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ESSENTIALS OF BACTERIOLOGY 



rubbed upon a glass slide with a drop of sterilized water or 

 bouillon, and from this a little is taken on cover-glass, as 

 before. 



The cover-glass with its drop is now placed on the glass 

 slide, carefully pressing out all bubbles. Then a drop of 

 cedar-oil is laid on top of the cover-glass, and the oil-immer- 

 sion lens dipped gently down into it as close as possible to the 

 cover-glass, the narrow blender shutting of the Abbe conden- 

 ser, for this being an unstained specimen, we want but little 

 light. We now apply the eye, and if not in focus, use the 

 fine adjustment or the coarse, but always away from the 

 object i. e. } toward us since the distance between the speci- 



Fig. 12. A "concave slide" with " hanging drop" (McFarland). 



men and the lens is very slight, it does not require much 

 turning to break the cover-glass and ruin the specimen. 

 Having found the bacterium, we see whether it is bacillus, 

 micrococcus, or spirillum, discover if it is motile or not. 

 The phenomenon of agglutination is observed in this way. 



Hanging Drop (Fig. 12). When the looped platinum 

 needle is dipped into a liquid, a very finely formed globule will 

 hang to it ; this can be brought into a little cupped glass slide 

 (an ordinary microscopic glass slide with a circular depression 

 in the center) in the following manner: The drop is first 

 brought upon a cover-glass; the edges of the concavity on the 

 glass slide are smeared with vaselin, and the slide inverted 

 over the drop; the cover-glass sticks to the smeared slide, 



