63 



finds that in both of them there arc traces of copper, and 

 of iron, but that the amount of both metals is actually 

 greater in the colourless than in the green gills. 



Cases of sudden poisoning following upon the con- 

 sumption of oysters have frequently been ascribed to the 

 oysters having a green colour which v\^as supposed, with 

 little or no reason, to be due to impregnation with a 

 copper salt. The river Roach, in Essex, has long been 

 known to produce in winter green oysters which, on 

 account of their colour, are not sold in England but are 

 sent to the French and other continental markets. It 

 has been shown several times that copper has nothing to 

 do with the greening of these oysters. However, that 

 conclusion is constantly doubted, and such cases as the 

 following are quoted : — In 1713 a certain Ambassador 

 gave a great supper at the Hague, and, we are told, as a 

 luxury procured green oysters from England. The guests 

 who eat them are said to have been seized with severe 

 colics and to have been cured with great difficulty. It is 

 also said, however, that the merchant had palmed upon 

 the Ambassador some common oysters tinted with copper 

 instead of the true greens. Another historic case is that 

 of the trial which took place at Eochefort in 1862 of a 

 merchant who had sold green oysters imported from 

 England and which were said to contain copper. 



Other cases are on record of green oysters which 

 are supposed to have taken up copper from old mines 

 under the sea, as at Falmouth, or from the copper bottoms 

 of ships, and so have become poisonous. Mr. G. C. 

 Bourne of Oxford who has investigated the Falmouth 

 oysters tells me that their greenness is in his opinion due 

 to a green Desmid upon which the oysters feed in 

 quantity. It is said that these oysters lose their colour 

 on being transplanted to the mouth of the Thames. 



