OF THE ARTERIES. 285 



ford a passage to the blood, gradually shrinks, and ultimately 

 disappears more or less completely. 



420. The vital properties of the arteries, like those of the 

 other parts, are relative both to their own nutrition and to 

 their action in the organism. The force of formation is mani- 

 fest in them by their accidental productions, and less in the 

 reparation of their lessions. Irritability is susceptible to a 

 certain degree; sensibility is much less obvious. 



421. Arterial irritability,* called also tonicity, contractili- 

 ty, vital force of the arteries, power of contraction, or the 

 force by which the parietes of the arteries, during life, draw 

 towards its axis without even having distended, has been a 

 subject of great controversy among physiologists. 



Haller, who admits that the middle coat of arteries is of a 

 muscular nature, confesses that his experiments have taught 

 him nothing positive on their contractility, and that these 

 vessels have not always given evidence of the effects produced 

 on them by chemical and mechanical stimulants. Bichat, 

 Nysten, and Magendie, have all denied the irritability of the 

 arteries. Bichat founds his opinion on the circumstance, that 

 mechanical irritation within or without the vessel does not 

 produce motion; if an artery be open lengthwise, its edges 

 do not curl; if it be separated from the body, it evinces no 

 mark of contractility; if it be dissected layer by layer, its 

 fibres are not perceived to palpitate ; if the finger be intro- 

 duced into an artery during life, it is not firmly grasped by it; if 

 an artery be intercepted between two ligatures, it experiences 

 only a motion communicated to it. The contraction produced 

 by acids, is a horny induration, and the action of alkalies is 

 next to nothing. 



The greater number of anatomists and physiologists, how- 

 ever, are of a contrary opinion, founding it on a great number 

 of facts. Verschuir and Hastings have observed mechanical 



* See Chr. Kramp, de vi vitali arteriarum. Argent, 1785. C. H. Parry, 

 An exper. inquiry info the, puke and oilier prop, of arteries, &c. Bath, 1816. 

 Oh. H. Parry, Additional experi. on the arteries, &c. Lond. 1819. Hast- 

 ings, be. cit. 



