OF THE GALVANIC CURRENT ON THE MOTOR NERVES OF MAN, 
981 
Changes of current-strength depend upon various conditions which we have not 
been able to determine satisfactorily for the want of a sufficiently delicate galvano- 
metric record. Pending such a determination, which will be necessary when we come 
to the investigation of the time factor in electrotonic and post-electrotonic processes, 
we record the alterations which we have hitherto observed. When the electrodes are 
first applied the current grows gradually to a maximum, owing to the permeation of 
the skin with moisture, and, perhaps, to the accompanying vascular turgidity. On 
applying the electrodes to the skin previously prepared by soaking, the current at 
once reaches a maximum from which it declines at first rapidly, then more and more 
slowly. On renewed make of the same current instantly after interruption the 
galvanometer shows that the current has not recovered its strength. On renewed 
make after another interruption of 30-60 seconds the galvanometer indicates that the 
current has recovered. If a current that has been allowed to flow until the galvano¬ 
meter needle has ceased to fall is suddenly reversed, the current-strength is indicated 
to be greater in the new direction. These effects are such as would be produced, at 
least partially, by polarisation of the electrodes, and that this is so can be shown in 
the usual way by leaving the electrodes only connected with the galvanometer, either 
in direct contact with one another, or with the body intervening. Current is indicated 
in either case, greater of course in the former. We observe another fact indicating a 
fallacy to which the estimation of after-effects is especially liable, viz.: that after a 
given duration of current, with a given deflection of the needle, a given interval is 
followed by a greater deflection which rapidly subsides to the original deflection—a 
phenomenon which may repeat itself several times in succession, and obtains whether 
the electrodes are kept in broken or in closed circuit during the interval. Without 
committing ourselves to any positive statement, we may remark that our observations 
led us to suppose that during the passage of the galvanic current, an opposed electro¬ 
motive force is developed within the body which rapidly subsides. But however this 
may be, the importance of these alterations of current-strength as a source of fallacy 
are obvious, and they especially concern the question of after-effects. We have not 
been able as yet to assign to them their exact share for and against the manifestation 
of the after-effects. But we have, we think, succeeded in demonstrating the rough 
facts in spite of the fallacy, and it will be one of the objects of a future paper to find 
numerical expression for this vague quantity. 
Finally we may mention a further possible source of error, which however cannot be 
eliminated should it exist, viz.: the unequal alteration by the current of the conduc¬ 
tivity of the nerve and of the surrounding tissues. It is conceivable that the conduc¬ 
tivity of the surroundings of nerve should be increased in a greater proportion than 
Strome,” &c. Deutsches Archiy f. Klin. Med., 1876, p. 264). He lays stress upon the fallacies arising 
from alterations in the current-strength, and used the galvanic test only. He states that K.C.C. is 
increased after K.D., and variable after A.D.; that A.C.G. is increased after K.D., and variable after A.D, 
He does not seem to have determined any alteration of the opening contraction. 
