ELECTROTOXUS. 231 



a second record, this time with commutator 6 turned to the 

 more distant electrode. 



Read off the difference between the two this will give the 

 time consumed by the nervous impulse in travelling from the 

 one point of stimulation to the other. Calculate the rate in 

 metres per second as before. 



Blectrotonus. Electrotonic variation of nervous excitability. 



Required: Indue torium for single induction shocks, two Daniell 

 cells, Pohl's commutator, muscle chamber with noil - polarisable and 

 platinum electrodes, 11 wires, 3 keys. Nerve muscle preparation. 



s 



FIG. 45. Eleetrotonus. Position of keys, &c., on the table. Stimulating circuit 

 P, S to E the platinum electrodes near the muscle M. Polarising key K. C com- 

 mutator. N non-polarisable electrodes on nerve above E. L Leclanch6 cells. 



Set up as follows (Fig. 45) : 



(a) The stimulating circuit. Connect the S circuit to the 

 binding screws of the platinum electrodes on the outside of 

 the muscle chamber. 



(b) Polarising circuit. Arrange as in the diagram. Connect 

 the positive pole of the battery to the key (break) and wire 

 the poles to the commutator C, and the pair of terminals 

 nearest the muscle chamber to the terminals of the non- 

 polarisable electrodes of the latter. 



