THE RESPIRATORY SYSTEM 155 
appears a richness of nuclei, of round, moderately well 
stained character, among which one may see a few gran- 
ular and red blood cells. Soon the. epithelia of adjacent 
alveoli increase in number and a fibrinocellular exudate 
appears, at first probably in the smaller sacs. However 
when the lesion is intensive the course of events must be 
rapid for the identity of a. group of primary alveoli is soon 
lost and the exudate may extend to the larger air space. 
(Fig, 11) In severe or late cases a decision as to the 
course of origin is often impossible. The most instructive 
point of this part of the study is the closing of primary 
alveoli by the swelling of their septal ends and the early 
occlusion of the secondary alveolus by a catarrho- 
fibrinous or even pus-like material. It is quite possible 
that a similar course of events transpires in the path- 
ogenesis of human pneumonia, the superficial avian form 
being comparable to the aspiration form, the interstitial 
form comparable to the septicemic variety. 
Abscess and Gangrene of Lung. 
Abscess and gangrene of the lung are degenerative 
processes dependent upon embolism, or inspiration of 
infective matter and it is usually assumed that gangrene 
succeeds upon abscess when the blood or air supply of a 
part of the pulmonary tissue has been obstructed 
mechanically or by inflammation. A review of our 
material adds little to the etiology or pathogenesis of 
these two lesions, well recognized as they are by veterina- 
rians. As opposed to human beings, lower animals prob- 
ably suffer more from them, for an explanation of which 
one can probably look to the B. necrosis or necrophorus, 
an organism quite common in feed, and acknowledged to 
be of great importance as a secondary invader during 
specific infectious diseases. It has been found in embolic 
abscesses and in the organs in calf diphtheria and similar 
other conditions. It has been cultivated here twice, once 
from a lung abscess, once from Kangaroo disease. It 
