286 THE VITAL FUNCTIONS. 



the arteries are, in most places, so connected 

 witli 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 consider 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 winding 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 ve- 

 locity 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 this is when we come to very 

 large animals. The aorta of a whale is larger in 

 the bore than the main pipe of the water-works 



