(The method depends upon the assumption that members of the typhoid and coli groups find their way through the porcelain filter from the interior to the surrounding bouillon at a quicker rate than the associated bacteria.) B. ~Enteritidis Sporogenes.~-- 1. Transfer 5 c.c. of the emulsion from the filter candle to a sterile test-tube and plug carefully. 2. Place the test-tube in the interior of the benzole bath employed in separating out spore-bearing organisms (_vide_ page 257), and expose to a temperature of 80° C. for twenty minutes. 3. Number ten tubes of litmus milk consecutively from 1 to 10. 4. Remove the test-tube from the benzole bath and shake well to distribute the spores evenly through the fluid. 5. To each tube of litmus milk add a measured quantity of the suspension corresponding to the amounts employed in isolating the coli group (_vide_ page 437). 6. Incubate each tube anaerobically at 37° C. Anaerobic conditions can be obtained by putting the cultures up in Buchner's tubes or in Bulloch's apparatus. If, however, whole milk has been used in making the litmus milk the layer of cream that rises to the surface will be sufficient to ensure anaerobiosis; whilst if separated milk has been employed it will be sufficient to pour a layer of sterile vaseline or liquid paraffin on the surface of the fluid. 7. Examine after twenty-four hours' incubation. Note (if B. enteritidis sporogenes is present)-- (a) Acid reaction of the medium as indicated by the colour of the litmus or its complete decolourisation. (b) Presence of clotting, and the separation of clear whey. (c) Presence of gas, as indicated by fissures and bubbles in the coagulum, and possibly masses of coagulum driven up the tube almost to the plug. 8. Replace the tubes which show no signs of growth in the incubator for a further period of twenty-four hours and again examine with reference to the same points. 9. Remove those tubes which give evidence of growth from the Buchner's tubes and carefully pipette off the whey; examine the whey microscopically. 10. Inoculate two guinea-pigs each subcutaneously with 0.5 c.c. of the whey and observe the result. ~Vibrio Choleræ.~-- 1. Number ten tubes of peptone water consecutively from 1 to 10. 2. To each of the tubes of peptone water add a measured quantity of the suspension, corresponding to those amounts employed in isolating the members of the coli group (_vide_ page 437). 3. Incubate aerobically at 37° C. for twenty-four hours. Examine the tubes carefully for visible growth, especially delicate pellicle formation, which if present should be examined microscopically for vibrios, both by stained preparations or by fresh specimens with dark ground illumination. 4. Inoculate fresh tubes of peptone water from such of the tubes as exhibit pellicle formation--from the pellicle itself--and incubate at 37° C. for twenty-four hours.