Gangrene is known also as _necrosis_, although this term is usually limited to gangrene of bone. It is known also as _mortification_, and to the older writers, especially when soft parts die and separate in sloughs, as _sphacelus_. _Gangrene means death of tissue in visible and more or less circumscribed masses._ It is distinguished from ulceration not on account of molecular disintegration, particle by particle, but because of death _in toto and synchronously_ of a large, perhaps innumerable, number of cells. Gangrene is described as due to causes which may be: A. =Traumatic=, including the so-called thermal causes as essentially mechanical injuries. Under this head are included cases where _injury_ is the primary cause, whether this injury is the crushing of a limb, the separation or occlusion of its main bloodvessels, the division of its main nerves, or the crushing or pulpefying of its entire structure by machinery or accident; also those so-called _thermal_ cases which are due to intense heat or intense cold. To these might be added the _chemical_ causes, comprising injuries by powerful caustics, alkalies, or acids, which are known to cause speedy death of every living tissue with which they come in contact. Gangrene from _frostbite_ is often of the moist type. There is scarcely a limit to its extent, either in area or depth. It is due primarily to thrombosis, which is followed by a purplish color of the skin, by loss of local warmth, and numbness. Naturally it involves the ears, nose, fingers, and toes. But after alcoholism and exposure one or more entire limbs may be involved. With moist gangrene there is danger of septic infection (_q. v._). After formation of a line of demarcation the line of amputation may be made to follow it closely, but the best results are obtained by higher division, at points of election, where tissues are less sensitive and less infiltrated.