432 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the finger of one hand upon the common carotid artery, and that of the other 

 upon the dorsal artery of the foot at the instep, he will perceive that the pulse 

 corresponding to a given heart-beat occurs later in the foot than in the neck. 

 This phenomenon is readily comprehended by considering that room for the 

 " pulse-volume " injected by the heart is made in the root of the arterial system 

 botlTby local expansion and by a more rapid displacement of blood into the 

 next arterial segment. This next segment, in turn, accommodates its increased 

 charge by local expansion and by a more rapid displacement ; and this same 

 process involves segment after segment in succession, onward toward the 

 capillaries. The expansion of the arterial system, then, is a progressive one, 

 and, as the phrase is, spreads as a wave from the aorta onward to the arteri- 

 oles. The rate of transmission of the "pulse-wave" from a point near the 

 heart to one remote from it, may be calculated. This is done by comparing 

 the time which elapses between the occurrence of the up-stroke of the pulse 

 in the nearer and in the farther artery with the distance along the arterial 

 system which separates the two points of observation. In one case, for exam- 

 ple, that of an adult, the absolute amount of the postponement of the pulse 

 that is, the time required for the transmission of the pulse-wave from the 

 heart itself to the arteria dorsalis pedis, was 0.193 second. 1 The time of 

 transmission of the pulse-wave from the heart to the dorsalis pedis is often 

 longer than in this case, amounting to 0.2 second or a little more. If we 

 reckon the duration of the ventricular systole at about 0.3 second, it is evi- 

 dent that the fact of the postponement of the pulse in the arteries distant from 

 the heart does not invalidate the general statement that the arterial pulse is 

 synchronous with the systole of the ventricles. 



The general estimates of the rate, as opposed to the absolute time, of trans- 

 mission of the pulse-wave vary, in different cases, from more than 3 meters 

 to more than 9 meters per second. As the blood in the arteries does not pass 

 onward at a swifter rate than about 0.5 meter per second, it is clear that the 

 wave of expansion moves along the artery many times faster than the blood 

 does ; and that to confound the travelling of the wave with the travelling of 

 the blood would be a very serious error, easily avoided by bearing in mind 

 the causes of the pulse-wave as already given. 



Investigation by the Finger. The feeling of the pulse has been a valu- 

 able and constantly used means of diagnosis since ancient times. Indeed, the 

 ancient medicine attached to it more importance than does the practice of 

 to-day. But it is still advisable to warn the beginner that he may not look 

 to the pulse for " pathognomonic " information; that is to say, he may not 

 expect to diagnosticate a disease solely by touching an artery of the patient 

 under examination. The pulse is most commonly felt in the radial artery, 

 which is convenient, superficial, and well supported against an examining 

 finger by the underlying bone. Many other arteries, however, may be util- 

 ized. 



Frequency and Regularity. The most conspicuous qualities of the pulse 

 1 J. N. Czerraak : Oesammelte Schriften, 1879, Bd. i. Abth. 2, p. 711. 



