A l:?> r\^^ ^. ^ ^'\ ViJ- ""i^ f'-,'' .♦.'.•5 :• ;•:■>! i i,»i<> :•!•.■> ^•i>.i!^':^^v! i ^^. -^^ v^ ^ '■^^ ^ o 0^ .-■^^ '> V -6^ \. .n ,c'V- c' V- V X*" '^^. % ^^ ^ -^^ V- ."&-' '-<<. a'^ '^/^ ^^^' '■^. c.^- OO'' 0' .^^.. ■X^' >P v\ \0^r. .A -r^ .\^ <^. 0^ \# ^ ^ .'^-' '=^ '-> " .^ -0 •\ r \ "ci-. V .^^0. > ■ -^''^^^-'"^ '^' \> ^ ^ - " ^c^. •^^ /v" * ^/' ,V S^^^ .V S'' '"^. .^^ ^ a\ r'% ^^^ .^ V ^ -Tt c^. .0 o 0^ 6^ '% .^ ^£^K'^ % ^ '0 o5 -n^ ^">o -A, V ■»- ■W, o. '. "> V ^°^- <^ j> * » 'Z^ 'V- A^ \ / . . S '^ ^'^ ,x- 'O 9 \ \ ^ s ' ' / ^^:^ x^^' '/'. .sO .^^ ^^. aV d^r. PSYCHOLOGY L PSYCHOLOGY BY BURTIS BURR BREESE PROFESSOR OF PSYCHOLOGY IN THE UNIVERSITY OF CINCINNATI ILLUSTRATED CHARLES SCRIBNER'S SONS NEW YORK CHICAGO BOSTON \ <\V^ Copyright. 1917, 1921, by CHARLES SCRIBNER'S SONS NOV 23 1921 g)CI.A6271-)3o PREFACE The present text aims to give a comprehensive view of the facts, principles, and theories of human psychology. Accordingly, the student will find that it represents the various points of view of modern psychology — the analytic and the descriptive, the structural and the functional, the genetic and the physiological. At the same time the em- pirical results of experimental psychology are used as far as possible. Thus at the beginning the student is given a broader foundation for the understanding of mental life than could be given by a more limited point of view. From the very outset an attempt has been made to dif- ferentiate the metaphysical and the empirical tendencies in psychology-. It is important that the student should know when he is indulging in naive metaphysical speculation, and when he is dealing with the results of scientific observation or the theories based upon such observation. While I am in sympathy with the present attempt now being made in some quarters to emphasize the objective and quantitative aspects of consciousness, nevertheless I confess the belief that the qualitative aspect is still worthy of psycho- logical consideration, and that, in order to get at this quahta- tive aspect, the method of introspection is still a valid method of psychological procedure. I am very much indebted to Mr. Schachne Isaacs, In- structor in P5}xhology, University of Cincinnati, for prepar- ing the index, for reading the manuscript and proofs, and for many helpful suggestions in the preparation of the text. Acknowledgments are due for the use of illustrations taken from the following text-books: Vilhger's *' Brain and Spinal Cord," J. B. Lippincott Co.; Quain's "Elements \1 PREFACE of Anatomy," Longmans, Green and Co.; AngelFs ''Psychol- ogy,'' Henry Holt and Company; Howell's "Text-Book of Physiology,"' \V. B. Saunders and Company; Pillsbury's "'Essentials of Psychology" and Titchener's "Text-Book of Psychology," The Macmillan Company; Thorndike's ''El- ements of Psychology"; Ladd and Woodworth's ''Physio- logical Psychology" and Judd's "Psychology," Charles Scrib- ner's Sons. B. B. B. University of Cincinnati, June, 191 7. CONTENTS CHAPTER PAGE I. Introductory i Divisions of Psycholog>\ The Procedure of Psychology. Consciousness. Subject-Object Nature of Consciousness. Soul. iVIind. Self. II. The Nervous System 21 Consciousness and the Nervous System. The Gross Struc- ture of the Brain. The Autonomic Ner\'ous System. Ner\-e- Cells. Nature of the Nerv^ous Impulse. Kinds of Neurones. ^Vhite and Gray Matter. The Fibre Connections of the Brain. Localization of Function. III. Attention 53 Forms of Attention. Neural Basis of Attention, Shifting of Attention. Range or Span of Attention. Effect of Atten- tion. ]Motor Accompaniments of Attention. Feeling of Effort in Attention. Interest and Attention. IV. Sensation 87 Sensation as an Element of Consciousness. Pure Sensations. Physiological Basis of Sensation. The Nature of the Ner\e- Impulse. Evolution of Sense-Organs. The Stimuli. After- Effects of Stimulus. Sensory Adaptation. Attributes of Sensation. Quality. Intensity. Extensity. Duration. Other Attributes. Kinds of Sensations. V. Organic, Kinesthetic, and Cutaneous Sensa- tions no Organic Sensations. Kinaesthetic Sensations: Muscle, Ten- don, and Joint Sensations; Sensations from Vestibule and Semicircular Canals. Cutaneous Sensations: the End- Organs; the Brain Centres; Pressure-Sensations; Pain- Sensation; Sensations of Cold and Warmth. vii VIU CONTENTS CHAPTER PAGE VI. Olfactory and Gustatory Sensations . . . 130 Olfactoty Sensations: End-Organ; the Stimulus; Classifica- tion. Gustatory- Sensations: End-Organ; Gustatory Ner\'es and Brain Centres; Stimulus; Classification of Gustatory Sensations; Retardation; ^Mixtures, Contrasts, Adaptation; Threshold; Complexes. VII. Auditory Sensations 144 End-Organ. Brain Centres. The Stimulus. Noises. Tones. Compound Tones. Timbre. Beats. Combination Tones. Intensity. Extensity. Musical Tones, Consonance, and Dissonance. VIII. Visual Sensations 166 The Retina. The Optic Nerve and Optic Centres. Stimulus. Kinds of \'isual Sensations. Brightness of Colors. Purkinje Phenomenon. Saturation. Complementary Colors. The Color Pyramid. Color ^Mixtures. Light and Color Adapta- tion. Successive Contrasts. Simultaneous Contrasts. Color Zones of the Retina. Color-Blindness. Color Theories. The Young-Helmholtz Theory. Hering Theory. Ladd- Franklin Theor>\ IX. Perception 19} Perception of Objects. Complication. Recognition. Mean- ing. Illusions. Hallucinations. Perception of Space: De- velopment of Space Perception; Third Dimension; Space Errors and Illusions; Localization and Projection of Audi- tor}- Sensations. Perception of Time: Elements of Time Per- ception; the Psychical Present; Sensory Material of Time Perceptions; the Psychical Present and the Logical Present; the Past and the Future; the Measure of Time. X. Memory 238 The Image. Definition of Memor}-. Organic ^Nlemorj-. In- dividual Differences in Memory-. The Training of the Mem- ory. Methods of ^Memorizing. Forgetting. Defects of Memory. Function of Memory. XI. IiL\GINATION 260 Memory and Imagination. Kinds of Imagination. Repro- ductive Imagination. Productive Imagination. Types of Imagination. Visual Type. Auditory Type. Motor Type. CONTENTS IX CHAPTER PAGE Mixed Types. Methods of Determining the Types of Im- agination. Imagery in Synaesthesia. Concrete and Symbolic Imagination. Image and Idea. Training of Imagination. Imagination as a Means of Supplementing the Present. Imagination and Behavior. XII. Association 277 Formation of Associations. Motor Connections. Mental Connections. Associative Recall. The Laws of Associa- tion. Contiguity. Similarity. Partial and Total Recall. Falsification of Association. Association Tests. Physio- logical Basis of Association. XIII. Conception 299 Thinking. The Concept. The Formation of the Concept. The Psychological and the Scientific Concepts. The Gen- eral and the Individual Concept. The Analysis of the Con- cept. The Image. Consciousness of Meaning. The Inten- sion and Extension of Concepts. The Genesis and Develop- ment of the Concept. Language. Origin of Language. Thought and Language. XIV. Judgment 321 Judgment and Perception. The Nature of Judgment. Judg- ment as Apperception. Judgment as Belief. Judgment as the Ascription of Meaning. Judgment as Comparison. Judgment as Evaluation. Kinds of Judgments. Analysis and S>Tithesis. Judgment and Concept. Judgment as the Fundamental Cognitive Activity. XV. Reasoning 338 Inference. Inference and Perception. Inference and Judg- ment. Inference and Concept. The Nature of Reflective Thought, or Reasoning. The Steps in Thinking. Kinds of Reasoning. Reasoning and the Syllogism. Imageless Thought. The Neural Basis of Reason. XVI. Affection and Feeling 356 Affection. The Nature of Affection. Kinds of Affection. Attributes of Affection. Adaptation. Affection and Sensa- tion. Pain and Affection. Affection and Perception. Af- fection and the Ideational Processes. Affection and Bodily Expressions. Neural Basis of Affection. The Significance X CHAPTER CONTEXTS FACE and Function of Affection. Feeling. Classification of Feelings. Mood. Temperament. Emotions. Sentiments. Passion. XVII. Emotions 377 James-Lange Theory of Emotions. The Instinctive Reac- tions and Emotions. Conditions Which Give Rise to Emo- tions. Significance of Emotions. Classification of the Emo- tions. Emotions and Memory. XVIII. Consciousness and Behavior 397 Volitional Action. Genesis of Motor Activity. The Connec- tion between Conscious States and Action. The Law of Dynamogenesis. Control. Effect of Motor Activity upon Consciousness. XIX. Will 419 Conation. Will. Will as Self -Determination. Will and Knowledge. Will and Character. Freedom of the Will. XX. The Self 432 The Unity, Continuity, and Identity of Personal Conscious- ness. The Subject Self, or Ego. The Empirical Self. Origin and Growth of the Self. Contents of the Self. Conscious- ness of the Self. Self and Sensation. Self and Perception. Self and Attention. Self and Interest. Self and Feeling. Self and Will. Sleep and the Self. Dreams and the Self. Disturbances of the Self. Mental or Psychic Blindness. Automatic Writing. Somnambulism. Hypnosis. Double Personality. Insanity. Bibliography 463 Index 471 \ PSYCHOLOGY PSYCHOLOGY CHAPTER I INTRODUCTORY Psydiology is that study whose task it is to point out and organize the observable facts of conscious life, and to formulate the theories, or h>jpo theses, necessar}^ to explain these facts. In this study it is important that the student should distinguish clearly between fact and h^-pothesis — be- tween what is obtained through scientific observation and what is logically constructed through speculation. Psychol- ogy was in its earliest stages a branch of philosophy, and was more inclined to speculate about the nature of consciousness than to observe and systematize the facts connected with it. This is illustrated in the attempts to explain consciousness in terms of the soul, a metaphysical being beyond actual obser- vation. Modern psychology concerns itself more with the facts and less wdth the ultimate nature of consciousness. If we consider all the facts which come from actual ob- servation we may put them into three groups: 1. Facts about matter. 2. Facts about life. 3. Facts about consciousness. The first group forms the subject-matter of the material sci- ences; the second group forms the subject-matter of the bio- logical sciences; and the third group forms the subject-matter of psychology. Divisions of Psychology. — There are a number of special forms of psychology determined by the fields of mental life 2 PSYCHOLOGY from which the psychologist draws his material, and by the methods and points of view he employs in his study. With respect to the fields of consciousness we have: 1. Adult human psychology. 2. Child psycholog>\ 3. Social psychology. 4. Abnormal psychology. 5. Animal psychology. With respect to methods and special points of view we have : 1. Descriptive psychology. 2. Experimental psychology. 3. Genetic psychology. 4. Functional psychology. 5. Physiological psychology. 6. Psychophysics. 7. Comparative psychology. Adult Human Psychology considers the consciousness found in the adult human being. It points out the common quali- ties, processes, and modes of activity found in human beings general]}-. Since individuals differ from each other in men- tal characteristics, a study of these differences is also impor- tant. This study has been termed individual psychology. Cliild Psychology deals with the conscious states of the child. It takes account of the stages of mental development through which the child passes. Since the genesis of con- sciousness is important here, child psychology is a part of genetic psychology-; and since a large part of the child's life is spent in school under a formal educational system, child psycholog}- and genetic psychology often take the form of educational psychology. Social Psychology has to do with conscious experiences which are made possible by the presence of an individual mind in a group of other minds. Such experiences are due to what has been termed social consciousness. Out of it spring language, laws and customs, myths and religion — all of w^hich INTRODUCTORY 3 are dependent upon the existence of a community of individ- uals. The use of the terms ''social consciousness" and ''coi lective mind" must not be understood to indicate the assump- tion of the existence of another kind of consciousness other than that found in individuals. These terms refer only tc the conscious states in individuals which are due to a com- munity of minds. Communities of people have the same language, customs and fashions, rehgion and mythology. The conscious experiences back of these institutions we as- sume to be the same in all individuals. Since much of our mental life is social, social psychology overlaps normal adult psychology and draws its material from it. A subdivision of social psycholog}^ variously named as race psychology, ethnic psychology, or folk psychology, is interested in the mental characteristics of different races or peoples. It may include the comparison of the mental traits found in different peoples. We may compare the Japanese, on the one hand, with the Russians on the other; or the primitive races, like the Ameri- can Indians or Malays, with the more civilized races. A still further subdivision might take up the study of classes, pro- fessions, and occupations. Abnormal Psychology deals with abnormal mental states, such as hypnotism, double or multiple personaHty, fixed ideas, hysterias, mania, melanchoHa, dementia, paranoia, idiocy. Here also should be included the study of deficient and exceptional minds — the weak-minded and the genius. The criminal mind belongs in this list, because most criminals are abnormal. Animal Psychology takes as its subject-matter the mental states of animals. The absence of language in animals limits the possibilities of studying the consciousness which we know exists there. Man can describe his experience in language, but animals cannot. However, the behavior of the animal is a clew to the kinds of consciousness it has. We may therefore study its behavior and so, indirectly, its conscious- aess. Since we may proceed from the lowest animal forms 4 PSYCHOLOGY to the highest, animal psychology may be genetic in its point of view. Descriptive Psychology is really a method of studying con- sciousness. It analyzes, describes, and classifies conscious experiences. Experimental Psychology is laboratory psychology. Lab- oratory methods and physical apparatus are used as means of controlling and studying mental states. Of course, the psychologist cannot measure or weigh the conscious states of his subjects. He cannot even observe them directly. He may, however, measure the time during which a conscious state exists. He may measure or weigh the physical stimuli and correlate the results with the intensities of the conscious experiences. He may also note the physiological changes which take place in the body while the conscious states are going on. For all this he uses instruments of precision, but nowhere in his laboratory has he an instrument that will measure a mental st^te itself. A large part of this study de- pends upon the introspective report given by the subject. Genetic Psychology considers the successive stages of men- tal growth and the evolution in the individual and in the race. We may use a pair of terms that are common to biol- ogy and psychology to designate the two Knes of development — phylogenesis , or racial development, and ontogenesis, or indi- vidual development. These terms really refer to the growth and development of organisms as a whole — both mind and body. Mental development in phylogenesis includes all the stages of conscious Hfe which appear in the evolution of ani- mal forms from the lowest to the highest. These stages of development may be considered either as a series now exist- ing, or as a series constituting the successive stages of evolu- tion from the earliest time to the present. Mental develop- ment in ontogenesis includes the stages of development which take place in an individual from birth to death. The biolo- gist finds a relation between ontogenesis and phylogenesis wnicn he states as the principle of recapitulation. According INTRODUCTORY 5 to ''n.s principle, the individual in embryo passes through the same stages of development that the race has passed through. Thus, biological recapitulation suggests a problem for genetic psychology: Does the child in his mental development pass through the stages of mental development that the race has passed through ? ^ The chief problem of genetic psychology, however, is that of making out the stages of mental develop- ment of the individual. Functional Psychology looks upon consciousness as a process. Formerly the mind was supposed to possess the functions of knowing and willing. Later a third function, that of feeling, was added. Knowing, feeling, and wilHng are, from the point of view of functional psychology, the functions of the mind. A more recent functional point of view asserts the presence in the mind of a purposive factor which deter- mines the direction and nature of conscious processes. While external conditions (stimuli) do this to a certain extent, it is claimed that these factors are not sufficient to explain con- scious activity adequately. A conscious agency, therefore, is assumed to account for the character of our conscious states. Physiological Psychology considers consciousness as either the direct outcome or the correlate of brain activity. Physio- logical psycholog}' does not, however, necessarily commit itself to a materialistic philosophy. For consciousness may be non-material or spiritual in its nature and yet be depen- dent upon the brain for an opportunity to manifest itself. The brain may be only the medium or agent for conscious- ness and not its real cause. But whether its philosophy is materialistic or spiritual, it bases its particular point of view and its method upon the observable fact of correlations be- tween consciousness and nervous processes in. the brain. It accordingly takes the activity of the nervous tissue as its starting-point, acquaints itself with the facts of the anatomy, histology, and physiology of the nervous system, and at- ^For a discussion of this question the student is referred to "Mental De- velopment in the CMld and the Race," by James Mark Baldwin. 6 PSYCHOLOGY tempts to find out what happens in the brain when we are conscious, or, more exactly, to find out what the correlations are between the ner\^ous activities on the one hand and men- tal states or activities on the other. It really combines a large part of neurology (that which has to do with the higher brain centres and their connections) with psychology proper. One of its important problems is the localization of brain centres for the different conscious processes. For example, it finds the centre for sight in the occipital lobes of the brain, the centre for hearing in the superior convolution of the tem- poral lobes, and so on. In the present state of knowledge of the physiology of the nervous tissue there is relatively Httle known concerning the nerv^ous action in the brain. At the present time, then, physiological psychology can be little more than the statement of a series of neurological facts on the one hand, and of conscious facts on the other. Psychophysics is the study of the relations which exist between consciousness and the world of physical objects which are capable of acting as sense-stimuli. It is a partner- ship between physics and psychology, and is included under experimental psychology as now carried on in the psychologi- cal laboratorv. Comparative Psychology has taken at least two directions. In some quarters it has been identical with animal psychology and has occupied itself with the comparison of the mental life found in the various t}'pes of animals. This might well include a comparison of the mental Hfe of the animal forms with that of man, but this is a problem for the future. A ■v\dder significance has been given in other quarters to com- parative psychology in that it is considered as a comparison of the normal human adult consciousness with that found in the child, in abnormal man, in social groups, and lq animals respectively. The Procedure of Psychology. — Although the array of psychologies seems rather long and perplexing, the matter becomes really very simple when we remember that they are INTRODUCTORY / all studies of consciousness, and that consciousness is found only in human beings and animals. Nearly all these forms of psychology are simply special methods, or points of view, used in the study of animal and human consciousness. A general psychology, such as we are entering upon, takes for its subject-matter the highest type of consciousness — that of the adult human being. But it may make use of any of the different special methods and points of view, or even of the subject-matter of the different psychologies, in so far as it is helpful in understanding the mental life of normal man. The fundamental method of psychology is observation: first, the observation of the mental states and processes tak- ing place in our 0"wti minds, and second, the observation of the behavior of others by means of which we may infer the presence and nature of their mental states. These two forms of observation are necessary in psychology. Without the first we could never have an intimate first-hand acquaintance with the facts of consciousness, and without the second we would know nothing of consciousness outside our own minds. The first form of observation gives us direct knowledge of our own conscious life and has been termed — introspection, i. e., looking within. Introspection is the observation of our own mental states. This self-observation does not, however, presuppose a new process or method of observation intro- duced by the psychologist. Introspection does not differ fundamentally from the observation employed in the other sciences. The difference lies only in the material upon which it works. Introspection in psychology is observation of men- tal facts, while observation in the other sciences is observa- tion of material facts. Introspection has sometimes been taken to be an inner consciousness in distinction to an outer consciousness which knows the outer world of objects. But there is no vaHd ground for such a distinction. All conscious- ness, whether it be awareness of mental states or of material objects, is of the same character. The distinction of inner and outer has no meaning when applied to consciousness it- 8 PSYCHOLOGY self. The awareness of a material object is just as much inner consciousness as the awareness of a mental state. Both are contents of consciousness. The ability to introspect im- proves with training and practice. The novice in psychology is quite as helpless as the beginning student in biology when given his first high-power microscope. Expertness is needed no less for the accurate observation of mental states than for the accurate observation of material specimens in biology, physics, or chemistry. Objections have been urged against introspection as a scientific method on the ground that its results cannot be verified. The claim has been made that the results of intro- spection cannot be confirmed because no one can observe directly the conscious states of another. On the other hand, the objects of material sciences are said to be common prop- erty. Any one may observe them and confirm the reports of others. This distinction of the private nature of consciousness and the public nature of objects is not as far-reaching as it seems at first sight. All the sciences are built up by means of observation. But every observation is the observation of some one person. The observation itself is always a private and personal affair. Difi'erent observations can be brought together and made to agree only when reduced to a common imit of measurement. By means of this unit of measurement imiformity may be established, and this is the most important thing in all observation. In the material sciences the uni- formities are found in terms of units of quantity — the milli- metre, the gram, et cetera. In psychology the uniformities are in the terms of quality — quality of experience. The units of quaHty are descriptive units, or language symbols. The facts of consciousness discovered by means of introspection may be reduced to the common terms of descriptive language. If when measured by these common terms the experiences of different observers show uniformity, that is sufficient verifi- cation. Restating this point, we may say that the so-called mate- INTRODUCTORY 9 rial objects of the sciences always fall within some one's pri- vate experience. The material object which I observe is my object, and the material object which you observe is your object. You can never experience my object and I can never experience your object. They become common to both of us only when they are described in the same terms, i. e., re- duced to the same symbols. Likewise, my consciousness and your consciousness become common property when described and communicated through the medium of language. The reliability of these descriptions depends, of course, upon the degree of accuracy with which the symbols of language are used. There is, to be sure, greater opportunity for variation and error in the language description of psychical facts than in the quantitative units of measurement of the material sciences. But even in the material sciences there is variation and error. No two observers report exactly the same results from the observation of material objects. The method of in- trospection in psychology and the method of observation employed in the material sciences are alike in their funda- mental procedure. They both reduce the results of individ- ual and personal observation to the common terms of mea- surement or description, and by means of the uniformities discovered verify the facts. When a number of investigators co-operate and compare the results of their introspection, and repeat them again and again, a mass of cumulative evi- dence is obtained that is entirely trustworthy. Another objection to introspection has been offered on the ground that the observation of mental states cannot take place without changing their nature. This objection is based upon the assumption that the consciousness of mental states is not the same as the consciousness of material objects. This assumption, as we have seen, is not well founded. We have spoken of this before, but let us remind ourselves again that the observation of mental states is not a different kind of observation from that by which we know the material world. The physicist interprets his experience in one way lO PSYCHOLOGY and the psychologist in another, hut the interpretation is a construction li'hich is put upon the experience after it is over. In the one case we are interested in the experience as an object belonging to an independent material world. In the other case we are interested in the experience as a part of our 'Tonsciousness. At the moment of obser\'ation both the object and the mental state are given in our awareness. The second form of observ'ation in the procedure of psy- chology supplements introspection. It is the obser\-ation of behavior. From these external manifestations we may not only infer the presence of consciousness, but its nature. \%en a man smiles we judge that he is pleased. \Mien a young child cries we know that it is experiencing pain. We can estabhsh the fact that there is a large number of corre- spondences between the two series of events. Bodily move- ments and attitudes are the outward signs of conscious states. The quiver of the eyeHd, the tremor of the muscles about the mouth, the faint blush upon the cheek, the pecuHar quahty and intonation of the voice, all betray to the practised ob- ser\-er the nature of the conscious states back of them. In vounsf children and animals obser\'ation of behavior is the only means we have of gaining knowledge of their mental states. Consciousness. — \\Tiat consciousness ultimately is we do not know any more than we know what hfe ultimately is. Many theories have been formed about its real or intrinsic nature, but so far these theories have been of little value to the science of psycholog}'.^ When the psychologist asserts his inability to define con- sciousness ultimately he does not intend to imply that psy- ^ Such inquiry really belongs within the p^o^-ince of metaphysics and not in psycholog\\ We may, however, note two opposing theories concerning the ultimate nature of consciousness that have been generally held: 1. The spirituahstic h}'pothesis. 2. The materialistic hj'pothesis. The spiritualistic hx-pothesis holds consciousness to be states of an unex- tended permanent being of immaterial or spiritual nature. The materialistic INTRODUCTORY II chology is different from the other sciences in respect to the definition of its fundamental subject-matter. No science is able to define its subject-matter ultimately. What matter really is remains as great a mystery as ever, even though the sciences of physics and chemistry attempt to define it vari- ously in terms of energy, or in terms of the atom, the ion, or the electron. These are metaphysical conceptions, and they tell us no more about the real nature of matter than the spir- ituahstic or the materialistic hypothesis tells us about the real nature of consciousness. Biology, too, is unable to define life ultimately, although it has been tempted into metaphysi- cal speculation about it. This is illustrated by the attempt in some quarters to conceive Hfe as a manifestation of *' vital force'' — a principle of mysterious and unfathomable essence thought to be the cause of life phenomena. Even the at- tempt to reduce life to some form of refined chemical reac- tion is none the less pure speculation. Just as the material and biological sciences have now given up speculation about the transcendental nature of matter and life, so psychology no longer speculates about the transcendental nature of con- sciousness. While we are unable to reduce consciousness to anything more fundamental than itself, we are able to define it as observable fact. When we say that we are conscious we mean that we have experiences that we know directly. Every moment of our waking lives we are conscious: we see fights and colors, or hear sounds, or taste foods, feel pleasures or pains, perceive objects, image forms, remember past events, or form judgments, reason, feel glad or sad, or angry, love or hate, resolve, decide, and experience impulses to act. Any or all of these are states of consciousness. We can observe them directly. We can analyze those that are complex into hypothesis regards consciousness as a form of nerve-energy which, so far, we have not been able to observe and measure. But whatever the metaphysical basis of consciousness may be, the facts of consciousness remain the same as far as observation of them goes. 12 PSYCHOLOGY simple conscious states and can weave them into a system of relationships. Some of the earlier English psychologists used the term consciousness to signify awareness of one's own mental states and processes. Locke defined it as the ''perception of what passes in a man's own mind," and Reed as "that immediate knowledge which we have of all the present operations of our own mind." But more recently that meaning has been dis- carded and now the term consciousness is used to indicate any and all mental experience; not only the awareness of our own mental states, but also awareness of objects and relations in the outer world; not only the mental experience of man but the mental experience of all sentient beings. Subject-Object Nature of Consciousness. — One of the most troublesome points to keep clear in discussing the na- ture of consciousness is the distinction which we are logically forced to make between the subject side of consciousness and the object, or content, side. To be conscious impHes some one who is conscious. To have a sensation or thought seems logically to involve a subject to which the sensation or thought is presented. What thinks the thought? What has and owns the sensation? Professor James's answer, ''that the thoughts themselves are the thinkers," does not satisfy the logical need of our thinking. This question appears in vari ous forms in the study of conscious phenomena. We cannot attempt really to answer it without entering the field of meta- physics, but psychology has the right to make any assump- tion concerning it that is in accord with the facts of con- sciousness. The spiritualistic hypothesis of consciousness assumes a being of psychical nature, a permanent ego, or knower, to which all consciousness as content is presented. This double aspect of consciousness has given rise to two different points of view concerning consciousness: 1. Consciousness as the act of the subject. 2. Consciousness as content of experience. It is important for the student to keep clearly in mind INTRODUCTORY I 3 these two possible meanings of consciousness, because in psy- chology the term is sometimes used in one sense and some- times in the other, and often the meanings are confused. The first meaning considers only the subject and its activity in attending, perceiving, feehng, willing, et cetera. The sec- ond meaning considers only the content of experience, or, in common terms, that which is experienced — a sensation, a percept, a memory image, an emotion, et cetera. For exam- ple, the content of consciousness is that which is presented to us as different experiences. The experience of red is different from that of green. The experience of the taste of sugar is different from the experience of the sound of middle C on the piano. The experience of an emotion is different from the experience of a memory image. Such experiences make up the content of consciousness. It is not possible in an introductory psychology to avoid the use of consciousness as subject and consciousness as con- tent, but it is possible to know when we are using the one and when the other. As an illustration of the two meanings of consciousness found in the literature of psychology we may instance the widely differing definitions offered for some of the most common concepts. For example, if the student will read the definitions of attention in a number of text-books on psychology, he will find that in some attention is defined as the ''power of the mind to concentrate, select, and prolong consciousness," while in others it is defined as ''clearness, vividness, or distinctness of mental content, accompanied by a complex of muscular strain and effort.'^ It is plain that in the former case consciousness is conceived as a subject or agent manipulating the contents of its experience, while in the latter case consciousness is merely content. It is the content side of consciousness which furnishes the facts of scientific psychology, because the content of our ex- perience is the only part of consciousness that lends itself to observation. It is the only part about which we can have definite, empirical knowledge. On the other hand, the so- 14 PSYCHOLOGY called subject of consciousness always lies outside the world of observable facts. It is a logical construction which should be used in psychology only as a convenient hypothesis. In referring to the subject of consciousness as a logical construc- tion, we mean that it is a factor which appears only after we begin to think about the facts of consciousness and attempt to explain them rationally. It is, therefore, a product of thought, and not a directly observable reality. Those who have attempted to avoid the hypothesis of a spirituaHstic subject of consciousness or have denied its exis- tence, usually substitute for it the assumption that conscious- ness is really some form of nervous energy. They assert that there is no necessity of assuming anything more than this nervous energy in a living and acting brain to account for the phenomena of consciousness. Whether we accept the hy- pothesis of a psychical or spiritual subject of consciousness, or that of the material nature of consciousness, really makes little difference within psychology itself so long as we are consistent in holding to one or the other. The observable facts remain the same in either case. The sensation of red is just what it is experienced to be, whether it is referred to a psychical subject or to a form of nervous energy. If con- sciousness is a form of nervous energy, then the brain or nervous system is the unifying principle which has and owns the conscious states. Now, we know by actual observation that conscious states as content of experience exist only at the moment of their experience. Then, according to the materialistic conception, they become, when they cease to be experienced, merely states or conditions of the nervous system. They may be revived again when the nervous ma- terial which has given rise to them is stimulated into activity. This conception tacitly assumes a mode of transformation be- tween material brain processes and conscious experience that is beyond the realm of observable fact. Even if it were pos- sible to observe all the details of the brain-cell processes, and to follow them to their last chemical or physical activities, INTRODUCTORY I 5 they would still be just what they are — material processes. The particular manner or mode of their transformation into conscious states is never revealed to us as observable fact. The central point in this materiahstic hypothesis is the asser- tion that conscious states are really and ultimately some form of nervous energy in the brain, and that therefore the brain is the ultimate ground of existence for all consciousness. The student should not confuse this assumption with the observable fact of the dependence of conscious phenomena upon the brain or nervous system in a living organism. The assumption attempts to explain the ultimate or real nature of consciousness by reducing it to nervous energy. On the other hand, the establishment of the fact of the dependence of consciousness upon the nervous system does not involve the question of what its ultimate ground of being is, but rests its case upon the observable facts of consciousness on the one hand, and the observable facts of brain states and activities on the other. Soul. — In popular thought it is often the soul which plays the part of the subject of consciousness. Here we meet the idea that it is the soul that knows and feels and wills. But the popular conception of the soul really involves so many transcendental and metaphysical attributes that it cannot be used profitably in psychology. If the term is used at all there, as it oftentimes is, it must be shorn of many of its metaphysical imphcations and made identical with the mere subject of consciousness. The old and popular meanings are apt, however, to associate themselves with its use, even in a restricted sense. So it is better to avoid the term in psychology.^ Singularly enough the term soul has sometimes been used to signify the content side of consciousness. This concep- tion makes it the sum total of one's thoughts and feelings. But this is altogether unjustifiable, because it twists the term ^ It is a narrow and pedantic view which for this reason denies its existence as an ultimate reality. 1 6 PSYCHOLOGY too far from its popular and original meaning. Its use as the subject of consciousness is preferable, for then it retains some of its old meaning as a permanent being, or entity, behind our consciousness experiences. Mind. — The double aspect of consciousness appears again when we try to get a clear idea of what is meant by mind. Very commonly it is used to designate that which owns the conscious states. Thus we speak of a sensation, a perception, an image, a feeling, or an emotion as in the mind, or we may say that the mind has the sensation, the perception, et cetera. In this way we think of the mind as a continuous, if not per- manent, psychical being persisting through the var^^ing states of consciousness and holding them together, and possessing powers, capacities, attributes, and dispositions which are al- ways in existence, even when not active. Used in this sense, it turns out to be the same conception as that of the subject or knower of consciousness, and it is therefore metaphysical in its real meaning. In this sense the mind is that something that knows and feels and walls, but what that something is, is never given to us as an observ^able fact. On the content side of consciousness mind is the sum total of aU our mental states. Sensations, images, memories, judg- ments, feelings, desires, vohtions, et cetera — all these organ- ized, systematized, and unified in such a way that they hang together as an individual whole. This is the mind that we know directly. Since, however, the content of experience is known only in the present moment, and since each present- moment experience is in a way separate from all others, we might think at first glance that there could be no unity or organization in the contents of experience themselves, and that without a unifying subject the contents of consciousness would remain a mere series of isolated bits, strung out in a time sequence. In fact we very frequently find references to the subject of consciousness as that something, the sole function of which is to organize the various elements of our experience into some sort of unity. Without this something INTRODUCTORY 1 7 it is claimed that no organization or unity can exist. But the present moments of experience do contain actual and observable material which binds them together. For in- stance, if I recognize a man to-day whom I met last week, the present moment of consciousness has ia it not only the pres- entation of the man to-day, but the memory of the man last week. Thus the present-moment experience has in it as a part of its content the element of memory which binds it to the past experience. Recognition is present in the sensory presentation of the man to-day as a consciousness of famihar- ity which relates the present content to past content. In a full and complete recognition there is consciousness of the identity in the two experiences, and of the time relationship between them. Moreover, the two experiences fall within a larger and relatively unchanging content which we shall dis- cuss later as the self. This larger content is always involved in any single experience incorporating it within a system of conscious relationships. Therefore, no single experience stands by itseh even on the content side of consciousness. While the experiences appear to come to the individual in a series of sequences, they really interpenetrate each other and form an organized continuum. Self. — On the subject side of consciousness self, mind, and subject are really synonymous terms. The subject self is that which persists through all the changing experiences of the individual and is therefore the psychical being to which all these experiences are presented. Like the mind, it is sup- posed to possess powers, capacities, attributes, and disposi- tions which account for its outward and observable charac- teristics and manifestations. But on the content side of consciousness the self is the most central, intimate, and persistent core of experience of an individual — those experiences which form the complex mass of conscious content not always directly attended to, but subconsciously present; that content which changes slowly but grows and develops as we become more familiar l8 PSYCHOLOGY with our own nature and the world about us. It is made up of our bodily sensations and sensuous appetites, our private feelings and insistent memories, our real desires and familiar thoughts and ideas. These elements are not all present at any one moment, but change with the changes of our daily life. The organic or bodily sensations and feelings are, how- ever, fairly constant, and form a relatively permanent centre about which the other self-contents revolve. Sometimes one and sometimes another group of experiences combines with this constant factor of bodily sensations, and thereby makes up the changing aspects of the self. The business man leaves his family seK behind and puts on another self when he enters upon the duties of the day. He passes from one set of habit- ual and familiar background experiences to another. He shows a different side of his character at the club, on the golf-links, or at an evening reception. Yet there is a certain identity running through these different groups of self -expe- riences which unifies them into a single system of experience. Certain of these experiences are more persistent than others, and form a background against which all new experiences are projected. Although, as we have seen, the terms mind and self point out the same ultimate reality, as subject of consciousness, they are used with different meanings or restrictions. As far as the naive metaphysics of psychology go there is practically no differentiation between the mind and self. They are both the subject which knows and feels and wills, and whatever powers and attributes are assumed for the one are usually attributed to the other. But on the content side of con- sciousness there is a definite Hmitation. Mind is an organiza- tion and unity of conscious content in an individual, while self is a central group within the larger organization of the mind. The preceding discussion has made plain the fact that there are two distinct tendencies in psychology — the philo- sophical and empirical. The one leads us into the world of speculation and metaphysical reahty. The other limits us INTRODUCTORY I 9 to the world of observable facts. The one induces us to infer and beheve in the existence of an enduring ego, mind, or soul. The other deals only with the observable content of consciousness. The one appeals to our interest in the larger problem of the ultimate reahty and meaning of our experi- ences. The other limits us to an arbitrarily chosen field of facts — the facts of consciousness which are abstracted only for the purpose of study. While it is our desire to follow the empirical tendency, it is not our intention thereby to take away, or even to diminish the student's interest in the question of the ultimate nature of consciousness. What con- sciousness really is, how it came to exist, and what its place is in the universe — are questions worthy of our higher reason and philosophical insight. No petty round of facts ought to ensnare and tame man's desire to know the whole truth. We believe that the world is larger than the facts given us by the methods of science. But before we attempt to take the broader outlook, our first task is to master the facts just as they are given to us — to pick out those that are significant and to analyze them into their elements and find out the laws that govern their behavior, to evaluate them properly and or- ganize them into a system. This is the task that empirical psychology sets before itself. In a general study of human consciousness such as we are going to undertake there are several points of view to be kept in mind: 1. Conscious states must be analyzed and described. In doing this we take the structural point of view and ignore the functional aspect of consciousness. 2. We must point out the laws of mental activity accord- ing to which conscious states conjoin and form streams of thought or feehng. Here consciousness is considered as a process and the point of view is functional. 3. The relation of consciousness to the brain and its nerve processes should be determined. When we attempt to do this our point of view is physiological. 20 PSYCHOLOGY 4. Changes in consciousness that accompany changes in the physical world which act as stimuU should be noted. This demands the psychophysical point of view. 5. Finally we must not neglect the relation of conscious- ness to behavior. We shall not attempt to follow these points of view sep- arately. Sometimes one and sometimes another will be uppermost in the following discussions. CHAPTER II THE NERVOUS SYSTEM Although the study of the structure and function of the nervous system is not properly a part of psychology, it is, nevertheless, important for the understanding of the processes of conscious hfe to know something of the elementary facts in the anatomy, histology, and physiology of the brain. This seems necessary since we assume that all consciousness is in some way dependent upon the action of the nervous system. The brain is connected through nerve-fibres with all parts of the body. Some of these fibres (sensory fibres) come from the sense end-organs which are played upon by the external forces in the environment, and some of them (motor fibres) go out to the muscles which bring about adaptive movements of the body. Biologically the brain and its nerve-connec- tions are merely the means through which external stimula- tions are transformed into organic behavior. Changes in the outer world act upon the sensory nerve-ends and set up nerve-impulses which are carried to the brain, where they are projected outward into appropriate muscular and glandu- lar activities. But accompanying these physiological brain and ner\'e processes there is something else which is not discoverable in them, and of which physiology can take no account, however much its methods may be refined and perfected. This some- thing is consciousness. When light-rays strike the retina we see. When air- vibrations enter the ear we hear. Besides the sensations which arise when external objects stimulate the sensory end-organs there are other conscious experiences which accompany the neural processes within the brain. These experiences are the higher conscious states of percep- tion, imagination, memory, judgment, reason, feelings, emo- 21 22 PSYCHOLOGY tions, etc. Although conscious states depend upon brain states, we must not confuse these two forms of existence — the mental and the physical. Consciousness is not the brain, or any of its neural processes. Even though we were able to follow and observe a nerve-activity to its last analysis within the brain-cells, we could never discover an element of con- sciousness in it. What the exact relation between the mind and the brain is we do not know. We can only assert that the mind is dependent upon certain brain-activities. Consciousness and the Nervous System. — There are sev- eral groups of facts which mdicate the dependence of con- sciousness upon the nervous system: 1 . Consciousness depends upon the action of sense-organs. Without the sensitive nerve-endings in eye, ear, nose, mouth, skin, and deeper tissues of the body, we could never be aware of anything. All the higher forms of consciousness are based upon the sensory experiences which are mediated by the ner\'e-endings in the sense-organs. 2. Certain drugs, like alcohol, ether, hashish, etc., which disturb the action of the nervous tissue in the brain, also affect consciousness. 3. Bodily diseases, especially those producing high fever, seriously interfere wdth the conscious processes. 4. Diseased conditions of the brain — tumors, brain-hem- orrhages, lesions, disintegration of the nervous tissue, etc., are followed by disturbances or loss of certain forms of con- sciousness. Thus a tumor in the occipital region of the brain may cause the loss of visual memories. A lesion in the left temporal lobe is followed by the loss of the ability to under- stand spoken words. 5. If we compare the different forms of animal life, from the lowest to the highest, we find that the most highly devel- oped consciousness goes with the most complex and highly developed nervous system. Development of the Central Nervous System. — The cen- tral nervous system is made up of the brain and the spinal THE NERVOUS SYSTEM 23 Medullary plate Chorda Cuticle-plate r— Ectoderm Mesoderm ■Entoderm cord. The brain is the mass of nerve- tissue found within the cranial case, while the spinal cord is the long tube of nervous tissue within the vertebral canal. The brain sends out twelve pairs of cranial nerves whose fibres go to the sense-organs and muscles of the head, face, and some of the vital organs of the body. From the spinal cord issue thirty-one pairs of spinal nerves whose fibres go to the sensory sur- faces and muscles of the body. The cranial and spinal nerves are com- posed of sensory and motor fibres which constitute the afferent and ef- ferent pathways between the body and the central ner^^ous system. We can best understand the struc- ture of the nervous system by follow- ing its embry ©logical growth. Nerve- tissue develops from the ectoderm or outer layer of embryonic cells. Very early in the growth of the embryo, after it has elongated, a longitudinal groove, the medullary groove, forms in the medullary plate, or beginning nerv^e-tissue. The edges of this groove come together and form the neural tube, which extends along the length of the vertebral column and into the cranial cavity. The cavity enclosed within the neural tube is the spinal canal. This canal, at its upper extremity, later forms the irregular ventricles of the brain. The walls of the upper, or anterior part of the neural tube thicken enormously and form the brain. The walls of the lower part thicken to a less degree but more uniformly and form the spinal cord. Within the cranial cavity the neural tube forms by ring-like constric- tions and dilatations into three primary brain vesicles, known as anterior, middle, and posterior vesicles. These three pri- mary vesicles give rise to the fore-brain, mid-brain, and hind- brain respectively. Medullary groove I €^r~Medu.llary ridge Medullary tube Central canal Fig. I. — Diagram repre- senting the formation of the medullary tube from the outer germ- la3'er, (Taken from Villiger's "Brain and Spinal Cord.") Cerebral hemisphere - Thalamus ^Miii-brain^ vesicle Hind-brain vesicle Fore-brain vesicle Mid-brain Cerebellum Medulla oblongata Spinal cord Fig. 2. — A, Diagram "showing the brain- vesicles; B, Diagram showing parts of embryonic brain Cerebrum Cergbellum SpintU cord LatercU Ventricle Aqueduct of Sylvius VentricH Spinal cancH , Fig. 3. — Diagram showing the brain- ventricles THE NERVOUS SYSTEM 25 / « / jFore {Brainy' Olfactory Lobe Pituitary "Body Mid Brainy Hind Brain Cord Fig. 4. — Diagram showing a cross-section of the brain. (Highly diagramatic.) f Anterior < Fore-brain < Olfactory bulbs and tracts. Cerebral hemispheres. Corpora striata. Lateral ventricles. Neural tube < i Pineal body. Thalami. Optic tracts. Third ventricle. (Corpora quadrigemina. Crura cerebri. Aqueduct of Sylvius. Pons Varolii. Hind-brain J Medulla oblongata. Cerebellum. Fourth ventricle. ^ Spinal cord. 26 PSYCHOLOGY The Gross Structure of the Brain. — The brain is divided by a median fissure into two s>Tnmetrical hemispheres. The division is not complete, however, for at the bottom of the fissure a broad band of fibres, the corpus callosum, unites the two halves of the brain. The median fissure extends the whole length of the cord and divides it less prominently into right and left halves. The surface of the brain is furrowed by fissures or sulci, which serve to increase the cortical area. The ridges be- tween the fissures are called convolutions. Two of the fis- sures, deeper than all the others, make convenient landmarks on each cerebral hemisphere. They are the lateral fissure (fissure of Sylvius) and the central fissure (fissure of Rolando). It is sometimes convenient to divide each cerebral hemi- sphere into lobes. The frontal lobe occupies the anterior, the occipital lobe the posterior, the parietal lobe the upper central, and the 'temporal lobe the lower central part of the cerebral hemisphere. The island of Reil forms the fifth lobe of the cerebral hemisphere. The cerebellum, sometimes called the httle brain, Hes below the cerebrum on the dorsal side of the brain. Below and in front of the cerebellum is the medulla oblongata, which is an enlargement of the spinal cord at its upper end. Almost encircling the medulla oblongata is the pons, a thick band of fibres joining the two halves of the cerebellum. The cerebral hemispheres are the largest and most con- spicuous parts of the fore-brain. The other principal parts, the corpora striata, the pineal body, and the thalami, are over- laid and concealed from view by the folds of the cerebral hemispheres. The hemispheres also enfold the parts of the mid-brain, the corpora quadrigemina, and the crura cerebri, which He below the thalami. The pons, medulla, mid-brain, and thalami constitute the brain-stem. A medial cross-sec- tion of the brain will show all these parts except the corpora striata. From the ventral and basal side of the brain are given off Cer, Fig. s. — The figure on the left shows the general relations of the central nervous system to the bones of the skull and spine. The figure on the right displays the general contours of the central system as seen from in front. The great gangUonated cord of the s5Tnpathetic system is showTi attached to one side of the spinal nerves; the other side has been cut away. Cer., the cerebral hemispheres; O, the olfactory centres; P, the pons Varolii; M, the medulla oblongata; Cb., the cerebellum; Sp.C, the spinal cord; /, the olfactory nerv^e; //, the optic nerve; ///, the oculo-motor nerve; IV, the trochlear nerve; V, the trigeminus nerve; VI. abducens nerve; VII, the facial nerve; VIII, the auditory nerve; IX, glosso- pharyngeal nerve; X. the vagus nerve; XI, spinal accessory- ; XII, the hypoglossal nerve; C. the first cervical spinal nerve; Di. the first dorsal, or thoracic, nerve; L\. the first lumbar nerve; 5i . the first sacral nerve; X\, filum terminale; C5', superior cervical ganglion of the sympathetic; C5', middle cervical ganglion of the sjonpathjetic; C5', and D.S", junction of the inferior cer\ncal and the first dorsal, or thoracic, ganglion of the sympathetic; DS^^. the eleventh dorsal, or thoracic ganglion, of the syin pathetic; LS^. the first lumbar ganglion of the same system; 55", the first sacral ganglion al.so of tb>-* sym Dathetic (From Angell's " Psychology.") Frontal lobe Precentral gyre Central fissure Postcentral gyre Parietal lobe Occipital lobe Fig. 6. — ^The upper surface of the cerebral hemispheres. (From Ladd and Woodworth, after Sobotta-McMurrich.) Central fissure Superior frontal gyre Middle frontal gyre Precentral gyre Inferior ) frontal gyre SuPramargtnal gyre Angular gyre Postcentral gyre Superior temporal gyre Middle temporal gyre Inferior temporal gyre Cerebellum Fissure of Sylvius Fig. 7.— Lateral surface of the left cerebral hemisphere. (From Ladd and Woodworth, after Edinger.) Paracentral lobule Cingulale fissure Central fissure ^^ Precuneus Parieto-orcipital fissure Limbic lobe Cuneus Sup. frontal &yre Calcarine fissure Lingual gyre Cerebellum Optic chiasm Mammillary body Fig. 8. — ^Mesial surface of the right cerebral hemisphere. (From Ladd and Woodworth, after Edinger.) Fig. q. — Under surface of the brain. (From Ladd and Woodworth, after Van Gehuchten.) The Roman numerals at the left margin of the figure indicate the twelve cranial nerves; liyp. hy- pophysis; cA, optic chiasm; c. warn., mammillary body; />c, pedunrlf* of the cerebrum; pr, pons; 0, olive; py, pyramids; CI, first spinal nerve. 30 PSYCHOLOGY the twelve pairs of cranial nerves. Some of these nerves carry only sensory fibres, some only motor fibres, while others carry both sensory and motor fibres (mixed nerves) . NAMES AND GENERAL FUNCTION OF THE CRA- NIAL NERVES I, Olfactory: Sensory fibres from olfactory sense-organs. II. Optic: Sensory fibres from the visual sense-organs. HI. Ocido-motor : Motor fibres to several muscles of eyes. IV. Trochlear: Motor fibres to superior oblique muscles of eyes. V. Trigeminal: Sensory fibres from cutaneous sense-organs of face, scalp, mouth, tongue, and teeth. Motor fibres to muscles of mastication. VI. Ahducens: Motor fibres to external rectus muscles of eyes. VII. Facial: Sensory fibres from gustatory end-organs in tongue. Motor fibres to muscles of face, scalp, and external ears. VIII. Auditory: Sensory fibres from auditory end-organs in cochlea (cochlear branch), and from semicircular canals of ear (vestibular branch). IX. Glossopharyngeal : Sensory fibres from gustatory end-organs. Motor fibres to tongue and pharynx. X. Pneumo gastric, or vagus: Sensory fibres from respiratory, cir- culatory, and digestive organs. Motor fibres to pharynx, larynx, oesophagus, stomach, respi- ratory organs, and intestines, also inhibitory fibres to heart. XI. Spinal-accessory : Motor fibres to muscles of neck and shoulders. XII. Hypoglossal: Motor fibres to muscles of tongue. The spinal neroes (31 pairs) are given off from the sides of the spinal cord. Each nerve is attached to the cord by two roots — a posterior root and an anterior root. The posterior root is composed chiefly of sensory fibres from cell-bodies in the spinal ganglia. The anterior root is composed of motor fibres whose cell-bodies lie within the gray matter of the cord. The two roots join shortly after leaving the cord and form a complete spinal nerve. The spinal nerves are divided into cervical (8 pairs), thoracic (12 pairs), lumbar (5 pairs), sacral (5 pairs), and coccygeal (i pair). THE NERVOUS SYSTEM 31 The brain, the cord, the cranial nerves, and the spinal nerves make up the cerebrospinal neroous system. 4_2 Fig. 10. — A, ventral, and B, lateral, view of a portion of the cord from the cervical region, i, ventral median, and 2, dorsal median, fissures; 5, ventral fibres leaving the cord; 6, dorsal fibres entering the cord; 6^, spinal ganglion; 7, spinal nerve after the union of the dorsal and ventral fibres. (From Ladd and Woodworth, after Schwalbe.) The Autonomic Nervous System. — Besides the cerebro- spinal nervous system there is another relatively independent nervous system known as the autonomic nervous system. This is composed of a double chain of nerve-gangha and nerve-fibres extending on both sides of the vertebral column from the base of the skull downward to the end of the column. In addition there are nerve-gangha in the thoracic, abdominal, and pelvic cavities; also isolated ganglia located in the heart, in the walls of the arteries, and in the eye-cavities. While the autonomic system is connected with the cerebro- spinal ner- 32 PSYCHOLOGY ^Dendrites Collaterals Axon Fig. II. — Nerve-cell from the cerebral cortex. vous system, it is a relatively independent and self-directing system. It is due to its action that the vital and automatic processes of respiration, circula- tion, digestion, and the glandular processes are carried on without burdening the central nervous system. Nerve-Cells. — The nervous system is composed of millions of nerve-cells too small to be seen except by the aid of a power- ful microscope. The nerve-cell is composed of a protoplasmic cell-body and its prolongations or fibres. These prolongations are of two kinds: axons and den- drites. The whole nerve-cell (cell- body, axon, and dendrites) constitutes a nervous unit known as the neurone. Each cell-body gives off many dendrites, but in most cases only a sin- gle axon. The axon is smooth and regular in contour and preserves the same diameter throughout its course. It ends in a brush or terminal arborization. In some cases it gives off, along its course, branches or collaterals, and these end also in terminal arborizations. Axons vary greatly in length. While those which terminate within the brain are short, those which lead to outlying parts Dendrites Fig. 12. — Multipolar nerve-cell from the cerebral cortex. In a cell of this type the axon is short and has many branches. PR-^^ gnP kl.PD Fig. 13. — ^A section through the brain cortex. Greatly magnified. (From Thomdike's "Elements of Psychology," after KoUiker.) 34 PSYCHOLOGY may be half the length of the body. The true nerve sub- stance of the axon (the axis cylinder) is protected by a medullary sheath which disappears near the cell-body and at Fig. 14. — Nerve-cell showing fibrils. (From Ladd and Woodworth, after Bethe.) a, b, c, d, the stumps of several dendrites; Ax, stump of the axon. Fig. 15. — Short pieces of two nerve- fibres. (From Ladd and Woodworth, after Schafer.) The axis cylinder appears gray; the myelin sheath is stained black; the primitive sheath ap- pears white. R, node of Ranvier; c, the nucleus of one of the sheath-cells. the terminals of the axon. Outside the medullary sheath is usually found a thin covering known as the neurilemma. The dendrites are rough and branch more gradually from *3?f» Fig. i6. — Motor-cell from the ventral horn of the cord, with scheme of the course of its axon. (From Ladd and Woodworth, after Barker.) n, the nucleus, with nS nucleolus; d, dendrites, only the stumps of which are shown; a.h., hUlock from which the axon arises; at tn, the axon becomes invested with the myeUn sheath; n.R., a node with branching of the axon; m\ a muscle in which the axon terminates in tel., the motor end-plate. 36 PSYCHOLOGY each other, giving off antler- like processes. The size of the dendritic processes becomes rapidly smaller as they leave the cell-body. The nerve-cells are supported and held in place by neurogHa-cells whose numerous processes form a frame work in which the true nerve- cells rest. Dendrites Fig. 17. — Diagram showing the probable way in which neurones are connected. The function of the cell-body seems to be that of rein- forcing and inhibiting the nerve-impulses which pass through it. The dendrites carry the impulses to the cell-body and the axon transmits the impulse away from the cell-body — to the dendrites of other neurones or to the glands and muscles of the body. There is one exception to this rule. The fibres which carry sensory impulses from the different sense-organs to the cell-bodies in the spinal gangHa resemble axons in structure. How the nervous impulse is transmitted from one neurone to another is not definitely known. Many investigators be- lieve that each neurone is a distinct individual unit, and that where neurones form a functional chain, the axonic terminals of one neurone merely approach the dendrites or cell-body of the next neurone. These points of contact or contiguity THE NERVOUS SYSTEM 37 between neurones over which the nerve-impulse is passed from one to the other are called synapses. Since the axons and dendrites have many branches, the terminations of one rebiS ^J-C7arfce's coturnj^ Spinal End organ in MfingUon/ Muscle ~^ _^\End organ in Skin Muscle Motor neurones in Ventral horns Fig. i8. — Diagram of some of the comiections between sense-organs and muscles through . ^ cord and brain. The student should understand that this diagram is far too simple to represent all the facts of nerve-connections. axon may connect with the dendrites of a number of other neurones. Thus an impulse may spread to large areas of the brain and under different conditions take different path- 38 PSYCHOLOGY ways through the cord and brain. A single fibre from the spinal ganglion makes connections with fifty or sixty differ- ent neurones in the gray matter of the cord. Nature of the Nervous Impulse. — Just what the nature of the nervous impulse is we are not able to say. The most popular theory regards it as a form of chemical activity analogous to the action in a train of gunpowder, which when lighted at one end transmits the combustion throughout its entire course. It has been suggested, also, that the nervous impulse is electrical in nature. But the rate of nerve trans- mission (not more than 300 feet per second) is much too slow for that of any known electrical action. Kinds of Neurones. — Neurones may be classified accord- ing to their function into (i) sensory or afferent neurones, (2) motor or efferent ftetirones, and (3) associational or central neurones. The sensory neurones receive stimulation from the outside world and conduct sense-impulses to the sensory centres of the brain. The motor neurones project impulses outward from the brain to the muscles and glands. The cen- tral neurones form chains for connecting the different parts of the brain, as for instance from the sensory to the motor areas. When neurones pass from one-half of the brain or cord to the other half they are spoken of as commissural neurones. The cell-bodies of the central and motor neurones lie within the brain and spinal cord, while the cell-bodies of the sensory neurones are found near the sense-organs or in the spinal ganglia outside the brain and cord. When a large number of cell-bodies are grouped closely together the group is spoken of as a ganglion. The separate nerv^e-fibres are (except at their terminals) bound together in bundles or 'nerves. They are referred to as medulla ted and non-medullated nerves, according as the fibres which compose them are meduUated or non-medullated. White and Gray Matter. — The white matter of the brain, cord, and nerves is made up of medullated nerve-fibres. It is THE NERVOUS SYSTEM 39 Subit. nigra Eipfo- t