because
certain ulcers have special seats of election--for example, the varicose
ulcer in the lower third of the leg, the perforating ulcer on the sole
of the foot, and so on.

#The Healing Sore.#--If a portion of skin be excised aseptically, and no
attempt made to close the wound, the raw surface left is soon covered
over with a layer of coagulated blood and lymph. In the course of a few
days this is replaced by the growth of _granulations_, which are of
uniform size, of a pinkish-red colour, and moist with a slight serous
exudate containing a few dead leucocytes. They grow until they reach the
level of the surrounding skin, and so fill the gap with a fine velvety
mass of granulation tissue. At the edges, the young epithelium may be
seen spreading in over the granulations as a fine bluish-white pellicle,
which gradually covers the sore, becoming paler in colour as it
thickens, and eventually forming the smooth, non-vascular covering of
the cicatrix. There is no pain, and the surrounding parts are healthy.

This may be used as a type with which to compare the ulcers seen at the
bedside, so that we may determine how far, and in what particulars,
these differ from the type; and that we may in addition recognise the
conditions that have to be counteracted before the characters of the
typical healing sore are assumed.

For purposes of contrast we may indicate the characters of an open sore
in which bacterial infection with pathogenic bacteria has taken place.
The layer of coagulated blood and lymph becomes liquefied and is thrown
off, and instead of granulations being formed, the tissues exposed on
the floor of the ulcer are destroyed by the bacterial toxins, with the
formation of minute sloughs and a quantity of pus.

The discharge is profuse, thin, acrid, and offensive, and consists of
pus, broken-down blood-clot, and sloughs. The edges are inflamed,
irregular, and ragged, showing no sign of growing epithelium--on the
contrary, the sore may be actually increasing in area by the
breaking-down of the tissues at its margins. The surrounding parts are
hot, red, swollen, and oedematous; and there is pain and tenderness both
in the sore itself and in the parts around.

#Classification of Ulcers.#--The nomenclature of ulcers is much involved
and gives rise to great confusion, chiefly for the reason that no one
basis of classification has been adopted. Thus some ulcers are named
according to the causes at work in producing