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. 7. Prepare a 10 per cent. solution of basic fuchsin in 95 per cent. alcohol, allow to stand 20 hours, decant and filter the supernatant fluid. This is a stock solution. 8. When ready to make plates melt 100 cc. of agar in streaming steam or on a water bath. Dissolve 1 gram of lactose in 15 cc. of distilled water, using heat if necessary. Dissolve 0.25 gram anhydrous sodium sulphite in 10 cc. water. To the sulphite solution add 0.5 cc. of the fuchsin stock solution. Add the fuchsin-sulphite solution to the lactose solution and then add the resulting solution to the melted agar. The lactose used must be chemically pure and the sulphite solution must be made up fresh. 9. Pour plates and allow to harden thoroughly in the incubator before use. 2. COLLECTION OF SAMPLE. Samples for bacterial analysis shall be collected in bottles which have been cleansed with great care, rinsed in clean water, and sterilized with dry heat for at least one hour and a half at 170° C., or in the autoclav at 15 lbs. (120° C.) for 15 minutes or longer after the pressure reaches 15 lbs. Great care must be exercised to have the samples representative of the water to be tested and to see that no contamination occurs at the time of filling the sample bottles. 3. STORAGE AND TRANSPORTATION OF SAMPLES. Because of the rapid and often extensive changes which may take place in the bacterial flora of bottled samples when stored even at temperatures as low as 10° C., it is urged, as of importance, that all samples be examined as promptly as possible after collection. The time allowed for storage or transportation of a bacterial sample between the filling of the sample bottle and the beginning of the analysis should be not more than six hours for impure waters and not more than twelve hours for relatively pure waters. During the period of storage, the temperature shall be kept as near 10° C. as possible. Any deviation from the above limits shall be so stated in making reports. 4. DILUTIONS.