288 PHYSIOLOGY 



simply leading off an intact living axis cylinder through the dead 

 portion of the nerve, which acts as an ordinary moist conductor. On 

 making a fresh section just above the previous one, the process of 

 dying is again set up, and the demarcation current is restored to its 

 original strength. If, while the demarcation current is at its height, 

 we stimulate the other end of the nerve with an interrupted current, 

 the needle of the galvanometer swings back towards zero, i.e. there 

 is a negative variation of the resting current. 



In order to demonstrate the wave -like progression of the electrical 

 change from the excited spot along the nerve, it is necessary, as in the 

 case of muscle, to make use of a very sensitive capillary electrometer 

 or a string galvanometer. It is then found that the change progresses 

 along the nerve at the same rate as the nervous impulse, i.e. 28 to 

 33 metres per second in the frog. But it lasts only an extremely 

 short interval of time at each spot, viz. six to eight ten- thousandths 

 of a second. Thus the length of the excitatory wave in nerve is about 

 1 8 mm. 



