d
centrifugalise thoroughly. On removing the pipette from the centrifuge,
the red cells will be collected in a firm mass at one end, and above
them will appear the clear serum.

10. By marking the blood pipette above the level of the serum with the
glass cutting knife and snapping the tube at that point, the blood-serum
becomes readily accessible for testing purposes.

If larger quantities of blood are required, the animal, after puncturing
the vein, should be inverted, an assistant holding it up by the legs.
Blood to the volume of several cubic centimetres will now drop from the
punctured vein, and should be caught in a tapering centrifuge tube, the
tube transferred to the incubator at 37 deg. C. for two hours, then
placed in the centrifugal machine, counterpoised and centrifugalised
thoroughly. The three most important of the antibodies referred to which
can be demonstrated with a certain amount of facility are agglutinin,
opsonin and bacteriolysin; and the methods of testing for these bodies
will now be considered.

AGGLUTININ.

Agglutinin is the name given to a substance present in the blood-serum
of an animal that has successfully resisted inoculation with a certain
micro-organism. This substance possesses the power of collecting
together in clumps and masses, or agglutinating watery suspensions of
that particular microbe.

~Dilution of the Specific Serum~:

_Apparatus required_:

Sterile graduated capillary pipettes to contain 10 c. mm. (Fig. 17).
Sterile graduated capillary pipettes to contain 90 c. mm. (Fig. 17).
Small sterile test-tubes 5 x 0.5 cm.
Normal saline solution in flask or test-tube.
Pipette of specific serum.
Glass cutting knife, or three-square file.
Glass capsule, nearly full of dry silver sand, or roll of plasticine.
Grease pencil.

METHOD.--

1. Take three sterile test-tubes and number them 1, 2 and 3.

2. Pipette 0.9 c.c. sterile normal saline solution into each tube, and
stand tubes upright in the sand in the capsule, or in the plasticine
block.

3. Make a scratch with the glass cutting knife on the blood pipette
above the upper level of the clear serum, and snap off and discard the
empty portion of the tube.

4. Remove 0.1 c.c. of the serum from the blood pipette tube, and mix it
thoroughly with the fluid in tube No. 1; and label ~s.s.~, (specific
serum), 10 per cent.

5. Remove 0.1 c.c. of the solution from tube No. 1 by means of a fresh
pipette, and mix it with the c