THE ELECTRIC CONDUCTIVITY OF MAMMALIAN NERVE 
63 
resistance across the fibres is much greater than along them, and any structure 
other than a peripheral nerve, not having parallel fibres, would on that account 
have a relatively high longitudinal resistance. The ulnar nerve has a relatively 
small amount of connective tissue envelope and lymph space, and its higher 
conductivity may be due to this fact. 
A few determinations of the specific gravity of a nerve, by use of glycerine 
solutions of different densities, have given the values 1*030 lor the sciatic, 1*042 tor 
the ulnar, and 1*045 ^ or a separate strand of the sciatic. The values given above for 
specific conductivities should properly be multiplied by these numbers respectively, as 
the volume and specific conductivity were computed on the basis of a specific gravity 
equal to i*ooo. The changes in specific gravity produced by five minutes' immersion 
in distilled water, and in a gramme-molecular solution of KC1, were about 0*005 in 
case of the sciatic nerve, and a little more in case of the ulnar. 
The effects of immersion on the weight and on the electric conductivity of a 
nerve were found to be exceedingly definite functions of the strength of solution used. 
Weak solutions, while lowering the specific gravity, increase the absolute weight of 
a nerve ; and concentrated solutions, while raising the specific gravity, decrease the 
absolute weight. This means that water diffuses from the weak solutions into the 
interior of the nerve, and from the interior of the nerve into strong solutions. The 
strength of solution that produces no change in the weight of the sciatic nerve is 
about one-eighth of the gramme-molecular solution (the latter being, for KC1, 7*45 
per cent). 1 
The ratio of the weight after five minutes' immersion to the weight of the 
fresh nerve is as follows, in case ot each strength of solution : — 
Distilled water 
1'033 
1 '40th j 
jramme- 
•molecular solution oi KG ... 
I*OI7 
1 /20th 
99 99 
1-015 
1 I 1 oth 
99 
99 99 
1 -006 
1 /8 th 
9 9 
99 91 
0-996 
0-15 
99 9 9 
°'993 
1 /5 th 
99 99 ••• 
0-972 
1 4-th 
99 
99 99 
°'953 
1 jz 
99 99 
0-948 
1 
» 
99 99 
0-928 
2 
99 
99 99 " " * 
0-901 
The specific conductivity of a nerve is increased by immersion in strong 
solutions, and decreased by immersion in weak solutions. The concentration 
necessary in order to cause no change in the conductivity ot the immersed nerve is 
I. In case of the ulnar nerve, the strength of solution necessary to cause no change in weight was somewhat greater, 
according to my determinations, but there is here a slight source of error, due to the fact that the ulnar nerves were kept longer 
before being immersed. This error does not prejudice the values for the specific conductivity, for the latter was found not to 
change during over an hour's stay in the moist chamber. 
