736 NATURAL HISTORY OF AQUATIC ANIMALS. 



under my observation recently. What is now alluded to is the yellowish, verging toward 

 a reddish cast, which is sometimes noticed in the gills and mantle of both the American and 

 European species. This, in all probability, like the green color, is due to the reddish-brown 

 matter which is contained in much of the diatomaceous food of the animal. 



Mr. J. M. Carley has also called my attention to these variations, and was inclined to attribute 

 them to the soil in the vicinity of the beds. But if the classical writers are to be trusted, to the 

 green, yellow, and white fleshed sorts we must add red, tawny, and black fleshed ones. Pliny 

 tells us of red Oysters found in Spain, of others of a tawny hue in Illyricum, and of black 

 ones at Circeii, the latter being, he says, black both in meat and shell. Horace and other writers 

 awarded these the palm of excellence. (O'Shaughnessy.) However, the black appearance may 

 only have been due to an abundance of the natural purple pigment in the mantles of the animal, 

 which varies very much in different forms; some, judging from the dark purple color of the whole 

 inside of the shell, must have the whole of the mantle of the same tint. The amount of color in 

 the mantle, especially at its border, varies in local varieties of both the American and European 

 species, as may often be noticed. 



Sometimes almost the whole of the outside surface of the mantle is charged with dark purple 

 pigment cells. That copper is not usually the cause of the green color of Oysters I also have the 

 additional testimony of Prof. W. K. Sullivan, of Dublin, who says : 



"As the green color of the mantle of Oysters from certain localities just referred to is 

 commonly attributed to copper, and as such Oysters are consequently believed very generally to 

 be poisonous, and their value therefore greatly depreciated, I made the most careful search for 

 traces of that metal in the muds which I had received from grounds known to produce green- 

 bearded Oysters. Oysters and other mollusca placed in solutions containing copper and other 

 metals absorb them and retain them in their tissues. I have had two or three opportunities of 

 examining Oysters which had assimilated copper, owing to mine-water containing it being allowed 

 to flow into estuaries at places close to oyster-beds. In every case the copper was found in the 

 body only of the Oyster, which it colored bluishg-reen, and not in the mantle or beard, which was 

 not green. In the green-bearded Oysters which I have had an opportunity of examining, the body 

 was not green, and no trace of copper could be detected in any part of the animal. The color, 

 too, was not the same as that of the true copper Oysters, but rather that which would result from 

 the deposition of chlorophyl or other similar chloroid vegetable body in the cells." 



The American consumer, however, need not be alarmed about the presence of copper in our 

 species, as there are no beds on our eastern coast into which the washings from mines ever flow, 

 as we have no workable deposits of copper near any of our beds, as in Cornwall, England. Besides, 

 I am inclined to doubt the statement of Professor Sullivan that Oysters or other mollusks can 

 absorb copper salts until their tissues are " colored bluish-green." Every competent histologist 

 knows how very readily organisms are killed by the action of inorganic acids and salts, several of 

 which are constantly used by biologists in fixing histological characters. Liebig, in his "Animal 

 Chemistry," long ago pointed out that the oxides and metallic compounds of antimony, arsenic, 

 copper, and lead had a very remarkable affinity for protoplasm, producing its immediate death. 

 In consequence, he suggested a very high chemical equivalency for living matter. This has since 

 been confirmed by the studies of Loew and Pokoruy, who found that silver nitrate would produce 

 a reaction with protoplasm if diluted to the extent of one part to a million of water. 



PROBABLE CAUSE OF THE GREEN COLOR. It is highly probable that the green color of the 

 Oyster is due to the absorption from its food of a harmless vegetable pigment. In this country 

 green-bearded Oysters occur at Lynn Haven Bay, Hongers and York itivers, Virginia, on the 



