CIRCULATION. 139 



either narrow or obliterate, like sphincters, the months of the veins at the out- 

 set of the systole, and that these fibres thus take the place of valves. If the 

 closure be complete, all the blood ejected by the systole mustenter the ventricle, 

 and a momentary standstill of blood and rise of pressure in the vein- just with- 

 out the auricle must accompany its brief systole. A recent observer believes 

 the flow into the auricle to be interrupted even more than once during its cycle. 1 

 If the venous openings be not closed but only narrowed during the systole 

 of the auricles, the transfer of all or most of the ejected blood to the ventricle 

 must depend upon the pressure being lower therein than at the venous openings. 

 A slight regurgitation into the veins would, like the complete closing of their 

 mouths, cause a momentary checking of their blood-flow just without the auri- 

 cle, and a slight rise of pressure. Such a checking of the flow has in some 

 cases been observed and ascribed to regurgitation. 2 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 lowuess 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. 92) 

 to depend upou 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 ha- also 

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

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

 rhythmic fluctuations; in other words, that the pulse undergoes extinction :it 

 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 heat, in the elas- 

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

 of such changes; and that, therefore, the character- 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 sudden 



1 W. T. Porter : op. cil., p. 534. 



* Francois-Franck : "Variations de la viteeae du Bang dana !«'s veines sous ['influence 

 de la svstole de l'oreillette droite," Archives <!•■ physiologie normale >t pathologique, 1890, \>. •">!:. 



