TUBERCULOSIS 285 



source of infection for calves and liog-s. Allowing hogs to run 

 after cattle is sure to result in infection of a large percentage of 

 them, if there are any o^oen cases of tuberculosis in the herd. 



Predisposing Causes. — Any condition that may lessen the 

 resistance of the body or enable the tubercle bacillus to survive 

 the exposure outside the body favors the development of the 

 disease and the infection of the healthy animals. Crowded, 

 poorly ventilated, filthy stables lower the disease-resisting power 

 of the animal, and favor the entrance of the germs into the body. 

 Under such unsanitary conditions, tuberculosis spreads quickly 

 among dairy cattle, and a large percentage of the animals de- 

 velop the generalized form of the disease. Sanitary stables and 

 yards do not prevent the spread of the disease among animals 

 that live in close contact with one another. Fresh air and sani- 

 tary surroundings only check the spread and retard its progress. 



Introduction of Tuberculosis into the Herd. — The common 

 method of introducing tuberculosis into the herd is through the 

 purchase of animals having the disease. Such animals may be 

 in apparent good health at the time of purchase, and be affected 

 with generalized or open tuberculosis. 



A source of infection is by unknowingly buying cows that 

 have reacted to the tuberculin test. The indiscriminate use and 

 sale of tuberculin are largely responsible for the large number 

 of reacting animals that have been placed on the open market. 

 This dishonest practice has resulted in the rapid spread of the 

 disease in certain localities. For years a large percentage of 

 the l)reeding herds have been infected, and the writer has met with 

 several herds of dairy and beef cattle that became tubercular 

 through the purchase of tubercular breeding animals. 



Symptoms. — There is no one symptom by which w^e may 

 recognize tuberculosis in cattle and hogs. ISTone of the symptoms 

 shown by a tubercular animal are characteristic, unless it is in 

 the late stage of the disease. In a well-cared for animal, the 

 lymphatic glands iu the different regions of the body, the lungs, 



