170 



PRACTICAL PHYSIOLOGY. 



[XXVII. 



(5.) Screw the Du Bois key to the table, place the copper elec- 

 trodes under the sciatic nerve, and connect their other ends each 

 with the outer binding screw of the brass bars of the Du Bois key. 

 Close the key, and observe that no contraction of the leg muscles 

 occurs. 



(c.) Connect a Daniell's cell with the Du Bois key. Open the 

 key to allow the constant current to pass through the nerve for 



FIG. 98. Du Bols-Ueymond's Platinum Electrodes. The nerve is placed over the two 

 pieces of platinum, P, which rest on glass ; B. Universal joint ; V. Support. 



three or four minutes, and observe that there is no contraction as 

 long as the constant current is passing. Close the key, i.e., short- 

 circuit the battery, and at once a contraction occurs. Bemove the 

 battery, close and open the key. Contractions occur, but they 

 gradually get feebler as the polarisation ceases. The contractions 

 are due to polarisation of the electrodes. 



(d.) If non-polarisable electrodes are used, this does not happen. 



11. Non-Polarisable Electrodes. See Lesson XLI. 



