262 CHEN CHONG CHEN AND LEO F. RETTGER 

 CARBOHYDRATE FERMENTATION 



A. Acid production 



The production of acids and gas by intestinal bacteria was 

 observed by Buchner as early as 1885. He found that the main 

 end products of sugar decomposition by his "Darmbacillus G" 

 were carbon dioxide and fatty acids. Since this time the fermen- 

 tation reaction in a culture medium has been extensively utilized 

 for the purpose of characterization and classification of bacteria. 

 Its principles have been so firmly established that it is considered 

 one of the very important reactions in the differential studies of 

 organisms of more or less similar as well as widely-divergent 

 types. 



At first the acid test was limited to a narrow field, namely, 

 the separation of the colon from the typhoid type of bacteria, 

 as is well illustrated in the early use of the litmus-lactose agar 

 of Wurtz (1892) ; but at the present time no systematic study of 

 an organism is complete without a resume of its fermentative 

 properties if it is found to have such. Our chief interest in this 

 paper is, of course, in the colon-aerogenes group of bacteria. 



In 1893 Theobald Smith separated the colon bacilli into two 

 groups, according to their action on sucrose. The work of Dur- 

 ham (1900), however, inaugurated the real beginning of the use 

 of the fermentation method in systematic classification. He 

 employed glucose, lactose and sucrose, and characterized B. 

 communis verus as glucoso-lactoso-non-sucroso fractor, B. colt 

 communior as glucoso-lactoso-sucroso fractor, and B. lactis aerog- 

 enes as polysaccharid fractor. Ford (1901) chose the same sugars 

 for his classification. He divided the colon group into B. coli, 

 B. lactis aerogenes, and B. cloacae. 



McConkey (1905) divided the lactose-fermenting group into 

 the four well-known divisions, based principally upon the action 

 on sucrose and dulcitol, namely: (1) sucrose— dulcitol— (B. acidi 

 lactici type) , (2) sucrose — dulcitol + (B. communis type) , (3) 

 sucrose + dulcitol + (B. communior type), and sucrose +- 

 dulcitol — (B. aerogenes type). This classification for a long 

 time served as a frame-work for investigators in this field. Wins- 



