154 BACTERIOLOGY. 



ized to render the bacteria, visible and admit of the use 

 of contrast stains. 



Weigert's modification of Gram's method for sections. 

 Stain the sections in the Koch-Ehrlich aniline-water 

 gentian-violet 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 

 solution used by Gram ; take up the excess of the solu- 

 tion 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 gentian-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 decolor- 

 ization is sufficient (repeated 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 



