406 BACTERIOLOGY. 



Biologically bacterium xeorsis is readily differentiated 

 from bacterium diphtheria 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 * claims that a positive differentiation of the or- 

 ganisms 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 assisted 

 in differentiating between bacillus diphtherias and the 

 confusing forms. He has found that by the use of a 

 particular staining method the appearance of bacterium 

 diphtherise is characteristic. His differential method 

 comprehends the following manipulations : the culture 

 to be tested should be grown upon Loffler's blood-serum 

 mixture solidified at 100C. ; it should develop at a 

 temperature not lower than 34 C. and not higher than 

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

 not older than twenty-four hours. A cover-glass prep- 

 aration made from such a culture is stained as follows : 



i Knapp: Jour Med. Research, vol. xil, p. 475, 1904. 

 sNelsser: Zeitschrlft fur Hygiene und Infektionskrankheiten, iW, 

 Bd. xxiv, 



