332 SWINE PRACTICE 



ences. This resistance is probably due to the waxy coat they possess. 

 Direct sunlight destroys them when freely exposed for twenty to 

 thirty minutes, but they retain their vitally and virulence for from 

 ten to twenty days when exposed to diffuse daylight. "When desiccated 

 and not exposed to light they may retain their virulence for four 

 months or even longer. In decomposing tubercular tissues they re- 

 main virulent for a long time. In milk they retain virulence for. ten 

 days. Dry heat at 212 degrees Fahrenheit destroys them in one hour ; 

 moist heat at the boiling temperature will destroy them in fifteen 

 minutes. They are also destroyed by chemical disinfectants, the 

 length of time for exposure depending upon th concentration of solu- 

 tion and the nature of the tissue or discharge incorporating the bacilli. 

 Gastric juice does not destroy the tubercle bacilli, and bile has little 

 or no injurious effect upon them. 



The inoculation of healthy, susceptible animals with virulent bacilli 

 produces tuberculosis, the extent of the lesions produced depending 

 upon the virulence of the bacilli injected and upon the resistance of 

 the inoculated animal. 



Source of infection. — Tubercle bacilli are eliminated from the 

 affected animals, at least when there are open lesions in organs, the 

 secretions or excretions of which pass to the outside world. Thus the 

 tubercle bacilli are eliminated in the feces from animals having tuber- 

 culous ulcers of the intestinal mucosa. Open tuberculous lesions of 

 the respiratory tract would permit of the elimination of the tubercle 

 bacilli in the discharge from the air tubes and also in the feces, for 

 the chances are that the pharynx would become contaminated by the 

 pulmonary or tracheal discharge and this infection would be carried 

 with food or drink and ultimately pass from the body in. the feces. 

 Tubercle bacilli from lesions in the liver or pancreas may also be 

 eliminated in the feces. 



Tubercle bacilli from open tubercular lesions of the urogenital 

 organs are eliminated in the urine, seminal fluid, or other discharges 

 from these organs. Infection is directly eliminated from open, cuta- 

 neous, tuberculous lesions, and tubercle bacilli may be eliminated in 

 the milk, especially if tuberculous lesions exist in the mammary 

 gland. 



The dissemination of tubercle bacilli in the body and the possibility 

 of their elimination through any channel is facilitated by leukocytes. 

 Thus tubercle bacilli in the lung may be incorporated and retained 

 by leukocytes that are later eliminated by the mammary cells, and the 



