6. Allow the film to dry in the air.

7. Stain with one of the polychrome blood stains (see page 97).

8. Examine microscopically.

b. The ~bacteriological examination of the blood~ is directed solely to
the demonstration of the presence in the circulating blood of the
organisms previously injected into the animal. For this purpose several
cubic centimetres of blood should be taken in an all-glass syringe from
an accessible vein corresponding to one of those suggested as the site
of intravenous inoculation--and under similar aseptic precautions.

1. Sterilise an all-glass syringe of suitable size, and when cool draw
into the syringe some sterile sodium citrate solution and moisten the
whole of the interior of the barrel; then eject all the citrate solution
if less than 5 c.c. blood are to be withdrawn; if more than 5 c.c. are
required retain about half a cubic centimetre of the fluid in the
syringe. This prevents coagulation of the blood.

The sodium citrate solution is prepared by dissolving:

Sodium citrate 10 gramme.
Sodium chloride 0.75 grammes.
In distilled water 100 c.c.

Sterilise by boiling.

2. Prepare the animal as for intravenous inoculation (see page 363) and
introduce the syringe needle into the lumen of the selected vein.

3. Slowly withdraw the piston of the syringe. When sufficient blood has
been collected direct the assistant to release the proximal compression
of the vein; and withdraw the needle.

4. Remove the needle from the nozzle of the syringe and deliver the
citrated blood into a small Ehlenmeyer flask containing about 250 c.c.
of nutrient broth.

5. Label, incubate and examine daily until growth occurs or until the
expiration of ten days.

c. The ~serological examination of the blood~ is directed to the
demonstration of the presence of certain specific antibodies in the sera
of experimentally infected animals, and within certain limits to an
estimation of their amounts.

The chief of these bodies are:

Antitoxin.
Agglutinin.
Precipitin.
Opsonin.
Immune body or Bacteriolysin.

None of these substances are capable of isolation in a state of purity
apart from the blood serum, consequently special methods have been
elaborated to permit of their recognition. In every instance the
behaviour of serum from the experimental animal, which may be termed
"specific" serum, is studied in comparison with that of serum from an
unin