Atrophy is the opposite to hypertrophy. Want of blood or of the supply of nervous energy will cause an organ to shrink away. So a palsied hand often, in time, withers to half its original size. Atrophy occurs naturally, all over the body, with old age. First the fat is absorbed, then the muscles, and afterward other parts.

Degeneration

Instead of lessening in size, however, from loss of life-force, an organ may grow larger, with change of substance. This is organic degeneration. The substance taking the place of the natural tissue of the part is always inferior in character to that tissue. Thus fat may take the place of muscle, as in " fatty degeneration of the heart." Or bone-like material may form in place of the proper substance of the arteries; making " ossification " of those vessels. Or the liver or kidney may be enlarged, the normal cells of either organ being replaced by a material like the areolar ("cellular") tissue of the surface of the body under the skin. Tubercle, of the lungs or other parts, is essentially a kind of degeneration; although it often follows attacks of inflammation. Acute and chronic inflammation of various organs is frequently followed by hardening or softening; both of these being modes of degenerative alteration.