780 JOURNAL OF TIlE SOCIETY OF COSMETIC CHEMISTS Add 40 g to 1 000 ml of water and soak for 15 min. Mix and sterilize at 121 ø for 15 min. Mix well before pouring. For general purpose Nutrient Agar, Blood Agar Base no. 2 is recom- mended. Commercial form: Oxoid CM271 1.04 Blood Agar Add defibrinated sterile horse blood to sterile nutrient agar that has been liquefied by heating and then cooled to `52 o. The final concentration of blood should be 5-10%. Haemolysis is best observed in layered blood agar plates. For such plates, a layer of nutrient agar is poured into the petri dish and allowed to set the blood-containing medium is then poured on top of the nutrient agar. 1.05 MacConkey Agar Peptone 20 g Sodium chloride 5 g Sodium taurocholate 5 g Water 1 000 ml Dissolve the peptone, sodium chloride and sodium taurocholate in the water by heating. Adjust to pH 8.0. Boil for 20 min. Cool and filter. Agar 20 g Lactose 10 g Neutral red, 1% aq. soln. 10 ml Add and dissolve the agar by boiling and adjust to pH 7.4. Add the lactose and indicator solution. Mix and sterilize at 11,55 ø for 20 min. The quantity of indicator required depends on the depth of colour preferred. Sodium taurocholate, sodium tauroglycocholate or other satisfactory bile salt may be used. The use of 0.1% Teepol (an anionic detergent) in place of bile salt in MacConkey agar has been recommended. Commercial form: Oxoid Granules CM7 or Tablets CM8. 1.06 MacConkey Broth (Modified) Peptone 20 g Sodium chloride 5 g Sodium taurocholate ,5 g Water 1 000 ml Bromcresol purple, 0.2% soln. ,5 ml Lactose 10 g

HYGIENIC MANUFACTURE AND PRESERVATION 781 Dissolve the peptone, sodium chloride and sodium taurocholate in the water by heating. Adjust to pH 8.0 and boil for 20 min. Cool, filter, and adjust to pH 7.4. Add the lactose and indicator solution, mix and distribute into tubes containing inverted Durham's tubes. Sterilize at 115 ø for 15 min. Commercial form: Oxoid Granules CMSa or Tablets CM{3a. 1.07 Plate Count Agar (Tryptone Glucose Yeast Extract Agar) Tryptone 5 g Yeast extract 2.5 g D-Glucose 1 g Agar 15 g Water to 1 000 ml Add the ingredients to the water and dissolve by steaming. Adjust to pH 7.0, dispense as required and sterilize at 121 ø for 15 min. Commercial form: Oxoid Granules CM325 or Tablets CM32(3. 1.08 Robertson's Cooked Meat Medium Minced meat 1 000 g 0.05 N Sodium hydroxide soln. 1 000 ml Add the minced meat to the sodium hydroxide solution. Mix well and heat to boiling. Simmer for 20 min with frequent stirring. Skim off the fat and check pH which should be about 7.5. Strain through gauze or muslin, squeeze out excess liquor, and dry the meat particles at a temperature below 50 ø. For use, place sufficient dried meat in a screw-capped container to a depth of about 2.5 cm and add sufficient Nutrient Broth to give a depth of above 5.0 cm. Sterilize at 115 ø for 20 min. Avoid rapid release of pressure in the autoclave after sterilization. Although called Robertson's Cooked Meat Medium, the method of preparation differs considerably from the original. Commercial form: Oxoid Granules CM81 or Tablets CM82. 1.09 Sabmt, raud Dextrose Agar Mycological Peptone (Oxoid L40) 10 g Dextrose 40 g Agar 15 g Water to 1 000 ml Dissolve in a steamer and adjust pH to 5.0. Sterilize by autoclaving at 115 ø for 10 min. Commercial form: Oxoid Granules CM41 or Tablets CM42.