CIRCULATION. 429 



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, for, 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 just 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, 2 and of course becomes still more so when 

 the latter is intact, sinking in this case to perhaps 11.2 millimeters. 3 What 

 is striking in connection with the " quick-charging " of the ventricle is that 

 the greatest and longest negative pressure in the auricle coincides, as we should 

 expect, with the earlier part of its diastole, and therefore with the systole of 

 the ventricle, when the auricle is cut off from it by the shut valve. 4 By 

 this suction within the auricle the flow from the veins into it probably is 

 heightened, and the store of blood increased which accumulates in the reservoir 

 to await the opening of the valve. The quick-charging mechanism itself is 

 quickly charged. Nor should it be forgotten that the work of the ventricle 

 contributes in some degree to this suction within the auricle. The heart is 

 air-tight in the chest, which is a more or less rigid case. At each ventricular 



1 von Frey und Krehl: op. cit., p. 61. 



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



3 Goltz und Gaule : op. cit., p. 109. 



4 von Frey und Krehl, op. cit., p. 53. Porter, op. cit., p. 52a 



