HYGIENIC MANUFACTURE AND PRESERVATION 783 Sodium chloride 100 g Water to 1 000 ml (pH 7.6 approx.) Commercial form: Oxoid Granules CM93 or Tablets CM94. 1.14 Selenite F. Broth The selenite in this medium serves the same purpose as tetrathionate in tetrathionate broth and has been preferred to it. Sodium acid selenite (NaHSeO 3) 4 g Peptone 5 g Lactose 4 g Disodium hydrogen phosphate (Na 2HPO 4.12H 20) 9.5 g Sodium dihydrogen phosphate (NaH2PO4.2H20) 0.5 g Sterile water 1 000 ml Dissolve the ingredients with aseptic precautions, and distribute the yellowish solution in 10 ml amounts in sterile screw-capped bottles, steam at 100 o for 30 min. Excessive heat is detrimental to the medium and auto- claving must not be used to sterilize it. A slight amount of red precipitate may form but this does not interfere with the properties of the medium. The pH of the medium should be 7.1 and the phosphates may be varied slightly if necessary to attain this. Salts of selenium are very toxic to animals and man, and must be handled xvith care. Some organic compounds of selenium and hydrogen selenide are volatile and toxic if inhaled. Commercial form: Oxoid Granules CM39 or Tablets CM40 (Modified). 1.15 Bacto-brilliant Green Agar. Difco Dehydrated Medium. Bacto-Yeast extract 3 g Proteose peptone no. 3, Difco 10 g Sodium chloride 5 g Bacto-lactose 10 g Saccharose, Difco 10 g Bacto-phenol red 0.08 g Bacto-brilliant green 0.0125 g Bacto-agar 20 g Bacto-Brilliant Green Agar is a selective medium recommended for the isolation of Salmonella, other than typhosa, either directly or after prelim- inary enrichment.

784 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS To rehydrate the medium, suspend 58 g of Bacto-Brilliant Green Agar in 1000 ml cold distilled water and heat to boiling to dissolve the medium completely. Distribute in tubes or bottles and sterilize in the autoclave for 15 min at 121 ø. A longer period of sterilization will tend to decrease the selectivity of the medium. The final reaction of the medium will be pH t3.9. Commercial form: Bacto-Brilliant Green Agar 0285-02 [Baird and Tatlock (London) Ltd.•. 1.16 Thioglycolate Broth (Modified Brewer) Peptone 15 g Yeast extract 5 g Sodium chloride 5 g Agar 1 g Thioglycolic acid 1 g Water 1 000 ml Dissolve the solids in the water with the aid of gentle heat. Add the thioglycolic acid and adjust to pH 8.5 with N/1 sodium hydroxide solution. Sterilize at 115 ø for 10 min. To prevent darkening of the medium, screw- caps should be loosened during autoclaving. Glucose 5 g Methylene blue, 1% aq. soln. 0.2 ml Adjust to pH 7.2. Add the glucose and dye solution. Mix well and sterilize at 115 ø for 10 min. This medium should be stored in screw-capped containers in the dark at 4 ø. If more than 20% of the medium shows a green colour before use, it should be heated in a boiling water bath or steamed for 5-10 min, and allowed to cool undisturbed. This treatment must not be repeated. Commercial form: Oxoid Granules CM23 or Tablets CM24. 1.17 Cetrimide Agar Proteose peptone no. 3 (Difco) 20 g New Zealand agar 15 g Glycerol 10 g Water to 1 000 ml Adjust this basal medium to pH 7.2 and sterilize at 121 ø for 15 min. To