56 



ELECTRICAL STIMULI. 



[BOOK i. 



called a muscle-nerve preparation. The most convenient muscle 

 for this purpose in the frog is perhaps the gastrocnemius, which 

 should be dissected out so as to leave carefully preserved the 

 attachment to the femur above, some portion of the tendon (tendo 

 achillis) below, and a considerable length of the sciatic nerve with 

 its branches going to the muscle. Fig. 1. 



FIG. 1. A MUSCLE-NERVE PREPARATION. 



m, the muscle, gastrocnemius of frog ; n, the sciatic nerve, all the branches 

 being cut away except that supplying the muscle; /, femur; cL clamp; t. a tendo 

 achillis ; sp. c. end of spinal canal. 



44. We may apply to such a muscle-nerve preparation the 

 various kinds of stimuli spoken of above, mechanical, such as 

 pricking or pinching ; thermal, such as sudden heating ; chemical, 

 such as acids or other active chemical substances, or electrical ; 

 and these we may apply either to the muscle directly, or to the 

 nerve, thus affecting the muscle indirectly. Of all these stimuli 

 by far the most convenient for general purposes are electrical 

 stimuli of various kinds ; and these, except for special purposes, 

 are best applied to the nerve, and not directly to the muscle. 



Of electrical stimuli again, the currents, as they are called, 

 generated by a voltaic cell are most convenient, though the 

 electricity generated by a rotating magnet, or that produced by 

 friction, may be employed. Making use of a cell or battery of cells, 

 Daniell's, Grove's, Leclanche', or any other, we must distinguish 

 between the current produced by the cell itself (the constant 



