ISOLATION OF SPECIFIC PATHOGENES 93 



demonstrate that even a small number of virulent 

 organisms can bring about an almost wholesale infection. 

 Indeed, if the virulent organism were as abundant as 

 some results would indicate (Remlinger and Schneider, 

 1897), the human race would long since have been 

 exterminated. A negative result in testing for typhoid 

 bacilli has no significance and there is danger that it 

 may be misinterpreted if the fact that it has been made 

 comes to public knowledge. In spite of this danger, 

 however, and in spite of the laborious and time-con- 

 suming nature of the process, the increasingly large 

 number of positive isolations in recent years indicate 

 that it is well worth trying in cases of special importance. 

 The search for the typhoid bacillus should of course 

 never supersede the examination for colon bacilli, 

 since the latter are so much more numerous in water 

 and so much more easily identified. Because of these 

 facts, colon bacilli will continue to be our best index 

 of pollution, while the positive isolations of the typhoid 

 bacillus will supply additional proof of the deadly 

 character of a water containing it. 



Other Bacteria of the Typhoid Group Related to 

 Intestinal Disease. The typhoid bacillus and the colon 

 bacillus (which will be fully discussed in succeeding chap- 

 ters) stand at the opposite ends of a series of many dif- 

 ferent varieties of organisms which are intermediate in 

 their properties between B. typhi and B. coli, all being 

 non-spore-forming, non-liquefying rods, which produce 

 a more or less characteristic growth on solid media. 

 Durham (1898) divided these forms into three main 

 divisions, grouped, respectively, about B. typhi, B. 



