52 CIRCULATION OF THE BLOOD 



blood gushes forth from a severed artery by spurts. 

 These spurts take place at the moment when the ventricle 

 contracts, not when it expands. 



5. The auricles can be shown to have somewhat 

 the same relation to the ventricles that the ventricles 

 have to the arteries. In the dying heart of an animal, 

 the ventricles cease beating before the auricles. If 

 the tips of the ventricles are removed so as to expose 

 their cavities, then each beat of the auricles will be 

 seen to be followed by a corresponding spurt of blood 

 from the opened cavity of the ventricles. In other 

 words, at each beat or contraction of the auricle, blood 

 is driven into the corresponding ventricle. 



6. In the intact heart the contraction of the auricles 

 is followed by that of the ventricles. The same blood, 

 therefore, that is driven into the ventricles by the con- 

 traction of the auricles is subsequently driven into the 

 arteries by the contraction of the ventricles. 



7. Once the blood has entered one of the great arteries 

 -whether the aorta or the pulmonary artery it cannot 



return along the path by which it came. Its movement 

 in that direction is absolutely stopped by valves. This, 

 as we have seen, had been successfully demonstrated by 

 previous investigators and notably by Leonardo. 



8. But Harvey introduces a new point in connection 

 with the conclusion of paragraph 7. He points out that 

 this process must be continuous. This leads him to a 

 very crucial discussion. Consider the capacity of the 

 heart. Let us suppose the ventricle holds but 2 ounces 

 of blood. The pulse beats 72 times a minute and 72 X 60 

 times an hour. In the course of one hour, therefore, the 

 left ventricle will throw into the aorta or the right ventricle 

 into the pulmonary artery no less than 72 X 60x2 =8640 

 ounces =38 stones 8 Ib. In other words, in one hour the 

 ventricle will throw into the great artery more than three 



