Contrary to Lillie's hypothesis, we have direct evidence that the rate of nerve-conduction may be independent of the electrical conductivity of the electrolytic solution surrounding the nerves, for I have found (1915)* that if sea-water be diluted with 0.415 molecular the rate of nerve-conduction is only slightly more depressed than if the sea-water be diluted with distilled water, or with dextrose; yet the main tains a nearly normal electrical conductivity, while with distilled water or dextrose it declines in nearly the same ratio as the dilution. Nor do the experiments I have made with solutions containing some but not all the cations of sea-water support Lillie's view. Thus if the rate of nerve-conduction in 0.647 molecular NaC1 be 55, it becomes 100 in 85.3 c.c. of 0.6 molecular NaC1+14.69 c.c. of 0.39 molecular Here the electrical conductivity of the solution is somewhat reduced, while the rate of nerve-conduction is much augmented. This is, of course, a striking instance of Loeb's law of the antagonism between a univalent and a bivalent cation, even though the bivalent cation in this case is magnesium, well known to be a depressant, especially for muscular activity in Cassiopea.
The temperature coefficient of nerve-conduction is 2.5 times as great as that of the electrical conductivity of the sea-water, as appears in table 6.
The rate of nerve-conduction in Cassiopea in heated sea-water was first determined by Harvey (1911) who found it to accelerate in a right line ratio up to 35° to 38°C., at which point there was an abrupt decline in rate. These results were later confirmed by Mayer (1914), and Cary (1916). The average of the best experiments is shown in table 6.
The high temperature coefficient of the rate of nerve-conduction suggests that we may be dealing with a chemical reaction involving a compound composed of sodium, calcium, and some proteid element; the degree of ionization of which is considerably affected by tempera ture in the manner suggested by W. B. Hardy (1900), Quincke (1902), and Bayliss (1915).* Possibly, also, the negative electrical potential associated with the wave of nerve-conduction may increase the surface tension of the alka line colloidal particles, thus reducing their size, rendering them more soluble, and thereby increasing the concentration of the reacting ions.
In this connection, A. Mayer, A. Schaeffer, and E. Terroine (1907)t state that in a large number of alkaline organic colloids, the addition of a further negative charge, in the form of OH' ions, caused a decrease in the size of the particles. Moreover, Hulett (1901)$ has shown that the solubility of particles of barium sulphate is about inversely propor tional to the size of the particles; and as colloidal particles are more or less soluble, one would expect their solubility to increase as the average diameter of the particles decreased.
Nerve-conduction is due to a chemical reaction involving the cations of sodium, calcium, and potassium. Magnesium is non-essential.
The probably high temperature coefficient of ionization of this ion pro teid may account in some measure for the high temperature coefficient of the rate of nerve-conduction, which I find is 2.5 times as great as that of the electrical conductivity of the sea-water surrounding the nerve.
Our observations do not support the "local action" theory of R. S. Lillie (1916) ; for this maintains that the rate of nerve-conduction must be a function of the electrical conductivity of the conducting tissue and of the electrolytic solution surrounding the nerve. It is found, however, that the rate of nerve-conduction is practically identical, whether we dilute sea-water with 0.415 molecular MgCh or with distilled water— in other words, whether we maintain a practically constant electrical conductivity or reduce it in nearly the same ratio as the dilution.
Table 7, illustrated by figure 14, shows rates of nerve-conduction in the subumbrella tissue of Cassiopea xamachana in Tortugas sea-water of P,, 8.1 to 8.2 diluted with aerated distilled water of P„ about 8.0 at 29° C. The rate in pure sea-water at the same temperature as the diluted sea-water is assumed to be 100. The experiments were conducted at Tortugas, Florida, on July 4 to 11 and July 19 to 25, 1916.
Table 8 shows the rates of nerve-conduction in subumbrella tissue of Cassiopea xamachana in Tortugas sea-water of P. 8.1 to 8.2 diluted with non-aerated distilled water of about 6 (H-ion concentration 0.9 X at 29° C. The rate in undiluted sea-water is taken to be 100. The experiments were conducted at Tortugas, Florida, in June and July 1916.