QUALITATIVE BACTERIOLOGICAL ANALYSIS. 217 



originally it was agglutinated by the serum, diluted 1-70,000 ; 

 the B. coli maintained its characters unchanged. After fifty- 

 one days association the B. typhosus colonies were found to 

 develop more slowly than before, and the B. coli colonies were 

 smaller and resembled those of B. typhosus. After eighty-two 

 days association the B. typhosus remained as before, but the 

 B. coli isolated from the neutral peptone water, though it still 

 fermented sugar media, had lost the power of producing indol. 

 In the acidified flask, however, the B. coli maintained its 

 characters unchanged. After 100 days it was difficult to 

 distinguish the colonies of B. coli and B. typhosus from the 

 neutral flask ; all the colonies failed to produce gas and indol 

 and to agglutinate with anti-typhoid serum. In the flask con- 

 taining the acidified water, however, the B. coli still gave the 

 indol reaction, and fermented lactose, and the B. typhosus did 

 not react with anti-typhoid serum. A week later the colonies 

 from the neutral water were exceedingly feeble in their growth, 

 and, as before, failed to produce indol or gas or to agglutinate 

 with anti-typhoid serum. In the acidified water the B. typhosus 

 had now disappeared, and only B. coli could be isolated, which, 

 however, still produced indol and gas. In these experiments 

 there was a very marked difference between the results obtained 

 in the neutral and acid waters ; in the former medium the 

 B. coli and B. typhosus speedily lost their special characteristics ; 

 but in the latter the B. coli maintained its power of forming 

 gas and indol right up to the end of the experiment, and the 

 B. typhosus only lost its power of reacting to anti-typhoid 

 serum after 100 days association with B. coli. Control 

 experiments were then made to see if the B. coli and 

 B. typhosus lost any of their special characteristics when 

 growing separately in the neutral peptone water. After four 

 months the two organisms were still found alive, and they both 

 maintained their specific reactions. Other races of B. coli and 

 and B. typhosus when grown together in neutral peptone water 

 were not found to be affected in the same way as the B. coli 

 and B. typhosus which were used for the first experiments. 

 Remy then endeavoured to decide whether the colonies which 

 had perfectly negative reactions when isolated after 100 

 days from the neutral peptone water were B. coli or 



