Quotation from: Manual of Surgery

Written by: Alexander Miles and Alexis Thomson

_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.