THE NERVOUS SYSTEM. 439 



their atrophy is ascribed to want of use. The loss of the hoof 

 after division of the nerves is said by Mr. Youat to occur only 

 when considerable inflammation is present at the time ; that the 

 horse, having no sensation in the part, knocks it about, and in- 

 creases the inflammation to such a point, according to him, that 

 the hoof is detached : he assures me that, if no severe inflam- 

 mation is present at the time of the operation, the hoof is not 

 lost. 



Now, such among these effects of division or incapacitation in 

 any way of parts of the nervous system as cannot be attributed 

 to indirect circumstances, do not, in my opinion, militate against 

 the numerous general facts already mentioned of the independence 

 of the organic properties and functions upon the nervous system. 

 I do not see that we are justified in considering these results as 

 more than instances of the sympathetic influence of one part 

 upon another. All parts influence each other and the whole sys- 

 tem exclusively of their peculiar functions. The encephalo-spinal 

 nervous system must be like all other parts in this respect : and 

 yet every result of their injury on other parts is strangely re- 

 garded as a proof of dependency upon them. Besides its functional 

 powers and influences, its condition, even as to its structure and 

 organic functions, must sympathetically affect other parts, a 

 fact too often overlooked, and thus power has been presumed for 

 it without reason. When the kidneys are in such a state that they 

 produce sugar, a mental impulse is destroyed, and the power of the 

 genitals is lost. Under diabetes a man usually has no sexual im- 

 pulse and is impotent, yet no one supposes that the faculty of the 

 brain known as sexual desire, or the vigour of the genitals, depends 

 upon the kidneys. The brain is besides especially connected with 

 every other part of the body, and is one of the most important or- 

 gans which exist. The effect, therefore, which anyinjury of it must 

 have over other parts must be very great. But children live and 

 eat and preserve their temperature for many days, though born 

 without brains ; and we have seen what was borne by brutes in 

 the experiments of Duverney and his imitators. Nay, we have 

 seen that injury of nerves not supplying a part will injure it ; just 

 as the extremities may be absent or removed without injury to 

 the functions at large, and yet diseased states or severe injuries 

 of them may destroy the system. Injury of nerves, just as of 

 any other organs in proportion to their importance, may affect 

 parts, not which they supply, but with which they are connected : 



