THE CIRCULATION OF THE BLOOD 



143 



which the blood may take 

 in flowing from the arte- 

 rial to the venous reser- 

 voir. The blood stream, 

 indeed, may be compared 

 with a stream supplying 

 water power to a series of 

 mills in a manufacturing 

 town. The larger arteries 

 from the main source of 

 pressure (the heart) cor- 

 respond to the headrace 

 from above the dam, while 

 the larger veins correspond 

 to the tailrace. The water 

 flows from the one into 

 the other only through the 

 smaller sluices, or pen- 

 stocks, which supply the 

 mills. So in the vascular 

 system a part of the blood 

 pumped into the arterial 

 reservoir, or aorta, finds 

 its way into the venous 

 reservoir by way of the 

 skin, another part by way 

 of the digestive organs, 

 another by way of the 

 brain, still another by 

 way of the kidneys, and 

 so on ; but the flow in 

 every case is essentially 

 the same, namely from a 

 reservoir of high pressure 

 to one of lower pressure. 



FIG. 70. 



Diagram 



of the organs 



of the circulation 



L, pulmonary circulation; M, circulation 

 through the organs suspended by the mes- 

 entery, the blood being carried to the liver 

 P before it returns to the heart. The circu- 

 lation through other organs, such as brain, 

 muscles, skin, and kidneys, is indicated. 

 Lymphatics are represented by dotted lines 



