The Organism as a Whole, from a Physicochemical Viewpoint

Thus within a few minutes after the fertilization of the egg and before or immediately after the first cleavage, the anterior and posterior, dorsal and ventral, right and left poles are clearly distinguishable, and the substances which will give rise to ectoderm, endoderm, mesoderm, muscles, notochord, and nervous system are plainly visible in their characteristic positions.1 We may finally allude briefly to the fact that when once a number of tissues are differentiated each one may influence the other by calling forth tropistic reactions. Thus the writer showed that in the yolk sac of the fish Fundulus the pigment cells lie at first without any definite order but that they gradually are compelled to creep entirely on the blood-vessels and form a sheath around them with the result that the yolk sac assumes a tiger-like marking.1 Driesch2 has pointed out that the mesenchyme cells are directed in their migration; and it seems that the direction of the growth of the axis cylinder is determined by the tissues into which it grows. The idea of tropistic reactions in the formation of organs has been discussed by Herbst. 3

6. As a consequence of further changes definite anlagen or buds originate later in the embryo which are destined to give rise to definite organs. Thus in the tadpole early mesenchyme cells are formed which are the anlagen for the four legs, which will grow out under the proper conditions. These anlagen are specific inasmuch as from the anlage of a foreleg only a foreleg, and from the anlage for a hindleg only a hindleg, will develop. Braus4 has proved this by trans-

a Driesch, H., Science and Philosophy of the Organism, L, p. 104. 3 Herbst, C., Formative Reize in der tierischen Ontogenese. Leipzig, plantingthe anlage of a foreleg to different parts of the body. No matter into which part of the body they are transplanted the mesenchyme cells for the foreleg will give rise to a foreleg only; even if they are transplanted into the spot from which the hindlegs grow out under natural conditions. There is therefore nothing to indicate "regulation."

The same is true for the formation of the eye and probably in general. Y/e have to consider the formation of the various organs of the body as being due to the development of specific cells in definite locations in the organisms which will grow out into definite organs no matter into which part of the organism they are transplanted. It is at present unknown what determines the formation of these specific anlagen. They may lie dormant for a long time and then begin to grow at definite periods of development. We shall see later that we know more about the conditions which cause them to grow.

7. The fact that the egg, and probably every cell, has a definite structure should determine the limits of the divisibility of living matter. In most cases the complete destruction of a cell means the cessation of life phenomena. A brain or kidney which has been ground to a pulp is no longer able to perform its functions; yet we know that such pulps can still perform some of the characteristic chemical processes of the organ; e. g., the alcoholic fermentation characteristic

of yeast can be caused by the press juice from yeast; or characteristic oxidations can be induced by the ground pulp of organs. The question arises as to how far the divisibility of living matter can be carried without interfering with the total of its functions. Are the smallest particles of living matter which still exhibit all its functions of the order of magnitude of molecules and atoms, or are they of a different order? The first step toward obtaining an answer to this question was taken by Moritz Nussbaum,1 who found that if an infusorian be divided into two pieces, one with and one without a nucleus, only the piece with a nucleus will continue to live and perform all the functions of self-preservation and development which are characteristic of living organisms. This shows that at least two different structural elements, nucleus and cytoplasm, are needed for life. We can understand to a certain extent from this why an organ after being reduced to a pulp, in which the differentiation into nucleus and protoplasm is definitely and permanently lost, is unable to accomplish all its functions. 2

The observations of Nussbaum and those who repeated his experiments showed that although two different structures are required, not the whole mass of an 3 It must not be overlooked that in bacteria and the blue algae no distinct differentiation into nucleus and protoplasm can be shown. To these organisms, therefore, the experiments of Nussbaum cannot be applied. infusorian is needed to maintain its life. The question then arose: How small a fraction of the original cell is required to permit the full maintenance of life ? The writer tried to decide this question in the egg of the sea urchin. He had found a simple method by which the eggs of the sea urchin (Arbacia) can easily be divided into smaller fragments immediately after fertilization. When the egg is brought from five to ten minutes after fertilization (long before the first segmentation occurs) into sea water which has been diluted by the addition of equal parts of distilled water, the egg takes up water, swells, and causes the membrane to burst. Part of the protoplasm then flows out, in one egg more, in another less. If these eggs are afterward brought back into normal sea water those fragments which contain a nucleus begin to divide and develop.1 It was found that the degree of development which such a fragment reaches is a function of its mass; the smaller the piece, the sooner as a rule its development ceases. The smallest fragment which is capable of reaching the pluteus stage possesses the mass of about one-eighth of the whole egg. Boveri has since stated that it was about one twenty-seventh of the whole mass. Inasmuch as only the linear dimensions are directly measurable, a slight difference in measurement will cause a great discrepancy in the calculation of the mass. Driesch's

results disagree with the statement of Boveri and support the observation of the writer. If we raise the question why such a limit exists in regard to the divisibility of living matter, it seems probable that only those fragments of an egg are capable of development into a pluteus which contain a sufficient amount of material of each of the three layers. If this be correct, it would certainly not suffice to mix the chemical constituents of the egg in order to produce a normal embryo ; this would require besides the proper chemical substances a definite arrangement or structure of this material. The limits of divisibility of a cell seem therefore to depend upon its physical structure and must for this reason vary for different organisms and cells. The smallest piece of a sea-urchin egg that can reach the pluteus stage is still visible with the naked eye, and is therefore considerably larger than bacteria or many algas, which also may be capable of further division.

8. The most important fact which we gather from these data is that the cytoplasm of the unfertilized egg may be considered as the embryo in the rough and that the nucleus has apparently nothing to do with this predetermination. This must raise the question suggested already in the third chapter whether it might not be possible that the cytoplasm of the eggs is the carrier of the genus or even species heredity, while the Mendelian heredity which is determined by the nucleus

adds only the finer details to the rough block. Such a possibility exists, and if it should turn out to be true we should come to the conclusion that the unity of the organism is not due to a putting together of a number of independent Mendelian characters according to a "pre-established plan," but to the fact that the organism in the rough existed already in the cytoplasm of the egg before the egg was fertilized. The influence of the hereditary Mendelian factors or genes consisted only in impressing the numerous details upon the rough block and in thus determining its variety and individuality; and this could be accomplished by substances circulating in the liquids of the body as we shall see in later chapters.

I. The action of the organism as a whole seems nowhere more pronounced than in the phenomena of regeneration, for it is the organism as a whole which represses the phenomena of regeneration in its parts, and it is the isolation of the part from the influence of the whole which sets in action the process of regeneration. The leaf of the Bermuda "life plant"— Bryopliyllum calycinum — behaves like any other leaf as long as it is part of a healthy whole plant, while when isolated it gives rise to new plants. The power of so doing was possessed by the leaf while a part of the whole, and it was the "whole" which suppressed the formative forces in the leaf. When a piece is cut from the branch of a willow it forms roots near the lower end and shoots at the upper end, so that a tolerably presentable "whole" is restored. How does the "whole" prevent the basal end of the shoot from forming roots as long as it is part of the plant? A certain fresh-water flatworm has the

piece is excised between the head and the pharynx a new head is formed at the oral end, a new tail at the opposite end, and in the middle of the remaining old tissue a new mouth and pharynx is formed. How does the "whole" suppress all this formative power in the part before the latter is isolated? It almost seems as if the isolation itself were the emancipation of the part from the tyranny of the whole. The explanation of this tyranny or of the correlation of the parts in the whole is to be found, however, in a different influence. The earlier botanists, Bonnet, Dutrochet, and especially Sachs, x pointed out that the phenomena of correlation are determined by the flow of sap in the body of a plant. These authors formulated the idea that the formation of new organs in the plant is determined by the existence of specific substances which are carried by the ascending or descending sap. Specific shootproducing substances are carried to the apex, while specific root -producing substances are carried to the base of a plant. When a piece is cut from a branch of willow the root-forming substances must continue to flow to the basal end of the piece, and since their further progress is blocked there they induce the formation of roots at the basal end. Goebel2 and de Vries have

a Goebel, K.t Einleitung in die experimenlelle Morphologic der Pflanzen, accepted this view and the writer made use of it in his first experiments on regeneration and heteromorphosis in animals. * At that time the idea of the existence of such specific organ-forming substances was received with some scepticism, but since then so many proofs for their existence have been obtained that the idea is no longer questioned. Such substances are known now under the name of "internal secretions*' or "hormones"; their connection with the theory of Sachs was forgotten with the introduction of the new nomenclature. It may be well to enumerate some of the cases in which the influence of specific substances circulating in the blood upon phenomena of growth has been proven. One of the most striking observations in this direction is the one made by Gudernatsch on the growth of the legs of tadpoles of frogs and toads. 2 The young tadpoles have no legs, but the mesenchyme cells from which the legs are to grow out later are present at an early stage. From four months to a year or more may elapse before the legs begin to grow. Gudernatsch found that legs can be induced to grow in tadpoles at any time, even in very young specimens, by feeding them with the thyroid gland (no matter from what

1 Loeb, J., Untersuchungen zur physiologischen Morphologie der Tiere. I. Heteromorphose. Wurzburg, 1891. II. Organbildung und Wachsthum. 1892. Reprinted in Studies in General Physiology. Chicago, 1906. | animal). No other material seems to have such an >' effect. The thyroid contains iodine, and Morse1 states that if instead of the gland, iodized amino acids are fed to the tadpole the same result can be produced. We must, therefore, draw the conclusion that the normal outgrowth of legs in a tadpole is due to the presence in the body of substances similar to the thyroid in their action (it may possibly be thyroid substance) which are either formed in the body or taken up in the food.

Thus we see that the mesenchyme cells giving rise to legs may lie dormant for months or a year but will grow out when a certain type of substances, e. g., thyroid, circulates in the blood. There may exist an analogy between the activating effect of the thyroid substance and the activating effect of the spermatozoon or butyric acid (or other parthenogenetic agencies) upon the egg, but we cannot state that the thyroid substance activates the mesenchyme cells by altering their cortical layer.

The fact that the substance of the thyroid may induce general growth in the human is too well known to require more than an allusion in this connection. When growth stops in children as a consequence of a degeneration of the thyroid, feeding of the patient with thyroid again induces growth. It may also suffice tnerely to call attention to the connection between acromegaly and the hypophysis. acted as a regulator of the phenomena of metamorphosis in animals, but it was possible to show by simple experiments that the central nervous system does not play this r61e and that the regulator must be the blood or substances contained therein. In the metamorphosis of the Amblystonia larva the gills at the head and tail undergo changes simultaneously, the gills being absorbed completely. The writer showed that in larvae in which the spinal cord was cut in two, no matter at which level, — the sympathetic nerves were in all probability also cut — the two organs continued to undergo metamorphosis simultaneously. x Uhlenhuth found that if the eye of a salamander larva is transplanted into another larva the transplanted eye undergoes its metamorphosis into the typical eye of the adult form, simultaneously with the normal eyes of the individual into which it was transplanted.2 These and other observations of a similar character leave no doubt that substances circulating in the blood and not the central nervous system are responsible for the phenomena of growth and metamorphosis.

An interesting observation on the r61e of internal secretion in growth was made by Leo Loeb.3 When the fertilized ovum comes in contact with the wall of the uterus it calls forth a growth there, namely the formation of the maternal placenta (decidua). This author showed that the corpus luteum of the ovary gives off a substance to the blood which alters the tissues in the uterus in such a way that contact with any foreign body induces this deciduoma formation. The case is of interest since it indicates that the substance given off by the corpus luteum does not induce growth directly, but that it allows mechanical contact with a foreign body to do so while without the intervention of the corpus luteum substance no such effect of the mechanical stimulus would be observable. The action of the substance of the corpus luteum is independent of the nervous system, since in a uterus which has been cut out and re transplanted the same phenomenon can be observed. Bouin and Ancel1 have shown that the corpus luteum, which in the case of pregnancy continues to exist for a long time, is responsible for the changes in the mammary gland in the first half of pregnancy, when an active cell proliferation takes place in the gland. This process can be interrupted by destroying the corpus luteum artificially. During the second half of gravidity no further cell proliferation takes place, but the cells begin to secrete milk while during the period of cell proliferation such secretions do not occur.

Claude Bernard and Vitzou had shown that the period of growth and moulting of the higher Crustacea is accompanied by a heaping up of glycogen in the liver and subdermal connective tissue. Smith1 found that during the period between two moultings, when there is no growth, the storage cells are seen to be filled with large and numerous fat globules instead of with glycogen. He also found that in the Cladocera "the period of active growth is accompanied by glycogen — as opposed to fat — metabolism. ' ' He observed, moreover, that if Cladocera are crowded at a low temperature the fat metabolism (with inhibition to growth) is favoured, while at high temperatures and with no crowding of individuals the glycogen metabolism is favoured. In the latter case a purely parthenogenetic mode of propagation is observed, while in the former sexual reproduction takes place. The effect of crowding of individuals is possibly due to products of excretion, which then act on growth and reproduction indirectly by changing the "glycogen metabolism" to "fat metabolism."

All these cases agree in this, that apparently specific substances induce or favour growth, not in the whole body, but in special parts of the body. Sachs suggested that there must be in each organism as many specific organ-forming substances as there are organs in the body. ence of such "organ-forming" substances (which may or may not be specific) and of their flow in definite channels explains the inhibitory influence of the whole on the parts as well as the unbridled regeneration of the isolated parts.

2. We have seen that the resting egg can be aroused to development and growth by substances contained in a spermatozoon or by certain other substances mentioned in the preceding chapter. We will assume that plants contain a large number of cells or buds which are comparable to the resting egg cell, but which can be aroused to action by certain substances circulating in the sap; and that the same is effected for animal cells by substances in the blood. In plants the cells which can be aroused to new growth have very often a rather definite location while in lower animals they are more ubiquitous. For .experimental purposes organisms where these buds have a definite location are more favourable, since we are better able to study the mechanism underlying the process of activation and inhibition (correlation). When a leaf of the plant Bryophyllum calycinum is cut off and put on moist sand or into water or even into air saturated with water vapour, new plants will arise from notches of the leaf. This is the usual way of propagating the plant and in no other part of the leaf except the notches will new plants arise. These notches therefore contain cells comparable to seeds or to unfertilized eggs or to the mesenchyme

FIG. 1 6. Growth of roots and shoots in few notches of an isolated leaf of Bryopliyllum ca.ycinum be present in the leaf; but as long as it is connected with a normal plant they will be carried by the circulation to the growing points of the stem and of the roots and they cannot reach the notches; while when we detach the leaf, either a new distribution or a new flow of liquids will be established whereby the substances reach some of the notches ; and in these notches new roots and a new shoot will be formed. When we cut off a leaf and put it into moist air, not all but only a few of the notches will, as a rule, grow out (Fig. 16);

but when we isolate each notch leaving as much of the rest of the leaf as possible attached to it, each notch will give rise to a new plant.1 (Fig. 17.) We see, therefore, that it does not even require a whole plant to cause inhibition but that we may observe the tyranny of the whole over the parts in a single leaf. The explanation is as follows : When we isolate a leaf, some of the notches will commence t o grow into new plants and this growth will arrest the develop-

to roots and a shoot, but the growth will be other notches of less rapid than in Fig. 16. Figs. 16 and 17 were two leaves taken from the same node of a plant. their development was suppressed by the whole plant. The explanation is the same; those notches which begin to grow first will attract the flow of substances to themselves, thus preventing the other notches from getting those substances. This idea is supported by the fact that if all the notches are isolated from the leaf each notch will give rise to a slowly growing 1 Loeb, J., Bol, Gazette, 1915, lx., 249,

plant, while if the leaf is not cut into pieces, and a few notches only grow out, their growth is much more rapid. In all these experiments the idea that the "isolation** in itself is responsible for the growth still presents itself. It can be disposed of by the following experiment which never fails. Three leaves of Bryophyllum calycinum are suspended in an atmosphere saturated with water vapour but their tips are submersed in water (Figs. 1 8, 19, 20). The first leaf, Fig. 20, is entirely separated from its stem, the second leaf, Fig. 19, remains connected with the adjacent piece of stem, and the third leaf, Fig. 1 8, remains also connected with this piece of stem but the latter still possesses both leaves. The first leaf, Fig. 20, produces new roots and shoots in the submerged part in a few days; the second leaf, Fig. 19, produces no roots or shoots for a long time. This might find its explanation by the assumption that the first leaf, being more isolated than the second, regenerates more quickly. But this explanation becomes untenable owing to the fact that the third leaf, Fig. 18, being less isolated than both (possessing a second leaf in addition to the stem), forms new roots and shoots also more quickly than the second leaf. The phenomena become intelligible in the following way. The fact that in the second leaf shoots and roots are formed very late, if at all, finds its explanation not in the lessened isolation of this leaf, but in the fact that the formation of a new shoot or of a callus in the piece of stem takes place

more quickly than the formation of roots and shoots in the notches of a completely isolated leaf. The stem acts therefore as a centre of suction for the flow of substances from the leaf and this prevents or retards the formation of roots and shoots in the notches. In the isolated leaf of Bryophyllum calycinum no callus formation takes place and hence no flow of the sap away from the leaf will occur. This will allow one or more of the notch buds of this leaf to grow out and then a flow will be established towards these growing buds.

In the third specimen, Fig. 1 8, the presence of two leaves suppresses or, as a rule, retards the growth of a shoot on the stem and possibly also the flow from one leaf may block to some extent the flow from the opposite leaf if the piece of stem is very short. This puts the leaves in a condition not as good as that in leaf Fig. 20, but better than in leaf Fig. 19.' In the normal plant the buds in the notches of the leaf remain dormant since the flow of the ''stimulating" substances takes place towards the tips of the stem and root, and because these substances are retained there in excess. This is probably the real basis of the mysterious dominance of the "whole" over its "parts" or of the anlagen of the tip of the stem over those farther below. When a piece of the stem of Bryophyllum is cut off and its leaves are removed, the two apical buds will grow out first. This "dominance" finds its explanation probably in the anatomical structure and the mechanism of sap flow which tend to bring the "stimulating" substances first to the anlagen in the tip. In Laminaria Setchell has been able to show directly that regeneration always starts from that tissue which conducts the nutritive material.

1 With larger leaves the experiment may also succeed in moist air. and remove all the leaves, new shoots will be formed from the two apical buds of the stem, and roots will arise from the most basal nodes ; provided that the stem is suspended in air saturated with water vapour. The growth in such a stem deprived of all leaves is slow. If we remove all the leaves on such a piece of stem except the two at the apical end, the stem will form only roots, but these will develop much more rapidly than on a stem without leaves. If we remove all the leaves except the two at the basal end, the stem will only form shoots (at the apical end) but these will develop much more rapidly than in a leafless stem. Hence the leaves accelerate the growth of roots towards the basal end and inhibit it towards the apical end; and they favour the growth of shoots towards the apical end and inhibit it in the nodes located nearer the base.

We thus see that while the stem inhibits the growth of the leaves connected with it, the latter accelerate the growth in the stem. Both facts can probably be explained on the same basis ; namely, on the assumption that it is the flow of substances from the leaf to the stem which inhibits the growth of the notches and accelerates the growth of the buds in the stem. On this assumption it would also follow that the leaves send root-forming substances towards the basal and shootforming substances towards the apex of the stem. It also seems to follow from recent as yet unpublished experiments by the writer that the root-forming substances

are associated or identical with the substances which cause geotropic curvature in the stem. These observations show that the phenomena of correlation or of the influence of the whole over the parts is due to peculiarities of circulation or the flow of sap ; and that the isolation prevents the sap from flowing away to other parts of the plant. There is no need for assuming the existence of a mysterious force which directs the piece 3. Phenomena of inhibition or correlation such as we have described in Bryophyllum are not lacking in the regeneration of animals, as experiments on Tubularia show.1 Tubularia mesembryanthemum (Fig. 21) is a hydroid consisting of a long stem terminating at

the other end in a polyp. The writer found that if we cut a piece from a stolon and suspend it in an aquarium it forms as a rule a polyp at either end (Fig. 22), 1 Loeb, J., Untersuchungen zur physiologischen Morphologic. I. Heteromorphose. 1891. II. Organbildung und Wachsthum. Wurzburg, 1892. but the velocity with which the two polyps are formed is not the same, the polyp at the oral end of the piece being formed much more rapidly — a day or one or two weeks sooner — than the aboral polyp. The process of polyp regeneration at the aboral pole could, however, be accelerated and its velocity made equal to that of the regeneration of the oral polyp by suppressing the formation of the latter. This was accomplished by depriving the oral pole of the oxygen necessary for regeneration, e. g.t by merely putting the oral end of the piece of stem into the sand. It was, therefore, obvious that the formation of the oral polyp retarded the formation of the aboral polyp. This inhibition might have been due to the fact that a specific organ-forming material needed for the formation of a polyp existed in sufficient quantity in the stem for the formation of one polyp only at a time. This idea, however, was found to be incorrect since when the stem was cut into two or more pieces each piece formed a polyp at once at its oral pole and regenerated the aboral polyps also, but again with the usual delay. It seemed more probable then that the cause of the difference in the rapidity of polyp formation at both ends lay in the fact that certain material flowed first to the oral pole and induced polyp formation here but that this flow was reversed as soon as the polyp at the oral pole was formed or as soon as the formation of the oral polyp was inhibited by lack of oxygen. The partial