214 BACTERIOLOGICAL EXAMINATION OF WATER. 



developed. In later experiments by employing surface alkaline 

 glucose-litmus-agar plates instead of surface gelatine plates, I 

 have been able to sharply differentiate colonies of B. coli from 

 those of B. typhosus, and so obviate the defects of the earlier 

 experiments. By this means I found that when one loopful of 

 an agar growth of B. typhosus was mixed with one loopful of an 

 agar growth of B. coli in ten cubic-centimetres of sterile tap 

 water, the B. typhosus could be easily isolated after twenty- 

 eight days. The bacillus so obtained had lost none of its 

 cultural characteristics, and as regards its reaction to the specific 

 agglutinins contained in Berne serum it appeared, if anything, 

 more susceptible to agglutination after the four weeks existence 

 with B. coli than when it was first introduced into the tube. 

 The original culture was completely agglutinated by Berne 

 serum diluted 1-1000, and only partially agglutinated by the 

 same serum diluted 1-10,000 ; but the culture of B. typhosus 

 after association with B. coli was found to be completely 

 agglutinated by the Berne serum when diluted 1-10,000. 

 Attempts were then made to study the duration of life of the 

 B. typhosus in unsterilised tap-water to which B. coli was also 

 added. A loopful of B. typhosus was added to 10 c.c. of 

 unsterilised tap-water and twenty-four hours later a loopful of 

 B. coli was introduced. The tube was maintained at the room 

 temperature, and loopfuls withdrawn from time to time were 

 plated out on the alkaline glucose-litmus-agar medium. The 

 typhoid bacillus was easily isolated after twenty-one days. In 

 all these experiments the B. typhosus was present in large 

 quantity, and it seemed probable that the B. coli did not 

 multiply to any extent. When B. typhosus and B. coli were 

 added to peptone water, it was found that the B. coli under- 

 went rapid multiplication and no signs of the B. typhosus could 

 be discovered after seven days. Also when a loopful of a typical 

 typhoid stool was diluted in 10 c.c. of sterile tap- water and 

 examined at once, B. typhosus was found to be present in 

 considerable numbers ; but after seven days had elapsed the 

 typhoid bacillus could not be found. 



Sidney Martin has investigated the growth of the typhoid 

 bacillus in the presence of particular soil organisms. Most of 

 the experiments were made with bacteria isolated from 



