OYSTERS AND TYPHOID 257 



fatal, includes colic, nausea, vomiting, with more or less prostration. The onset is 

 generally sudden, and the attack lasts a comparatively short time. 



(c) Dysenteric Symptoms may occur which simulate the symptoms of group (6), 

 but are more severe. In this group, between it and (6), may be classified the cholera- 

 like conditions which sometimes occur. 



(d) Specific Disease, such as typhoid fever or cholera.* 



In all cases there is, of course, an incubation period, which is usually longer in 

 duration than that occurring in ptomaine poisoning. 



Infection of Oysters. The mode of infection of oysters by 



pathogenic bacteria is briefly as follows: The sewage of certain 



coast towns is passed untreated into the sea. At or near the outfall, 



oyster-beds are laid down for the purpose of "fattening" oysters. 



Thus they become contaminated with saprophytic and pathogenic 



germs conte^" u the sewage. It will be at once apparent that 



sevpi"* 1 . ' * U T .dry questions require attention before any deductions 



-vvix as to whether or not oysters convey virulent disease 



^sinners. 



The precise conditions which render one locality more favourable 

 than another in respect to oyster culture are not fully known. But 

 it has been observed that they do not flourish in water containing 

 less than 3 per cent, of salt. Hence they are absent from the 

 Baltic Sea, which, owing to the fresh river-water flowing into it, 

 contains a small percentage of salt. Oysters appear, in addition, to 

 favour a locality where they find their chosen food of small ani- 

 malcula and particles of organic matter. Such a favourable locality 

 is the mouth of a river, where tides and currents also assist in 

 bringing food to the oyster. Unfortunately, however, in a crowded 

 country like England, such localities round our coast are frequently 

 contaminated by sewage from outfalls. Thus the oysters and the 

 sewage come into intimate relation with each other. 



Professor Giaxa carried out some experiments in 1889 at Naples 

 which appeared to show that the bacilli of cholera and typhoid 

 rapidly disappeared in ordinary sea-water. Other observers at about 

 the same time, notably Foster and Freitag, arrived at an opposite 

 conclusion. Klein also found the cholera bacillus four days after 

 the removal of the oysters from water purposely contaminated with 

 them. In 1894 Professor Percy Frankland, in a report to the 

 Koyal Society, declared "that common salt, whilst enormously 

 stimulating the multiplication of many forms of water bacteria, 

 exerts a directly and highly prejudicial effect on the typhoid bacilli, 

 causing their rapid disappearance from the water, whether water 

 bacteria are present or not." Boyce and Herdman found that up 

 to a certain point oysters could render clear sewage-contaminated 



* The general question of mollusc poisoning is treated of by Mosny in the Revue 

 d' Hygiene, December 1899 to March 1900. Mosny also furnished the .French 

 Government with reports on the subject 



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