COMMON AILMENTS OF CATTLE 327 



germs of the disease with the manure. From this source 

 some of the germs may find their way into the milk, making 

 it possible for the milk to be infected even when no germs 

 come through the udder. 



Tuberculosis in a cow may run its course quickly, result- 

 ing in the death of the animal, but this seldom occurs. As a 

 rule, it progresses slowly and the animal may have it for 

 years without any indication of ill health. All this time the 

 animal is a menace to the health of the people. The dis- 

 ease may attack any part of the animal's body, but is most 

 common, as with persons, in the lungs. 



It should be thoroughly understood that it is impossible 

 to judge from external appearances, except in extreme cases, 

 whether the animal is affected or not. Neither can any 

 examination of the milk that can be made be depended 

 upon as a reliable test of the presence of the disease. For- 

 tunately we have in the substance known as tuberculin an 

 almost infallible agent for determining the presence of the 

 disease even in the smallest degree. Before many years it 

 will unquestionably be required by law that every cow sup- 

 plying milk for human food be tested with tuberculin and 

 found free from tuberculosis, as is now done by a few cities. 

 Even leaving the question of human health out of considera- 

 tion, the dairy cow owner should have his animals tested 

 and keep his herd free from this disease for pecuniary reasons. 

 The breeder of pure-bred stock who can guarantee his ani- 

 mals to be free from tuberculosis finds it a valuable recom- 

 mendation. The breeder in starting a herd should by all 

 means start with clean animals ; then if every one added to 

 the herd later be tested, it is an easy matter to keep the 

 disease out. It is advisable, however, to have the entire 



