TUBERCULOSIS— CONSUMPTION 433 



Necropsy. — ^The lesions of tuberculosis may appear in any 

 organ in the body with the exception of the teeth. The loca- 

 tion of the lesion may depend upon the kind of animal, mode 

 of infection, and whether the disease is primary (local), or 

 secondary (generalized). In the ox, tuberculosis is usually 

 confined to the lungs, serous membranes, and lymph glands. 

 In swine the digestive tract with corresponding lymph glands 

 is most frequently involved. In the horse the lymph glands 

 (mesenteric, retroperitoneal) are generally elected. How- 

 ever, exceptions to this rule are frequently noted; in gener- 

 alized (spread via blood) tuberculosis the nodules may occur 

 in any organ, even being found in muscle. The influence of 

 the mode of infection is difficult to determine, since it has 

 been proved that subcutaneous inoculations in calves (even 

 at the tail tip) with tubercle bacilli were followed by pul- 

 monary lesions. 



The most characteristic lesion in tuberculosis is the tuber- 

 cle which has undergone caseous degeneration. The lesion 

 may vary in size from a small millet seed (miliary tubercle) 

 to a cheesy mass larger than a human head, due to the con- 

 fluence of numbers of smaller foci. While the individual 

 tubercle is at first of a translucent, gray appearance, later 

 from the degeneration, which begins in its center, it assumes 

 a yellow color. The formation of nodules tending to caseate, 

 particularly if corresponding lymph glands are similarly 

 affected, is characteristic of tuberculosis. 



Ox. — As noted, the lungs, serous membranes, lymph glands, 

 especially the bronchial and mediastinal, are most commonly 

 involved. 



Lungs. — In the lungs nodules or nodes of varied size, of 

 firm to fluctuating consistency, with usually well-defined out- 

 line, invade the tissue. On cut surface the dry, yellow, 

 friable caseation surrounded by a thick capsule is found, or, 

 on the other hand, the contents are soft, puriform, thick- 

 fluid, covered by a thin, connective-tissue layer. The color is 

 grayish-yellow to pronounced yellow. The size will vary 

 from that of a millet seed to a clenched fist, or, by confluence, 

 a whole lobe of lung tissue may be found changed to a case- 

 ous mass. In old cases calcification of the tubercle occurs, 

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