162 THE AMERICAN MONTHLY [July, 



If bacteria aie examined in the hanging-drop shortly before the for- 

 mation of spores in many of them refracting bodies are found wiiich 

 have not yet a size equal to that of spores. When the preparations, 

 dried and fixed by passing them through the flame three times, are 

 stained with an aqueous or dilute alcoholic staining solution, the bac- 

 teria in this stage are found to be stained, not so equally as before, but 

 some parts are more deeply colored. This condensed protoplasm 

 takes tlie dye more readily than the protoplasm not thus concentrated. 

 Then follows the stage in which the refracting corpuscles become much 

 more equal in size, but they still stain well ; and finally the stage in 

 which similar refracting corpuscles .are present in the unstained prepa- 

 rations, but these no longer take up the color. Now the spores have 

 first obtained an insusceptibility to the dye through the formation of a 

 membrane diflicult of penetration, which prevents the absorption ot 

 the coloring matter. 



In the cover-glass preparations, which have been passed through the 

 flame three times, the bacteria and nuclei are well stained. If they 

 are passed through the flame more times, say six, the bacteria are 

 stained successively worse, but the nuclei still absorb the dye as does 

 also the condensed protoplasm of the bacteria which has not yet formed 

 spores. At this stage, besides the nuclei, granular elements can often 

 be seen which may easily impress one as belonging to the badly stained 

 bacteria. If the preparations are passed through the flame still more 

 times, say ten, then both the nuclei and the condensed protoplasm lose 

 their susceptibility to the dye, and the spores gain it. In the case of 

 some of the bacteria of putrefaction, it is sufiicient to pass the prepa- 

 ration through the flame only seven times, but in others ten times are 

 required. (In the dry-oven a similar stage is reached in from fifteen 

 to thirty minutes at i8o° to 300° C.) The spores then take up aqueous 

 solutions of red, violet, blue, brown, and green basic aniline-dyes. 



This isolated staining for the proof of the resistance of the spores, 

 as Buchner intended, is perhaps sometimes to be used ; but, since in 

 this way nothing is learned concerning the relation of the spores to the 

 bacteria, it is better to use a double stain. The procedure is almost 

 the same, quantitatively increased, as that for staining the tubercle ba- 

 cilli. Either the preparations, passed through the flame three times, 

 are stained with a strong alkaline solution from twelve to twenty-four 

 hours and afterward stained with vesuvin, or the aniline-water-dye so- 

 lutions are used, of which that of Neisser, previousl}' described, has 

 proved to be the most convenient and satisfactory. Stain in hot ani- 

 line-water fuchsin, decolorize with nitric acid, then stain with 

 methyl-blue. 



Some spores, are stained, moreover, by saturated aqueous or dilute 

 alcoholic solutions, if they are at the same time heated. The difler- 

 ence of spores in respect to their susceptibility to dyes, seems to be 

 scarcely less than that of the bacteria themselves. 



Slides Received. — We desire to return thanks to the donor for the 

 following interesting slide : 



Diatoms, prepared by A. F. Bartges, Esq., Akron, Ohio. 



