260 THE VITAL FUNCTIONS. 



That we may form an adequate conception of the 

 immense power of the ventricle, or prime mover in 

 the circulation of the blood, we have but to reflect 

 on the numerous obstacles impeding its passage 

 through the arterial system. There is, first, the 

 natural elasticity of the coats of the arteries, which 

 must be overcome before any blood can enter them. 

 Secondly, the arteries are, in most places, so con- 

 nected with many heavy parts of the body, that 

 their dilatation cannot be effected without, at the 

 same time, communicating motion to them. Thus, 

 when we sit cross-legged, the pulsation of the artery 

 in the ham, which is pressed upon the knee of the 

 other leg, is sufficiently strong to raise the whole 

 leg and foot, at each beat of the pulse. If we con- 

 sider the great weight of the leg, and reflect upon 

 the length of the lever by which that weight acts, 

 we shall be convinced of the prodigious force which 

 is actually exerted by the current of blood in the 

 artery in thus raising the whole limb. Thirdly, 

 the w^inding course, which the blood is forced to 

 take, in following all the oblique and serpentine 

 flexures of the arteries, must greatly impede its 

 motion. But notwithstanding these numerous and 

 powerful impediments, the force of the heart is so 

 great, that, in defiance of all obstacles or causes of 

 retardation, it drives the blood with immense velo- 

 city into the aorta. The ventricle of the human 

 heart does not contain more than an ounce of blood, 

 and it contracts at least seventy times in a minute; 

 so that above three hundred pounds of blood are 

 passing through this organ during every hour that 

 we live. " Consider," says Paley, " what an affair 



