ON THE LIFE CONDITIONS OF THE OYSTER. 663 



Two points of interest have arisen in this connection. In the first 

 place the relation of iron to the greenness of the healthy French oyster 

 (' Huitre de Marennes ') ; and secondly, the extent to which copper is 

 responsible for the pale green colour of American and other oysters, a 

 diseased condition accompanied by a leucocytosis discovered and especially 

 studied by Herdman and Boyce. The presence of minute quantities of 

 copper and of iron as normal constituents of all oysters has also been 

 shown by the analytical data obtained. 



The results recorded have been made at Professor Herdman's request, 

 and have proceeded side by side with his investigations. Now that 

 these are completed, a summary of the work from a more purely chemical 

 standpoint may be of interest, especially since the occurrence of these 

 metals — copper and iron — either from the point of view of the origin of 

 colouration or of the cause of poisoning has from time to time been the 

 subject of discussion. 



The Analytical Method employed. — Electrolytic methods of analysis 

 Avere adopted both for the determination of iron and copper : these 

 methods, I have already shown,' possess mai-ked advantages for the esti- 

 mation of minute quantities of metal, especially if derived from organic 

 matter, for they are quite fi'ee from any prejudicial influences traces of 

 organic matter may exert, such as arise when volumetric or colorimetric 

 methods are employed. In each determination the bodies or gills only of 

 six or more oysters were carefully washed, dried between filter paper to 

 i-emove as much adherent moisture as possible, and then carefully dried 

 in porcelain dishes in the air bath at 100° C. When this drying was as 

 complete as possible, the oysters were heated in the air bath until 

 thoroughly carbonised, the carbon carefully burnt off over the free flame, 

 and the residue finally ignited in a porcelain crucible. Special care was 

 taken to exclude dust during both the drying and the ignition. The ash 

 was then thoroughly extracted with a mixture of 25 c.c. hydrochloric acid 

 and 25 c.c. sulphuric acid (1 : 2) on the water bath, and the resiilting 

 solution filtered and concentrated. The residue was free from both 

 copper and iron. The acid solution obtained was electrolysed for copper 

 with the usual precautions, a spiral of fine platinum wire weighing about 

 5 grme. being employed as the cathode. The iron was determined in the 

 residual solution, after neutralisation with ammonium hydrate, kc, acidi- 

 fying with a few drops of oxalic acid solution, and boiling with ammonium 

 oxalate : 4 grme. of the oxalate were added in each case, the precipi- 

 tated calcium oxalate (which is quite free from iron) filtered off" and 

 thoroughly washed and the resulting solution electrolysed, the metallic 

 iron being also deposited on a spiral of platinum wire. A blank experi- 

 ment with all the reagents employed was made, and the amount of metal 

 found (0-0002 grme. iron) deducted in each case. Also the deposited 

 metal, both iron and copper, Avas dissolved off" the electrode by acid, the 

 solution obtained tested by the ordinary reagents and the spiral re- 

 weighed, as a check upon the determinations, since the quantities found 

 were extremely small. 



The Green Colour of French Oysters, ' Huitres de Marennes' and the 

 Presence of Iron in Oysters. — The early observations of Dumas (1841) and 

 of Berthelot (1855) showed that the green colour of 'Huitres de 

 Marennes ' is not due to chlorophyll, and that although every oyster con- 



' Brit. Assoc. Sep., 1893, p. 726. 



2 



