64 



It has been conclusively shown by various investigators, 

 since Dumas in 1841 and Berthelot in 1855, that the green 

 colour is not due to Chlorophyll and that although every 

 oyster contains a very small amount of copper in its blood 

 there is no reason to believe this becomes increased to a 

 poisonous extent in any oyster, and that the green colour 

 of the French cultivated oysters (" huitres de Marennes ") 

 is not due to copper. 



Gaillon in 1820 came to the conclusion that the green 

 colour is due to the microscopic food which the oyster 

 gets from the water of the " claire " or oyster park. He 

 called the organism in question Vibrio ostrearius ; it is 

 now known to be a Diatom — Navlcida fas if o?' mis, var. 

 ostrearia, Grunow. Since then other French investigators, 

 and notably Valenciennes in 1841, have corroborated 

 Gaillon's conclusion and have shown that in addition to 

 the branchiap, the inner surfaces of the labial palps, the 

 alimentary canal beyond the stomach, and to some extent 

 the liver, become coloured green. 



It has been proved experimentally by Puysegur,* 

 Bornet, Decaisne and others that white oysters can be 

 greened rapidly — in 26 hours — by keeping them in clean 

 soup plates and feeding them with water containing the 

 Navicula. These interesting experiments were carried out 

 at Le Croisic in Brittany, and were afterwards repeated 

 in Paris ; and the result seems entirely opposed to the 

 old suggestion that iron salts in the soil at the bottom of 

 the "claire" are the cause of the greening, which was 

 alluded to twenty years ago by Bouchon-Brandely and 

 has quite recently been revived by Carazzi at Spezia. 



Ryder,! in America, was also in 1880 investigating the 

 greening of oysters, with much the same results as those 

 of Puysegur. He went a step further, however, and 



* Revue Maritime et Coloniale, 1880. 



tU. S, Fish Coium. Report lor 1882 (puljlished 1884). 



