428 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



without help from the auricles, in unloading the latter and the veins, that the 

 auricles recommence their beats. 1 



On the other hand, it is clear that the auricle is not without importance as 

 a force-pump for completing the filling of the ventricle, even if it can be dis- 

 pensed with for a time. In curves of the blood-pressure during asphyxia taken 

 simultaneously from the auricle and the ventricle, there may be noted the influ- 

 ence exerted upon the ventricular curve by ineffectiveness of the auricular sys- 

 tole. It is found that, in this case, that slight but accelerated rise of pressure 

 may fail which normally just precedes, and merges itself in, the large swift rise 

 of the ventricular systole. It is found, too, that, under these circumstances, 

 the total height of this systolic rise may be diminished. 2 We shall see pres- 

 ently how, when the pulse becomes very frequent, the importance of the auric- 

 ular systole may be increased. We have seen already (p. 424) that normally it 

 may probably effect the closure of the cuspid valves. 



Time-relations of the Auricular Systole and Diastole. The auricular 

 systole is not only weak, but brief, being commonly reckoned at about 0.1 of a 

 second (see p. 416). If this be correct for man, at the average pulse-rate of 

 72 the auricular systole would comprise only about one-eighth of the cycle; 

 would be only one-seventh as long as the auricular diastole ; and only about 

 one-third as long as the ventricular systole which immediately follows that of 

 the auricle. 



The Auricle a Mechanism for Facilitating the Venous Flow and 

 for the " Quick-charging " of the Ventricle. Further points in regard to 

 the systole of the auricles can best be treated of incidentally to the general 

 question, What is the principal use of this portion of the heart ? The answer 

 is not so obvious as in the case of the ventricles. It may, however, be stated 

 as follows : The auricle is a reservoir, lying at the very door of the ventricle. 

 That door, the cuspid valve, remains shut during the relatively long and un- 

 varying period of the ventricular systole and the brief succeeding period of fall- 

 ing pressure within the ventricle. These periods coincide with the earlier part 

 of the auricular diastole. During all this time the forces which cause the 

 venous flow are delivering blood into the flaccid and distensible reservoir of 

 the auricle, and can thus maintain a continuous flow. But the blood of which 

 the veins are thus relieved during the period of closure of the cuspid valve, 

 accumulates just above that valve to await its opening. When it is opened 

 by the superior auricular pressure, the stored-up blood both flows and is drawn 

 into the ventricle promptly from the adjoining reservoir. From this time 

 on, auricle and ventricle together are converted into a common storehouse for 

 the returning blood during the remainder of the repose of the whole heart, 

 which coincides with the later portion of the long auricular diastole. The 

 next auricular systole completes the charging of the ventricle ; and a second 

 use of this systole now becomes apparent, for the sudden transfer by it of 

 blood from auricle to ventricle not only completes the filling of the latter, but 



1 von Frey und Krehl : op. cit., pp. 49, 59. G. Colin : Traite de physiologic comparee des ani- 

 maux, Paris. 1888, vol. ii. p. 424. 2 von Frey und Krehl : op. cit., p. 59. 



