136 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



that the work of the heart may entirely suffice to maintain the circulation with- 

 out aid from any subsidiary source of energy. It must now he added that the 

 ventricles can, for a time, maintain the circulation without the aid of the auric- 

 ular systole — a clear proof that this systole is not a sine qua non for the 

 working of the cardiac pump. 



If in an animal, not only anaesthetized but so drugged that all its skeletal 

 muscles arc paralyzed, artificial respiration be established and the chest be 

 opened, the circulation continues. If the artificial respiration be suspended 

 for a time, the lungs collapse, asphyxia begins, and the blood accumulates 

 conspicuously in the veins and in the heart. Presently the muscular walls 

 of the auricles may become paralyzed by overdistention, and their systoles 

 may cease, while the ventricles continue at work and may maintain a circu- 

 lation, although of course an abnormal one. After the renewal of artificial 

 respiration, it may not be till several beats of the ventricles have succeeded, 

 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 ease, 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. 132) 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. 124). 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 Plow 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 

 i- not so obvious as in the ease 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- 



1 veil Frey unci Krehl: op. cit., pp. 49,59. G. Colin: Train' </< plni.<i<>l,>iiif rompurir rfrx ,mi- 

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



