5. Measure out and add to the medium Sodium sulphite, 10 per cent. aqueous solution 25 c.c. 6. Tube and sterilise as for nutrient agar. ~Brilliant Green Agar (Conradi).~-- 1. Liquefy and measure out into a sterile flask Nutrient agar 1000 c.c. 2. Adjust reaction to +30 by the addition of normal phosphoric acid; and filter. 3. Measure out and mix thoroughly with the fluid medium Brilliant green (Hoechst) 1 per thousand aqueous solution 6.5 c.c. 4. Measure out and add to the medium Picric acid (Gruebler), 1 per cent. aqueous solution 6.5 c.c. 5. Tube and sterilise as for nutrient agar. ~Brilliant Green Bile Salt Agar (Fawcus).~-- 1. Weigh out agar 20 grammes and emulsify in 100 c.c. cold distilled water. 2. Wash the emulsion into a "tared" 2-litre flask with 500 c.c. distilled water. 3. Dissolve the agar by bubbling live steam through the flask. 4. Cool, clarify with egg and filter. 5. Weigh out Sodium taurocholate 5 grammes Peptone 20 grammes and add to the medium in the flask. 6. Weigh out Lactose 5 grammes and add to the medium in the flask. 7. Adjust reaction to +15 and filter if necessary. 8. Measure out Brilliant green, 1 per thousand aqueous solution 20 c.c. and mix thoroughly with the fluid agar. 9. Measure out and add to the medium Picric acid, 1 per cent. aqueous solution 20 c.c. 10. Tube and sterilise as for nutrient agar. ~China Green Agar (Werbitski).~-- 1. Liquefy and measure out into a sterile flask Nutrient agar 1000 c.c. 2. Adjust the reaction accurately to +13 and filter. 3. Measure out and mix thoroughly with the fluid agar China green 0.2 per cent. aqueous solution 15 c.c. 4. Tube and sterilise as for nutrient agar. ~Malachite Green Agar (Loeffler).~-- 1. Liquefy and measure out into a sterile flask Nutrient agar 1000 c.c. 2. Weigh out Dextrose 10 grammes. and dissolve in nutrient agar. 3. Adjust the reaction to +3, and filter. 4. Measure out and mix thoroughly in the fluid agar Malachite green, 0.1 per cent. aqueous solution 16 c.c. for ~"weak"~ medium. _4a._ To the filtered agar add Malachite green, 2 per cent. aqueous solution 25 c.c. for ~"strong"~ medium. 5. Tube and sterilise as for nutrient agar. ~Double Sugar Agar (Russell).~-- 1. Liquefy and measure out into a sterile flask Nutrient agar 1000 c.c. 2. Add 100 c.c. litmus solution to the fluid agar. 3. Weigh out and dissolve in the fluid agar. Lactose 10 grammes Dextrose 10 grammes. 4. Render the reaction of the medium neutral to litmus paper by the cautious addition of normal caustic soda. 5. Tube in quantities of 10 c.c. and sterilise in the steamer at 100° C. for twenty minutes on each of three successive days. 6. Store for use in a cool dark place. _B. Diphtheriæ._ ~Glycerine Blood-serum.~--