Infection of Milk. 73 



the disease sooner or later spreads from the originally 

 affected animal to others in the herd. Close contact, 

 and close confinement in ill ventilated stables facilitate 

 the spread of the disease, and sooner or later, other ani- 

 mals acquire the trouble. This may all occur while all 

 animals appear in a healthy condition. 



The symptoms of the disease in the earlier stages 

 are quite indefinite. As the disease progresses, the nu- 

 tritive functions appear to be disturbed, and sooner or 

 later, the body weight begins to decline, and finally 

 marked emaciation ensues. Accompanying this condi- 

 tion, especially when the disease is in the lungs, is a 

 cough, which is generally aggravated with active ex- 

 ercise. While the run-down condition permits fre- 

 quently of the detection of the disease in the advanced 

 stages, it is wholly impossible with any accuracy to 

 diagnose the trouble in the incipient stages. It is at 

 this stage that the tuberculin test comes to the aid of 

 the stockman. 



Tuberculin test. This test is made by the injecting 

 beneath the skin of the animal a small quantity (about 

 2 c. c.) of tuberculin, and noting the temperature of 

 the animal, before and after the injection. Tuberculin, 

 a product of the growth of the tubercle bacillus, when 

 injected into the body causes a marked rise in tem- 

 perature, in the case of an animal affected with the dis- 

 ease, and no such elevation in the case of a healthy ani- 

 mal. The process of preparing tuberculin makes it ab- 

 solutely free from danger, so far as liability of produc- 

 ing the disease, or in any way injuring the animal, is 

 concerned. Fig. 19 shows the temperature range of 

 both reacting and non-reacting animals. While the 



