38 



GENERAL BACTERIOLOGY 



(/*) it should be converted to such, as this is the unit in micrometry. 



References. G. 100-108. 



Special Directions. 



a. Determine the value of the ocular micrometer and fill out 

 blanks in following table : 



h. Measure the bacteria on the preparations made in Exercise 18 

 and sketch a few individuals from each. 



In making drawings, represent a micron by two and one-half 

 millimeters on paper. This will give a magnification of 2,500 diame- 

 ters, represented thus : X 2,500. 



EXEECISE 21. HANGING-DROP PKEPAEATION. 



General Directions. These are made by adding a small portion 

 of bacterial culture from solid media to a drop of water on a clean 

 cover-glass, or, in case of fluid media, by placing a small loopful of 

 the culture medium on the cover-glass. A hollow ground glass slide 

 having the rim of the cavity previously coated with vaseline, is 

 inverted and lowered over the cover-glass enclosing the drop. With 

 a careful, quick movement the preparation is now brought right 

 side up. 



a. 



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Fw. 12. Hanging-drop preparation, a, Hanging drop; 6, Vaselin. 



