ALKALI-FORMING BACTERIA FOUND IN MILK. 



17 



Table 8. — The cultures which fermented lactose in synthetic media and the milk reactions 

 by titration of the same cultures. 





Lactose synthetic 

 media. 



Reaction of milki cultures 

 after— 





A. 



C. 



7 days. 



14 days. 



30 days. 



Control 



Ph. 

 6.9 



Ph. 



6.8 



C.c. 

 22.0 



C.c. 

 22.0 



C.c. 

 22.0 



10 



6.7 

 6.7 

 6.7 

 6.7 



6.7 

 6.7 

 6.6 

 6.7 



6.6 

 6.7 

 6.7 



6.1 

 6.1 

 6.1 



4.8 



6.4 

 6.4 

 6.4 

 6.0 



5.9 

 6.3 

 6.1 



2.0 

 2.8 

 4.6 

 10.2 



5.6 

 3.0 

 5.2 

 5.2 



15.0 

 13.0 

 5.4 



10.6 

 7.4 

 7.0 



21.0 



6.6 

 7.8 

 2.8 

 9.6 



13.6 

 7.2 



6.8 



17.0 



12 



15.4 



49 



12.8 



107 



45.2 



112 



10.2 



113 



15.8 



120 



8.4 



123 



19.0 



137 



39.6 



141 



17.8 



143 



16.2 







1 100 c. c. of milk titrated with tenth-normal NaOH. 



In the study of the fermentation of sugars by the alkah-formmg 

 bacteria care must be exercised to use a medium in which organic- 

 acid salts are not present, for they are readily oxidized to alkaline 

 carbonates, which may mask an acid fermentation of the sugar. 

 A synthetic medium is of the greatest assistance in this connection. 



FERMENTATION OF ALCOHOLS. 



In a study of the fermentation of sugars it is customary to include 

 some of the polyatomic alcohols, such as adonite, dulcite, mannite, 

 and glycerin. It was found that these polyatomic alcohols were not 

 particularly good sources of carbon for the alkali group of organisms 

 when used in a synthetic medium composed of sodium-ammonium 

 phosphate 2 grams, potassium chlorid 0.1 gram, test alcohol 2 grams, 

 and distilled water 1,000 cubic centimeters. None of the cultures 

 fermented adonite or dulcite, but, as is shown in Table 9, 5 cultures 

 fermented mannite and 3 fermented glycerin. In mannite the maxi- 

 mum change in hydrogen-ion concentration was from Ph 7.1 (control) 

 to Ph 6.1 and in glycerin from Pg 6.9 (control) to Pg 6.4. 



The monoatomic alcohols are not commonly used as test fermenta- 

 tion substances, but it was thought advisable to determine whether 

 some of them could supply carbon for the alkali-forming bacteria. 

 Four of the monoatomic alcohols, namely, methyl, ethyl, propyl^ 

 and amyl, were tested with different amounts in the sodium-ammo- 

 niiun phosphate medium just described. As nothing was known 

 regarding the effect of different concentrations of these alcohols on 

 the bacteria, 3 different sets of media with 10, 5, and 3 grams, re- 

 spectively, of alcohol to the liter were used. The cultures were incu- 

 bated 7 days at 30° C. and any change over Pg 0.2 in a hydrogen-ion 

 104410°— 10— Bull. 782 3 



