64 LETTERS TO BROTHER JOHN. 



as possible. The little knobs, with which the sym- 

 pathetic is studded, have been considered by some 

 as so many little independent brains, whose office 

 it is to supply the organs of nutrition with motive 

 power : and they say that this arrangement was 

 made in order to remove these organs beyond the 

 influence of the will, which has its seat in the brain. 

 The absolute necessity that these organs should not 

 be under the controul of the will, and the fact that 

 they are not, together with the additional fact that 

 this pair of nerves does not supply them with 

 motive power, seems, I think, to favour this no- 

 tion. But, however this may be, it will be suffi- 

 ciently accurate, for our present purpose, to con- 

 sider all nervous influence as derived from the 

 brain, and from the spinal marrow, which is 

 merely an elongation of the brain. 



The brain itself I believe to be a secretory gland, 

 of which the nerves are the excretory ducts, and 

 the nervous fluid the secretion; and it is formed, 

 like all other secretory glands, by a most wonder- 

 ful convolution of inconceivably minute arterial 

 branches. The artery which principally supplies 

 these branches is the basilary. Thus the brain, 

 like every other structure, consists of arteries, 

 nerves, and veins; and there is little doubt but 



