ABOUT OYSTER-CULTURE. 257 



the " green matter " of Priestley, which may be detected 

 in all water exposed to the action of light. 



Some authorities have sought for the cause in the con- 

 fervce and relvce which multiply so rapidly in those " parks" 

 where the supply of water is not frequently renewed ; 

 others think that the colouring principle belongs to the soil. 



The most likely explanation seems to be that which M. 

 Coste, the distinguished pisciculturist, has put forward. 

 He is of opinion that the green oyster owes its peculiar 

 tint and characteristic flavour to a " disease of the liver." 

 Such is also the belief of M. Valenciennes; according to 

 whom, the immediate cause of the discoloration is a 

 peculiar animal substance, due to a particular condition 

 of the oyster. 



The largely increased demand for this favourite mol- 

 lusc, and the gradual exhaustion of many of the best 

 oyster-banks, have led to the adoption of artificial means 

 of increasing the supply. 



The art, or science, of oyster- culture was introduced, 

 as we have seen, by a wealthy Roman, named Sergius 

 Grata, who in his time was famed for his epicurean 

 tastes, and attained the curious title of " master of 

 luxury." He was something more, however, than a 

 gourmand, for Cicero speaks of him as " ditissimus, 

 anio3nissimus, deliciosissimus." It is said of him that 

 he patriotically asserted the superiority of the shell-fish 

 bred in the Lucrine Lake ; though, under the empire, 

 they were less valued than those imported from Britain. 

 He owed his surname, Grata, or Aurata, either to his 

 fondness for gold-fish (Auratce pisces), or to his habit of 

 wearing two very large gold rings. 



