4. Kill one guinea-pig at the end of the second week and make a complete post-mortem examination. 5. If the result of the examination is negative or inconclusive, kill a second guinea-pig at the end of the third week and examine carefully. [Illustration: FIG. 215.--Cadaver of guinea-pig experimentally infected with B. tuberculosis.] 6. If still negative or inconclusive, kill the third guinea-pig at the end of the _sixth_ week. Make a careful post-mortem examination. Examine material from any caseous glands microscopically and inoculate freely on to Dorset's egg medium. NOTE.--Every post-mortem examination of animals infected with tuberculous material should include the naked eye and microscopical examination of the popliteal, superficial and deep inguinal, iliac, lumbar and axillary glands on each side of the body, also the retrohepatic, bronchial and sternal glands, the spleen, liver and lungs (Fig. 215). (B) 1. Intimately mix all the available cream and deposit from the milk sample, and transfer to a sterile Erlenmeyer flask. 2. Treat the mixture by the antiformin method (_vide_ Appendix, page 502). 3. Inoculate each of two guinea-pigs, intraperitoneally, with half of the emulsion thus obtained. 4. Kill one of the guinea-pigs at the end of the first week and examine carefully. 5. Kill the second guinea-pig at the end of the second week and examine carefully. 6. Utilise the remainder of the deposit for microscopical examination and cultivations upon Dorset's egg medium. NOTE.--No value whatever attaches to the result of a microscopical examination for the presence of the B. tuberculosis unless confirmed by the result of inoculation experiments. ~6. Streptococcus Pyogenes Longus.~-- (A) 1. Spread serial surface plates upon nutrose agar. Also plant serial cultivations upon sloped nutrient agar (six tubes in series). 2. If the resulting growth shows colonies which resemble those of the streptococcus, make subcultivations upon agar and in bouillon, in the first instance, and study carefully. (B) 1. Plant a large loopful of the deposit D^{2} into each of three tubes of glucose formate bouillon, and incubate anaerobically (in Buchner's tubes) for twenty-four hours at 37° C. 2. If the resulting growth resembles that of the streptococcus, make subcultivations upon nutrient agar. 3. Prepare subcultivations of any suspicious colonies that appear, upon all the ordinary media, and study carefully. If the streptococcus is successfully isolated, inoculate serum bouillon cultivations into the mouse, guinea-pig, and rabbit, to determine its pathogenicity and virulence. ~7. Staphylococcus Pyogenes Aureus.~-- 1. Examine carefully the growth upon the serial blood serum cultivations prepared to isolate B. diphtheriæ and the serial agar cultivations to isolate streptococci after forty-eight hours' incubation.