STIMULATION OF MUSCLE AND NERVE 151 



nerve, make and break the galvanic current 

 again. 



A moderately strong galvanic current will now 

 produce an opening tetanus (anodal stimulation 

 of a region the irritability of which has been 

 raised by the sub-minimal tetanizing current). 

 Other effects are a lengthening of the latent 

 period, and an increased dependence on the 

 duration of the galvanic current (see page 138). 



Eeverse the pole-changer, so that the tetanizing 

 electrodes fall in the cathodal region. Eepeat 

 the experiment, comparing the results of cathodal 

 stimulation without and with the sub-minimal 

 tetanizing current. 



With sub- minimal tetanization, an increase in 

 the height of the closing contraction, when the 

 galvanic current is not too strong, will be seen ; 

 when the galvanic current is stronger, closing 

 tetanus will also be observed. 



Polar Excitation in Injured Muscle. Smoke a 

 drum. Make non-polarizable electrodes. Con- 

 nect a dry cell through a simple key and 

 pole-changer (with cross-wires) with the non- 

 polarizable electrodes. Prepare a sartorius mus- 

 cle with bony attachments. Fasten the pelvic end 

 in the muscle clamp. Tie a thread to the tibial 

 end, and fasten the thread to the upright pin of 

 the muscle lever, so that the muscle is extended 



