 
 electric storage element. A simple picture of a nervous 
 process needed for our imagination of nervous function. 
 
 THE design of Figure 16 allows infinitely many 
 modifications and elaborations without deviat- 
 ing from the general principle upon which it 
 is based. This principle may be stated in the 
 following words. Each sensory and each motor point 
 of the body contains one of the ends of a neuron which, 
 accordingly, may be called either a sensory neuron or a 
 motor neuron. The other ends of each pair of a sensory 
 and a motor neuron are connected by what may be called 
 a. connecting neuron. The whole, represented in the figure 
 in the shape of an arch, for example, S^ S\ M\ Ma, may 
 be called a reflex arch. Each reflex arch is composed of 
 at least one sensory, one motor, and one connecting neuron. 
 
 46 
 
REFLEX 47 
 
 The number of neurons, however, forming a reflex arch, 
 need not be limited. Any line in our diagram, the sensory 
 neuron SaSl, for exaniple, might a,ctually be a chain 
 composed of several neurons. But for our present purpose 
 of constructing a simple diagram typical of the design 
 of the nervous system, this possibility need not be dwelt 
 upon: Further, several sensory neurons may run to- 
 gether into a common meeting point, as S^Sj, S^S], 
 and S'iSl in Figure 17. And the same may be true for 
 several motor neurons, as MlMi, and MjJf j in the same 
 figure. Nevertheless we may say, since to generahze 
 is our present business, that each reflex arch is composed of 
 a sensory, a connecting, and a motor neuron. We must 
 say a word, however, as to why we have called these arches 
 reflex arches. The term reflex has been a physiological 
 term for centuries. The early physiologists used it to 
 signify the great quickness and definiteness with which 
 certain actions occur compared with the slowness and 
 variability of others. To take an example from human 
 life, if we bring the tip of the finger suddenly close to the 
 eye of a stranger sitting opposite us in the street car, he 
 surely and most quickly shuts his eye. Such an action 
 seems to deserve the name of reflex action. It occurs, 
 or seems to occur, as promptly and definitely as our own 
 features are r^ected back towards us when we look at 
 ourselves in a mirror. But if we ask the stranger to lend 
 us a dollar, he puts his hand in his pocket — if he does it 
 at all — only after a good deal o1^ hesitation, of delay. 
 This does not seem to deserve the name of reflex action. 
 Modern physiology, however, has gradually put less 
 and less emphasis on the quickness of the response 
 in the case of so-called reflexes, and more on its deflnite- 
 ness. For example, in such reflexes as coughing, or vom- 
 iting, or intestinal action there is not necessarily any great 
 
48 HUMAN BEHAVIOR 
 
 quickness, but a great definiteness of response. Now, we 
 may most naturally regard the definiteness as being deter- 
 mined by the fact that of the innumerable motor outlets 
 of the excitation just one is superior to all others in being 
 reached over the shortest path, offering the least resis- 
 tance. Such a path may be represented by one of the 
 arches of our diagram, since each arch assigns to each sen- 
 sory point just one motor outlet of specially low resistance. 
 We may, then, call these arches reflex arches, but we 
 must remember that by giving them this name nothing 
 is proved or disproved, nothing is made clearer than it 
 would be otherwise, — we have merely referred to a tra- 
 ditional physiological term when occasion seemed to offer. 
 Each reflex arch contains four points. We may give 
 them diflferent names by calling them peripheral points 
 (So and Ma, for example) and central points {S\ and M\, 
 for example). These terms "peripheral" and "central" 
 must not, however, be understood literally. The peri- 
 pheral points are not always located on the anatomical 
 periphery of the body, the skin; — some sensory points are 
 located in the skin and some in the inner parts of the body, 
 whereas the motor points, in muscle flbers, are neces- 
 sarily without exception beneath the skin. Neither are 
 the central points always located in a central part of 
 the body. The words peripheral and central are used in 
 a loose sense, as a telephone station in a city is called 
 central, although it may be located far from the centre 
 of the city. We may then speak, not only of a peripheral 
 sensory point and a peripheral motor point, but also of a 
 central sensory point (S^) and a central motor point {M]^. 
 This does not signify that these points are in a strict 
 sense sensory and motor, but merely that one of them (S^) 
 is nearer to a sensory than to a motor point of the body, 
 3,nd the other (Afo) is nearer to a motor than to a sensory 
 
CENTRAL POINTS 49 
 
 point of the body. It is easily seen, then, that in the dia- 
 grams of our figures several central -sensory points are 
 collected, so to speak, by neurons (central sensory neurons) 
 into a central sensory point of a higher order. For exam- 
 ple, Sl and Sl are collected into Sl^. This is done in 
 a manner not different from that in which the peripheral 
 sensory points Sj, and Sj are collected into Sl. The 
 central motor points are also collected (by central motor 
 neurons) into central motor points of a higher order, 
 for example. Ml and M^ into Ml,,. The same prin- 
 ciple of design is then applied again. From the cen- 
 tral sensory point to the central m3tor point of the second 
 order there are several paths •— a direct one (SltMat) 
 and more indirect ones, for example S% S^sc Ml^^ ^Ib- 
 We find there the same manner of connection 
 which we found for Sl and Mo, which too had a direct 
 and a less direct path of communication. The whole 
 design, complicated as it looks at first, is really built 
 upon a very simple principle, applied consecutively in 
 regular order, — the principle, that from a sensory to 
 its corresponding motor point there are always direct 
 and less direct paths of communication, and that the less 
 direct paths serve the purpose of connecting each sensory- 
 motor system of conductors with other systems of a similar 
 kind by the aid of a common path, always represented 
 graphically by a horizontal line. 
 
 The letters and digits added below or above each 
 S or M very simply indicate the peripheral points with 
 which the point in question is most directly connected 
 (for example, S^cd with Sj, Sl, S^, S^, S^, and S'i ) and the 
 total number of unit conductors making up any such 
 connection (for example, three neurons for Slcdt two 
 for Sli). Where the number of units differs for differ- 
 ent peripheral points, the digit is added, not to S or M 
 
50 HUMAN BEHAVIOR 
 
 but to a, b, c, etc., as the case demands. For example, 
 in the diagram of Figure .17, S/i,\^ indicates that the dis- 
 tance from this point to S^ is one of only two unit lengths, 
 but to Sj of three lengths, and to S^ also of three lengths. 
 
 We spoke of the physiological term reflex. We may 
 use this opportunity to refer now to another traditional 
 term, that of instinct. When one observes that a bird, 
 without having been taught by experience or by other 
 birds, builds a nest before laying any eggs, one usually 
 says that the bird has done this instinctively. Here again 
 there is a certain promptness and definiteness of action as 
 in the case of a reflex action, but promptness and definite- 
 ness of a different kind. Let us try to make clear of what 
 kind. The bird does not many times lay eggs which are 
 doomed to perish because there is no place to receive 
 them, until some time it happens to prepare a nest before 
 the act of laying. But before the first egg is laid, the nest is 
 prepared in quite a definite way, well suited for the 
 hatching of the young. Of course, there are certain 
 physiological processes in the bird's body which, previous 
 to laying, cause excitations in definite sensory neurons, 
 and these excitations are conducted to the motor neu- 
 rons controlling the act of building. Why are they con- 
 ducted just here and not to any other motor neurons? 
 Obviously, because of short connections, of relatively small 
 resistance, between these motor and these sensory neurons. 
 But the figure of speech of a "mirror-like reflection" is not 
 applicable. We cannot comprehend an instinctive 
 activity by simply referring to a reflex arch, — it is too 
 complex and variable for that. It is definite only in the 
 sense that it occurs at a time when innumerable stimuli 
 acting on innumerable reflex arches make us regard almost 
 any other kind of muscular activity as just as probable as 
 the one which actually occurs, some of them stimuli 
 
INSTINCT 51 
 
 without the presence of which the act of building would 
 not have occurred, some, however, quite irrelevant to the 
 act of building. For example, a suitable site for the nest 
 and suitable building material must impress themselves 
 upon the eyes. But even this site and this material 
 might have called out innumerable other responses just 
 as well. The specific excitation of the instinct, caused by 
 the internal physiological stimulus aforementioned, there- 
 fore cannot be the all-sufficient cause of the action, but 
 must be rather of the nature of a selecting and collecting 
 agent, weakening and rejecting those excitations whose 
 presence is unnecessary, or whose reflex responses would 
 interfere with the instinctive action, strengthening and 
 uniting all those excitations whose presence is necessary 
 for the performance of the instinctive action. Let us 
 now try to comprehend the effect of the specific excitation 
 of the instinct by the application of the diagram of 
 Figure 17. 
 
 Let Sd Sj represent all those sensory neurons any exci- 
 tation of which is likely to interfere, if the corresponding 
 reflex responses are allowed, with the performance of 
 the instinctive activity. To illustrate this by a concrete 
 example, think of flying. It is clear that any long continued 
 flight would make nest building an impossibility, even 
 though short flights are with many birds an essential 
 part of the building activity. Here a selection is needed, 
 excluding, on the whole, such motor responses as flight. 
 Let, further, Sj Sl and S^ S] represent all those sensory 
 neurons whose excitation is necessary for the instinctive 
 activity. For example, the bird's eyes must see the 
 site and the material. Here a collection is needed, including 
 in the activity the motor responses upon such things 
 as a building site and building material. Let S^ S ^ repre- 
 sent the sensory neuron whose excitation is what we 
 
52 HUMAN BEHAVIOR 
 
 called the specific excitation of the instinct, which selects 
 and collects among the nervous processes coming from the 
 other sensory points. How, then, can we comprehend 
 the influence of the excitation coming from Sa upon the 
 motor activities at the points M^, M„ and Mj? Obviously, 
 the excitation coming from Si must be prevented from 
 reaching the corresponding motor point Mj,. The excita- 
 tions coming from Sj and from Sc, however, must not be 
 prevented from reaching their corresponding motor points 
 Ml, and M^, but their effectiveness must be enhanced as 
 much as possible: — the bird must not do any other 
 things, but pick up building material and drop it at the 
 site of the nest in the proper manner leading to the form a- 
 tion of a nest. 
 
 It seems clear that this acting as a selecting and collecting 
 agent as we said above, can be best understood by assum- 
 ing that the excitation coming from S^, being so strong 
 that the direct discharge over S\ and M\ into Ma overflows 
 the channel of its reflex arch, partly travels upwards from 
 the point S\. Because of the connections naturally 
 existing it can reach equally well both Ml and M\ 
 over shorter paths than it could reach any other points 
 (e. g., M\ ) leading towards motor organs. Thus it en- 
 hances the muscular contractions at both the motor points 
 ilfj and M^. The connections of the generalized design 
 of Figure 16, however, do not fulfil this condition. They 
 would favor Mi, over M^. The connections representing 
 the instinct must be like those of Figure 17, which is 
 • derived from Figure 16, in the main by simply omitting 
 certain conductors, as a comparison of the two figures 
 imniediately reveals. If we travel in Figure 17 from So 
 to any motor point other than M^ over the shortest pos- 
 sible route, we can travel only over S\, Sa^i,'/, and 
 Ma'b'c' to either M^ or ilfjor M^. In this case the entire 
 
A SELECTING AND COLLECTING AGENT 53 
 
 path from the_sensory to the motor points has a total 
 length of six units. Had we traveled from S^'t^' up to 
 S/b'^c*d* and M/!,*c*d* and thence to any other motor 
 point, for^ example, to M'^, the path would have had a total 
 length of at least^eight units. The control by the strong 
 and overflowing excitation from S^ of the function of the 
 motor points Jf j and M^, the collecting agency of the in- 
 stinct, is thus graphically represented by the relative 
 shortness of the connecting conductors. On the other 
 hand, the inhibiting influence of the excitation coming 
 from Sa upon the function of the reflex arch S^M^ is 
 graphically represented by the bare existence of a connection 
 by means of the connecting nem-on S/i*c*d* ^a^b"* i*"- 
 This connection must make it possible for the nervous 
 process coming from S^ to capture, as it were, the nervous 
 process coming from S^, thus preventing it from reach- 
 ing Mi. But we are still far from understanding this in- 
 hibiting, selecting influence. The diagram of connection 
 by conductors in Figure 17 is only one of the assumptions 
 necessary for the explanation of instinctive activity. We 
 shall return to this problem in the following lecture. It is 
 necessary that we investigate first what other assumptions 
 we have to make to understand theoretically what nervous 
 activity means. 
 
 We have already compared the nervous system with a 
 signal system, a telephone system by means of which 
 messages may be sent. We must understand more clearly 
 what kind of a signal system it is. It is important, how- 
 ever, that we keep clearly before our mind that it is only a 
 system for signaling, not a system for the transmission of 
 power. It can not be compared, for example, with the elec- 
 tric light and power circuit of a city, furnishing to many 
 houses in many streets power which is generated in a cen- 
 tral station. An animal's muscular power does not take 
 
54 HUMAN BEHAVIOR 
 
 its source in the nervous conductors attached to the mus- 
 cles. The power is derived from the digested food through 
 mediation of the blood circulation. The power is thus 
 stored in the muscles, ready to be expended at the proper 
 signal. The nervous excitation is the signal, the message 
 that the power should be expended. To be sure, the 
 amount of power expended is not altogether independent 
 of the force of the signal, of the intensity of the mes- 
 sage received. But that the power is not derived from 
 the messenger is clear from the fact that when a muscle is 
 exhausted, no nervous excitation can make it contract. 
 
 What, then, is the excitation which is propagated 
 through a nervous conductor in order to serve as a signal 
 to a muscle fiber. This, however, is not really a good ques- 
 tion. What it is, in other words, what name is to be 
 applied to it, is directly of little significance. What it 
 can be likened to, is the question which we should rather 
 ask. What thing with which we are familiar in the ordi- 
 nary functions of life, acts like a nervous conductor through 
 which an excitation is taking its path? 
 
 Fifty years ago, when a master desired to call his servant, 
 he rang the bell in the servant's room by means of a rigid 
 wire connection extending over pivoted angles from his 
 own to the other room. Now, let nobody think that this 
 comparison is absurd from the start. Everybody knows, 
 of course, that there are no wires and pivots in any nervous 
 system. But we have already emphasized that it is 
 of minor importance what there is, that we are concerned 
 rather with what goes on there. Does the signaling 
 going on in the nervous system permit comparison with 
 the signaling done by pulling a bell cord? Now, it does not. 
 If for no other reason, for this, that the bell attached to 
 a perfectly rigid wire or rod begins to ring the very 
 moment the other end is pulled. But when an excitation is 
 
ANALOGIES OF CONDUCTION 66 
 
 caused at one end of a nervous conductor, it is not at the 
 same moment also at the other end, but measurably la- 
 ter, — the later, the greater the distance between the 
 two points. We must look, therefore, for a different com- 
 parison. 
 
 Everybody knows the grand musical instrument in 
 which the player, pressing down the keys, opens at consi- 
 derable distances from the keyboard the valves which 
 make the various sources of sound speak. In the pipe or- 
 gan too the messages were sent until comparatively recent 
 times from the keys to the valves by means of rigid connec- 
 tions, as from the master's room to the bell in the ser- 
 vant's room. No delay is permissible in the response "of 
 the pipes to the touch of the fingers on the keys. The 
 rigid connection, therefore, seemed to be the only possible 
 one. Nevertheless, the modern organ has been freed of 
 all rigid connections. A narrow tube runs from the key 
 to the pipe valve. The motion of the key opens a tiny 
 auxiliary valve which admits compressed air from the 
 main reservoir to the tube just mentioned. At the 
 other end of the tube is a tiny bellows which is raised 
 by the compressed air and thus operates the pipe valve. 
 Now, what use can we make of our knowledge of this 
 familiar mechanism? We shall see at pnce that we can 
 thus elucidate certain fundamental facts of the function 
 of the nervous system. The pneumatic mechanism does 
 not operate the pipe valve at the very moment when the 
 key is moved by the finger, but at a measurably later 
 time, — the later, the longer the connecting tube. How- 
 ever, the time interval is short enough to be negligible 
 in musical practise, provided the connecting tube is not 
 extraordinarily long. The time interval is practically 
 independent of the density of the compressed air in the 
 reservoir. It is simply proportional to the length of the 
 
56 HUMAN BEHAVIOR 
 
 tube, provided the tube is plain and does not contain in 
 its course any additional mechanisms. The corresponding 
 facts are found in the function of the nervous system. The 
 muscle fiber does not contract at the very moment when 
 the sensory point is excited, but some time later, — the 
 later, the longer the nervous path connecting the sensory 
 and the motor point. Yet, the time interval is, in the 
 case of a reflex, quite negligible according to our standards 
 of time in ordinary life, — so much so, that for centuries, 
 until modern methods of measuring exceedingly short 
 time intervals were invented, the time was regarded as 
 absolutely zero, that is, the response was indeed believed 
 to occur at the very moment when the sensory point was 
 excited. It has further been shown by experiment, 
 that the contracting of the muscle fiber does not occur 
 any sooner if the excitation of the sensory point is made 
 stronger. 
 
 With aU this, however, we do not want to suggest 
 that a neuron is a narrow tube through which a fluid is 
 pressed. We have emphasized before that we are merely 
 searching, for fanuliar functions with which we may com- 
 pare the nervous functions in order to assist our power 
 of imagination and reflection. Let us use this opportunity 
 to tell briefly what physical processes have actually been 
 found by the neurologists to go on in the nervous conduc- 
 tors. Whenever anything of the nature of an excitation 
 occurs in a neuron, an electrical phenomenon is observed. 
 But it is generally admitted that this electrical phe- 
 nomenon is not the excitation itseK. There is no such 
 thing as an electrical insulation surrounding a neuron, 
 which would enable an electrical current to pass along 
 a neuron. And further, the velocity with which the exci- 
 tation is conducted is almost infinitely small when com- 
 pared with the velocity of electricity in its conductor. 
 
STREAMING OF IONS 57 
 
 During the time a nervous excitation is conducted one way 
 and back through an elephant or other large animal, elec- 
 tricity can circle the globe. The electrical phenomenon 
 must be, therefore, a purely accidental accompaniment of 
 the conduction of an excitation. It is highly probable that 
 the conduction of the excitation is a process of a chemical 
 nature. The substance of a neuron, consisting of highly 
 unstable organic compounds, must be well adapted to 
 the conduction of chemical changes. It is also well known 
 that the conduction of chemical changes frequently 
 involves, as by-products, so to speak, electrical phenomena. 
 Indeed these electrical phenomena accompanying the 
 conduction of chemical changes have been used technically 
 and have become of the greatest industrial importance 
 in the so-called accumulators or electrical storage batteries. 
 An accumulator is essentially a conducting fluid on the 
 sides of which there are two related, yet different chemical 
 substances, most commonly lead compounds. One of 
 these substances has a tendency to take up a certain 
 more elementary substance; the other has a tendency 
 to give off this same elementary substance. The same 
 elementary substance is one of the components of the con- 
 ducting fluid. What happens is this: A stream of element- 
 ary substance flows — or, whatever it may actually do, is 
 imagined to flow — from one end of the conductor to the 
 other, and this flow, the wandering of molecules or ions, 
 as it is usually caUed, is accompanied by an electrical 
 phenomenon. We are, then, probably justified in regard- 
 ing the conduction of an excitation through a neuron as, 
 not identical with, but at least analogous to the wandering 
 of ions through the conducting fluid — ^the electrolyte, 
 to use the technical term — of a storage battery. 
 
 Concerning the chemical and physical properties 
 of the neurons hardly anything further is known which 
 
58 HUMAN BEHAVIOR 
 
 could make the function of these wonderful structures 
 clearer. It is not especially remarkable that the chemistry 
 of the neuron, although it has attracted in recent years 
 the attention of investigators, has made little progress. 
 We need only remember that the neuron is a microscopic 
 structure, and that for a chemical analysis a more than 
 microscopic quantity of the substance to be analyzed is 
 required, and we understand why no one yet knows how 
 the excitation actually wanders from one end of a neuron 
 to the other end and thence to the other neurons. For the 
 very reason that the chemistry of the neurons is a thing 
 of the future, we may picture to our own imagination 
 the processes going on in the neurons in terms not neces- 
 sarily chemical, in any kind of terms with which we are 
 familiar and which enable us to understand the function 
 of the nervous system as being a complex of a few — as 
 few as possible — simple functions. We have pictured 
 it as a process like the one going on in a connecting tube 
 of a pneumatic organ. Let us now draw further conclu- 
 sions from this assumption. 
 
FIFTH LECTURE 
 
 Advantage of comparing the nervous process with a pro- 
 cess of streaming. Analogy of the jet-pump. The whole 
 nervous system permeated by any nervous process, but not 
 with uniform intensity. Suction at motor points; openings 
 made at sensory points. Velocity of the relief of tension. 
 Conditions of the intensity of streaming at any definite 
 point of the system. Exhaustion. Resistance increasing 
 with, and even more rapidly than, the flux. Overflow not 
 identical with universal permeation. The selective function 
 of an instinct explained by the principle of deflection, the 
 collective by that of overflow. 
 
 SPEAKING of the fundamental facts to which one 
 customarily refers by the term instinct, we showed 
 (page 53 and Figure 17) that one of them consists 
 in the capturing of the nervous process going on 
 in one reflex arch (S^ M^ ) by the nervous process going on 
 in another reflex arch (Sa M^, in such a manner that the 
 former process, coming from S^, could not reach its normal 
 end in the motor point M^. Does it help us to understand 
 this possibility of one nervous process capturing another, 
 deflecting it from its normal course, if we compare nervous 
 processes with the conducting mechanism of a pneumatic 
 organ? It does indeed, although no such capturing takes 
 place in an organ. The little bellows operating a pipe 
 valve is filled by air streaming through the connecting 
 tube. Now, it is one of the most interesting facts of 
 
 59 
 
60 HUMAN BEHAVIOR ^ 
 
 physics that a stream can deflect another stream with which 
 it is in contact. This is equally true for gaseous and 
 liquid substances, there being in this respect no funda- 
 mental difference between them. We are all familiar 
 with many kinds of apparatus using this principle of 
 deflection. Think of the various sprayers for spraying 
 perfumes or substances for inhalation, or for spraying 
 with insecticides the vegetables growing in the fields. 
 In these sprayers the liquid to be distributed is usually 
 taken — deflected, if we wish to say so — from the vessel 
 in which it is contained, by a stream of air. Or think of 
 the jet-pump, draining, perhaps, the cellar under our 
 house, or exhausting air from a glass bell in our laboratory. 
 It is not necessary for us here to discuss these phenomena 
 from the standpoint of theoretical physics, to explain 
 them mathematically. It is sufficient to mention them 
 as familiar facts. In all these cases it is irrelevant, of 
 course, whether the deflected stream really streams 
 originally with a positive or a negative velocity or 
 happens to have a zero velocity, that is, happens to 
 stand still, as in most of the examples mentioned above. 
 We can speak of deflection in every case. 
 
 Now, if the wandering of an excitation through a neuron 
 is comparable to the streaming of a fluid, we understand 
 at once the possibility of the deflection of one nervous 
 process by another. This deflection of a nervous process 
 from its ordinary course is then no longer a strange pheno- 
 menon, but has become like an old acquaintance. We 
 no longer ask any curious questions about it. We might, 
 possibly, inquire after the physiological details of this 
 function of the contact point or points of the two nervous 
 paths, where the deflection is brought about. But our 
 curiosity in this respect is not very great as long as we do 
 not even know the kind of chemical changes which are 
 conducted through the neuron. 
 
ANALOGY OF THE JET-PUMP 61 
 
 We have spoken of a chain of neurons as if it were a 
 tube through which air (or any fluid) is pressed from a 
 reservoir containing air under higher pressure. There 
 are, however, some disadvantages in picturing a nervous 
 process in this way. There is actually nothing which 
 resembles a reservoir from which any power or any sub- 
 stance enters, by way of a sensory point, into a chain of 
 neurons in order to be pushed along; and this pushing by 
 pressure might suggest a wrong idea of the function of 
 the nervous system. Some one might think that, what- 
 ever it is that is pushed from a sensory to a motor point, 
 it will take — like a rolling ball — only one way and entirely 
 avoid all other possible ways. Thus, indeed, one finds 
 nervous processes most commonly described in the older 
 literature of neurology. The question would then have 
 to be asked why such a process can take, now one, now 
 another path, why it does not always take the same, 
 since there is no god, no supernatural entity, in our ner- 
 vous system to act as switchman, to sever the connections 
 of the first path and to establish new paths, by voluntary 
 action. This question is then unanswerable; the fact 
 appears like a miracle. We must not think, therefore, 
 of a nervous process as ever taking strictly a single path. 
 We must, on the contrary, think of any nervous process 
 as permeating the whole nervous system, but only along 
 a certain path with great intensity, along all others with 
 very small intensities. Only thus can we understand the 
 function of the nervous system as a unitary function. It 
 is, therefore, better not to think of the nervous process as 
 something being pushed, but rather as a fluid filling the 
 whole network of neurons and being attracted by, sucked 
 in the direction of, all the motor points of the body. It 
 is true, to those who are accustomed to imagine in mathe- 
 matical terms movements of a liquid or a gas, there is no 
 
62 HUMAN BEHAVIOR 
 
 essential difference between a stream of a fluid caused by 
 pressure at one end and a stream caused by suction at the 
 other. But those not accustomed to mathematical reflec- 
 tions on such phenomena, will probably remember the 
 all-permeating nature of any process in the nervous 
 system more easily if they think of the cause of the stream- 
 ing as something located in the totality of the motor 
 points. 
 
 Let us, therefore, make the assumption, that the nervous 
 system functions as if the neurons were tubes filled with a 
 fluid, as if at all the motor points there were a constant 
 suction tending to draw the fluid in the direction of each 
 and every motor point, and as if an excitation of any 
 sensory point were equivalent to a greater or smaller, 
 but always minute, opening of the tube at this point, thus 
 allowing a streaming motion of the fluid within the tube 
 system. When a system of tubes like the diagram of 
 Figure 16, with one-way valves at all the meeting points 
 of tube-units, is closed at all those points which we have 
 called sensory points, no streaming of the fluid is possible 
 in any of the tubes, in spite of the suction at all the motor 
 points. Another effect, however, results from the suction. 
 The whole fluid in the tubes must assume a definite 
 tension, whose force must become equal to that of the 
 suction. Then the tension remains constant until a 
 stimulus is applied to a sensory point, or, as we have said, 
 until one of the tubes is slightly opened at a sensory point. 
 One must not think that immediately when the opening 
 occurs, the whole column of fluid begins to stream. What 
 happens first, is a relief of the tension at the point where 
 the opening is made. Then, as in every elastic substance, 
 so in the fluid, the relief of tension passes on. Only when 
 the relief of tension has reached the point where the force 
 of suction is effective, that is, the motor point, can the 
 
RELIEF OF TENSION 63 
 
 actual streaming begin. The velocity with which the 
 relief of tension travels through the fluid, is exactly what 
 is ordinarily called the velocity of sound in an elastic 
 substance. In a neuron we have to call it the velocity 
 of the nervous process, — whatever the nature of that process 
 may be. The velocity of the nervous process, which may 
 be regarded as a constant nvmsrical value, and the length 
 of the conductor leading from the sensory to the motor 
 point determine, therefore, the time which elapses between 
 sensory excitation and the start of the motor response. 
 
 The relief of tension, and the subsequent streaming, in a 
 system like Figure 16, can take simultaneously many 
 paths in the direction of a motor outlet. Which of all 
 these paths is chiefly taken, is determined by the relative 
 resistance of the conductors. We must not imagine, — 
 as we have emphasized before and restate here in more 
 detail — that the relief of tension rolls on like a ball, strik- 
 ing an obstacle, rebounding, running into an open channel, 
 and so on, finally reaching one motor point exclusively. 
 The relief of tension travels to every motor point which 
 is directly or ever so indirectly connected with the sensory 
 point in question. That it reaches motor points of direct 
 connection sooner than those of indirect connection, is 
 clear; but this time difference does not especially concern 
 us at present. The streaming, subsequent to the relief 
 of tension, also occurs everywhere, — ^in every neuron 
 which is a chain in any path from the sensory point to any 
 motor point. But the intensity of the streaming, the 
 flux at any definite point within the nervous system, is 
 necessarily determined by the relative resistance of the 
 total path over this point (not the resistance of any single 
 point) from the sensory to the motor point and the resist- 
 ances of all the other paths leading from the same sensory 
 point to all the motor points. To get a more definite 
 
64 
 
 HUMAN BEHAVIOR 
 
 image of such a complicated phenomenon, let us think 
 of two incandescent electric lamps illuminating our room, 
 which in the ordinary manner are placed parallel into the 
 circuit. Suppose the wiring provides for two twenty 
 candle-power lamps, but we suddenly replace one of them 
 by a 200 candle-power lamp of correspondingly less 
 resistance. Immediately we see a diminution of the 
 brightness of the other lamp, because its higher resistance 
 keeps the current from passing through it in its normal 
 strength. Now imagine that in Figure 18, which is 
 
 Fig. 18 — Possible modification of details in nervous architecture. 
 
 merely a modification of Figure 16 on the same structural 
 principles, each neuron would be replaced by a thirty 
 volt lamp and that then the point S^ would be placed in 
 contact with the positive line, and all the M points in 
 contact with the negative line of a hundred and ten volt 
 electric circuit. It is clear that the three lamps of the 
 reflex arch S^ M^ would then glow visibly, but that the 
 other lamps of the system would hardly glow at all, 
 although a weak current must pass through them. Simi- 
 
PERMEATION OF THE SYSTEM 65 
 
 larly, the muscular activity in the animal body becomes 
 conspicuous only in the corresponding motor point, al- 
 though a weak streaming must occur in the direction of 
 every motor point in any way connected with the sensory 
 point where the excitation starts. 
 
 If we thus picture the nervous process as a streaming of 
 a fluid in a system of tubes, made possible by an opening 
 at one of the sensory points, we must, of course, imagine 
 this opening to be, even when at a maximum, very small 
 relative to the volume of a tube unit. Otherwise the 
 tube, or even the whole system, would quickly become 
 empty, exhausted. The nervous system; however, is by 
 no means quickly exhausted, but can be active for many 
 hours before taking a complete, or nearly complete, rest 
 during the period of sleep. The opening at a sensory 
 point being exceedingly small, the streaming of the fluid 
 must be very weak. This does not matter, since the flux 
 in various neurons is significant only through its relative, 
 not its absolute magnitude. 
 
 Two fundamental facts, with reference to the so-called 
 instinctive activities of animal organisms, were to be 
 explained : the deflection of one nervous process by another, 
 and the simultaneous enhancement of the activity of 
 several motor points. We have found that the former 
 becomes comprehensible if we regard any nervous process 
 as possessing the properties of a streaming fluid, provided 
 the meeting points of the neurons, about whose functional 
 properties we possess no actual knowledge whatsoever, 
 are assumed to function in a manner comparable to the 
 functioning of the simple mechanical device which is 
 called a "jet pump." The simultaneous enhancement of 
 the activity of several motor points can be satisfactorily 
 explained as we have explained it in the preceding lecture, 
 simply by an overflow and the inherited peculiarity of 
 
66 HUMAN BEHAVIOR 
 
 nervous connections. If the excitation starting from Sa 
 in Figure 17 is not in the ordinary way practically confined 
 to the reflex arch Sa Ma, but exceeds the capacity of the 
 reflex arch and overflows, it will reach on a higher level 
 the connecting neuron Sa^b^/ Mahc^ and hence pass down 
 over the central point M\c to both the motor points Mi, 
 (and also Jf j)and M^. Since the overflow flnds an outlet 
 from the level of Sia\^c' down, it does not reach the higher 
 level of &iho*i- This is important, for, if the overflow 
 from 8a reached this level, the excitation starting from 
 8a would enhance the activity of the motor points M^ and 
 Mi , instead of decreasing it by deflection, in accordance 
 with our previous assumption concerning the significance 
 of Mb, Mc, and M^ in the instinct under discussion. The 
 deflection of the nervous process S^M^, however, can be 
 insured by a sufficient difference in level between the 
 connecting neurons which in Figure 17 are represented 
 by 8aV/ MaW and by S„%*// MaW'i'. This differ- 
 ence in level, of course, is not limited to what it appears to be 
 in the simplified diagram of Figure 17. Only one question 
 is thus left, namely, how we can speak of an overflow of a 
 reflex arch (S^ M^ upwards, caused by the intensity of the 
 excitation (at Sa), with the result that the activity of 
 certain other motor points {M^ and M^ is not, as would 
 -be expected from the principle of deflection, weakened by 
 the strong nervous process (from 8^, but on the contrary 
 enhanced. This is a question of so much importance that 
 we cannot proceed without having answered it with 
 perfect clearness. It is particularly important to make 
 clear the difference between an overflow and the fact that 
 in the case of every nervous process very weak currents 
 always go over innumerable paths other than the main 
 path of the process. 
 
 It is obviously not sufficient to state simply that the 
 stronger nervous process deflects all weaker ones. There 
 
OVERFLOW 67 
 
 are exceptions to this rule, as in the present case. Every 
 case in which, because of a very great excitation at a 
 sensory point, the motor response is not practically 
 restricted to the corresponding motor point, but becomes 
 positively apparent also at other motor points, is an ex- 
 ception to the principle of deflection. The stronger 
 process, instead of canceling the motor effects at all motor 
 points other than its own, while it may cancel many of 
 them, enhances at least some of them, indeed may bring 
 about some motor effects at points whose corresponding 
 sensory points are not receiving any stimulation at all. 
 Now, this can be understood only by assuming that there 
 is an absolute limit to the flux in any neuron, or, — what 
 amounts practically to the same and agrees better with 
 our previous assumptions, — that the resistance of any 
 neuron is not independent of the flux within it, but in- 
 creases more and more rapidly as the flux increases. We 
 are familiar with a similar phenomenon in electric con- 
 ductivity. As the current increases, the conductor gets 
 hot; and in the case of most substances its resistance 
 becomes the greater, the greater the temperature. Let 
 us imagine that there is a similar, only much more rapid, 
 increase of the resistance with the increase of the flux in a 
 conductor, and our problem is solved. If, under this 
 condition, the excitation at Sa in Figure 17 reaches a 
 sufficiently great height, the intensity of the flux in the 
 motor neuron M\Ma reaches practically an absolute 
 maximum, and the overflow, which thus becomes inevit- 
 able, must seek the motor outlet which offers the least 
 resistance because of the least length. This is in the 
 present case the outlet over Sa%%' Ma^^^ ^u into JIf j, 
 Ms, and M^. Of course, there can be, then, no question 
 of any deflection of an independent nervous process in 
 Sft Ml or S( iff. Whether there is any such nervous 
 
68 HUMAN BEHAVIOR 
 
 process or not, the overflow from jS^ into Mi, and M^ would 
 occur anyway. At the same time, however, the nervous 
 process S^M^, if S^ happens to be simultaneously stimu- 
 lated, is deflected into Mb and M^, provided the overflow 
 from Sa has not reached the level of Sa''b*c*d* -^o'ft^c^d''- 
 Overflow and deflection, therefore, are not fundamental 
 principles which logically exclude each other. Their 
 conditions merely enter now and then into a conflict, a 
 state of affairs which is found in all natural laws. Let 
 us keep in mind, then, that we do not mean by overflow — 
 as someone might conclude who has not read our present 
 discussion carefully — the fact that any nervous process 
 permeates, although for the most part exceedingly weakly, 
 the whole nervous system, far beyond the limits of a narrow 
 path: — we mean an overflow caused exclusively by an 
 intensity of flux taxing the capacity of a nervous path to 
 its limit. 
 
 We have called an instinct a s elect ive and collective 
 agency_ iiLjhe functioning of the nervous system. It is 
 clear that the principle of deflection explains the selective, 
 the principle of overflow the collective part of the function 
 of an instinct, provided the inherited connections of 
 sensory and motor points are such as represented dia- 
 grammatically in Figure 17. 
 
SIXTH LECTURE 
 
 Tension of the total muscular system not interfering with 
 special activities. The motor point not identical with the 
 point that is moved. Fewer reflexes, more instincts in higher 
 animals. The compounding of nervous elements into groups, 
 of these groups into larger groups, and so on, into a single 
 nervous system. The nervous system of a worm. Nerve 
 centers. Lower and higher centers. The nervous system of a 
 crayfish. The brains offish, frog, bird, and mammal. The 
 nervous system of man. The cerebral heniispheres of man. 
 
 SINCE we have had occasion to mention again at 
 the end of the last lecture the fact that every 
 nervous process permeates, although for the most 
 part very faintly, the whole nervous system and 
 thus, in a manner, reaches every motor point, we may 
 explain briefly, that this does not conflict with our obser- 
 vations of actual animal behavior. A slight degree of 
 tension of all our muscles in no way interferes with speciflc 
 activities involving a few deflnite muscles. Indeed in 
 practically all our normal activities we find that at least 
 one group of muscles other than those which actually 
 pull is quite noticeably under tension, namely the so-called 
 antagonistic muscles. Raise your arm in order to take 
 off your hat. It can be easily observed, and there is no 
 ■doubt whatsoever, that during the upward movement of 
 the arm not only those muscles are under tension which 
 pull the arm towards the head, but also those which under 
 
 69 
 
70 HUMAN BEHAVIOR 
 
 other conditions might pull the arm towards the body. 
 The latter muscles, if we put our fingers on them, do not 
 feel relaxed, flabby, but somewhat stifiF. Only, the former 
 muscles feel stiffer, they are under greater tension, and 
 the arm, therefore, follows the direction determined by 
 them. Under these circumstances, a general but faint 
 permeation of the whole nervous system by any nervous 
 process, however definite the activity for whose sake this 
 process exists, involves by no means a contradiction. 
 
 Speaking of muscles, it may be well to make a remark 
 here which will help to avoid possible misunderstandings 
 later. When a nervous excitation causes a movement of a 
 definite part of the body, for example, of the arm, the 
 motor point of the nervous path is not necessarily located 
 in that part of the body, in the arm. Indeed, if a move- 
 ment of the arm as a whole is in question, the motor 
 point (more correctly, of course, points) must be in the 
 muscles located at the shoulder and the front or back of 
 the chest. The muscles located in the arm can not move 
 the whole arm, but only the lower arm. The muscles 
 located in the lower arm can not move the lower arm, but 
 only the hand and the fingers. These examples may 
 suffice to call attention to the fact, which is self-evident, 
 that in highly developed animals the motor point must 
 not generally be looked for in that part of the body of 
 whose activity the nervous process is said to be the signal. 
 
 We have thus far spoken of the fundamental facts of 
 behavior in higher animals under two headings, that of 
 reflex and that of instinct. We call an animal the higher, 
 the fewer simple reflexes it has — relatively — and the more 
 instincts. Since this difference in the relative number 
 of simple and compound reflexes, that is, of reflexes proper 
 and instincts, depends, according to our previous exposi- 
 tions, on definite structural peculiarities of the nervous 
 
INSTINCTS IN HIGHER ANIMALS 
 
 71 
 
 system, it seems interesting and promising to compare 
 lower and higher animals with regard to the structure of 
 their nervous systems. It is not a priori necessary, but 
 probable, that these structural differences become apparent 
 to the eye of the anatomist and zoologist, and if they do, 
 they permit the correctness of our previous expositions 
 to be tested. 
 
 As our lowest type may serve the nervous system of an 
 earth worm. Figure 19 shows the arrangement of the 
 more bulky masses of the nervous system, omitting the 
 many fibers which are found scattered over the body and 
 which obviously serve as sensory and motor neurons. 
 
 Fig. 19 — The bulk of the nervous system of an earth worm. 
 
 What we see in the figure represents, therefore, in the 
 main, merely the bulk of those connecting neurons which 
 are added to the sensory and motor neurons in order to 
 complete the reflex arches, and of those which serve to 
 establish connections among the reflex arches, in accord- 
 ance with the principles which we have discussed. We 
 have seen that the frequent necessity of a body acting as 
 a whole, the necessity of local responsiveness as found in the 
 reflexes, and the presence of selecting and collecting agents 
 
72 HUMAN BEHAVIOR 
 
 called instincts, have as a consequence a structure of the 
 nervous system like the diagrams of Figures 16, 17, and 
 18. Let us, at present, remember especially Figure 18. 
 We notice there a number of sensory and motor points. 
 Some of the reflex arches are united by the connecting 
 neuron Sahcd ^abcd- The significance of the formation 
 of such a group is obviously, together with the insurance 
 of local responsiveness for each reflex arch, a unification 
 of the group of reflex arches for the purpose of co-opera- 
 tion. It is clear that co-operating reflex arches, as a rule, 
 belong to, and so far as possible are located in, the same 
 part of the body. Any part of the body which deserves 
 to be called a limb or an organ, say, one finger, needs 
 unitary activity of the totality of its own reflex arches for 
 the sake of its own protection if not for other ends. This 
 part of the body, then, is as a whole subject to the principle 
 of local responsiveness, but must also be able to co-operate 
 with other organs, to form with them anatomically and 
 functionally a larger organ. For example, our fingers 
 are united in our hand, not only anatomically, but also 
 functionally, that is, by their nervous connections, thus 
 making the hand a larger organ. We know that it is 
 easier to make a fist than to bend each finger separately. 
 These considerations lead us to expect groups of reflex 
 arches to be united as we see two such groups united in 
 Figure 18, where the central sensory points Sfj^^ and 
 S^fg and the central motor points -3/ ojcd and M^fg are 
 connected as if they were peripheral sensory and motor 
 points. The larger organ which is only thus made "an 
 organ," enabled to function as a unit in addition to 
 possessing local responsiveness of its sub-divisions, must 
 again, perhaps, be united with other organs. That is, 
 the whole mass of nervous conductors, sensory or motor, 
 must again be united with similar masses — we might just 
 
GROUP FORMATION 
 
 73 
 
 as well say, systems— into a larger "nervous system." 
 Where this building reaches its final culmination, depends 
 exclusively on the anatomical development, the anatomical 
 complication, and, accordingly, the demands of the body 
 for nervous conductors to suit its functional needs. A 
 simple way of representing this compounding of sensory 
 and motor elements into groups, of these groups into 
 larger groups, of these into still larger groups, and so on, 
 finally into a single large system, is shown in Figure 20. 
 
 Fig. 20 — Low and high centers: group formation in the nervous system. 
 
 That the total mass of all nervous conductors thus forms 
 a single system, and not two or three or more mutually 
 independent systems, follows from the necessity of each 
 animal body being able to act as a whole. In the figure, 
 each group is composed of only two members, for sim- 
 plicity's sake. In the body each group must actually 
 contain, of course, a very large number of elements, in 
 accordance with the special anatomical and functional 
 demands. This large and varying number is represented 
 in the diagram almost throughout by two. The dotted 
 lines of the figure will be explained a little later. 
 
74 HUMAN BEHAVIOR 
 
 Let us now make the application to the earth worm. 
 Let us see what kind of a picture we can expect the earth 
 worm's nervous system to present to our eyes. Since 
 the worm 's body is long and narrow, we expect that suc- 
 cessive pieces, from the front to the rear, should function 
 in relative independence. To make this still clearer, let 
 us remember how the worm moves forward. The ab- 
 dominal side of the body possesses tiny bristles pointing 
 backwards, so that the body does not easily slide backwards 
 on the ground. If, then, a fraction of the body, at the 
 front end, lengthens in the manner which everybody 
 knows from observation, the front end must be pushed 
 forward. Suppose now the first half of this front end, 
 the head, so to speak, remains inactive on the ground, 
 but the second half actively shortens, and an equally long 
 piece directly behind actively lengthens. The effect 
 must be that the elements of the piece directly behind 
 the head are, more or less, pushed forward. If now the 
 piece which has just lengthened, contracts lengthwise, 
 and the directly following piece lengthens at the same 
 time, while all the rest of the body remains inactive on 
 the ground, the elements of the third piece are pushed 
 forward, more or less. When in the same way every 
 successive piece has been moved forward, we can say that 
 the worm as a whole has made a step forward. It is 
 immediately clear that the nervous system of this animal 
 must be so constructed that the successive pieces can 
 function in relative independence. They must be ner- 
 vously furnished in such a manner that they can function 
 like so many separate organs, that they possess as wholes 
 what we have called local responsiveness. This means 
 that the reflex arches of each piece must be united into a 
 group, schematically like the groups of reflex arches in 
 Figures 18 and 20. We learn from the figures that this 
 
NODES OF THE CORD 75 
 
 unification of the reflex arches adds a considerable number 
 of nervous conductors to those making up each group of 
 reflex arches, — conductors which must be found rather 
 close together, for the sake of the unifying function in 
 question. We must expect, then, to find along the worm, 
 here and there, something like clumps or nodes of nervous 
 substance. Look at Figure 19, where these nodes are 
 apparent. The nervous cord which runs lengthwise through 
 the body shows a number of points where something is 
 added. Where the cord is a plain cord, the addition is 
 simply a swelling, a node, for example, at a. Where the 
 cord is a double cord, in the front part of the body, for 
 example, at b, the addition appears as a kind of tie 
 between the parallel divisions, giving the whole a 
 ladder-like form. These morphological details, of course, 
 do not concern us much at present. The important fact 
 is that we actually find the addition, at fairly regular 
 intervals, of nervous substance to the cord, which con- 
 firms our view that the whole nervous cord must be 
 organized in successive groups of reflex arches. 
 
 The most conspicuous of these clumps of nervous tissue 
 are the two belonging to the head of the worm, at c. It 
 may be well to mention that the two parallel divisions of 
 the nervous cord are here, between these two nodes, more 
 widely separated, in the shape of an oval, because the 
 alimentary canal, from the mouth, passes through between 
 the two divisions of the nervous cord. If we can speak, 
 in the case of the earth worm, of instincts, that is, if there 
 are nervous functions sufficiently complicated in their 
 sensory and motor aspect and also sufficiently unitary to 
 be called instincts, they must be related to the head rather 
 than to any other part of the body. The head is, even 
 in the earth worm, the most complicated and most im- 
 portant motor organ. Food is taken in by the head. 
 
76 HUMAN BEHAVIOR 
 
 The direction of locomotion is determined largely by the 
 direction taken by the head. The head, therefore, must 
 contain many important groups of muscles; but also 
 many important sensory points, for the taking in of food 
 and the direction of locomotion are determined by the 
 nervous stimulations coming from the external objects 
 surrounding the head. It is quite natural that all these 
 important sensory and motor points must be connected 
 by a highly complicated — and therefore somewhat bulky 
 — system of nervous conductors, forming out of the many 
 reflex arches as many different functional groups with 
 manifold interrelations as the life activities of the animal 
 require. This, then, is the cause of the accumulation of 
 nervous tissue in the head, which far surpasses the accumu- 
 lation of nervous tissue at any of the other nodes of the 
 cord just mentioned. That there are two such accumula- 
 tions in the head is, from our point of view, a mere accident. 
 It is, of course, the consequence of the anatomical distribu- 
 tion of the head organs. If the anatomy of the head were 
 different, both masses of nervous tissue might appear 
 united into a single node correspondingly larger. And 
 if the anatomy of the head were still different, there might 
 be three, four, or more nodes, each correspondingly 
 smaller. 
 
 A name for these nodes has long been adopted, which 
 we must use here too in order to adjust ourselves to the 
 common usage of language. They are called nerve centers. 
 We need not discuss the value of this particular name, — 
 it has become so common that we cannot escape using it. 
 However, it is well to keep any literal meaning of the term 
 entirely out of mind. A "center" has no more literal 
 meaning for us in the nervous system than a "central"' 
 has in a telephone system. We know what it is convenient 
 to mean by it, in the one case as in the other. It is cus- 
 
NERVE CENTERS 77 
 
 tomary to speak, not only of nervous centers in general, 
 but of higher and lower nerve centers. The significance of 
 this distinction can now be easily understood. If a "nerve 
 center" is a system of neurons serving the purpose of 
 uniting reflex arches into groups and such groups again 
 into more comprehensive groups, it must be called the 
 higher, the farther removed it is from the sensory and 
 motor points of the body. Still, the word center can be used 
 in a btoader or in a narrower sense. In Figure 20, we may 
 call all the neurons enclosed within one of the dotted lines 
 a center. Which of them is higher, more removed from 
 the peripheral sensory and motor points, is immediately 
 clear to the eye. Or, we may take the term center in a 
 narrower sense and include only the connecting neuron 
 between a central sensory point (for example, Sfj) and 
 its corresponding central motor point {M^^ ), and the 
 adjoining parts of those neurons which from this central 
 sensory and this central motor point run in the peripheral 
 direction. In this sense the neuron S^iM%, plus the 
 adjoining parts of the four neurons S\,S\i, S\S^i, M^tMl, 
 MabMf, would be a nerve center as represented in this 
 diagram. (The reader is requested to supply the lettering 
 of Figure 20 according to the rules given on page 49.) 
 In this narrower sense likewise the distinction between 
 higher and lower nerve centers is immediately clear 
 to the eye. The nerve center of which we just spoke, 
 containing the points S%, and M%„ is much lower than 
 the nerve center containing the points S* and M^. It 
 seems that we may use the term nerve center in either 
 sense without fear that any consequences arise which 
 might make our future discussions ambiguous. 
 
 We need not prove that the so-called higher animals 
 possess higher nerve centers than the lower animals, for 
 the greater complication of their nervous system and the 
 
78 HUMAN BEHAVIOR 
 
 resulting greater complexity of their life activities is the 
 very reason why certain animals are caUed higher in com- 
 parison with others which then, of course, are called lower 
 animals. But just on account of this fundamental signific- 
 ance of the terms lower and higher animals, it is exceeding- 
 ly interesting to study the appearance of the bulk of the 
 nervous system in a series of higher animals as we have 
 studied it in a rather low animal, the earth worm. Let 
 
 Fig. 21 — Nervous system of a crayfish. 
 
 US now use as an example a crayfish (Figure 21), which 
 has a somewhat higher position in the animal scale than a 
 worm. There is no essential difference between the 
 nervous system of the crayfish and that of the earthworm. 
 We notice, however, that the bulky parts of the nervous 
 system, the nerve centers, are relatively bigger. This is 
 to be expected, since the crayfish has numerous appendages, 
 specialized organs which must co-operate for various ends 
 and could not co-operate if their systems of reflex arches 
 were not combined by connecting neurons into a sufficient 
 number of systems of a higher order. 
 
 The vertebrates have their more important sensory and 
 motor organs still more concentrated in the head than 
 the articulate and lower animals. The reflex arches of 
 each of these organs must be united into a group, and 
 these groups, again, must enter into manifold combina- 
 tions in order to serve the more varied needs of a more 
 complex organism. Accordingly we find in the head of a 
 
THE BRAIN 
 
 79 
 
 fish that particularly large accumulation of nerve centers 
 which we call the brain (Figure 22). That this group 
 formation of reflex arches, this development of higher 
 and higher centers is most conspicuous in the head, is the 
 direct result of the greater importance of the sensory and 
 motor organs of the head than of the other parts of the 
 body. The important reflex arches of the head must be 
 well co-ordinated among themselves, but the systems of 
 nervous conductors thus formed must also be well co-ordi- 
 nated with the less important reflex arches in other parts 
 ■ of the body. However, among the latter reflex arches 
 
 A B 
 
 Fig. 22 — Brain of a fish; double view. 
 
 there are a certain class which do not require a particularly 
 close connection with the reflex arches of the head. They 
 are the reflex arches which serve the so-called vegetative 
 or visceral functions of the body. Let us make this clear 
 by examples. The approach to a particular article of 
 food is controlled mainly by the reflex arches of the head : 
 it is a response to sights, sounds, odors received by the 
 sense organs of the head. But the approach could not 
 take place without the co-operation of the reflex arches on 
 which the locomotor organs depend for their function; 
 and these organs are to be found in the remainder of the 
 body rather than in the head. On the other hand, there 
 is scarcely any reason why the intestinal activity of digest- 
 ing the food should be enhanced or impaired or otherwise 
 influenced during this or any other specially directed 
 
80 HUMAN BEHAVIOR 
 
 locomotion of the body, or why this special locomotion 
 should be influenced by the intestinal activity, save the 
 extreme cases of an empty or an already overloaded 
 stomach, to use familiar language. We are not surprised, 
 then, to find in any animal the visceral or interoceptive 
 nervous system rather separated from the locomotor or 
 exteroceptive nervous system, and to find in the nervous 
 accumulation of the head which we call the brain "the 
 center" not so much of the whole nervous system as of the 
 latter part only, of the exteroceptive system. 
 
 In comparing different vertebrates, let us consider 
 of the whole nervous system this part accumulated in the 
 head, the brain, alone and compare the relative size of its 
 main subdivisions. For this purpose we give to the 
 sub-divisions their ordinary names. We notice, in 
 Figure 22, that there are five sub-divisions, of which 
 three, the frontal ones, are more obviously divided into a 
 right and a left part than the other two. To these accumu- 
 lations of nervous tissue the term ganglion might be 
 applied, as also to any of the bulkier parts of the nervous 
 systems of the crayfish and the earth worm in Figures 
 21 and 19. Or they may be called lobes, a term frequently 
 applied to sub-divisions of the brain. Thus, in Figure 22, 
 ol means "optical lobe," of "olfactory lobe. "|^ In the 
 same figure m stands for the^" medulla, " joining the cord, 
 also called bulb because of its, shape, cb for " cerebellum " 
 or small brain, CER for "cerebrum" or large brain. 
 
 A B 
 
 Fig. 2? — Brain of a frog; double view. 
 
GROWTH OF THE CEREBRUM 
 
 81 
 
 Compare with these ganghons of the fish the same 
 ganghons of the frog, as shown in Figure 23. Their 
 relative size has changed in favor of one, the cerebrum. 
 This is still more obvious in a still higher animal, a bird. 
 
 A B 
 
 Fig. 24 — Brain of a bird; double view. 
 
 The two halves of the cerebrum, the so-called hemispheres, 
 are now, especially in the view of Figure 24, B, the most 
 conspicuous part of the whole. The same development 
 continues when we pass, in Figure 25, to a mammal. 
 The hemispheres of the cerebrum begin to look as if they 
 were the whole brain. The optical lobes have indeed 
 
 Fig. 25 — Brain of a lower mammal; double view. 
 
 been so completely overlapped by the ever growing 
 hemispheres that they have disappeared from sight. This 
 continued growth of the same single ganglion — quite 
 aside from a continuous, but less marked growth of all 
 others — through the various stages of evolution of the 
 vertebrates illustrates a principle different from that 
 
82 
 
 HUMAN BEHAVIOR 
 
 which requires a bulkier nervous system for an animal 
 possessing a greater number of sensory and motor points. 
 This continued growth of a single ganglion can have a 
 meaning only if the ganglion thus growing does not serve 
 any peripheral points directly, but exclusively indirectly, 
 by interconnecting unified neuron groups and unifying 
 them into secondary and further derived groups, as shown 
 diagrammatically in Figure 20. The growth of this 
 ganglion, then, enables the animal more and more to 
 
 Fig. 26 — Nervous system of man; double view. 
 
THE HUMAN BRAIN 83 
 
 read at any motor point to an excitation occurring at any 
 sensory point whatsoever, without losing its indispensable 
 local responsiveness. 
 
 If we compare (Figure 26) the bulky part of the nervous 
 system of man, that is, the part which can be cut out of 
 the body with comparative ease, and the bulky part of 
 the nervous system of a worm (Figure 19), we see that 
 they are not unlike in appearance except for the fact 
 that to a nervous system like that of the worm man has 
 added the enormous mass of nervous tissue of the cerebral 
 hemispheres (and, we might add, to a lesser extent the 
 cerebellum) serving no other purpose than that explained 
 in the last paragraph. Along the two sides of the spinal 
 cord, in Figure 26, there are two rows of ganglions some- 
 what separated from the cord. They obviously group 
 the reflex arches of each side and thus make the organs 
 on one side of the body relatively independent of each 
 other and of those of the other side. Many of our activi- 
 ties, it is true, are of the symmetrical kind, requiring 
 co-operation of the motor organs symmetrically situated. 
 But not a few of our activities are one-sided. The reflex 
 arches of a certain region of either side are therefore united 
 in a ganglion before coming into connection with the 
 nervous conductors of the spinal cord. 
 
 Figure 27 shows the enormous development of the 
 cerebral hemispheres in man as compared with those of 
 the lower vertebrates represented in Figures 22, 23, 24 
 and 25. The cerebrum has grown to such an extent that 
 it hides practically all the other parts of the brain, so 
 conspicuous in the fish, the frog, and the bird. The 
 cerebral hemispheres, which in the mammals have fallen 
 sideways over the other original ganglions of the brain, 
 have further grown especially in the forward direction, 
 thus covering their own lateral parts and forming the 
 
84 
 
 HUMAN BEHAVIOR 
 
 large Sylvian fissure (at S in Figure 27). Only toward the 
 back a piece of the cerebellum is still left uncovered; 
 The cerebrum has become practically the whole brain. 
 Its growth, taking place in the brain exactly there where 
 the most pronounced growth took place during the im- 
 mediately preceding period of evolution, has every time 
 served to make possible interconnection of the highest 
 centers by still higher centers, thus bringing about an 
 ever increasing possibility of any imaginable group of the 
 seemingly most unrelated motor points being functionally 
 
 Fig. 27 — Brain of man; double view, 
 governed by any group of seemingly most unrelated 
 sensory points. We need not suppose, however, that in 
 this process of complication identical with unification, 
 evolution has reached its highest possible mark. We 
 should over-estimate our race if we thought so. There 
 are many indications — some of them we shall have to 
 mention later — that the functions of innumerable reflex 
 arches and groups of reflex arches are even in the human 
 race still practically independent of, never governed by, 
 the function of those, belonging to the majority, which 
 are already effectively unified by their connections with 
 the brain and especially with the cerebral hemispheres. 
 
SEVENTH LECTURE 
 
 Learning. The susceptibility of nervous conductors. 
 Variations of the nervous path. (1) Two kinds of variation 
 of response. {2) Sensory condensation. (3) Motor con- 
 densation. Graceful motion. Inhibition. How a child 
 comes to fear a fire. 
 
 THUS far we have spoken of animal activities 
 only under two heads, as reflexes, and as 
 selected groups of reflexes, that is, instincts. 
 Both these kinds of activities may be given 
 a common name. We may call them hereditary activi- 
 ties, because the characteristic response foUowiag 
 each particular stimulation is in these cases com- 
 pletely determined by the strictly biological inheri- 
 tance of the individual from his ancestors, — is in no way 
 shaped by the geographical and social inheritance resul- 
 ting from the fact that the individual has been given by 
 his ancestors life and the training of his youth in a particu- 
 lar geologic-physical and social environment. This shaping 
 during life of the individual's manner of acting may be 
 referred to by the word "learning," or by the word 
 "habit." We are, perhaps, inclined to use the word 
 "learning" chiefly in connection with social institutions, 
 "schools" of all kinds, "habit" chiefly in connection with 
 altogether fortuitous circumstances. For us, however, 
 in this treatise, these words are synonymous. Regarded as 
 phases in the behavior of the human or animal individual, 
 
 85 
 
86 HUMAN BEHAVIOR 
 
 acquiring a habit and learning are identical. In each 
 animal we find — the higher the species to which the indi- 
 vidual belongs, the more numerous — learned or habitual, 
 in addition to hereditary, activities. Our next task is 
 the description of the changes which hereditary nervous 
 activities undergo in order to become habit, — ^the descrip- 
 tion of the process of learning, or rather, of the various 
 kinds of processes of learning. 
 
 It is plain that any shaping during life of an individual's 
 sensori-motor activity presupposes: first, that there is a 
 variation in the succession of sensory excitation and motor 
 response, and secondly, that this variation is fixed and 
 thus caused to reappear. The variation is possible only 
 if the main flux of the excitation once takes a path differ- 
 ent from the one which is to be expected according to 
 the shortest hereditary connection of sensory and motor 
 points. The fixation of this path is possible only if 
 (we might also say: fixation means that) nervous conduc- 
 tors are in some way susceptible to excitations traveling 
 through them, so that one of the reasons why an excitation 
 may be thought to choose a particular path, is simply 
 this, that it has once before taken this path. Of course 
 this statement may, and must, be made more definite 
 with respect to our assumption that the main path of 
 the nervous flux is the path of least resistance. We must 
 say, then, that the susceptibility of nervous conductors 
 consists in their resistance being reduced by a flux occur- 
 ring in them,— this resistance to stay reduced for a consider- 
 able time after the flux has terminated. We may add, 
 at once, remembering that the counterpart of learning is 
 forgetting and that forgetting is a gradual process : that 
 we have the right to assume that the reduced resistance 
 of any nervous conductor slowly rises again to its original 
 measure. 
 
NERVOUS SUSCEPTIBILITY 87 
 
 The question then is: do the pictures of streaming 
 which we have used in order to have before our mind a 
 clear idea of nervous activity and its peculiarities, aid us 
 also in imagining the susceptibility of a neuron as one of 
 its natural properties? It seems that this question can 
 be answered unhesitatingly in the affirmative. We are 
 hardly more familiar with any other natural event than 
 that of a stream broadening, washing out its channel; 
 and a dry river bed being gradually obliterated by being 
 filled with debris and dust is not a very unusual phenom- 
 enon either. Our picture of nervous activity, with regard 
 to the susceptibility of conductors, is therefore quite consis- 
 tent. The question is then left, if it is also consistent 
 with regard to the possibility of a variation of the main 
 path along which the excitation is conducted. Now, this 
 question has been answered already, in our discussion of 
 instinct. We said that an instinct is not only a collecting, 
 but also a selecting agency, and we explained the selection 
 of a path for an excitation, by referring to the familiar 
 physical principle underlying the action of a jet-pump. 
 No further assumption is necessary, only a reference to 
 an assumption already made. A variation of the main 
 path taken by an excitation can, accordingly, be the result 
 of a second nervous process deflecting the first by dint 
 of its own greater intensity. That a variation of the ner- 
 vous path can be brought about also by other factors, with- 
 out any deflection, will appear later. 
 
 We may distinguish several classes of variation of the 
 nervous path. If the stimulation as well as the motor re- 
 sponse is so simple that the whole nervous activity can be 
 called a reflex, the variation of the nervous path can consist 
 either in the motor response occurring at a motor point 
 which is not the point corresponding to the sensory point 
 stimulated or in the very same motor response following 
 
88 HUMAN BEHAVIOR 
 
 the application of a stimulation to a point which is not 
 the corresponding sensory point. Let us use variation 
 of response as a technical term for this kind of variation 
 of the nervous path. Naturally, we can apply the same 
 term also to cases in which the nervous path is neither at 
 its sensory nor at its motor end quite so simple. Indeed, 
 looking for a striking concrete example, we can hardly 
 help giving one in which the nervous path is complex. A 
 small chUd, taking beer into his mouth, spits it out, 
 reflexly, — or rather instinctively, for the motor activity 
 may be quite complex. Any bitter substance stimulates 
 definite sensory organs of the mouth, and the motor res- 
 ponse of the facial and other muscles is that which we call 
 spitting. The bitter substance is thus removed. The 
 large number of people who habitually drink beer can have 
 acquired this habit only by a variation of response taking 
 place and becoming fixed. Once, instead of spitting, 
 the very different motor response of swallowing occurred, 
 as a variation, and this variation, becoming fixed, became 
 the habit of drinking beer. In this example a different 
 response came to foUow the same stimulation. As an 
 example of the same response following a different stimu- 
 lation we may mention this. A baby, during the first 
 three or six weeks of his life, responds to any sudden noise 
 by quickly closing his eyes. It is. easy to observe this. 
 One need only clap his hands or whistle in order to see the 
 baby wink. On the other hand, one may closely approach 
 the baby's open eye with a finger or a stick without caus- 
 ing the slightest winking, unless the eye is actually touched. 
 When the baby is a few months old, all this has changed. 
 Noises rarely call forth the response of winking, but 
 when any object is brought near the eye, the latter is 
 closed. This reaction then remains our habit all through 
 our adult life. Once, of course, the variation must have 
 
VARIATION OF THE PATH 89 
 
 occurred for the first time, — the variation of the nervous 
 path which consists in a visual stimulation taking the 
 place of an auditory stimulation, while the motor response 
 remaias the same. 
 
 If the stimulation is complex and the motor response 
 correspondingly complex, the variation of the nervous 
 path can consist in the complex response being called out 
 by a greatly simplified stimulation, possibly a stimulation 
 of a single sensory point. The habitual nervous activity 
 then becomes similar to an instinct, for a complex reaction 
 in response to a simple stimulation is, as we have seen, 
 characteristic of an instinct. In order to have a brief 
 term for this kind of a variation of the nervous path, let 
 us call it sensory condensation, thus referring to the fact 
 that at the sensory end of the system of nervous conductors 
 the flux (when represented reversely in a diagram) no 
 longer spreads out, but is condensed into a narrow channel. 
 
 An example, rather complex in all its aspects, but very 
 familiar and therefore well illustrating our case, is the 
 following. In playing a certain piece of music on the piano, 
 at a particular place in the music each one of several fingers 
 has to perform a definite movement, — ^what movement, is 
 indicated by as many notes as there are fingers to move. 
 The beginner, in order to strike the correct chord, looks 
 at every note. But after some time of practice, we observe 
 that he plays exactly the same complicated chord even 
 when some of the notes, without his knowledge, have been 
 erased or changed by us. Obviously these notes are no 
 longer needed for the response, and a simpler stimulation 
 now brings about the same motor response. Typewriting, 
 reading, proofreading, weaving, attending to any machine, 
 — any kind of skillful activity can illustrate this same kind 
 of variation of the nervous path. The complex activity 
 is ultimately called forth by a part of the original stimu- 
 
.90 HUMAN BEHAVIOR 
 
 lation; sometimes to the detriment of the subject, as when 
 a proofreader overlooks a typographical error, reading the 
 whole word although not all of the word is there to act 
 on his eyes. 
 
 If the motor response is complex (because it is an in- 
 stinctive response or the stimulation is complex), the 
 variation of the nervous path can consist in the response 
 being greatly simplified, possibly reduced to a response at 
 a single motor point. Thus it would become similar to a 
 reflex response, were it not, perhaps, for the complexity of 
 the stimulation. In order to have a brief term for this kind 
 of variation of the nervous path, let us call it motor con- 
 densation, thus referring to the fact that at the motor end 
 of the system of nervous conductors the flux no longer 
 spreads out, but is condensed into a narrow channel. 
 Watch a child receiving his first instruction in writing 
 and you will frequently observe, not merely a moderate 
 activity in the shoulder, wrist, and finger joints, as when 
 an adult is writing, but in addition to an excessive activity 
 in these joints a tense bending of those fingers of the writing 
 hand which do not hold the pen, and also of the fingers 
 of the other hand, even a twisting of the head and the feet 
 as if no writing were possible without them. We say in 
 such a case that the person acts awkwardly. The dis- 
 appearance of awkwardness is generally equivalent to 
 the dropping of all movements unnecessary for the end in 
 question. A graceful motion is simply a motion no ele- 
 ment of which appears to be superfluous. The acqui- 
 sition of graceful motion means motor condensation. 
 
 Of course, our distinction of three classes of variation 
 of the nervous path, variation of response, sensory conden- 
 sation, and motor condensation, does not imply that 
 each of these variations must occur in separation from 
 the others. On the contrary, we must expect to find 
 
INHIBITION 91* 
 
 ' in actual life usually mixtures of them. As example of 
 such a mixture may serve the behavior of a person falling 
 into a river. If this is his first experience of the kind, 
 the motor response is exceedingly complex. The hands 
 move about in all directions, but chiefly they are thrown up 
 in wild attempts to catch anything which might be in 
 reach — a straw, as the proverb says — while the feet make 
 movements which, when slowly executed, might be useful 
 in climbing a tree, but which can serve no very useful 
 purpose in the surrounding fluid. The skillful swimmer, 
 on the other hand, merely makes a few moderate down- 
 ward strokes with his outstretched arms and hands, 
 and thus reaches the surface and stays there, possibly 
 not moving his feet at all. The variation of the nervous 
 path in this case obviously consists in a variation of 
 response as well as a motor condensation. As a matter 
 of fact, a sensory condensation is also involved, for during 
 the process of learning to swim many stimulations of 
 various sensory points (perhaps a teacher's words and 
 example) are effective, which later become superfluous. 
 The process of learning, the acquisition of a habit, has 
 a negative aspect of great importance, so far as the motor 
 end of the nervous activity is concerned. What a person 
 does not do, whether he reacts towards his physical or 
 social environment in a definite way or remains inactive 
 in this way, is frequently of the greatest consequence to 
 others. When I am walking along a highway and meet 
 strangers, my chief interest is in not being attacked 
 and robbed. What they positively do, concerns me but 
 little, possibly not at all. How important the negative 
 aspect of human activity is appears from the fact that 
 the great moral law of the decalogue contains almost 
 exclusively negative rules. Our scientific interest, therefore, 
 can not be restricted to the positive aspect of an individual's 
 
92 HUMAN BEHAVIOR 
 
 motor activity, It is clear, even from the mere outline 
 of nervous activity as given thus far, that the negative 
 aspect of the motor result of a nervous process can 
 never be a reduction of a nervous excitation to nothing, 
 but only a deviation to a motor point other than the 
 one at which we had a certain right, according to our 
 knowledge of the nervous connections, to expect its 
 motor response. When we are interested in a person's 
 or animal's not doing a certain thing, we use as a tech- 
 nical term the word "inhibition." From the point of 
 view of this treatise, inhibition means that the indi- 
 vidual does something else instead of what we thought 
 or feared he might do, while we do not care what it is that 
 he actually does. From a purely neurological point of 
 view the term inhibition in this sense is superfluous. 
 Nevertheless we shall have to use it because of its great 
 significance from the social point of view, for many social 
 institutions of great importance, for example all those 
 connected with crime and criminal law, cannot do without 
 this concept of inhibition. The law which inhibits murder 
 by stating "Thou shalt not kill" does not state what we 
 shall do instead of killing. The law giver is not concerned 
 with our action provided it does not consist in killing. 
 But it is of great value to us in any sociological application 
 to be aware of the fact that, at the bottom, the prevention 
 of crime is not a problem of preventing action, but alto- 
 gether a problem of substituting a socially valuable reaction 
 to a certain stimulation for a socially harmful reaction. 
 Thus far, we have hardly done more than define the 
 terms, variation of response, with its negative aspect 
 inhibition, sensory condensation, and motor condensation. 
 We must now make clear in detail, in specific instances 
 illustrating these cases, what goes on in the nervous sys- 
 tem when the nervous path is modified and this modifica- 
 
EDUCATION 
 
 93 
 
 tion becomes fixed, — to make sure that the fundamental 
 assumptions hitherto put down are suflBcient for an under- 
 standing of the behavior of any animal, even the highest, 
 or that they must be supplemented in a particular way. 
 Let us study in detail, first, the fundamental nervous 
 processes underlying the "education" of the proverbial 
 child who learns to fear the fire. This is a variation of 
 response. The instinctive activity called out by the flame 
 impressing the sensory points of the eyes consists in 
 a drawing nearer of the body or its limbs to the flame. 
 The habit which exists in later life is a withdrawing of 
 the body or its limbs from the flame. The variation 
 
 Sj. FmgfrTip 
 
 Drawing in h^ l^a Stretching out ^ 
 
 Fig, 28 — Burnt child fears the fire. 
 
 of the nervous path, therefore, must consist in this, that 
 the excitation coming from the eyes, which at first 
 passes into certain muscles, for example, those stretch- 
 ing out the arm, later passes into the very antagonis- 
 tic set of muscles, drawing in the arm. In Figure 28 we 
 represent this schematically as if the eyes stimulated 
 were only a single sensory point (So) and each of the 
 muscle sets only a single motor point (Ma approaching. 
 Mi receding). The only difference from our previous 
 method of drawing the figures is that the two reflex arches 
 open in opposite directions, right and left, instead of both 
 
94 HUMAN BEHAVIOR 
 
 downwards. Sa and M^ are corresponding points. It 
 is natural, therefore, that the child's finger is stretched out 
 toward the light. The problem is how we can explain 
 that later the path S^SlSltMlbMlM^, marked in the 
 figure by a zigzag line, has a lesser resistance than the path 
 SaSlMlMa, so that then the finger is withdrawn as soon 
 as the flame becomes simply visible. We have stated 
 that such a change must mean the fixation of a variation, 
 and this variation may be the result of a second nervous 
 process deflecting the first one from its original course, 
 in the direction of Ma, to another course in the direction 
 of Ml,. The second nervous process, therefore, must 
 have Ml, as its motor end. What kind of a sense organ 
 is then represented by the sensory point S^,- corresponding 
 to this motor point il/j? We know that the drawing 
 of limbs toward the body, while resulting from many differ- 
 ent stimulations, is especially the result of pain stimulation. 
 An animal suffering from strong pain of any kind does 
 not stretch out its limbs, but draws them in, curves them, 
 and the whole body too, if possible. It writhes. We know 
 further, from direct and indirect experience, that pain 
 stimulation is quite generally the essential factor in any 
 kind of variation of response. S^ represents, therefore, the 
 pain nerve ends of the finger stretched out. In what way, 
 then, in our diagram of Figure 28, do the two nervous 
 processes, from the eyes and from the finger tip, infiuence 
 each other? 
 
 In order that one of two nervous processes defiect the 
 other from its course, they must obviously exist in 
 the nervous system (Figure 28) simultaneously. This 
 does not imply, however, that one of them may not begin 
 before the other. In our case, Sa is stimulated first, 
 and only because of the excitation traveling from S^ to Ma 
 and causing the finger to approach the flame, occurs 
 
BURNT CHILD 95 
 
 stimulation of Sj by the flame. From this moment on 
 Sa and Si, are stimulated simultaneously. Whether 
 now the finger is moved into the flame or away from it, 
 depends, so far as it is a strictly mechanical event, simply 
 on the relative force with which the one (at M^) or the other 
 (at Ml,) of the antagonistic sets of muscles contracts. 
 This muscular force here depends on the relative intensity 
 of the nervous flux towards Ma and towards Mj. It 
 seems rather obvious that the excitation at Sj, caused 
 by the burning of the finger in or near the flame, must be 
 exceedingly strong, so that, as a purely mechanical effect, 
 the reaction must be that of a withdrawal. But even 
 if the two reactions were not as mechanical phenomena 
 mutually exclusive, — even if they were not antagonistic, 
 but anatomically independent movements, — the laws of 
 nervous function alone would practically suppress the one 
 in favor of the other, because the stronger nervous process 
 would sufficiently deflect the flux of the weaker nervous 
 process. It is this suppression of one nervous process 
 by another nervous process (and not at all the mechanical 
 annihilation of one muscular pull by another) which we 
 are here concerned with. Let us see how this is brought 
 about. 
 
 The flux originating from S^ divides at the point Sl. 
 The larger part of it takes the path SlMl; a smaller 
 part the path SlSli,M%Ml, because the resistance 
 of the latter is, according to the diagram, three times 
 that of the former. It is evident that at the point if fj, 
 too, a division of the flux must take place. Although the 
 resistance of the path M^iMlMi, is no greater than that 
 of the path M^i,M\Ma, most of the flux must go on 
 from M^j, in the direction of M\, because the flux over 
 S\ MlMa, according to our assumptions, acts as suction 
 upon the contents of the conductor M%,M\, whereas 
 
96 HUMAN BEHAVIOR 
 
 no similar force acts in the direction of Ml. Practically 
 all of the flux which originates from S^ finds its outlet 
 therefore in Ma, only an insignificant fraction going to ilf j. 
 But immediately the excitation of the point Ma brings 
 about the strong stimulation of Sj, the outstretched 
 finger being burnt. A strong flux now goes on from Sj 
 to Mi, mostly over SJMl, partly over SlSl^MltMl; 
 but even the part taking the latter path is strong compared 
 with the flux originating from Sa- At once all the condi- 
 tions are changed which determine the flux originating 
 from Sa- The strong current over SjSajMfj draws the 
 contents of the conductors S^Sat and SaSl. Consequen- 
 tly most of the flux from Sl takes the direction of S^i,; 
 little takes the direction of M]. From Mfj, again, most 
 of the flux is drawn, by the strong current over Sjilf jMj, 
 in the direction of Ml; little in the direction of Ml, since 
 the weak current over SlMlMa draws only weakly in 
 this direction. All this will appear even more natural 
 to us when we recall that in our physical analogy, the 
 jet-pump, the suction effect is not simply proportional 
 to the velocity of the fluid, but to the square of the velocity. 
 We have the right to assume, therefore, that the flux of a 
 weak nervous process is very readily consumed by the 
 deflecting effect of one which is only considerably stronger. 
 Consequently, in spite of the continuance of the stimula- 
 tion at Sa (the eyes), there is now practically no motor 
 excitation at Ma (no tendency to stretch out). 
 
 How is the fixation of this variation brought about, 
 to the effect that later, when S^ is stimulated, the 
 response occurs at Mi„ without any stimulation at all 
 occurring at Sj? We have assumed that each neuron 
 is susceptible to any flux occurring within it, so that its 
 resistance is lessened in proportion to the flux and the 
 time during which it continues. Under the assumption 
 
FEARS THE FIRE 97 
 
 of such a susceptibility the fixation of the variation of 
 response is a plain enough matter. The direct path 
 from Sa to Ma is made up (in the diagram of Figure 28) of 
 three units of length, the path from S^ to 3f j of five units. 
 The reduction of the resistance of the latter path need not 
 be by any means j[enormous, in order to m&,ke the flux in 
 the direction of M^ so weak as to be practically insignificant. 
 
EIGHTH LECTURE 
 
 Substitution of a direct for a devious nervous path. 
 Nervous tension inducing growth. Automatic action. Peri- 
 odic levels of learning. Two meanings of forgetting. Pos- 
 itive and negative susceptibility of neurons. The curves 
 of learning and forgetting. 
 
 THERE is, concerning the fixation of a new 
 path, a very important problem still left. 
 We have reason to believe that La addi- 
 tion to the fixation just mentioned, there is 
 another kind of fixation. Consider this example. 
 When we ask an educated person what six times 
 seven is, the answer is forty-two. When we ask 
 him what six times seventy-seven is, the answer 
 is four hundred and sixty two. Either answer will 
 doubtless be given with the same definiteness and 
 correctness. But there is a great difiFerence in the prompt- 
 ness. While the first answer is enounced directly, the 
 second is enounced only after a considerable delay. 
 The explanation seems obvious. Either path is somehow 
 fixed, but the former, because of the promptness of the 
 response, seems to be much shorter than the latter. As 
 we have just seen, a new path resulting from a variation 
 by deflection is naturally a relatively long path, since 
 the possibility of variation depends on the mediation of 
 centers higher than those of the path to be varied. The 
 fixation of the new path in the manner described does not 
 
 98 
 
DEVIOUS PATHS 99 
 
 change its length and can not, therefore, change the time 
 interval between the stimulation and the response, — the 
 so-called reaction time. Thus, there must be a second 
 kind of fixation of a path, which implies a shortening of 
 the path. We can explain this by the aid of a compara- 
 tively simple hypothesis. This hypothesis must be 
 the assumption of a property of the nervous system 
 which permits the growth of neurons in places where there 
 were previously none, and thus the shortening of a long 
 path by substituting a direct path for a devious and round- 
 about one. The neurological facts known, point indeed 
 in the direction of such an assumption. 
 
 All growth of living tissues, alike in the vegetable and 
 animal world, is of either one or the other kind, by cell 
 division or by growth of the individual cells. Different 
 kinds of tissues, however, show a remarkable difference 
 with respect to these two kinds of growth at the different 
 ages of an animal. In certain tissues, cell division can 
 occur all through life. The necessity of this in certain 
 tissues is clear, for example, in those tissues of which our 
 skin consists. When we have received a considerable 
 wound, involving the. loss of some skin, the cells at the 
 edges of the wound divide. The resulting new cells 
 increase in size and divide again; and so on until the opening 
 is completely covered with new skin. Without cell 
 division any new skin could hardly be formed, since there 
 is a limit to the si^e which individual cells may normally 
 attain. But scarcely any animal goes through life without 
 frequently receiving wounds. In other tissues cell divi- 
 sion becomes impossible after the animal has reached a 
 certain age. Since the muscles are of special significance 
 for animal behavior, let us take the muscles as an 
 example. It seems that in human muscles cell division be- 
 comes impossible after the age of from twenty to twenty- 
 
100 HUMAN BEHAVIOR 
 
 five years. From this follows the important fact that, in 
 order to become an athlete, a person must exercise his 
 muscles and thus induce both cell division and cell growth 
 before the age of twenty-five years at the latest. If 
 he has failed to do this, the number of muscle cells 
 which he possesses is so small that exercise, because of the 
 limited growth of the individual cells, will now only slight- 
 ly increase the bulk and therefore the total strength of 
 his muscles. This age limit for cell division differs in 
 tissues of various kinds. 
 
 The bulk of the nervous system consists of nervous 
 tissue proper, that is, the conducting tissue, and of suppor- 
 ing tissue. In the latter, cell division may occur at any 
 age. In the nervous tissue proper, however, cell division, 
 that is the multiplication of neurons, stops before man 
 begins his postnatal Kfe. It has been found that about 
 three months before birth man has as many neurons as 
 he will ever have in his Kfe. At this time, however, the 
 vast majority of these neurons are in the undeveloped 
 condition which we have already described. They are 
 little balls without any branches and therefore of little 
 value for the conduction of any excitation. They 
 develop into complete conductors at various times during 
 life. Some develop early, in order to serve those muscular 
 activities which the baby needs immediately on entering 
 into life, for example, the activities of sucking and swallow- 
 ing. Others develop during the succeeding years of child- 
 hood and youth. It is a peculiar fact, however, that 
 even in old age there are still many undeveloped neurons 
 present in the human brain. The conclusion offers itself 
 that these undeveloped neurons enable their owner to 
 acquire, even at an advanced age, certain new nervous 
 functions. The numerical possibility . that such unde- 
 veloped neurons will always, to the time of death, be 
 
UNDEVELOPED NEURONS 101 
 
 present and ready to take service, appears from the 
 fact that the total number of neurons in the human brain 
 is enormous, uncountable. They have been estimated 
 at from three to four thousand millions. How long would 
 it take us to count so high, if it took but a second to pro- 
 nounce each successive number? A day of twenty-four 
 hours contains 86,400 seconds, a hundred years only 
 3153f million seconds. We could not do the counting 
 in a life time. Thus it does not matter much if we take 
 a few millions of undeveloped neurons with us into the 
 grave, provided that we are thus at any time of our life 
 capable of new adaptations, of new useful habits. Capable 
 also of regaining nervous functions which we have lost 
 in consequence of a lesion within our brain, — say, a bullet 
 having passed through our brain. In such a case, if we 
 are lucky enough to remain alive, we are found to be inba- 
 pable of performing certain skilful movements and of 
 reacting in any way to certain stimulations. If a piece 
 of our brain is destroyed, it does not regenerate like a 
 piece of our skin. Its room is filled out with supporting 
 tissue, but the nervous tissue proper, the neurons lost, are 
 lost forever. The functions lost, however, may be entirely 
 or partly regained, just as if they were new habits. 
 
 We found it necessary to assume that a new nervous 
 path, a variation by deflection, may first be fixed in 
 its original length and later greatly shortened. We 
 can now explain how this shortening fixation can come 
 about. Suppose a new habit is being formed by the 
 variation of a path, leading now, instead of to the point 
 Mp which corresponds to S^ (Figure 29), by way of a 
 higher center to a non-corresponding point, say M^. 
 Sp and Mg are supposed to belong to two reflex arches 
 which are very remotely connected, over central sensory 
 and central motor points of a very high order, so that the 
 
102 
 
 HUMAN BEHAVIOR 
 
 resulting path is of a very round-about and zigzag nature. 
 Figure 29 may be regarded as diagrammatieally represent- 
 ing this path,without, however, suggesting that the path in 
 the brain would actually present itself to the eye as a 
 symmetrical figure like this. What is important in the 
 
 Fig. 29 — AutomatiG action: Short-circuiting in the nervous system 
 
 diagram is only that in various places, for example, at 
 Sp, two points of the path are by chance very near each 
 other. Let us assume that in such a case we have between 
 the two points a peculiar, growth inducing, biological 
 condition, just as we should have, if the path were a 
 metallic conductor carrying a high potential current, an 
 electrical tension likely to break through the insulating 
 substance in sparks. This simple hypothesis is suflBcient 
 to explain the second kind of fixation of the variation of 
 a nervous path. The biological tension, so to speak, 
 between Sp and M^ causes one or more of the undeveloped 
 nerve cells to grow and send out branches in either direction 
 of the tension. The consequence of this development 
 of a new connecting neuron is a shortening of the path 
 leading from Sp to M^ by practically putting out of func- 
 tion the part above Sp M\ , owing to the higher resistance 
 
SHORT-CIRCUITING 103 
 
 of this upper loop. The result of the new growth is that 
 the response at Mg to stimulation of Sp occurs with greater 
 quickness and also with greater definiteness, exclusiveness, 
 for less of the flux from S^ can now reach motor points 
 other than M^, 
 
 The same kind of shortening of the path may occur 
 later between S| and M^. Here again the biological 
 tension may cause the development of a new connecting 
 neuron out of an undeveloped nerve cell. The length of 
 the total path leading from Sp to M^ may thus be reduced 
 to almost that of a reflex arch. The response at M^ to a 
 stimulus at S^ must then occur with the same quickness 
 and definiteness as a reflex. That habits can become 
 very much like reflexes is well known. In the drilling 
 of a soldier good examples can be found by any observer. 
 Action of this kind is called automatic. It scarcely 
 differs from reflex action in any respect, save in its origin, 
 which is not hereditary. Its resemblance to reflex action 
 is fllustrated also by the resistance which automatic action 
 offers to the destructive influences of certain diseases 
 of the brain. When a nervous disease has made a man's 
 actions entirely illogical, certaia automatic actions still 
 occur with the same promptness as most reflexes, for 
 example, oaths — in people who have acquired the habit 
 of swearing in early life. This indicates the probability 
 that our hypothesis agrees with what actually occurs 
 in the brain. Since the disease attacks the higher centres 
 of the brain before the lower centres, the development of 
 automatic action seems to consist in the functional 
 cutting out of higher centres from the path, as explained 
 in the diagram of Figure 29. 
 
 If the distance between S^ and M^ had been less than 
 between S| and M\, the shortening of the path might 
 immediately have occurred here. This possibility agrees 
 
104 
 
 HUMAN BEHAVIOR 
 
 with the observation that habitual reactions whose per- 
 formance at first requires a considerable reaction time, 
 are sometimes made quicker only in numerous stages, some- 
 times become completely automatic almost at one time. 
 Our whole view concerning the shortening of a newly 
 acquired nervous path is thus supported by innumerable 
 experimental studies in the acquisition of skiU, for example, 
 in typewriting or in telegraphing. If the growing efficiency 
 of a person learning to write on the machine is represented 
 in a curve, we do not obtain a constantly rising curve, 
 but one which rises to a certain level, remains on this level 
 for some time, rises to a higher level, remains on it for some 
 time, and so on, as illustrated in Figure 30. Such an im- 
 
 Fig. 30 — Steps in acquiring skill: Periodic levels of learning. 
 
 provement by steps is to be expected if the fixation of the 
 variation of response is not merely a fixation of the new 
 path over higher centers, but at the same time a repeated 
 shortening by cutting oflP loops from the original winding 
 path. Each time when a loop is cut off, the test of the 
 person's efficiency must reveal a rather sudden improve- 
 
LEVELS OF LEARNING 105 
 
 ment. After this improvement, however, the efficiency 
 cannot but remain practically stationary, until another 
 neuron, perfecting its development, cuts off another loop 
 and thus raises the efficiency rather suddenly again to a 
 higher level. 
 
 Let us return to what we called the susceptibility of 
 the neurons . On it is based every possibility of a variation 
 of the nervous path, that is, every possibility of learning. 
 We know that the opposite of learning, forgetting, is of 
 as much consequence in actual life as learning. If we 
 call forgetting the opposite of learning, we should do so in 
 only one sense, namely, in so far as a path, instead of 
 becoming fixed, is being obliterated. In another sense 
 the opposite of learning, of a new reaction more useful 
 than the old, is a new reaction less adapted to our needs 
 than the old, as when we "forget" to lock the door in 
 leaving our house. This, obviously, is a case of inhibition, 
 of nervous deflection, rather than of true forgetting. In 
 so far as obliteration is opposed to fixation we are inclined 
 to explain obliteration by a property of the neurons 
 similar, but opposite to that on which fixation is based. 
 We might speak of a negative as well as of a positive 
 susceptibility. We said previously that the susceptibility 
 of nervous conductors consists in their resistance being 
 reduced by a flux occurring in them, and added that the re- 
 duced resistance of any nervous conductor very slowly rises 
 again to its original measure. The reduction may be called 
 positive suscepiibilty since it is a reaction to function, the 
 rise negative susceptibility since it is a reaction to a lack 
 of function. 
 
 In accordance with our statements thus far, the magni- 
 tude of the positive susceptibilty must be determined by 
 two factors, the intensity of the nervous process and its 
 duration. In the analogous case the river bed is washed 
 
106 HUMAN BEHAVIOR 
 
 out the more, (1) the more water flows through it 
 in a unit of time, and (2) the longer this flow continues. 
 On the other hand, the negative susceptibility depends 
 only on one factor, the time during which no ner- 
 vous process occurs in the neuron. It is interesting, 
 therefore, to compare the quantitative results of experi- 
 mental studies of the progress of learning, which is the 
 effect of the positive susceptibility, with those of the prog- 
 ress of forgetting, which is the effect of the negative 
 susceptibiKty. 
 
 The increasing efficiency of reaction in the process of 
 learning is always represented by a curve like that of 
 Figure 31, rising first rapidly, then more and more slowly, 
 
 liciency 
 
 Fig. 31 — Learning dependent on time. 
 
 provided that we have in mind one continuous process 
 without any intervening periods of rest. In a longer 
 process of learning spreading over days or months, and 
 containing many extended periods of rest, the efficiency 
 rises, as we have seen, in the manner of Figure 30. 
 We notice that in a continuous process of learning, lasting 
 say, haK an hour, the first few minutes are the most 
 valuable. During the following minutes less and less 
 is gained in efficiency, and the last few minutes add so 
 little to the result that we might just as well have stopped 
 earlier. This fact is established beyond doubt by experi- 
 ment and agrees also with the ordinary experience of 
 any one who has to practice anything, for example, the 
 
LEARNING AND FORGETTING 
 
 107 
 
 school-boy memorizing a foreign vocabulary. To read 
 over the whole task five minutes a day for a suflBcient 
 number of days to complete it, is much more economical 
 with regard to the total time required, than to complete 
 the task in one continuous memorizing. If we continue 
 the process only for five minutes, we do not make use of 
 the uneconomical part of the time curve farther to the 
 right in the figure. At first glance, the facts represented 
 in this curve seem to overthrow our analogies. Why 
 should a flux, broadening and deepening its channel, 
 do this the longer the less? But the matter becomes clear 
 when we remember that in a neuron, with its limited 
 resources, the flux cannot remain continuously on the 
 same level of intensity. The neuron does not become 
 less and less susceptible to the flux, but the flux becomes 
 in spite of an undiminished intensity of stimulation less 
 and less intensive. The total result, then, must be in 
 accordance with Figure 31. 
 
 Fig. 32 — Forgetting dependent on time. 
 
 The decreasing efficiency of reaction in forgetting is 
 represented by a curve like that of Figure 32. This 
 agrees well with our analogies. We compared the negative 
 susceptibility with the fate of a river bed through which 
 no water flows any more, and which is gradually obliterated 
 
108 
 
 HUMAN BEHAVIOR 
 
 by being filled with debris and dust. Such a filling in is 
 usually very pronounced at first, when the banks of the 
 river bed are still steep, less and less considerable later, 
 so that traces of the original depression of the ground 
 may continue for an exceedingly long period. Although 
 the analogy is remote, it shows that the curve may well 
 be expected to have the shape of Figure 32. 
 
 This curve, however, of Figure 32 does not indicate 
 what changes, if any, the efficiency undergoes during the 
 time directly following the period of practise, during the 
 first few seconds or minutes, let us say. Now, it is a 
 matter of common experience, that anything we have 
 just learned stays with us, as a rule, for a few minutes 
 
 Effi 
 
 iciency 
 
 Time 
 
 V 
 
 Fig. S3 — Forgetting immediately after practice. 
 
 with hardly lessened efficacy and is only then forgotten 
 at a rapid rate. Perhaps the complete curve ought to 
 be drawn as it appears in Figure 33, remaining almost 
 on a level for a short time, then falling very quickly and 
 
NO IMMEDIATE FORGETTING 109 
 
 later falling more and more slowly. The usual experiments 
 concerning the rate of forgetting do not tell anything 
 about the first few minutes since they are made only 
 with the intention of recording the loss from day to day. 
 But the ordinary experience is in this case definite and 
 general enough to assume that the loss during the very 
 first few minutes — ^not to speak of seconds — is practically 
 nothing. Let us here record the fact without attempting 
 to explain it. 
 
NINTH LECTURE 
 
 Sensory condensation in piano playing. Proportional 
 reduction of the resistance of higher and lower centers 
 connecting the same corresponding points. The positive 
 {and negative) susceptibility of a higher center greater than 
 that of a lower center. Motor condensation in grasping. 
 
 WE have studied and explained in de- 
 tail one of the three kinds of varia- 
 tion of the nervous path, the simple 
 variation of response. Let us study 
 next that kind which we called sensory conden- 
 sation. Musical practise may serve as an example. 
 A child learning to play the piano, at a certain place in 
 his piece, wants to strike two keys without having to look 
 at both the corresponding notes in the score — no matter 
 whether looking at both is possible or, because of their 
 distance apart in the score, impossible. He begins by 
 looking at one of the notes, seeing, let us say, the 
 other one in indirect vision and therefore indistinctly. 
 He reacts to the former by a perfectly definite finger stroke. 
 But the other note, not clearly separated from its sur- 
 roundings by the perceiving eye, calls forth an incorrect 
 or insufficient movement. The child tries again, and now, 
 of course, looks at the note whose movement was not 
 properly executed. Everything is reversed. The finger 
 movement which was previously done badly is now done 
 well, and the movement which was previously done well 
 
 110 
 
SENSORY CONDENSATION 
 
 111 
 
 is done badly. After many trials, on the whole alternating 
 as to the note favored by the eye, and as to the finger 
 crowned by success, the child becomes able to perform both 
 movements simultaneously with equal definiteness although 
 he is looking at only one of the notes — ^no matter which one 
 he is looking at. How do we explain this process of 
 sensory condensation? 
 
 In order to explain it we make use of a diagram very 
 similar to that of Figure 28, which helped us to explain the 
 simple variation of a child learning to avoid contact with 
 fire. For simphcity's sake, we represent the stimulation by 
 the note looked at as a single strong nervous process 
 taking its origin from Sj (in Figure 34), and the stimulation 
 
 Musical 
 Note I 
 5b> 
 
 Musical 
 
 Note I 
 
 :erl 
 
 FlngerH l^b i^a Rn 
 
 Kg. 34 — Sensory condensation explained, 
 by the note seen indirectly as a single weak nervous 
 process taking its origin from S^. We learned from Figure 
 28 that the motor response to this double stimulation, 
 strong at Sj and weak at S^, occurs only at M^. In 
 the child's second trial everything is reversed. The 
 stronger process is the one starting from S,, and the weaker 
 the one starting from Sj, so that the motor response 
 occurs only at M^. This goes on, the motor response 
 occurring alternately at Mb and Ma- The question 
 is what kind of changes the resistances of the various 
 neurons undergo. 
 
112 .. HUMAN BEHAVIOR 
 
 Plainly, when Sa and Sj are stimulated for the first time 
 simultaneously and the motor response occurs at the 
 point Ifj (see Figure 28), the neurons S%,Mli and M%,Ml 
 suffer a slightly greater reduction of their resistances 
 than in case S^ is stimulated alone. But it does not make 
 any difference to the reduction of the resistance of the 
 neuron S\M\, whether S^ is stimulated alone or S^ too. 
 The flux from Sj divides at the point S\ and goes on to 
 M\ partly over the direct, partly over the indirect route. 
 Let us assume for the present, quite arbitrarily (we shall 
 soon discuss this assumption separately), that the relative 
 resistance of each of the four neurons S\MI, S\S^, S^jM"^, 
 M%M\ in case the flux comes exclusively from the sensory 
 point Sj, remains absolutely constant, so that none of 
 these neurons is then in any respect favorably influenced, 
 compared with the other three. When, however. So is 
 stimulated at the same time with Sj, two of these four 
 neurons are, with respect to the reduction of their resis- 
 tances in consequence of their positive susceptibihty 
 imdoubtedly in a more favorable position than the other 
 two. The favored ones, Sfjlf^ and M^^Ml, in 
 which occurs the additional flux deflected from the reflex 
 arch SaMa, are marked in Figure 34 by a zigzag line. 
 Soon, as we have seen in our example of the piano-playing 
 child, the reverse stimulation occurs. S^ is now stimula- 
 ted strongly, St at the same time more weakly. Of the 
 four neurons SlM^, SlSlh, SliM^j,, and MIi,M\, two 
 are now with respect to the reduction of their resis- 
 tance specially favored, namely S%,M^f, and M%,M\. 
 They are marked in Figure 34 in the same way by a zigzag 
 line. If these two events happen alternately (this is 
 the important condition, without which the outcome 
 would be a mere variation of response) in a sufficient 
 number of repetitions, the finalTesult can be read off 
 
LOW AND HIGH CENTERS 113 
 
 from the diagram of Figure 34. The relative resistances 
 will be gradually changed so that ultimately any flux 
 starting from either S^ or Sj exclusively, will take, in the 
 main, the path over S%M%, divide at the point M%, almost 
 equally, and cause a response at Ma as well as at Mj, (a 
 striking of both the piano keys), — ^practically as if neither 
 the neuron SaJf a- nor Sjitf J were any longer in existence. 
 
 Thus this kind of a variation of the nervous path — sen- 
 sory condensation — ^would have been explained, but only 
 under the assumption just made that the relative resistance 
 of any higher nerve center connecting the same correspond- 
 ing points (for example Sj and Mi,) as any lower nerve center 
 remains constant, however much the absolute resistance 
 of all these centers may be reduced by a continuation 
 or repetition of an isolated stimulation of the sensory point 
 in question. This is the same assumption, only generalized, 
 which we made with regard to four special neurons, 
 and upon which we based our reasoning in the explanation 
 of sensory condensation. This assumption is by no 
 means self-evident. On the contrary, one might expect 
 something very different. -If Sj alone is stimulated, 
 the flux in the neuron SlMl must be about three times 
 as strong as in any of the neurons SjSaj, SabMai,, and 
 M%,Ml, since the path from S\ to Ml over these three 
 neurons in series offers a greater resistance than the 
 direct path over the single neuron SIM\. In conse- 
 quence of the greater flux, the resistance of the neuron 
 8\MI might be expected to be reduced, by and by, 
 relatively much more than the total resistance of the 
 other three neurons is reduced. 
 
 This last consequence, however, is biologically impossible. 
 It would mean, in this special case, that the resistance 
 of the neuron SlMl would tend to become so much 
 reduced in comparison with any other nervous connection 
 
114 HUMAN BEHAVIOR 
 
 between the points Sl and Ml, that the reflex arch 
 would be practically separated from its connection with 
 the points Sfj and M^. In general terms it would 
 mean that all the reflex arches tend to become functionally 
 separated from the higher nerve centers. Why 
 should any animal have higher nerve centers, if the 
 natural tendency of any nervous function from the 
 beginning of individual life were to make the conduction 
 of excitations over any higher centers more and more 
 diflBcult and even impossible? The animal, then, might 
 just as well, from the beginning of its life, possess no 
 nervous conductors whatsoever, other than the reflex 
 arches. It is clear, then, that we have, on quite general 
 biological grounds, the right to assume that the relative 
 resistance of any higher nerve centre connecting the same 
 corresponding points as any lower nerve centre, in the 
 case of isolated stimulation of the sensory point, remains 
 constant. That is, in our special case (Figure 34), we 
 have the right to assume, as we did, that when Sj, alone 
 has been stimulated, and the flux has occurred, in accor- 
 dance with the length of the conductors, more strongly 
 over sl and Ml directly, more weakly over S%, and M^, 
 the ratio of the resistances of any two of the four connec- 
 ting neurons involved always remains identical. Only 
 simultaneous stimulation of a second sensory point can 
 bring about a change of the relative resistances,^ — favoring 
 the one or the other according to the special circumstances 
 of the case. Our explanation of this case of sensory 
 condensation is therefore complete. 
 
 The assumption made concerning higher and lower cen- 
 ters, which we found necessary on general biological 
 groimds, may be stated also in diflferent words. If the 
 lower nerve center (take as an example the connecting 
 neuron SlMl in Figure 34) does not, in spite of the 
 
RELATIVE SUSCEPTIBILITY 115 
 
 greater flux within it, suffer any greater reduction of its 
 resistance than the higher center {SlSliM%,Ml) , the 
 positive susceptibiHty of the lower center is obviously 
 less than the positive susceptibility of the higher center. 
 
 If this holds good for the positive susceptibility, we 
 have reason to ask if it applies also to the negative suscep- 
 tibility. That it does, seems to follow from the familiar 
 fact that any ability is lost through the normal process 
 of forgetting the less readily, the greater the number of 
 instinctive, low-centered relations contained in it. For 
 example, we forget how to recite historical dates more 
 easily than we forget how to skate. Perhaps, then, we 
 are justified in stating the assumption quite generally 
 thus: The neurons of higher centers have a greater suscep- 
 tibility than those of lower centers. 
 
 We have still to explain the third kind of variation 
 of the nervous path, — that kind which we called motor 
 condensation. The condensation of the motor activity 
 can be explained in practically the same way as a variation 
 of response. We have learned from Figure 28 that, when 
 Sa is rarely stimulated alone, but frequently together 
 with Sf, and then less strongly than Si,, the path leading 
 from Sa to Ml, tends to offer less and less rfesistance 
 and finally to surpass greatly in conductivity the path 
 from Sa to Ma- It is plain that when this stage of devel- 
 opment has been reached, simultaneous stimulation 
 of Sa and Sj can scarcely under any condition of relative 
 intensity result in a simultaneous response at both 
 the motor points Ma and Mf,, but exclusively in a re- 
 sponse at Ml,. 
 
 But not all cases of learning which deserve the name of 
 motor condensation are so simple. Let us take as a concrete 
 and not too complicated example the baby who, during 
 several months, can grasp small articles only by closing 
 
116 HUMAN BEHAVIOR 
 
 his whole hand, but afterwards learns to grasp a small 
 article, for example a shirt button, between his thumb 
 and index finger, like a grown person. At the sight of a 
 sufficiently conspicuous object the young baby stretches 
 out his arm. As a consequence of this reflex movement 
 the fingers are stimulated by contact with the object. 
 When the tip or any other part of the inner surface 
 (from the nail toward the palm of the hand) of any finger 
 is stimulated by touch, the finger reflexly bends. After 
 a few months the baby learns to respond to the mere 
 sight of an object by the initial part of the movement 
 of closing the hand; that is, the fingers begin to bend while 
 the arm is still being stretched out, before they have 
 had any contact with the object. What gives, at this 
 stage, the grasping a particular appearance of clumsiness 
 is the fact that the thumb does not aid in grasping, but is 
 left practically functionless. To understand this is not 
 difficult if we recall the statement just made that the 
 original (reflex) bending of any flnger results from 
 touch stimulation of its inner surface. When the arm is 
 stretched out and the hand naturally drops on the object 
 presented, the thumb is not stimulated, as the other four 
 
 Fig. 35 — Thumb and finger movement, 
 fingers are, on its inner surface, but on its side. This 
 is the natural consequence of the anatomical location of 
 the thumb, which moves, as the arrow in Figure 35 indi- 
 cates, in the plane vertical to the plane of movement of 
 the other fingers. Accordingly, the thumb has a less 
 strong tendency to bend refiexly and, after the other fingers 
 have bent, is prevented by them from bending. 
 
MOTOR CONDENSATION 117 
 
 Compare with this clumsy mamier of grasping the 
 skill which the same child shows less than a year later, 
 in taking hold of a small object. While the arm is being 
 stretched out, in response to the sight of the thing, the 
 thumb and the index finger assume positions opposite 
 each other, ready to take the object between them. The 
 other three fingers remain all the time at rest, in whatever 
 position they happened to be at the start. If the object 
 is of medium size, the middle finger assists the index 
 finger. Only if the object is large, do all the four fingers 
 come into action. In any case the thumb assumes a 
 position opposite the fingers while the hand is still approach- 
 ing the object, that is, in response to the mere sight of 
 the object. 
 
 This whole process of learning can be made clear by 
 the aid of a comparatively simple diagram. Sg represents, 
 in Figure 36, the eye. The neurons SlMl and M1,,M\ 
 leading toward the motor organ which stretches the index 
 finger, are marked as not yet developed. The shortest 
 motor outlet from S^ is therefore Mj, the motor organ 
 stretching the arm. In consequence of this stretch- 
 ing of the arm, the points Si, S^, S/, and Sg, representing 
 the finger tips, are stimulated. The reflex response at 
 Mi, Me: Mf, and Mg is a bending of the four fingers and 
 enclosing the object by them. The nervous processes 
 from Si, Sg, Sf, and Sg attract, by dint of their own. 
 intensity, the process coming from So and force it to 
 take largely the path over SltSliciefgM^cdefg^aefg and 
 thence into Mi, Mg, Mf, and Mg. The resistance of 
 this path decreases until, after repeated occurrence of 
 this deflection and the fixation of the path, the excitation 
 caused at some time at S^ travels in the direction of 
 Mi, Me, Mf, and Mg and causes the beginning of a bending 
 even before any of the finger tips have been touched. 
 
118 HUMAN BEHAVIOR 
 
 Oabcdefg 
 
 Sab:^ 
 
 I Ubcdefg 
 
 Ma Mb Sg Sf Se Sd Sc Mc Nd Ne hf Mg 
 
 Mg. 36 — JLearning how to grasp. 
 
 Sa, Eye — Ma, Stretching index finger — Mb, Stretching arm — Sc, 
 Tip of thumb — Sd, Tip of index finger — Mc, Bending thumb — Md, 
 Bending index gnger — Zigzag, Neurons undeveloped at birth. 
 
 This accomplishment becomes the subject of a new 
 influence at some time during the second half of the first 
 year. The neurons marked in Figure 36 by zigzag lines 
 reach by this time their full development and estabUsh 
 a new hereditary connection. When now the eye is 
 stimulated, not only the arm but also the index finger is 
 . stretched out. This reflex appears at about the same time 
 that the flrst articulated sounds (usually dental and 
 guttural — "da" and "ga") are instinctively enounced by 
 the baby, — a coincidence the significance of which we shall 
 discuss at a later time. The result of this stretching of 
 the index finger, with the other fingers in their ordinary 
 slightly bent position, is touch stimulation of the tip 
 of the index finger exclusively. Since the other fingers 
 remain unstimulated, the index finger alone bends. If the 
 
GBASPING 119 
 
 object is small, this bending movement of the index 
 finger touching it is likely to pull the object toward the 
 hand. When this is actually done, the object comes into 
 contact with the outer surface of the other fingers and the in- 
 ner surface of the thumb . The former contact is irrelevant, 
 because it occurs on the outer surface; but the contact with 
 the thumb is followed by a reflex bending of the thumb, 
 so that the object is squeezed between the thumb and 
 index finger. This means, in the diagram of Figure 36, that 
 the two nervous processes from S ^ to Af ^ and from S^ to M^ 
 deflect the nervous process coming from Sa by dint 
 of their greater intensity and force it to take the path 
 over S%„i,fg, M%,a^g, and M\f^ into M^ and Mi. If 
 this whole occurrence happens repeatedly, the resis- 
 tance of the path from So into Mc and into Mi is 
 so much lowered that finally, at the appearance 
 of the object, the excitation travels not only to 
 Ma and to Jkfj, but largely also to Mc and Mi and causes 
 a motor response here too, although slightly later than 
 at Ma and Mj, because of the difference of the distance. 
 This makes it plain, why toward the end of the first year 
 the child responds to the mere sight of an object by 
 stretching out his arm and at the same time making 
 the thumb and index finger ready to receive the 
 thing which has been presented to the eye. The 
 motor expansion, the clumsy use of the whole hand, has 
 been succeeded by the motor condensation, the use 
 of two fingers only. 
 
TENTH LECTURE 
 
 Order of acquisition of the first four classes of habits. 
 Control of the sense organs of the head. Direction and 
 extent of the fixation movement of the eye. Improvement by 
 experience of the fixation movement of the eye. A variation 
 of response resulting from a close succession of nervous 
 processes just as from a deflection of one by another. Co- 
 ordination of the eyes. How an infant learns to face a 
 sounding object. Control of the hands and arms. Learning 
 to raise the arm in response to a visual object above the eyes. 
 Loose co-ordination of eye and hand. 
 
 WE have considered the change of behavior, 
 which we call learning, in its positive as 
 well as in its negative aspect. We have 
 recognized that learning and unlearning 
 (inhibition) are only the positive and the negative aspect 
 of the same nervous function. We have further convinced 
 ourselves that the three classes of change of behavior, 
 which seem to include all possible kinds, variation of 
 response, sensory condensation, and motor condensation, 
 are at bottom the same nervous function, which in its 
 simplest form we have called variation of response. The 
 above explanation of this nervous function, however, is 
 appHcable only in case one nervous process which influen- 
 ces another, begins before the other has ceased, that is, in 
 case of simultaneity. Learning as applied to successive 
 nervous processes Avill be explained farther below. We shall 
 
 180 
 
FIRST HABITS 121 
 
 first make ourselves acquainted with the most fundamental 
 reflex activities of childhood from which human learning 
 develops. The study of this development will show us 
 in what respects the explanations of human behavior 
 given thus far are sufficient and in what respects they 
 need to be supplemented. 
 
 Childhood is the very age of learning in human life. 
 Great as the accomplishments of human beings may 
 appear which are acquired in schools and colleges, they 
 are as a matter of fact small when compared with those 
 of the first six or seven years, before the individual is 
 systematically trained by his teachers. It is of the utmost 
 importance for the teacher to understand how learning 
 proceeds before it is systematically directed, in order to 
 avoid the forcing of the individual into an educational 
 system which is unrelated — or even opposed — ^to the 
 natural way in which man acquires his habits in early 
 childhood. The first habits acquired by the baby are 
 those connected with the use of the sense organs of the 
 head. Then the baby learns to use his arms and hands. 
 Toward the end of the first year or soon thereafter he 
 learns to use his feet for walking and running, and toward 
 the end of the second year to use his vocal organs for 
 speech. Of course, we do not mean that each one of these 
 classes of activities must become perfect before the next 
 begins, but merely that they usually become conspicuous 
 in this order. Besides, it is well to keep in mind that 
 individual differences are exceedingly common, so that 
 these four stages of development are not in every child 
 equally obvious. 
 
 Of the sense organs of the head, the eyes are those whose 
 efficient use depends most on proper motor adjustments, 
 — much more so than the ears or the sense organs j^of the 
 mouth. The chief reflex of the eye consists in a turning of 
 
122 HUMAN BEHAVIOR 
 
 the center of the eye, the "fovea," the area of most 
 distinct vision, in the direction of the most effective 
 object of visual stimulation, in a "movement of fixation" 
 as we may call it. It is quite natural that this response 
 at first is often rather inadequate in accuracy of direction 
 and particularly of extent, — ^the center of the eye moves 
 either beyond the point where it could receive the optical 
 rays from the object in question or not far enough to 
 reach this point. Gradually, however, the movement 
 becomes more and more adequate. Yet it never becomes 
 absolutely exact even in adult life. Even the grown 
 person, in order to fixate an object, must, practically 
 without exception, correct the first sweeping movement 
 of fixation by smaller ones before a suflSciently accurate 
 adjustment of the fovea is obtained. Figure 37 gives an 
 example of a complex eye movement of this kind, the 
 first sweep of the object's image being from Sa to Sj. 
 
 Kg. 37 — Fixation movement of the eye. 
 On Retina: F, Fovea — Sa, Point stimulated before fixation movement — 
 
 Sb, Point stimulated after fixation movement. 
 On Field of Vision : F, Point to be fixated — Sa, Point fixated before 
 
 movement — Sb, Point fixated after movement. 
 
 Two things need explanation. First: why the eye ball 
 moves always in the direction of the stimulus. Secondly: 
 why the eye ball stops at the moment when the fovea is 
 approximately opposite the stimulus. The first is easily 
 explained. The various sensory points of the retina are 
 doubtless connected with the eye muscles by reflex arches 
 in such a way that, when any point of the retina is especial- 
 ly stimulated, the excitation takes its path toward those 
 muscles or groups of muscles which pull the eye in the 
 
EXTENT OF EYE MOVEMENT 123 
 
 proper direction. In this respect no learning is necessary. 
 The direction is determined reflexly. The second question 
 is less easily answered. Why does the eye movement stop 
 as soon as the fovea has approximately reached a point 
 opposite the object? One feels inclined to think that 
 during the fixation movement of the eye the object, 
 suddenly striking with its rays the fovea, sets up there a 
 particularly effective excitation which either results reflexly 
 in a muscular contraction capable of fixing the eye in 
 the position just reached, or stops the movement by 
 inhibiting the nervous process which causes it. Such 
 explanations could still be offered as recently as ten years 
 ago. But the research of the most recent years has dis- 
 credited them. For some reason or other sensory excita- 
 tions received while the eye moves, fail to become effective 
 and, therefore, can not in any way stop the movement. 
 The extent of the sweeping movement of the eye must also 
 be determined reflexly and in advance of the motion — 
 probably by a strong excitation reaching the muscles which 
 puU the fovea in the proper direction and a relatively 
 weak excitation reaching the antagonistic muscles. If the 
 inherited connections of every point of the retina with 
 the various groups of muscles are su6h as to determine 
 through their resistances a definite ratio of the two anta- 
 gonistic muscular effects just mentioned, the eye must 
 clearly stop at a definite point, — where the antagonistic 
 motor effects balance each other. Figure 38, for clearness ' 
 sake, suggests how the nervous conductors might be 
 arranged in order to bring about this result; but we do 
 not, of course, assert that they are arranged just in this 
 way. The figure contains only two motor points, ilf x, and 
 Mg, representing, say, the muscles which pull the eye to 
 the left and those which pull to the right. The sensory 
 points represent a series from one side of the retina, at 
 
124 
 
 HUMAN BEHAVIOR 
 
 M, 
 
 s; s: 
 
 "L ^L ^L \ ^L '^R "R ^R "R "R 
 Fig. 38 — Simultaneous innervation of antagonistic muscles. 
 
 M„ 
 
 Si , (the right side, opposite the left edge of the field 
 of vision) to the other side, at Sr. It is evidentj that a 
 nervous process starting, for example, from S^ must go 
 mainly to M^, traveling thus over the smallest number of 
 neurons possible; but a considerable fraction of it must 
 pass over S^rMlr to Mr. A nervous process starting, 
 for comparison, from S^ can send only a smaller part of 
 its total flux to Ml, since the resistance of the path from 
 Sl to Af X, is greater than that of the path of fewer neurons 
 from Sl to Ml '■ so a larger fraction of the flux takes the 
 now shorter path over SlrMlr to Mr. The farther we go 
 to the sensory points at the right of the figure, the more 
 we find Mr favored in comparison with Ml- Thus the eye 
 must come to a standstill at different angles according to 
 the sensory point excited and the corresponding ratio of 
 the excitation of the antagonistic muscle groups. 
 
 This is simple enough thus far. However, this ratio 
 does not seem to be established by inheritance with any 
 great exactness, so that there is still left the problem which 
 is of special interest to us in this study, namely, how we 
 can explain the great improvement in the accuracy of the 
 fixation movement which is to be observed during the 
 first weeks and months of life, — ^how the child learns to 
 execute these sweeping fixation movements with so much 
 more accuracy in direction and extent after a few months 
 
IMPROVEMENT OF EYE MOVEMENT 125 
 
 of experience. The very purpose of our present study is, 
 not to take learning as a phenomenon which is too common 
 to need explanation, but to arouse our curiosity about it 
 and to satisfy this by making the process of learning as 
 plain as the running of a steam locomotive. 
 
 We may restrict our discussion to the extent of the 
 movement stopping at, or before, or beyond a certain 
 point, but always on the straight line passing through it. 
 A movement along a line leaving the point to be fixated 
 more or less at one side, is obviously simply the com- 
 ponent, geometrically, of two movements, two muscular 
 effects, and does not involve any additional principle of 
 explanation. We shall, then, have to solve the following 
 typical problem: If in earliest childhood, the fixation 
 movement brings the image, let us say, from S^, in Figure 
 37, to Sj, some distance beyond the fovea, why is it that 
 after some experience the sweep is so much shorter that 
 the image is brought from Sa to the nearest neighborhood 
 of the fovea? 
 
 Figure 39 will aid us ih understanding how the fixation 
 movement of the eye can be improved by experience — 
 in understanding, at the same time, what the often mys- 
 terious word "experience" really signifies. So represents 
 the sensory point where the image of the object first 
 appears on the retina, M^ the motor point which signifies 
 pulling the fovea in the direction of the optical image. 
 Mi represents the motor point which signifies pulling the 
 fovea in exactly the opposite direction. In order to bring 
 about the proper movement of approximately the right 
 extent, both Ma and Mf, must be excited, — ^but Ma more 
 strongly (if equally, there would be no movement at all). 
 Mi only strongly enough to bring the eye ball after some 
 time to a standstill, through the balancing of the opposite 
 forces of muscular tension. The antagonistic muscles, 
 
126 
 
 HUMAN BEHAVIOR 
 
 in such a case, must act upon the eye ball in the same way 
 in which two rubber bands of different tension, attached 
 to and pulling, say, a piece of cork in opposite directions, 
 would act. We have assumed that the tension resulting 
 from Ma is relatively too great, so that the image, instead 
 of falling upon the fovea, now falls at a point Sj, some- 
 what beyond the fovea. It is easy to understand from 
 
 A 
 
 n 
 
 a 
 
 Sb 
 
 M, 
 
 Fig. 39 — Improvement of the fixation movement of the eye. 
 
 Figure 39 why stimulation of S<, should result in a stronger 
 excitation at Jf^ and a weaker one at Jfj. But why 
 should, at a later recurrence of the stimulation of S^, 
 after the "experience" has become effective, the excita- 
 tion at Mjj be relatively greater, thus balancing the effect 
 of Ma sooner and preventing the fovea from moving as 
 far as the first time, stopping it nearer the correct point 
 of fixation, the point F in Figure 37.? The answer to this 
 question is the solution of our problem. 
 
THE CORRECTING MOVEMENT 127 
 
 In order to give the answer, we must consider the 
 correcting movement. As soon as the eye stops after 
 having swept too far, Sj, is stimulated by the new optical 
 impression, and — everything being exactly reversed — 
 the fovea is pulled in the opposite direction. Let us see 
 what neurons conduct the excitation whenever Sj is 
 stimulated. They are, eight in number, marked in Figure 
 39 partly as broad, partly as double lines. A moment 
 ago Sa was stimulated and the excitation took its path 
 over some of these very neurons, namely, over those 
 drawn in broad lines. The effect of that excitation, 
 reducing the resistance of the neurons, lasts for some 
 time before the negative susceptibility begins to restore 
 the former resistance, as discussed previously and illus- 
 trated in Figure 33. Therefore, when now Sj is stimulated 
 and the excitation coming from Sj reduces the resistance 
 in all the neurons through which it passes, the resistance 
 of the neurons drawn in broad lines not merely begins to be 
 reduced, like the resistance of the neurons drawn in 
 double lines, but is further reduced. In the total system of 
 Figure 39, the neurons drawn in broad lines thus suffer a 
 relatively greater reduction of their conductivity than aU the 
 others. It is easy to see that our problem is herewith 
 solved, for when now at any time the retiual point S^ 
 is again struck by an optical image, a greater fraction 
 than originally of the excitation from Sa can pass over 
 Sab^ab ^^d J^ab^l into the non-corrcsponduig point 
 Ml,, causing a stronger muscular tension at M^ and an 
 earlier balancing of the antagonistic forces which bring 
 about the sweeping movement of fixation. 
 ;«.To remove all doubt as to the correctness of this con- 
 clusion let us look again at the broad lines of Figure 39. 
 The short route from Sa tojMa consists of three neurons, 
 of which one is favored by the effect in question ; that is, only 
 
128 HUMAN BEHAVIOR 
 
 one-third of the total length of the path. The longer route 
 from Sa to Ma and the route from S^ to Mi,, however, 
 consist each of five neurons, of which three are favored 
 by the eflfect in question; that is, as much as three-fifths 
 of the path. It is clear that the total result of this widen- 
 ing of one-third of the length of one path and of three- 
 fifths of the length of the other path is to the advantage 
 of Mi, to the disadvantage of Ma- The ordinary superiori- 
 ty in intensity of response (to stimulation of SJ of Ma 
 over M{, is based on the greater conductivity of the reflex 
 arch SaSlMlMa, which has now been relatively diminished. 
 Any relatively greater reduction of the resistance of the 
 higher center SltM^i must favor the ordinarily quite 
 weak response of the non-corresponding point if 5, to the 
 disadvantage of the corresponding point Jf „. The motor 
 effect of Mi now balances the effect of Ma a little earlier, 
 brings about the stopping of the eye movement a little 
 earher. That is, the next fixation movement is more 
 correct. 
 
 We see, then, that the improvement of any particular 
 nervous function by "experience" of the individual is an 
 altogether natural phenomenon, — no more mysterious, 
 although different in kind, than the gradual improvement 
 of the draft in a cold chimney after the fire has been 
 burning for some time. A few fundamental laws which 
 we assume as governing nervous activity are sufficient 
 to explain this learning by experience, without any 
 necessary reference to "conscious" experience. The 
 present case is clearly a variation of response, for we have 
 now a relatively strong motor effect where (at Mi, in 
 response to a stimulation of S^) we had originally only a 
 weak part of the total effect. But we notice the important 
 fact that the variation has come about without a deflection 
 of one nervous process by a simultaneous one taking 
 
VARIATION BY SUCCESSION 129 
 
 place. We see, then, that the same variation which can 
 be the result of a deflection, can also be the consequence 
 of a succession of nervous processes, provided the law 
 illustrated in Figure 33 is applicable, the law that any 
 reduction in resistance remains for a short time (a few 
 seconds at least) uninfluenced by the negative susceptibili- 
 
 ty. _ _ 
 
 We have explained how the improvement of the accur- 
 acy of the fixation movement comes about, which dimin- 
 ishes the need for movements of correction succeeding 
 the first sweep. Simultaneously another improvement 
 takes place, — that of the co-operation of the two eyes. 
 During the first days of a baby's life it may not infre- 
 quently be observed that the eyes move independently 
 of each other, thiat one moves to the right while the other 
 stands still or moves even to the left. This is but natural 
 since a striking object may not impress one eye as strongly 
 as the other, indeed may be invisible to one eye if it 
 happens to be near the right or left edge of the total field 
 of vision. How, then, is the nervous system "educated" 
 so that later both eyes always move together to the right 
 or left, even when the object is, in advance of the move- 
 ment, invisible to one eye.'* 
 
 In Figure 40, Mi and M^ represent those motor points 
 whose simultaneous excitations cause the simultaneous 
 and similar movements of the two eyes. Whenever Si 
 and Sf are stimulated simultaneously and with equal 
 intensity, as it happens most frequently, the simultaneous 
 excitations of the two motor points are self-evident. 
 But why are, after a few months of life of the individual, 
 the motor points simultaneously excited even when one 
 of the sensory points is unstimulated.? This is clearly a 
 case of sensory condensation. It may be thought to come 
 about in the following way. 
 
130 
 
 HUMAN BEHAVIOR 
 
 Whenever Si is stimulated alone, by far the largest 
 part of the excitation takes its path over the reflex arch 
 directly to Mi. A smaller, though considerable, part, 
 however, takes the indirect path over SfMf and even 
 over SiMfr, mostly in the direction of Mi, but to some 
 extent also in other directions, for example, toward M,.. 
 
 Si Ml Sr Mr 
 
 Left Eye Right Eye 
 
 Fig. 40 — Co-ordination of the two eyes or any two organs. 
 
 Whenever S, is stimulated alone, by far the largest part 
 of the excitation takes its path over the reflex arch directly 
 to Mr- A smaller, though considerable, part, however, 
 takes the indirect path over S^M], and even over S^M^., 
 mostly in the direction of M„ but to some extent also 
 in other directions, for example, toward Mi. In either 
 case, when S; or S, is stimulated alone, the relative resist- 
 ance of the lower and higher neurons involved remains 
 unchanged, in accordance with the law which we assumed 
 in the preceding lecture. But when Sj and S, are stimu- 
 
CO-ORDINATION OF THE EYES 131 
 
 lated at the same time, those neurons which belong to the 
 system of Si as well as to that of S^ are favored over all 
 the others with respect to the reduction of their resistance, 
 since a double excitation — and therefore a stronger flux — 
 passes through them. These neurons are drawn in Figure 
 40 in double lines. The relatively greater reduction of 
 the resistance of these neurons may amount to but little 
 in a single case of "experience." But it must become 
 quite considerable in a few months, since simultaneous 
 stimulation of both eyes by the same object is naturally 
 a very common occurrence. When the resistance of the 
 double drawn neurons has become much reduced, an ever 
 increasing amount of the flux takes its path, instead of 
 over a reflex arch, over the higher center SffMf,, which 
 forms the connecting bridge between the two eyes. Ac- 
 cordingly, an ever increasing part of the flux finds its way 
 from Mfr down into M^ even when S; happens to be 
 stimulated alone, or into Mi when S^ happens to be 
 stimulated alone, until finally the response occurs regularly 
 at both Ml and M^ no matter whether both- the sensory 
 points are stimulated or only one of them. That is, the 
 movements of the eyes have become perfectly co-ordinated. 
 The co-ordination of the eyes is an example of that 
 kind of variation of the nervous path which we have called 
 sensory condensation. Another example of sensory con- 
 densation which we have studied in detail is that of a child 
 learning to execute, on the piano keyboard, two finger 
 movements in response to only one note. The explanation 
 in detail of the two examples is somewhat different owing 
 to the fact that in the former case the sensory condensa- 
 tion results from a two-fold stimulation of unequal intensi- 
 ties, the one and the other sensory point being alternately 
 more strongly excited, whereas in the present case both 
 sensory points are usually stimulated with the same 
 
132 HUMAN BEHAVIOR 
 
 intensity. We have thus seen that sensory condensation 
 can result under various circumstances, provided only 
 that the reflex arches involved are connected — and not 
 too remotely — ^by higher nerve centers. 
 
 Next to the eye, the ear is the sense organ of the head 
 which is most interesting because of its motor adjustments. 
 We are naturally inclined to assume that there is here a 
 reflex similar to the turning reflex of the eye, — ^that, when 
 a sound strikes one of the ears more strongly than the 
 other, the face turns reflexly toward the source of sound. 
 This would mean that, by inheritance, of the muscles 
 turning the head those on either side are more closely 
 connected with the one ear than with the other ear. The 
 purpose of this head movement would be, not so much a 
 better adjustment of the organ of hearing, as of the organ 
 of sight, — the eyes when facing the source of sound would 
 be more likely to receive from it an effective visual stimu- 
 lation. Such a reflex response, however, a turning of the^ 
 face in the direction of a sound, does not seem to exist. 
 When a child is five to six months old, this response is 
 quite common, but during the first three months it does 
 not occur. One may, of course, assume that the refiex 
 does not mature until several months after birth, and 
 support this assumption by the fact that some instincts 
 and reflexes mature even years after birth. However, 
 reflexes whose maturity is undoubtedly delayed — take 
 for example the sexual — are obviously delayed because 
 their appearance directly after birth would be useless. 
 But turning the head in the direction of a sound would not 
 be entirely useless even in earliest infancy. We may 
 therefore, as long as the question is left undecided by the 
 physiologists and anatomists, regard it as most probable 
 that the turning of the face in the direction of a sound is 
 not a reflex, but a habit which is usually estabUshed three 
 
LEARNING TO FACE A SOUND 133 
 
 or four months after birth. Our problem, then, is to 
 explain how the individual learns to respond thus to 
 sounds which stimulate the two ears unequally. 
 
 There can hardly be any doubt that the habit of turning 
 the face toward a source of sound is a variation of response 
 — one of that kind in which the same response occurs, but 
 another stimulus has been substituted for the original one. 
 The original stimulus is visual. The fixation reflex of the 
 eyes can be observed as functioning a few weeks after 
 birth; and the reflex turning of the head can be seen to 
 support and supplement the eye movement at the same 
 early age, — in response to sight, for reflex movements of 
 the head in response to tactual stimuli occur even a few 
 days after birth, when the baby, held to the mother's 
 breast, hunts, so to speak, for the nipple. Objects which 
 appear in indirect vision and therefore call forth the 
 fixation reflex, are frequently sources of sound, — ^for 
 example, the mother's face. That is, the baby's ears 
 are stimulated at the same time as the eyes. If the 
 nervous flux coming from the ear more strongly stimulated, 
 and including, by deflection, most of the flux from the 
 other ear, has no particular reflex outlet, it must take its 
 path, other things being equal, mostly in the direction of 
 any other strong nervous process existing at the same time 
 and therefore attracting it. It must take its path in the 
 direction of that motor point which in response to the 
 visual stimulation turns the head to face the source of 
 sound. There is no danger that the reverse might occur, 
 that the nervous flux coming from the eye might be 
 attracted by the flux from the ear, for we are working 
 under the assumption that the flux from the ear has no 
 low-resistance reflex outlet and, therefore, cannot attain 
 any such great intensity as that from the eye. When the 
 deflection from the ear to the head-turning muscles has 
 
134 HUMAN BEHAVIOR 
 
 occurred often enough and the resistance along this path 
 has been effectively lowered, the habit which we intended 
 to explain is established. The head then turns even in 
 response to a source of sound which may remain perma- 
 nently invisible. That the habit is not established until 
 several months after birth, is caused probably by the 
 absence, at an earlier time, of connecting neurons which 
 are capable of serving as a chain of conductors. It is a 
 well established fact that the majority of the higher nerve 
 centers capable of serving such remote connections are 
 immature at birth and fairly mature only three months 
 later. 
 
 The next large group of activities we proposed to study 
 are those of the hands and arms. We have already seen 
 how, from the reflex of a bending of the fingers in response 
 to a stimulation of their inner surfaces, the delicate and 
 skillful grasping of the older child and of the adult develops. 
 We have also mentioned that the arm is reflexly stretched 
 out in response to a stimulation of the eye. With respect 
 to the arms, there are several further details which are 
 interesting enough to be mentioned here. 
 
 Fig. 41 — Raising the hand. 
 
 With an adult, the raising of the hand in response to 
 sight, as when we take a book from a shelf above our head 
 (Figure 41), is a very common movement. During the 
 
BABIES AND APES 135 
 
 first months a similar response to sight, moving the hand 
 in the direction from the feet to the head, does not occur. 
 The movements — like many other properties — of a human 
 baby have often been compared with those of full-grown 
 animals, for example, the apes; and, since the apes are 
 climbers, one might conclude that the movement of Figure 
 41, which is common in climbing, must be frequently 
 observed in babies. We see here, that, as a matter of fact, 
 one has to be very critical in such comparisons. The apes 
 are indeed climbing animals and, as such, are compelled 
 to execute the arm movement in question quite frequently; 
 but only in adult life, — ^the baby apes do not climb any 
 more than human babies, but cling to their mothers who 
 carry them about. The comparison is therefore not 
 really between babies and apes, but only between human 
 babies and monkey babies. When the very young baby 
 stretches out his arms, in response to a visual impression, 
 it is always either at right angles to the longitudinal 
 axis of the body or more downwards, toward the feet, 
 never more upwards, toward the head. The same is 
 probably true for the monkey baby. 
 
 How, then,, does the baby learn to raise his hands in 
 response to a visual stimulation? In order to answer 
 this question, we must inquire whether there is during 
 the first few months any reflex raising of the hands, and 
 whether there is any possibility of this reflex being varied so 
 that a visual stimulation takes the place of the stimulation 
 of this reflex. There is a reflex of throwing up the arms, 
 namely, in response to the appUcation of cold to the skin 
 of the body During the flrst days the new-born baby is — 
 however strange this may seem — ^rather insensitive to all 
 stimuli applied to the skin, be they heat or cold or pressure 
 or the prick of a needle. But after the third week, if the 
 baby is suddenly uncovered and exposed to a draft of cold 
 
136 HUMAN BEHAVIOR 
 
 air, or placed on a cold linen cloth, or immersed in cool 
 water, he may be seen to throw up his arms violently. 
 
 How, then, can these upward movements of the arms 
 become associated, so to speak, with visual impressions? 
 Incidentally the hands, during the upward movement, 
 impress themselves as visual images upon the eyes, — 
 upon the lower parts of the retinas, since all rays are 
 crossed at the entrance to the eye. While the nervous 
 process of the above mentioned reflex goes on, another 
 nervous process thus starts from the lower region of the 
 retina. The latter may be assumed to be especially 
 intensive because it is caused by an object in motion. 
 Although it is not perfectly known how this is brought 
 about, it is a perfectly familiar fact that on the peripheral 
 parts of the retina an object in motion produces a specially 
 effective nervous process, much more effective than those 
 resulting from the impressions of motionless objects. It 
 therefore draws all the other visual nervous processes 
 into its own channel and is the only visual nervous process 
 which we have to take into account. The reflex motor 
 effect of this process is probably a turning of the eye 
 upwards. A considerable part of this visual nervous 
 process is now likely to be deflected from its course by the 
 other nervous process, still going on, into the direction 
 of the motor organs which served the violent throwing up 
 of the arms. Accordingly the resistance of the path lead- 
 ing over higher nerve centers from the lower part of the 
 retina to the muscles raising the arm is reduced; and when 
 this reduction of the resistance of the path has become 
 sufficiently great, the hand will be stretched upwards in 
 response to a visual stimulus coming from an object in 
 front of the head and more or less above the eyes — a 
 reaction which is quite common in the half-year old 
 chUd. This variation of the nervous path is simply a 
 
HANDS AND EYES 137 
 
 further example of that kind of a "variation of response" 
 in which the same response is called forth by a new kind 
 of stimulus. 
 
 Of course, the establishment of an habitual upward 
 movement of the hands in response to a visual stimulation 
 does not necessarily interfere with the reflex of turning 
 the eyes upwards in response to the same kind of stimula- 
 tion. In order to establish the habit only a part of the 
 nervous flux of the reflex need be deflected into the new 
 motor outlet; and the final result may be a co-existence, a 
 loose co-ordination of the two upward movements of the 
 hands and the eyes. A similar loose co-ordination of 
 eye and hand movements in a horizontal direction, to the 
 right and left, can be observed in children as early as the 
 third month. 
 
ELEVENTH LECTURE 
 
 Control of the feet. The ability to walk equal to 
 rising plus balancing. Reflex of straightening the leg. 
 Reflex of squatting. Balancing with hand support preceding 
 free balancing. Balancing on one leg preceded by balancing 
 on both. Walking not a simple instinct, but a compound of 
 reflexes united largely by experience. Balancing sideways 
 preceding balancing fore and aft. Stretching the foot 
 reflexly toward a thing which impresses the eye. Locomo- 
 tion resulting from this reflex. Creeping. Creeping on 
 two legs preceded by creeping on one. Influences of 
 creeping on walking. Sitting up. Finger-sucking super- 
 ceded by other habits. Free standing rarely preceded by 
 walking. One-sidedness and general clumsiness of first 
 walking. Encouraging a child to stand: a purely negative 
 event. The so-called instincts of constructiveness and 
 destructiveness: rather habits. 
 
 WHATEVER may be— practicaUy and 
 scientifically — the relative importance 
 of arms and legs, hands and feet, the 
 control of the feet, the acquisition of 
 the ability of locomotion in the up-right position, 
 has always attracted the chief interest of the amateur 
 observers of child life, the parents and nurses. When the 
 child can walk, their interest in observation almost 
 ceases. And yet, most animals possess the ability of 
 locomotion practicaUy from birth, so that, in this res- 
 
 138 
 
WALKING 139 
 
 pect, the year old child merely attains the level of a new- 
 born animal. The control of the hands when once fully 
 attained, places the child on a level which no animal 
 ever reaches. Nevertheless, walking attracts more 
 attention than the control of the hands, probably be- 
 cause the changie-'from the perfectly helpless condition 
 of human ■ infancy to an animal-like condition lessens 
 the responsibility of the child's care-takers so much 
 more suddenly than any of the changes which raise 
 the child above the level of animal life. 
 
 The complete ability of locomotion in the upright 
 position involves two distinct abihties of muscular action : 
 the abUity to rise from a lying to a standing position and 
 the ability to balance on either leg. The ability to rise 
 is only imperfectly developed as long as holding on an 
 object, a chair or the like, is necessary in order to rise. 
 This imperfect ability usually precedes by several months 
 the child's ability to rise to his feet from the floor without 
 the aid of any supporting object. The ability to balance 
 on (either) one leg is naturally preceded — as a rule — ^by the 
 ability to balance on both legs, which, on the whole, is 
 more easily acquired. 
 
 The governing reflex of the whole group in ques- 
 tion seems to be that of straightening the legs in 
 response to pressure against the soles. A child about 
 nine months old, or even considerably younger, 
 may absolutely "refuse" to be held on anybody's arms 
 in a sitting, flexible position. The reflex of straightening 
 the legs causes a stiffening of the body. The mother then 
 naturally places the child, no longer easily held in her arms 
 when in this straight position, with his feet on her knees, 
 or a table, or the floor. The child then stands, in a way, 
 but retains this standing position only because he is 
 kept from tumbling by his mother's arms. Soon the 
 
140 HUMAN BEHAVIOR 
 
 child learns to use his own hands, in the control of which 
 he has by this time already acquired considerable skill, 
 in order to keep from tumbling. He grasps whatever is 
 in sight and reach and thus learns to keep in a standing 
 position. Another reflex reaction is soon added to those 
 of grasping the things which are seen and of straight- 
 ening the legs when the soles are touched: that of 
 changing from a standing to a squatting position, in 
 response — ^probably — to sensory excitations in the muscles 
 and joints of the legs when supporting the body. The 
 following periodic activity must then frequently take 
 place. The child changes from a standing to a squatting 
 position while having his mother's clothes or any other 
 object in his grasp. Being in the squatting position he 
 no longer receives the sensory excitations which caused 
 squatting. Consequently the excitation of the soles of the 
 feet regains its former relative power and straightening 
 of the legs occurs. At the same time the touch of the 
 objects in the child's hands causes a bending of the 
 arms, an action derived perhaps from the reflex of put- 
 ting things into the mouth, so that the whole action 
 might be described by saying: the child gets up, pulling 
 himself up by his hands. This may be followed again by 
 squatting, again by raising himseK, and so on. Since the 
 squatting, when the body is held' in the upright position 
 by the hands having grasped an object, readily changes 
 into kneeling, the periodic action may be : kneeling, stand- 
 ing, kneeling, standing, and so on. Further, when there 
 are solid objects which the hands can grasp, the body 
 is easily pulled up from a lying to a kneehng position, so 
 that there may be a change from lying to standing, and the 
 reverse, provided only that the grasping hands can come 
 into play. 
 
 When the child stands before an object, holding on with 
 both hands, it naturally happens that now and then one 
 
FROM LYING TO STANDING 141 
 
 of the hands loses its grasp. If this happens while his 
 legs are perfectly straight, he is likely to tumble down 
 toward the side of the other hand; and then he will get up 
 again. But if it happens while the legs are in a slightly 
 bent position, intermediate between standing and squat- 
 ting, it means only that the weight of the body is thrown 
 on one side and that the leg of this side is straightened 
 in response to the increased pressure on the sole. Thus 
 the body is again balanced and kept from tumbling. This 
 ability to balance the body is then further improved in 
 two ways. First, the resistance of the nervous path from 
 the sensory points of the sole to the muscles straightening 
 the leg is lessened, possibly by the mere maturing of the 
 inherited reflex. Accordingly, sensory excitations of much 
 smaller intensity, caused by much weaker pressure on 
 the sole when the body is barely beginning to lose its 
 balance, are capable of bringing about the motor res- 
 ponse which restores the balance. Secondly, the nervous 
 processes starting from the excitations of the sensory 
 points in the muscles, tendons, and joints of both legs are, 
 by motor condensation, caused to contribute to the motor 
 response which restores the balance temporarily impaired. 
 This second kind of improvement, when further developed 
 in later years into an independent "variation of response", 
 becomes our ability to stand on one leg and to balance 
 our body on one leg in dancing or skating. When the 
 child has had a certain amount of practise in retaining its 
 upright position, both hands may lose their grasp on the 
 supporting object without causing any tumbling. The 
 equilibrium of the body is then at any time restored by 
 the newly acquired motor responses as soon as it is lost. 
 We say that the child has "learned" to stand alone. 
 
 Let us return to the moment described in the beginning 
 of the last paragraph. While the child is standing before 
 
142 HUMAN BEHAVIOR 
 
 an object, holding on with both hands, one of the hands 
 loses its grasp and consequently the leg on the other side 
 is straightened. The body as a whole, perhaps, is thus 
 somewhat raised, and with it that leg which remained 
 slightly bent. But now this leg, hanging and subject 
 to the effect of gravity, straightens somewhat; and when 
 the body regains its vertical position and the foot of this 
 leg touches the ground, it straightens perfectly, owing 
 to the reflex repeatedly mentioned. The weight of the 
 body is thus thrown again — lightly — ^upon the other leg. A 
 swinging movement of the body may thus result, from the 
 left to the right, from the right to the left. It is clear that 
 this movement needs only a slight modification to become 
 a regular walking movement. Children who are just be- 
 ginning to walk, do indeed, usually, walk in this pendulum- 
 like fashion, comparable to the walking of a sailor. One 
 finds here and there in psychological literature the asser- 
 tion that the walking of a child is the result of an instinct 
 consisting in a tendency of the legs to swing fore and back 
 in directions opposite to each other, and that these instinc- 
 tive movements can be observed in a baby a few months 
 old when held suspended. While such opposite fore and 
 back swinging movements of the legs may sometimes be 
 observed, it seems doubtful if they have much significance 
 for the acquisition of the ability to walk, since one does not 
 walk in suspension, but on a supporting surface. In any 
 case, it is possible to derive the alternate movements 
 of the legs in walking from the reflex of straightening each 
 leg in response to pressure against the sole, without assum- 
 ing any specific "instinct of walking." 
 
 We described how a child may learn to stand 
 alone, balancing himself sideways. But in order 
 to stand really alone he must also keep from losing 
 his balance in the forward and backward . directions. 
 
BATANCING 143 
 
 From falling forward he may be kept by the very 
 reflex of straightening mentioned before. When the 
 body begins to move forward, less weight is placed 
 on the heels and more on the soles. Accordingly the 
 foot straightens, the heel is raised above the ground and 
 the body is kept from moving forward since the centre of 
 gravity is now behind the point of support. On the other 
 hand, when the body begins to move backward, more and 
 more weight is placed on the heels, the pressure on the 
 soles vanishes, and the muscles which keep the legs straight 
 relax. The knees then bend forward and thus a part of the 
 weight of the body is thrown in front of the previous center 
 of gravity, thus restoring the balance. Just as the swing- 
 ing of the body to the left and right, so these kinds of 
 movement have great significance for walking. In the 
 walking movements of a grown person the raising of the 
 heel of one foot may raise with the whole body the other 
 foot from the floor and cause it by the mere force of 
 gravity to swing forwards. 
 
 We have been trying to explain how a child learns to 
 balance its body in the upright position without having 
 to hold to an object. Before this accomplishment of 
 standing free, the child usually begins to walk along by 
 pieces of furniture, changing the hold of his hands as he 
 walks on. What reflex is the basis of this locomotion? 
 It seems that, in response to a visual stimulation, not only 
 the hand but the foot, too, stretches toward the thing 
 which impresses the eye. On the basis of such a reflex 
 locomotion is easily explained. Imagine a child standing 
 before a bench, holding on with both hands, and an object, 
 say, a pencil, lying on the end of the bench to the right. 
 The effect of the stimulation of the eye by the pencil is 
 a stretching of the right arm and the right leg to the right. 
 The body then falls to the right until the right foot again 
 
144 HUMAN BEHAVIOR 
 
 touches the ground. The body is now somewhat displaced 
 to the right. The feet are farther apart than normally 
 and are therefore, in consequence of special reflexes which 
 we need not discuss, brought together to their normal 
 position, but of course, without any essential change of 
 the body sideways. Now the whole stretching of the 
 right hand and the right foot to the right may be repeated 
 several times, until the hand grasps the object. This 
 walking along the pieces of furniture or the walls of a 
 room can therefore be very simply explained. 
 
 At about this time in a child's development another 
 kind of locomotion is likely to make its appearance, — creep 
 ing. As the baby happens to lie on his stomach, his eye is 
 stimulated by an object and the arms are reflexly stretched 
 forward, — but not the arms alone, the legs too are 
 stretched, these backward, of course; and later a draw- 
 ing in of all the extremities simultaneously may 
 occur as an alternative response to the visual stimu- 
 lation. We can not apply here simply the term reflex, 
 but must say that the baby possesses an instinct, 
 since the simultaneous stretching of the arms forward 
 and the legs backward, and alternately the simul- 
 taneous drawing in of all four extremities, are the result 
 of selective grouping of nervous paths. That the 
 alternation of stretching, drawing in, stretching, and so on, 
 continues for some time can be explained by assuming 
 that the sensory points of the muscles, tendons, and joints 
 stimulated in either one position are by inheritance very 
 closely connected with the motor points whose activity 
 brings about the other position. The result of the simul- 
 taneous drawing in and simultaneous stretching of the 
 arms and legs is not necessarily, but may be, locomotion, 
 provided either the front or rear extremities find a better 
 hold on the ground. At first, it happens not infrequently 
 
CREEPING 145 
 
 that this is the case with the hands rather than the feet, and 
 the somewhat ridiculous observation is then to be made of 
 a baby pushing himself away from the object exciting the 
 eye. Once now, when the arms and legs are being drawn 
 in, it happens that in consequence of an unusually strong 
 nervous process one of the legs, drawn in with unusual 
 force, gets under the body. When now, instinctively, the 
 arms and legs are stretched, this leg, resting with the 
 knee on the ground and bearing the weight of the body, can 
 not slide over the ground, but pushes the body forward. 
 The eyes are thus brought nearer the exciting object and, 
 therefore, receive the same stimulation as before, only 
 still stronger. The nervous process resulting from this 
 stimulation now tends to take the path into the leg drawn 
 under the body rather than into the other, because it is 
 attracted in this direction. It is deflected by the flux 
 resulting from the excitations of the sensory points of 
 the knee and the muscles and tendons of the leg drawn 
 under the body, whose corresponding motor points are, 
 of course, in the muscles of the same leg. Thus the 
 alternate stretching and drawing in occurs chiefly in this 
 leg. The baby learns to creep on one leg. 
 
 Why does not the baby, one may ask, learn just as 
 readily to creep, at once, on both legs? The answer to 
 this question is not that this is impossible, — only that it is 
 less likely. During the first year the legs move, in the hip 
 joint, much more readily sideways, than in later life. This 
 is due to the position of the fetus before birth, which chan- 
 ges but gradually after birth and enables infants even for 
 years to put their toes into the mouth, a feat impossible 
 in later life, as we all know. When the baby is lying on 
 the stomach and the legs are drawn in, the legs are not 
 likely to get under the body, but move outwards, in frog 
 fashion. At the ninth or tenth month, however, the child 
 
146 HUMAN BEHAVIOR 
 
 begins to roll over, and when now, in consequence of an 
 unusually strong stimulation, the drawing in of the legs 
 is accompanied by a rolling movement of the body toward 
 one side, a chance is given for one of the legs to get under 
 the body. It is most natural, therefore, that the creeping 
 on one leg should be learned first. After some skill has 
 been attained in this, the other leg is likely to get under 
 the body too, and the baby then creeps on both legs. 
 We stated that creeping usually makes its appearance 
 about the time when the baby has learned to pull himself 
 up and to walk along pieces of furniture. Creeping now 
 has a pronounced influence on the child's progress in 
 upright locomotion, in either of two ways. (1) As soon as 
 the child has learned to creep on both legs — or knees, if 
 we prefer this word, — ^he easily gets from the lying 
 to the upright position without depending any longer on 
 pieces of furniture or other objects which he can grasp, 
 for the change from creeping to squatting is easy. With- 
 out being able to stand up from the ground freely, walking 
 is of but limited usefulness. Thus creeping contributes, 
 though indirectly, toward perfection in upright locomotion. 
 (2) If, however, free walking is not yet a firmly established 
 habit, the newly acquired form of locomotion, creeping, 
 may so seriously interfere with the acquisition of that other 
 habit as to hold it back for several months. Children 
 who early become skilled creepers, usually learn to 
 walk freely two or three months later than those children 
 who little or never creep. This is comprehensible enough. 
 The creeping child is not so exposed as the walking child 
 to falling and to the consequent pain stimulation with its 
 varied and strong motor responses, interfering by deflec- 
 tion with the learning process. Further, creeping brings 
 the young child more quickly to the object which stimu- 
 lates the child's eyes than unskilled walking, and thus as- 
 
CREEPING AND WALKING 147 
 
 sures the repetition of the creeping movement by the rep- 
 etition of the stimulus from nearer by, much more than 
 walking assures the repetition of the walking movement. 
 In other words, the very nature of the case makes 
 rapid improvement of skill in creeping more likely than 
 of skill in walking; and when one form of locomotion has 
 once been well learned, the other kind of locomotion, 
 not yet well learned, is excluded by the simple rule of the 
 effect of different resistances of various nervous paths, 
 until, at a later time, new conditions arise. Some have 
 drawn the practical conclusion, that therefore parents 
 must prevent their children from creeping whenever they 
 are seen to try it, before having become skilled walkers. It 
 seems so simple : if creeping delays walking, stop the creep- 
 ing and hasten thereby the walking. This conclusion, 
 however, implies several important assumptions. First, 
 walking is assumed to be the only kind of locomotion 
 needed by a human being. This is somewhat doubtful. 
 Not that we wish to assert that grown people ought to 
 make frequent use of creeping movements, but it is highly 
 probable that a complete analysis of our motor activities 
 in later life would show of the elementary activities 
 which are exercised in creeping many applications in 
 new combinations. If this is true, the suppression of this 
 exercise during infancy would be a grave mistake. 
 Secondly, one must not think that the suppression of 
 creeping before walking must be harmless since, after 
 walking is thoroughly established, the child may be per- 
 mitted to creep and thus exercise the same activities. 
 Who knows whether exercise, then, brings about the 
 same results in the education of the nervous system 
 which it might have brought about previously? As long 
 as we know nothing about this question, it is hazardous 
 to try to improve upon nature because we, as parents, 
 
148 HUMAN BEHAVIOR 
 
 happen to be exaggeratedly proud of our children's early 
 accomplishments in walking and indifFerent to all other 
 kinds of motor accomplishments. Different children differ 
 greatly in different talents, and we know that their suc- 
 cess in life depends largely on the proper training of the 
 most pronounced talent of the individual. It is 
 possible, even highly probable, that a special talent 
 means merely a special form of interconnection of 
 the fundamental reflexes common to all; and such 
 special interconnection may early show itself in 
 such phenomena as this, where creeping does or does 
 not precede walking. We might then really inter- 
 fere with the child's most* favorable development if 
 we try to arrange the fundamental reflexes in groups 
 different from those intended by nature. 
 
 To these arguments, of course, some one might rejoin 
 that he does not feel convinced that to prevent a child 
 from creeping during a few months can be of such con- 
 sequence, positively or negatively, to his later intellect- 
 ual and moral development. Very well then, we can 
 answer that to make a child walk freely at the age of 
 twelve months, instead of letting him use for locomotion 
 creeping during the thirteenth and fourteenth and free 
 walking only from the fifteenth month, does not seem to 
 be of much significance for his later life either. The safest 
 course in education — ^in this simple case as in the most 
 complex problems of educational theory — is probably the 
 one which interferes least with the development designed 
 by nature and which trusts nature rather than tradi- 
 tional ideals of education or, worse, parental vanity, un- 
 less we have the most certain — experimental — evidence 
 thatj in this or that way nature can be improved upon. 
 
 Before leaving the discussion of creeping, let us mention 
 two further accomplishments connected with its develop- 
 
FREE SITTING UP 149 
 
 ment. The creeping child has acquired a second position 
 of rest in addition to that of lying : he can rest at any time 
 in a sitting position. It is true that children can sit, with 
 support in the back and at the sides, when a few weeks 
 old, and that they can sit on the floor without any further 
 support when about six months old. But the ability to 
 sit does not include the ability to seat himself, to sit 
 up. The latter comes with creeping. The creep- 
 ing child can sit up on the plain floor on which no objects 
 offer themselves to his hands to be taken hold of. 
 Thus when tired, he can take for resting the sitting as well 
 as the lying position, and he often takes the former 
 owing to the multitude of sensory-motor reactions of 
 the nervous system which are only in this position possible. 
 For example, the child when sitting can freely turn his 
 head. 
 
 The creeping child further acquires a play of his hands 
 formerly impossible. During the first half year, whenever 
 the child takes anything in his hands, he almost invariably 
 puts it into his mouth, and often, when he has nothing 
 in his hands, he puts one or more fingers in his mouth. 
 These reactions become less frequent when the child begins 
 to creep and sit up. Objects can now call forth numer- 
 ous other responses. The child learns to push or throw 
 away things, to creep after them and take them again; 
 and this more complicated game, more likely to bring about 
 repetition of activity by the repetition of stimulation 
 of the eye and, consequently, more likely to become a 
 strong habit, gradually supersedes the simple reflex of put- 
 ting things into the mouth. It is the exceptional child 
 that retains the finger sucking habit after the acquisition 
 of locomotion. 
 
 We stated above that children learn to stand freely, 
 that is, to balance the body continuously in the upright 
 
150 HUMAN BEHAVIOR 
 
 position, before they learn to move in this position. While 
 this is generally true, there are also exceptional cases 
 where children, being held in the upright position, are 
 suddenly attracted by an object, perhaps the mother's 
 voice, and start off running successfully five or six steps 
 until they have reached the object. In such a case 
 a child really learns to walk before he has learned to stand 
 without support. However, as a rule, a child learns first 
 to stand; and then, standing, in response to a stimulation 
 of his eyes by an object, he moves one leg slightly toward 
 the object, shifts his weight so that it rests on this leg and 
 draws the other leg after, secures his balance, then moves 
 again the first leg toward the object, and so on. One 
 might call this form of locomotion walking on one leg only. 
 In a week or two this one-sidedness gires place to the regu- 
 lar form of walking in which both legs take part equally . 
 For many months thereafter, however, a child's walk 
 remains clumsy because the legs are kept so far apart, 
 owing to the anatomical fact already mentioned that 
 this opening of the legs sideways is the normal position 
 until birth, which but gradually changes into that of the 
 older child and adult, and also to the fact that balanc- 
 ing is easier in this position. 
 
 If walking is thus the outgrowth of standing, it is well 
 to "encourage" free standing as much as possible after 
 the baby has learned to stand while holding to things. 
 What does it mean to "encourage" him? Let us reduce 
 the process to its essential elements. (1) The child, when 
 beginning to tumble, reflexly draws in his legs. (2) He 
 has often tumbled, when standing and losing the hold of 
 his hands. (3) Subsequently, by a " variation of response " 
 he draws in his legs at once (in other words, he sits down) 
 when standing and losing thehold of his hands. But hecan- 
 not practice balancing his body if he sits down. Therefore 
 
ENCOURAGEMENT 151 
 
 (4) we give his hands the same or similar sensory impres- 
 sions as if they were supporting the body. For example, 
 we let the standing child grasp for support a small stick or 
 pencil which we are holding, and then, gradually, we cease 
 to hold it. The child then balances and, although nothing 
 supports him, receives almost the same stimuli in his hands 
 and eyes as if he were still supported by the stick in his 
 hands. The process of balancing suffers no sudden inter- 
 ference by a new stimulation (caused by the withdrawal 
 of an object from his hands) and its reaction of sitting 
 down. The "encouragement" which we give the child 
 is therefore a purely negative event in the education of 
 his nervous system : we keep an obstacle out of the way. 
 After the establishment of free locomotion, further 
 activities make their appearance, which are often referred 
 to as the constructive and destructive instincts. It 
 seems very doubtful, however, whether it is justifiable 
 to speak of such instincts. A child, let us say, picks up 
 one of a number of wooden blocks lying about in his room. 
 He receives the visual stimulation of a similar block, and 
 since the nervous path is still favored by the reduction of 
 the resistance due to the previous stimulation, reacts in 
 the same way, walks towards it and puts on it his hand 
 in which he still has the first block. Since now, he cannot 
 pick up the second block, he opens and raises his hand and, 
 there, has before him a structure, one block upon another. 
 Since this double block is a more striking stimulus than any 
 of the single ones, it is quite natural that he returns to it, 
 after having picked up one more of the blocks lying about. 
 Is not all the so-called constructive activity simply a more 
 or less complicated habit of the same kind as this very 
 simple example.? This habit of gathering and piling up 
 must develop from the reflexes and habits which we have 
 studied thus far, provided the child is surrounded by things 
 
152 HUMAN BEHAVIOR 
 
 which are sufficiently similar so that two or more of them 
 together make a similar, but more intensive sensory 
 impression than a single one; and what child does not live 
 under such surroundings? It is hardly necessary, then, 
 to assume a mysterious particular instinct of constructive- 
 ness. That the habit of taking to pieces, which is to be 
 derived from the ordinary reflex of grasping, becomes 
 united with this habit of putting together is plain enough, 
 for taking apart brings about ever new opportunities for 
 putting together. Thus develop constructiveness and 
 destructiveness as co-operating habits. 
 
TWELFTH LECTURE 
 
 Repetition of motor activity characteristic of learning 
 in childhood. Variation of the order of earliest accomplish- 
 ments. Speech organs: whispering and singing. First 
 speech sounds. General and specific resistances of neurons. 
 The motor outlet of a group of successive nervous processes 
 determined by the temporal order of the qualitatively different 
 processes. The general resistance as well as the specific 
 resistance reduced by any special fiux; but the reduction of 
 the specific resistance outlasting that of the general resistance. 
 Possibility of a particular distribution of specific resistances 
 resulting from experience. 
 
 OF the motor activities of early childhood we 
 have briefly discussed thus far the adaptive 
 movements of the sense organs of the head 
 and the fundamental activities of the hands 
 and feet. All the processes of learning which we mentioned 
 can easily be placed in the classes distinguished by our 
 theory of nervous activity. Most of them are simply 
 variations of response, some are kinds of condensations. 
 That the learning process is so quick in all these cases is 
 largely due to the fact that the reflexes in question quite 
 naturally lead either to an exact repetition of the stimulus 
 or to a stimulus similar to the first and even more powerful 
 — as when a baby piles up blocks. Even when a new 
 stimulus caused by the first reaction is dissimilar to the 
 
 153 
 
154 HUMAN BEHAVIOR 
 
 first, it may take the path to the same motor point, either 
 according to the law of deflection, or because of the 
 temporarily lessened resistance in that direction, or 
 owing to both these causes. It has become customary to 
 refer to these repetitions of motor activity by the term 
 "circular reaction." Such a special term is useful as it 
 emphasizes the typical character of learning in early 
 childhood in comparison with learning in later life, when 
 the conditions are more complex and repetition of the 
 motor activity rarely results. But let us not forget that 
 the term "circular reaction" is not itself an explanation and 
 would be an additional mystery unless we explain the 
 facts themselves as we have very briefly attempted to do. 
 
 Let us emphasize that, whenever we spoke of a particular 
 kind of movement as preceding in human growth another 
 kind, we wished to indicate merely the most common 
 serial order of development, and that individual deviations 
 from this order, displacing relatively for four or five 
 months this or that element of action, are common too. 
 Parents should neither be alarmed nor think that they 
 have special reasons for paternal pride if they observe 
 that their children do this or that several months later 
 or earlier than other people's children, or that similar 
 differences appear among their own children. Human 
 life during the first — and even second — ^year is so elemen- 
 tary, that any conclusions with respect to the enormously 
 complex life of the future have as much value as the 
 oracles of antiquity. 
 
 The new-born baby is so helpless a creature that, if 
 experience did not teach the contrary, one could hardly 
 believe that such a being could survive the accidents with 
 which he must be daily confronted. When he has reached 
 the age of fifteen months, it seems much less improbable 
 that he will succeed in the struggle with the world. He 
 
SPEECH 155 
 
 has learned to use his sense organs, he has acquired the 
 ability of locomotion which he daily improves by adding 
 further skill in walking, running, and climbing, and he 
 has learned to use his hands so that only further exercise 
 is wanted to enable him to shape the world in accordance 
 with his needs. Yet, at this age it is stUl easy to recognize 
 that all the diversified human power is merely a complex 
 of a small number of natural laws because we can still 
 trace the child's power back to its sources. Of course, 
 the few muscular activities which we have mentioned as 
 characteristic of the behavior of the infant, are not really 
 so simple as we have — intentionally — represented them, 
 but are movemefnts executed each by a large group of 
 muscles and permit eafch many modifications, according 
 as the one or the other muscle in the group receives the 
 stronger nervous impulse. During the second year the 
 complications grow almost into the infinite, especially 
 during the second haK of this year, when the child learns 
 to use more and more effectively its speech organs. Never- 
 theless, we shall convince ourse ves that even now nothing 
 happens but what can be derived from the laws of nervous 
 activity previously stated and a few additional laws 
 which we shall state below. 
 
 It may be well here to make a brief statement as to what 
 the essential factors of speech production are. There 
 are two main classes of sound producing organs. The 
 first class contains only the pair of vocal chords in the 
 throat, at the end of the wind pipe. The vocal chords are 
 comparable to an ordinary musical wind instrument. 
 They produce, when the mouth organs leave the out- 
 streaming air unobstructed, pure musical tones. With- 
 out the* vocal chords one cannot sing. With the vocal 
 chords in a normal condition, one could sing evefn though 
 the mouth organs were completely lacking. The vocal 
 
156 HUMAN BEHAVIOR 
 
 chords might therefore be called the singing organ. On 
 the other hand, the totality of the mouth organs, including 
 even the nasal cavities, might be called the whispering 
 organ. We can make ourselves understood even though 
 we may be unable to sing; for example, when we are 
 hoarse, we can still whisper. Our ordinary speech is a 
 compound of whispering and singing, only that the latter, 
 the "song" of speech, is not, in a musical sense, melodious. 
 
 The first cry of the baby, immediately after birth, is a 
 song, in the sense n which we have just used this word. 
 It is only two or three months later that the growth of the 
 nervous system has progressed far enough to make possible 
 the reflex production of speech sounds. Naturally, first 
 those speech sounds are called forth, which require the 
 smallest amount of sensori-motor activity, of muscular 
 contraction. These are the guttural sounds, produced 
 by the mouth organs located farthest back, near the 
 throat, and the dent^,'! sounds, in the production of which 
 the teeth (or gums) co-operate with the tongue. Neither 
 guttural nor dental sounds require the lips. It is natural 
 again, that of the various guttural and dental sounds 
 those are produced first which require the smallest amount 
 of muscular work. We are therefore most likely to hear 
 first such sounds as ga or goo and da or doo, later the sounds 
 of k, t, etc. The accompanying vowel depends, in accord- 
 ance with the laws of acoustics, on the measurements of 
 the cavity which the mouth happens to form at the 
 moment. Labial sounds occur several months later, 
 since the tension of the lips requires more muscular work : 
 we then begin to hear b and m and nasal n. The popular 
 notion that the first words pronounced by a baby are 
 papa and mama, is an illusion. 
 
 One of our tasks in connection with speech is to explain 
 how stimulation of the ear by different words, for example, 
 
TEMPORAL ORDER OF STIMULATION 157 
 
 by the syllables ga and da, can call forth definite and 
 different motor responses not on"y of the speech organs, 
 but of any motor organs of the body. Here we are con- 
 fronted by a difficulty which hitherto, in order to avoid 
 complication of the discussion, we have intentionally 
 evaded, but which we must now face. The question. 
 Why does excitation occur at a definite motor point? 
 we have always answered thus: Because over the path 
 from the definite sensory point excited to this motor 
 point the nervous flux finds less resistance than on any 
 other path. Now, it is plain that stimulation of the ear 
 by the syllables ga or da can not mean the stimulation of 
 two different sensory points. It is true that the theories 
 concerning the physiological processes in the ear show 
 wide differences of opinion; but that the difference of da 
 and ga is simply a local difference of sensory points from 
 which the two nervous processes start, no physiological 
 theory is likely to assert. That a nervous flux takes the 
 path toward one motor point rather than toward another, 
 must depend, not exclusively on the sensory point whence 
 it comes, but sometimes also on qualitative differences of 
 the flux itself. The importance of the role played by 
 qualitative differences of nervous processes becomes still 
 more apparent when we consider the fact that words 
 differ, not only in the quality of the various stimuli, but 
 especially in the temporal order in which the sounds follow 
 each other. For example, the main difference between 
 the words cat and tack consists in the difference of the 
 temporal order of a small number of sound qualities. 
 There is no doubt that such non-spatial differences of 
 stimulation are sufficient to bring about spatial differences 
 ■ in the motor response. 
 
 In order to explain these facts, it is not enough to speak 
 of the resistance of a neuron. We must speak of a general 
 
158 HUMAN BEHAVIOR 
 
 resistance and specific resistances to particular kinds of 
 flux. How is it possible for a single conductor to have 
 several specific resistances? We can understand this if 
 we assume, as we have previously done, that a nervous 
 flux is a wandering of ions. In a highly complex chemical 
 substance like that which makes up nervous tissue, many 
 kinds (hundreds or even thousands) of molecules may 
 serve as ions. Our purely mechanical analogies, of course, 
 become insufficient at this point, for, as soon as we assume 
 different kinds of ions, we would have to use as analogy 
 a stream of which not always the whole substance, but 
 sometimes only these, sometimes only those of the parti- 
 cles composing the substance may be in motion, while 
 other particles uniformly distributed through the whole 
 substance may remain at rest. This is something like 
 the streaming in filtering and in osmosis, but even more 
 complicated than such processes. 
 
 The assumption of specific resistances of any neuron is a 
 brief expression of the fact that the motor outlet of a nervous 
 process may be determined by the quality of the flux. Now 
 we must find a way of expressing by a picture the fact 
 that the motor outlet of a definite group of processes 
 quickly succeeding each other may be determined by the 
 particular temporal order of the qualitatively different 
 processes, in order to make plain that, for example, the 
 response to the word cat may and does differ from the 
 response to the word tack. Let us use for this purpose 
 the diagram of figure 42. In this figure S° represents a 
 peripheral sensory point; S^ a central sensory point from 
 which several neurons pass on in different central direc- 
 tions; ilffjc and M^gf central motor points from each 
 of which numerous neurons pass on in different peripheral 
 directions. Imagine that the words cat and tack consist 
 of two sounds, let us say, ca and ta, and that the difference 
 
GENERAL AND SPECIFIC RESISTANCE 159 
 
 of the two words lies in the order of succession of these 
 two sounds. While this is only very approximately true, 
 the simplification thus brought about is justified by 
 our purpose. Suppose that the nervous process belonging 
 to the sound ca is x, that the nervous process belonging 
 to the sound ta is y, and that in Figure 42 the neurons 
 S^Sa!,c> ^IbMlbc, MJefM}, and M}Mf have an extra- 
 ordinarily low specific resistance for the flux x (as indicated 
 
 Fig. 42 — Motor response dependent on temporal order of stimulation. 
 
 in the figure by the letter x inclosed in a circle) and the 
 neurons S^SJef, S^fMJef, MI^MI, and M\M , an 
 extraordinarily low resistance .for the flux y (as indicated 
 by the letter y inclosed in a circle). Our task is to explain 
 why the motor response occurs at M ^ when from S° the 
 flux X precedes the flux y, and at the different point Mf 
 when the temporal order of x and y is reversed, — to show 
 that this difference of response is possible. We shall show 
 it in exact mathematical terms. 
 
160 HUMAN BEHAVIOR 
 
 Suppose the fluid quantity passing through one neuron 
 in a unit of time to be equal to G in case general resistance 
 is effective, equal to S in case specific resistance is effective; 
 and that in the latter case the flux is greater, so that S 
 is larger than G, perhaps a multiple of G. Suppose further 
 that the resistance between two "levels" of the nervous 
 system distant the length of one neuron is equal to the 
 reciprocal value of the fluid quantity passing in a unit of 
 time. Then, for the flux x, the resistance between S^ 
 and Mfjc is | since the fluid quantity for each of the two 
 neurons S^S'iic and S^hcMtbc is S and the resistance of 
 each neuron accordingly §. The fluid quantity passing 
 parallel through the neurons which lead from M^j^ to the 
 periphery is, for the flux x, G multiplied by the number 
 of branches from itfoto which we shall call N. The 
 resistance between Mabc and the periphery is then jj^ 
 multiplied by 2, since each branch has the length of two 
 neurons. The total resistance, for the flux x, between S^ 
 and the motor periphery represented by the total group 
 of motor points Ma, Mj„ etc. (let us call it L, being on the 
 left side of the diagram) is therefore 
 
 T ^2j 2 _ 2(NG+S) 
 
 ^ S"^NG NGS 
 
 For comparison, we must now determine the resistance, 
 for the flux x, between S^ and the motor periphery repre- 
 sented by the total group of motor points M^, M^, etc. 
 (let us call it R, being on the right side of the diagram). 
 The resistance between S^ and M'^^f is §. The resistance 
 between -M^/ and the motor periphery is to be found as 
 follows. The fluid quantity passing parallel through 
 the neurons which lead from M^^^f to the level one neuron 
 nearer the periphery, is S plus (N-l)G, since one of the 
 neurons branching off from -M^^/ has for x a specific resist- 
 ance, g, and the (N— 1) other neurons have the general 
 
GENERAL AND SPECIFIC RESISTANCE 161 
 
 resistance g. The resistance between -ML/ and the 
 periphery is then the reciprocal value s+(N^r:i)G> to be 
 multiphed by 2 since each branch has the length of two 
 neurons from M^^f to the periphery. Consequently: 
 
 B_2i 2 ^2( S+NG-G+G _ 2 fS+NG) 
 
 ^ G^S + (N-1)G G(S+NG-G) ~G(S+NG-G) 
 
 In order to compare the magnitude of L with that of R, 
 let us form the ratio: 
 
 L_ 2(NG+S)XG(S+NG-G) _ S+NG-G 
 R NGSX2(S+NG) NS 
 
 Let us consider this formula in a few special cases. It 
 appears that, when there is only a single motor branch 
 at -Mote as well as at M^gf, that is, when N equals 1, L 
 attains its maximum value, is equal to R, for 
 
 L_ S+G-G _-. 
 R S ^ 
 
 With increasing N, the ratio g grows smaller, for each 
 unit added to N is multiplied in the numerator only by G, 
 but in the denominator by the larger value S. If N 
 becomes a very large number, the ratio 
 
 L_ S+NG-G 
 R NS 
 
 approaches more and more g, which is the lower limit of 
 this resistance ratio, for in the numerator the constant 
 value (S— G) becomes then infinitesimal relative to NG, 
 so that the ratio reduces to 
 
 limit fe=g|=|<l 
 
 We see, thus, that the advantage of the left side of the 
 conductive system of Figure 42, which is equivalent to 
 smallness of the resistance ratio ^, for the flux x, depends 
 on two conditions, (1) on the degree by which the specific 
 resistance | is reduced below the general resistance ^, or, 
 in other words, by which the flux intensity S surpasses 
 
162 HUMAN BEHAVIOR 
 
 the flux intensity G, (2) on the number N of the specific 
 motor points belonging to the system. Now immediately 
 after the termination of the flux x, the flux y takes its 
 origin from the same point S°. In order to give x, 'n this 
 theoretical discussion, no unfair advantage over y, we 
 have supposed our conductive system of Figure 42 to 
 offer to y all those resistances in the direction of "left- 
 right" which it offers to x in the direction of "right-left. " 
 Accordingly, as the flux x found the lesser resistance from 
 S° toward the left, so y would find the lesser resistance 
 from S" toward the right, if nothing had preceded. Actual- 
 ly the flux X has preceded the flux y immediately, and this 
 fact, obviously, must be the cause which prevents the 
 flux y from taking mainly the path toward the right of 
 the diagram. To this causal relation we have to give 
 expression in an assumption in the form of a general 
 statement. We assume that any special kind of flux, 
 say X, reduces not only the specific resistance, for x, of 
 the neurons in which it occurs, but also the general resist- 
 ance of these neurons; but we assume, in addition, that 
 the reduction of the general resistance disappears under 
 lack of function much more quickly than the reduction of 
 the specific resistance. 
 
 Let us see what necessitates the latter half of this 
 hypothesis: clearly, the admittance that any specific 
 resistance of any neuron can be the result of function as 
 well as of mere inheritance. If the reduction by function 
 of the general resistance did not disappear more rapidly 
 than the reduction of the specific resistance, no neuron 
 could be said to have any specific resistance distinct 
 from its general resistance, save directly by inheritance. 
 On the other hand, our assumption implies that during a 
 short time directly after the termination of a particular 
 flux, the general resistance may be regarded as being as 
 
GENERAL AND SPECIFIC RESISTANCE 163 
 
 much reduced as the specific resistance. It is plain that 
 this is of the utmost importance for any immediate suc- 
 cession of two or more qualitatively different nerve 
 processes. 
 
 Let us make the application. The flux x from the 
 point S , taking its path largely over the left side of the 
 system of Figure 42, is immediately succeeded by the 
 flux y, likewise from the point S°. If y had not been 
 preceded by x, it would have found toward the right, 
 over S^ef, a resistance less, in proportion to the ratio 
 
 j^s ~ ' than toward the left, over Sabc- But the general 
 resistance of the left side having ust been reduced, in 
 consequence of the flux x, there may be for y no more 
 resistance to the left than to the right. Suppose, then, 
 for simplicity's sake, that the flux y divides equally at the 
 point S^, where the flrst branching occurs. The part 
 passing to the right divides again at M^^f. It divides 
 about equally into N parts, since none of the neurons 
 leading from M^^f to the N motor points has a specific 
 resistance for the flux y. The part passing from S^ to the 
 left, divides at M^bc also into N parts, — but into unequal 
 parts, since the neurons M^i,cM\ and M\M^ have a 
 specific resistance for the flux y, all the others only the 
 general resistance. If N is a rather high number, that 
 is, if the peripheral branches are very numerous, the 
 ratio of the flux reaching M^ to the flux reaching any 
 other single motor point on either side of the dia- 
 gram, must be approximately as S to G. (The ratio § 
 is the limit.) 
 
 Summarizing now the total motor influence of x and y 
 together, we reach the foHowing conclusion. Of x but 
 little flows into the motor points to the right. The main 
 flow reaches the motor points on the left side, including 
 Mc, but distributes itself equally over all these. Of y 
 
164 HUMAN BEHAVIOR 
 
 a much larger (proportional to q) part flows into M^ 
 than into any other motor point of the system. There- 
 fore, the main motor response to the total stimulation x 
 and y in this immediate succession occurs at Mc- If the 
 succession had been y and x, the main motor response, 
 owing to the symmetrical relations of all the conditions 
 concerned, would have occurred at Mf. We have thus 
 demonstrated that the mere temporal relation of two stim- 
 uli {x and y) may result in a spatial determination (at M^) 
 of the motor response. 
 
 We wanted to explain the fact that a human being 
 reacts to the word cat in one way, to the word tack in 
 another way. In the diagram of Figure 42, which we 
 have used for the explanation, we have supposed certain 
 conductors to possess a specific resistance for one kind 
 of flux, others a speciflc resistance for another kind. But 
 that nature should by inheritance completely provide for 
 such details of stimulation by such details of resistance 
 distribution as those of this figure, is highly improbable. 
 Our explanation is satisfactory only if we can show that a 
 resistance distribution like that of Figure 42 may result 
 from "experience" during the individual's life. 
 
 In the middle of Figure 43 we find a reflex arch whose 
 central points are named Sl and M]. This is one repre- 
 sentative of the whole class of reflex arches connecting 
 the sensory points in the muscles and tendons of the 
 speech organs with the motor points in the muscles of 
 these same organs. These reflexes are undoubtedly of 
 more importance for the talking instinct of the young of 
 the human species than any other class of reflexes affecting 
 the speech organs. In our figure the sensory point of 
 the reflex arch has been marked by the word kinesthetic. 
 This name is, of course, really too broad in its meaning, 
 since it includes all sensory points found within any of the 
 
GENERAL AND SPECIFIC RESISTANCE 165 
 
166 HUMAN BEHAVIOR 
 
 motor organs. More correct, but rather long, would be 
 the name "kinesthetic of the speech organs. " The motor 
 point of the same reflex arch has been marked by the word 
 speech. Below it we find in the figure the syllable ca, 
 which is to indicate that the kinesthetic sensory stimulation 
 and the motor activity are both those of the speech 
 organs pronouncing the syllable ca. One of the results 
 of this motor activity is the production of the sound ca, 
 the stimulation of the ear by this sound. The nervous 
 process thus starting from the ear is deflected by the 
 kinesthetic nervous process and takes its path from S^ 
 over S^i, M%, and Ml into the speech organs. Thus 
 the child may be supposed to learn to pronounce the word 
 ca in response to the sound, to "imitate" the word habit- 
 ually. But he learns to imitate also other words, for 
 example ta. In this case the nervous process takes its 
 path from the point Sj in a different direction, say, over 
 (Sf J, M^e, and M] into the motor point marked in the 
 figure by "speech" and "ta. " 
 
 It is plain that the child, living in a human environment, 
 is stimulated by the sound ca most frequently when such 
 things as a "cat" or a "cap" or others whose names 
 begin with the same sound, are present and stimulate the 
 eye with unusual force, more strongly than the other 
 things which happen to be there too. Consequently, 
 the strong nervous process coming from the eye deflects 
 the weaker one coming from the ear, makes it take its 
 path from S% up to Slicd over ilfo6c<i down to Jfoj. and 
 thence to the motor periphery. Thus a specific resistance 
 must be established for the flux corresponding to the sound 
 ca, in the neurons leading from S] to M^i,; but practically 
 no specific resistance for any flux corresponding to any 
 of the sounds foUowing ca in cat, cap, etc., since the 
 sound ca, common to all these words, occurs with so much 
 
GENERAL AND SPECIFIC RESISTANCE 167 
 
 greater frequency. Thus the point Sl becomes, so to 
 speak, a branching point of specific resistances, for ca to 
 the left in the figure, for ta by a similar process to the 
 right, and for many other sounds in other directions which 
 are not explicitly drawn in Figure 43. This is exactly 
 what we pre-supposed for the point S^ in Figure 42, with- 
 out showing, at the time, how it could originate. The 
 promise in this respect we have now made good. We 
 still have to show, however, how in Figure 42 from the 
 point Mabc to a special motor point (M^) a second kind of 
 specific resistance can establish itself. Figure 43 answers 
 our question. Whenever a cat is before the eye, the 
 nervous process from the ear is drawn towards Ma (in 
 Figure 43); and this nervous process contains regularly 
 the specific flux corresponding to the t-sound. According- 
 ly, the nervous path MabMlMa must have a very low 
 specific resistance for this flux, compared with any other 
 path branching off from M^i- This explains the second 
 presupposition embodied in Figure 42, for we had supposed, 
 there, that one of the N branches from M^ic to the 
 periphery possessed a very low specific resistance for a 
 second kind of flux. We were, therefore, entitled to the 
 suppositions in Figure 42, and can rightly assert that we 
 have demonstrated that the temporal order of qualitatively 
 different stimuli may determine the motor point which 
 responds. 
 
THIRTEENTH LECTURE 
 
 A simple sensory excitation bringing about a temforally 
 complex response. Some, but by no means all, temporally 
 complex responses to a simple sensory excitation explainable 
 on the basis of geometric-Tnechanical rivalry of motor organs. 
 Multiform variation of response. Importance of kinesthetic 
 sensory activity. Two stages in the development of speech. 
 Reflex pointing and utterance of a dental sound. Left- 
 handedness during the first months of life. Right-handed 
 reflex pointing. Right-handedness and speech. Accented 
 and gesticulating languages. 
 
 WE have discussed the fact of a temporally 
 complex stimulation, a word, producing 
 one response at a definite motor point. 
 But the reverse is of no less importance, 
 — the fact of an absolutely simple sensory excitation 
 bringing about a temporally complex response, for ex- 
 ample, since we are just discussing speech, bringing about 
 the pronunciation of a word, or of a whole sentence. We 
 must not imagine, however, that the pronunciation of 
 every — even the simplest monosyllabic — word presents a 
 problem of this sort. When a child one year old 
 begins to pronounce such syllables as ga or da, 
 nothing is required to bring about the proper motor 
 activity but an equal, or about equal, division of the 
 simple nervous process into several branches simultan- 
 eously. This is theoretically nothing new, a pure case of 
 
 168 
 
TEMPORALLY COMPLEX RESPONSE 169 
 
 sensory condensation. The muscles active in such a case 
 in producing the second sound, the vowel, may be inner- 
 vated at the same time with those active in producing 
 the first, the consonant. Everyone can easily make the 
 experiment which proves this. Get ready with your 
 mouth organs to say ga, but stop short before the expira- 
 tory "explosion." Then do the same for the syllable 
 goo. You notice a great difference of position of the 
 mouth organs and of tension of the various muscles, 
 although the consonant beginning the word is identical 
 in both cases. The mouth organs, it appears, are ready 
 at once to produce both sounds, consonant and vowel; 
 and it may be altogether a matter of geometric-mechanical 
 conditions — an organ being incapable of moving at once 
 in two opposite directions — that actually the consonant, 
 since it cannot occur simultaneously, precedes or follows 
 the vowel. Try the case of the vowel preceding the 
 consonant. Get ready to say og or ot. Again the mus- 
 cles, especially those of the tongue, have entirely different 
 tensions before even the vowel o is heard; that is, the 
 muscular tensions needed for the second sound begin at 
 the same time as those needed for the first. It is possible — 
 indeed probable — ^that in the pronunciation of such words 
 as god and dog there is no difference at all in the temporal 
 order of the nervous activities involved, but a mere dis- 
 tribution of the relative resistances of the nervous branches 
 serving simultaneously as conductors, to the effect that, 
 in the one case, the muscular "g-tension" is stronger than, 
 and thus becomes outwardly effective before, the "d- 
 tension, " in the other case the reverse, — the o-tension 
 being of intermediate intensity in either case. 
 
 Let us admit that this is the true explanation of the 
 pronunciation of many a word, but let us also be aware 
 that this does not include the assertion that, whenever 
 
170 
 
 HUMAN BEHAVIOR 
 
 any word is pronounced, its pronunciation results just in 
 this way. Nothing can be more misleading than the 
 tendency to beheve that a certain event, in the complexi- 
 ties of human life, must regularly have the same cause. 
 There is no question that the pronunciation of a long, 
 polysyllabic word — not to mention a sentence — can not 
 be the outcome of a purely geometric-mechanical rivalry 
 of the several speech organs crowded together in and about 
 the mouth and excited with different intensities. If a 
 short word often does come about by this rivalry, it often 
 may and does come about in the way typical for long 
 words and sentences. What is this latter way? 
 
 Let us imagine, in the following discussion, a child so 
 far advanced in experience that he responds to any simple 
 speech sound impressing his ear by producing a similar 
 sound with his own speech organs. In Figure 44, S^ 
 denotes {k equals kinesthetic) a sensory point within the 
 
 Sbcdk 
 
 Mb Mf fid Mk Sk 
 
 Fig. 44 — Multiform variation of response. 
 
 muscular and tendinous organs of speech, or, rather, 
 that whole group of sensory points which are stimulated 
 by the tensions of the speech organs during the production 
 of any definite sound, say, the word baby. The motor 
 ending of the reflex arch S^ Mk is of no direct interest to 
 us; we might imagine that Jf;(, represents the motor activ- 
 ity of saying "baby," which leads again to stimulation of 
 
TEMPORALLY COMPLEX RESPONSE 171 
 
 Sj, but we must note that in the following figure another 
 point, Ma will be supposed to take this function. We 
 know that from S^ over a higher center, Stcdk ^bcdk> ^ 
 route of low resistance may be established in the direction 
 of numerous motor points, M,,, M„ M^, etc., — each of 
 which represents here rather a group of motor points 
 active in the production of one definite speech sound than 
 a single point. To take a concrete example, — a child 
 happens to say "baby" and the mother's answering 
 "cry," "hungry," "tired," etc., causes the child to pro- 
 nounce one of these same words in succession to "baby." 
 While the word baby is — ^probably repeatedly — produced, 
 the kinesthetic nerve process starts from Sk- At the 
 same time the auditory process (not represented in the 
 figure) resulting from the mother's answer leads to the 
 imitative motor activity at either if j, or M„ etc. Of 
 these two processes, the former is attracted and deflected 
 by the latter, and the child, instead of saying once more 
 "baby," says now "cry," another time "hungry," etc., 
 whatever the mother has said. The deflection of the 
 nervous process originating at iS^;., from S\ upwards (in 
 Figure 44) , leads then to a multiform variation of response. 
 The actual response at any future time, on the basis of 
 this variation of the nervous path, to a stimulation of S^ 
 occurs either at Mb> or at M„ or at M^, etc., according as 
 adventitious circumstances happen to favor the one or the 
 other of these points. That the variation must be multi- 
 form, is plain enough, for many kinds of word successions 
 having the same first word must needs occur in the experi- 
 ence of a child surrounded by older people. What, then, 
 may be such an adventitious circumstance as just men- 
 tioned, making the selection among the motor outlets of 
 the multiform nervous path.'' Here we approach the real 
 problem set before us at the end of the previous paragraph. 
 
172 
 
 HUMAN BEHAVIOR 
 
 Figure 45 is an elaboration of the directly preceding 
 figure. S° is a sensory point at which, we suppose, an 
 absolutely simple nervous process originates, for example, 
 the sound of a baby crying at a distance. At S'^ a branch- 
 ing of the nervous conductor brings about a division of 
 the process to the left and right. We suppose that the 
 resistance to the left is less, so that the main flux occurs 
 in this direction, much less to the right, as indicated in 
 the figure by the conductors to the left being drawn in 
 
 Fig. 45 — A simple stimulus calling forth a temporally complex response. 
 
 double lines. The motor response occurs practically only 
 at Ma, notwithstanding a certain amount of muscular 
 tension elsewhere, especially at Mi,. Now, imagine both 
 these points. Ma and M^, to represent tw;o groups, partly 
 overlapping, of muscular organs of speech. The sound 
 actually pronounced is then the one corresponding to 
 Ma', the other, corresponding to ilf j, is excluded by geo- 
 metric-mechanical rivalry, the same organ being incap- 
 able of moving in two opposite directions and follow- 
 ing, by necessity, the stronger pull, — a very ordinary 
 event in animal life. The pronunciation, through 
 its muscular tensions, stimulates a whole group of the 
 kinesthetic sensory points in the organs of speech; and 
 
TEMPORALLY COMPLEX RESPONSE 173 
 
 the group of sensory points thus affected is exactly, let 
 us say, the one which we have formerly called S/,. Then 
 a second word must be pronounced in response to the 
 stimulation of S/^; and of the many responses possible, 
 at M,,, or at M^, or at M^, etc., the one must actually 
 occur which is favored by the adventitious circumstance 
 that directly before this moment a nervous flux, although 
 weak, has passed from S^ over Sl and Ml through the 
 neuron Ml M,,. That is, under the conditions embodied 
 in Figure 45, a simple stimulation of S° must result in a 
 temporally complex response, a succession of two muscular 
 activities, first at M^ and then at M),. 
 
 Still the question is left if in our demonstration just 
 completed we had a right to pre-suppose such a branching 
 of the nervous conductors as represented by Figure 45 
 at the point S^, which means that saying "cry" (M^) 
 is a rival, but weaker, response to a certain stimulation 
 at S° (e. g., a sound coming from a distance) that is 
 actually responded to by saying "baby" (Ma). We had 
 a right to pre-suppose this for the following reason. The 
 child in question is sufficiently advanced in experience to 
 respond to a simple speech sound heard by pronouncing 
 it imitatively, — ^this we have assumed. We only have to 
 ask, therefore, whether he has the opportunity of hearing 
 grown people say both "baby" and "cry" frequently 
 while a crying baby impresses the sensory point S°. Of 
 course, this must be the case, and surely, too, the word 
 "baby" is under these conditions more frequently used 
 than the word "cry," so that of the two paths estabHshing 
 themselves from S^ upward the one leading to Ma must 
 have its resistance reduced much more than the one leading 
 to Mi. 
 
 We have shown, thus, how experience can train the 
 nervous system in such a way that one simple stimulation 
 
174 HUMAN BEHAVIOR 
 
 is responded to by a succession of motor activities, by a 
 temporally complex action. We do not assert that every 
 training of this kind must conform with figure 45. There 
 may be hundreds or thousands of other possibilities of 
 bringing about a similar result. To have demonstrated 
 one such possibility, as an example, is sufficient for our 
 present purpose. Let us use this opportunity, however, 
 to point out a fact of much general importance for all 
 training of temporally complex reactions, namely, the 
 necessity of kinesthetic sensory activity. If it were not 
 for temporally complex reactions, kinesthetic sensory 
 points would be rather superfluous. Why should any 
 animal respond by particular reactions to tension in its 
 muscles and tendons? The biological purposes of activity 
 are, mainly, protection and nutrition. Neither is, as a 
 rule, served directly by an animal 's reacting upon internal 
 tension. But a definite temporal order in a very complex 
 reaction could hardly be acquired, as Figure 45 shows, 
 without the mediation of kinesthetic sensory points, 
 enabling the first motor activity to determine — in co-opera- 
 tion with further conditions — the second, the second to 
 determine the third, and so on. The greater the com- 
 plexity of an animal's anatomy, the greater is the need of 
 temporal order in its compound motor activities. Thus, 
 indirectly, the kinesthetic sensory points come to serve 
 the purposes of nutrition and preservation, to be ultimately 
 as indispensable as the sensory points on the surface of 
 the body. But a direct reference to any purpose can 
 hardly ever be found in the kinesthetic sensory activity, 
 except where — as it happens especially in the highest 
 animal, in man — the performance of a skillful motion 
 becomes itself a purpose, severed from all "practical" 
 significance, for example, in athletic sports. 
 
 On the basis of our views concerning the nervous 
 conditions of speech functions, we may adopt a distinction 
 
KINESTHETIC SENSORY FUNCTION 175 
 
 which is often made by those interested in the growth of 
 speech. We may distinguish two stages in the develop- 
 ment of speech, the early prattle of a child, consisting 
 mainly of monosyllabic words, and the more highly 
 developed — often, but only with partial justice, called 
 exclusively the "imitative" — formation of longer words 
 and sentences. The early prattle of a chUd depends on a 
 branching of the nervous process so that numerous motor 
 points receive the excitation simultaneously or almost 
 simultaneously. The branching of the nervous conductor 
 is then similar to that in the special process of learning 
 which we have called sensory condensation. But this 
 branching may be completely inherited. The speech 
 organs usually produce both a consonant and a vowel, 
 but one precedes the other owing to geometric-mechanical 
 rivalry. Even sounds consisting of two consonants and 
 a vowel may be produced in this way, like gook. And 
 polysyllabic words too: very easily reduplications like 
 dadadada, or words like goocka, booppa, hoppa. Such 
 words are characteristic of the second year of life. It is 
 a mistake to think, however, that the term imitative is in 
 no way applicable to this stage. In this — ^in the main 
 monosyllabic— prattle, as in his later talking, the child is 
 influenced by what he hears grown people pronounce. 
 The second stage, from the end of the second year 
 continuing really aU through life, is governed by kines- 
 thetic sensory functions, as illustrated in Figure 45; and if, 
 as often in the nervous disease of aphasia, the kinesthetic 
 functions are interfered with, the grown person retires to 
 the prattling stage. Let no one think, however, that the 
 simpler function, governed by geometric-mechanical 
 rivalry of the speech organs, has ceased to exist in the 
 second stage. Many kinds of lapses of speech in grown 
 people and in children prove the contrary. When a child 
 
176 HUMAN BEHAVIOR 
 
 says tome instead of come or dood instead of good, it is not 
 necessarily, as one might be inclined to believe, because 
 he can not pronounce gutturals, — they are the class of 
 consonants most easily produced. Most probably, in such 
 a case, the nervous function described in Figure 45 is not 
 perfected, and simultaneous innervation, by means of a 
 mere branching of the nervous conductor, governs the 
 pronunciation. Then we understand why tome should be 
 pronounced instead of come, for the branching of the 
 nervous conductor is more ready to serve t and m together, 
 both of which are produced by the speech organs located 
 in the front of the mouth and co-operating naturally 
 in many ways, than to serve k and m together, of which 
 the former is produced by speech organs located in the 
 back part of the mouth and therefore less naturally 
 co-operating with the other. That any imaginary diflBcul- 
 ty of producing guttural sounds need not have anything 
 to do with the case, is demonstrated by the example of a 
 German-speaking child who insisted upon saying kragen 
 instead of tragen, — certainly not because gutturals are 
 more easily pronounced than dentals, but because the 
 other significant consonants of the word, the German r 
 and the g, are both gutturals, with a common nervous 
 conducting apparatus. 
 
 In our ninth lecture we mentioned the reflex of pointing 
 with the index finger at a thing which impresses the eye. 
 We said that this reflex appears at about the same time 
 when the first articulated sounds (usually guttural and 
 dental — ga and da) are instinctively produced by the 
 baby. But the act of pointing is not accompanied by a 
 guttural, but by a dental sound — the baby pointing and 
 saying dadada. We recall, too, the interesting fact that 
 in all Germanic languages the demonstrative pronouns 
 begin with a dental sound. Why does the baby say da 
 
REFLEX POINTING 177 
 
 when pointing at anything, and not ga? The answer is 
 to be found in the same considerations which we have 
 just applied. The act of pointing sets in motion one of 
 the extremities of the body. The nervous process, one 
 of whose divisions goes into this extremity, can naturally 
 reach by one of its other divisions more easily the muscles 
 of the frontal part of the mouth, belonging to the periphery 
 of the body, than the muscles of the throat, belonging to a 
 different, an internal, system of muscular activity. Try 
 yourself to accompany a pointing movement by a dental 
 or a guttural sound. The latter seems less natural. 
 
 When the reflex of pointing first occurs, we notice that 
 the pointing is done far more frequently with the right 
 than with the left hand, whereas previous to this time the 
 right hand is by no means favored in action. The func- 
 tional connections between the reflex of pointing, the 
 growth of speech, and the development of right-handed- 
 ness, are so interesting that we must discuss them more in 
 detail. A baby two or three months old, in using the 
 hand, for example in order to put the fingers into the 
 mouth, unquestionably gives preference to the left 
 hand in about two-thirds of all cases. That is, one 
 observes during the first few months about two activities 
 of the left to one of the right hand. Toward the middle 
 of the first year this preference disappears, and both 
 hands are now used with about equal frequency. This 
 is also the time when speech sounds, although hardly 
 yet imitative, become more frequent. During the second 
 year — say, at the fifteenth month, making allowance for 
 the enormous individual differences — the right hand 
 begins to predominate, and about the same time speech 
 enters upon that rapid development which insures to this 
 art its being the distinguishing feature of a human being 
 as compared with an animal. As little as it possesses 
 
178 HUMAN BEHAVIOE 
 
 speech in the human sense, can any animal be said to 
 be right-handed or right-sided. In animals both sides of 
 the body function about equally. 
 
 It is probable, although not absolutely certain, that the 
 totality of these facts may be explained in the following 
 way. The left hemisphere of the normal human brain, 
 as has been known for nearly a century, has functions 
 different from those of the right hemisphere; not merely 
 in so far as the right hemisphere is more closely connected 
 with the left side of the body and the left more closely 
 with the right side of the body, but through its significance 
 for the functioning of the speech organs. Certain nervous 
 paths, most probably those leading from the kinesthetic 
 sensory points of the speech organs, have their higher 
 centers in the temporal part of the left hemisphere exclu- 
 sively, and when a person suffers from aphasia, it is in 
 this part where a lesioli is regularly found in a post- 
 mortem examination. It is clear, then, that the growth 
 of speech during the second year of life is coincident with 
 and dependent on the inner development of this part of the 
 brain; and since this part of the brain is also closely con- 
 nected with the hands, but more closely with the right 
 than with the left hand, it is to be expected that speech 
 functions bring about activities of the right hand. Thus 
 we understand why certain movements of the baby's 
 speech organs are accompanied by pointing movements 
 of the right hand, and why ^own people, too, so fre- 
 quently accompany their talk by gestures of the right 
 hand. 
 
 As to the time of the development of the right hemi- 
 sphere of the brain in comparison with the left, we are 
 entitled to a conclusion from analogy. The human 
 brain with its complex functions is not fully developed 
 until years after birth. The brain of larger animals of a 
 
LEFT-HANDEDNESS OF INFANCY 179 
 
 longevity comparable to that of man, with its simpler, 
 but no less important functions, is fully developed some 
 months after birth. May not a similar rule govern the 
 development of the left and the right hemispheres? The 
 temporal part of the left hemisphere, with its highly 
 complex speech functions, is not fully developed until 
 years after birth — so much we knbw. By analogy we con- 
 clude that the symmetrically corresponding part of the 
 right hemisphere, with its simpler, though no less import- 
 ant functions, develops to maturity at a much earlier 
 period. If this is so, activity of that hand which is 
 governed by the right hemisphere, must become con- 
 spicuous at a much earlier period than activity of the 
 other hand. Indeed, the left hand, whose musces are 
 closely connected with the temporal part of the right 
 hemisphere, is the preferred member in the activities of 
 the first few months after birth. Thus the fact that a 
 normal human child is at first left-handed and then 
 changes into being right-handed, to remain so during his 
 life, appears plain enough. 
 
 Movements of the speech organs are likely to be accom- 
 panied by pointing movements or other gestures of the 
 right hand, or of both hands because of the nervous 
 co-ordination of the hands, so we said. Some languages, 
 especially the English, habitually put an enormous vigor 
 into the enunciation of one definite sound of each word 
 or sentence. The English language, that is, is a strongly 
 accented language. According to our law of nervous 
 deflection we might expect that the strong nervous flux 
 leading to the enunciation of the accented sound should 
 interfere with the execution of the hand gesture. It 
 seems that this explains the absence, or at least remark- 
 able infrequency, of gesticulation in speakers using the 
 English language. In the French language, on the other 
 
180 HUMAN BEHAVIOR 
 
 hand, there is no accent worth mentioning, and the reflex 
 gestures of the speaker are therefore fully preserved. 
 Accent is thus a substitute for gesture. This explanation 
 seems more generally applicable than the customary one 
 referring to racial differences of temperament as the exclu- 
 sive cause of the difference in question. Such a difference 
 of "temperament" would remain both ethnologically and 
 psychologically rather mysterious. 
 
FOURTEENTH LECTURE 
 
 Spatial perception. Inherited responses to spatial form. 
 Acquisition of unitary groups of conductors serving all 
 objects of the same design. Mutual attraction of nervous 
 processes of equal strength. Melody and harmony. Two 
 kinds of tonal similarity. Neurons applying their specific 
 resistances in various degrees to a variety of processes. 
 Rhythm equals subjective grouping of objectively uniform 
 excitations. Habits of performing group motions consisting 
 of one chief and one or several preparatory movements. 
 No counting in rhythmical perception. Why all common 
 rhythms are of the doublet and triplet kind. 
 
 THE function of the nervous system is said, by 
 some, to have three aspects. But to distingiush 
 them one must narrow his view to an exclusive 
 consideration of the sensory function, the motor 
 function, or the collecting and redistributing function of 
 the system, of which none can have any separate exis- 
 tance. How artificial the separation of these functions 
 is, appears from our previous discussions. The function 
 of the nervous system is always one which carries sensory 
 excitations to motor points over short or long, relatively 
 simple or complex paths. A distinction of different 
 aspects of this single function merely offers convenient 
 headings under which to place chapters of a prolonged 
 discussion. Thus we may say that we are now to consider 
 a certain sensory aspect of nervous function, namely that 
 
 181 
 
182 HUMAN BEHAVIOR 
 
 which is customarily referred to by psychologists under 
 the name of the perception of space. The sensory points 
 here in question are mainly those of the cutaneous surface 
 of the body and the retinas of the eyes. The problem 
 which concerns us is, broadly stated, this: How can we 
 explain the fact that group stimulations of a particular 
 geometrical design, occurring now here, now there on the 
 sensitive surface, are capable, within limits, of calling forth 
 identical motor responses although the sensory elements 
 stimulated may be either entirely different or only 
 partly identical? 
 
 Fig. 46 — The simple perception of'space. 
 
 To state the problem less abstractedly, let us take an 
 example. A triangle is before our eyes. We move, and 
 the triangle appears on a different part of the field of 
 vision, at B instead of at ^, in Figure 46. The sensory 
 elements stimulated in both cases are partly different, 
 partly identical, as the figure shows immediately. We 
 move again and the triangle appears again on a different 
 part of the field of vision, at C. This time altogether 
 different sensory elements are stimulated. In aU three 
 cases our reaction is about the same; if it is a speech 
 reaction it consists probably in our pronouncing the word 
 triangle. Whatever the reaction may be, on general 
 
SPATIAL PERCEPTION 
 
 183 
 
 principles of theoretical explanation we must be able to 
 conceive of it, because of its definiteness and identity, 
 as the result of a nervous flux proceeding somewhere 
 within the nervous system from a definite single point. 
 Our problem, then, consists in showing the possibility of 
 all the nervous processes which come either from A, or 
 from B, or from C, uniting in the same single point within 
 the nervous system. From this point on toward the motor 
 periphery the nervous process may then undergo all the 
 influences hitherto described in general, leading to all 
 kinds of variations and combinations of motor effects. 
 
 op 
 
 5y 
 
 ■JZ 
 
 Su 
 
 ^rk, 
 
 I 1 I I 1 
 
 Sa Sb Sc Sd Se 
 
 Fig. 47 — Sensory points serving form stimulations. 
 
 Figure 47 contains two classes of points which are 
 marked with letters. The points marked S^, Sy, S^, S„, Sp 
 are those among which the central point just mentioned 
 is to be found. They are quasi-sensory points, not located 
 in the sensory periphery of the nervous system, yet to be 
 regarded, in the light of all our previous discussions of 
 function, as if they were truly sensory points. In them 
 are collected the conductors which unite the genuine 
 sensory points Sa, Ss, S„ Sd, Sg into the groups spoken 
 of above as essential for the so-called perception of space. 
 In the point S^ of the figure two true sensory points are 
 grouped together, Sa and Sj. One of these, Sj, is also 
 
184 HUMAN BEHAVIOR 
 
 grouped with S^ in the quasi-sensory point Sy. All three, 
 Sa, Sj, Sc, are united in the quasi-sensory point Sp. From 
 each of the points S^, Sy, Sp a definite chain of neurons, 
 not given in the figure, leads to a definite motor outlet. 
 Suppose, now, that three other sensory points are united 
 in another quasi-sensory point Sp/ (not shown in the figure), 
 three others in Spff, etc., and that from all these quasi- 
 sensory points Sp, Sp', Sp", etc., the excitation is carried 
 to the same motor point Mp. Thus group stimulation 
 of a particular geometrical design, though occurring now 
 here, now there on the sensitive surface, can by way of 
 Sp, Spi, Sp>', etc., lead to the same motor response at Mp. 
 Only this question is left, whether we have the right to 
 assume that by both inheritance and experience, neuron 
 connections like those of Figure 47 can exist. 
 
 As to inheritance, observation of the reactions of young 
 animals as well as infants proves that we have this right. 
 The present writer has repeatedly observed that children 
 a few months old, with no experience whatsoever as to 
 danger from animals, reacted definitely and strongly with 
 shrinking, tension of the facial muscles, and crying when 
 shown the face of a stuffed puppet representing a little 
 
 Fig. 48^Spatial stimulation with inherited response. 
 
 pig of simple features like those of Figure 48. Since the 
 reaction was the same in the case of different children and 
 of somewhat different puppets, the conclusion is to be 
 drawn that it was a reaction to the common features of 
 
INHERITED RESPONSE TO FORM 185 
 
 tliese puppets, consisting in a circular head, two conspi- 
 cuous circles within, the eyes, and a conspicuous triangle, 
 the snout, as shown in the figure. Obviously, then, the sen- 
 sory points of the child's eyes are by inheritance combined 
 into a large number, perhaps thousands, of groups so that 
 all the points stimulated by an appearance, in upright 
 position, more or less like that of Figure 48, send their 
 excitations to a single motor point or a single central 
 point whence the flux is redistributed to cause the definite 
 reactions mentioned. There are probably also many other 
 kinds of such groups, of other shapes, inherited by each 
 individual of the human and animal race. In animals, 
 too, similar definite reactions to the appearance of an 
 object never experienced before have been reported by 
 various observers. 
 
 The other question is whether a grouping of sensory 
 points like that of the diagram of Figure 47 and the further 
 grouping (above mentioned) of such points as Sj, Sp', Sp'>, 
 mentioned above as serving the same geometrical design 
 on the sensitive surface, can be acquired during life. For 
 this it is merely necessary that whf n a definite group of 
 the sensory points on the retina or skin is stimulated by 
 an object, a definite motor response is strongly called forth 
 by a certain additional property of the same object or by 
 any other property of the total situation. If this is the 
 case, the nervous processes, in accordance with the law 
 of deflection, must all be drawn into a single channel, the 
 one leading to the motor response just referred to. That 
 is, somewhere within the nervous system, they must all 
 be united, as processes coming from So, Sj, and S^ may be 
 united in Sp. Now, the next moment, the same object 
 may stimulate other sensory points, partly identical with 
 or entirely different from the former. What enormously 
 simplifies the whole problem is the fact that of all the 
 
186 HUMAN BEHAVIOR 
 
 groups which might be stimulated by the same object, only 
 those relatively few are ever likely to be stimulated which 
 are displaced without any rotation, like the triangles in 
 Figure 46. This new stimulation by the same object may 
 result from either a movement of the object or a movement 
 of the eyes or of the whole body. The objects which move 
 are usually animals, moving over the ground without 
 rotating around any horizontal axis within their body. 
 Accordingly, their images on our retina do not suffer any 
 rotation. If it is our body that moves, it does not rotate 
 either, nor do our eyes, so that the image is again displaced 
 on the sensitive surface without any rotation to speak of. 
 The flux from the sensory points now stimulated is by 
 deflection carried into the same motor point. Thus a 
 large number of conductor groups of low resistance leading 
 to the same motor point must be estabUshed — ^all these 
 groups having in common that the sensory points form a 
 geometrical design of the same position with respect to the verti- 
 cal; for other positions could be brought about only by 
 rotation around a horizontal axis, which is a relatively 
 infrequent occurrence in nature. Such a response having 
 once been established — or else being inherited — it can be 
 varied like any simple response by further experience. 
 For example, the first response of a child to the sight of 
 a cat may be one of shrinking; later, by variation, it may 
 be one of approaching and petting the animal. 
 
 This is simple enough. The only question which might 
 stUl be asked in order to make this kind of reaction — ^to 
 spatial stimulation — ^perfectly plain, is this : Why does the 
 main flux, in case Sj and S^ (in Figure 47) are stimulated 
 together with equal intensity, pass in the direction of 
 Sy^ Why does it not pass in the direction of Sp as well? 
 Secondly, why does it not scatter almost equally in the 
 directions of S„ Sy, and S^? To answer this question 
 
ACQUIRED RESPONSE TO FORM 187 
 
 we need only refer to the law that nervous processes 
 mutually attract each other. If one of them is stronger 
 than the other, the result is a deflection of the weaker one 
 from its course. If they are equally strong, the result is 
 a union whenever the conditions of the case make a union 
 of the several processes possible. Thus the two processes 
 coming from Sj and Sc, instead of scattering in the direc- 
 tions of S^, Sy, and S^, unite in the only neuron in which 
 they can unite most directly, the one leading to Sy, whence 
 the flux goes on directly or indirectly toward the motor 
 periphery. Saying that the flux takes its path over Sy, we 
 mean, as always, strictly only that the major part takes 
 this path and the muscular re9,ction depending on Sy 
 overpowers all other muscular reaction. If So is stimulated 
 together with Sj, and S^, the three processes can not unite 
 either in Sx or in Sy, but only in Sp. Accordingly, the 
 muscular reaction is determined by Sp. That in conse- 
 quence either of inheritance or of experience definite 
 motor responses succeed group stimulations of a particular 
 geometrical design, is thus made plain on the basis of 
 our general assumptions. 
 
 Another one among the peculiarities of the so-to-speak 
 sensory aspect of nervous function, of much interest to 
 the psychologist because of its significance for the theory 
 of esthetics, is the perception of melody and harmony in 
 music. Certain tones, affecting the ear either in succes- 
 sion or in simultaneity, bring about motor reactions like 
 those which generally, in any division of sense, are the 
 effect of stimulations of similar kind — similar in a greater 
 or lesser degree. Neglecting the fact that these reactions 
 to music are chiefly emotional — ^to the question what 
 emotional means we shall return later — ^we may use here 
 the following quite possible and very concrete example. 
 That the example is not taken from every one's daily 
 
188 HUMAN BEHAVIOR 
 
 experience may be excused by the fact that common behav- 
 ior hardly ever contains any unemotional reaction upon 
 musical tones. Suppose somebody has been trained to per- 
 form a particular responsive act whenever he hears the 
 same tone twice with a short time interval between. The 
 responsive act may consist in his saying simply "same 
 tone" or "the tones are alike." We notice that he re- 
 sponds in this particular way frequently even when the 
 second tone is an octave of the first, and also, though 
 less frequently, when the second tone is a fifth of the 
 first. Obviously, then, the nervous flux of the octave is, 
 not identical with, but similar to that of the first tone 
 stimulation; and the nervous flux of the fifth is also sim- 
 ilar, though in a lesser degree, to that of the first tone 
 stimulation. 
 
 If the first tone had been one of, say, four hundred 
 vibrations and the second tone one of four hundred and 
 five, it would not appear strange that the second nervous 
 excitation should have affected the nervous system like 
 the first. On an earlier page we spoke of the specific 
 resistance of neurons. It goes without saying that any 
 neuron having a specific resistance for the flux which is 
 caused by the auditory sensory points being jerked four 
 hundred times in a second, has this specific resistance also 
 for a flux caused by slightly more, or less, frequently 
 occurring jerks. But here observation teaches us that 
 one neuron must apply the same specific resistance 
 to a flux caused by jerks occurring in the ear twice ("oc- 
 tave") or one and a half times ("fifth") as frequently, 
 — only in various degrees with various ratios. Rejecting 
 all speculation on this point, we are compelled to accept 
 the bare fact that with respect to the specific resistance 
 of a neuron a simple ratio of jerks can take the place of a 
 near number of jerks in the auditory organ. A full know- 
 
MUSIC 189 
 
 ledge of the chemistry of the nervous flux may in the future 
 make the evident fact plain to our understanding. 
 
 It does not follow, however, that in every neuron with- 
 out exception a simple ratio must have this effect. On the 
 contrary, there is good reason to believe that only a minori- 
 ty of all the neurons connected with the ear function thus, 
 for there are even people — those who are entirely unmu- 
 sical — in whom practically no "ratio" reactions of this kind 
 are found, who, we may assume, possess no neurons what- 
 soever of this vicarious function. In infancy, too, this 
 function in auditory excitation seems to appear later than 
 the other, so that we may regard it as a comparatively re- 
 cent acquisition of the race. Now, if all the neurons do not 
 apply their specific resistances to simple-ratio stimulation 
 of the ear equally as to near-number stimulation, the sub- 
 ject's ultiniate motor response, the muscular reaction 
 proper, need not be identical in every case of similar and 
 of simple-ratio stimulation of the auditory organ. An 
 example will show what conditions are favorable to a re- 
 sponse of this sort,^ — the nature of the just preceding reac- 
 tion especially. Let a tone and its octave stimulate a 
 person's auditory organ. Suppose that, a fraction of a 
 minute before, many of those neurons have carried exci- 
 tations which do not apply their specific excitations to 
 simple-ratio stimulations of the ear :- — two slightly mistuned 
 tones may just have affected the ear. Then these neurons 
 owing to their recent functioning, rather than the others, 
 will function now again and the motor reaction to the two 
 tones must be the usual one to two "tones quite different, " 
 because of their difference in the number of jerks. Our 
 general explanation of that property of the nervous sys- 
 tem which is the basis of all music (of melody and har- 
 mony) by no means involves us — as one might fear — ^in the 
 difficulty that the motor reaction to tones of a simple 
 
190 HUMAN BEHAVIOR 
 
 ratio of vibration rate must inevitably be always the 
 same as the motor reaction to tones of similar vibration 
 rate. 
 
 No attempt will be made here to answer the question 
 as to the origin of the fact that a limited number of the 
 neurons of the human nervous system apply their specific 
 resistance in various degrees to a variety of auditory nervous 
 processes provided that the frequencies of the jerks re- 
 ceived by the ear form certain simple ratios. Too much 
 printer's ink has already been wasted on proposed answers 
 to this question, of which none appears thus far entirely 
 plausible. 
 
 A third peculiarity of the sensory aspect of nervous func- 
 tion, which we shall discuss here, is the .rhythm which is 
 often observable — not in animals but in man — in the mo- 
 tor reactions when the stimuli occur at fairly regular inter- 
 vals but without being combined into any groups by phys- 
 ical accentuation, objectively. We mean by rhythm the 
 subjective grouping, the fact that a definite, unitary re- 
 sponse corresponds, not simply to each single stimulus, 
 but rather to a group of stimuli, — this group recurring 
 in the sensori-motor activity with regularity for some time. 
 
 Take this example. I am sitting at the open window 
 through which the regularly recurring puffs of a distant 
 steam engine reach my ear. Suddenly I am imagining 
 the strains of a waltz. The puffs of the engine seem to 
 turn into the successive chords of the music and, at the 
 same time; seem to have lost their former absolute regulari- 
 ty. They incite me to beat with my hand; but the move- 
 ments of the hand are not all equal. Six of them fall into 
 a group, and this group again consists of two parts of three 
 beats each. The first of the six beats is executed with 
 great vigor and mainly from the shoulder joint. The 
 following two are executed with a much weaker movement 
 
RHYTHM 191 
 
 of the hand, and then too, the upper arm takes 
 hardly any part in the motion, which occurs from the 
 elbow joint rather, or even merely from the wrist. The 
 total time occupied by these two beats is slightly less than 
 double the time of the first beat. The fourth beat (the 
 first of the second part) is comparable to the first of the 
 group, but has the same properties in a slightly lesser de- 
 gree. The fifth and sixth are comparable to the second and 
 third. We call this the perception of rhythm^ — of a 
 particular rhythm in this particular case. How do I 
 come to be affected in this peculiar way by absolutely 
 regular puffs of a steam engine.'' 
 
 This habit of reacting is acquired by each individual in 
 innumerable different ways. Let us at once give a concrete 
 example. Imagine a gardener having planted a double 
 row of plants like the stars of Figure 4fl. In order to keep 
 
 Fig. 49 — How the habit of rhythm may be acquired. 
 
 the loose earth, just thrown around the roots of each plant, 
 from drying, it is necessary to compress it and thus render 
 effective the capillary attraction which draws the mois- 
 ture from the lower soil. The quickest way of doing 
 the work is to walk along the center line of the double row 
 and to step, with the full weight of the body, on each of 
 the places which need compression, using, of course, 
 alternately the right and the left foot. Now, try to 
 walk ahead, doing this, and observe how your legs most 
 naturally act during this procedure. While you are 
 standing on your right foot, the muscles of your right leg 
 are strained in such a way as to keep the leg straight and 
 able to support the weight of the body, but not in such a 
 
192 HUMAN BEHAVIOR 
 
 way as to throw readily the weight of the body upon the 
 other foot. For this a complete readjustment of the mus- 
 cles of the right leg is requisite. To bring about the 
 muscular readjustment, you most naturally let the body 
 fall lightly upon the left foot and let it swing back to the 
 right. Thus you assume that new position on the right 
 foot in which the tension of the various muscles is ad- 
 justed so that the fuU weight of the body can be thrown 
 on the left foot forcefully and skillfully. The left foot 
 now hits exactly the spot in the left row on the ground 
 where the compression of the soil is needed. 
 
 What, then have you really done instead of stepping 
 simply from the right foot upon the left? You have made 
 two intermediate steps of a much less forceful kind, merely 
 preparatory to the proper stepping on the loose soil. Be- 
 fore you now step on the next spot in the right row, you 
 make again two preparatory steps, and so you continue 
 your agricultural work most easily (that is, most naturally) 
 and most effectively. Between each two compressing 
 movements there are always two different preparatory 
 movements, both of an easy character. Why just two 
 different preparatory movements? Obviously because 
 man is a symmetrically built and two-legged animal. If 
 man were built like a horse, the total muscular activity 
 might, and probably would, be rather different. Surely, 
 if man were a three-cornered animal, the case would be 
 entirely different, — most probably he would not even have 
 any tendency then to plant his garden in double rows. 
 
 One must not think that all this cannot have much signi- 
 ficance for rhythm, since most people who have rhythm 
 have never planted any garden in the way indicated. This 
 is true. The one example of human activity was only to 
 show that the activities of man in general tend to be habit- 
 ually of such a nature that the main motion is preceded 
 
GROUP ACTIVITY 193 
 
 by a double or single (example below) preparatory 
 movement of a less forceful kind. Thus the human nervous 
 system becomes accustomed to muscular innervations 
 arranging themselves in a group of three (or two) successive 
 innervations of which one is strong. The individual 
 possessor of the nervous system then has the habit of 
 performing group activities rather than entirely uniform 
 motions which follow each other like the puffs of an engine. 
 He may then be said to have the habit of rhythmical 
 perception, that is, the habit of reacting by a group activity 
 to a series of perfectly uniform stimulations like our series 
 of puffs, which directly, by their objective properties, in no 
 way incite any group activity. That animals do not acquire 
 any such habit of rhythm is readUy understood if we only 
 consider that horses or dogs do not habitually perform any 
 systematic labor at all comparable to that mentioned above 
 of a gardener. But in man's life systematic labor plays 
 an important part — ^and not only labor, but also systematic 
 play, like dancing a waltz. When the nervous system 
 has once thoroughly acquired the habit of a particular 
 group activity, this activity may by a " variation of re- 
 sponse " quite readily show itself in a part of the body 
 where it was not, and in a motion in which it was not, 
 acquired, as when I beat with my hand the rhythm of a 
 waltz while my feet are at rest. It may by a further 
 variation of response result in my naming an auditory 
 impression as when, in reply to a certain question, I speak 
 or write: "This is a waltz," without hnving in the least 
 had recourse to counting up to three, the distinguishing 
 number of that rhythm. 
 
 Our example of the gardener illustrated the acquisition 
 of the habit of triplet activity. We have also referred to 
 the existence of the habit of doublet activity. If we 
 are permitted to take our example again from agricultural 
 
194 HUMAN BEHAVIOR 
 
 work — it is still easier to find examples in the shop 
 or factory — ^we may imagine a gardener who has planted 
 a single line of plants and has now to compress the 
 soil at the successive spots. Suppose he does this 
 with his left foot. He must then make before each 
 compressing movement of the left leg one preparatory 
 movement of the right leg (or three if he chooses, 
 one of the right, one of the left, and one again of the right 
 leg) in order to assume the proper position to the right 
 of each plant. We thus have one weaker muscular 
 innervation between each two of the main innerva- 
 tions, a group activity composed of two motions, one 
 strong, one weak. 
 
 Our most common rhythmical perceptions are of the 
 doublet and triplet kind. There are also familiar rhythms 
 composed of four, six, eight, twelve, and sixteen units. 
 These are simply compounds of doublets and triplets. 
 For example, a group of twelve is a doublet of six, and 
 this group of six again is a doublet of three; or the 
 group of twelve may be a triplet of four, etc. We are very 
 familiar with such groups in dancing. It is a common, but 
 on that account no more correct, belief that people dance 
 because of an inherited " sense of rhythm, " a special instinct 
 which impels them to perform group movements of two, 
 three, four, six, eight, etc., elements. The truth seems to 
 be rather that we have a sense of rhythm because we dance 
 than the reverse, that we dance because of an instinct 
 of rhythm. Dancing is a group activity of our muscles 
 which is easily learned because of its relative simplicity 
 and its adaptation to the human anatomy. Since this 
 activity is so easily learned and performed, it is used for 
 sport, for play. Thus it becomes one of the sources of the 
 general habits of rhythm. 
 All common rhythms are reducible to doublets and trip- 
 
NOT INSTINCT, BUT HABIT 195 
 
 lets by division with two or three. There is nothing mys- 
 terious in the fact that groups of five, seven, or nine units 
 are not common rhythms. This is merely the conse- 
 quence of the fact that systematic labor or play does not 
 readily employ the human body with its two hands and 
 two feet in such a way as to lead to the acquisition of a 
 habit of combining, say, four different weak, preparatory 
 motions with a strong, fifth motion into a single group. 
 If one invents a certain playful activity of five or seven 
 elementary motions — one of them being strong, the rest 
 serving as different preparatory movements — and exercises 
 it until it becomes perfectly habitual, he acquires a rhyth- 
 mical perception of a quintuplet or of a septuplet which 
 appears no less natural and quasi-inborn than the rhyth- 
 mical perceptions of a triplet and doublet. Such has been 
 the present writer's personal experience. 
 
 Let us understand, then, that the so-called "percep- 
 tion" as well as the execution of rhythm, as a nervous 
 function, is simply successive group activity, involving 
 in each case the successive innervation of a definite num- 
 ber of different muscle sets. One reason why in the text- 
 books rhythm is so shrouded in mystery is clearly this, 
 that it is usually thought of as an instinctive nervous 
 reaction to number instead of being regarded as a (numeri- 
 cal) habitual group of successive sensori-motor activities 
 unified by their leading to a single end. Number enters 
 into such a function really only as a conception of the 
 scientist who describes it, not of him in whom the func- 
 tion occurs. 
 
FIFTEENTH LECTURE 
 
 Imitation. Auditory and visual imitation at different 
 stages of life. Kinesthetic imitation not inherited; of little 
 importance even when acquired. Emotional reactions. 
 Either contraction or relaxation prevailing in either organic 
 or skeletal muscles. Emotional reactions inherited. Emo- 
 tional reactions either of direct or of indirect ■ value, for 
 example, as signals for social interaction; especially in 
 primitive man and in animals. Civilized man, deriving 
 little benefit from his emotional reactions, practically unable 
 to control them by experience. 
 
 WHILE discussing speech we had to men- 
 tion the fact that certain activities of 
 the speech organs occurring in response 
 to auditory stimuli have the pecuHarity 
 of bringing about sounds very much Uke those which 
 served as stimuli in the first place. In any such case 
 where the motor response repeats the stimulation we speak 
 of imitation. " Imitation, " therefore, is not the name of a 
 force, but of a mode of reaction. Here the subject has 
 imitated the sound heard . But imitation, of course, is not 
 restricted to auditory stimulation. In auditory stimula- 
 tion it makes its first appearance as one of the great 
 factors of human education, — during the second year of 
 life. Visual imitation attains its maximum of importance 
 about a year later. While auditory imitation plays a 
 part of ever decreasing significance as life advances, 
 
 196 
 
AUDITORY AND VISUAL IMITATION 197 
 
 visual imitation determines our actions in all stages of 
 life. The infant imitates the speech sounds which are 
 produced by children and older people in his presence. 
 The eight or ten year old child has almost ceased to 
 imitate the speech of others. How slight the tendency 
 to imitate speech has become in grown people, all those 
 know from experience, to their regret, who have ever 
 learned or taught a foreign language. Grown people 
 will do a hundred other things rather than repeat over 
 and over again a phrase just heard, as small children do, 
 — the secret of children's rapid success. It is quite 
 natural, however, that auditory imitation is so strong 
 during the second and the following few years and so weak 
 later. The chUd must learn to speak early in life, and he 
 learns by imitation. When this is once accomplished, 
 imitation is no longer necessary. Aside from learning, 
 auditory imitation has no value of its own. With visual 
 imitation the case is quite different. It is true that a 
 good many skillful movements may be and are learned 
 by visual imitation; however, the imitative act itself, aside 
 from all learning, has an enormous biological value all 
 through life, in old age no less than in middle age and 
 infancy. When we see a crowd gather on the street, we 
 immediately run to the spot ourselves, — ^not because we 
 still have to learn how to run to a point seen, but because 
 it is of immense value for our social life to do at any time 
 what we see other people do, exceptions notwithstanding. 
 There can hardly be any doubt that auditory imitation 
 is largely the result of inheritance. All the elementary 
 sounds are imitated because the necessary paths of small 
 resistance are inherited. The apes, having practically 
 the same vocal organs, do not, in our zoological gardens, 
 acquire human speech, obviously because this factor of 
 nervous inheritance is lacking. One might argue that 
 
198 HUMAN BEHAVIOR 
 
 the existence of the so-called "baby talk" demonstrates 
 the importance of experience in auditory imitation. It 
 is true that baby talk is the result of the child's experience, 
 not of his inheritance. But baby talk is not acquired by 
 imitation on the child's part. The infant babbles in 
 response to all kinds of stimulations, auditory or not 
 auditory. The sounds thus produced are imitated by the 
 parents and used by them in the baby's presence with 
 reference to particular situations. The child then learns, 
 by this experience, the meaning created by his parents 
 for these sounds, which are in the main reduplications; 
 that is, he learns to use these simple words in these particu- 
 lar situations, — ^by imitation on the part of his parents. 
 Thus he acquires the talk peculiar to the nursery. It is 
 clear, then, that the existence of baby talk is no argument 
 in favor of any importance of experience in auditory 
 imitation. Inheritance brings about adequately the 
 imitation of all elementary speech sounds. To combine 
 these elements into complicated groups composed of 
 many successive elementary sounds, requires indeed 
 both experience and reflex imitation on the child's part, 
 — we have studied the process in a previous lecture. The 
 imitation of the elementary sounds, however, is regulated 
 by inherited reflexes. 
 
 In visual imitation, on the other hand, there seems to 
 be little dependence on special inherited reflexes. Even 
 the simplest movements which are executed by visual 
 imitation seem to depend on experience. We have dis- 
 cussed in an earlier chapter the simplest reflex movements 
 of the hands and feet. There is in them no imitation of 
 any movement seen. Only when the child begins to 
 make new movements by experience, can imitation be 
 observed. And even in these earliest movements learned 
 by experience there is hardly any imitation. The child 
 
EXPERIENCE IN IMITATION 199 
 
 learns, for example, the upward movement of his hands 
 which we make in order to take a thing from a shelf above, 
 — but not by imitation, as we have found. He learns to 
 creep, to stand, to walk, but not by imitation. It is only 
 after he has acquired these skillful movements of his 
 hands and feet, that visual imitation becomes conspicuous. 
 Now we observe that the little child, barely able to walk, 
 joins us when we are standing with our back against the 
 wall and takes his place at our side, leaning his back 
 likewise against the wall. Now he puts his hat on when 
 we put our hat on. Now he places an open book on the 
 music stand of the piano before he strikes the keys with 
 his little fingers, because he has seen us open our music 
 before striking the keys with our fingers. Visual imita- 
 tion, therefore, depends altogether, or practically alto- 
 gether, on experience; there is scarcely any inherited visual 
 imitation. 
 
 We have discussed auditory imitation and visual 
 imitation. Shall we add, as a third important class, 
 kinesthetic imitation? If we apply the term imitation 
 to every sensori-motor process which brings about directly 
 a repetition of its stimulation, we might speak also of 
 kinesthetic imitation. But whoever would restrict the 
 term to cases where the stimulation results from an 
 extra-corporeal (visible or audible) phenomenon, should, 
 not use this phrase, for kinesthetic stimuli are not external, 
 but physiological phenomena. He might then, instead 
 of adding a third class of imitation, speak of circular 
 sensori-motor processes. In an earlier chapter we have 
 already had occasion to mention that circular reactions 
 are of much importance in the acquisition of skillful 
 movements because they hasten, through repetition of 
 the same nervous activity, the establishment of paths of 
 low resistance. The question which interests us here is 
 
200 HUMAN BEHAVIOR 
 
 this: Is kinesthetic imitation, if we are permitted to 
 apply the term, largely inherited? 
 
 One might think that the inheritance of kinesthetic 
 imitation, of the occurrence of the motor response in the 
 very muscles in which the sensory excitation occurred, 
 is self-evident from the nature of the case, for two reasons.- 
 Did we not state the great importance of kinesthetic 
 excitation for habits of temporally complex, that is, of 
 serial, reactions? Secondly, should not nervous connec- 
 tions of low resistance be inherited between sensory 
 points and motor points located side by side in the body, 
 when many such connections are inherited between widely 
 separated sensory points and motor points? Both these 
 are false arguments. As to the latter, it is clear enough 
 that in the lowest organisms, having no nervous system, 
 the motor response occurs primarily at the point itself 
 which has received the stimulation. It does not foUow, 
 however, that after differentiation of the tissues the sensory 
 and motor points, because they are originally identical, 
 must be closely connected by nervous paths. It is true 
 that in the peripheral parts of the body the sensory and 
 motor neurons of the same region usually run parallel in 
 big bundles, the so-called nerves. But within the central 
 nervous system they separate; and they are connected 
 to form short reflex arches only where the functional needs 
 of the organism unite them, as in the case of all other 
 sensory and motor neurons. The former argument has 
 no greater strength. Not everything of great importance 
 is necessarily inherited. Further, in so far as kinesthetic 
 excitation plays a part in the execution of habitual serial 
 reactions, we have no imitation, for each kinesthetic 
 stimulation in a serial reaction brings about a contraction 
 of a new set of muscles, and a different Idnesthetic stimu- 
 lation. On the other hand, where we have repetition of 
 
NO KINESTHETIC IMITATION 201 
 
 a truly inherited sensori-motor process, we have imitation, 
 but it is not kinesthetic. For example, when a child 
 learns to pile up blocks, (compare Lectures 11 and 12) 
 there is a circular reaction, — imitation in so far as the 
 child imitates a model (a block standing) by creating a 
 thing like it ( a block or pile of blocks standing) ; but the 
 stimulation of the circular process is visual, not kinesthetic. 
 Far from admitting, then, that kinesthetic imitation is 
 largely inherited, we are led to deny almost its very 
 existence, even as acquired by experience. Indeed, if it 
 were inherited, it would greatly retard the acquisition of 
 useful habits of reaction. For example, the child, instead 
 of learning how to build a house of blocks, would continue, 
 through the influence of such imitation, to move his hand 
 up and down in the same manner without being influenced 
 by the fact that blocks other than the one in his hand 
 are lying about. Kinesthetic imitation, if inherited, would 
 reduce man's biological significance to something like 
 that of mechanical toys in a child's world, capable 
 only of performing the same jump in endless repetition. 
 There is little probability, then, that such a function 
 should be acquired during life. Kinesthetic excitation as 
 a biological factor seems to be confined to serial motor 
 activity, consisting in a succession of different acts; there, 
 indeed, kinesthetic excitation is indispensable. 
 
 While the larger part of the motor activity of an animal 
 consists of reactions upon the objects of the environment, 
 brings about, indeed, in the case of visual or auditory 
 imitation, a duplication of an environmental phenomenon, 
 there are also motor activities which do not seem to affect 
 the objects of the environment at all, and directly, most 
 certainly, do not affect them; which are confined to the 
 inner world of the organism. Motor responses of this 
 class are often called emotional reactions. There is an 
 
202 HUMAN BEHAVIOR 
 
 enormous literature debating the question what the 
 emotions are aside from these internal reactions of the 
 organism, what they are as purely introspective pheno- 
 mena. Let us be satisfied with the simple statement 
 that in most, if not all, conditions of animal life which are 
 called emotional, internal reactions occur; and let us, 
 without entering into a discussion of introspective "emo- 
 tions," give a broad classification of them and a brief 
 discussion of their biological significance. 
 
 In order to understand these internal reactions properly, 
 we have to discuss not only muscular contraction, but also 
 muscular relaxation, and to regard the latter as a factor 
 as positive as the former. Lacking space, we cannot 
 here, and need not for our present purpose, enter into a 
 discussion of the physiological mechanism by which relaxa- 
 tion as well as contraction is brought about. Let us 
 regard either simply as the motor response to a proper 
 excitation of sensory points. We have then at once two 
 large classes of internal reactions, according as relaxation 
 or contraction of the internal organs dominates, — we say 
 "dominates" as it is entirely possible that relaxation of 
 some organs be accompanied by contraction in others. 
 A subdivision of each of these classes is found by reference 
 to the two classes of muscles in our body, the "organic" 
 muscles which perform the mechanical work of our internal 
 organs, and the skeletal muscles which control the position 
 of the members of the body, relative to each other, and 
 their motion. The important fact that in the large 
 majority of all cases of reaction in the organic muscles 
 reactions in the skeletal muscles occur simultaneously, 
 is comprehensible enough. In general, whenever the 
 skeletal muscles tend more than ordinarily to relax, the 
 motion of the body will be unusually weak; and whenever 
 the skeletal muscles tend more than ordinarily to contract. 
 
EMOTIONAL REACTIONS 203 
 
 the motion of the body will be unusually vigorous. Thus 
 we should obtain among those motor responses with which 
 we are at present concerned, four main classes: (1) Relaxa- 
 tion of organic muscles combined with vigorous motion. 
 (2) Contraction of organic muscles combined with vigorous 
 motion. (3) Relaxation of organic muscles combined 
 with weak motion. (4) Contraction of organic muscles 
 combined with weak motion. It is to be understood, 
 however, that in no case do we include all the organic 
 muscles or all the possible motion of the members of the 
 body. Let us see, now, to what extent this classification 
 aids us in characterizing familiar types of emotional 
 reaction in animals and in man. 
 
 Unusual contraction or relaxation of the organic muscles 
 becomes apparent chiefly in the blood vessels, the heart, 
 the stomach, the intestine, the bladder, and the skin. 
 If the ring-shaped muscles of the smaller blood vessels 
 relax, the vessels take up a larger amount of blood forced 
 into them by the heart. The skin, containing innumerable 
 small blood vessels, then looks red. Our first class, there- 
 fore, is illustrated by a person who looks red, whose skin 
 is warm owing to the presence of a large quantity of 
 warm blood, and whose motion is very vigorous. We 
 recognize in him what we commonly call the emotion of 
 joy or the emotion of anger. Whether we apply the one 
 or the other name, depends on the special situation, which 
 may call forth — so far as the skeletal muscles are con- 
 cerned — either movements of dancing, shouting, clapping 
 the hands, and the like, or movements of attack. That 
 the sensory excitation caused by the situation affects not 
 only the skeletal muscles, but also such muscles as those 
 in the walls of the blood vessels, is, by the way, a good 
 illustration of the fact which we have previously emphasiz- 
 ed, namely, that our nervous system is one, in spite of the 
 
204 HUMAN BEHAVIOR 
 
 special physiological and anatomical names applied for 
 various reasons to its parts. This unity of the nervous 
 system can also be demonstrated by such a simple experi- 
 ment as this. Address a person suddenly with the ques- 
 tion, "Why do you blush?" The response will consist, 
 of course, in words spoken; but in addition, frequently, 
 the person will be observed to blush, although ordinarily 
 stimulation of the auditory organ is not capable of causing 
 a relaxation of the muscles in the blood vessels of the face. 
 The situation in question, in which we find that person 
 who looks red, etc., probably causes activities of the skel- 
 etal muscles which are of a direct objective purpose, for 
 example, running. But it causes also activities of the 
 skeletal muscles which are of no direct purpose, for 
 example, the tension of the facial muscles, the grinning, 
 of a person in joy or rage, often represented by carica- 
 tures like Figure 50. Since all the muscular functions 
 with which we are concerned at present, are inherited, 
 not acquired by experience, we may ask how we can 
 understand the evolution of such seemingly useless reflexes. 
 That in anger, where an ■ animal attacks another animal, 
 or in joy, where an animal applies to good use an object 
 which he has succeeded in. obtaining, vigorous motion is 
 biologically of great value, is self-evident. But of what 
 use is grinning? 
 
 Fig. 50 — Tension of the facial muscles in joy or anger. 
 
 One answer to the question is this. In anger, grinning 
 may mean simply getting ready to bite, for the mouth is 
 
JOY AND ANGER 205 
 
 an important weapon of attack of animals and of primitive 
 man; and in joy, since the most important article applied 
 to good use is an article of food, grinning may mean simply 
 getting ready to bite off and chew. But it may have still 
 another biological meaning. It may be of indirect value 
 by helping to bring about social interaction — ^positive or 
 negative, friendly or hostile — through rendering the 
 situation quickly understood by other members of the 
 animal species. 
 
 Let us give further examples to illustrate the in- 
 direct, purely social, value of movements or attitudes. 
 In an infant the stimulation of hunger may cause reflex 
 movements of the hands upwards, with the result that 
 the fingers get into the mouth and are sucked, or that the 
 finger nails, when the hands are withdrawn, scratch the 
 face. Although these results are directly without any 
 value to the child, they are indirectly of the very greatest 
 value, for their sight stimulates the parents to definite 
 activities, for instance, to providing the necessary food 
 for the baby. A mother describing these reactions would 
 surely say that the baby is "so hungry that he tries to 
 put his hands into his mouth," or "so angry at the delay of 
 his dinner that he scratches himself. " This social value is 
 not the least significant explanation of the evolution of 
 reflexes which are directly of little value. There is still 
 left to explain why in situations of joy or anger the blood 
 should rush into the skin. Perhaps this is merely a symp- 
 tom of the unusually strong circulation of the blood through 
 the whole body, useful for continued activity of the 
 muscles which, for physiological reasons, would soon be 
 incapacitated for work without being washed out con- 
 stantly by the blood current. But the redness of the 
 skin, just as the tension of the facial muscles, the grinning, 
 has also an indirect value of much importance, a value for 
 social interaction. A red-faced man in a given situation 
 
206 HUMAN BEHAVIOR 
 
 causes the situation to impress other men in a way by no 
 means identical with the way in which they are aflFected 
 by the situation whUe the man in its center looks pale. 
 
 The second class of these peculiar motor responses was 
 distinguished by contraction of organic muscles combined 
 with vigorous motion. We recognize the symptoms of what 
 is called the emotion of fear. That the stomach, the 
 intestine, the bladder, and other internal organs contract 
 in a fearful situation, that the heart beats with unusual 
 force, is a familiar fact. Contraction of the smaller blood 
 vessels causes the blood to disappear from the skin and 
 the latter to become pale. Contraction of the minute 
 muscle fibers distributed all through the skin, gives it 
 the appearance ordinarily called "goose flesh"; and where 
 the skin is hairy, this contraction causes the hair to "stand 
 on end." The skin, having lost its blood,. cools off, and 
 this cooling in turn calls forth reflexly shivering, the 
 ordinary physiological response to cooling of the skin. 
 The vigorous motion, adapted to the particular situation, 
 shows itself in the individual's running faster than he is 
 ordinarily able to. Vigorous motion, however, is only 
 one external symptom of an extraordinary tendency to 
 contract. Some degrees further, and th's tendency results 
 in a cataleptic state, a continuous contraction of all 
 muscles, making all motion impossible. One person or 
 animal responds to a dangerous situation by running, 
 another is "turned into stone." 
 
 If we now ask of what biological value these inherited 
 reactions are, we find the answer very readily so far as 
 the extraordinary tendency of the skeletal muscles to 
 contract in response to a dangerous situation is concerned. 
 The faster the animal runs away from the dangerous 
 situation, the safer it is. On the other hand, if the mus- 
 cular contraction progresses up to the cataleptic, perfectly 
 
FEAR 207 
 
 motionless, state of the body, the animal is again relatively 
 safe in case the danger comes from another animal being 
 in the neighborhood, owing to the fact that a motionless 
 body is less readily perceived by the eye — not to speak 
 at all of the ear — than a moving body. Many species of 
 birds and small mammals can be observed to assume this 
 motionless attitude when surprised by a man or a hostile 
 animal, especially when the dangerous being is not yet so 
 near that the exposed animal is within direct reach. Many 
 a hunted animal escapes the hunter by this mode of reflex 
 reaction. 
 
 Why the organic muscles should tend to contract, 
 however, is less clear. Apparently, their contraction in a 
 dangerous situation can be of no direct value. A certain 
 amount of indirect value, on the other hand, with respect 
 to social interaction, is obvious, especially when the ex- 
 posed animal is in the cataleptic state. The skin having 
 lost its blood, the exposed animal resembles more nearly 
 a dead animal; and this resemblance may save it. For 
 example, it is reported that certain bears will leave a 
 seemingly dead man's body unmolested; not to reiterate 
 the anecdotes of hunters who gave no attention to an 
 animal whose possession they felt sure of, because it was 
 already dead, but who discovered suddenly that it had run 
 away. Even an animal being chased by another may 
 appear more formidable than it really is, on account of its 
 fur or feathers standing on end, or may retard the enemy 
 by the ejection of disgusting substances. 
 
 Our third class of responses was distinguished by relaxa- 
 tion .of organic muscles combined with weak motion. 
 This is of all the four classes the least important one. We 
 experience it after having eaten a hearty dinner, — but this 
 is not everyone 's habitual occupation. Of vast importance 
 is the fourth class, distinguished by contraction of organic 
 
208 HUMAN BEHAVIOR 
 
 muscles combined with weak motion. It is exactly the 
 opposite of the first class (joy) and is, indeed, the reaction 
 to any kind of disappointment, — ^what we most commonly 
 call the emotion of sorrow. We can at once derive the 
 symptoms and comprehend the biological value of this 
 reaction if we recall that in animal life and in the life 
 of primitive man the most ordinary kind of disappoint- 
 ment consists in the want of food. Imagine a winter 
 month: every article which might serve as food covered 
 by snow and impossible to find, for weeks or longer, until 
 the weather changes. An animal which, under these 
 circumstances, would continue to run about for food, 
 would soon fall dead from exhaustion. However adverse 
 the situation, the body can survive living on the sub- 
 stances stored away in its own tissues, if it only consumes 
 this limited supply economically. For this the first 
 requirement is that all muscular activity be reduced to a 
 minimum. Thus we understand why the nervous system, 
 in a disappointing situation, tends to leave the skeletal 
 muscles in a state of relaxation. A person in great sorrow 
 is so far from being master of his skeletal muscles that 
 he drops as if he were completely paralyzed, like Romeo 
 in Friar Laurence 's cell : 
 
 "Wert thou as young as I, Juhet thy love. 
 
 An hour but married, Tybalt murdered. 
 
 Doting like me, and like me banished. 
 
 Then mightst thou speak, then mightst thou tear thy 
 hair. 
 
 And fall upon the ground,' as I do now, 
 
 Taking the measure of an unmade grave." 
 A disappointed person looks like Figure 51 (the opposite 
 of Figure 50), since the relaxation of the facial muscles 
 causes the angles of the mouth to be pulled down by the 
 weight of the lower jaw. 
 
DISAPPOINTMENT 209 
 
 Why should the nervous system, in a disappointing 
 situation, tend to cause contraction of the orgdnic muscles? 
 Recall the animal just spoken of, disappointed in its food 
 supply. If it does not exercise its muscles, little or no 
 heat is produced, for the skeletal muscles are, physiologi- 
 cally, the very furnaces of the body. If little heat is 
 produced, the loss of heat must be safeguarded against. 
 Thus the biological value of the contraction of the muscles 
 in the walls of the blood vessels becomes evident. The 
 
 Fig. 51 — -Relaxation of facial muscles in disappointment. 
 
 contraction of the vessels prevents the blood from circu- 
 lating much in the periphery of the body where cooling 
 mainly takes place. The coohng by the conduction of 
 heat through the tissues covering the body is little to be 
 feared as long as the warm blood is kept in the inner parts 
 of the body and prevented from circulating through the 
 periphery. The actual cooling of the skin, exciting the 
 sensory points of the skin, causes the reflex and habitual 
 response of the animal's seeking shelter, again reducing 
 the loss of heat, of physiological energy. Thus con- 
 traction of the organic muscles keeps the animal alive 
 until a change of the external conditions enables it to 
 resume its ordinary manner of life. 
 
 Less plain than these reflexes seems the fact that 
 often a disappointed person weeps. From our 
 statements thus far one should rather expect a person in 
 joy to weep, provided we derive weeping from an unusual 
 
210 HUMAN BEHAVIOR 
 
 blood pressure in the lacrimal glands, an unusual fulness 
 of the blood vessels owing to the relaxation of the organic 
 muscles. Indeed, people weep when joy reaches a high 
 degree. That people weep in disappointment becomes 
 plain when we recall the generally accepted notion that 
 weeping gives relief from excessive sorrow. Only we 
 should rather say: when the nervous system, through 
 normal exhaustion, commences to respond to the disap- 
 pointing situation less excessively, then weeping occurs. 
 The tears here are actually not a cause, but an effect of 
 relief. The organic muscles, excessively contracted for 
 some time, at the moment when exhaustion of the nervous 
 system commences, relax completely and the blood 
 pressure in the lacrimal glands suddenly rises far beyond 
 the normal. 
 
 All these responses of the organic muscles, with or 
 without simultaneous activities of the skeletal muscles, 
 of which we have discussed here only those which can be 
 most easily classified, are the result of nervous connections 
 between certain sensory and certain motor points and 
 group formation among these connections, inherited by 
 each iudividual of the species. The extent to which they 
 can be modified by experience is slight, almost zero. 
 This is, perhaps, to be regretted, since in the life of modern 
 civilized man they have largely lost the biological useful- 
 ness attributable to them under primitive conditions of 
 social life. Nevertheless, however advanced the present 
 evolution of man's nervous system, in his inability to 
 control these responses by experience, man practically 
 shares the fate of the animals. 
 
SIXTEENTH LECTURE 
 
 The speech function serving as a generalizing function. 
 Abstraction a kind of generalization. Advantages of the 
 written language in generalization for individual use and for 
 communication. Science the sum total of all generali- 
 zations which mankind has tested and collected. Written 
 symbols becoming a class of (artificial) objects to which 
 man learns to respond as formerly he learned to respond 
 alone to the objects of nature. Arithmetic. The general- 
 ization "force" in mechanics: a creation of man like all 
 other generalizations. Advantage of handling words 
 rather than things. Danger of speculation. 
 
 WE have already discussed speech, but 
 only as an instance of temporally complex 
 sensori-motor activity. We shall now 
 discuss the speech function as that ner- 
 vous function upon which the distinguishing features of 
 human as compared with animal life are based. Science 
 is justly regarded as the chief characteristic of modern 
 human life. Since generalization and abstraction are the 
 foundations of science, we shall have to show by concrete 
 examples what nervous activities are meant when we speak 
 of generalization and abstraction. 
 
 (1) A child, in the presence of such things as bread, fruit, 
 edible roots, meat, impressing his eye, (So, Sj, S„ S^ in 
 Figure 52) learns to pronounce the word "food" (M^in 
 Figure 52). The nervous function is simply a variation 
 of response. A new response takes the place of those 
 
 211 
 
212 
 
 HUMAN BEHAVIOR 
 
 which at first succeeded these stimuli and which are indi- 
 cated in the figure by the dotted lines leading to motor 
 points without lettering. Instead of handling the things 
 
 Oa Ob Oc Od Ow I iw 
 Fig. 52 — Naming takes the place of handling. 
 
 in accordance with his previous instincts and habits, he 
 speaks the word which is used by older people as the com- 
 mon name of these things. (2) On the other hand, when 
 the child's ear is struck by the sound of the word "food" 
 (Sj„ in Figure 53), he learns to respond, if otherwise than 
 by saying "food" {M^ in' Figure 53), exclusively by 
 
 
 
 
 n^feh 
 
 w 
 
 
 )wM 
 
 < 
 
 f^ 
 
 > 
 
 Sw Mw Me Mf Mg rih 
 
 Fig. 53 — ^Handling takes the place of talking. 
 
 such muscular activities as are adapted to the preparation 
 for eating of bread, fruit, edible roots, meat, and similar 
 articles and to their consumption by the mouth (Af „ Mf, 
 Mg, Mj^. This is also simply a variation of response. 
 The word heard — in any of the nervous functions bringing 
 
GENERALIZATION 213 
 
 about the responses of handling these things — takes the 
 place of the things seen, indicated in the figure by'the dotted 
 lines starting from sensory points without lettering. From 
 now on, whenever the word has struck the ear, the muscles 
 which co-operate in properly handling these things get 
 ready to work rather than other muscles to handle other 
 things which also impress the eye at the time. The ner- 
 vous paths serving the latter impressions are at a disad- 
 vantage in not being "cleared for action" by the sound 
 of the word exciting the ear. 
 
 Under (1) we mentioned the speech movement enoun- 
 cing the word food, under (2) the speech sound of the word 
 food striking the ear. It is plain, then, since the sound of 
 the word strikes also the own ear of the person enouncing 
 it, that the motor response of speaking and the resulting 
 excitation of the ear becomes a double link inserted between 
 the mere sight of the article of food and its proper handling. 
 
 Sight of thing ^handling 
 
 Sight of thing — ^-speaking — hsound of word ^handling 
 
 This insertion of a new link into the chain of functions 
 seems an unnecessary, uneconomical complication due to 
 the individual's experience, so that experience in this case 
 would be harmful rather than useful. It would indeed 
 be an undesirable superfluity of nervous and muscular 
 activity, were it not for the fact that the inserted link is 
 practically the same however different the visual appear- 
 ances of the articles of food — ^they are all called by this name 
 — and however different the ways of handling and preparing 
 them before putting them into the mouth — ^they are all 
 called out by the same word food. The insertion between 
 two nervous processes— let us call them A and B — of 
 such a link of activity, always identical in spite of untold 
 variations of A and of B, is exactly what we call, in another 
 
214 HUMAN BEHAVIOR 
 
 terminology, in that of logic, generalization. All the 
 visual appearances of things eatable, on the one hand, and 
 all the motor responses of eating (including therein the 
 necessary preparations), on the other, are held together by, 
 are, so to speak, under the command of, a single, though 
 originally not quite simple, biological function of the speech 
 reaction class. We understand immediately why in the 
 nervous life of animals there can be little, if any, generali- 
 zation since animals do not possess speech. 
 
 Let us imagine another instance. I, being still an inex- 
 perienced child, am occupying a definite position. Another 
 being, animal or human, is occupying another position, 
 more or less distant from mine. I have a solid article, no 
 matter of what kind, in my hand, or between my teeth, 
 or in a pocket, or beneath my feet. A certain stimulation 
 — easily imaginable and therefore needing no definition — 
 causes me to perform such a motion that the article is 
 transferred from its place near me to a new place near the 
 other being. While my own motion, as well as the 
 article changing place, impresses my eye, or directly after 
 this impression, the word "give" happens to be spoken 
 in my environment. I imitate the sound and thus learn 
 to respond to the situation of an article being transferred 
 by my own motion from me to anotljer being, by saying 
 "give." But I also learn to respond to the auditory 
 impression "give" by such a motion transferring an 
 article from me to another being. Here, the sum of the 
 motor excitation "give" and the sensory excitation "give" 
 (briefly speaking the speech function "give") is — ^not, as in 
 the former case of "food," a link inserted between the plain 
 sensory impression of a thing and the motor response of 
 properly handling it — but a seemingly superfluous repre- 
 sentative of that whole nervous process which has as its 
 issue the motion transferring an article. 
 
ABSTRACTION 215 
 
 Transferring Y-transferring continued 
 
 Traniferring— — ^saying "give" ysound of "give" ^-transferring continued 
 
 This representative, accompanying its constituent, would 
 indeed be an unnecessary complication of nervous activity, 
 were it not for the fact that the additional function is 
 practically the same however diflferent the manner of 
 motion transferring the article in question: by stretching 
 out the hand, throwing, kicking, dropping from an elevated 
 place, rolling down a hill side, not to mention sending 
 it by a messenger, by mail, or by any other device of 
 modern transportation. This establishment of a definite 
 function identical in spite of untold variations of the sen- 
 sori-motor activities which it represents — ^they are all called 
 giving — is obviously also a generahzation. Or, in the termi- 
 nology of logic, it is an ahstraction. Abstraction, then, 
 is a special case of generalization — ^generalization, not with 
 reference to objects, but with reference to relations (spatial 
 transference, in the instance discussed). 
 
 The difference between the biological functions in ordin- 
 ary generalization and in this special kind of generalization, 
 abstraction, might be described thus. In ordinary general- 
 ization the .object handled is of main significance.! The 
 manner of handling it is of importance only in so far as 
 the object is distinguished from objects of a different class 
 by the proper mode of handling it, — ^for example, "food" 
 is an object to be eaten by the responsive animal. In 
 ahstraction the mode of handling is of main significance. 
 The object itself is important exclusively in so far as, 
 if there were no object whatsoever, no handling of it 
 could have occurred. 
 
 The purpose of our present discussion is not to give a 
 lesson in logic. Our intention is to show briefly, but 
 conclusively, that practically no generalization or abstrac- 
 tion is possible without speech, and to make clear by con- 
 crete examples what is meant biologically by such terms 
 
216 HUMAN BEHAVIOR 
 
 as generalization and abstraction. In order to make the 
 significance of the speech function for the nervous activity 
 of the individual living body — over and above the social 
 significance of speech as a mere system of signals for co- 
 operation in actual labor — still clearer, let us make a third 
 application to a concrete case of human life. 
 
 A child, having had both the speech experiences above 
 described of "food" and of "give," happens to meet 
 another person, say, a beggar, who addresses him with the 
 words "food, give." The natural consequence is, first, 
 that the child looks about until his eyes are arrested by an 
 article belonging to the class of "food, "say, a piece of 
 bread. Then he approaches the bread and would now 
 respond to its sight simply by the most firmly established 
 habit, by taking and eating it, had his ears not been 
 stimulated by the sound of the word "give" too. So he 
 responds to the total stimulation of sound and sight by 
 giving the piece of bread to the other person. Similar 
 occurrences take place quite frequently in the child's life; 
 but the words heard are not always only food and give. 
 Now and then the address will be "food, give, hungry." 
 Thus the child learns, by what we have called a variation of 
 response, to react to the word "hungry" in the same way 
 as to the sentence (if these two words may be called a sen- 
 tence) "food, give. " He learns to react to the word hungry 
 by looking about for edible things, taking hold of them, and 
 transferring them to the other person. What a wealth 
 of possible actions is thus placed under the control of the 
 single word "hungry"! The fully experienced human 
 being, hearing this word, looks about until an edible 
 thing strikes his eyes. But if his eyes do not perceive 
 anything eatable, other activities follow. He may put 
 his hands into his pockets to search for food. He may walk 
 home in order to find food there. He may open 
 
SIGNIFICANCE OF ABSTRACTION 217 
 
 his chest or cabinet, take money from it, and go to the store 
 where food is for sale. Or he may go out to his fields, 
 cut his wheat, and store it away under the roof of a barn in 
 order to be able to give food at a later time when the sound 
 hungry may strike his ear again. Not having any wheat 
 mature on his fields, he may take out his horses and imple- 
 ments and plow the ground on which wheat is only to be 
 sown. He may attend, as a student, an agricultural college 
 where he learns how to grow wheat most successfully on 
 his farm. He may vote in favor of his government spend- 
 ing money for the support of such a college. Further think 
 of the innumerable possible activities which make pro- 
 vision for the transportation of the food from place to 
 place, from the producer to the consumer! To enum- 
 erate even those activities which are more directly 
 controlled by the word hungry, would require a volume. 
 Of the activities which we have mentioned, some are 
 rather remotely dependent on the abstraction "hungry". 
 The more remotely they are dependent on it, the more 
 numerous, of course, are the other abstractions on which 
 they are also — ^more or less directly — dependent, so that, 
 then, the actual motor response becomes more and more 
 the resultant of many components, of all the activities 
 controlled by all the abstractions. 
 
 We have thus far spoken of the word "hungry" only 
 as denoting a sound, stimulating the ear and controlling 
 by means of the nervous paths diverging from the ear a 
 vast number of highly complicated motor responses. We 
 said above, that the word hungry was often heard together 
 with the words food and give. At such a time it must 
 have been imitated by the chUd in question. Thus the 
 pronunciation of the word hungry has become one of 
 the possible motor responses to the total situation. It is 
 plain, however, that the same word, hungry, is also heard 
 
218 HUMAN BEHAVIOR 
 
 in other situations, especially frequently at the time when 
 the subject together with the other members of the family 
 takes one of his regular daily meals. At that time the 
 sensory points of the stomach are likely to be excited 
 by the physiological condition which is called hunger. Ac- 
 cordingly, the subject learns to say "hungry" in response 
 to the sensory excitation of hunger. Whenever he res- 
 ponds thus, he produces the sound of the word, and this 
 sound impresses his ear. Most naturally, then, the total 
 (motor and subsequently sensory) speech function of the • 
 word "hungry" becomes an intermediate link between 
 the sensory excitation of hunger and that vast number of 
 responses mentioned above, all serving, with greater or 
 lesser directness, to dispel hunger not only in others but 
 in himself. 
 
 What, then, is the value of abstractions to man.'' They 
 serve to make ready, instead of the simple reflex or in- 
 stinct corresponding to the stimulation, an enormous num- 
 ber of complex motor responses among which a selection is 
 made by the other sensory factors of the situation and the 
 motor tendencies of the abstractions belonging to them. 
 This complex nervous activity, which is the distinguishing 
 feature of man's life as compared with that of animals, 
 is made possible by the acquisition of speech. 
 
 In this development, now, of generalized (abstract) 
 nervous functions an enormous step in advance is made 
 when mankind invents script. Not only can the written 
 language — except for the greater brevity of speech than of 
 writing — ^in the functions described above almost complete- 
 ly take the place of the spoken language; it can even ac- 
 complish much that is denied the spoken language. First, 
 it enhances preservation of the individual's generalizations 
 (including his abstractions) for his own later use. Secondly, 
 it remove^ practically all limits of space and time from 
 
SPEECH AND SCRIPT 219 
 
 communicating one individual's generalizations to other 
 individuals. 
 
 As to the preservation of any generalization for the 
 individual's own use, it is plain that, as long as generaliza- 
 tion is mediated only by the spoken language, it depends 
 exclusively on the properties of his own nervous system. 
 Just so long will the generalization persist, as a path of 
 low resistance, established by the speech function, leads 
 from the sensory points of, say, hunger to a common central 
 point, and another one from a common central point to 
 that vast number of responses previously indicated. But 
 such a path of low resistance can continue to exist only 
 if it is constantly re-established, so to speak; for we know 
 that a path whose resistance has been lowered by individual 
 experience tends to resume gradually its original high 
 resistance. After the individual has acquired — by a simple 
 variation of response — to the, sight of the written word the 
 same manifold possibility of responding as to the sound 
 of the same word, the time limit of preserving the generali- 
 zation depends no longer on the delicate properties of his 
 nervous system, which is so easily influenced by new 
 experiences as well as by normal and abnormal physical 
 processes like fatigue and disease, but on the physical 
 properties of the material on which he has written the 
 word. It is true that, quite recently, one has learned by 
 phonographic records to preserve even the spoken word. 
 But the limitations of this method are obvious, and, 
 whatever may be its significance for the future, in the past 
 at least the individual has had to depend for the preserva- 
 tion of his generalizations on the written word, the memo- 
 randum-book. Of course, we use here and in the follow- 
 ing the term "word" in a very wide sense, including there- 
 in all written symbols of any kind, especially those of 
 mathematics, even all kinds of geometrical drawings, and 
 
220 HUMAN BEHAVIOR 
 
 the diagrams and symbolic letters of physics, chemistry, 
 and all other sciences. 
 
 Secondly, we stated that by the substitution of the 
 written for the spoken word communication of the indivi- 
 dual's generalizations to other individuals has transgressed 
 almost all limits of space and time. As we read a letter 
 despatched from the opposite side of the globe, we learn 
 what generalizations were most powerful in the nervous 
 system of the individual who signed the letter, at the 
 time — weeks ago — when it was written. As we peruse the 
 book of an author long since deceased, we learn what 
 generalizations of his own he thought desirable to commu- 
 nicate to his contemporaries and those who were to live 
 after him. As we uncover the tombs of the Egyptian 
 kings, we learn what generalizations chiefly determined 
 their actions thousands of years ago, while they were 
 preparing for the common destiny of all individual life, 
 for death. Posterity, opening our books, may learn what 
 generalizations afiPected our nervous system so strongly 
 that, in addition to using them in our individual life, we 
 had them reproduced in the printer's oflBce. Thus all 
 mankind becomes a unit, spatially and temporally. The 
 individual's experiences are no longer useful to him and to 
 the few people of his direct environment alone. All 
 other individuals of the present and future may profit 
 by them. Thus only, mankind becomes in the world 
 of animal life that power the vastness of which nothing 
 perhaps testifies as much as the existence of poetry and 
 religion. But to the growth of this power neither poetry 
 nor religion contributes directly. Its systematic further- 
 ance is the task of science. Science is the sum total of 
 all those generalizations which the experience of mankind 
 has invented, selected, and collected as the most useful 
 for the control of the muscular response called forth by 
 sensory excitation. 
 
SCIENCE 221 
 
 The statement of the last sentence calls for further 
 elaboration since the work of a scientist, especially to 
 those not very familiar with it, seems to be altogether 
 different from that of the ordinary man, say, the farmer 
 plowing his field, — seems to belong to a category of activity 
 other than that of motor (muscular) response to sensory 
 excitation. 
 
 When, in the evolution of civilization, the writing of 
 words and other symbols of generalization has firmly 
 established itself in a sufficiently large group of men, in 
 a tribe or a nation, the written symbols become a special 
 class of important objects to which, however artificial 
 their origin, man has to learn to respond in order to be 
 successful in the struggle for life, as formerly he had to 
 learn to respond to those objects alone which have their 
 origin in nature. Moreover, young people selecting 
 a class of objects to which to devote their lives as specialists 
 may now not only select from the natural objects, but may 
 choose even this class. Their life work, then, consists 
 in responding to written symbols by writing symbols and, 
 of course, also by pronouncing them, as in oral teaching. 
 The scientist's work, aside from experimenting, that is, 
 testing the value of his generalizations by skilful appeals 
 for an answer to nature, consists in combining, on writing 
 paper, symbols already existing into new groups and in- 
 venting for each group of generalizations which has been 
 demonstrated by experiment to be a useful combination of 
 symbols, a new name, that is, a new symbol of generaliza- 
 tion. All this is, clearly, motor activity in response to 
 sensory excitation. The only distinguishing features 
 are these, that the scientist's motor activity does not 
 require muscles of any great strength, and that it does 
 require an enormous amount of learning, of variations of 
 response, before it can begin to be of any value to humanity. 
 
222 HUMAN BEHAVIOR 
 
 Let us take an example from the most ancient of all the 
 sciences, which, notwithstanding its age, is still and will 
 always be the foundation of all others, — from arithmetic. 
 No one doubts that the most ancient symbols for larger and 
 smaller groups of things were diagrams of familiar objects. 
 The Roman numerals V and X, for example, are dia- 
 grams of one hand with fingers spread out and of two hands 
 united in opposite positions at their wrists. Even if these 
 diagrams, originally, signified only a quantity portable 
 in one hand and a quantity portable in both, they would 
 already be generalizations, for many are the things or 
 substances which can be carried by hand. If not at once, 
 at a later period, these diagrams came to signify five 
 and ten. They are then a step further removed from 
 natural experience; they have assumed to a further degree 
 the meaning of a generalization (or, if you prefer, of an 
 abstraction). When a person counts, up to five or any 
 other number, he enounces in regular order one of the words 
 of a series which he must previously have learned, while he 
 removes to a position of repose, say, with his finger on the 
 table, or with his turning eye in the subjective field of 
 vision, just one more each time of the objects counted. 
 The series of words spoken in doing this (that is, the series 
 of numbers) is a generalization since it represents innumer- 
 able different manners of successively removing the objects, 
 only two of which (by the finger and by the eye) have 
 been mentioned above. When written symbols like our 
 Arabic figures are substituted for the spoken words, new 
 generalizations are made possible. What is the sig- 
 nificance of the plus sign? If we write it in 7+8, we invite 
 the reader to count a group of seven things of his own 
 choice and another group of eight as if they were only a 
 single group of countable things. The plus sign, 
 then, is a generalization for any kind of sensori-motor 
 
ARITHMETIC 223 
 
 activity arranging the things as if they were a single series 
 and counting them thus. The minus sign is a generalization 
 of a similar kind. In 7-4, for example, we express the 
 question: How many times more do you count after 4, till 
 you enounce 7? The minus sign, then, is a generalization 
 for any kind of sensori-motor activity arranging the 
 things of one series as if they were two series. The mul- 
 tiplication sign presupposes the experience of the plus 
 sign. By writing 3X7 we invite the reader to perform 
 the work of adding 7 plus 7 plus 7. Modern mathema- 
 tics has greatly increased the number of such generali- 
 zations, — think only of logarithms, not to mention higher 
 mathematics. Yet by degrees they can all be reduced 
 to the relatively simple sensori-motor activity of counting 
 a series of things. 
 
 Another example of a scientific generalization might 
 be taken from mechanics. Remember the formula J^m»^, 
 generally used in measuring our experience of "force." 
 Man, in his intercourse with nature, learns how to resist 
 moving objects and also how to utilize the motion of ob- 
 jects (a hammer, for example) for his own purposes. He 
 learns that he has to exert more muscular energy if the 
 object resisted is heavier, and also that his work is more 
 effective if he uses a heavier tool. He generalizes his 
 experiences of resistance to objects and of work by the aid 
 of objects — experiences to which he has already given the 
 general name of "force " — ^by pronouncing the word " mass " 
 in order to express their quantitative aspect. In writing 
 this word he abbreviates it by writing simply m. By 
 further experience man learns that he has to exert more 
 muscular energy and also that his work is more effec- 
 tive, if the object in question moves more quickly. 
 These experiences, in addition, he generalizes in writing 
 by uniting the symbols "mass" and "velocity "in a single 
 
224 HUMAN BEHAVIOR 
 
 formula, connecting them by a sign of multiplication. 
 At our present time, however, one does not write simply 
 mxv, but mxi?, multiplying v with itself. This is done 
 because the formula mx»^ in algebraic relations with other 
 formulas expressing other important experiences with 
 heavy bodies, is in general more convenient. Still, this 
 greater convenience was only gradually recognized 
 by scientists. Two hundred years ago the question was 
 debated in heated controversies between the most distin- 
 guished scientists whether the symbol mv or the symbol mv 
 was a more useful tool of generalizing human experience, 
 or, as they expressed it, — talking as if force were a measur- 
 able thing among the other objects in nature, instead of 
 a mere generalization invented by man — "whether 
 force was proportional to velocity or to the square of 
 velocity. " 
 
 At present the latter formula is generally preferred, 
 but slightly modified by the addition of the factor 3^. 
 This simplifies again the algebraic operations, for the for- 
 mula 3^m» can be put down directly as equal to a certain 
 other very important formula of mechanics. The useful- 
 ness of the equation thus formulated is the only reason 
 why our scientists have become accustomed to using 
 exclusively the formula l^mv^ in their generalizations of 
 the quantitative aspect of the qualitative generalization of 
 "force." (We may mention, by the way, that the use 
 of the equation in question gradually brought about a 
 change of name of the generalization 3^m«)^, so that it is 
 nowadays called "work" in the text-books of physics.) 
 
 Force, therefore, is by no means, as some speculative 
 philosophers would make us believe, a reality given by 
 nature, and truly measurable only by a single formula, 
 but a mere abstraction created by man to suit his needs, 
 and expressed by that combination of algebraic symbols 
 
WORDS AND THINGS 225 
 
 which best suits his needs, practical and theoretical, — 
 an abstraction from experiences so varied and complex 
 that without this generalization we could not respond to 
 the quantitative aspect of any one of them with any defi- 
 niteness, we could not measure them. 
 
 In school and all through life we find ourselves compelled 
 to respond to traditional audible and visible symbols of 
 generalization as well as to the situations presented by 
 nature. We gradually learn to respond to these kinds 
 of stimulations most successfully: we acquire scientific 
 habits. An example of a halbit of responding to symbols 
 of generalization — or rather an example of a large group of 
 such habits — ^is the multiplication table. To the phrase 
 "seven times nine" we at once add, by habit acquired, 
 the word "sixty -three," without having first to do any 
 counting, thus saving a large amount of time. In a 
 similar way one learns, long before he acquires the 
 multiplication table, to combine words into sentences and 
 sentences into periods, and to draw conclusions expressed 
 in further sentences, without first having to devote time 
 and energy to perceiving the things which are meant by 
 those generalizing words and sentences. The enormous 
 advantage of substituting this handling of words for the 
 cumbrous handling of things is clear enough, but the 
 danger of speculation is clear too, — ^the danger of combining 
 words and of thus drawing conclusions, that is, of expect- 
 ing the things to agree with the last group of words 
 manufactured by us, for no better reason than this, that 
 we know our succession of sentences to have been construc- 
 ted according to the rules of grammar, syntax, and logic. 
 This danger does not exist in the case of the multiplication 
 table. Here, in our most elementary quantitative generali- 
 zations, things always agree indeed with our conclusions. 
 
2^6 HUMAN BEHAVIOR 
 
 But our purely qualitative generalizations are so inexact 
 that the things, when we perceive them, often turn out to be 
 quite different from what we, guided only by our habits 
 of handling words, expected to find them. 
 
SEVENTEENTH LECTURE 
 
 The generalizing function changing from a nervous and 
 muscular into a purely nervous function. Relation between 
 processes in the higher nerve centers and strictly subjective 
 experiences. Nervous functions of generalization especially 
 likely to have also the subjective aspect. For the generalizing 
 nervous function in another person's brain we substitute 
 an imaginary mental state. The nervous correlates of sensa- 
 tion and imagery. Associations of successive and of simul- 
 taneous mental states. Attention. Pleasantness and un- 
 pleasantness. Insufficiency of introspective psychology. 
 
 WE have discussed, in some detail, the 
 biological significance of spoken and 
 written language. We stated that prac- 
 tically no generalization is possible with- 
 out speech. We showed that generalization, regarded as 
 a biological function, comes about by the insertion of an 
 additional link in the series of organic processes previously 
 existing, and that the link added is a double link, a motor 
 response, speaking, and a sensory excitation, the sounding 
 word. One must not conclude, however, that conse- 
 quently in every process of generalization the subject 
 must actually speak the word upon which this generaliza- 
 tion is based, that is, must innervate and move his speech 
 organs. No doubt, generaUzktion in general has its 
 origin in actual speech. But the speech function in all 
 generalizations tends to change during use from a nervous 
 
 227 
 
228 
 
 HUMAN BEHAVIOR 
 
 and muscular function to a purely nervous function; and 
 a highly educated individual may even originate generali- 
 zations without at all calling his speech organs into play. 
 
 Sb a Sd Sw Mw Me Mf 
 
 Fig. 54 — ^Generalization without actual speech. 
 
 Figure 54 helps us to understand the dropping out of the 
 muscular function. The figure is a composite of Figures 
 52 and 53. In discussing the latter figures we showed 
 that an excitation by any article of food of any one of the 
 sensory points to the left (in Figure 54) may call forth a 
 response at any one of the motor points to the right by 
 mediation of M^ and S^, since the reaction at M^, the 
 organ of speech, results in a sound and thus in a physical 
 stimulation of S^, the ear. 
 
 In this way any article of food appearing before the 
 eye or another sense organ tends to call forth any 
 action of preparing for a meal and eating. Now, a glance 
 at Figure 54 teaches that the generalization, as soon as 
 established, no longer needs the peripheral points S^ and 
 M^, essential to its creation. A nervous excitation start- 
 ing from Sa, Sj, Sc, or S^ can directly over Sa^aw -*f?/gto 
 take its path to Mg, Mf, Mg, and if j,. The functional 
 relation to the points S^ and Jf „ of this direct path is then 
 merely historical, consisting in the fact that a fart of the 
 path from, say, Sa to M;, (namely, the part from the point 
 
THE OBJECTIVE— THE SUBJECTIVE 229 
 
 Sabcdw to the point M^fg,,^) has in the past been traveled over 
 by nervous processes coming from S^. A fact of this kind 
 we shall soon find to be of a particular significance. 
 
 We have just seen that no actual speaking, nor writing 
 either, is required for the functioning of a generalizatidn 
 once established. The biological function of generaliza- 
 tion may be regarded as purely nervous. Moreover, it 
 is a nervous process inevitably taking its path over 
 higher — very high — nerve centers. Between nervous pro- 
 cesses in the higher nerve centers and strictly subjective 
 experiences, that is, the individual's states of consciousness, 
 there is an important relation. We have good reason to 
 believe that a mental state never occurs unless there is at 
 the same time a nervous process taking its path through 
 the higher nerve centers. It is probably not correct to 
 call the relation between a mental state and a process in a 
 higher nerve center causal, which would mean that the 
 one occurs first and the other after, or the other first and 
 the one after. More probably they are strictly simultan- 
 eous; but we are as yet unable to prove it because science 
 has not yet invented an instrument by means of which we 
 can observe the process going on in our o.wn brain while 
 we have the mental state corresponding to it. If they are 
 strictly simultaneous, we have the right to describe them 
 by saying that they are really only one phenomenon 
 occurring in the world, but that this phenomenon has two 
 aspects. In so far as it can be observed by any and all 
 individuals, including the one whose brain is affected, 
 who are in possession of the proper instruments (not yet 
 invented), we call it an objective phenomenon, a nervous 
 process. In so far as it is (and can be) known exclusively 
 by the one individual whose brain is affected, we call it a 
 subjective phenomenon, a mental state. We understand, 
 then, that among aU the possible nervous functions those 
 
230 HUMAN BEHAVIOR 
 
 of generalization are especially likely to have also the 
 second, the subjective aspect, because they occur in very 
 high nerve centers. 
 
 This brings us back to the considerations with which 
 wfe started out in the first lecture. We stated there that 
 in pronouncing a moral judgment on a boy who has 
 obstructed the track of a train, we seem to be interested 
 chiefly in his thoughts, although only his actions, never 
 his thoughts, can be known to us by observation. When 
 in school, we seem to be interested chiefly in what our 
 teacher thinks of us, although only his actions can be 
 observed by us. The path is now open for our under- 
 standing this. 
 
 The proper valuation of the boy 's or the teacher 's action 
 depends on the application of the proper generalization. 
 It really does not matter much whether the boy placed 
 a plank on the track by using his hands, or caused a 
 rock to roll on the track by using his feet, or, by using 
 his speech organs to pretend a different purpose, made a 
 friend put a stick of dynamite there. What matters 
 is only the fact that all these events are likely to 
 cause the dera,ilment of a car. The derailment, again, 
 is not of so much importance for our judgment as the 
 fact that the derailment may be the cause of many differ- 
 ent events, the saving of a train from passing on a bridge 
 with underwashed foundations, the killing and maiming 
 of numerous passengers by the destruction of the car, and 
 innumerable others. Our judgment, then, is impossible 
 without generalization. It is itseK a generalization of a 
 high order. It expresses our decision as to what generaliz- 
 ing function determined the boy 's motor activity, whether 
 he said to himself (remember in Figure 54 the points M^ 
 and SJ.) : "I will save" or "I will kill." 
 
SUBSTITUTION OF A MENTAL STATE 231 
 
 As we found in the preceding lecture, however, it is not 
 necessary that the boy actually pronounces the word. 
 It leads to the same motor result if the particular generaliz- 
 ing function on which our judgment has decided, is purely 
 nervous, a nervous process passing through a certain 
 higher center in the boy's brain. Therefore, if our judg- 
 ment were in every respect what it ought to be according 
 to the standards of exact science, it .would plainly express 
 that this generaUzing process occurred in this high center 
 of the boy's nervous system. But, unfortunately, these 
 nervous processes in the higher centers are only hypotheti- 
 cal, owing to the fact that the instruments for their ob- 
 servation have not yet been invented. That they will have 
 been invented in a hundred years, or sooner, or later, 
 does not help us. So we help ourselves by substituting 
 in our imagination for the boy's nervous process which 
 today the undeveloped state of physiology will not let us 
 know, an assumed reality which we do not, shall not, 
 cannot ever know, a mental state of the boy, his willing to 
 save, or to kill. The right to substitute this assumed 
 mental state, in spite of its being forever unknowable, 
 for the nervous process, which is insufficiently known 
 only because of the insufficient development of scientific 
 technic, we derive from the fact that a (sUghtly familiar) 
 nervous process like the boy 's is in each of us, individually, 
 regularly coexistent with a perfectly familiar state of 
 willing to save or to kill. 
 
 In a similar way we substitute in our imagination for 
 the nervous process determining our teacher's actions a 
 mental state taken from the store-house of our subjective 
 experiences. Objectively, scientifically, we know only 
 our teacher's actions. We are not so much interested, 
 however, in the particular act as in the class to which it 
 belongs. We do not, for example, care so much whether 
 
232 HUMAN BEHAVIOR 
 
 he uses his writing hand or his talking mouth to praise us, 
 as we care for the general fact that he praises us and does 
 not blame us. It is, therefore, the generalizing nervous 
 function in a high center of the teacher 's brain that concerns 
 us. And for this nervous function we substitute, for 
 reasons stated, an imaginary mental state, — imaginary 
 since, not being ours, it is unknowable to us. 
 
 From this it must be clear that there can be little 
 scientific progress in our knowledge of the interrelations 
 between human beings until we shall be able to compre- 
 hend better the nervous processes of generalization which 
 almost exclusively determine these interrelations, our 
 social intercourse. But since we shall undoubtedly 
 continue, for a long time to come, to substitute in our 
 discussions of social events for the generahzing nervous 
 processes imaginary mental states, it is important that 
 we understand how in our individual life nervous processes 
 and mental states are connected. We emphasized on 
 page 20P that (in Figure 54) a part of the path of the 
 generalizing function had in the past been traveled over 
 by nervous processes coming from S^. Let us note that 
 stimulation of S^ is stimulation by a word, and let us 
 remember the extraordinary part played in any generahzing 
 function of our individual consciousness by word imagery. 
 We draw the conclusion that our consciousness of the 
 word-image, when any of the points Sa, Sj, S„ or Sd in 
 Figure 54 is stimulated and responded to by any of the 
 points Me, M^, Mg, or Mj,, has its nervous correlate in the 
 fact that a part of the nervous path taken by the excitation 
 has previously been traveled over by a nervous excitation 
 coming from the sensory point S^, corresponding to the 
 particular nature of this word image (auditory, visual, 
 etc.), while S^, remains at present unstimulated. 
 
CORRELATES OF MENTAL STATES 23S 
 
 Thus we can at once establish a general rule concerning 
 the nervous correlate of ' sensation, on the one hand, and 
 of imagery, on the other. Sensation, we know from our 
 individual experience, requires proper sensory stimulation, 
 but requires also, we have good reason to beheve, that 
 the nervous excitation takes its path, not directly over 
 a reflex arch, but over higher nerve centers; otherwise 
 there is no consciousness. It is a common condition, 
 then, for the existence of either sensation or imagery, 
 that the nervous process does not remain in the lowest 
 centers, but takes its path over higher nerve centers. The 
 difference, whether our consciousness is a sensation or an 
 image, depends on this: If the nerve center which is 
 conducting a nervous excitation, is at present serving the 
 sensory point corresponding to the mental state in question, 
 that mental state is what we call a sensation; if the center 
 has only in the past served the sensory point corresponding 
 to the mental state in question, that mental state is what 
 we caU an image. 
 
 Introspective psychology, that is, the psychology which 
 restricts its observations to (the observing individual's) 
 consciousness and attempts to comprehend human life 
 by comprehending the one individual's life, has long ago 
 formulated one important law, that of the association 
 of mental states. An association may be one of successive 
 or of simultaneous mental states. In the former case, 
 "association" means that the partictilar mental states 
 tend to recur in the same order, or, more rarely, in reversed 
 order. In the latter case, "association" means that the 
 particular mental states tend to occur together at one 
 moment rather than temporally separated from each other. 
 Let us state, in the terms of nervous function employed 
 in these lectures, the nervous correlate of the law of 
 association. 
 
234 HUMAN BEHAVIOR 
 
 A nervous process starting from a certain sensory point, 
 say, Sa in Figure 16, terminates an'd is succeeded by another 
 nervous process starting from Sj. This second process 
 is then not uninfluenced by the first. A larger fraction 
 of its flux takes its path over the connective neuron Sf j 
 Mai, than would have done so if the other flux had not a 
 moment ago been conducted partly by this neuron. (We 
 have discussed this same fact in Lecture 10 with a 
 somewhat different end in view, namely, in order to show 
 that a nervous process can be more or less deflected not 
 only by a simultaneous stronger one, but also by any directly 
 preceding one.) When now, at any later time, Sa is stimu- 
 lated again, more of the flux passes up from Sl to Sajil/oi, 
 than the first time, since the resistance of the higher center 
 SahMli, affected by two nervous processes, has been re- 
 duced relatively more than that of the lower center SlMl. 
 If we represent by SlMl a relatively high center, (relative 
 to the whole system), the flux in SlMl must be ac- 
 companied by consciousness. The nature of this con- 
 sciousness is determined by the nature of the sensory 
 excitation at So. The flux in the stiU higher neuron 
 SabMab is accompanied by the same consciousness, but 
 also by the consciousness corresponding to the nature 
 of the sensory excitation at S^, because SojMaj has been 
 traveled over previously by a nervous process coming from 
 Si. It is clear that the mental state "b" must begin 
 later than the mental state "a" since the relief of tension 
 starting from Sa can not reach the point Soj as soon as 
 the point Sa- The successive association of the two 
 mental states is therefore a simple consequence of our 
 assumptions concerning the laws of nervous function. 
 
 What we have just said about two mental states of a 
 successive association, holds equally for three, four, etc. 
 Nothing new is to be found in these cases, except that, the 
 
ASSOCIATION 235 
 
 greater the number of different sensory excitations (for 
 example, add S^ and S^ in Figure 16), the higher are the 
 nerve centers coming, more or less, into play (up to 
 Stbcd.^abcd in the Same figure). This is evident enough. 
 Another fact, however, deserves probably a brief discus- 
 sion, that of reproduction of the mental states in the order 
 opposite to the one in which they were acquired. The 
 classic treatise of Ebbinghaus "On Memory" proves the 
 existence also of a tendency for reproduction in the 
 reversed order. The nervous correlate of this tendency 
 is easily derived from the same example which we have 
 just used. If St alone is stimulated, after the succession 
 of stimulus "a" and stimulus "b" has had its opportun- 
 ity for changing the relative resistances of the higher 
 centers in Figure 16, the nervous excitation travels, not 
 only over SImI but also considerably over Sli,Mli,- 
 The flux in the centers SImI and SltM^i, is then accom- 
 panied by two mental states, "b" occurring first because 
 the center SlMl can be reached from Sj in less time than 
 Sai-Moj. That is, the mental state "b" calls up the 
 mental state "a" although in aU the instances of twofold 
 stimulation "b" was invariably preceded by "a." 
 
 Ebbinghaus rightly points out, however, that this re- 
 production of mental states in the order opposite to that 
 of their acquisition by the individual is quite rare. He 
 explains it by calUng attention to the fact that, as a rule, 
 the two mental states are members of a series and are 
 followed by other mental states. In the alphabet, for 
 example, " b " but rarely calls up " a, " because its tendency 
 to call up "c" is still greater. Let us explain the same 
 fact in terms of nervous function by the aid of Figure 55. 
 If in the mental process of memorizing the letters of the 
 alphabet or any other series Sg is stimulated soon after a 
 flux from Sp has occurred in the center S^gM^j, the part 
 
236 
 
 HUMAN BEHAVIOR 
 
 of the flux which does not take its path from Sg to the 
 right but upwards, must divide so that more passes in 
 the direction of Sp^ and over the center Sp^M^^ than 
 in the direction of Sj, and over the center S^^M^f. We 
 may say, then, that from any of the points S^ a larger 
 
 S^ 
 
 riQ7 
 
 Sp Mp Sq Hq S7 ^7 
 
 Fig. 65 — Two directions in successive association. 
 
 flux travels up to the left than up to the right. This is 
 indicated in Figure 55 by double and single lines. It is 
 then immediately clear that during the memorizing any 
 one of the neurons marked S M receives from the right 
 below a stronger flux than from the left below. For 
 example, S^^Mpq receives relatively a strong flux from 
 Sp a weak flux from S^; and S^fM^^ receives a strong flux 
 from Sf, a weak flux from Sg. On some later occasion S^ 
 alone is stimulated, say, for the sake of a test. The flux 
 divides at Sj. A part travels over Sjilf J, another part 
 over S^jM^j, a third over SlfM%. Our problem is to 
 show whether of the mental states other than "q, "namely 
 "p" and "r," the one or the other has a higher degree of 
 consciousness. Obviously, the degree of consciousness 
 depends on the relative flux which has previously passed 
 over the higher centers Sl^M^^ and Sl,M% from Sp 
 
ATTENTION 237 
 
 and Sf. Above we found that the previous flux over the 
 higher centers from S, was relatively strong, from Sp rela- 
 tively weak. Accordingly, the mental state "q" tends to call 
 up the associated mental state "r" rather than the associ- 
 ated state "p." Thus we have explained this rule of 
 introspective psychology in terms of nervous function. 
 
 To explain in terms of nervous function the simultaneous 
 association of mental states, it is only necessary to refer 
 to our discussion of that kind of variation of the nervous 
 path which we called motor condeilsation. If a number 
 of sensory excitations unite in a higher center in order to 
 pass into a common motor outlet, the condition for a 
 simultaneous association of definite mental states is 
 fulfilled. Whenever now, even from a single sensory 
 point, a nervous process travels over that center, the 
 mental states corresponding to all those sensory excita- 
 tions must simultaneously enter consciousness. 
 
 Aside from the time-honored law of association, only 
 one other generally recognized law of mental life has been 
 discovered by purely introspective psychology, the law 
 of attention. By attention is meant "the peculiar fact 
 that of a great number of conscious impressions or ideas 
 simultaneously oflFered to the mind, only a few can ever 
 be carried through and become effective." It is plain 
 that, in terms of nervous function, this is the law of 
 deflection of weaker nervous processes by a stronger one. 
 The stronger nervous process determines the dominant 
 aspect of the total mental state. The weaker ones, if 
 deflected from their own course before having reached 
 any centers of a higher level, are not accompanied by any 
 consciousness whatever.. The higher the center reached 
 by any of these nervous processes before it enters the 
 path of the stronger process, the more pronounced, 
 relatively, the corresponding consciousness; the greater. 
 
238 HUMAN BEHAVIOR 
 
 obviously, also its chance of becoming later the prevailing- 
 nervous process itself and determining the animal's next 
 action. Thus we must expect to find by introspection 
 in our individual mind as a rule a single mental state 
 dominant together with a large number of others of vary- 
 ing degrees of consciousness. The law of attention, which 
 has caused introspective psychology so much discomfort, 
 and which Herbart attempted in vain to clear up by his 
 "mechanics of ideas," thus becomes clear enough as 
 soon as we comprehend its nervous correlate. 
 
 Introspective psychology has long struggled to under- 
 stand the relation between the feelings of pleasantness and 
 unpleasantness (not meaning by the latter term "pain," 
 which is a sensation) and human behavior. It seems ad- 
 visable to approach the problem from- another point of 
 view, studying objective nerVQUs functions, hypothetical 
 as they may be for the present, rather than the intro- 
 spections of the individual which by their very nature 
 can never be anything but subjective. We can distin- 
 guish two classes of conflict between two nervous processes 
 of which one originates while the other is still going on. 
 Either, the first is stronger, deflects the second and by 
 absorbing it grows still stronger. This corresponds to 
 our experiences of pleasantness, for in all such experiences, 
 however varied in other respects, we continue the same 
 form of behavior more and more vigorously. Or, the 
 second nervous process is stronger, weakens the first by 
 deflection, and finally absorbs it completely. This cor- 
 responds to our experiences of unpleasantness, for in all 
 such experiences our behavior suffers interference until 
 it is completely replaced by another form of behavior, 
 when the unpleasantness ceases. The nervous correlate 
 of feeling may then be described in the following words. 
 The nervous correlate of pleasantness and unpleasantness 
 
PLEASANTNESS— UNPLEASANTNESS 239 
 
 is the increase or decrease of the intensity of a previously 
 constant nervous process if the increase or decrease is 
 caused by a force acting at a point other than the point of 
 sensory stimulation. The condition of the second half 
 of this sentence is necessary because our experiences of 
 feeling do not depend on a change in the intensity of a 
 stimulus, but on the interference of nervous processes in 
 higher nerve centers. 
 
 Introspective psychology, disregarding behavior, for cen- 
 turies has been satisfied with remarking that pleasant 
 experiences are the experiences of helpful situations, 
 unpleasant ones those of harmful situations,. This is true 
 enough, for the animal body is so equipped by nature with 
 nervous connections of sensory and motor points that 
 reactions to a helpful situation continue and grow stronger, 
 reactions to harmful situations are weakened until they 
 discontinue. But there are exceptions to this rule which 
 destroy its whole value for any mental or social science, 
 for it is an undeniable fact that the pleasure-seeker may 
 sacrifice his life to pleasure. Not the study of the in- 
 dividual's consciousness, of "the structure of the mind," 
 but the study of the nervous laws of behavior will enable 
 us to understand the significance of human action for 
 human life in the individual and in society. The scientific 
 value of introspective psychology consists merely in the 
 fact that it aids us in discovering the laws of nervous 
 function.* 
 
 How unreliable the results of introspective psychology 
 are, can be learned, for example, from the attitude of 
 
 *A more detailed account of the relations between mental states and 
 nervous functions may be found in my articles "The Nervous Correlate 
 of Pleasantness and IJnpleasantness" and "The Nervous Correlate of 
 Attention," Psychological Review 15, 201-216, 292-322, 358-372; 16, 36- 
 47. 1908-9. Compare also an elaboration of this theory and appli- 
 cation to sociology by L. L. Bernard, "The Transition to an Objective 
 Standard of Social Control," The University of Chicago Press, 1911. 
 
240 HUMAN BEHAVIOR 
 
 psychologists toward the question as to the relative 
 importance of the kinesthetic sense. When, during the 
 nineteenth century, sensory neuron endings were dis- 
 covered in muscles and tendons, some psychologists made 
 use of the new sense in order to explain numerous pheno- 
 mena whose explanation had formerly been impossible. 
 Immediately they were opposed by others who asserted 
 that the kinesthetic sense was of practically no significance 
 since in their individual consciousness they could not, 
 introspectively, discover any kinesthetic sensations or 
 images at all. We saw in Lecture 13 that kinesthetic 
 sensory activity is quite indispensable for the training of 
 any temporally complex reaction, for example, speech. 
 Introspective psychologists, however, are rarely among 
 those people who — like mechanics, skilled factory workers, 
 sportsmen, and athletes — acquire new habits of temporally 
 complex reaction late in life. Their own habits of this 
 kind were all acquired in early childhood and have long 
 ago become completely automatic, — short-circuited, so 
 to speak. Since the nervous processes of these reactions 
 no longer pass over higher centers, there can then be little 
 consciousness, especially no consciousness of kinesthetic 
 sensation or imagery. It does not follow, however, that 
 this consciousness was absent in their first few years of 
 life when they received all the motor skill they possess; 
 and it does not follow that the kinesthetic sense during 
 any period of life is insignificant as a nervous function. 
 This is, perhaps, the best example one can find of the 
 failure of introspection in the explanation of human 
 behavior. 
 
 Enormous is the amount of introspective research 
 embodied in the publications belonging to the mental and 
 social sciences from Aristotle to the present day, enormous 
 the energy which has been spent on careful analysis of 
 
INTROSPECTIVE PSYCHOLOGY 241 
 
 introspective records by the application of generalizations, 
 of abstractions. But if one attempts to collect results of 
 these investigations which are generally recognized — 
 or recognized at least by a majority of the scientists of the 
 present day — ^as contributing toward an understanding of 
 human life in the individual and in society, he is struck 
 by the fact that there is almost nothing to be collected. 
 A few abstractions are recognized as valuable for the 
 science of general psychology: memory, association, 
 attention. In the special mental sciences, ethics, 
 education, sociology, politics, political economy, little — 
 aside from purely statistical facts — seems to be more than 
 personal opinion. There appears to be only one hope 
 that a real mental and social science, comparable to natural 
 science, will ever come about, the hope based on the 
 observation that just as far as the facts and laws of 
 introspective psychology have hitherto been correlated 
 with — replaced by — ^facts of behavior and its laws, has 
 confusion and obscurity given place to order and clearness 
 in the mental sciences. There is hope, then, that by future 
 progress in our knowledge of the laws of human behavior 
 more order and clearness will be there introduced. 
 
TRANSLATIONS 
 
 Adolf Hildebrand, The Problem of Form in Painting 
 and Sculpture; translated and revised with the author's 
 co-operation by Max Meyer and Robert Morris Og- 
 den. G. E. Stechert & Co., New York. 90 cents net. 
 The famous sculptor of Munich, Germany, describes 
 in this book the mental processes which dominate his 
 own artistic activity. 
 
 Hermann Ebbinghaus, Psychology; translated and edited 
 
 by Max Meyer. D. C. Heath & Co., Boston. $1.25, 
 
 An introductory text for college students and general 
 
 readers. Easily readable, up to date, comprehensive. 
 
 Adapted to one semester courses. 
 
7 2' ,,*^'4jlXc''( <!o^ 
 
 J^- z' r ii-^tn^i/^i 'Wv.» f ■• (,I»,.p • 
 
Wiiiiiilll 
 
 ilili'/HrMMi'-'lJit'l',