Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

catalytical and polarizing effect is as certain/// in progress. But the visible physiological effects that are manifested by contrac- tion, occur rather at the moment when the density of the current suddenly rises from zero to a certain height, as is the case on establishing the circuit, and also when the density of the cur- rent descends again from a certain height to zero, as occurs on breaking the circuit. Setting out with these facts, Dr. Du- bois-Reymond gives us a great electro-physiological law for tho motor nerves in the following terms: " The motor nerve is not excited by the absolute amount of the density of the current of electricity, but merely by the variations which occur in the density of that current from one instant to the other; and tho physiological effect is the greater, the more considerable are the variations of the density of the current; that is, in proportion as the variations take place less or more rapidly, or as they aro more considerable in a given space of time."* But we can say still further, that it is not absolutely neces- sary to actually break the current that is traversing a nerve in order to produce contractions ; for these physiological effects are brought about even by the minor variations in the density of tho electric current, as is shown by moving one of the electrodes a little farther from the other while the current is flowing, and while both electrodes remain on the skin ; or by now pressing the electrode more or less ; or it can also be done by increasing the current from switching on other scries of cups through the key-board, or by quickly taking a portion away, or by diverting a portion of the current. But this power will be shown still more, if the direction of the current is suddenly reversed every second, as by the current turner of the key-board, although tho current is constantly flowing ; besides, this latter effect is observed to be more and more powerful, for a time at least, until the nerve is over-fatigued, or exhausted, when it will be observed to diminish ; but that diminishing I do not call paralyzing in any sense of the tcord, more than hard work is paralyzing; unless they are carried to great extremes as to * Untersuchunger uber thieristhe Elektricitat, Berlin, 1848, vol. i. p. 258.