INFECTIOUS DISEASES OF CATTLE. 405 



collapses. Subsequently it becomes filled with, yellowish, cheesy mat- 

 ter, which greatly distends the small air tubes and air vesicles (bron- 

 cho-pneumonia). The connective tissue between the lung lobules, 

 around the tubercles, and around the air tubes becomes thickened and 

 indurated. In the larynx and the bronchi tubercles may vegetate 

 upon the mucous membrane, and ulcers may result from their break- 

 ing down. The inflammatory irritation which the growth of the 

 tubercles on the surface of the lungs arouses gives rise to adhesion of 

 the lungs to the ribs and diaphragm. This adhesion is sometimes so 

 firm and extensive that the lungs appear grown to the chest wall. 



When, therefore, the lungs in advanced stages of the disease are 

 cut open we observe large, yellowish masses, from one-quarter to thi-ee- 

 quarters of an inch in diameter, of a cheesy texture, in which calcified, 

 gritty particles are embedded and which are surrounded by very firm 

 connective tissue. The neighboring lung tissue, when collapsed and 

 involved in broncho-pneumonia, has the color and consistency of pale- 

 red flesh. The air tubes, large and small, stand out prominently on 

 the cut surface. They are distended with a pasty, yellowish, cheesy 

 mass, surrounded and enveloped in thick mucus, and their walls 

 greatly thickened. The larger bronchi may be sacculated, owing to 

 the distention produced by the cheesy contents. 



The disease usually attacks the bronchial glands, which are situated 

 on the trachea and bronchial tubes at the bifurcation. The changes 

 in the glands are the same as those going on in the lung tissue, and 

 they frequently reach an enormous size. 



The tubercle formation on the serous membranes covering the lungs 

 and chest wall (PI. XXXIX, fig. 2), which may go on at the same time 

 with the lung disease or independent of it, has been called "pearly 

 disease," on account of the peculiar appearance of the tubercles. 

 These begin as very minute, grayish nodules, which give the originally 

 smooth, lustrous membrane a roughened appearance. These minute 

 tubercles enlarge, become confluent, and project above the surface of 

 the membrane as wart-like masses, attaining the size of pease. In this 

 stage their attachment to the membrane is by means of delicate fibers. 

 The attachment is loose, so that the tubercle hangs by a short pedicle 

 or neck and may be moved slightly to and fro. Large masses are fre- 

 quently formed by a coalescence of many tubercles and the secondary 

 formation of the same. These may be found on the lungs, the ribs, 

 and the diaphragm. These tubercles likewise undergo degenerative 

 changes. The center partly softens and partly calcifies into a grayish 

 mortar-like mass, and are gritty. Associated with the formation of 

 tubercles on the pleura, those glands situated back of the center of the 

 lungs between the two main lobes (posterior mediastinal) become greatly 

 enlarged and the center cheesy. (PI. XXXVI.) They may compress 

 the esophagus and interfere with swallowing. The size attained by 

 these tumors and new growths is well illustrated by the fact that, 



