Comparative Physiology of the Brain and Comparative Psychology

association which is in line with the necessity for sense-impressions for the remembrance of words. Before he was able to pronounce a word he had to go through the motion of writing it. When asked the colour of the leaves, he had to go to the window and look at a tree, and then he had to go through the motion of writing the word green with his finger before he could give the correct answer. When not allowed to use his fingers for this purpose, he used his toes, and when this was forbidden, he made the writing motions in his mouth with his tongue. When all three motions were forbidden, he was not able to find the word.1 He did not write phonetically, but ortho- graphically. It would be absurd to think for a mo- ment that in this case one single centre, or one single tract between two centres, was injured. The whole apparatus was equally affected. I believe that the associative mechanism of the patient differed only in decree from the associative mechanism of a

normal being. Wolff pointed out that for each act of remembering there is one association more power- ful than the rest. But for a normal being the weaker associations are sufficient for the reproduction, while in our patient only the strongest one sufficed. One may ask how it happens that we so seldom hear of such simple, clear cases as those published by Rieger and Wolff. I believe the majority of physicians who deal with such patients have neither the scientific

1 It was not necessary for him to see what he wrote or to actually write ; it was sufficient to go through the motions of writing. analysis of the case. Wolff's patient had been in the hands of half a dozen specialists, and they discovered only the peculiar writing motions that the patient used. This of course led them to false conclusions. If the analysis in such a case is incomplete, the results must be misleading. 3. It is worth while to compare the mental con- dition of these patients with that of lower animals. The two patients mentioned above forgot immedi- ately what was said to them. If the correct associa- tion did not occur to them after a short time, the question had to be repeated. There was, however, one exception. Objects or occurrences which were intimately connected with their instincts they remem- bered— for instance, money matters. We can imagine that conditions maybe similar in lower animals — e. g., wasps, which either forget easily or only seem to re- member certain things which are intimately connected with their instincts — e. g., the location of the nest.

A qualitative difference has been supposed to exist between the associative memory of man and that of animals. These patients may help us to arrive at a decision in regard to this question. When the patient was asked the colour of blood, the question aroused associations which caused him to provide the visual impression of blood. If we compare with this the fact that a wasp is no longer able to find its nest when the latter is covered with a small blossom, we might imagine that there is a qualitative difference

between the associative memory of the wasp and of man. It might be argued that man possessed the power of creating new associations, i. e., the ability of substituting or changing the existing conditions, in order to make a new process of association possible. But this ability is not entirely lacking in animals. When in Thorndike's experiment a cat goes volunta- rily into a certain cage and waits there to be offered a fish, we have to deal with the same apparent ability of creating new associations. On the other hand, the superiority of man in this direction can be accounted for by the fact that his capacity for forming and re- taining new associations is very much greater than that of animals.

The question, What is the colour of blood ? pro- duces not only one association - - the word red- - but a number of other associations, for instance, the asso- ciation of a wound and the association of the produc- tion of a wound. If at that time the sense-impression of a pustule occurs, the association arises that the opening of the pustule causes the appearance of blood. All experiments point to the fact that this overwhelming abundance of associations which even

a disabled human brain can form is lacking in animals. One impression may arouse only a very limited num- ber of associations. This is evident from Thorndike's experiments on dogs and cats (3), and from Whit- man's observations on pigeons (4). This small capacity for associations makes the reactions of animals appear machine-like and less intelligent. I think that the greater capacity of the human brain for associations and the greater celerity with which these associations are formed and retained are sufficient to explain why mankind has been able to control nature, while animals remain at its mercy.

In a pamphlet on Instinct and Intelligence, Father E. Wasmann, S.J., a well-known entomologist, has raised the question as to whether or not animals pos- sess intelligence (5). The answer to such questions varies with the definition of the word intelligence, and hence such discussions result in a discussion of words and definitions. Such scholastic discussions are very serviceable for the defence of a dogma or an opinion. Wasmann's pamphlet belongs in this category. But we cannot overlook the fact that the steady progress of science dates from the day when Galileo freed sci- ence from the yoke of this sterile scholastic method. The aim of modern biology is no longer word-discus- sions, but the control of life-phenomena. Accordingly we do not raise and discuss the question as to whether or not animals possess intelligence, but we consider it our aim to work out the dynamics of the processes of association, and find out the physical or chemical con- ditions which determine the variation in the capacity of memory in the various organisms.

i. RIEGER, K. Beschreibung einer Intelligenzstorung in Folge einer Hirnverletzung, etc. Verhandl. der Wurzburger physikalisch medicinischen Gesellschaft, Bd. xxii. and xxiii., 1889 and 1890. 2. WOLFF, GUSTAV. Ueber krankhafte Dissoziation der Vor- stellungen. Zeitschrift fur Psychologic und Physiologic der Sinnes- organe, Bd. xv., 1897. 4. WHITMAN, C. O. Animal Behaviour. Biological Lectures Delivered at Wood's Holl, 1898. Boston, Ginn & Co. 5. WASMANN, E. Instinct und Intelligenz im Thierreich. Freiburg, 1897.

i. The facts have thus far shown that the reflexes are determined chiefly by the structure of the sense- organs, or of the surface of the body, and the arrange- ment of the muscles. The central nervous system participates in these functions only as a conductor. The true problem with which the physiology of the reflexes is concerned is the mechanics of protoplasmic conductivity. This problem is no longer a biological problem but a problem of physical chemistry.

The only specific function of the brain, or certain parts of it, which we have been able to find is the activity of associative memory. There is at present a tendency to consider the anatomical and histological investigation of the brain as the most promising line for the analysis of these functions. It seems to me that we can no more expect to unravel the mechan- ism of associative memory by histological or morpho- logical methods than we can expect to unravel the dynamics of electrical phenomena by a microscopic study of cross-sections through a telegraph wire or by

counting and locating the telephone connections in a big city. If we are anxious to develop a dynamics of the various life-phenomena, we must remember that the colloidal substances are the machines which produce the life-phenomena. But the physics of these sub- stances is still a science of the future. The new methods and conceptions created by physical chemis- try give us the hope that a physics of the colloidal substances may be looked for in the near future. At present we can only consider data of secondary im- portance for the mechanics of associative memory. The first group of these data is furnished by the study of the functions of the sense-organs.

Helmholtz emphasised the fact that our senses only furnish us symbols of the external world. Every physical process that affects a sense-organ produces changes in the organ. These changes are determined by the peripheral structure or by the specific " energy " of the sense-organs, as physiologists since Johannes Miiller call it. Whether a blow, an electric current, or ether-vibrations of about 0.0008-0.0004 mm. wave- length stimulate the retina, the sensation is always a specific one, namely, light, while a blow or an electric current produces sensations of sound in the ear. This so-called law of the specific energy of the sense- organs is not peculiar to the sense-organs ; it applies, as was emphasised by Sachs, to all living matter; it even holds good for machines. It is in reality only another expression for the fact that the eye, the ear,

and every living organ are able to convert energy in but one definite form- -that is, that they are special machines. The determination of the way in which this transformation of energy occurs in the various organs would be the explanation of the specific energy of the various senses. Physiology gives us no answer to the latter ques- tion. The idea of specific energy has always been regarded as the terminus for the investigation of the sense-organs. All the more credit is due Mach and Hering for first having advanced beyond that limit with their chemical theory of colour-sensations. Mach has recently expressed the opinion that chemical conditions lie at the foundation of sensations in general (i).

For the eye we may consider it as probable that light produces chemical effects. Various substances are formed and decomposed in the retina, and the chemical processes of the formation and decomposi- tion of these substances determine the licrht- and colour-sensations. The ether-vibrations of certain wave-lengths influence these decompositions in a de- finite manner. The electro-magnetic theory of light will probably in this case lead to further discoveries. Effects similar to those produced by light are also brought about by the electric current. The current itself can pass through the retina only by means of electrolysis, and it may be that the increase in the concentration of ions (wherever their progress is Mocked) brings about the light- and colour-sensations

caused by the current. It is not impossible that the so-called visual substances — that is, the photo-sensi- tive substances — are electrolytes. We can thus under- stand how the electric current produces sensations of light and colour in the eye. But it is more difficult to account for the fact that pressure or a blow on the eyeball produces the sensation of a flash. Carey Lea has found that on photographic plates pressure pro- duces changes of the same character as weak light.

The specific energy of the eye would accordingly amount to nothing more than the fact that an increase in the concentration of ions or certain other chemical substances in the retina causes the sensation of light and colour, no matter whether the changes are caused by vibrations of the ether, by the electric current, or by a blow on the eye. The stimuli which are trans- mitted to the brain from the eye will hence show ex- actly the variety and peculiarities which correspond to the variety and peculiarities of the chemical pro- cesses in the retina.

The same holds good for the stimuli which are transmitted to the brain from the organs of taste and from the nose. The chemical nature of the causes that produce the sensations of smell and taste is so apparent as to require no proof. We find greater difficulty in dealing with the sense- organs of the skin. Yet it is conceivable that a chem- ical basis may also exist for the activity of these senses. This idea finds support in a train of thought, by which I attempted to explain the peculiar influence of grav-

ity on the orientation of animals and plants and their formation of organs (2). In these cases, a change in the orientation of the organs produces a change in the chemical condition. If the chemical processes in these instances consist in fermentative processes, the amount of the chemical change in the unit of time must be a function of the number of the ferment-mole- cules and of the fermentable molecules that come in contact. If we assume that both are present in dif- ferent morphological constituents of the living cells, that the ferment, for instance, is present in the nu- cleus, the fermentable substance in the protoplasm of the cell, it is apparent that a change in the position of the cell or a pressure upon it will bring new mole- cules of the protoplasm in contact with the nucleus. In this way the metabolic activity may be increased. Such changes in the peripheral nerve-endings of the skin mieht result in innervations and reflexes. But

this is all so vague that it only indicates the possibil- ity of the chemical character of the process. It seems forced, if not altogether impossible, to apply this theory to the cochlea of the ear. We could imagine that the vibrations of sound produce corresponding vibrations in the endings of the auditory nerve, by which new molecules are brought into contact with each other. But I cannot see how this assumption could account for the different pitches or the phenom- ena of consonance. While a chemical theory is pos- sible or probable for certain sensations, e. g., light, taste, and smell, it is very doubtful whether such a

theory can be applied to the other sense-organs. But it is certain that if we wish to make any progress in this direction we must follow the lead of Mach and Hering, and must cease to consider the so-called law of the specific energy of the sense-organs as the terminus of our investigation of the processes of sensation. 2. If we wish to find out the dynamics of associa- tion we must study the effects which simultaneous processes have upon each other. Let us consider periodic and aperiodic processes.

If we turn a wheel with one hand without thinking of the manner or velocity of the rotation, and at the same time repeat a poem to ourselves without moving the lips, the number of the revolutions shows a simple numerical relation to the number of the arses of the verses. In German, where the arsis is pronounced with greater emphasis than the thesis, the number of the rotations of the wheel generally equals the num- ber of the arses. Briicke first called attention to this relation. Thirteen years ago I made a large number of experiments (not published) concerning this sub- ject that yielded the same result. But I found, fur- ther, that if one intentionally turns the wheel rapidly and recites slowly, the number of rotations is a simple multiple of the arses. Two, three, or even more re- volutions are made in the interval of one arsis. If one recites very rapidly and turns the wheel very slowly, the number of the arses becomes a simple multiple of the number of revolutions. In the latter case, the

number of revolutions is often the same as the num- ber of verses. If we assume that in thinking the poem the respiratory innervations which follow the rhythm can be represented as harmonic curves, and that the same holds good for the innervations which are responsible for the turning of the wheel, it follows from these facts that harmonic processes of inner vation occurring simultaneously affect each other in such a way that the periods of both processes are either equal or in the ratio of simple multiples of each other. 1 1 requires great determination to withstand this law. I consider it possible that where this succeeds the de- viation from the law is only apparent, not real. In reality it might be possible that one of the two har- monic processes was stopped temporarily. The facts, however, suffice to show that two harmonic processes of innervation for different parts of the body, occur- ring simultaneously, influence each other and are most liable to form processes of equal period.

The same is true not only for two or more simulta- neous processes of motor innervation, but also for simultaneous sensory processes and motor innerva- tions, as is proved by dancing. The rhythm of the music and the period of the motor innervations of the legs and body coincide. 3. A priori it would follow from these facts that two simultaneous aperiodic processes will in general interfere with or inhibit each other. That this is to a certain extent true is shown by the experience that we cannot do two things well at the same time. We

must add, however, the provision that the two things are aperiodic. If they be periodic, the opposite is true. We cannot solve an equation while jumping over a broad ditch. According to Fechner's inter- pretation of this fact the brain at any time has only a certain amount of energy at its disposal. In jump- ing over a ditch all the energy is supposed to pass into the muscles and nothing is left for the process of thinking. I showed fourteen years ago that Fech- ner's conception was not correct. The inhibition of a process of thought by simultaneous muscular ac- tivity is greater when we innervate one arm than when we innervate both arms simultaneously. Ac- cording to Fechner, however, the greater the number of muscle-groups that were innervated the more energy must be consumed in the brain. In these ex- periments I measured the maximal pressure which the flexors of the hand are able to exert on a dynamo- meter. This pressure does not decrease when the other hand or all the muscles are innervated simul- taneously, but even increases (3). The further appli- cation of this method explained the fact that we cannot well be mentally and physically active at the same time.

If we begin by solving a moderately difficult prob- lem in mental number work, and if we attempt when in the midst of the task to attain the highest dynamo- metrical pressure with the hand, the pressure re- mains from 20-30^ below the maximum that we otherwise attain when we devote our attention to the pressure alone (3, 4). It often occurs, however, that the maximal pressure is obtained while reckoning. In this case the experimenter certainly interrupted his reckoning while pressing. This is shown by the fact that in this case either the task is not solved cor- rectly or the problem is entirely forgotten by the subject experimented upon. It was a great excep- tion if the maximal pressure was attained and the task also solved correctly. The experiments result quite differently, however, when the experimenter first begins by pressing, and the problem is given when the maximal pressure has already been reached, so that it is only necessary to keep up the pressure. In this case I noticed no, or only a very slight, in- fluence of both activities : the person could reckon correctly, although with effort, and the curve either did not descend, or descended but little lower than without the reckoning.

Thus we see that a simultaneous, static innerva- tion, no matter how strong, does not prevent the reckoning ; that, on the other hand, a rapidly increas- ing maximal motor innervation disturbs the process of reckoning perceptibly. I have attempted to dis- cover whether a sudden stoppage of motor innerv- ation— that is, a sudden relaxation of the statically contracted muscles — disturbs the process of reckon- ing. This is not the case. Whatever may be the explanation of these phe- nomena, we see that two simultaneous, maximal, aperiodic processes of innervation which require an

effort disturb each other. On the other hand, if they have not a maximal intensity they can take place simul- taneously. I found tJiat easy tasks or the reproduc- tion of simple matters of memory did not lower the maximum of the pressure. 4. These experiments recall the disturbances of associative memory which were discussed in the preceding chapter. By causing powerful processes of motor innervation to go on, we interfere with all associations, except those which have occurred very frequently. This was the characteristic of the patients mentioned in the preceding chapter. But at the same time it does not exhaust the case. The processes of innervation in the brain of these patients were possibly mutilated not only in intensity but also in other dimensions or directions.

Perhaps the cases of the inhibition of reflexes also belong in this same category of phenomena. We have mentioned that a dog with severed spinal cord shows pendulum-movements of the hind-legs when they are allowed to hang down. But if we press the skin of the tail gently the pendulum-movements of the legs at once cease (Goltz). Some authors seem to be under the impression that a shock-effect must consist in the exhaustion of the parts under the in- fluence of the shock. This is not necessarily true. The shock-effect may be due to a phenomenon of interference or to a comparatively slight physical change which results in a mutilation of the processes of innervation.

The role which the intensity plays in the case of two simultaneous processes of innervation recalls the influence two simultaneous wave-motions have upon each other. A superposition of two waves is only possible as long- as the amplitude is not too great. It looks as if two processes can occur simultane- ously in our brain only when their intensity is weak enough to allow a superposition. It is perhaps allowable to pursue this possible analogy of the processes of innervation with wave- motions a step farther and apply it to the process of association. A process remains associated with those processes in our brain which occur quite or almost simultaneously. Let us imagine that every process in our central nervous system has a definite form in so far as it can be represented by a curve in which the time-elements are represented by the abscissas and the intensity of the processes by the ordinates. If two processes take place simultaneously and their intensity is not too strong, they superpose each other. The traces which this process leaves in our central nervous system correspond to the curve which is de- termined by the superposition of both elementary curves. If one of the processes takes place later on, the other process also is reproduced by resonance. On the other hand, a very complicated process may reproduce simpler processes, which are contained in the former as constituents and have already oc- curred once before in their simple form. Our ex- perience concerning sound-sensations shows indeed