EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 19 



In bacteriological work a rather "low power" f or | inch 

 objective, and a high power yV i^^h oil-immersion objective 

 are needed. A J or ^ inch dry objective may also occasionally 



Fig. 3. — ^Microscope. 



be useful. The magnification with the | or f inch objective is 

 about 75 to 100 diameters; with the J to ^ inch 300 to 500 

 diameters ; with the ^ immersion 750 to 1000 diameters. The 

 magnification varies according to the eye-piece used, as well 



