CHAPTER XVIII 



CIRCULATION AND RESPIRATION 



374. The Circulation of the Blood. Just as the work 

 of Newton is the foundation of modern Physics, and 

 as Lavoisier's explanation of burning was the beginning 

 of modern Chemistry, so Harvey's discovery that the 

 blood circulates through the body was the starting point 

 of modern Physiology. Harvey, an English physician, 

 made his discovery about 1616. The blood has several 

 very important functions. The food that is digested in 

 the alimentary canal must be carried to the individual 

 cells all over the body (cf. 369); the blood carries it. 

 The oxygen that is taken into the body at the lungs must 

 also be taken to the cells; so the blood has the power of 

 carrying oxygen. The cells in the exposed parts of the 

 body (those near the skin, for example) must be kept 

 warm, so that the protoplasm can continue its work; 

 hence the blood is a carrier of heat, and keeps up the 

 body's temperature. The reaction between the food and 

 oxygen, which takes place at the cells, gives energy, but 

 it also produces waste materials (cf. 366 and 371). 

 These must not accumulate, or they will poison the body. 

 Hence the blood serves as the great sewer into which the 

 wastes of the cells are discharged. 



A system carrying liquids through the body needs a 

 pump, or heart. The other organs of circulation are the 

 arteries, veins, and capillaries. There are also spaces 



372 



