AGf~ICULTURAL RESEARCH, PUSA.

The reaction is carried out in a manner similar to
an agglutination test (vide p. 197).
The activity of the serum is at an optimum when
heated at 54°-56° C. For the test the patient's serum
is therefore heated at 55° C. for half-all-hour, and a
series of concentrations is prepared in small test-tulles
(3 >: "} in.) as follows (physiological saline solutio]) heing
used as the dilucnt) :o
o
1 i,1 2 1 iu 4 1 ill 8 1 ill 16 1 ill 32
0'4 C.c. of each concentration is a convenient. qmmtitv
for the test, and to caeh tube ollc-half of this yolllnlc
(0'2 c.c.) of the antigen suspension is added. If the
optimum dilution of the autigen is 1 in 18, then a
1 in 6 suspension is used; it is prepal'ed by mixing
rapidly equal quantities of the undiluted antigcn and
saline solution, allowing the mixture to stand for ten
minutes, and then adding sufficient saline to give thc
required dilution (i.e. 1. in 6). The mixtures of serum
and antigcn are transferred to nal'l'OW agglut.ination
tubes, incubated at 37° C. for four hoUl's, and allowed to
stand overnight at room temperature, when readings
are made of the results. A final reading should he
madc after thirty-six hours. In reading thc results,
the tubes should he held in front of a shaded lamp so
that they are brightly illuminated without the glare
of the lamp reaching thc eyes. A control tube containing
antigcn suspcnsion and saline lmt. no serum should
be inclurled. ·With strongly reacting scra, flocculation
may occur even in tuhe 0. With weak scra definite
flocculation may occur only in tube CD. " Zone
phenomena" arc sometimes noticed, especially with
sera after three days or morc from the tim.c of withdrawal
of thc blood-i.e. flocculation is less with lower
dilutions of serum than ·wit.h highel' dilutions.
The rcacti,on mn be hastened by shaking the mixtures
of serum and antigen for five to ten minutes hefore
incubation. This ean easily be done after the addition