58 Physiology. 



blood out, the auricles are slowly filling by the steady 

 inflow through the veins. 



Systole and Diastole. The contraction of the heart is 

 called the systole, and its dilation is the diastole. 



Dilation of the Ventricle. As soon as the ventricle has 

 completed its contraction it dilates, and most of the blood 

 that has accumulated in the auricle simply falls into the 

 ventricle. The dilating ventricle makes a slight suction, 

 so the blood is in part drawn into the ventricle. During 

 the remainder of the pause the blood accumulates in the 

 ventricle and auricle till the auricle again contracts and 

 the action is repeated. This is true of both halves of the 

 heart, which work at the same time, the two auricles con- 

 tracting together, and then the two ventricles. The rjght 

 heart pumps dark blood while the left heart pumps bright 

 blood. The left ventricle is thicker walled and stronger 

 than the right. 



Work and Rest of the Heart Immediately after the 

 contraction of the auricle comes the contraction of the 

 ventricle. The pause is as long as the contractions of 

 the auricle and ventricle put together. In other words, 

 the heart is resting half the time. It is often said that the 

 heart never rests. Its periods of work and rest are so short 

 and follow each other in such rapid succession that it is 

 hard for us to realize that there is a resting time between 

 each two beats, and that this resting time is as long as the 

 working time. 



Overworking the Heart. During violent exercise the 

 heart is likely to be overworked trying to pump blood 

 enough to supply the overworked muscles. One very 

 important part of training an athlete is to strengthen the 



