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102                 PATHOGENIC BACTERIA.

flagella to show well, so that it is recommended to prepare
a second dilution by placing a "small drop of distilled
water upon a cover and taking a small portion from the
first cover to the second, spreading it over the entire sur-
face. The material is allowed to dry, and is then fixed
by passing it three times through the flame. When this
is done with forceps there is some danger of the prepara-
tion becoming too hot, so Loifler recommends that the
glass be held in the fingers while the passes through the
flame are made.

The cover-glass is now held in forceps, and the mordant,
Solution A, is dropped upon it until it is well covered.
The cover is warmed until it begins to steam, and the
stain replaced as it evaporates. It must not be heated too
strongly ; above all things, must not boil. This solution
is allowed to act from one-half to one minute, is then
washed in distilled water, then in absolute alcohol until all
traces of the solution have been removed. The real stain
—Loffler recommends an anilin-water fuchsin (Ehrlich's
solution)—which should have a neutral reaction, is now
dropped on so as to cover the specimen, and heated for a
minute until vapor begins to arise; it is then washed off
carefully, dried, and moimted in Canada balsam. To
obtain this neutral reaction enough of the i per cent,
sodium-hydrate solution is added to an amount of the
anilin-water-fuchsin solution having a thickness of sev-
eral centimeters to begin to change the transparent into
an opaque solution. Such a specimen may or may not
show the flagella. If not, before proceeding farther it is
necessary to study the products of the bacterium in cul-
ture-media. If by its growth the organism elaborates
alkalies, Solution C, in proportion from i drop to i
in 16 of the mordant A, must be added, and the
process repeated again and again until the proper amount
is determined. On the other hand, if the organism by
its growth produces acid, Solution B must be added,
drop by drop, until i in 16 crn. have been attained, and
numerous experiments made to see when the flagella