pipettes, except that the point of the
blowpipe flame must be used in order to obtain the sharp shoulder at
either end of the central bulb. The terminal tubes must retain a
diameter of at least 1 mm., in order to avoid capillary action during
the collection of the fluid.

[Illustration: FIG. 15.--Blood pipettes and hair-lip pin in a
test-tube.]

[Illustration: FIG. 16.--Blood-pipette in metal thermometer case.]

For sterilisation and storage each pipette is placed inside a test-tube,
resting on a wad of cotton-wool, and the tube plugged in the ordinary
manner. As these tubes are used almost exclusively for blood work, it is
usual to place a lance-headed hare-lip pin or a No. 9 flat Hagedorn
needle inside the tube so that the entire outfit may be sterilised at
one time.

For the collection of small quantities of blood for agglutination
reactions and the like, many prefer a short straight piece of narrow
glass tubing drawn out at either extremity to almost capillary
dimensions. Such pipettes, about 8 cm. in length over all, are most
conveniently sterilized in ordinary metal thermometer cases (Fig. 16).

~Graduated Capillary Pipettes~ (Fig. 17).--These should also be made in
the laboratory--from manometer tubing--of simple, convenient shape, and
graduated by the aid of "standard" pipettes (in hundredths) to contain
such quantities as 10, 50, and 90 c. mm., and carefully marked with a
writing diamond. These, previously sterilised in large test-tubes, will
be found extremely useful in preparing accurate percentage solutions,
when only minute quantities of fluid are available.

[Illustration: FIG. 17.--Capillary graduated pipettes.]

~Automatic ("Throttle") Pipettes.~--These ingenious pipettes, introduced
by Wright, can easily be calibrated in the laboratory and are
exceedingly useful for graduating small pipettes, for measuring small
quantities of fluids, in preparing dilutions of serum for agglutination
reactions, etc. They are usually made from the Capillary Pasteur
pipettes (Fig. 13, a). The following description of the manufacture of
a 5 c. mm. pipette will serve to show how the small automatic pipettes
are calibrated.

1. Select a pipette the capillary portion of which is fairly roomy in
bore and possesses regular even walls, and remove the cotton-wool plug
from the open end.

2. Heat the capillary portion near the free extremity in the by-pass
flame of the bunsen burner and draw it out into a very fine hair