OF THE GALVANIC CURRENT ON THE MOTOR NERVES OF MAN. 
963 
effects varied in kind and degree.* Helmholtz’ hypothesis undoubtedly accounts 
for some of these apparent contradictions, which may be due to the fact that when a 
proximal region, or series of points, in a nerve is submitted to the polar action of a 
given electrode, there exists a distal region, or series of points, in that nerve which is 
submitted to polar influence of the opposite sign to that of the electrode (using the 
terms “ distal” and “ proximal” with reference to the electrode as centre). 
But if this hypothesis is true in the case of the polarising current, it must hold 
also for the testing current, whether galvanic or induced, since the laws of diffusion 
are the same for both, and one cannot ensure the coincidence of excitation and polari¬ 
sation by separate electrodes. Another contingency capable of vitiating the results 
obtained by this same method is, that derived currents may be established through 
the testing electrode of sufficient strength to alter the irritability of the nerve. We 
adopted the theory of a mixed polar action for both polarising and testing currents, 
as a working hypothesis at the beginning of our experiments, relying upon the 
following considerations to justify its assumption:— 
(1.) The presence of an anodic make contraction speaks in its favour, since, given 
the axiom of Pflltger and Chauveau, that make contraction is kathodic, break 
contraction anodic, it follows that with anodic make there coexists an associated 
kathodic make. 
(2.) The elementary fact that, over certain points of nerve, the muscles that contract 
at anodic make are not the same as those that contract at anodic break also speaks in 
its favour, since it indicates that at the two events the points of excitation are not 
identical. 
To denote the nerve-regions that are subjected to the two kinds of influence, we 
use the terms “polar” and “peripolar ” The area of electrical influence within which 
the density is sufficient to produce physiological effect is schematically represented as 
consisting of a polar region immediately beneath the electrode, in which the electrical 
relation is of the same sign as that of the electrode, and of a surrounding peripolar 
region in which the electrical relation is of the opposite sign (Diagram I.). We shall 
use this representation for the most convenient expression of our facts; it must 
* Our experiments with this method were few, and for the reasons given in the text we do not lay any 
stress upon the results obtained. These were as follows :— 
With the galvanic kathode above or below the negative polarising electrode the make contraction 
(K.C.C.) was diminished. On breaking the current a contraction appeared (K O.C.P). 
With the galvanic anode above or below the negative polarising electrode the break contraction 
(A.O.C.) was diminished; the make contraction (A.O.C.) variable. 
On testing with the make and break induction currents the effect of the kathode of either was 
diminished in the neighbourhood of the polarising kathode, increased in that of the polarising anode; the 
effect of the anode was increased in the neighbourhood of the polarising kathode; variable in that of the 
polarising anode. 
With reference to the after-effects, they appeared to show increase after diminution of effect; diminu¬ 
tion after increase. 
