PATHOLOGY 363 It is when we come to the several tissues that we meet with the most striking reminders of persisting de velopmental characters, the most universal fact of the kind being the indwelling embryonic character of the common binding tissue. In that tissue, indeed, we have a constant reminder that in the midst of the very highest or most perfected modes of cellular life we are but a step removed from the most rudimentary. Thus in the brain and in the retina the elaborate nervous mechanism is supported on a framework of connective tissue ; there is a morbid con dition of these organs, called glioma, in which the con nective tissue, or neuroglia, absolutely usurps the place of the nervous mechanism of which it is ordinarily the mechan ical support ; and this it may so completely do, as in disease of the pons Varolii, that even the outward form and mark ings of the part are not interfered with. An equally striking instance of a return to embryonic characters and predominance may sometimes be observed in the primi tive nuclei of muscle ; the muscle-fibres will be found to have surrendered their high function, to have retraced the steps of their development, and to have sunk their identity in a rudimentary form of cell-life. Thus the body nowhere loses altogether the memory of the past, even when the periods of development and growth are, strictly speaking, ended. Among the normal processes of mature life there are such as amount to a recrudescence of structure and function ; and an analogous recrudescence in the tissues is one of the most fundamental facts in the processes of disease. There are several advan tages in proceeding in an exposition of pathological prin ciples from this evolutional or developmental basis. It enables us to take up, in an order not unsuited to their importance, the sections relating to repair, to new growth of tumours, to errors of growth, such as rickets, to errors of blood-making, and the like. At the outset comes the process of repair, for which Paget has formulated the embryological principle as follows : " 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." 3. THE PROCESS OF KEPAIE. onta- The spontaneity of certain polyps under injury is a ty of good example of the indwelling power of all the cells and tissues to return to the established order, to the order and harmony which had been slowly acquired, and of which the memory is vividly retained. Trembley cut a hydra longitudinally, and "in an hour or less," says Paget, " each half had rolled itself and seamed up its cut edges so as to be a perfect hydra. He split them into four ; he quartered them ; he cut them into as many pieces as he could ; and nearly every piece became a perfect hydra. He slit one into seven pieces, leaving them all connected by the tail, and the hydra became seven-headed, and he saw all the heads eating at the same time. He cut off the seven heads and, hydra- like, they sprang forth again." The recovery of perfection may be more gradual. Thus, Sir J. G. Dalyell (as quoted by the same writer) cut a specimen of Hydra tula in halves ; each half regained the perfect form, but only very slowly, and, as it were, by a gradual improvement of parts that were at first ill formed. In Tubularia indivisa, after the natural fall of its head, the stem was slit for a short distance down ; an imperfect head was first produced, at right angles to the stem, from one portion of the cleft ; "after its fall another and more nearly perfect one was regenerated, and, as it grew, im proved yet more. A third appeared, and then a fourth, which was yet more nearly perfect, though the stem was thick and the tentacula imperfect. The cleft was almost healed, and now a fifth head was formed, quite perfect ; and after it, as perfectly, a sixth and a seventh head. All these were produced in fifteen months." This spontaneity resides in every living thing, and its efforts are directed by the memory of what the species had come through in reaching its place in the scale of organization ; it is able, indeed, to make perfect reparation for injuries or losses only where the cells are little differentiated into tissues, or where the tissues are little specialized for diverse func tions. In all animals, and most notably in the higher, this spontaneity is most effective for repair in the periods of development and growth. With reference to the degree of reparative power possessed, Paget formulates the rule as follows : " The amount of reparative power is in an inverse ratio to that of the development, or change of structure and mode of life, through which the animal has passed in its attainment of perfection, or on its way thitherward." Healing by Granulations. It will now be convenient to advance Granu- in medias res, and to give some account of the process of repair in lation- inan, where there is a breach of continuity in the course of the repair, blood-carrying and lymph-carrying vessels, of the nerves, sinews, binding tissue, bone, fat, and skin. What is the effort that they each and all make to adapt themselves to the circumstances, in the case, let us say, of a stump after amputation ? (The repair be tween the two ends of a broken bone will be discussed separately.) Disregarding the cases where the most perfect coaptation of parts is secured by the surgeon, and selecting the extreme case where the wound is "left to granulate," the following is the order of events. The divided vessels being sealed up either by ligature or by clots of blood (which are in the end absorbed), there oozes from the raw surface a blood -tinged serous - looking fluid. Becoming paler by degrees, it sets on the surface as a greyish-white film or glazing, especially on the exposed surface of muscle. The film of surface- glazing will be found to contain numerous corpuscles embedded in it resembling the colourless corpuscles of the blood. They have probably the same formative or reparative value as the granulation- cells proper, but it will appear from the facts about to be given that they are practically superseded by the latter in all cases where a wound is "left to granulate." After an interval of two or three days of apparent rest reddish points are seen on the edges of skin, on the muscular substance, and on the marrow of the bone ; these are the beginnings of the granulation -tissue, which in the end covers the whole surface and grows until it fills up the gap somewhat beyond the level of the edges of skin. When the growth of granu lations projects considerably beyond the skin it is known as "proud flesh. " Usually the surface begins to skin over when the defect of substance has been sufficiently made good, the new skin showing as a delicate bluish border or frill to the old skin. This frill becomes broader and broader until the growing points meet in the centre, and the continuity of the skin is restored. Meanwhile the granulation - tissue beneath has been changing into more charac teristic forms of mature tissue, although the status quo antea is never quite restored. Notwithstanding the regularity of this process, and its daily occurrence in surgical practice, there is an almost incredible amount of conflicting opinion as to its details, radical differences as to the source or sources of the reparative material, and as to the mode of development of the new blood-vessels and of the new skin ; and these differences of opinion must be the measure of the difficulty of analysis where the interference takes place in the highly com plex and subtly integrated life of man. Direct observation of the reparative process does not of itself suffice to discover the law of it ; it is necessary to seek elucidation from the nearest analogies, both among the regular processes of life and growth and among the deviations therefrom. Among the former there is in particular one rich source of analogous detail to be found in the periodical new formation on the surface of the uterus for the purposes of the embryo in the placenta ; among the latter are certain kinds of tumours and cysts. Hunter sought for a parallel to the new vessels of granulation-tissue in the first formation of vessels in the embryo ; but these arise in the continuity of development, and not as a somewhat abrupt incident in the mature life. On the other hand, the formative process of the placenta is an example and a unique example of an extensive new growth of vascular tissue occurring periodically in the adult, and as somewhat of an interruption on the ordinary course of life. It matters little for this parallelism whether we accept the extreme position of Ercolani, that a total destruction of the uterine mucosa precedes the placental new growth, or whether we adopt the more likely view that the new formation takes place under an intact surface. In either case we have to do with a remarkable spontaneity of the body, a spontaneity which
