STAINING OF BACTERIA IN TISSUES. 149 



solution for five or six minutes ; wash out in water or 

 physiological salt solution (0.6 to 0.7 per cent, solution 

 of sodium chloride in distilled water) ; transfer them 

 with the section-lifter to the slide ; take up the excess 

 of fluid by gently pressing upon the flat section with 

 blotting-paper; treat the section with the iodine solu- 

 tion used by Gram ; take up the excess of the solution 

 with blotting-paper ; cover the section with aniline oil — 

 this not only differentiates the component parts of the 

 section, but dehydrates as well ; wash out the aniline 

 oil with xylol, and mount in the usual way in xylol- 

 balsam. Or, decolorization with iodine may be omitted, 

 and the sections, after staining in the aniline-water gen- 

 tian-violet for five or six minutes or longer, if necessary, 

 are transferred to the slide without being washed in 

 water or salt solution, or if so only very slightly and 

 rapidly, dried as completely as possible with filter-paper, 

 then are decolorized with a mixture of aniline oil (one 

 part) and xylol (two parts). This is the delicate part of 

 the process and can be watched under the low power of 

 the microscope ; when decolorization is sufiicient (re- 

 peated applications of the aniline oil and xylol mixture 

 are generally necessary), pure xylol replaces the mixture, 

 and the specimen is finally mounted in xylol balsam. 

 Unless all the aniline oil is replaced by the xylol the 

 specimen will not keep well. In this process the aniline 

 oil is really the decolorizer and has the valuable 

 property of absorbing a certain amount of water, so 

 that dehydration with alcohol is avoided. This method, 

 while it stains certain bacteria in tissues very satisfac- 

 torily, is nevertheless designed especially for the stain- 

 ing of fibrin. Fibrin and hyaline materal will be 

 stained deep blue, bacteria a dark violet. 



