ANIMAL ELECTRICITY. LECTURE IV. 9 I 



body by dipping a finger into each vessel, any acci- 

 dental inequality on the two sides does not affect the 

 instrument. Such being the case I polarise myself for 

 an instant by dipping a pair of fingers into the battery 

 vessels R L, and quickly transfer the same pair of 

 fingers to the galvanometer vessels, R' L' and as 

 you see, the spot is sharply deflected to the left. That 

 is a mixed effect of polarisation that may be wholly 

 external, at the way-in and way-out of current between 

 skin and fluid ; it merely serves to show the direction 

 in which to expect the effect of internal polarisation if 

 it exists. To this end — and this is the experiment 

 proper — I polarise myself again In the same way 

 through the same fingers dipped Into R and L, but 

 for a little longer to make sure of the effect ; then I 

 put my possibly polarised tissues Into the galvano- 

 meter circuit by dipping another pair of fingers Into 

 the vessels R' L', thus avoiding the external polari- 

 sation of the first pair of fingers. There is now a 

 considerable deflection, not quite so sharp as before, 

 but in the same direction, independent of external 

 polarisation at the skin, and significant of internal 

 polarisation in the tissues below the skin. Finally 

 repeating the experiment with reversed direction of 

 current, a reversed effect Is obtained. But to show 

 this without fail it Is necessary to let the current flow 

 for a rather longer time In order to wipe out the effect 

 of the previous polarisation. 



I shall not now enter Into any details as to the 



