262 MICROBES, 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—Grenacher’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, 
ete. 
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, ete. 
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 
