658 Tuberculosis 



the fragmented bacilli are no more capable of resisting heat than 

 others. 



The bacilli not infrequently present projecting processes or 

 branches, this observation having changed our views regarding the 

 classification of the organism, which is probably erroneously placed 

 among the bacilli, belonging more properly to the higher bacteria. 



The organism is not motile, and does not possess flagella. 



Staining. The tubercle bacillus belongs to a group of organisms 

 which, because of their peculiar behavior toward stains, are known 

 as "saurefest" or acid-proof. It is difficult to stain after it has 

 lived long enough to invest itself with a waxy capsule, requiring that 

 the dye used shall contain a mordant (Koch). It is also tenacious 

 of color once assumed, resisting the decolorizing power of strong 

 mineral acids (Ehrlich). 



Fig. 270. Bacillus of tuberculosis, N showing branched forms with involution 



(Migula). 



Koch* *first stained the bacillus with a solution consisting of 

 i cc. of a concentrated solution of methylene bjue mixed with 20 

 cc. of distilled water, well shaken, and then, before using, receiving 

 an addition of 2 cc. of a 10 per cent, solution of caustic potash. 

 Cover-glasses were allowed to remain in this for twenty-four hours 

 and subsequently counterstained with vesuvin. Ehrlich subse- 

 quently modified Koch's method, showing that pure anilin was a 

 better mordant than potassium hydrate, and that the use of a 

 strong mineral acid would remove the color from everything but 

 the tubercle bacillus. This modification of Koch's method, given 

 us by Ehrlich, probably remains the best method of staining the 

 bacillus. 



* " Mittheilungen aus dem Kaiserlichen Gesundheitsamte," 1884, n. 



