478 GENERAL ANATOMY. 



the nervous system acts. This fact escaping observation, a 

 multitude of hypotheses have been proposed, varying with the 

 prevailing doctrines at each epoch. 



An attempt has been made to explain nervous action by 

 mechanical hypotheses, either by supposing that the nervous 

 fibres could vibrate in the manner of cords, or by admitting 

 such vibrations only in their elementary fibrils, or in the spi- 

 nal fibrils which have been supposed, or finally by an oscilla- 

 tion of elastic globules, the existence of which has been ima- 

 gined. 



Other explanations have been founded on the supposition of 

 a nervous fluid, either material and visible, or more generally 

 an incoercible fluid; and, in this latter supposition, it has been 

 called sometimes ether, sometimes phlogistic or magnetic, lu- 

 minous, electric, latterly galvanic, according to the objects 

 which have engaged at different epochs the attention of natural 

 philosophers. 



Reil has proposed on this subject an hypothesis which con- 

 sists in deriving the nervous action from a chemico-vital pro- 

 cess. He attributes in general the action of organic parts to 

 their form and composition. The form and composition of 

 organic parts being changed, their action is always so; and 

 whenever the action is changed, there are changes observable 

 in the parts; so, that as a general rule, the change of action is 

 a consequence of the change of composition in the parts: nerv- 

 ous action then supposes a change in the nervous substance. 

 What appears particularly favourable to this hypothesis of 

 Reil, is the abundance of arterial blood which is distributed 

 in the nervous system, and especially in the gray substance, 

 the volume of which is always proportionate to the nervous 

 activity (759). 



762. We may, independently of every hypothesis, consider 

 the nervous action as a general fact, and observe its phenomena 

 and conditions. The phenomena of innervation are insensible 

 in the nerve, as those of muscular contraction are in the muscle: 

 nothing is visible there; however, some facts seem to indicate 

 that there occurs in the nervous substance, when in action, a mo- 

 tion of some kind, in order to produce sensation. The sensation 



