ch the serum has been separated
is of sufficiently large diameter to permit of their use.

~The Macroscopical Reaction:~

Sterile graduated capillary pipettes to contain 90 c. mm.

Eighteen to twenty-four-hours-old bouillon cultivation of
the organism to be tested.

Three test-tubes containing the 10, 1, and 0.1 per cent.
solutions of specific serum (about 90 c. mm. remaining in
each).

Tube containing 50 per cent. solution of pooled serum.

Sedimentation pipettes (_vide_ page 17) or teat pipettes.

METHOD.

1. Pipette 90 c. mm. of the bouillon culture into each of the tubes
containing the diluted serum; and the same quantity into the tube
containing the pooled serum.

2. Fill a sedimentation tube (by aspirating) or a teat pipette from the
contents of each tube. Seal off the lower ends of the sedimentation
tubes in the Bunsen flame.

3. Label each tube with the dilution of serum that it contains--viz., 5,
0.5, and 0.05 per cent.

4. Place the pipettes in a vertical position, in a beaker, in the
incubator at 37 deg. C., for one or two hours.

5. Observe the granular precipitate which is thrown down when the
reaction is positive, and the uniform turbidity of the negative reaction
as compared with the appearances in the control pooled serum.

OPSONIN.

Opsonin is the term applied by Wright to a substance, present in the
serum of an inoculated animal, which is able to act upon or sensitise
bacteria of the species originally injected, so as to render them an
easy prey to the phagocytic activity of polymorphonuclear leucocytes. In
the method for demonstrating opsonin about to be described, a comparison
is made between the opsonic "power" of the pooled serum and the specific
serum.

_Apparatus:_

Small centrifuge and tubes for same (made from the barrels
of broken capillary pipettes by sealing the conical ends in
the bunsen flame).

Capillary Pasteur pipettes.

India-rubber teats.

Grease pencil.

Bunsen burner with peep flame.

Electrical signal clock (see page 39) stop watch, or watch.

Rectangular glass box or tray to hold pipettes.

Incubator regulated at 37 deg. C.

3 x 1 slides.

Piece of light rubber tubing.

Rectangular block of plasticine.

Flask of normal saline solution.

Flask of sodium citrate (1.5 per cent.) in normal saline
solution.