reparation. This number is recorded as
the denominator of a vulgar fraction of which the numerator is the
number recorded for the specific serum. This fraction, expressed as a
percentage of unity = the _opsonic index_.

IMMUNE BODY.

Immune body or amboceptor is the name given to a substance present in
the serum of an infected animal that has successfully resisted
inoculation with some particular micro-organism, and which possesses the
power of linking the complement normally present in the serum to
bacteria of the species used as antigen in such a manner that the
micro-organisms are rendered innocuous, and ultimately destroyed. The
presence of the immune body in the serum can be demonstrated _in vitro_
by the reaction elaborated by Bordet and Gengou, known as the complement
fixation test, the existence or the absence of the phenomenon of
complement fixation being rendered obvious macroscopically by the
absence or presence of haemolysis on the subsequent addition of
"sensitised" red blood corpuscles, (e. g., a mixture of crythrocyte
solution and the appropriate haemolysin--two of the three essentials in
the haemolytic system, _vide_ page 326).

_Apparatus Required:_

Sterile pipettes 1 c.c., (graduated in tenths).

16 x 2 cm. test-tubes.

9 x 1 cm. test-tubes.

Test-tube racks for each size of test-tube.

_Reagents Required:_

Normal saline solution.

Erythrocyte solution (human red cells, page 329) = E.

Haemolytic serum (for human cells) = H.S.

Complement (fresh guinea-pig serum) = C.

Specific serum from inoculated animal, inactivated = S.S.

Control pooled serum from normal animals of same species,
Inactivated = P.S.

_Antigen_ (cultivation upon solid medium of the organism
(e. g., B. typhosus) which has already served as antigen
in the inoculation of the experimental animal) = A.

To prepare the antigen for use, emulsify the whole of the bacterial
growth in 5 c.c. normal saline solution.

Shake the emulsion in a test-tube with some sterilised glass beads to
ensure a homogenous emulsion, and sterilise by heating to 60 deg. C. in
a water-bath for one hour.

METHOD.--

1. Take five small test-tubes, and number them 1 to 5 with a grease
pencil.

2. Into tubes Nos. 1, 3, 4 and 5 pipette 0.1 c.c. of complement.

3. Into tubes Nos. 1 and 2 pipette 0.2 c.c. of the serum to be tested.

4. Into tube No. 4 pipe