Varicose veins in immediate relation to the base of a large chronic ulcer usually become thrombosed, and in time are reduced to fibrous cords, and therefore in such cases haemorrhage is not a common complication.  In smaller and more superficial ulcers, however, the destructive process is liable to implicate the wall of the vessel before the occurrence of thrombosis, and to lead to profuse and it may be dangerous bleeding.

These ulcers are at first small and superficial, but from want of care, from continued standing or walking, or from injudicious treatment, they gradually become larger and deeper.  They are not infrequently multiple, and this, together with their depth, may lead to their being mistaken for ulcers due to syphilis.  The base of the ulcer is covered with imperfectly formed, soft, oedematous granulations, which give off a thin sero-purulent discharge.  The edges are slightly inflamed, and show no evidence of healing.  The parts around are usually pigmented and slightly oedematous, and as a rule there is little pain.  This variety of ulcer is particularly prone to pass into the condition known as callous.

In anaemic patients, especially young girls, ulcers are occasionally met with which have many of the clinical characters of those associated with imperfect venous return.  They are slow to heal, and tend to pass into the condition known as weak.

Ulcers due to Interference with Nerve-Supply.—­Any interference with the nerve-supply of the superficial tissues predisposes to ulceration.  For example, trophic ulcers are liable to occur in injuries or diseases of the spinal cord, in cerebral paralysis, in limbs weakened by poliomyelitis, in ascending or peripheral neuritis, or after injuries of nerve-trunks.

The acute bed-sore is a rapidly progressing form of ulceration, often amounting to gangrene, of portions of skin exposed to pressure when their trophic nerve-supply has been interfered with.

[Illustration:  FIG. 15.—­Perforating Ulcers of Sole of Foot.

(From Photograph lent by Sir Montagu Cotterill.)]

The perforating ulcer of the foot is a peculiar type of sore which occurs in association with the different forms of peripheral neuritis, and with various lesions of the brain and spinal cord, such as general paralysis, locomotor ataxia, or syringo-myelia (Fig. 15).  It also occurs in patients suffering from glycosuria, and is usually associated with arterio-sclerosis—­local or general.  Perforating ulcer is met with most frequently under the head of the metatarsal bone of the great toe.  A callosity forms and suppuration occurs under it, the pus escaping through a small hole in the centre.  The process slowly and gradually spreads deeper and deeper, till eventually the bone or joint is reached, and becomes implicated in the destructive process—­hence the term “perforating ulcer.”  The flexor tendons are sometimes destroyed, the toe being dorsiflexed by the unopposed