152 EXPERIMENTAL PHYSIOLOGY. 



(b.) Use the same preparation, cover the leg with the skin 

 of the frog, or wrap it in blotting-paper saturated with nor- 

 mal saline. Expose the fresh cut end of the nerve to the 

 vapour of strong ammonia; there is no contraction of the 

 muscle, but the ammonia kills the nerve. Instead of doing 

 this, the whole leg may be laid on a card, covered with 

 blotting-paper moistened with normal saline, with a hole in 

 it just sufficient to allow the sciatic nerve to pass through 

 it. The card is placed over a test-tube containing a drop 

 of ammonia ; the nerve hanging in the vapour of the latter 

 is speedily killed, but there is no contraction of the muscle. 

 Apply the ammonia to the muscle, it will contract. 



LESSON XXVIII. 



SINGLE AND INTERRUPTED INDUCTION 



SHOCKS TETANUS CONSTANT 



CURRENT. 



1. Electrical Stimulation. Single Induction Shocks. Apparatus. 

 Frog, Daniell's cell, induction machine, two du Bois keys, 

 five wires, flexible electrodes. 



(a.) Arrange a cell and induction machine, for single in- 

 duction shocks according to the scheme, Fig. 54. Flexible 



Fig. 54. Scheme for Single Induction Shocks. B, Battery; K, K', 

 keys ; P, primary, and S, secondary coil of the induction machine ; 

 N, nerve; M, muscle. 



electrodes are fixed to the short-circuiting key (K') in the 

 secondary circuit, and over them the nerve is to be placed. 



(b.) Expose the sciatic nerve in a pithed frog, place the 

 electrodes preferably a pair fixed in ebonite, and so shielded 



