96 OYSTERS, AND ALL ABOUT THEM. 



thrown out mostly as carbonate, on meeting nascent carbonic acid at 

 the secreting cells. Lime salts, of whatever form, are deposited only 

 in vitally inactive tissues, such as bone matrix, chitin, or tissues that 

 have undergone degeneration. Although the tissue be dead, depo- 

 sition may go on." 



Liebig says : "The quantity of calcareous matter, from which the 

 continued and immense construction of shell is derived, appears to be 

 infinitesimally small sea water containing I2 * 40 o of its weight of carbo- 

 nate of lime, this being the principal ingredient of molluscous shells." 



