126 



FERTILIZATION 



Sodium in 



Potassium 

 out 



(0) 



o 



time 



(b) 



■N^-' 



(c) 



-\ 



(d) 



(e) 



FIG. 27. — An action potential travelling along a nerve fibre from left to right, 

 with two electrodes, connected to a voltmeter V, on the nerve surface. 



