Comparative Physiology of the Brain and Comparative Psychology

small quantity of CaCl2 or KC1, or both, be added, the centre stops beating. The centre would beat in sea-water were it not for the presence there of Ca, K, and possibly other ions (3). The centre contains some scattered ganglion-cells. It might be argued that the presence of these cells makes the rhythmical contractions in a pure NaCl solution pos- sible. It is easy to prove that such is not the case. The striped skeletal muscles of a froor do not contract

rhythmically in blood or serum. I have shown that this is due to the presence of Ca ions in these liquids. If the muscle be put into a pure NaCl or NaBr solution of the same osmotic pressure as the blood, the muscles contract rhythmically (4). Yet these muscles contain no ganglion-cells. Hence it is not the presence or absence of ganglion - cells which determines the spontaneous rhythmical contractions, but the presence or absence of certain ions. Na ions start or increase the rate of spontaneous rhythmical contractions ; Ca ions diminish the rate or inhibit such contractions altogether. How can these ions have such an influence? In order to explain this we must go back to the fundamental character of protoplasmic motion. Protoplasmic

The amputated margin continues to contract rhythmically, while the bell no longer contracts. motions are due to changes in the physical character of the colloidal material in the protoplasm. These changes may consist in changes in the state of matter or in the absorption of water by these colloids, or in secondary changes derived from those before men- tioned. We know that the physical qualities of the colloids are influenced greatly by the nature and osmotic pressure of the ions in the surrounding solu- tion. For that labile equilibrium of the colloids which is required for spontaneous rhythmical contrac- tions, the Na, Ca, and K ions must be present in definite proportions in the tissues. This proportion must be different for the centre and the margin of a Hydromedusa. While for the margin the proportion in which these three ions exist in the sea-water is adequate, for the centre of a Hydromedusa more Na ions and less Ca ions are required. Hence, if we put a centre without the margin into normal sea-water it does not beat, but it will beat when put into a pure NaCl or NaBr solution of the same osmotic pressure as sea-water. In the pure NaCl solution Na ions of the solution will enter into the tissues and take the place of some of the Ca ions. This will give the col- loids of the muscles those qualities which allow rhyth- mical contractions. If too many Na ions enter the tissues of the centre it will lose its irritability. The latter will, in this case, be restored again by adding a trace of CaCl2 to the solution. It thus happens that the problem of spontaneous activity is no longer a question of the presence or absence of the ganglion-

cells, but of the physical qualities of the colloidal sub- stances in the tissues. But must we conclude from this that the Na ions are the cause of the spontaneous rhythmical contractions of the Medusae ? I think not. The ions only bring about a certain labile equi- librium in the condition of the colloids of the con- tractile tissue which allows the true cause of the contractions to be effective. But what is this cause ? J. Rosenthal seems to have been the first to call attention to the fact that it is in no way essential for a rhythmical phenomenon to have a rhythmical cause, and that constant conditions can lead to rhythmical effects. If a small, constant stream of water flows into a pipette, it will pass out rhythmically in drops. The weight of the drop must be greater than the

surface-tension in the periphery of the opening of the outlet before the drop can break off. As long as the quantity of water running into the pipette, in the unit of time, remains below a certain limit, it will be some time before the drop will be heavy enough to fall. Quincke has given a simple and elegant method by which it is easy to produce rhythmical contractions in air bubbles (5). I will describe the experiment as shown in my lectures. A glass plate P (Fig. 4) is placed in a dish B, filled with water. The lower, narrow end of the thermometer tube T is under and at the middle of the air-bubble, while the upper end rests in a dish A filled with 95 per cent, alcohol. The alcohol rises in a fine stream toward the centre of the bubble. As soon as the alcohol comes in contact with the bubble, the alcohol spreads out on the limit between the air and the water, because the sum of the surface- tensions between air and alcohol and alcohol and water is less than the surface-tension between air and water. By the decrease in the surface-tension the bubble becomes flatter and broader. Inconsequence of the vortex movements in the water that are pro- duced by the spreading, the flow of the alcohol to the bubble is interrupted. The layer of alcohol around the bubble diffuses rapidly into the surrounding water, and the bubble becomes again higher and narrower. The alcohol can flow to the bubble again now that the vortex-movements have ceased, and the flattening of the bubble again takes place, and so on. Under the above-mentioned conditions I obtained about

eighty pulsations per minute- -/. e., about the period- icity of the heart. Now, as regards the origin of the rhythmical activ- ity of Medusae, of the heart, and of respiratory activity, we can imagine that a constant fermentative produc- tion of certain compounds in the automatically active cell corresponds to the constant flow of alcohol in Ouincke's experiment. These substances may be of such a nature that they occasion spreading-phenomena or some other physical change in the colloids of the muscle. But a certain quantity of these substances must be present before this change occurs, hence the periodicity of the contractions. But whether it be a constant fermentative production of some substance or not, the ultimate constant cause for the production is the heat or the intensity factor of the same — the temperature. It now can no longer surprise us that Romanes found that the centre of an Acalepha is able to beat rhythmically in normal sea-water if severed from the margin. As long as we assume that the ganglion-cells are the essential element in spontaneity, this experience on Acalephse would be difficult to ex- plain. As it is, we are only obliged to conclude that in Acalephae there is less difference between the col- loidal substances of the margin and centre than in Hydromedusae.

2. Not only the spontaneous character of locomo- tions is commonly considered to be due to ganglion- cells, but the coordinated character of these motions as well. Let us see how far this notion is correct. Romanes found that if the whole margin of the umbrella of a Hydromedusa be cut off, and only a tiny piece left, this is sufficient to keep up the spontane- ous activity of the jelly-fish in sea-water. From this it would appear that any element of the margin may be considered a centre for the rhythmical contractions of the whole Medusa. But if this be the case, how does it happen that the whole umbrella contracts sim- ultaneously, and why do we not find one part of the margin in systole and the other in diastole ? This coordination is by no means to be taken for granted. It is present only in healthy specimens, and is wanting in injured or dying specimens, a fact to which Roma- nes called attention. The problem of the mechanism of this coordination has been dismissed by many au- thors by the assumption of a " coordinating centre " that is supposed to control this coordination. We shall shortly be in a position to decide whether coor- dination in lower animals is controlled by a special " centre of coordination," or whether it is not rather the result of simple laws of stimulation and conduction.

Romanes found in Acalephae that coordination ceases when all direct connection between the nervous centres has been interrupted by radial incisions in the umbrella, the various sectors no longer contracting simultaneously. The same thing results in Hydrome- dusae, if conduction through the nerve-ring is inter- rupted. In such cases, the radial incision must reach well toward the centre of the bell. If, however, such incisions are made in the umbrella without injuring

the margin and the nerve-ring, no disturbance of coordination ensues. It seems that the continuity of the structures located in the marginal portions of the umbrella is necessary for the coordinated activity. Now how does it happen that so long as the continuity is preserved all the elements act synchronically, while the synchronism disappears if the continuity is inter- rupted?1 In order to answer this question, we must turn our attention to an organ which shows the phe- nomena of coordinated rhythmical activity in a strik- ing manner — namely, the heart. If the heart of a frog be divided into several pieces, they will all be rhythm- ically active, but the number of contractions will vary in the different pieces. The sinus venosus beats most rapidly, and the number of its contractions in a unit of time equals that of the heart before it was divided. T Juts we see that the whole heart beats in the rhytJim of the part that has the maximum number of contrac- tions per minute. From this we must assume that the coordination of the heart's activity is due to the fact that the part which contracts most frequently, forces the other parts to contract in the same rhythm. They will be forced to do this if the activity of the sinus venosus acts as a stimulus upon the other parts. A centre of coordination is therefore entirely unneces- sary.

1 It should be emphasised that incisions through the margin alone do not interfere with coordination in Gonionemus, but that it is necessary to continue the incisions to the centre of the swimming-bell. But even under such circum- stances the animal may still contract in a coordinated way. strips of a mammalian heart to beat. He also draws from his observations the conclusion that there is no reason for assuming the existence of a centre of a coordination (6). In Medusae, also, a synchronical contraction of all the parts takes place if the stimulus from the portion first active can travel rapidly enough to the rest of the margin. This is only possible when the margin is uninjured. It is evident, however, that the neighbouring tissue as well as the nerve-ring is in- volved, because the radial incision must reach well toward the centre of the bell if we wish to stop the coordination. In this case the wave of stimulation must pass around the incisions, a process which in- volves so much time that the separate parts are able to contract independently, and the synchronism is lost. In injured or dying Medusae, where the contact of the cells is less close, uncoordinated, rhythmical activity occurs.

In order to test this idea further, I proposed to Dr. Hargitt, who was working in my laboratory, that he attempt to graft two Hydromedusae, and observe whether they continue to contract synchronically or independently after healing. For this purpose it was necessary to remove the margin of the Medusae. Two of them were then placed with their wounded surfaces in contact, and kept in this position. Figure 5 shows two Gonionemi grafted in this way. They grew together along the entire line of contact with the exception of a small part at O. New tentacles would probably have developed there in time had we not

killed the animals in order to preserve them. In other experiments, the two animals did not heal together so completely. It happened in the case where the animals had grown together most completely, as represented in Figure 5, that they contracted synchronically like one animal two days after the operation. The animals, on the other hand, that had not grown together to such an ex- tent did not contract synchro- nically. I believe that if one could succeed in healing two hearts together completely, they would also beat synchro- nically.

The assumption of a " centre of coordination " situated in the ganglia of the margin of a Medusa thus becomes un- necessary. In the frog's heart, the sinus venosus beats faster than the auricle, ven- tricle, and bulbus aortae. Hence, each contraction of the sinus venosus acts as a stimulus, which causes a contraction of the auricles, and the contraction of the latter is the stimulus which causes the contraction of the ventricle and bulbus aortae. It would follow from this that if we could cause the bulbus aortae in the frog's heart to beat as fast as the sinus venosus we

Two Gonionemi grafted to- gether. Two days after the operation synchronous con- tractions of both animals were observed. might see a reversal of the heart-beat. Nature has made this experiment for us on a large scale in the Ascidian's heart (Fig. 6). contraction do not spread out con- stantly in one di- rection, as in the hearts of other an- in the direction from a to b, and then from b to Contraction alter- a. If the heart be cut open at c, the left half nate in it If for contracts only in the direction from a to c, the , . ,

hundred times in succession from left to right, sending the blood to the right, this activity is followed by per- haps three hundred pulsations from right to left, which cause the blood to flow through the blood- vessels in the opposite direction. These contractions are followed again by a large number of pulsations from left to right, etc. Mr. Lingle made the follow- ing experiments on the Ascidian's heart at Wood's Holl in 1892. If a b (Fig. 6) be an Ascidian's heart and it be divided at c, both pieces, a c, and b c, con- tract uninterruptedly in a constant direction, the former in the direction from a to c, and the latter in the direction from b to c. Mr. Lingle found, further- more, that the source of the automatic activity is

confined to two small regions (a and b, Fig. 6) which correspond to the sinus venosus and the bulbus aortse of the frog's heart. When we excise these two pieces from the heart they continue to beat without inter- ruption, while the long part between the two pieces no longer pulsates (in sea-water at least). These ex- periments, it seems to me, leave no room for doubt that the change in the direction of the contraction in the Ascidian's heart is determined by each of the two ends getting the upper hand alternately, and forcing the other centre to act in its rhythm for a time. This " getting the upper hand " might possibly mean no- thing more than that one end gains the time in which to send off a wave of contraction before the other end begins to contract. For this it is only necessary that a single heart-beat of the leading end be delayed or fail entirely, a phenomenon that also appears oc- casionally in the human heart. In this way the other end of the heart gains time in which to send out a wave of contraction, and its automatic activity will continue to be the stimulus for the activity of the first end until a delay occurs in one beat or until one beat is skipped, thus allowing the first end time again to become automatically active, and so on.

Last year I asked the members of the class in gen- eral physiology at Wood's Holl to find out whether the latter view was correct. Their observations were as follows : Suppose at a certain time a to be the active and b the passive end of the heart. After a short time a begins to beat more slowly or ceases to beat altogether. During the pause, the end b suc- ceeds in sending out a wave of contraction which reaches a before it has had time to send out a wave of its own. One sees occasionally at the time of a reversal that at first both ends send out contraction- waves which may meet in the middle of the heart. At the next heart-beat, the end which is about to stop delays the sending out of the wave a little more, and at the next heart-beat the wave starting from the other end can pass over the whole heart without being blocked.

Hence the coordination of movements in Medusae (or in the heart) is not due to a hypothetical centre of coordination situated in the ganglion-cells, but to the fact that the element which is first active acts as a stimulus upon its next element, and so on. 3. It may be shown that even more specialised forms of coordination do not depend upon the pre- sence or interference of ganglia. When the back of a frog is touched with acetic acid, the frog wipes off the acid with its foot. If one leg is tied, it uses the other for this purpose. The turtle acts in a similar manner when acetic acid is applied to the back of its shell. It cannot reach the stimulated spot, but the legs move dorsally under the shell as far as possible towards it. Physiology has contented itself in regard to these phenomena by pointing to the complicated nature and impenetrable structural secrets of the central nervous system. Yet the same reactions oc- cur in a Hydromedusa, in which case the term

" central nervous system " has only a conventional significance. Romanes found that if we stimulate a spot a (Fig. 7) on the concave side of the umbrella of a Tiaropsis indicans with a needle, the manubrium is brought to the stimulated spot (Fig. 7), as though the animal wished to remove the stimulating object (2). This move- ment takes place as follows: A bending of the manubrium as T Well as Of the bell manubrium is brought to the stimulated spot,

ensues in that mer- somewhat as a decapitated frog tries to wipe off idian of the um- brella which passes through the stimulated point a. It seems as though all the muscle-fibres cooperated in bringing the manubrium to the stimulated spot. The central nervous system has nothing to do with this reaction, for Romanes found that it continued after excision of the whole margin with the nerve- ring. On the other hand, if we make an incision in the umbrella parallel to the margin and stimulate a spot below the line of incision, movements of the manubrium, although not pronounced ones, ap- pear in the direction of the quadrant where the stimulated spot is located, but an exact localisation

is impossible. Romanes concludes from this that there are radial lines of differentiated tissue pass- ing through all parts of the bell and that it is their function to transmit impressions to the manu- brium. He assumes that this tissue is of a nervous character. I believe that the whole phenomenon can be explained without the as- sumption of a special differ- entiation of nervous tissue in radial directions. It seems to me that the following as- sumption is possible : Every localised stimulus leads to an increase in the muscular tension on all sides, which is most intense near the stimulated spot. Now if we decompose each of the lines of increase of tension (aa' ab' ac' ad' ae1 , Fig. 8) radiating from the stimul- ated spot, into a meridional component aa' dd' bb' , etc., and an equatorial component, it is evident that the lat- ter can have no influence on the manubrium. Only the meridional components can have an influence, and of these the one passing through the stimulated spot is the largest. This fact must necessarily cause a bend- ing of the manubrium toward the stimulated spot. It also shows why an incision parallel to the mar- gin of the umbrella makes an exact localisation impos- sible and only allows uncertain movements towards the stimulated quadrant.

analogous reflex in a frog or turtle are of a more com- plicated character. Nature works with very simple tools. The tool employed in the reflex of localisa- tion is the curvature produced by stimulation, — con- tact, for instance. We meet with this in its simplest form in plants, in which the side that comes in con- tact with a solid body becomes concave. Plants cer- tainly possess no central nervous system containing mysterious reflex structures. In their case, irritabil- ity and conductibility suffice as an explanation. In Medusae the method appears more complicated only in so far as in them the contractile tissue is real mus- cle-fibre. In the frog, the only further complication is the fact that the conduction takes place through a special kind of tissue — namely, nerve-tissue. In its first anlage, this central nervous system is of a very simple segmental character. I believe that the cent- ral nervous system preserves this simple character better than any other tissue. The muscles undergo considerable displacement during the development, but the changes occurring in the central nervous sys- tem by no means equal those occurring in the mus- cular system.

It seems thus possible to explain the above-men- tioned phenomena of coordination in Medusae by means of the simple facts of irritability and conduct- ivity without attributing any other functions to the ganglion-cell except those which occur in all conduct- ing protoplasm. 1. O. u. R. HERTWIG. Das Nervensystem und die Sinnesorgane der Medusen. 2. ROMANES, G. J. Jellyfish, Starfish and Sea Urchins. The International Science Series, 1893. 3. LOEB, J. On the Different Effects of Ions upon Myogenic and Neurogenic Rhythmical Contractions, etc., American Journal of Physiology, vol. iii., 1900.

4. LOEB, J. Ueber lonen, welche rhythmische Zuckungen der Skelettmuskeln hervorrufen. Festschrift fur Fick. Braunschweig, 5. QUINCKE. Ueber periodische Ausbreitung an Fliissigkeits- oberfldchen, etc. Sitzungsberichte der Berliner Akademie der Wis- sensch., 1888, ii., S. 791. 6. PORTER, W. T. The Coordination of the Ventricle. The American Journal of Physiology, vol. ii., 1899. i. If we wished to observe the order of the natural system in this book, we should not let the Ascidians follow the Medusae. We consider it more profitable, however, to discuss simple cases before taking up the more complicated ones. Having reached the con- clusion, at the end of the preceding chapter, that the spontaneous coordinated activities in Medusae are not due to specific morphological structures of the gan- glion-cells, we will now attempt to find out whether the reflex actions of animals depend upon the struct- ure of the central nervous system or of the peripheral parts. In Ascidians the central nervous system con- sists of a single ganglion (d, Fig. 9). This ganglion is situated between the oral and aboral tubes (a and &• Fig. 9).

Ciona intestinalis (Fig. 9), a large, transparent Ascidian, possesses a very characteristic reflex. If either the oral or aboral opening be touched, both openings close, and the whole animal contracts so that it becomes small and round. This reflex is de- termined by two groups of muscles, first by ring- muscles in the oral and aboral openings, second by longitudinal muscles, which run lengthwise through the animal. By the contraction of these muscles the animal is protected from the en- trance of foreign bodies into the body cavity. This reaction is a typ- ical reflex act, and is eminently purposeful. According to the pre- vailing ideas concern- ing the decisive role that the ganglion plays in reflexes, the pro- cedure is as follows :

If the oral or aboral opening be touched, the stimulation is conducted through the peripheral nerves to the ganglion, where a mysterious reflex mechanism is brought into play, which gives the muscles the command to contract in a manner corresponding to the nature of the stimulus. Ferrier, for instance, in his text-book, mentions the one ganglion of the Ascidians as illustrative of the significance of the ganglion in reflexes. a oral, b aboral opening ; c, foot, d, location of ganglion.

For some time after the operation, in most cases for about twenty-four hours, the animals remained con- tracted. At the end of this period they began to re- lax again. To my great surprise, I found that the typical reflex continued. If we let a drop of water fall on such an animal, the typical reflex act is pro- duced just as in the normal animal. Hence the reflex cannot be determined by specific structures of the ganglion. But what does determine the reflexes, and what is the function of the ganglion ?

The answer to the first question must be that the reflex is determined by the structure and arrange- ment of the peripheral parts, especially the muscles. The mechanical stimulus throws the muscles directly into activity, and the stimulation is transmitted from muscle-element to muscle-element directly, as in the heart or the ureter. But is the central nervous system superfluous in this animal ? We get the answer to this question if we determine the threshold of stimul- ation. The threshold of stimulation for producing this reflex is higher in animals which have been operated upon than in normal animals. As the source of the stimulus, I used the kinetic energy of drops of water, which fell from a pipette upon the animal. Since the weight of the falling drop in the pipette is always the same, the minimum of the height from which a falling drop can produce a contraction is a convenient measure of the irritability ; the latter is of course equal to the reciprocal value of the thresh- old of stimulation. In one case there were in an

aquarium (equally near the surface), a Ciona freshly operated upon and a normal Ciona. The minimum height from which a contraction could be produced was as follows for the normal animal (a) and the animal operated upon (<£) : In two other animals used for the experiment I obtained the following values : It seems to me that the difference in the irritability arises from the fact that in the normal Ascidian the stimulation is conducted through the nerves and the

ganglion, in which case less energy is required. In the Ascidian operated upon, however, the muscles are stimulated directly, and the conduction of the stim- ulation probably takes place from muscle-cell to muscle-cell, just as in the heart. We know, more- over, that the direct irritability of muscle-fibres is not so great as that of the nerves. Hence the nerves and the ganglion only play the part of a more sensitive and quicker conductor for the stimulus (i).