CHAPTER XVIII. 



THE TUBERCLE BACILLUS. 



The tubercle bacillus is to be distinguished from all 

 others, with the exception of the leprosy bacillus, by 

 its peculiar behaviour towards staining reagents. It 

 is only imperfectly stained with the ordinary solutions, 

 even when they are used for a considerable time. The 

 best results are obtained by using aniline water solu- 

 tion of fuchsine, the use of which is fully described in 

 Chapter IX,, and therefore need not be entered into 

 here. It may, however, be mentioned that less satis- 

 factory results are obtained if the bacilli in the tissues 

 are treated with Ziehl's carbolic fuchsine, and it is best 

 therefore invariably to make use of the aniline water 

 staining solutions. 



The tubercle bacillus is a very delicate, slender 

 rodlet, from xswo to tboo nam. in length, and of 

 minute width. The cells are hardly ever quite 

 straight, but are generally curved or bent ; they are 

 sometimes also divided in a peculiar manner. Especi^ 

 ally in stained preparations it has been remarked that 

 between intensely coloured portions completely colour- 



2U 



