CIRCULATION 



383 



blood returning to the heart. At the same time, the waste 

 materials added to the blood by the tissues are partly got 

 rid of by some of the blood being sent through the liver and 

 kidneys {Liv. and Kid.). 



The blood is then poured back through the veins into a 

 subsidiary pump — the pulmonic heart (P.H.) — ^by which it is 

 pumped through the lungs, there to obtain a fresh supply 

 of oxygen, and to get rid of the carbon dioxide excreted 

 into it by the tissues. Finally the blood, with its fresh 

 supply of oxygen from the lungs, and of nourishing sub- 



OZ 



LUNG 



CAf 



Art. 



Fig. 162.— Scheme of the Circulation. S.H., systemic heart sending blood 

 to the capillaries in the tissues, Caj). The blood brought back by 

 veins, and the exuded lymph by lymphatics, Ly., passing through 

 glands ; blood sent to the alimentary canal, Al.C, and from that to 

 the liver, Liv. ; blood also sent to the kidneys, Kid. ; the blood before 

 again being sent to the body is passed through the lungs by the 

 pulmonic heart, P.H. 



stances from the alimentary canal, is poured into the great 

 systemic pump — the left side of the heart — again to be 

 distributed to the tissues. 



Thus the circulation is arranged so that the blood, 

 exhausted of its nourishing material by the tissues, is 

 replenished in the body before being again supplied to the 

 tissues. 



The sectional area of the vascular system varies 

 enormously. The aorta leaving the heart has a compara- 

 tively small channel. If all the arteries of the size of the 

 radial were cut across and put together, their sectional area 



