Comparative Physiology of the Brain and Comparative Psychology

The difference between Flourens's and Schrader's observations lies in the fact that Flourens considered this condition permanent, while Schrader showed that it lasts only a few days or until the " shock-effect " of the operation has passed off. The objection might be raised that Schrader did not entirely remove the hemispheres, but this was not the case. Schrader's experiments are masterpieces in regard to the perfec- tion of the mode of operation. The contradiction in the statements of the two authors is due to the fact, as it so often is in brain-physiology, that the minor effects of the operation in one case were strong, in the other slight, or that one author based his opinion upon the most severe disturbances, the other upon the slightest disturbances. The latter is the only re- liable method in physiology of the brain, because in addition to the disturbances caused by the loss of part of the brain, the shock-effects on the rest of the central nervous system also appear in the mosaic of symptoms. Schrader's experiments are models in regard to technique, but this cannot be said of Flourens's experiment, to which fact the excellent investigator Magendie vainly called attention.

In Schrader's experiments, a few days after the operation, spontaneity not only returns, but is evert in- creased. The animal wanders about in tJie room un- tiringly the greater part of the day. It is not blind, for its movements are determined by visual impres- sions. Like the frog without cerebral hemispheres, it turns out to avoid obstacles. " Dusty window-glass, transparent bell-jars placed in their way were avoided just as much as chairs and table legs, or boards of different colours." It is evident that optic space-per- ception still continues, even when the cerebral hemi- spheres (and with them the associative memory) have disappeared entirely. If such a pigeon is placed in an uncomfortable position, it flies to another place with perfectly coordinated movements. Schrader gives the following description : " We place our pigeon on the cloth-covered stopper of a large bottle. The stopper is large enough to support the animal on both feet, and is placed in the middle of a large, empty room, so that the pigeon is one to two metres above the floor. For some minutes the pigeon sits with its head drawn in, its feathers ruffled, in a condition of sleep or inhibition ; then it shakes itself and begins to turn around and look about ; finally it stoops and with an exertion looks down on the floor as if it wished to measure the height. It makes preparations to fly down, stops again, however, turns about once more, and again directs its attention to the floor. The dura- tion of this play varies, but at last it flies down in a slight curve and alights easily on the floor. If a cross-bar is placed at the same height, one or two metres from the bottle, the pigeon flies determinedly to the bar and seats itself there. If a chair be used instead of a bar, the pigeon is seated on the arm" (4). These experiments show that these pigeons are able to measure distance by visual impressions also.

solving of the problem as to whether sensations of space are purely a matter of memory, as Helmholtz, among others, assumes, or whether they are deter- mined by inherited structural conditions, as Hering, for instance, maintains. The question is of great im- portance for the further investigation of the mechanics of the brain, and for this reason we mention it in passing. It has been assumed that space-sensations are acquired because the new-born infant does not immediately show signs of orientation in space. The fact is overlooked that the new-born infant comes into the world incomplete — that is to say, certain structures become complete during the first year or even later. The same erroneous conclusion was drawn in regard to walking. The child was supposed to " learn " to walk. The fact that the chick can walk when it comes out of the egg would have sufficed to prevent this error on the part of the empiricists, if physiolo- gists had earlier appreciated the importance of com- parative physiology. The difference between the chick and the human suckling consists in the fact that the structural development of the former is more complete at the moment of hatching than the struct- ural development of the latter at the time of its birth. The child can begin to walk only when the nerves, muscles, etc., have reached the required de- gree of development. The same is true of visual space-perception. The newly hatched chick has vis- ual perception ; that is, it picks at points that differ from their environment in colour and intensity of light.

It does not learn this reaction any more than a plant learns its heliotropic reactions, and it is no more necessary for the suckling than for the chick to learn space-reactions. They come " of themselves " as soon as the embryonic development of the suckling has ad- vanced far enough. This conception, to which com- parative physiology forces us, is further supported most effectually by Schrader's observation (and by those of earlier authors, for instance, Longet) that visual space-perception in birds continues after the cerebral hemispheres have been removed. The pos- sibility that this holds good for birds and not for mammals is refuted by a statement of Christian! in regard to rabbits. The fact, however, that space- reactions can be modified by the memory, that we can " learn " to shave before a mirror, for instance, or can " learn " to grasp things in spite of prismatic glasses, does not contradict this conception any more than the acquired accomplishments of the dancer con- tradict the fact that normal walking is not a matter of memory. The fact that coordinated progressive movements on the turn-table occur in the direction of the plane of the rotation, and those produced by a gal- vanic current occur in the direction of the curves of the current, also speaks for this nativistic conception. From this digression we will now return to Schra-

der's experiments. The pigeon described above as wandering about the room all day, sleeps at night. Sleep has nothing to do with consciousness and mem- ory, for it occurs in plants. It is not surprising then that the animal without cerebral hemispheres shows the difference between sleeping and waking. The great difference between the normal male pigeon and the pigeon that has lost its cerebral hemi- spheres is shown forcibly by the following facts : During the period of heat the male pigeon courts the female with cooing, but if a female pigeon is placed before the cooing male whose hemispheres have been removed, it remains unheeded. This entire lack of memory is the chief point in which the animal without cerebrum differs from the normal animal. " For the former everything is only a mass in space, it moves aside for every pigeon or attempts to climb over it, just as it would in the case of a stone. All authors agree in the statement that to these animals all objects are alike. They have no enemies and no friends. They live like hermits no matter in how large a com- pany they find themselves. The languishing coo of the male makes as little impression upon the female deprived of its cerebrum as the rattling of peas or the whistle which formerly made it hasten to its feeding place. Neither does the female show interest in its young. The young ones that have just learned to fly pursue the mother, crying unceasingly for food, but they might as well beg food of a stone " (4).

Taking all the reactions of the pigeon without cerebral hemispheres together, it seems to me that the conclusion may be drawn that loss of the cerebral hemispheres causes the loss of the associative mem- ory. Inherited reactions remain after the loss of the cerebrum, but that which is acquired by the activity of memory during the life of the individual is lost forever. In order to emphasise this loss of memory after ex- tirpation of the hemispheres, we will quote the follow- ing observation made by Schrader on a falcon. The falcon, as everyone knows, is a good hunter. Schrader placed some mice, and a falcon from which the hemi- spheres had been removed in the same cage. Every time that a mouse moved the falcon jumped on it and caught it in its claws, if the movement occurred with- in its field of vision. The normal falcon in such cases devours the mouse, but for the falcon without cerebral hemispheres the matter wras at an end when the mouse was caught. The activity of the associative memory was lacking and the mouse was forgotten as soon as it ceased to move. When the falcon moved, the mouse escaped, but if the mouse moved again the process was repeated. Any inanimate object that moved would, of course, be caught in the same way. The falcon and mice remained together until one day the mouse de- voured the back of the living falcon. Deprived of its memory the falcon was entirely defenceless (2).

One disturbance takes place in animals that have lost the cerebrum which does not belong in the same class with disturbances of memory, namely, the inabil- ity to take food unassisted. In frogs and, according to Steiner's observations, also in fishes (5), the ability to take food independently continues to exist after excision of the cerebral hemispheres. Birds without cerebral hemispheres starve unless they are fed. Schrader came to the conclusion that this is due to a disturbance of the motor innervation, for they are un- able to swallow a pea placed in the front part of the beak ; to be swallowed it must be placed well back toward the throat. From the results of these experi- ments on frogs, I believe that we might go one step farther than Schrader and conclude that, in this case, the tension is decreased in certain groups of muscles which are necessary for taking food independently. We shall again meet with such a decrease in the ten- sion of certain muscles after lesion of the cerebral hemispheres. This decrease in tension is, however, a secondary effect of the operation on the remaining srgmental tracts of the central nervous system, and is not determined by loss of the cerebrum. It is very probable too that if Schrader's experiments are con- tinued birds may be found in which disturbances in eating will not occur.

3. The bold attempt to remove both hemispheres entirely from a full-grown dog and then to keep it alive not only for months but for years has been attempted and carried on successfully by Goltz (6). The results of his experiments in a few words are as follows : In such a dog all those reactions in which the associative memory plays a role are lacking perma- nently, while the simple reactions that only depend on inherited conditions remain just as in pigeons and in other animals.

wakes. It moves spontaneously — that is, without visi- ble external stimulus. The only abnormal feature in the progressive movements of the dog without cere- bral hemispheres was its extreme restlessness. When not asleep it moved about in the cage unceasingly, and this perhaps accounts for the fact that such ani- mals show a tendency to lose flesh. The postures peculiar to dogs in urinating and defalcation were still assumed by these dogs. The reactions to sensory stimuli were normal in so far as no associative mem- ory was necessary. Meat and milk were devoured greedily, but if made bitter with quinine they were ejected. The dog growled and snapped if its paw was pinched. If its foot was placed in cold water it was removed at once. If one paw was injured the dog was still able to go on three legs. If it was asleep it could be waked by blowing a horn in the next room. If in a dark room it closed its eyes when a strong light was suddenly allowed to strike it. It seemed more wide-awake and restless when it was hungry and more quiet after it had been fed. In regard to eating, the dog without cerebral hemispheres was more nor- mal than Schrader's doves. To make the dog eat, it was only necessary to hold the plate up to its nose, so that the nose came in contact with the meat. The facts that motor disturbances exist and that such dogs do not turn out for obstacles, behaving in this regard like blind dogs, may be regarded as shock- effects on the brachial and optic segments, produced by the operation. The dog could still bark and howl.

But everything requiring associative memory was gone. The dog was not able to seek its food. It recognised neither its master nor its playmates. It could hear but could not discriminate between scold- ing and petting. It was impossible for it to get itself out of any uncomfortable situation. The period of heat was no longer noticeable. The effects are simi- lar to those upon pigeons, with the difference that the secondary effects of the operation on the remaining parts of the central nervous system are greater in dogs. The reasons for this may be purely technical or anatomical, or may be due to a greater sensitive- ness of the central nervous system in dogs. We may mention in this connection that hemorrhages in the human cerebral hemispheres are often accompanied by a complete paralysis of the extremities, while this is never the case in clogs.

The fact that in animals which normally possess no memory, loss of the hemispheres occasions little dis- turbance, and the fact that in animals possessing memory, the latter disappears upon destruction of the hemispheres, prove that the hemispheres are an essen- tial organ for the phenomena of associative memory. 4. Pfluger expressed the opinion many years ago that an animal that has lost its brain still possesses consciousness (7). He drew this conclusion from the reactions of decapitated animals. If the tail of a de- capitated eel be rubbed gently on one side the tail presses itself against the finger, but if touched with a burning match it is turned away. From these and

similar observations, which are doubtless correct, Pfluger concluded that the spinal cord possesses con- sciousness. Pfluger's statements gave rise to a lively discussion. His opponents could not refute his con- clusions entirely, but they advanced arguments to show that the spinal cord does not possess consciousness. Goltz's ingenious experiments deserve special mention in this connection (3). They show that the decapi- tated frog is not able to rescue itself from an unpleas- ant situation. A blinded but otherwise normal frog and a frog without cerebral hemispheres were placed together in a trough filled with water and the water

heated gradually. When the temperature of the water rose, the blinded frog became restless, jumped about, and attempted to escape from the trough. The frog without cerebral hemispheres, on the other hand, re- mained quiet and the heat rigor overcame it in the attitude it assumed when put into the trough. This of course speaks against the presence of consciousness in the spinal cord. But since this did not directly prove the erroneousness of Pfluger's conclusions, opin- ions remained divided. I believe we are now in a position to prove that Pfluger's observations not only allow but demand an entirely different explanation, and that it is wroncr to make them a criterion for the exist-

ence of consciousness. The experiment with the tail of the eel is a case of tropism. The eel is positively stereotropic. It is forced to bring every part of its body as far as possible in contact with solid bodies, like Nereis, many insects, the stolons of Hydroids, and the roots of many plants. It lives chiefly in cracks. This is no more a process of consciousness than the boring of a root in the sand. It exists in every segment of the eel, and if touched on one side with the finger positively stereotropic curvations toward the finger ensue. The stimulus of rubbing increases the tension of the muscles on the stimulated side. But while it is positively stereotropic it is not positively thermotropic. If a burning object is applied it produces a relaxation of those muscles which move the body toward the stimulated side.1 The body is thus moved toward the opposite side. In this case too consciousness plays no more part than it does in the tropic reactions of a plant. The whole discussion of the " spinal-cord-soul " was needless, and might have been avoided if Pfluger had realised that those phe- nomena which the metaphysician calls consciousness are a function of the mechanism of associative mem- ory. In that case the question would have been :— Does the decapitated animal still possess associative memory, or are its reactions all due to inherited struct- ures and irritabilities ? With the aid of comparative physiology it would have been found that all the reac- tions of such an animal may occur in forms which possess no associative memory. The mechanisms which allow an associative memory in Vertebrates seem to be located in the cerebral hemispheres. In

! If Pfluger had made his experiments on decapitated snakes he would have obtained different results. Exner mentions that such animals press their body against a fiery coal just as well as against the finger (13). Invertebrates they will probably be found in the supracesophageal ganglion. 5. The spinal-cord-soul is not the only instance in which biologists have been led astray by their blind acceptance of metaphysical notions. A second and perhaps more general instance is the assumption that consciousness exists in every animal and is present to a certain degree even in the egg. Many authors ob- ject to the idea that a thing like consciousness or the soul should get into the body suddenly at a certain stage of development. What they consider true for the ontogenetic development they also assume for the phylogenetic development, and they are led to believe that each animal possesses consciousness. All these speculations collapse as soon as we free ourselves from the influence of metaphysics, and realise that the term consciousness or soul is applied by meta- physicians to phenomena of associative memory, and that the latter depends upon a physical mechanism which must be just as definite as, for example, the dioptrical apparatus of our eye. I do not think that anybody maintains that every animal must have an apparatus which unites the rays of light emanating from a luminous point to an image point on the sur- face of its body, simply because certain animals have such an apparatus. Moreover, I do not believe that even our biological metaphysicians assume that this dioptrical apparatus exists already in the human egg, and that the latter is already capable of visual space- perception, because it would be too awkward to as-

sume that visual space-perception should begin at a definite period of embryonic or post-embryonic de- velopment. And yet the matter is in no way different for psychic phenomena, if we realise that what we call psychic is only a metaphysical term for functions of associative memory. Just as our dioptrical apparatus can only begin to function after the eye has reached a certain stage of development, the mechanism of as- sociative memory can only begin to function after the brain has reached a certain stage of development. And just as only certain animals are provided with apparatus for visual space-perception, only certain ani- mals are provided with the mechanism necessary for associative memory.1 I think it is time for us to re- alise that some of the phenomena of embryonic de- velopment are not continuous processes but decidedly discontinuous. This is, of course, less obvious if we limit our study of the organism to methods of stain- ing and sectioning, but it becomes very striking if we add some physiological methods. A pure -§- n NaCl solution is extremely poisonous to the eggs of Fundulus during the first twelve hours. After that it is decidedly less harmful. There is then a discon- tinuity in the physical or chemical conditions of that embryo at about twelve hours after fertilisation. An- other discontinuity is connected with the beginning of circulation. Before circulation begins a -| n KC1 solution is no more harmful to the embryo of Fundulus

1 These considerations dispose also of the conception of consciousness in plants or of the barbarous notion of consciousness in molecules and atoms. than a | n NaCl solution. As soon as the heart be- gins to beat, the KC1 becomes much more poisonous than the NaCl solution. A similar discontinuity is noticed if we try the effects of lack of oxygen. As soon as the circulation begins, the Funclulus embryo becomes quite suddenly much more sensitive to a lack of oxygen. The functional changes in the embryo itself are sudden and not gradual or continuous. The

heart-beat, for example, starts at a certain time, sud- denly, after a certain stage of development has been reached. The idea of a steady, continuous development is in- consistent with the general physical qualities of proto- plasm or colloidal material. The colloidal siibstances in our protoplasm possess critical points. If we in- crease the pressure of a gas below a certain tempera- ture, at a certain critical point the gas becomes liquid. The colloids change their state very easily, and a number of conditions- -temperature, ions, en- zymes— are able to bring about a change in their state. Such material lends itself very readily to a discon- tinuous series of changes, while a gradual steady development, such as most Darwinians assume, is practically excluded.

We, of course, concede that the associative memory shows different degrees of development or perfection in different animals. These different degrees are mainly differences in capacity and resonance. By difference in capacity I mean a difference in the number of associations of which the brain is capable. By difference in the resonance I mean the ease with which associations are produced. It is necessary, for example, in the case of a great complex of sensations, that the images of memory which correspond to cer- tain constituents of that complex are easily repro- duced, and in the case of a very elementary sensation greater images of memory, which contain that ele- mentary sensation as a constituent, should be repro- duced. The quality of resonance is perhaps the more important, as long as the capacity does not fall below the average. The intelligent man differs from the stupid man, among other things, in the ease with which by means of the associative memory he makes the analysis or synthesis of the complexes of sensation : that is, in the slow or stupid man only such images of memory are called up associatively as were con- nected before with the entire stimulating complex ; while in the quick thinker complexes of memory are also produced associatively which are connected with single elements of the stimulating complex.

6. After what has been said, it is clear that the ab- solute mass of the brain cannot be the principal factor in determining intelligence (10). In different races of dogs, for instance, the brain varies just as much as the weight of the body. Dogs of a small breed may, however, be more intelligent than dogs of a large breed. It also follows from this that the relation of mental activity to the metabolism of the central nervous system is totally different from that of mus- cular activity to the metabolism of the muscle. The

power-rate of activity of the muscles is proportional to their mass, and something similar may be true of the glands. The results obtained by weighing the brain of man have proved, conclusively, that the mass of the cerebrum, unless it falls below a certain mini- mum, in no way affects the degree of intelligence. The same facts prove that the number of ganglion- cells bears no direct relation to the degree of intelli- gence. The small dog has fewer ganglion-cells than the large dog, inasmuch as the size of the cells varies comparatively little in dogs of different size.

Speck, who has called attention to this difference between muscles and brain (8), has also made another important discovery, namely, that in case of lack of oxygen associative memory first disappears. He in- haled air deficient in oxygen from a gasometer, and counted during his experiments. As soon as the partial pressure of the oxygen of the air fell below 8 % of one atmosphere, he forgot to count very soon and then fainted, although the other functions of his body showed no change. Speck concludes from this that the cerebral hemispheres are most sensitive to a lack of oxygen. It is not absolutely necessary to conclude from this that the cerebral hemispheres have relatively the greatest metabolism of all the organs. It is possible that lack of oxygen affects the physical qualities of colloids in the brain in such a way as to make the functioning of the mechanisms of associative memory impossible. I have shown that lack of oxygen leads to a liquefaction of the cell-walls

in certain forms, and it seems to be pretty generally true that the formation of solid cell-walls becomes impossible under such conditions (11). It is possible that in the case of lack of oxygen, physical changes in the state of certain constituents of the brain are prevented which are necessary for the activity of memory. Some physiologists seem to be of the opinion that when the brain contains a good deal of blood the body has a special feeling of happiness. I recall a popular lecture by a prominent psychiatrist in which he maintains that when the cerebral hemispheres con- tain a great deal of blood the proprietor of this brain enjoys the absolute happiness (?) of an intoxication from champagne. This psychiatrist evidently ima- gines that the greater the supply of blood is, the better the brain is nourished, and that with the in- creasing nourishment of the brain the feeling of happiness increases. Among the food-substances which are offered to the brain in large quantities by the dilatation of the arteries oxygen takes the first place. It was formerly assumed that the oxygen- supply determined the metabolism, but we now know definitely that internal processes in the tissues determine the consumption of oxygen, probably processes of fermentation. If a certain quantity of oxygen is present in the brain, the superfluous oxygen has no effect. The same is probably true of all the other food-constituents. Under normal conditions the oxygen-supply in the brain is sufficient as long as

the circulation is normal. It harmonises with these facts that mental activity does not influence the phenomena of oxidation, as Speck has proved by very careful experiments. But from this we must not con- clude that the activity of the brain takes place with- out chemical changes, only that the chemical changes which are determined by mental activity are too slight to be recognised. The statement that dilatation of the blood-vessels of the brain produces a sensation of happiness is not based upon any fact that has been proved scientifically.

7. The amoeboid changes in the ganglion-cells have been utilised to account for the phenomena of asso- ciation. As far as normal processes of association are concerned, these amoeboid changes cannot play any role, as they are much too slow. We notice migrations of the cones and the pigment in the retina, yet the idea that these protoplasmic motions play any role for space- or colour-perception has to be abandoned for the same reason. Other authors hold that conditions of incomplete association, as in the case of dreams, or interruption of association, as in the case of deep sleep or narcotics, are due to a partial or complete discon- nection of the ganglion-cells by a shortening of the processes. It does not seem to me that the obser- vations which we thus far possess prove anything of that character (9, 12).

1. SCHRADER, MAX E. G. Zur Physiologic des Froschhirns. Pflugers Archiv, Bd. xli., 1887. 2. SCHRADER. Die Stellung des Grosshirns im Reflexmechan- ismus. Archiv fur experiment. Pathologic und Pharmakologie, Bd. xxix., 1892. 3. GOLTZ, F. Beitrdge zur Lehre von den Nervencentren des Frosches. Berlin, 1868. 4. SCHRADER, MAX E. G. Zur Physiologic des Vogelgehirns. Pflugers Archiv, Bd. xliv., 1889. 5. STEINER, J. Die Functionen des Centralnervensystems und ihre Phylogenese. II. Abth. : Die Fische. Braunschweig, 1885.

7. PFLUGER, E. Die sensorischen Functionen des Ruckenmarks. Berlin, 1853. 11. LOEB, J. Untersuchungen uber die physiologischen Wir- kungen des Sauerstoff mangels. Pflugers Archiv, vol. Ixii., 1895. 12. BAWDEN, H. H. A Digest and a Criticism of the Data upon which is Based the Theory of Amoeboid Movements of the Neuron. The Journal of Comparative Neurology, vol. x., 1900. 13. EXNER, S. Entwurf zu einer physiologischen Erklarung der psychischen Erscheinungen. Leipzig and Wien, 1894, p. 85.

i. It follows from the facts of the preceding chap- ter that the cerebral hemispheres are a necessary organ for the phenomena of associative memory. We are not quite justified in saying that they are the specific organ for this function. It may be possible, although not probable, that other parts of the brain are also required for this purpose. It is certain that the spinal cord is not needed for this function, for animals whose spinal cord is severed, or from whom the greater part of it has been removed, show no de- ficiency in the process of associative memory.

The cerebral hemispheres form an appendage of the segmental central nervous system. They are con- nected with at least some of the segmental ganglia by special nerve-fibres. As these different bundles of fibres enter the cortex at different places, it is obvious that if we stimulate the various spots of the surface of the cortex with electric currents of the smallest in- tensity necessary to produce a reaction, we must notice different effects. If, for instance, a current of minimal intensity be sent through the spot D (Fig.

39), where the fibres from and to the brachial segment of the cord of a dog enter the cortex, contractions of certain muscles of the fore- leg must follow. If we stimulate the region A (Fig. 39), which is connected with the sensory or motor ganglia of the eyes, motions of the latter must be produced. It is, moreover, evident that if we injure the spot D in the cortex we must get some- what different after-effects from those produced when A is injured. In the former case we must expect motor disturbances in the use of