XIII.] THE FROG. 257 



cut the muscles of the limb will contract : whether 

 or not, however, they will contract violently while 

 the interrupted current is going through the 

 nerve. 



[If an induction-coil is not at hand a hit of clean 

 copper wire twisted round a strip of zinc, with the 

 points of contact moistened with dilute acetic acid, 

 may be used to stimulate the nerve ; smart tapping 

 or pinching with a pair of forceps will also excite it, 

 but by such means the nerve is soon killed.] 

 The above experiments shew : 



c. That the muscle is irritable and contractile : cer- 

 tain external agencies (stimuli) excite some 

 change in it, the result of which is a muscular 

 contraction. 



d. The nerve is irritable : certain external agencies 

 excite some change in it, which in this particular 

 case manifests itself by a contraction of the 

 muscles connected with the nerve. 



e. The nerve possesses conductivity : although it is 

 stimulated at some distance from the muscles, 

 yet the change excited by the stimulus travels 

 along it to them. 



M. 17 



