442 TRANSACTIONS LIVERPOOL BIOL6GICAL SOCIETY. 



Now we see at once that there is no agreement as to 

 the series of reactions which are to be regarded as 

 proving the presence of Bacillus coli. Some few tests, 

 the fermentation of glucose and lactose (these are really 

 all that everyone agrees upon), are common to all the 

 series, but for the rest their adoption appears to be a 

 matter of the amount of time that may be spent upon the 

 identification. 



Generally speaking, public health bacteriologists in 

 this country adopt Houston's "Flaginac" test. The 

 mussel, or other shell-fish, is cut up and (after other 

 operations to which I return later) is inoculated in 

 MacConkey's bile-salt broth. The organisms growing 

 in this liquid are then separated from each other by 

 "plating-out" in gelatine, or some other medium. 

 Colonies of the microbes growing on this medium are 

 then selected for further study. As a rule, the analyst 

 endeavours to select colonies which he regards as those 

 formed by B. coli, but this procedure is, as Houston 

 (1904, p. 173) says, " a speculative venture even to the 

 expert." Real B. coli colonies may, then, be neglected. 

 After isolation, the organism is identified by growth on a 

 number of media, and it has been shown (Houston, 

 1904, p. 105) that it " cannot be said with certainty 

 which tests should be employed, and how many of them." 



Nowadays, however, most public health bacteriolo- 

 gists probably employ Houston's four tests (1) fermenta- 

 tion of lactose broth, (2) fluorescence in neutral-red 

 broth, (3) formation of indole, (4) fermentation and 

 clotting of milk. This is the series of reactions which 

 Houston employed in his work for the Sewage 

 Commission, but it does not appear that he regards it as 

 always essential for the definition of B. coli. Thus 

 " a coli-like microbe, to be considered typical, must 



