ON GREEN OYSTERS. 79 
gives the brilliant blue solution characteristic of the compound 
of copper and ammonia. On the other hand, the “ huitres de 
Marennes ” are not uniformly coloured green, but have only 
the gills and labial tentacles so coloured (see Pl. VII, fig. 10), 
and, moreover, the deep blue-green gill may be treated 
to any extent or in any way with ammonia and not a 
trace of blue solution can be obtained. 
These facts should alone have been sufficient to cause the 
rejection of the popular copper-theory of green Oysters, and 
would no doubt long since have done so, were it not for two 
remarkable facts. These are: 
lst. Oysters do normally contain a certain very minute 
quantity of copper in their blood. 
2nd. Common Oysters have been stained green by fish- 
mongers with copper-salts in order to imitate the natural green 
Oysters. 
In reference to the first of the above statements, it is to be 
noted that many Mollusca and many Arthropoda have been 
shown by Frederiq, followed by other observers, to possess as a 
constituent of their blood a proteid known as hemocyanin, 
into the constitution of which as much as 1 per cent. (ash) of 
copper enters. The detection of minute quantities of copper 
by Bizio (Instit. of Venice, 1845) in the tissues of Oysters may 
therefore be accepted. The copper so found was the copper of 
hemocyanin, normally present in both green and colourless 
Molluscs. 
The second statement as to the fraudulent staining of Oysters 
admits of no doubt. So far back as 1718 a case is on record, 
and cited by Dr. Johnston in his ‘Introduction to Conchology.’ 
A fishmonger at the Hague was ordered to supply green 
Oysters. Not being able to obtain any, he stained common 
Oysters green with copper. The persons who ate them were 
seized with severe colic. The fishmonger confessed his fraud. 
A few years ago a similar fraud was practised at Rochefort, 
in France. The authors of the fraud, and those interested in 
maintaining the reputation of the green Oysters of Marennes, 
were unable to confute the evidence of the chemist, who 
