_Name and Definition._ The word _croup_ by which this disease is known
over the whole of Europe and a great part of America is, essentially
_Scotch_, and is familiarly used in the Lowlands of Scotland to
signify—_to croak_. The disease consists in an acute inflammation or
high vascular irritation of the larynx, associated with spasms of its
muscles and commonly though not invariably with a firm layer of
exudation on the surface of the mucous membrane. In some cases
undoubtedly croup is but a form of the contagious pseudo-membranous
affection diphtheria, the germs of which grown on a surface freely swept
by continuous currents of pure air, retain too much of an ærobic habit
to penetrate deeply into the tissues. (See Authors, “Malignancy
mitigated by Oxygen,” Medical Record, 1881, p. 673). It does not follow,
however, that croup is always due to even a weakened germ. So far as yet
appears it may develop independently of any particular pathogenic germ,
from some violent local irritant in a predisposed subject. Croup
therefore may be treated here as a presumably noninfectious disease.
Being a very rare disease in horses its manifestation in ruminants will
first be noticed.