446 



MUSCLE PHENOMENA. 



ance than the nerve, the current takes the short path through the 

 key, and none of it, or so little as not to be worth considering, 

 passes through the nerve. It is at the make and break that 

 muscular contractions occur, and then only ; the contraction being 

 stronger when the circuit is closed than when it is opened. It 

 has been demonstrated that if a current is permitted to pass 

 through a nerve, and gradually increased, and again gradually 

 decreased, no contraction of the attached muscle occurs ; the make 

 and break must be sudden. 



Induced Current. This is a more powerful stimulus to the 



FIG. 250. Du Bois Reymond's inductorium : B, primary ; B', secondary coil ; H, 

 guides in which B' slides, with scale; D, electromagnet; E, vibrating spring; i, 

 wire connecting wire of D to end of primary; A, A', binding screws to which are 

 attached the wires from battery ; A' is connected with the wire of the electro- 

 magnet D, and through it and i with the primary. 



nerves than the galvanic current produced in a voltaic cell, such 

 as that of Daniell. 



In Fig. 249, b represents a battery the current of which can 

 be permitted to pass or not through the primary coil p by closing 



FIG. 251. Unpolarizable electrode; A, hook-shaped; B, V-tubes; (7, straight;, 

 I?, clay in contact with tissue ; S, saturated zinc sulphate solution ; Z, amalgamated 

 zinc wire (Stewart). 



or opening the key k. If near this coil a secondary coil, *, is 

 placed, with its electrodes connected with a muscle, at the 

 moment the key k is closed in the primary circuit a current is in- 



