176 ELECTROTONUS [CH. XV. 



electrometer are directly opposed to those of Stewart. , The following simple 

 experiment devised by Gotch appears to be quite conclusive that conductivity like 

 excitability is lessened at the anode when the current is made. Three non-polaris- 

 able electrodes are employed (fig. 173), the current is first closed from A 2 to K, and 

 the time which intervenes before the muscle contracts is measured ; it is then 

 closed from Aj to K, and the time again measured. In both cases, excitation 

 occurs at K, but the time of response in the second case (A x to K) is longer, because 

 in that case the nerve impulse has to traverse a region of nerve at A x in which the 

 power of conduction is lessened. 



A 2 A! 



FIG. 173. Diagram to illustrate Gotch's experiment with triple electrodes. 



Sometimes (when the preparation is specially irritable) instead of 

 a simple contraction a tetanus occurs at the make or break of the 

 constant current. This is due to chemical (electrolytic) changes pro- 

 duced by the current, and is liable to occur at the break of a strong 

 ascending current which has been passing for some time into the 

 preparation, or at the make of a strong descending current; both 

 being conditions which increase the excitability of the piece of nerve 

 nearest to the muscle ; this is called Ritter's tetanus, and may be 

 stopped in the first case by throwing in the current in the same 

 direction, or in the second case by throwing in a current in the 

 opposite direction, i.e., by conditions which lessen the irritability of 

 this piece of nerve. 



The same general laws hold for muscle as well as for nerve, but 

 are more difficult to demonstrate ; the main fact, however, that the 

 kathode is the stimulating electrode at the make, and the anode at 

 the break, may be easily shown by the following experiment: if a 

 curarised, that is, a physiologically nerveless muscle, is arranged, as 

 in the experiment, for demonstrating the muscle-wave (see fig. 122, 

 p. 100), and a non-polarisable electrode placed at each end, the muscle- 

 wave at the make of a constant current starts at the kathode and 

 at the break it starts at the anode. 



An induced current in the secondary circuit of an inductorium 

 may be regarded as a current of such short duration that the opening 

 and closing are fused in their effects. This is true for all induction cur- 

 rents, whether produced by the make or break of the primary circuit. 

 The kathode will always be the more effective in causing contraction. 



EESPONSE OF HUMAN MUSCLES AND NERVES TO ELECTRICAL 

 STIMULATION. 



Perhaps the most important outcome of this study of the response 

 of muscle and nerve to electrical stimulation is its application to the 

 muscles and nerves of the human body, because here it forms a most 

 valuable method of diagnosis in cases of disease. 



