DISCOURSE ON METHOD. 57 



that if the blood be withdrawn from any part, the 

 heat is likewise withdrawn by the same means ; and 

 although the heart were as hot as glowing iron, it 

 would not be capable of warming the feet and 

 hands as at present, unless it continually sent 

 thither new blood. We likewise perceive from this, 

 that the true use of respiration is to bring sufficient 

 fresh air into the lungs, to cause the blood which 

 flows into them from the right ventricle of the heart, 

 where it has been rarefied and, as it were, changed 

 into vapours, to become thick, and to convert it 

 anew into blood, before it flows into the left 

 cavity, without which process it would be unfit for 

 the nourishment of the fire that is there. This 

 receives confirmation from the circumstance, that it 

 is observed of animals destitute of lungs that they 

 have also but one cavity in the heart, and that in 

 children who cannot use them while in the womb, 

 there is a hole through which the blood flows from 

 the hollow vein into the left cavity of the heart, and 

 a tube through which it passes from the arterial 

 vein into the grand artery without passing through 

 the lung. In the next place, how could digestion be 

 carried on in the stomach unless the heart com- 

 municated heat to it through the arteries, and along 

 with this certain of the more fluid parts of the 

 blood, which assist in the dissolution of the food 

 that has been taken in? Is not also the operation 

 which converts the juice of food into blood easily 

 comprehended, when it is considered that it is dis- 

 tilled by passing and repassing through the heart 

 perhaps more than one or two hundred times in a 



