364 REPORT— 1897. 



all — of our oysters and mussels are grown or kept under most insanitary 

 conditions, and so may, when taken as food, without the necessary precau- 

 tions, from unhealthy localities, cause disease or poisoning. The con- 

 clusions on the public health question are entirely in accord with what we 

 (Boyce and Herdman) recommended in a former report (Ipswich, 1895) as 

 the two requisite sanitary measures, namely, first, the inspection of all 

 grounds upon which shelliish are grown or bedded, so as to ensure their 

 practical freedom from sewage ; and, secondly, the use, when necessary, of 

 what the French call ' d^gorgeoirs ' — tanks of clean water in which the 

 ■oysters should be placed for a short time before they are sent to the 

 consumer. 



Copper in Oysters. 



There are two other points in the Medical Officer's Report to which 

 •we must allude. The first is that Dr. Bulstrode's report corroborates our 

 account of the pale green disease which we have discussed in our pre- 

 vious papers, and which we refer to more fully below. He has independ- 

 ently met with a condition in oysters from the South Coast of England 

 which is clearly the diseased condition we had described. This is the 

 more important as Dr. Carazzi in the paper referred to above seems 

 inclined to doubt our account of the pale green disease. The second 

 point is that Dr. Thorpe, who examined some green oysters obtained 

 by Dr. Bulstrode at Falmouth, found tliat they contained a notable 

 amount of copper. This observation has raised once more the question, 

 which was by many considered settled, as to whether large amounts 

 of copper might be taken up by the oyster, and as to whether any of 

 the green forms of oyster owe their colour to copper. 



We have alluded in former reports ' to the great difference of opinion 

 that has existed in the past as to the green colour of certain oysters, and 

 there can be no doubt that that difference of opinion has l)een largely due 

 to the fact that the observers worked with different kinds of oysters. Some 

 investigated Marennes oysters {0. edulis) and found that with dark blue- 

 green gills they were in a perfectly healthy state, that they contained very 

 little copper, and that some iron was present in the pigment. In all that 

 they were perfectly correct ; but that does not prove that the pale green 

 American oyster {0. virginica) is also in a healthy state, and that its green 

 ■colour is due to iron and not copper. If there is one thing more than 

 another which this investigation has taught us, it is caution in drawing 

 general conclusions from what is found in one oyster or one brand of 

 oysters. At an early period of the investigation we were inclined to agree 

 with some previous investigators that copper, though present in small 

 quantity in all oysters, had nothing to do with the green colour ; but now 

 we have to definitely announce that we find copper in considerable quan- 

 tity in the green American oysters, that the copper reaction coincides 

 histologically with the green granular leucocytes, and that consequently 

 the copper may be regarded as the cause of the green colour. 



Professor Bizio records that he found (in 1835 to 1845) copper in 

 oysters at Venice ; and he suggests that the colour of the Marennes 

 oyster is due to a compound of copper. Subsequent work upon Marennes 

 oysters, in which little or no copper was found, may have seemed to throw 



' Brit. Assoc. Bep., 1896, p. 668 ; and Beport Lancasliire Sea-fsheries Laboratory 

 for 1895 and 1896. 



