MICROSCOPICAL EXAMINATION OF BACTERIA. 47 



bottle. Turn the cover-glass on to a slide, remove 

 excess of water with filter paper, and wipe the 

 exposed surface ; examine with Zeiss' DD (about 

 230 diams.), and if a higher power be required, 

 which is usually the case, place a droplet of cedar 

 oil on the cover glass, and examine with an im- 

 mersion lens. 



If the specimen is to be made permanent, fix the 

 cover-glass at one corner with the thumb, and with 

 a soft rag carefully wipe off the cedar oil ; then 

 float off the cover-glass by running in distilled 

 water at its margin, and having made a little ledge 

 with a strip of filter-paper, place the cover-glass up 

 against it upon one of its edges and leave it to dry. 

 When perfectly dry mount in Canada balsam, or 

 put it away in a cover-glass box provided with a 

 label of contents. 



A culture from a solid medium may be stained 

 and examined in the same way after spreading it 

 out with a needle into a thin film, with or without 

 the addition of a droplet of sterilised water. 



In many cases it is necessary or preferable to 

 apply the stain for a much longer period. This is 

 effected by pouring some of the staining solution 

 into a watch-glass, and allowing the cover-glasses 

 to swim on the surface, with their prepared side, of 

 course, downwards. Throughout all these manipu- 

 lations it is necessary to bear in mind which is the 

 prepared surface of the cover-glass. 



Double coloration of cover-glass prepara- 



