THE CIRCULATION. 



235 



Auricular diastole is about 0.64 seconds, hence its time is 

 longer than that of a systole of the auricle. It has been found by 

 Einthoven and Geluk by the most accurate measurements in fifteen 

 human hearts that ventricular systole may take 0.312 to 0.346 

 seconds, whilst diastole may be 0.385 to 0.518 seconds. If the fre- 

 quency of the heart is greater the time taken by each revolution is 

 shorter, but the diminution is mainly in the diastole, when the heart 

 rests and recovers its systolic power. Whatever may be the rate of 

 the heart-beat, the auricular and ventricular systoles do not vary 

 much, but in a rapidly acting heart the pause is short, in a slow 

 beating heart it is long. 



The diastole of all the four cavities of the heart is longer than 

 their systole, and it is about a half second from the end of the con- 

 traction of the ventricles to the commencement of the contraction 

 of the auricles, a period of cardiac rest. It has been estimated that 

 the human heart works about nine hours and rests .about fifteen 

 hours in a day. 



The rhythmical succession of these acts constitutes the cardiac 

 revolution. By their function the vital fluid the blood is kept 

 in constant circulation within the body so that every portion of the 

 economy receives its proper nourishment. The processes of metabo- 

 lism are balanced, the various organs and glands of the body per- 

 form their needed functions, and the whole animal lives and thrives. 



The events in a cardiac revolution can be tabulated as fol- 

 lows : 



1st period. 



Auricular systole. 

 Accomplishment of ven- 

 tricular diastole. 



2d period. 



Ventricular systole. 



Closure of mitral and 

 tricuspid valves. 



Opening of semilunar 

 valves. 



The blood is thrown in- 

 to the aortic and pul- 

 monary arteries. 



Cardiac impulse. 



Diastole of the arteries 

 and the pulse. 



Auricular diastole. 



3rd period. 



General diastole of the 

 heart. 



Closure of semilunar 

 valves. 



The blood pours into 

 the auricles, and a 

 little into the ventri- 

 cles. 



To physiologists, the first period in the movement of the heart 

 coincides with contraction of the auricles. The clinicians take the 

 first period at the moment of ventricular systole. 



