CHAPTER V 

 THE CIRCULATION 



A CARRIER must move. To enable the blood to carry food 

 and oxygen to the cells and waste materials from the cells, 

 and also to distribute heat, it is necessary to keep it mov- 

 ing, or circulating, in all parts of the body. So closely 

 related to the welfare of the body is the circulation 1 of the 

 blood, that its stoppage for only a brief interval of time 

 results in death. 



Discovery of the Circulation. The discovery of the circulation of 

 the blood was made about 1616 by an English physician named Harvey. 

 In 1619 he announced it in his public lectures and in 1628 he published 

 a treatise in Latin on the circulation. The chief arguments advanced 

 in support of his views were the presence of valves in the heart and 

 veins, the continuous movement of the blood in the same direction 

 through the blood vessels, and the fact that the blood comes from a cut 

 artery in jets, or spurts, that correspond to the contractions of the heart. 



No other single discovery with reference to the human body has 

 proved of such great importance. A knowledge of the nature and pur- 

 pose of the circulation was the necessary first step in understand- 

 ing the plan of the body and the method of maintaining life, and 

 physiology as a science dates from the time of Harvey's discovery. 



Organs of Circulation. The organs of circulation, or 

 blood vessels, are of four -kinds, named the heart, the 

 arteries, the capillaries, and the veins. They serve as con- 



1 The term " circulation " literally means moving in a circle. While the blood 

 does not move through the body in a circle, the term is justified by the fact that 

 the blood flows out continually from a single 'point, the heart, and to this point is 

 continually returning. 



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