and make into a thick paste with 150 c.c. distilled water. 3. Add this paste to the distilled water in the flask. 4. Dissolve the ingredients by bubbling live steam through the mixture. 5. Weigh out Aesculin 1.0 gramme Ferric citrate 0.5 gramme and dissolve in a second flask containing 100 c.c. distilled water. 6. Mix the contents of the two flasks--adjust the weight to the calculated medium figure (in this case 1031.5 grammes) by the addition of distilled water at 100°C. 7. Clarify with egg and filter. 8. Tube and sterilise as for nutrient agar. ~Bile Salt Agar (MacConkey).~-- 1. Weigh out powdered agar, 15 grammes (= 1.5. per cent.), and emulsify with 200 c.c. _cold tap_ water. 2. Weigh out peptone, 20 grammes (= 2 per cent.), and emulsify with 200 c.c. _tap_ water previously warmed to 60°C. 3. Mix the peptone and agar emulsions thoroughly. 4. Weigh out sodium taurocholate, 5 grammes (= 0.5 per cent.), dissolve it in 300 c.c. _tap_ water, and use the solution to wash the agar-peptone emulsion into a tared 2-litre flask. 5. Bubble live steam through the mixture for twenty minutes. 6. Adjust the weight of the medium mass to the calculated figure for one litre (1040 grammes). 7. Cool to 60° C. and clarify with egg as for nutrient agar (_vide_ page 168). 8. Filter through papier Chardin, using the hot-water funnel. 9. Weigh out lactose, 10 grammes (= 1 per cent.), and dissolve it in the agar. If desired, add 5 c.c. of a 1 per cent. (= 0.5 per cent.) aqueous solution of neutral red. 10. Tube, and sterilise as for nutrient agar. ~Litmus Nutrose Agar (Drigalski-Conradi).~-- This medium should be prepared in precisely the same manner as the Nutrose agar described on page 172 substituting meat extract for serum water, and increasing the percentage of agar added per litre to 3 per cent. ~Fuchsin Agar (Braun).~-- 1. Liquefy and measure out into a sterile flask: Nutrient agar 1000 c.c. 2. Weigh out: lactose 10 grammes and dissolve in the fluid agar. 3. Adjust the reaction to -5 and filter. 4. Measure out and mix thoroughly with agar: Fuchsin, alcoholic solution 5 c.c. The fuchsin solution is prepared by mixing: Fuchsin (basic) 3 grammes. Absolute alcohol 60 c.c. Allow to stand twenty-four hours, then centrifugalise thoroughly and decant the supernatant fluid into a well-stoppered bottle. 5. Measure out and add to the nutrient agar, sodium sulphite, 10 per cent. aqueous solution, freshly prepared 25 c.c. 6. Tube and sterilise as for nutrient agar. 7. Store in a dark cupboard. ~Fuchsin Sulphite Agar (Endo).~-- 1. Liquefy and measure out into a sterile flask: Nutrient agar 1000 c.c. 2. Weigh out Lactose 10 grammes. and dissolve in the fluid agar. 3. Adjust the reaction to +3 and filter. 4. Measure out and mix thoroughly with the fluid agar. Fuchsin, alcoholic solution (_vide supra_) 5 c.c.