Comparative Physiology of the Brain and Comparative Psychology

One of the most remarkable conclusions of Bethe is the assumption that the roads of the ants have two paths which differ chemically from each other, one leading from and one toward the nest. Bethe tried to prove this by experiments that had been undertaken before by Lubbock, who obtained no definite results. Bethe arranged a broad ant-street so that it led over a turn-bridge. He revolved this bridge 180°, when the ants were passing to and from the nest, and found that it was impossible for the two armies to continue on their way. He again turned the bridge 180° so that the tracks had the original orientation. The ants continued in the direction they were pursuing when disturbed. An observation made by Forel also agrees with this : " An ant that is picked up from the path while moving and then put down again is al- most sure to take the same direction, no matter what orientation is given to its body." This, however, only holds good for a street which is often travelled. A weak track which leads in one direction is qualified to lead in the opposite direction, as is shown by the fact that an ant which has found a new supply returns to the nest the same way that it came. It is evidently the load and lack of load which determine which path the ant will take (that is, to or from the nest). The load causes the ant to go to the nest reflexly ; the lack of a load causes it to £O from the nest. Bethe comes

to the conclusion that the reactions of ants, which have always been considered psychic phenomena, are merely reflex processes comparable to the tropisms. 5. Although I heartily sympathise with Bethe's re- action against the anthropomorphic conception of animal instincts, I yet believe that he is mistaken in denying the existence of associative memory in ants or bees. The fact that bees find their way home through the air cannot depend upon any trace left in their path. It can only depend upon memory and, as I believe, upon visual memory. If the bee-hive be removed while the bees have swarmed out, they will return to and gather at the spot where the entrance to the hive used to be. Bethe is not willing to admit that this indicates the existence of a visual image of memory of the locality of the nest, professing to con- sider it possible that unknown forces guide the bee reflexly.

I have recently had a chance to observe the activity of solitary wasps and have come to the conclusion that these animals are guided back to their nest by their memory. My observations were made on Ammophila, a spe- cies of wasps, whose habits have been carefully stud- ied and described by Mr. and Mrs. Peckham (7). Ammophila makes a small hole in the ground and then goes out to hunt for a caterpillar, which, when found, it paralyses by one or several stings. The wasp carries the caterpillar back to the nest, puts it into the hole, and covers it with sand. Before this is done, it deposits its egg and the caterpillar serves the young larva as food.

wasps employ of finding their way to the nest, which absolutely excludes the assumption that they are guided reflexly by known or unknown stimuli, and which indicates that they find their way through memory. An Ammophila had a hole in a flower-bed in my front yard. The wasp, of course, left the yard Hying. To\ ,irds noon I saw an Ammophila running on the sidew ilk of the street in front of the yard carrying a caterpillar in its mouth. The weight of the caterpillar prevented it from flying. The yard is separated from the street by a cemented stone wall. I noticed that the wasp repeatedly made an attempt to climb upon the wall, but kept falling down. Suspecting that it might have its nest in the yard I was curious to see whether and how it would find the nest.

It followed the wall until it reached the neighbour- ing yard, which had no wall. It now left the street and crept into this yard. Then crawling through the fence which separated the two yards, it dropped the caterpillar near the foot of a tree, and flew away. After a short zigzag flight it alighted on a flower-bed in which I noticed two holes. It soon left the bed and flew back to the tree, not in a straight line but in three stages, stopping twice on its way. At the third stop it landed at the place where the caterpillar lay. The caterpillar was then dragged to the hole, pulled into it, and covered with sand.

As the wasp only walks to the hole when carrying a caterpillar, it is impossible to say that it followed a trace and was guided reflexly when it carried the cat- erpillar to the nest. The repeated attempts to climb the wall of the yard which first attracted my atten- tion indicate that the wasp remembered the location of the nest. The fact that it returned to fetch the caterpillar indicates that it remembered having dropped it, and also where it had been dropped. The zigzag character of its flight shows that it was not guided reflexly.

While these animals without doubt possess asso- ciative memory they possess little " intelligence." I mentioned that the Ammophila covered the hole in which it had buried the caterpillar. In order to cover it, the wasp had to pick up little grains of sand in the neighbourhood of the hole and carry them in its mandibles to the hole. Once, while it had its back turned to the nest and was picking up a grain of sand, I covered the hole with a clover blossom. The wasp was no longer able to find the hole. It ran and flew about in the most excited manner, returning each time to the place where the hole had been, without being able to discover it. I finally removed the flower, and the wasp immediately found the hole and continued covering it with sand. The blossom with

which I covered the hole weighed considerably less than the caterpillar which the wasp carried with such ease between its mandibles. The fact that the wasp keot returning to the spot where the hole was, indi- cates again the existence of memory in these animals. Bethe's conclusions have been criticised by Was- mann (8) as far as ants, and by von Buttel-Reepen (9) as far as bees, are concerned. I think that bees and ants possess associative memory. In their re- actions, however, reflex or instinctive elements and memory elements are mixed together. The task re- mains 10 discover how much of a role associative memory plays in the various habits of bees, ants, and wasps.

6. The possibility of associative memory must be conceded in the case of spiders, certain Crustacea, and Cephalopods, but it is in all probability wanting- in Coelenterates and in worms. We saw that Act- inians refuse water-soaked paper wads and take meat, though our organs of taste cannot distinguish betv/een the two. Some authors would have called this an expression of intelligence because the Actinian can "discriminate" and "make a selection." Accord- ing to this, consciousness and intelligence should be attributed to the chemical elements, for they unite only with certain other elements. The term " power of discrimination " is often merely an ill-chosen ex- pression for the fact that different causes have differ- ent effects. This difference of the effects may in some cases depend on associative memory, but in order to find out these cases we must first prove that the forms under consideration have associative memory. In Actinians, however, all attempts to prove the exist- ence of associative memory have been fruitless. This is shown in the experiments on Cerianthus mentioned above, in which I succeeded in producing, below the

normal head, a second head, which had an oral disc and tentacles but no mouth (Fig. 12, p. 52). The ten- tacles never learned that no mouth was present, but continued when meat was offered to make the attempt to force it into an opening that did not exist. Some reactions of lower animals cannot be repeated indefinitely. We must not conclude, however, that this is due to processes of association and that the animal has learned certain effects. It is a well-known fact that many worms that live in cases suddenly withdraw into their cases when a shadow is cast on them. I analysed this process and showed that the shadow has nothing to do with the phenomenon. It is due to a reaction against negative variations in the intensity of the light, comparable to the " break-con- traction " of a muscle. The experiment does not suc- ceed if repeated an indefinite number of times in succession. Nagel concludes from this that these worms possess " the ability to judge." " The animal recognises that the shadow cast so frequently does not signify the approach of an enemy or of any other danger" (Nagel). In reality these reactions are in- herited forms of irritability that have nothing to do with experience. The reason that the reaction ceases if repeated frequently is due to a simple after-effect of the stimulus, a case that we often meet in the physi- ology of both animals and plants. The assumption that such low animals as eyeless worms and snails possess ideas or even the one idea of " an approach- ing enemy or other impending danger " is entirely

arbitrary. Graber also maintained that animals that go to the light do so because they love it, and another author thought that animals fly into the flame out of curiosity. It is not worth while to follow up such an- thropomorphisms in the biological literature. Biol- ogy is as much justified in ignoring them as modern physics is in ignoring the fact that savages explain the locomotive by supposing a horse to be concealed within it. On the contrary, biology should concern itself with a systematic investigation of the differ- ent animals in regard to the existence of associative memory. The total results of such an investigation will furnish the material for a future comparative psychology.

7. Our conception meets with an apparent difficulty in the fact that stimuli which call forth sensations of pain in us produce also reactions in lower animals which have no memory. These reactions are natur- ally regarded as the expression of sensations of pain. The injured worm writhes and wriggles, and it is diffi- cult to rid ourselves of the impression that these movements are the expression of severe pain. Yet W. W. Norman proved that this conclusion is by no means justified (5, 10). He found that if an earth- worm is divided transversely, only the posterior piece makes these writhing movements, while the anterior piece crawls off as if nothing had happened. It would, of course, be absurd to assume that the pos- terior piece alone is capable of a sensation of pain, while the anterior piece, which contains the brain,

experiences no such sensation. If we continue the ex- periment and divide the posterior piece in the middle, the anterior part crawls off calmly while the posterior part again makes writhing movements. We obtain the same results if we divide the anterior piece. No matter how the worm is divided, the piece in front of the place of division shows coordinated crawling movements, while the piece behind the place of divis- ion makes writhing movements. It is not even neces- sary to cut the worm. If we only touch it with the point of a pencil the posterior part wriggles, the ante- rior part elongates. The only conclusion that can be drawn is that the stimulus of cutting produces a dif- ferent effect when it extends forward through the worm, from the effect which it produces when it ex- tends backward. The movements do not indicate that the animal possesses sensations of pain.

Similar observations can be made in other Annelids. In Planarians I had already observed that they give no evidence of pain when they are divided trans- versely. The forward piece crawls or swims as if nothing had happened, occasionally merely hasten- ing its movements. But even in insects and Crustaceans pieces can be cut off without any reaction from the animal which might be interpreted as the expression of a pain- sensation. Janet has observed that the abdomen of a bee can be cut off while the bee is sucking honey without causing any interruption in its occupation. In 1888 I noticed

something similar in a small Crustacean, Gammarus, during copulation. The abdomen of the male can be cut off while it is seated on the female without caus- ing it to release the female. In fact, unless my mem- ory deceives me, these males without abdomen, when torn away from the female, were ready to hold another as soon as they could find one. Norman has added a great many similar observations on insects and Crustaceans (10). The result of all these observa- tions is that either these Invertebrates do not react to injury in a way which indicates the existence of pain-sensation, or that, if there seem to be such re- actions, they do not justify the assumption of the existence of pain-sensations.

We cannot be surprised that among those repre- sentatives of the lower Vertebrates which have no associative memory, or only traces of it, similar con- ditions exist. Hermann and other physiologists maintain that the reactions of lower Vertebrates under the influence of an ascending current are due to pain-sensations, while the descending current is said to have a sooth- ing effect. Garrey and I came to the conclusion that, in both cases, different sets of muscles were thrown into activity (see Chapter XL). In order to test Hermann's view, we experimented on larvae of Am- blystoma whose spinal cord had been cut between the head and the tail-end of the body. We found that in the ascending current only the tail-end of the ani- mal showed those reactions which Hermann and the

other physiologists had considered as the expression of pain-sensations. I may mention further that when the motions following the stimulation of the semicir- cular canals were first observed they were considered by some authors as the expression of pain-sensations. Norman observed that sharks and flounders react in no way against very severe operations, c. g., the laying bare of the semicircular canals, provided that respiration was not interfered with (10). As soon as the water-supply to the mouth was cut off, they made violent motions, which are characteristic for the condition of beginning asphyxiation and which have nothing in common with conscious acts. Sharks and flounders belong to that class of Vertebrates which have practically no associative memory.

It therefore seems to me that our experience con- cerning the pain-sensations of animals does not con- tradict our view regarding the limits of associative memory or the consciousness of the metaphysicians. Of course I do not expect to convince the senti- mentalists and Darwinians. The former will say that their " feeling ' tells them that an earthworm is capable of pain-sensations. My reply to these is that the burden of proof rests upon them. If a per- son maintains that there is a gaseous Vertebrate in the air it is plainly his duty to prove its existence, and not the duty of all the other scientists to disprove it. Otherwise we might be called upon to waste our lives in disproving the statements of any insane person or impostor. The Darwinians will doubt the possibility

that pain-sensations or any definite characters should appear in certain forms without existing- (although in a rudimentary form) in the whole animal kingdom. To these we shall reply in the next chapter (p. 251). 8. At the end of the chapter on instincts we mentioned that in those animals which possess asso- ciative memory the instinctive reactions may be modified or complicated by the influence of the associations. This influence can be so powerful that the instincts are warped or suppressed altogether. By education and experience the memory of man is filled with a number of associations which can inhibit any reflex or instinctive motor process. To a certain extent these inhibitory associations are necessary for the preservation of the life of the individual. More- over, it is necessary to provide the child with associa- tions which prevent "dissipation," e. g., the cultivation of one or a few instincts at the expense of others. The greatest happiness in life can be obtained only if all the instincts — that of workmanship included— can be maintained at a certain optimal intensity. But while it is certain that the individual can ruin or di- minish the value of its life by a one-sided develop- ment of its instincts- - e. g., dissipation, — it is at the same time true that the economic and social condi- tions can ruin or diminish the value of life for a great number of individuals.1

1 It is no doubt true that in our present social and economic condition more than ninety per cent, of human beings lead an existence whose value is far be- low what it should be. They are compelled by want to sacrifice a number of instincts, especially the most valuable among them, that of workmanship, in Although we recognise no metaphysical free-will, we do not deny personal responsibility. We can fill the memory of the young generation with such asso- ciations as will prevent wron^doin^ or dissipation.

If in a human being such associations are lacking, it points to an organic deficiency or to an insufficient education, for which in some cases the parents, in the majority of cases, our present social conditions, are responsible. Punishment is, perhaps, justifiable in so far as it may bring about inhibitory associations or may be able to strengthen the inhibitory associations of weaker members of society. Inhibitions to be effect- ive, however, must be cultivated in youth, as the time at which the penal code is enforced is usually too late for any lasting benefit. Cruelty in the penal code and the tendency to exaggerate punishments are sure signs of a low civilisation and of an imperfect educational system.

order to save the lowest and most imperative, that of eating. If those who amass immense fortunes could possibly intensify their own lives with their abun- dance, it might perhaps be rational to let many suffer in order to have a few cases of true happiness. But for an increase of happiness only that amount of money is of service which can be used for the harmonious development and satisfaction of inherited instincts. For this comparatively little is necessary. The rest is of no more use to a man than the surplus of oxygen in the atmos- phere. As a matter of fact, the only true satisfaction a multi-millionaire can possibly get from increasing his fortune, is the satisfaction of the instinct of workmanship, or the pleasure that is connected with a successful display of energy. The scientist gets this satisfaction without diminishing the value of life of his fellow-beings, and the same should be true for the business man.

1. MACH, E. Contributions to the Analysis of the Sensations. The Open Court Publishing Co., Chicago, 1^97. 2. LOEB, J. Beitriige zur Gehirnphysiologie der W tinner. Pflugcrs Archiv, Bd. Ivi., 1894. Zur Psychologic und Physiologic der Aktinicn. Pfliigers Archiv, Bd. lix., 1896. Zur Theorie der physiologischcn Licht- und ScJiivcrkraftivirkungen. Pfliiger's Archiv, Bd. Ixvi., 1897. 3. LOEB, J. Wcitere Bcmcrkungen iiber den Hcliotropismus der Thicre und seine Uebcreinstiiiiinnng mit dcm Hcliotropismus der Pflanzen. Pluger 's Archiv, Bd. xlvii.

4. BETHE, A. Dtirfen wir den Ameisen und den Bienenpsychische Qualitdten zuschreiben? Pfliiger's Archiv, Bd. Ixx., 1898. 5. NORMAN, W. W. Diirfcn wir aus den Rcactionen nicdcrcr Tliicre auf Schmerzcmpfindungen derselben schliessen 1 Pflugcr' s Archiv, Bd. Ixvii., 1897. 7. PECKHAM, G. W. and E. G. On the Instincts and Habits of the Solitary Wasps. Wisconsin Geological and Natural History Survey, 1898. 8. WASMANN, E. Die psychischcn Fdhigkcitcn der Ameisen. Zoologica, vol. xi., 1899.

9. v. BUTTEL-REEPEN. Sind die Bienen Reflexmaschinen? Biologischcs Centralblatt, vol. xx., 1900. 10. NORMAN, W. W. Do the Reactions of the Lower Animals against Injury Indicate Pain- Sensations ? The American Journ. of Physiology, vol. iii., 1900. i (. MACH, E. Die Analyse der Empjindungen und das Verhdlt- niss des Physischen zum Psychischen. Jena, 1900. i. The view that consciousness is only a meta- physical term for the phenomena determined by the mechanisms of associative memory finds support in the results of experiments on higher animals. Extir- pation of the cerebral hemispheres causes complete loss of associative memory. After this operation, no- thing remains that could possibly be interpreted by the metaphysicians as a phenomenon of consciousness.

If the cerebral hemispheres of a Rana esculenta or temporaria be extirpated, the frog seems on the whole to be unchanged. This has been proved beyond question by Schrader (i). Such a frog catches flies, buries itself in the mud when the cold season comes, and changes its habitation from the land to the water, like a normal frog. None of these processes, how- ever, are functions of associative memory ; they de- pend upon inherited structures. The frog either has no associative memory or it is so insignificant that it does not in any way affect the behaviour of the frog. This explains the fact that the loss of the cerebral

hemispheres, which produces so great a change in the personality of a higher animal, has much less effect on a froe. In the shark, nothing in the habits or reac- tions of the normal animal shows the existence of associative memory. Most of its reactions are inher- ited and composed of segmental reflexes. We find, correspondingly, that it shows very little change after the extirpation of the cerebral hemispheres, for in spite of their loss the segmental reflexes are pre- served.

It would be a mistake to assume that the loss of the cerebral hemispheres in no way affects the animal. Its loss has a certain effect upon the segmental re- flexes. Nereis has no associative memory, yet it shows a certain lack of inhibition after the loss of the supra- cesophageal ganglion (see Chapter VI.). Something similar is noticeable in lower Vertebrates whose cere- bral hemispheres are removed. For instance, in ad- ders all segmental reflexes are preserved after loss of the cerebral hemispheres. Schrader found, however, that such animals no longer show any " fear " -it was not possible to frighten them although all the opticus- reflexes still functioned (2). From this we must con- clude that the effects of those stimuli which extend from the opticus-segment into the central nervous system are different, so long as the cerebral hemi- spheres exist, from what they are when the hemi- spheres have been extirpated. Something of this kind also shows itself in the frog. Goltz has found that the frog without cerebral hemispheres is better

suited for demonstrating reflexes than the frog with cerebral hemispheres. If the skin on the back of a normal frog is touched, it may or may not croak. Goltz showed that this croaking reflex never fails in a frog whose cerebral hemispheres have been excised (3). In the normal frog, however, touching the skin of the back produces, in addition, another reflex : it shows a tendency to leap away. The normal frog as well as the frog without cerebral hemispheres is a re- flex animal — that is, its reactions are chiefly segmen- tal reflexes. But there is this difference between the two : In the animal with cerebral hemispheres the same stimulus can produce more than a single reflex, and this fact adds to the greater complication and capriciousness of the reactions of the animal. On the other hand, the cerebral hemispheres can also restrict the play of the segmental reflexes. The clasping re- flex of the male frog in the act of copulation is a segmental reflex of the arm-segments during the period of heat. It seems that sexual substances de- termine this reflex, since it cannot be shown to exist in animals that are castrated before the period of heat. Now male fro^s that have lost the cerebral

hemispheres are much more indifferent in the choice of the object they clasp during the period of heat than animals with cerebral hemispheres. 2. In birds the conditions are different from those which exist in frogs and sharks. We are indebted to Schrader for an exact and, in many respects, classic investigation of the effect of the extirpation of the cerebral hemispheres on birds (4). The work of this investigator, Goltz's article on the clog- without cere- bral hemispheres, and Goltz's and Ewald's article on the dog with shortened spinal cord are among the best on the physiology of the central nervous system. Until their work appeared, it was a dogma (and is still in many text-books) that animals which have lost the cerebral hemispheres can no longer move spon- taneously. Flourens is responsible for the statement. Schrader first disproved it in regard to the frog and then succeeded in disproving it in the case of birds. " None of the animals under observation [pigeons] showed a sleep-like condition longer than three to four days [after excision of the cerebral hemispheres]. According to Rolando and Flourens, animals which have undergone this operation, except when certain stimuli are applied to the skin, remain absolutely quiet. At first, this is true. The pigeons remain standing, where they are placed, with ruffled feathers, the head drawn in, the eyes closed, and often on one leg. Occasionally they shake themselves, clean their feathers with their beak, stretch sleepily, and in the act of defalcation take a few steps. If left undis- turbed, nothing else is to be observed. When thrown up into the air, they fly down diagonally, strike ob- stacles, and fall rather than alight on the floor, where they at once sink back into their stupor again. If the skin is stimulated, they take a few steps, but in so doing are liable to run into obstacles" (Schrader, loc. cit.).