EMBRYOLOGY. MEDICAL AND BIOLOGICAL DIRECTION IN THE MEDICINE OF NEW TIME 1640-1918

 

History of medicine

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MEDICAL AND BIOLOGICAL DIRECTION IN THE MEDICINE OF NEW TIME (1640-1918)

EMBRYOLOGY

 

Embryology (from the Greek. Embrion - embryo, logos - teaching) has historically formed as a study on embryogenesis - fetal development from the moment of fertilization to birth. In the process of becoming, the content and scope of this science expanded considerably - the development and structure of germ cells and the early postembryonic period were also the subject of its study. Modern embryology studies three periods of individual development: pre-strain-breathing (progenesis), embryonic (actually embryogenesis) and early post-embryonic (postnatal) ontogenesis.

 

The first ideas about the prenatal development of the fetus arose in the ancient world and are presented in the writings of philosophers and doctors of ancient India, ancient Egypt and ancient Greece ("Hippocrats Collection"). Some of them (for example, Anaxagoras, V in. BC. E.) Believed that in the father’s or mother’s “seed” in the miniature there are all parts of the future fetus, i.e. there is a small, invisible man the development process only increases in size (the idea of ​​preformism; from the Latin. praeformare - to form in advance).

 

Aristotle (384-322 BC) was the first to criticize these ideas. He argued that the organs of the future fetus develop from a fertilized egg through successive transformations (the idea of ​​epigenesis; from Lat. Epi - above and genesis - origin). This position of Aristotle persisted in science without significant changes until the XVII century.

 

The concepts of preformism and epigenesis for a long time existed in parallel, and preformism held dominant positions, especially in the 17th — 18th centuries. (Fig. 113). This was facilitated by the imperfection of microscopic research methods and a mechanistic understanding of the idea of ​​development. Claiming that the future organism in miniature pre-existed in the egg, preformists (and among them were prominent researchers of their time: A. Leeuwenhoek, J. Swam-merd, M. Malpighi, A. Galler, etc.) explained the development, but denied it.

 

The first treatise in the history “On the formation of the fetus” (“De formatione foetu”, 1600) was composed by I. Fabrizius. He described and depicted in 32 engravings the stages of fetal development in humans and various animals (guinea pig, dogs, cats, pigs, etc.), as well as the chicken fruit in a separate work “On the formation of eggs and chicken” (“ De formatione ovi et pulli , 1621).

 

The birth of embryology as a science is associated with the name of William Harvey (Harvey William, 1578-1657) - an English doctor, a physiologist and an embryologist. In 1651 he published an essay "Studies on the Birth of Animals" ("Exercitationes de generation ammalium"), which was reprinted many times. Having studied the development of chicken and some mammals, Harvey refuted the idea of ​​spontaneous generation and put forward reasoned arguments against the doctrine of preformism. He summarized the idea of ​​the egg as the source of the development of all animals. However, due to the imperfections of the microscopic technique, Harvey was unable to see the egg of mammals.

Very close to the discovery of the egg came the Dutch anatomist and physiologist Repey de Graaf (Graaf, Regnier de, 1641 - 1673). Having lived a little over 30 years, Graaf made a significant contribution to the development of anatomy, physiology, histology and embryology. His name is associated with the improvement of many research methods, for example, the use of siphons and | enemas in anatomy. Graaf first studied the seminiferous tubules and identified them as “vessels that make seed”.

 

In 1672, he described the open vesicles of the female genital glands (Fig. 114), which he mistakenly took for eggs, whence the name ovaries (ovarium) originated. It was possible to establish the truth only a century and a half later, when K. M. Baer, ​​using a more advanced microscopic technique, showed that graph bubbles are only cavities where eggs are formed and where they are released from as a result of ovulations. Nevertheless, the first microscopes made an invaluable contribution to the history of embryology. An important milestone was the research of M. Malpighi, one of the founders of embryology, who first sketched the early stages of the development of the chicken. In 1672, he presented to the Royal Society his works “On the Formation of Chicken in the Egg” (“De Formatione Pulli in Ovo”) and “On the Development of the Eggs (“ De Ovo incubato ”), in many respects one time spent on time. They contained] 12 tables with 86 figures and explanatory text.

 

Of great importance for embryology studies as an evolved science was the research of an embryologist and Caspar Friedrich Wolff (Wolff, Caspar Friednch, 1733–1 / V4] German by origin, he accepted an invitation to Petersburg Academy of Sciences in 1767 and worked in Russia .

KF Wolf delivered a decisive blow to the concept of preformism, developing and experimentally substantiating the theory of epigenesis (the term proposed by Wolf). Having carefully studied the early stages of chicken development, he proved that a chicken egg does not contain a preformed embryo. Moreover, Wolf identified two leaflets of germinal tissue in it and showed that the lower one, coagulating into a tube, forms a digestive canal that does not exist in the early stages of development.

By analogy with this observation, Wolf suggested that the central nervous system is formed from the upper leaf and that all other organs are formed as a result of the gradual structural differentiation of the organism in the process of intrauterine development.

 

K.F. Wolf outlined his views in his dissertation Theory of Generation (Theoria Generations, 1759) and the work “On intestinal formation in chicken” published in Russia (De Formatione Intestinorum, 1768–1769).

The works of Volif laid the success of Russian embryology, the prominent representatives of which were L. I. Tredern, X. I. Pander, K. M. Baer, ​​A. O. Kovalevsky, I. I. Mechnikov and others.

 

Karl Maksimovich Baer (Baer, ​​Karl Ernst von, 1792–1876), academician of the Petersburg Academy of Sciences and its honorary member, occupies a special place among the founders of embryology (Fig. 115). He discovered the basic laws of vertebrate embryogenesis and made important theoretical generalizations. KM Baer first saw and described the mammalian and human ovum (1827), discovered the blastula, investigated and described the development of all the major organ systems of vertebrates from the germ layers. Having established the law of similarity of embryos of various classes of vertebrates, he showed that in the process of prenatal development, the properties of the type, then class, order, etc., are first discovered Species and individual traits appear at later stages of embryogenesis. He also showed that the human embryo develops by analogy with all vertebrate animals. The research of K. M. Baer finally proved the inconsistency of the concept of preformism.

The works of K.-M. Baer laid the foundations for the comparative embryology of vertebrates. The honor of creating this science belongs to A. O. Kovalevsky and I. I. Mechnikov.

 

Alexander Onufrievich Kovalevsky (1840–1901) —academic of the Petersburg Academy of Sciences — proved the relationship between vertebrates and invertebrates and developed a unified theory of the development of germ layers for all members of the animal world, which is still the main generalization of embryology.

Ilya Ilyich Mechnikov (1845- 1916) —Academic of many world academies, Nobel Prize winner (1908), in the period from 1865 to 1886 he worked in Odessa together with A. O. Kovalevsky and published a number of capital works on comparative and evolutionary embryology .

In the XIX century. along with general and comparative embryology, the physiological direction in embryology has been widely developed, connected with the use of physiological experimental methods.

 

Embryology has become one of the most important biological disciplines. Its application in medicine is not limited to the field of anatomy and histology, it is of practical importance for the development of preventive medicine and the control of hereditary diseases, for the development of new methods of testing pharmacological drugs. Great prospects for embryology are associated with the development of genetics and many other areas of medical science.

 

 

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