THE EVENTS OF THE HUMAN CARDIAC CYCLE 103 



or in that which it is claimed occurs subsequent to the S.C. 

 closure. 



During the systole of the ventricle, the auricular pressure falls 

 and the blood pours into that chamber. There is no exit for the 

 stream and the reservoir must gradually fill. If the systolic 

 plateau is prolonged or the filling is rapid, it is reasonable to expect 

 that the pressure in the auricle will rise, for any influences, other 

 than the passive one, which tend to dilate the auricle, must of 

 necessity be diminishing during the last phases of ventricular 

 systole. When in a venous or auricular curve, there is a rise 

 which can but be attributed to events occurring before the ter- 

 mination of systole, it is rational to attribute it to this auricular 

 filling and to a stasis wave passing back into the veins. As yet 

 no curves indicative of the changing velocities in the large veins 

 have been obtained. 



The second possible factor in the production of the " v " 

 wave, namely, the upward spring of the auriculo-ventricular 

 junction at the beginning of diastole, must be dealt with at greater 

 length. 



The direction of movement of the different parts of the heart 

 wall has been for many years the subject of contention, and there 

 is accumulated evidence that the earlier observations, in which the 

 heart was exposed, were fallacious. The experiments which chiefly 

 concern us are those of Briicke ( 5 ) and Haycraft ( 21 ). The method 

 employed was the same in each case, and is in all probability a 

 very accurate one. Needles were used, and the chest wall and 

 heart muscle was transfixed. The needles carried light straw 

 levers from the movements of which the excursion of the heart 

 wall could be observed. As a result it was shown that in systole 

 the apex is the only fixed point of the musculature, and that all 

 other parts tend to move towards the mid-line and apex. The 

 auriculo-ventricular line is considered by most authorities to have 

 a decided downward movement in systole, and a corresponding 

 upward fling in diastole. Keith, who regards the mouths of the 

 great vessels as other fixed points, has recently laid much stress 

 on this movement of the A-V line. According to this author, 

 whose researches are in the main anatomical, the systole of the 

 ventricle causes expansion of the auricle, and diastole of the ven- 

 tricle its collapse. The auricle is opened like a concertina, and 

 the upward movement of the A-V line in diastole is said to pro- 



