278 LETTERS TO BROTHER JOHN. 



As we breathe for the purpose of oxidizing the 

 black blood, then the oftener we are compelled to 

 breathe, the better ; because every time we breathe, 

 a portion of black blood becomes oxidized, and tit 

 for use. The increased rapidity of breathing con- 

 sequent upon exertion is an increased rapidity in 

 the function of oxidizing the blood, one of the 

 most important of all the living actions. 



Besides all this, every time the blood has com- 

 pleted its circle of circulation, a part of the great 

 office of nutrition has been accomplished. The more 

 rapidly the blood, therefore, is, by natural means, 

 circulated through the body, the more rapidly does 

 the process of nutrition go on. 



You may compare the living actions to the 

 actions of a hand-cornmill, the heart representing 

 the first wheel, which puts into motion all the other 

 wheels : and bodily exertion may represent the man 

 who turns the crank attached to the first wheel. 

 Now, the more rapidly the man turns the crank, the 

 more rapid will be the motion of the first, second, 

 third, and all the other wheels; and the more ra- 

 pidly will the corn be ground. At the same time, 

 if the crank be turned with inconsiderate fury, the 

 machinery may be deranged, and the mill broken. 

 So, bodily exertion is not to be furious. A horse 



