20 
OYSTERS AND DISEASE. 
to US as healthy as those which are colourless. They are frecjuently thin, with the 
liver shrunken, but we were unable to find evidence of any parasite or other irritative 
cause of the disease, either by staining or by cultivation. On the other hand, it is 
evident from experiment that an irritation of the surface of the mantle will determine 
the presence of leucocytes at the point. We have shown this by trephining the shell, 
and by removing pieces of shell to form " windows," which we closed by paraffined 
water-tight corks. We have also carefully removed one valve without causing any 
hemorrhage, and have kept the oysters, which were healthy yellow Americans, alive for 
more than a week. On the first day green leucocytes began to appear on the mantle. 
On the second day they were more abundant, especially on and around the adductor 
muscle and over the heart. This condition increased for about two days more, and then 
began to disappear. The leucocytes causing the green spots were granular and actively 
amoeboid. 
At an early period of the investigation we were inclined to agree with some 
previous investigators that copper, though present in small quantity (on the average 
0.006 grains) in all oysters, had nothing to do with this green colour ; but last year we 
definitely announced* that we had found copper in considerable quantity (up to four 
times the normal amount) in these green American oysters, and that the copper reaction 
coincided histologically with the green granular leucocytes, and that consequently the 
copper may fairly be regarded as the cause of the green colour. 
In the next section we give an account of our chemical analyses of the copper 
and the iron present in these and other oysters ; and in the succeeding section on the 
micro-chemistry we show the evidence upon which we base our statement that the 
superabundant copper of these oysters is contained in the granular green leucocytes. 
* Proc. Roy. Soc, vol. LXII., p. 30 (1897). 
