CONTAGIOUS PLEURO-PNEUMONIA IN CATTLE 417 
in the lines are dilated like lacune and filled with a serous or fibrinous 
fluid. In robust animals, the exudate in the alveoli is firm; but is of 
a more serous character in animals of a weak constitution. In the 
former case, a section made through the lung will be found to be 
granular. Besides these changes, the other lymph vessels of the 
lungs are dilated, their walls are infiltrated with cells and their lumen 
is in a state of thrombosis. The blood vessels frequently show 
thrombi and small hemorrhagic infarcts. The contents of the finer 
bronchi are often infiltrated with numerous white corpuscles. The 
bronchial glands and frequently the mediastinal glands are inflamed 
and swollen. ; 
After the disease has existed for some time, the affected parts of the 
lungs undergo induration, cicatrization, caseation, calcification, 
necrosis or suppuration. At first the interstitial infiltration becomes 
dense, solid and dry and changes into firm connective tissue which 
makes a crunching noise while it is being cut with the knife. In other 
places we have fatty degeneration, caseation, calcification or suppura- 
tion, in which the enclosed lobules of the lungs, in consequence of the 
existing suppuration, become gangrenous, and form sequestra sur- 
rounded by sequestral cavities which have smooth walls. The dead 
portions of the lungs may remain unchanged in these cavities for a 
long time. Frequently they become softened to the consistency of a 
greasy, yeast-like paste. Sometimes, when they are comparatively 
small, they become absorbed, and a scar is formed. The hepatized 
lobules of the lungs rarely regain their normal condition after the 
absorption of the exudate. More frequently they atrophy or collapse, 
undergo atelectasis, calcification or softening, become necrotic or sup- 
purating or form cavities. On the pleure we find thick and wart-like 
hypertrophies of connective tissue, which frequently cause the lungs 
to adhere to the sides of the chest. 
The changes in the lungs and pleure are the most important 
general lesions in pleuro-pneumonia. It is stated that we may some- 
times meet with an interstitial fibrinous exudate on the liver with 
atrophy of the liver cells; serofibrinous effusions into the articulations, 
tendon sheaths, subcutis, dewlap and brisket; intestinal catarrh; 
erosions of Peyer’s patches and ulcers on the gastro-intestinal mucous 
membrane. 
Meyer and also Boynton have called attention to the changes 
brought about in the muscle by the intermuscular injection of lymph 
from the thoracic cavity of an infected animal. Boynton concludes 
that: 
