3. Place the beaker in a water-bath and proceed as in preparing meat extract--i. e., heat gently at 40° C. for twenty minutes, then rapidly raise the temperature to, and maintain at, the boiling-point for ten minutes. 4. Strain the mixture through butter muslin into a clean flask. 5. Weigh out peptone, 5 grammes, and emulsify with about 200 c.c. of the hot fish water; incorporate thoroughly with the remainder of the fish water in the flask. 6. Heat in the steamer at 100° C. for twenty minutes to complete the solution of the peptone. 7. Filter through Swedish filter paper. 8. When the fish bouillon is cold, if it is to be used as fluid medium, make up to 1000 c.c. by the addition of distilled water. If, however, it is to be used as the basis for agar or gelatine media store it in the "Double Strength" condition. 9. Tube and sterilise as for nutrient bouillon. As an alternative method "Marvis" fish food (16 grammes) may be substituted for the 500 grammes of fresh fish. ~Fish Gelatine.~-- 1. Measure out double strength fish bouillon, 500 c.c., into a "tared" 2-litre flask. 2. Add sheet gelatine, 100 grammes, cut into small pieces. 3. Bubble live steam through the mixture for fifteen minutes to dissolve the gelatine. 4. Weigh the flask and its contents; adjust the weight to the calculated figure for one litre of medium (1135.5 grammes) by the addition of distilled water at 100° C. (_vide_ page 166). 5. Cool to below 60°C., and clarify with egg. 6. Filter through papier Chardin. 7. Tube, and sterilise as for nutrient gelatine. Shake well after the final sterilisation, to aerate the medium. ~Fish Gelatine-Agar.~-- 1. Weigh out powdered agar, 5 grammes, and emulsify it with 200 c.c. double strength fish bouillon. 2. Wash the emulsion into a "tared" 2-litre flask with 300 c.c. fish bouillon. 3. Weigh out sheet gelatine, 70 grammes, cut it into small pieces and add it to the contents of the flask. 4. Bubble live steam through the mixture to dissolve the gelatine and agar. 5. Weigh the flask and contents. Adjust the weight to the calculated figure for one litre of medium (1110.5 grammes) by the addition of distilled water at 100° C. (_vide_ page 166). 6. Cool to below 60° C. and clarify with egg. 7. Filter through papier Chardin. 8. Tube, and sterilise as for nutrient gelatine. Shake well after the final sterilisation, to aerate the medium. _Media for the Study of Yeasts and Moulds._ ~Pasteur's Solution.~-- (Reaction alkaline). 1. Weigh out and mix the ash from 10 grammes of yeast; ammonium tartrate, 10 grammes; cane sugar, 100 grammes. 2. Dissolve the mixture in distilled water, 1000 c.c. 3. Tube or flask, and sterilise as for nutrient bouillon. ~Yeast Water (Pasteur).~-- 1. Weigh out pressed yeast, 75 grammes; place in a 2-litre flask and add 1000 c.c. distilled water. 2. Heat in the steamer at 100° C. for thirty minutes. 3. Filter through papier Chardin.