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CHAP. VIII. 



Relations of the Organic Life in the Nervous System. 



1. LIFE, or the organic spirit in the nervous system, 

 maintains its own identity, or assimilates itself from blood, in the 

 same manner as in the other structures. But the properties of life 

 in this system appear to have an intercourse so rapid, so frequent, so 

 important in its results, so subtile, so mysterious, so difficult of in- 

 vestigation, that this system on these accounts deserves rather to be 

 particularized than some others. 



2. The assimilating life in the nervous system is that which 

 belongs to the seat, to every seat in which life is maintained. This is 

 to be inferred on the ground before stated, that properties which 

 maintain themselves by assimilation depend only, 1st, on their own 

 existence, and, 2nd, upon a supply of that material from which their 

 existence is renewed. Hence the assimilating life of the nerves is 

 every where independent of the other parts of the system, at least it 

 has no direct dependence; the indirect will be hereafter spoken of. 



3. Such a conclusion is furnished a priori t and we find it to 

 agree with facts to a considerable extent. The nerves are the 

 organs of the animal functions, or those of sense and motion : a de- 

 pendence is obvious, in the exercise of these functions, upon their 

 centres, as the brain, spinal marrow, &c.; accordingly, we find that 

 if the nerves of a voluntary muscle are divided, that muscle no longer 

 obtains those properties which are derived from the centre of its 

 nerves, and which enable it to perform voluntary motion ; the faculty 

 of sensation is also suspended or destroyed in the inferior distribution 

 of the divided nerves. Not so with the organic assimilating life: 

 the terms of the maintenance of this are not violated, its organic 

 spirit survives the division of the nerves distributed in its seat, it 

 is supplied with blood, and it preserves its identity, maintaining the 

 cohesion of the structure, and exhibiting its usual characteristics. 



4. Thus far the distinction and the independence of the assimi- 

 lating life of nerves is plain to our experience. But we are called 

 upon, in order to extend or correct our view of this same indepen- 

 dence, to consider facts of the following kind. If a sciatic nerve 



