196 BACTERIOLOGICAL EXAMINATION OF WATER. 



with anti-typhoid serum and also by growing at C., at which 

 temperature the B. typhosus does not develop. 



The B. lactis serogenes resembles the B. typhosus in the 

 appearance of its colonies, but it is not agglutinated by anti- 

 typhoid serum. It also develops indol, coagulates milk, and 

 produces gas in glucose media. 



The B. cavicida described by Brieger also resembles the 

 B. typhosus in the appearance of its colonies, but it develops 

 indol and produces gas in glucose media. 



The B. fluorescens non-liquefaciens group of organisms 

 occasionally gives rise to difficulties, as the surface colonies have 

 a superficial resemblance to those of the B. typhosus. As a 

 rule, the marked venation on the surface colonies and the green 

 colour of the gelatine around them enables a diagnosis to be 

 made without difficulty. Sometimes, however, the venation is 

 not marked and the green colour is not developed for many 

 days. Under these conditions a mistake may be made, as these 

 bacilli do not produce gas, coagulate milk, nor give rise to gas 

 in glucose media. They are, however, not agglutinated by 

 anti-typhoid serum in a high dilution, though some members 

 of the group are agglutinated by the serum when diluted 

 1-80. 



The B. Acidi Lactici produces surface colonies somewhat 

 like those of B. typhosus, but it is a spore-bearing organism, 

 coagulates milk, produces indol, and forms gas in glucose 

 media. 



The B. Urese also gives rise to surface colonies which closely 

 resemble those of the B. typhosus. It is distinguished by not 

 reacting to the agglutination test and by its power of convert- 

 ing urea into ammonium carbonate. 



The B. Psittacosis, which has been isolated from Parrots, 

 belongs to the typhoid group of organisms. It is an actively 

 motile bacillus, which does not stain by Gram's method. The 

 colonies on gelatine plates closely resemble those of the B. 

 typhosus. It does not ferment lactose, nor curdle milk, nor 

 produce indol in Witte's peptone and salt solution. It, how- 

 ever, produces a coloured growth on potato like the B. coli, 

 which serves to distinguish it from the B. typhosus. 



