no LABORATORY GUIDE IN BACTERIOLOGY 



3. Cover with the stain for 10 to 15 seconds. 



4. Wash in water. 



5. Dry and mount in balsam. 

 Second method (Welch's method) — 



1. Prepare a film from a 24-hour milk culture by 

 smearing a loopful thinly over a coverglass. 



2. Cover with glacial acetic acid for IS to 2oseconds. 



3. Wash the acetic acid off with carbol fuchsin. 



4. Wash off the stain with 0.8 per cent NaCl solu- 

 tion. 



5. Dry and mount in balsam. 



Third method (Rosenow's method) {Jour. Am. 

 Med. Assoc, 191 1, 56, p. 418) — 



This method is applicable for staining capsules in 

 tissues as well as cultures. If the material is too thick 

 or viscid it must be diluted with a suitable amount of 

 distilled water. Cultures from agar, blood serum, etc., 

 should be mixed on a cover slip with a loopful of serum. 



o) Prepare a thin film, and dry in the air. 



b) When dry, cover with a 5 to 10 per cent solution 

 of tannic acid for 10 to 20 seconds. 



c) Wash in water and dry with blotting paper. 



d) Cover with carbol gentian violet or anilln gentian 

 violet for one-half to one minute. Carbol gentian 

 violet is prepared by mixing one part saturated alco- 

 holic solution of Griibler's gentian violet with 4 parts 

 of an aqueous 5 per cent phenol solution. 



e) Wash in water. 



/) Stain with Gram's iodin solution for one-half to 

 one minute. 



g) Decolorize in alcohol. 



