OF THE HUMAN" SUBJECT. 49 



adopted, it is in reality wholly unnecessary ; if the transit 

 through the flame is made sufficiently slowly to really heat the 

 glass, there is a risk of inducing still further shrinkage of the 

 bacteria. Not only is the practice unnecessary for preparations 

 made from agar cultures, but from careful comparative experi- 

 ments, the author has found it equally without advantage in the 

 case of such as are made from liquefied gelatine or from broth ; 

 the film will remain adherent even if the dye has to be heated 

 on the glass, provided always that it is not afterwards violently 

 washed beneath a stream, but in a vessel, of water ; to such cul- 

 tures the addition of water is not required ; the loop is simply 

 dipped into the fluid and distributed over the cover-glass. 



The next procedure is that of staining For this purpose 

 aniline dyes are alone used ; none others are sufficiently intense. 

 The three chief are carbol fuchsin, aqueous solution of gentian 

 violet, and aqueous solution of methylene blue ; for special pur- 

 poses modifications are necessary, the most important of which 

 are Gram's method and those for staining spores, capsules, and 

 flagella. Of these dyes carbol fuchsin* holds the first place, and 

 takes the same position for bacterial staining that hematoxylin 

 does for histological : it not only dyes all known bacteria, but 

 gives, as a rule, cleaner preparations, in consequence of its being 

 more readily washed out from extraneous material. 



The cover-glass should be quite covered with a high bead of 

 the stain. This may be done from a drop bottle, but the author 

 invariably filters the stain directly on to the cover-glass through 

 a small cone of filter-paper held across its overlapping parts in a 

 pair of forceps. The stain having remained on from five to fif- 



* Fuchsin, 1 gram: absolute alcohol, 10 c.c. Dissolve and add lOOc.c. of a 5 

 per cent, aqueous solution of carbolic acid. 



