CIRCULATION. 431 



cases been observed and ascribed to regurgitation. 1 A systolic narrowing with- 

 out closure of the venous mouths would leave room also for the view already 

 given, that so far is regurgitation from taking place, that even during the sys- 

 tole of the auricles blood enters them incessantly, and the venous flow is never 

 checked. In this case the systole of the auricle would still empty it partially 

 into the ventricle, owing to the lowness of the pressure there. 



The time has not arrived for a decision as to all these questions, which are 

 surrounded by practical difficulties ; but fortunately they do not throw doubt 

 upon the functions of the auricle -as a reservoir and pump which may be 

 swiftly filled, and may swiftly complete the filling of the ventricle which it 

 adjoins. 



O. THE ARTERIAL PULSE. 



Nature and Importance. The expression " arterial pulse " -is restricted 

 commonly to those incessant fluctuations of the arterial pressure which corre- 

 spond with the incessant beatings of the ventricles of the heart. These rhyth- 

 mic fluctuations of the arterial pressure have been explained already (p. 385) 

 to depend upon the rhythmic intermittent injections of blood from the ven- 

 tricles ; upon the resistance to these injections produced by the friction within 

 the blood-vessels ; and upon the elasticity of the arterial walls. It has also 

 been explained that the interaction of these three factors is such that the blood, 

 in traversing the capillaries, comes to exert a continuous pressure, free from 

 jjiythmic fluctuations ; in other words, that the pulse undergoes extinction at 

 the confines of the arterial system. It is at once apparent that the pulse may 

 be affected by an abnormal change, either in the heart's beat, in the elas- 

 ticity of the arteries, or in the peripheral resistance, or by a combination 

 of such changes ; and that, therefore, the characters of the pulse possess 

 an importance in medical diagnosis which justifies a brief further discus- 

 sion of them. 



A pulsating- artery not only expands, but is lengthened. The suddeu 

 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 

 of 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 

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

 larger surface of contact. 



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



1 Francois- Franck : "Variations de la vitesse du sang dans les veines sous 1'influence 

 de la systole de 1'oreillette droite," Archives de physiologic normale et pathologique, 1890, p. 347. 



