USE OF OIL-IMMEKSION LENS. 5 



one to two minutes. If desired, the stain can be 

 dropped on the cover glass. 



(/) Remove and wash in water; dry thoroughly and 

 mount the cover glass in Canada balsam. 



Examine the specimen with a -^ oil-immersion lens, 

 using the plane mirror and open diaphragm, with the 

 Abb6 condenser. 



Use of Oil-Immersion Lens. 



In using the oil-immersion lens, first place a drop of 

 immersion oil on the centre of the film to be examined, 

 and placing the preparation on the centre of the micro- 

 scopic stage, fix one end of the slide with a clip. Lower 

 the lens with the coarse adjustment, till it touches the 

 drop. With the eye to the ocular, in stained prepara- 

 tions, lower very slowly till the field becomes colored. 

 In unstained preparations always use the fine adjust- 

 ment after the lens touches the oil. Now, with the fine 

 adjustment carefully lower the lens till the field comes 

 clearly into view. The slide can be readily moved 

 about at the undipped end. Before removing slide 

 always raise the objective well out of the oil with the 

 coarse adjustment. 



2. Examine in like manner the liquefying gelatine 

 cultures of Bacillus pyocyaneus and of Sarcina lutea, 

 substituting Loeffler's methylene blue as staining agent, 

 the films being left in the stain from two to three 

 minutes. 



3. Examine in like manner the broth culture of 

 Torula rosea, using Loeffler's methylene blue as stain. 



