The Organism as a Whole, from a Physicochemical Viewpoint

out how much CaCl2, was required to allow them to swim permanently at the surface. In order to interpret these figures correctly we must remember that we are dealing with two different antagonisms, one between the salts with univalent and*' bivalent metals and the other between Mg and Ca.«* The former antagonism is satisfied by the addition of Mg, inasmuch as enough Mg was present for this purpose in all solutions. What was lacking was the balance between Mg and Ca. The experiments in Table XIX therefore answer the question of the ratio between Mg and Ca. If we consider only the concentrations of Mg between 2.5 and 10.0 c. c. % m MgCl2 — which are those closest to the normal concentration of Mg in the sea water — we notice that CCa must vary in proportion to CMg. If we now combine the results of this and the previous paragraph we may

express them in the form of the theory of physiologically balanced salt solutions, by which we mean that in the ocean (and in the blood or lymph) the salts exist in such ratio that they mutually antagonize the injurious action which one or several of them would have ij they were alone in solution.* This law of physiologically balanced solutions seems to be the general expression of the effect of changes in the constitution of the salt solutions for marine or all aquatic organisms.

This chapter would not be complete without an intimation of the r61e of buffers in the sea water and the blood, by which the reaction of these media is prevented from changing in a way injurious to the organism. These buffers are the carbonates and phosphates. Instead of saying that the organisms are adapted to the medium, L. Henderson has pointed out the fitness of the environment for the development of organisms and one of these elements of fitness are the buffers against alterations of the hydrogen ion concentration.2 The ratio in which the salts of the different metals exist in the sea water is another. It is obvious that the quantitative laws prevailing in the effect of environment upon organisms leave no more room for the interference of a " directing force" of the vitalist than do the laws of the motion of the solar system.

2 Henderson, L., The Fitness of tJie Environment. See also Michaelis, L., Die Wasserstoffionenconzentration. Berlin, 1914. I. It is assumed by certain biologists that the environment influences the organism in such a way as to increase its adaptation. Were this correct it would not contradict a purely physicochemical conception of life ; it would only call for an explanation of the mechanism by which the adaptation is brought about. There are striking cases on record which warn us against the universal correctness of the view that the environment causes an adaptive modification of the organism. Thus the writer pointed out in 1889 that positive heliotropism occurs in organisms which have no opportunity to make use of it,1 e. g.t Cuma rathkii, a crustacean living in the mud, and the caterpillars of the willow borer living under the bark of the trees. We understand today why this should be so, since heliotropism depends upon the presence of photosensitive substances, and it can readily be seen

1 Loeb, J., Der Heliotropismus der Tiere und seine Ubereinstimmung mil dem Heliotropismus der Pflanzen. Wurzburg, 1890 (appeared in that the question of use or disuse has nothing to do with the production of certain harmless chemical compounds in the body. A much more striking example is offered in the case of galvanotropism. Many organisms show the phenomenon of galvanotropism, yet, as the writer pointed out years ago, galvanotropism is purely a laboratory product and no animal has ever had a chance or will ever have a chance to be exposed to a constant current except in the laboratory of a scientist. This fact is as much of a puzzle to the selectionist and to the Lamarckian (who would be at a loss to explain how outside conditions could have developed this tropism) as to the vitalist who would have to admit that the genes and supergenes indulge occasionally in queer freaks and lapses. The only consistent attitude is that of the physicist who assumes that the reactions and structures of animals are consequences of the chemical and physical forces, which no more serve a purpose than those forces responsible for the solar systems. From this viewpoint it is comprehensible why utterly useless tropisms or structures should occur in organisms.

2. A famous case for the apparent adaptation of animals to environment has been the blind cave animals. It is known that in caves blind salamanders, blind fishes, and blind insects are common, while such forms are comparatively rare in the open. This fact has suggested the idea that the darkness of the cave was the cause of the degeneration of the eyes. A closer investigation leads, however, to a different explanation. Eigenmann has shown that of the species of salamanders living habitually in North American caves, two have apparently quite normal eyes. They are Spelerpes maculicauda and Spelerpes stejnegeri. Two others living in caves have quite degenerate eyes, Typhlotriton spelcsus and Typhlomolge rathbuni. If disuse is the direct cause of blindness we must inquire why Spelerpes is not blind.

Another difficulty arises from the fact that a blind fish Typhlogobius is found in the open (on the coast of southern California) in shallow water, where it lives under rocks in holes occupied by shrimps. The question must again be raised: How can it happen that in spite of exposure to light Typhlogobius is blind? The most important fact is perhaps the one found by Eigenmann in the fishes of the family of Amblyopsidae. Six species of this group live permanently in caves, are not found in the open, and have abnormal eyes, while one lives permanently in the open, is never found in caves, and one comes from subterranean springs. The one form which is found only in the open, Chologaster cornutus, has a simplified retina as well as a comparatively small eye, in other words, its eye is not normal. This indicates the possibility that the other representatives which are found only in

caves also might have abnormal eyes even if they had never lived in caves. Through these facts the old idea becomes questionable, namely, that the cave animals had originally been animals with normal eyes which owing to disuse had undergone a gradual hereditary degeneration. Recent experiments made on the embryos of the fish Fundulus have yielded the result that it is possible to produce blindness in fish by various means other than lack of light. x Thus the writer found that by crossing the egg of Fundulus with the sperm of a widely different species, namely, Menidia, blind embryos were produced very frequently; that is to say such embryos had the degenerate eyes characteristic of blind cave fishes. Very often no other external trace of an eye, except a gathering of pigment, could be found, while a close histological examination would possibly have resulted in the demonstration of rudiments of a lens and other tissues of the eye.

Another method of producing blind fish embryos consists in exposing the egg immediately, or soon after fertilization, to a temperature between o° and 2° C. for a number of hours. Many embryos are killed by this treatment, but those which survive behave very much like the hybrids between Fundulus and Menidia, i. e., a number of them have quite degenerated eyes. If the eggs have once formed an embryo they can be kept at the temperature of o° for a month or more without giving rise to blind animals. Occasionally such rudimentary eyes were also observed when eggs were kept in a solution containing a trace of KCN. Stockard has succeeded in producing cyclopean eyes in Fundulus by adding an excess of magnesium salt to the sea water in which the eggs developed or by adding alcohol, and McClendon has confirmed and added to these results.

The writer tried repeatedly, but in vain, to produce Fundulus with deficient eyes by keeping the embryos in the dark. Sperm and egg were not allowed to be exposed to the light yet the embryos without exception had normal eyes. F. Payne raised sixty-nine successive generations of a fly Drosophila in the dark, but the eyes and the reaction of the insects to light remained perfectly normal. Uhlenhuth has recently demonstrated in a very striking way that the development of the eyes does not depend upon the influence of light or upon the eyes functioning. He transplanted the eyes of young salamanders into different parts of their bodies where they were no longer connected with the optic nerves. The eyes after transplantation underwent a degeneration which was followed by a complete regeneration. He showed that this regeneration took place in complete darkness and that the transplanted eyes remained normal in salamanders kept in the dark for fifteen

months. Hence the eyes which were no longer in connection with the central nervous system, which had received no light, and could not have functioned, regenerated and remained normal. The degeneration which took place in the eyes immediately after being transplanted was apparently due to the interruption of the circulation in the eye, and the regeneration commenced in all probability with the re-establishment of the circulation in the transplanted organ.

In our own experiments it can be shown that the circulation in the embryo was deficient in all cases where the eyes degenerated. The hybrids between Fundulus and Menidia have often a beating heart but rarely a circulation (although they form blood); and the same phenomenon occurred in the embryos which were exposed to a low temperature at an early period of their lives. Hence all the facts agree that conditions which lead to an abnormal circulation (and consequently also to an abnormal or inadequate nutrition of the embryonic eye) may prevent development and lead to the formation of blind fishes. Eigenmann states that no blood-vessels enter the eye of the blind cave salamander Typhlotriton. The presence or absence of light does not usually interfere with the circulation or nutrition of the embryonic eye, and hence does not as a rule lead to the formation of degenerated eyes.

fish owe their deficiency not to lack of light but to a condition which interferes with the circulation in the embryonic eye. Such a condition might be brought about by an anomaly in the germ plasm or in one chromosome, the nature and cause of which we are not able to determine at present ; but which, since it occurs in the germ plasm or the chromosomes, must be hereditary. This would explain why it is, that animals with perfect eyes may occur in caves and why perfectly blind animals may occur in the open. It leaves, however, one point unexplained; namely, the greater frequency of blind species in caves or in the dark and the relative scarcity of such forms in the open.

Eigenmann has shown that all those forms which live in caves were adapted to life in the dark before they entered the cave.1 / These animals are all negatively heliotropic and positively stereotropic, and with these tropisms they would be forced to enter a cave whenever they are put at the entrance. Even those among the Amblyopsidae which live in the open have the tropisms of the cave dweller. This eliminates the idea that the cave adapted the animals for the life in the dark.

Only those animals can thrive in caves which for their feeding and mating do not depend upon visual mechan- ~xCue*not has proposed the term preadaptation for such cases and this term expresses the situation correctly. Cue"not, L., La Genese des Especes animates. Paris, 1911. isms; and conversely, animals which are not provided with visual mechanisms can hold their own in the open, where they meet the competition of animals which can see, only under exceptional conditions. This seems to account for the fact that in caves blind species are comparatively more prevalent than in the open.

In other words, the adaptation of blind animals to the cave is only apparent; they were adapted to cave life before they entered the cave. Many animals are obviously burdened with a germinal abnormality giving rise to imperfection and smallness of the eye — the hereditary factor involved may have to do with the development of the blood-vessels and lymphatics of the eye. Such mutants can survive more easily in the cave, where they do not have to meet the competition of seeing forms, than in the open. In man also an hereditary form of blindness is known, the so-called hereditary glaucoma. It has nothing to do with light, but the disease seems to be due to an hereditary anomaly of the circulation in the eye.

Kammerer1 has recently reported that by keeping the blind European cave salamander Proteus anguinus under certain conditions of illumination he succeeded in producing two specimens with larger eyes. According to him the eyes of Proteus may develop to a certain point and then retrogress again. He states that by keeping young salamanders alternately for a week or two in sunlight and in a dark room where they were exposed to red incandescent light, two males formed somewhat larger eyes. The first year no alteration was visible. In the second year a slight increase in the size of the eyes was noticeable under the skin. In the third year the eye protruded slightly and this increased somewhat in the fourth year.

There is thus far only one case on record in animal biology in which the light influences the formation of organs. The writer found that the regeneration of the polyps of the hydroid Eudendrium does not take place if the animals are kept in the dark, while the polyps will regenerate if exposed to the light;1 and the time of exposure may be rather short according to Goldfarb. 2 It is possible that Proteus resembles in this respect Eudendrium; it should be stated, however, that of many different forms tried by the writer over a number of years, Eudendrium was the only one which gave evidence of such an influence of light. Of course it is not impossible that the light might influence reflexly the development of blood-vessels in the eyes of certain animals, e. g., Proteus, and thus allow the eyes of Proteus to grow a little larger.

We therefore come to the conclusion that it is not the cave that made animals blind but that animals with a hereditary tendency towards a degeneration of the eyes can survive in a cave while they can only exceptionally survive in the open. The cause of the degeneration is a disturbance in the circulation and nutrition of the eye, which is as a rule independent of the presence or absence of light. We may by way of a digression stop for a moment to consider the most astonishing and uncanny case of adaptation; namely, the formation of the transparent refractive media, especially the lens in front of the retina. It is due to these media that the rays which are sent out by a luminous point can be united to an image point on the retina. One part of this process is understood ; namely, the formation of a lens. Wherever the optic cup of the embryo is transplanted under the epithelium the latter will be transformed into a transparent lens. When the upper edge of the iris is injured in the salamander so that the cells can multiply, the mass of newly formed cells also becomes transparent and a lens is formed. This indicates the existence of a substance in the optic cup which makes the epithelial cells transparent; and which also limits the size of the lens which is formed. The lens is not always a perfect optical instrument, on the contrary, it is as a rule somewhat defective. Of course, a great many details concerning the process of lens regeneration have still to be worked out.

3. It is well known that most marine animals die if put into fresh water and vice versa; and in salt lakes or ponds with a concentration of salt so high that most marine animals would succumb if suddenly transferred to such a solution we have a limited fauna and flora. The common idea is that marine animals become adapted to fresh water or vice versa; or to the conditions in salt lakes; especially if the changes take place gradually. Yet it can be shown that the existence of these different faunas can be explained without the assumption of an adaptive effect of the environment. The writer has worked with a marine fish Fundulus whose eggs develop naturally in sea water which, however, will develop just as well in distilled water; and the young fish hatching in distilled water live and grow in this medium. Most of the adult fish die after several days, when put suddenly into distilled water, but they can live in fresh water which contains only a trace of salt. They can also live in very concentrated sea water, e. g., twice the normal concentration. Suppose that a bay of the ocean containing such fish should suddenly become landlocked and the concentration of the sea water be thus raised to twice its natural amount; the majority of forms would die and only Fundulus and possibly a few other species with the same degree of resistance would survive. An investigator examining the salinity of the water and not knowing the natural resistance of Fundulus to changes in concentration would be inclined to assume that he had before him an instance of a gradual adaptation of the

fish to a higher concentration of the sea water; whereas the fish was already immune to this high concentration before coming in contact with it. This fish seemed a favourable object from which to find out how far an adaptation to the environment really existed; and the result was surprising. By changing the concentration of the sea water gradually it is possible to raise the natural resistance of the fish only a trifle, not much over ten per cent. The concentration of the natural sea water is a little over that of a m/2 solution of NaCl+KCl+CaCl2 in the proportion in which these three salts exist in the sea water. When adult Fundulus are put into a 10/8 m solution of NaCl+KCl+CaCl2 in the proportion in which these salts occur in sea wrater they die in less than a day, but when put from sea water directly into a 8/8 m or 9/8 m solution they can live indefinitely. It was found1 that if the concentration of the sea water was raised gradually (by m/8 a day) the fish on the fifth day could resist a 10/8 m solution of NaCl+KCl+CaCl2 for a month (or possibly indefinitely; the experiment was discontinued after that period). When a 10/8 m solution was allowed to become more concentrated slowly by evaporation (at room temperature) all the fish died rapidly when the concentration was 12/8 m or even below. In higher concentrations they can live only a day or two. These experiments show that while the

fish is naturally immune to a 9/8 m NaCl+KCl+CaCl2 solution, by the method of slowly raising the concentration it may be made to tolerate a 10/8 m or n/8 m solution, but not more. These fish when once adapted to a 10/8 m solution can be put suddenly into a very weak solution, e. g., a m/8o NaCl, without suffering and when brought back into a 10/8 m solution of NaCl+ KCl+CaCl2 they will continue to live. If they remain for several days in the weak solution their power of resistance to 10/8 m NaCl+KCl+CaCl2 solution is weakened.

What change takes place when the fish is made more resistant and why is its normal resistance so great? The answer based on the writer's experiments seems to be as follows: Fundulus is comparatively resistant to sudden changes in the concentration of the sea water between m/8o and 9/8 m because it possesses a comparatively impermeable skin whose permeability is not seriously altered by sudden changes within these limits of concentration; while if these limits are exceeded and the fish are brought suddenly into too high a concentration the skin becomes permeable and the fish dies, the gills becoming unfit for use or nerves being injured by the salt which diffuses into the fish.

The fact, that by slowly raising the concentration to 10/8 m the fish may resist this limit, is in reality no adaptation. There is no sharp limit between the injurious and non-injurious concentration. We have seen that the fish is naturally immune to a 9/8 m solution. It is also naturally immune to a 10/8 m or 1 1/8 m solution if we give it time to compensate the injurious effects of a 10/8 m solution by the repairing action of its blood or kidneys. Beyond this no rise is possible. In reality adaptation does not exist in this case.

In former experiments the writer had shown that a pure NaCl solution of that concentration in which this fish naturally lives kills it very rapidly, while it lives in such a solution indefinitely if a little CaCl2 is added. The explanation of this fact is that the pure NaCl solution is able to diffuse into the tissues of the animal while the addition of a trace of CaCl2 renders the membrane practically impermeable to NaCl. The question then arose whether it was possible to make the fish more resistant to a pure NaCl solution of sufficiently high concentration and how this could be done. On the basis of the idea of an adaptive effect of the environment we should expect that by gradually raising the concentration of a pure NaCl solution the latter would gradually alter the animal and 'make it more resistant. The method of procedure suggested was therefore to put the fish first in low and gradually into increasing concentrations of NaCl. This method was tried and found futile for the purpose. Fundulus when put from sea water (after having been washed) into a 6/8 m NaCl solution die in about four hours. When kept previously in a weaker NaCl solution they die if anything

more quickly. But it is possible to make them live longer in a 6/8 m solution of NaCl ; we have to proceed, however, by a method which is in contrast with the ideas of the adaptive influence of the environment. When the fish are first treated with sea water (or with a mixture of NaCl+KCl+CaCl2) of a higher concentration so that they become adapted to a 10/8 m solution of NaCl+KCl+CaCl2 or to 10/8 m sea water, they become also more resistant to an otherwise toxic solution of NaCl. Fish taken directly from sea water were killed in less than four hours when put into a 6/8 m NaCl solution, while fish of the same lot previously adapted to 10/8 m sea water in the manner described above lived two or three days in a 6/8 m NaCl solution. x

It is not impossible that it was the high concentration of calcium in the 10/8 m sea water which rendered the fish more immune to a subsequent treatment with NaCl. We know why a pure NaCl solution kills them and we also know why the addition of CaCl2 protects them against this pernicious effect. It is rather strange that where the conditions of the experiments are clear we find nothing to indicate an adaptive effect of the environment. 4. Ehrlich's work on trypanosomes seems to indicate a remarkable power of adaptation on the part of organisms to certain poisons. If the writer understands these experiments correctly they consisted in infecting

a mouse with a certain strain of trypanosomes, and treating it with a certain arsenic compound, which inhibited somewhat the propagation of the parasites but did not kill them all. Four or five days later trypanosomes from this mouse were transmitted to another mouse and after twenty-four hours this mouse was treated with a stronger dose of the same arsenic compound; and this process was repeated. After the third transmission or later, the trypanosomes can resist considerably higher doses of the same poison than at first and this resistance is retained for years. Ehrlich seems to have taken it for granted that he had succeeded in transforming the surviving trypanosomes into a type which is permanently more resistant to the arsenic compound than was the original strain.

The writer is not entirely convinced that in these experiments a possibility was sufficiently considered which is suggested by Johannsen's experiments on the importance of pure lines in work on heredity. Ac- cording to this author a strain of trypanosomes taken at random should, in all likelihood, contain a population consisting of strains with different degrees of resistance. If a high but not the maximal concentration of an arsenic compound is repeatedly injected into the infected mice the weaker populations of trypanosomes are killed and only the more resistant survive. These of course continue to retain their resistance if transplanted to hosts of the same species. According to this

interpretation the arsenic-fast strain may possibly have existed before the experiments were made, and Ehrlich's treatment consisted only in eliminating the less resistant strains. On the other hand, it has been shown that if an arsenic-fast strain of trypanosomes is carried through a tetse fly it loses its arsenic-fastness. This fact may possibly eliminate the applicability of the pure line theory to a discussion of the nature of the arsenicfastness, but it seems that further experiments are desirable.