280 METHODS OF IDENTIFICATION AND STUDY 



Media Required: 



Peptone water containing various percentages (gen- 

 erally 2 per cent.) of each of the substances referred 

 to under "sugar" media (page 177), also tubes of 

 peptone water containing i per cent, respectively of 

 each of the following: 



Organic salts: Sodium citrate, formate, lactate, malate, 



tartrate. 



METHOD. 



1. Prepare tube cultivations in each of the above 

 media. 



2. Observe from day to day up to the expiration of 

 ten days if necessary. 



3. Note growth, reaction, gas production. 



2. Acid Production. 



(a) Quantitative. 

 Medium Required: 



Sugar (glucose) bouillon of known "optimum" reaction. 

 Apparatus and Reagents Required: 



As for estimating reaction of media (vide page 150). 



METHOD. 



1. Prepare cultivation in bulk (100 c.c.) in a flask; 

 also "control" flask of medium from same batch. 



2. After suitable incubation, heat both flasks in the 

 steamer at 100 C. for thirty minutes to sterilise. 



3 . Determine the litre of the medium in " inoculated ' ' 

 and "control" flasks as described in the preparation of 

 nutrient media (vide page 151). 



4. The difference between the titre of the medium 

 in the two flasks gives the total acid production of the 

 bacterium under observation in terms of normal NaOH. 



NOTE. If the growth is very heavy it may be a difficult matter 

 to determine the end-point. The cultivation should then be 

 filtered through a Berkfeld filter candle previous to step 2, and 

 the filtrate employed in the titration. 



