ACID-FAST GROUP 



311 



under certain conditions, in the animal tissues in particular, this 

 acid-fast property may be temporarily lost. The acid-fast char- 

 acter is apparently due to the presence of a wax-like substance in 

 the bacterial cell. The cells from which this has been removed by 

 ether and benzol are no longer acid-fast. 



There are certain morphological differences commonly to be 

 observed between bovine and human tubercle bacilli. The 

 former are shorter, straighter, and thicker than the latter. They 

 are also less apt to show the irregular or granular staining noted 

 above. These characters are, of course, not sufficient to differen- 

 tiate isolated bacteria of the two types, but cultures can usually 

 be identified readily by an ex- 

 perienced observer. Whether 

 or not one type may be trans- 

 formed into the other type 

 by animal inoculation or by 

 cultural methods is a moot 

 question. Some investigators 

 claim to have isolated typical 

 human bacilli from animals 

 that have been inoculated 

 with bovine bacilli, others 

 hold that there is no evidence 

 of the transformation of the 

 one type to the other. How- 

 ever this may ultimately be 

 decided, it is certain that each 



type retains its characters with a considerable degree of con- 

 stancy. The existence of two well-marked varieties is unques- 

 tioned. The bacillus of avian tuberculosis resembles the bovine 

 type closely in its morphology and staining reactions. 



Isolation. The isolation of B. tuberculosis from lesions is 

 attended with considerable difficulty. This is even more pro- 

 nounced when an attempt is made to secure the organism from the 

 sputum or the feces where it exists in mixed culture. 



It may be isolated from infected organs by securing bits of the 

 tissue and rubbing over the surface of inspissated blood-serum or 

 other suitable medium. The method worked out by Theobald 



Fig. 127. Bacillus tuberculosis, bo- 

 vine, in a section of the peritoneum 

 (Frankel and Pfeiffer). 



