ISOLATION OF SPECIFIC PATHOGENES 87 



Of the comparative advantages of these methods 

 it is still too early to speak with finality. Up to the 

 present time the use of caffein and lactose bile has 

 apparently been followed by the best results, and it 

 seems likely that of the precipitation methods that 

 employing the oxychloride of iron is the best. The suc- 

 cessful use of malachite green and brilliant green in the 

 isolation of typhoid and paratyphoid bacilli from fasces 

 suggests that the more general adoption of these media 

 in water examinations would possibly prove fruitful. 



Identification of the Typhoid Bacillus. At the end 

 of the process the identification of the pure cultures 

 isolated is again subject to considerable uncertainty. 

 The typhoid bacillus belongs to a large group which 

 contains numerous varieties differing from each other 

 by minute degrees. The inability to reproduce the 

 disease by inoculation in available test animals owing 

 to their natural immunity is a serious drawback; 

 and the specific biochemical characters of the organism 

 are, as it happens, mostly negative ones, as shown by 

 comparison with B. coU, to which it is supposed to be 

 allied. 



COMPARISON OF THE CHARACTERS OF B, COLT AND 

 B. TYPHI 



(HORROCKS, I901) 

 B. COLI B. TYPHI 



(i) Surface Colonies, Gelatin (i) Much thinner than those 



Plates. — Thicker, and grow more of B. coli, and grow more slowly, 



rapidly than those of B. typhi. After forty-eight hours' incuba- 



After forty-eight hours' incubation tion at 22° C. they are hardly 



at 22° C. they are usually large visible to the naked eye. 

 and characteristic. 



