ON GREEN OYSTERS. 77 
The chief value of Valenciennes’ contribution to this subject 
is, however, to be found in the chemical examination of the 
colouring matter of the green Oyster, which he carried out with 
the aid of Dumas, the celebrated chemist. He found that the 
green pigment of the Marennes Oysters was insoluble in water, 
in alcohol, in ether, in weak alkalies, or in weak acids; in fact 
it was found to be insoluble without the use of agents which 
destroy or fundamentally alter it, such as strong acids. He 
conclusively proved that the pigment did not contain copper, 
and M. Dumas studied it further, in order to ascertain whether 
it might be a compound similar to Prussian blue, and reported 
that it had no relation to the ferrocyanides. Accordingly 
Valenciennes came to the conclusion that the pigment of the 
green Oyster had nothing to do with metallic salts, and was due 
to an organic compound quite distinct from all green sub- 
stances hitherto known. This, again (though its import was 
not recognised by Valenciennes) was a conclusion in favour of 
Gaillon’s hypothesis, since it was thus demonstrated that chlo- 
rophyll, the pigment of the Ulve and common green Algz, 
from which some persons supposed the Oyster to derive its green 
colour, had nothing to do with it. 
Gaillon, however, had given no proper account of the pigment 
of the Navicula ostrearia, and it might well have been 
assumed by Valenciennes and others that the Navicula 
ostrearia owed its bluish-green tint to chlorophyll or to that 
and the water-soluble phycocyan (not properly recognised till 
many years later), and accordingly that this organism was ex- 
cluded with all others by the peculiar characters of the pigment 
observed in the Oyster, from being considered as its source. 
Valenciennes suggested the view that the peculiar green 
colouring matter which he characterised was manufactured by 
the Oyster itself in the intestine and liver, and was absorbed 
thence and deposited in the Oyster’s gills. 
In this condition the subject has remained! ever since the 
1 At Easter, 1877, 1 had the good fortune, in company with my friend 
Thiselton Dyer, to meet M. Bornet, the eminent algologist, at Le Croisic. 
M. Bornet subsequently sent to Mr. Dyer a dried gathering of Navicula 
