The Dynamics of Living Matter

Other experiments gave similar results. The experiments show that the influence of temperature upon the rate of contractions in different hearts is practically the same, and that a rise, of 10° C. increases the rate to a little more than twice the original figures. It was found that temperatures above 25° C. injure the heart rather soon, and for this reason the rate of contraction was regular at a temperature of 30° C. for the first fifteen or twenty minutes only.

These experiments show that the heartbeat is caused by chemical processes which go on constantly. O. Hertwig * has made experi- ments on the influence of temperature upon the time required for the development of the eggs of the frog. He compared the time required to reach three successive stages in the development at the tempera- tures of 6°, 10°, 15°, 20°, and 24°. The temperatures were not kept perfectly constant. From Hertwig's results E. Cohen calculated f that the influence of temperature followed the law of van't Hoff and Arrhenius.

When the temperature of the protoplasm becomes sufficiently low, e.g. approximately o° C., the velocity of the chemical reactions becomes so small that the manifestations of life cease. Cold-blooded animals can at any time be revived from this condition of latent life by raising their temperature. The lack of water acts similarly to a low tempera- ture. This is the reason why seeds can be kept alive so long. Lack of water may reduce the reaction velocity of the hydrolytic processes in seeds at ordinary temperature so considerably that it may become practically zero.

The question may be raised whether lowering of the temperature can ever kill an organism, or whether there exists a low temperature limit for life phenomena. From our viewpoint the criterion for death is the nonreversibility of the changes brought about by the agency in question. We must therefore ask, Does lowering of temperature bring about irreversible changes in the protoplasm, as does a raising of the temperature ? The answer seems to be that for many cold-blooded animals there is no lower temperature limit in the sense of our defini- tion, and if death occurs at a low temperature, it is due to secondary and entirely accidental effects connected with the freezing of the water in the cells. It is known that the formation of ice crystals in the cells may mechanically injure and kill them. This seems to be the case in the freezing of plants. Another accidental irreversible change is con- nected with the thawing of animals that have been frozen. It seems to be certain that a frog after being frozen cannot be brought back to life again if the temperature is raised suddenly, while it may live if allowed to thaw slowly. Barring these two secondary and mechani-

cal complications, the lowering of temperature does not seem to bring about irreversible changes in the condition of protoplasm, which are incompatible with life. This seems to be in harmony with the fact that living matter contains no colloidal solutions which are transformed into irreversible gels by cooling. Gelations which are brought about by cooling seem ta be, in general, reversible processes, e.g. the gelation of gelatine. Experiments made recently by Pictet and others show that various cold-blooded animals and bacteria may be cooled to very low tem- peratures without being killed. Many, possibly most, warm-blooded animals seem, however, to behave differently. If their blood is cooled for some time to a temperature of 15° C. or below, they cannot again recover. If this fact which is generally stated is correct, it shows that in the warm-blooded animals a reversible, fatal change occurs at such a lowering of their temperature, although we have not the slight- est conception which substance or variable is responsible for this re- sult. It is interesting that, according to Setchell, the Cyanophycece of the hot springs also die when suddenly brought into water whose temperature is below 40°. It is possible that we are dealing in this case also with some secondary effect connected with the lowering of temperature.

The variables thus far mentioned do not yet exhaust the range of possibilities in which temperature influences life phenomena. The coefficient of partition of one substance between two others may vary with the temperature. This is the case, e.g. for the coefficient of par- tition of chloralhydrate between oil and water. This coefficient in- creases with the temperature, which means that with an increasing temperature more chloralhydrate will leave the watery liquids of the body and go into the tissues which are rich in fat, e.g. nervous elements. In consequence of this fact a frog which is poisoned with chloralhy- drate at room temperature may become normal again upon cooling, as chloralhydrate must in this case go from the nervous elements into the watery liquids of the body. The following fact belongs possibly in the same category. It is known that decapitated frogs show an increase in irritability when kept for some time on ice. If the reaction velocity were decisive for the reflex irritability, it should be expected that, with an increase in temperature, the irritability would increase. Could it be possible that in this case the coefficient of partition of some toxic or inhibiting substance formed in the body varies in the same sense with the temperature, as in the case of chloralhydrate? If this were the case the fact might become intelligible that with decrease in temperature the reflex irritability is increased.

There are, however, a number of biological effects of temperature for which we cannot yet indicate the physical or chemical variable. It is generally known that in many hibernating northern chrysalids the velocity of metamorphosis is increased if the chrysalids are exposed for some time to a temperature of o°. This fact is possibly related to the experience, that treatment with ether can hasten the develop- ment of buds and plants. An equally puzzling effect of heat is the influence a low temperature has upon the production of wings in Aphides. As long as the temperature is high and the moisture sufficient, plant lice are wingless; but if the temperature be lowered, wings begin to grow. In this case the lowering of temperature favors the growing of an organ, an effect which is rather paradoxical in view of the fact that the phenomena of development seem to be plainly a function of the reaction velocity of underlying chemical processes.

The late Dr. Greeley * showed that a certain group of Infusorians, Monas, can at any time be caused to form spores by exposing them for a short time to a low and afterward to a higher temperature. Forms of irritability can also be varied through the influence of temperature. I have shown that positively heliotropic Copepods can be made nega- tively heliotropic by raising the temperature, and negatively helio- tropic Copepods can be made positively heliotropic by lowering the temperature. This will be more fully discussed in the next lecture. In passing I may mention that certain changes — seasonal variations — can be brought about by changes in temperature. f

The electromagnetic theory of light has led to the idea that there must exist besides the already known ether waves other waves on both sides of the scale. Hertz discovered the method by which we can experiment with ether waves of several centimeters or more with the same certainty as was before possible with the shorter waves, which are able to produce sensations of heat or light. The question had to be put whether or not Hertzian waves had any physiological effect. I made eight years ago an extended series of investigations on this sub- ject, and the first experiments seemed to speak in favor of the idea that the Hertzian waves have effects upon the nerves; but I was able to show by a closer analysis that these apparent effects of these waves were not due to the oscillatory character of the discharge, and that the same results could be brought about by nonoscillatory discharges.^

If we wish to study the physiological effects of ether waves, we may therefore confine ourselves to the waves of shorter length. Among these waves those are especially interesting for us whose length is 0.8 p and less, inasmuch as these waves affect our retina, and produce those chemical effects in green plants which make assimilation in these plants possible. Among the various known effects of these waves two are of impor- tance for us; namely, the photochemical effect and the radiation pressure. The latter seems to be of great importance as far as cos- mical phenomena are concerned, as Arrhenius has shown; but I do not believe that they play any role in life phenomena, as Radl seems to assume,* who believes they are responsible for the heliotropic effects of light. This view is, as I believe, contradicted by the fact that radiation pressure is independent of the wave length, while the heliotropic effects are eminently a function of the wave length. This latter influences, however, the photochemical effects, and for this reason it seems advisable to consider the possibility that the biological effects of light are indirectly chemical effects. It seems that every chemical reaction which is influenced by ether waves at all can be influenced only by waves of a definite, limited period. As in this case radiating energy is transformed into chemical energy, the light waves can have no effect unless they are absorbed. We find indeed that in all cases only such light waves produce a chemical or biological action as are absorbed ; but the reverse statement, that wherever in an organ- ism an absorption of light occurs (e.g. in pigment spots) a biological effect must be produced, is not correct.

In order to give an idea of the possible chemical effects of light, a few instances may be quoted. Ultraviolet rays cause the formation of ozone from the oxygen of the air, as can be beautifully demonstrated with the aid of the Heraeus mercury quartz lamp. According to Vogel, violet rays cause the oxidation of guaiacum and give it a blue color, while red rays reduce it and make it appear yellow. The oxidizing and reducing effects of light seem to be of special physiological im- portance. Thus Duclaux attributes the well-known sterilizing effect of light upon bacterial cultures partly, at least, to the formation of acids which are produced by the light in the nutritive medium. He has shown that fats are oxidized and hydrolized under the influence of light, and that the acid thus formed acts antiseptically. According to the same author, sugars are oxidized in an alkaline medium by light. Hydrogenperoxide is also found among the products formed under the influence of light in culture media.

* Radl, Untersuchungen liber den Phototropismus der T/iiere, Leipzig, 1903. It is perhaps of special biological significance that the oxidation of many dysoxidizable substances occurs more rapidly in the light than in the dark. Schonbein and recently Jorissen have shown that alde- hydes are oxidized more rapidly in the light than in the dark; the same is true for oil of turpentine. According to Richardson and For- teg, amylalcohol is oxidized quicker in light than in the dark. Bod- lander is inclined to attribute these effects of light to a dissociation of oxygen; his assumption is based upon the electromagnetic theory of light.*

It is a common biological conception that the occurrence of pigment in animals or plants bears a close relation to biological effects of light ; we may perhaps for this reason quote an observation which bears on this problem. The observation was made by H. W. Vogel.f The silver salts and especially the bromide of silver of common negatives are preeminently sensitive for rays between blue and ultraviolet. If, however, eosin or cyanin is added in traces, the maximum of the photo- graphic effect moves toward the side of the longer waves in the spec- trum.

After this preliminary orientation we shall discuss briefly the bio- logical effects of light. The most important biological role of light lies in the assimilatory activity of green plants. The transformation of the CO2 of the air into sugar (and starch) in the green plant occurs only under the influence of light. This assimilation occurs in chloro- phyll granules (or on their surface) inside the cells of green plants (or certain animals). All attempts thus far made to separate a substance from the chlorophyll which is able to form sugar from the CO2 of the air have f ailed. | Narcotics like ether and chloroform which inhibit the motor activities of the cell also inhibit the chlorophyll action. (This indicates also that the narcotics have another action than a mere physi- cal one, as Overton assumes.) Yet it is not unlikely that in respect to chlorophyll, a similar experience will be made to the one made in regard to zymase; namely, that mere technical difficulties at present prevent the isolation of the assimilating catalyzer in the chlorophyll granules from the living cell.

The chemical side of the process of assimilation is unknown. Baeyer suggested that from H2CO3 at first formaldehyde, HCOH, is formed which by polymerization yields C6HJ2O6. Hoppe-Seyler § expressed the idea that chlorophyll undergoes first a combination with H2CO3 * Bodlander, Ueber langsame Verbrennung. (Ahrens' Sammlung chemischcr und chemisch-technischer I'ortrage}, Stuttgart, 1899. which, under the influence of light, falls apart in such a way as to yield chlorophyll (or the catalyzer contained therein), O2, and a third prod- uct, the latter being sugar or a substance from which sugar may be formed. It is obvious that Hoppe-Seyler's idea represents that con- ception of the action of the catalyzer which is more and more supported by the facts.

The different parts of the spectrum do not accelerate the process of assimilation equally well; chlorophyll absorbs the rays between B and C of the spectrum, and also the rays beyond F. Engelmann has shown by a very ingenious method that the rays between B and C cause the most vigorous assimilation, that the effectiveness of the rays between D and E is a minimum, and that a second maximum exists beyond F* Those rays are therefore the most effective for the pro- cess of assimilation which are most vigorously absorbed by the chlorophyll.

It is as yet uncertain whether the light influences directly any other synthetic processes than those which lead to the formation of sugars and starch. f The lack of light must make itself felt in an indirect way in any process in the plant for which the formation of carbohydrates is a prerequisite, e.g. the formation of proteins. The life of animals does not depend so directly upon the presence of light. This is evidenced by the fact that animal life occurs in caves. Life at the bottom of the ocean also occurs practically in the dark, inasmuch as the light furnished by phosphorescence is only slight. It has occasionally been stated that eggs of animals develop better or quicker in the light than in the dark; but a closer analysis of such statements has shown invariably, thus far, that they are due to an experimental error. Some authors managed by faulty methods to ex- clude the air also with the light, and others did not exclude or consider the influence of microorganisms in their experiments. Driesch's experiments have failed to show any influence of light upon the develop- ment of eggs; and my own experiments in that direction have also thus far yielded only negative results. The fact that the eggs of mam- mals develop in the uterus, shows sufficiently that eggs can develop in the dark.

In years of experimenting I have found only one form of animals in which diffused daylight has an influence upon the formation of organs ; namely, Eitdendrium, a hydroid.J When stems of Eudendrium are t As fungi can form proteids in the dark when a carbohydrate is contained in the cul- ture medium, it seems at least possible that light is not directly required for the formation of proteids in green plants. brought from the ocean to the aquarium, the old polyps die in a few days. If the aquarium is exposed to sufficiently strong light, new polyps are formed, while this formation does not occur in weak light or the dark. It seems, however, as if the formation of stolons could occur also in the dark. The different parts of the visible spectrum are not equally effective. Behind screens of red glass the formation of polyps was less favorable than behind screens of blue glass, even if the degree of brightness of both kinds of glass seemed to be the same.

MACHINES which are constructed artificially are arranged in such a manner that the energy which they require is provided by the hand of man. Through the blind play of the forces of nature durable machines can be created only if their supply of energy is regulated automatically. As an example of that type of machine we may men- tion the waterfall. The waterfall is a machine which transforms dis- tance energy into kinetic energy and heat, and the permanency of this machine is guaranteed by the physical conditions that determine the continued flow of water to the cataract. The green plants represent another type of such machines ; namely, machines which, among others, transform radiating energy into chemical energy. The permanency of this kind of machines is guaranteed by the presence of an automatic arrangement in such plants, whereby their stems grow toward the light. The automatic turning of the stems of many plants toward the light is called heliotropism. We shall go a little deeper into the analysis of these phenomena, inasmuch as heliotropism and similar phenomena give, to a large extent, an insight into the mechanism of automatic self- preservation of organisms.

The stems of many plants in the open grow vertically upward, while the same stems when raised in a room which receives light from only one side grow toward the window. Roots which contribute toward the maintenance of the plant by absorbing the necessary salts from the soil show very frequently (though not always) the opposite behavior. When exposed to light they bend and grow away from the source of light. This behavior is determined only by rays of a certain wave length of the visible spectrum and possibly by some ultraviolet rays. The dark heat rays have no such effects.

We do not yet know with the same degree of certainty, as in the case of the process of assimilation, the relative heliotropic efficiency of each part of the spectrum; but from experiments with colored screens it appears that the more refractive green, blue, and violet rays of the spectrum are more effective heliotropically than the less refractive red and yellow rays. There exists thus apparently a division of labor, the longer light waves accelerating assimilation, the shorter waves ac- celerating heliotropism. This can be demonstrated with the aid of screens, inasmuch as behind red screens the plants assimilate well, while they do not bend or bend only slowly, toward the source of light ; while behind a blue screen they bend actively toward the light, their assimilation being diminished.

We call organisms which bend or grow toward the source of light positively heliotropic or phototropic, and those that bend or grow away from it negatively heliotropic. As far as the mechanism of the heliotropic bending is concerned, we must remember that in most cases it occurs most effectually in the tips of branches or roots. As this region is also the growing region, botanists frequently state that the process of heliotropic bending is a function of growth. This, however, is certainly not true for grasses, in which the bending occurs in the nodes which are flexible, while in the less flexible internodes no bending occurs. It seems therefore as though the phenomena of growth were not essential in the heliotropic reaction, and that the reason that the tips react better to light than the older parts is perhaps due in part to the fact that the latter are not so soft and flexible.

How can light bring about heliotropic curvatures? Let us suppose that light strikes a plant on one side only, or more strongly on one side than on the opposite side, and that it be absorbed in the superficial layers of tissue of that side. In this case we assume that on that side certain chemical reactions occur with greater velocity than on the opposite side. What these reactions are is unknown; we may think provisionally of oxidations. This change in the velocity of chemical reactions either produces a tendency of the soft elements on that side to contract a little more than on the opposite side, or creates otherwise a greater resistance to those forces which have a tendency to elongate or stretch the plant, e.g. hydrostatic pressure inside the cells, or imbibition of certain tissue elements. The outcome will be that one side of the stem will be stretched more than the opposite side, and this will bring about a curvature of the stem. Where the latter is soft at the tip, the bending will occur only, or chiefly, in that region; and as the degree of softness decreases rapidly from the tip downward, the result will be that the tip will bend toward the source of light. This result may possibly be aided by a greater photosensitiveness of the extreme tip of the stem, although I am not aware that this is an estab- lished fact.

Through the process of bending, both sides of the stem come under the influence of light, and this fact determines the extent of the bend- ing. As soon as the tip of the stem is bent to such an extent as to ex- pose the symmetrical sides or elements of the stem equally to the light, the bending must cease ; and the tip of the stem must continue to grow in this direction. The reason for this is obviously the fact that if the symmetrical elements of the tip are struck by the ray of light at the same angle, the photochemical effects in symmetrical elements must be the same, and the tendency to contract or the resistance to elonga- tion must be the same on both sides. In this case the tip or rather its axis of symmetry will continue to grow in the direction of the rays of light. It is, of course, taken for granted in this discussion, that the plant is exposed to only one source of light. What has thus far been said refers to positively heliotropic organs, e.g. stems, which bend toward the source of light if illuminated from one side only. The same reasoning applies also to negatively heliotropic organs, e.g. roots, with the difference only, that in the latter case the photochemical effects result in a relaxation or a decreased resistance to the stretching forces on that side of the organ where the light strikes. It appears as if there might exist a chemical or physical difference between stem and root; it might be possible that while the light accelerates oxidation in one organ it accelerates reduction in the organ with opposite heliotropism. It might also be possible that the chemical effects of light are the same in the stem and the root of a plant, but that the colloids in the root are affected by these substances in the opposite sense from those of the stem. We have no data which enable us to test these suggestions.

Wortmann * has made sections through the tips of stems and roots which were exposed to light from one side only. He found that the cells on that side of the stem which was directed toward the light possess denser protoplasm than the cells on the opposite side; in roots it was the reverse. Wortmann concluded from this that the protoplasm itself is heliotropic in the stem and that it creeps toward the illuminated side, while in the root the reverse process takes place. Botanists have raised the objection that a creeping of the protoplasm from cell to cell could not occur so rapidly on account of the great resistance offered to such a process. I wonder whether the changes which Wortmann observed are not of a character similar to those observed by Darwin in the basal cells of the tentacles of Drosera, an insectivorous plant, which he designated as aggregation.! In the unstimulated condi- tion these cells are filled with a homogeneous watery liquid of a pur-

* Wortmann, Botanische Zeitung, 1887. t Darwin, Insectivorous Plants. plish color. The walls are lined with a layer of colorless circulating protoplasm. If, however, the cells are investigated after a prolonged stimulation of the glands of the plant, the basal cells of the tentacle no longer contain a homogeneous liquid, but solid masses of various shape which have the purplish color and are surrounded with an almost colorless liquid. These changes do not necessarily depend upon the bending of the tentacles, but only upon the stimulation of the glands. This process of aggregation (which may be a gelation) is reversible, and after a period of rest the original appearance of the protoplasm is reestablished. By way of digression we may mention that Darwin observed that the process of aggregation traveled from the stimulated gland to the contracting tentacle, and that what he observed here directly may occur invisibly in the stimulated nerve fiber. It is possible that in the positively heliotropic organs a process of aggregation occurs in the cell on the side of the light, while in negatively heliotropic organs the reverse occurs on the light side; and this may be the explanation of Wortmann's observations. On the side where the protoplasm be- comes denser (or undergoes aggregation?) the cellulose walls become subsequently thicker than on the opposite side.

The same phenomena of heliotropism which we find in plants we find also in sessile animals ; and the identity of the heliotropic reactions in these two groups of organisms is so complete that it would be at any time possible to demonstrate the phenomena and laws of plant heliotropism in such animals, and vice versa. One of the best animal forms in which to show this identity is Eudendrium, a hydroid. As stated in the preceding lecture, the polyps of this hydroid soon fall off when it is brought from the ocean into the aquarium ; but in a few days new polyps are formed, and as soon as this occurs the little stems in the region below the polyp bend toward the source of light, when illumi- nated from one side only (see Figs. 20 and 21). The region in which this curvature occurs is situated immediately below the polyps, and it happens that in this region also the main growth of the stem occurs. The bending of the polyp or the tip of a branch continues until the symmetrical points of the stem are struck by light at the same angle. If there is only one source of light this occurs when the axis of symmetry falls into the direction of the rays of light. As soon as this happens the stem continues to grow in the direction of the rays of light.

In Eudendrium just as in plants the more refractive blue rays are more effective than the red rays; behind a red screen' the heliotropic curvatures in Eudendrium do not occur at all, or only slowly, while be- hind a blue screen they occur as rapidly as in mixed daylight. In Eudendrium we are able to convince ourselves that the region behind the polyp in which the heliotropic curvatures occur possesses contractility, and the forces underlying protoplasmic contraction are responsible for the heliotropic curvature. The heliotropic curvature consists here in the stem undergoing a stronger contraction or short- ening on the more strongly illuminated side of the polyp than on the opposite side. When the aquarium is turned by an angle of 180° soon

FlGS. 20, 21. — Positive heliotropism of the polyps of Eudendrium. The new polyp-bearing stems all grow in the direction of the rays of light which is indicated by an arrow in each figure. (From nature.) after the curvature occurs, the stem turns and bends in the opposite direction.* Sachs mentions that in the stems of plants also the helio- tropic curvature can be again reversed, provided the experimenter does not wait until the bent region of the stem has become too hard. The heliotropic curvature in Eudendrium is therefore a phenomenon of contractility and not a phenomenon of growth, although growth may accidentally occur at the same time.

* These observations were made in 1895 at Woods Hole, and were mentioned briefly in Pfliiger's Archiv, Vol. 63, p. 273, 1895. We find heliotropic curvatures in animals where there can be no doubt that the curvature is due solely to a process of contraction, and not to a process of growth. Spirographis Spallanzani is a marine Anne- lid from 10 cm. to 20 cm. long, which lives in a rather rigid yet flexible tube. The latter is formed by a secretion from glands at the surface of the animal. The tube is attached by the animal with its lower end to some solid body, while the other end projects into the water. The worm lives in the tube and only the gills, which are arranged in a spiral at the head end of the worm, project from the tube. The gills, how- ever, are quickly retracted, and the worm withdraws into the tube when touched or if a shadow is cast upon it.