272 LETTERS TO BROTHER JOHN. 



efficient agent by which all the living phenomena 

 are effected, it surely can require no great stretch 

 of faith to feel convinced at once, that if this agent 

 be allowed to dose at his post, infinite mischief must 

 ensue ; and that whatever is capable of keeping 

 its energies in constant activity, is of the very 

 highest value to the welfare of the system. And 

 further, that whatever circumstances such as, sloth, 

 and the other habits which I have enumerated as 

 conducive to a languid circulation whatever cir- 

 cumstances are calculated to lull its energies to 

 repose, are, in the highest degree, detrimental. 

 And the influence which bodily labour exercises 

 over the circulation, every body knows ; it is felt in 

 every pulse of the body. Besides, the heart is a 

 muscle, similar in its nature to the muscles of the 

 arm or leg. Exercise, therefore, has the same 

 influence in strengthening the heart (and, of course, 

 through it, the circulation) as it has in strength- 

 ening the muscles of the leg or arm: and most 

 men are well acquainted with its influence in this 

 respect. 



But there is yet another view of the subject, 

 which I shall now open to you. 



You know that our relation to external things is 

 established by virtue of the sensibility of our 



