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