_Application of Galvanism to the organs of hearing and of sight._
By applying Galvanism to different parts of the face, a flash of light
is excited in the eyes, which is stronger or weaker according to the
nature of the parts to which it is directed. These organs, though
delicate, are always affected in such a manner that the mechanism of
the eye sustains no injury from the metallic arcs when they are made
to communicate with only two plates of different metals. I received an
account of this phænomenon at Milan, several years ago, from the
celebrated Volta, who produced it by applying a conductor of zinc in
such a manner, that one end of it touched the bulb of the eye, and the
other the tip of the tongue armed with a plate of tin. In
administering Galvanism for diseases of the eyes, it is much better to
employ the pile. To excite the appearance of a flash of light, it is
not necessary that the eyes should be open; it takes place even if
they are shut, and covered with a bandage in a darkened apartment.
Some of the partisans of Euler, perhaps, may here maintain, that this
phænomenon of Galvanism is a deception, and that no light can be
really excited in such cases, as the production of light depends on
the emanation of rays from a luminous body which penetrate into the
interior part of the eye. But without entering into the examination of
this question, which is foreign to my principal object, I shall only
observe, that long before the theory of Galvanism was known, the
celebrated Darwin had found that when the eyes are shut, there are
certain internal stimulants which are capable of producing the
appearance of light and of colours.
In no case is the difference between Galvanism and electricity more
apparent than in the application of the former to the sight. Very
little benefit had been obtained by means of a metallic point inclosed
in a glass tube, which directed the electric charge from a jar to the
cornea; and besides, the shock of a Leyden jar applied directly to so
delicate an organ as the eye could not but be attended with danger.
Galvanism applied to the exterior part of the eye, in the same place
where a stream of electricity would have had no influence whatever,
has always produced a certain effect on the organ of sight, as is
proved by the following experiments.
EXPERIMENT I.
If you touch with one hand the bottom of the pile, and at the same
time apply to the summit different parts of the face moistened with
salt water, a flash of light will be excited in the eyes. The same
result will be obtained, if instead of touching the bottom of the pile
with the hand you touch it with the sole of your foot. No flash of
light is observed when the Leyden flask is employed in the same
manner.
EXPERIMENT II.
Having observed the preceding phænomenon in myself, and excited it in
others, I was desirous of proving it in regard to several persons at
the same time during the course of my public lectures, and for that
purpose I made use of the following apparatus. I arranged two metallic
plates in a horizontal position, at the distance of nine inches from
each other, so that six persons with their hands dipped in salt water
could touch the lower plate, and the upper one with the tips of their
tongue. A charged Leyden flask placed between the two plates being
then discharged, the whole of the persons experienced a violent shock,
but perceived no flash of light. It is well known however that, when a
similar arc is formed with the interposition of a very strong pile, a
flash of light is constantly observed; though the force in the second
case is much less than that excited by the explosion of the Leyden
flask. The same result will be obtained by bringing the upper plate
into contact with the nose.
EXPERIMENT III.
As my pupils took much interest in this research, some of them
suspected that the light of the apartment might perhaps have effaced
that excited by the electricity. I therefore made the apartment
entirely dark; and one of them taking a Leyden flask applied it to the
point of the nose of another person with whom he was in communication,
by laying hold of him with the other hand. By these means a very
strong shock was given, but no flash of light was observed. This
experiment was repeated, making the person who received the shock of
the Leyden flask to remain some time before in the dark, that his eyes
might be better enabled to perceive any faint light that might be
excited: but the result was still the same. To those who refer
Galvanism to the common laws of electricity, it will be difficult to
comprehend the cause of the different action exercised by the latter
on the organ of sight. But as it is not my intention at present to
enter into any discussion on this subject, I shall leave it to
philosophers to assign a reason for this phænomenon, and only observe,
that the properties above indicated will be sufficient to authorize
medical practitioners to prefer, in certain cases, the administration
of Galvanism by the pile to that of common electricity.
Before I proceed directly to the medical administration of Galvanism
to the organ of sight, I think it necessary to distinguish four
classes of blind persons whose cases ought to be considered
separately.
The first belongs to those who from their birth have been deprived of
the valuable blessing of sight.
The second comprehends those become blind in consequence of some great
læsion, or some derangement in the solids or in the fluids which
constitute the mechanism of the eye.
The third, those who have become blind by some morbid action, though
the mechanism of the eye has been little affected, and though no
impediment has occurred but in regard to the action of the optic
nerve.
The fourth class comprehends those who, though not actually deprived
of sight, have it much weakened in consequence of disease, or of some
other cause.
The administration of Galvanism does not hold forth much hope of a
cure to persons belonging to the first two classes. I however resolved
to attempt some experiments on this subject at Bologna; but though
there were a great many blind in that city, I found that they had
become so by the malignant influence of the small pox. This
observation will, I hope, be of service to the pursuits of the
celebrated Dr. Jenner, and of all those who exert themselves to
promote the beneficial practice of vaccine inoculation.
Being deprived, at Bologna, of any opportunity of trying the effects
of Galvanism in cases of persons born blind, I galvanised several who
had lost their sight at a very early age. I first applied the
Galvanism to the arms of five blind persons, some of whom had lost
their sight thirty, and others forty years and even more. By this
method they were familiarised with the idea of its mechanical action,
and learned to distinguish it from every other sensation. I then
applied Galvanism to the lips, and to the tip of the nose, in a
darkened apartment; but in three instances only the patients had a
real perception of light, to which they had been so long strangers. I
then applied it to cases of amaurosis, and at first had confident
expectation of effecting a perfect cure. One of my patients was a
woman, whom this disorder had deprived of the sight of one eye, while
that of the other was much weakened. After administering the Galvanism
different ways, I observed that the eye totally blind began to have a
perception of light, and that the sight of the one which was weakened
became much stronger. I then took a book, which I held at a
considerable distance from her; and removing it gradually further as
the Galvanism was administered, I observed, in consequence of this
method, that the patient’s sight daily improved. But I must freely
confess that the success obtained, though at first flattering, was not
of long duration; and that when the Galvanism was discontinued a great
deal of the benefit which had been obtained was again lost. On this
account, I was discouraged from administering Galvanism any more in
such cases. I am however of opinion, that by varying the method of
administration it may be attended with some utility. I shall here
observe, that having once had occasion to administer common
electricity in a similar case of amaurosis, I was never able to excite
the perception of a flash in the eyes of the patient, though the
electricity was applied directly to the eye itself.
I have had few opportunities of applying Galvanism in diseases of the
organs of hearing. Besides, I thought it almost needless to try a
method which had been already brought to a state of perfection by some
of the most celebrated professors of Germany and Berlin. I admired in
particular a very ingenious machine, invented for that purpose by a
German philosopher, and lately constructed in England by Mr. John
Cuthbertson, an eminent philosophical and mathematical instrument
maker, and celebrated for having constructed the large electrical
machine of Harlem. The apparatus consists of a metal lever, which by
means of certain wheels and machinery rises and falls every minute or
second, and at each time of falling forms a communication between
certain parts of the patient and the pile. In consequence of this
arrangement, the interrupted action of the Galvanism is renewed every
time that the communication between the patient and the pile is
re-established. Before my departure from London, I made several
changes and improvements in the usual construction of this apparatus,
in order to give it as much simplicity as possible. The following is
the manner in which I caused it to be constructed lately for my own
use. One extremity of the lever which forms the communication (Plate
III. fig. 1.), is fixed to the base or negative end of the pile, and
the other terminates in a small hammer, so placed as to strike a bell,
which by means of a bason of water is in communication with certain
parts of the patient, while an arc extends from the patient to the
summit or positive end of the pile. In consequence of this
arrangement, every time that the small hammer strikes the bell the
Galvanic action of the pile is repeated. In cases of deafness, I cause
the patient to hold in one hand an insulated metallic arc, one end of
which is brought into contact with the affected ear, and the other
with the positive end of the pile; and to immerse the other hand in a
bason of salt water placed above the bell. When this disposition has
been made, the wheel-work is turned round, which gives motion to the
lever; and every time that the hammer strikes the bell, a
communication is formed between the positive and negative ends of the
pile: consequently there will then be a circulation of the fluid, and
the Galvanism will exercise a direct action on the organ of hearing.
The apparatus, constructed in this manner, appears to me to be reduced
to great simplicity: and therefore I propose to extend the use of it,
by employing it to administer medical Galvanism to other diseased
parts of the body.
Before I conclude this article, I must suggest a hint respecting the
application of Galvanism to diseases of the teeth, founded on
information communicated to me on this subject by Mr. Fowler, an
eminent dentist of London. When the caries is concealed from the
sight, Mr. Fowler employs the following method to discover the
affected tooth. He first insulates the patient; and having put into
his hand the electric chain, he applies a small piece of wire to the
_dens sapientiæ_, drawing it gradually over its surface: he then
applies it to the next tooth, repeating the operation, and proceeds in
like manner with the rest till he comes to the diseased tooth, which
discovers itself by a violent pain producing an involuntary commotion
in the body. It is always remarked, that when this tooth is extracted
it exhibits a carious part not before visible. This method, therefore,
is of great importance, as it frequently happens in such cases that
the dentist, not being able to distinguish the diseased tooth from the
rest, is obliged to draw some that are sound before he can discover
it.