56 HUMAN PHYSIOLOGY 



CHAPTER IV 



THB STORY OP THE HEART 



THE CIRCULATION. In order that the nourishment 

 obtained from the food should be duly placed at the 

 service of every organ, tissue, and cell of the body, 

 it must be duly circulated through the frame. This 

 function we find accordingly to be performed 

 through the medium of the heart as a central 

 pumping engine, and by the bloodvessels or tubes 

 which are directly or indirectly in communication 

 with the heart itself. The blood, as the common 

 currency of the body, must find its way to every 

 nook and corner of the system, and we shall note 

 that a very perfect mode of distribution of the 

 nutrient fluid is secured by the arrangements to be 

 presently described as existing in the shape of the 

 heart and bloodvessels. It is of importance to note 

 in the first instance that it is a "circulation" of 

 blood we are dealing with, and not a mere flow. The 

 difference between these two things is obvious. If 

 we stand on the banks of a river and watch the 

 water passing us, we note that the water will not 

 return again, but will flow to the sea or lake in which 

 the river ends. Circulation, on the other hand, 

 implies a return of that which is circulated to the 

 starting-point, or at least includes a journey or cycle 

 which tends in a sense to repeat itself. In the case 

 of the distribution of blood through the body, the 

 idea of a circulation is really represented; for if we 



