SEA-FISHERIES LABORATORY. 93 



can really be studied, as the process of identification is very 

 laborious. Lately the investigation has been necessarily 

 abandoned because of the impossibility of procuring the 

 chemical substances used in the test-media (formerly obtained 

 from the firm of Merck, of Darmstadt). 



But even in several hundreds of strains of organisms 

 isolated, at least several dozens of distinct or " particular 

 species " of bacteria were found and less than 5 per cent, of 

 those provisionally called sewage organisms, that is glucose- 

 and lactose-fermenting bacteria, were really Bacillus coli 

 communis. 



Then the question arises as to what is a " strain " or 

 " particular species " of bacillus, and it is evident that the 

 criteria of "purity of strain," or "identity of species" cannot 

 be the same among the bacteria as among higher organisms, 

 say parasitic worms ; that is, with regard to accepted methods 

 of identification. 



It is probable that among the many "particular species" 

 of micro-organisms isolated from mussels, a number of these 

 are of the same significance as regards the possible dissemina- 

 tion of epidemic disease. But it seems probable that the 

 " habits " of these faecal organisms are not identical. Some 

 of them are resistive to changes of environment, and others 

 easily succumb to such, changed conditions. Therefore the 

 nature of the mixture of intestinal organisms inhabiting 

 sewage, sea-water or mussels may change very rapidly as one 

 after another of the " particular species " ceases to reproduce 

 and dies out in the new environment. Thus we ought to be 

 able to recognise from the nature of a sample of the micro- 

 organisms isolated from mussels or sea- water, what was the 

 probable date of pollution, and therefore the gravity of the 

 pollution from the public health point of view. 



But because of the laborious nature of the investigations 

 necessary to give this information, we are not yet able to give 



G 



