288 TUBERCULOSIS 
Moreover, since the cow does not expectorate, she does swallow the 
secretions from her mouth. The tubercle bacilli will thus be 
carried to the stomach, and through the intestine, from whence 
they will be voided with the excrement. If the disease is located 
in the intestine the bacilli will be sure to be discharged with the 
excrement. In these ways the excrement of tuberculous cattle is 
sure to be impregnated with the bacilli, Now the conditions of 
the ordinary cow stall, even in the best cow barn, are such as to 
make it almost inevitable that the infectious material will soon be 
distributed through the whole barn. The excrement may be 
carried over the floor, perhaps, for some distance to the opening 
used for its exit, and the farmer’s boots will always collect more 
or less and carry it through the barn. The particles adhering 
to his boots will be sure to be knocked off when dry, and will thus 
be carried everywhere that the farmer goes. They will be certain 
to be dislodged near a healthy cow and may become mixed with 
her food which is commonly thrown on the floor in front of her; or 
the particles may become dry and be distributed through the barn 
as dust. In short it is inevitable that the bacilli voided with the 
excrement will in time come in contact with every healthy animal 
kept in the same barn. 
Once distributed from infected animals, the bacilli may find 
entrance into the healthy animals, by a variety of channels. Some 
find entrance to the lungs, either by the dust particles or by the 
bacilli-laden moisture drops from coughing animals, which are 
breathed by healthy animals. The bacilli which find their way 
into the watering trough will be swallowed, and the same will be 
true of those which the animal takes into its mouth by licking its 
infected neighbor. These two means of entrance are doubtless 
responsible for most cases of bovine tuberculosis, and it is very 
easy to understand how a single diseased animal in a barn may, 
in time, infect most of the herd. 
Abundance of Bovine Tuberculosis.— Tuberculosis is widely 
distributed among cattle, although it is by no means universally 
