quine
pleuropneumonia; influenza pectoralis equorum; pleuropneumonia;
influenzal pneumonia; Brustseuche (German).

Contagious pleuropneumonia is an acute contagious disease of horses
manifesting itself either as a croupous pneumonia or a pleuropneumonia
with complications in the form of serous infiltrations of the
subcutaneous tissues and tendons.

_Etiology._--Investigators of this disease incriminated various kinds of
microorganisms as the cause of this affection. Transmission experiments
were usually negative with these organisms. This was also the case in
attempts to transmit the disease by feeding with affected parts of the
lungs, intestinal contents, and nasal discharge; likewise by
intravenous or subcutaneous injections of blood and of emulsions made
from nasal discharge, urine, the lung, and other organs.

The most recent experimental results of Gaffky and Lueber proved that at
least at the beginning of the disease the bronchial secretion contains
the infection. Upon killing horses affected with the typical forms of
the disease on the third or fourth day of the affection the air passages
are usually found to be filled with a yellowish, tenacious, germ-free
secretion with which they succeeded in infecting healthy colts. The
virus has not been isolated. The possibility of its being a protozoan is
suggested by the above-named investigators through their observations of
round or rod-shaped bodies in the round cells of the secretions.

Two organisms were formerly especially considered to play an important
part in the cause of the disease, the _Streptococcus pyogenes equi_,
which has been isolated from most cases of the disease, and the
_Bacillus equisepticus_, which by some investigators was considered to
be the cause of contagious pleuropneumonia. Although there is no doubt
as to the presence of these microorganisms in most of the cases, their
association with the cause of this disease, however, is now doubted,
especially since attempts to transmit the disease with pure cultures of
these germs failed to reproduce the typical form of the disease. They,
however, are of great significance in connection with the pathological
changes occurring in connection with the infection and probably are the
determining factor in the course of the disease. They exert their action
after the animal has already been attacked by the true virus, and then
produce the inflammatory changes attributed to these secondary invaders