a piece of black walnut, say 14 in. long by 5
in. wide, 3/4 thick, having in the centre a bed to accommodate a carbon
plate, say 5 in. long by 2 in. wide, 1/4 thick. From the centre of this
bed a gimlet hole pierces the board. The denuded end of an insulated
wire is drawn through this gimlet hole from without inward (toward the
bed) and twisted in the form of a spiral to prevent its slipping back,
as well as to insure its more certain connection with the carbon. The
carbon is now placed in the bed, and kept there by a piece of muslin
drawn over it and tacked down. The wire should be of sufficient length
to reach the battery. I shall speak further on of the use to be made of
the surface board.

_c_) _The Water._ The quantity of water may be the same as that in an
ordinary bath. In those cases alone where it is intended to localize the
current by means of the surface board, and to concentrate it _very
strongly_ in one spot, the water in the tub should be left low enough to
leave the particular spot to be treated uncovered by this; the surface
board can then be applied to this spot without the loss to the current
of strength, through derived currents, inevitable in its application
under water.

The temperature of the water may range from 85 deg. to 105 deg.
Fahrenheit. As a rule the comfort of the patient may be consulted in
this respect. There are certain cases, however, where an especially high
or low temperature is indicated, and where the extremes mentioned have
to be touched.

_d_) _Chemicals._ Where these are added to the water of the bath, it is
for one of three purposes: viz. 1)--To exercise a direct therapeutic
influence on the patient, either internally by being absorbed, or
externally by their action on the skin; 2)--Through chemical affinity to
aid in eliminating certain metallic substances from the body; or 3)--To
further the absorption of morbid deposits. The various indications in
these respects will be treated of in their proper places.

_e_) _The Batteries._ In the choice of this, the most important part of
the electro-balneological apparatus, the greatest circumspection is
necessary. Inferior instruments and such as are liable to get out of
order frequently, have time and again been the means of discouraging the
beginner in electro-therapeutics, and causing him to abandon the study
of an art, the pursuit of which would have well repaid him for all his
labor. Fortunately our manufacturers here in