BACTERIUM XEROSIS 473 



Differentiation of Members of the Group. Knapp 1 claims 

 that a positive differentiation of the organisms may be 

 made by merely inoculating the Hiss media containing dex- 

 trin and saccharose. If the dextrin is alone fermented, the 

 organism is bacterium diphtherise, if only the saccharose is 

 fermented, the organism is bacterium xerosis, and if neither 

 of these carbohydrates is fermented, the organism is bac- 

 terium pseudodiphtheriticum. 



Through the suggestion of Neisser 2 we are assisted in 

 differentiating between bacillus diphtherise and the confusing 

 forms. He has found that by the use of a particular staining 

 method the appearance of bacterium diphtherias is charac- 

 teristic. His differential method comprehends the following 

 manipulations: the culture to be tested should be grown 

 upon Loffler's blood-serum mixture solidified at 100 C.; 

 it should develop at a temperature not lower than 34 C. 

 and not higher than 36 C.; and it should not be younger 

 than nine and not older than twenty-four hours. A cover- 

 glass preparation made from such a culture is stained as 

 follows : 



(a) It is subjected to the following mixture for from one 

 to three seconds: 



Methylene-blue (Griibler's) 1 gram 



Alcohol (96 per cent.) 20 c.c. 



When dissolved, mix with 



Acetic acid 50 c.c. 



Distilled water 950 c.c. 



(b) After thoroughly rinsing in water, it is stained for 

 from three to five seconds in vesuvin (Bismarck-brown), 



1 Jour. Med. Research, 1904, xii, 475. 



2 Zeitschrift fur Hygiene und Infektionskrankheiten, 1897, Bd. xxiv. 



