TUBERCULOSIS 



163 



The introduction of a single infected animal 

 into the herd is likely to inoculate the whole 

 herd, as the tubercle germs are thrown off with 

 the saliva and other excretions. These germs 

 when dry will live in the dark for months and, 

 settling upon the hay and other feed, are trans- 

 mitted from animal to animal. Skim-milk from 



Fig - . 44. Tubercular nodules from the abdominal cavity of a cow. 



creameries and whey from cheese factories are 

 other sources of infection. Here the milk from 

 infected cows is mixed in a common tank with 

 other milk and the whole supply thus becomes 

 contaminated. In this way the disease is often 

 spread throughout an entire neighborhood. 



