CONTAGIOUS DISEASES OF CATTLE. 451 



soon follows, the nearest lymphates becoming affected. The 

 mode of spread is by continuity of tissue, and by lymphatic veins, 

 arteries, and 'by the affection, of one part from another. The 

 germs may pass through the lungs, thence by the pulmonary 

 capillaries to the systemic circulation. "We are able to recognize 

 the presence of tuberculosis in the dead animal by the character- 

 istic tubercles — the formations which give the disease its name. 

 These tubercles are small, hard masses, which may be present in 

 almost any part of the body, but are most frequently found in 

 the lungs, pleura, peritoneum, liver, intestinal walls, and the 

 lymphatic glands belonging to these organs. The tubercle is, at 

 first, a small, grayish, opalescent mass, the size of a millet seed, 

 which may be single or a number may be found side by side, thus 

 making a large, diseased area. As the tubercle or tubercular 

 mass grows older it becomes yellow, and forms a cheesy mass. 

 Especially is this noticed in connection with tubercles in the 

 lungs. We have here the yellow and the gray. The gray are 

 semi-transparent nodules of a grayish-white color, varying in size 

 from a pin-head to a hemp seed or shot. They are somewhat 

 spherical in shaj)e, and usually possess a well-defined outline. The 

 yellow are much larger. I have seen in the lungs of cattle large 

 cavities filled with a yellowish thick fluid mass known as tu'bercu- 

 lar abscesses. Some of them are larger than walnuts. They are 

 irregular in outline. AVhen the tubercles are situated in the 

 pleura or peritoneum, the growths are usually hard and nodular. 

 The normal smooth and glistening surface is dotted or thickly 

 studded with sound, hard masses, ranging from the size of a 

 mustard seed to that of a grape. In the liver the tubercular 

 masses are similar to those of the lungs. Immense numliers of 

 these tubercles may conglomerate to form a collection of diseased 

 products, as large as an apple between the lungs and chest wall; 

 masses even larger are found. If one of the diseased lymphatic 

 glands be cut across, it will be noticed that small, yellow spots 

 dot the cut surface. Sometimes the whole center of the gland is 

 taken up by this cheesy substance. In other cases the gland be- 



