ANIMALS. 



173 



The bones, also, become every day more 

 solid. In the embryo they are as soft almost 

 as the muscles of the flesh ; but by degrees 

 they harden, and acquire their natural vigour; 

 but still, however, the circulation is carried 

 on through them, and, how hard soever the 

 bones may seem, yet the blood holds its cur- 

 rent through them, as through all other parts 

 of the body. Of this we may he convinced, 

 by an experiment, which was first accidental- 

 ly discovered by our ingenious countryman 

 Mr. Belcher. Perceiving at a friend's house, 

 that the bones of hogs, which were fed upon 

 madder, were red, he tried it upon various 

 animals by mixing this root with their usual 

 food ; and he found that it tinctured the bones 

 in all ; an evident demonstration that the jui- 

 ces of the body had a circulation through the 

 bones. He fed some animals alternately 

 upon madder and their common food, for some 

 time, and he found their bones tinctured with 

 alternate layers, in conformity to their man- 

 ner of living. From all this he naturally con- 

 cluded, that the blood circulated through the 

 bones, as it does through every other part of 

 the body; and that, how solid soever they 

 seemed, yet, like the softest parts, they were 

 furnished through all their substance, with 

 their proper canals. Nevertheless, these ca- 

 nals are of very 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 ;. their vessels are almost 

 imperceptible; and the circulation through 

 them is proportionably slow. But, in the de- 

 cline of life, the blood which flows through 

 the bones, no longer contributing to their 

 growth, must necessarily serve to increase 

 their hardness. The channels that every 

 where run through the human 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 de- 

 grees diminished, 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 

 considered 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 contribute 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 mo- 

 tion of the joints also must, of consequence, be- 

 come more difficult. Thus, in old age, every 

 action of the body is performed with labour ; 

 and the cartilages, formerly so supple, will now 

 sooner break than bend. 



" As the cartilages acquire hardness, and un- 

 fit the joints for motion, so also that mucous li- 

 quor, which is always separated between the 

 joints, and which serves, like oil to a hinge, to 

 give them an easy and ready play, is now 

 grown more scanty. It becomes thicker, and 

 more clammy, more unfit for answering the 

 purposes of motion ; and from thence, in old 

 age, every joint is not only stiff, but awkward. 

 At every motion this clammy liquor is heard 

 to crack ; and it is not without the greatest 

 effort of the muscles that its resistance is over- 

 come. I have seen an old person, who never 

 moved a single joint, that did not thus give no- 

 tice of the violence done to it." 



The membranes that cover the bones, the 

 joints, and the rest of the body, become, as we 

 grow old, more dense and more dry. Those 

 which surround the bones, soon cease to be 

 ductile. The fibres, of which the muscles or 

 flesh is composed, become every day more ri- 

 gid ; and while to the touch the body seems, 

 as we advance in years, to grow softer, it is, 

 in reality increasing in hardness. It is the 

 skin, and not the flesh, that we feel upon'such 

 occasions. The fat, and the flabbiness of that, 

 seems to give an appearance of softness, which 

 the flesh itself is very far from having. There 

 are few can doubt this, after trying the differ- 

 ence between the flesh of young and old ani- 

 mals. The first is soft and tender, the last is 

 hard and dry. 



The skin is the only part of the body that 

 age does not contribute to harden. That 

 stretches to every degree of tension ; and we 

 have horrid instances of its pliancy, in many 

 disorders incident to humanity. * In youth 



21* 



