In   should be used at the different temperatures at *which sec-
i ,   tions are usually cut, but I can indicate at least one point
IPeR  with considerable accuracy. Small sections can always be
1ip   made to chain when cut from a good paraffin of 450 C. melt-
itiat  ing-point in a room  in which the thermometer stands at 160
tyi  to 170 C.   (The temperatures quoted apply to the case of
* rooms heated by an open fire, and probably would not apply
1.  to the case of rooms heated by closed stoves, such as are usual
in Germany.) At 15' C. the paraffin will be found a trifle
O  hard. At 220 C., the proper melting-point of the paraffin
will probably be found at about 480 C., but my observations
at these temperatures are less extended. Secondly, the knife
a  should be set square. Thirdly, the block of paraffin should
h     be pared-down very close to the object, and should be cut so
as to present a straight edge parallel to the knife edge; and
the opposite edge should also be parallel to this. The block
should in no case be cut so as to present a pointed side, as
)  recommended by the Naples Zoological Station. Fourthly,
i the sections ought to be cut rapidly, with the swiftest strokes
i that can be produced. It is evident that this condition can
b    only be conveniently realised by means of a sliding microtome;
but it is by no means necessary to have recourse to special
mechanical contrivances, as in Caldwell's automatic micro-
tome.    The Thoma microtome well flooded        with  oil is
sufficient.
655. Parabolic Mirror for Correction of too Hard or too
I Soft Paraffin (H. Fol's method ').-If, after cutting has begun,
the paraffin be found to be too hard, it may be softened by the
following simple and ingenious expedient :-A lamp provided
with a parabolic reflector is set up near the microtome in such
a position that the heat-rays.of the flame are thrown by the
reflector on to the imbedded object. The right temperature
is obtained by adjusting the distance of the lamp.
tig I Fol, ' Lehrbuch d. verg1. mikr. Anat.,' p. 123. Leipzig, Engelmann,
11884.
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