tissues should remain in the mixture about twenty-four hours.

7. Transfer the tissues to a vessel containing pure melted paraffin.
Place this vessel in a paraffin water-bath regulated for 2 deg. C. above
the melting-point of the paraffin used, and allow the tissues to soak for
some four to six hours to ensure complete impregnation. The paraffin
used should have a melting-point of not more than 58 deg. C. For all
ordinary purposes 54 deg. C. will be found quite high enough.

8. Imbed in fresh paraffin in a metal (or paper) mould.

(a) Arrange a pair of ~L~-shaped pieces of metal on a plate of glass to
form a rectangular trough (Fig. 72).

(b) Pour fresh melted paraffin into the mould from a special vessel
(Fig. 73).

(c) Lift the piece of tissue from the paraffin bath and arrange it in
the mould.

(d) Blow gently on the surface of the paraffin in the mould, and as
soon as a film of solid paraffin has formed, carefully lift the glass
plate on which the mould is set and lower plate and mould together into
a basin of cold water.

(e) When the block is cold, break off the metal ~L~'s; trim off the
excess of paraffin from around the tissue with a knife, taking care to
retain the rectangular shape, and store the block in a pill-box.

When several pieces of tissue have to be imbedded at one time, shapes of
stout copper, 10 cm., 5 cm., and 2.5 cm. square respectively, and 0.75
cm. deep (Fig. 74) will be found extremely useful. These placed upon
plates of glass replace the pair of L's in the above process. When the
paraffin has set firmly the screw a should be loosened to allow the
two halves of the flange b to separate slightly--this facilitates
removal of the paraffin block.

[Illustration: FIG. 74.--Paraffin mould.]

8. Cement the block on the carrier of a "paraffin" microtome (the Minot,
the Jung, or the Cambridge Rocker) with a little melted paraffin.
Greater security is obtained if the paraffin around the base of the
block is melted by means of a hot metal or glass rod.

9. Cut sections--thin, and if possible in ribbands.

~Mounting Paraffin Sections.~--

1. Place a large drop of 30 per cent. alcohol on the centre of a slide
(or cover-slip) and float the section on to the surface of the drop,
from a section lifter.

2. Hold the slide in the fingers of one hand and warm cautiously over
the flame of a Bunsen burner, touching the under surface of the glass
from time to time on the back of the other hand. A