APPENDIX I. 105 



by Professor Helmholtz, but with some slight modi- 

 fications, that the speaker has introduced for the 

 sake of convenience, g is the gastrocnemius muscle 

 of a frog, fastened by the thigh-bone in the clamp c, 

 which can be raised or lowered by the screw 8. 

 Through the tendo-Achillis a hook is thrust, and to 

 this, by an insulating piece t, a brass lever / k is 

 attached, turning on the axis &, and, near its end Z, 

 supported by a platinum point resting on a platinum 

 plate p. Just underneath the muscle, a scale-pan is 

 suspended from the lever, on which any suitable 

 weight may be placed. At the end I of the lever an 

 amalgamated copper point dips into a mercury cup 

 m. G is the galvanometer-coil; and it is hardly 

 necessary to mention that the readings are made 

 with mirror, telescope, and scale. B l is the battery 

 belonging to the chronoscopic circuit. This circuit 

 is formed by B 1 , G, m, j>, L, and the place of contact 

 , where for the present it is interrupted. For 

 several reasons, which it would take too long here 

 to explain, the chronoscopic current cannot be em- 

 ployed for directly stimulating the nerve by its 

 beginning, and this has to be done indirectly, in the 

 following way : 



n o q is an insulating lever turning on the axis o, 

 and bearing at n a platinum plate connected with B 1 . 

 This plate corresponds to a platinum point at the 

 end of the brass lever L, which in its turn is con- 

 nected with jp, so that by pressing down L, the 

 chronoscopic circuit is made. But by pressing down 

 the extremity n of the lever n o q, its extremity q is 

 simultaneously raised, and thus another circuit is 



