36 ELEMENTARY PHYSIOLOGY. V. 



local and relatively slow, and in lasting during the 

 whole time of the passage of the current and for a short 

 time afterwards. 



When the protracted contraction is obvious, turn the 

 bar of the commutator in the opposite direction, so that 

 the direction of the current is reversed. On closing the 

 in-circuit key, it will be seen that the protracted con- 

 traction is now on the left-hand side of the tendinous 

 insertions, i.e. at the opposite ends of the muscle seg- 

 ments, which are now the cathodes (cf. Fig. 16, B). Put 

 the bar of the commutator in the mid-line and close the 

 in-circuit key; move the bar first in one direction and 

 then in the othen It will be seen that the contraction 

 caused by sending the current in one direction, at once 

 ceases on sending the current in the opposite direction, 

 i.e. the contraction is inhibited at the anode. 



If the current is kept on for some time, a weak similar slow con- 

 traction is sometimes seen at the break of the current; this will be 

 at the anode. 



The quick contraction at the make and at the break starts from 

 the cathode and the anode respectively, but it is conducted so 

 rapidly through the rest of the muscle that no difference in the time 

 of the contraction at the two ends can be seen by the eye. 



3. Polar stimulation of nerve. The apparatus re- 

 maining as in the previous experiment place the sciatic 

 nerve of the nerve muscle preparation across the elec- 

 trodes, pin down the knee joint and keep the nerve and 

 muscle moist with saline solution. Put the slider of the 

 rheochord at 10 and stimulate with ascending and de- 

 scending currents, i.e. with currents running from and 

 to the muscle respectively, repeat with the slider at 20, 

 and so on till a contraction is obtained at make with 



