STIMULATION OF MUSCLE AND NERVE 153 



short time, test the irritability to weak, ascend- 

 ing (i. e. cathode at pelvic end) currents. 



The closure of ascending currents will give 

 extraordinarily large contractions. 



The cause of this change in irritability is not 

 the presence of dead contractile tissue, for elec- 

 trodes can be wrapped in dead muscle and used 

 to stimulate normal muscle without loss of irri- 

 tability being noticeable. 



When the end of the fibre is killed, the patho- 

 logical change passes gradually through the 

 whole of the fibre. 



POLAR INHIBITION BY THE GALVANIC CURRENT 



It remains now to consider the inhibitory 

 action of the galvanic current, to which attention 

 was called on page 142. 



Heart. Connect a dry cell through a simple 

 key with the and 1 metre posts of the rheochord. 

 Connect non-polarizable electrodes through a pole- 

 changer with cross-wires (Fig. 30), with the slider 

 and the positive post of the rheochord. Pith the 

 brain, not the cord, of a frog, and place the animal, 

 back down, in the holder (Fig. 29, page 112), and 

 expose the heart, without unnecessary loss of 

 blood, according to the method described on page 

 112. Open the delicate membrane (pericardium) 



