224 Mv. A. W. E. O'Sliauglincssy on Green Oysters. 



for which he proposed the name of Vibrio ostrearius. These 

 creatures he described as gelatinous, linear in shape, pointed at 

 the extremities, rounded in the middle, being also contractile in 

 that part, and charged with a quantity of green fluid. He says 

 that they inhabit the water of the tanks or " parks ^^ in which 

 the oysters are preserved, in such immense abundance at certain 

 periods of the year that they can only be compared to the 

 grains of dust which rise in clouds and obscure the air in dusty 

 weather. 



In a resume of his observations on this subject which he con- 

 tributed to the ^Journal de Physique,' tome xci. (1820) p. 222, 

 he observes that the change of colour takes place only in the 

 " parks " or reservoirs of salt water, where the oysters are kept 

 on being brought from the sea. These "parks," which are about 

 4 feet in depth, 200 to 250 feet in length by about 50 feet in 

 breadth, are capable of containing from 500,000 to 600,000 

 oysters : such are those of Marennes, Oleron, Courseulles, Caen, 

 Havre, Dieppe, Treport, &c. At certain seasons of the year, 

 particularly from April to June, and again in September, the 

 water becomes, in some of these reservoirs, of a dark-green tint; 

 even the small stones at the bottom of the tanks are covered 

 with small green points or excrescences. Then, says M. Gaillon, 

 the oysters which are destined to assume the same colour are 

 placed, with great care, one by one, and side by side, in order 

 that none may rest upon any of the others, and the supply of 

 fresh currents of water is suspended for a longer or shorter 

 period, according to the required intensity of the green. 



M. Gaillon rejects the supposition that the change of colour 

 is the result of disease, on the ground that, having compared 

 the green oysters with those of the normal tint, he found all the 

 organs quite as healthy in the former as in the latter. 



To the opinion which has often been entertained, that the 

 green colour is due to the numerous minute particles of marine 

 plants which either themselves form the food of the oyster or 

 communicate their colour to the water absorbed by it, he objects 

 that the plants which most commonly find their way into the 

 reservoirs are the Ulva compressa and the Conferva littoralis, 

 which are known to turn yellow with age, and which, if mace- 

 rated and left for several days in jars of salt or even fresh water, 

 will not communicate the least tint of green to the fluid, whereas 

 both the mouth and stomach of the oyster are totally unfitted 

 for such food as Ulvre or Confervse, 



By the aid of the microscope, M. Gaillon discovered that the 

 little green excrescences with which the stones at the bottom of 

 the tank were constantly studded were nothing more than a 

 heap of the tiny animalcules which filled the water in myriads. 



