IRON AND COPPER IN OYSTERS. 



27 



down copper from old mines, and the mud of which was found by Thorpe to contain 

 0.148 per cent, of copper. Normal sea-water contains such an excessi vdy small quantity 

 of copper that it was not found possible by Dr. Kohn to detect its presence, even 

 electrolytically, in a litre of sea-water, after concentration. 



Taking, finally, the green leucocytosis found in some American oysters, the six 

 greenest and six whitest of 120 of these oysters, as re-laid on our coast, were chosen 

 for analysis ; also a quantity of the greenest portions of the greenest oysters was 

 selected from another batch, and compared with the corresponding portions of the 

 whitest oysters. The iron was not determined in the latter comparison, owing to the 

 possible contamination by that metal in the cutting. 



The following were the results obtained : — 



The excessive quantity of copper in the selected green oysters is 3.75 times that- 

 in the white ones, calculated per oyster, and 3.63 times calculated on the ash. In the 

 selected parts the total copper present calculated on the ash is high in both cases, and 

 the green parts again show a marked excess in the proportion of 2.1 to i. The copper 

 and iron in the white specimens are about normal, but the increased quantity of iron 

 in the green is marked, being 2.5 times that of the former. Still there is relatively a 

 large excess of copper as compared with iron in the green oysters, as is evident from 

 the analyses, the ratio being i.i : i for the white, and 1.8 : i for the green. 



It is to be concluded, therefore, that the green colour of these diseased American 

 oysters is coincident with the distribution of the excessive quantity of copper present, 

 and that the copper is in consequence to be regarded as the cause of the colour. The 

 histo-chemical investigations given further on confirm this conclusion. 



Manganese was also found by Dr. Kohn to be present in several of the kinds 

 of oysters analyzed. Its detection is readily effected in the electrolytic method of 

 analysis, as it separates at the anode as peroxide. Colne oysters contain 0.14 mgrme. 

 per oyster, a quantity rather smaller than the amount of iron present. 



We must now turn to Dr. D. Carazzi's recent papers, in which he tries to show 

 that the green colouration in oysters is in all cases a healthy condition, caused by the 

 absorption of iron as a nutrient material from the surrounding medium by means of the 

 surface epithelial cells, such as those of the branchiae and palps. A good deal that is 



