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XII (D)
CONTINUATION
(AS A
PAPER)
§. 52. There is therefore a well markedwell-marked difference between the nerves called movement nerves and the sensation nerves. The
experiments Q and R on the tongue, just mentioned, show us obviously, that nervesthat nerves are affected and irritated by the electric fluid
set in circular motion by the action of metals of different species applied with one extreme to the humid parts, and communicating
between them with the other extreme. Those experiments show the office or proper
function of the nerves affected and traversed by the said current, i.e. the muscular movements or
sensations.
$. 53. From that we must then again conclude, according to the
deductions drawn from so many experiments and observations (§. 17, 20, 40-56), that the proper, direct action of the electric fluid is not to irritate the muscles so that
contractions are immediately excited but rather torather to stimulate the nerves encountered on its passage and to
set their activity in motion. Indeed if the electric fluid set in motion in the described manner directly excites muscular movement, why should
it not produce more or less strong movements in the tongue, a muscle so mobile, when in
experiment Q it invades, penetrates and transverses quite a wide stretch of it? It seems that we would see, if not the whole tongue, at least the part
between the two metal armatures go into convulsions and contortions, and bend from side to
side. But nothing like that happens: we feel a simple sensation of taste, due to the nature and
function offunction of the numerous, delicate nerves included in its tip that are the main site for taste. Those nerves are moreover closemoreover close to the surface, so that they can be easily reached and excited by the electric
fluid.
Do we want to obtain movements of this very tongue? We need only to arrange the experiment in such a way that the nerves having this task,
which go from its root to the internal parts, are in the route of the electric current so that
some of them are invaded by it. This can be realised by experiment R and others described
above (§ 50, 51). Having cut the tongue out of an animal, close to its root, we
applied on the cut itself one of the metal armatures, particularly a piece of tin
foil.
§. 54. Though these experiments on the tongue (excited
to most lively movement or affected by the sensation of taste corresponding to the nerves
irritated by the current of the electric fluid) are sufficientare sufficient for establishing the indicated distinction (§. 52) of the two classes of nerves, I was not at all happy
at not being able to excite in the same way some other sense apart from taste. I then made some attempts and I succeeded completely with sight(a) and only to some extent with the sense of
touch. We will see now some of the ways ofways of doing such experiments, that could be easily repeated by anybody with no
difficulty.
Exp. S. Let us put ourselves, if not in a perfect darkness, far from the too strong light
of day. Let us apply precisely on the bare eyeball one end of a ribbon of tin foil, or of the tinned paper improperlypaper improperly called
"silver paper" (Cambric-paper), in such a way that the other extreme is hanging
freely. Let us then apply to the lips or better we introduce
into the mouth a silver spoon, or any strip of this metal, of gold or even copper or
ironor iron – silver is, however, the best of all. Any time the two metal armatures are put in mutual contact, or the two metals are put in communication by means of another metal, the, the eye will be struck by a more or less strong sensation of light,
which disappears immediately like a flash of lightning if the metals are kept in contact.
Exp. T. If instead of leaving the armatures at rest, their contact is broken and re-established with more or less rapidity, the light pulses are
repeated, and one gets a sensation of undulating light. If the separations and
reconnections follow each other with great speed, we notice annotice an almost continuous light, through a series of small shocks or
the friction of one blade against the other obtaining trembling and little jumps.
§. 55. Though the vivid lightning in experiment S happensS happens only at the moment
when the metals touch, and disappears immediately, it remains nevertheless, as long as the circle is not broken, a dim light but so weak that it is perceived
only in the complete darkness that happens, as if a black sheet is placed on the eyes, at the moment of the separation of the metals. In order to perceive this change to complete darkness, it is necessary that the eye
be placed in a fully dark environment; if it is not, then the eyelids must be kept closed against the armature touching the eye balleyeball. It
seems, moreover, that at the moment of separation of the metals another lightning
flash, but very weak, occurs, followed by said complete darkness.
§. 56. This persistence of the sensation that lasts as long as the touching of the metals
(the rest of the circle remaining uninterrupted) and the termination of the sensation at the moment of
interruption, present a quite surprising phenomenon. This is more evident in the experiments with the tongue, where the sensation of taste lasts and increases up to a certain point if the tin and the silver, continuing to be applied, the first to the tip or
edge of the tongue, the, the second to another part, are kept in communication. The sensation ends, all of a sudden but not completely, as soon as the communication is broken. The phenomenon, I say,
by well considering this result, is very surprising, since it proves that the circulation of the electric fluid (caused by the application of two different metals to conductors of another class, such as the humid conductors, and the junction of the said metals so that a circle is obtained, composed
of two arcs, one all metal, the other non-metallic) continues permanently, as long as the circle is
not broken. Consequently the action of the two metals is not an electric discharge of short duration followed by an equilibrium state. It is rather a sustained action deriving from
some sort of force exerted continuously by metals, with greater or less energy according to their nature, on the electric fluid of the materials in contact. We will come back to this
point.
§. 57. I have already found, following my experiments (at the period
when I sent my 2nd letter to Mr. CAVALLO), that all effects,
be they muscular contractions or the sensation of taste, were considerably strong when opposing
an armature of silver or gold with an armature of zinc instead of one of tin, which
I had used previously. It is the same with the eye. The pulses of light are more vivid if we apply to the ball, instead of the tin paper, the rounded end of a zinc
strip, and this is put in communication with the other tag of silver or gold kept in the mouth, both
when the armatures were in put direct contact or with the interposition of other
metals.
§. [58.]
1 Exp. U. The preceding experiment can be performed inversely, by applying silverapplying silver or gold to the eye, tin or zinc to the mouth. We get approximately the same effects, with this
added advantage that it is thus possible to excite both the sensation of light in the eye and the acid taste on the tongue, if weif we apply
the tongue appropriately to the zinc or tin strip. Whereas with contact to the silver the tongue does not feel the acid taste but another
bland one, difficult to perceive, as I will have the opportunity to discuss
later.
Exp. V. We can also experiment with both eyes at once, by applying the tin or better the zinc onto one and the silver onto the other one. All succeeds equally well, the light pulse being stronger, due to the double
sensation2.
§. 58. We are not going to try to discover and determine the route taken by the electric current in all the experiments, i.e. to know theknow the exact fibres or
vessels which it prefers to follow. Suffice it to say that in its circuit from the fore part of the eye to the internal part of the mouth it must encounter the back of the eye
itself. Consequently the retina or the nervous membrane that is the organ of sight, cannot avoid the incursion of the electric fluid. This happens
any time the metal armature is applied immediately to the eye balleyeball and not
to the exterior of the eyelids. In such a case the easiest way for the flow of the electric fluid seems to be the ball itself, due to the
humours contained in it. On the other hand, if the armature is applied to the eyelids, the electric fluid can follow a detour and follow other
routes on the exterior of the eye, i.e. finding vessels and conducting fibres more or less far from it. This is the reason why the experiment is uncertain and variable; why the sensation of light is sometimes not obtained, or it is rather weak when the eyelids are not kept well open and the armatures touch the ball and the eyelids at once; and why the effect is totally lacking if the armature is applied only to the
eyelids.
§. 59. We could be surprised to see that the current of
electric fluid can excite the sensation of light, even when it does not go through the eye nor through the retina, in a word without affecting the natural seat of
sight. Nevertheless we can conceive that this can happen in the event of it encountering on its passage some expansion of the optic nerve. Why could not this nerve stimulated, even out of the eye, be affected by the sensation proper to its nature? This is the way to explain the following experiment, communicated to me by Mr.
CAVALLO, following the experiments on the eye described in a letter of mine of May 1793. I give here this experiment with the addition of some details, and also other analogous, most curious experiments I was led to
conduct.
Exp. X. Let us introduce well into the nostrils a tag of gold or silver on one side, one of tin or better of zinc
into the other. Any time these two
strips are put in mutual contact, or through a third metal of any kind, we will feel the sensation of light, though weaker, as in the preceding experiments, and this in both eyes or in one only, depending on
whether both the armatures, or only one, are applied well inside close to the root of the
nose.
Exp. Y. A weak pulse of light is obtained if only one of the metals is placed inside the nose, the other one being kept in the
mouth, when the two metals are put in mutual communication.
Exp. Z. The same effect, though weaker, is obtained if the two armatures are placed in two
different parts inside the mouth, be it the gums on one side or the other, the tongue or the upper
gums, or better the two jaws, particularly the parts closest to the root of the tongue.
§. 60. In the two experiments X and Y, where one or both the armatures are applied to the interior of the nostrils, the explanation of the weak light sensation excited is easily found in the communication of some kind between nerves included in the upper parts of the nostrils and the optical nerve. Such communication is reciprocally shown when the action of a vivid light impacting on the eyes irritates the inside of the nostrils and produces a sneeze. It seems a little more difficult to explain how the same sensation of light is caused in
experiment Z, where the two metals are applied only at the internal part of the
mouth. However, it can be conceived that the electric fluid, in its path for completing the circuit most easily, partitions, partitions itself in several vessels and conducting fibres and, leaving the shortest
route, at least partially, in order to follow the best
of those conductors, it can catch some expansions of the optical nerve. It can then stimulatethen stimulate them
enough to excite the aforementioned sensation of
light, which in this case is, moreover, very weak.
§. 61. Coming back to the experiments in which the electric current is
directed by the suitable position of metal armatures to cross directly through the eye
and strike the retina itself (the very seat of the sense of vision), where it excites a much more vivid sensation of light. We can
well imagine that different circumstances can have an influence on the greater or lesser intensity of the sensation, such as the more or less precise application of the metal
tag to the eye ball, the position and extension of such application, the cleanliness of the applied surface, the more or less abundant fluid wetting the eye, etc. Moreover there are differences
in the eyes of different people, that will make them more or less sensitive in these experiments. I have nevertheless found nobody with good or bad sight
who could not experience theexperience the sensation of pulsing light, provided the experiment is well done, i.e. the metals have been well
chosen, properly applied and put in contact.
§. 62.I am moreover certain that the experiment will succeed even with
people that are blinded by cataract, or any other disease except the insensitivity or paralysis of the optic nerve.
These results could actually be of some help in determining the type of
disease. If well used, who knows, they might even lead to the discovery of some remedy for
the paralysis itself, whether more or less advanced. But let us leave this to the
Doctors.
§. 63. When one of the metal armatures is properly applied to the eye ball, it is not necessary to apply the other one toone to the
lips, the tongue, any other part inside the mouth, or the nostrils, as in the experiments described,
to obtain the sensation of light, i.e. the more or less vivid light pulse at the moment
when the two armatures are put in mutual communication,
directly, directly or throughor through an intermediate metalintermediate metal arc.
Similarly, to excite sensation of taste,
when the zinc or tin is applied to the tip of the tongue, it is not necessary to apply the silver or gold to the back of that tongue nor to any other part of the mouth. This second armature can be applied withapplied with success to any other part of the body even far apart, provided it is humid inside and outside.
For not only thick, dry clothes but also a single linen sheet, thin non-moistened
paper, and even not damp skin, suffices to slow down the electric current
considerably, or even halt it. In all the experiments described it has rather small force or tension (I
prefer using this term, as I have on several occasions). It is therefore incapable of overtaking
any serious obstacle, as I will explain better elsewhere.
Exp. AA. Having chosen the two metals, e.g. silver and zinc, we can keep one of them in
one hand, previously wetted if it is not naturally humid, and bring it into contact with the other,
which has been applied to an eye or the tip of the tongue. At each touching we will
experience the sensation of light in the first case, of taste in the second.
These sensations will only be less vivid due to the fact that the electric fluid
set in motion by these contacts must traverse a longer distance from the tongue or from the eye
to the hand than the distance from the tip of the tongue to its back or parts close in the mouth, or from the mouth to the eye. Such a longer distance involves a more resistant route, since
humid conductors areconductors are far from being perfect conductors, and this cannot but slow
down the electric fluid current.
Exp. BB. Let twoLet two, three or more people make a chain
by holding (well dampened) hands or otherwise communicating between them through watery conductors, e.g. with ropes or with
strips of cloth or cardboard soaked with water, or by putting their hands in some vessels. The first person
in the chain has his eye or the tip of his tongue properly armed with strip of tin or better of zinc. The last person
with a piece of silver in his hand puts the two metals in mutual contact: The sensation of sudden light (repeated if the contact is repeated) or taste will be felt, though
the sensation will be the weaker the longer is the chain carrying the electric stream.
It will be weaker if theif the hands and bodies composing the chain are less humid or the hands are less strongly
held.
§. 64. It should be noted here that, no, no matter how humid these
bodies in the chain are, no matter how firm the contact, it will neverwill never be equivalent to
true continuity. This kind of break or imperfect continuity, like all such conductors
which are not as perfect conductors as the metals, but much inferior, puts some obstacle
in the path of the electric fluid, so that it is somewhat slowed and retarded. Nevertheless the sensations of taste and
light can still be excited to a remarkable degree with a chain of 8 or 10 people, keeping their hands well humid and strongly grasped.,. if the first has the
tip of his tongue or his eye ball armed with a piece of zinc, and the last holds a piece of silver and completes the circle
by putting the two metals in contact.
§. 65. There is more: in the same manner that one of the armatures can be placed far from the eye and
the tongue (§. 63-64), we can even place the other armature at
a distance. We can place both of them onto another humid
body, or water in general: without directly touching any part of the animal body.
It suffices that the eye or the tip of the tongue be placed in the unbroken chain
of humid conductors that will be passed through by the electric fluid set in motion by
the action of two different metals when, through their contact, the circle is completed. It suffices for the nerves excitable for
vision or for taste to be part of the chain that the electric current is obliged to follow. Among the numerous experiments I am going to describe
a few as examples for all other similar ones.
Exp. CC. One person applies the ball of his eye to one end of a
strip of leather or cardboard well soaked with water. This strip touches a zinc tag with
its other end, at several points. This same person gives his hand to a second person (I once again
warn that in this kind of experiment it is necessary to wet the hands if they are dry)
whose other hand is immersed in a large basin if water, in which there is also immersed a
piece of silver. At the moment that the pieces of zinc and silver are put in mutual communication, directly or through the interposition of any other metal or a number of metals, the eye that is in contact with the soaked
strip will perceive a pulse of light. This will happen any time that, having separated the two metals, they
are again put in contact.
Exp. DD. Let two, three or several people form a chain,
by holding (damp) hands or joined by other well-moistened materials, or through
expanses of water, or mixed types of joining. Let the first person in the chain put the tip of
his tongue in a large glass of water, in which a piece of zinc or a strip of tinned foil is also immersed,
Let also the last person hold in his hand a piece of cardboard, leather, linen, or any other well-soaked material, to which is applied, close to his hand or at any distance, a
tag of silver. Finally let this silver piece be put in contact with the other of zinc or
tin. The tongue placed in the water will perceive very well the acid taste, this sensation increasing during the first moments and then remaining constant, as long as the circle
is not broken (§. 56).
§..66. It is now easy to understand that, through suitable arrangements, it is possible to excite at once both the sensation of light and of taste, both in the same person and inand in two or moreor more. It is also possible to excite
convulsions in several frogs. Anybody can imagine a thousand different ways of arranging
such experiments. I wish nevertheless to describe one more experiment, representing many others.
Exp. EE. In a long chain of several people holding
hands, we may have some that communicate through their eye balls, others through the
tip of their tongues; others through the direct contact of a finger, or via a piece of cardboard or other
well-soaked material; finally others through prepared frogs (i.e. cut in such a manner that the
thighs are connected to the trunk only by the sciatic nerve) forming equally communication rings. As soon as the first person
in the chain, holding in his humid hand a tag of zinc, and the last person a piece of silver, put the two metals in contact thus completing the circle, simultaneously are excited the convulsions in the legs of the frogs, the light in the eyes and the taste
on the tongue tips, i.e. the movement and sensations proper to the nerves that are encountered on its route by the electric fluid
set in motion by the action of the metals.3
§. 67. I had already observed (§. Exp. AA, BB) that the longer
the route or the arc of humid conductors that the electric fluid has to pass through, the, the less efficient is the action of this current on the nerves. I have nevertheless succeeded in exciting strong convulsions in several frogs at once, interlaced with 14, 16, 20
people. This is a nice, very surprising experiment. It is necessary for the purpose to have a non-humid floorhumid floor, otherwise all the electric current, or a large part of it, will make the tour, from the first person
holding the zinc to the last holding the silver, through the floor instead of passing through the long chain of people. It
may happen, if the floor is too humid, that, that the experiment
could fail even with a chain of two or three people, particularly if the feet of one are very close to the feet of
another and theand the soles are very damp.
§. 68. As I have already said (§65 and 66), these experiments can be varied in a thousand
ways. It will always be found that the conditions to be met for success are essentially the
following:
-
A circle of two conductor arcs must be established, one metallic, the other of materials
soaked with water or with some other conducting liquid, which must not be oily.
-
The metallic arc must not be of only one metal, but must consist
of two or more pieces, in such a manner that the two extremes (at least the surfaces touching the
ends of theof the non-metallic arc) be of metals of two different species.
-
Such a conducting circle should not contain the smallest interruption, no interposed insulator or bad conducting body, such as a not soaked piece of wood,
leather or cardboard.
This is all that is needed disturb the electric fluid and set it moving due to
the activity proper to all metals, but different in different metals. The movement is through all the entire circle. There are no other conditions required for
arousing, as one intends, sensation, sensation or movement nerves, only that
IV the non-metallic arc, i.e. the arc conducting only
by its humidity, constituted by a single piece or with several contiguous pieces,
be arranged in such a way that thethat the nerves includednerves included are
practically the only conductors in the communication path.
§. 69. This last condition is nevertheless not so essential as the
others, which are absolutely necessary. Its influence is only to make stronger or less strong, more or less sensitive, the irritation of said nerves, depending
on a more or less large amount of the electric flow in the circuit being obliged to pass through them. Their excitation
is brought to its highest degree when the nerves are the only path offered. On the other hand the excitation is insufficient, when the stream finds a large
enough route offering the easiest way outside the nerves. I will come back to this point later.
§. 70. As far as the metal arc is concerned, no, no matter its length,
size, shape, the number and variety of pieces composing it, provided they are all metallic and
touch each other exactly. The action depends exclusively on the diversity of the metals at its extremes where the contact is with the
ends of the non metallic arc, i.e. the conducting humid arc (the action is strongest if the two
end metals are zinc and silver, mediocre if they are silver and lead, less than mediocre if lead and iron, and very small if silver and copper, copper and iron, iron and lead, lead and tin). The action is what can be obtained with such combinations of
metals applied to the ends of the non metallicnon-metallic arc communicating between them directly or with the interposition of other metals, no matter
what they are.
§. 71. The condition for the non-metal arc, i.e. the arc conducting through its humidity, is not the same as for the metallic arc. The length of such
an arc is not indifferent, and even less the number of the pieces composing it.,. e.g. the people composing the chain. These circumstances contribute considerably
to diminishing or slowing the electric current, in making less powerful the action on the nerves through which it must flow, as already shown and explained (Exp. AA, BB and §.64. 64). But what is more harmful is if this non-metal arc, from its beginning to its end or only in some parts, is too narrow, if the pieces are touching each other
at a small number of points, etc., as I will explain below.
On the other hand, the metal arc can be made for whatever length of a very
thin wire, the number of pieces can be large, they can touch each other in few points withpoints with a small reduction ofreduction of the action. The reason of this large difference is easily understood by considering how the metals are so more excellent conductors than the humid materials or the same water.
§. 72. I will perhaps be better understood if I represent the things with some models or types, particularly for the most complicated cases resulting from the combination of several metallic and nonand non-metallic parts.
Fig.1
is the simplest of all. A is the humid conducting arc
consisting of one only piece. B is the metallic arc composed of two different metals, i.e.
a silver rod B and theand the other of zinc C, applied at bc to the piece A and touching each other
at d. With such disposition the electric current is excited and moves round very easily, in the direction cbd.
Fig 2 differs from the preceding one only by the interposition
between the two metals B C of a third piece D, which here is of iron, but could be indifferently any other metal; the effect is the same as if B C
touched each other directly.
Fig 3 differs from the preceding two only by a larger number of pieces D E F interposed
between B C at the ends of the metallic arc. Such interposition does not change and noticeably
decrease the electric current and its action (§. 70-71). It is still approximately as if B and C were
in direct contact.
Fig. 4. Here the non-metal arc is composed of several pieces, of many
bodies conducting by humidity. This does not change the direction of the current
but slows it down and decreases its action (Exp. AA, BB and §.§.64, 71).
In Fig.5, finally, both the metal and the non-metal arcs are composed
of several pieces. The electric current is decreased due only to the length and number of pieces AA included in the non-metallic arc, and the small extension and
imprecise contacts at points aa (see quoted §§.)
We can see that in all these types the conditions of §. 68 I, II, III, are all exactly fulfilled. Nothing is lacking for the electric fluid to be
set in motion by the action of the two different metals (applied on one side at both ends of the non-metallic
conducting arc, and communicating between them on the other side) and going all round with more or less facility and rapidity according to the circumstances indicated.
To make sure that this current excites muscular movement, or the sensation of light or
taste, we have only to satisfy condition IV (see quoted §.). This will be obtained if the
single piece A in figures 1,2,3, or any of the A's in figures 4 and 5 is,
for instance, a prepared frog, if at some of the ends of these humid pieces, where two touch
at a, there is an eye ball or the tip of a tongue (this directed towards the current coming from the zinc, if an acid taste is desired).
§. 73. In the preceding we have only considered a metal arc, and a
different, non-metal one in our conducting circle, having always collected and connected among them
on one side all the humid pieces, on the other all the metal pieces, as can be seen in the five figures.
But4 what will happen if humid conductors are interposed
between pieces in the metallic arc, or if in the chain of humid pieces some metals
are included, or if the circle is composed of several metallic arcs and non-metallic ones
alternately?
It easy to see that the number and the…..5
72. Such are the conditions for all the experiments, where the conducting circle is formed with only two arcs, one metallic, the other all non- metallic. But what will happen if we interpose put humid conductors to between the pieces of the metallic arc, or if we introduce some metals into the chain of the humid damp conductors in the non- metallic arc some metals, if the conductors conducting circle is composed with of several metal and non metal arcs placed alternatively? We see that the number and the ways for this interpolation can vary infinitely. Can we establish rules and conditions, determining to determine the cases in which we could certainly obtain effectsresults, and those in which we would not at all obtain effects at all, or we would get very small results and/or with difficulty? Yes, through the application of my principles.
Here It suffice it here to say that the effect is lacking, i.e. that there will not have be any sensation of light or of taste, if the metals of different species do not touch each other directly, being interposedbut are separated by a humid conductor of any kind. Both the metals are then between two conductors of this other class, as if e.g. a third person is placed between the silver blade strip and the zinc one of zinc, kept held by two people, a third person is placed. We can understand thatunderstand that, no matter how strong the force proper to the silver and to the zinc of attracting or pushing the electric fluid, though different in the two metals, such force must first of all develop for each metals in opposite sensedirections, since each touches, both at the left and at the right, two humid conductors, otherwise it wouldn't happen anyno breaking of equilibrium would occur, and noy electric current.
For obtainingTo obtain this current it is needed necessary that each of the two metals should touches two humid conductors at on one side only, e.g. the zinc, e.g. at on the left, the silver at on the right, to two humid conductors, and that the other sides touch each other, directly or through other interposed metals.
Let u's now suppose that the metals action develop in theirexert their action on mutual contact, so that it is there that the electric fluid really receives really the push, or that it develops inon the contact with the respective humid
conductors6 , e.g. that e.g. the zinc pushes7
forward the electric fluid forward and that the silver on the contrary attracts it, or that also it too pushes the fluid, but with less force,. This as I believe to be more probable (assuming that the power force of the metals as motors of the electric fluid is the same for all, or that it differs only for in degree some degrees). No matter what the supposition adopted supposition, it can be understood that the electric fluid is moved in one direction and determined constrained to go through the all whole
circle.
((73) We also understand…)
.Hence, when It happens then that two different metals e.g. silver and zinc, communicating, communicating among between them, form a single metallic arc,. Iif theyif they are applied, the one to the right, the other to the left, to the extremities of another arc composed withmade up of humid conductors, an electric current is determined to make all the tour, if the circle has no interruptions. I have learned through experiments, that I will report later, what is the direction of the current is for each pair of metals used. It sufficesSuffice it to say here that with silver and zinc, the electric fluid flows from the zinc into the humid piece, it arrives and enters into the silver, passing and then returns to the zinc.
Where then really develop does8 the forces of the metals really develop? Is it in their mutual contact and by virtue of the that same contact? Is it there that the electric fluid really receives really the pushits impulse, there is the action that urges it to jump from the silver into the zinc? Or is rather the origin and the cause is rather in the contacts with the respective humid conductors? It isIs it here that the metals exploit display their activity, that the zinc, in, in the example here considered, pushes forward the electric fluid forward, while the silver is attracting it. Or that the silver is also pushing the electric fluid, but with less force? This seems to me more likely. Yes, I believe more easily that the virtue and power of the metals, as motors of the electric fluid, is the same for all, and that it differs only for itsin degree, and that
after all9 it is actingacts against conductors very far from the metals, and much less perfect. Such are the humid conductors, compared with metals of different species. With this supposition the metals, though different, in their mutual contact behave as simple conductors. They act as motors in the contact with conductors of the other class. In the other supposition, they would be motors in their mutual contact depending from on their mutual difference…...
Although I prefer…10
The same is goes for the effects and for the required
conditions11.
These principles, suggested by the experimentsexperience, have been indicated byindicated by myself in several circumstancesplaces, but I believe useful to expose here a better developmentmust develop them here a little better.
(§. 73) Metals are not simple Conductors, but real motors of electricity. When they are brought to certain contacts, they shake the electric fluid, move it and in certain circumstances they can put set it in continuous movement. Each different metal has a different activity for both in the manner and for the force with which it tends to displace the said fluid, and for puttingset it in motion, when it is applied at to one side only to another of a conductor of the another class, i.e. to a conductor through humidity. But if the same metal touches equally with its two extremities, at on the left and at the right, two humid conductors, i.e. if it is comprised withinincluded between two of them, being the two actions on the electric fluid being equal in the two parts, the electric fluid being is urged to move in two opposite directions and cannot decide for either, it is not determined for any one and. So no current is generated, though the said conductors are continuous completing the circle, not having reasons for the current to move to the right or to the left. This is the reason why a single piece of metal, or two of the same species, don't do not produce anything (§. ).
No effect is produced, and for the same reason, with two different metals, even with those that differ the most as motors of electricity, i.e. silver and zinc, if each of them is interposed to two humid conductors;, since the action in the opposite directions is balanced for each of them, the equilibrium still holds.
It is therefore necessary that each of the two metals, that which being of different species are different also in their activity, are be applied onlyapplied only at one of their extremities to whatever humid conductor. They must also touch each other at the other extremities end with no interposition, here, of humid conductors. T, the interposition of other metals, of no matter what species, being permitteddoes not harm, as I will explain soon. Only It is only the interposition of conductors of the other class that destroys or perturbs disturbs the effect according to the circumstances, the effect. In a word, they must form an all metal arc. When the things are as said, e.g. a silver blade strip and a zinc blade one communicate with each other forming a single metal arc while they are applied, one to its right the other to its left, to the extremities of the other arc formed with the said humid conductors, and no interruption exists, all the conditions indicated previously are satisfied (§:… ). It is then not difficult to understand that, due to the assumed different activity of the two metals, an, an electric stream is determined to make the full tourmade to go round the whole circuit...
§. Experiments that I will report later below have taught metell what is the direction of the current is for each pair of metals used. It suffices here to say, fFor a better understanding of what I am going to exposeexplain, suffice it to say here that with silver and zinc (two of the most different in their action on the electric fluid) the fluid flows from the zinc to the humid conductor to which the metal is applied, and through such that conductor (it could be a single or be composed ofcomposed of several pieces) enters in the silver applied to the other extremity end of such the arc for passingto pass back again to the zinc, etc. Such is the tour and the direction. For what concernsAs far as the other metals are concerned, they behaves like the silver and the zinc, i.e. the direction of the electric current is always from the zinc to the other metal through the interposed humid conductors, returning from this other metal to the zinc. Only the amount of the fluid making the tour, or the force of the current, is smaller if, keeping the zinc, the silver is replaced with by copper, or iron, or lead, or tin. Such a decrease of force follows gradually the same order or grading, so that the current is most weak (and consequently also its effect on the nerves, i.e. the excitation ofexciting the sensation of taste or of light, or the muscular movements) if the tin is opposed to the zinc, particularly, particularly the tinned paper. The same applies when are combined two other metals are combined that are ranged one after theafter the other, in the said order that I have established according to the grading of their respective virtues and that determine for each combination which one of the two metals sends the electric fluid through the arc of humid conductors, to the other that receives it at the other extremity end of the arc, for givingbefore sending it back to the first, etc. As far as the direction is concerned, it is always the superior one that sends the electric fluid, through the interposed humid conductor, to the inferior. This transfuses it directly to the superior (the metal arc being assumed with no interruptions) for completing the tour circuit and following it incessantly. Such a current is so the more much vigorous, so muchthe more distant are the two metals in the following table:
Zinc
Tinned paper
Lead
Iron
Silver
This scale must have a greater number of steps, and indeed effect I have already inserted several other metallic materials, such as the antimony bars and the bismuth between the lead and the iron, the copper sheet and the platinum between the iron and the silver.
From L 10:
§. Whenever, having well organised everything, the said effects have been obtained at the first contact, after having broken the circle (either by separating two metals or by leaving releasing the companion’s hand, or by extracting one of the circle’s ends of the circle from under a humid body, or out of the water) the connection is re-established, a repetition of the same phenomena concerning motions movements and sensations occurs. This cannot be surprising. Rather, it should be surprising that sometimes the convulsions of the frogs – that had quietened down while the circle was kept whole – reappear as well at the moment the circle is broken. I’ll I will explain that phenomenon later on, with even more remarkable circumstances, and I wi’ll show how this provides us with a further proof of what I have already anticipated advanced (§… )), namely that the current of electric fluid continues its round without interruption, as long as the circle is not broken. The continuing taste, even increasing on the tongue, directly proves this point (§ )§ . ). The same is true for contractions of the prepared frog, that which relax nothave no reprieve and constitute a real tetanus, or else re-start again and again for some time, until the nerves somehow get used to the continuing current and – so to speak – attain a final balance and come to rest. One should not therefore assume, when convulsions appear to quieten down, that the current flow of electric fluid is over. The sensation of taste will show you that it is always sustaining itself, that it is continuing on its way. ; Iit is suspended and terminated only by the separation of the conductors. This separation, that reduces itself to insertion of inserting a resistant medium, of an insulator, stops it all of a sudden: nay, it is not enough to say that such insuperable obstacle stops the current of electric fluid, it can’t cannot suddenly stop it without having it rebound back, without having it reverse its flow. It is therefore this sudden reflux that, coming on the frog’s sciatic nerves that had in a way become adapted to the first current and had reached a resting position, …..,12 these these nerves, irritated again by the new shock due to the sudden backwards movement, so that they cause the contractions of the related muscles.
§. Yet, it should also excite as well the flash in the eye and the taste on the tongue. W; what about itthis? Does one have such sensations at the moment the two metals are separated, just as at the moment they are joined? I answer:
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Firstly, that the electric fluid coming by such reflux to the excitable nerves, whatever they may be, has little strength, so that it may happen that in some circumstances (in fact, not always) it will have the capacity of irritating the prepared frog’s sciatic nerves, since the nerves having been completely handbared, it does not have the capacity of producing an appreciable enough effect on the nerves of taste and of sight, which are not isolated nor yet
uncover...13
so that the electric fluid – when reaching them – is less concentrated and more diffused by a number of other conducting fibres.
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Secondly, that some slight flash of light is sometimes really produced in the eye at the moment of separating the two metals, as I have already made my readers notedrawn attention to (§. ). As for the sensation of taste, since it continues (§. ) as long as the circle of conductors is unbroken, so that it’ is alive at the moment of interruption, it follows that the reflux of the electric flow due to such interruption cannot cause an appreciable sensation on that already affected organ, which only feels a great reduction, and soon the complete ending of the previous sensation.
§. After all, one cannot even expect the frog’s convulsions to happen in the same way at the circle’s interruption as at the circle’s re-creation, or by separating, as by joining the metals, although they do often happen as a consequence of both, nor can one expect them to be equally strong in both cases. They usually appear to be feebler, as it is quite natural, at on interruption; and the cases where they this happens in this way are much rarer; although there are instances, in which they are obtained quite well through said separation and hardly, if ever, by joining. I think I am able tocan explain these anomalies in a satisfactory way by referring to facts, and to applications deduced by from these facts, that will shed much light on the action of the electrical fluid in animal economy. But this is not the place to do it.
§. I come back to the sensations excited, the muscles’ movements, and in particular to the taste on the tongue and the flash in the eye when the complete circle of conductors is re-established.
Up to now we have assumed that the circle was broken by separating the two metals from each other. But it can be broken in different ways – detaching those same metals from the humid bodies, to which the are applied, or even by separating from each other the humid bodies forming the other part of the circle – e.g., by taking one’s hand away from the companion’s hand; or by extracting it from under on top of the drenched damp body, or out of the water. Now, however the interruption or discontinuity of the circle may have been effected, the phenomena are identical; i.e., there is in some circumstances a convulsive movement in the frog’s legs as a consequence of the temporary shock produced on the nerves by the reflux of the electric fluid that I recalled above (§. ); a slight changing change in the sensation of sight (... ) and a marked decrease in, – if not a total cessation -– of, the sensation of taste on the tongue. But if all goes the same way; , whetherlet the circle’s circuit interruption between the two metals, or between one metal and the damp conductor, or between the two damp conductors, in a few wordsshort, let whether the metallic arc be interrupted rather than the damp arc: , then the effects do not resemble in every point the onesthose that are observed when the circle is completed by joining the separate parts. This is because when the two metals are united, the effect in its entirety is produced at the time moment of connection, even if this is effected in one point only, provided connection is exact (which implies some pressure, in particularespecially if the metals are unpolished or rough), so that the convulsions in the frog’s legs are as violent, the flash in the eye as brilliant, the feeling of taste on the tongue as strong, as if the two metals touched each other in at different points on over an extended surface. On the contraryother hand, when either metal is brought into contact with any damp conductor, whatever this mayit beit be, or even more when two such damp humid conductors are joined to each other, in order to obtain a greater effect it is necessary to apply them over suitably extended surfaces; otherwise no convulsions will be excited, and anyand any sensations felt experienced will be feeble. Differences due to this fact are mostly remarkable in experiments involving the tongue. I will now give one or two examples.
Exp. A silver blade strip will beis partially immersed in the water contained in a glass or similar vessel (provided the vessel is not made of metal), the water partially overflowing in part. The blade’s part of the blade that stays outside of the water is joined to a tin blade, or to a zinc blade, and the tip of tongue is applied to this second blade. Up to now, no particular sensation of taste is felt. Touch now the water in the vessel with the tip of your fingers, and the mere beginning of an acid taste is felt. F; from this almost imperceptible degree the taste increases when the finger isn immersed more deeply in the water, or when two or three fingers or finally the entire hand is immersed, until the taste is not only very distinct, but even quite strong.
Exp. There is no need of silver blades strip if the vessel is a silver one. It is then sufficient for the tin or zinc blade to be put onto the vessel or to touch in some way its external surface in some way. The remainder of the experiment is as above.
Exp. Take two non-metal vessels full of water. Immerse in one a zinc bladestrip into one, in the other one a silver one into the other, and take bring the parts of the blades that are out of the water nearer to each other, until they come in contact. Then putImmerse then the tip of your tongue into the water in the first vessel,; give your hand to a second person . person. ,T this second person will give the hand to a third one’s hand, etc, etc. (all people will taketaking care to have their hands moistwet);. F finally, let the last person gradually immerse little by little first one finger, then two, three, the whole free hand in the water of the second vessel. You will once more feel the acid taste increasing by degrees, from very feeble and imperceptible to middling strong.
Exp. Let everything be as in the previous experiment. L; let the hand of the last person be already immersed in the vessel where the silver is, and the tongue in the vessel where the zinc is;: L let the two metals be in contact; and let only the circle be interrupted only by the separation ofseparating the hands of two people in the chain. If these people will suddenly unite again theirjoin hands again, in such a way that a wide contact surface be obtained, the tongue will instantaneously feel a strong taste (and if prepared frogs had been put in the chain, they would be subject to violent shocks). On the contraryother hand, if the same two people start by touching each other slightly, in at a few points, the effect will be almost absent or anyway very feeble; and the taste will be felt only as the contact of the two hands will becomes more precise and extended.
Exp. I take a zinc cup with a silver foot; having filled it with water., I immerse in it the tip of my tongue in it. I; in this position, I touch the silver foot with one or two fingers (previously moistened) ).the silver foot; There is a feeble sensation of a vague taste. I take the silver foot with one or even two hands, and squeeze it: the taste is enhanced;. I feel a very decided acid taste, quite much stronger than previously.
§. I believe there is no need I do not believe I need to say there will be no sensation at all if the hand, instead of embracing the silver foot, will embraces the zinc cup,; just as there is none whenever one uses only one metal (or two metals of the same type) to create the circlecircuit. It would be also useless to report on a greater number of experiments to prove the proposition presented above, i.e., that communications effected only by a few contact points either between metal and moist conductor or between two moist conductors do not appear to be sufficient for a free and prompt ready flowing of the electric fluid. The reason is that contact of two considerably large surfaces is needed, while in the case of two metals a contact between a few points is as effective that as one ofover a large surface. I will rather explain this difference. I find it easily in the much greater conducting capacity of metals than of water or other moist bodies. The first ones are such good, such perfect conductors, that a metal wire as long as it pleases, with a diameter d’ of ¼ to d’ 1/10 of a line, will neither noticeably stop nor delay in a sensible way the strong discharge of from a Leyden bottleflask, or at least it does not forbid prevent this discharge to from happening so suddenly that the commotion shock is felt. On the contrary, water and the dampest bodies, which are censed to beconsidered good enough conductors, are so poor by comparison to with metals that if a small flow, or a cylinder of water with a diameter of one line or more, and some inches long, a drenched soaking cardboard strip one or two lines wide, are put in the circuit, if they don’t completely hinder the discharge of from the bottle flask they at least slow it down, reducing the speed and the impetus of the electric current so that the commotion shock will not happenoccur, or else a much smaller one will appear, etc. The lack of conductibility of these bodies, that I would prefer to call imperfect conductors rather than bad conductors, can be balanced by making them as that much wider, so as to offer by such means a way free enough for the passage of the electric current. In fact a large cylinder, or other mass of water, a wide hemp rope of hemp, or a wide enough strip of drenched damp cardboard, are capable of conducting very well the said commotionshock very well, that was not conducted by thin lines of the same bodies. It would then seem, then, that, since a small flow of water could conduct only a small quantity of electric fluid at a time (without any comparison,incomparably less that a metal wire of the same dimensions) there have to be many such flows amongstreamlets into which the electric fluid could subdivide itself so that a considerable quantity be transported with sufficient promptness. In other words, the path made by a few thin flows of water is too narrow for the electric fluid to pass though as a current. G, given their imperfect conductibility; a large number of them are necessary.
This allows us to understand also why in the experiments here discussed, where the simple action of different metals moves the electric fluid and produces a continued continual current, the moist bodies that are part of a conducting circle circuit must be applied one to the another and provide several contact points at the two ends of the metal arc completing said circle by reasonably extended surfaces. Moreover, these moist bodies must not have a too small a volume at any point of over their whole length, while the metals forming the said metallic arc (as already indicated) may be as thin as it is preferred and just touch each other atin a few points, provided only that they have a contactquite extended enough contact with the moist bodies.
§. It follows that the more imperfect part of the conducting circle, namely the one made of moist materials, in other words the non-metallic arc, due to the very fact that it is not so conductive must present a wide path without being at any point squeezed or excessively restricted; . Consequentlyand as a consequence (nay, even more important) these materials must be well applied both at the two ends of the metallic arc and among themselves, so as not to delay excessively the flow of electric fluid excessively, but to allow it a free passage. This wide path all along the non-metal part of the circle, without any
narrowing... 14... is a most important condition.
What! Somebody will say, is the path not narrowed, and the passage very much restricted, at the point where the only communication is provided by the frog’s two crural nerves of the frog, or even by one only? And isn’t the contact not limited to just a few points when just merely the tip of the tongue is applied to one of the two metals or to the water? And yet, the greatest effects are obtained in this way. Isn’t that not a contradiction? Not at all:. O on the contrary, what I just said provides the explanation of for this thingsituation. In fact, while on the one hand, while the electric current, being restricted in the narrow channel of a few nerves or of a small number of fibres, is slowed down by the excessive resistance found due to the imperfect permeability of the medium, on the other hand those very nerves, reacting, suffer so much more the from the effort of the electric current against them and , from its more concentrated action, if we hold it true that action and reaction are always paired.
Thus, when the non-metallic conducting arc is quite long or made of several parts, i.e. made by of several people or other damp bodies, all these bodies must touch over extended surfaces and in at no point all along the chain must there be any restriction or contact limited to a few points, except at or near the position of the nerves where we want to concentrate the action of the electric fluid flowing through the circle. This is in order to obtain the greatest effects, i.e., the strongest movements of the muscles, if the nerves touched are the onesthose related to such movements, or the strongest sensation of taste or of light, if the nerves interested concerned are the onesthose pertaining to taste or to vision. In short, the electric fluid must pass with ease where it is not requested required to make an appreciable impression on the nerves, so that is its passage be as free as possible, and yet restricted where we want the nerves to be irritated so that the irritation be as strong asproportionately stronger the greater is the effort it must make and , the difficulty it must has to meet in order to pass.
This kind of obstacle to the fluid’s passage, which anyway only slows it down, causes the fact that beyond one of these narrow paths (such as, e.g., the sciatic nerve of a frog, remaining the only connection of the legs to the trunk) the electric current excited aroused by the contact of the two metals does not have the strength of excitingto excite a lively sensation of taste on the tongue, or of light in the eye; and that the sensations excited become feebler and feebler until they cannot be felt any more, if in the circle it meets several such restricted and embarrassingnarrow, troublesome passages in the circle. Thus it happens that, when three, four or five people tightly holding well their well-moistened hands, complete a circle by means of a metal arc, the first person holding such the arc and the last one touching the zinc with the tip of his tongue, the tongue will, without fail, sense the acid taste, if not strongly at least remarkable noticeably enough, while the same person will feel very little, or even nothing at all, if instead of the other people in the circle an identical number of prepared frogs is are substituted. These small bodies interposed make up shorter lengths of chain, that should more easily be traversed by the electric current; but since this current must pass restricted only within the nerves that connect the legs of the prepared frogs to the trunks, it irritates them in a violent way and excites their convulsions, etc. while irritating the nerves, inducing the convulsions of in all the leg muscles in the legs. T; the current is much more embarrassed and slowed down in its passage through such thin channels than when traversing the whole body of a man, etc.
§ Anyway, the nerves controlling movement appear to be much more excitable from by the electric fluid traversing them than the nerves controlling the various sensations, considering that several frogs connected to each other or to people keep being overcome bythrown into convulsions (Exp. ), even though the electric current’s flowing through the narrow passages of each one must be very much slowed down by all these restrictions; while two or three such narrow paths make the action of the same current imperceptible to the eye and to the tongue.
It should yet again be noted that in the frogs prepared in the said manner describedway the whole current flow
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are limited to united within the sciatic nerves alone, and passes though the whole length of them. W; while hereas in the experiments where the goal is to excite the sensation of light or of taste, either traversing the eye or penetrating the tip of the tongue, the current could can only traverse a few nerve fibres of the nerves, and then for a limited length;, and instead of making its way, well properly confined within the nerves alone, it must extend itself to so many other fibres and conducting vessels surrounding the nerves. It would be necessary for these nerves related to sensations to be naked and isolated so that the electric current would be obliged to enter those channels alone, as it happens for the crural (sciatic) nerves of the prepared frog, etc. So I’m not going to decide that the nerves of movement are by nature more excitable than the nerves of sensation by the flow of the electric fluid; this might depend only on circumstances, in particular on the afore-mentioned preparation of the said nerves of movement. In fact if the movement nerves of movement are not prepared as mentioned and all things arranged so that the electric fluid will be obliged to pass all united together within the nerves alone; if they keep being surrounded by other fibres and vessels (as when the frog has just been just killed and the bowels only have been taken awaymerely disembowelled, the leg’s muscles being left intact) then convuslions convulsions are excited with much greater difficulty, even greater than for the feeling of taste on the tongue or the flash of light in the eye. Isn’t this not due to the fact that, when there are more conducting fibres for the passage of the electric fluid, less fluid is left to pass through the pathby way of the sciatic nerves? Still the way path is not so large as yetwide enough yet; the quantity of electric fluid passing through the nerves is still large enough to irritate them with some strength. This half-prepared frog can still suffer convulsions not only if we immediately directly apply the two metals, one to the back and one to the legs, and then bring the metals into mutual contact; but also if it creates a communication communicating link between two people is created who, holding the two metals in their hands, thereby joining each other complete the circle, etc., provided the two metals are the ones provided with stronger activity such as zinc and silver or gold (otherwise the experiment will not succeed). In the same way the experiment will never succeed, even though the best metals might be used, if the frog has not been eviscerated in which there are too many and too wide conductors for electric current to concentrate in the nerves. I say, never, if the frog is placed between two people or between other moist conductors, so that the imperfect conducting arch that the electric fluid should traverse will be a long one (and this, added to the obstacle due to the imperfect continuity where connections are effectedaffected, will, of itself, slow down by itself the flow of the electric fluid, as already saw seen in detail - § ...). Otherwise, if we apply the two well chosen metals – i.e., a sheet of tin or even better of zinc to one part and of silver or of gold to the other part of the same non-eviscerated frog – to a whole, and intact frog, we can very well happen to observeeasily excite convulsions (Exp. ).
§ To make all the above more evident, let us perform some experiments on the same frogs, completely prepared, only half-prepared or and not prepared at all, by using the usual normal artificial electricity. I have already reported some results and I summariszed the actions conduct of such experiments (§ 5-8). I will now describe some other experiments in greater detail.
Exp. Let one person, having moistened his fingers, hold the head or the front legs of a whole and intact frog; a second person holds one or both the hind legs of the same frog, and with a one finger of the other hand (or by means of a moistened strip of cardboard) he touches the globe ball of the eye of a third person. Have a fairly large Leyden bottle flask so charged that, not being able to give the smallest sparklespark, the charge will just be sensed by a Cavallo’s or Bennet’s Electrometres Electrometer – it might just separate the two gold leaves by a few lines or, have them mark 8 or 10 degrees. Since isolating bladesinsulating strips mounted on the two faces must be electrically charged, even such feeble Electricity requires a fairly considerable quantity of electric fluid;. T this is a consequence of the very great capacity of the two blades strips due to the opposite electricities on the opposing surfaces that which by their mutual balance sustain each other. This same feeble electricity, suddenly discharged through the three people and the frog, will not excite any perceptible commotion shock in the people’s arms, but it will excite a flash in the touched eye, and convulsions in the frog’s legs.
It is therefore evident that since the people’s arms provide too large wide a path, too free a passage to for such electric current, this does not produce any perceptible irritation on the nerves, that on the other handThe nerves are less dispersed in the much smaller body of the frog so that a greater quantity of the electric fluid will be obliged to pass through the spinal cord and the crural nerves and there produce an irritation strong enough to excite the muscles’ movements and the convulsions. LastFinally, the passage is even smaller in the eye, so that the electric fluid creates a correspondingly stronger excitation of the sight’s nerves of sight. I say a "stronger "one;: I in fact, a sensation of light is felt even when the bottle’s charge in the flask is so feeble that it will not excite any movement in the frog, if this is whole and intact.
Exp. Prepare everything as in the previous experiment, with this difference only, that the frog’s head and abdomen will have been cut away so as to leave only the loins with the crural nerves (appearing uncovered and lying on the "os sacrum") will connect the back to the legs. Then, by a discharge similar to the previous one, much stronger convulsions will be excited in this half-prepared frog, while the flash in the eye will be feebler. This means that the current of the electric fluid, forced though the restricted path of the loins, and even more concentrated through the crural nerves, irritates them much more and is delayed in its passage by such an obstacle, so that when it comes to the eye its energy has been correspondingly decreased.
Exp. Some convulsions can still be obtained from the frog cut up as above (but this with much difficulty, while no flash will be observed by the eye) if the Leyden bottle jar is subjected to a charge 4, 6, 8 times feebler than in the two previous experiments, i.e., corresponding to 1 or 2 degrees only on Bennet’s BENNET’s electrometer and not perceivable on any other electrometer. Useless to sayIt hardly needs saying that, if such a charge is already too feeble to excite any sensation in the eye, such sensations cannot be expected with still feebler charges.
Exp. If a part of the frog’s loins is cut away – one half, two thirds etc., without damaging the crural nerves, an even feebler charge, barely perceivable even with the BENNET Bennet’s electrometer, will be capable of exciting convulsions in the frog’s legs.
Exp. LastFinally, if the "os sacrum" is taken away together with the remaineder of the loins, only leaving the crural nerves as a connection between legs and trunk, a charge fromof the bottle flask just between 1/8 and 1/16 10 of a degree on said Electrometer, which is totally imperceptible, is capable of exciting the said aforementioned convulsions. Thus it can be seen that very little is sufficient to excite the muscle’s movements in the fully prepared frog (the same holds for any other animal, etc.) when it so happens that the electric current must has to make its way through the nerves controlling such movements and must all pass all united through them.
Exp. On the other hand, if several such prepared frogs are inserted in the circle, either all consecutively or alternating with people, it will be found that such an exceedingly feeble charge is not sufficient; that it is necessary to use a (however slightly) stronger electricity, and that its efficacy will be as much smaller as the electric fluid discharged from the bottle jar will have not only to go a longer way, but also to pass through a larger number of such extremely restricted paths, which contributes much more to slowing down its passing.
Exp. It will also be seen that this exceedingly feeble charge is made totally devoid deprived of efficacy not only by the least interruption of in the circle or by insertion ofng any ill-conducting body – however thin – such as e.g., a piece of fine linen, a membrane, a piece of thin paper provided they are have not been well moistened, but also when the hands holding each other and touching to the frog’s body are not damp, or if the contacts are effected at a few points only, etc.
§ Here is how experiments made performed with the usual artificial electricity are useful to explain the others ones, where the effects come from a similar electricity produced by the simple contact of two metals of different types with each other and with conductors of a different class (i.e., the moist conductors), just as we have noted in the other experiments.
Coming back to the different degrees of excitability of the nerves under the action of electric stimuli, either by the means we are dealing with or even by any other form of artificial electricity, it is quite remarkable that the nerves pertaining to sight, as well as the ones related to voluntary motions, react most strongly, and in fact almost only, when they are first affected by the current of electric fluid, while they are not much affected afterwards during all the time it continues uninterrupted. While on the contrary the nerves of taste do not feel anythingfeel nothing (or almost noanything) during for a short instant only, i.e., if the electric current is not continued. Thus, the violent convulsions excited in the frog at the same very moment the conducting circle is completed, are usually quite soon calmed and at most reappear – though less strongly – from time to time (.. .),as long as the circuit has not been interrupted , even if as long as the circle has not been interrupted the current of electric fluid continues being sustained, as it is proved by many other experiments (.. .). In a similar way, the lively sensation of light in the eye is instantaneous and passes like lightning; and all that barely remains is the sensation of a very feeble light during all the time the contact of the two metals (one applied to the mouth the other to the eye) is continued. The same is not true for the sensation of taste on the tongue; this is barely perceivable at the beginning, and gradually increases during for some seconds, after which it keeps sustained with the same strength, as long as the conducting circle is not interrupted (.. .); this is in fact – let’s repeat it again – - a proof that the electric current is maintained during all this time.
This allows us to see (and it seems to be quite general) that the sensation of taste requires that the exciting cause of excitement be16 applied continuously for some time on the organ of taste, while an instantaneous action, a passing shock on the nerves of taste is not (or almost not) perceivableperceptible. The capacity of feeling and the excitability of the nerves of sight and of the nervesthose controlling voluntary movements are such that the strongest impression and the greatest effects happen at the first moment, at the first shock. Having stated that point, one can understand why the continued convulsions of the frog’s legs, as well as the almost continued continuous sensation of light – even of a flaming light – are obtained only by alternating interruptions and re-conjunctions of the conducting circle by means of separations and contacts rapidly repeated (exp. ), rather than by keeping such contacts and maintaining the circle circuit whole. On the contrary, for the feeling of taste such interruptions are very unfavourable, and the feeling never becomes strong enough if the communication along the entire circle is not kept at least for a few seconds.
In the same way it is (also) possible to explain (understand) why the instantaneous discharge of an electrified conductor, or better of a very feebly charged Leyden bottle flask very feebly charged excites the flash of light very well the feeling of a flash, having it pass through the back of the eye, and excites the convulsions in the legs when it goes through the frog’s sciatic nerves, while whereas it excites the sense of taste very little, if at all, the feeling of taste, when penetrating and traversing the tip of the tongue. In order to perceive that sensation of an acid taste it is necessary to direct against the tip of the tongue a continued continual stream of electric fluid against the tip of the tongue, by exposing it (the tongue) to the blow and the electrical emanation from the point of the conductor on the machine that is being activated, or by keeping it in contact with such this conductor.
§ I will come back to discussing these experiments with the artificial electricity produced by machines seen in parallel to the experiments we area dealing with at present, in which the play game depends on the action of two metals put in contact with each other and applied, by their opposite ends, to moits humid bodies completing the circle. I will also show even more clearly – by the perfect similarity of the effects, point by point, of the required conditions, of circumstances and modification (a similarity that can be already detected in particular from experiments ((...) ) – that the cause in both instances is identical, namely, here as there, something like a torrent of electric fluid. Just now I still have to speak oftalk about the different excitability of the various senses:, i.e., to discuss that if the taste is much less delicate than the sight, in particular regardingwith respect to the fact that it cannot be so promptly excited, a similar tardiness and a greater grossness coarse ness can be found in one other sense, that is more similar to it, i.e.,viz. the sense of touch. Yet, as I have already announced (§. ), I managed to excite the sense of touch by the same means, by which I had excited taste and sight. It is thus only the senses of smell and of hearing that have up to now resisted my attempts up to now.
It is may be easily guessed imagined that we should choose such parts of the body, where the sense of touch is very delicate, and at the same time use the strongest means. These means are the metals that provide greatest activity when they are opposed, namely silver or gold on the one sidehand, "silver" paper covered with tin or even better zinc on the other side. Now, the most delicate parts of the body that were successfully subjected to my experiments are the globe ball of the eye, the internal rim of the lids, and most of all the parts nearest to the lachrymatory glands.; Ttherefore I excited a more or less painful and burning sensation in such parts, by tougching them with the most active metals, a more or less painful and burning sensation. Similarly, in the interior of the nostrils the sensation of a small pinprick is produced, and another disagreeable sensation at the root of the tongue and the back of the mouth, when one of the metal armatures is applied there, but these sensations are usually too feeble and obscuredull.; I am sure that a stronger sensation (even stronger than in the delicate parts of the eye) would be excited in open wounds, where the flesh is very irritableeasily irritated and without protection, but this is an experiment I did have not madke. I will describe some of the experiments involving the eye, since only these are well marked and even sometimes too strong to be tolerated without pain. It will then be sufficient to describe some of the experiments on the eye.
Exp. Thus, when – having applied to the eye (in particular, to the corner nearer to the nose) an one end of the blade made of zinc strip, and having taken the silver strip in the one’s damp hand the other blade made of silver (or better still, having placed it into the mouth) or vice-versa – when the two blades are brought into mutual contact, after the passing flash of light excited at the back of the eye at the moment of contact (Exp. ), little by little a sensation of pain and of
heath begins little by little (obviously, provided everything stays in its place and the communication is not interrupted). This sensation feeling increases not only during for a few seconds, as it happens with the sensation of taste in similar experiments involving the tongue (Exp. ), but during for one or two minutes, until it almost becomes unbearable and even produces a slight local inflammation. Even when this does not happen, at least the pain continues long after the experiment is over. One could suspect this to bewas the effect of pressing and grazing the metal against the delicate parts of the eye; but this assumption will soon be dismissed when the experiment will beis made of keeping the same bladestrip applied to the lachrymal gland and holding the other one either in the hand or in the mouth, just avoiding to bringbringing the two blades strips into mutual contact with each other either directly or through a third metal. In that case, really, only the effect of mechanical pressure will be felt, without anything of that burning pain excited in the above experiment; again, nothing is felt if one uses two blades of the same metal – silver and silver, zinc and zinc, tin and tin, however they may be applied to the parts of the eye and of the mouth and be brought in contact with each other. Finally, very little is felt if instead of using on the one side silver or gold on one side, and on the other side zinc or paper covered in tin (metals that have the greatest activity when brought in mutual contact) one employs silver or gold on the one hand, and copper or iron on the other one, or yet iron and zinc, copper and tin foil, etc.
§ These combinations of less effective metals are still capable of exciting the sensations of light in the back of the eye, and or of taste on the tip of the tongue, even though much feebler than do the other, better assorted combinations – in particular that of zinc with silver or gold. Thus if they do not have almost any perceptible effect on the external parts of the eye, we should state that the sense of touch in those same parts is by far not by far as excitable as the sense of sight or of taste (at least, where the action of the electric fluid is concerned), and that
moreover it is not as promptly excitable by comparison with the "last taste" (§. ), which is in turn much slower and more latelater-coming than the sense of sight (§. ).
§. It was has been seen how I manage to mimic almost perfectly, by the usualusing normal, artificial electricity (...), most of the effects produced by the simple contact of metals of different types, that – As all circumstances and requested conditions prove, these metals certainly do not act – as all circumstances and requested conditions prove – if not byby means of another form of still artificial electricity, up to now unknown, by some impulse given to the electric fluid, or some such action that moves this fluid to pass from one of the metals (e.g., from the zinc) in the touching moist conductor, to go all along such said conductor, or along a series of such conductors communicating with each other, until it reaches the last conductor in the chain and from this passes to the last metal (e.g., silver) and finally from such the silver gets back into the zinc, when these two metals are brought in contact. Thus the whole circle has been traversed. As I said, it wasit has been seen how, by using normal artificial electricity, which has long been well-known, I manage tocan mimic almost perfectly by the usual artificial electricity, known since a long time, most effects produced by that other artificial electricity only recently discovered by totally new means,; an electricity that could be properly called originating from metals. I; its effects are the convulsions in the voluntary muscles, and the sensation of light in the organ of sight (§ ). One can then imagine that I try have tried to mimic the other effects as well, i.e., the sensation of taste and thea painful feeling or pinching (Ital. Pizzicottare, bruciore) in the eye, usingwith the same artificial electricity produced by the Electrophoruse machine, or by the bottles flasks, etc., the other effects as well, i.e., the sensation of taste and the painful feeling or pinching (Ital. Pizzicottare) in the eye.
§. To start with, I did not succeed with the instantaneous electric discharges either offrom insulated isolated conductors or of Leyden bottles jars in any of the ways hereafter described (...). ; And I should not have expected to succeed having observed that the sense of taste and even more the sense that of touch are not perceivably perceptibly affected by an electric current (I speak of a current even plentiful but provided with very little strength or tension, such as it is not perceived by any electrometer except by the animal Electrometer) , that which only lasts a short time, at least the space of a few seconds (§. ).
§. Thus I decided to employ the sustained electricity provided by the Conductor of the Machine used. Let us present the eye in front of the pointed end of such said Conductor, at a convenient distance so as to avoid the discharge of a lively spark (which would make too strong an impression too strong and quite different from the one we wish to perceive) and to have the eye (which will be kept wide open) simply affected by what is called the "electric feather" or cone of light (invisible in full daylight) accompanied by a sparkling crackling sound and by a whisper breath of wind or fresh windcool breeze. As I was saying, let us present the eye near enough to receive at least the impression of this slight electric windbreeze, the way it is done to dispense administer electricity for some illnesses of that organ. I; if this impression is sustained for some time it is well known that the eye feels a sense of pain, of pricking, initially light but always increasing and capable of continuing long enough after the experiment ends so as to produce a slight inflammation. Well: , this sensation, which can go with all its variations
17, is as similar as possible to that felt in the other experiments where, without using the machine, the electricity originating from the metals is used (...).
§. In the same way, if the electric wind or feather created by the Conductor of from the machine is received on the tip of the tongue and the machine continues producing electricity in plenty, we will feel the same acid taste, gradually increasing, as that excited by the artifice of metals (§. ). The only difference is that the taste is not as strong in these experiments as that felt in the other experiments with the sheet of tinfoil, and even more that ofwith zinc, applied to the tip of the tongue and touched with silver or gold. ;I it reaches at most the degree obtained with iron or lead, opposed to silver, or zinc opposed to lead. But anyway what’s the importance of strength, if the quality of the sensation is the same, if more specifically the taste is the same?
§. Having concluded all that, I still was not satisfied. The comparison parallel between the experiments of with the usual artificial electricity and those of with intrinsic or spontaneous electricity due to the metals, and between the effects produced by either on the sense organs of senses , is not exact, unless the first one is reduced to act as in all points, and the second one without the feather, without the wind, without any of the other usual signs of electricity, in other words with a strength or tension below the sensitivity of the most delicate electrometer apart from the animal electrometers, incapable of overcoming getting across the smallest interval from one conductor to the next one, etc. Concerning muscles’ movements, and even the sensation of light, I have showned how these could be easily obtained by means of artificial electricity, such as that from a Leyden bottlejar, just feeble at to the right point (Exp. ). Otherwise for the other sensations of taste on the tongue, of irritation and pricking in the delicate parts of the eye, as I have already said, such an instantaneous discharge is not sufficient; for these lazy senses a continuous torrent of electric fluid is necessary. If this is present, the saidthese sensations can arise and gradually increase, even though the torrent may effect the discharge only with very feeble strength, smaller than the least degree on the electrometer, provided the quantity of fluid discharged or passing at any instant through the nerves is not extremely small (it must not, in fact, be infinitely small), that is, it is not lower than that produced at the instant of itsmoment of discharge by a Leyden bottleflask, or a Battery, charged at to 1/10 or 1/20 of a degree on the Bennet’s electrometer (exp. ).
To achieve such conditions, I made another this further different endeavour.
Exp. I applied the tip of my tongue, or else the my eye, depending on whether I wanted to excite the sensation of taste, or that of pain, to the conductor of the electric machine that I worked was turning vigorouslywith vigour...…
(Translated from French by: Mariagiovanna Sami and Luigi Dadda, Politecnico di Milano, February 2001)
Revised by John Coggan, Oxford University.
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