VENOUS AND PULMONARY CIRCULATION. 115 



it is the same with the feet and legs after long-continued 

 standing, and varicose veins appear on the limbs of persons 

 whose profession obliges them to remain on their feet. 



In following the course of the blood on its return to the 

 heart, we mid a venous system belonging to the liver and 

 intestines; the portal system to which reference has already 

 been made which carries the venous blood from the diges- 

 tive canal and from the spleen to the liver. This system is 

 remarkable from the fact that it is ramified at both ex- 

 tremities; at the intestinal extremity the radicles or roots, 

 and at the hepatic the branches, are found. From this it has 

 been inferred that the bile is secreted from the blood of the 

 portal vein and not from the blood of the hepatic artery; but 

 this question still remains unsettled. 



The inferior vena cava, after receiving the blood from the 

 lower regions of the body, turns toward the heart like the 

 superior vena cava, but before reaching it, the blood receives 

 by the subclavian veins the lymph and chyle which have 

 been brought to it by the two grand trunks of the lymphatic 

 system; the elements of nutrition drawn from the intestine 

 come to replace those which have just been given up for 

 assimilation. Thus partially reconstituted, the blood pours 

 back through the venae cavae into the right auricle of the 

 heart, and the auricle by contracting throws it into the right 

 ventricle. 



At last the blood has returned to the heart, and although 

 it is enriched by the assimilable products of digestion, it is 

 still incomplete, and must be transformed in order to become 

 perfect arterial blood, while at the same time the combustion 

 of a portion of its principles will produce the heat which is 

 soon to be distributed to the organism. It is in the lungs 

 that this elaboration of the blood is to take place hematosis 

 or sanguification. 



Pulmonary circulation. The right ventricle contracts, and 

 the flood of venous blood closes the tricuspid valve, and 

 passes into the pulmonary artery. This artery and all its 

 ramifications contain black or venous blood, while the pul- 

 monary veins, as we shall soon see, convey red or arterial 

 blood ; it is therefore to their direction, from the heart to the 



