OF THE NERVOUS SYSTEM IN GENERAL. 479 



resulting from the impression made by the light upon the eye 

 is not instantaneous; the vibration or the pressure of the eye 

 in darkness gives the sensation of light, &c. Many other 

 facts collected by Darwin seem to indicate that there is in sen- 

 sation a molecular movement of the nervous substance which 

 is not instantaneous. On the other hand, many facts seem to 

 indicate that the nervous system is the forming and conducting 

 organ of an imponderable agent analogous to electricity or 

 galvanism. This nervous agent, whose existence was fore- 

 seen by Reil, recognised by Humboldt and by Aldini, ad- 

 mitted and sustained with so much talent by Cuvier, allows 

 an easy explanation of all the phenomena of nervous action, 

 and particularly the relation which exists between the benumb- 

 ing nervous action of electrical fishes and galvanic phenomena 

 on the one hand, and ordinary nervous action on the other; 

 the possibility of exciting galvanic phenomena by the nerves 

 and muscles alone; the possibility of exciting muscular con- 

 tractions, the chymifying action of the stomach, the respira- 

 tory action of the lungs, &c., by replacing nervous influence 

 with galvanic action; the existence of a nervous atmosphere, 

 acting from a distance on the nerves and muscles, and across 

 the solution of continuity of divided nerves; the wrinkling 

 which takes place in the muscular fibre in contraction, and 

 the relation of the ultimate nervous fibres, transverse with re- 

 spect to these wrinkles, is a phenomenon which approaches 

 certain electro-magnetic phenomena, &c. 



These opinions have appeared so probable to Rolando, that 

 he has sought the source of the nervous agent of contraction 

 in the cerebellum, which, on account of its laminae, has ap- 

 peared to him to act in the manner of a voltaic pile, and has 

 admitted in sensation a molecular motion of the pulp. 



However that may be, the nervous power is weakened and 

 exhausted by intellectual operations, by the exercise of the 

 senses, of the muscles and of the encephalon, and still more 

 by pain; it is restored by rest, food, and sleep. Its energy, 

 generally and particularly, is relative to the entire mass of the 

 nervous system and of its parts, and especially to the mass of 

 the gray substance, which is the most vascular; it is relative 

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