CHAPTER VI 



METHODS USED IN THE MICEOSCOP1C STUDY AND STAINING OF 



BACTERIA 



MICROSCOPIC STUDY OF BACTERIA 



BACTERIA may be studied microscopically, in the living and un- 

 stained state, and, after the application of dyes, in colored prepara- 

 tions. For the manipulation of bacteria for such study, glass slides 

 and coverslips of various design are used. These must be perfectly 

 clean if the preparations are to be of any value. 1 



The Study of Bacteria in the Living State. Living bacteria may 

 be studied in what is spoken of as the " hanging-drop" preparation. 

 For this purpose a so-called hollow slide is employed, in the center 

 of which there is a circular concavity about three-quarters of a 

 centimeter to one centimeter in diameter. The preparation is 

 manipulated as follows: if the bacteria are growing in a fluid 

 medium, a drop of the culture fluid is transferred to the center of 

 a cover-slip. If taken from solid media, an emulsion may be made 

 in broth or in physiological salt solution, and a drop of this trans- 

 ferred to the cover-slip, or the bacteria may be emulsified in a drop 

 of salt solution, or broth, directly upon the cover-slip. The con- 

 cavity on the slide, having first been rimmed with vaseline, by 

 means of a small camel's-hair brush, the cover-slip is inverted over 



1 Although the silicates of which glass is composed are extremely stable, never- 

 theless alkaline silicates which are said to separate out on the surface, together 

 with grease and dirt left upon the glass by handling, during blowing and cutting, 

 necessitate cleansing before use. This may be accomplished by a variety of 

 methods. A simple one suitable for general application is as follows: (1) The 

 slides and coverslips are thrown singly into boiling water and left there for 

 half an hour; (2) wash in twenty-five per cent sulphuric acid; (3) rinse in 

 distilled water; (4) wash in alcohol; (5) wipe with a clean cloth and keep 

 dry under a bell-jar. Another method convenient for routine use is to immerse, 

 after thorough washing in soap-suds and acid, in ninety-five per cent alcohol and 

 to leave in this until the time of use. 



Ill 



