ISOLATING THE TYPHOID BACILLUS. 441 



METHODS OF ISOLATING THE TYPHOID BACILLUS. 

 Bacillus iyphosus is so variable in many of its bio- 

 logical peculiarities, and is so closely simulated in cer- 

 tain respects by a group of other organisms to which it 

 appears to be botanically related, that its identification, 

 especially outside the infected body, is usually a matter 

 of considerable difficulty and uncertainty. For these 

 reasons many efforts have been made to discover specific 

 reactions for the organism, and with this end in view 

 many methods have been devised for its isolation from 

 water, faeces, sewage, and other matters believed to con- 

 tain it. None of them, however, has given general satis- 

 faction, 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 deposited. 1 



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



