418 BA CTERIOLOG Y. 



Biologically bacterium xerosis is readily differentiated 

 from bacterium diphtherias because of the scant growth 

 that takes place on the ordinary culture-media. On 

 agar-agar the growth appears as small transparent colo- 

 nies which have little tendency to coalesce. On gelatin 

 the growth is slow, and frequently shows as minute, iso- 

 lated colonies along the needle track. In litmus-milk a 

 slight degree of acidity is produced. In bouillon the 

 growth is so slight as to leave the medium practically 

 unaltered. The growth on potato is slight and invisible. 



Differentiation of Members of the Group. Knapp 1 

 reports that the serum-water media of Hiss, to which 

 different carbohydrates have been added, serve to differ- 

 entiate between bacterium diphtherice, bacterium pseudo- 

 diphtheriticum, and bacterium xerosis. Bacterium diph- 

 therias ferments dextrose, mannite, maltose, and dextrin 

 with formation of acid and the coagulation of the medium. 

 Saccharose is not fermented. Bacterium xerosis fer- 

 ments dextrose, mannite, maltose, and saccharose, with 

 formation of acid and coagulation of the medium. Dex- 

 trin is not fermented. Bacterium psendodiplttJieritieum 

 does not ferment any of these carbohydrates. Knapp 

 claims that a positive differentiation of the organisms 

 may be made by merely inoculating the Hiss media 

 containing dextrin and saccharose. If the dextrin is 

 alone fermented, the organism is bacterium diphtheria, if 

 only the saccharose is fermented, the organism is bacte- 

 rium xerosis, and if neither of these carbohydrates is fer- 

 mented, the organism is bacterium pseudodiphtheriticum. 



Through the suggestion of Neisser 2 we are fortu- 



1 Knapp : Jour. Med. Research, vol. xii., p. 475, 1904. 



2 Neisser: Zeitschrft fur Hygiene und Infektionskrankheiteu, 1897, 

 Bd. xxiv. 



