270 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



It will be seen that such a comparative series of 

 analyses indicates the value of the method adopted here 

 for the quantitative determination of the number of 

 sewage organisms present in shellfish. Where topo- 

 graphical and other considerations render the pollution of 

 the shellfish most probable, there we find that the numbers 

 of colon bacilli present in the stomachs of the molluscs 

 are the greatest; and conversely where, as far out from 

 land, we should expect great freedom from pollution, 

 colon bacilli are either very rare or are absent altogether. 

 The direct incubation of material of this kind on neutral- 

 red bile-salt, lactose agar, in the manner indicated here, is 

 indeed the simplest, and apparently the most reliable 

 biological test for the presence of sewage microbes that 

 has yet been devised. A negative result is, undoubted^, 

 a sure indication of freedom from such contamination. 



It is to be noted, too, that the enteritidis test is far 

 less useful as an index of contamination than the B. coli 

 one. In all the analyses made here, some reaction 

 (though not always a " typical " one) has been obtained 

 from anaerobic milk cultures, though bacilli of the colon 

 group may have been absent altogether. This is to be 

 expected, for in such tests we cultivate the spores of an 

 obligatory or facultative anaerobe of some kind, and 

 these spores are far more resistant than the colon bacilli, 

 and most probably have a very general distribution, 

 though they do not form a part of the normal bacterial 

 contents of uncontaminated shellfish. 



Note. — A question recently raised by the Chairman of the Gen. 

 Purp. Sub-Corn, was referred to me by Dr. Jenkins, viz. : Are sewage- 

 contaminated mussels unhealthy? I have never seen any certain 

 indications that a considerable degree of admixture of sewage with the 

 water in which mussels are living does any harm to the latter. They 

 indeed appear at times to thrive on sewage. 



