248 
THOMPSON YATES LABORATORIES REPORT 
The potential differences between the electrodes were measured before and after 
the experiments ; no experiments are recorded in which any such were found, and, as 
has been previously stated, this latterly has never been the case. 
A complete set of such measurements having been taken, the experiment was 
performed. Electrodes A and D were connected together through the plug key, so 
as to allow the injury current to traverse the arc AD. When this was done it was 
always found that the potential difference between the intermediate points, B and C, 
was greatly altered. The alteration remaining constant as long as AD was closed, and 
disappearing immediately when this arc was broken. 
The performance of the experiment was followed by the making of a simple 
calculation from the data then obtained, by which it was sought to reveal the relation 
which might exist between the alteration in the potential difference between points 
B and C and the resistance between these points in the path of a current traversing 
the arc DA and the nerve AD as a complete circuit. 
The basis of this calculation was the value of the resistance between points 
B and C, and also the resistance in the whole circuit inclusive of the nerve AD. 
It is necessary, before proceeding to the details of the actual experiments, to 
consider the comparative value and meaning of the measured resistances of the pieces 
of nerve — AD and BC. 
There is no difficulty in determining the required resistance of the whole circuit, 
and thus of the piece of nerve AD to the terminal points of which the observation 
arc is applied. For the resistance in this case is necessarily measured by the 
resistance to a current entering and leaving the nerve at the points A and D, that is 
at the points and traversing the same path as the current determined by the position 
of the arc. 
The measurement of resistance of the short piece of nerve BC is different, since 
the current used to measure this resistance must enter and leave the nerve at points 
B and C, and encounter a 'transverse' resistance in so doing which is not encountered 
by a current passing, as in the assumed conditions of the experiment, from A to D 
and through points B and C, situated within the longitudinal resistance. 
