332 



THE CIRCULATION. 



Elongation and 

 increased curvature 

 of an ARTERY IN 

 PULSATION. 



Fir. 110. becoming enlarged in every direction. Especially 



in arteries having a distinctly curved or serpen- 

 tine course, this elongation and increase of curva- 

 ture may be observed at the time of each pulsa- 

 tion. It is perceptible, for instance, in emaciated 

 persons, in the temporal artery, or even in the ra- 

 dial at the wrist, and may readily be seen in the 

 mesenteric arteries in the abdomen of the living 

 animal. At every contraction of the heart, the 

 curves of the vessel on each side become more 

 strongly pronounced. In the case of the radial or 

 other artery, running over a bony surface, the vessel 

 may even partially rise out of its bed at each pulsa- 

 tion. In old persons the arterial curvatures become 

 permanently enlarged from frequent distension ; and 

 all the arteries tend to assume, with the advance of 

 age, a more serpentine and spiral course. 

 Time of the Arterial Pulse. The shock of an arterial pulsation, as 

 perceived by the finger, varies a little in time, according to its distance 

 from the centre of the circulation. If we place one finger upon the 

 chest over the apex of the heart, and another over the carotid artery at 

 the middle of the neck, we can distinguish little or no difference in time 

 between the two impulses ; the distension of the carotid being sensibly 

 simultaneous with the heart's contraction. But if the second finger be 

 placed upon the temporal artery, instead of the carotid, there is a per- 

 ceptible interval between the two beats. The impulse of the temporal 

 artery is felt to be a little later than that of the heart. The pulse of the 

 radial artery at the wrist also appears to be a little later than that of 

 the carotid, and that of the posterior tibial at the ankle joint a little 

 later than that of the radial. The greater the distance from the heart 

 at which the artery is examined, the later is the pulsation perceived by 

 the finger laid upon the vessel. 



But it has been conclusively shown that this difference in time of the 

 arterial pulsations, in different parts of the body, is rather relative than 

 absolute. The impulse is communicated at the same instant to all parts 

 of the arterial system ; but the apparent difference between them, in this 

 respect, depends upon the fact, that, although all the arteries begin to 

 be distended at the same moment, yet those nearest the heart are ex- 

 panded suddenly, while for those at a distance the distension takes place 

 more gradually. The impulse given to the finger marks the condition 

 of maximum distension of the vessel ; and this condition occurs at a 

 later period, according to the distance of the artery from the heart. 



The contraction of the left ventricle is a brisk and sudden motion. 

 The blood driven into the arterial system, meeting with a certain amount 

 of resistance from that already filling the vessels, does not instantly 

 displace a quantity equal to its own mass, but a certain proportion of 

 its force is used in expanding the distensible walls of the vessels. In 



