METHODS OF OBSERVING BACTERIA. 85 



the blue color is wholly or almost lost, after which it can 

 be counter-stained with eosin, Bismarck brown, vesuvin, 

 etc., washed, dried, and mounted in Canada balsam. 

 Given briefly, the method is : 



Stain with Khrlich's solution two to five minutes ; 



Gram's solution for one-half to two minutes ; 



Wash in 95 per cent, alcohol until decolorized ; 



Counter-stain if desired ; wash the counter-stain 

 off with water ; 



Dry; 



Mount in Canada balsam. 



Method of Staining Spores. It has already been 

 remarked that the peculiar quality of the spore-capsules 

 protects them from the influence of stains and disinfect- 

 ants to a certain extent. On this account they are much 

 more difficult to color than the adult bacteria. Several 

 methods are recommended, the one generally employed 

 being as follows : Spread the thinnest possible layer of 

 material upon a cover-glass, dry, and fix. Have ready 

 a watch-crystalful of Ehrlich's solution, preferably made 

 of fuchsin, and drop the cover-glass, prepared side down, 

 upon the surface, where it should float. Heat the stain 

 until it begins to steam, and allow the specimen to 

 remain in the hot stain for five to fifteen minutes. The 

 cover is now transferred to a 3 per cent, solution of hydro- 

 chloric acid in water for about one minute. Abbott rec- 

 ommends that the cover-glass be submerged, prepared 

 side up, in a dish of this solution and gently agitated 

 for exactly one minute, then removed, washed in water, 

 and counter-stained with an aqueous solution of methyl 

 or methylene blue. 



In such a specimen the spores should appear red, the 

 bacilli blue. 



I have not generally found that spores color so easily, 

 and for many species the best method seems to be to 

 place the prepared cover-glass in a test-tube half full of 

 carbol-fuchsin : 



