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tance, I proceed to review the conjec- 

 tures that have been formed as to the 

 cause of these curious, sudden, and power- 

 ful contractions. Not to speak of ex- 

 ploded hypotheses, I trouble you only 

 with those which are modern. 



First, then, the contraction has been 

 supposed to be the effect of some chemical 

 change occurring in the part. This opinion 

 is I think invalidated by the reiterated con- 

 tractions which may be produced in the 

 limbs of some animals when removed from 

 the body, even during twenty-four hours, 

 if excited by voltaic electricity, and conse- 

 quently when no supply of materials can 

 be supposed to exist within the limb, to 

 produce such reiterated chemical changes. 

 The opinion is still further refuted by 

 observing, that these vivacious contractions 

 will equally take place, upon the same excite- 

 ment, in the exhausted receiver of an air 



