ISOLATING THE TYPHOID BACILLUS. 427 



of a technical procedure, which in principle, with some 

 important additions, is almost identical with that of 

 Stoddart. In this method also advantage is taken of 

 the fact that in semi-solid nutrient media the greater 

 motility of the typlioid bacillus enables it to diifuse more 

 readily through the medium than can the less active 

 colon bacillus. The endeavor of Hiss was to discover 

 a method whereby this peculiarity would be favored, 

 or at least not checked, in the typhoid, and more or 

 less suppressed in the colon bacillus. A series of experi- 

 ments demonstrated that if peptone be omitted and glu- 

 cose be added to the semi-solid medium, the absence of 

 the former important nutritive substance and the excess 

 of acidity resulting from the fermentation of the latter 

 had only slight eifect upon the characteristic develop- 

 ment of the typhoid bacillus (a diffuse clouding of the 

 medium), while the influence upon the growth of the 

 colon bacilli was to prevent, in many cases, their ten- 

 dency to cloud the medium by sharply restricting their 

 growth to the point at Avhich they A^ere deposited.^ 

 The composition of the medium used is : 



Agar-agar . . 5 grammes. 



Gelatin . . 80 " 



Liebig's beef-extract 5 



Sodium chloride . 5 



Glucose . ■ 5-10 



Water ■ 1000 c.c. 



The gelatin should be added after the agar-agar and 

 other ingredients are dissolved ; the volume of the mass 

 is then brought to 1000 c.c, and finally the reaction is 

 corrected. This should be equivalent to a degree of 

 acidity that would require 15 c.c. of a normal sodium 



• Hiss : Journal of Experimental Medicine, 1897, vol. ii. No. 6, p. 677. 



