234 L. A. EOGERS, W. M. CLARK AND H. A. LUBS 



literature to the occurrence in feces of B. cloacae and B. proteus 

 and it is likely that bacteria of this type would have been isolated 

 if special methods had been employed for this purpose. 



The fermentation of carbohydrates. The most convenient 

 method for determining the extent of an acid fermentation is to 

 measure the resulting hydrogen ion concentration fin terms of 

 Ph). Some of the reasons for this have been treated in previous 

 papers from this laboratory and need not be repeated here. 



The procedure used was the following: The medium was com- 

 posed of 1 per cent Witte pepton 0.5 per cent K2HPO4, 1 per 

 cent of the carbohydrate or alcohol. This medium was dis- 

 tributed (in 10 cc. portions) in test tubes, sterilized by the inter- 

 mittent method, inoculated from agar slopes and incubated for 

 five days at 30°. The ?„ values before and after fermentation 

 were determined by the colorimetric procedure described by 

 Clark and Lubs (1917a). A sufficient number of electrometric 

 measurements Avere made to show that in the particular medium 

 used the colorimetric ?„ values were consistent and essentially 

 correct. 



The substances studied were glucose, lactose, sucrose, raffinose, 

 melibiose, arabinose, inulin, mannitol, dulcitol, adonitol, and 

 glycerol. Of these inulin and glycerol were commercial "c.p." 

 samples. The other compounds were exceptionally pure samples 

 furnished to us by Dr. Hudson of the Bureau of Chemistry. 

 We take this opportunity to express publicly our appreciation of 

 Dr. Hudson's kindness in affording us the rare opportunity to 

 study the fermentation of sugars whose identification and purity 

 is assured. 



In the presence of most of these compounds the organisms 

 within forty-eight hours either produce a vigorous acid fermenta- 

 tion or else very little change in the reaction of the medium. 

 When a vigorous acid production occurs there is little doubt but 

 that an acid fermentation of the carbohydrate is taking place. 

 The converse proposition, that where no distinct acid production 

 occurs the carbohydrate is not being utilized, is not so certain. 

 There is a distinction here between the utilization of a substance 

 and a particular mode of utilization which has not always been 



