THE POLLUTION OF THE SEA 29 



these articles of food within a period antecedent to the onset 

 of illness consistent with the hypothesis that they were the 

 carriers of the infection. It is usually impossible in such cases 

 to cause a bacteriological examination of the presumed medium 

 of infection to be made. A knowledge of the source from which 

 the shellfish were obtained does not help greatly , since all mussel- 

 beds are sewage-polluted to some extent. Finally it is very 

 difficult to exclude all other possible sources of infection such 

 as water, milk and vegetables, though there are criteria which 

 enable an epidemiologist to distinguish between an outbreak 

 due to water or milk, and that due to the accidental pollution 

 of other articles of food by flies, or by enteric carriers, or by 

 contamination in situ as in the case of shellfish. Nevertheless 

 there are " classic " investigations on record where the cause 

 (shellfish) of the outbreak of disease has been traced beyond 

 doubt, and there are other lines of evidence. The residuum 

 of enteric fever in this country — a residuum reducible with 

 very great difficulty in spite of sanitation — points to the 

 presence of some cause or source of infection untouched so far 

 by public health measures. The rise in the incidence of the 

 disease in the autumn and early winter months, immediately 

 after the beginning of the season of fishing for mussels, is also 

 very significant. On the whole one cannot doubt that the 

 consumption of shellfish (raw or cooked, for cooking is a very 

 imperfect means of sterilisation) is a competent cause of the 

 maintenance of outbreaks of enteric fever, yet the application of 

 this thesis in any particular case, and the attachment of legal 

 responsibility to any particular vendor, fisherman, or locality, 

 must be very difficult, or even impossible in the present con- 

 dition of our knowledge. 



It is here that one feels justified in complaining of the very 

 imperfect results of the investigation made by the Sewage 

 Commission and of the equally poor results of public health 

 investigation during the last dozen years or so. It is hopeless 

 to attempt to prove the unwholesomeness of any particular 

 mussel, cockle, or oyster la}dng by trying to demonstrate the 

 presence of the specific organism of enteric fever in the molluscs 

 in question. Bacillus typhosus can only be recognised with 

 difficulty after a laborious analysis. It is very exceptionally 

 that it has been found in shellfish taken from natural layings 

 and its actual occurrence there must be exceptional ; for like 



