564 



REPORT — 1898. 



tains a certain very small amount of copper in its blood in the form of 

 ' haimocyanin,' as determined by Fredericq, the green colour of the French 

 cultivated oyster is not due to this metal. Ray Lankester ' in 1886 con- 

 firmed the latter statement, and states in his investigation on the histo- 

 logical condition of the colour that there is neither copper nor iron in the 

 refractory blue pigment ' marennin ' of the coloured portions of the 

 oyster. Berthelot, however, suggested that the green colour was probably 

 due to iron, and more recently Chatin and Muntz ^ have extended and 

 corroborated this statement. 



From their analytical results these observers conclude that both the 

 green and brown colourations of various types of French oysters are due 

 to the presence of iron, and that the depth of colour bears a close pro- 

 portion 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 

 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. 



Appended are some of their results, to which I have added a column 

 showing the ratio of the iron in the body, minus gills, to that contained in 

 the gills. 



The relative proportion of iron in the gills hardly bears out the con- 

 clusions arrived at ; it is the same in pale-green and brown-green oysters, 

 and in both, but little greater than in the white. On the other hand, the 

 total iron, both in the gills and in the rest of the body, shows a marked 

 increase, apparently corresponding to the depth of the colouration. The 

 iron was determined in these experiments by potassium permanganate, 

 but the absolute quantities of metal found are not stated. The calcu- 

 lation of the results per 100 parts of dried organic matter is apt to be 

 misleading. In my own experiments it was not found possible to get 

 anything approaching constant weights in this way, and the results are 

 entirely out of accord with those of Chatin and Muntz. 



The following table gives the quantities of iron found in French as 

 compared with white American oysters, three pairs of gills being analysed 

 in each case. 



These figures show conclusively that there is more and not less iron in 

 the gills of the white American oysters than in the French, and this 

 irrespective of the basis on which the result is calculated. The ash is 

 undoubtedly the most reliable factor to calculate on, provided the oysters 



' Qvart. Journ. Micrus. ScL, 1886, 26, 71. 

 = Compt. Rend., 1892, 118, 17, and 56. 



