[Illustration: FIG. 40.--Ulcerating Gumma of Lips.
(From a photograph lent by Dr. Stopford Taylor and Dr. R. W. Mackenna.)]
_The tertiary ulcer_ may be situated anywhere, but is most frequently
met with on the leg, especially in the region of the knee (Fig. 42) and
over the calf. There may be one or more ulcers, and also scars of
antecedent ulcers. The edges are sharply cut, as if punched out; the
margins are rounded in outline, firm, and congested; the base is
occupied by gummatous tissue, or, if this has already separated and
sloughed out, by unhealthy granulations and a thick purulent discharge.
When the ulcer has healed it leaves a scar which is depressed, and if
over a bone, is adherent to it. The features of the tertiary ulcer,
however, are not always so characteristic as the above description would
imply. It is to be diagnosed from the "leg ulcer," which occurs almost
exclusively on the lower third of the leg; from Bazin's disease (p. 74);
from the ulcers that result from certain forms of malignant disease,
such as rodent cancer, and from those met with in chronic glanders.
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