ELECTRIC RESPONSE 7 
that their electric conditions have also become different. 
They are no longer iso-electric. There is thus a more or less 
permanent or resting difference of electric potential between 
them. A current—the current of injury—is found to flow 
in the nerve, from the injured to the uninjured, and in the 
galvanometer, through the electrolytic contacts from the 
uninjured to the injured. As long as there is no further dis- 
turbance this current of injury remains approximately con- 
stant, and is therefore sometimes known as ‘the current of 
rest’ (fig. 2, b). 
A piece of living tissue, unequally injured at the two ends, 
is thus seen to act like a voltaic element, comparable to a 
copper and zinc couple. As some confusion has arisen, on the 
question of whether the injured end is like the zine or copper 
in such a combination, it will perhaps be well to enter upon 
this subject in detail. 
If we take two rods, of zine and copper respectively, in 
metallic contact, and further, if the points A and B are con- 
nected by a strip of cloth s moistened with salt solution, it 
will be seen that we have a complete voltaic element. A 
current will now flow from B to A in the metal (fig. 8, a) and 
from A to B through the electrolyte s. Or instead of connect- 
ing Aand B by a single strip of cloth s, we may connect them by 
two strips s s’, leading to non-polarisable electrodes EE’. The 
current will then be found just the same as before, i.e. from 
B to A in the metallic part, and from A through s s’ to B, the 
wire W being interposed, as it were, in the electrolytic part of the 
circuit. If now a galvanometer be interposed at 0, the current 
will flow from B to A through the galvanometer, i.e. from right 
to left. But if we interpose the galvanometer in the electro- 
lytic part of the circuit, that is to say, at W, the same current 
will appear to flow in the opposite direction. In fig. 3, c, the 
galvanometer is so interposed, and in this case it is to be 
noticed that when the current in the galvanometer flows from 
left to right, the metal connected to the left is zine. 
Compare fig. 3, d, where A B is a piece of nerve of which 
the B end is injured. The current in the galvanometer 
