as to thoroughly mix its contents. Plug
the mouth of each tube with cotton wool, and place entire set in the
incubator at 37 deg. C. for one hour.

8. Remove the tubes from the incubator and into each tube pipette 0.1
c.c. complement (guinea-pig's serum) and replace tubes in incubator at
37 deg. C. for further period of one hour.

9. Remove the tubes from the incubator, and if complete haemolysis has
not taken place in every tube, stand on one side, preferably in the ice
chest, for an hour.

10. Then examine the tubes.

Complete haemolysis is indicated by a clear red solution,
with no deposit of red cells at the bottom of the test-tube.

Absence of haemolysis is indicated by a clear or turbid
colourless fluid, with a deposit of red cells at the bottom
of the test-tubes.

The smallest amount of haemolytic serum that has caused complete
haemolysis is known as the minimal haemolytic dose (_M. H. D._) and if
haemolysis has occurred in all the tubes down to No. 7--the m. h. d. of
this particular serum is .005 c.c. = 200 minimal haemolytic doses per
cubic centimetre. Such a serum is strong enough for experimental work;
indeed, for many purposes, complete haemolysis down to tube 6 will
indicate a serum sufficiently strong(= 100 m. h. d. per cubic
centimetre). If, however, only the first one or two tubes are completely
haemolysed, this is an indication that the rabbit should receive further
injections in order to raise the haemolytic power to a sufficiently high
level.

STORAGE OF HAEMOLYSIN.

If, and when the haemolysin content of the rabbit's serum is found to be
sufficient, destroy the animal by chloroform vapour.

Remove as much of its blood as possible from the heart under aseptic
precautions into sterilized centrifuge tubes.

Transfer the tubes of blood to the incubator at 37 deg. C. for two
hours--then centrifugalize thoroughly.

Pipette off the clear serum, and fill in quantities of 1 c.c., into
small glass ampoules or pipettes, and hermetically seal in the blowpipe
flame, care being taken to avoid scorching the serum.

Place the ampoules when filled with serum and sealed, in a water-bath at
56 deg. C. for 30 minutes. This destroys the complement, i. e.,
inactivates the serum, and at the same time, provided the various
operations have been carried out under aseptic precautions, ensures its
sterility. A longer exposure reduces the haemolytic power.

Place the ampoules in a clos