CAUSE OF THE GEEEIf COLOE OF THE OTSTEE. 735 



There is therefore no doubt but that a delicate balance of power is maintained by these rivals 

 which is best for the health of the community. The stability of permanent oyster-beds, it must 

 be remembered, furnishes the right conditions for the survival of many types. It is a place where 

 they find both a home and jilenty of food. It is the very favorableness offered by these places 

 which tends to induce them to congregate and multiply, and it becomes a serious question whether 

 the artificial establishment of banks will not in time cause the proper types to congregate and 

 multiply so as to afford the needed food supply for the Oysters. That destructive members of the 

 community may also be attracted is admitted, but if the beds are established in shallow waters, as 

 I have previously suggested, the destruction of such unwelcome intruders may be very readily 

 effected. "Drills" and boring-sponges are naturally to be thought of as types which should be 

 destroyed, while diatoms, infusoria, small polyps, bryozoa, minute algae, etc., are to be favored in 

 every way. Those forms again which the oyster-culturist knows are only there for the purpose 

 of getting a good living with little trouble to themselves ought to be destroyed. 



It might be an advantage to introduce certain desirable forms onto a bank, which might be 

 supposed to be useful as a food supply. Infusoria and diatoms not previously existing might be 

 introduced in this way ; this, I think, would be especially easy in the case of the former where 

 the type was one which is fixed during its adult life. 



216. ON THE CAUSE OF THE GREEN COLOR OF THE OYSTER. 



BxPBKiMENTS AT WASHINGTON AND PHILADELPHIA. — I have frequently read accounts of 

 Oysters which had become green-fleshed iu certain localities, and it has also been asserted that 

 competent chemists had discovered poisonous green substances of metallic origin in such speci- 

 mens. Tests made at the Smithsonian Institution by Professor Endlich in 1879 failed to disclose 

 anything poisonous in some green Oysters which had excited the suspicion of the Board of Health 

 of the city of Washington. This investigator, it is desirable to state, resorted to every test known 

 to him in order to discover if anything poisonous was present, and failing to discover any harmful 

 substance concluded that the color must be due to some inert material. In order to see if the color 

 was due to the presence of some green compound of copper. Prof. H. C. Lewis, of the Academy of 

 Natural Sciences of Philadelphia, kindly made some delicate tests for me, using small dried frag- 

 ments of an Oyster very deeply tinged with green in various regions, especially iu the liver, con- 

 nective tissue, and mantle. The fragments were burned in a bead of microcosmic salt and chloride 

 of sodium on a clean platinum wire in a gas flame j this test did not give the characteristic sky- 

 blue flame which should have been developed had there been the minutest trace of copper present. 



It is therefore clear that the substance, whatever it may be, is not a corrosive metallic poison 

 derived from copper, which if present would almost undoubtedly be detected by a peculiar acrid 

 metallic taste, which would be experienced when one ate such Oysters. In making some practical 

 tests as to the relative qualities of such Oysters as compared with white-fleshed ones, oppor- 

 tunities for which were kindly furnished me by Mr. J. M. Oarley, of Fulton Market, I failed to 

 detect the slightest difference of flavor. Such also is Professor Leidy's verdict, who informs 

 me that he made a similar experiment, and a restaurateur, with whom I discussed the matter, 

 declared that he was in the habit of selecting them for his own eating, preferring their flavor to 

 that of the white 0.\ sters. 



Vaeiations in color. — If it be objected that the green color indicates an unhealthful 

 condition of the animal, it may be stated that other color variations of the flesh have fallen 



