208 THE HUMAN BODY. 



aorta, and the other with the pulmonary artery, and in its 

 circuit the blood returns to the heart twice. Leaving the 

 left side it returns to the right, and leaving the right it 

 returns to the left; and there is no road for it from one 

 side of the heart to the other except through a capillary 

 network. Moreover, it always leaves from a ventricle 

 through an artery, and returns to an auricle through a 

 vein. 



There is then really only one circulation; but it is not 

 uncommon to speak of two, the flow from the left side of 

 the heart to the right through most of the body being 

 called the systemic or greater circulation, and from the 

 right to the left through the lungs the pulmonary or lesser 

 circulation. But since, after completing either of these 

 alone, the blood is not again at the point from which it 

 started, but is separated from it by the septum of the 

 heart, neither is a "circulation" in the proper sense of the 

 word, for a circulation implies that any object at the end 

 of its course is again exactly where it was at the com- 

 mencement. 



The Portal Circulation, A certain portion of the blood 

 . which leaves the left ventricle of the heart through the 

 aorta has to pass through three sets of capillaries before it 

 can again return there. This is the portion which goes 

 through the stomach and intestines. After traversing the 

 capillaries of those organs it is collected into the portal 



Through what does blood always leave the heart? To what does 

 it return? How many circulations are there really? What is meant 

 by the systemic circulation? What by the pulmonary? Why is 

 neither a true " circulation" in the proper sense of the word? 



How many sets of capillaries does some blood pass through in a 

 complete circulation? What portion of the blood is it? What vessel 

 does it enter after traversing the capillaries of the stomach and in- 

 testines? 



