88 LETTERS TO BROTHER JOHN. 



injurious to your health; not from my dictum, but 

 from the simple exercise of your own reason. 



I beg that you will consider what I am about to 

 say on the subject of these laws with great attention ; 

 examine the proofs and arguments carefully, but 

 fairly. For I tell you, at the outset, that if you 

 admit the existence of these laws, you will not 

 afterwards be at liberty to question or doubt the 

 truth or propriety of what I shall say with regard 

 to diet and regimen. For the existence of con- 

 tractility and sensibility are like the axioms of 

 Euclid; they are self-evident truths, of which any 

 one may convince himself by experiment. For 

 instance, a dead man may easily be made to move 

 his limbs, to breathe, to frown, &c., by exciting 

 the appropriate muscles to contract by means of 

 galvanism. And the laws to which these properties 

 are subject, and of which I am now to speak, are, 

 if I prove them, of the nature of the propositions 

 of the First Book of Euclid. If these be true, the 

 propositions of the Second Book must be true also, 

 of necessity the truths of the Second Book arising 

 out of the truths of the First. As, for instance, if 

 you admit that twice two are four, you must of 

 necessity, also, admit that the half of four is two. 

 So, if you admit what I am about to say of these 



