ZOOLOGY. 611 



per iu oysters. But Mr. Gaillard, from scieutific cousiderations, himself 

 concluded that this was because some process was fraudulently em- 

 ployed to color the oysters, and that it consisted merely iu immersing 

 them in a solution of a salt of copper, and leaving them in it till they 

 were saturated by it. 



Mr. Puys6gur sought by experiment to ascertain whether copper was 

 absorbable by the mollusk, and found that— 



1. "An oyster which is placed in a bath of sulphate of copper is not 

 colored at all." 



2. " Death quickly follows when they are plunged into such a mix- 

 ture." 



He did not deny that chemists may have found copper in oysters, but 

 his own direct experiments did not verify the absorption of the metal 

 by the animals. 



Copper, then, being out of the question, he sought to learn what was 

 the cause. 



Various observations and experiments were instituted, for a detail of 

 which reference must be made to the original memoir of the author. 

 His conclusions are thus summarized : 



"There remains no longer any doubt as to the fact that the viridity of 

 oysters is entirely due to the absorption or digestion of the soft parts of 

 the Naviculw held in suspension by the surrounding water ; this definite 

 experience also completely overturns the hypotheses which attribute 

 it to the influence of the soil, to the mixture of fresh and salt water, to 

 northeast winds; in a word, all the other conjectural causes to which 

 this simple phenomenon has been childishly atrributed are shown to be 

 inadequate. 



" It is evident, moreover, that the coloring matter is directly absorbed 

 by the mollusks, and that the process takes place inside of tlie animals. 

 If, in fact, dissolution of the coloring matter tojk place in sea-water, 

 the water would be tinged as soon as the diatoms were blanched, Now, 

 this is not the case. In fresh water, on the contrary, the coloring mat- 

 ter is immediately dissolved, and as a result the diatoms are blanched. 

 A single drop of water placed on a slide containing the diatoms causes 

 them to lose their color instantly. Finally, if a piece of filtering paper 

 is saturated in the fresh water which has been placed on the diatoms, 

 and it is afterwards dried, it will present absolutely the same color as 

 the green oysters. 



" These laboratory observations are, moreover, perfectly in accord 

 with the phenomena observed by the oyster-culturists. Heavy rains 

 cause the greenness of the claires to disappear, and the dry and salt- 

 laden northeast winds, which augment the saturation of the waters, are, 

 on the contrary, favorable to the production of the green coating in the 

 claires." 



Mr. Ryder supplemented Mr. Puysegur's researches by observations 

 of his own. His investigations convinced him of the correctness of Mr, 



