The Organism as a Whole, from a Physicochemical Viewpoint

Let us assume that the negatively heliotropic animal is at an equal distance from the two unequal lights and placed so that at the beginning of the experiment its median plane is at right angles to the line connecting the two lights, but with its head turned away from them. In that case the velocity of reaction in the symmetrical photosensitive elements of the eyeless larvae is greater on the side of the stronger light. Since the animal is negatively heliotropic this will result in a greater relaxation or a diminution of the energy production of the muscles turning the head of the animal towards the side of the stronger light. Hence the animal will automatically deviate from the straight line towards the side of the weaker light. By the alteration of the position of its body the photosensitive elements exposed to the stronger of the two lights

will be put at a less efficient angle and hence the rate of photochemical reaction on this side will be diminished. The deviation from the perpendicular in which the animal will ultimately move will be such that as a consequence, the rate of photochemical reaction in symmetrical elements is again equal. The ultimate direction of motion will, according to our theory always be such that the mass of chemical products formed 'under the influence of light in symmetrical photosensitive elements during the same time is equal.

Patten also investigated the question whether the same difference of percentage between two lights would give the same deviation, regardless of the absolute intensities of the lights used. The absolute intensity was varied by using in turn from one to five glowers. The relative intensity between the two lights varied in succession by o, 8J£, 16%, 25, 33^, and 50 per cent. Yet the angular deflections were within the limits of error identical for each relative difference of intensity of the two lights no matter whether, I, 2, 3, 4, or 5 glowers were used. The following table shows the result.

Such constancy of quantitative results is only possible where we are dealing with purely physicochemical phenomena or where life phenomena are unequivocally determined by purely physicochemical conditions. 5. It seems difficult for some biologists, even with the validity of the Bunsen-Roscoe law proven, to imagine that the movements of the animals under the influence of light are not voluntary (or not dictated by the mysterious "trial and error" method of Jennings).1

1 According to this theory the animal is not directly oriented by the outside force, e. g. the light, but selects among its random movements the one which is most " suited " and keeps on moving in this direction. This idea is untenable for most if not all the cases of tropisms and has been But one wonders how it is possible on such an assumption to account for the fact that the angle of deflection of the larva of the fly when under the influence of two lights of different intensities should be always the same for a given difference in intensity; or why the time for curvature in Eudendrium should vary inversely with the intensity of illumination. It is, however, possible to complete the case for the purely physicochemical analysis of these instincts. John Hays Hammond, Jr., has succeeded in constructing heliotropic machines which in the dark follow a lantern very much in the manner of a positively heliotropic animal. The eyes of this heliotropic machine consist of two lenses in whose focus is situated the " retina " consisting of selenium wire. The two eyes are separated from each other by a projecting piece of wood which represents the nose and allows one eye to receive light while the other is shaded. The galvanic resistance of selenium is altered by light; and when one selenium wire is shaded while the other is illuminated, the electric energy (supplied by batteries inside the machine) which makes the wheels turn (these take the place of

refuted by practically all the workers in this field, e. g., Parker and his pupils, Bohn, H. B. Torrey, Holmes, Bancroft, Ewald, and others. It is only upheld by Jennings and Mast; and is accepted among those to whom the idea of a physicochemical explanation of life phenomena does not appeal. Torrey and Bancroft (for the literature the reader is referred to Bancroft's paper, Jour. Exper. ZooL, 1913, xv., 383) have shown directly that the theory of trial and error is not even correct for the organism for which Jennings has developed this idea; namely Euglena.

the legs of the normal animal) no longer flows symmetrically to the steering wheel, and the machine turns towards the light. In this way the machine follows a lantern in a dark room in a way similar to that of a positively heliotropic animal. Here we have a model of the heliotropic animal whose purely mechanistic character is beyond suspicion, and we may be sure that it is not "fondness" for light or for brightness nor will-power nor a method of "trial and error" which makes the machine follow the light.

6. It may also be of interest to know that in heliotropism the motions of the legs are automatically controlled by the chemical changes taking place in symmetrical elements of the retina. In order to prove this point we will turn to the phenomenon of galvanotropism. The galvanic current forces certain animals to move in the direction of one of the two electrodes just as the light forces the heliotropic animals to move towards (or from) the source of light. The change in the concentration of the ions at the boundary of the various organs, especially the nerves, determines the galvanotropic reactions. When the shrimp Pal&monetes is put into a trough with dilute salt solution through which a current of a certain intensity flows, the animal is compelled to move towards the anode.1 It can walk forwards, backwards, or side wise. Here we can observe directly

that the effect of the current consists in altering the tension of the muscles of the legs in such a way as to make it easy for the animal to move toward the anode and difficult to move toward the cathode. Thus if the current be sent side wise through the animal, say. from left to right (Fig. 45), the legs of the left side assume the flexor position, those of the right the extensor position. With this position of its legs the animal can easily move

to the left, i. e.t the anode, and only with difficulty to the right, i. e., the cathode. This change in the position of the legs occurs when the animal is not moving at all, thus showing that the galvanotropic movements take place not because the animal intends to go to the anode, but that the animal goes to the anode because its legs are practically prevented by the galvanic current from working in any other way. This is exactly what happens in the heliotropic motions of animals. x

To understand what happens when the current goes lengthwise through the body it should be stated that Palamonetes uses the third, fourth, and fifth pairs of legs for its locomotion. The third pair pulls in the forward 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 tail to head, and the strength be increased gradually, a change soon takes place in the position of the legs (Fig. 46). In the third pair the tension of the flexors predominates, 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

1 That the mechanisms by which heliotropic and galvanotropic orientation is brought about are identical was shown by Bancroft in Euglena (Bancroft, loc. cit.). the forward motion is rendered easy, the backward motion is difficult. Hence it can easily move toward the anode, but only with difficulty toward the cathode. If a current be sent through the animal in the opposite direction, namely, from head to tail, 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 move backward easily and forward with difficulty, and it is thus driven to the anode again. The explanation which Loeb and Maxwell proposed for this influence of the current on the legs assumes that there are three groups of ganglion cells in the central nervous system of these animals which are oriented according to the three main axes of the body; (i) right-left and left-right, (2) backward, and (3) forward. It depends upon whether the ganglion cells or the nerve elements are in anelectrotonus, which muscles are bent and which relaxed. It would lead us too far to recapitulate the theory in this place, and the reader who is interested in it is referred to Loeb and Maxwell's paper.1 The importance of the observations lies in the fact that they show that any element of will or choice on the part of the animal in these motions is eliminated, that the animal moves where its legs carry it, and not that the legs carry the animal where the latter "wishes" to go.

7. This may be the place to dispel an error which has sometimes crept into the discussion of the tropistic reactions of animals. It has been stated occasionally that it is the energy gradient and not the automatic orientation of the animal by the light which makes the positively heliotropic animal move towards the source of light and the negatively heliotropic away from it. Thus the positively heliotropic animal would be compelled to move towards the source of light as a consequence of the fact that the intensity of the light increases the more the nearer the animal approaches the source of light. If the source of light be the reflected sky-light the difference of intensity at both ends of a microscopic organism is so slight that it is beneath the limit capable of influencing the motions.

A simple experiment published by the writer in 1889 suffices to dispel the idea that the energy gradient determines the direction of the motion of an animal in tropistic reactions. Let direct sunlight (S, Fig. 47) fall through the upper half of a window (w w) upon a table, and diffused daylight (D) through the lower half of the window on the same table. A test-tube a c is placed on the table in such a way that its long axis is at right angles to the plane of the window; and one half a b is in the direct sun-

light, the other half in the shade. If at the beginning of the experiment the positively heliotropic animals are in the direct sunlight at a, they promptly move toward the window, gathering at the window end c of the tube, although by so doing they go from the sunshine into the shade.1 This experiment is in harmony with our idea that the effect of light consists in turning the head of the animal and subsequently its whole body toward the source of light. By going from the strong light into the shade the reaction velocity in both eyes is diminished equally and hence there is no reason for the animal to change its orientation, though its progressive motion may be stopped for an instant by the change. But at the boundary between sunlight and daylight a sudden change from strong to weak light occurs. If the energy gradient determined the direction of the positively heliotropic animal, the motion should stop at the boundary from strong to weak light, which may happen for an instant but which will not interfere with the progressive motion of the animal.

8. Graber had found that when animals are put into a trough covered half with blue and half with red glass, those that are "fond" of light go under the blue, those that are "fond" of darkness go under the red glass. The writer pointed out that this result should be expected on the basis of his theory of heliotropism, if the assumption be correct that the red light is considerably less efficient than light which goes through blue glass (such glass also allows green rays to go through). The botanists had already shown that red glass is impermeable for the rays which cause heliotropic reactions of plants, and the writer was able to show the same for the heliotropic reactions of animals. Red glass acts, therefore, almost like an opaque body for these animals.

A closer examination of the most efficient rays for the heliotropic reactions of different organisms has revealed the fact that for some organisms a region in the blue X = 460— 490 w, for others a region in the yellowish-green, near about X = 520— 530^ is the most efficient.1 For many plants and for some animals, like Eudendrium and the larvae of the worm Arenicola, a region in the blue is most efficient; for certain, if not most, animals a region in the yellow-green is most efficient. Among unicellular green algae, Chlamydomonas, has its maximal efficiency in the yellowish-green and Euglena in the blue. According to observations by Mast, some green unicellular organisms like Pandorina, Eudorina, and Spondylomorum seem to behave more like Chlamydomonas, while certain others behave more like Euglena . 2 Wasteney s and the writer suggested

that there are two groups of heliotropic substances, one with a maximum of photosensitiveness in the blue, the other in the yellowish-green; and that the latter group may or may not be related or identical with the visual purple which is most rapidly bleached by light of a wave length near X = 520 — 530 \J.\L. The ophthalmologist Hess1 has utilized the heliotropic reactions of animals in an attempt to prove that all animals from the lowest invertebrates up to the fishes inclusive suffer from total colour-blindness. This statement was based on the observation that for most positively heliotropic animals the region in the yellowishgreen near X = 520 ^ seems the most efficient. Since this region of the spectrum appears also as the brightest to a totally colour-blind man, he concluded that all these animals are totally colour-blind. There is no reason why heliotropic reactions should be used as an indicator for colour sensations; if totally colour-blind human beings were possessed of an irresistible impulse to run into a flame Hess's assumption might be considered, but no such phenomenon exists in colourblind man. Moreover, v. Frisch2 has shown by experiments on the influence of the background on the colouration of fish as well as by experiments on bees and

on Daphnia that the reactions of these animals to light of different wave-lengths indicate different effects besides those of mere intensity. Thus v. Frisch could train bees to go to a blue piece of cardboard distributed among many cardboards of different shades of grey. Bees thus trained would alight on any blue object even if it contained no food. It would be impossible to do this with totally colour-blind organisms. 9. Heliotropic reactions play a great r61e in the preservation of individuals as well as of species. In order to understand this r61e it must be stated that the photosensitive substances appear often only under certain conditions and that their effect is inhibited under other conditions. Thus among ants the winged males and females alone show positive heliotropism, x while the wingless workers are free from this reaction. This positive heliotropism becomes violent at the time of the nuptial flight and this phenomenon itself seems to be a heliotropic phenomenon since it takes place in the direction of the light. When the queen founds her nest she loses her wings and becomes negatively heliotropic again. Kellogg2 has shown that the nuptial flight of the bees is also a purely heliotropic phenomenon. When a part of the hive remote from the entrance is illuminated the bees rush to the light and can thus be prevented from swarming. These phenomena suggest

that the presence of some substance secreted by the sex glands may cause the intensification of the heliotropism which leads to the nuptial flight. In certain species of Daphnia, fresh-water copepods, and of Volvox, a trace of C02 suffices to make negatively heliotropic or indifferent specimens violently positively heliotropic.1 Certain forms of marine copepods and the larvae of Polygordius can be made positively heliotropic by lowering the temperature2 and the larvae of the barnacle can be made negatively heliotropic by strong light. 3 It is quite possible that a change in the sense of heliotropism by temperature and light is to some extent at least responsible for the periodic depth migrations of heliotropic animals. Many if not all positively heliotropic animals can be made negatively heliotropic by exposure to ultra-violet light. 4

A most interesting example of the r61e of heliotropism in the preservation of a species is shown in the caterpillars of Porthesia chrysorrhcea. The butterfly lays its eggs upon a shrub. The larvae hatch late in the fall and hibernate in a nest on the shrub, as a rule not far from the ground. As soon as the temperature reaches a certain height, they leave the nest; under natural conditions, this happens in the spring when the first leaves have begun to form on the shrub. (The larvae can, however, be induced to leave the nest at any time in the winter provided the temperature is raised sufficiently.) After leaving the nest, they crawl directly upward on the shrub where they find the leaves on which they feed. Should the caterpillars move down the shrub, they would starve, but this they never do, always crawling upward to where they find their food. What gives the caterpillar this never-failing certainty which saves its life, and for which a human being might envy the little larva ? Is it a dim recollection of experiences of former generations? It can be shown that it is the light reflected from the sky which guides the animal upward. When we put these animals into a horizontal test-tube in a room, they all crawl toward the window, or toward a lamp ; the animal is positively heliotropic. It is this positive heliotropism which makes them move upward where they find their food, when the mild air of the spring calls them forth from their nest. At the top of the branch, they come in contact with a leaf, and chemical or tactile influences set the mandibles of the young caterpillar into activity. If we put these larvas into closed test-tubes which lie with their longitudinal axes at right angles to the window, they will all migrate to the window end, where they stay and starve, even if their favourite leaves are close behind them. They are slaves of the light.

The few young leaves on top of a twig are quickly eaten by the caterpillar. The light, which saved its life by making it creep upward where it finds food, would cause it to starve could it not free itself from the bondage of positive heliotropism. The animal, after having eaten, is no longer a slave of the light, but can and does creep downward. It can be shown that a caterpillar, after having been fed, loses its positive heliotropism almost completely and permanently. If we submit unfed and fed caterpillars of the same nest contained in two different test-tubes to the same artificial or natural source of light, the unfed will creep to the light and stay there until they die, while those that have eaten will pay little or no attention to the light. Their sensitiveness to light has disappeared; after having eaten they become independent of light and can creep in any direction. The restlessness which accompanies the condition of hunger makes the animal creep downward — which is the only direction open to it — where it finds new young leaves on which it can feed. The wonderful hereditary instinct, upon which the life of the animal depends, is its positive heliotropism in the unfed condition and its loss of this heliotropism after having eaten. The latter phenomenon is in harmony with the experiments which show that the heliotropism of certain species of Daphnia disappears when the water becomes neutral.

of green plants could not exist if their stems were not positively, their roots negatively, heliotropic. It is the positive heliotropism which makes the top grow toward the light, which enables the leaves to get the light necessary for assimilation, and the roots to grow into the soil where they find the water and nutritive salts. 10. While we do not wish to deal here with the different tropisms it should be stated that aside from heliotropism, chemotropism as well as stereotropism play the most essential role in the so-called instinctive actions of animals. It is a problem of orientation by the diffusion of molecules from a centre when a male butterfly is deviated from its flight and alights on the wooden box in which is enclosed a female of the same species. We have already alluded to certain phenomena of chemotropism in Chapter IV. Certain organisms have a tendency to bring their bodies as much as possible on all sides in contact with solid bodies; thus the butterfly Amphipyra, which is a fast runner, will come to rest under a glass plate when the plate is put high enough above the ground so that it touches the back of the butterfly. The animals which live under stones or underground or in caves are as a rule both negatively heliotropic and positively stereotropic. Their tropisms predestine or force them into the life they lead.

is as a rule developed not in the whole organism but only in certain segments of the body. Thus the eyes are located in the head. But when the action of one segment becomes overpowering the whole organism follows the segment. It has been customary among physiologists to speak of reflexes in such cases. Thus, e. g., the arms of the male frog develop a powerful positive stereotropism on their ventral surface during the spawning season. It would avoid confusion to realize that there is nothing gained in applying to this tropism the meaningless term "reflex"; it is better to call them tropisms since the organism as a whole is involved. If necessary we might speak of segmental tropisms. The act of seeking the female as well as that of cohabitation are in many cases combinations of chemotropism and stereotropism. The development of these tropisms depends upon the presence of certain specific substances in the body, a fact emphasized already in the case of heliotropism. In case of the development of the segmental stereotropism of the male frog at the time of spawning it has been shown that it depends on an internal secretion from the testes.

It has been suggested by some authors that the tropistic reactions are determined by some feeling or emotion on the part of the organism. We have no means of judging the emotions of lower animals (except by "intuition"). The writer suggested in 1899 in his book on brain physiology that emotions may be determined by specific substances which also determine the tropistic reaction (as well as phenomena of organ formation, although this latter phenomenon has nothing to do with the subject of instincts); and the excellent work of Cannon1 has shown the r61e of adrenalin in the expression of fear. It is, therefore, both unwarranted and unnecessary to state that hypothetical emotions determine the tropistic reactions.

I. The term environment in relation to an organism may easily assume a mystic r61e if we assume that it can modify the organisms so that they become adapted to its peculiarities. Such ideas are difficult to comprehend from a physicochemical viewpoint, according to which environment cannot affect the living organism and non-living matter in essentially different ways. Of course we know that proteins will as a rule coagulate at temperatures far below the boiling point of water and that no life is conceivable for any length of time at temperatures above 100° C., but heat coagulation of proteins occurs as well in the test-tube as in the living organism. If we substitute for the indefinite term environment the individual physical and chemical forces which constitute environment it is possible to show that the influence of each of these forces upon the organism finds its expression in simple physicochemical laws and that there is no need to introduce any other considerations.

We select for our discussion first the most influential of external conditions, namely temperature. The reader knows that there is a lower as well as an upper temperature limit for life. Setchell has ascertained that in hot springs whose temperature is 43° C., or above, no animals or green algae are found.1 In hot springs whose temperature is above 43° he found only the Cyanophycecs, whose structure is more closely related to that of the bacteria than to that of the algae, inasmuch as they have neither definitely differentiated nuclei nor chromophores. The highest temperature at which Cyanophycecs occurred was 63° C. Not all the Cyanophycece were able to stand temperatures above 43° C., but only a few species. The other Cyanophycece were found at a temperature below 40° C., and were no more able to stand higher temperatures than the real algse or animals. The Cyanophycece of the hot springs were as a rule killed by a temperature of 73°. From this we must conclude that they contain proteins whose coagulation temperature lies above that of animals and green plants, and may be as high as 73°. Among the fungi many forms can resist a temperature above 43° or 45°; the spores can generally stand a higher temperature than the vegetative organs. Duclaux found that certain bacilli (Tyrothrix) found in cheese are killed in one minute at a temperature of from 80°

to 90°; while for the spores of the same bacillus a temperature of from 105° to 120° was required.1 Duclaux has called attention to a fact which is of importance for the investigation of the upper temperature limit for the life of organisms. According to this author it is erroneous to speak of a definite temperature as a fatal one; instead we must speak of a deadly temperature zone. This is due to the fact that the length of time which an organism is exposed to a higher temperature is of importance. Duclaux quotes as an example a series of experiments by Christen on the spores of soil and hay bacilli. The spores were exposed to a stream of steam and the time determined which was required at the various temperatures to kill the spores.

In warm-blooded animals 45° is generally considered a temperature at which death occurs in a few minutes; but a temperature of 44°, 43°, or 42° is also to be considered fatal with this difference only, that it takes a longer time to bring about death. This fact is to be considered in the treatment of fever. It is generally held that death in these cases is due to an irreversible heat coagulation of proteins. Ac- cording to Duclaux, it can be directly observed in micro-organisms that in the fatal temperature zone the normally homogeneous, or finely granulated, protoplasm is filled with thick, irregularly arranged bodies, and this is the optical expression of coagulation. The fact that the upper temperature limit differs so widely in different forms is explained by Duclaux through differences in the coagulation temperature of the various proteins. It is, e. g. known that the coagulation temperature varies with the amount of water of the colloid. According to Cramer, the mycelium of Penicillium contains 87.6 water to 12.4 dry matter, while the spores have 38.9 water and 61.1 dry substance. This may explain why the mycelium is killed at a lower temperature than the spores. According to Chevreul, with an increase in the amount of water, the coagulation temperature of albuminoids decreases. The reaction of the protoplasm influences the temperature of coagulation, inasmuch as it is lower when the reaction is acid, higher when the reaction is alkaline. The experiments of Pauli show also a marked influence of salts upon the temperature of coagulation of colloids.