cutting the lung or other organs where an interstitial
support is needed. For a very thin object, a cork fitting any kind of a
tube is to be split, and the object placed between the two parts; the
cork is then thrust into the tube, and a sufficient degree of firmness
will be obtained to allow cutting. The sections should always be
manipulated with camel's hair brushes.

Much practice will be required before dexterity is attained.

_Methods of preserving the tissues_.--All water must be removed from the
tissue, either by drying or by immersing it in rectified spirits, and
then in absolute alcohol, and the alcohol driven off by floating it upon
oil of clove or turpentine. The substances used to preserve the tissues
are Canada balsam, Dammar balsam, glycerine, Farrant's solution,
potassium acetate, spirits, naphtha, and creosote.

The section is to be floated on to the slide or placed in position with a
camel's hair brush. It should be spread out, and then examined under the
microscope for the purpose of improving its position if necessary, or of
removing any foreign particles. A drop of the preserving medium is then
placed upon it, and another placed on the cover and allowed to spread
out. The cover is then taken by a pair of pincers and inverted over the
object, and one edge brought to touch the slide at one part of its
margin. The cover is then gently lowered, and the whole space beneath the
cover filled and the tissue completely saturated. If air bubbles show
themselves, raise the cover at one corner and deposit a further quantity
of the medium.

The slide should be set aside for a few days. First, the excess of the
medium must be removed; if it is glycerine, much of it can be removed by
a piece of blotting paper, but the cover must not be touched, for it is
easily displaced; that near the cover can be replaced by a camel's hair
brush. A narrow ring of glycerine jelly should be placed around the edge
of the cover, to fix it before the cement is applied. When this has set,
a narrow strip of cement is to be put on, just slightly overlapping the
edge of the cover and outside the margin of the jelly. Until it has been
perfectly secured, a slide carrying glycerine must never be placed in an
inclined position, as its cover will slide off.

_Preservative media_.--Canada balsam may be prepared as follows: Place
some pure Canada balsam in a saucer, and cover with paper to exclude
dust; dry it in an oven at a temperature of