140 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



increase in the contents of an artery which causes the pulse therein, is accom- 

 modated not merely by the increase of calibre which produces the " up-stroke " 

 of the arterial wall against the finger, but also by an increase in the length 

 df the elastic vessel. If the artery be sinuous in its course, this increase in 

 length suddenly exaggerates the curves of the vessel, and thus produces a 

 slight wriggling movement. This is sometimes very clearly visible in the 

 temporal arteries of emaciated persons. On the other hand, the increase in 

 the calibre of the artery is relatively so slight that it is invisible at the profile 

 even of a large artery, dissected clean for a short distance for the purpose of 

 tying it. Such a vessel appears pulseless to the eye, although its pulse is 

 easilv felt by the finger, which slightly flattens the artery and thus gains a 

 larger surface (if contact. 



Transmission of the Pulse. — If an observer feel his own pulse, placing 

 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 

 both by 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 !) meters per second. As the blood in the arteries does not pass 

 onward at a -witter 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 t<> confound the travelling of the wave with the travelling of 

 1 J. N. Czermak: Gcsamm.Uc Schrifim, 1S79, Bd. i. Abth. 2, 8. 711. 



