Standard methods for the examination of water and sewage

Editorial note — BACTERIOLOGICAL EXAMINATION.

Reading edition

H. (a) Peptone Medium for the Methyl Red Test. To Make One Liter.

1. To 800 cc. of distilled water add 5 grams of Proteose-Peptone, Difco., or Witte’s Peptone (other peptones should not be substituted), 5 grams c. p. dextrose, and 5 grams dipotassium hydrogen phosphate (K₂HPO₄). A dilute solution of the K₂HPO₄ should give a distinct pink with phenolphthalein.

2. Heat with occasional stirring over steam for twenty minutes.

3. Filter through folded filter paper, cool to 20° C. and dilute to 1,000 cc. with distilled water.

4. Distribute 10 cc. portions in sterilized test-tubes.

5. Sterilize by the intermittent method for 20 minutes on three successive days.

I. Tryptophane Broth for Indol Test.

To 1,000 cc. of distilled water add 0.3 gram tryptophane, 5 grams dipotassium hydrogen phosphate (K₂HPO₄), and 1 gram peptone. Heat until ingredients are thoroughly dissolved, tube (6 to 8 cc.), and sterilize in autoclave for 15 minutes after the pressure reaches 15 pounds. Some American peptones are standardized to contain a uniform amount of tryptophane. If such peptone is used the tryptophane in the above formula may be omitted and the peptone increased to 5 grams.

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