THE MICROTOMIST'S VADE-MECUM

is by no means as good. Any addition of paraffin oil, tur-
pentine, &c., to soften the paraffin, renders it granular and
brittle, and is decidedly injurious to its cutting qualities."
231. Paraffin and Chloroform (Giesbrecht's method ').-
Chloroform is the readiest solvent of paraffin, and is at the
same time the most easily evaporated.       These properties
render possible the following procedure. Objects to be im-
bedded are saturated with absolute alcohol, and then brought
into chloroform (to which a little sulphuric ether has been
added if necessary, in order to prevent the objects from
floating). As soon as the objects are saturated with the chlo-
roform, the chloroform and objects are gradually warmed up
to the melting point of the paraffin employed, and during the
warming small pieces of paraffin are by degrees added to the
chloroform. So soon as it is seen that no more bubbles are
given off from the objects, the addition of paraffin may cease,
for that is a sign that the paraffin has entirely displaced the
chloroform in the objects. This displacement having been a
gradual one, the risk of shrinkage of the tissues is reduced to
a minimum. (The paraffin mass should be kept for some
time at its melting point over a water-bath, or better, in a dry
oven, in order that the chloroform may be completely driven
off, as the presence of chloroform makes the paraffin too soft
for thin section cutting.)
The discovery of chloroform as a solvent for paraffin is, I
believe, due to Biitschli and Blochman. . Undoubtedly the
procedure above described is one of the most exact methods
of interstitial imbedding yet made known.
Sections are cut dry; if they have a tendency to roll they
must be held down on the section-knife with a small, flat,
camel's-hair brush or other suitable instrument.   .
232. Paraffin and Chloroform (Biitschli's formula2).-A
I ' Zool. Anz.,' No. 4 (1881), p. 484.
2 ' Biol. Central.,' i (1881), pp. 591-2. ' Journ. Roy. Mic. Soc.' (N.S.),
vol. ii, p. 708.

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