tery.

Stöhrer's Bat- Rub the quicksilver well over the plate with a piece of sponge until it is quite bright; replace the plate for a moment in the acid, and notice if any bubbles of gas are evolved; if so, the amalgamation is imperfect, and more quicksilver will be required. If no gas is generated, rinse the plate for a moment in tepid water, and stand it aside to dry. At the same time the carbons should be soaked for about five minutes in tepid water (not hot), to dissolve the zinc salts with which they become encrusted. They may be also scrubbed with an old nail or toothbrush. Clean all metallic connexions with emery paper, and do not screw the carbons and zincs together again until they have been allowed to dry for twelve hours. Charge each cell with a solution of one part of strong sulphuric acid to nineteen of water, and put in each a pinch (about as much as a pinch of snuff) of sulphate of mercury, which will greatly contribute to preserve the amalgamation of the zincs. Dr. Stöhrer constructs this battery in several sizes, varying from thirteen to forty pairs of elements (fig. 7), adapted for hospital use; and in a portable form (fig. 8) of essentially the same construction, but smaller and lighter. It is a most efficient and serviceable instrument, and equal to all the requirements of electro-therapeutics. Its price is from 67. to 157. 15s.

Pulver

macher's Chain Battery.

Pulvermacher's Chain Batteries.-As before stated,

the fundamental requisite of a voltaic current for

macher'sChain

therapeutic application is its constancy. To ob- Pulver-
tain this property and at the same time a cheap Battery.
and portable instrument, has been for years the
effort of manufacturers. The most ingenious
arrangement of the largest number of elements in
the smallest space is to be found in Pulvermacher's
chains. But in action they are inconstant. Steeped
in vinegar they yield currents of high tension, but
their action rapidly declines, and they become much
weakened in a very short time. They may in the
absence of a better instrument be occasionally
of use for purposes of diagnosis, employed with
electrodes in the same way as other batteries; but for
therapeutical applications they are unsuitable, and
worn upon the body
the body as advocated by the inventor
they exercise little or no benefit, except perhaps in
some cases where they appear to act from their
electrocutaneous excitation as counter-irritants. I
am led to make these remarks and to describe these
forms of battery from the very numerous letters of
inquiry that I receive regarding them. The prin-
ciple of their formation is that of the combination.
of a great number of elements, from 300 to 400,
having butsmall surface. The original and best known
forms of the chains are shown in figs. 9 and 10. The
elements of which the chains are now constructed are
formed of a cylinder of copper plate perforated with
longitudinal openings, and within this cylinder is a
cylinder of zinc without perforation. The zinc is

Pulvermacher'sChain

Battery.

separated from immediate contact with the copper by a few stout threads. An unbroken link which forms part of the copper cylinder serves as the means for joining the several segments. This construction permits the withdrawal and renewal of the zinc when necessary.

Requisites of a Faradic Instrument.

FARADISM.

The essential requisites for a faradic instrument are: 1. The possession of a primary and secondary coil, constructed after certain proportions of thickness and length of wire.* 2. A sufficient range of power. 3. An exact means of graduation. 4. Con

* The distinction between the primary and secondary coil therapeutically, is mainly a question of the greater tension of the current of the secondary coil, enabling its current to penetrate easily several thicknesses of muscle.

stant readiness for action, and capability of being placed out of action without trouble and loss of time.

large Volta

Duchenne's large Volta-faradic apparatus.-In this Duchenne's instrument the two coils forming the systems of faradic Instruinduction are composed of two copper wires differ- ment. ing in diameter and length, and covered with silk.

Duchenne's large Volta-Faradic Instrument.

The thicker and shorter of the two wires is rolled around a bundle of soft iron wire so as to form a coil (the primary coil). The ends of this wire terminate upon two small plates of platinum at the level of the knobs E, L, fig. 11, which are the positive

Duchenne's large Volta

ment.

and negative poles of the battery enclosed in the

faradic Instru- drawers u and u'. The finer and longer wire is rolled round the thicker and shorter coil and forms the secondary coil. Its ends terminate at the two springs of the commutator of the coils (E, fig. 14). This commutator is for the purpose of transmitting rapidly and alternately the current either of the primary or secondary coil to the conductors attached to the knobs P and Q, (fig. 11), according as the needle (F, fig. 14) is turned to the right or left, as is shown on a plate situated above the needle. The battery which works the instrument is composed of three pairs of elements contained in the drawers u and u', two pairs in the upper and one in the lower. Each pair consists of a carbon plate (c c', fig. 12) fixed to a cell of hard caoutchouc, and of a

zinc plate, z z', of the same surface as the carbon and separated from it by a cloth diaphragm. The platinum wires which form the carbon contacts are arranged as in the smaller instrument (fig. 17, page 30), while the zinc contacts differ in each of the pairs-1. In the lower drawer (u, fig. 11) a strip of