6. Filter through papier Chardin, using the hot-water funnel. 7. Tube, and sterilise as for nutrient agar. (Leave the reaction unaltered.) ~Serum Sugar Media (Hiss).~-- In these media the fermentation of carbohydrate substance by bacterial action is indicated by the coagulation of the serum proteids in addition to the production of an acid reaction. ~Serum Dextrose Water (Hiss).~-- 1. Measure out into a litre flask Serum water (See page 170) 1000 c.c. 2. Weigh out Dextrose 10 grammes and dissolve in the serum water. 3. Filter through Swedish filter paper. 4. Measure out and add to the medium Litmus solution (Kahlbaum) 50 c.c. 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. Lævulose, galactose, maltose, lactose, etc., can be substituted in similar amounts for dextrose and the medium completed as above. ~Omeliansky's Nutrient Fluid~ (_For Cellulose Fermenters_).-- 1. Weigh out and mix Potassium phosphate 4.0 grammes Magnesium sulphate 2.0 grammes Ammonium sulphate 4.0 grammes Sodium chloride 0.25 gramme 2. Dissolve in distilled water 4000 c.c. 3. Flask in quantities of 250 c.c. 4. Weigh out and add 5 grammes precipitated chalk to each flask. 5. Sterilise in the steamer at 100° C. for twenty minutes on each of three successive days. _Media for the Study of Chromogenic Bacteria._ ~Milk Rice (Eisenberg).~-- 1. Measure out nutrient bouillon, 70 c.c., and milk, 210 c.c., and mix thoroughly. 2. Weigh out rice powder, 100 grammes, and rub it up in a mortar with the milk and broth mixture. 3. Fill the paste into sterile capsules, spreading it out so as to form a layer about 0.5 cm. thick, over the bottom of each. 4. Heat over a water-bath at 100° C. until the mixture solidifies. 5. Replace the lids of the capsules. Sterilise in the steamer at 100° C. for thirty minutes on each of three consecutive days. (A solid medium of the colour of _café au lait_ is thus produced.) ~Milk Rice (Soyka).~-- 1. Measure out nutrient bouillon, 50 c.c., and milk, 150 c.c., and mix thoroughly. 2. Weigh out rice powder, 100 grammes, and rub it up in a mortar with the milk and broth mixture. 3. Fill the paste into sterile capsules, to form a layer over the bottom of each. 4. Replace the lids of the capsules. 5. Sterilise in the steamer at 100° C. for thirty minutes on each of three consecutive days. (A pure white, opaque medium is thus formed.) _Media for the Study of Phosphorescent and Photogenic Bacteria._ ~Fish Bouillon.~-- 1. Weigh out herring, mackerel, or cod, 500 grammes, and place in a large porcelain beaker (or enamelled iron pot). 2. Weigh out sodium chloride, 26.5 grammes; potassium chloride, 0.75 gramme; magnesium chloride, 3.25 grammes; and dissolve in 500 c.c. distilled water. Add the solution to the fish in the beaker.