|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
MOST IMPORTANT SCIENTIFIC DISCOVERIES
Fundamentals of Embryology. History and essence of scientific discovery
Directory / The most important scientific discoveries "Ab ovo" is an old Latin proverb. It means "from the egg", "to start from the beginning". How does human and animal life originate, where does it begin? Fragmentary embryological observations were already made by Aristotle. However, as early as the 200th and 000th centuries, the so-called theory of transformation or evolution dominated. According to this theory, the future organism preexists in the egg ready, with all its parts. These parts are not visible in the early stages only because they are very small and transparent. A direct consequence of this theory was the assumption that in the microscopic germ there already preexist those germs that it subsequently produces; embryos are also nested in these embryos, and so on - whole generations of future organisms are preformed in each egg. Since at that time naturalists, whatever theories they came up with, tried to harmonize them with the Holy Scriptures, some idle minds began to calculate how many embryos were embedded in the ovaries of the foremother of the human race, Eve, and determined their number to be approximately XNUMX million . Moreover, since the development of an egg requires fertilization, that is, the union of the egg with the gum, the question arose: in which of the connecting elements are the embryos embedded, in the egg or in the gum? This question divided scientists into two schools: the ovists, who asserted that the embryos are embedded in the egg, and the gum serves only to stimulate development, and the spermatics, who were convinced that the embryos are in the gum, and the egg only supplies nutritional material for them. Only in the second half of the 1734th century did the famous "Theoria Generations" by the Berlin physician Caspar Friedrich Wolf (1794-1812) appear, which laid the foundation for the theory of epigenesis, that is, the gradual formation of the organs of the embryo from an initially simple (according to Wolf, even unorganized) basis. This work marks an era in embryology, but the thoughts carried out in it were not appreciated when Wolf's dissertation appeared. The dissertation itself, having passed almost unnoticed, was so thoroughly forgotten that it was not until XNUMX, when Meckel found it and translated it from Latin into German, that the theory of epigenesis received due attention. The same Wolf laid the foundation for the theory of germ layers, or sheets, showing that the embryo consists of layers, each going to the development of certain organs. This discovery of Wolf was also not at first appreciated. Oken, among other things, criticizing the work of Wolf, says: "This cannot be, since the organism does not arise from leaves, but from bubbles." In 1817, Pander, while developing the chicken, published his research, which contained a lot of valuable data and confirmed Wolf's theory of epigenesis and germ layers. But Pander's work, like Wolf's dissertation, was not understood by his contemporaries. The one who is rightfully considered the founder of embryology did not understand it either - Carl Baer. Karl Ernst Baer (1792–1876) was born in the town of Pip, in the Gerven district of the Estland province. Little Carl early began to be interested in various objects of nature and often brought home various fossils, snails and the like. At the age of seven, Baer not only could not read, but did not know a single letter. Subsequently, he was very pleased that "he did not belong to the number of those phenomenal children who, because of the ambition of their parents, are deprived of a bright childhood." Then home teachers worked with Karl. Eleven-year-old Carl is already familiar with algebra, geometry and trigonometry. In August 1807, the boy was taken to a noble school at the city cathedral in Revel. In the first half of 1810, Karl completed the course of the school. He enters Dorpat University. Here Baer decides to choose a medical career. When Napoleon's invasion of Russia followed in 1812 and MacDonald's army threatened Riga, many of the Derpt students, including Baer, went, like true patriots, to the theater of operations. In 1814, Baer passed the examination for the degree of doctor of medicine. He presented and defended his dissertation "On Endemic Diseases in Estonia". But still realizing the insufficiency of the knowledge gained, he asked his father to send him to complete his medical education abroad. Baer went abroad, choosing to continue his medical education in Vienna, where such famous people of the time as Hildebrand, Rust, Beer and others taught. In the autumn of 1815, Baer arrived in Würzburg to another famous scientist, Dellinger. All his life, Baer kept the liveliest gratitude to Dellinger, who spared neither time nor labor for his education. Then he enters as a dissector to Professor Burdakh, at the Department of Physiology at the University of Königsberg. As a dissector, Baer immediately opened a course on the comparative anatomy of invertebrates, which was of an applied nature, since it consisted mainly of showing and explaining anatomical preparations and drawings. Since then, Baer's teaching and research activities have entered their permanent groove. He led the practical classes of students in the anatomical theater, taught courses in human anatomy and anthropology. Baer also finds time to prepare and publish special independent works. In 1819, he managed to get a promotion: he was appointed extraordinary professor of zoology, with an assignment to start building a zoological museum at the university. In 1826, Baer was appointed ordinary professor of anatomy and director of the anatomical institute, relieving him of his duties as a dissector until now. That was the time of the rise of the scientific activity of the scientist. Baer's greatest success was in embryological research. When Baer worked for Dellinger, the latter invited him to study the development of the chicken - a classic object of embryology due to the availability of material and the size of the egg. Baer at that time still hesitated in choosing a career, and the work required a large investment of time and money. So he persuaded his friend Pander to take on the job. Having received Pander's dissertation, published without drawings, he could not understand it. And only when Pander sent him a more complete edition of his work, supplied with drawings, Baer somewhat clarified its content. However, he only achieved a full understanding of it when he undertook an independent study of the history of the development of the chicken. This incomprehensibility of Pander's work depended, firstly, on an unclear exposition, and secondly, apparently, on the fact that the author, conscientiously observing and describing everything that he saw, did not have any guiding, generalizing idea. Baer, starting to study the embryology of the chicken, was, thanks to his extensive comparative anatomical training, in completely different conditions than Pander. Already possessing an idea of the type of vertebrates, he was prepared to capture the features of this type in embryonic development. And so, observing that early stage of development, when two parallel ridges form on the germinal plate, subsequently closing and forming a brain tube, Baer concludes that "the type directs development, the embryo develops, following the basic plan according to which the body of organisms of this class is arranged ". He turned to other vertebrates and in their development found a brilliant confirmation of his thought: no matter how different vertebrates are, dorsal ridges and the neural tube formed from them appear everywhere, everywhere the digestive canal is formed by a grooved bend of the lower germinal layer, everywhere the navel is formed on the abdominal side facing the yolk. Turning to the development of other types of animals, Baer saw that even there, in each type, there is an early order and mode of development. So, in articulated animals, a transverse dissection of the embryo is noticed very early, the ventral side, and not the dorsal side, is formed and turns outward, and if there is a navel, then it is located on the back. The enormous significance of Baer's History of the Development of Animals, published by Baer in 1828, lies not only in the clear elucidation of the main embryological processes, but mainly in the brilliant conclusions collected at the end of the first volume of this work under the general title of Scholia and Corollaria. The English scientist Huxley, who in 1855 translated a passage from these "scholia" into English, expresses in his preface his regret that in his country a work containing the most profound and sound philosophy of zoology and even of biology in general has been unknown for so long. Another famous zoologist, Balfour, says that all the studies on vertebrate embryology that came out after Baer can be considered as additions and corrections to his work, but cannot give anything so new and important as the results obtained by Baer. Let us point out only some of these results. Asking himself the question about the essence of development, Baer answers it: all development consists in the transformation of something that previously existed. "This proposition is so simple and unsophisticated," says Rosenberg, the author of an excellent speech on Baer's merits, "that it seems almost meaningless. And yet it is of great importance." The fact is that in the process of development, each new formation arises from a simpler pre-existing basis. So, for example, the lung arises as a protrusion of the originally simple digestive tube; the eye is like an outgrowth of the cerebral bladder; the auditory labyrinth is formed as a deepening of the skin, lacing off from it in the form of a sac, and so on. Thus, an important law of development is revealed, that at first general bases appear in the embryo, and more and more special parts are isolated from them. This process of gradual movement from the general to the specific is known today under the name of differentiation. By elucidating the principle of differentiation of the embryo, Baer thereby put an end once and for all to the theory of preformation, or evolution, and ensured the final triumph of Wolff's principle of epigenesis. Baer's other general proposition, which is in close connection with the one just considered, says: the history of the development of the individual is the history of a growing individuality in all respects. Again, at first glance, an obvious conclusion. In reality, however, this conclusion was not easy to obtain, and its content is far from unimportant. “Experience shows,” says Baer, “that conclusions are more correct when their results are previously achieved by observation; if it were otherwise, then a person would have to receive a much larger spiritual inheritance than it actually is.” The main significance of Baer's just-drawn conclusion becomes immediately clear if it is stated in somewhat more detail. The fact is that a developing being, as Baer noted, initially reveals only belonging to one or another type. Then little by little signs of a class appear, that is, if, for example, we observe the development of a vertebrate, then it becomes clear whether we are dealing with a future bird, a mammal, and so on. Even later, the characteristics of the order, family, genus, species are clarified, and, finally, after all, purely individual characters appear. In this case, the embryo does not pass through a continuous series of forms corresponding to ready-made beings of varying degrees of perfection, as natural philosophers imagined the development of animals, but rather separates, delimits more and more from all forms, except for the one towards which its development tends. Baer, establishing with his embryological studies the principle of gradual divergence of signs, prepared the emergence of the idea of the kinship of organs in the form of a complex, abundantly branched genealogical tree: “The earlier stages of development we study, the more similarities we find between different animals. Therefore, the question arises: are not all animals the same in essential features at the very beginning of their development and is there not one common initial form for them? .. According to the conclusion of our the second scholia, the embryo can be considered as a bubble with which the yolk gradually grows in the egg of birds ... in the egg of the frog it appears even earlier than the type of vertebrate is found, and in mammals from the very beginning it surrounds an insignificant mass of yolk.But since the embryo is not nothing but a whole animal, only underdeveloped, then it can be asserted, not without reason, that the simple form of the bubble is the common basic form from which all animals have developed, and not only in an ideal sense, but historically. For anyone who is more or less familiar with embryology, it is clear from this extract that Baer quite correctly noticed and evaluated a very important embryonic phase, currently known as the blastula. Author: Samin D.K.
▪ Theory of chemical structure ▪ The laws of planetary motion ▪ Saussure's linguistic concept
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Purification of drinking water from drugs
▪ section of the site Firmware. Article selection ▪ article Through the sleeves. Popular expression ▪ article How could many samurai be forced to kill themselves at the same time? Detailed answer ▪ Quince article is oblong. Legends, cultivation, methods of application ▪ article Contours for KB antennas. Encyclopedia of radio electronics and electrical engineering ▪ article Talking coin. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page