FORCE OP THE HEART. 205 



teries, 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 dila- 

 tation cannot be effected without, at the same time, commu- 

 nicating motion to them. Thus, when we sit cross-legi^cd, 

 the pulsation of the artery in the ham, which is pressed upon 

 the knee of the other leg, is sufficiently strong to raise tlie 

 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 cur- 

 rent 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 not- 

 withstanding 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 

 velocity into the aorta. The ventricle of the human heart 

 does not contain more than an ounce of blood, and it con- 

 tracts 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 at London Bridge; and the water roaring 

 in its passage through that pipe is inferior in impetus and ve- 

 locity to the blood gushing through the whale's heart. An 

 anatomist who understood the structure of the heart, might 

 say before hand that it would play; but he would expect, 

 from the complexity of its mechanism, and the delicacy of 

 many of its parts, that it should always be liable to derange- 

 ment, or that it would soon work itself out. Yet shall this 

 wonderful machine go on night and day, for eighty years 

 together, at the rate of a hundred thousand strokes every 

 twenty-four hours, having at every stroke a great resistance 

 to overcome, and shall continue this action for this length 



