CHAP. IL] THE CONTRACTILE TISSUES. 



59 



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. 



FlG. 1. A MUSCLE-NEBVE 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 prick- 

 ing 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 



