THE ACID FAST GROUP 379 



to tuberculin for a few days thereafter, or in some cases 

 for a longer period. This fact has been made use of by dis- 

 honest cattlemen in securing certification of freedom from 

 tuberculosis in animals. The veterinarian who makes the 

 test, however, may overcome the results of such previous 

 injection by the use of larger doses of tuberculin or by the 

 use of the intradermal test. 



It should be noted furthermore, that in some cases, ani- 

 mals that are in the last stages of the disease or are con- 

 siderably emaciated may fail to show the reaction. The 

 presence of large numbers of organisms constantly in the 

 body has made it impossible for the animal to react nor- 

 mally to the injection of the tuberculin. Naturally the fact 

 that animals showing very marked symptoms of the disease 

 may occasionally fail to show the reaction while animals 

 having only slight lesions, perhaps only an obscure nodule 

 in a lymph node, may show marked reaction, has led to 

 considerable skepticism on the part of practical farmers 

 with reference to the test. When properly understood, 

 however, it may be regarded as reliable. 



Transmission. Tuberculosis in man is transmitted most 

 commonly by inhalation of infectious droplets thrown off in 

 coughing, through contaminated drinking vessels and in 

 some cases undoubtedly by the eating of food containing 

 the tubercle bacillus. The bacteria leave the body with the 

 sputum or feces and occasionally with the urine. 



Tuberculosis exists in animals and man either as a closed 

 or an open type. In closed tuberculosis the bacteria are 

 present in organs or tissues that have no direct communica- 

 tion with the surface of the body. The presence of tubercle 

 bacilli, for example, in the lymph nodes, would not neces- 

 sarily lead to their being discharged by the body. In open 

 tuberculosis the bacteria are growing in tissues which com- 

 municate readily with the surface of the body, in the lungs, 

 in the liver or in the walls of the alimentary tract. In 



