BACTERIOLOGY. 161 



3. Sodium chloride , , . > 5 grams 



4. Water 1000 c.c. 



Boil until ingredients are dissolved (fifteen to 



twenty minutes) ; add water from time to time to 

 keep up the 1 ,000 c.c.; allow to cool slightly; meas- 

 ure out 1,000 c.c., and place them in a large flask. 



Determine the Reaction. Process: Take phenolph- 

 thalein as an indicator and normal 20 sodium hydrox- 

 ide as an alkali ; take 5 c.c. of the medium and 40 

 c.c. of distilled water; put 12 drops of the indicator 

 into the mixture and proceed to add the alkali from the 

 burette until the indicator shows sufficient quantity of 

 the alkali, which can be observed by watching the color 

 of the fluid as it changes from a colorless to a red. 

 Calculate from this how much sodium hydroxide will 

 be required to alkalinize the whole liter of medium; 

 then add and boil forty-five minutes. Keep up the 

 level by adding water; filter and distribute in the ves- 

 sels you are going to use. Sterilize fifteen minutes each 

 day for three successive days in the Arnold sterilizer. 



PEPTONE SOLUTION. 



Take sodium chloride, 0.5 grams; take peptone, i.oo 

 gram; water, 100 c.c. 



We will make other media from time to time as they 



are needed. Everything is sterilized. 

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