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 : 



&. 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. 



EXERCISE 21. HANGING-DROP PREPARATION. 

 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. 



2 



FIG. 12. Hanging-drop preparation, a, Hanging drop; &, Vaselin. 



