262 MICEOBES, FERMENTS, AND MOULDS. 



to stain the living bacteria in a drop of water, under 

 a cover-glass. A small drop of the staining liquid is 

 slowly diffused into the preparation, and gradually 

 tinges the bacteria without giving any sensible colour 

 to the liquid which contains them. When the comma 

 bacillus of cholera is thus treated, it is still capable of 

 motion after the lapse of twenty-four hours, and it will 

 continue to develop if the stage of the microscope is 

 heated to 25. 



In sections which have been hardened or dried in 

 alcohol the bacteria have ceased to live, but they may 

 be stained with the following reagents Grenadier's 

 borassic carmine, hematoxylin, and tincture of iodine 

 may be respectively employed, according to the species 

 of microbe which is to be stained : Micrococcus, the 

 flagellum of bacteria, Bacillus amylobacter, moulds, 

 etc. 



Aniline dyes, with an alkaline or acid basis, are 

 very numerous and varied ; methyl- violet and gentian 

 in oil of aniline, or in aqueous solution, rosine, saffronine, 

 Bismarck brown, purpurine, etc. 



It is often desired to effect a double staining of the 

 section, the tissues, for example, being stained red, and 

 the bacteria violet, or conversely. Picrocarminate of 

 ammonium gives this effect by the following process : 

 After staining the preparation with methyl-violet, it 

 is dipped for a moment in the iodide solution, and 

 washed in water or weak alcohol ; it is then steeped 

 for some minutes in the picrocarminate, of which the 



