328 THE OUTGO OF ENERGY 



The Electrotonic Current as a Stimulus. As 

 would naturally be expected, the ' electrotonic 

 current may be an effective stimulus. Bring the 

 end of an extirpated nerve A into contact with 

 the distal portion of the nerve of a nerve-muscle 

 preparation, B, as in Fig. 57, and place on the 

 other end of A non-polarizable electrodes joined 

 through a key to a battery of two cells. Make 

 the galvanic current. 

 Muscle B will contract. 



The galvanic current polarizes nerve A, and 

 the electrotonic current thereby 

 -~o) set up passes into the nerve of 

 B through the contact, and occa- 

 sions in nerve B an impulse 

 which descends to the muscle 



Fig. 57. 



and stimulates it to contract. 



Paradoxical Contraction. Expose the bifur- 

 cation of the sciatic nerve into tibial and peroneal 

 branches. Polarize either of these branches. 

 (The electrodes should not be placed too near 

 the bifurcation.) 



On making and breaking the polarizing cur- 

 rent, the muscles supplied by each branch will 

 contract. 



In this instance, the extrapolar region of the 

 branch polarized lies in part in the main trunk. 

 The electrotonic current there spreads into the 



