THE CIRCULATION. 



287 



to Carpenter, the pulse of the foetus, before birth, is about 140, and 

 that of the newly-born infant 130. During the first, second, and 

 third years it gradually falls to 100; by the fourteenth year to 80; 

 and is reduced to the adult standard by the twenty-first year. At 

 every age, mental excitement may produce a temporary acceleration, 

 varying in degree with the peculiarities of the individual. 



As a rule, the rapidity of the heart's action is in inverse ratio to its 

 force. A slow pulse, within physiological limits, is usually a strong 

 one, and a rapid pulse comparatively feeble. This is especially notice- 

 able in the lower animals, when the force of the heart's action is 

 experimentally measured by the arterial impulse ; an increased fre- 

 quency of the cardiac pulsations being almost invariably accompanied 

 by a diminution in their strength. The same is true in disturbance 

 of the heart's action from morbid causes ; the pulse in febrile or other 

 debilitating affections becoming weaker as it grows more rapid. An 

 excessive rapidity of the pulse is an indication of great danger, and, 

 in the adult male, a continued rate of 160 per minute is almost inva- 

 riably a fatal symptom. 



Increased Curvature of the Arteries in Pulsation. In the disten- 

 sion of the arteries under the force of the ventricular systole, these 

 vessels are elongated as well as widened ; and especially in those 

 having a distinctly curvilinear or serpentine course, an elongation and 

 consequent increase of curvature is observable at each pulsation. This 

 may be seen in emaciated persons, in the temporal 

 artery, or in the radial at the wrist, and is very 

 marked in the mesenteric arteries in the abdomen of 

 a quadruped. A superficial artery, running orer a 

 bony surface, may be partially lifted out of its bed 

 from this cause, at each pulsation. In old persons 

 the arterial curvatures become permanently enlarged 

 from frequent distension ; and all the smaller arteries 

 tend to assume, with the advance of age, a more ser- 

 pentine course. 



Characters 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 one finger be placed 

 upon the chest over the heart's apex, and another Elongatiou and in _ 

 over the carotid artery at the middle of the neck, 

 little or no difference in time is perceptible be- 

 tween the two impulses ; the distension of the caro- 

 tid being sensibly simultaneous with the heart's contraction. But if 

 the second finger be placed on the temporal artery, its impulse is felt 

 to be a little later than that of the hsart. The pulse of the radial 

 artery at the wrist is also later than that of the carotid, and that of the 

 posterior tibial at the ankle later than that of the radial. The greater 

 the distance from the heart, the later is the pulsation of the artery. 



creased curvature 

 of an ARTERY IN 

 PULSATION. 



