The standard azolitmin solution shall be a 1 per cent. solution of Kahlbaum’s azolitmin. Add the azolitmin powder to the water and boil for five minutes. The solution may need to be corrected in reaction by the addition of sodium hydrate solution so that it will be approximately neutral and will give a distinctly blue plate when 1 cc. is added to 10 cc. of neutral culture medium in a Petri dish. It may be distributed in flasks or test-tubes and sterilized as is culture media.
h. Litmus-lactose-agar.
Litmus-lactose-agar shall be prepared in the same manner as nutrient agar with the addition of 1 per cent. of lactose just before sterilization. The reaction shall be a faint pink with phenol red, or, if on titration with phenolphthalein the reaction is not already between neutral and +1, adjust to neutral. One cc. of sterilized litmus or azolitmin solution shall be added to each 10 cc. of the medium just before it is poured into the Petri dish, or the mixture may be made in the dish itself.
i. Endo’s Medium.[[209]][[214]][[215]] To Make One Liter.
1. Add 5 grams of beef extract, 10 grams of peptone and 30 grams of agar dried for one-half hour at 105° C. before weighing, to 1,000 cc. of distilled water. Boil on a water bath until all the agar is dissolved and then make up the loss by evaporation.
2. Cool the mixture to 45° C. in a cold water bath, then warm to 65° C. in the same bath without stirring.
3. Make up lost weight, titrate, and if the reaction is not already between neutral and +1 adjust to neutral.
4. Filter through cloth and cotton until clear.
5. Distribute 100 cc. or larger known quantities in flasks large enough to hold the other ingredients which are to be added later.
6. Sterilize in the autoclav at 15 lbs. (120° C.) for 15 minutes after the pressure reaches 15 lbs.