The Organism as a Whole, from a Physicochemical Viewpoint

or full completion of the formation of the oral polyp acted as an inhibition to the further flow of material to this pole. This idea was supported by an observation made independently by Godlewski and the writer that if a piece of stem be cut out of a Tubularia, and if the piece be ligatured somewhere between the two ends, the oral and the aboral polyps are formed simultaneously. This would be comprehensible on the assumption that the retarding effect which the formation of the oral has on the* aboral polyp was indeed of the nature of a flow of material towards the oral pole.

Miss Bickford1 found that the difference in time between the formation of the two polyps disappears also when the piece cut from the stem becomes so small that it is of the order of magnitude of a single polyp. In that case two incomplete polyps are formed simultaneously at each end (Fig. 23). The new head in the regeneration of Tubularia arises, as Miss Bickford observed, from the tissue near the wound. At some distance from the wound in the old tissue two rows of tentacles arise, which are noticeable as rows of longitudinal lines inside the stem before the head is formed. Driesch noticed that the newly formed head is the smaller the smaller the whole

piece. (This is true, however, only in rather small pieces.) There is, therefore, in small pieces a rough proportionality between size of head and size of regenerating piece. Driesch1 uses this interesting fact to prove the existence of an entelechy, while we are inclined to see in it an analogue to the observation of Leo Loeb, that the velocity of the process of healing in the case of a deficiency of the epithelium decreases when the size of the uncovered area diminishes. While we do not wish to offer any suggestion concerning the mechanism of these quantitative phenomena — they may be related in some way with the velocity of certain chemical reactions — we see no reason for assuming that they cannot be explained on a purely physicochemical basis.

The writer noticed that certain pigmented cells from the entoderm of the organism always gather at that end where a new polyp is about to be formed. These red or yellowish cells always collect first at the oral end of a piece of stem. It may be that certain substances given off by the pigmented cells at the cut end are responsible for the polyp formation, but this is only a surmise. Another suggestion made by Child,2 is that there exists an axial gradient in the stem whereby the cells

1 Driesch, H., Science and Philosophy of the Organism, i., 127, 2 Child, C. M., " Die physiologische Isolation von Teilen des Organismus," Roux's Vortrage und Aufsdtze, Leipzig, 1911. regenerate the more quickly the nearer they are to the oral pole. If this were correct, and we cut a long piece from the stem of a Tubularia and bisect the piece, the oral pole of the anterior half should regenerate more quickly than the oral pole of the posterior half. According to the writer's observations on a Tubularian (T. croced) growing in the estuaries near Oakland, California, both oral ends regenerate equally fast in such cases.

4. The phenomena of regeneration in Cerianthus membranaceus, a sea anemone, can be easily understood from the experiments on Tubularians, if we imagine the body wall of Cerianthus to consist of a series of longitudinal elements running parallel to the axis of symmetry of the animal from the tentacles to the foot. The number of these elements may be supposed to correspond to the number of tentacles in the outer row of the normal animal. Each such element behaves like a Tubularian, with this difference, however, that the elements in Cerianthus are more strongly polarized than in Tubularia, and that each one is able to form a tentacle at its oral pole only. This fact can be nicely illustrated in the following way : if a square or oblong piece (abed, Fig. 24) be cut from

the body wall of a Cerianihus in such a way that one side, a c, of the oblong is parallel to the longitudinal axis of the animal, tentacles will grow on one of the four sides only; namely, on the side a b.1 (Fig. 25.) The other three free edges are not able to produce tentacles. If an incision be made in the body wall of a Cerianthus , tentacles will grow on the lower edge of the incision (Fig. 26). The writer tried whether or not by tying a ligature around the middle of a piece of an Actinian this polarity could be suppressed; but the experiments did not succeed, inasmuch as the cells compressed by the ligature died, and were liquefied through bacterial action so that the pieces in front and behind the ligature fell apart. It is therefore impossible to decide whether or not a current or a flow of substances in a certain direc-

1 Loeb, J., "Untersuchungen zur physiologischen Morphologic der Tiere." tion through these elements is responsible for this polarity, though this may be possible. The writer found, however, that one condition is necessary for the growth and regeneration of tentacles which also plays a role in the corresponding phenomena in plants, namely turgidity. The tentacles of Cerianihus are hollow cylinders closed at the tip, and by liquid being pressed into them they can be stretched and appear turgid. If, however, an incision is made in the body, the tentacles above the incision can no longer be stretched out. In one experiment the oral disk of a Cerianthus was cut off; very soon new tentacles began to grow at the top, and after having reached a certain size, an incision was made in the animal. The tentacles above the incision collapsed in consequence and ceased to grow, while growth of the others continued. On the lower edge of the incision new tentacles began to grow.

It seems also possible that Morgan's well-known experiment on regeneration mPlanaria can be explained by a flow of substances. He1 found that if a piece a c d b be cut out of a fresh-water Planarian at right angles to the longitudinal axis (Fig. 27), at the front end a new normal head, at the back end a new tail, will be regenerated (Fig. 28) ; but that if a piece a c d b be cut from a Planarian obliquely (Fig. 29) instead of at right angles to the longitudinal axis a tiny head is formed at the foremost corner of the piece a and a tiny tail at the hindmost corner b (Fig. 30) . Why is it that in the oblique piece the head is formed in the corner and not all along the cut surface as is the case when the cut is made at right angles to the longitudinal axis? The writer is inclined to believe that the right answer to this question has been given by Bardeen. x This author has pointed out the apparent role that the circulatory (or so-called digestive) canals in Planarians play in the localization of the phenomena of regeneration, inas-much

as the new head always forms symmetrically at the opening of the circulatory vessel or branch which is situated as much as possible at the foremost end of the regenerating piece of worm. He assumes that through muscular action the liquids of the body are forced to stream toward this end, and that this fact has some connection with the formation of a new head. There can be no doubt that the facts here mentioned agree with Bardeen's suggestion. The oblique pieces in Morgan's experiments which at first have the heads and tails

outside the line of symmetry of the middle piece, gradually assume a normal position (Figs. 31, 32). The writer is inclined to believe that this is due to mechanical conditions. The head a e c of such an oblique piece is asymmetrical, the one side a e being less stretched than the other e c. The higher tension of the piece e c will have the effect of bringing e nearer c, since we know that acid formation and hence energy production increases in proportion to surface, i. e., it must be the greater the more it is stretched. The reverse is true for the tail df b, and the effect here will be that/

will be pulled nearer d. In this way purely mechanical conditions are responsible for the fact that the soft tissues of the animal are gradually restored to their true orientation. As a final possible example of the influence of internal secretion or substances contained in the blood may be mentioned the following curious observation of Przibram.1 In a crustacean, Alpheus, the two chela3 (pincers) are not equal in size and form, one being very much larger than the other. Przibram found that when he cut off the larger pincer in such crustaceans the remaining pincer assumes in the next moulting the size and shape of the removed large pincer; while in place of the removed pincer one of the small type is produced. Hence a reversal of the two pincers is thus brought about. If later on the large pincer is again cut off the process is repeated and the original dissymmetry is restored. Przibram was able to show that the nervous system has no connection with this phenomenon.

The elements which have entered into the discussion thus far are, first, the flow of substances in preformed channels; second, the existence of general or specific substances required for the growing or regenerating organ. A third element is to be added; namely the "suction" effect upon these substances of a developing organ. Thus we see that if one or a few of the notches in a leaf of Bryophyllum grow out the other notches of the leaf are inhibited from growing. There is enough material present in the leaf for all the notches to grow into shoots as is proved by the fact that all will grow out if they are isolated from each other. This was explained on the assumption that the notches of a whole which happen to develop first, create a flow of these substances from the rest of the leaf to themselves and thus prevent any getting to the other notches. We stated that this is supported by the fact that the few notches growing out in an undivided leaf grow more rapidly than the many shoots growing from each notch of a divided leaf. But why should a growing shoot or a growing point in general produce such a suction? I think this may be possible on the assumption that the consumption of these substances by the growing organs causes a low osmotic pressure of these substances in the growing region and this fall of osmotic potential will act as a cause for the further flow. This brings about the apparent "suction" effect of the growing elements upon the flow of substances.

5. We mentioned that when a piece is cut from a Planaria between pharynx and head a new mouth is formed in the middle. It should also be mentioned that according to Child the piece after regeneration is smaller than it was before.1 This indicates that material in the old cells has been digested or has undergone hydrolysis in order to furnish the nutritive material for the new head and tail, since the piece cannot take up any food from the outside before a mouth is formed. These phenomena of autodigestion — the process itself will be discussed in the last chapter — seem to occur in many (if not all) phenomena of regeneration. It may

be that the collecting of red cells at the end in a Tubularian where regeneration is about to begin has to do with the furnishing o f material by selfdigestion, since these cells are partly at least destroyed i n the process. It is of interest to look for more examples of autodigestion accompanying phenomena of regeneration. The writer has observed more closely the transformation of an organ into more undifferentiated material in Campanularia (Fig. 33), a hydroid.1 This organism shows a remarkable stereotropism. Its stolons attach themselves to solid bodies, and the stems appear on the side of the stolon exactly opposite the point or area of contact with the solid body. The stems 1 Loeb, J., Am, Jour. Physiol., 1900, iv., 60.

grow, moreover, exactly at right angles to the solid surface element to which the stolon is attached. If such a stem be cut and put into a watch glass with sea water, it can be observed that those polyps which do not fall off go through a series of changes which make it appear as if the differentiated material of the polyp were transformed into undifferentiated material. The tentacles are first put together like the hairs of a camel's-hair brush (Fig. 34), and gradually the whole fuses to a more or less shapeless mass which flows back into the periderm (Fig. 35). It follows from this that in this process certain solid constituents of the polyp, e. g., the cell walls, must be liquefied. This undifferentiated material formed from the polyp may afterward

flow out again, giving rise to a stolon or a polyp; to the former where it comes in contact with a solid body, to the latter where it is surrounded by sea water. These observations suggest the idea of reversibility of the process of differentiation of organs and tissues, in certain forms at least. We have to imagine that some of the cells or interstitial tissue is digested and that as a consequence the organ loses its characteristic shape. Giard and Caullery have found that a regressive metamorphosis occurs in Synascidians, and that the animals hibernate in this condition. The muscles of the gills of these animals are decomposed into their individual cells. The result is the formation of a parenchyma which consists of single cells and of cell aggregates resembling a morula. x

Driesch, 2 experimenting on the regeneration of an Ascidian, found that when he cut off the gills and siphons of the animal the portion removed was able to regenerate a whole animal. The gill-piece excised contained no heart, no intestine, and no stolon, and all these organs were regenerated from the gills. In a number of cases the regeneration took place by bud formation at the edge of the wound, but in other cases the gills were transformed into an undifferentiated mass of tissue from which the missing parts of the animals arose by budding and new gills were formed.

It is probable that the two cases are only quantitatively different. In both, autodigestion of certain cell constituents and possibly of whole cells must take place in order to obtain material for the formation of the lost part of the Ascidian. If an interstitial tissue is digested it becomes a question of how much of this tissue undergoes hydrolysis. If there is little destroyed the old shape of the gills remains, if too much is digested the old gills become a shapeless mass in which a certain number of the old cells are maintained and give rise to the new animal by cell division. The material for the new organs must of course be furnished from old cells which have been digested.

If regeneration takes place in pieces which take up no food the newly formed organs must originate from material absorbed from cells of the animal which are hydrolyzed and whose material serves as food for those cells which grow. Very often this process of digestion takes place without loss of the total form of the organ and is overlooked by the pure morphologists. In Campanularia also the process of collapse described above is only apparent in a fraction of the cases as in Driesch's observations on Clavellina. x It is also possible that the red and yellow entoderm cells which gather at the end where the new polyp forms furnish the material which is utilized for the process of growth of the cells from which the tentacles arise (with or without giving off specific "hormones" besides).

1 One author, Miss Thatcher, in trying to repeat these observations, did not notice the total collapse of the tissues and concluded that my observations must have been wrong. The writer is fairly certain that his observations were correct. 6. We have mentioned the ideas concerning a design, or "entelechy, " acting as a guide to the developing egg and have shown that this revival of Platonic and Aristotelian philosophy in biology was due to a misconception; namely, that the egg consisted of homogeneous material which was to be differentiated into an organism. For this supernatural task supernatural agencies seemed required. But we have seen that the unfertilized egg is already differentiated in a way which makes the further differentiation a natural affair. This idea of a quasi superhuman intelligence presiding over the forces of the living is met with in the field of regeneration, and here again it is based upon a misconception. The lens of the eye is formed in the embryo from the epithelium lying above the so-called optic cup (the primitive retina). Where this retina touches the epithelium the latter begins to grow into the cup, the ingrowing piece of epithelium is cut off and forms the lens, which probably under the influence of substances secreted by the optic cup becomes transparent. Certain animals like the salamander are able to form a new lens when the old one has been removed by operation, but the new lens is formed in an entirely different way; namely, from the upper edge of the ins. G. Wolf, who observed this regeneration used it to endow the organism with a knowledge of its needs; the idea of a Platonic preconceived plan or an Aristotelian purpose suggested itself. But it can be shown that the

organism does in this case what it is compelled to do by its physical and chemical structure. Uhlenhuth1 has shown by way of tissue culture that the cells of the iris cannot grow and divide as long as they are full of pigment granules as they normally are. When the fine superficial membrane of the iris is torn the pigment granules fall out and the cells can now grow and multiply. If the lens is taken out of the eye of the salamander the fine membrane of the iris is torn and the pigment cells at the edge (especially the upper edge) lose their pigment granules which fall down on account of their specific gravity. As soon as this happens the cells will proliferate. A spherical mass of cells is formed which become transparent and which will cease to grow as soon as they reach a certain size. The unanswered question is: Why does the mass of cells become transparent so that it can serve as a lens? The answer is that young cells when put into the optic cup always become transparent no matter what their origin; it looks as if this were due to a chemical influence exercised by the optic cup or by the liquid it contains. Lewis has shown that when the optic cup is transplanted into any other place under the epithelium of a larva of a frog the epithelium will always grow into the cup where the latter comes in contact with the epithelium; and that the ingrowing part will always become transparent. This leaves us then with one puzzle still: Why is the 1 Not yet published.

growth of the lens limited? The limitation in the growth of organs is one of the most important problems in growth and organ formation, though unfortunately our knowledge of this topic is inadequate. 7. The botanist J. Sachs was the first to definitely state that in each species the ultimate size of a cell is a constant, and that two individuals of the same species but of different size differ in regard to the number, but not in regard to the size of their cells.1 Amelung, a pupil of Sachs, determined the correctness of Sachs's theory by actual counts. Sachs, in addition, recognized that wherever there were large masses of protoplasm, e. g., in siphoneas and other cceloblasts, many nuclei were scattered throughout the protoplasm. He inferred from this that "each nucleus is only able to gather around itself and control a limited mass of protoplasm/'2 He points out that in the case of the animal egg the reserve material — fat granules, proteins, and carbohydrates— are partly transformed into the chromatin substances of the nuclei, and that the cell division of the egg results in the cells reaching a final size in which each nucleus has gathered around itself that mass of protoplasm which it is able to control. Morgan3 and Driesch4 tested and confirmed the idea of Sachs for

the eggs of Echinoderms. We stated in the previous chapter that Driesch produced artificially larvae of sea urchins of one-eighth, one-fourth, and one-half their normal size by isolating a single cleavage cell in one of the first stages of segmentation of the fertilized seaurchin egg. He counted in each of the dwarf gastrulae resulting from these partial eggs the number of mesenchyme cells and found that the larvae from a one-half blastomere possessed only one-half, those from a onefourth blastomere only one-fourth, and those from a one-eighth blastomere only one-eighth of the number of cells which a normal larva developing from a whole egg possessed. Moreover, he could show that when two eggs were caused to fuse so as to produce a single larva of double size, the gastrulae of such larvae had twice the number of mesenchyme cells. Driesch drew the conclusion from his observations that each morphogenetic process in an egg reaches its natural end when the cells formed in the process have reached their final size.

Since each daughter nucleus of a dividing blastomere has the same number of chromosomes as the original nucleus of the egg, it is clear that in a normally fertilized egg each nucleus has twice the mass of chromosomes that is contained in the nucleus of a merogonic egg, i. e.t an enucleated fragment of protoplasm into which a spermatozoon has entered and which is able to develop. Such a fragment has only the sperm nucleus. This phenomenon of merogony was discovered by Boveri and was elaborated by Delage.1 Boveri, in comparing the final size of the cells in normal and merogonic eggs after the cell divisions had come to a standstill, found that this size is always in proportion to the original mass of the chromatin contained in the egg; the cells of the merogonic embryo, e. g., the mesenchyme cells, are only half the size of the same cells in the normally fertilized embryo. Driesch furnished a further proof of Boveri's law, that the final ratio of the mass of the chromatin substance in a nucleus to the mass of protoplasm is a constant in a given species. Driesch compared the size of the mesenchyme cells in a sea-urchin embryo produced by artificial parthenogenesis with those of a normally fertilized egg and found them half of the size of the latter. When the fertilized eggs and the parthenogenetic eggs are equal in size from the start, — which is practically the case if eggs of the same female are used, — the process of the formation of mesenchyme cells comes to a standstill when their number in the normally fertilized eggs is half as large as the final number in the parthenogenetic egg.a Boveri's results as well as those of Driesch were obtained by counting the cells formed by eggs of equal size and not by simply measuring the size of the cells. It is most remarkable that certain apparent exceptions

to Boveri's law which Driesch has actually found had been predicted by Boveri. These facts show that the growth of an organ comes to a standstill when a certain size is reached or a certain number of cells are formed. We cannot yet state why this should be, but we are able to add that the formation of a lens of normal size in the regeneration of the eye is in harmony with the phenomena in the embryo. There seems therefore no reason for stating that the regeneration of the lens cannot be explained on a purely physicochemical basis. The only justification for such a statement on the part of Wolf is that he was not in possession of the more complete set of facts now available through the work of Fischel and Uhlenhuth.

The healing of a wound is a process essentially similar to the regeneration of the lens. Normally the cells which begin to proliferate after a wound is made in the skin lie dormant, inasmuch as they neither grow nor divide. When a wound is made certain layers of epidermal cells undergo rapid cell division. Leo Loeb1 has studied this case extensively. He found that if the skin is removed anywhere, epidermis cells from the wound edge creep upon the denuded spot and form a covering. This may be a tropism (stereotropism) or it ^ may be a mere surface tension phenomenon. Next a I rapid process of cell division begins in the cells adjacent to the wound these cells having been heretofore dormant.

He is inclined to attribute this increase in the rate of cell division to the stretching of the epithelial cells, and he is supported in this reasoning by the observation that the larger the wound the more rapid the process of healing.1 During wound healing the mitoses first increase markedly in the old epithelium. With the closure of the wound a sudden fall in the mitoses takes place. The closure of the wound causes an increase in the number of epithelial rows over the defect. This increase is therefore reached at an earlier period in the larger wound since the process of mitosis is more rapid here. Leo Loeb thinks that the pressure of the epithelial cells upon each other leads to a rapid diminution in the mitotic proliferation.2

2 The excessive formation of epithelial cells in the healing of wounds has led the older pathologists to the generalization that if something is removed in the body an excessive compensation will take place. The formation of antibodies has even been explained on this basis by Weiggert and Ehrlich in their side-chain theory. As a matter of fact, this generalization is entirely incorrect and in regeneration of starfish, actinians, flatworms, annelids, and possibly in all forms the reverse is true; e. g.t if we cut off the anterior half of the body in Cerianthus less is reproduced than was cut away namely only tentacles and the mouth, but not the missing piece of the body. Weiggert's conception of regeneration was probably based on the phenomenon of the healing of wounds, but the excessive epithelium formation in this case is not the expression of a general law of regeneration but of the peculiar mechanical conditions which lead to mitoses. It would be a very strange coincidence indeed if a theory of antibody formation based on such an erroneous generalization should be correct

Should it be possible that this is more generally the case, e. g.t also in the lens after it has reached a certain size? The conditions limiting growth require further investigation. It is hardly necessary to point out that in these cases we are seemingly dealing with cases of the inhibition of growth which cannot be explained by the tyranny of the whole over the parts, and that there must be conditions at work other than the mere flow of substances which can cause a cessation of growth. This can be illustrated by certain observations on the egg.