( 21 ) 
VIII.— IRON AND COPPER IN OYSTERS. 
Dr. Charles A. Kohn has kindly made for us, from time to time, chemical 
analyses of oysters from various localities, and in different conditions of colouring^ ; in 
the following account we quote freely from his notes, and the reports* he has given us, 
and from our conversations with him on the results of the experiments. 
The early observations of Dumas (1841) and of Berthelot (1855), which showed 
that the green colour of French oysters (" Huitres de Marennes ") is not due to chloro- 
phyll, and not to copper, though possibly to iron, have been recently extended by A. 
Chatin and A. Muntz.f From their analytical results these observers conclude that 
both the green and the brown colourations of the various types of French oysters are 
due to the presence of iron, and that the depth of colour bears a close proportion to 
the quantity of iron contained. The colourations are chiefly apparent in the gills, but 
extend also to the labial palps and parts of the alimentary canal. Chatin and Muntz 
base their conclusions, in the first place, upon the fact that they find considerably more 
iron in the gills than in the rest of the body of green oysters, and secondly, upon the 
occurrence of a larger quantity of iron in the gills of green than of white oysters. 
The cause and origin of this colouration is a physiological problem of much 
interest, but the confirmation or refutation of Chatin and Muntz' results also appeared 
of importance in connexion with the investigations on Oysters and Disease, and therefore 
the following experiments on the occurrences of copper as well as of iron in various 
kinds of oysters were undertaken. The point at issue is not so much the nature of 
the colouring matter, nor whether it does or does not contain a small quantity of iron, 
but simply whether the coloured parts of the green oysters contain proportionately 
such an excess of the metal that the colour can be attributed to its presence. This 
has not been found to be the case. The determination of the copper appeared to be 
of some interest, since poisonous effects have often been attributed to its presence, 
although earlier observers have shown that a small quantity is a normal constituent of 
the blood of the oyster. 
Electrolytic methods of analysis were adopted both for the determination of iron 
and copper ; these methods Dr. Kohn has already shown {Brit. Assoc. Reports, 1893, 
p. 726) possess marked advantages for the estimation of minute quantities of metal, 
* Sec also the Brit. Assoc. Reports. t Conipt. Rend. 1894, CXVIII., pp. 17 and 56. 
