THE GENUS DIPLOCOCCUS III 



and serum reactions, which establishes the individuality 

 of the genus beyond reasonable doubt. 



The first important biochemical test which distin- 

 guishes the diplococci from the streptococci is their dif- 

 ference in fermentative powers. This property was at 

 first studied in a curiously roundabout way. Libman 

 (1900 and 1901) noted that when bacteria are grown 

 on media containing serum and sugars there may occur 

 a white opacity connected with the precipitation of some 

 constituent of the serum; and showed that this action 

 was due to acid production. Hiss (1902), in a fruitful 

 series of investigations, found that both pneumococci and 

 streptococci uniformly ferment the monosaccharides, dex- 

 trose, levulose, and galactose. The pneumococci always 

 ferment the disaccharides, lactose, saccharose, and mal- 

 tose, and the streptococci generally do so, altho some cul- 

 tures fail. The pneumococci produce acid in serum 

 media containing dextrin, starch, glycogen, or inulin, as 

 manifested by the resulting coagulation of the serum pro- 

 teids; while the streptococci generally fail to do so with 

 the first three polysaccharides and always fail with inulin. 

 Finally, the pneumococci produce, in a diluted alkalin 

 ox-serum, to which no sugar has been added, sufficient 

 acid to cause coagulation. Berry (1907) has recently 

 shown that the inulin reaction of the pneumococcus, like 

 other characteristics, is subject to considerable variations. 

 Cultivation of this organism on artificial media causes 

 modifications of the diplococcus morphology toward the 



