26 



OYSTERS AND DISEASE. 



These results show that copper is present normally in both green and in white 

 oysters in small quantity, but that the greenness of the gills of French oysters is certainly 

 not due to this metal — in fact they contain only the merest trace. 



Experiments which wc have made on the feeding of oysters with very dilute 

 saline solutions of iron and of copper salts, entirely confirm these analytical data. 

 Beyond a certain amount of post-mortem green staining, the oysters did not acquire 

 any green colour. We give the details of these feeding experiments further on. 



There are, however, some green oysters (not the " Huitres de Marennes ") which, 

 as we have already stated, contain much more copper than those analyzed above. They 

 are probably under abnormal conditions. Such cases are certain Falmouth oysters, and 

 the American oysters with the green leucocytosis. 



Dr. Thorpe has shown that some green oysters picked out by Dr. Bulstrode at 

 Falmouth and Truro contained as much as 0.02 grains per oyster on the average — 

 some contained much more ; while we find that the green American oyster from Fleetwood, 

 where the greenness is due to the leucocytes, has on the average 0.0229 grains of 

 copper per oyster — between three and four times the normal amount. 



We have been able to obtain some of these green oysters from Falmouth for 

 examination and analysis. Six Falmouth oysters {O. edulis), the bodies of two of which 

 were of a distinct arsenic green colour, were dried at 100" C. and then digested with 

 water, and subsequently with dilute hydrochloric acid. The extract contained about 

 half the total copper present, showing that the metal is partially, at any rate, 

 mechanically retained in or on the body of the oyster,* probably as a basic carbonate. 



The analytical results were as follows : — 



The total copper present here is almost nine times the normal quantity, and 

 about half of this is easily removed by dilute acid. It is quite likely that the remainder 

 of the excess is partially or wholly simply entangled in the food passages of the oyster. 



The occurrence of copper in oysters, under such conditions, in some parts of 

 Cornwall is due to the locality, and might quite possibly attain injurious proportions. 

 The oysters analyzed were obtained from a creek which is locally supposed to bring 



*Dr. Thorpe, in a letter to Nature (1896, p. 107), referring to the large proportion of copper in these 

 Falmouth oysters, speaks of it as "obviously caused by the mechanical retention of cupriferous particles." 



