ker than 0.08 to 0.10 mm., the
glass must not be brittle or faulty, and must in this thickness easily
allow of considerable bending, without breaking. Every unevenness of the
slip renders it useless for our purposes. The glasses must previously be
particularly carefully cleaned, and all fat removed. It is generally
sufficient to allow the slips to remain in ether for about half-an-hour,
not covering one another. Each one still wet with ether is then wiped
with soft, not coarse, linen rag or with tissue-paper. The slips now are
put into alcohol for a few minutes, are dried in the same manner as from
the ether, and are kept ready for use in a dust-tight watch-glass.
Bearing in mind, that these cover-slips are not cut out from a flat
piece but from the surface of a sphere, it is evident that only with
glasses thus prepared, can it be expected that a capillary space should
be formed between two of them, in which the blood spreads easily. For
with the smallest unevenness or brittleness of the glass it is an
impossibility for the one to fit every bend of the other. And it is only
then that the slips can be drawn away one from another, without using a
force which breaks them.

To avoid fresh soiling of the cover-slips, and above all the contact of
the blood with the moisture coming from the finger, the cover-glass is
held with forceps[4] to receive the blood. We recommend for the under
cover-glass a clamp forceps _a_, with broad, smooth blades; the ends may
be covered with leather or blotting-paper for a distance of about 1/2
in. For the other cover-slip a very light spring forceps _b_, with
smooth blades, sharp at the tips, is used, with which a cover-glass can
be easily picked up from a flat surface. The lower slip is now fixed by
one edge in the clamp forceps, and held ready in the left hand. The
right hand applies the upper glass with the forceps _b_ to the drop of
blood as it exudes from the puncture, and takes it up, without touching
the finger itself. The forceps _b_ is then quickly brought to _a_ and
the slip with the little drop of blood allowed to fall lightly on the
other. In glasses of the right quality the drop distributes itself
spontaneously in a completely regular capillary layer. With two fingers
of the right hand on the edge of the upper glass, it is now carefully
pulled from the lower, which remains fixed in the clamp, without
pressing or lifting. Frequently only one, the lower, shews a regular
layer, but oc