INADEQUACY OF PFLUGER'S LAW 581 



of both ascending and descending currents, but not at the 

 break of either. Extending the clear inference of the 

 previous case to cover this, it was supposed that here, too, 

 the kathode at one time near to, and at another far from, the 

 responding muscle excited at make. But this is not so 

 conclusive, since the anode might equally well be regarded 

 here as causing the excitation at make. Indeed this 

 supposition that a very weak anode might cause excitation 

 at make derives some support from Heidenhain's experi- 

 ments. For, using a weak E.M.F., he found make-excitation 

 to occur in the first stage only, when the current was 

 ascending that is to say, when the anode was near the 

 responding muscle. This result would tend to show that 

 there was a possibility of the reversal of normal polar effects 

 when the acting E.M.F. was weak. With regard to this 

 particular effect of minimal currents, there are considerable 

 differences of opinion. The obtaining of such an effect is 

 probably only possible when the nerve-muscle preparation is 

 in an exceptionally favourable condition of excitability, a 

 state of things not always possible to secure in the isolated 

 specimen. It therefore occurred to me that the effect of 

 a feeble anode in enhancing excitability might be demon- 

 strated conclusively in the case of the vigorous intact animal. 

 With this consideration in view, I carried out a number of 

 experiments on certain of my students and myself. 



If we make a slight wound, say one square cm. in area, on 

 the back of the hand, and apply a solution of salt, which is 

 not too strong, a constant sensation is induced which cannot 

 be called painful, but may best be described as smarting or 

 irritating. If now we apply one non-polarisable electrode 

 on this wound, and the other on a distant and indifferent 

 point, then, on applying an E.M.F. to the circuit, charac- 

 teristic variations of sensation will be induced, depending 

 on whether the wound-spot is made anode or kathode 

 (fig- 359)- Employing an E.M.F. of 2 volts, it will be found 

 that when the spot is made kathode, the sensation, which 

 was previously one of mere general irritation, becomes 



