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.