30 LECTURE I. 



goaded ; and thus again demonstrated that 

 the muscles of its jaw were endowed with 

 an irritabiUty of the more common cha- 

 racter. 



Having thus briefly described the prin- 

 cipal phsenomena of muscular action, for I 

 forbear to notice others of less importance, 

 I proceed to review the conjectures that 

 have been formed as to the cause of these 

 curious, sudden, and powerful contractions. 

 Not to speak of exploded hypotheses, I 

 trouble you only with those which are mo- 

 dern. 



First, then, the contraction has been sup- 

 posed 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. 



