So long as we retain these names it will be impossible to find a single
basis for classification; and yet many of the terms are so descriptive
and so generally understood that it is undesirable to abolish them. We
must therefore remain content with a clinical arrangement of ulcers,--it
cannot be called a classification,--considering any given ulcer from two
points of view: first its _cause_, and second its _present condition_.
This method of studying ulcers has the practical advantage that it
furnishes us with the main indications for treatment as well as for
diagnosis: the cause must be removed, and the condition so modified as
to convert the ulcer into an aseptic healing sore.

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 Röntgen 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