280 BACTERIOLOGY. 



On potato they grow in practically the same way, 

 though the development is much more limited. They 

 are here of nearly the same color as the potato on which 

 they are growing. When cultivated for a time on potato 

 they are said to lose their pathogenic properties. 



On milk-agar-agar they are of so nearly the same 

 color as the medium that, unless they are growing as 

 the mealy-looking masses, considerably elevated above 

 the surface, their presence is less conspicuous than when 

 on the other media. 



In bouillon they grow as a thin pellicle on the sur- 

 face. This may fall to the bottom of the fluid and con- 

 tinue to develop, its place on the surface being taken 

 by a second pellicle. 



Under all conditions of artificial development the 

 cultures of this organism are always very dry and 

 brittle in appearance, though in truth the individuals 

 adhere tenaciously together by a very glutinous sub- 

 stance. 



The tubercle bacillus does not develop on gelatin? 

 because of the low temperature at which this medium 

 must be used. 



MICROSCOPIC APPEARANCE OF THE TUBERCLE 

 BACILLUS. Microscopically the organism itself is a 

 delicate rod, usually somewhat beaded in its structure, 

 though rarely it is seen to be homogeneous. It is either 

 quite straight or somewhat curved or bent on its long 

 axis. In some preparations involution-forms, consist- 

 ing of rods a little clubbed at one extremity or slightly 

 bulging at different points, may be detected. Branching 

 forms of this organism have been described. It varies 

 in length sometimes being seen in very short segments, 

 again much longer, though never as long threads. On 



