Moist gangrene therefore differs from dry gangrene in that the arrest of circulation takes place more or less suddenly when the tissues are suffused with blood. The dry form of gangrene does not occur regularly in the diseases in which it might be expected, and though a true wet gangrene is not found, neither is the typical mummification. Moist gangrene may occur in diabetes, in senility and in Reynaud’s disease, and probably assumes this form on account of the sudden onset of inflammation in the part from some slight abrasion, or from weak heart action. C+AUSES OF GANGRENE+ _Traumatic._ The sudden cessation of the blood supply to a part in consequence of a cutting or crushing accident, will obviously produce the moist form of gangrene. It is not essential that the part be entirely severed, or even nearly so, for if only the main artery is severed, gangrene will ensue. The crushing or pressure upon a large vein will act similarly, owing to there being no outflow possible, back pressure will cause the total arrest of circulation in the part. _Constitutional Diseases._ Certain diseases affect the lumen or calibre of the blood vessels, gradually diminishing and finally arresting the stream of blood carried through them. In these diseases it would be logical to invariably expect dry gangrene. This does not regularly occur, for the reason just given, and the mere presence of a moist or dry condition therefore cannot be regarded as diagnostic. In diabetes, either form may obtain, and a diagnosis can be assured by the discovery of sugar in the urine. The thickened condition of the arteries leading to senile gangrene must be thought of and proven in aged subjects. Dry gangrene is the rule in arteriosclerosis. Reynaud’s disease, or synthetic gangrene, is due to a vasomotor spasmodic condition of the terminal vessels and is of central nerve origin. The tips of the toes and fingers, of both sides, are the most common sites, though the lobes of the ears, cheeks and tip of the nose may be affected. A coldness of the parts, with mottling of blue and white, and a subsequent diffuse blueness, becoming darker and finally black, are characteristic signs of this disease, and the dry form of gangrene is usual. _Obliterating Endarteritis_, is a condition in which the walls of an artery become inflamed and thickened, thus obliterating its lumen. _Thromboangiitis Obliterans_ is similar to the above and differs only in that a thrombotic growth occurs in an artery obliterating its lumen. _Thrombosis and Embolism._ Thrombosis and embolism cause a sudden or gradual stoppage of the blood stream in a vessel, and in consequence, either moist or dry gangrene occurs, depending on the time required for the obstruction to become complete. The stoppage of the outflow because of thrombosis in a large vein, will cause moist gangrene; the part being unable to drain, will, by back pressure, arrest circulation.