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but such a minute one, that it is altogether imperceptible to the naked eye and can only be demonstrated microscopically. In this case we generally make use of the expression, atrophy of muscle, although the process which has attacked the individual primitive fasciculi, does not in any way differ in its nature from the processes which we at other times term softening of muscle.

This is the reason, why the term softening, which must be reserved for coarse pathological anatomy, cannot simply be applied to histological processes, and why it is better to say necrobiosis, when we have to do with these more delicate processes. The common feature of all the varieties of the necrobiotic process is, you know, that the affected part at the close of the process is destroyed, nay annihilated.

A second class of passive processes is formed by the simply degenerative forms, in which, at the conclusion of the process, the affected part is in some condition or other less fitting it for action, and has generally become more rigid. This group might therefore be termed hardenings [indurations) and thus a group be formed distinguishable even externally from the necrobiotic processes. Only the term induration also would easily be misunderstood, inasmuch as in this class likewise many conditions occur, in which the hardness of the organ on the whole at least does not become more considerable, but only isolated, very minute parts undergo change, so that no very striking effects are apparent to the sense of touch.

Allow me now to hold up to you as types a few of the processes belonging to this class, which are of the greatest importance in a directly practical point of view.

Among the necrobiotic processes the one which is unquestionably the most widely spread and the most important in the course of all cellular disturbances, is fatty metamorphosis, or as it has also long been wont to be called, fatty degeneration. This process is attended by a continually increasing accumulation of fat in different organs. Even the old notion of fatty degeneration involved the idea of a continually increasing change of such a nature that pure fat at last took the place of whole parts of organs. It has turned out, however, that this old notion, which is even now retained by many in the language of pathology, includes a great number of completely different processes, and that errors would inevitably be committed if it were sought to interpret the whole group from a pathogenical point of view, in a simple manner.

The history of fat in its relation to the tissues may, generally speaking, be considered under three aspects. We find namely one class of tissues in the body, which serve as physiological reservoirs for fat, and in which the fat is contained as a kind of necessary appurtenance, without however their own permanency being in any way endangered by its presence. On the contrary, we are actually accustomed to estimate the well-being of an individual by the amount of fat contained in certain tissues, and to regard the degree of fulness presented by the individual fat-cells as a criterion of the successful progress of the interchange of matter generally. This forms therefore a complete contrast to the necrobiotic processes, in which the part in consequence of the accumulation of fat really altogether ceases to exist.

A second series of tissues do not constitute regular reservoirs for fat, on the contrary fat is found in them only at certain times and transitorily, for after a short tune it again disappears from them, without their being on that account left in an altered state. This is the case in the ordinary absorption of fat from the intestinal canal. When we drink milk, we expect in accordance with old experience that it will gradually pass from the intestines into the lacteals, and thence be conveyed into the blood; we PHYSIOLOGICAL FATTY METAMOEPHOSIS. 321

know that the passage of digested matters from the intestines into the lacteals takes place through the epithelium and the villi, and that some hours after a meal the epithelium and the villi are full of fat. Now, with respect to such a fat-containing villus or epithelial cell, we take for granted that in the natural course of events it will at last yield up its fat, and after some time again become perfectly free from it. This is a fatty infiltration of a purely transitory character.

Finally, we have a third series of processes, namely, those which lead to necrobiosis and which have of late frequently been regarded as peculiarly pathological ones. But, as it has been shewn to be the case in all other conditions that pathological processes are not specific ones, but, on the contrary, that others analogous to them exist in normal life, so also the conviction has been acquired that this necrobiotic development of fat is an entirely regular and typical process in certain parts of the body, nay that it is even met with in very obvious forms in physiological life. The most important types of this process we find on the one hand in the secretion of milk, the sebaceous matter of the skin, the cerumen of the ears, &c, and on the other in the formation of the corpus luteum in the ovaries. In all these parts a development of fat takes place precisely in the same manner that we meet with it in the necrobiotic fatty metamorphosis occurring from morbid causes, and in what we call sebaceous matter, milk or colostrum we have formations analogous to the pathological masses of fat which constitute fatty softening. If in any person milk is manufactured in the brain instead of in the mammary gland, this constitutes one form of cerebral softening; the product may morphologically exactly correspond with what in the mammary gland would have been quite normal. The great difference, however, is this, that, whilst in the mammary gland the cells which perish are replaced by a succession of new cells, the disintegration of elements in an organ which is not arranged so as to furnish such a succession, leads to a permanent loss of substance. The same process which in one organ yields the happiest, nay the sweetest, results, brings along with it in another, painful lesions.

If then you picture to yourselves these three different physiological types, we have in the first case an accumulation of fat in the cells in such a way, that at the close of the process every single cell is entirely full of it. This yields us the type of the so-called adipose cellular tissue, or simply, adipose tissue, as it occurs in such large masses especially in the subcutaneous tissue, where it on the one hand gives rise to beauty, particularly in the female figure, and on the other to the pathological conditions of obesity or polysarcia. Fat-cells always possess a membrane and fatty contents, but the fat so completely fills up the interior, and the membrane is so extremely thin, delicate and tense, that usually nothing else is seen than the drop of fat, and thus it was, until very recently, still a matter of discussion

Fig. 107.


whether the fat-cells really were cells. It is in reality very difficult to come to a distinct decision upon the subject, but

Fig. 107. Adipose cellular tissue from the panniculus [adiposus]. A. Ordinary subcutaneous tissue, with fat-cells, some interstitial tissue, and at b vascular loops; a, an isolated fat-cell with membrane, nucleus and nucleolus. B. Atrophic fat in phthisis. 300 diameters.


supporting testimony of a very beautiful character is supplied in the course of natural processes. When a person becomes thinner, the fat gradually disappears, the membrane loses somewhat of its tension, is no longer so thin and delicate, and thus becomes more clearly manifest, being sometimes distinctly separated from the drop of fat, and even provided with a recognizable nucleus (Fig. 107, A, a). We have here therefore a real, complete cell with nucleus and membrane, though the contents have been almost entirely supplanted by the fat it has taken up. This so-called adipose cellular tissue is a form of connective tissue (p. 48), and when it undergoes retrogressive metamorphosis, it is clearly seen to be reduced to connective or mucous tissue, for between the cells a small quantity of intercellular substance again becomes apparent (Fig. 107, A, b, B).

This species of adipose tissue it is, gentlemen, which under certain circumstances not only gives rise to poly. sarcia and obesity, from continually increasing quantities of connective tissue becoming involved in this accumulation of fat, but is also the foundation of all anomalous fatty structures, for example, of lipomata. The different forms of these structures, and particularly real fatty tumours, are distinguished from one another only by the greater or less quantity of interstitial connective-tissue, which the tumour contains, and upon which their greater or less consistence depends. It is the same form of accumulation of fat which we see appear in morbid conditions in a series of cases which, in compliance with old tradition, are still called fatty degeneration; and it is indeed particularly the fatty degeneration of muscles which in many instances presents nothing else than a more or less advanced development of adipose cellular tissue between the primitive muscular fasciculi. It is a similar process to that which we meet with in the fattening of animals, and which is often exhibited in simply fattened muscles in the human body.

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