MOLLUSCA. 147 



evident at the present day that this substance 

 derived from uric acid is identical with the purple 

 of the ancients. Dr. Sacc has used it as a dye very 

 recently, and obtained tolerably good results ; and 

 Dr. Schlumberger has endeavoured to prove that the 

 varied hues of parrots, humming-birds, pheasants, 

 etc., are owed in great measure to murexide. At the 

 present time, large quantities of murexide have been 

 obtained from guano, which contains much uric acid, 

 for the purpose of dyeing. It is a splendid sub- 

 stance when pure, presenting in one direction beau- 

 tiful metallic green reflections, and in others brown 

 and purple tints. 



But to this we must add, that, up to the present 

 time, no rigorous chemical experiments have been 

 made with the purple colouring matter extracted 

 from sea snails, and the curious manner in which it 

 is developed under the influence of the sun's rays 

 seems to indicate that it is really distinct from 

 murexide, however much the latter may re- 

 semble it. 



Many snails are sought for and bred as articles 

 of food or medicine. Among the terrestrial species, 

 Helix pomatia, or the Apple snail (Fig. 14), known 

 in France as the Grand escargot, is cultivated to a 

 considerable extent, and is eaten, principally during 

 Lent, in France, Belgium, Germany, and other 

 parts of Europe. Indeed, the taste for this animal 



