204 BA CTERIOL OGY. 



when the bacteria are stained in the ordinary manner. 

 Special stains have been devised for causing the color to 

 penetrate through the resistant spore. Thus in Abbott's 

 method the cover-slip after having been prepared in the 

 usual way is covered with a dye and held over the Bun- 

 sen flame until the fluid steams. This is continued for 

 one or two minutes. It is then washed and dipped in a 

 decolorizing acid solution, such as a 2 per cent, alco- 

 holic solution of nitric acid, until all visible color has 

 disappeared, then it is washed off and dipped for ten sec- 

 onds in a solution containing 10 parts saturated alco- 

 holic solution of eosin and 90 of water. The bacilli 

 will then be rose-colored and the spores blue. Some- 

 times, however, the spores refuse to take the stain in 

 this manner. We then can adopt Moeller's method, 

 which is designed still further to favor the penetration 

 of the coloring-matter through the spore membrane. 

 He macerates the spores in a solution of chromic acid 

 before staining them. The prepared cover-slip is held 

 for two minutes in chloroform, then washed off in water, 

 then placed from one-half to three minutes in a 5 per 

 cent, solution of chromic acid, again washed off in 

 water, and now restained by adding to it carbolic 

 fuchsin, which is steamed for several minutes. The 

 staining fluid is then washed off and the preparation 

 decolorized in a 3 per cent, solution of hydrochloric 

 acid or a 5 per cent, solution of sulphuric acid. The 

 preparation is finally stained for a minute in methyleue- 

 blue solution. The spores will be red and the body of 

 the cells blue. The different spores vary greatly in 

 the readiness with which they take up the dyes, and 

 we have, therefore, to experiment with each variety 

 as to the length of time they should be exposed to the 



