EXCITATION OF NERVES. 201 



Strength of interrupter shocks. Slide the S coil to 

 35 cm and note its position when the first manifestations of 

 stimulation are apparent. 



The distance of the S coil will be greater than with the 

 single shocks. This is chiefly due to the quicker and more 

 regular make and break of the P circuit, especially when 

 using a Leclanche cell, which does not, under these circumstances, 

 remain close circuited for so long a time, and in consequence 

 the potential of the battery does not drop to any appreciable 

 extent. 



It is also due to the rapid repetition of shocks which, if 

 applied singly, are ineffective. 



Effect of stimulating 1 different nerves. Stimulate the 

 roots of the sciatic separately, near the spine, with interrupter 

 shocks. 



Also the peroneal and the tibial branches. Next the trunk 

 of the sciatic with various strengths of current, and note the 

 difference produced upon the class of muscle called into play, 

 i.e., extensor and flexors. 



Excitation of a muscle by various stimuli other than 

 a nervous one. 



(a) Mechanical. Strike the gastrocnemius smartly with the 

 handle of a scalpel, the muscle will contract. The blow must 

 be a sharp one. 



(b) Chemical. Dissect out the sartorius muscle, hold it with 

 forceps over a glass rod which has been dipped in ammonia 

 so that the vapour may play on the muscle. The muscle 

 will curl up in a continued contraction (contracture). Ammonia 

 kills nerve without stimulating it. 



Excitation of nerve by various forms of stimuli. 



(a) Mechanical. Whenever a nerve is cut, a twitch of its 

 muscle is evidence of its stimulation. In this manner when 



