74 



ACTION OF THE HEART. 



dilates, and most -of the blood that has accumulated in the 

 auricle simply falls into the ventricle. The dilating ventricle 

 exerts a slight suction, so the blood is in part drawn into the 

 ventricle. During the remainder of the pause the blood accu- 

 mulates in the auricle and ventricle till the auricle again con- 

 tracts, and the cycle is repeated. 



Auricle 



Fig. 23. Diagram of the Heart, Showing the Action of the Values. 



The time taken by the different parts of the heart-beat, as 

 near as can be measured, are about as follows : 



Since the heart beats seventy-one or seventy-two times each 

 minute, each beat takes about eight-tenths of a second (.8) ; of 

 these eight-tenths the auricle takes for its contraction one- 

 eighth of the time ; that is, one-tenth of a second (.1) ; the con- 

 traction of the ventricle occupies three-eighths of the time, or 

 three-tenths of a second (.3), while the pause fills the rest of 

 the time ; that is, four-eighths, or one-half, of the whole time 

 of the entire heart-beat, or four-tenths of a second (.4). Let 

 us call the time required for the complete heart-beat the 

 heart's day. Of course this day is very short, less than a 

 second. If we suppose it to be twenty-four hours, we can 



