BACTERIA OF MILK 



81 



If N/10 NaOH were used, the factor in the numerator would 

 be .009 mstead of .0045. 



5. Does the acidity eventually decline ? Why ? 



6. Procure commercial tablets of lactic-acid-formiug bacteria 

 and inoculate pasteurized milk. Carefully compare the odor and 

 taste of samples inoculated with different strains. 



Exercise 117. Fermentation Test 



This is a convenient method of showing whether bacteria of 

 the putrefying or the Coli-Aerogenes groups are present in milk 

 in excess. 



Fig. 35. Constant-temperature water bath for making fermentation 

 and other tests 



1. Procure samples of milk from different sources and of dif- 

 ferent degrees of purity. Put 25 cc. of each sample into a large 

 test tube which has been carefully cleaned and sterilized. Plug 

 the tubes with cotton and "put them into a rack which fits a 

 water bath (Fig. 35). 



