2. Weigh out lead acetate, 1 gramme (= 0.1 per cent.), and dissolve it in the bouillon. 3. Tube, and sterilise as for bouillon. ~Nitrate Bouillon.~-- 1. Measure out nutrient bouillon, 1000 c.c. (_vide_ page 163, sections 1 to 6). 2. Weigh out potassium nitrate, 5 grammes (= 0.5 per cent.), and dissolve it in the bouillon. 3. Tube, and sterilise as for bouillon. NOTE.--The nitrate of sodium or ammonium may be substituted for that of potassium, or the salt may be added in the proportion of from 0.1 to 1 per cent. to meet special requirements. ~Iron Peptone Solution (Pakes).~-- 1. Weigh out peptone, 30 grammes, and emulsify it with 200 c.c. tap water, previously heated to about 60°C. 2. Wash the emulsion into a litre flask with 800 c.c. tap water. 3. Weigh out salt, 5 grammes, and sodium phosphate, 3 grammes, and dissolve in the mixture in the flask. 4. Heat the mixture in the steamer at 100° C. for thirty minutes, to complete the solution of the peptone, and filter into a clean flask. 5. Fill into tubes in quantities of 10 c.c. each. 6. Add to each tube 0.1 c.c. of a 2 per cent. neutral solution of ferric tartrate. (A yellowish-white precipitate forms.) 7. Sterilise as for nutrient bouillon. ~Lead Peptone Solution.~-- Prepare as for iron peptone solution but in step 6 substitute 0.1 c.c. of a 1 per cent. neutral aqueous solution of lead acetate. ~Nitrate Peptone Solution (Pakes).~-- 1. Weigh out Witté's peptone, 10 grammes, and emulsify it with 200 c.c. ammonia-free distilled water previously heated to 60°C. 2. Wash the emulsion into a flask and make up to 1000 c.c., with ammonia-free distilled water. 3. Heat in the steamer at 100° C. for twenty minutes. 4. Weigh out sodium nitrate, 1 gramme, and dissolve in the contents of the flask. 5. Filter through Swedish filter paper. 6. Tube, and sterilise as for nutrient bouillon. ~Litmus Bouillon.~-- 1. Measure out nutrient bouillon, 1000 c.c. (_vide_ page 163, sections 1 to 6). 2. Add sufficient sterile litmus solution to tint the medium a dark lavender colour. (Media rendered +10 will usually react very faintly alkaline or occasionally neutral to litmus.) 3. Tube, and sterilise as for bouillon. ~Rosolic Acid Peptone Solution.~-- 1. Weigh out rosolic acid (corallin), 0.5 gramme, and dissolve it in 80 per cent. alcohol, 100 c.c. Keep this as a stock solution. 2. Measure out peptone water (Dunham), 100 c.c., and rosolic acid solution, 2 c.c., and mix. 3. Heat in the steamer at 100° C. for thirty minutes. 4. Filter through Swedish filter paper. 5. Tube, and sterilise as for nutrient bouillon. ~Capaldi-Proskauer Medium, No. I.~-- 1. Weigh out and mix Sodium chloride 2.0 grammes Magnesium sulphate 0.1 gramme Calcium chloride 0.2 gramme Monopotassium phosphate 2.0 grammes 2. Dissolve in water 1000 c.c. in a 2-litre flask 3. Weigh out and mix Asparagin 2 grammes Mannite 2 grammes