Staining 309 



peculiar to spores. Spores also resist heat strongly, but 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 prob- 

 ably erroneously placed among the bacilli, belonging more 

 properly to the higher bacteria and probably being related 

 to the actinomyces. 



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



Staining. The tubercle bacillus is difficult to stain, 

 requiring that the dye used shall contain a mordant (Koch) ; 

 it is also tenacious of the color once assumed, resisting the 

 decolorizing power of strong mineral acids (Ehrlich). 



The peculiarity of staining the bacillus delayed. its dis- 

 coverv for a considerable time, but, now that we are 



Fig. 91. Bacillus of tuberculosis showing branched forms with invo- 

 lution (Migula). 



familiar with it, gives us a most valuable differential char- 

 acter, few other organisms reacting in the same way. 



Koch first stained the bacillus with an aqueous solution 

 of a basic anilin dye, a little potassium hydrate being added 

 as a mordant, subsequently washing the specimen with 

 water and counterstaining it with vesuvin. Ehrlich sub- 



