APPARATUS FOR PHYSIOLOGICAL USE. 249 



FIG. 9. a, hind leg of frog. A silk cord is attached to the tendon of the 

 muscle of the calf (Tendo AchiU&s), by which, when it contracts, it pulls upon 

 the lever 5, and thus compresses the air in the receiving tympanum c. Immedi- 

 ately below d the electrodes are shown, by which the induction current acts on 

 the sciatic nerve, d, recording tympanum with its writing lever ; m, steel bar 

 on which it is supported ; e, rack and pinion by which the recording tympanum 

 can be lowered half a centim. , after each experiment ; //> wires of battery cir- 

 cuit ; g, trigger by which, as the arm h passes, the circuit is closed ; k, primary 

 coil of the induction apparatus ; I, secondary coil ; n, wires of the induction 



