THE INJURY CURRENT OF NERVE 
3°9 
undoubtedly was based upon the opinion that the injury current was caused by an 
inequality in the 'internal' and 'external' solutions of the nerve, and might there- 
fore be expected to depend upon the ratio existing between them, e.g. : — 
Internal solution 
External solution 
But such an expectation is not based upon a knowledge of the value of the 
potential difference to be obtained from such arrangements of solutions, which varies 
not directly with this ratio but with its logarithm ; although for a short range the 
two methods of variation might agree, and a too limited examination might lead to 
the inference that the more simply relation was in existence. 
Let us therefore take the ratios discovered in these four experiments (Experi- 
ment I, -31 ; Experiment II, '62 ; Experiment III, i"2i ; Experiment IV, 1 - 5 1 ) to 
exist between the final and initial values of the potential difference, and examine not 
these figures themselves, but the numbers of which they are the logarithms. 
Experiment I — C31 = log. 2 
Experiment II — 0-62 = log. \~2 
Experiment III — 121 = log. \6'i 
Experiment IV — 1 • 5 1 — log. 32*5 
Such a collection of figures becomes of immediate interest when it is appreciated that 
the concentrations of the experimental solutions used in these experiments bear the 
following ratios to one another : — 
Experiment I Experiment II Experiment III Experiment IV 
32 16 4 2 
it is at once realized that a definite relation has been discovered which unites together 
completely the very different effects of the solutions of hydrochloric acid used in these 
experiments. 
k 
Final potential difference = initial potential difference x log. - ; where 
'k' is a constant for all the experiments, and 'n' is the concentration 
of the solution in gram-molecules per litre — 
Eft, = E« log. - 
n 
Needless to say, such a formulated expression of opinion can be readily tested by the 
use of the data from each of the four experiments, and that in each case the use of 
these data should lead to the discovery of the same value for ' k.' 
N 
