NATURAL HISTORY. 19 



" The man who consecrates his hours 

 By rigorous effort, a?id an honest aim, 

 At once he draws the sting of life and death." Youxo. 



is fVJows : If a piece of timber supported on two point*. 



bear a weight upon it, it sustains this weight by different qualities in 

 its different parts. For example, divide it into three equal parts, 

 A, B, ; ths uppsr p.irt, A, supports the weight by its solidity and 

 resistance to compression ; the lowest part, B, on the other hand, 

 resists by its toughness or adhesive quality. Between the portions 

 acting in so different a manner, there is an intermediate, neutral, or 

 central part, C, which may be taken away without materially weak- 

 ening the beam, which shows that a hollow cylinder is the form of 

 strength. 



48. How is it that the joints of the body undergo so much use 

 for many years without diminution of their action ? 



This durability is attributable to tho provision which is made for 

 preventing wear and tear, first, by the polish of the cartilaginous 

 surfaces ; secondly, by the healing lubrication of the mucilage, and 

 in part to that astonishing property of animal constitutions, assimi- 

 lation, by which in every portion of the body, let it consist of what 

 it may, substance is restored and waste repaired. 



49. The union of joints even where no motion is intended or required, carries 

 narks of mechanism and mechanical wisdom. The teeth, especially the front teeth, 

 are one hone fixed in another, like a peg driven into a board. The sutures of th 

 skull are like the edges of two saws clapped together in such a manner as 

 jhat the teeth of one enter the intervals of the other. We have sometimes onebonp 

 Lipping over another, and planed down at the edges ; sometimes, also, the tliir. 

 lamella of one bone re-curved into a narrow furrow of another. In all of whn-h 

 varieties we discover the same design ; namely, firmness of jiuulion w uhout 

 'umsiness o. *cam. 



