It is unnecessary in a work of the present character to call attention to all the possible circumstances under which fat is present in the body as the result of degeneration. Mention may be made of the acute parenchymatous (fatty) degeneration of new-born children, of the results of excessive bleeding, and of pernicious anæmia otherwise occasioned. The fatty degeneration of the uterus after parturition, of paralyzed muscles, and of tumors, the atrophic fatty degeneration of the liver in chronic {79} passive congestion (nutmeg liver), are all well-known examples. To these may be added the fatty degenerations associated with amyloid and interstitial processes. It is apparent that in most of these instances the common features of rapid tissue-metamorphosis and deficient oxidation are present, and, being present, offer a ready explanation for the appearance of the fat. The clinical importance of fatty metamorphosis requires consideration in connection with the description of the diseases in which its occurrence is a constant feature. As the presence of fat in cells is not necessarily pathological, so an interference with the function of the cell is not invariably implied by its presence. When its existence is suggestive of a local destruction of albuminates, a diminution of cell-activity is a necessary consequence. Such diminished activity must produce different results as the cells are those of muscles, of vessels, or of glandular organs. Even if fat is found in cells under conditions favoring such a suggestion, it does not follow that the destruction of the cell must result. Not only is it possible that the fat may be reserved for eventual oxidation, and its place in the protoplasm be filled by normal constituents, but it is also possible that the fat may be eliminated, as such, from the body. The latter event is made apparent by the experiments of numerous observers referred to by Cohnheim, who have found free fat in the urine after its introduction into the venous current. _Cheesy Metamorphosis, Cheesy Degeneration, Caseation._ Virchow introduced the term cheesy metamorphosis, tyrosis, to designate the process resulting in the incomplete absorption of pus and the production of apparently similar changes in certain other occasional constituents of the body. The characteristic cheesy appearances were regarded as due to the inspissation of the material concerned, in consequence of the absorption of its fluid. With this inspissation there was frequently associated a partial fatty degeneration, and the cheesy matter represented dead material, which might undergo further changes, of which softening and calcification were the more important.