THE INJURY CURRENT OF NERVE 
249 
This objection invalidates all conclusions made as to the resistance of nerve 
measured between two points upon its longitudinal surface, just as the measurement 
of the resistance between two points upon the surface of an insulated, or rather badly 
insulated cable, is of no value, when one is seeking information as to the conductivity 
which the cable offers to currents traversing the same section of cable but passing 
in the interior of the cable from and to points beyond the terminals of the small stretch 
considered. 
There can be no question but that the direct measurement of the resistance of 
short pieces of nerve is rendered in this way fallacious, it seems possible, however, 
that a study of the extent of the fallacy may be of interest. Direct experimental 
evidence justifying the rejection of such measurements may be taken from the 
observation of differences in the resistance per centimetre of long and short stretches 
of nerve. For if a piece of nerve is laid upon several electrodes, and the resistance of 
the whole piece of nerve and of its parts separately measured, it is always the case 
that the directly measured total resistance is less than the same resistance computed 
by the addition of the resistances of the several parts ; a fact undoubtedly due to the 
repeated inclusion of the transverse resistance in the measurements of the shorter 
stretches. The finer the calibre of the nerve and the longer the distance between each 
pair of electrodes the less true this statement becomes, obviously because there is 
then a closer approach to ' infinity ' of resistance of each small piece of nerve. The 
fact is, however, readily demonstrated upon the sciatic nerve of the frog, and 
disappears in such a nerve upon ' cooking,' in company with the excess transverse 
resistance. The fact is very apparent in large calibred mammalian nerve. 
Preliminary Experiment. Sciatic Nerve of Dog 
The nerve was laid upon five electrodes — A, B, C, D, E 
The resistances by sections ... AB 6,150 ohms. 
BC 7,890 „ 
CD 10,450 „ 
DE 11,450 „ 
Addition ... 35,940 ohms. 
Resistance of AE, directly measured ... 24,000 ,, 
Difference ... 11,940 ohms. 
i.e., an excess of 48 per cent, above the direct estimation. 
The facts from similar experiments upon vagus nerves (dogs) are tabulated 
below to show in the briefest possible manner the magnitude of the error introduced 
into the examination of the resistance of short stretches of nerve. 
