CONTAGIOUS PLEURO PNEUMONIA. 
163 
fluid is of a viscid yellow color, full of albumen, and coagulates on 
exposure to air; its quantity is in direct ratio with the amount of 
lung tissue involved, and is never absent in any case. The cause 
of this great effusion is due to the mucous congestion which oc¬ 
curs in the inflamed serous membrane. The pleura is inflamed, 
swollen and thickened, often to an inch or more. The microscopi¬ 
cal preparations which I made while fresh showed this thickening 
to be due to a large deposit of fibrous exudation, heavily charged 
with lymphoid cells, partly organized and partly soaked or infil¬ 
trated by serum, which produced an enormous oedema of this new 
formed tissue, as well as of the sub-endotheliel connective tissue 
of the pleura proper, so that sections could only be made by 
means of the freezing microtome. If put in alcohol, the mem¬ 
brane shrunk very much, and thin sections examined under the 
microscope presented nothing else than a dense fibrilar mass. The 
liquid when examined under the microscope shows few cellular 
elements, these being represented by some desquamated endothe¬ 
lial cells, usually fatty, degenerated and some leucocytes. Examina¬ 
tion of one of the numerous flakes found suspended in the serum 
showed them made up of leucocytes, fibrine and multitudes of 
micrococci. The inflammation first starts in the mucous membrane 
of the smaller bronchia and air vesicles, which are irritated by the 
specific virus taken in through the respiratory tract. This irrita¬ 
tion sets up an inflammation, the product of which is a true crou¬ 
pous exudation, which produces occlusion of the affected vesicles 
and bronchules, from which the inflammatory product spreads 
rapidly by means of the lymphatic circulation, which has an extra¬ 
ordinary development in this class of animals. By means of this 
remarkable lymphatic development in the lungs of the ox tribe, 
the irritation'readily reaches that part of the pleura which is im¬ 
mediately over the seat of the original inoculation, and when once 
this is established it spreads with ama.zing rapidity, not only over 
the sound portion of the lungs, but also by contiguity of tissue to 
the pleura costalis. When this has taken place the sound portion 
of the lungs is involved in two directions, centrally and superfi¬ 
cially; that is to say, by the. broncho-vascular lymphatic circula¬ 
tion, and from the pleura downward into the substance of the 
