276 AGRICULTURAL BACTERIOLOGY 



There is no fever or pain in the tubercular udder, as in the 

 case of acute inflammations. 



Distribution of the tubercle bacillus. The organisms are 

 eliminated in the sputum discharged from the mouth in 

 the act of coughing, in the feces, and to some extent in the 

 milk. In the stable the material from the digestive tract 

 becomes dry, and the dust therefrom with the adherent tu- 

 bercle bacilli may be drawn into the air-passages of healthy 

 animals. The fodder or water may be contaminated with 

 infectious material, or the transmission of the organism 

 may be direct, through the diseased animal licking herself 

 and then being licked by a healthy animal. The milk be- 

 comes infected through the introduction of manure and 

 dust, and also from tubercular udders. The feeding of 

 such milk to calves and hogs readily serves to infect them. 

 Hogs also acquire the disease from following cattle in the 

 feed lot or from manure. The reproductive organs are 

 rarely diseased, and calves from tubercular dams are usually 

 healthy. 



The spread of the disease in the herd may be rapid or 

 slow, the determining factor being the prevalence of cases 

 of open tuberculosis. It is a popular view that the disease 

 will not spread among cattle kept out of doors or in stables 

 well ventilated and lighted. Experience shows these views 

 to be wrong, and that when open cases, or spreaders, as they 

 are called, which give out large numbers of the organisms, 

 are present, the disease will spread rapidly under condi- 

 tions ideal in other respects. 



Infection of the herd. The infection of the herd takes 

 place through the introduction of a tubercular animal, or 

 through the use of contaminated products, such as the milk. 

 In the more acute communicable diseases, the transmission 

 of the organism from place to place may be accomplished by 

 the transportation of contaminated objects, but in the case 



