THE CIRCULATION OF THE BLOOD AND LYMPH 99 



influence on the rate, which is greater in the standing than in the 

 sitting posture, and greater in the latter than in the recumbent 

 position. And this is true even when muscular action is as far 

 as possible eliminated by fastening the person to a board. The 

 pulse is further affected by the respiratory movements, especially 

 when they are exaggerated in forced breathing, being accelerated 

 during each inspiration (p. 269). It is also increased by the 

 taking of food, and especially of alcoholic stimulants, by muscular 

 exercise, in fever and many other pathological conditions, and 

 by a high external temperature. A warm bath, for example, 

 causes a very distinct acceleration of the heart ; and Delaroche 

 found that in air at the temperature of 65 C. his pulse went up 

 to 160. A cold bath may depress the pulse-rate to 60, or even 

 less. During sleep it may fall to 50. It is greatly influenced by 

 psychical events, and that in the direction either of an increase 

 or a decrease. Finally, it ought to be remembered as of some 

 practical importance that the pulse-rate in women and children, 

 but particularly in the latter, is less steady than in men, and 

 more apt to be affected by trivial causes. And it is a good general 

 rule to let a short interval elapse after the finger is laid on the 

 artery before beginning to count the pulse, so that the acceleration 

 due to the agitation of the patient may have time to subside. 



Rate of Propagation of the Pulse-wave. When pulse- 

 tracings are taken simultaneously at two points of the arterial 

 system unequally distant from the heart, by two sphygmographs 

 whose writing-points move in the same vertical straight line, 

 it is found that the ascent of the curve begins later at the more 

 distant than at the nearer point. Since waves like the pulse- 

 wave travel with approximately the same velocity in different 

 parts of an elastic system like the arterial ' tree/ this ' delay ' 

 must be due to the difference in the length of the two paths. 

 The difference in length can be measured ; the time-value of 

 the ' delay ' can be deduced from the rate of movement of the 

 recording surface ; dividing the length by the time, we arrive 

 at the rate of propagation of the pulse-wave. The average rate 

 has been found to be about 7 metres per second in man in the 

 arteries of the upper limb, and 8 metres in those of the lower 

 limb, the difference being due to the smaller distensibility of 

 the latter. In sleep the velocity diminishes almost a metre a 

 second. It increases in arterio-sclerosis, where the distensibility 

 of the arteries is diminished, and in chronic nephritis with hyper- 

 trophy of the heart, in which the blood-pressure is increased. 

 The mean velocity of the pulse-wave is about the same as the 

 speed of a moderately fast steamship (say, 17 miles an hour), 

 but less than that of a wave uf ;ther sea in y strong gale. , The 

 velocity of the pulse-wave mus*t net- be confounded with- tha\- 



72 



