Degeneration

Degeneration, in Pathology, certain alterations of the tissues of which the body is composed, which have been described by the morbid anatomist and pathologist. Lardaceous, waxy, oramyloid degeneration occurs in cases of long-continued suppuration. and affects mainly the liver, kidneys, spleen, and intestines. On microscopic examination of the diseased parts a new deposit of colourless retractile "amyloid" material is found to be present for the most part in the walls of the small arteries. The exact composition of this amyloid matter is not known; it seems to be allied to the substances known as proteids. Fatty degeneration is a term of somewhat undefined significance. It is applied to mere overgrowth of fatty tissue, to the distension of cells with oil drops, as in fatty degeneration of the liver, and to the breaking up of the protoplasm of cells which is met with in such a condition as fatty degeneration of the heart. Calcareous degeneration is of particularly common occurrence in the internal coats of arteries. In extreme instances the artery may become converted into a perfectly rigid tube. It is a condition met with in advanced life, and may result in rupture of the vessel, or in gangrene, from failure of the artery to respond to the varying needs of the parts supplied by it with blood. Other forms of degeneration which may be mentioned are mucous and colloid degeneration, pigmentary degeneration, and uratic degeneration.

In Biology, the operation of the disuse of parts, through the laws of economy of nutrition and of acceleration of development, to produce a simpler structure. It is especially characteristic of organisms that lead a parasitic or otherwise sedentary life, in which case it will affect organs of locomotion, organs of special sense, which especially subserve the capture of food, and even the nutritive and food-elaborating organs themselves. Under other circumstances, increased facilities for growth, for longevity, or for asexual reproduction may lead to degeneration so far as sexual characters are concerned. It is a moot question whether the reduction of organs which undoubtedly results from their disuse, by the law of economy of nutrition, is directly inherited, it being an acquired character, or whether individuals arising by spontaneous variation with reduced organs merely survive as the most fit. When, however, a structure is aborted or suppressed, its abortion or suppression tends, according to the law of acceleration of development, to occur at a slightly earlier period in the life of each successive generation. Parasitism (q.v.), for instance, may at first be only occasional and partial; but among flowering plants, when habitual, it means obtaining elaborated food made up of organic substances and rendering the action of chlorophyll (q.v.) upon atmospheric carbon-dioxide unnecessary. The leaves and stems of many parasites accordingly contain little or no chlorophyll and are brown, the leaves also being commonly much reduced in size. The same changes occur in some plants which are saprophytes (q.v.), living among dead leaves or other decaying organic matter. Entozoa, or internal parasitic worms, illustrate several phases of extreme degeneration, being in some cases destitute even of a mouth. In the Ichthyophthira, crustaceans which become parasitic upon fish, the embryo has eyes and swimming organs which are lost in the adult, as is also the case with the barnacles, which are merely sedentary and not truly parasitic. One of the most striking cases of degeneration is that of the ascidians [Tunicata], which possess a true vertebrate notochord in their larval stage and afterwards lose it, being in fact a side branch of the ancestral Vertebrata degenerating when adult to the grade of the lowest mollusks. Apogamy (q.v.), or the loss of the sexual process, accompanied by increased means of vegetative reproduction, as in the mushroom, is another case of degeneration, and the reversion of the bee-orchis to self-pollination, whilst belonging to a group all specially adapted for insect pollination (q.v.), may be regarded in the same light.