22 
A. W. CLEMENTS. 
<* 
the great majority of cases occluded, but in some cases a fine 
probe may be pushed through them. Finally these projections 
slough off, and their ends becomes covered by the connective tis¬ 
sue, which grows from the lung, surrounding the necrosed mass; 
Sometimes ulceration may take place in a bronclious at the border 
of the diseased portion before complete occlusion has taken place, 
and so establish direct communication between the contents of the 
cyst and the healthy lung. This is the only way in which there is 
bronchial communication with a pleuro-pneumonia cavity. A 
bronclious is often seen leading toward a cyst, but instead of pen¬ 
etrating the wall it passes to the side of it. The new formation 
of peri-bronchial connective tissue, together with the pressure of 
the walls of the cavity, serve to completely occlude the bronchi. 
What causes the necrosis is hard to say. One would think 
that the plugging of the blood vessels leading to the part would 
be sufficient, but we see the same necrotic processes, on a very 
much smaller scale, in the bronchial glands. Perhaps the virus 
which causes the disease has the property of producing necrosis, 
and at the same time of plugging the blood vessels. As soon as 
sequestration is complete, disintegration of the necrosed mass takes 
place, and the cavity becomes filled with serum or, more com¬ 
monly, with a purulent material, in which more or less of the 
sequestrum remains. 
What I have said refers to typical pleuro-pneumonia. Unfor¬ 
tunately many cases which we are called upon to diagnose are by 
no means typical. For example, a herd of cows came to Balti¬ 
more from outside of the quarantine limits, from a region where 
pleuro-pneumonia was not supposed to exist. Soon after arrival 
two of them presented symptoms of acute contagious pleuro-pneu- 
monia. One was slaughtered, and at the post-mortem the follow¬ 
ing lesions were found: double pleurisy, both lungs enlarged and 
solid on pressure. On section of the lungs the following appear¬ 
ances were noticed: there was interlobular exudation precisely 
like that seen in acute pleuro-pneumonia contagiosa, but it affected 
the greater portion of both lungs, and there was no hepatization 
of the parenchyma except in a very small area of one lung, and 
there the consolidation was of the broncho-pneumonia type. When 
number two was slaughtered, much the same appearances were 
