bdominalis)

Pipette end with the remainder of the specific serum
labelled ~s.s.~

Tubes containing the three solutions of the specific serum,
10, 1, and 0.1 per cent. respectively.

Pipette end with pooled normal serum labelled ~p.s.~

METHOD.--

1. Make five hanging-drop preparations, thus:

(a) One loopful of bouillon cultivation + one loopful pooled serum;
label "Control."

(b) One loopful culture + one loopful undiluted specific serum; label
50 per cent.

Mount these two cover-slips on a double-celled slide.

(c) One loopful bouillon culture + one loopful 10 per cent. serum;
label 5 per cent.

Mount this on single-cell slide.

(d) One loopful bouillon culture + one loopful 1 per cent. serum;
label 0.5 per cent.

(e) One loopful bouillon culture + one loopful 0.1 per cent. serum;
label 0.05 per cent.

Mount these two cover-slips on a double-celled slide.

2. Note the time: Examine the control to determine that the bacilli are
motile and uniformly scattered over the field--not collected into
masses.

3. Next examine the 50 per cent. serum preparation.

If agglutinin is present and the test is giving a positive reaction, the
bacilli _will_ be collected in large clumps.

If the test is giving a negative reaction, the bacilli _may_ be
collected in large clumps owing to the viscosity of the concentrated
serum.

4. Observe the 5 per cent. preparation microscopically.

If the bacilli are aggregated into clumps, positive reaction.

If the bacilli are _not_ aggregated into clumps, observe until thirty
minutes from the time of preparation before recording a negative
reaction.

5. Examine the 0.5 and 0.05 per cent. preparations.

These may or may not show agglutination when the result of the
examination of the 5 per cent. preparation is positive, according to the
potency of the specific serum; and by the examination of a series of
dilutions a quantitative comparison of the valency of specific sera from
different sources, or of serum from the same animal at different periods
during the course of active immunisation may be obtained.

NOTE.--The graduated pipettes supplied with Thoma's
haematocytometer (intended for the collection of the specimen
of blood required for the enumeration of leucocytes), giving
a dilution of 1 in 10--i. e., 10 per cent.--may be
substituted for the graduated capillary pipettes referred to
above, if the vessel in whi