GO HISTORY OF 



different capacities during the different stages 

 of life. In infancy they are capacious, and the 

 blood flows almost as freely through the bones as 

 through any other part of the body ; in manhood 

 their size is greatly diminished, the vessels are 

 almost imperceptible, and the circulation through 

 them is proportionably slow. But in the decline 

 of life, the blood, which flows through the bones, 

 no longer contributing to their growth, must ne- 

 cessarily serve to increase their hardness. The 

 channels that every-where run through the hu- 

 man frame, may be compared to those pipes that 

 we every-where see crusted on the inside, by the 

 water for a long continuance running through 

 them. Both every day grow less and less, by the 

 small rigid particles which are deposited within 

 them. Thus, as the vessels are by degrees dimi- 

 nished, the juices also, which were necessary for 

 the circulation through them, are diminished in 

 proportion ; till at length, in old age, those props 

 of the human frame are not only more solid, but 

 more brittle. 



The cartilages, or gristles, which may be con- 

 sidered as bones beginning to be formed, grow 

 also more rigid. The juices circulating through 

 them, for there is a circulation through all parts 

 of the body, every day contributes to render 

 them harder ; so that these substances, which in 

 youth are elastic and pliant, in age become hard 

 and bony. As these cartilages are generally 

 placed near the joints, the motion of the joints 

 also must, of consequence, become more difficult. 



