THE STAINING OF BACTERIA 



103 



It is most convenient to keep saturated alcoholic solutions 

 of the stains made up, and for use to filter a little into about 

 ten times its bulk of distilled water in a watch-glass. A solution 

 of good body is thus obtained. Most bacteria (except those of 

 tubercle, leprosy, and a few others) will stain in a short time in 

 such a fluid. Watery solutions may also be made up, e.g., a 

 saturated watery solution of methylene-blue or a 1 per cent, 

 solution of gentian-violet. Stains must always be filtered before 

 use ; otherwise there may be deposited on the preparation 

 granules which it is impossible to wash off. The violet stains 

 in solution in water have a great 

 tendency to decompose. Only small 

 quantities should therefore be prepared 

 at a time. 



The Staining of Cover-glass Films. 

 Films are made from cultures as 

 described above. The cover-glass may 

 be floated on the surface of the stain 

 in a watch-glass, or the cover-glass 

 held in Cornet's forceps with film side 

 uppermost may have as much stain 

 poured on it as it will hold. When 

 the preparation has been exposed for 

 the requisite time, usually a few 

 minutes, it is well washed in tap water 

 in a bowl, or with distilled water with 

 such a simple siphon arrangement as 

 that figured (Fig. 42). The figure 

 explains itself. When the film has 

 been washed the surplus of water, is 

 drawn off with a piece of filter-paper, 

 the preparation is carefully dried high 

 over a flame, a drop of xylol balsam 

 is applied, and the cover-glass mounted 

 on a slide. It is sometimes advan- 

 tageous to examine films in a drop of 



water in place of balsam. The films can be subsequently dried 

 and mounted permanently. 



Films of fluids from the body (blood, pus, etc.) can be 

 generally stained in the same way, and this is often quite 

 sufficient for diagnostic purposes. The blue dyes are here 

 preferable, as they do not readily overstain. In the case of such 

 fluids, if the histological elements also claim attention it is best 

 first to stain the cellular protoplasm with 1-2 per cent, watery 



FIG. 42. Siphon wash- 

 bottle for distilled water 

 used in washing prepara- 

 tions. 



