3. _Perverted surface nutrition_, for example, in connection with varicose veins of the extremities, where, aside from any perverted trophoneurotic influence, there is stagnation of blood, saturation of tissues with serum, and final leakage of the same, even to the surface. Varicose veins of the leg which lie near or underlie ulcerating surfaces become thrombosed and obliterated, so that such ulcers rarely bleed. On the other hand, a passive hyperemia here leads to edema, perversion of nutrition, failure to repair trifling surface injury, and a surface is left which of itself rarely, if ever, heals. 4. So-called _pressure sores_ or _bed-sores_, which in some cases may be regarded as having a traumatic origin, but which, nevertheless, would not occur from purely traumatic influences without predisposing tissue changes. The bed-sore is probably the best illustration of this. Simple ulcer is known as bed-sore, while a sloughing ulcer of this kind is frequently alluded to as _decubitus_. Such ulcers are usually found over those regions of the body made most prominent by bony projections, upon which undue pressure is made when debilitated patients have lain for a long time in bed. 5. Ulcer is the frequent result of numerous _skin diseases_, into whose etiology as yet bacteria have not been introduced--_e. g._, pemphigus, eczema, etc. 6. Ulcer is the occasional result of _embolic_ or other _disturbance_ of the principal artery of the part, by which nutrition is cut off and tissue death results. 7. _Bites of insects_ or other _parasites_ or of noxious animals frequently lead to ulceration. 8. Certain more specific forms of ulcer are described by some writers, apparently with more or less reason, among them being _chancroid_, _perforating ulcer of the foot_, etc. (Chancroid is described in Chapter X.) Trophic ulcers of the fingers or hand are also seen, particularly after injury to or division of nerve trunks in the arm or forearm. Perforating ulcer of the foot is a circumscribed circular ulcer with thickened edges, often nearly concealed by overhanging skin. It may be found in any part of the sole of the foot, but is most common near the first joint of the great toe. The borders of the ulcer are usually anesthetic. It is frequently seen in diabetics. By some it is associated with trophic nerve disturbance; by others it is regarded as having a specific etiology of its own. The probability, however, is that it is simply a subvariety of pressure sore.