Book - Russian Embryology (1750 - 1850) 19
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Blyakher L. History of embryology in Russia from the middle of the eighteenth to the middle of the nineteenth century (istoryia embriologii v Rossii s serediny XVIII do serediny XIX veka) (1955) Academy of Sciences USSR. Institute of the History of Science and Technology. Translation Smithsonian Institution (1982).
Publishing House of the Academy of Science USSR
Translated from Russian
Translated and Edited by:
Dr. Hosni Ibrahim Youssef # Faculty of Veterinary Medicine Cairo University
Dr. Boulos Abdel Malek
Head of Veterinary Research Division
Arab Republic of Egypt
The Smithsonian Institution and the National Science Foundation, Washington, D.C, by The Al Ahram Center for Scientific Translations 1982
The Smithsonian Institution and the National Science Foundation, Washington, D.C by The Al Ahram Center for Scientific Translations (1982)
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Chapter 19. Theoretical Introduction to the Second Volume of Uber Entwicklungsgeschichte
The second volume of Baer's basic work includes the third part, "Lectures on the origin and development of organic bodies, read to physicians and prospective students of nature in the form of an introduction to a deeper study of the history of development," and the fourth part, "Studies of the history of human development ,"^ The third part begins with a theoretical introduction, which presents the basic principles of the history of development. Baer then moved to a systematic statement of the embryological data for all classes of vertebrates.
A superficial acquaintance with the third part can give the impression that he repeated the first part. Such a conclusion is not fair, because the first part stresses the chronology of development and the individual steps characterized by the condition of the different organs. The third part represents a related description of development of the organs and their systems.
For the characteristics of Baer's general opinions, the fairly extensive theoretical introduction, entitled "Statement of the Task," holds great interest (Â§ 1). Baer began with the cardinal question about what organic life is, remarking that scientific information about life is incomplete because of the impossibility of accurately indicating the beginning of this process. When the question, "What, in essence, is the life of the organic body," is asked, a typical answer would conclude that life derives from something different, possibly from some sharply outlined individuality. To the layman such explanations, which relate life either to the long running oxidation process or to an electric phenomenon, will cause great delight. This delight is fed by the belief that such information brings understanding of the essence of life, because such unique processes of inorganic nature are considered accessible to complete apprehension. By this means, it would be possible to indicate accurately life's beginning and end.
The fourth part is not included in the second volume of the Russian version? in it are listed only the human embryos investigated by Baer. (Ed.: Nor is the fourth part in the original German edition. It was printed later, as explained in Chapter 21.)
All such explanations Baer considered absolutely unsatisfactory for the physiologist, because they are concerned with only one particular phenomenon of the life process. The physiologist should teach that life should be explained not from something else, but from life itself. Turning to the inorganic world, Baer noted that the time will come when the physicists themselves should recognize that on performing their experiments they remove individual physical phenomena from the context of the general nature of life. It is known that "not a single chemical process takes place without galvanic activity, nor any galvanic without magnetic activity, that light and heat are mutually dependent; and therefore, it is to be hoped that, as until now the physiologist compares the complex phenomena of organic life to physical processes, some day he will compare physical phenomena with those in the living organism and will gain understanding from them" (II la 3). At that time, Baer predicted that the complaint concerning unclear life phenomena should end. It is customary to look at their reciprocal relations and take them as they are, without forced, frequently laughable explanations and references to the unique phenomena in inorganic nature.
Baer's statements reflect his ideology, which was not free from the effect of the, to him modern, idealistic philosophy. But his ideas reflected a protest against the simplified mechanical understanding of processes, the inorganic as well as the organic, and the spontaneous approach to the idea about the general or universal connection of all phenomena.
The difficulties in investigating inorganic phenomena are not so great, but understanding organic life is more imperfect because it is not possible to determine accurately the moment of its appearance in each separate individual. Hence the origin and development of organic bodies seems particularly obscure and strange. However, Baer noted, the beginning of individual life is not more obscure than any other life phenomenon, but what is directly apprehended seems to be much more understandable than that unavailable for perception. Every year the tree gives rise to buds, and sprouts grow from them. This fact, for people who do not study nature, does not arouse curiosity, while the quick growth of the tree from the seeds creates an unsolved enigma. In a similar way they do not see anything strange in that each man, each animal and plant feeds and grows over time. However, the nourishment is nothing other than a constant change; man today is not man of yesterday. It is possible to say that growth is nourishment with the formation of a new mass, that it is a continuation of conception, and that conception in its turn is nothing other than the origin of individual growth.
In the spiritual constitution of man, it is common to search for an entirely defined origin of all things, a defined border between being and not being, when it is actually possible that in nature there is nowhere an absolute beginning. Nature is characterized only by eternal change. With living beings it is natural to assume that the beginning of a new organism corresponds with the moment of fertilization. In order to pursue this beginning moment, writers had resorted to wit and imagination. They had assumed that at the time of fertilization the new creature appears as a result of an electric shock, or through the union of two heterogenous substances, or by means of some magic power. However, since the microscope had not been improved or vision extended, after fertilization it was possible to see only what was seen before fertilization. Only after some time was a new plant or new animal recognized, but already in a condition of later growth. Undoubtedly, however, before fertilization nothing had existed that represented the primary form of the emerging animal or plant; so an independent organic body resulted from its conversion. Consequently, the beginning of the individual does not correspond with fertilization, and the rudiment of the fetus already preexists in the parents. At fertilization the conditions allow it to grow quicker. In other words, the initial existence of the fetus should have been sought either in the mother's or in the father's body.
The ovary of the mother contains parts, such as the ova, which give the beginning to a new individual. It was possible to assume preformation in the ova. From the other side, after the invention of the magnifying lens, observers found in the male an enormous number of small, spontaneously moving animals, i.e. live bodies. This observation was extremely welcomed by the supporters of preformation. The fact of the enormous quantity of these bodies in the male testicles was difficult to explain. Defenders of preformation believed that the moment of fertilization millions of the male bodies (called cercaria) violently fight with each other, until those lucky few live conquerors penetrate into the vesicle of the female ovary. It is only a pity, Baer speaks ironically, that these bodies do not have jaws to bite each other. In general they do not have even the most remote similarity to the higher animals, but consist only of a small head and a long tapering tail.
"After a brief flourishing," Baer continued, "this hypothesis, like the hypothesis of preformation in the egg, was forgotten and faded throughout half a century. Only recently two very accurate observers, Prevost and Dumas, have revived it as a result of a thorough investigation of the testicular beasts." About the cercaria, Baer cited the words of Prevost and Dumas that "not the complete hen or cow is formed from the cercaria, but only the nervous system, while the others grow from the female reproductive material" (II Id, 5). Actually, Baer continued, the cephalic brain, in combination with the spinal cord, has a form somewhat similar to the cercaria magnified a million times" (II Id, 6) The first part of Prevost 's and Dumas 's work^ was received, according to Baer, with complete confidence. However, when Prevost found similar bodies in the reproductive organs of snails and the cockle-shell, in which there is neither a cephalic brain nor a spinal cord, then the authors
2. J(ohn) L(ouis) Prevost and J(ean-Baptiste) Dumas, NOUVELLE THEORIE DE LA GENERATION (New theory of generation) (Paris, 1824). ANNALES DES SCIENCES NATURELLES, 1 (1824), pp. 1-29, 167-187, 274-292.
were required to have oratorical art to explain that they were incorrectly understood? they say that they did not affirm that the narrow system is directly formed from the testicular bodies which penetrate into the ovum, and considered that this penetration is necessary as a preparation to its formation. By this explanation, however, they themselves frustrated their hypothesis. (II, Id, pp. 12-13 (p. 6))
Next Baer strove to show that the task of explaining the defined beginning of individual development will not be solved if we assume the preexistence of future generations in the bodies of the parents, because, in this case, we must assume that all living creatures, right up to the last generation, were created at the same time as the first individuals. Consequently, in the chick ovary all the chicks that are to be formed must be present, and in the ovary of each one of them must be again all their future offspring, and so on. These offspring included in each other, because of their infinitely small sizes, are unavailable for observation by our optical facilities. Although the hypothesis, as Baer said, is next to nonsense, nevertheless it was defended by many famous naturalists. This represents a clear example of the confusion into which one can fall if he bases opinions on suggestions and not on observations. If this point of view were correct, then it should have been recognized that inevitably the time would come when all life on earth would end because all creation had been already formulated. Continuing ironically this "theoretical argument," which in part relies on religious belief, Baer wrote that after the exhaustion of preformed generations the Creator would then begin his work again, since the first effort of creation appeared to be so imperfect. From the characteristics of preformation, Baer drew his listeners' attention to the fact that, in spite of the slowly progressing accumulation of facts in the history of development and the great -difficulties in extracting such facts, the accomplishments of science are highly significant. Observations show the incorrectness of the aforementioned ideas about reproduction and development. Baer expressed his belief that already there was enough data to recognize nature's methods for forming new organisms. The new investigations of the history of development, Baer said, were still poorly known, and the old ones obscured by preconceived ideas; therefore it is necessary to present the facts from the history of development.
3. J. L. Prevost, "On the Generation of Painters Mould," ANN. SCI. NAT., 7 (1826), p. 447-455.
Baer considered his task as giving the combined work of the history of reproduction and development and showing that they, in one sense, are not preformed and, in another sense, do not develop as was usually thought, all at once from a formless mass.
Baer noted in this case that he recognized well the difficulty of talking about an object still so alien to contemporary scholastic and university education. He feared that he would not be understood on the level that he wished, because his listeners had more experience with hypotheses rather than with facts. Knowing how the classical trend of education had fenced German students off from studying the phenomena of nature, Baer, not without irony, said that he even assumed the structure of the bird's egg to be unknown to his listeners.
For among my respectful listeners there are probably few who do not know that the cackle of geese once saved the Capitol. With the exception of medical persons, there are probably few who are aware of the contents of a goose egg, and a qualified German teacher, above all, would not know that poultry lay eggs if he did not have it from Pliny or Phaedrus. (II, If, 8).
About birds' eggs, Baer continued, the basis of our knowledge of growth and development of animals is obtained from the fortunate opportunity of continued studies . What we know of the development of other animals is for most classes, especially the mammals, to which the physical aspects of man also belong , so isolated, that it can only be understood by comparison with the development of birds. (II, If, p. 16 (p. 8 ))
And although Baer, as a result, anticipated that the features of similarity of birds and other vertebrates, as well as their specific peculiarities, might be inherent only to avian development, he later did not pay attention to his own warning. Describing the development of the egg in the ovary, the structure of the fertilized egg, the formulation of embryonic organs and membranes and so on in reptiles, birds, and mammals, Baer strove not to keep finding complete parallels. Sometimes he did not see those new formations characteristic of the higher classes of vertebrates. Note that it is impossible to forget about Baer's great service. He was the first to show with complete distinctness the fruitful comparative method in embryology, although he himself used it only within the class of vertebrates and did not see the possibility of comparing regularity of development in animals belonging to different morphological types.
In order that his listeners could establish an objective judgment, and in order that they would not draw general conclusions for their own dogmatism, Baer suggested the following. He intended to begin by stating the history of bird development, then to compare the most essential from the history of development of other classes of animals in order to get to the most important problem â€” the elucidation of reproduction and development.
The last division of the book, treating general questions of embryology, was never written, and because the second volume of UBER ENTWICKLUNGSGESCHICHTE was printed without the author's participation, the missing part remained only a reference in the introduction.
Cite this page: Hill, M.A. (2021, April 15) Embryology Book - Russian Embryology (1750 - 1850) 19. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Russian_Embryology_(1750_-_1850)_19
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