94 



selection of the respective bacteria are those frequently found in milk, 

 cream, and butter. By the selection of these bacteria and using a medium 

 which is naturally present in milk products, we are able, in a great 

 measure, to avoid introducing disturbing factors on the end products, 

 also factors foreign to our previous work concerning the changes pro- 

 duced in stored butter. 



Our preliminary study included the following bacteria: B. proteus 

 vulgaris, B. viscosus, B. butyricus, B. mycoides, B. lactis acidi, B. mesen- 

 tericus, B. liquifaciens, B. fluorescens putidus, B. subtilis, B. megather- 

 ium, and B. coli. The medium was sterilized milk to which the pure 

 cultures were added and kept at room temperature. The pure cultures 

 were previously grown in the same media and transfers were made 

 three times before being used for experiment. At intervals of three 

 days an analysis of the inoculated milk was made. The following prod- 

 ucts were determined each time the analysis was made: acidity, alde- 

 hyde number*, lactore (polariscope), ammonia (Folin's method), and 

 nitrogen compounds not precipitated by phospho tungstic acid. This was 

 continued for five periods or during a period of sixteen days. (First 

 period four days.) 



The following table shows the changes in the nitrogenous constitu- 

 ents of the milk and the change in lactose by the different bacteria at 

 the end of the sixteenth day. 



TABLE III. 



Showing the per cent, of gain of ammonia (NH3) and amid nitrogen ba.sed on total nitrogen 

 and the loss of lactose based on the total lactose. 



* The aldehyde number gave no more information concerning protein hydrolysis 

 than did phospho-tungstic acid. 



