Chap. XII] GENERAL CIRCULATION OF BLOOD 215 



tion. The purpose of the pulmonary circulation is to carry the 

 blood which has been through the system, giving up oxygen and 

 collecting carbon dioxide, to the air sacs of the lungs, where the 



Pulmonary artery. 



Superior ca\a or vein 

 from head and necl<. 



Right auricle. 

 Inferior vena cava- 



Right ventricle. - 



Portal circulation. 



Second renal circu- 

 lation. 



Pulmonary capillaries. 



Pulmonarj' veins. 



Aorta. 



Arteries to head and 

 neck. 



Left auricle. 

 Left ventricle. 



Gastric and intostinal 

 vessels. 



;.7— ...First renal circulation. 



Systemic capillaries. 



Fig. 137. — Diagram of the Circulation. (Halliburton.) 



red corpuscles are recharged with oxygen, and the carbon dioxide 

 is feduced to a standard amount. 



The systemic circulation. — The more extensive circulation, 

 from the left ventricle to all parts of the body, and the return to 

 the right auricle, is known as the systemic circulation. The pur- 

 pose of the systemic circulation is to carry oxygen and nutritive 

 substances to all parts of the body, and gather up waste products. 



This double circulation, pulmonary and systemic, is constantly 

 and simultaneously going on, as each half of the heart is in a literal 

 sense a force pump. The contraction of both ventricles drives a 

 certain quantity of blood, probably amounting to six ounces, with 

 great force into both the aorta and pulmonary artery. 



Factors governing circulation. — The perfect circulation of the 

 blood is dependent upon certain factors, the chief of which are : 

 (1) the heart-beat, (2) the elasticity and extensibility of the arterial 

 walls, (3) the position and direction of the valves, (4) the large 



