26 



rest of the body is somewhat more (1 : 2) than that found 

 in Dutch oysters (1:3'7) but much less than in American 

 oysters which are white (1'4:1). The comparison is pur- 

 posely made on the absolute quantity of metal in the gills 

 and the rest of the body, as any other basis for calculation 

 is fallacious. Chatin and Muntz reckon on the weight 

 of the dried organic matter present, but it was not found 

 possible to get anything approaching constant weights in 

 this way. This may to some extent account for the 

 differences in our results, but I should also like to point 

 out that although the ratio of iron in the gills and the 

 rest of the body in green and in brown oysters is from 

 1:1'8 (feebly green) up to 1:2"3 (very green) they also 

 instance white oysters with a proportion of 1:1"6. It is 

 certainly somewhat strange that they find more iron in 

 the gills than in the rest of the body in all cases, which 

 is not the case in my own experiments. But the quanti- 

 ties of metal present are so small, that since they do not 

 state how many oysters were taken for analysis and 

 employ the permanganate method for the estimation of 

 the iron, it is difficult to say what degree of absolute 

 accuracy their results represent and therefore to judge in 

 how far their analytical data justify their conclusions. 



" From two points of view the above results show that 

 the greenness of the gills of French oysters is certainly 

 not due to iron : — 



(1) Because the gills of the green oysters contain less 



iron than the rest of the body ; 



(2) Because the proportion of iron in the gills as 



compared with the rest of the body in white 

 (American) oysters is greater than in the green. 

 " That the method is rehable is shown by two determin- 

 ations of the iron in the gills of American oysters one 

 giving 2" 3 and the other 1"8 mgrme. of iron per six pairs 



