Richard Fowler

“ EXPERIMENT I. I have before said that if a living and entire frog be set upon a plate of zinc, contractions can very seldom be produced in any part of its body by passing a rod of silver over it, so that the silver, the frog, and the zinc, may be all in contact with each other. ”

“ EXPERIMENT V. Having tied one of the crural arteries of another frog, I filled its stomach, immediately afterwards, with a saturated solution of opium in water. The difference between the strength, and the continuance of the contractions, excited by the metals, in the two legs of this frog, was not so great as in the former; yet still the difference was considerable in favour of that leg in which the artery remained free. ”

“ But with zinc, and gold, silver, or molybdena, I have frequently succeeded in exciting contractions in the 6 foot of a frog, upwards of a day after they had ceased to be excited, by arming the nerve with tin foil, and using some other metal as a conductor, in the way the experiment is commonly performed.
When the bulk of the metals is large, and the quantity of surface, of an animal with which they are in contact, is considerable, I think, the contractions are both stronger and more readily excited, than when the reverse of this is the case. ”

“ A doubt must always remain, whether nerve has not been present; and from this doubt will arise another still more difficult to solve, whether the influence produced or excited by the metals have passed through the nerve to the muscles? or if it have merely acted as a stimulus to the nerve, serving to rouse that unknown energy, by which nerves are known in certain circumstances to excite muscles to contraction. ”

“ The contractions of animals excited by electricity have a tendency to destroy that power upon which contractions depend. But the contractions excited, by the application of the metals, have, in all my experiments, had the directly opposite effect. The more frequently contractions have been, in this way, excited, the longer do they continue excitable: and the longer are the parts, upon which such experiments are made, preserved from putridity. ”

“ If the contact of two 26 different metals were alone sufficient to excite contractions; contractions should always take place, whenever a good conductor is interposed between the metals, and the nerve alone. But I have, in no instance, observed this to be the case. In the experiment, where the crural nerve must be supported upon a silver probe, it is necessary that the piece of silver, with which the zinc is brought in contact, should communicate either immediately, or through some good conducting medium, with the muscles of the foot, or leg, before any contraction takes place. ”

“ From this well devised experiment, he concludes, likewise, that animal electricity is the principle of life. That, on the side where the nerve remained entire, it was withdrawn from the muscles, and deposited in the brain. That, from the impossibility of this taking place on the other side, where the nerve was divided, it had continued in the limb, and enabled it to contract.
If it were indisputably true, as I once believed, that contractions could be excited in a limb without the metals having any communication with it, except through the medium of a nerve ”

“ That some kind of disagreeable sensation is occasioned by it, even in frogs, independent of that which must necessarily arise from irritation, and the contractions of their muscles, is evident from their restlessness, and expressions of uneasiness. In other animals, as I shall afterwards have occasion to shew, these expressions are still less equivocal: and, in man, we can ascertain both their degree and their kind. That they differ considerably from such as are 52 produced by electricity, will be proved when I come to speak of the effects of this influence upon our senses. ”

“ In establishing a communication between two opposite electricities, as, for example, between the two sides of a charged phial, it is matter of indifference to which the conductor is first applied. But it is by no means so, in the case of muscles and armed nerves. For, if one branch of a conductor be applied to the tin-foil arming a nerve, before the other branch has been applied to the muscles, it frequently fails to excite contractions. If first applied to the muscles, this is very seldom the case. ”

“ The contractions produced seemed to be strong in proportion to the extent of the surfaces of the metals in contact, strongest when a large plate of zinc is laid horizontally upon a large plate of silver or gold. If the zinc be suffered to remain in contact with the silver, for a little time, the contractions of the leg cease. The zinc may then be slid over the silver, till it even touch the leg without renewing the contractions: but, in withdrawing the silver, the leg contracts at the instant the silver parts from it! ”

“ Powers of Nerves, and of Muscles, are derived. As yet, the question whence the nerves and muscles of animals derive their respective properties, remains in a state of doubt. By many, the brain has been considered as the source not only of the several energies exerted by nerves, whether appropriated to sensation, to the excitement of muscles subservient to the will, or distributed to organs exempted from its influence; but likewise of that unascertained 104 power, by which muscles contract on the application of a stimulus. ”

“ Cotton is a non-conductor of electricity.
Oils of all kinds are so far from conducting, that if the fingers of the person holding 18 either the probe, or the zinc, have perspired much, even this operates as a complete obstruction to the passage of the influence: the instant the perspired matter has been wiped away, and the fingers have been dipped in water, it again passes, and excites contractions. ”

“ I find, that if a piece of zinc be applied to the tongue, and be in contact with a piece of silver, which touches any part of the lining of the mouth, nostrils, ear, urethra, or anus, the sensation resembling taste is felt on the tongue. ”

“ If, after having divided at the pelvis a frog recently killed, the sciatic nerves be freed from cellular membrane up to their origin from the spine, and all the parts below 99 this, except themselves, be cut away, the muscles on each side of the spine, for some little way up, may be brought into contraction by touching the nerves alone with the two metals in contact. This experiment has not always succeeded with me, and never unless the frog had been recently killed. So long as the hind legs remain undivided from the nerves, it never succeeded; the only contractions produced being in the legs. ”

“ But it should be recollected that the evidence of one accurate, and positive experiment, is not in the least invalidated by twenty unsuccessful ones, especially upon animals of warm blood; where the irritability of their muscles is so very fleeting, and the result liable to variation from so many, as yet, unknown causes. The irritability of the arteries, for example, is now completely established, yet Haller’s experiments led him to deny it. ”

“ This argument appears, to me, to do away all support, which the hypothesis may seem to derive from the experiment, before quoted, of applying the metals equally to 40 both sciatic nerves, after one of them had been divided; I may however remark, that the pain necessarily excited by arming a nerve, whose communication with the brain was not interrupted, would fully account for the more rapid exhaustion of the muscles, to which it belonged, compared with such as had not been acted upon by so strong an additional stimulus. ”

“ A strong presumptive proof, in my humble opinion, that these animals are endowed with a most exquisite organ of sense, and, consequently, that they are not, as has been supposed, destitute of a nervous system. ”

“ That both the frequency, and the strength of the heart’s contractions are affected by passions of the mind, is a fact known to every one; but what is much more to the purpose, since 72 we know so little either of mind or of its mode of influencing the body, we know that many derangements of the brain, such as apoplexy, hydrocephalus, phrenitis, &c. together with all kinds of mechanical injuries, (and what are these, but so many stimuli irritating the brain, and consequently the nerves sent to the heart?) affect the motions of the heart most materially and obviously. ”

“ Whatever has a tendency to blunt the sensibility of the tongue, as laudanum, a strong solution of opium in water, distilled spirits, acids, &c. diminishes the effect of the metals. Acids, I think, diminish it least.
85 On placing different metals in the meatus auditorius externus of both my ears, and establishing an insulated metallic communication between them, I felt, or fancied that I felt, a disagreeable jirk of my head. The metals used were a silver probe, a roll of tin-foil, and a common brass conductor belonging to an electrical machine. ”

“ The advocates for the first opinion observe, that whenever the brain is considerably injured, or its free communication, by means of nerves, with moving parts is interrupted, a deprivation both of sense and motion is the uniform consequence: and, further, that the several organs, both of sense and of motion, appear to suffer detriment 105 from the over strained exertions of the brain in thinking, equal to that which they experience from their own exertions. ”

“ And indeed I am not sure, if, in examining the newly discovered influence, by such a test, a sufficient quantity of electricity might 49 not be produced merely by the motion of the animals, subjected to the experiment, to occasion some fallacy in the result. Certain, however, it is, that although this influence did not affect the electrometer in these experiments, it produces infinitely stronger effects upon an animal, than any which can be produced by a quantity of electricity sufficient to affect an electrometer to a very high degree. ”

“ The experiment sometimes succeeds when neither the brain nor the spinal marrow have been laid bare, and when even the skin has not been divided, but, when the frog is placed upon a plate of zinc, and one of the ends of a bent silver wire is 164 placed upon any part of its spine, while the other is made to touch the plate. ”

“ Every experiment and observation, which has been made upon the subject of nutrition, and of the reproduction of parts, clearly demonstrates that nerves and muscles, in common with every other part of the body, derive their structure from the arteries ”

“ But when the person holding the zinc, held the nerve of the interposed leg; and I held the foot, both legs contracted with equal strength. From this experiment it is evident, that Galvani’s influence had passed either from the muscles, or the zinc and silver; and in the direct course of the nerves of both legs.
16 I was now in possession of an easy method of ascertaining the different substances, which do, or which do not, afford a passage to this new influence.
All the metals when pure appear to be excellent conductors; not quite so good when in the ore ”

“ In by far the greater number of animals, we are precluded from the possibility of discovering nerves by their minuteness; yet the actions of these animals, not merely excited by mechanical irritation, but so obviously directed to the attainment of an end, oblige us to infer their existence even where our senses, aided by the best glasses, do not enable us to detect them. ”

“ Dr Whytt’s experiment on this subject is one of the most decisive with which I am acquainted. He found, that opium operates much more slowly in destroying the heart’s motion in frogs, deprived of their brain and spinal marrow, 73 than it does when these animals ate entire. Several of my own experiments, though not made expressly with this view, gave the same result with those of Dr Whytt. M. Fontana tells us, he has discovered the heart of the wheel polypus to be a voluntary muscle. ”

“ It is however known to every one, that a blow, and that pressure upon the eye, are capable, as I have before observed, of producing a similar effect. And the following case, which Bonetus quotes from Hermannus Cummius, if it may be credited, affords an almost positive proof, that vision depends upon the stimulus given to the retina by the activity of blood vessels in some part of the eye. ”

“ Thrust in a rod of zinc between the zinc and the cheek, and a rod of silver between the silver and the other cheek. Bring their outer ends slowly into contact, and a smart convulsive twitch will be felt in the parts of the gums situated between them, accompanied by bright flashes in the eyes. And these will be distinctly perceived before contact, and a second time on separating the ends of the rods, or when they have again attained what may be called the striking distance. If the rods be alternated, no effect whatever is produced.
Care must be taken, not to press the pieces hard to the gums ”

“ As little are we authorised to suppose, that the contractions were produced in consequence of the metals attracting the electrical fluid from the leg: for, since the leg was insulated, it is impossible that it should have received a new supply of electricity, after having been deprived by the metals of what it naturally possessed ”