ANIMALS. 59 



loads than assists it. This is formed from fat, 

 which generally, at the age of thirty-five or forty, 

 covers all the muscles, and interrupts their acti- 

 vity. Every action is then performed with greater 

 labour, and the increase of size only serves as a 

 forerunner of decay. 



The bones also become every day more solid. 

 In the embryo they are as soft almost as the mus- 

 cles and the flesh ; but by degrees they harden, 

 and acquire their natural vigour ; but still, how- 

 ever, the circulation is carried on through them ; 

 and how hard soever the bones may seem, yet the 

 blood holds its current through them as through 

 all other parts of the body. Of this we may be 

 convinced by an experiment, which was first acci- 

 dentally discovered by our ingenious countryman 

 M. 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 evi- 

 dent demonstration that the juices 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 confor- 

 mity to their manner of living. From all this 

 he naturally concluded, 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 fur- 

 nished through all their substance with their pro- 

 per canals. Nevertheless, these canals are of very 



