1 66 BOVINE TUBERCULOSIS 



may appear to be in good health. In the earlier stages the 

 progress of the disease may become arrested and complete 

 recovery follow ; in the majority of cases, however, it pro- 

 gresses, sooner or later, to a fatal termination. In the later 

 stages, the animal shows its presence by more or less charac- 

 teristic symptoms. 



SOURCES OF INFECTION 



When the tubercles ulcerate, or break down, their contents 

 escape into the air passages or intestines and are thrown out 

 by these channels. The bacilli are contained in these dis- 

 charges, often in great numbers. If they are coughed up and 

 fall upon fodder of some kind which is eaten by another 

 animal, here is an excellent chance for infection. If manure, 

 or discharges from the lungs, containing bacilli, fall where 

 they become dry and are later powdered by trampling or some 

 other means, the bacilli then rise in the dust and may be 

 inhaled and start the disease in the lungs of other animals. 

 Cattle by licking themselves and one another furnish a way 

 for the spread of bacilli. If bacilli are contained in the milk, 

 calves fed upon it are exposed to infection. It is possible that 

 an animal may be born with tuberculosis and so be said to 

 inherit the disease from a tuberculous parent ; such cases are, 

 however, comparatively rare. The ground for the general 

 belief that the disease is inherited, viz., the fact that the 

 offspring of tuberculous parents frequently die of tuberculosis, 

 is explained in this way : What is inherited is not the disease 

 itself, but a constitution or condition of the system, which 

 lacks the normal resistance of perfect health, and which yields 

 readily to the invasion of tubercle bacilli. 



TRANSMISSION 



Can the disease be transinitted fro7n cattle to vian or from 

 mail to cattle? There is no need to dwell on the importance 

 of this question. In its general history and behavior the dis- 

 ease appears to be the same in man and cattle ; but there are 

 bacteriologists who believe that there may be a difference. 

 This, however, does not seem at present to be clearly estab- 

 lished. With this belief in a difference is associated the 



