IRRITABILITY AND CONDUCTIVITY 179 



Muscle B, which is stimulated only through 

 its nerve, will contract before muscle A, which 

 is stimulated directly. Hence, the specific irri- 

 tability of nerve is greater than that of muscle, 

 provided (1) that the intensity of the stimulating 

 current is equal for both nerve and muscle, and 

 (2) that the irritability of the two muscles does not 

 differ, and (3) that the stimulation of the nerve 

 of B is not by unipolar induction. The first 

 source of error may be excluded, because the 

 density of the current passing through the por- 

 tion of nerve lying on muscle A is certainly not 

 greater than the density of the current passing 

 through the muscle itself. The second possibil- 

 ity is tested as follows : 



Reverse the muscles and repeat the experi- 

 ment. 



The result will not be altered. 



The third source of error is excluded as follows. 



Tie a ligature about the nerve of B, between 

 muscles A and B. The physiological conduc- 

 tivity of nerve B is thereby destroyed, and the 

 nerve impulse cannot pass ; but the physical con- 

 tinuity of the nerve, and hence its power to con- 

 duct electricity, is still present. 



The strongest induction currents applied to 

 muscle A will now fail to produce contraction 

 of B. 



