ACTION OF THE HEART. 97 



menced at that period in each action which immediately pre- 

 cedes the beat of the heart against the side of the chest, and, 

 by a very small interval more, precedes the pulse at the wrist. 

 For at this time the whole heart is in a passive state, the walls 

 of both auricles and ventricles are relaxed, and their cavities 

 are being dilated. The auricles are gradually filling with 

 blood flowing into them from the veins ; and a portion of this 

 blood passes at once through them into the ventricles, the 

 opening between the cavity of each auricle and that of its cor- 

 respond ing ventricle being, during all the pause, free and 

 patent. The auricles, however, receiving more blood than at 

 once passes through them to the ventricles, become, near the 

 end of the pause, fully distended ; then, in the end of the pause, 

 they contract and empty their contents into the ventricles. The 

 contraction of the auricles is sudden and very quick ; it com- 

 mences at the entrance of the great veins into them, and is 

 thence propagated towards the auriculo- ventricular opening ; 

 but the last part which contracts is the auricular appendix. 

 The effect of this contraction of the auricles is to propel nearly 

 the whole of their blood into the ventricles. The reflux of 

 blood into the great veins is resisted not only by the mass of 

 blood in the veins and the force with which it streams into the 

 auricles, but also by the simultaneous contraction of the mus- 

 cular coats with which the large veins are provided for some 

 distance before their entrance into the auricles ; a resistance 

 which, however, is not so complete but that a small quantity 

 of blood does regurgitate, i. e., flow backwards into the veins, 

 at each auricular contraction. The effect of this regurgitation 

 from the right auricle is limited by the valves at the junction 

 of the subclavian and internal jugular veins, beyond which the 

 blood cannot move backwards ; and the coronary vein, or vein 

 which brings back to the right auricle the blood which has 

 circulated in the substance of the heart, is preserved from it 

 by a valve at its mouth. 



The blood which is thus driven, by the contraction of the 

 auricles, into the corresponding ventricles, being added to that 

 which had already flowed into them during the heart's pause, 

 is sufficient to complete the dilatation or diastole of the ven- 

 tricles. Thus distended, they immediately contract : so im- 

 mediately, indeed, that their contraction, or systole, looks as 

 if it were continuous with that of the auricles. This has been 

 graphically described by Harvey in the following passage : 

 " These two motions, one of the ventricles, another of the au- 

 ricles, take place consecutively, but in such a manner that 

 there is a kind of harmony, or rhythm, present between them, 

 the two concurring in such wise that but one motion is appar- 



