Methods of Studying Bacteria. 



17 



The microscope in bacterial investigation. In order to 

 verify the purity of the cultures, the microscope is in con- 

 stant demand throughout all the different stages of the 



c l 



Fra 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 fil- 

 aments 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) ; *, an obligate anaerobe, that develops only in 

 absence of air. 



isolating process. For this purpose, it is essential that the 

 instrument used shall be one of strong magnifying powers 

 (600-800 diameters), combined with sharp definition. 

 The microscopical examination of any germ is quite as 

 2 



