A change in structure or in chemical composition of a tissue or organ, by which its vitality is lowered or its function interfered with. Degeneration is of various kinds, the chief being fatty, where cells become invaded by fat globules; calcareous, where calcium is deposited in tissue so that it becomes chalky in consistency; and mucoid, where it becomes semi-liqueﬁed.
Causes of degeneration are, in many cases, very obscure. In some cases heredity plays a part, with particular organs – for example, the kidneys – tending to show ﬁbroid changes in successive generations. Fatty, ﬁbroid, and calcareous degenerations are part of the natural change in old age; defective nutrition may bring them on prematurely, as may excessive and long-continued strain upon an organ like the heart. Various poisons, such as alcohol, play a special part in producing the changes, and so do the poisons produced by various diseases, particularly SYPHILIS and TUBERCULOSIS.