H.S.^{4} H.S.^{4} H.S.^{4} H.S.^{4} H.S.^{4} -------------------------------------------------------------------------- Incubate at 37° C. for one hour. -------------------------------------------------------------------------- (?) No hæmolysis. |__________________________________| Hæmolysis. 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 hæmolytic doses of hæmolysin, add to the erythrocyte solution on the test-tube. 3. Allow the erythrocyte and hæmolysin 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°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 derivatives). Platinum loop. Aluminium "spreader." Grease pencil. Sterile capillary pipettes (Fig. 13, a). Sterile glass capsules, large and small. Cover-slips or slides. Bottles of fixing fluid (_vide_ page 114) for pieces of tissue intended for sectioning.