156 PHYSIOLOGY OF BACTERIA 



substrates. These substrates are similar, but not iden- 

 tical. Other microorganisms produce different fermen- 

 tations in different sugars: mannite bacteria reduce 

 fructose, but not glucose, to mannitol; Leuconostoc 

 produces slime only in sucrose solutions; the Pneumococ- 

 cus group ferments different sugars to different products. 

 On the other hand, the same substrate may be fer- 

 mented by the same organism to different products, 

 owing to outside conditions. Some of these are due to 

 the chemical composition of the medium. The best 

 known example is that of the different fermentations 

 by yeast (p. 50), in a normally acid medium, in an 

 alkaline medium, and in a medium containing Na2S203. 

 The change of the gas ratio of Bad. coli by the presence 

 of oxygen (p. 64) might also be included here. A 

 change of acidity effects some other fermentations as 

 well, as might be seen from the importance of pH 

 control in the acetone fermentation (Arzberger, Peterson 

 and Fred, 1920). 



(6) CHANGES DUE TO TEMPERATURE 



It has been shown before (p. 151) that the endpoint 

 of fermentation is greatly influenced by the temperature. 

 Pronounced changes of the type of fermentation by 

 temperature are not known, but the by-products of 

 fermentation are influenced. It is well known that the 

 ripening at high temperatures of the cream for churning 

 gives a sharp, undesirable flavor. Bioletti (1908) stated 

 that the quality of California wines could be greatly 

 improved if the wine manufacturers would employ lower 

 temperatures. Sarkaria and Hammer (1928) observed 

 distinct but not very pronounced changes in the type of 

 metabolism of proteolytic bacteria if they were cultivated 

 at different temperatures. 



