86 



PHYSIOLOGICAL PHYSICS. [Chap.vm. 



and, the electrotonising current being downward, the 

 stimulus is applied in the neighbourhood of the - - pole, 

 in the region, that is, of MYOPOLAR KATELECTROTONUS. 

 In the second case the stimulus is also myopolar, but 

 in the neighbourhood of the + pole, therefore MYO- 

 POLAR ANELECTROTONUS. The other two cases are seen 

 by the diagram to be CENTRO-POLAR ANELECTROTONUS, 

 and CENTRO-POLAR KATELECTROTONUS. Therefore, both 

 circuits being open, incline the commutator c (Fig. 44) 



Meet _ISt 



IcfSftF 



Cenlrn< 



Fig. 46. Results of Electrotonus. 



so that the constant current may be down the nerve ; 

 incline the double commutator to stimulate near the 

 muscle, that is, by wires 3 and 4 ; then open the key 

 of the induction coil, so as to send shocks to the 

 nerve; slowly approximate the secondary coil to the 

 primary, till the strength of the induction shocks is 

 just sufficient to cause the muscle to twitch the tele- 

 graph signal. At this point close the mercury key K, 

 and send on the constant current ; electrotonus is 

 established in the nerve ; the region of the negative 

 pole, where the stimulus is being applied, is thrown 

 into a state of increased excitability, and consequently 

 the current, before just sufficient to twitch the muscle, 

 now throws it into tetanus ; tetanus appears. In- 

 terrupt both currents. 



