CHAPTER VI 



METHODS USED IN THE MICROSCOPIC 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 preparations. 

 For the manipulation of bacteria for such study, glass slides and cover- 

 slips 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 transferred to the cover-slip, or the bac- 

 teria may be emulsified in a drop of salt solution, or broth, Directly upon 

 the cover-slip. The concavity on the slide, having first been rimmed 

 with vaseline, by means of a small camel's-hair brush, the cover-slip is 

 inverted over the slide in such a way that the drop hangs freely within 

 the hollow space. The preparation is then ready for examination under 

 the microscope. 



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, neces- 

 sitate 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 cover- 

 slips 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. 



93 



