126

PATHOGENIC BACTERIA.

to a faintly alkaline reaction. Definite varying degrees
of alkalinity can be secured by adding measured quan-
tities of the soda solution beyond that necessary to bring
about the beginning alkalinity. In using phenolphtha-
lein one should remember that the first sign of rose color
marks a change to alkalinity, and that this is a higher
degree of alkalinity than that required to turn red litmus
blue.

The bouillon thus prepared is a clear fluid of a straw
color, much resembling normal urine in appearance. It

FIG. 21.—Funnel for filling tubes with culture-media (Warren).

is dispensed in previously sterilized tubes with cotton
plugs—about 10 c.cm. to each—and is then sterilized by
steam three successive days for fifteen to twenty minutes
each, according to the directions already given for frac-
tional sterilization. (See p. 109.)