ISOLATING THE TYPHOID BACILLUS. 427 



related, that its identification, especially outside the 

 infected body, is a matter of considerable difficulty and 

 uncertainty. For these reasons many eiforts have been 

 made to discover specific cultural reactions for the or- 

 ganism, and with this end in view many methods have 

 been devised for its isolation from water, faeces, sewage, 

 and other matters believed to contain it. None of them, 

 however, have given general satisfaction, and many have 

 proved wholly untrustworthy. Those worthy of some 

 degree of confidence are as follows : 



Hiss's METHOD. In this method advantage is taken 

 of the fact that in semisolid nutrient media the greater 

 motility of the typhoid bacillus enables it to diffuse 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 effect 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 which they were de- 

 posited. 1 



The composition of the medium used is : 



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



