A. #Arrangement of Ulcers according to their Cause.#—­Although any given ulcer may be due to a combination of causes, it is convenient to describe the following groups: 

Ulcers due to Traumatism.—­Traumatism in the form of a crush or bruise is a frequent cause of ulcer formation, acting either by directly destroying the skin, or by so diminishing its vitality that it is rendered a suitable soil for bacteria.  If these gain access, in the course of a few days the damaged area of skin becomes of a greyish colour, blebs form on it, and it undergoes necrosis, leaving an unhealthy raw surface when the slough separates.

Heat and prolonged exposure to the Rontgen rays or to radium emanations act in a similar way.

The pressure of improperly padded splints or other appliances may so far interfere with the circulation of the part pressed upon, that the skin sloughs, leaving an open sore.  This is most liable to occur in patients who suffer from some nerve lesion—­such as anterior poliomyelitis, or injury of the spinal cord or nerve-trunks.  Splint-pressure sores are usually situated over bony prominences, such as the malleoli, the condyles of the femur or humerus, the head of the fibula, the dorsum of the foot, or the base of the fifth metatarsal bone.  On removing the splint, the skin of the part pressed upon is found to be of a red or pink colour, with a pale grey patch in the centre, which eventually sloughs and leaves an ulcer.  Certain forms of bed-sore are also due to prolonged pressure.

Pressure sores are also known to have been produced artificially by malingerers and hysterical subjects.

[Illustration:  FIG. 14.—­Leg Ulcers associated with Varicose Veins and Pigmentation of the Skin.]

Ulcers due to Imperfect Circulation.—­Imperfect circulation is an important causative factor in ulceration, especially when it is the venous return that is defective.  This is best illustrated in the so-called leg ulcer, which occurs most frequently on the front and medial aspect of the lower third of the leg.  At this point the anastomosis between the superficial and deep veins of the leg is less free than elsewhere, so that the extra stress thrown upon the surface veins interferes with the nutrition of the skin (Hilton).  The importance of imperfect venous return in the causation of such ulcers is evidenced by the fact that as soon as the condition of the circulation is improved by confining the patient to bed and elevating the limb, the ulcer begins to heal, even although all methods of local treatment have hitherto proved ineffectual.  In a considerable number of cases, but by no means in all, this form of ulcer is associated with the presence of varicose veins, and in such cases it is spoken of as the varicose ulcer (Fig. 14).  The presence of varicose veins is frequently associated with a diffuse brownish or bluish pigmentation of the skin of the lower third of the leg, or with an obstinate form of dermatitis (varicose eczema), and the scratching or rubbing of the part is liable to cause a breach of the surface and permit of infection which leads to ulceration.  Varicose ulcers may also originate from the bursting of a small peri-phlebitic abscess.