THE MICROTOMIST tS VADE-MECUM

subsequent staining, and of hindering less than any other the
application of chemical tests.
The action of all the usual fixing agents (osmic acid,
chromic acid, alcohol) is intensified and made more rapid by
employing the solutions hot. Alcohol may sometimes be used
boiling with advantage. Mayer finds that some Tracheata
can only be satisfactorily fixed by means of boiling absolute
alcohol.
7. Alcohol.-One-third Alcohol.-Alcohol is most usually
employed for fixing purposes diluted to a strength of 33-3 per
cent. This formula, which has now become classic, is due to
Ranvier, who was the first to point out its wide applicability,
and the excellence of the results obtained by it. Alcohol of
the strength of 33-3 per cent. is known in France as "Alcohol
au tiers," which is the name given to it by Ranvier himself;
in Germany as " Drittelalcohol " or " Ranviersche alcohol
dilutus; " in Italy, as " alcool al terzo." I propose to speak
of it as " one-third alcohol."
8. One-fourth and one-fifth Alcohol.-For some purposes
(e.g. retina) it has been found that still weaker alcohols give
better results, viz. 25 per cent., or even 20 per cent.; but the
strength of 33 per cent. is certainly the most generally
useful.
Tissues should remain in these alcohols, as a general rule,
for at least twenty-four hours; they may be stained (with
picro-carmine, or, better) with some alcoholic staining medium.
They must never be treated with water, or any aqueous
liquid, except picro-carmine or alum-carmine, or methyl
green.
9. Strong Alcohol.--Stronger alcohols are employed with
advantage in some few cases ; thus, for the study of voluntary
muscle, 50 per cent. and 100 per cent.; for Spongida, and
larve of Spongida, absolute alcohol often gives better results
than any other reagent; it is recommended for the preparation
of Magelona (Vermes).

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