THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES GIFT OF SAN FRANCISCO COUNTY MEDICAL SOCIETY An Essay on the Physiology of Mind An Interpretation Eased on Biological^ Morphological^ Physical and Chemical Considerations BY Francis X.^Dercum A.M., M.D., Ph.D. Member of the American Philosophical Society; Fellow of the College of Physicians of Philadelphia; Member of the Academy of Natural Sciences of Philadelphia; Professor of Nervous and Mental Diseases in the Jefferson Medical College, etc Philadelphia and London W. B. Saunders Company 1922 Copyright, 1922, by W. B. Saunders Company YIADE IN U. S. A. PRESS OF SAUNDERS COMP, PHH.AOEl.PHIA Biomedical Library This Essay is Reverentially Inscribed to the Memory of JOSEPH LEIDY to whom especially we owe our Knowledge of the Behavior of the Rhizopoda 577957 FOREWORD IN this essay the writer has endeavored to present the basic facts of those reactions of the organism to the environment which under given conditions manifest the qualities which we speak of as "mind." As far as possible elemental truths have been sought in a con- sideration of the structure of the constituent substance of the organism, the living proto- plasm. The physical peculiarities of the latter, its ceaseless chemical change, its simultaneous up-building and reduction, its reactions and its lack of reactions to the incident forces of the physical world, have, in turn, been called to the attention of the reader. Secondly, the behavior of simple unicellular forms of life has been compared with and in a measure correlated with the behavior of the individual cells of multi- cellular forms. In due course, also, have been considered those peculiarities of structure of the living protoplasm which cause the arrest of certain, a very limited number, of the incident forces of the environment; protoplasm as a whole is "transparent" to and remains totally unaffected by an infinitude of forces active in the universe. 4 FOREWORD In turn the writer has taken up the problems of the reception and transmission of the forms of energy which protoplasm is capable of re- ceiving, the conversion of these incident forces into other forms, and the transmission and the release of energy by the protoplasm itself. Naturally, this discussion is preceded by a consideration of elementary responses to im- pacts, by a consideration of the differentiation in metazoa of special structures for the recep- tion and transmission of the latter, and for the resulting expression in motion; and, finally, by a consideration of the elaboration and differentia- tion of these phenomena in the more complex metazoa. At first the responses of the organism are very general in character. Soon, however, they become limited and special, and later acquire the character of being fixed, stereotyped, and invariable. Later still, owing to an increase an increase which finally becomes vast in the number of the integers concerned in transmission and owing to the preservation in these integers of certain primitive and undiffer- entiated properties, the responses lose this quality of fixation. They become capable of variation and acquire the quality of being more and more adaptable and adjustable to the impacts received; the responses become more FOREWORD 5 and more the exact or, rather, the increasingly approximate equivalents of the impacts. The recondite problems of consciousness now present themselves and its elemental phenomena first occupy our attention. Finally, the writer directs attention to some of the remarkable physical facts definitely known in regard to the responses of the organism, facts which possess, a profound significance and which must pro- foundly influence our conceptions both of the structure of protoplasm and of the limitations which this structure imposes. Here appears the great question: "What and how much does our structure permit us to know?" In conclusion the writer wishes to say for the lay reader into whose hands this essay may fall, that as far as practicable the language employed has been as simple as the nature of the subject permits. Unfortunately, however, many tech- nicalities are unavoidable, though, whenever possible, the meaning of these has been indicated in the text. F. X. D. 1719 WALNUT STREET, PHILADELPHIA, PA. January, 1922. CONTENTS Attitude Toward the Subject 11 Reactions of Unicellular Forms and of the Individual Cells of Multicellular Forms 12 Primitive Responses of Movement in Multicellular Forms 15 Differentiation of a Contractile Cell 16 Transmission of Impacts 19 Primitive Pathways of Transmission 21 Differentiation of a Receiving Cell 23 Differentiation of an Intermediate Cell 24 Position of the Primitive Transmitting Apparatus. Position Later Assumed in the More Complex Metazoa 24 Structure of the Primitive Transmitting (Nervous) Network 26 Differentiation of a Synaptic Nervous System 27 The Neurone 28 Polarity of Transmission 30 Mechanism of Response 31 Differentiation of Responses 33 Impacts Which Living Protoplasm is Capable of Receiving 34 Chemical Impacts ; 34 Impacts from Movements and Coarse Vibrations in the Surrounding Medium 35 The Otic Vesicle, the Ear, the Lateral Line 35 Impacts of Light, of Heat 37 Limited Capacity of Living Protoplasm ' for the Reception of the Incident Forces of the Environ- ment. Significance of this Fact 39 Differentiation of the Receptors. Physical Character of their Function 42 7 8 CONTENTS PAGE Methods of Response by the Organism 47 Establishment of Definite Pathways of Transmission. The "Common Paths" 48 Segmental Relations of the Central Nervous Appa- ratus 49 Segmental Relations of the Cephalic Extremity and the Special Sense Receptors 50 The Nose Brain, Eye Brain, Ear Brain, Skin Brain, Visceral Brain 50 The Chemical Sense. Automatism of Response in the Approach to or Withdrawal from Foreign Bodies 51 Roles of the Other Senses 54 Automatic Character of the Spinal Responses 55 The Palaeo-encephalon; the Brain Stem; Responses Fixed, Invariable 56 The Neo- or Telencephalon; the Cortex; Responses Variable and Adaptable 57 Absence of Segmental Relations of the Telencephalon 57 Pathways of Ingress and Egress to the Telencephalon 58 Functions of the Cortex; the So-called Centers. As- sociation Pathways. Relation of the Various Parts of the Cortex to Each Other. Possibilities of Adaptation and Adjustment of Responses 60 The Responses of the Cortex Being Variable the Neurones Cannot Be in Fixed Relations with Each Other 62 Amceboidism of Cortical Neurones; Historical Data. Discussion 63 The Neuroblast. Chemotaxis; Neurobiotaxis 67 The Synapses. Polarization of the Neurone 70 Further Discussion of the Amoeboidism of the Neurone 71 Synaptic Delay 72 The Electro-endosmotic Layer 74 Amoeboid Transmission. The Neurone Threshold. . 78 CONTENTS 9 PAGE The Principles that Determine Neurobiotaxis and the Principles that Determine the Direction of Trans- mission. Old and New Pathways of Transmission 79 Changes in the Neurone. Release of Energy. Ava- lanche Conduction 81 Consciousness. Sentiency. The Lower Forms of Life; the Lower Vertebrates; the Higher Verte- brates. The Role of the Pallium; the Role of the Palseo-encephalon 83 In Mammals Fixed Responses Play no Role in Consciousness 86 Disappearance of Consciousness in Acquired Autom- atisms 87 Consciousness Present Only in Responses of Adapta- tion and Adjustment 88 Phenomena of Transmission Through the Cortex. Relations of These Phenomena to Consciousness. . . 89 Nature of Consciousness 90 Principles that Govern Transmission 93 The Train of Activity. The Field of Consciousness. Community of Consciousness, Sense of Self 95 Memory; its Automatism. Instincts 96 Perception; Apperception; Thought 99 The Conscious and the Unconscious Fields. Physi- ology of the Latter 101 The Re-forming of Old and the Formation of New Combinations Among the Neurones; Originality; Imagination 103 Relative Dynamic Power of the Conscious and Un- conscious Fields. Dynamic Levels. Attention; Concentration; Initiative; Will Power 105 Sentiency. Sensation. Role of the Telencephalon. . 106 Special Sensations Derived from Physical Impacts. Extero-, Intero-, and Proprioceptors. Pleasure, Pain. The Emotions; Affects.. . 107 10 CONTENTS PAGE Physical Conceptions in the Interpretation of Mind 114 Significance of the Element of Time 115 Significance of Weber's Law 116 Inferences as to the Changes in the Structure of Protoplasm in Response to Changes in the Outside World 118 Limitations of Possibilities : a, Only Such Changes as Protoplasm is Capable of Receiving; b, These Changes Correspond Only Imperfectly to Changes in the Outside World 119 Memory Pictures; Composite Pictures; Abstract Conceptions; Abstract Thinking; Dangers 120 Final Word as to the Biological Interpretation of Mind : Objections to the Greek Word tyuyj and Its Derivatives. Objections to the Latin Word Spiritus and Its Derivatives. . . 122 ADDENDUM The Pathological Physiology of Mind 126 Hysteria, Hypnosis, Dreams 127 Delirium^Confusion, Stupor 131 Hallucinations, Illusions, Delusions 132 Variability of Neurone'Relations 133 The Biological Endogenous Deteriorations. The Precocious Dementias. The Paranoid States 134 The*Appearance and Significance of Fixation 138 Melancholia, Mania 139 INDEX... 143 AN ESSAY ON THE PHYSIOLOGY OF MIND AN INTERPRETATION BASED ON BIOLOGICAL, MORPHOLOGICAL, PHYSICAL, AND CHEMICAL CONSIDERATIONS To the writer it has seemed that all of the phenomena embraced by human experience, no matter what their character, must be approached from the standpoint of cold, unemotional, sci- entific observation and analysis. This neces- sitates as a preliminary an attitude of mind in which preconceived ideas, prejudices of what- soever character, previous beliefs, and concep- tions are set aside. In no field is this more important that in the study of the phenomena embraced under the term "mind." Long the subject of the discussions of metaphysicians and in later times of psychologists, the phenomena of mind have been approached as though they were altogether peculiar in their character and 11 12 THE PHYSIOLOGY OF MIND being; as though a difference essential and in- trinsic separated these phenomena by a wide and hopeless gap from all other phenomena of nature. Let us see whether such an attitude, such a preconceived notion, is justified. When we turn our attention to some of the lower forms of life, for example, to the pro- tozoa, and notably to the simple expression of life as witnessed in the amoeba, we find that the organism reacts in an already complex manner to the environment; thus, when the pseudopod of an amceba conies in contact with a foreign body one of two things occurs: either the pro- toplasm of the pseudopod flows around the for- eign body and thus takes the latter into the interior of its own substance, or the pseudopod is withdrawn. Here we have undoubtedly a "selective" action. If the foreign substance is capable of serving as food, it is appropriated; if not, it is rejected. Should the foreign body be made up both of material capable of serving as food and of material incapable of serving such a purpose, the two are separated; after a time the first disappears, apparently becomes a part of the substance of the amceba; the second is ejected. No one, I believe, would be so ven- THE PHYSIOLOGY OF MIND 13 turesome as to interpret these phenomena as the volitional acts which they so closely re- semble. Evidently they are merely the result of the physical (or physico-chemical) reaction of the protoplasm of the amoeba with the ma- terial of the foreign body. Our increasing knowl- edge of the functions of the cells in the higher animals has taught us that not only have these cells the special functions pertaining to the tis- sues of which they are parts but also that they retain, in addition, the primordial property of selecting, digesting, and assimilating their own food. It would appear that the cells of the various tissues possess each a special structure, a special metabolism; that is, each cell contains special ferments by means of which it builds itself up, adds to its own substance out of the general material of the blood plasma. The cells thus have the power of "selecting" foreign materials, of fragmenting them, and of utilizing them for purposes of reconstruction or as sources of energy. The purely physical character of these changes are, of course, beyond question. Fats are split into alcohol and fatty acids; car- bohydrates are broken up; albumin is con- verted into peptones; the latter are split into 14 THE PHYSIOLOGY OF MIND amino-acids and these again into still simpler bodies. In turn, the cells give up into the blood-stream substances so far reduced that they are no longer sources of energy, can no longer play a role in the metabolism of the cell. Not only have the cells of multicellular forms retained the power of selecting, appropriating, and discarding the various materials concerned in their metabolism, but such cells as are not fixed in the tissues, e. g., the white corpuscles of the blood, have retained in addition the power of independent movements and of act- ually extending and retracting portions of their substance in every way comparable to the pseudopods of the amoeba. Surely no one would ascribe the action of the individual cells of the multicellular animals to volition. Both the "selective" action and the power of reduc- ing the material selected into components suit- able for appropriation into its own substance are properties inherent in living protoplasm and which the tissue cell shares with the most prim- itive unicellular forms. No volitional, no so- called "psychic" act can be considered as enter- ing into the phenomena. It seems almost super- fluous to repeat that they are clearly the result THE PHYSIOLOGY OF MIND 15 of purely physical and chemical processes. They merely instance the action of colloidal sub- stances upon each other and upon other sub- stances; an action in which the ions of the con- tained crystalloids no doubt also play a part; in short, the problem is one of chemistry, of elec- tromagnetic or equivalent reactions. We have in the selection and appropriation of food by the cells of the tissues an instance of the retention by the individual cells of multi- cellular organisms of the primitive properties of the single cell of unicellular forms. When we turn our attention in multicellular forms to other properties which have likewise to do with the reaction of the organism to the environment, other equally interesting facts become apparent. Let us begin with sponges. According to Parker, 1 "Some sponges, such as the Stylatella, appear, when out of water, to be more or less shrivelled or contracted and under other cir- cumstances to be plump and well rounded out. The differences which, for reasons to be men- tioned presently, are known not to be due to the simple physical loss of fluid, are apparently 1 G. H. Parker, Sc.D., "The Elementary Nervous System," Phila- delphia and London, J. B. Lippincott Company, p. 26. 16 THE PHYSIOLOGY OF MIND dependent upon a general contractility of the whole flesh of the sponge which, though slight, may nevertheless enable the sponge to change its form somewhat." Again, the dermal mem- brane of sponges which is a tissue which has not become differentiated into cells, but remains syncytic, has the property of closing the pores of the sponge apparently by flowing over and coalescing, thus forming "over the external end of the pore canal an extremely thin sheet, the pore membrane, near the middle of which the pore has disappeared." 1 The movement of the pore membrane "is hardly to be described as purely amoeboid. It seems to represent a stage of differentiation between amceboid motion and simple muscle contraction which may well in- dicate the kind of contractility that the com- mon flesh of the sponge possesses." 2 In addi- tion, the pores may be closed hi some sponges not only by the formation of a pore membrane but also by the closure of the canal leading to the pore the pore canal itself. "This is prob- ably due, according to Wilson, to a contraction of the epithelial lining in the pore canal acting after the fashion of a sphincter." 3 The cells of 1 See Parker, loc. cit., p. 34. 2 Loc. cit., p. 36. 3 Loc. cit., p. 35. THE PHYSIOLOGY OF MIND 17 this epithelial lining "are in every way com- parable to a primitive form of smooth muscle- fiber. Their superficial position places them in contact with the water passing through the canal and, as they respond to differences in this water, they are without doubt capable of direct stimulation." To repeat, then, we have in the sponges not only a general contractility of the organism as a whole, together with an amoeboid movement of the dermal membrane, but also a sphincter-like action in the canals due to spe- cialized cells. The latter correspond to the smooth muscle cells of other metazoa. They have, of course, no nerve supply and are de- pendent for their stimulation to contraction on the physical contact with the changing water and its contained substances. It is interesting to note that in the higher animals muscle-fibers still exist which like these primitive muscle cells of sponges are capable of responding to direct physical stimulation inde- pendently of any nervous influence. This has been clearly demonstrated, for instance, by a number of observers to be the case in the iris. In fishes, amphibians, birds and mammals, and probably in the eyes of cephalopods, the sphinc- 18 THE PHYSIOLOGY OF MIND ter of the pupil may be regarded as normally subject to direct stimulation by light, notwith- standing the fact that it is also under nervous control. 1 Similarly, the vertebrate heart mus- cle appears to be equally subject to direct phys- ical stimulation. While the adult heart is abundantly supplied with nerves and, indeed, itself contains an abundance of nerve-cells, no such facts obtain, so far as is known, in regard to the developing heart of the embryo. Indeed, in the chick the heart appears in about twenty- three hours of incubation and begins to pulsate about six hours later, at a time when the neural crests and neuroblasts have not. yet been dif- ferentiated. Hence, there is every reason to believe that in the beginning it is absolutely free from possible nervous influence and that its beat is purely myogenic. 2 Many similar in- stances of muscle activity independent of ner- vous influence might be cited. It is true ap- parently of the heart of the tunicate, of the muscle-fibers of the amnion of the chick, and of the circular and acontial fibers of sea-anemones. 3 We have, then, as one of the primary facts of 1 See Parker, loc. cit., pp. 50-53. - Loc. cit., pp. 53-56. 3 Loc. cit., pp. 59-61. THE PHYSIOLOGY OF MIND 19 the reaction of the organism to the environ- ment a response in movement. This is expressed in the amoeba in the movements of its pseudo- pods, and, in such multicellular forms as the sponges, in the movements of the syncytic dermal membrane, in the contraction of the cells about the canals, and in the movement of the body of the animal as a whole. The next question that presents itself is as to the capacity of living protoplasm for the trans- mission of motion through its own substance. It is not my intention to take up at this point the reaction of protoplasm to light, to heat, to electricity, or to sound, but rather its reaction to those more grossly mechanical forces implied by the impact of foreign bodies. In the sense here employed mere contact implies such an impact. To begin, if transmission of a mechan- ical impact actually takes place, it would not be surprising to find that this transmission is rela- tively slow. Proteins are extremely complex compounds. They are made up of many amino-acids; as many as seventeen. Emil Fischer, it may be recalled, succeeded in com- bining as many as nineteen amino-acids in the synthetic construction of an artificial protein- 20 THE PHYSIOLOGY OF MIND It is a legitimate inference from these and other facts that the structure of living protoplasm is that of an exceedingly complex colloid, the dis- perse and continuous phases of which must necessarily bear multiple and complicated rela- tions of surface and interfacial tension and of electrical charge to each other. It would seem that considerable time relatively must neces- sarily elapse for the diffusion or transmission of a mechanical impact through such a substance. That transmission or diffusion takes place from one part of a protozoan to another part as a result of impact or contact is exceedingly probable. In the amoeba the transmission ap- pears to be more or less widely diffused, for not only a pseudopod but the organism as a whole may move toward the food. The diffusion, however, appears to be very slow. In simple multicellular forms such as the sponges trans- mission likewise takes place. Thus, Parker states 1 that if a pin is stuck into a finger of Stylatella at 1J cm. from the osculum, the osculum will close in about ten minutes; and further, that ".the sluggish transmission upon which this reaction depends represents without 1 See Parker, loc. cit., p. 42. THE PHYSIOLOGY OF MIND 21 doubt that elemental property of protoplasmic transmission from which true nervous activity has been evolved. It may, therefore, not in- appropriately be called neuroid transmission." 1 Similarly, in other animals a transmission of motion through non-active and non-nervous protoplasmic tissue can be demonstrated as when motion is transmitted from one field of cilia to another, although quiescent or non- ciliated tissues lie between. According to Parker, "it appears that the ordinary tissues of animals, at least their ciliated epithelia, may exhibit sluggish forms of transmission that are so like those seen in sponges as to admit of being classed under the single head of neuroid trans- mission." 2 Obviously, it is greatly to the advantage of an organism when special pathways for trans- mission are differentiated. Such pathways make their appearance in the primitive nervous appa- ratus of coelenterates. This nervous apparatus has been elaborately studied in jelly-fishes and sea-anemones. In the former, impressions stimuli upon the marginal bodies are diffused through deeper lying muscle-cells, so that a 1 See Parker, loc. cit., p. 64. 2 Loc. cit., p. 75. 22 THE PHYSIOLOGY OF MIND contraction takes place in the large circular sheet of muscle that forms the sphincter-like organ midway between the centrally located mouth and the edge of the bell. This contrac- tion reduces the cavity of the bell and by thus driving the water out of this cavity forces the animal forward. 1 In the sea-anemones an impulse a mechan- ical stimulus applied to the surface of the ani- mal results in a retraction of the oral disc. Investigations have shown that the impulse both in the jelly-fish and the sea-anemone is diffused through a well-defined nervous net- work. When this nerve tissue is studied it is found to consist of a diffuse and continuous network which also contains cells. The fact that the network is continuous and diffuse sug- gests an analogy to the syncytic tissue of the dermal layer of the sponges. In keeping, how- ever, with what one would expect, the evolu- tion of special pathways for transmission, leads judging by the time of the response to an increased speed of transmission; the response, which is very slow in sponges, is much more rapid in the ccelenterates. 1 See Parker, loc. cit., p. 103. THE PHYSIOLOGY OF MIND 23 Let us now turn our attention once more to the primitive muscle-cell in the pore canals of the sponges. This muscle, as we have seen, sug- gests the smooth, unstriated muscle-cell of the higher animals; indeed, such a muscle-cell is still found in some of the tissues of the latter existing as a prototype independent of nervous influence. A muscle-cell independent of .ner- vous influence reacts directly, as we have seen, to a stimulus applied to it. This is unques- tionably the case in the muscle-cell in the pore canal of the sponge, in which the stimulus is the flowing water and the substances contained in the latter; similar facts obtain in the case of the other independent smooth muscle-cells that have been instanced. In the sea-anemones and the jelly-fishes, however, the muscle-cell no longer receives its stimulus directly from the environment. There is now interposed an epi- thelial cell which receives the stimulus and transmits it to the muscle-cell. This epithelial receiving cell acts as a "sense" cell and is termed the "receptor," while the muscle-cell to which it conveys the stimulus is known as the "effector." Later a third structure appears inter- posed between the receiving cell and the muscle- 24 THE PHYSIOLOGY OF MIND cell. The function of the new structure, a cell termed by Parker "protoneurone," appears to be to diffuse and to distribute to the muscle- cell or cells the stimulus derived from the re- ceiving cell. Its function is that of an inter- mediary. Evidently we have presented here an arrangement which is the prototype of the sensjory, nervous, and muscular system of the higher animals. Certain other important considerations now present themselves. In the higher animals the nervous system, which in sea-anemones and jelly-fishes is largely superficial, existing in the epithelial layers of the animal, becomes grad- ually more and more deeply seated and better protected. This is seen in the higher inver- tebrates and vertebrates alike. In invertebrates there is a gradual retreat, a migration, of the nervous apparatus into the interior of the ani- mal; in vertebrates, as evidenced by embry- ology, a portion of the epidermal layer, a por- tion doubtless corresponding to a primitive area of receptor or sensory epithelium, becomes grooved and finally inclosed by the infolding of the edges of the groove. Interesting as these facts are, a still more THE PHYSIOLOGY OF MIND 25 important consideration remains. The nervous system of ccelenterates, as we have pointed out consists of a diffuse and continuous network which also contains cells and which is grossly analogous to the syncytic tissue of the dermal layer of sponges. Restating the facts thus far considered, we find that the most elemental form of response by an organism to the en- vironment next to the movement of the pseu- dopod of an amoeba consists in the contraction of an epithelial cell, a cell analogous to a smooth muscle-cell, directly in response to a stimulus. The next stage consists, as also pointed out, in the appearance of another epithelial cell which does not itself contract, but receives the im- pression or stimulus and transmits it to the contractile cell. In this primitive arrangement the first or receiving cell, the receptor, is at- tached directly to the muscle-cell, the effector. As a matter of fact, a number or a group of re- ceiving cells are attached to a number or a group of muscle-cells. Further, this arrange- ment "is complicated by the fact that the cen- tral branches of the receptive cells are not only applied to the muscle-cells, but form among themselves a network of communication whereby 26 THE PHYSIOLOGY OF MIND the impulses that arise from a few receptive cells may be transmitted to many muscle-cells instead of being limited to a restricted group." 1 The final stage consists in the differentiation of additional cells now interposed between the primitive receiving cell and the muscle-cells. The network now becomes exceedingly com- plicated, but it presents this distinguishing feature, its fibers are continuous. The cells which it contains are clearly primitive nerve- cells and, as already stated, Parker has applied to them the term "protoneurones." Further, there is no separation of these protoneurones from each other such as occurs in the neurones of vertebrates. There is a free interchange be- tween them of the fibers of the network. There is therefore a wide diffusion of transmission which is totally different from the transmission along definite paths as seen in vertebrates. It is interesting to note, however, in this connec- tion that even in vertebrates nerve nets, diffuse and continuous, are found in certain struc- tures, namely, in the walls of the intestine and in the heart and blood-vessels. The nerve cells found in these structures present all the char- 1 See Parker, loc. cit., pp. 200, 201. THE PHYSIOLOGY OF MIND 27 acteristics of protoneurones, and as in the coelenterates form a continuous network. 1 It is, however, with the differentiated neurone of the central nervous system of vertebrates that we are most concerned. Here the cells which give rise to nerve-cells are in the embryo entirely distinct and separate, and it is only by developing extensions or processes that one nerve-cell comes into relation with other nerve- cells; but there is never any fusion or exchange of fibers between them. Each nerve-cell is a separate and distinct histological integer. It is a unit which is made up of the cell body and the cell processes. By means of the latter it comes into proximity with other nerve-cells often far distant. The processes terminate in brush-like tufts, basket-like formations, and in other ways. The approximated end-formations of two nerve- cells is spoken of very appropriately as a syn- apse. The nerve-cell, in general terms, is made up of a cell body and two kinds of processes; at one extremity are found one or multiple proc- esses leading to the cell body; these are known as the dendrites; at the other extremity is found a process leading from the cell body; this is 1 See Parker, loc. cit., pp. 118, 128. 28 THE PHYSIOLOGY OF MIND known as the axone. To this entire structure Waldeyer in 1891 applied the term "neurone,'' which has been universally accepted and is now in common use. Occasionally there is more than one axone; quite frequently, too, the axone gives off small side branches, usually near the cell body; these are known as collaterals. For a discussion of nervous function clear conceptions of nervous structure are absolutely essential. To repeat, then, the neurone cor- responds morphologically to one cell; it is an anatomical and genetic unit. It comes into close relations with other neurones, but remains anatomically distinct and separate. The point or, rather, the structure at which the juxta- position of the processes of two neurones takes place the synapse assumes, therefore, a spe- cial importance in the problem of transmission. 1 Not only the independence of the individual neurone but the presence of the synapse dis- tinguishes the nervous system of the higher animals from that of the ccelenterates, and it 1 Instead of the cells coming into relation by the approximation of the end-tufts of the axone of one cell to the dendrites of another, the end-tufts of the axone of one cell may terminate about the body of the second cell, but in neither case is there any fusion or continuity of struc- ture. THE PHYSIOLOGY OF MIND 29 may, therefore, be spoken of as a synaptic ner- vous system in contrast with the nerve-net of the coelenterates which is essentially syncytic. A very important fact now becomes mani- fest. In the nerve net of the coelenterates trans- mission is essentially diffuse in character. Only in a very limited degree is the response to a stimulus differentiated. According to Parker, a stimulus e. g., a fine glass rod applied to a single spot on the body of a sea-anemone may be followed by a contraction of its whole mus- culature. 1 However, if the stimulus be less vigorous and limited e. g., if light be thrown on one side of the animal it responds usually by turning its oral disc toward the light. Again, stimulation of its tentacles by food will cause its transverse mesenteric muscles to contract and thus open its oesophagus. Further, transmis- sion though diffuse in certain nerve-nets takes place more readily in one direction than in another; e. g., in the tentacles of the sea- anemone, in which transmission is much more freely accomplished in a proximal direction than in a distal one. This slight tendency to spe- cialization in the responses exhibited by the 1 Loc. cit., pp. 99, 100, 07. 30 THE PHYSIOLOGY OF MIND sea-anemone is to be looked upon as the fore- runner of the extremely specialized and limited responses met with in the higher animals. How- ever, while a nerve-net may transmit more freely in one direction than another, it really transmits in all. Transmission in one direc- tion, that is, polarity of transmission, exists in a very imperfect degree in the nerve-net. In the sy nap tic nervous system, however, it is not only established, but is absolute. For example, while it is possible to elicit a response to a stimulus applied in the course of an afferent neurone of the spinal cord, as in obtaining a spinal reflex, no amount of stimulus applied to the efferent neurone, for instance, to the cen- tral end of a divided motor spinal root, will elicit any response whatever. Were it not for the synapses and the consequent polarity of the neurone, a stimulus so applied should dif- fuse to other neurones in the cord; e. g., to sen- sory neurones and from these again to motor neurones, and thus lead to a response; but none takes place. It is to the synaptic nervous system of the vertebrates that we will now direct our atten- tion. We have already seen that the smooth THE PHYSIOLOGY OF MIND 31 muscle-cell of the pore-canal of the sponge re- sponds to a direct stimulation. In the coelen- terates a receiving cell is interposed between the muscle and the stimulus. The muscle mani- fests the response; it is the effector; the receiv- ing cell is the receptor. At the next stage of differentiation, as already pointed out, another cell is interposed which now transmits the im- pulse from the receptor to the effector. In ver- tebrates this constitutes the simplest expression of a response, or, to use the physiological term, a reflex. An impression is made on the cuta- neous surface, is transmitted along the dendrite of the afferent neurone; thence to the cell body of the latter; thence along its axone to its end- tufts which are in relation with the dendrites of the transmitting cell and form with the latter a synapse; thence to the body of the transmitting cell (the motor cell in the ventral horn of the cord), and thence by the axone of this transmitting cell to the end-plate on the muscle-fiber. The mechanism of the response does not, however, remain as simple as this; for other neurones, intercalary neurones, are fur- ther interposed; thus a neurone may be inter- posed between the afferent cell or receptor, the 32 THE PHYSIOLOGY OF MIND sensory neurone, and the motor neurones. The effect of such an intercalary neurone may be twofold: first, it may reinforce, i. e., increase the volume and' intensity of the transmission; secondly, it may come into relation with neu- rones other than the ones between which it is interposed and thus make possible a more ex- tensive and a more complicated response. An a priori consideration would suggest that there are necessarily great variations in the sim- plicity or complexity of the responses as well as w r ide variations in the degree with which such responses are fixed or stereotyped. These in- ferences, I need hardly add, are in accord with fact. In the spinal reflexes, for instance, we have examples of relative simplicity and stereotypy of response. In the knee-jerk we have an ex- ample of an exceedingly simple and fixed re- sponse. It is invariably the same and inde- pendent of volition; it is subject, of course, to variations in diffusion and degree dependent upon secondary factors, but its character never changes. The neural mechanism upon which it depends is relatively simple. However, the very simplicity and stereotypy of the knee reflex bespeaks a response that has THE PHYSIOLOGY OF MIND 33 become differentiated and limited, and it serves our present purpose merely as offering an ex- ample of a simple mechanism of spinal re- sponse. It is exceedingly probable that in the course of development differentiations of lim- ited relationships between intercalary neurones and efferent neurones ensued relatively late, and that the primitive arrangement was one which permitted of the more or less wide diffusion of the stimuli received by the afferent neurones. In keeping with this we note in the fish in re- sponse to such stimuli movements which in- volve the musculature of the entire trunk. Evi- dently the mechanism of response must at first have been very general in character. It must have consisted in the linking of intercalary neu- rones and 'the consequent formation of path- ways of transmission general in character, and, furthermore, common to the transmission of stimuli received from many different receptors. Having laid a foundation for the conception of the mechanism by means of which stimuli are received and transmitted, let us now turn our attention briefly to the stimuli which the or- 34 THE PHYSIOLOGY OF MIND ganism is capable of receiving. Thus far we have considered merely the most primitive of all stimuli, namely, contact with foreign bodies. Such contact constitutes an impact grossly mechanical or physical in character. Evidently, living protoplasm is, in addition, exposed to actions that are chemical, to the movements and course vibrations of the medium in which it is immersed, as well as to the various forces that pervade the physical world. Protoplasm is, of course, destroyed by any chemical action that radically interferes with its structure. Living protoplasm, as pointed out, is an exceedingly complex colloid; it is relatively unstable and is constantly undergoing change. It is being constantly built up and yet is being constantly oxidized and reduced. Such changes necessarily mean an interplay within comparatively narrow limits. If living proto- plasm is exposed, for instance, to the gross ac- tion of an acid or an alkali, its destruction necessarily follows. There is, however, a wide range in which chemical action can take place without such result. Such non-destructive ac- tion would naturally be influenced, first, by the nature of the substance diffused through the THE PHYSIOLOGY OF MIND 35 surrounding medium, and secondly, by the de- gree of its dilution. The reaction of the proto- plasm to such influences cannot, of course, be observed by us through the microscope, but that such chemical actions do take place is evidenced to us in our own persons by our senses of taste and smell. Further, it will be- come apparent as we proceed that the reaction of the organism to the chemical impressions of the environment have profoundly influenced the development of the nervous system. When we turn our attention to the move- ments and vibrations of the medium in which the protoplasm is immersed, we at once find numerous evidences that the protoplasm reacts to such influences. In the very simplest forms, such as the protozoa, the coarse movements of the water currents and the like possibly facili- tate the changes implied by oxidation, but do nothing else. Soon, however, in the metazoa we observe the appearance of small cavities- vesicles which contain one or more particles of solid mineral matter and which constitute an apparatus by means of which the movements, the vibrations, of the surrounding medium are taken up arrested as it were and thus for- 36 THE PHYSIOLOGY OF MIND cibly transmitted to the body of the organism. Such an apparatus, though it is termed an ear, an otic vesicle, may take up movements far coarser than those which in ourselves give rise to sound. Again, in fishes there is, in addition to a well-differentiated ear, an apparatus which extends in linear form from the head on each side of the body to the tail. It is known as the lateral line system and consists of a tube having at intervals an open space closed by a mem- brane beneath which is found a structure in- distinguishable in its essential features from a macula acustica. Each such macula contains epithelial cells bearing hair-like appendages and each is surmounted by a small jelly-like mass containing a few granules of mineral matter. It is exceedingly probable that this apparatus, existing as it does in addition to the ear, has to do with the reception of vibrations other than those of sound; namely, waves and movements of relatively great length. 1 It would appear, then, that in addition to the chemical impressions of the environment, the movements and vibrations of the surrounding 1 See, among others, Dercum, Proceedings Academy of Nat. Sci., Philadelphia, 1879, p. 152. THE PHYSIOLOGY OF MIND 37 medium are taken up in greater or less degree by living protoplasm. These movements seem to play an indifferent role in the protozoa and in plant life, but in metazoa an apparatus sooner or later makes its appearance, the function of which is to arrest and to transmit, and, in many instances, to magnify what is purely a mechan- ical or physical impression. Similarly, living protoplasm has the function of taking up other incident forces. Especially is this the case in regard to light. The simpler forms of life -e. g., the amoeba and other protozoa are largely transparent to light. It is probable that the light vibrations so trans- mitted influence notwithstanding the chemical changes in the protoplasm; indeed, this is so evident in plant life as to admit of no question. However, very early we note in many protozoa the appearance of a small mass of red or dark red pigment, a so-called eye spot or stigma, a mass which clearly is not, or is less, transparent to light than the remaining protoplasm, and whose action is apparently to arrest and trans- form the light vibrations and, possibly, to trans- mit this transformed energy to the general pro- toplasmic mass. Clearly we have here a mech- 38 THE PHYSIOLOGY OF MIND anism, a modification of structure, analogous to the formation of the otic vesicle, the function of which with its contained mineral granules (otoliths) is obviously to arrest and transmit coarse physical vibrations. Heat likewise greatly influences the activity of living protoplasm. The reactions of amcebae and other protozoa to variations in tempera- ture are well known. Whether in given forms the eye spots, the stigmata, play here also a role is not known, though it is, of course, not improbable. However, the presence of the stigmata is clearly not necessary to the tem- perature reactions of the primitive organism. All things considered, special structures for the "taking up" of heat rays do not appear to be developed until late in the evolution of the metazoa, and our knowledge of them is largely inferential. Regarding their actual existence, however, there can be no doubt; of this our ability to appreciate hot and cold and, indeed, many gradations of temperature, offers indis- putable evidence. A very striking fact now becomes apparent, namely, that the various mechanisms for the special reception of the incident forces of the THE PHYSIOLOGY OF MIND 39 environment are exceedingly small in number. They are limited to receptors for contact, for coarse movements and vibrations of the sur- rounding medium, for chemical changes, and for the forces of light and heat. This is essentially the arrangement in the higher metazoa and notably in our own persons. This, however,' leaves the organism without any provision for the reception appreciation of vast ranges of vibrations of whose existence we have in con- sequence only an inferential knowledge. Be- sides contact, touch will give us information only of coarse vibrations numbering less than 30 per second; thence, vibrations from 30 to 30,000 per second are appreciated by the ear. Now ensues a great hiatus, for the organism is unable to appreciate any vibrations between 30,000 per second and 3000 billion per second. Vibrations from 3000 billion to 800,000 billion are appreciated as radiant heat; 400,000 billion to 800,000 billion are appreciated as light. For vibrations from 800,000 billion to 6,000,000,000 billion, embracing the ultra-violet rays and the z-rays, there is no appreciation whatever. 1 1 Herrick, Introduction to Neurology, second edition, p. 77. 40 THE PHYSIOLOGY OF MIND When we consider the vast range and number of the forces at work in the universe, the ex- ceedingly limited capacity of the organism to become cognizant of its environment becomes very apparent. Living protoplasm fails utterly to develop receptors for these unnumbered manifestations of energy. Protoplasm seems to be "transparent" to them. Have we not a hint here as to the structure of protoplasm? If deluged by them in great volume it may be de- stroyed, but as ordinarily exposed in the course of nature to electricity, the ultra-violet ray, the x-ray, and other rays it remains unaffected. It is very suggestive, too, that it is practically transparent to light rays and is obliged to de- velop a pigment, the stigma, the visual purple. Similarly, it is largely negative to coarse vibra- tions and requires the development of a vesicle with its contained otolith. In order that the significance of the above facts may be fully appreciated . let us recall to our minds once more the nature of living proto- plasm. It is, as we have already pointed out, an exceedingly complex colloid, built up of many complex amino-acids distributed through varied disperse and continuous phases. It is a very THE PHYSIOLOGY OF MIND 41 unstable compound, for it is constantly under- going changes. It is constantly being oxidized and reduced, but is as constantly being built up. Foreign materials, proteins, fats, and car- bohydrates are through its fermentative (i. e., chemical, electro-physical) action fragmented until they become identical in character with the molecules of the original protoplasmic mass and become part of its substance. During this process and in the further continuance of the chemical change, that is, in the continued proc- ess of oxidation, energy is liberated. The older particles are finally chemically so far reduced that they become inert and then spontaneously make their exit by solution into the surrounding medium. It is this continuous chemical change with its accompanying evolution of energy that constitutes the phenomenon presented by living matter. 1 Evidently, if so complex and unstable a com- pound as living protoplasm when first evolved had been vulnerable to the innumerable in- cident forces of the universe, it could never have survived. Curiously, it has been almost 1 The mineral salts ions of the crystalloids undoubtedly arrange themselves during this process in accordance with electrophysica' principles, and no doubt play an important rdle. 42 THE PHYSIOLOGY OF MIND wholly negative in its reaction to these. Ex- tremes of heat and cold, coarse physical de- struction, have been the most it had ordinarily to contend with. Excessively rarely have other agencies interfered with its existence. Its very "transparency" has been its salvation. Perhaps it is its complexity, its semifluidity its very in- ability to take up manifold modes of motion- its colloidal plasticity, its peculiar molecular structure, that have made possible the passage through it of such a vast array of forces with- out change in its substance. After all, these forces do influence it and play a role in its physics and chemistry, but certainly that role, as it occurs in nature not in the laboratory- is not a destructive one. We have already considered (see p. 23) the evolution or adaptation in metazoa of a sur- face cell to receive external impressions, e. g., of contact, and which receiving cell (receptor) transmits the impact or impulse to a contig- uous contractile cell (muscle-cell, effector) either directly or it may be through an intermediate cell or cells. Evidently these primitive surface cells were capable of receiving all of the im- pressions which the protoplasm itself was cap- THE PHYSIOLOGY OF MIND 43 able of receiving. These impressions consisted primarily of those of contact and of coarse vibration. That substances contained in the medium in which the organism was immersed also affected the surface cells chemically is extremely probable. It seems equally clear that the surface cells were also affected by the vibrations which give rise to sound and by those which give rise to heat and light. In both of the latter instances, however, it is evident that the degree and extent in which the impacts could be taken up depended upon the presence of special and probably, at first, purely incidental factors; on the one hand, on the presence of coarse mineral particles, and on the other of particles of pigment; i. e., of particles derived from the original protoplasm and so changed as to be able to arrest in a measure the incident forces. In addition, then, let us repeat, to contact and coarse vibrations, the primitive surface re- ceiving cell also received those impacts termed "chemical." These impacts, molecular in char- acter, are those which, as already pointed out, give rise in ourselves to the sensations of smell and taste. It would seem that the reception of 44 THE PHYSIOLOGY OF MIND chemical impressions was almost as primitive if not quite as primitive a quality as the reception of contact and coarse vibrations. On a priori grounds we would almost expect the chemical sense or senses to have assumed a relatively high degree of importance; and this, indeed, is found to be the case, judging from the facts of vertebrate morphology. It would appear that relatively early certain receiving cells became especially adapted to receiving chemical im- pressions and that this finally became their special and sole function. It is important at this point to note a distinction between the senses of smell and taste. The sense of smell is excited by objects external to the organism, usually by objects at some distance, and the impressions received from which cause the or- ganism to approach or to move away from the object. The sense of taste, on the other hand, deals with objects that have entered the oral cavity or at least come into close contact with it and which bring about responses within the body of the animal, namely, visceral responses dealing with digestion. As expressed by Sher- rington, the sense of smell is exteroceptive, while taste is interoceptive. Clearly, it is the extero- THE PHYSIOLOGY OF MIND 45 ceptive sense of smell which deals directly with the environment and as such it greatly out- ranks in importance the sense of taste. In keeping with this we find in fishes that almost the whole of the cerebral hemisphere is an organ of smell, while the portion devoted to the sense of taste is much smaller and appears to be in close anatomical relation with the portion the visceral area 1 devoted to impressions re- ceived from the viscera. However, in fishes the receptors for taste are found also outside of the oral cavity about the mouth and, indeed, in some forms are rather extensively distributed externally; so that in fishes the sense of taste is not as strictly interoceptive as with ourselves, but also in part exteroceptive. The great im- portance of smell as an exteroceptive sense be- comes evident when we reflect upon the very great range in the number and variety of the impressions, the infinitely small size of the par- ticles concerned, and the relatively great dis- tance at which they may be appreciated. Taste, on the other hand, has to do only with substances in immediate contact with the re- ceptors, while the variety of impressions pos- 1 See Herrick, loc. cit., pp. 119, 273. 46 THE PHYSIOLOGY OF MIND sible is exceedingly small; namely, merely salty, sour, bitter, and sweet. Flavors, it should be remembered, are appreciated only through the sense of smell. Just as in the course of development special receptors were differentiated for chemical im- pressions, special receptors were differentiated for the reception of sound and light, and to which have been adapted various structures for in- tensifying and elaborating the impressions re- ceived. A consideration of the latter factors would take us too far afield and, further, is not necessary for our purpose. Suffice it to say that highly specialized receptors with highly complex additions have in the course of time made their appearance, and that they are all expressive of a common truth, namely, that they receive and transmit into the interior of the organism cer- tain definite impacts from the external world. That there are more than five pathways for the ingress of these impacts need not here be pointed out; the consideration of others than those thus far discussed may be safely deferred for the present. Having emphasized the purely physical char- acter of the role played by the receptors, let us THE PHYSIOLOGY OF MIND 47 turn our attention once more to the transmis- sion of the impacts through the organism. How does the organism respond to the multitude of impressions received? What are the reasons therefore? In how far are responses fixed? In how far are they variable? The simplest form of response, as we have already seen, is the response of a muscle-cell to direct stimulation; the next in the course of evolution is the reception by an epithelial cell, a receptor, of the impact, and the transmission of the latter to a contiguous muscle-cell, an effector; the third state consists in the inter- polation between the receptor and the effector of another cell whose function is that purely of transmitting the impact from the first cell to the second. This third cell may have relations, however, with several effectors, and thus the response induced may be less simple and pro- portionately extended. This intermediate cell has been termed by biologists the "adjuster." It should, of course, have a definite name, but to the writer it has seemed that the word "ad- juster," implying as it does independence of action or possibly volition, is open to objection. The action of the intermediate cell is purely 48 THE PHYSIOLOGY OF MIND physical and, needless to say, automatic. Its presence, however, opens up, as we will see, enormous possibilities as to the degree and the character of the response. As already pointed out (see p. 31), other transmitting cells, inter- calary neurones, are in the course of develop- ment farther interposed. The role of the latter in increasing the volume and intensity of the transmission and in adding to the complexity of the response we have already indicated. Evidently the presence of the intercalary neurones has made possible the establishment of definite pathways of transmission. Impacts derived from many sources would tend to form average pathways of transmission to the ef- fectors. To use the words of Sherrington, "That portion of the synaptic nervous system which is termed 'central' is the portion where the nervous paths from various peripheral organs meet and establish paths in common, i. e., 'common paths ' ' The central nervous system of vertebrates is primitively a longitudinal tubular structure which lies above another longitudinal tubular structure upon which the nutrition of the animal depends, namely, the alimentary canal. The material admitted to THE PHYSIOLOGY OF MIND 49 the latter traverses its entire length. Evidently the reception of material which may serve as food is of primal importance to the animal. Given the "polarity" of the latter i. e., the differentiation of a cephalic and a caudal ex- tremity it follows that the interplay of re- ceptors and effectors to bring about the intake of food at the cephalic end is a necessary out- come of the action of the individual receptors and the establishment of common paths of transmission. The primitive nervous system of vertebrates was in its essentials a tube in which the nerves coming from the peripheral surfaces terminated synaptically in neurones in the walls of the tube; probably there was an arrangement in segments, certain nerve aggregations corre- sponding to certain areas. These tubal centers were doubtless connected with each other by intercalary neurones which communicated syn- aptically with each other to form "internuncial paths." In this way many muscles would prob- ably be made to respond simultaneously or suc- cessively to an impression made upon a limited number of cutaneous receptors. If we turn our attention to the cephalic end of the animal, we note the presence of certain aggregations of 50 THE PHYSIOLOGY OF MIND neurones about the tube which stand in definite relation to certain receptors situated about the head, the relation being very much the same as the segmental relation in the tube lower down. Here, to restate .the fact, definite cutaneous levels of receptors are related to the neurone aggregations at the same levels, each such ar- rangement constituting a segment. The first aggregation of neurones that we meet with in the primitive vertebrate forms is that constituting the olfactory lobe which is in close relation with the receptors in the olfactory mucous membrane. Back of the olfactory lobe we note the presence of a lobe related to the receptors in the eye; next an aggregation re- lated to the receptors in the ear, and so on. Naturally these facts find their simplest ex- pression in the fish. Speaking of the dog-fish, Herrick states 1 that we may recognize in this fish a "nose brain," an "eye brain," an "ear brain," a "visceral brain," and a "skin brain." Each "brain" is related, let us repeat, to certain receptors and to these only. Further, each set of receptors and its corresponding central neu- rones is adapted to the reception of certain im- 1 See Herrick, loc. cit., p". 121. THE PHYSIOLOGY OF MIND 51 pacts or stimuli only; thus the receptors for the olfactory lobes can receive only chemical im- pressions; the receptors for the optic lobes only the impacts of light; those for the ear only the impacts of sound, and so on. In other words, each receptor can accept only its own special stimulus; the latter is known technically as the "adequate" stimulus. We are impressed at once by the relatively enormous size in the fish of the olfactory lobes. We are justified in inferring that the chemical sense in fishes is most important. Its receptors are placed immediately above the oral cavity and its function in the approach of the organ- ism to food and in the intake of food is quite obvious. W T e note that the chemical impacts, i. e., odors, are often received from great dis- tances. The question arises why does the organism as a whole respond to the reception of such impacts by an approach? Here we are forced in a measure into the field of speculation. However, the phenomenon must be purely physical and therefore capable of a physical interpretation. Once more we are referred to the reactions of living protoplasm to the impacts of the external world. Evidently these impacts 52 THE PHYSIOLOGY OF MIND can be roughly divided into two groups: first, those whose motions can be taken up by the protoplasm with little or no consumption of its own substance, and, secondly, those in which the vibrations or molecular movements im- parted by the impacts tend to disrupt, to dis- organize, or destroy its structure. Evidently, chemical impressions which are in harmony or in consonance with the protoplasm of the ol- factory receptors, or, to state it in other words, whose chemical or physical motions are ac- cepted and transmitted by the receptors with no or a minimal change in the protoplasm of the latter, establish a direction of least resist- ance. Possibly this reaction, in its essence, does not differ from that which leads the amceba to throw out a pseudopod toward a neighbor- ing mass of food. In the latter (as we have already seen on p. 13) we have reason to believe that the phenomenon is purely physical or dynamic. Internuncial fibers connect the olfactory lobes with the centers lower down, namely, with the neurones in the spinal cord which innervate the muscles on either side of the trunk. In response to an impression received primarily through the THE PHYSIOLOGY OF MIND 53 olfactory receptors these muscles contract. The neurones which supply the two sides are syn- aptically so related that when the muscles of one side of the trunk contract, contraction of the muscles of the other side is inhibited. The result is an alternate contraction of the muscles of the two sides, which causes the body of the animal to be propelled forward as in swimming. The neurone relationships which necessitate the alternate contractions and alternate inhibitions or relaxations of the two sides are in part direct and in part indirect through the cerebellum. With these subsidiary problems we are, how- ever, not at present concerned. Should the chemical impressions be harmful or of such a nature as to portend harm, it is easy to understand how reverse movements should occur and the a.nimal be moved away. Everything depends upon the development of the internuncial paths. The latter are clearly association paths which when once fully de- veloped respond accurately and, it is needless to add, automatically to the olfactory im- pressions. Further, it is very probable that in the course of evolution these olfactory impres- sions would not necessarily be limited to those 54 THE PHYSIOLOGY OF MIND which merely affected the protoplasm of the receptors for good or for ill, but for those which affected the tissues of the organism as a whole. While the reader may find objection to the above explanation, the fact remains, I think, beyond reasonable question that the approach or re- treat of the fish in response to olfactory im- pressions is a purely automatic phenomenon. When we turn our attention to the eye, the ear, and the lateral line system of the fish, other important and interesting facts suggest them- selves. Thus it is exceedingly probable that the field of vision is primarily one for the perception of moving objects rather than for those which are stationary. Food, already perceived by its odor, makes also in moving an impression on the retina. Owing to the internuncial path- ways the action of the olfactory apparatus in bringing about contraction of the muscles in swimming would now be reinforced. A similar effect would be exerted if the object also made a sound and so excited the ear, or produced coarse waves in the water and so excited the lateral lines. Whatever explanation we adopt, whether we consider the olfactory impacts the chemical THE PHYSIOLOGY OF MIND 55 molecular movements of smell as establishing a line of least resistance, or whether we adopt the explanation of these impacts establishing an "attraction," the conclusion is alike inevitable that the resulting approach of the fish toward the food is, let us repeat, automatic. Similarly the reaction of the other "brains" to their spe- cial receptors the eye brain, the ear brain, the skin brain must be alike physical and auto- matic. It may, I think, be safely assumed that the other functions of the fish in which the nervous system plays a part, such as digestion, respira- tion, circulation, and nutrition, are similarly automatic; in fine, that all the neural functions are automatically performed. The question arises can we draw a like conclusion as regards the nervous system of the higher vertebrate forms, including man? Let us see what the facts justify. The automatic character of a spinal response or reflex must be admitted without question. Secondly, this response is fixed and invariable. A similar interpretation must, I think, be ex- tended to the responses which involve the brain stem, namely, the medulla, the pons, the crura 56 THE PHYSIOLOGY OF MIND cerebri, the thalamus, and the corpus striatum; indeed, the brain stem is frequently spoken of as a segmental apparatus, just as we apply the conception of a segmental apparatus to the spinal cord. It is also spoken of as the palseo- encephalon (Edinger) as it represents the prim- itive vertebrate brain. To the brain stem we must add the cerebellum whose activities are alike "invariable, innate, structurally predeter- mined." 1 This leaves us as the only structure permitting a variable response the cerebral cortex. It may be here noted that such modifications of the invariable response as an animal betrays in its behavior under changed external condi- tions, such as absence or surplus of food or of oxygen, or such changes in response as may have their origin in changed physiological states within the organism itself, are not here included in the expression "variable" response, but rather such responses as would suggest, other things equal, a volitional act, i. e., "choice" on the part of the animal. "Choice" in this sense is manifested by such elementary forms as the amoeba, and, as we have seen, by the individual 1 See Herrick, loc. cit., p. 124. THE PHYSIOLOGY OF MIND 57 cells of the body tissues. How this apparent choice is to be explained on purely physical and chemical principles we have also seen. Let us now take up the "variable" responses of the higher vertebrates for detailed consideration. The end of the primitive neural tube, the telencephalon, also spoken of as the neo-en- cephalon, has no segmental relationships. It can, therefore, only be in relation with, and grow in relation with, the other portions of the neural tube. Its neurones in their development and multiplication can only establish relation- ships with the neurones of the primitive seg- mental brain; ingress and egress are possible only through the latter. Not having segmental relationships, the neurones of the end-brain are necessarily limited to the function of intercalary neurones. If the end-brain grows in response to the stimulus of function and the facts of embryology, comparative anatomy, and pale- ontology show that it has so grown it means that a multiplication of intercalary neurones has taken place, and as a corrollary an increas- ing variability that is, an increasing "adapta- bility" of response. An increasing adaptabil- ity of the responses of the organism to the con- 58 THE PHYSIOLOGY OF MIND stantly changing condition of its existence can only become possible through the multiplica- tion of intercalary neurones. This multiplica- tion permits alike of an increased complexity and an increased adjustment of the responses. Finally, it is obvious that in speaking of the function of the end-brain, the cortex, we should speak not of the variability of the responses, but of the adaptation of the responses. In turn, it becomes evident that the responses of the end-brain, the telencephalon, have their origin in the relation which its neurones bear to those of the primitive segmental brain, to the neurones of the spinal segments, and to each other. Transmission into the end-brain takes place through the "between brain," the thal- amus. Here we find that through the develop- ment of intercalary neurones, special way sta- tions, nuclei, have made their appearance. In the cells of the latter various axones bearing tactile, visual, auditory, and other impacts ter- minate synaptically; thence other axones con- stituting the so-called "sensory projection fibers" pass upward to the cortex. The nuclei in the thalamus which play this role of way stations and one of whose functions is doubtless that of THE PHYSIOLOGY OF 1N/EIND 59 reinforcement are spoken of as "cortical de- pendencies"; in vertebrates lacking a corre- sponding cortical development they naturally have no existence. 1 Responses make their exit from the cortex in axones which terminate synaptically not in neurones in the corpus striatum but in neurones in the brain stem and spinal segments. The latter group of axones constitute the motor pro- jection fibers and are also spoken of as the upper motor pathway or pyramidal tract. Like the nuclei of the thalamus, the neurones of the corpus striatum doubtless have an action of re- inforcement, but it is probable that they do much more than this; in lower vertebrates their nuclear arrangement appears to be such as to permit of relatively complex responses; for ex- ample, in birds, in whom the striatum is large and the cortex meagre. In higher vertebrates they appear to constitute a ready-made mechan- ism (neurone combinations) for various auto- matic movements controlled or inhibited by the cortex; certain it is, also, that the corpus stri- atum is in part concerned in the purely dynamic 1 All of the afferent impulses save those coming from the olfactory lobes find their way into the telencephalon through the thalamus. 60 THE PHYSIOLOGY OF MIND function of the maintenance of muscle tone. It is clearly evident that in the higher vertebrates such responses as have their origin in the stri- atum or are transmitted by it are definitely fixed; on the other hand, such responses as arise in the cortex and are transmitted by the axones terminating in the brain stem and spinal seg- ments are variable or adaptable. The responses so transmitted are adapted to the environmental happenings. They are the resultants of, and, other things equal, equivalent to, the various and multiple impacts received by the organism. Having established the avenues of ingress and egress and having considered the nature of the responses, the question now arises, "What takes place in the cortex itself? The sensory projec- tion fibers terminate synaptically in certain re- gions or areas of the cortex. These areas are commonly spoken of as cortical centers for smell, taste, vision, hearing, tactile, and other impressions. For the present it will suffice to regard them purely as gateways or avenues of entrance to the general cortex. Similarly, the neurones of a certain area that of the ascend- ing frontal convolution in man give rise to axones which constitute the motor projection THE PHYSIOLOGY OF MIND 61 fibers. This leaves extensive regions which have no access to the external world either in the way of receiving impacts or of transmitting them save through such connections, direct or indirect, as they may have with the receiving or the emissive areas. The facts of anatomical structure show that there are extensive and numerous pathways association tracts which connect different parts of the cortex with each other. Some of these fibers form extensive and long bundles or fasciculi; others are relatively short; others still connect immediately or closely adjoining areas of the cortex. In fact, the arrangement is such that any one part of the cortex is directly or indirectly connected with every other part. Finally, extensive commis- sural fibers bring about an intimate union of the two cerebral hemispheres. When we reflect that the human cortex contains upwards of ten thou- sand million neurones 1 and that each neurone bears numerous dendrites and that each neu- rone sends out one axone, sometimes two, and several collaterals, all terminating in numerous tuft-like subdivisions, we can realize that the 1 According to Herrick, loc. cit., p. 27, "some 9280 million," i. e. t approximately 10,000,000,000. 62 number of possible combinations becomes al- most infinite. That this leads to great "vari- ability" of the response, or to restate the fact in other words, to great possibilities in the adapta- tion of the response becomes very evident. A given adaptation, as we will see later, is the resultant of the impacts received and of the previously existing cortical neuronic combina- tions. Finally, the conclusion is inevitable that the response to the impacts must be automatic. Such response is clearly automatic when but one neurone is interposed between a receptor and an effector, and the factors do not change when the interposed neurone becomes multiple. A further fact now becomes apparent, namely, that as a result of a given impact a very large number of neurones may and probably do be- come involved in the transmission; the trans- mission doubtless takes place not only through many hundreds, but through many thousands of cortical neurones. In the course of the transmission a gateway of exit is finally reached, and thence a response is transmitted via the brain stem or cord to the effectors. Another inference now presents itself, an in- ference unavoidable and conclusive, and which THE PHYSIOLOGY OF MIND 63 is of the very greatest importance; and that is, if the response is "variable," if it is "adjust- able," and therefore capable of change, the neu- rones of the cortex cannot bear the same fixed relations to each other as do the neurones of the brain stem and cord. Many years ago in 1895 in thinking over the problems presented by hysteria, it occurred to the writer that possibly a hysterical paralysis e. g., of an arm could be accounted for by a retraction of the processes of the neurones in the "arm center" of the motor area of the cor- tex, so that these neurones would no longer be in physiological relation with the rest of the cor- tex. In other words, it occurred to the writer that possibly the neurones of the cortex had some power of movement as far as their ter- minal processes, the dendrites, and end-tufts are concerned; so that the latter could in some de- gree be retracted or extended. An examination of the literature revealed that the idea of move- ment on the part of the neurone had already occurred to three other writers, one in Germany and two in France. The first to advance such a view was Rabl-Riickard, 1 who in 1890 sug- 1 Rabl-Riickard, Xeuro!og. Centralblatt, April, 1890, p. 199. 64 THE PHYSIOLOGY OF MIND gested that nerve-cells have an amoeboid move- ment; and he, at the same time, pointed out the significance of such a view in enabling us to explain the mechanism of psychic processes. His ideas attracted no attention, but in 1894 Lepine, 1 in a paper on a case of hysteria of a peculiar form, advanced practically the same theory. His idea was that the neurones were capable of movement, and to such an extent as to enable them to alter the degree of their rela- tion to each other. Some six months after- wards another French writer, Mathias Duval, 2 advanced the same theory in a communication made to the Societe de Biologic. Lepine had been unaware of the theory advanced by Rabl- Rlickard and Mathias Duval, and was equally unaware of the views advanced by Lepine. A week after Duval had advanced his theory, Lepine, 3 before the same society, repeated his former arguments in its support. I myself pre- sented the theory of the movement of the neu- rone in a paper read before the College of Phys- icians of Philadelphia in January, 1896, 4 and in 1 Lepine, Revue de Medecine, Aout, 1894, p. 713. 2 Duval, Comptes Rendus de la Societe de Biologic, Fevrier, 1895, pp. 74, 86. 3 Lepine, Comptes Rendus de la Societe de Biologic, 1895, p. 85. 4 Trans. College of Physicians, Philadelphia, 1896. 65 June of that year read an address on the same subject before the American Neurological Asso- ciation. 1 In the meantime, in the spring of 1896, the theory had been again advanced by two other French physicians, Azoulay and Pupin. This view was not accepted by Ramon y Cajal. 2 He, however, saw the necessity of ad- mitting a change in the relations of the neurones to each other, and offered the explanation that it was the neuroglia cells which moved and not the neurones. He maintained that the processes of the neuroglia cells represent an insulating and non-conducting material, and that during the stage of relaxation these processes penetrate between the arborizations of the nerve-cells and so make difficult or impossible the passage of nerve currents; on the other hand, in the stage of contraction the processes of the neuroglia cells are retracted and they then no longer sepa- rate the processes of the nerve-cells, and the latter are thus permitted to come into contact. Evidently Ramon y Cajal admitted the very thing against which he contended, for if the nerve-cell processes are at one time not in con- 1 Trans. Amer. Neur. Assoc., August, 1896. 2 Ramdn y Cajal, Revista de Medicina y, Cirugia Practicas, Mayo, 5, 1895, p. 497. 66 THE PHYSIOLOGY OF MIND tact and at another are in contact, they cer- tainly move. It matters not whether the mo- tion is an active or a passive one. Finally, while movements of neurones have not been observed in vertebrates, one very suggestive observation was made in 1890 by Wiedersheim. 1 He saw in the living animal, an entomostracan, leptodora hyalina, the nerve-cells in the oesophageal gan- glion move. The oesophageal ganglion may in a sense be regarded as the brain of the animal, inasmuch as it receives the fibers of the optic nerve, and Wiedersheim actually saw these cells move and change their shape. He described the movement as slow and flowing, and pictures in his paper the various shapes assumed by the nerve-cells at different times. While it is a far cry from the nerve-cells of invertebrate forms to those of the vertebrates, the nerve-cells of the former, the protoneurones, illustrate, as we have seen, elemental truths, and the observation of Wiedersheim is in harmony with the view that the relations of the primordial neurones are not fixed as we find them in the segments of the cord and brain stem of vertebrates, but permit of change with each other. It would appear that 1 Wiedersheim, Anatomischer Anzeiger, 1890, p. 693. THE PHYSIOLOGY OF MIND 67 this motility or facility of change lost in the cord and brain stem has been preserved in the telencephalon. Further, we are so in the habit of looking at nerve-cells in mounted and stained sections of the cord and brain that we are apt to transfer the idea of fixation of structure subconsciously to our conceptions of the living cells and pro- cesses, and to overlook some of the marvelous truths which they present. The neurone has its origin in a simple undifferentiated cell, the neuroblast; in the course of its development it sends out processes, some of them of enormous length, which in their growth often pass along devious routes to a definite destination. For instance, certain cells of the motor area of the cortex send forth processes, the axones, which grow through great distances to come finally into relation with neurones in definite segments of the spinal cord; and again, other neurones, both motor and sensory, send out processes which bring the various portions and areas of the body into definite relations with them; that is, the axones grow out until they reach definite effectors or definite end-organs of the body sur- face and elsewhere. That this phenomenon 68 THE PHYSIOLOGY OF MIND must be the expression of purely physical or chemical causes there can be no doubt. Defi- nite causes must be at work, such, for instance, as determines the growth of the roots of plants toward water. "Many organs of the adult body are known to secrete specific soluble chemical substances termed 'hormones,' which diffuse throughout the lymph or blood and call forth functional activity in remote organs. It is pos- sible that during development of the body, the organs, as soon as definite stages of growth are reached, secrete similar substances which diffuse through the surrounding tissue and each of which has a chemotactic affinity for a certain type of developing neurones. Thus, the developing muscles may secrete a substance to which the motor neurones of the spinal cord react by a growth of their embryonic axones toward the source of the stimulating material." 1 This phe- nomenon is known as chemo taxis. The thought also suggests itself that possibly this process does not cease absolutely with the evolution of the organism, but in some measure continues in the fully developed organism in accordance with changing conditions. 1 See Herrick, loc. cit., pp. Ill, 112. THE PHYSIOLOGY OF MIND 69 Again, it has been found that in the course of the evolution of vertebrate forms nerve-cells change their positions. Numerous groups of cell bodies with specific functions move from their primitive positions to new locations. Our knowledge of their migrations is due mainly to Kappers. It would seem that cell bodies "tend to migrate in the direction from which they habitually receive their stimuli, i. e., in the direction taken by their dendrites. If there is a change in the direction from which a given nucleus (i. e., a group of cells) receives its chief stimuli, the nucleus as a whole will tend to move toward the new source of excitation and away from the old. 1 The change in position is obviously expressive of a physical reaction to a stimulus, and the phenomenon has received the name of "neurobiotaxis." Both the facts of chemotaxis and neurobiotaxis throw an inter- esting light on the active, living, growing char- acter of the neurone; changing and capable of change. Indeed, capacity for change and adaptation seems inherent in the primitive neuroblast. At times continuous changes and fresh adaptations may be the result; at others, 2 See Herrick, loc. cit., p. 112. 70 THE PHYSIOLOGY OF MIND fixation or relative fixation may be estab- lished. Let us again turn our attention to the rela- tions between the neurones, i. e., to the synapses. Kappers 1 points out that the relations of neu- rones to each other vary somewhat. In some the relation may be practically one of con- tinuity, as when the neurofibrils of one neurone pass directly into those of the second; as is often the case in the vestibular apparatus. Such an arrangement may be expected in the Mauthner cell in the catfish a large cell in relation with the vestibular nerve in which transmission probably takes place directly between the ax- ones of one cell and the dendrites of another. Between other cells the relation may be merely that of contiguity or, it may be added, of propinquity. At the time of the passage of a reflex a delay in transmission occurs at a syn- apse. Kappers thinks that differences in delay may be due to differences in the synapses. Probably this delay is greater when the his- tological relation consists merely of contiguity and greatest when this contiguity or approxi- 1 Kappers, Versuch einer Erklarung des Verhaltens an der Synapsis, Psych, en NeuroL, Bladen, 1917, H. 6, p. 440; also Brain, July, 1921, p. 125. THE PHYSIOLOGY OF MIND 71 mation must first be established. The last would naturally result when a new pathway was being formed, or in the case of one that was only occasionally used. Kappers regards the transmission through the neurone in one direction only i. e., the polarization of the neurone as a neurobio tactic phenomenon. He declares that the formation of dendrites and axones is the result of the reaction to stimuli; the axone is a formed product of the stimuli current; it grows with the current, is formed by the cur- rent. The dendrite is likewise a formed product of the stimuli current. In the passage of the current from cell to cell, the axone terminals of the first cell are drawn toward the dendrites of the second cell, and the dendrites of the second cell are drawn toward the axone terminals of the first. The mere act of the transmission of an impulse brings about an approach, the whole process being neurobiotactic. Sherrington 1 regarded it as improbable that the phenomena of the synapse are dependent upon an amceboidism of the neurones, and he did so for the following reason: The length of the delay caused in a reflex by a synapse^. e. 9 1 Sherrington, The Tntegrative Action of the Nervous System, 1911, p. 24. 72 THE PHYSIOLOGY OF MIND the latent period is inversely proportional to the intensity of the reflex. Sherrington found that if the latent period of a reflex produced by delivery of the stimulus in its full strength be compared with the latent period of the reflex produced in two stages i. e., by an "initial" stimulus and an "incremental" stimulus the latent period resulting in the two stimuli reflex is longer than in the first, namely, when only one maximal stimulus is applied. This result he regarded as an argument against an amoeboid movement on the part of the neurones; a bridge once having been constructed by the initial stimulus, there should be no additional loss of time. However, Sherrington' s results also showed that the latent period of the incremental stim- ulus is always shorter than that of the initial stimulus. As Kappers points out, this fact can only be explained by supposing that something takes place as a result of the initial stimulus which does not take place as a result of the in- cremental stimulus; and to Kappers there seems no good reason for supposing that the added time of the initial latent period is not con- sumed by the approach of the colloidal particles of the terminal processes. Kappers declares THE PHYSIOLOGY OF MIND 73 that the amoeboidism, and, in any case, the neurobiotactic phenomena of nerve-cells, have not for a long time been mere hypotheses, but are actual facts. The interrelations of the neurones have been the subject of much speculative thought and study. Sherrington who, as just seen, denies the amceboidism of the neurone, expresses himself as follows: 1 "At the nexu's between cells, if there be not actual confluence, there must be a surface of separation. At the nexus between efferent neurone and the muscle-cell, electrical organ, etc., which it innervates, it is generally admitted that there is not actual confluence of the two cells together, but that a surface sepa- rates them; and a surface of separation is phys- ically a membrane." "If the conductive element of the neurone be fluid, and if at the nexus between neurone and neurone there does not exist actual confluence of the conductive part of one cell with the con- ductive part of the other e. g., if there is not actual continuity of physical phase between them there must be a surface of separation. Even should a membrane visible to the micro- 1 See Sherrington, loc. cit., pp. 16, 17. 74 THE PHYSIOLOGY OF MIND scope not appear, the mere fact of non-con- fluence of the one with the other implies the existence of a surface of separation. Such a surface might restrain diffusion, bank up os- motic pressure, restrict the movement of ions, accumulate electric charges, support a double electric layer, alter in shape and surface tension with changes in difference of potential, alter in difference of potential with changes in surface tension or in shape, or intervene as a membrane between dilute solutions of electrolytes of dif- ferent concentration or colloidal suspensions with different sign of charge." Regarding this hypothetical membrane Kap- pers is of the opinion that by a synaptic mem- brane we need not understand an actual mem- branous structure, but "merely an electro- endosmotic layer." Again, obviously such a membrane if morphologically demonstrable would consist of the apposition or fusion of two cell walls and, further, the physical prin- ciples involved endosmosis and the possible passage of electrically charged ions would apply especially to neurones with fixed synaptic relations and perhaps in less degree to neurones whose relations were changeable. In any event, THE PHYSIOLOGY OF MIND 75 it is quite probable that the physical principles involved would not differ in essence from those that determine the approach of the pseudopod of an amoeba to a nitrogenous or other food particle. Leaving for the time being the consideration of this "electro-endosmotic layer" or synaptic ''membrane" and the consideration of the phys- ical or chemical principles involved, let us turn our attention once more to the reactions of the cortical neurone, the neurone of the telen- cephalon, to the stimuli, the impacts, trans- mitted to it from the segmental brain. In one of my earlier papers, read before the American Neurological Association in June, 1896, I thus expressed myself: 1 "A sequence of sound vibrations impinging upon the peripheral auditory neurones pro- duces in them a change, which in turn affects the relations which their neuraxones bear to the auditory nuclei, and secondarily to the auditory cortical neurones. Not only are the latter affected by the impressions received from the afferent neuraxones, but they, in turn, re- 1 Dercura, Presidential Address delivered before The American Neurological Association (The Functions of the Neurone), The Journal of Nervous and Mental Disease, Vol. XXI, No. 8, 1896, p. 522. 76 act in such a way as to change their relations to each other, and the new positions assumed by them will depend largely upon the fact as to whether a similar sequence of impressions has passed through them before. If so, the old combinations will be re-formed. From the cortical, auditory center there now pass through the general cortex a series of combinations among the neurones, also along the oldest and best-travelled lines, so that a given sequence of musical sounds may suggest at first a familiar air, a moment later a vivid recollection of an opera once heard and seen. In this simple il- lustration is embraced the physiology of per- ception, of conception, of memory, and the ex- planation of the very sequence of thought itself." Setting aside for the time being the dis- cussion of the factors of sensation and of con- sciousness embraced in the above^ interpreta- tion, let us take up more in detail the various other phenomena presented. First, we are im- pressed by the fact that time is consumed in the transmission of the impact from the moment of its reception until it finds motor expression. This is known as the reaction time. We have THE PHYSIOLOGY OF MIND 77 already briefly considered the delay which occurs at a synapse. It appears to be time consumed in the preparation of the synapse for trans- mission, i. e., in the "setting" of the synapse (to use Sherrington's term), and which con- sists possibly in the formation of protoplasmic extensions, in the passage of ions, or in the establishment of induction. Many studies have been made as to the time lost in the passage through gray matter of various reflexes, and it would appear that the simpler the reflex, the shorter the reaction time, and the more complex the reflex or response, the longer the reaction time; thus a simple spinal reflex in the frog re- veals a loss of 0.008 second (Wundt) or 0.014 and 0.021 second (Buchanan), while the sim- plest reaction times measured in the psycholog- ical laboratories vary between 0.1 and 0.2 sec- ond, 1 and the reaction times as measured by physicians between a "stimulus word" and a "reaction word" range from one to two seconds and sometimes longer. The time consumed is evidently lost in some physical process, as al- ready indicated. The transmission of impact from neurone to neurone means the overcoming 1 See Herrick, loc. cit., p. 104. 78 THE PHYSIOLOGY OF MIND of inertia or resistance at the beginning of each neurone, i. e., at its dendrite. Each synapse, so to speak, presents a new "neurone threshold" (Sherrington). The positions of neurones and their relations to each other are, as we have seen, determined by the principle of neurobio taxis. According to the latter, the dendrites are directed or, rather, are drawn toward the sources of stimulation, i. e., the sources from which the impacts are re- ceived; the axones likewise are drawn toward the dendrites of the succeeding cell and, in given instances, in the course of phylogeny even the entire neurone may move. Here we are concerned, however, merely with the be- havior of the dendrites and axone terminals. No doubt the transmission, the diffusion, of an impact, to definite neurones, is determined by neurobiotactic principles, and in this is to be found the explanation of "association." In their early phylogenetic relationships the trans- mission of impact from neurone to neurone was doubtless determined by propinquity, and in the multiplication of intercalary neurones there gradually appeared the "common paths" (see p. 48). Definite groups of neurones, therefore, THE PHYSIOLOGY OF MIND 79 became associated in the transmission of given impacts, e. g., of sound, as in the illustration quoted above. The transmission did not, how- ever, cease in the so-called cortical center for hearing in the temporal lobe, but was trans- mitted along "association" paths to other re- gions of the brain. What determines the direc- tion of the transmission? Why do the impacts break through definite thresholds and thus give rise to certain associations? Doubtless the tendency in the primitive nervous system was to a general diffusion of impacts, but auto- matically, as in the instance of the establish- ment in the fish of the common effector paths concerned in swimming as a result of the com- mon action of the receptors of smell, sight, and hearing in determining the approach of the fish to food (see p. 54), so impacts entering the cortex by way of the organ of hearing would probably diffuse more readily toward the cor- tical areas for vision than to those of touch, smell, or taste; as in the higher vertebrates, impacts of sight and sound from a given source are very frequently simultaneous. That there should be a lowering of thresholds between si- multaneously aroused groups of neurones would 80 THE PHYSIOLOGY OF MIND naturally follow. Activity of neighboring groups of neurones would necessarily mean an in- creased amoeboidism. If one group only be aroused, pathways having once been established, there would be a transmission to the others which were still quiescent. At any rate, what- ever be the explanation, it can, I think, be safely assumed that association i. e., trans- mission to other neurones takes place in ac- cordance with physical principles, and, second, having once taken place, they take place more and more readily with repetition. In other words, to use a physiological term, they be- come "facilitated." The special trend followed by the cortical neurones in their transmission-associations doubtless depends upon a number of factors. If the experiences are old and often met with, the same or similar associations are repeated; if they are new experiences, no doubt new com- binations are formed, new pathways estab- lished. It is probably this quality of neurone activity which makes possible additions to our knowledge; it becomes thus the basis of all training and education. However, the function of the neurone of the THE PHYSIOLOGY OF MIND 81 cortex is not merely that of transmission. The reception of the impact means not only the passage of the latter through dendrites, cell body and axone, but also a change in the sub- stance of the neurone; a change physical and chemical which results in the evolution of energy. An active consumption of substance, probably the result of an increased oxidation, takes place, and a corresponding amount of energy is added to the impulse transmitted. It is easy to understand that when the latter finally reaches the effectors i. e., finds motor expres- sion it may differ greatly both in amount and character from that originally impinging upon the receptors. A very small stimulus may liberate a large amount of energy. Each neu- rone is a storehouse of energy which needs but the transmitted tap of the impact to release it. Evidently a series of neurones in relation with a receptor will intensify the impressions im- pinging upon the latter. Such an arrangement is especially evident in the olfactory lobe and doubtless accounts for the recognition by the organism of impacts so excessively minute as are those which impinge upon the olfactory re- ceptors. Ramon y Cajal has in this connection 82 THE PHYSIOLOGY OF MIND employed the expression "avalanche conduc- tion." Doubtless a similar truth obtains in re- gard to the intercalary neurones next in series. i. e., those concerned primarily in the central transmission of the impact, and also and finally, in regard to those in relation with the effectors. That the impact in its course of transmission through the various neurones avalanche con- duction or other undergoes, in addition, con- versions in character, is modified, transformed into different equivalents is probably equally true; but the discussion of this interesting ques- tion is deferred for the present. One truth, however, remains apparent, and that is that the 10,000 million intercalary neurones of the cortex add merely to the complexity of the re- sponse; the purely physical, automatic char- acter of the latter remains unchanged. This automatism is as true of the higher vertebrates as it is of the lower. The reaction of the fish to the environment is clearly automatic (see p. 54), and the development of the telencephalon merely makes that automatism more complex. A discussion which can no longer be deferred is that of consciousness. In a consideration of THE PHYSIOLOGY OF MIND 83 nervous phenomena, the problem of conscious- ness of necessity obtrudes itself, and, although in a study of the simple problems it may be ignored, it must finally be squarely faced. When we turn our attention to the protozoa and more especially to the amceba, we realize at once that a discussion whether such an organ- ism is conscious, whether it has sensation, feeling, a sense of being, becomes futile. We have seen reason to believe (see pages 12, 14) that the reactions of the amoeba to the environment, like that of the white blood- corpuscles and the other individual cells of the metazoa, are due to purely physical and chem- ical causes. If such structures have a sense of being, it must be one that is shared by the sub- stance and energy of the universe generally; in- deed, it must be participated in by that ulti- mate expression of substance and energy, the electron itself. Are we to infer that "senti- ency" makes its appearance when the combina- tion of a given number of amino-acids results in the formation of a substance that is the seat of a continuous chemical change featured by a simultaneous upbuilding and reduction (see p. 40), a continuous change that is itself a direct 84 THE PHYSIOLOGY OF MIND result of its reaction to its environment? or, are we to defer this conception of sentiency until special arrangements for the reception and trans- mission of impacts make their appearance? The difficulty increases when we approach the more complex metazoa. In the contemplation of the ccelenterates we may be content to set aside the question of "feeling," but are we justified in doing this in the case of insects with their obviously complex sense organs and central nervous aggregations? Again, are we justified in assuming that the cuttlefish in spite of his elaborate eye does not "see," has not "light sensation" of some kind or other? Assuredly it is unphilosophical to assume that the fish in spite of its enormous olfactory brain does not "smell," or being possessed of eyes and ears, that it does not "see," does not "hear." True, the impacts received by the "nose brain," the "eye brain," the "ear brain," and the "skin brain" are all transmitted into the common paths concerned in swimming, i. e., in bringing about automatic approach to or withdrawal from objects in the water; yet, though the "eye brain" may glow with the sensation of light and the "ear brain" ring with the sensation of sound, THE PHYSIOLOGY OF MIND 85 the consciousness of the fish must be something very different from that experienced by our- selves. In what does this difference consist? Evidently it concerns the function of the telen- cephalon. Let us for the time being turn our attention to the responses to impacts in the higher ver- tebrates. In amphibians the situation has changed but little from that in fishes; the re- sponses are still the invariable, non-adjustable responses of a segmental brain. The same may be said of reptiles; variable or adjustable re- sponses are negligible factors. When we turn to birds, the situation has apparently slightly changed. In addition to their very remarkable and complex automatic "instinctive" responses, there appears to be a capacity, though an ex- ceedingly limited one, for adjustable responses. In birds the pallium the cortex of the telen- cephalon is still very rudimentary, and if the bird does any "thinking" he must do it with his thalamus and striatum. That he does very little is quite evident from the behavior of birds ordinarily; that he exceptionally does some is equally evident from the occasional behavior of certain birds, e. g., the parrot. Further, it is 86 THE PHYSIOLOGY OF MIND exceedingly probable, as we shall see later on, that the complex instincts of birds, as well as those of mammals, had their origin in adjustable responses. It would appear that the structures of the primitive brain, the palaeo-encephalon, the seg- mental brain, as we term it, is of such a char- acter as to permit of adjustable responses in only a limited degree. However, that such ad- justable responses did take place in it originally and still do take place in it in birds and per- haps in lower forms, though in very small measure, is exceedingly probable. In mam- mals, however, the function of the segmental brain, like that of the spinal cord, is limited to non-adjustable responses. Like the spinal cord, the segmental brain has been reduced to a fixed mechanism. Such capacity for variable or ad- justable responses as it may have originally possessed has been usurped by the telencephalon. Whatever may be the state of consciousness in vertebrates other than mammals, it is quite certain that in the latter fixed responses play no r61e in consciousness; this is true of the re- sponses in the spinal cord, and it is doubtless equally true of the responses in the segmental THE PHYSIOLOGY OF MIND 87 brain. Here again the telencephalon has played the role of usurper, for the function of con- sciousness, as we know it, is limited to the telencephalon. When we now turn our attention to this function of the telencephalon, the following in- teresting facts and inferences present them- selves. To begin, various acts themselves the outward expression the effector result of the intercalary function of the telencephalon, and which when first performed are attended by consciousness, may lose this quality when fre- quently repeated. Acts the performance of which is at first accompanied by a conscious effort, may by frequent repetition become largely and in some instances wholly "automatic," i. e., may finally be unattended by consciousness either in whole or in part. Many of the acts acquired in early life the use of utensils in eating, the adjustments of clothing, the move- ments of writing, the movements concerned in playing a musical instrument are all acts usually at first performed slowly and with dif- ficulty, but later with increasing ease until con- sciousness no longer enters into them. The same movements frequently repeated necessitate the 88 THE PHYSIOLOGY OF MIND constant repetition of the same association the same combination among the neurones, and sooner or later the movements acquire all the character of fixed responses. The first inference that is justified is that consciousness disappears in proportion as fixa- tion is established. Fixation of response means the disappearance of consciousness. This in- ference leads to another no less interesting, an inference that follows as a corrollary, namely, that consciousness is present only in the "ad- justable" responses; that is, only in those re- sponses which are attended by a changing, an actively varying relationship among the neu- rones. An impact transmitted from the cord and segmental brain into the telencephalon brings about definite changes in the synaptic relations of the neurones to which the impact is first transmitted. Thence the impact is transmitted to other intercalary neurones, in- deed, to many series of the latter in the manner already indicated. The transmission of the im- pact, subject to reinforcement, may continue until motor centers i. e., until neurones in re- lation with effector (motor) neurones of the segmental brain or cord are reached, when an THE PHYSIOLOGY OF MIND 89 outward or motor expression results; or the transmission may continue to diffuse variously through the cortex without a so-called motor area being involved. Whatever the course of the transmission, it is inevitable that the neu- rones concerned are involved in sequence. The axone- terminals of the first neurone approach and are approached by the dendrites of the second (see p. 71). The second neurone effects a like synaptic approach with the third, the third with the fourth, and so on. It follows that just as soon as an impact has been transmitted by a neurone i. e., just as soon as it has com- pleted its discharge (see p. 81) its axone ter- minals and the dendrites of the receiving cell are again retracted, i. e., the synaptic relation- ship is broken and the neurone is again at rest. It is, I believe, a legitimate inference that a neurone at rest can have no relation with con- sciousness; a neurone at rest, so to speak, is un- conscious. It follows, therefore, that con- sciousness is only present in the neurones that are actively concerned in transmission. Con- sciousness is itself a phenomenon of cortical transmission. Let us at this point consider some of the ele- 90 THE PHYSIOLOGY OF MIND mental facts of consciousness as they reveal themselves to our individual experience. What- ever consciousness may be, it is something that is constantly changing. A sensation, a percep- tion, a thought is experienced. A sensation per- sists as long as the impacts that give rise to it continue; a perception as long as the object perceived throws its impacts upon the receptors; a thought resolves itself into a train of sequences. Each individual instant of time, however, whether it is concerned in a momentary sensa- tion derived from a single impact or whether the sensation be made up of many succeeding in- stants of impacts, becomes past history the moment it is experienced; it immediately enters the past. The same statement applies, of course, to a perception, to a thought; in fact, to any mental process. While consciousness is con- stantly changing from the immediate present to the immediate past, it is of necessity also con- stantly passing into the immediate future. Bergson 1 expresses the same facts as follows: "For consciousness there is no present, if the present be a mathematical instant. An in- 1 Bergson, Mind Energy, transl. by H. Wilson Carr, Henry Holt & Co., New York, 1920, p. 8. THE PHYSIOLOGY OF MIND 91 slant is the purely theoretical limit which sepa- rates the past from the future. It may, in the strict sense, be conceived, it is never perceived. When we think we have seized hold of it, it is already far away. What we actually perceive is a certain span of duration composed of two parts our immediate past and our imminent future." 1 Surely these elemental facts are in accord with the principles governing transmission through the cortical neurones. This transmis- sion is a progressive, continuous thing; receding from the point of entrance of the impact and at the same time continuously advancing. In con- sidering transmission, however, it is important to bear in mind that in addition to the mere fact of transmission there is the further fact of the release of energy (see p. 81), a release in which each neurone successively takes part. As a result, an impact, thus continuously re- inforced, becomes widely diffused. This dif- fusion, however, does not take place indiffer- ently in all directions, but in accordance with definite principles. To begin with, it is obvious 1 Thus far only is the writer in accord with Bergson's interpretation of consciousness. From this point on Bergson enters a maze of mysticism. 92 THE PHYSIOLOGY OF MIND that transmission follows the direction of least resistance. Evidently the latter will be in the course* of the most frequently travelled paths, those paths in which the amoeboid approach of axone terminals and dendrites has been most frequently established, or, to phrase it in other words, in which "synaptic resistance" has been most frequently overcome. Further, it is prob- able that the transmissions, other things equal, at first followed the most direct routes to the gateways of exit; the demands for adjustment of the responses to the environment were in the * primitive mammalian forms doubtless rela- tively simple; as they are to this day in moles and rabbits, insectivora, rodents, and the like. However, the organism in response to the in- creasing demands made upon it by the environ- ment, reacted by increasing its power of adap- tation; it underwent, as we say, evolution. The telencephalon grew, its neurones became more numerous, and its power of adjusting to the environment the responses it transmitted was correspondingly increased. Numerous "as- sociation tracts," great and small, gradually made their appearance, so that every part of the cortex became connected with every other THE PHYSIOLOGY OF MIND 93 part (see p. 61). Notwithstanding this increas- ing complexity and increased power of adjust- ment, notwithstanding the great facility for in- tercommunication, an impact entering the tel- encephalon is not diffused universally through- out the entire cortex. Doubtless dependent upon the nature of the impact the exciting cause and the special environment in which the organism happens to be placed, as well as upon other factors already considered (see p. 79), the transmission pursues a course more or less defined. The transmission is not, however, entirely limited to this course, for the neurones successively involved doubtless discharge their energy not only into those in the direct path- way of the transmission but also into neighbor- ing neurones not directly concerned. There is, so to speak, a lateral transmission, but one of less dynamic power, and which finally dies out within a variable range of the primary activity. Consciousness follows the main train, but also includes a limited and fading field to either side to all sides, one might say. In a sense, con- sciousness is analogous to the visual field with its sharply defined central vision and its grad- ually fading peripheral areas. The "field of con- 94 THE PHYSIOLOGY OF MIND sciousness" becomes less and less distinct as the main train of activity perception, thought, emissive impulse is departed from. Gradually it fades into the subliminal, the subconscious, the unconscious. Again, the "train of activity" is continuous, unbroken, during the waking period. Further, the inpour of impacts is incessant, and a given " train" may be reinforced, deflected, or modi- fied in various ways. Cessation of the "train of activity" means, of course, cessation of the synaptic transmission, a discontinuance of the "amceboid approach" of axone terminals and dendrites. Such a discontinuance means un- consciousness and, physiologically, sleep. In one of my papers, 1 read in 1897, I expressed myself as follows: "Evidently the neurones when functionally active must be in relation with each other. Their processes must be either in contact or nearly so. Evidently this condi- tion is a prerequisite of consciousness. Now what happens when the nerve-cells are ex- hausted by fatigue, when their volume and their cell contents have been diminished, as we have 1 Dercum, Application of the Theory of the Movement of the Neuron^ Univ. Med. Magazine, April, 1897. See also C. L. Dana, J. A. M. A., April 24, 1920, p. 1141. THE PHYSIOLOGY OF MIND 95 every reason to infer is the case, from the ex- periments of Hodge? Evidently their processes become retracted and they are no longer in re- lation with each other. The neurone isolated from the rest by retraction must be without function. General retraction of neurones must mean absence of function, must mean uncon- sciousness, must mean sleep. In other words, in sleep the neurones have their processes re- tracted; in consciousness their processes are extended." 1 Let us turn our attention to some of the other considerations that present themselves. Evidently the extent of the field of conscious- ness must depend upon the number of neurones called into activity, and this, in turn, must de- pend upon the impacts received, upon the number, intensity, and character of the latter. Further, it is the summation of the activities of all the neurones aroused at a given time which constitutes at that time the conscious indi- viduality. The latter must, therefore, be re- garded as multiple, as made up of many in- 1 Lugaro's suggestion that during sleep there is a general diffuse extension of all nervous processes instead of a retraction would sub- stitute activity for rest, and is, so it would appear, dynamically incon- sistent with arrest of function. 96 THE PHYSIOLOGY OF MIND tegers, and of varying from time to time both in extent and character. The group activity, the united activity of many neurones probably gives rise to a community of consciousness, a sense of self as something distinct from the outside world. A discussion of the degree with which man shares this property with other ani- mals would be nugatory. Its possession, how- ever, by the latter to any extent must depend upon the presence of "variable," that is, "ad- justable" responses. Without these a sense of self would obviously be impossible. Further, this "community of consciousness" must neces- sarily vary in extent from time to time within physiological limits; that it varies greatly in pathological conditions we will see later on. The community of action of the cortical neu- rones must inevitably give rise to the function of memory. To make my meaning clear let me use the following illustration: A sequence of sound vibrations impinges upon the auditory receptors and in due course the impacts are transmitted to the "auditory center" in the temporal lobe of the cerebrum. Here the neu- rones assume relations with each other corre- sponding to the impacts received, the character, THE PHYSIOLOGY OF MIND 97 intensity, and other qualities of the latter; the impacts are also transmitted to neighboring and possibly distant areas. If a similar series of impacts has been transmitted by the neurones before, similar or the same combinations will be re-formed, and as a corollary there will follow a recognition by the neurones concerned in the communal relation of consciousness as some- thing experienced before. That memory is a purely dynamic function there can, I think, be no question. The capacity for memory must depend upon" the facility among the neurones for re-forming old combinations, and this facility must be increased by repetition. In a sense memory is the expression of the same tendency to fixation of neurone combinations as has given rise to the fixed relationships in the palseo- encephalon. Perhaps some of the "instincts" and "race memories" have their basis in com- binations of such frequent recurrence in the ancestry that they have acquired all the poten- tiality of inherited structure. One of the most instructive phenomena illus- trating the dynamic character of memory is that presented by memory temporarily de- layed. It is a matter of common experience that 98 THE PHYSIOLOGY OF MIND a name which cannot at once be recalled appears in consciousness after the lapse of a fraction of a second or, indeed, at times after the lapse of many seconds, and at a time when the train of thought is already occupying another channel. It would seem that the impact leading to the memory recall had set in motion a group of neurones along paths only occasionally used or long unused, or along paths subject for the time being to sy nap tic resistance. The significant facts are that time is required for the act, and that the presentation of the name occurs auto- matically. Another significant illustration of the dynamic quality of memory is offered by the abnormal memory occasionally observed in certain defective children, the so-called "idiot savants." The latter may be able to give cita- tions at great length of matter which they have heard only once and of the meaning of which they have no comprehension; not infrequently such citations are in foreign languages, of which the child is likewise ignorant. Such abnormal memories suggest a pathological tendency to fixation of the combinations; perhaps a disease of the synapses. Further, it is not improbable that in these children the tendency to fixation THE PHYSIOLOGY OF MIND 99 of the cortical responses is directly related to their idiocy. It would appear that a certain plasticity, release, and freedom of combination are essential to normal function. Referring again to instincts, it is not im- probable that some instincts are inherited modes of reaction to the environment that had their origin in responses which early in the phylogeny of the race were adjustable and which, owing to constant repetition, became fixed and relegated to the subconscious field. However, other phenomena apparently instinctive are doubtless due to the mere physical reaction of the organism to the environment as pointed out by Jacques Loeb. 1 In these reactions, like- wise, the responses being fixed, they play no role, or at most only an indirect role in con- sciousness. In our discussion of the transmission of im- pacts through the telencephalon, and especially in our discussion of memory, we have already laid the foundation for the explanation of vari- ous detailed mental phenomena such as per- ception, apperception, association, as expressed 1 Jacques Loeb, Forced Movements, Tropisms, and Animal Conduct, Lippincott & Co., Philadelphia, 1918. 100 THE PHYSIOLOGY OF MIND in the train of thought, and the transmission of the impact through the avenues of exit to the effectors. In the act of perception the neurones of the cortex which are the recipients of a given series of impacts form combinations among themselves corresponding to the impacts re- ceived. The transmission, of course, does not cease here, but continues, as already indicated, by association, intracortical and subcortical, many neurones being called into activity. The combinations successively formed are some of them new, others are combinations which are the same as or similar to combinations formed upon previous occasions. The result is that the incoming combinations resulting from the act of perception assume relations in part to past combinations and. in part to combinations wholly or partly new. In other words, it is the function of the common or community con- sciousness of the neurones concerned in this activity to collocate the impression received. It is this which constitutes the act of appercep- tion. The train of thought automatically fol- lows. The very act of collocation constitutes the train of thought. It is thought, no matter how diversified or complex the transmission may THE PHYSIOLOGY OF MIND 101 become. If it finally eventuates in a discharge through an emissive gateway, its further prog- ress to the effectors is, of course, outside the field of consciousness. It is evident, let us resume, that the neurones of the telencephalon are roused into action by the impacts transmitted to them from the seg- mental brain. As a result, the neurones in- volved in a given transmission extend their processes and enter into synaptic relations with other neurones, into which they also discharge. It is the active neurones alone, as already pointed out, which are concerned in conscious- ness. Those which are quiescent are those into which transmission has not taken place, and consequently cannot manifest consciousness. In contrast with the field of consciousness, they therefore occupy the unconscious field. It is further evident that in the progress of a trans- mission through the cortex, neurones previously quiescent and therefore in the unconscious field are brought into action and now become part of the conscious field, and at the same time other neurones through which transmission has been completed again become quiescent and lapse into the unconscious field. In other words, the 102 THE PHYSIOLOGY OF MIND conscious and unconscious fields are constantly changing; that which at one moment is con- scious field at the next moment is unconscious field, and vice versa. Again, when a transmission passes through a group of neurones, the latter react by forming combinations among themselves corresponding to the impacts received (see p. 76). A repeti- tion of the same or similar impacts means the re-formation of the same or similar combina- tions (see p. 80). This implies the establish- ment of pathways of least resistance, and it would seem that a single transmission of an impact is sufficient to establish such a path- way. In other words, the passage of transmis- sions establishes "associations" among the neu- rones. These are manifest only when the neu- rones are active, and are merely potential when the neurones are quiescent. It would appear that when the latter are stimulated by a trans- mission, previous combinations are automat- ically reproduced. In this lies, I believe, the explanation of the physiology of the uncon- scious field. 1 The latter is a vast storehouse of 1 1 do not like the expression "unconscious mind" ; the words are self-contradictory. THE PHYSIOLOGY OF MIND 103 past experiences. These are represented not by gross changes of structure, but merely by po- tential possibilities. Whether certain combina- tions associations are re-formed depends en- tirely upon whether the neurones concerned are reached by a given transmission. Further, it is, I believe, a legitimate inference that the number of neurones in action at a given time is an exceedingly small part of the sum total of the neurones of the cortex. It is very probable that the number concerned in the field of consciousness in the train of trans- mission, in the train of thought is relatively insignificant when compared with the ten thou- sand millions of the total. Finally, when we consider the number and complexity of both the axone terminals and of the dendrites, and the fact that every part of the cortex is in rela- tion with every other part, we can perhaps form a faint conception of the practically limitless possibilities of association. Not only may the latter consist of combinations representing im- pacts the same as or similar to impacts already transmitted but also of combinations entirely new. The organism is constantly exposed to new and changing relations to the environment, 104 and to these demands the organism reacts by a constant readjustment in its responses. The individual from infancy on, from his very ear- liest experiences, throughout his training and education, up to the complex experiences of adult life, is constantly making fresh adjust- ments, i. e., new combinations, new associations among his neurones. There can be no doubt that the power of the continued making of new combinations differs in individuals. In the larger number the com- binations that are formed resemble those that are formed by other individuals under the same circumstances, i. e., who are exposed to the same impacts. In others, a relatively small number, the combinations differ in a degree sometimes slightly, sometimes widely, from those formed by the average individual. It is the novel character of the associations formed among the neurones that constitutes "origin- ality." If the novelty of the association be very pronounced, it gives rise to "imagination"; originality and imagination are close kin. The field of consciousness i. e., the train of transmission is, of course, of relatively greater dynamic power than the unconscious field into THE PHYSIOLOGY OF MIND 105 the neurones of which it successively discharges. Whether into the field of activity itself fresh impacts, impacts derived from other sources than that which originally gave rise to the transmission, find entrance, is purely a question of dynamics. If the dynamic level of the active field be relatively high, the ingress of disturbing impacts is excluded and the original transmis- sion pursues its way undisturbed and untram- meled. In such case it is open only to impacts derived from the same source that gave rise to it and which continually reinforce it. It is this which constitutes "attention." Lack of atten- tion, the inability for sustained attention, is due to the ingress of interfering transmissions and, other things equal, is expressive of a lower dy- namic level i. e., of weakness. Similarly, the relatively high dynamic level of the conscious field especially when joined with novel associations gives rise to "initiative," to the outward expression, to the discharge through the emissive gateways of the cortical energy. Between "initiative" and "will" or "will power" there is again a close kinship. Given the exclusion of interfering transmissions as in attention, or in that higher degree of at- 106 THE PHYSIOLOGY OF MIND tention to which we apply the term "concen- tration," and given a high dynamic level of the train of transmission the field of conscious- ness "will power" is the necessary outcome. The dynamic level of the field of consciousness i. e., the output of energy must inevitably depend upon the intensity of the metabolic processes, the chemical changes, going on in the substance of the neurones and upon the number of the neurones taking part. To the conception of the purely automatic character of the phenomena of transmission, of the amoeboid movements and the serial dis- charges in short, of the physico-chemical changes which constitute the train of conscious- ness, we must now add another, or rather re- call to our minds a quality of the neurone al- ready in part considered. Consciousness im- plies "sentiency" (see p. 84) as a property of the neurone. Consciousness without this prop- erty would cease to be consciousness. Sensa- tion is a self-evident condition of consciousness and is inseparable from it. Now we have al- ready considered some of the fundamental reac- tions of living protoplasm to the incident forces of the environment, the gradual evolution of THE PHYSIOLOGY OF MIND 107 special receptors, and the evolution of special portions of the primitive brain, the "segmental brain," into which the impacts are transmitted. These are differentiated in the fish into an "olfactory brain," an "eye brain," an "ear brain," a "skin brain" (see p. 50). The infer- ence becomes unavoidable that these structures respectively experience the sensations of odor, light, sound, and touch (see p. 84). The ques- tion now arises what role does the telencephalon, the great usurper, play in this respect. From the evidence of structure, only one inference is possible, namely, that the impacts from the various receptors are transmitted to the cortex. If transmitted to the cortex they must be still farther transmitted, diffused, according to the principles indicated in the preceding pages. We have no reason to infer that the mode of motion of the impact is thereby changed, i. e., in pass- ing from the neurones of the segmental brain to those of the telencephalon or in the passage from the gateway of ingress to other areas of the cortex; and, if this be true, it can only be that sound, for instance, is experienced in every neurone reached by the transmission; or light, or smell, or touch, as the case may be. When, 108 THE PHYSIOLOGY OF MIND as is frequently the case, transmissions are re- ceived simultaneously from several special sense receptors, the impacts do not interfere with each other. Both the sound and the object that produces it may be perceived at the same time; one through the receptors, for hearing and the other through the receptors for vision. Cor- responding neurone associations, as already in- dicated, are formed. So it is doubtless when the impacts are received from many receptors; for instance, of sound, sight, smell, taste, touch, all at the same time. This would seem to be a necessary result of the elemental reactions of protoplasm to the incident forces of the en- vironment; a matter which we have already fully discussed (see p. 33 et seq.). It would appear to be a logical conclusion that, in a sense, the entire cortex sees, hears, smells, tastes, and feels wherever it is traversed by the transmission. The so-called cortical centers appear merely to be avenues of ingress and egress to the general cortex, as already pointed out. To be sure, the cortex varies in its different parts in its detailed structure and presents peculiarities in both the receptive and emissive areas; e. g., in the 'Visual area" in the THE PHYSIOLOGY OF MIND 109 occipital lobe and in the centers of the "motor area." Here peculiarities of structure are found whose function is that apparently of the rein- forcement of transmissions. However, the neu- rone of the telencephalon appears to have re- tained along with its lack of fixation, along with its amoeboid movement, the general elemental qualities inherent in the primitive neuroblast, elemental qualities which are shared by the en- tire cortex. Other things equal, this lack of fixation of function, like the absence of fixation of the neurone itself, appears to have been and still is a necessary condition of its continued evolution. Differentiation and specialization, therefore, while it has taken place in the cortex, has not interfered with the continued adapta- tion and adjustment of responses and the con- tinued forming of new associations or combina- tions. Sensations are only experienced by the neurones taking part in the transmission, and these sensations doubtless depend for their kind upon the special receptors by which the im- pacts are received. The kinds of impact are much more numerous than would be implied by a consideration merely of the senses of smell, taste, vision, hearing, and touch. There are, 110 THE PHYSIOLOGY OF MIND first, the subdivisions of vision; namely, the per- ception of moving objects, of form, and color; secondly, the addition to the receptors for hearing of those for equilibrium and sense of position, and, lastly, the addition to touch of the senses of pressure, temperature, and pain. In addition to the receptors which receive im- pacts from sources external to the body, there are receptors which receive impacts arising within the body. Sherrington, as already stated, has termed the first "exteroceptors" and the second "interoceptors." Besides these there is a third group of receptors situated in muscles, bones, and joints, which give information as to the state of these structures when the parts concerned are moved. These Sherrington has termed "proprioceptors." It is quite clear, let us repeat, that the specific sensations aroused are dependent upon specific impacts received. In addition to these, how- ever, the neurone when active i. e,, when tak- ing part in the train of consciousness also ex- periences other sensations, namely, those com- prised by pleasure, pain, the emotions or af- fects. These may be slight, moderate, or in- tense in degree. In their production the in- THE PHYSIOLOGY OF MIND 111 ternal secretions, the hormones, and the sym- pathetic and autonomic nervous systems play an important role; at times the active cause is to be sought in toxic substances bred within the body or taken in from without. There is every rea- son to believe that the impacts which give rise to sensations of pleasure and pain affect primar- ily neurones in the segmental brain, the palseo- encephalon, namely, "cortical dependencies" in the thalamus (see p. 58). That they are transmitted to the telencephalon and that they play a role in consciousness and pro- foundly influence the train of neurone activity in the cortex goes without saying. The hor- mones or toxins probably act upon the sympa- thetic nervous system, upon the neurones of the thalamus, and the neurones of the cortex; it is probable that in the latter, in many in- stances, they act upon the synapses. If this be the case, transmission must be profoundly in- fluenced. On the one hand, it may be greatly retarded or inhibited, as in depressed mental states, e. g., in melancholia, in which we have probably to do with a toxic hormone as the cause both of the mental pain and the retarda- tion of the mental processes. How much the 112 THE PHYSIOLOGY OF MIND retardation of itself may serve as a cause of mental pain is an interesting question; probably it also plays a role. Interference with the syn- apses doubtless retards the "discharge of en- ergy" to the neurones next in succession, and this "blocking" or retardation of function may itself be a cause of pain in the neurone. In the opposite condition, that of mania, the normal resistance offered by the synapses is greatly lessened; there is a general release of inhibition and it is not improbable that the re- sulting increase of discharge, the heightening of function, is directly related to the "expansion," the pleasurable, aggressive, mental attitude so characteristic of this condition. Speculation as to the details possible or prob- able in the play of the emotions may lead us astray, but perhaps a few thoughts as to some of the fundamental physical principles which may underlie such elementary phenomena as pleasure and pain may not be amiss. For ex- ample, certain sequences and certain combina- tions of sound give us the pleasurable sensa- tion which we term "music." The thought suggests itself that the impacts transmitted to the neurones, i. e., the vibrations, are of such a THE PHYSIOLOGY OF MIND 113 character as to be taken up by the molecules of the neurones without causing a disruption of their structure, or at most, only a minimal con- sumption of substance. It is probable that sounds which are harsh, discordant, cacapho- nous, are painful because they actually cause destruction of the neurone molecule. Con- sumption of substance accompanies all dis- charge of function (see p. 81), but impacts that result in motions that are possible to or in harmony with the structure of the neurone molecule are probably accompanied by pleasur- able sensations. Possibly in some such thought as this is to be found the explanation of the pleasure and pain experienced through the other senses. May we perhaps be permitted to extend this conception to pleasurable and painful emotions? How markedly the latter are at times attended by the evidences of physical exhaustion i. e., consumption of sub- stance need hardly be pointed out. The relation between general nutrition and a sense of well-being is well known. Many factors, however, enter into the problem, and a detailed consideration of the affective qualities of mind would lead us too far afield. Suffice it to say 114 THE PHYSIOLOGY OF MIND that the elemental qualities of pain and pleasure were in primitive forms doubtless related, on the one hand, to injurious or destructive influ- ences, and, on the other, to the intake of food and other physical compliance with the needs of the organism. Later, in the course of evolu- tion, there ensued specializations and differen- tiations of impressions, impressions derived both from the external world and from the body of the organism itself. At the same time special receptors, both extero- and intero- ceptors, together with special neurone path- ways were evolved. Later, with the increasing development of the telencephalon, there came a further differentiation in the impressions and their corresponding neurone reactions and an increase in the adjustment of the response, i. e., in the behavior of the individual. Into the final result there may have entered, on the one hand, physical pain or physical pleasure; or on the other, joy, satisfaction, sorrow, dis- appointment; or, it may be, a refined feeling of altruism or perhaps of an almost impersonal regret. In the preceding pages the writer has en- deavored to apply purely physical conceptions THE PHYSIOLOGY OF MIND 115 to the interpretation of mind. The view that mental phenomena are in their essence physical finds confirmation in the facts of so-called psychophysics. These embrace especially the results of the experimental study of the time relations of mental processes and of the phe- nomena underlying the sense impressions. While a consideration of these phenomena in detail would here be out of place, let it suffice to say that as regards the first, namely, the time relations or reactions the time re- quired for the response to sense impressions they are significant in the fact, first, that any time at all is required, and secondly, that this time is in distinct relation to the complexity of the experiment and the condition of the individual; i. e., whether the latter be in good health, whether he be fatigued, or perhaps under the influence of some stimulant or drug, or the subject of disease. Clearly, all these factors are physical in their nature. In this connec- tion the interesting facts of the "personal equation" in the making of astronomical and other scientific time observations also present themselves. We are forcibly reminded, too, of the part which the synapses play in the 116 THE PHYSIOLOGY OF MIND delay of responses; though it goes without saying that some time must necessarily also be consumed in the transmission through the dendrites, bodies, and axones of the neurones. It is, however, in the field of the experimental studies upon sense impressions that the most significant and most convincing results have been achieved. It was found, for instance, that a sensation aroused by a given impres- sion having been noted, an increase in that sensation can only be brought about by a proportionate increase in the intensity of the impression. It was found, further, that in order to bring about such an increase of sensa- tion, the increase of intensity of the impres- sion made upon the receptors mu'st be in a geometric ratio to the increase of sensations; that is, the intensity of the sensation increases in an arithmetic progression, the intensity of the stimulus in a geometric proportion. Thus, a man capable of distinguishing between the weight of 16 ounces and 17 ounces, cannot distinguish between 32 and 33 ounces, but only between 32 and 34 ounces. Again, a man capable of distinguishing between 20 and 21 grammes, testing a weight of 250 grammes THE PHYSIOLOGY OF MIND 117 cannot tell when an increase is reached until 12.5 grammes are added. If he looks at a light of 10 candle-power he cannot become conscious of an increase in the intensity of the light until 2 candle-power are added; if he looks at a 60 candle-power flame 12 candle-power must be added; if it is a 2000 candle-power light, 400 candle-power must be added. 1 Similar facts obtain as regards the appreciation of intensity of sounds and as regards intensities of pressure. As regards the senses of taste and smell, of temperature, and the various somatic and visceral sensations, the conditions are such as to preclude very satisfactory experi- mentation. However, in regard to the senses in which such studies are possible, there can be no doubt as to the facts. A physiologist of a past generation, Weber of Leipzig, discovered these facts more especially in regard to auditory and cutaneous sensations, and they constitute what is today known as Weber's law. Many studies have since been made and various interpretations advanced, e. g., by Wundt and by Fachner, and the facts may be briefly sum- marized as follows: an increase of sensation 1 Ebbinghaus, Abriss der Psychologic, 1909, pp. 66, 67. 118 THE PHYSIOLOGY OF MIND depends, as above stated, upon a proportionate increase of the stimulus; the increase of sensa- tion is in arithmetic progression, that of the stimulus in geometric progression; or, to state it in other words, the sensation increases in proportion to the logarithm of the stimulus. Clearly we have here a hint not as to the relations between physical impressions and a spiritual world, as various interpretations would lead us to believe, but a hint as to the structure of the proteins that make up the neurone and the physical laws which these proteins must obey. In a sense Weber's law is as purely physical as the one which tells us that light is inversely as the square of the distance and must be equally accepted. The facts of Weber's law, however, lead it seems .to the writer to inferences far more fundamental and im- portant. We have already seen that the num- ber and character of the impacts which living protoplasm can take up is comparatively small. Only in an extremely limited degree do the changes induced in the protoplasm represent the changes the multiplicity of forces in the outside world. To this conception Weber's law adds another; namely, that such changes THE PHYSIOLOGY OF MIND 119 as are represented are only approximate; the very constitution of the protein molecules for- bids an even and continuous recognition of the increasing intensity of impacts. If this is true of the recognition of so simple a quality as in- crease of intensity, may it not be true also of other qualities of the impacts? The thought that suggests itself is that the changes induced in living protoplasm by the impacts are, first, only such as the protoplasm is capable of receiv- ing and, secondly, that these may and probably do in themselves correspond only imperfectly to the changes going on in the outside world. We can only be conscious of the changes in the protoplasm of our own substance, i. e., the changes in the proteins of our neurones; our knowledge of the outside world is necessarily limited to these changes and must of necessity be imperfect. Further, our knowledge is purely inferential. That multiple qualities of the out- side world produce no changes in the proteins of the neurones we have already seen; that other qualities induce changes which only im- perfectly represent those of the outside world is, it must be conceded, equally true. What are we to say of the memory pictures and of 120 THE PHYSIOLOGY OF MIND the general and abstract conceptions based upon these? Of the memory pictures it may be said that they can at best represent only more or less approximately actual past re- sponses to impacts. Of the general concep- tions i. e., the composite pictures resulting from accumulated responses it may be said that they are at best imperfect approximations to general external truths, and are liable to vary and change with additions to the impacts and corresponding fresh responses; that is, with an increasing experience. When we approach the field of abstract conceptions we clearly tread upon dubious ground. In reality, abstract conceptions represent nothing that actually exists in the outside world. At most they are artificial pegs upon which to hang the logic of our ideas. And, as regards our logic, is not this faculty dependent upon our own structure, upon the arrangement of our neurones, and upon their contained proteins and other substances? In how far is it to be trusted? Does it not at times lead us into gross absurdities? We need but recall the time- worn story of the race between the hare and the tortoise. Each interval of space existing THE PHYSIOLOGY OF MIND 121 between the two is divisible, and no matter how small the space may become it is still divisible; indeed, it is inconceivable that the space should become so small that it should not be still further divisible; and so it becomes logically impossible for the hare ever to catch the tortoise. Similar vagaries of neurone activity doubtless lie at the basis of such abstractions as the fourth, fifth, and sixth dimensions of space. As regards the fourth dimension, Ein- stein, after pointing out the relations of a given body to the three dimensions of space, points out that all bodies in the universe are in motion, and as it takes time for a given body to move from one point to another, time is the fourth "dimension" of space. To my way of think- ing, it would be better to say that time is an essential factor in all conceptions of spatial relations 1 ; or to put the fact into simpler lan- guage, merely to say that "all space is filled with moving matter." Time and the three dimensions of space are abstract conceptions, but the conception of "dimensions" having once been admitted, it becomes logically cap- 1 In a sense, every measurable element is a dimension, and in this sense time is a fourth dimension of space. 122 THE PHYSIOLOGY OF MIND able of indefinite multiplication; hence the fifth, sixth, and further dimensions of space. Is there not here an analogy to the logic of the race between the hare and the tortoise? In one instance there is indefinite division, in the other, indefinite multiplication. Evidently the logical process must be con- stantly curbed, held in check, inhibited by the correcting influence of the impressions received from the external world. We know that the hare does pass the tortoise, and we know also, no matter what our mathematical friends may say, that the multiplication of the "dimensions" is in crass contradiction with the orientation of our senses, i. e., with human experience. A biological interpretation of mind leads, I believe, to a more wholesome, a saner concep- tion of its functions and limitations. It may be noted that in this essay, up to the present moment, the word "psyche" or its equivalents and derivatives have not been employed. At the very outset the necessity was pointed out of laying aside preconceived ideas, prejudices, THE PHYSIOLOGY OF MIND 123 and beliefs. To introduce at this point an "immaterial" something, of unknown and un- ascertainable character, to insert such a some- thing into the problem renders the latter hopelessly unintelligible. Further, when we pause to consider the intrinsic meaning of the word psyche and its equivalents, most sugges- tive inferences present themselves. The Greek word ^V%YI has the primitive meaning of the breath: indeed, given the Greek pronunciation, the sound is literally that of the escaping breath. In primitive times the "breath" was looked upon as the vital principle, and its final escape in the act of dying as the departure of that vital principle. The ^f>7 naturally and subconsciously represented the idea of an "immaterial" constituent of our beings. A similar interpretation is applicable to the Latin word spiritus, the primitive meaning of which is likewise air, exhalation, breath, and its root still forms the integral parts of the words respiration, inspiration, expiration. The Latin word "mens" is free from such objections, for it literally means the mind, the under- standing, the intellect, and to me it has seemed much more fitting to employ its de- 124 THE PHYSIOLOGY OF MIND rivatives than those derived from -^V%YI or from spiritus. In conclusion, I may perhaps be permitted to say that there is nothing in the position here assumed which should shock or give pain to any one. The study of the recondite problems of human existence is in a sense a study that is imperative and should be pushed to its ulti- mate conclusions. Our knowledge of the, con- stitution of the universe as revealed by the marvelous truths of radio-activity, of the struc- ture of the atom, and by the field opened up by Einstein's discoveries and theories, is but an expression of this tendency; surely it should not be denied us in the study of mind. The modern study of the atom reveals it to be but an expression of energy, indestruct- ible, persistent, unknowable. Does not this cause the difference between the old con- ceptions of ''material" and "immaterial" to disappear? Does it not make unnecessary as it is impossible a "dual" conception of the universe? Finally, we should remember, that as regards religious conceptions, each human being is entitled to hold such faith as he chooses, and, further, that it is the necessary THE PHYSIOLOGY OF MIND 125 and essential attribute of religious faith that it should be incapable of scientific proof. A relig- ious faith that would be capable of mathemat- ical demonstration would be no faith at all. AN application of the facts and deductions embraced by the within essay to mental disease is both obvious and interesting, and the writer has thought it fit to add the following para- graphs. In the body of the essay, the writer has pointed out how the retraction of the dendrites and axones of the neurones explains the palsies and anaesthesias of hysteria. In other words, the functional break is referred to the synapses. A similar explanation applies to the palsies and anaesthesias of hypnosis which, as Gilles de la Tourette long ago pointed out, is merely hysteria artificially evoked. All of the phe- nomena of these states are undeniably mental, i. e., cortical in their origin. This is true alike of the motor, sensory, visceral, as well as the more strictly mental reactions. In hypnosis, for instance, a partial sleep is induced in which the admission of impacts from the various 126 THE PHYSIOLOGY OF MIND 127 receptors is inhibited save from those of the sense of hearing. The instructions, i. e., the suggestions, are made orally by the operator 1 ; all other avenues of contact with the outside world are for the time being closed. The train of neurone activity, therefore, which is set in motion by the suggestions of the operator pursues its way unchecked, uncorrected, for the impressions ordinarily received through vision or the other senses cannot gain access to the train of neurone activity, the field of consciousness. That under such circumstances the subject should prove to be exceedingly susceptible to the suggestions of the operator is not surprising; even when the suggestions are in crass contradiction with the situation in which the subject happens to be placed and with his previous experiences. The patient suffering from hysteria while not in any sense asleep, as in hypnosis, yet resembles the hypnotized subject in being abnormally susceptible to suggestion. Both Charcot and Gilles de la Tourette long ago stressed this factor in then* descriptions of hysteria. It was Babinski, however, who espe- 1 Except, of course, in special instances. 128 THE PHYSIOLOGY OF MIND cially pointed out the fact that the symptoms have their origin in suggestions that may arise from causes within as well as from causes with- out the patient. Especially instructive also were the facts which Babinski presented in regard to the production of special symptoms by the medical examination itself. He pointed out, for instance, that the reason hysterical hemiansesthesia predominates on the left side of the body is because the physician, being usually right-handed, has the brush or sesthesi- ometer in his right hand, and, facing the patient and asking the usual questions, he naturally tests the left side of the patient's body first, thus suggesting the very anaesthesia he is try- ing to discover. Similar facts obtain in regard to the induction of other sensory losses and other symptoms. The fact, however, of gre:.t- est importance is that the same or similar procedures may be practised upon normal per- sons, but without the slightest result. In other words, the hysterical subject accepts suggestions both direct and indirect; the normal person re- pels them. The personality of the hyster- ical patient is a very vulnerable one. Hysteria is, indeed, a neuropathy of degeneracy. Its 129 symptoms are always expressive of a biological inferiority, and, in keeping with this fact, it presents a large element of heredity. Charcot and his pupils regarded hysteria as always inherited; all other causes have merely the value of provocative agents. It would appear that, as in hypnosis, impacts received by other receptors than those which serve as the enter- ing avenue of the suggestion, fail to reach or to adequately enter the train of transmission, the field of consciousness. That when the field is entered as a result of psychotherapy or other cause, or when the suggestion giving rise to the symptom ceases to be operative, the symptom disappears, is a matter of common experience. It is not my intention here to consider the mechanism of hysteria in detail, such, for instance, as is illustrated by the immediate disappearance of the hysteria of litigation when the claim is settled or other- wise disposed of, or, of cases in which other "mental compensation" equally powerful oc- curs; for this would take us too far from our subject. The discussion of the phenomena of hypnosis and of hysteria leads naturally to the discus- 130 THE PHYSIOLOGY OF MIND sion of dreams; the latter, it should be added however, may be entirely normal manifestations As in hypnosis and hysteria, there is in a dream a field of cortical neurones active during a period in which impacts received by the special sense and perhaps other receptors are denied access. A field of cortical activity, a "train of trans mission" arising during sleep, may have its origin in one of two ways: First, transmis- sion of impacts into the telencephalon by way of the special sense receptors being suspended during sleep, transmission can only arise from impacts received from the viscera or from the soma generally; i. e., from the interoceptors or proprioceptors. Secondly, it is exceedingly probable that a train of transmission may be started by direct stimulation of the neurones by substances circulating in the blood; for example, by hormones present in unusual amount or modified in character, or by toxins resulting from overfatigue or introduced from without. The neurones, too, as a result of fatigue or other cause, may be abnormally irritable. It is exceedingly probable that toxins act primarily upon the terminals of the den- drites and end-tufts of the axones, ?. e., upon THE PHYSIOLOGY OF MIND 131 the synapses. It can readily be comprehended how in this way a train of transmission, a field of cortical activity, may arise. The train of transmission no matter how arising, being un- inhibited, i. e., uncorrected, by impacts received from the external world, now diffuses along pathways of least resistance; former neurone combinations are re-formed, many former ones are compounded; unusual and bizarre combi- nations result. Considerations such as the above lead not unnaturally to a consideration of states of delirium and confusion. Here we have to deal with problems of infection, intoxication, and exhaustion; and doubtless with the action of toxins and poisons directly and primarily upon the synapses and secondarily upon the bodies of the neurones. Irregularly occurring, con- stantly changing combinations, discharges and retractions appear to feature the conditions; more active and pronounced in delirium; de- layed, slower in confusion; and abolished in stupor. In keeping with this interpretation we find delirium featured by hallucinations, illusions, and unsystematized, fragmentary de- lusions. An hallucination is doubtless excited 132 THE PHYSIOLOGY OF MIND by the direct action of the toxin on the neurones of a special sense receiving area of the cortex; quite commonly it involves the auditory or the visual area. The disturbance forcing itself into the train of neurone activity already existing is naturally regarded by the latter, the "communal consciousness" (see p. 96), as something coming from without, and the noises, words, or phrases heard or the object seen are referred to the outside world. That in delirium errors of perception also occur is not surprising. An illusion excluding, of course, errors in the receiving apparatus, the special sense organ- is due to a faulty combination of the neurones of the cortex in response to the impacts received, or to an imperfect or aberrant correlation (in- tegration) with combinations previously formed ; thus occur mistakes in the recognition of objects and persons. That the resulting state of the communal consciousness should be one of con- fusion more or less active according to the intensity of the disturbance is what we should under the circumstances be led to expect. It is one of the essential features of delirious and confused states that there is an absence of fixation of any of the symptoms. The pic- THE PHYSIOLOGY OF MIND 133 ture is one constantly changing, constantly varying; in an active delirium the picture changes with kaleidoscopic suddenness; in con- fusion much more slowly; while in stupor the deadening weight of intoxication and exhaus- tion abolish all manifestations whatever. In certain mental diseases fixation, on the contrary, sooner or later makes its appear- ance. In order that its significance may be fully appreciated a digression will be necessary. There is a group of mental diseases which have their beginnings before the foundation of the organism is laid. The building material is imperfect, poor in quality, vitiated, so that the resulting structure crumbles and gives way under its own strains. Mental symptoms make their appearance relatively early, and this caused the early French writers, notably Morel, to speak of it as demence precoce, a name which Arnold Pick long after rendered into the now generally accepted term "dementia prsecox." As might be expected, the number of factors which enter into the impaired heredity of the patients is exceedingly large and varied, e. g., mental and nervous disease, syphilis, alcoholism, criminality, prostitution, vagabondage, eccen- 134 THE PHYSIOLOGY OF MIND tricity; in fact, all forms of degeneracy, mis- fits, and failures. Dementia prsecox is essentially an affection of endogenous deterioration. It should really be spoken of in the plural, as the insanities of adolescence, because in keeping with the many and varied hereditary factors entering into its causation, it manifests itself in many forms. Long ago two groups were isolated by Kahlbaum, which he termed respectively "hebephrenia" and "catatonia," and to these Kraepelin later added a third, "paranoid dementia." Later still Kraepelin distinguished ten different forms instead of three, but in this he has not been generally followed; and doubtless largely because, as Kraepelin himself admits, there are between the various forms so many transitional forms that they cannot be sharply delimited. For practical purposes the segregation into hebephrenia, catatonia, and paranoid dementia is quite commonly accepted. Hebephrenia is a relatively simple form, which occurs, on the whole, in the younger individuals; catatonia is distinguished more especially by the addition of certain motor phenomena and also presents slight evidences of "systematiza- THE PHYSIOLOGY OF MIND 135 tion" of the delusive ideas, and occurs, on the average, in somewhat older patients. Para- noid dementia is distinguished by a more pronounced systematization and occurs, on the average, in a still older group. That many transitional forms are met with need hardly be restated. 1 Space and the objects of this Addendum do not permit of a consideration of the symp- toms of dementia prsecox. Suffice it to say that the known facts in our possession point clearly to an auto toxic state and exhaustion. 2 The onset of symptoms is gradual, usually bearing the character of a confusion, some- times with varying elements of systematiza- tion and, let us repeat, of weakness and ex- haustion. That a progressive deterioration and a final dementia should ensue seems quite natural; and it is this that occurs in the larger number of cases. 1 Because of his interpretation of dementia prsecox as a cleavage or fissuration of the mental functions, Bleuler invented and proposed the name "schizophrenia," which he believes to be preferable to dementia prsecox. However, cleavages and fissurations of the personality are not confined to dementia prsecox, but also occur in other forms of mental disease as well as in the neuroses. Both the term and the affection lack the specificity that would justify its use. 2 Dercum, The Story of Dementia Praecox, New York Med. Jour., Aug. 12, 1916; also Clin. Manual of Mental Dis., p. 108. 136 THE PHYSIOLOGY OF MIND The behavior of the neurones, their synapses, and cell bodies, in confusion we have already considered. The researches of Fauser and others point among other things to the ingress into the blood of an abnormal hormone from the sex glands. Together with this we have a nerve substance inherently defective and feeble in resistance. As a natural result there is present, in addition to the confusion, a more or less marked adynamia of the field of cortical activity, the train of transmission. The level, .the intensity, of the metabolic processes of the neurones is lowered. In keeping with this there is slowness of speech and poverty of thought which eventuate in mutism, in fixed positions, stereotypy, automatism, persevera- tion, verbigeration; or it may be stupor. The train of transmission is reduced to a shallow, a narrow, a monotonously trickling stream, which may for a time cease altogether. Now and anon, tributary currents join what is left of the main stream, but they do so irregularly, at unusual points, and at variance with the orderly sequence of neurone combinations. While the cortex is adynamic as a whole, it may happen that the field of cortical activity THE PHYSIOLOGY OF MIND 137 is more greatly reduced than other portions. Under normal conditions the train of trans- mission, as already pointed out, diffuses, dis- charges into other and still inactive areas. However, if the level of the active field is greatly diminished and other portions of the cortex become, as a result of the toxic causes at work, spontaneously active, and if they possess relatively greater dynamic power, the direction of the diffusion may be reversed and these new activities may flow into the less resistant field. It is not necessary to suppose that they represent "complexes" that have been "repressed," to use the language of the Freudians. They may, of course, represent a variety of things; on the one hand, "wishes" and things desired, and, on the other, things of which the patient stands in fear and dread; but not necessarily either. We have already traced the origin of a hal- lucination, e. g., of hearing, and how it breaks into the train of transmission and how it is naturally regarded by the already existing communal consciousness as something coming from without. In a similar manner, other groups of neurone combinations may, as a result of 138 THE PHYSIOLOGY OF MIND their greater dynamic level, diffuse their energy into the less active field. That phenomena of cleavages and fissurations of the personality should under these circumstances result is what might be expected, but this is no reason, as has already been pointed out, for giving to dementia prsecox the specific name of schizo- phrenia. Let us return now to a consideration of fixa- tion which in certain mental diseases sooner or later makes its appearance. We have seen how in delirium and confusion there occurs an ever-changing and ever-varying combina- tion among the neurones. Sy nap tic relations are continuously and irregularly made and broken. We have seen, also, that in dementia prsecox, especially in the younger group, the mental picture is that of a confusion, but that in the older groups "systematization" of the delusive ideas may in some degree be present. By systematization is meant the arrangement of the ideas into logical sequence; in other words, a systematized delusion is one which has a logical structure. Now, it is the essence of an THE PHYSIOLOGY OF MIND 139 insane delusion that the person holding it is incapable of accepting evidence concerning it; i. e., such evidence as is accepted by ordinary men or by normal minds. This can only mean that the neurone combinations concerned in the delusions are inaccessible. It is entirely justifiable to assume that we have here to deal with relations between neurones which recur with such ease and constancy as to be potentially fixed in character. Inaccessibility to conflict- ing trains of neurone- combinations is a neces- sary result. Any impulse approaching the neurones concerned merely results in the re- formation of the old combinations. In keep- ing with this we meet with another fact, and that is, that a delusion once fixed becomes permanent. This is typically illustrated by the history of the various forms of paranoia, and, indeed, in general terms, it may be stated that the appearance of systematized delusions in a given mental case is always an unfavorable omen. The application of the physiological prin- ciples developed in the within essay to melan- cholia and mania has already been indicated (see p. 111). In melancholia the retardation 140 THE PHYSIOLOGY OF MIND may properly be ascribed to a depressing action upon the function of the synapses of a toxic hormone. Possibly to this, as well as to the general action of the toxin upon the neurone bodies, the mental suffering is to be attributed. It would seem a not illogical inference to regard the painful delusions so frequently present, as secondary outgrowths, as the explanations devised by the patient to account for his suffer- ings. At all events, the mental distress is the essential feature, as witness the cases of simple though severe melancholia without delusions. In the phase of mania, as already pointed out, the resistance of the synapses is greatly dimin- ished; there is a general release of inhibition. It would seem that as a result of the toxic hormone or other cause at work, the neurones evolve and discharge their energy with unusual ease and that the latter flows with lessened resistance along the cell processes. The patient is expansive, aggressive, boisterous, boastful, buoyant. He talks incessantly and with great rapidity; he rapidly embraces the objects and persons in a room in the scope of his percep- tions, but fastens his attention upon nothing. Illusions of objects and persons, due in part THE PHYSIOLOGY OF MIND 141 to the fragmentary and imperfect character of the perceptions and in part to abnormal associations, are a natural consequence. The associations are usually striking, unexpected; often they consist of meaningless rhymes, simi- larly sounding words or syllables, puns, mere assonances. There is an enormous increase in the flow of ideas; but the latter are evanes- cent, fugacious, unessential; what we hear is richer in words than in ideas. The expansion and the enormously increased association of mania is in keeping with heightened- nervous outflow, the increased energy discharged by the neurones. Along with this are the motor excitement and the unusual, the bizarre, the pathological char- acter of the associations. We can understand, perhaps, why the nervous overflow should pass along unaccustomed channels; perhaps, also, why the associations lose their intimate, elaborate, and finer qualities; why they should become coarse or relatively so. Normal acts require time, and probably in proportion to the amount of detail. In mania the discharges appear to be diffused en masse and probably along the larger pathways in which the least 142 THE PHYSIOLOGY OF MIND resistance is encountered. Possibly there is here an explanation of the coarseness and superficiality of the associations. Finally, it is probable that fatigue early impairs the synapses upon which the finer adjustments depend, so that as the case progresses coarse and flaring associations alone are present. A concluding paragraph upon the mental disturbances, the dementias, which ensue upon the gross destructive action of poisons, such as lead and alcohol, and upon the destruction- of the neurones by the ravages of the Spirochaeta pallida and other agents, hardly seems neces- sary. The action of these is obvious and the details do not here concern us. INDEX ABSTRACT conceptions, 120 thinking, 120 Act of apperception, 100 of collocation, 100 Activity, train of, 94 Adaptation in metazoa of surface cell, 23, 42 of responses, 58, 62 Addendum on pathological physi- ology of mind, 126 Adequate stimulus, 51 Adjuster, 47 Affects, 110 Alimentary canal, 48 Altruism, 114 Amino-acids in proteins, 19 Amoeba, reaction to environment, 12 Amoeboid approach, 94 movement of dermal membrane of sponges, 16 transmission, 78 Amoeboidism of cortical neurones, 63 of neurone, 71, 73 Apperception, 99 Association, 99 paths, 53 pathways, 61 Attention, 105 Automatic character of spinal re- sponses, 55 Automatism, acquired, disappear- ance of consciousness in, 87 Automatism of memory, 97 of response in approach to or withdrawal from foreign bodies, 51 Avalanche conduction, 81, 82 Axone, 28, 71 Azoulay, 65 BABINSKI, 127, 128 Bergson, 90 Biological endogenous deteriora- tions, 134 interpretation of mind, 122 Blocking, 112 Brain, ear, 50, 107 eye, 50, 107 nose, 50, 107 skin, 50, 107 stem, 56 visceral, 50 Buchanan, 77 CATATQNIA, 134 Cell, contractile, differentiation of, 16 intermediate, differentiation of, 24 metabolism, 13 receiving, differentiation of, tS reducing power of, 14 selecting power of, 13 Centers, cortical, 60 Central nervous system, segments] relations of, 49 143 144 INDEX Cephalic extremity and special sense receptors, segmental rela- tions of, 50 Cerebral cortex. 56, 57. See also Cortex. Charcot, 127, 129 Chemical impacts, 34 received by surface cell, 43 sense, 51 Cbemotaxis, 68 Ccelenterates, pathways for trans- mission in, 21 transmission in nerve net of, 29 Collaterals, 28 Collocation, 100 Common paths of transmission, 48, 49,78 Communal consciousness, 132 Community of consciousness, 96 Complexity of proteins, 19 Composite pictures, 120 Concentration, 106 Conceptions, abstract, 120 of dimensions, 121 Conduction, avalanche, 81, 82 Confusion, 131 Conscious and unconscious fields, relative dynamic power of, 104 Consciousness, 83 communal, 132 disappearance of, in acquired automatisms, 87 field of, 93, 95, 101 in higher vertebrates, 85 in lower forms of life, 83 in lower vertebrates, 84 in responses of adaptation and adjustment, 88 nature of, 90 relation of phenomena of cortical transmission to, 89 Contact with foreign bodies as stimuli, 34 Contractile cell, differentiation of, 16 Contractility of sponges, 16 Cortex, functions of, 60 relation of parts of, 61 responses of, and relations of neurones, 62-, 63 transmission through, phe- nomena of, 89 Cortical centers, 60 dependencies, 59, 111 neurones, reactions of, 75 amoeboidism of, 63 transmission, phenomena of, rela- tion to consciousness, 89 DANGERS of abstract thinking, 120 de la Tourette, 126, 127 Delirium, 131 Delusions, 131 Demence precoce, 133 Dementia, paranoid, 134 prsecox, 133, 134 Dendrites, 27, 71 Dercum, 36, 63, 64, 65, 75, 94, 135 Dermal membrane of sponges, 16 Diffusion, 20 Dimensions, conception of, 121 Disappointment, 114 Discharge of energy, 112 Dreams, 130 origin of, 130 Duval, 64 Dynamic levels, 105 power, relative, of conscious and unconscious fields, 104 quality of memory, 97, 98 INDEX 145 EAR, 36 brain, 50, 107 Edinger, 56 Effector, 23, 25 Egress, pathways of, from telen- cephalon, 59 Einstein, 121, 124 Electro-endosmotic layer, 74 Element of time, significance of, 115 Emotions, 110 Endogenous deteriorations, biolog- ical, 134 Energy, discharge of, 112 release of, 81 Environment, reaction of organism to, 12-19 Expansion, 112 Exteroceptive sense, 44, 45 Exteroceptors, 110 Eye brain, 50, 107 spot, 37 action of, 37 FACHNER, 117 Fauser, 136 Field of consciousness. 93, 95, 101 physiology of, 102 unconscious, 101 Fischer, Emil, 19 Fixation, appearance and signifi- cance of, 138 Foreign bodies, contact with, as stimuli, 34 impact of, reaction of proto- plasm to, 19 Fourth dimension, 121 Freudians, 137 HALLUCINATIONS, 131 Heat, impacts of, 38 10 Heat, influence of, on activity of protoplasm, 38 Hebephrenia, 134 Heredity in hysteria, 129 Herrick, 39, 45, 50, 56 61, 68, 69,77 Higher vertebrates, consciousness in, 85 Historical data, 63 Hodge, 95 Hormones, 68 Hypnosis, 126 Hysteria, 63, 126 heredity in, 129 Hysterical paralysis, theory of, 63 IDIOT savants, 98 Illusions, 131 Imagination, 104 Impacts, chemical, 34 from movements and coarse vibrations in surrounding me- dium, 35 groups of, 52 of heat, 38 of light, 37 physical, special sensations from, 107 received by living protoplasm, 34 Incremental stimulus, 72 Ingress, pathways of, to telenceph- alon, 58 Initial stimulus, 72 Initiative, 105 Instincts, 97 Intercalary neurones, 31, 48 effect of, 32 Intermediate cell, differentiation of, 24 Internuncial fibers, 52 paths of transmission, 49 Interoceptive sense, 44 146 INDEX Interoceptors, 110 Invertebrates, nervous system of, 24 Iris, response to direct physical stimulation, 17 JELLY-FISHES, nervous apparatus in, 21 pathways for transmission in, 21 Joy, 114 KAHLBAUM, 134 Kappers, 69, 70, 71, 72, 74 Knee reflex, 32 Knee-jerk, 32 Kraepelin, 134 LATERAL line system, 36 Lepine, 64 Light, impacts of, 37 influence on activity of proto- plasm, 37 Limitations of possibilities, only such changes as protoplasm is capable of receiving, 119 these changes correspond only imperfectly to changes in outside world, 119 Loeb, Jacques, 99 Lower forms of life, consciousness in, 83 vertebrates, consciousness in, 84 Lugaro, 95 MACULA acustica, 36 Mammals, fixed responses and consciousness in, 86 Mania, 112, 139 Mauthner, 70 Mechanism of response, 31 Melancholia, 111, 139 Memory, 97 dynamic quality of, 97, 98 its automatism, 97 pictures, 119, 120 Mental pain, 112 Metabolism of cells, 13 Metazoa, adaptation of surface cell in, 23, 42 Mind, 11 biological interpretation of, 122 interpretation of, physical con- ceptions in, 114 pathological physiology of, ad- dendum, 126 phenomena of, 11 Morel, 133 Motor area, 109 projection fibers, 60 Movement, response in, 19 Movements and coarse vibrations in surrounding medium, impacts from, 35 Multicellular forms, primitive re- sponses of movement in, 15 reactions of individual cells of, 13 Muscle activity independent of nervous influence, 17, 18 Muscle-cell in pore canals of sponges, 23 Music, 112 NEO-ENCEPHALON, 57 Nerve net of ccelenterates, trans- mission in, 29 Nerve-cells, 27 change in positions of, in verte- brates, 69 movement of, in invertebrates, 66 processes of, 27 Nervous network, structure of, 26 INDEX 147 Nervous system, central, of verte- brates, neurone of, 27 of invertebrates, 24 of vertebrates, 24 synaptic, 29 differentiation of, 27 of vertebrates, 30 syncytic, 29 Neurobiotactic phenomenon, 71 Neurobiotaxis, 69, 78 principles that determine, 78 Neuroblast, 67 Neuroid transmission, 21 Neurone, 28 amreboidism of, 71, 73 changes in, 81 combinations, 59 development of, 67 of central nervous system of vertebrates, 27 origin of, 67 polarization of, 70, 71 relations, variability of, 133 threshold, 78 Neurones, cortical, amoeboidism of, 63 intercalary, 31, 48 effect of, 32 of cortex, relations of, 62, 63 relations between, 100 reforming of old and formation of new combinations among, 103 Nose brain, 50 OBJECTIONS to Greek word and its derivatives, 123 to Latin word spiritus and its derivatives, 123 Olfactory brain, 107 impressions, 53 lobes in fish, 51 Organism, response by, methods of, 47 Originality, 104 Otic vesicle, 36, 38 Otoliths, 88 PAIN, 110 mental, 112 physical principles of, 112 Palseo-encephalon, 56 role of, 86 Pallium, role of, 85 Paralysis, hysterical, theory of, 63 Paranoid dementia, 134 states, 134, 135 Parker, 15, 18, 20, 21, 22, 26, 27, 29 Pathological physiology of mind, addendum, 126 Pathways, association, 61 of ingress to and egress from telencephalon, 58 of transmission, definite, estab- lishment of, 48, 49 old and new, 80 primitive, 21 Perception, 99 Personal equation, 115 Phenomena of mind, 11 Physical conceptions in interpreta- tion of mind, 114 Pick, Arnold, 133 Pictures, composite, 120 memory, 119, 120 Pleasure, 110 physical principles of, 112 Polarity of transmission, 30 Polarization of neurone, 70, 71 Pore canal, 16 epithelial lining of, 16 of sponges, muscle-cell in, 23 membrane, 16 INDEX Precocious dementias, 134 Primitive pathways of transmis- sion, 21 responses of movement in multi- cellular forms, 15 transmitting apparatus, position of, 24 network, structure of, 26 Proprioceptors, 110 Protein, complexity of, 19 Protoneurone, 24, 26 function of, 24 Protoneurones, 66 Protoplasm, living, capacity of. for transmission of motion through its own substance, 19 changes in structure of, in response to changes in out- side world, 118 function of, 37 impacts received by, 34 influence of heat on activity of, 38 of light on, 37 limited capacity of, for recep- tion of incident forces of environment, 38. 39 nature of, 40 reaction to medium, 35 structure of, 20, 40 transparency of, 37, 40, 42 Pseudopod, reaction to environ- ment, 12 Pupin, 65 RABL-Riickard, 63, 64 Race memories, 97 Ramo"n y Cajal, 65, 81 Reactions of individual cells of multicellular forms, 13, 14 Reactions of organism to chemical impressions of environment, 34 to environment, 12-19 of unicellular forms, 12 word, 77 time, 76 Receiving cell, differentiation of, 23 Receptor, 23, 25 Receptors, differentiation of, 42 limited number of, 39 physical character of function, 42 Reducing power of cells, 14 Reflex, 31 knee, 32 spinal, 32 Regret, 114 Release of energy, 81 Response, automatism of, in ap- proach to or withdrawal from foreign bodies, 51 by organism, methods of, 47 forms of, 47 in movement, 19 mechanism of, 31 Responses, adaptable, 57 adaptation of, 58, 62 differentiation of, 33 exit of, 59 fixed, 56, 88 invariable, 56 of adaptation and adjustment, consciousness in, 88 of cortex and relations of neu- rones, 62, 63 of movement, primitive, in multi- cellar forms, 15 origin of, 58 possibilities of adaptation and adjustment of, 62 INDEX 149 Responses, spinal, automatic char- acter of, 55 variable, 56, 57 in higher vertebrates, 57 Roles of other senses, 54 SATISFACTION, 114 Schizophrenia, 135, 138 Sea-anemones, nervous apparatus in, 21 pathways for transmission in, 22 Segmental apparatus, 56 relations of central nervous system, 49 of cephalic extremity and special sense receptors, 50 of telencephalon, absence of, 57 Selecting power of cells, 13 Selective action, 12 Self, sense of, 96 Sensation, 106, 109 of smell, 43 of taste, 43 Sensations, special, from physical impacts, 107 Sense cell, 23 chemical, 51 of self, 96 of smell, exteroceptive, 44, 45 of taste, interoceptive, 44, 45 Senses of smell and taste, distinc- tion between, 44 r&les of, 54 Sensory projection fibers, 58 Sentiency, 83, 106 Sherrington, 44, 48, 71, 72, 73, 77, 78, 110 Significance of element of time, 115 Skin brain, 50, 107 Sleep, 94, 95, 126 Smell, sensation of, 43 Smell, sense of, 44 Sorrow, 114 Sound, transmission of, 36 Sphincter-like action in canals of sponges, 16 Spinal reflexes, 32 responses, automatic character of, 55 Sponges, 15 amosboid movement of dermal membrane of, 16 contractility of, 16 dermal membrane of, 16 muscle-cell in pore canals of, 23 reaction to environment, 16 sphincter-like action in canals of, 16 Stigma, 37 action of, 37 Stimuli, 34 Stimulus, adequate, 51 word, 77 Stupor, 131 Stylatella, 15, 20 Surface cell, adaptation of, in metazoa, 23, 42 chemical impacts received by, 43 Synapse, 27, 28 Synapses, 70 Synaptic delay, 71 membrane, 75 nervous system, 29 differentiation of, 27 of vertebrates, 30 resistance, 92 Syncytic nervous system, 29 Systematization, 138 TASTE, sensation of, 43 sense of, 44 150 INDEX Telencephalon, 57 absence of segmental relations of, 57 pathways of ingress to and egress from, 58 role of, 107 Thought, 100 Time, element of, significance of, 115 Tourette, 126, 127 Train of activity, 94 Transmission, 20 common paths of, 48, 49 in nerve-net of coelenterates, 29 internuncial paths of, 49 neuroid, 21 of impacts through organism, 47 pathways of, definite establish- ment of, 48 49 old and new, 80 polarity of, 30 primitive pathways of, 21 principles that govern, 91 through cortex, phenomena of, 89 Transmitting apparatus, primitive, position of, 24 in more complex metazoa, 24 network, primitive, structure of, 26 Transparency of protoplasm, 37, 40,42 UNCONSCIOUS and conscious fields, relative dynamic power of, 104 field, 101 physiology of, 102 Unconsciousness, 94, 95 Unicellular forms, reactions of, 12 VERTEBRATES, higher, conscious- ness in, 85 lower, consciousness in, 84 nervous system of, 24 synaptic nervous system of, 30 Visceral brain, 50 Vision, subdivisions of, 110 Visual area, 108 WALDETER, 28 Weber, 117, 118 Weber's law, significance of, 116- 118 Wiedersheim, 66 Will, 105 power, 105, 106 Wilson, 16 Wishes, 137 Wundt, 77, 117 UNIVERSITY CALIFORNIA T.rn. A rerel< Tt- : fHE LIBRARY WIVERSITY OF CALIFORNIA LOS ANGELES Ae 12 Bwmeduol Library A 000 329 320 6