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MOST IMPORTANT SCIENTIFIC DISCOVERIES
electricity in animals. History and essence of scientific discovery
Directory / The most important scientific discoveries By the second half of the eighteenth century, the study of electrical phenomena had already provided material for the conclusion about the important role of electricity in biology. The experiments of John Walsh and Larochelle proved the electrical nature of the impact of the stingray, and the anatomist Gunther gave an accurate description of the electrical organ of this animal. Walsh and Gunther's research was published in 1773. Thus, by the time Galvani's experiments began in 1786, there was no shortage of attempts at a physical interpretation of mental and physiological phenomena. The ground for the emergence of the doctrine of animal electricity was completely prepared. The whole life of Galvani (1737-1798) was spent in the Italian city of Bologna. His life was not rich in events. It is curious that he graduated from the university with a degree in theology and only after defending his dissertation became interested in medicine. This happened under the influence of his communication with his father-in-law, the famous doctor and professor of medicine Carlo Galeazzi. Despite his degree, Galvani abruptly changed his profession and again graduated from the University of Bologna, but already in the medical department. Galvani's master's work was devoted to the structure of human bones. After her successful defense, Galvani began teaching medicine. In 1785, after the death of Galeazzi, Galvani took his place as head of the department of anatomy and gynecology. While working at the university, Galvani was simultaneously engaged in physiology: he owns interesting works in which he proved that the structure of a bird's ear practically does not differ from a human one. The discovery, as often happens, happened by accident. In his treatise, Galvani writes: “I cut and dissected a frog ... and, meaning something completely different, I placed it on a table on which an electric machine was located ... One of my assistants, with the tip of a scalpel, accidentally very easily touched the internal femoral nerves of this frogs ... Another noticed that this succeeds when a spark is removed from the conductor of the machine. Surprised by a new phenomenon, he immediately drew my attention to it, although I was planning something completely different and was absorbed in my thoughts. " As rightly pointed out later VoltaFrom the physical point of view, there was nothing new in the very fact of the startling of the paw of a dissected frog during an electric discharge. The phenomenon of electrical induction, namely the phenomenon of the so-called return stroke, was analyzed by Magon in 1779. However, Galvani approached the fact not as a physicist, but as a physiologist. The scientist was interested in the ability of a dead drug to show vital contractions under the influence of electricity. He studied this faculty with the greatest patience and skill, studying its localization in the preparation, the conditions of excitability, the action of various forms of electricity, and in particular of atmospheric electricity. The classical experiments of Galvani made him the father of electrophysiology, the importance of which in our time can hardly be overestimated. At the same time, Galvani came to a remarkable discovery. Waiting in vain for muscle contraction in clear weather, he, "tired ... of vain waiting ... began to press the copper hooks stuck in the spinal cord to the iron grate" ... "Although I," he writes further, "often observed contractions , but not one of them corresponded to a change in the state of the atmosphere and electricity ... When I transferred the animal to a closed room, placed it on an iron plate and began to press a hook passed through the spinal cord to it, the same contractions, the same movements appeared. Thus, Galvani, having carried out a series of experiments, comes to the conclusion that there is a new source and a new type of electricity. He was led to this conclusion by the experiments of compiling a closed circuit of conducting bodies and metals and a frog preparation. The following experiment turned out to be especially effective and effective: “If you hold a hanging frog with your fingers by one foot so that the hook passing through the spinal cord touches some silver plate, and the other foot can freely touch the same plate, then as soon as this the foot touches the said plate, the muscles begin immediately... to contract, while the foot gets up and rises and then, falling again on the plate, at the same time comes into contact with the latter, again for the same reason, rises up, and, thus, continues further alternately rising and falling, so that this foot, to the considerable admiration and joy of watching it, seems to begin to compete with some kind of electric pendulum. In such a rather complicated form, a new source of electricity was discovered, creating a long-term discharge in a conducting closed circuit. For objective reasons, the physiologist Galvani could not even allow the thought that the cause of the phenomenon lies in the contact of dissimilar metals. The scientist suggested that the muscle is a kind of battery of Leyden jars, continuously excited by the action of the brain, which is transmitted through the nerves. The theory of animal electricity provided a basis for practical electromedicine, and Galvani's discovery caused a sensation. Among the followers of the Bolognese anatomist was Volta. Alessandro Volta (1745–1827) was born in Como, Italy. Since the age of 18, Alessandro has been corresponding with Nolle on physics issues. A year later, he writes a Latin poem about modern physical and chemical discoveries. The first work of 1764 is devoted to the Leiden jar, the next work of 1771 is "Empirical research on the methods of exciting electricity and improving the design of the machine." In 1774, Volta became a teacher of physics in his native city. In 1777 he invented the electrophore, then the capacitor and the electrophorus with a capacitor. But that's not all. On his "account" is the invention of an electric pistol, a hydrogen lamp, a eudiometer. In 1777, Volta was appointed professor of physics at Pavia. In the eighties he invents the flame probe. For the invention of the pillar, he received an award from Napoleon and was elected a member of the Institute. In his first articles, published in the early nineties, Volta shares Galvani's point of view. But a future departure from this theory is soon outlined, and the physical moments of the effect come to the fore. First, Volta establishes that, in an appropriate way, "a dissected frog represents, so to speak, an animal electrometer, incomparably more sensitive than any other most sensitive electrometer." Then the scientist determines the importance of the contact of dissimilar metals. "Such a difference in metals is certainly necessary; if both plates are made of the same metal, then it follows that they differ, at least in the way they are applied ..." (i.e., in the state of the contact surface). Volta further shows that the current of the electric fluid is due to the contact of dissimilar metals and can produce not only muscle contractions, but also other irritations of the nerves. Finally, Volta establishes the polarity of the effect: changing the plates in places causes a change in taste from sour to alkaline. In the light of these facts, the theory of Volta's muscular Leiden jar seems to be untenable. In the future, Volta finally breaks with the theory of animal electricity. It gives a physical interpretation of the effect. In a letter to Cavallo, Volta writes: "... I have discovered a new, very remarkable law, which does not actually apply to animal electricity, but to ordinary electricity, since this transition of an electric fluid, a transition that is not instantaneous, as a discharge would be, but constant and continuing as long as the communication between the two plates is maintained, takes place regardless of whether this plate is superimposed on a living or dead animal substance, or on other non-metallic, but good enough conductors, such as water or bodies soaked in it. And earlier, on February 10, 1794, in a letter to the same Cavallo, Volta directly begins with the question: “What do you think about the so-called animal electricity? As for me, I have long been convinced that all action arises initially due to the contact of metals with some kind of wet body or the water itself. Physiological irritations of the nerves are the result of a passing current, and these irritations are all the stronger, the farther apart the two metals used are from each other in the row in which we put them here; zinc, tin foil, ordinary tin in plates, lead, iron, brass and various quality bronze, copper, platinum, gold, silver, mercury, graphite. This famous series of voltages of Volta and the law of voltages discovered by him form the core of the whole effect. Animal organs, according to Volta, "are purely passive, simple, very sensitive electrometers, and it is not they that are active, but metals, i.e., that the initial impulse of the electric fluid occurs from the contact of the latter, in a word, that such metals are not simple conductors or current transmitters, but real engines of electricity..." In one of the notes to this article, Volta again emphasizes that he came to the idea of contact voltage more than three years ago and already in 1793 he gave his series of metals. Thus, the essence of the effect lies, according to Volt, in the property of conductors "to cause and set in motion an electric fluid where several such conductors of different classes and grades meet and touch each other." “Hence it turns out that if three or more of them, and moreover different, together form a conducting circuit, if, for example, between two metals - silver and iron, lead and brass, silver and zinc, etc. - introduce one or more conductors, precisely from that class which is called the class of wet conductors, since they are a liquid mass or contain some moisture (animal bodies and all their fresh and juicy parts are included in them), if, I say, a conductor of this second class is in in the middle and comes into contact with two conductors of the first class of two different metals, then as a result of this a constant electric current arises in one direction or another, depending on which side the effect on it is stronger as a result of such contact. So clearly and clearly Volta formulated the conditions for the emergence of direct current: the presence of a closed circuit of various conductors, and at least one must be a conductor of the second class and come into contact with various conductors of the first class. In response, galvanists cited experiments in which muscle movements were excited by an arc of a homogeneous conductor and even, as in Valli's experiments, by contact of various preparations without a metal conductor. Volta pointed out to this that there is inhomogeneity in these experiments as well. The ends of one conducting arc are different, it is almost impossible to achieve their complete uniformity, a contact difference can also occur when different conductors of the second class come into contact. "... Non-metallic conductors, liquid conductors or containing moisture to one degree or another, those that we call second-class conductors, and they alone, when combined with each other, will be activators, like metals, or first-class conductors in combined with second-class guides..." In the future, Volta, in order to eliminate any doubts about not the physiological, but the purely physical essence of the matter, excludes animal preparations, which until then served as current indicators. He develops a technique for measuring contact potential differences with his capacitor electrometer. Volta reports these classical experiments in a letter to Gren in 1795 and Aldini in 1798. On March 20, 1800, Volta wrote his famous letter to Banks describing his pole, an invention that revolutionized the science of electricity. P.S. Kudryavtsev writes in his book: “The nature of the discovered effect was very complex, and at the then level of physical and chemical sciences and physiology it was impossible to reveal the picture of the phenomenon. In the dispute about the nature of the phenomenon, both sides were essentially right. Galvani became the founder of electrophysiology, and Volta - the founder of the doctrine of electricity. In the labyrinth of contradictory experiments and observations, Volta found the right path, found an experimental physical law of voltages, gave the correct description of the electric current circuit. There were still great disputes ahead on the cause and nature of the contact potential difference, but there were already doubts about its existence did not remain, and in the voltaic column, science received a powerful research tool, which it did not hesitate to use. Author: Samin D.K.
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