40 METHODS OF STUDYING MICROORGANISMS 



from which this single organism comes the bacteri- 

 ologist spreads it on a glass slide and colors it by 

 certain aniline or vegetable dyes, of which there is 

 a large number. It is practically impossible certainly 

 to identify any bacterium by a simple examination of 

 a stained preparation under the microscope. The 



FIG. 10. Culture tubes. (Park.) 



observer, however, does form a tentative opinion as 

 to its probable nature, and proceeds to introduce some 

 of the material into a nutrient medium which he con- 

 siders best adapted to its development. Among these 

 are broth, milk, potato, coagulated blood serum, and 

 broth stiffened (when cool) with gelatin and the 



