Nerve-Conduction in Diluted and in Concentrated Sea-Water. 183 



with tliis potassium-chloride solution, both at 25 C., the ratio of 

 their electrical conductivities became as 1 to 4.179. 



The salinity of the sea-water was determined by titration with silver 

 nitrate, using potassium chromate as an indicator and titrating against 

 a sample of standard sea-water from Professor Knudsen's laboratory. 



The fact that the rate of nerve-conduction increases in a straight - 

 line ratio in comparison with the increase of electrical conductivity 

 suggests a causal relation between the two, as was pointed out by Ralph 

 S. Lillie, 1916, 1 but the same ratio exists between the concentration of 

 the dissociated cations Na% Ca", Mg", and K% surrounding the nerves 

 and the rate of nerve-conduction ; and thus the rate may be dependent 

 upon the concentration of these electrolytes rather than upon their 

 electrical conductivity as such. Thus, in experiments made in 1917 

 upon Cassiopea, we find that if the electrical conductivity of 0.601 m* 

 NaCl be taken as 1.00, that of an isotonic solution composed of 81.1 

 c.c. of 0.601 m. NaCl + 14.36 of 0.39 m. MgCl 2 is 0.932; yet if the rate 

 in the pure sodium chloride be 100, that in the NaCl+MgC! 2 is 115. 

 Thus the rate has increased while the electrical conductivity has dimin- 

 ished. This experiment is a striking illustration of Loeb's law that a 

 bivalent cation tends to offset the injurious effects of a univalent cation 

 and even magnesium, a well-known depressant, acts as a stimulant 

 for rate of nerve-conduction in association with sodium. 



Comparing the effects of these solutions with that of normal sea- 

 water, all being practically isotonic one with the other, we find: 



Rate of nerve-conduction is 100 in natural sea-water of 36.24 



0/00 salinity, 8.22 P H , and 1.00 relative electrical conductivity. 



Rate of nerve-conduction is 79.6 in 0.601 //>. NaCl of 8.2 P H , 



and 0.996 relative electrical conductivity. 



Rate of nerve-conduction is 92.2 in 81.1 c.c. of 0.601 m. NaCl+ 

 14.36 of 0.39 m. MgCl 2 of 8.2 P H , and 0.94 relative electrical 

 conductivity. 



It may be of interest to see that diluted sea-water is less depressant 

 for nerve-conduction than abnormally concentrated sea-water. 



The injurious effects of concentrated sea- water upon regeneration 

 and growth have been studied by Loeb 2 and by Goldfarb, :j and there is 

 a general resemblance between their curves and ours for the rate of 

 nerve-conduction, excepting that for regeneration somewhat dilute 

 sea-water seems to be more favorable than normal sea-water, whereas 

 in nerve-conduction the highest rate is obtained in slightly concen- 

 trated sea-water. 



, R. S., 1916, American Journal Physiology, vol. 41, pp. 126-136. 

 2 Loeb, J., 1891, Organbildung und Wachsthum, 82 pp., Wi'irzburg. 



3 Goldfarb, A. J., 1914, Papers from the Tortugas Laboratory, Carnegie Inst. Wash. Pub. 

 No. 183, pp. 83-94. 



