NATURAL THEOLOGY. 1G3 



This is a general account of the apparatus ; and 

 the simplest idea of its action is, that by each con- 

 traction a portion of blood is forced by a syringe 

 into the arteries ; and, at each dilatation, an equal 

 portion is received from the veins. This produces, 

 at each pulse, a motion, and change in the mass 

 of blood, to the amount of what the cavity contains, 

 which in a full-grown human heart I understand 

 is about an ounce, or two table-spoons full. How 

 quickly these changes succeed one another, and by 

 this succession how sufficient they are to support 

 a stream or circulation throughout the system, may 

 be understood by the following computation, abridg- 

 ed from Keill's Anatomy, p. 117, ed. 3: "Each 

 ventricle will at least contain one ounce of blood. 

 The heart contracts four thousand times in one 

 hour: from which it follows, that there pass through 

 the heart, every hour, four thousand ounces, or three 

 hundred and fifty pounds of blood. Now the whole 

 mass of blood is said to be about twenty-five pounds: 

 so that a quantity of blood, equal to the whole mass 

 of blood, passes through the heart fourteen times 

 in one hour, which is about once in every four 

 minutes." 



Consider 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 im- 

 petus and velocity, to the blood gushing from the 

 whale's heart. Hear Dr. Hunter's account of the 



