414 Growtk and -Decline of tie "Body. [Book IX* 



hue of middle life, and this into the wrinkled and 

 ihrunk appearance of old age. Similar changes are 

 taking place in other parts of the body, and the coats 

 of the arteries gradually becoming thicker and ftronger 

 with refpecl to thofe of the veins ; thefe latter become 

 more diftended, and the livid hue of venous plethora 

 fucceeds to the vivid tint of the arterious. A difpo- 

 fition to folidity invades the body in the progrefs of 

 life, and that which in the child was pliant cartilage^ 

 becomes in the old man brittle bone. 



The quantity of earth in the compofition of the dif- 

 ferent parts of the body is continually increafing ; the 

 mufcles become infenfible to the ufual ftimuli j the vi- 

 gour of the circulation is diminimed; and in the few, 

 the very few, who efcape the numerous pitfalls of dif- 

 eafe and accident, this rigidity and infenfibility increaf- 

 ing, neceflari-ly puts an end to exiftence. 



That modern difcoveries, or the improvement of 

 the medical art, mould be able to protract for any 

 confiderable period our mortal exiftence, is a notion 

 that will only be entertained by thofe who are ignorant 

 of the phyfiology of the animal frame, and indeed of 

 every other branch of fcience. It is the natural confe- 

 quence of extenfive knowledge to abate our confidence ; 

 while impudence, dogmatifm, and vain and vifionary 

 peculation, are the genuine offspring of ignorance. 

 Medical ikill may indeed be fuccefsfully applied in oc- 

 cafionally arrefting the progrefs of thole difeafes, which 

 might otherwife prematurely interrupt our mortal ca- 

 reer j yet even in thefe inflances, thofe who have 

 ftudied moft, and practifed moft, will be the moft fen- 

 fible of the impotence of human knowledge in this 

 important art j but he who is at all acquainted with 

 the delicate and fragile texture of the human -frame 



muft 



