Comparative Physiology of the Brain and Comparative Psychology

10. The Basis of Social Relations. By DANIEL G. BRINTON. $1.50 Comparative Physiology of the ^ Brain and Comparative Psychology It is the purpose of this book to serve as a short introduction to the comparative physiology of the brain and of the central nervous system. Physiology has thus far been essentially the physi- ology of Vertebrates. I am convinced, however, that for the establishment of the laws of life-phenomena a broader basis is necessary. Such a basis can be furnished only by a comparative physiology which includes all classes of the animal kingdom. My ex- perience in the course on comparative physiology at Wood's Holl seems to indicate that the transition from the old to the comparative physiology can be most readily accomplished through the physiology of the central nervous system.

The physiology of the brain has been rendered unnecessarily difficult through the fact that meta- physicians have at all times concerned themselves with the interpretation of brain functions and have introduced such metaphysical conceptions as soul, consciousness, will, etc. One part of the work of the physiologist must consist in the substitution of real physiological processes for these inadequate con- ceptions. Professor Ernst Mach, of Vienna, to whom

this book is dedicated, was the first to establish the general principles of an antimetaphysical science. I have added at the end of each chapter a list of the chief papers of which I have made use. Although far from complete, this may serve the beginner as a guide for the further study of the subjects touched upon. The book appeared first in German and was trans- lated by Anne Leonard Loeb. As a number of new facts have been found since the German edition ap- peared, and as it seemed desirable to formulate my antimetaphysical standpoint more precisely, I have made extensive alterations.

My thanks are due to a number of friends who have offered suggestions, — most of all to my pupil, Miss Anne Moore. 2. DlAC.RAM OF THE BELL OF AURELIA AURITA, (AFTER GLAUS.) . iS 8. DIAGRAM FOR EXPLAINING THE LOCALISING REFLEX IN MEDUSAE 32 13. AN ACTINIAN (CERIANTHUS) THAT HAD BEEN PLACED IN A TEST- 17. MECHANISM OF THE TURNING OF A STARFISH THAT HAS BEEN LAID AT LAST COLLECT IN A CORNER OF THE AQUARIUM AND PERISH IN THE VAIN ATTEMPT TO Go THROUGH THE GLASS. (AFTER

i. The understanding of complicated phenomena depends upon an analysis by which they are resolved into their simple elementary components. If we ask what the elementary components are in the physio- logy of the central nervous system, our attention is directed to a class of processes which are called re- flexes. A reflex is a reaction which is caused by an external stimulus, and which results in a coordinated movement, the closing of the eyelid, for example, when the conjunctiva is touched by a foreign body, or the narrowing of the pupil under the influence of light. In each of these cases, changes in the sensory

nerve-endings are produced which bring about a change of condition in the nerves. This change travels to the central nervous system, passes from there to the motor nerves, and terminates in the muscle-fibres, producing there a contraction. This passage from the stimulated part to the central nervous system, and back again to the peripheral muscles, is called a reflex. There has been a growing tendency in physiology to make reflexes the basis of the analysis of the functions of the central nervous system, consequently much importance has been at- tached to the underlying processes and the necessary mechanisms.

The name reflex suggests a comparison between the spinal cord and a mirror. Sensory stimuli were supposed to be reflected from the spinal cord to the muscles ; destruction of the spinal cord would, ac- cording to this, make the reflex impossible, just as the breaking of the mirror prevents the reflection of light. This comparison, however, of the reflex pro- cess in the central nervous system with the reflection of light has, long since, become meaningless, and at present few physiologists in using the term reflex think of its original significance. Instead of this, another feature in the conception of the term reflex has gained prominence, namely, the purposeful char- acter of many reflex movements. The closing of the eyelid and the narrowing of the pupil are eminently purposeful, for the cornea is protected from hurtful contact with foreign bodies, and the retina from the

injurious effects of strong light. Another striking characteristic in such reflexes has also been empha- sised. The movements which are produced are so well planned and coordinated that it seems as though some intelligence were at work either in devising or in carrying them out. The fact, however, that a de- capitated frog will brush a drop of acetic acid from its skin, suggests that some other explanation is necessary. A prominent psychologist has maintained that reflexes are to be considered as the mechanical effects of acts of volition of past generations. The ganglion-cell seems the only place where such me- chanical effects could be stored up. It has there- fore been considered the most essential element of the reflex mechanism, the nerve-fibres being regarded, and probably correctly, merely as conductors.

Both the authors who emphasise the purposeful- ness of the reflex act, and those who see in it only a physical process, have invariably looked upon the ganglion-cell as the principal bearer of the structures for the complex coordinated movements in reflex action. I should have been as little inclined as any other physiologist to doubt the correctness of this concep- tion had not the establishment of the identity of the reactions of animals and plants to light proved the untenability of this view and at the same time offered a different conception of reflexes. The flight of the moth into the flame is a typical reflex process. The light stimulates the peripheral sense organs, the

stimulus passes to the central nervous system, and from there to the muscles of the wings, and the moth is caused to fly into the flame. This reflex process agrees in every point with the heliotropic effects of light on plant organs. Since plants possess no nerves, this identity of animal with plant heliotropism can offer but one inference — these heliotropic effects must depend upon conditions which are common to both animals and plants. At the end of my book on helio- tropism I expressed this view in the following words : " We have seen that, in the case of animals which possess nerves, the movements of orientation toward light are governed by exactly the same external con- ditions, and depend in the same way upon the external form of the body, as in the case of plants which possess no nerves. These heliotropic phenomena, conse- quently, cannot depend upon specific qualities of the central nervous system (i)." On the other hand, the objection has been raised that destruction of the ganglion-cells interrupts the reflex process. This argument, however, is not sound, for the nervous reflex arc in higher animals forms the only protoplas- mic bridge between the sensory organs of the surface of the body and the muscles. If we destroy the gan- glion-cells or the central nervous system, we interrupt the continuity of the protoplasmic conduction between the surface of the body and the muscles, and a reflex is no longer possible. Since the axis-cylinders of the nerves and the ganglion-cells are nothing more than protoplasmic formations, we are justified in seeking

in them only general protoplasmic qualities, unless we find that the phenomena cannot be explained by means of the latter alone. 2. A further objection has been raised, that al- though these reflexes occur in plants possessing no nervous system, yet in animals where ganglion-cells are present the very existence of ganglion-cells neces- sitates the presence in them of special reflex mechan- isms. It was therefore necessary to find out if there were not animals in which coordinated reflexes still continued to exist after the destruction of the central nervous system. Such a phenomenon could be ex- pected only in forms in which a direct transmission of stimuli from the skin to the muscle is possible, in addition to the transmission through the reflex arc. This is the case, for instance, in worms and in Ascidi- ans. I succeeded in demonstrating in Ciona intesti- nalis that the complicated reflexes still continue after removal of the central nervous system (2).

A study, then, of comparative physiology brings out the fact that irritability and conductibility are the only qualities essential to reflexes, and these are both common qualities of all protoplasm. The irritable structures at the surface of the body, and the arrange- ment of the muscles, determine the character of the reflex act. The assumption that the central nervous system or the ganglion-cells are the bearers of reflex mechanisms cannot hold. But have we now to con- clude that the nerves are superfluous and a waste ? Certainly not. Their value lies in the fact that they

are quicker and more sensitive conductors than undif- ferentiated protoplasm. Because of these qualities of the nerves, an animal is better able to adapt itself to changing conditions than it possibly could if it had no nerves. Such power of adaptation is absolutely necessary for free animals. 3. While some authors explain all reflexes on a psychical basis, the majority of investigators explain in this way only a certain group of reflexes --the so- called instincts. Instincts are defined in various ways, but no matter how the definition is phrased the mean- ing seems to be that they are inherited reflexes so purposeful and so complicated in character that no- thing short of intelligence and experience could have produced them. To this class of reflexes belongs the habit possessed by certain insects of laying their e°f£s on the material which the larvae will afterwards

require for food. When we consider that the female fly pays no attention to her eggs after laying them, we cannot cease to wonder at the seeming care which nature takes for the preservation of the species. How can the action of such an insect be determined if not by mysterious structures which can only be contained in the ganglion-cells? How can we explain the in- heritance of such instincts if we believe it to be a fact that the ganglion-cells are only the conductors of stimuli ? It was impossible either to develop a mechanics of instincts or to explain their inheritance in a simple way from the old standpoint, but our con- ception makes an explanation possible. Among the

elements which compose these complicated instincts, thetropisms (heliotropism, chemotropism, geotropism, stereotropism) play an important part. These trop- isms are identical for animals and plants. The explanation of them depends first upon the specific irritability of certain elements of the body-surface, and, second, upon the relations of symmetry of the body. Symmetrical elements at the surface of the body have the same irritability ; unsymmetrical ele- ments have a different irritability. Those nearer the oral pole possess an irritability greater than that of those near the aboral pole. These circumstances force an animal to orient itself toward a source of stimulation in such a way that symmetrical points on the surface of the body are stimulated equally. In this way the animals are led without will of their own either toward the source of the stimulus or away from it. Thus there remains nothing for the ganglion- cell to do but to conduct the stimulus, and this may be accomplished by protoplasm in any form. For the inheritance of instincts it is only necessary that the egg contain certain substances — which will de- termine the different tropisms--and the conditions for producing bilateral symmetry of the embryo. The mystery with which the ganglion-cell has been sur- rounded has led not only to no definite insight into these processes, but has proved rather a hindrance in the attempt to find the explanation of them.

It is evident that there is no sharp line of demarc- ation between reflexes and instincts. We find that authors prefer to speak of reflexes in cases where the reaction of single parts or organs of an animal to external stimuli is concerned ; while they speak of instincts where the reaction of the animal as a whole is involved (as is the case in tropisms). 4. If the mechanics of a number of instincts is explained by means of the tropisms common to ani- mals and plants, and if the significance of the gan- glion-cells is confined, as in all reflex processes, to their power of conducting stimuli, we are forced to ask what circumstances determine the coordinated move- ments in reflexes, especially in the more complicated ones. The assumption of complicated but unknown and perhaps unknowable structures in the ganglion- cells served formerly as a convenient terminus for all thought in this direction. In giving up this assump- tion, we are called upon to show what conditions are able to determine the coordinated character of reflex movements. Experiments on galvanotropism of ani- mals have proved that a simple relation must exist between the orientation of certain motor elements in the central nervous system and the direction of the movements of the body which is called forth by the activity of these elements. This perhaps creates a rational basis for the further investigation of coordi- nated movements.

5. We must also deprive the ganglion-cells of all specific significance in spontaneous movements, just as we have done in the case of simple reflexes and instincts. By spontaneous movements we mean movements which are apparently determined by inter- nal conditions of the living system. Strictly speaking, no movements of animals are exclusively determined by internal conditions, for the atmospheric oxygen and a certain temperature or certain limits of tem- perature are always necessary in order to preserve the activity beyond a short period of time.

We must discriminate between simple and conscious spontaneity. In simple spontaneity we must consider two kinds of processes, namely, aperiodic spontaneous processes and rhythmically spontaneous or automatic processes. The rhythmical processes are of import- ance for our consideration. Respiration and the heart-beat belong to this category. The respiratory movements prove without possible doubt that auto- matic activity can arise in the ganglion-cells, and from this the conclusion has been drawn that all automatic movements are due to specific structures of the ganglion-cells. Recent investigations, how- ever, have transferred the problem of rhythmical spontaneous contractions from the field of morphology into that of physical chemistry. The peculiar quali- ties of each tissue are partly due to the fact that it contains ions (Na, K, Ca, and others) in definite proportions. By changing these proportions, we can impart to a tissue properties which it does not ord- inarily possess. If in the muscles of the skeleton the Na ions be increased and the Ca ions be reduced, the muscles are able to contract rhythmically, like the heart. It is only the presence of Ca ions in the

blood which prevents the muscles of our skeleton from beating rhythmically in our body. As the mus- cles contain no ganglion-cells, it is certain that the power of rhythmical spontaneous contractions is not due to the specific morphological character of the ganglion-cells, but to definite chemical con- ditions which are not necessarily confined to gang- lion-cells (3). The coordinated character of automatic movements has often been explained by a " centre of coordina- tion," which is supposed to keep a kind of police watch on the different elements and see that they move in the right order. Observations in lower animals, however, show that the coordination of automatic movements is caused by the fact that that element which beats most quickly forces the others to beat in its own rhythm. Aperiodic spontaneity is still less a specific function of the gang- lion-cell than rhythmical spontaneity. The swarm- spores of algae, which possess no ganglion-cells, show spontaneity equal to that of animals having ganglion-cells.

6. Thus far we have not touched upon the most important problem in physiology, namely, which mechanisms give rise to that complex of phenomena which are called psychic or conscious. Our method of procedure must be the same as in the case of in- stincts and reflexes. We must find out the ele- mentary physiological processes which underlie the complicated phenomena of consciousness. Some physiologists and psychologists consider the purpose- fulness of the psychic action as the essential element. If an animal or an organ reacts as a rational man would do under the same circumstances, these authors declare that we are dealing with a phenomenon of consciousness. In this way many reflexes, the in- stincts especially, are looked upon as psychic func- tions. Consciousness has been ascribed even to the spinal cord, because many of its functions are pur- poseful. We shall see in the following chapters that many of these reactions are merely tropisms which may occur in exactly the same form in plants. Plants must therefore have a psychic life, and, follow- ing the argument, we must ascribe it to machines also, for the tropisms depend only on simple mechan- ical arrangements. In the last analysis, then, we would arrive at molecules and atoms endowed with mental qualities.

We can dispose of this view by the mere fact that the phenomena of embryological development and of organisation in general show a degree of purposeful- ness which may even surpass that of any reflex or instinctive or conscious act. And yet we do not consider the phenomena of development to be depend- ent upon consciousness. On the other hand, physiologists who have appre- ciated the untenable character of such metaphysical speculations have held that the only alternative is to drop the search for the mechanisms underlying consciousness and study exclusively the results of

operations on the brain. This would be throw- ing out the wheat with the chaff. The mis- take made by metaphysicians is not that they devote themselves to fundamental problems, but that they employ the wrong methods of invest- igation and substitute a play on words for ex- planation by means of facts. If brain-physiology gives up its fundamental problem, namely, the dis- covery of those elementary processes which make consciousness possible, it abandons its best possi- bilities. But to obtain results, the errors of the metaphysician must be avoided and explanations must rest upon facts, not words. The method should be the same for animal psychology that it is for brain-physiology. It should consist in the right understanding of the fundamental process which re- curs in all psychic phenomena as the elemental com- ponent. This process, according to my opinion, is the activity of the associative memory, or of association. Consciousness is only a metaphysical term for phenomena which are determined by associative memory. By associative memory I mean that mechanism by which a stimulus brings about not only the effects which its nature and the specific structure of the irritable organ call for, but by which it brings about also the effects of other stimuli which formerly acted upon the organism almost or quite simultaneously with the stimulus in question (4). If an animal can be trained, if it can learn, it possesses associative memory. By means of this criterion it

can be shown that Infusoria, Ccelenterates, and worms do not possess a trace of associative memory. Among certain classes of insects (for instance, wasps), the existence of associative memory can be proved. It is a comparatively easy task to find out which representatives of the various classes of ani- mals possess, and which do not possess, associative memory. Our criterion therefore might be of great assistance in the development of comparative psychology.

7. Our criterion puts an end to the metaphysical ideas that all matter, and hence the whole animal world, possesses consciousness. We are brought to the theory that only certain species of animals possess associative memory and have consciousness, and that it appears in them only after they have reached a certain stage in their ontogenetic development. This is apparent from the fact that associative memory depends upon mechanical arrangements which are present only in certain animals, and present in these only after a certain develop- ment has been reached. The fact that certain ver- tebrates lose all power of associative memory after the destruction of the cerebral hemispheres, and the fact that vertebrates in which the associative memory either is not developed at all or only slightly developed (e. g., the shark or frog) do not differ, or differ but slightly, in their reactions after losing the cerebral hemispheres, support this view. The fact that only certain animals possess the necessary

mechanical arrangements for associative memory, and therefore for metaphysical consciousness, is not stranger than the fact that only certain animals possess the mechanical arrangements for uniting the rays from a luminous point in one point on the retina. The liquefaction of gases is an example of a sudden change of condition which may be produced when one variable is changed ; it is not surprising that there should be sudden changes in the onto- genetic and phylogenetic development of organisms when there are so many variables subject to change, and when we consider that colloids easily change their state of matter.

It becomes evident that the unravelling of the mechanism of associative memory is the great dis- covery to be made in the field of brain-physiology and psychology. But at the same time it is evident that this mechanism cannot be unravelled by histo- logical methods, or by operations on the brain, or by measuring reaction times. We have to remember that all life phenomena are ultimately due to motions or changes occurring in colloidal substances. The question is, Which peculiarities of the colloidal sub- stances can make the phenomenon of associative memory possible ? For the solution of this problem the experience of physical chemistry and of the physiology of the protoplasm must be combined. From the same sources we must expect the solution of the other fundamental problems of brain-physio- logy, namely, the process of conduction of stimuli.

1. LOEB, J. Der Heliotropismus der Thiere und seine Ueberein- sti/nfnung mit dem Heliotropismus der Pflanzcn. Wiirzburg, 1890. A preliminary note on these experiments appeared January, 1888. 2. LOEB, J. Untersuchungen zur physiologischen Morphologie der Thiere II. Wtirzburg, 1892. 4. LOEB, J. Beitrdge zur Gehirnphysiologie der Wiirmer. Pflugers Archiv, Band Ivi., 1894. i. Experiments on Medusae or jelly-fish afford us an excellent opportunity for analysing the con- ditions for spontaneity and coordination, and for deciding whether or not these phenomena are depend- ent upon ganglion-cells. The subumbrella of the Medusae has a very thin layer of muscle-fibres which contract rhythmically. The contraction diminishes the size of the swimming-bell, and forces the water out. By means of the recoil the animal moves for- ward. In regard to the nervous system, we must discriminate between two classes of Medusae : first, the Hydromedusae (Hydroidea, Fig. i), and, second, the Acalephae, one representative of which (Aitrelia aurita, Fig. 2) is familiar to many laymen. The nervous system of the Hydromedusae consists of a double nerve-ring along the margin of the umbrella (d, Fig. r). The upper nerve-ring forms a flat layer in the ectoderm, and consists of thin fibres and gan- glion-cells. The lower nerve-ring has thicker fibres

and more ganglion-cells, and is connected with the upper ring by nerve-fibres. In addition to this ring, which is called the central nervous system, there is also a peripheral nerv- ous system, a plexus, consisting of nerves and scattered ganglion cells, spread out over the whole subumbrella (b, Fig. i), between the epithelium and the muscle-layer. The convex surface of the umbrella consists of a non-contractile, gelat- inous mass, and no nervous elements are to be found in it.

Acalepha^ (Fig. 2) have no continuous nerve-ring, but a row of separate nerve-centres (S, Fig. 2) extends around the margin of the umbrella, lying in the ectoderm, which covers the basis of the marginal bodies (sense organs). The number of these centres corresponds, at least in Aurelia aurita, with the num- ber of sense organs. This nervous system contains no ganglion-cells, but processes called nerve-fibres go out from special epithelial cells. The muscle-layer of the umbrella also is said to contain a peripheral nervous plexus (i).

umbrella; £, subumbrella with muscles; c, man- ubrium ; d, margin of the swimming-bell with the nerve-ring. Our first question is : Is the spontaneous locomo- tion of the Medusae, or the rhythmical contraction of their swimming-bell, a function of the ganglion-cells ? Romanes found - that if the margin of the bell of a Hydro- medusa (6, Fig. 3) be cut off, the rhythmical contraction of the centre of the bell (a, Fig. 3) ceases, while ring, continues to ex- ecute rhythmical contractions (2). The wound does not even cause a decrease in the number or in the strength of the marginal contractions. The exper- iment has been repeated by other authors with the same result. Any sort of wound can be made in the umbrella without disturbing the rhythmical con- tractions so long as the nerve-ring remains intact. Thus Romanes concluded that these rhythmical con- tractions of Hydromedusse originate in the nerve- ring or its ganglia. I have found recently that this whole problem is not so much a morphological problem as a problem of physical chemistry. The osmotic pressure of the sea-water is about equal to that of a -| n NaCl solution. I found that if the centre of a swimming-bell be put into a -| n NaCl or |- n NaBr solution it goes on beating rhythmically. But if a