424 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



aortic curve. So, too, the rise of pressure within the auricle produced by its 

 systole may suddenly be succeeded by a fall, the beginning of which must mark 

 the closure of the cuspid valve, which closure thus may correspond with the 

 apex of the auricular curve. 



In Figure 108, ordinate 1 indicates the closing, and ordinate 4 the open- 

 ing, of the mitral valve. These two points were found by help of the dif- 

 ferential manometer. Ordinate 2 indicates the opening, and ordinate 3 the 

 closing, of the aortic valve. These two points were marked with the help 

 of the curve of aortic pressure, also shown in Figure 108, each ordinate of 

 which has the same number as the corresponding ordinate of the ventricular 

 curve. In the arterial curve, 2 marks the beginning of the systolic rise, 

 and 3 the beginning of the dicrotic wave, which latter point is treated by 

 the observer as closely corresponding to the closure of the aortic valve. In 

 Figure 109 each ordinate has the same number, and, as regards the valve- 

 play, the same significance, as in Figure 108. Ordinate 1 corresponds to the 

 apex of a peak in the auricular curve (not here given) which represents the 

 end of the auricular systole. Ordinate 2 corresponds to the beginning of the 

 systolic ascent in the aortic curve (not here given). Ordinate 3 was found 

 by comparing, by means of two elastic manometers, the simultaneous pressures 

 in the ventricle and the aorta. Ordinate 4 corresponds, on the auricular 

 pressure-curve, to a point which marks the beginning of a decline of pres- 

 sure believed by the observer to succeed the opening of the cuspid valve. 

 In both the figures given of the ventricular curve, and in such curves 

 in general, the points which mark the valve-play occur as follows : The 

 closure of the cuspid valve corresponds to a point, not far above the line 

 of atmospheric pressure, where the moderate upward sweep of the ventric- 

 ular curve takes on the steepness of the systolic ascent. The systole of the 

 auricle is of little force, and the blood injected by it into the distensible ven- 

 tricle raises the pressure there but little ; that little, however, is more than 

 the relaxing auricle presents, and the cuspid valve is closed. Somewhere on 

 the steep systolic ascent occurs the point corresponding to the rise of the ven- 

 tricular above the arterial pressure, and therefore to the opening of the semi- 

 lunar valve. But other forces beside the arterial pressure must be overcome 

 by the contracting muscle ; and the ventricular pressure mounts higher yet, 

 and either stays high for a while, producing the plateau, or, in a peaked curve, 

 at once descends. In either case, not long after the beginning of the sharp 

 descent, the point occurs at which the ventricular pressure falls below the arte- 

 rial, and the semilunar valve is closed. Beyond this point the curve continues 

 steeply downward, but it is not till a point is reached not far above, or possibly 

 even below, the atmospheric pressure that the pressure in the ventricle falls 

 below that in the auricle, and the cuspid valve is opened. 



The Period of Reception, the Period of Ejection, and the Two Periods 

 of Complete Closure of the Ventricle. During the whole of the period 

 when the cuspid valve is open, the pressure is lower in the ventricle than in 

 the artery ; the arterial valve is shut ; and blood is entering the ventricle. 



