CIRCULATION. 137 



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 

 lessens the contents of the auricle, and so prepares it to act as a storehouse 

 during the coming systole of the ventricle. The auricle, then, is an apparatus 

 for the maintenance of as even a flow as possible in the veins and for the rapid 

 and thorough charging of the ventricle. It is clear that, for both uses, the 

 auricle's function as a reservoir is certainly no less important than its function 

 as a force-pump. 



The value of a mechanism for the rapid filling of the ventricle increases 

 with the pulse-rate, and with a very frequent pulse must be of great import- 

 ance, because now time must be saved at the expense of the pause, with its 

 quiet flow of blood through the auricle into the ventricle ; and the auricular 

 systole must follow more promptly than before upon the opening of the cus- 

 pid valve. If the pulse double in frequency, each cardiac cycle must be com- 

 pleted in one-half the former time; but we have seen that the ventricle 

 requires for its systole a time which cannot be shortened with the cycle to the 

 same degree as can its diastole. Of heightened value now to the ventricle 

 will be the adjoining reservoir, which is filling while the cuspid valve remains 

 closed, and from which, as soon as that valve is opened, the necessary supply 

 not only flows, but is sucked and pumped into the ventricle, tor, when increased 

 demands are made upon the heart, the usefulness of an increased frequency of 

 beat disappears if the volume transferred at each beat from veins to arteries 

 diminish in the same proportion as the frequency increases. No increase of 

 the capillary stream can then follow the more frequent strokes of the pump. 1 



Negative Pressure within the Auricle ; its Probable Usefulness. — The 

 course of the pressure-curve of the auricle, as shown by the elastic manome- 

 ter, is too complex and variable, and its details are too much disputed, for it 

 to be given here. But certain facts regarding the auricular pressure are of 

 much interest in connection with the use of the auricle which has jus! been 

 discussed. Once, and perhaps oftener, in each cycle, the pressure in the auricle 

 may become negative, perhaps to the degree of from —2 to— 10 millimeters of 

 mercury even in the open chest,-' and of course becomes still more so when 



1 von Frey und Kivlil ; op. tit., p. 61. 



2 de Jager : op. eit., p. 507. W. T. Porter: op. cit., p. 533. 



