The Dynamics of Living Matter

As far as the method of regeneration is concerned, Miss Bickford has found that it does not consist in the growth of a new polyp from the old material, but in a direct transformation of the material of the stem into a new polyp. Miss Bickford observed this directly under the microscope in small pieces from the stem of a Tubularian, which were not even of the size of a normal polyp. In such cases the whole mass of the piece was transformed into a polyp. f In the case of the smallest pieces the result was still more striking. At each free end of the small piece of the stem tentacles and a proboscis were formed (Figs. 43 and 44), but inasmuch as there was no material left for the formation of a stem in addition to two polyps, or not even for two entire polyps, a kind of Janus head was formed, two faces or probosces of a polyp looking in opposite directions. No new outgrowth occurred, but the old tissues arranged themselves into a new shape, forming a polyp, while before they had formed part of the stem. The most remarkable fact was the transformation of certain cells of the entoderm into secretory cells of the stomach.

It is not yet possible to tell exhaustively which forces have to do with this transformation. The stem is surrounded by a chitinous layer. I have never observed the formation' Beginning of the formation of two polyps in- side a piece from a stem of Tubularia. of a polyp inside of the intact stem, but only where the cells inside the chitinous layer come in contact with the sea water. The mere dothelium. The analogy with similar cases suggests the possibility that

these pigments are respiratory pigments, serving a purpose similar to, e.g., the red blood corpuscles in our body. If we now cut out a piece from the stem of the hydroid, the opening at either end closes in an hour (more or less according to the temperature) by the cells of the cut end spreading out over the opening concentrically.* According to my observations, no piece of a hydroid can regenerate unless this circula- tion is established. This may be due to the fact that the circulation serves as a means of supplying oxygen, and a liberal supply of oxygen seems to be an absolute prereq- uisite for all phenomena of regeneration and growth. Any piece of a Tubularian, however, which can establish a cir- i ^ culation can form a polyp. Thus, when a stem is split U lengthwise, the cellular masses may become disconnected FIG. 45. into several pieces. Each such piece may form a polyp at

When we ligature a stem in the middle, the circulation will be inter- rupted, inasmuch as at a place where the ligature is made the septum The same specimen a little later, after the formation of the polyps was com- pleted. The chitinous tube was removed. is not perforated. Very soon, however, after the ligaturing, a perforation at the septum on either side of the ligature occurs, and the circulation is again established. One might think that the current just described was responsible for the phenomena of polarity in Tubu- larians, inasmuch as this current carried away certain material from the aboral pole. The direct observation supports this idea to some extent. As I pointed out fifteen years ago, the place where a new polyp will be formed is always recognizable some time before the actual regen- eration occurs, by the collecting of the red or yellow pigment granules in greater density at that spot. It agrees with this statement that if a piece be cut out from the stem of a Tubularian and suspended in sea water, the red pigment always collects first in great masses at the oral end, where the polyp is formed first, and only later at the other end. In my earlier writings on heteromorphosis I pointed out that this seems to be in harmony with Sachs's idea, inasmuch as it indicates a migration and collection of definite substances at the end of a regenerating piece as the cause of the formation of a new organ. Morgan and Miss Stevens raised the objection that after the formation of the polyp the rem- nants of these red granules are thrown out by the polyp. This seems to me in no way to speak against the possibility that the red granules contribute some substances necessary to the formation of the polyp. As is well known, the red blood corpuscles perish regularly in the body, and their products of decomposition form constituents of the bile. Yet nobody would think of using this fact as an argument against the importance of the red blood corpuscles or the bile.

I am inclined to be- lieve that Morgan and Miss Stevens underestimate the fact which Sachs tried to emphasize, that chemical processes underlie the phenomena of regeneration. But I am far from believing that the circulation current is the only factor in the transport of substances through the Tubularian. It is possible that in Tubularia we are dealing also with a current of sap through specific tissue, as is found in plants. Setchell has made it probable that in Laminaria regeneration always starts from that tissue which conducts the nutritive material. It may be that there exists a flow of material from cell to cell in the entoderm or ectoderm of the Tubu- laria or both, and that this flow occurs naturally from the aboral to the oral end, but that it is reversed in the aboral piece of the stem when a ligature is made in the stem. Even if the fact that the pigment gran- ules are carried away from the rest of the stem and are gathered at the oral end be responsible for the polarity, it remains to be ex- plained what keeps the granules rather at that than at the opposite end. These details still have to be worked out, but I believe that we may

consider it as established experimentally that the conditions which de- termine the morphological polarity are due to something of the nature of a current inside of the Tubularian. The mysterious morphological polarity is thus reduced to a polarity which can be expressed in physical or physicochemical terms. We see that this result differs in one point from Sachs's hypothesis. The latter includes the effect of specific sub- stances, while this condition does not appear in the results of our experi- ments. It is, however, hardly necessary to state that our experiments by no means exclude this possibility. I have discussed the case of regen- eration in Tubularians at some length, not only because it is well known to me through my own experiments, but also because on account of its simplicity, it lends itself better to a reduction of dynamically unintelligible morphological data to the more rationally expressible physi- cal or physicochemical conditions.

Osterhout and I tried to test the effects of a ligature on plants, espe- cially on willow twigs. As we have already stated, a piece cut out from a willow twig forms roots first at the basal and shoots at the apical end. The process of regeneration in this case differs in several essential fea- tures from that in Tubularians. The formation of the new organs occurs in the willow twig not at the cut end but at the anlage of the roots and shoots, both of which exist here normally. All that the opera- tion does in this case is to cause the anlage of roots which would never have developed now to grow out into roots. The reader should realize that the anlage of the roots which begin to grow in consequence of the cutting off of the twig is not injured by the operation and is often far removed from the wound. The idea that this anlage grows out be- cause the sap which would otherwise flow downwards is now blocked by the cut, and becomes available for the anlage of the roots, looks very plausible in the light of the actual facts. As part of the sap flow can be suppressed by a tight ligature around the rind of a stem, Osterhout and I tried the experiment of ligaturing a number of willow twigs in the middle; The result was that a ligature caused the root anlage above it and the shoots below it to develop, which without the ligature would not have developed. In the case of the willow, we are also deal- ing with a flow of material through conductive tissue, i.e. tissue through which nutritive material is conducted.

The phenomena of regeneration in Cerianthus can be easily under- stood from the experiments on Tubularians, if we imagine the body wall of Cerianthus to consist of a series of longitudinal elements which run parallel with the axis of symmetry of the animal from the tentacles to the foot. The number of these elements may be supposed to corre- spond to the number of the outer row of tentacles of the normal animal. Each such element behaves like a Tubu- larian, with this difference, however, that the elements in Cerianthus are more strongly polarized than Tubularia. No heteromor- phosis has thus far been produced in these elements in Cerianthus, and 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. 46) be cut from the body wall of a Cerianthus in such a way that one side, ac, 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 ab* The three other

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. 47). I have recently tried whether or not by tying a ligature round the middle of a piece of an Actinian this polarity could not be suppressed. But the experiments did not succeed, inasmuch as the cells compressed by the ligature died, and through bacterial action were liquefied so that the pieces in front and behind the ligature fell apart. It is therefore impossible to decide whether or not a condition of the nature of a current or a flow of substances in a certain direction through these elements is responsible for this polarity, though I consider this probable. I 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 Cerianthus 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 (Fig. 47). I have found that the turgid condition of the tentacles is neces-

* Loeb, Unttrsuchungen zur physiologisch.cn Morphologie der Thiere. sary for their growth. 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 at d, Fig. 47. The tentacles above the incision between b and c, Fig. 47, collapsed in consequence and ceased to grow, while growth of the others between a and b continued. On the lower edge of the incision new tentacles began to grow.

Child* has elucidated to some extent these phenomena of turgidity. Every tentacle is a hollow cylinder, and this cylinder continues down- ward where it communicates with the body cavity. When liquid is pressed into the tube from the body cavity, the tentacles are stretched ; but if the liquid leaves the tube, the tentacles relax also. If an incision is made below a tentacle into the wall of the body of a Cerianthus, no more liquid can be pressed into that tentacle, and it relaxes. Child con- firmed my observation, that regeneration of the tentacles in Cerianthus is no longer possible when they relax. He added a number of pretty demonstrations of the necessity of the turgidity of the tentacles for regeneration. He found, for instance, that if an incision is made into the foot of a Cerianthus and the edges of the wound are prevented from healing together the tentacles lose their turgidity and are no longer able to grow. He found, also, that the ten- tacles degenerate under such conditions.

It is unknown at present how the turgidity can influence growth in the tentacles of an Actinian. The observations on Cerianthus are comparable with those on Tubularia if we realize that the body wall in Cerianthus consists of a series of hollow cylinders or spaces each of which ends in a tentacle. The idea of an animal body consisting of a series of comparatively independent longitudinal elements recommends itself also for the understanding of a phenom- enon of regeneration in Ascidians. The Ascidian, Ciona intestinalis, has eyes (ocelli) at the oral as well as at the aboral opening of the body (Fig. 48). We may imagine that each ocellus is the end of one of the

An incision was made at c and new ocelli develop at both ends of the cut. longitudinal elements to which reference was just made. If a lateral incision be made in the body at c, not too far from the openings, ocelli will be formed at each free end of these elements. Here the longi- tudinal elements show heteromorphosis, inasmuch as they are capable of forming ocelli at both ends. I am inclined to believe that in each of these cases the individual longitudinal element represents a conductor for nutritive material or specific morphogenic substances in the sense of Sachs. It must remain undecided for the present whether this flow occurs through the hollow space' or through the tissue or certain cells of the tissue.

It had been known for a long time that if the head and the tail be cut off from a fresh-water Planarian, at the front end a new normal head, at the back end a new tail, will be regenerated (Fig. 49). Morgan* made the interesting observation that if a piece acdf be cut obliquely (Fig. 50) instead of at right angles to the V longitudinal axis from a canals in Planarians play in the locali- zation of the phenomena of regeneration, inasmuch 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 the muscular action the liquids of the body are forced to stream toward this end, and that this fact has some connection with the form- ation 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 have at first the heads and tails outside the line of symmetry of the middle piece, gradually assume afterward a normal position (Figs. 51-54). I am inclined to believe as Child

Successive stages in the regeneration of the oblique piece adcf of Fig. 50. does that this is due to purely mechanical conditions. The head of such an oblique piece is asymmetrical, the one side ab being less stretched than the other side be. The higher tension of the piece be will have the effect of bringing b nearer c. The reverse is true for the tail def, and the effect will here be that e 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.*

It was of interest to find out whether heteromorphosis could be pro- duced in Planarians. At my request Dr. Van Duyne undertook experi- ments in this direction and succeeded in a few cases.f Figure 55 shows one of these instances. On the right side of the animal the posterior part had been cut off. A new head which was directed backward was regenerated in place of the amputated part. Morgan was more suc- cessful later on. He obtained a larger number of heteromorphoses by cutting short pieces out of a Planarian than by cutting out long pieces. J

* It is in mv opinion not only unnecessary but directly confusing to introduce for the explanation of these phenomena of restitution such mystical forces or conceptions as Noll's " Morphresthesia," and similar things. He mentions that in the short pieces less "polarity" exists than in the long pieces; but as the conception of heteromorphosis is the opposite of polarity, Morgan's statement is only a different way of expressing the same fact. I remember that when Miss Bickford made her experiments on regeneration in Tubularians in my laboratory, I was struck with the fact that in the very small pieces cut out of a stem the polyps at the oral and the aboral end developed practically simultaneously. Here, too, polarity was less pronounced in small pieces than in large pieces. I believe the reason for this lies in the role which processes of the character of a current or a flow of material play in these phenomena. The red pigment, and possibly other substances which are of importance for regeneration, gather not in one point but in an area of the length of several millimeters, where a polyp is to be formed. If the regener- ating piece is in itself only a few millimeters long, the pigment must remain scattered equally over the small piece, and hence the polarity must disappear. Something similar may occur in the case of a Planarian. If the piece is very small, the head-forming material will remain equally distributed through the whole length of the piece, and hence the chance for the simultaneous formation of the head at either end is greater than in a large piece.

It is a general experience that in order to get a duplication of organs, the regenerating animal must be split into two pieces. Thus, in order to obtain two larvae from one egg, the egg must be cut into two, or the heap of cells must be separated into two parts. One might believe that in order to get two heads in front of a Planarian, the front end would have to be separated into two by a longitudinal incision. Two heads, however, often develop in front of a Planarian whose head has been cut off without such an incision. The explanation is obvious on the basis of Sachs's hypothesis. If the gathering of certain substances at the front end is the cause of the formation of a head, and if we assume with Bardeen that these substances are carried to the cut by the circu- latory system, it is comprehensible that in two different spots at the front end substances necessary for the formation of the head may gather.

5. ON THE INFLUENCE OF THE CENTRAL NERVOUS SYSTEM UPON REGENERATION AND ON PHENOMENA OF CORRELATION IN REGEN- It is rather remarkable that the central nervous system plays an important role in phenomena of regeneration. In 1889 I noticed that in Thysanozoon Brochii, a marine Planarian, the isolated head containing the ganglia is capable of rapid regeneration while the body without the ganglia shows less, or a slower regeneration.* The taking up of food is not responsible for this difference, since the head cannot take up food. That the taking up of food is not essential for regeneration follows also from the observations on the regeneration of pieces cut from the walls of Cerianthus. We must not overlook the fact that the reversible chemi- cal processes in the cells of an animal are liable to provide material for regeneration in the same way as the taking up of food.

A number of observers — T. H. Morgan, Child, Lillie, and Lillian Morgan — have since found that the cesophageal ganglia exercise a con- siderable influence upon regeneration in marine Planarians. f It is therefore obvious that there exists a typical difference be- tween fresh-water and marine Planarians, since in the fresh-water Planarians the presence of the cesophageal ganglia is not required for complete and rapid regeneration. This difference in the influence of the cesophageal ganglia in marine and fresh-water Planarians upon regeneration finds a probable expla- nation in a fact to which Bardeen has called attention; namely, that the longitudinal nerves which go through the whole body of the Planarians are very rich in ganglia in the fresh-water Planarians and very poor in ganglia in Thysa- nozoon.

Herbst J has discovered the most beautiful case of hetero- morphosis thus far known; FIG. 56. -AFTER HERBST. the place of an eye which has been cut off, an entirely different organ, an antenna, can be formed (Fig. 56). Herbst proved, moreover, that the experimenter has it entirely in his power to determine whether the Crustacean shall regenerate an eye in the place of the eye which has been cut off, or an antenna. It depends upon the fact whether or not in the operation the optic ganglion is removed with the eye. If the optic ganglion is removed with the eye, an antenna is regenerated in the place of the eye. If the optic ganglion is left intact, a new eye is formed. These experiments were carried on successfully in Palaemon, Palaemonetes, Sicyonia, Palinurus, and other Crustaceans. Herbst says that the optic ganglion exercises a "formative stimulus" upon the hypodermic cells of the wound. It is certain that an explanation of the role of the ganglion can only be given in physical or chemical terms; that as long as this is not possible we possess no explanation.

Morgan has made a somewhat similar observation on earthworms, in which he found that a new head is only possible at the anterior cut end of the nerve cord.* The following case may be mentioned by way of illus- tration. A few of the anterior segments of an earthworm were cut off, H, Fig. 57, and from the remaining body a piece ab was cut from the anterior part of the nerve cord (see Fig. 57), while all the other tissues remained unaltered. The anterior cut end a of the worm healed, and no new head formed at this place. Instead, a new head was formed in some such cases at b, at the anterior cut end of the nervous system. If the head alone is cut off in an earthworm without the excision of the anterior piece of the nerve cord, a new head is formed at the anterior end of the body. In another series of experiments Morgan cut off the head H of an earthworm and in addition (Fig. 58) excised a piece be from the nerve cord, so that now two anterior cut ends, a, and c, Fig. 58, of the nerve cord existed. In a few of these cases two new heads were

AFTER MORGAN. AFTER MORGAN, formed, one at each of the anterior ends 01 Another example of the dependence of the regeneration of one organ upon the presence of another is found in the formation of the lens of the eye. As is well known, the formation of the lens in the eye is pre- ceded by the formation of the optic vesicles, and where the latter touch the ectoderm a proliferation of cells begins, from which later the lens is formed. Spemann* has shown in the salamander that if the optic vesicle does not reach the ectoderm, no lens is formed. The same author showed, moreover, that if in the embryo the optic vesicle is destroyed, no lens is formed, but that if afterward the optic vesicle is regenerated, a lens is formed as soon at this vesicle touches the ecto- derm. Lewis confirmed and enlarged Spemann's observations.!

He showed that the ectoderm in frogs can form a lens at any place in the body if the optic vesicle is transplanted and allowed to come in contact with the ectoderm. He suggests that definite chemical reac- tions may occur between certain substances of the optic vesicles and the cells of the ectoderm; that these substances determine the formation and the peculiar character of the cells of the lens. This suggestion is in harmony with the ideas of Sachs, and I am inclined to believe that it will lead to further discoveries. Lewis's experiments also throw light upon an earlier observation made on salamanders. It was found that if a lens is removed in a salamander it can be regenerated from the iris. Inasmuch as the edge of the iris is naturally in contact with the retina (optic vesicle), this is about what should be expected from Lewis's experiments.

It is well known that the skeletal muscles degenerate if separated from the centers of their motor nerves. Goltz and Ewald have cut long pieces from the spinal cord in dogs, and observed that all the mus- cles belonging to the excised segments of the spinal cord degenerated, as was to be expected. This may be due to some chemical change in the muscles, owing to their inactivity after the motor nerves are cut or sepa- rated from their ganglia. We have already discussed one case of an apparent action at a dis- tance in Tubularians, where the suppression of the process of regener- ation at the oral pole accelerated the formation of a polyp at the aboral pole. Przibram found a case of distance action which is not so easy to explain. $ In a Crustacean, Alpheus, the right and left chelae are not equal in size and form. The same type of chela is not always on the same side, but in about one half of the cases the one type is on the right side, in the other half, the other type. Przibram found that if the larger of these chelae is removed in such a Crustacean, the remain- ing chela assumes after the next moulting the shape of the removed chela, and the regenerating chela assumes the shape which the remain-

* Spemann, Sitzungsber. der physik. meet. Gesellschaft in Wiirzburg, 1901. ing smaller chela originally had. Thus the animal is normal again, but the relative position of the two chelae is now reversed. If later on in such an animal the larger chela is cut, the original order can be obtained again. E. B. Wilson has repeated the experiments of Przibram, and made the important discovery that the growth of the smaller chela after the removal of the larger one does not occur if the nerve of the former is previously cut.* The number of the successful operations wTas small, but the results were significant. This brings Przibram's experiments into a line with Herbst's and Morgan's.

It seems to follow from these facts that the nerves have a function which is different from that of a mere conductor of stimuli; namely, that of causing the growth or development of certain organs. It has been argued that these two functions are not different, inasmuch as in both cases the nerve acts only as a conductor of stimuli and that these stimuli determine the phenomena of regeneration mentioned here. Child ex- presses such a view, and Herbst's idea of " formative stimuli " is only a somewhat less definite expression of the same view. It seems to me that there exists a still different possibility ; namely, that the nerve may also act as conductor for certain substances which go from the periphery to the ganglion cells or in the reverse direction and are carried through the axis cylinder. Especially the observations of Lewis and possibly those of Herbst and Przibram suggest such a possibility. But before we admit the possibility that the axis cylinder can act as a conductor for the passage of definite substances, we must look for facts which war- rant such an assumption. Such facts are given by the beautiful dis- covery of Hans Meyer f that the tetanus toxin is carried from the wound to the central nervous system through the axis cylinder of the nerves, and neither through the blood vessels nor the lymphatics nor the sheaths of the nerves. It is hardly necessary to emphasize the fact that through this discovery an entirely new light is thrown upon the role which the nerves or ganglion cells may play in the phenomena of regeneration. The possibility now arises that the axis cylinder may act as a conducting path for certain substances which in some animals may be necessary for the starting of a process of regeneration or which may modify the nature of the organ which is to be regenerated.

A few words may finally be said about the well-known effects of certain organs like the hypophysis and the thyroid gland on phenomena of growth. Certain parts of the body - - namely, the lower jaw, the fore arm, the hand, and the leg from the knee down — may suddenly be- gin to grow even if the body had already reached its final size. This phenomenon, known as acromegaly, is comparable to the process of re- generation, inasmuch as the problem in this case is also what causes this sudden growth which normally does not occur. It has been ob- served that this disease is often connected with a degeneration of the hypophysis, a small organ of enigmatic function. An attempt has been made (Von Cyon) to cure this disease by feeding the patient on normal hypophyses. This idea is based on experiences made in regard to the thyroid gland. Complete extirpation or degeneration of the thyroid gland in growing persons causes a standstill of growth and sexual and mental development. It has been found that if such patients be fed on thyroid glands, the growth and development can be again started. This seems to speak in favor of the idea that the action of specific substances may cause the post-adult growth of arms and legs in the case of acromegaly. It may, however, be a case of growth due to nervous influences com- parable to the experiences of Przibram in Alpheus.

If we cut a piece ab, Fig. 59, from the stem 55 of Antennularia an- tennina (Fig. 60), a hydroid, and put it into the water in a horizontal position, new stems cd, Fig. 59, may arise on its upper side. The small branches on the under side of the old stem ab begin suddenly to grow vertically downward.* In appearance and function ^ these downward-growing elements are entirely dif- ferent from the branches of the normal Antennu- laria ; they are roots. FlG In order to understand