AGf~ICULTURAL RESEARCH, PUSA.

STAINING METHODS 151
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ing, when the slide has been wiped round the section,
the preparation is blotted and then heated with
the aniline-oil-xylol mixture, which clears as well as
dehydrates. The aniline-oil-xylol is then replaced by
xylol. This can be done conveniently by holding the
slide almost vertically and dropping xylol from a drop
bottle on to the slide just above the section. 1'he
xylol flows over the section and quickly removes the
aniline oil. The preparation is mounted immediately
in Canada balsam.
SIMPLE STAINS
These show not only the presence of organisms, but
also the nature of the cellular content in exudates.
METHYLENE BLUE
or the many preparations of this dye, LofIler's
methylene blue is perhaps the most useful:
Saturated solution oC methylene blue in alcohol 30 c.c.
Solution of caustic potash in water (1 : 10,000) 100 C.c.
(This caustic potash solution is made by adding 1 C.c. of it
1 per cent. solution to 99 C.c. of water)
Films.-Stain for three minutes, then wash with
water. This preparation does not readily over-stain.
Seci'ions.-Stain for :five minutes or longer. The
application of the alcohol during dehydration is
sufficient for differentiation. Aniline-oil-xylol can also
be used for dehydration and clearing.
POLYCHROME METHYLENE BLUE
This is made by allowing Loffier's methylene blue
to "ripen" slowly. The stain is kept in bottles,
which arc half filled and shaken at intervals to aeratc
thoroughly the contents. The slow oxidation of the
methylene blue forms a violet compound which gives
the stain its polychrome properties. The ripening
takes twelve months or more to complete. The
preparation is used in a manner similar to Lamer's