ACTION OF THE HEART. 367 



heart. Moreover, the first sound was observed to be of exactly the same 

 character with the second (the complicating effect of the impulse being here 

 withdrawn), except as to its intensity, which was less, and its duration, 

 which was greater. 



486. Hence, although these observations do not entitle us to dehy the par- 

 ticipation of the muscular contraction, and of the movement of the blood over 

 the ventricular walls, in the production of the first sound, they establish (if 

 correct), that the principal cause of it exists at the entrances to the arterial 

 trunks ; and it does not seem that any other reason can be assigned for it than 

 the prolon^d rush of blood through their orifices, and the throwing back of 

 the SemiluMir valves ; which, in suddenly flapping down again, produce the 

 second sound. That an exaggeration of the first sound, not essentially differ- 

 ing from it in character, is often produced by disease of the sigmoid valves, 

 wMch causes an obstruction of their orifice, has long been known ; and in such 

 cases, the character of the second sound is also changed. Indeed, M. Cruveil- 

 hier states it as, in his opinion, an uniform occurrence, that disease of the 

 Semilunar valves alters both sounds. When this disease is such as to prevent 

 the valves from effectually closing, a reflux of blood takes place into the ven- 

 tricle at the time of its diastole ; causing a rushing sound, more or less pro- 

 longed, to be heard in the intervals of the pulse, instead of with it. These 

 considerations appear to prove almost incontestably, that the cause of the first 

 sound, and Hiat of the second, are very closely allied ; and this view, which if 

 correct, is of great importance in the explanation of numerous morbid phe- 

 nomena, harmonizes well with the known effect of a slight obstruction in a 

 tube, through which fluid is being rapidly forced, in producing a prolonged 

 sound, very analogous to the first sound of the heart. The following table may 

 assist the student in connecting the sounds of the Heart with its movements. 



FIRST SOUND. Ventricular Systole, and Auricular Diastole. Impulse 

 of apex against parietes of chest. Pulsation in arteries. 



SECOND SOUND. First stage of Ventricular Diastole. 



INTERVAL. Short repose ; then Auricular Systole, and second stage 



of Ventricular Diastole. 



487. The course of the circulating fluid through the Heart, and the action 

 of^ts different valves, will now be briefly described. The Venous blood, 

 which is returned by the ascending and descending Vena Cava, enters the 

 right Auricle during its diastole ; and, when it contracts, is forced between the 

 Tricuspid valves, into the Ventricle. The reflux of blood into the veins, during 

 the auricular systole, is prevented by the valves with which they are furnished ; 

 but these valves are so formed, as not to close accurately, especially when the 

 tubes are distended ; so that a small amount of reflux usually takes place, and 

 this is much increased when there is any obstruction to the pulmonary circu- 

 lation. Whilst the right Ventricle is contracting upon the blood that has 

 entered it, the carnese columns, which contract simultaneously with its proper 

 walls, put the chordae, tendinese upon the stretch ; and these draw the flaps of 

 the Tricuspid valve into the auriculo-ventricular axis. The blood then getting 

 behind them, and being compressed by the contraction of the ventricle, forces 

 the flaps together in such a manner as to close the orifice ; but they do not 

 fall suddenly against each other, as is the case with the semilunar valves, since 

 they are restrained by the chordse tendinese ; whence it is that no sound is 

 produced by their closure. The blood is expelled by the ventricular systole 

 into the Pulmonary Artery, which it distends, passing freely through the Semi- 

 lunar valves ; but as soon as the vis a tergo ceases, and reflux might take place 

 by the contraction of the arterial walls, the valves are filled out h| the back- 

 ward tendency of the blood, and completely check the return ofjlny portion 



