The Dynamics of Living Matter

Many animals change the sense of heliotropism during their devel- opment. The larvae of Limulus polyphemus are positively heliotropic immediately after hatching, while they become negatively heliotropic in later stages. The larva? of the common house fly are negatively heliotropic at the end of their larval period, while this reaction neither exists in the earlier stages nor in the imago stage. It is not impossible that in all these cases the real cause for the changes in the sense and intensity of heliotropism is to be found in chemical changes which accompany sexual maturity or larval development. Larva? of Poly- gordius (a marine Annelid) are, when caught, negatively heliotropic; in about twro hours, however, they become positively heliotropic. I found that they could be made positively heliotropic at any time by cooling the sea water to about 7° C., or below. It was also possible to make positively heliotropic larvae negatively heliotropic by raising the temperature of the water. Larvae which were positively heliotropic at 24° were rendered negatively heliotropic by raising the temperature to 29° C. Larvae which were positively heliotropic at room tempera- ture became much more positively heliotropic when the temperature was lowered; while those which were already negative at room tem- perature remained so when the temperature was raised. f It was pos- sible to make the same larvae in succession negative or positive at desire ; it was only necessary not to raise the temperature too suddenly above 25°, as this apparently injured the animals. The immediate effect of temperature in this case was possibly a chemical one.

Results similar to those obtained by changing the temperature could be obtained by changes in the concentration of the sea water. When Polygordius was suddenly put into sea water diluted with fresh water, those that were positively heliotropic before became negatively heliotropic, while those that were already negative continued so. It * Kellogg has observed that bees also become outspokenly positively heliotropic at the time of their nuptial flight, Science, 1904.

sufficed for this purpose to add from 30 to 60 c.c. of fresh water to 100 c.c. of sea water. If, however, the concentration of the sea water was raised through the addition of i gr. NaCl, or the equivalent amount of some other salt, or of sugar, the animals became positively helio- tropic. Loss of water on the part of the animal acted therefore like cool- ing, and an increase in the amount of water like raising the temperature. I made similar observations concerning the changes in the sense of heliotropism in Copepods.

In some forms light itself seems to play a role in the sense of helio- tropism. The Nauplii of Salami's are positively heliotropic upon leaving the egg, but they soon become negatively heliotropic. Groom and I found that when the larvae were kept in a dark room which was illuminated by a gas flame, they remained positively heliotropic toward the flame. In strong light they soon became negatively heliotropic, and, as a rule, the quicker the stronger the light.* These experiments were made at Naples. Experiments which I made on Nauplii of Balanus in Berkeley showed that the reaction of these latter toward light differs somewhat from those found at Naples, and is much more complicated.

While in all these cases one would naturally suspect that chemical influences determine the sense and precision of heliotropic reactions of animals, the same is not so obvious in the following cases. Miss Towle found that Cypridopsis, an Ostracode, is at times negatively, at other times positively, heliotropic. The artificial transformation of positively heliotropic specimens into negatively heliotropic was not pos- sible. It was, however, possible to make negatively heliotropic speci- mens positively heliotropic by mechanical agitation. f S. J. Holmes observed that terrestrial Amphipods are positively heliotropic, while the Amphipods living in the water are negatively heliotropic. This led him to try whether or not terrestrial Amphipods would become negatively heliotropic when thrown into water. He found, indeed, that one of these terrestrial Amphipods, Orchesiia, when thrown into the water, becomes rapidly negatively heliotropic. In sea water these animals remain permanently negatively heliotropic, while in fresh water they become positively heliotropic again before they die.J

I have often wondered whether there are any differences in the be- havior of negatively and positively heliotropic animals aside from their behavior toward light. When larvae of Polygordius were kept in a ver- tical test-tube in a dark room, it often happened that one lot of these animals collected at the top, another at the bottom of the tube. When these two groups were separated in two different vessels and exposed to the light, it was found that those animals that had collected at the bottom of the tube in the dark room were invariably negatively helio- tropic, while the others were positively heliotropic. The reverse was also true; namely, that if positively and negatively heliotropic larvae of Polygordius were put into vertical tubes in the dark, the positively heliotropic specimens invariably gathered at the top, the others at the bottom of the tube. In Limulus larvae I noticed that when positively heliotropic they swam at the surface of the dish, while in the negatively heliotropic state they crept at the bottom. It is, however, questionable how far this observation can be generalized. In the Nauplii of Bala- nus I have noticed that negatively heliotropic larvee swim with the same velocity toward the room side as positively heliotropic animals move in the opposite direction.

Heliotropism, and especially positive heliotropism, is extremely common among animals, particularly pelagic animals. I have found pelagic larvae of fish which reacted in just as machinelike a manner to light as caterpillars or Crustaceans ; but in adult fish, and particularly in higher vertebrates, typical heliotropic reactions can no longer be demonstrated. It rarely happens that animals endowed with the mechanisms of associative memory react in such a machinelike manner to the elementary forces of nature as the heliotropic animals which we have discussed.

Heliotropism plays a wide role in determining the behavior of animals, and there are animals whose life becomes at certain periods of their existence, at least, a function of light. Since I have treated the bearing of heliotropism upon the theory of animal instincts in another place * it need not be repeated here. One source of endless misunderstandings and waste of time among scientists results from the indiscriminate application of one principle to all those cases which by accident have one feature in common with the cases covered by the principle, but differ in almost every other re- gard. We have already mentioned the absurdity of the idea that every kind of turning to the light should be a case of heliotropism. Helio- tropism covers only those cases where the turning to the light is com-

* Loeb, Comparative Physiology of the Brain and Comparative Psychology, G. P. Put- nam's Sons. pulsory and irresistible, and is brought about automatically or mechani- cally by the light itself. On the other hand, there are compulsory and mechanical reactions to light which are not cases of heliotropism ; namely, the reaction to sudden changes in the intensity of light. When the Serpula stretch out their gills, they instantly withdraw them if an opaque body passes between the animal and the source of light. Spiro- gr aphis behaves similarly. Instead of casting a shadow upon the animal, the same reaction may be produced by suddenly closing the shutters of the windows. It is thus evident that we are dealing here with the effect of a sudden decrease in the intensity of light compara- ble to the twitching of a muscle upon the breaking or sudden decrease in the intensity of a current. It should be noticed, however, that I never succeeded in bringing about the sudden contraction of Serpula or Spirographis by a sudden increase in the intensity of light.

There are other forms which react as well upon a sudden increase as upon a sudden decrease in the intensity of light, e.g. fresh-water Plana- rians and earthworms. In these forms a sudden increase in the in- tensity of light causes restlessness, while the reverse change causes the animals to come to rest. This may lead to the gathering of the animals in such parts of the vessel as represent relative minima in the intensity of illumination. When such an animal comes from a bright spot to a darker spot, it comes to rest ("falls asleep")- In consequence of this fact such a relative minimum must act like a trap in which the animals are caught. The consequence is that the number of animals collecting in such a place must always increase, inasmuch as any ani- mal which gets to such a spot by chance must remain there because its motions cease.

The fact that we are dealing here with the gathering of animals caused by light might easily mislead an investigator to mistake these reactions for negative heliotropism. It was a long time before I real- ized myself that I was dealing here with an effect of light which was specifically different from heliotropism. In the latter case the results are a function of the constant intensity, in the former a function of the quotient of the change of intensity over time. It is, however, easy to demonstrate the difference between the two kinds of gathering, experi- mentally. If negatively heliotropic animals be put into a cylindrical glass jar, and it be placed near a source of light, the animals move in the direction of the rays gathering at the negative end of the jar (b, Fig. 27). If fresh- water Planarians are put into such a circular glass dish, they show very little or no tendency to move in the direction of the rays of light, creeping along in an irregular manner and gathering not at the nega- tive or positive side of the jar, but on both sides, c and d (Fig. 27),

where, on account of the refraction of light, the intensity is a relative The fact can be demonstrated still differently: if one part of the aquarium is covered with an opaque body, these organisms gradually gather under the covered part, where they come to rest. If the cover is suddenly removed, they w~ w begin to become restless and creep about. In heliotropism we deal with an automatic orientation of the animal by light, which compels all the animals to move in the same direction. In animals like earthworms or Planarians this orienting effect of light is very slight, and the animals may or do move in every direction.

Of course, it is possible that sensitiveness to sudden changes in the intensity of light exists also in a heliotropic animal. Serpula uncinata is positively heliotropic, and yet contracts rapidly when the inten- sity of the light is suddenly decreased. In Planarians the sensitive- ness to changes in intensity prevails, while, according to G. H. Parker, they show a slight degree of negative heliotropism. IN the preceding lecture and in my former writings I had given a theory of tropisms which may be considered as an application of Fara- day's conception of lines of force. We may conceive space as being traversed by various kinds of lines of force, some of which are present permanently, and in the same direction, e.g. lines of gravitation ; while others may be present or absent, and may vary their direction, e.g. light rays, or electrical lines of force, etc. The bodies of living organ- isms possess as a rule a symmetrical structure, not only morphologically but also chemically, or dynamically. By this I mean that symmetrical points at the surface of the body of an organism possess practically the same chemical substances qualitatively as well as quantitatively, and hence the velocity and kind of chemical reactions must be the same for such symmetrical points. Asymmetrical points of the organism, however, possess a different chemical structure, and hence the velocity and kind of reaction does not need to be, and probably generally is not, the same.

It is presumed, and is in all probability true, that those forms of energy which influence orientation or the direction of the motion of an organism, do so because they alter the velocity or the character of the reaction. On account of the symmetrical structure the organisms are oriented automatically in any field of force which affects their chemical reactions neither too little nor too much, in such a way, that symmetrical points of the surface of the body are struck by the current curves at the same angle. In this case each element of the surface receives the same num- ber of current curves.

The way in which this automatic orientation of the organism is brought about has already been mentioned in a preceding lecture. If the current curves of radiating energy, e.g. light rays, strike an animal on one side only, or on one side more strongly than on the symmetrical side, the velocity or the kind of chemical reactions in the symmetrical photosensitive points of both sides of the body will be different. The consequence will be in a positively heliotropic animal a stronger ten- sion or tendency to contract in the muscles connected with the photo- sensitive points of the one side of the body than in those connected with the opposite side. It seems that in animals the region at the oral pole is, as a rule, more sensitive than the rest of the body. Consequently the tension of the muscles determining the position of the head or oral pole is more intensely affected by differences in the intensity of light than that of the muscles of the rest of the body. The head is conse- quently bent until its symmetrical photosensitive points are again struck at the same angle by the rays of light. The tension of the sym- metrical muscles of the head then again becomes equal, and the head must remain in this position unless other forces disturb its orientation. The rest of the body follows the orientation of the head, a point which is more fully discussed in my book on Brain Physiology.

Aside from the data given in the previous lecture on this subject, two more facts support this view. The one-sided section or destruc- tion of certain parts of the brain causes a diminution in tone in the muscles which turn the body toward one side. The consequence is that animals in which such an operation has been performed, no longer, or only with difficulty, are able to move in a straight line, moving instead constantly in a circle or spiral.* We speak in such cases of forced movements. The same condition which is brought about in a more permanent way by certain one-sided lesions of the brain can be pro- duced transitorily by a one-sided illumination of the photosensitive surface of a highly heliotropic animal, with this difference only, that the very difference in the tension of the muscles and the forced move- ment resulting therefrom leads to a remedy of the evil by bringing the symmetrical points of the animal back into a position where they are struck at the same angle by the lines of force.

The second fact in support of this conception is that when the photo- sensitive elements on one side of the body are eliminated,, the animal is compelled to move in a circle. S. J. Holmes f and Parker J have indeed found that such is the case. I will quote Parker's observation on the subject. His" experiments were made on a butterfly (Vanessa j G. H. Parker, The Phototropism of the Mourning-cloak Butterfly (Vanessa Antiopa), Mark Anniversary Volume, 1903.

antiopa). "Since the head is the portion stimulated by light, it is natural to suspect that the eyes are the particular parts concerned. Loeb has pointed out that the orientation of an organism in light is depend- ent upon the equal stimulation of symmetrical points on its body. Should the eyes be the parts stimulated, any interference with one of these ought to result in a disturbance of the direction of the butterfly's locomotion. Thus if the cornea of one eye were blackened, the insect in locomotion, being positively phototropic, ought to move as though that eye were in shade; namely, in a circle, with the unaffected eye toward the center. Specimens prepared by blacking the cornea of one eye showed the expected response. When the right eye was covered, the insects crept or flew in a circle, with the left side invariably toward the center; and the reverse took place when the other eye alone was blackened. These circus movements agree with those observed by Holmes in other positively phototropic Arthropods." These data ex- plain why in a field of force which affects the chemical processes in an animal neither too little nor too much, the animal is turned automati- cally until symmetrical points of its surface are struck equally by- the lines of force. As soon as this occurs the animals must keep this orientation, and therefore have no further choice in the direction of their motions.

Whether the oral pole is turned toward the source of the lines of force or away from it, depends upon whether the energy which streams along the lines of force alters the chemical reactions in such a way as to increase the tone of the muscles (or the contractile protoplasm) connected with the stimulated elements, or to decrease it. The light rays are not the only lines of force which bring about an automatic orientation of animals; the galvanic current curves act as lines of force, and we speak in that case of galvanotropic orientation, or galvanotropism. A number of plants and animals are oriented automatically by the lines of gravitation emanating from the center of the earth, and are compelled to put their axes or planes of symmetry into a vertical direction (geotropism). While in these cases the current curves are very marked, the same cannot be said in regard to the lines of force in a field of diffusion. The lines of diffusion determined by the particles emanating from a center of diffusion should be straight lines, but in reality currents of air or liquids cause disturbances of these ideal lines. It thus happens that in the case of chemotropism we can at the best expect only an approximate orientation.

There are some other tropismlike reactions of animals and plants which we shall discuss here, although they do not strictly belong in this chapter; namely, stereotropism and rheotropism. When animals are exposed to a galvanic current, compulsory re- actions may occur which agree with the compulsory reactions produced by light, with the difference that we have to substitute the current curves for the light rays. When parallel current curves strike a sym- metrical organ or organism sidewise, the contractile elements, e.g. muscles, on one side of the organ, or organism, undergo a higher degree of tension than on the other side; the outcome is a bending or turning of the organ or animal until its axis, or plane of symmetry, is in the direction of the current curves. As soon as this occurs, the symmet- rical elements of the surface of the body are struck at the same angle by the current curves and the kind and acceleration of chemical re- action is the same on both sides of the organism; consequently the symmetrical muscle elements show the same state of contraction. But the fact that the current curves penetrate throughout the whole animal causes often complications which prevent an ideal orientation such as we observe in the case of light.

A most striking case of galvanotropism was found recently by Ban- croft * in Polyorchis penicillata, a Medusa. "The method of experi- mentation consisted in cutting the Medusa in various ways, and placing the pieces in a trough of sea water through which the galvanic current was conducted with non-polarizable electrodes. The current strength varied from 25 to 2008. The responses were usually distinct with 258, but became more decided as the current was increased.

"If a meridional strip (Fig. 28) passing from the edge on one side through the center of the bell to the other edge be prepared and the current passed through transversely, tenta- cles and manubrium turn and point toward the cathode (Fig. 28). A reversal of the current initiates a turning of these organs in the opposite direction, which is usually completed in a few seconds. This can be repeated many times and the tentacles continue to respond after hours of activity. The manubrium, however, tires sooner and fails to respond. If the strip is placed

with its subumbrella surface upward and extended in a straight line parallel to the current lines (Fig. 29), the making of the current causes the tentacles at the anode end to turn through an angle of 1 80° and point toward the cathode. The tentacles at the cathode end become more crowded together, reminding one of the tip of a moistened paint brush, and also point more directly toward the cathode. The experiment may be varied in still other ways by cutting smaller or larger pieces from the edge of the swimming bell, but the response

as 10 point toward the cathode. The response depends in no way upon the connection of these organs with the swimming bell, muscles, or nerve ring, for it is obtained equally well with isolated tentacles and pieces of tentacles. Isolated tentacles when placed transversely to the current lines curve so as to assume a more or less complete U -shape, with their concave side toward the cathode. When placed parallel to the current, the tentacles do not curve" (Fig. 30). The latter observation shows very nicely the fact that the whole reaction is due merely to an increase in the tension of the muscles on the cathode side of the organ.

We are dealing here with the galvanotropic reactions of sessile organs where the whole reaction is merely a galvanotropic curvature. Wherever the current affects the locomotive organs of a free- swimming animal, besides the galvanotropic orientation of the animal, a swimming either toward the cathode or anode must occur.' As an example, the reaction of an Infusorian, Paramtfcium, may be quoted. Verworn observed that Para- mcecium, when put into a trough through which a galvanic cur- rent passes, is oriented in such FIG. 30.— AFTER BANCROFT. a way as to put its oral pole

toward the cathode. It swims in this orientation toward the cathode.* The mechanism of this reaction was discovered by Ludloff.f The locomotion of Paramcecium is brought about by cilia. As a rule, these cilia are directed backward (A, Fig. 31), and therefore their powerful stroke being directed backward, the animal is pushed forward. Ludloff found that if a Paramacium is struck sidewise by the current, the position of the cilia on the cathode side is re- versed; namely, they are now turned forward (Fig. 31, B); while on the anode side of the animal they remain practically unaltered. Instead of striking symmetrically on both sides of the animal, the cilia on the cathode side strike forward powerfully, those on the anode side backward. The animal is thus under the influence of a couple of forces which turn its oral pole toward the cathode side. As soon as it is in this condition the symmetrical cilia are struck equally by the current curves, and they must assume a symmetrical position. Such is, indeed, the case. They are now pointed forward at the oral end, at the aboral end backward (B, Fig? 31). As long as the current is not too strong, the oral region where the cilia point forward is rather small, and therefore the cilia which are pointed backward prevail, and the organism moves forward toward the cathode. That the motion of the organism to the cathode is exclusively due to the position of the cilia, and not to a stimulating effect

B. Forced position of the cilia when the Paramcecium is in a trough through which a constant galvanic current flows. The free ends of the cilia on the cathode side of the organism point in this case toward its oral pole. of the current at the anode, as Verworn had assumed, follows from observations made by Budgett and myself.* We found that in certain solutions, e.g. o.S per cent NaCl solution, the Param&cia show a tendency to swim backward. When exposed to a galvanic current in such a solution, they show a tendency to go to the anode. The explanation is that in such an organism the cilia are pointed forward under the influence of the solution. Bancroft found that when the current goes crosswise through such a Paramcscium, the cilia on the cathode side continue to point forward while those on the anode side assume their natural position, pointing backward. The animal is thus turned with its oral pole toward the cathode. As soon as this

occurs the cilia on both sides of the body, with the exception of a small number on the anode side, point forward, and the animal is therefore pushed backward to the anode. Maxwell and I have investigated a little more carefully the reactions of a Crustacean, Palamonetes, to a constant current.* When these animals are put into a trough through which a current passes (whose intensity is neither too weak nor too strong), all the animals move gradually toward the anode. The Crustacean can swim forward or backward and can walk forward, sidewise, or backward. The effect of the current does not in this case consist in a compulsory orien- tation of the organism, but merely in a compulsory change in the rela- tive position of the legs, or swimmerets. The result is always such as to facilitate the motion to the anode, and to render more difficult the locomotion to the cathode. " Pal&monetes uses the third, fourth, and fifth pairs of legs for its locomotion. The third pair pulls in the for- ward movement, and the fifth pair pushes. The fourth pair generally acts like the fifth, and requires no further attention. If a current be sent through the animal longitudinally, from head to tail, and the strength be increased gradually, a change soon takes place in the posi- tion of the legs. In the third pair the tension of the flexors predomi- nates, in the fifth the tension of the extensors. The animal can thus move easily with the pulling of the third and the pushing of the fifth pairs of legs, that is to say, the current changes the tension of the muscles in such a way that the forward motion is rendered easy, the backward difficult. Hence it can easily go toward the anode, but only with difficulty toward the cathode. If a current be sent through the animal in the opposite direction, namely, from tail to head, the third pair of legs is extended, the fifth pair bent ; that is, the third pair can push, and the fifth pair pull. The animal will thus go backward easily and forward with difficulty.

When Palamonetes swims for- ward, the swimming appendages, among which the tail fin must be counted, push backward forcibly and forward gently; in swimming backward the opposite occurs. If the current be sent through Pala- monetes in the direction from head to tail, the swimming appendages and the tail also are stretched backward, or dorsad, to their fullest extent. This proves that the tension of the muscles that move those organs backward is greater than that of their antagonists. The shrimp can thus swim forward toward the anode easily under the influence of such a current, but backward only with difficulty. If the current passes through in the opposite direction, from tail to head, the tail and the ventral appendages are turned forward. The tension and the

development of energy now predominate in those muscles which move the swimming appendages forward. In this way the animal can swim backward easily, while it is difficult or impossible for it to swim forward. " Palamonetes can also walk sidewise. This movement is pro- duced by the pulling of the legs on the side toward which the animal is moving (contraction of the flexors), while the legs of the other side push (contraction of the extensors). If a current be sent transversely, say from right to left, through the animal, the legs of the right side assume the flexor position, those of the left side the extensor position. The transverse current assists the animal in moving toward the right, toward the anode, and prevents it from moving toward the left, toward the cathode." *