IMPORTANT INFECTIOUS DISEASES 475 
of tubercle bacteria in the tissues of the animal. ‘Thc 
bacteria, or germs of tuberculosis, gain entrance to the 
organs of the body through air, drink or food. They 
most frequently attack the lungs, bronchial glands, liver, 
kidneys and intestines, but tuberculous areas may be 
found in almost any part of the infested animal. The 
disease is spread by germs escaping from diseased ani- 
mals and getting into the bodies of healthy ones. After 
the germs gain a foothold they will multiply and produce 
the disease, just as the seed of a noxious weed, if blown 
into a new field, will germinate and produce the weed 
there. Tuberculosis spreads from animal to animal on 
the same principle that weeds spread from one field to 
Se eer 
TupBercuLous Cow 
Note the emaciated condition, sickly attitude and coarse 
rough coat. 
another. .By using tuberculin, affected animals can 
usually be located. The simplest way to prevent the 
spread of tuberculosis is to prevent healthy animals from 
coming in contact with the diseased ones or eating or 
drinking after them. 
15. Control of infectious diseases——From time im- 
