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HUMAN PHYSIOLOGY 



the ventricle. At the close of the diastolic period the 

 ventricles as well as the auricles are moderately distended. 



TIM. 



FIG. 55. The heart cycle. The circumference of the circle is 

 divided into eight parts, each standing for 0.1 second. At (6) the heart 

 is in a passive state and swelling as it receives blood. Between (8) 

 and (1) the auricle thrusts on some blood to the ventricle which reaches 

 its maximum capacity at (1) (max.). Between (1) and (4) the ven- 

 tricle discharges to the arteries and is reduced to its minimum capacity 

 at (4). While the ventricle is emptying, the auricle is storing blood and 

 is large at (4). The diagram applies to either side of the heart. A.v.v. 

 stands for auriculo-ventricular valves, S'l.v. for semilunar valves. 



The first sign of contraction in the heart is noted in 

 the auricles. Careful observation has shown that there 



