802 
GALVANISM. 
muscles. This experiment may be performed 
entirely under water. 
Fig. 3 represents a living frog placed in 
an exhausted receiver, the animal being tied 
to a plate of silver by a silken string, and 
having a piece of tin foil on its back. As 
often as the circuit is completed, the con- 
vulsions ensue. 
The experiment may be performed with 
a flounder in a similar easy and harmless 
manner. Take a living flounder ; wipe it 
pretty dry, and lay it flat on a pewter plate, 
or upon a sheet of tin foil ; and place a piece 
of silver, as a shilling, a crown piece, &c. 
upon the fish. Then, by means of a piece 
of metal, complete the communication be- 
tween the pewter plate or tin foil and the 
silver piece : on doing which the animal will 
give evident tokens of being affected. 
It seems that such movements may be 
excited by the contact of metallic substances 
in all the animals ; at least they have suc- 
ceeded, but in different degrees, in a great 
variety of animals from the ox to the fly. 
Fig. 4 shows the method of producing- 
convulsions in cold-blooded animals, by 
the influence of warm-blooded animals. 
The right hand of the experimentalist is 
placed in the ear, previously moistened with 
salt and water, of an ox’s head, while in the 
other hand a prepared frog is suspended by 
the foot, and the sciatic nerves brought into 
contact with the ox’s tongue. Convulsions 
are immediately produced in the muscles of 
the frog. 
The human body, whilst undergoing cer- 
tain chirurgical operations, or its amputated 
limbs, have been convulsed by the application 
of metals. But the living animal body may 
be rendered sensible of the action of metallic 
application in an harmless way, and both the 
senses of taste and sight may be affected by it, 
but in different degrees according to the va- 
rious constitutions of individuals. 
Let a man lay a piece of metal, as zinc, 
upon his tongue, and a piece of some other 
metal, as silver, under the tongue ; on form- 
ing the communication between those two 
metals, either by bringing their outer edges 
in contact, or by the interposition of some 
other piece of metal, he will perceive a pe- 
culiar sensation, a kind of irritation, accom- 
panied with a sort of cool and subacid taste, 
not exactly like, and yet not much different 
from, that which is produced by artificial 
electricity. The sensation seems to be more 
distinct when the metals are of the usual 
temperature of the tongue. The silver or 
gold may be applied to any other part of the 
mouth, to the nostrils, to the ear, or to other 
sensible parts of the body, whilst the zinc is 
applied to the tongue ; and on making the 
communication between the two metals, the 
taste will be perceived upon the tongue. 
The effect is rather more remarkable when 
the zinc touches the tongue in a small part, 
and the silver in a great portion of its sur- 
face, than vice versa. Instead of the tongue, 
the two metals may also be placed in con- 
tact with the roof of the mouth, as far back 
as possible ; and on completing the com- 
munication, the taste or irritation will be per- 
ceived. 
Different persons are variously affected by 
this application of metals ; with some the 
sensation or taste is so slight as to be hardly 
perceived, whilst with others it is very strong 
and even disagreeable. Some persons feel 
merely a pungency, and not properly a taste. 
In order to affect the sense of sight by 
means of metals, let a man in a dark place 
put a slip of tin foil upon the bulb ot one of 
his eyes, and let him put a piece of silver, 
as a spoon or the like, in his mouth. On 
completing the communication between the 
spoon and the tin foil, a faint Hash of white 
light will appear before his eyes. This ex- 
periment may be performed in a more con- 
venient manner, by placing a piece of zinc 
between tire upper lip and the gums, as high 
up as possible, and a silver piece of money 
upon the tongue ; or else by putting a piece 
of silver high up in one of the nostrils, and 
a piece of zinc in contact with the upper 
part of the tongue ; for in either case the 
flash of light will appear whenever the two 
metals are made to communicate, either by 
the immediate contact of their edges, or by 
the interposition of other good conductors. 
By continuing the contact ot the two 
metals, the appearance of light is not con- 
tinued, it being only visible at the moment 
of making the contact, and sometimes, 
though rarely, at the instant of separation : it 
may therefore be repeated at pleasure, by 
disjoining, and again connecting; the two 
metals. When the eyes are in a state of in- 
flammation, the appearance of light is much 
stronger. 
W hen the science was advanced no farther 
than the knowledge of the above-mentioned 
facts, it was doubtful whether the convul- 
sions of prepared animal limbs, and the sen- 
sations which are produced by the application 
of metallic substances, were owing to some 
electrical property peculiar to the animal 
parts, which might perhaps be conducted 
through the metals from one part to the 
other; or to a small quantity of electricity, 
which might be supplied by the metals them- 
selves. The latter supposition however was 
soon verified by the result of various ex- 
periments, which prove in the most con- 
vincing manner that electricity is produced 
by the mere contact, not only of metallic 
substances, but likewise of other bodies. 
The electricity thus produced by the mere 
contact of two bodies is so very small as not 
to be perceived without great care, and 
without using some of those artifices tor dis- 
covering small quantities of electricity, which 
have been mentioned above. But the dis- 
coveries of the ingenious Mr. Volta have 
shewn a method of increasing that electricity 
to a most extraordinary degree. We shall 
now proceed to state those facts in as com- 
pendious a manner as the nature of the sub- 
ject will admit of. 
The ac tion of metallic substances upon the 
organs of living, or of recently dead animals, 
has been fully manifested by the above-men- 
tioned discoveries of Galvani and others ; 
but, previously to those discoveries, a variety 
of facts, frequently asserted, imperfectly 
known, and often disbelieved, indicated a 
peculiar action arising from a combination 
of different metallic bodies in certain cases. 
It had been long asserted, that when por- 
ter (and some other liquors also) is drunk 
out of u pewter pot, it has a taste different 
from what it has when drunk out of glass- 
or earthenware. 
It has been observed, that pure mercury 
r etaLns its metallic spl endour during a long 
time; but its amalgam with any other meUl 
is soon tarnished or oxidated. 
The Etruscan inscriptions, engraved upon 
pure lead, are preserved to this clay ; where- 
as some, medals of lead and tin, of no great 
antiquity, are much corroded. Works of 
metal, whose parts are soldered together by 
the interposition of other metals, soon tarnish 
about the places where the different metals 
are joined. 
When the copper sheeting of ships is fast- 
ened on by means of iron nails, those nails, 
but particularly the copper, arc readily cor- 
roded about the place of contact. 
It had been observed that a piece of zinc 
might be kept in water for a considerable 
time, with hardly oxidating at all ; but 
that the oxidation would soon take place if 
a piece of silver happened to touch the zinc, 
whilst standing in water. 
Since Galvani’s discoveries, the action 
arising from the combination of three con- 
ductors has been examined with great care, 
and with considerable success, especially by 
Mr. Volta, who lately discovered that the 
slight effect of such a combination may be 
increased to a prodigious degree by repeat- 
ing the combination ; for instance, if a com- 
bination of silver, zinc, and water, produce 
a certain effect, a second combination (viz. 
another piece of silver, another piece of zinc, 
and another quantity of water) added to the 
first, will increase the effect ; the addition 
of a third combination will increase the ef- 
fect still more, and so on. 
Previously to the description of the com 
struction of the very remarkable effects of 
those repeated combinations, which are now 
generally called galvanic batteries, it will ba 
necessary to state the principal laws, which 
have been pretty well ascertained with re- 
spect to the simple combinations. 
1. The conductors of electricity, which, 
strictly speaking, do almost all differ from 
each other in conducting' power, are never- 
theless divided into two principal classes. 
Those of the first class, otherwise called dry 
and perfect conductors, are the metallic subr 
stances and charcoaL Those of the second 
class, or the imperfect conductors, are water 
and other oxidating fluids, as also the sub- 
stances which contain those fluids. But as 
the substances of the second class differ in 
conducting power much more than those of 
the first class, so they may be subdivided 
into species. 
Mr. Volta arranges those substances in the 
following order, commencing with the least 
active ; observing, however, that this order 
is subject to a considerable deviation,, es- 
pecially with respect to the latter species, 
and according as they are combined with 
certain bodies of the first class. 
“ 1. Pure water; (It may be' ! observed, 
that water holding in solution common air, 
and especially oxygen gas, is much more ac- 
tive than water deprived of air by boiling or 
otherwise.) 2. Water mixed with clay or 
chalk; 3. A solution of sugar; 4. Alcohol; 
5. Milk ; 6. Mucilaginous fluids ; 7. Animal 
gelatinous fluids; 8. Wine; 9- Vinegar and 
other vegetable juices and acids ; 10. Saliva ; 
11.. Mucus from the nose; 12. Blood; 13-: 
Brains; 14. Solution of salt ; 15. Soap suds; 
16. Chalk-water; 17. Concentrated mineral 
acids; 18. Strong alkaline leys ; 19. Alkaline 
fluids ; 20. Livers of sulphur.” 
