Pathogenic Bacteria

100 PA THOGENIC BA CTERIA.

Stain with Ehrlich's solution two to five minutes ;
Gram's solution for one-half to two minutes ;
Wash in 95 per cent, alcohol until decolorized;
Counter-stain if desired ; wash the counter-stain

off with water;
Dry;
Mount in Canada balsam.

Method of Staining Spores.—It has already been
remarked that the peculiar quality of the spore-capsules
protects them from the influence of stains and disinfect-
ants to a certain extent. On this account they are much
more difficult to color than the adult bacteria. Several
methods are recommended, the one generally employed
being as follows: Spread the thinnest possible layer of
material upon a cover-glass, dry, and fix. Have ready
a watch-crystalful of Ehrlich's solution, preferably made
of fuchsin, and drop the cover-glass, prepared side down,
upon the surface, where it should float. Heat the stain
until it begins to steam, and allow the specimen to
remain, in the hot stain for five to fifteen minutes. The
•cover is now transferred to a 3 per cent, solution of hydro-
chloric acid in absolute alcohol for about one minute.
Abbott recommends that the cover-glass be submerged,
prepared side up, in a dish of this solution and gently
agitated for exactly one minute, then removed, washed
in water, and counter-stained with an aqueous solution
of methyl or methylene blue.

In such a specimen the spores should appear red, the
bacilli blue.

I have not generally found that spores color so easily,
and for many species the best method seems to be to
place the prepared cover-glass in a test-tube half full of
carbol-fuchsin:

Fuchsin, ^.

Alcohol, IO.

5 per cent, aqueous solution of phenol crystals, 100,