4. Weigh out peptone, 10 grammes; salt, 5 grammes; emulsify with 100 c.c. double strength meat extract previously heated to 60°C., and add to the contents of the flask. 5. Replace in the steamer for fifteen minutes. Then adjust the weight to the calculated figure for one litre (in this instance 1120 grammes) by the addition of distilled water at 100°C. 6. Estimate the reaction; control the result. Then add sufficient caustic soda solution to render the reaction +10. 7. Replace in the steamer at 100° C. for twenty minutes. 8. Cool to 60° C. Clarify with egg as for nutrient agar. 9. Filter through papier Chardin, using the hot-water funnel. 10. Tube, and sterilise as for nutrient agar. ~Agar Gelatine (Guarniari).~-- 1. Measure out double strength meat extract, 400 c.c., into a "tared" 2-litre flask, and add to it gelatine, 50 grammes. 2. Weigh out powdered agar, 3 grammes; emulsify with cold distilled water, 50 c.c., and add to the contents of the flask. 3. Dissolve the agar and gelatine by bubbling live steam through the flask for twenty minutes. 4. Weigh out Witté's peptone, 25 grammes; salt, 5 grammes, and emulsify with 100 c.c. double strength meat extract previously heated to 60°C., and add to the contents of the flask. 5. Replace in the steamer for fifteen minutes. 6. Weigh the flask and make up the medium mass to the calculated figure for one litre (1083 grammes) by the addition of distilled water at 100°C. 7. Neutralise carefully to litmus paper by the successive additions of small quantities of normal soda solution. 8. Replace in the steamer at 100° C. for twenty minutes. 9. Cool to 60° C. Clarify with egg as for nutrient agar. 10. Filter through papier Chardin, using the hot-water funnel. 11. Tube, and sterilise as for nutrient agar. ~Whey Gelatine.~-- 1. Curdle fresh milk by warming to 60°C., and adding rennet; filter off the whey into a sterile "tared" flask. 2. Estimate and note the reaction of the whey. 3. Weigh out gelatine, 10 per cent., and add it to the whey in the flask. 4. Bubble live steam through the mixture fifteen minutes to dissolve the gelatine; and weigh. 5. Estimate the reaction of the medium mass; then add sufficient caustic soda solution to restore the reaction of the medium mass (i. e., total weight minus weight of flask) to the equivalent of the original whey. 6. Cool to 60° C. and clarify with egg as for nutrient gelatine (_vide_ page 166). 7. Filter through papier Chardin. 8. Tube, and sterilise as for nutrient gelatine. ~Whey Agar.~-- 1. Curdle fresh milk by warming to 60°C., and adding rennet; filter off the whey into a sterile flask. 2. Weigh out agar, 1.5 or 2 per cent., and add it to the whey in the flask. 3. Bubble live steam through the mixture for twenty minutes, to dissolve the agar. 4. Cool to 60°C.; clarify with egg as for nutrient agar (_vide_ page 168). 5. Filter through papier Chardin, using the hot-water funnel. 6. Tube, and sterilise as for nutrient agar.