hour.
--------------------------------------------------------------------------
(?) No haemolysis. |__________________________________|

Haemolysis.

NOTE.--It is sometimes more convenient to _sensitise_ the
erythrocytes just before they are needed. This is done
forty-five minutes after the experiment has been started
(page 394, step 6), that is to say, before the completion of
the first period of incubation, thus:

1. Measure out into a sterile test-tube (or flask) five c.c.
of erythrocyte solution.

2. Measure out twenty minimal haemolytic doses of haemolysin,
add to the erythrocyte solution on the test-tube.

3. Allow the erythrocyte and haemolysin to remain in contact
for fifteen minutes at room temperature. The red cells are
then sensitised and ready for use.

4. When the tubes are removed from the incubator at the end
of the first hour (i. e., step 7) add 1 c.c. sensitised
red cells to each tube by means of a graduated pipette.

5. Mix thoroughly, return the tubes to the incubator at
37 deg. C. and complete the experiment as previously described
(steps 8 onward).

XIX. POST-MORTEM EXAMINATIONS OF EXPERIMENTAL ANIMALS.

The post-mortem examination should be carried out as soon as possible
after the death of the animal, for it must be remembered that even in
cold weather the tissues are rapidly invaded by numerous bacteria
derived from the alimentary tract or the cavities of the body, and from
external sources.

The following outlines refer to a complete and exhaustive necropsy, and
in routine work the examination will rarely need to be carried out in
its entirety.

NOTE.--Throughout the autopsy the searing irons must be
freely employed, and it must be recollected that one
instrument is only to be employed to seize or cut one
structure. This done, it must be regarded as contaminated
and a fresh instrument taken for the next step.

~Apparatus Required~:

Water steriliser.

{ Scalpels.
Surgical instruments: { Scissors.
{ Forceps.
{ Bone forceps.

Spear-headed platinum spatula (Fig. 199).

Searing irons (Fig. 198).

Tubes of media--bouillon and sloped agar.

Surface plates in petri dishes (of agar or one of its deriva