LETTERS TO BROTHER JOHN. 199 



him on matters connected with his own profession ; 

 because you are no judge therein you have no 

 means of knowing whether he answers you wisely or 

 foolishly: but talk to him on matters of general 

 learning and philosophy on subjects with which 

 you are yourself acquainted : you will thus easily 

 fathom the depth of his understanding : and you may 

 be quite sure, if he shew that he possesses a mind 

 capable of reasoning on the principles of science in 

 general, that he cannot be ignorant of that parti- 

 cular science which he has made his especial study. 

 For the practice of medicine is not an art, but a 

 science : it cannot be learned by rule or by rote, 

 as bricklayers learn to lay bricks, or a tallow- 

 chandler to make candles. In the treatment of 

 almost every disease, there is much to which no 

 rule will apply; and the correct or incorrect manage- 

 ment of which must entirely depend upon the phi- 

 losophical powers and general reasoning capabi- 

 lities of the mind of the practitioner who has the 

 treatment of the case under his care. 



But in that state of the body, that generally 

 enfeebled condition of health, of which I have been 

 speaking, every man must be his own physician : 

 for its cure or prevention must depend upon the 

 will of the sufferer upon the manner and habits of 



