Methods of Studying Bacteria. 



21 



of culture material and thus pure cultures of the various 

 germs are secured. These cultures then serve as a basis 

 for continued study and must be planted and grown upon 

 all the different kinds of media that are obtainable. In 

 this way, the slight variations in the growth of different 



1 



FIG. 4. Pure cultures of different kinds of bacteria in gelatin tubes, a, 

 growth slight in this medium; b, growth copious at and near surface. Fine 

 parallel filaments growing out into medium liquefying at surface; c, a rapid 

 liquefying form; d, a gas-producing form that grows equally well in lower part 

 of tube as at surface (facultative anaerobe); e, an obligate anaerobe, that devel- 

 opes only in absence of air. 



forms are detected and the peculiar characteristics are 

 determined, so that the student is able to recognize this 

 form when he meets it again. 



