[13] CAUSE OF THE GREENING OF OYSTERS. 805 



Taking- a survey of the lower groups of the vegetable world, which 

 coutain bluish-green pigments, and which are at the same time free- 

 swimming in their habits, so as to place them within reach of the sta- 

 tionary oyster as food, there is none which actually seems more likely 

 to be the source of the green tinge here discussed than tlie Diatomacem. 

 And as there is no other class of forms so commonly and constantly 

 met with in the alimentary canals of marine mollusks generally, I think 

 we might take it for granted, for this reason alone, that they are the 

 source of tbe coloration. In fact, it is rarely that I have met with any 

 other vegetable organisms in the stomachs of oysters except diatoms, 

 after having examined hundreds, by the excellent method of first re- 

 moving the recently- swallowed contents of the gastric cavity with a 

 pipette thrust into the mouth and through the short gullet. The " bill 

 of fare" of the animal can then be very deliberately studied under the 

 microscope after the contents of the pipette have been pressed out upon 

 and prepared for observation under a compressorium. This method 

 was also independently adopted by M. Certes in the course of his in- 

 vestigations upon the commensal fauna of the oyster, which led to the 

 discovery of the remarkable organism which he has called Trypanosoma 

 Balbianii, and which is almost as invariably present in the alimentary 

 canal of the oyster as the frustules of diatomaceous plants. While the 

 fact that diatoms impart a green tinge to oysters, which have been 

 erroneously supposed to be hurtful in that condition when consumed as 

 food, it is also very i^robably true that in the case of the common Mya 

 arenaria, the flesh of which is said to occasionally acquire a greenish 

 tint, the coloration is in like manner derived from the same source, viz, 

 the diatomaceous plants. 



