_Extravasation_ of blood is another cause connected with the bloodvessels, this coming usually from traumatic rupture, possibly from idiopathic causes. At any rate, the tension in the part may threaten its life because of the pressure which overcomes the circulation of blood. _Ligation_ of the main trunk of an artery is sometimes followed by gangrene, no matter how carefully done, collateral circulation being insufficient to sustain the nourishment of the part. In certain fractures, simple as well as compound, the blood supply of a part is rudely broken off by injury to a bloodvessel in such a way as to cause local or general death, either of a bone or of the entire limb. Flaps made for plastic purposes, arranged without sufficient regard to their proper blood supply, or so dressed after operation as to sustain undue pressure, are often so shut off from the heart as to die for want of blood. Finally, gangrene may be the result of _pressure_ either from splints, bandages, etc., or from _tumors_ increasing in size, or possibly, as in certain pressure sores, etc., from the mere weight of the body. Here, too, _chemical agents_ must be mentioned, referring now to the peculiar action of certain _foods or drugs_, particularly ergot. Thus antiseptic solutions, particularly carbolic acid, may be made strong enough to destroy the vitality of certain tissues. Carbolic gangrene (Warren) is a possibility not to be forgotten. Extravasation of urine, unless promptly recognized and appropriately treated, or especially as occurring when the urine is peculiarly toxic (ammoniacal) and the patient’s vitality reduced, as in confirmed alcoholics, is almost sure to produce gangrene which may easily terminate fatally. [Illustration: FIG. 14 Raynaud’s disease: digiti mortui. (Original.)] [Illustration: FIG. 15 Raynaud’s disease: perforating ulcer of foot. (Original.)]