CROUPOUS PNEUMONIA IN THE HORSE. 117 
by the most competent authorities to be the specific agent of 
this disease. It is identical with the micrococcus which Pasteur 
and Sternberg found in the saliva of certain individuals and 
which produces Septicaemia in the rabbit. The researches of 
Friedlaender, Weickselbaum and others show that it is by far 
the most constant organism in pneumonia. According to the 
dominant view pneumonia is an infectious disease caused by 
this diplococcus which has its main seat and produces its chief 
effect on the lung, and can under favorable circumstances invade 
the pleura, meninges and endocardium. It is a widespread 
organism, at times present in the buccal secretions of healthy 
animals, in the secretion of the nose and mouth it may be 
demonstrated by treating the ordinary cover glass preparation 
with glacial acetic acid, and then washing off the acid, dropping 
on aniline oil and gentian violet, which is to be poured off and 
renewed two or three times. The organism is seen to be some¬ 
what elliptical, lance-shaped coccus occuring in pairs, hence 
the term diplococcus. It is usually encapsulated. Inoculation 
experiments upon dogs, guinea pigs and mice have proven suc¬ 
cessful. The germ producing the well-known pathological 
changes occuring in croupous pneumonia. 
Morbid Anatomy: Since the time of Lannaec, pathologists 
have divided the stages of pneumonia into three well-known 
divisions of engorgement, red hepatization and grey hepatiza¬ 
tion. 
The stage of engorgement usually lasts but a short time, 
from twelve to thirty-six hours. The lung tissue is deep-red in 
color, more solid and on section the surface is bathed in blood 
and serum. Crepitation is still present although not so marked 
as in normal lung. 
In the stage of red hepatization the lung tissue is firm, solid 
and airless. On section the surface is dry, reddish-brown in 
color and the deeply congested appearance of the first stage is 
absent. In this stage the lung is very friable and is readily 
broken by the finger. Careful inspection shows the surface to 
be distinctly granular and the air cells filled with fibrinous 
