

THE HEART. 171 



would of itself have the effect of closing the valves even were the aorta 

 a rigid tube. But the aorta is extensible and elastic and the effects of the 

 movement of the column of fluid are combined with the effects of the move- 

 ment of the arterial walls ; the elastic action of the arterial walls, in a 

 manner which we shall discuss later on in dealing with the pulse, also leads to 

 a reflux. It has been urged that the reflux due to the negative pressure of 

 the mere movement of the column of blood being more rapid, occurs 

 independently of and earlier than the reflux due to the elastic recoil, the 

 former closing the valves, the latter securing their complete closure. Be 

 this so or no the valves are probably closed almost immediately after the 

 escape of the ventricular contents, though observers are not agreed upon 

 this point, some urging that the valves are not closed until so late a period 

 as the point d, just as relaxation is about to begin. In the curves we 

 are now considering, a notch, followed by a rise, or at least a more or less 

 abrupt change in the course of the curve at c', is sometimes observed in that 

 part of the curve which intervenes between the first large rise and the final 

 sudden fall ; and this secondary rise has been taken to indicate the closure 

 of the semilunar valves. Sometimes two such notches and peaks are seen, 

 and the occurrence of the two has been attributed to a want of synchronism 

 in the closure of the pulmonary and aortic semilunar valves, the latter 

 closing some little time before the former. But it is by no means clear that 

 these notches and peaks are thus due to the closure of the valves ; they 

 may possibly have another origin, they are riot always present, and, indeed, 

 it does not seem certain that the closing of the valves should necessarily 

 make an impress on the ventricular curve. 



123. In the performance of the ventricle, then (and what has been said 

 of the left ventricle applies also to the right ventricle), there appear to be 

 four stages : 



1. A rapid "getting up" of pressure within the ventricle, all the 

 valves being as yet closed ; this continues until the pressure within the 

 ventricle, becoming greater than that in the aorta, throws open the aortic 

 valves. 



2. The escape of the contents of the ventricle into the aorta, the contrac- 

 tion of the ventricular walls still continuing. 



3. Further maintenance of the contraction for some little time after the 

 main body, at all events, of the contents have passed the aortic valves ; by 

 this the complete emptying of the ventricle seems assured. 



4. Sudden and rapid relaxation of the ventricular walls. 



These four events together make up a large portion, and in a quickly 

 beating heart the greater portion, of the whole cardiac cycle. 



Meanwhile, that is, during the time from b' to , blood has been flowing 

 from the great veins into the auricle; during the interval from b' to d none 

 of this can pass into the ventricle since this is still contracted, but with the 

 commencement of relaxation from d onward there is no longer any obstacle ; 

 on the contrary, as we shall see, an inducement for the blood to pass from 

 the auricle into the ventricle. 



For a brief time, as we have seen, there is probably an unbroken flow 

 from the great veins (pulmonary or venas cavse) through the anricle into the 

 ventricle, leading to a steady but slight increase of the front-to-back diam- 

 eter, to a slight pressure of the apex on the chest-wall, and to a slight 

 increase of intra-ventricular pressure, especially shown in the curve of the 

 slowly beating heart of the horse (Fig. 55). In Fig. 57 the sudden rise due 

 to the ventricular systole is preceded by a rise b followed by a fall, forming 

 thus, as it were, a shoulder on the curve. This has been interpreted as indi- 

 cating the sharp transient auricular systole ; the sudden injection of the 



