FURNITURE, AND ITS USES. 231 



An adult, generally, has from twenty to 

 twenty-five of these inspirations in a minute, 

 as I have already observed. When we exer- 

 cise violently, as in running, the motion is 

 more rapid. So it is in childhood, and some- 

 times in a fever. When the lungs move faster, 

 the heart beats faster too, in the same propor- 

 tion ; the breathing and the contractions of the 

 heart always bearing an exact proportion to 

 each other. 



Now what is the object of all this motion ? 

 For what purpose is a pint of air drawn into 

 the lungs, and spread over fifteen square feet 

 of internal surface, every three seconds, and 

 another pint withdrawn from them as often ? 

 This I can, in part, tell you. 



USES OF BREATHING. In its healthy natu- 

 ral state, before it is sent out into all parts of 

 the body, the blood is composed of carbon, 

 oxygen, nitrogen and hydrogen. Of one hun- 

 dred parts of blood, fifty-three are carbon, 

 twenty-four oxygen, sixteen nitrogen, and 

 seven hydrogen. 



But when it has been circulated all over the 

 body, and has returned through the veins to 



