116 Alison on the Theory ascribing Secretion 



vanic, that we cannot understand how the mind should excite 

 under these circumstances strong galvanic actions in the 

 nerves. But the important fact is, that nervous actions may be 

 very readily excited by various physical agents, which certainly 

 have no effect whatever in exciting galvanism in any other 

 apparatus. Farther, these actions may be excited in the nerves, 

 long after their communication with the brain, (which is sup- 

 posed on this theory to be the main source of galvanic energy,) 

 is cut off; muscles being excited to contraction by stimuli ap- 

 plied ta their nerves fifteen days at least, according to the ob- 

 servation of Haller after the division of these nerves above the 

 point irritated. 



If, indeed, it were ascertained as matter of fact, that the irri- 

 tation of muscles through their nerves is always attended with 

 a notable evolution of galvanism, though it might be very dif- 

 ficult to explain the fact, it would be fair to argue, that the gal- 

 vanism, known to be evolved, was the cause of the contraction ; 

 but in the present state of our knowledge on the subject, there 

 being no proof whatever, that more galvanism passes from nerve 

 to muscle during the contraction produced by irritation than 

 at any other time, it seems to me fully as probable that muscles 

 should be so constituted as to contract in consequence of im- 

 perceptible changes, not galvanic, communicated to them by 

 their nerves, as that galvanism should be excited to a most in- 

 tense degree in nerves, merely by bruising them with a probe, 

 or pricking them with a pin, particularly after their commu- 

 nication witli the source whence they are supposed to draw their 

 galvanism is cut off. 



2. The effects which are produced upon muscles by changes 

 in the nervous system, are much more various than those which 

 have ever been observed to result from galvanism. Stimuli ap- 

 plied to the nerves supplying the voluntary muscles, excite 

 them very readily to contraction, but I believe no physiologist 

 has ever succeeded in exciting the involuntary muscles to con- 

 traction, by applying stimuli to their nerves. Galvanism applied 

 to either set of muscles directly excites them with nearly equal 

 facility. Alcohol applied to the brain augments the irritability of 



