256 BACTERIA IN OTHER FOODS 



other than typhoid fever occurred in persons who had eaten shell-fish, 

 whereas 54 per cent, of the cases of typhoid fever occurred in persons 

 who had recently eaten shell-fish. In 1903 the comparative figures 

 were 2 per cent, and 90 per cent, respectively.* 



Evidence necessary to prove Contamination of Oysters. — Evidence 

 of contamination of oyster-layings by sewage must be sought in 

 three directions : — 



(1) There must be personal inspection of the neighbourhood and 

 surroundings of the layings and storage ponds. The immediate 

 sanitary circumstances may be such that a definite conclusion can 

 be come to that the locality is dangerously unfit for the purposes of 

 the oyster industry, and no further examination by chemical or 

 bacteriological methods will be necessary. On the other hand, 

 local inspection may not reveal any probable source of dangerous 

 sewage contamination ; and to test the matter, it may be necessary 

 to make further examination in order to detect traces of pollution 

 which may have arisen from sources of contamination which were 

 not obvious to the eye. 



(2) In the event of the results of inspection being satisfactory, 

 the next step is to examine the water in which the oysters are laid, 

 in order to ascertain whether the chemical or bacteriological evidence 

 of sewage contamination is sufficiently strong to enable one to say, 

 in spite of the local inspection, that the sewage is not sufficiently 

 diluted and purified to obviate aU possible danger. 



(3) A bacteriological examination of the molluscs themselves 

 must be made, in order to ascertain whether they contain those 

 bacteria which are ordinarily associated with contamination by 

 sewage. 



It is hardly needful to add that, in order to estabhsh the fact that 

 infection has occurred or may occur from the consumption of polluted 

 oysters, it is necessary to prove disease in persons or animals who 

 have eaten some of the oysters. In any inquiry of this kind it is 

 essential to take into consideration, {a) clinical evidence, (b) the 

 history and circumstances of each case, and (c) the exclusion of 

 all other possible causes. 



Symptoms of Oyster-Poisoning. —Obviously, the diseased conditions set up by 

 the consumption of polluted oysters will vary according to circumstances. If the 

 pollution be the specific infection of typhoid fever, the clinical disease of typhoid 

 fever will supervene. The same applies to cholera. But in many cases on record 

 the illness resulting has been of a less specific character, and has simulated gastro- 

 enteritis, colic, certain nervous conditions, and so on. Hence it may be desirable 

 to make a provisional classification as follows : — 



(a) Nervous Conditions, which Mosny likens to curare poisoning. This type is 

 rare, always severe, and generally fatal. 



(h) Oastro-Enteritis. — This group, which is one of the most common and least 



* Public Health, 1903 (November), pp. 81 and 82. 



