GREEN OYSTERS. 19 



copper to simulate the natural tint, green oysters from Falmouth and elsewhere in 

 Cornwall have been suspected or accused of containing copper, derived from old mines 

 or metalliferous strata in the sea. Quite recently Dr. Thorpe * has found on the average 

 about 0.023 grains of copper oxide per oyster (in some cases much more) in specimens 

 from Falmouth and Truro. On relaying, the green Cornish oyster gradually loses 

 its colour, and is then found to contain only about 0.0062 grains of copper per oyster, 

 which is practically the normal amount (0.4 milligramme) which we find in white " native " 

 oysters from Whitstable. 



Dr. Thorpe-f says, " There is no question that the greenness of certain oysters, 

 especially of those found in Falmouth and Truro waters, is due to copper. The colour, 

 both in character and distribution is, however, quite different from that of the Marennes 

 oyster." We can corroborate this. It is in effect what we have been stating for the 

 last three years in our preliminary reports — that there are several kinds of green oysters ; 

 the " Huitre de Marennes " is one of them, the copper-containing green oyster is another. 



In the Falmouth oyster, containing an excessive amount of copper, we find that 

 much of the copper is certainly mechanically attached to the surface of the body, and 

 is in a form insoluble in water — probably as a basic carbonate. In addition to this, 

 however, the Falmouth oyster may contain a much larger amount of copper in its 

 tissues than does the normal colourless oyster. In these Falmouth oysters the cause 

 of the green colour appears to be the same as in the green American oysters. Some 

 of them also show {see PI. VI., Fig. 8) a green heart of exactly the same nature as 

 that of the green American oysters (PI. VI., Figs. 3, 7, 8). 



5. Green American Oysters. — This is the oyster at which we have chiefly worked. 

 It is brought to Liverpool in large quantities, and is laid down on various parts of the 

 neighbouring coast to be fattened and to be stored till required for the market. For 

 some years it has been noticed that certain of these re-laid Americans may become 

 green in the Autumn, the greenness being entirely different from that of the Marennes 

 and other oysters we have examined, and consisting in a large increase of the granular 

 green leucocytes of the blood in the heart, and in the sinuses and the tissues of the 

 mantle, and also on the surface of the mantle, but very rarely in the gills. The result 

 of this leucocytosis is that a more or less vivid green colouration is produced, which 

 may be almost anywhere on the surface of the body, although it is most frequently 

 over the liver, and the visceral (anterior) part of the body {see PI. VI., Figs. 3 — 7, and 9). 

 It may occur in patches or streaks, or very usually it is confined to the heart and blood 

 channels, which are then engorged with a pale chalky-green mass of the granular 

 leucocytes ; in some cases, owing to the universal injection of the vessels and smaller 

 blood spaces, the entire oyster has a greenish tinge (Fig. 6). 



The oysters in which this massing of the green leucocytes occurs do not appear 



* Local Govt. Bd. Report on Oyster Culture in relation to Disease, p. 105. 

 t Nalnre for Dec. 3rd, 1896, p. 107. 



