16 



OYSTERS AND DISEASE. 



account of the greenness of the Marennes oysters as being correct. Carazzi, in his 

 recent paper, makes a great point of the contents of Lankester's " secretion cells " 

 (" Beckerzellen ") of the branchiae being always colourless, and he speaks of the error 

 into which Lankester, Chatin, and others have fallen in considering these large globular 

 cells to be sometimes loaded up with green granules. In this Carazzi is undoubtedly 

 wrong. Although in ordinary colourless oysters the " secretion cells " are clear and 

 colourless, in most green-gilled oysters (those of the Roach River in England, and some 

 Dutch, as well as the Marennes) we find them to be distinctly green (PI. IV., Figs. 3, 

 4) ; and we are able to support Lankester in his views as to the origin of the colour, 

 which Carazzi has attempted to demolish. 



Carazzi says that an occasional green appearance in the secretion cells may be 

 due to an optical illusion, the green of the neighbouring epithelium appearing by 

 refraction to be in the large clear cell. We only mention this in order to state that 

 we have provided against any such optical illusion. We have seen the green colour 

 of the secretion cells quite distinctly, not only in surface views and in sections, but also 

 in the isolated cells, in teased preparations of the living tissue. We have been able to 

 show them in this condition to several of our colleagues, and all have agreed that the 

 green colour, although of course faint in single cells, is quite distinct. Even when the 

 neighbouring epithelium is slightly green, as it sometimes is, we are unable to admit 

 that the large secretion cells do not contain green granules. We have not only isolated 

 the cells, but in teased fresh preparations have isolated the large green granules ; and 

 after disorganizing these by pressure, have seen the green substance of the granules 

 collecting again to form green globules. There can be no doubt from our preparations 

 that the green colour is in the large granular cells. 



Our experience of the Marennes oysters is that the green colouration is disposed 

 as follows: — All over both surfaces of the four gills; on the ribbed or grooved adjacent 

 (adoral) surfaces of the four labial palps— that is, on the posterior faces of the anterior, 

 and the anterior faces of the posterior palps (the other sides of the palps are very 

 faintly coloured, if at all) ; occasionally the oesophagus to some extent (this is not at 

 all constant) ; more frequently the rectum (but sometimes a brown rectum is found in 

 a green-gilled oyster) ; the loop of intestine that coils around the stomach ; and, lastly, 

 the liver, to some extent. 



When a piece of the gill in the living state is put under the microscope, the 

 large green " macroblasts " are clearly visible. They are often arranged in longitudinal 

 rows — parallel to the long axis of the filaments — packed closely together (PI. IV., 

 Fig- 3) i sometimes they are a little spaced out, about their own diameter apart ; in 

 some places there are two rows on each filament in place of one, while in others they 

 seem scattered quite irregularly. These cells give an eosinophilous reaction. In a 

 previous paragraph (page 9) we have discussed the various forms of eosinophilous 

 cells, and have shown that the regular grouping of these cells tends to indicate that 



