BACTERIUM XEROSIS. 419 



nately enabled to differentiate between bacterium diph- 

 theria and the " pseudo " forms. He has found that 

 by the use of a particular staining method the 

 appearance of bacterium diphtheria? is strikingly 

 unlike that of the confusing forms. 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 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 : 



. It is subjected to the following mixture for from 

 one to three seconds : 



Methylene-blue (Griibler's) 1 gramme. 



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), 

 2 grammes, dissolved in 1 litre of boiling distilled water, 

 filtered, and allowed to cool. It is again rinsed in water 

 and examined as a water-mount, or it may be dried and 

 mounted in balsam. 



When so treated the diphtheria bacterium appears as 

 faintly stained brown rods, in which from one to three 

 dark-blue granules are always to be observed. The 

 dark granules are at one or both poles of the cell, are 

 more or less oval, and usually seem to bulge a little 

 beyond the contour of the bacterium in which they are 



