54 BACTERIOLOGICAL ANALYSIS. 



Add a saturated solution of sodium carbonate, drop 

 by drop, until the reaction becomes faintly alkaline, 

 using litmus paper as an indicator. 



(For greater accuracy in neutralization, phenolph- 

 thalein in 1% alcoholic solution may be used as an 

 indicator. To 10 cc. of the broth, add 2 drops of the 

 indicator and then drop in from a burette a diluted 

 solution of sodium carbonate, till the indicator shows 

 alkalinity. A ready calculation can then be made as to 

 the amount of the sodium carbonate solution it will be 

 necessary to add to the broth). 



Steam again in the sterilizer for \ hour and then fil- 

 ter into a flask. 



Steam this flask in the sterilizer for 20 minutes, on 

 3 successive days. 



Instead of using beef steak, Liebig's meat extract 

 may be employed, 3 grammes of this extract being dis- 

 solved in 1,000 cc. of water, with 10 grammes of peptone 

 and 5 grammes of salt. The after treatment is the 

 same as before described, except that it is better not to 

 filter for the last time, till the broth is cold. 



Glycerine Broth is ordinary broth to which 3 to 6% 

 of pure glycerine is added, before sterilization. 



Grape Sugar Broth or glucose broth is ordinary 

 broth to which 1 to 2% of grape sugar has been added. 



In Making Tubes place the broth (or liquefied jelly) 

 in a covered funnel with stop cock or clip attachments. 

 Add from 6 to 10 cc. to each test tube. The tubes are 

 then re-plugged, covered with tin foil and sterilized in 

 the steamer for 15 to 20 minutes on 3 successive days. 



