500 APPLICATION OF METHODS QF BACTERIOLOGY 



Biologically bacterium xerosis is readily differentiated 

 from bacterium diphtherise because of the scant growth 

 that takes place on the ordinary culture media. On agar- 

 agar the growth appears as small transparent colonies which 

 have little tendency to coalesce. On gelatin the growth 

 is slow, and frequently shows as minute, isolated 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 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 diphtheriae, 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 diphtherise 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 : 



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



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



