NATURAL THEOLOGY. 93 



the joints, viz. that here, the oil is not only dropped 

 but made." 



T. This is not the only superiority of the natural 

 contrivance. The more the joints are used, the more 

 abundantly is the oil supplied. It would be thought a 

 wonderful invention, if a wheel should be so made as 

 to supply more oil to the axis, in case the traveller 

 should see fit to accelerate his speed, or to take up a 

 companion. But this is done in our joints ; that is, 

 the lubricating fluid is poured out in increased quan- 

 tities when the joint is in use, and in proportion to 

 its use. 



B. What an exquisite provision ! This will ac- 

 count for the uneasy sensation we experience in mov- 

 ing our limbs, after neglecting exercise for a consider- 

 able time. The oil is deficient. 



T. A trifling item in the catalogue of evils we 

 bring upon ourselves by indolent habits. Let me ask 

 you what mode of fastening a joint you should sup- 

 pose would be the most safe ? 



B. I know of none so firm as what mechanics al- 

 ways employ, — a bolt. 



T. So, it is probable, a mechanic would say ; but 

 an anatomist would tell him that this would not have 

 answered in the animal structure, and is never em- 

 ployed. A strong band of gristle about the heads of 

 the bones is the fastening made use of; and it forms 

 almost the only instance in which nature has departed 

 from our mechanical expedients. 



B. The advantage, I now perceive, is very plain, 

 though it did not occur to me. Had the joints been 



