INFECTIOUS DISEASES 333 



milk become infected even though the mammary gland contain no 

 tuberculous lesions. 



From the foregoing it is evident that any of the discharges of tuber- 

 culous animals may contain the tubercle bacilli. In the United States 

 and in practically all other countries tuberculosis of cattle is prevalent, 

 particularly among cattle used for dairy purposes. 



The most frequent source of porcine tuberculosis is from tubercu- 

 lous cattle. Swine become infected from the infected cow's milk, feces, 

 nasal discharges, and the carcasses of tuberculous cattle that are given 

 them for food. A limited number of swine become infected from 

 garbag-e that contains the human tubercle bacilli. This has been 

 especially observed in swine fed upon garbag'e from tuberculosis san- 

 itaria, or hotels. An occasional case of uterine, ovarian, or testicular 

 tuberculosis is the result of direct infection by copulation. It is pos- 



Fig. 97. TUBERCULOSIS OP THE TONGUE. A, normal muscle; B, tuberculous 

 lesions; this is a rare condition in swine. 



sible that infection may be transmitted in the exhaled air from in- 

 fected to healthy swine. 



Channels of entrance. — The most frequent channel of entrance of 

 the tubercle bacilli in swine is the digestive tube, the infection being 

 introduced in food or water. An occasional case may become infected 

 by the inhalation of the bacilli and by direct transmission through the 

 genital organs. Mammary tuberculosis may be the result of cutaneous 

 infection or it may be transmitted from elsewhere in the body. 



The transmission of the tubercle bacilli from the mother to the 

 fetus is possible, but it is of rare occurrence. But a weakened con- 

 dition or susceptibility to the disease may and frequently is trans 

 mitted from the mother to the fetus. 



