154 THE CIRCULATION. 



ing pulse, and its unnatural excess of the hard and 

 tense one. 



The elastic and muscular contraction of an artery may 

 also be regarded as fulfilling a natural purpose when, the 

 artery being cut, it first limits and then, in conjunction 

 with the coagulated fibrin, arrests the escape of blood. It 

 is only in consequence of such contraction and coagulation 

 that we are free from danger through even very slight 

 wounds ; for it is only when the artery is closed that the 

 processes for the more permanent and secure prevention of 

 bleeding are established. 



From what has been said in the preceding pages, it 

 appears that the office of the arteries in the circulation is, 

 ist, the conveyance and distribution of blood to the several 

 parts of the body ; 2nd, the equalization of the current, and 

 the conversion of the pulsatile jetting movement given to 

 the blood by the ventricles, into an uniform flow ; $rd, the 

 regulation of the supply of blood to each part, in accord- 

 ance with its demands. In explanation of the mode in 

 which, by the combination of the elastic and muscular 

 coats of arteries, this three-fold office is accomplished, we 

 may use, as a summary of what has been already said, 

 the words of Mr. Hunter, who observes that, "there are 

 three states in which an artery is found, viz., \st, the 

 natural pervious state ; 2nd, the stretched ; and $rd, the 

 contracted state, which may or may not be pervious. The 

 natural pervious state is that to which the elastic power 

 naturally brings a vessel which has been stretched beyond 

 or contracted within the extent which it held in a state of 

 rest. The stretched is that state produced by the impulse 

 of the blood in consequence of the contraction of the 

 heart; from which it is again brought back to the natural 

 state by the elastic power, perhaps assisted by the mus- 

 cular. The contracted state of an artery arises from the 

 action of the muscular power, and it is again restored to 

 the natural state by the elastic." 



