172 LETTERS TO BROTHER JOHN. 



to discover the difference which distinguishes the 

 system of man from that of all others; and it is 

 indeed a momentous one ! It is this : that while all 

 the other systems of the universe are sustained and 

 governed by immutable laws, as gravitation, che- 

 mical affinity, instinct, &c. &c., the system of man 

 depends solely for support upon laws, the perfect 

 or imperfect fulfilment of which has been left de- 

 pendent on the capricious conduct of man himself. 

 For the laws which sustain the human system 

 are the laws of nutrition; and these are for ever 

 subject to disturbance by man's misconduct. For 

 instance: a man may voluntarily half starve him- 

 self or by his folly he may bring himself into a 

 position in which he is unable to procure sufficient 

 food or he may take greatly too much or he 

 may select for food such substances as are inca- 

 pable of being assimilated to his own structure 

 or he may annul the laws of nutrition entirely by 

 taking aliment of a poisonous quality. Now, it is 

 perfectly manifest, that under any of these circum- 

 stances the laws of nutrition must' be seriously 

 modified injuriously disturbed. And it is equally 

 clear, that these circumstances, in the instances 

 supposed, are the result of human conducf. The 

 systems of the lower animals are also sustained by 



