CHAPTER III.

REMINISCENCES OF EMBRYONIC ACTIVITY IN REPAIR AND IN NEW GROWTHS.

THE illustrations of developmental memory in the foregoing chapter are physiological, relating to reproduction or the preservation of the species. In order to exemplify on a sufficiently broad basis the principle of unconscious memory that we are about to apply to certain important groups of diseases, it will be necessary to give some brief account of two or three pathological instances of memory or recollection of embryonic phases inhering in the simple tissues.

"The powers for development from the embryo are identical with those exercised for the restoration from injuries; in other words, the powers are the same by which perfection is first achieved, and by which, when lost it is recovered." This is the statement of Paget, and it is illustrated by him in the first instance by reference to the remarkable reparative power in Hydra and other polyps. A further collection of instances of the power of restoring lost parts by the invertebrata, is given by Darwin to illustrate his hypothesis of pangenesis, or of countless gemmules each with its proper formative value.

In the repair of a wound or sore by granulations, the pre-existing tissues of the part are the basis of the repair; they undergo a transformation, they become formative, they furnish the materials out of which the lost structures are more or less perfectly restored. The power that they put forth is, as Paget says, the same as that exercised for development from the embryo. In other words, the tissues of an injured part revert to embryonic characters. Highly vascular tissues return most rapidly to the embryonic state : the distinction between the vessel-wall and the peri-vascular or inter-vascular tissue disappears; an area of tissue pervaded by vessels, changes into a corresponding area of what the late Professor Boll called "Gefasskeim-gewebe," that is to say, embryonic vasoformative tissue. The youngest phase of granulation tissue is of that nature, the new blood-vessels being channels in the midst of it bounded by rows of flattened cells. In the case of a severed tendon, a kind of tissue where the vascularity is small, we are better able to follow the activity of individual cells. The flattened cell-plates emerge from their obscurity to become solid cubical elements, and the identity of these with the granulation cells is obvious from the fact that they undergo their changes while retaining their natural position in the midst of the wavy bundles of fibres. The cell-plates of tendons are highly specialised derivatives of the embryonic mesablast; the perivascular cells and other connective-tissue elements are less specialised derivatives of the same.

Allalike return to their primitive embryonic characters; they become so much mesoblast again, and in so doing they become what Boll calls "Gefasskeim-gewebe."

Besides the making of vessels, the embryonic mesoblast has another and even more fundamental property -the making of blood; and, according to Stricker, the ordinary red blood may actually be seen to be produced in granulation tissue along with the new vessels. But the strength of the hæmatoblastic memory is shown even more strikingly in the production of a modified kind of blood-in the production of pus around the growing points of granulation tissue. Wherever the less intense or less hurried form of revived hæmatoblastic activity of connective-tissue cells can be studied, as in blood-cysts and cavernous bloodtumours, the hæmatoblast is seen to disengage its reddish protoplasm in the form of buds which become the red blood-discs; meanwhile its nucleus has been cleft into several fragments, which cling more or less closely to the buds of reddish substance as they proceed to detach themselves. But these nuclear particles have no permanent share in the red blood-discs; they come together again, and make up a cell with its nucleus divided into three or four, which is all that survives of the original hæmatoblast. In the fluid formed around the vascular points of granulation tissue, this residual element with nucleus cleft into three or four is the pus-corpuscle; the protoplasm originally surrounding it has been disengaged, but not in the form of definite reddish buds; it has simply

melted into the fluid part of pus, losing all traces of individuality. According to this reading of the phenomena, which I have expounded with descriptive details and figures elsewhere,* the well-known appearance of three or four nuclear particles in a pus-corpuscle is evidence of the essentially hæmatoblastic nature of the process, the same being a memory which the common binding-tissue and other adult tissues of mesoblastic origin never quite lose.

Again, in the repair of a broken bone we have evidence even down to old age that the "osteoblastic tendency or memory is strong in the tissues within and around a bone, above all in the periosteum and in the young or red marrow" (Art. "Pathology," l. c.).

It is well known that the tissues of repair, both those of the soft parts and the callus of bone, have close analogies to certain new growths of the tumour kind. But there is the grand difference between them that the new growth of repair is self-limited, whereas the new growth of tumours is indefinite. The former is a memory of development which is effaced after a time by the re-established continuity of mature life; the latter is a memory of development which fixes itself in the midst of the tissues as a habit. Practically the whole of the mesoblastic series of tumours can be shown to be due to revived embryonic activity; some of them may have sprung, as Cohnheim supposed that they all did, from actual centres of embryonic tissue left behind here and there in the * Art. “Pathology,”‹ Encycl. Brit.,' xviii, 1885, figs. 9, 10, 25, and 28.

body; but the larger number of them are owing to a reversion of some tissue of the connective series to its mesoblastic characters, just as in granulations, although the occasion is not usually so obvious as in granulation tissue.

Although there is a sufficiently clear line, for practical purposes, between the new growth of mesoblastic tumours and the new growth of repair; yet there are some among the former which come near to the reparative process in the tendency to self-limitation or in the comparatively slight hold that habit has obtained over them. The best instances are tumours with a cystic tendency. Wherever the revived embryonic activity is accompanied by evidences of embryonic function, we find cystic softening in the interior, the fluid being sometimes sanguineous but more often clear or turbid serum. The revived mesoblastic activity may proceed on the formative lines purely, or on the formative and functional combined; in the former case we have the memory of development becoming a habit, and in the latter case there is some chance of self-limitation.

The best instance of self-limitation going with mesoblastic function is in the case of those remarkable cavernous tumours or blood-tumours growing from the connective tissue of the liver, which have the well-known tendency to cicatrise in places. Wherever functional traditions of the mesoblast fail to assert themselves duly in a case of revived embryonic activity, we have a persisting and growing tumour—