1909.] 



Electrical State of Living Tissues. 



305 



this doubtful feature is eliminated when muscle-effects and skin-effects are 

 studied comparatively. 



A B_ 



I. Muscle — 



Heat 



Kxoitation or injury ^~ -s-— 



II. Nerve — 



Heat »- 



Excitation or injury ■*■ 



III. Skin- 

 Heat =*■ •< 



Excitation ; ; 



The arrows under A and B indicate the direction of currents in the tissue 

 in response to local warmth or local excitation at A and at B respectively : 

 e.g., if muscle, led off at A and B to the galvanometer, is heated at B, there is 

 current in the galvanometer from B to A, in the muscle from A to B as 

 indicated by the first arrow under B. Following the usual phraseology, we 

 say that B becomes " positive." The second arrow under B indicates that 

 there is current from B to A in the muscle when B is rendered active by 

 injury or excitation, or, according to usual phraseology, B becomes " negative." 



The arrows opposite the nerve indicate the analogous currents by local 

 warmth or by local excitation, identical in direction with those of muscle. 



The local skin currents both to heat and to excitation are of reverse 

 direction to those of muscle (and of nerve), e.g., if skin led off by electrodes 

 A and B applied to its external surface is warmed at B, there is current in 

 the galvanometer from A to B (" ingoing " current at B, or B " negative " to 

 A). If it is excited at B, there is current in the galvanometer from B to A 

 (" outgoing " current at B, or B " positive " to A). 



In the foregoing description the ordinary terms " negative " and " positive " 

 have been used. For my own part I find it conducive to clearness to think 

 of the active spot B as " electro-positive," giving current from B to A in the 

 tissue, rather than as " negative," giving current from B to A through the 

 galvanometer, and I call B " zincative." But the least ambiguous description 

 •of direction of current between A and B is afforded by the arrows. 



II. Of Nerve. 



A nerve disposed in a similar manner gives similar results, with this 

 difference, that the positive response to heat is relatively more evanescent 

 ■and more easily replaced by the negative response to injury. This 

 disappearance may occur so rapidly that a photograph taken after a few 

 trial deflections may exhibit only a series of injury responses (negative with 

 increasing negativity), the heat responses (positive with increasing negativity) 

 having occurred with the trial deflections. It is advisable, therefore, to take 



