164 NATURAL THEOLOGY. 



dissection of a whale : " The aorta measured a 

 foot diameter. Ten or fifteen gallons of blood are 

 thrown out of the heart at a stroke with an im- 

 mense velocity, through a tube of a foot diameter. 

 The whole idea fills the mind with wonder."* 



The account which we have here stated of the 

 injection of blood into the arteries by the contrac- 

 tion, and of the corresponding reception of it 

 from the veins by the dilatation, of the cavities of 

 the heart, and of the circulation being thereby 

 maintained through the blood-vessels of the body, 

 is true, but imperfect. The heart performs this 

 office, but it is in conjunction with another of 

 equal curiosity and importance. It was necessary 

 that the blood should be successively brought 

 into contact, or contiguity, or proximity with the 

 air. I do not know that the chemical reason 

 upon which this necessity is founded, has been 

 yet sufficiently explored. It seems to be made 

 appear, that the atmosphere which we breathe is 

 a mixture of two kinds of air : one pure and vital, 

 the other, for the purposes of life, effete, foul, and 

 noxious f that when we have drawn in our breath 

 the blood in the lungs imbibes from the air thus 

 brought into contiguity with it a portion of its 



^ The atmosphere contains, in every 100 parts, of oxygen 21 

 parts ; nitrogen or azote, 79 parts ; carbonic acid gas, a fractional 

 part. 



♦ Dr. Hunter's Account of the Dissection of a whale— (Phil. 

 Trans.) 



