METHODS OF STUDYING BACTERIA 



23 



be satisfactorily accomplished by staining the bacteria 

 and examining them by means of very high-power ob- 

 jectives, which dip into a drop of cedar oil placed 

 directly on the specimen to be examined. Such objec- 

 tives are spoken of as oil-immersion objectives; the one 



Oraduated 

 Draw-tube , 



Coarse Adjuster 



Pine Adjuster 



Objectives and 

 Nose-piece 



Stage 



Siihstarje with 

 Din])hrngm 

 and Condenser 



Fig. 7. — Bactcriologic microscope (Ball). 



in common use, the ^^ inch, when used with a No. 5 

 eye- piece, magnifies about 1200 times. For the staining 

 of bacteria we usually employ some of the coal-tar dyes^ 

 such as methylene-bluc, fuchsin, gentian-violet, etc. 

 The appearance of such stained bacteria is well shown 

 in Plate 1. The use of these stains has a further 



