THE INJURY CURRENT OF NERVE 303 
A temperature of 38° C. is not, however, so easily maintained as a temperature 
of 1 8° C, it is also a temperature at which the rate of decline of the injury current 
is very great, as would the rate of any process of diffusion also be. In an attempt 
to study the quantitative effect of immersion in various solutions, this declining value 
of the original phenomenon has to be borne in mind as carefully as in the case of any 
of the other measurements undertaken previously. Nor can this source of error be 
as easily dealt with as in the case of the examination of the distribution potential (see 
previous section on 'current of injury '). In that case the error was eliminated by 
taking two sets of measurements in a regular order. In this case no such method is 
applicable, since, as has been clearly stated, even a short immersion in any solution 
(which is not the ' isotonic ' one) leaves a fractional, but still important, effect 
behind it upon the concentration of the 'internal' as well as of the 'external' 
solution of the nerve. At first this point was not as clearly recognized as now, 
and experiments were made by the author in which immersions in the experimental 
solution were alternated with immersions in an isotonic solution : such experiments, 
although of some interest, have no quantitative importance, and have the disadvantage 
of appearing to correct an error which they largely leave unmodified, or only modify 
it in a new and undesirable fashion. 
The decline of the injury current is, therefore, an important consideration, and 
is most satisfactorily dealt with by immersions in solutions at a temperature unfavour- 
able to its marked occurrence. 
Data have already been given* from experiments in which the influence of tem- 
perature was studied, the data of the following experiment will serve here as an 
illustration : — 
EXPERIMENT X 
Sciatic Nerve of Cat 
(a) First nerve, removed immediately after death : — 
Potential difference at once ... ... ... 13*3 x io — ! Daniell 
After 2 5 minutes in 7 5 per cent. NaCl solution at 17* C. 12-5 „ 
(b) Second nerve, removed immediately after death : — 
Potential difference at once ... ... ... 13*3 ,, 
After 25 minutes in -75 per cent. NaCl solution at 38" C. 8"2 „ 
After a subsequent 5 minutes in '75 per cent, at 17° C. 8'i ,, 
In this experiment the two nerves were fortunately in the same original 
condition, and the degree of modification by immersion in the same solution at 
different temperatures is clearly seen. At a temperature of 38°C. the decline in the 
injury current is 39 per cent, of the original, at 17 0 C. the decline is only 6 per cent, 
in the same interval of time. 
J. S. Macdonald, Preliminary Communication, Proc. Roy. Soc, 67, 321. 
