452 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



reports made to the Lancashire and Western Sea- 

 Fisheries Committee has been, then, to isolate sewage 

 organisms from a sample of shell-fish and to estimate 

 the approximate mean number of these contained in a 

 single mollusc. A number of the organisms so isolated 

 are then sub-cultured, and their cultural characters are 

 determined. If, say, one-fifth of these organisms give 

 the reactions of Bacillus coli, we may then say that 

 one-fifth of all the sewage organisms isolated in the 

 primary cultures were B. coli, paying due attention, of 

 course, to the statistical errors involved. What we do 

 find in such a method of analysis is several categories 

 of organisms. I have given the reactions of 225 such 

 organisms in a former paper {Journal of Hygiene, 

 Vol. IX., No. 4, 1910), making use of MacConkey's 

 tables for the identification of intestinal bacteria 

 {Thorny son-Yates Laboratories Reports, Vol. IV., 

 Part I., 1901; and Journal of Hygiene, Vol. VI., 1906), 

 and refer the reader to this paper. 



If, however, a report on the liability of a natural 

 shell-fish producing area to sewage pollution consists not 

 only of a bacteriological analysis of the shell-fish them- 

 selves and the water in which they are living, but also 

 includes a detailed survey of all the natural conditions 

 —positions of sewer outfalls, direction and strength of 

 tidal streams and currents, wind drifts, rise and fall of 

 tide, &c, and also a critical consideration of the 

 epidemiological evidence available — then it may be 

 possible to dispense with the detailed examination of 

 the colonies of organisms isolated in the primary cultures. 

 If, for instance, a quantity of an emulsion corresponding 

 to one-tenth mussel fails to produce any change in bile- 

 salt glucose broth (see p. 481), we may accept this 

 reaction, without any reserve, as indicating that B. coli 



