A N D D E A T H. 475 



to which they adhere ; and, by this means, both 

 the circumference of the bone, and the diameter 

 of its cavity, are augmented. Thus the interior 

 parts of the two perioflca continue fucceflively 

 to produce bony plates, in the fame manner as 

 woody plates are produced from the bark of 

 vegetables. 



But, after the bone has acquired its full 

 growth, after the perioftea ceafe to furnifh ofie- 

 ous matter, then the nutritious juices, which 

 were formerly employed in augmenting the 

 bulk of the bone, ferve only to increafe its den- 

 fity. Thefe juices are depofued in the inter- 

 nal parts of the bones, and give them more 

 weight and folidity, as may eafily be perceived 

 by comparing the weight and deniity of an ox 

 with thofe of a calf. The fubftance of the bones 

 become, in procefs of time, fo compad, as not 

 to admit the circulation of thofe juices which 

 are neceffary for their fupport and nourifhment. 

 This fubftance, therefore, muft now undergo a 

 change fimilar to that which takes place in old 

 trees, after they have acquired their full folidi- 

 ty ; and this change is one of the firft caufes 

 which render the diflblution of the human body 

 inevitable. 



The cartilages, which may be regarded as foft 

 and imperfc(ft bones, likewife receive nutritious 

 juices, which gradually augment their denfity. 

 They become more and more folid as we ad- 

 vance in years j and, in old age, they are almofl 



as 



