QUALITATIVE BACTERIOLOGICAL ANALYSIS. 107 



two-day s-old culture was injected intra-peritoneally into guinea- 

 pigs of medium weight. He found that varieties of B. coli 

 isolated from pure waters sometimes killed the guinea-pigs, 

 while some of the varieties isolated from the impure waters 

 had no effect on the animals, and therefore concluded that the 

 isolation of a virulent B. coli from a water supply did not 

 necessarily indicate that the water had been contaminated with 

 faeces. 



