TUBERCLE BACILLUS. 575 



staining properties. When stained with the carbol staining 

 fuchsin of Ziehl and subjected to the action of * 

 mineral acids in dilute solutions the fuchsin is not 

 removed. After counterstaining with methylene 

 blue, the tubercle bacilli appear red,, whereas other 

 organisms, not "acid fast," are stained with the 

 methylene blue. It is not difficult to recognize the 

 bacilli in sections of tissue when the proper technic 

 is used, although the search is at times a laborious 

 one. In old processes the organism often can not 

 be recognized, and recourse to animal inoculation 

 may be necessary in order to demonstrate the ex- 

 istence of tuberculosis. . 



Much has demonstrated in such cases, however, 

 the presence of granular forms of tubercle bacilli 

 which are not acid fast but which stain by a modi- 

 fication of Gram's method. 



Ordinarily it is a difficult task to obtain the Cultivation 

 tubercle bacillus in pure culture, and the technic 

 we need not consider here. Even under the best 

 conditions growth is very slow, and may not be 

 recognizable to the naked eye for from six to ten 

 days. Coagulated bovine serum to which has 

 been added from 2 to 4 per cent, glycerin is the 

 most favorable culture medium. Good growth oc- 

 curs also in glycerin agar, in glycerin bouillon 

 and on potatoes. The optimum temperature is 37 

 C.; growth does not occur above 42 C. nor below 

 30 C. When a small amount of culture is planted 

 on the surface of glycerin bouillon it proliferates 

 slowly to form a heavy membrane. In time this 

 growth sinks from its own weight and a new mem- 

 brane forms. This process continues until large 

 masses have accumulated at the bottom of the 

 flask. 



