ACID-FAST GROUP 



315 



are generally susceptible to infection with B. tuberculosis. The 

 constant presence of the organism in the lesions of the disease 

 and its ability to reproduce the disease are sufficient evidence 

 that it is the true etiologic factor. 



Important differences in pathogenesis are to be noted among 

 the three varieties. The bovine bacillus is most pathogenic for 

 laboratory animals, the human next, and the avian least (except 



Fig. 129. Tubercular hypertrophy of the intestinal wall in the bovine 



(Chausse). 



for birds). Guinea-pigs inoculated subcutaneously with bovine 

 bacilli generally succumb in less than fifty days; those inoculated 

 with human bacilli generally live more than fifty days. Intra- 

 peritoneal injection of the bovine type is fatal in seven to eighteen 

 days, of the human type in from ten to thirty-eight days. The 

 difference upon intravenous injection of the rabbit is even more 

 marked with bovine bacilli death occurs within three weeks, 

 with human bacilli the animals usually live for several months 



