es immediately after use into tall glass
cylinders containing a 2 per cent. solution of lysol, and allow them to
remain therein for some days.

2. Remove from the jar and drain. Boil in water to which a little soap
has been added, for thirty minutes.

3. Rinse thoroughly in cold water.

4. Immerse in 5 per cent. nitric acid for an hour or two.

5. Rinse again in running water to remove all traces of acid.

6. Complete the cleaning as described under "new pipettes."

When dealing with graduated capillary pipettes employed for blood or
serum work (whether new or infected), much time is consumed in the
various steps from 5 onward, and the cleansing process can be materially
hastened if the following device is adopted.

Fit up a large-sized Kitasato's filter flask to a Sprengel's suction
pump or a Geryk air pump (see page 43). To the side tubulure of the
filter flask attach a 20 cm. length of rubber pressure tubing having a
calibre sufficiently large to admit the ends of the pipettes.

Next fill a small beaker with distilled water. Attach the first pipette
to the free end of the rubber tubing, place the pipette point downward
in the beaker of water and start the pump (Fig. 22).

[Illustration: FIG. 22.--Cleaning blood pipettes.]

When all the water has been aspirated through the pipette into the
filter flask, fill the beaker with rectified spirit and when this is
exhausted refill with ether. Detach the pipette and dry in the hot-air
oven.

~Slides and cover-slips~ (Fig. 23), when first purchased, have "greasy"
surfaces, upon which water gathers in minute drops and effectually
prevents the spreading of thin, even films.

~Microscopical Slides.~--The slides in general use are those known as
"three by one" slips (measuring 3 inches by 1 inch, or 76 by 26 mm.),
and should be of good white crown glass, with ground edges.

~New slides~ should be allowed to remain in alcohol acidulated with 5 per
cent. hydrochloric acid for some hours, rinsed in running water, roughly
drained on a towel, dried, and finally polished with a selvyt cloth.

[Illustration: FIG. 23.--Slides and cover-slips, actual size.]

If only a few slides are required for immediate use a good plan is to
rub the surface with jeweler's emery paper (Hubert's 00). A piece of
hard wood 76x26x26 mm. with a piece of this emery paper gummed tightly
around it is an exceedingly useful article on the microscope bench.

~Cover-slips.~--The most useful sizes ar