METHODS OF OBSER17NG BACTERIA. IOI

and boil it for at least fifteen minutes, after which it is
decolorized, either with 3 percent, hydrochloric or 2-5 per
cent, acetic acid, washed in water, and counter-stained bine.

Fiocca suggests the following rapid method: "About
20 c.cm. of a 10 per cent, solution of ammonium are
poured into a watch-glass, and 10-20 drops of a saturated
solution of gentian violet, fuchsin, methyl blue, or suf-
ranin added. The solution is wanned until vapor begins
to rise, then is ready for use. A very thinly-spread cover-
glass, carefully dried and fixed, is immersed for three to
five minutes (sometimes ten to twenty minutes), washed
in water,, washed momentarily in a 20 per cent solution
of nitric or sulphuric acid, washed again in water, then
counter-stained with a watery solution of vesuvin, chrys-
oidin, methyl blue, malachite green, or safranin, according
to the color of the preceding stain. This whole process
is said to take only from eight to ten minutes, and to give
remarkably clear and beautiful pictures.'7

Method of Staining- Flagella.—This is much more
difficult than the staining of either the bacteria or their
spores, because each species seems to behave differently
in its relation to the stain, so that the chemistry of the
micro-organismal products must be taken into considera-
tion.

The best method introduced is that of Loffler. In it
three solutions are used :

A. A 20 per cent, solution of tannic acid, 10 ;
Cold saturated aqueous solution of ferrous sulphate, 5 ;
Alcoholic solution of fuchsin or methyl violet, i;

B. A i per cent, solution of caustic soda.

C. An aqueous solution of sulphuric acid of such strength

that i c.cm. will exactly neutralize an equal quan-
tity of Solution B.

Some of the bacteria to be stained are mixed upon a
cover-glass with a drop of distilled water. This is the
first dilution, but is too rich in bacteria to allow the