:J4 A MANUAL OK BACTERIOLOGY 



3. Gentian violet. 



a. Saturated aqueous solution. 



Gentian violet 2 g. 



Distilled water 100 cc. 



b. Saturated alcoholic solution. 



Gentian violet 5 g. 



95 per cent alcohol 100 cc. 



Place in a stoppered bottle, shake frequently, and filter after 

 two hours. 



Exercise 59. General Method of Making Stained Preparations 



1. Clean a cover glass, holding it only by the edges. Remove 

 all greasy material, using alcohol or other solvents for the pur- 

 pose. After cleaning the cover glass, place it in the cover-glass 

 forceps (Fig. 18) and pass it rapidly several times through a 



Bunsen flame. 

 Circular cover 

 glasses 18mm. 

 in diameter are 

 most suitable 

 FKI. 18. Cover-^lass forceps for bacterio- 



logical work. 



2. With the platinum loop place a small drop (about the 

 size of a pinhead) of distilled water upon the center of the 

 cover glass. Transfer the bacteria to be examined with a sterile 

 platinum needle to the drop on the cover glass. Mix the bacteria 

 thoroughly with the drop and spread it as evenly as possible over 

 the cover glass, within 2 mm. of the edge. If the drop does not 

 spread well, the cover glass has not been successfully cleaned. 

 When the bacteria to be examined are taken from liquid media, 

 the platinum loop will be used and a drop of water on the cover 

 glass is unnecessary. 



It is difficult, especially for beginners, to get few enough bac- 

 teria to make a good preparation. It is well to make a second 

 mount from the first by transferring a part of a rather large 

 drop to a second cover glass. 



