58 



HUMAN PHYSIOLOGY 



in order that the results of the bodily wear and tear 

 with which it has become encumbered should be 

 duly excreted. 



THE COURSE OF THE CIRCULATION. The course 

 followed by the blood in its circulation may be ap- 

 propriately described at the present stage of our en- 

 quiries. Pure blood, returned from the lungs, enters 

 the left auricle (Fig. 14) of the heart, which is the 

 smaller and upper chamber of that side, the auricle 

 acting as a receiver of the blood. 

 From the auricle the blood 

 passes directly to the left ven- 

 tricle, this last being the pumping 

 chamber, and by the contrac- 

 tions of this cavity of the heart 

 blood is sent throughout the 

 whole body conveyed by the 

 arteries. Becoming impure in 

 the body the blood is returned 

 to the right auricle of the heart, 

 whence it passes to the right 

 ventricle, which in turn sends 

 it to the lungs for purification. 

 From the lungs the purified 

 blood passes to the left auricle, 

 and once more resumes its 

 circulatory journey. In connec- 

 tion with the circulation we have 

 to note the bloodvessels or tubes 

 which are employed to distribute blood through the 

 body. 



ABOUT THE BLOODVESSELS. The arteries (Fig. 14) 

 are bloodvessels which are in direct communication 

 with the left side of the heart, and into them the 

 left ventricle is perpetually pumping pure blood for 



Fig. 14. DIAGRAM OF 



THE COURSE OF THE 



CIRCULATION 



Impure blood is repre- 

 sented by the black 

 tint. 



