402 DISEASES OF CATTLE. 



In the lungs (Plate XXXIY) the changes observed vary according to the 

 ago and intensity of the disease process. They usually begin with the 

 appearance of very minute tubercles. These may appear in large num- 

 bers on the surface of the lungs or within the lung tissue. Later the 

 contents become cheesy and partly calcined. When these tubercles 

 are sufficiently numerous to become confluent large masses may be 

 formed, which undergo the same retrogressive changes of caseation 

 and calcification. In addition to the formation of tubercles in the luug 

 tissue certain other changes take place. There is usually present- bron- 

 chitis with abundant catarrhal secretion. This plugs up the smaller 

 air-tubes, and the lung tissue supplied by these tubes with air collapses. 

 Subsequently it becomes filled with yellowish, cheesy matter, which 

 greatly distends the small air-tubes and air vesicles (broncho-pneu- 

 nionia). 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 breaking down. The in- 

 flammatory irritation which the growth of the tubercles on the sur- 

 face 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 three- 

 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 011 

 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 dis- 

 tension 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, 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 con- 

 fluent, and project above the surface -of the membrane as wart-like 

 masses, attaining the size of peas. 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 frequently formed by a 



