4 OYSTERS AND DISEASE. 



Ryder in America was also, in 1880, investigating the greening of oysters, with 

 much the same results as those of Puysegur. He went a step further, however, and showed 

 that the colouring matter was taken up by the amoeboid blood-cells, and that these 

 wandering cells containing the pigment were to be found in the heart, in some of the blood 

 vessels, and in aggregations in " cysts " under the surface epithelium of the body.* He 

 describes the colour (in the ventricle) as a " delicate pea-green," and states that it is not 

 chlorophyll or diatomine : he suggests that it may be phycocyanine or some allied sub- 

 stance. This is undoubtedly the same green in the leucocytes and the heart which we now 

 find to contain a salt of copper. 



In 1885, Ray Lankesterf gave a useful summary of some of the earlier papers, and 

 discussed the main questions concerned. Moreover, he investigated the gilis of the green 

 oyster histologically, and described and figured for the first time cells laden with green 

 granules which occur in the epithelium of the gills and labial palps. He showed that such 

 cells are also present in the common oyster, where, however, they are not green, and that 

 these or similar cells may be found also wandering over the surface of the gills. He 

 considered these as "secretion" cells, but those on the surface are clearly the same structures 

 which Ryder a few years before had found in the blood, and are therefore leucocytes. 

 Lankester found the Navicula in the intestine of the green oyster ; and he reasserted 

 that there was no copper and no iron in the diatom's refractory blue pigment — which 

 he described under the name " Marennin," and identified with the pigment of the large 

 green " secretion cells " of gills and labial palps. 



This explanation of the "greening" has since been confirmed by Joannes Chatin,J 

 who has also described more fully the histology of the large green granular cells of 

 the gills, which he called " macroblasts." He showed that in brown oysters these same 

 cells contain brown granules. 



Lankester's amoeboid cells, laden with green granules and moving over the surface of 

 the gill, are almost certainly leucocytes or amcebocytes which have wandered out from the 

 body through the surface epithelium : such diapedeses are probably of frequent occurrence 

 in the Mollusca. Pelseneer§ (1892) and De Bruyne|| (1895), in recent papers, consider 

 that these cells act as phagocytes — which is quite probable — and we understand that 

 LankesterU would now accept this view himself. Dr. D. Carazzi of Spezia, however, 

 who has recently (1896 and 1897) written several rather controversial papers on the 

 subject, will have none of this, and states that the diapedesis is entirely a pathological 

 phenomenon. He attributes the green colour to the cylindrical epithelium solely, and 

 not to the " secretion cells," or " macroblasts," and regards the Marennin as a nutrient 



* Ryder's papers are found scattered through the U.S. Fish Commission publications from 1882 onwards. 



t Quart. Journ. Micros. Sci., vol. XXVI., p. 71. 



X Comptes-rendus, CXVI., p. 264 (1S93); and CXX., p. 884(1895). 



§ Hull. Soc. Malacol. Belg., t. XXVII., p. lxii. || Arch, de Biologie, t. XIV., p. 161. 



U See Nature for 9th May, 1895, p. 28. Joannes Chatin, in a more recent no:e (Comptes-rendus, Feb. 24, 1S96) 

 adopts a modified view that the phagocytes arc connective-tissue corpuscles distinct both from the blood-cells (leucocytes) 

 and the fixed macroblasts. 



