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DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 195
and the cathode in the lighter the natural osmotic current is not only
overcome but is reversed."
If a substance containing water, as a ball of wet clay or a piece of
muscular tissue, have an anode connected with a current of sufficiently
high potential attached to one side, with a cathode attached to the oppo-
site side, the watery contents of the substance are conveyed to and appear
in excess on the cathodal side; at the same time the anodal side be-
comes less damp ; also, if a capillary tube be filled with water and an
anode and a cathode be similarly arranged, the water flows toward the
cathode.
As a membrane or tissue may be considered to be a series of tubes
in close contiguity, it is apparent that the movement of fluids must take
place through them in the direction the current is passing.
These examples are an expression of electrical force. The applica-
tion of this law of the passage of fluids from a higher to a lower elec-
trical potential is the fundamental process which is employed in electrical
diffusion of medicaments. The depth to which medicaments may be
conveyed depends upon the conductivity of the tissue and that of the
medicament which is being ap])lied.
" The cataphoric action of electricity has often been made use of
experimentally to introduce drugs into the system through the skin.
In man quinin and potassium iodid have been thus introduced and
subsequently been detected in the urine."
As early as 1859 Dr. B. W. Richardson used this process to pro-
duce local anesthesia, and completely demonstrated its power in this
direction. It has also been clearly proven that when a solution of
cocain is applied to the skin, its characteristic action upon the mucous
membrane will not here take place. But when the anode is wet with
the solution and a galvanic current is passed through the e})idermis
to the cathode, placed upon an indiflerent surface, anesthesia is effected
over the surface covered by the anode and to an indefinite distance
inward.
This effect is not |)roduced by the current alone, which has been
abundantly proved by conclusive experiments, these having been fol-
lowed by demonstrations confirming the above statement. When the
medicaments so applied have anesthetic or analgesic ])roperties their
characteristic eflPects are produced.
When this principle is applied to the transfer of medicaments it is
found that they pass for an indefinite distance into the contiguous tissue
along with the current from the anc^dc toward the cathode, but with
some degree of diffusion ; the diffusion depending upon the resistance
of the tissue and upon the extent of the surface of the cathodal (nega-
tive) electrode.