172 Animal Husbandry 
in many cases good care is to be preferred to the use of medicine, 
p. 89. , 
285. Tuberculosis.— Perhaps no disease to which cattle are. 
subject is more discussed than tuberculosis. This is due-in 
large measure to the use of cattle to provide food for the hu- 
man race. There are perhaps few diseases so common among 
cattle as tuberculosis, particularly among those animals that are 
kept closely confined. 
Tuberculosis is a communicable germ disease, and is, therefore, 
preventable. The disease is caused by a small germ or bacterium 
known as Bacillus tuberculosis. This germ is, of course, invisible 
to the naked eye. 
286. Methods of infection. — As tuberculosis is a communi- 
cable germ disease, the methods of infection should receive much 
attention. This can be made clear by considering from two points 
of view: first, how the germs escape from diseased animals; and 
second, how sound animals become infected. All diseased ani- 
mals possess the germ. This germ escapes when the tissues it 
has destroyed are being discharged from the body. Thus, if the 
lungs are affected, the animal on coughing dislodges the germs, 
which may be forced directly out of the body or lodged in the 
mouth, when they leave the body with the saliva. In the cases 
in which the germs are found in the saliva they are left in the 
watering troughs, on the bottom of the mangers, on the grass, on 
other animals when licked by diseased ones, and in fact spread 
wherever the diseased animal goes. 
When the germs have escaped into the watering troughs, man- 
gers, on the grass, and the like, they are readily taken up by healthy 
cattle. In case the germs escape in the milk, whatever feeds upon 
it is liable to infection. The length of time that will pass after 
infection and before the disease visibly appears varies widely, 
even to months or years. The length of time the animal may 
possess the disease varies equally as much. With some it may 
prove fatal in a few months; others may carry it for years. 
