CHAPTER III. 

 STAINING METHODS. 



IN order to study a bacterial or blood specimen the first essential is 

 a properly prepared film; the matter of staining is of less importance. 

 The slide or cover-glass, after cleaning with soap and water or by special 

 solutions, should be polished with a piece of old linen. If a glass sur- 

 face is free of grease a loopful of water will smear out evenly and over 

 the entire surface. The only quick practical way to make the slide 

 or cover-glass grease free is to burn the surface for a moment in a Bunsen 

 or alcohol flame. The cover-glass must not be warped. To make a 

 preparation, apply a small loopful of distilled water on the slide or cover- 

 glass and, touching a colony with a platinum needle, stir the transferred 

 culture into the loopful (not drop) of water. The mistake is almost 

 invariably made of taking up too much bacterial growth. Fluid cul- 

 tures do not need dilution. Smearing the mixture over a large part of 

 the cover-glass or over an equal area of a slide, it is allowed to dry. If 

 very little water is used, the preparation dries readily. Otherwise it can 

 be dried in the fingers high over a flame. As soon as dry, the cover-glass 

 should be passed three times through the flame, film side up, to fix the 

 preparation. Slides may be fixed by passing them five times through 

 the flame, but the method by burning alcohol recommended for fixing 

 blood-films gives more satisfactory bacterial fixation. For routine work 

 the stain recommended is a dilute carbol fuchsin. Drop about 5 to 10 

 drops of water on the cover-glass, then add one drop of carbol fuchsin. 

 Allow the dilute stain to act from one to two minutes, then wash in 

 water, dry between small squares of filter-paper (4X4 inches), and 

 mount in balsam or the oil used for the i/i 2-inch immersion objective. 



By far the best mounting medium is liquid petrolatum. This not only has the 

 advantage of always being of proper consistence for mounts, as opposed to Canada 

 balsam, which must frequently be made thinner with xylol, but it is less sticky and 

 does not develop the acidity which causes balsam mounts of Romanowsky stains 

 to fade. Furthermore, it has superior optical qualities. It is also applicable for 

 mounting small insects and sporangia of moulds. For permanent preparations the 



3 2 



