Meyer - Essays on the History of Embryology 2
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Meyer AW. 1932 - Essays on the History of Embryology: Part I | Part II | Part III | Part IV | Part V | Part VI | Part VII | Part VIII | Part IX | Part X | Part XI | Arthur Meyer | Historic Embryology Papers
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Essays on the History of Embryology II
By A. W. Meyer, M. D.
Stanford University
- This is the second paper of 3. series of three articles. The first was printed in the December issue of California and Western Medicine, p. 447. January, 1932
Some Puzzling Things to Early Writers
ONE of the most puzzling things to the earlier writers was the fact that many creatures and also they themselves existed as male and female, and that both sexes were essential for procreation. The sexual secretions such as the semen of the male and the catamenia of the female could, to be sure, not escape attention. Similar phenomena in other mammals also were obvious, and the idea that menstrual blood not only took part in the formation of .the germ, but contributed its very substance, is a very old one indeed. It is mentioned in Susruta five hundred years B. C., and it lived on long after that in Aristotle and elsewhere. The male long was thought to contribute only the molding force and the Female the substance.
These ideas seem fanciful to us, but even William Harvey concluded that the womb conceives the embryo as the brain conceives a thought. Harvey believed that coitus merely excites conception in the uterus as desire is generated in the brain, and the present use of the words conceive and conception is not without significance in this regard.
It is said that Pythagoras[2] regarded semen as a foam of the purest blood and as an excess of nutriment, an idea that persisted to the days of Harvey, but Pythagoras and others, such as Alcmaeon. Democritus, and Parmenides, held that woman also produces semen. This idea may have had a various origin, but since they knew the spawn of the female fish and the milt of the male, as well as the sexual discharges of amphibia, it is not improbable that the superficial similarity between the testis and the ovary and between the cervical, uterine and tubal secretions and semen, may have been partly responsible for this idea. The outward effects of castration both accidental and intentional, in both sexes, on animals and on the human male, must also have been known and it is likely that cases of sex reversal had been observed at this time.
The ancient Greeks did not stop at speculation or accidental observation, however, for Alcmaeon, a disciple and contemporary of Pythagoras, made observations upon the eggs of birds and concluded that the yolk was the formative and the egg white the nutritive material. The true role of these substances still was unsettled in 1868, when the great embryologist His considered the matter. Although Alcmaeon rightly regarded the brain as the organ of thought, he, as Aristotle, concluded that semen was a product of the brain and Parolles in Alls Well, spoke of “spending his manly marrow in her arms.”
Aristotle says Empedocles thought that sex was determined by the temperature in the uterus. If hot a male results, if cool a female. He believed in the primacy of the heart in development, perhaps because the pulsating heart or punctum saliens is such a conspicuous object in an incubating egg. This conception of the role of the heart in development persisted until the sixteenth century. Anaxagoras rejected the idea of female semen, held also by Aristotle, perhaps because he believed that semen came from the blood, but Anaxagoras thought that male individuals arise from sperm produced by the right and females from that produced by the left testis, an idea rejected by Harvey, who thought that sex was determined by an internal, inherent agent wholly independent of the parents. The male and female were also once thought to develop in opposite sides of the uterus and a modified version of this idea was held also by Aristotle, and still is current among the laity of many lands today.
Democritus, a contemporary of Hippocrates, held that semen is a product of the whole body, an idea controverted by Aristotle who wrote: “For whereas they (the ancients) said that semen is that which comes from all the body, we shall say it is that whose nature is to go to all of it. and what they thought a waste product seems rather a secretion”; . . . “the ultimate secretion of the nutriment.” Aristotle stated, however, that “there is evidence that the semen is in the catamenia, for, as said before, this secretion appears in the male at the same time of life as the catamenia in the female . . ” and continues to say that “the spermatic secretions” are produced b_v “the uterus and pudenda and breasts,” including milk because it is a nutriment. Aristotle held that the loss of semen is exhausting because “the body is deprived of the ultimate gain drawn from the nutriment.” The embryo to Aristotle was “the first mixture of male and female” and the ovum an oviform body found in the uterus, as it was also to Harvey. Hippocrates thought that maleness and femaleness are determined by the excess of male or female semen present at the time of conception. Aristotle, on the contrary, concluded that “the male is such in virtue of a certain capacity-—and the female is such in virtue of a certain incapacity . . . to concoct the nourishment in its ultimate stage,” that is, blood.
Although Anaxagoras thought that the head and brain develop first, perhaps because the latter is the seat of thought, Democritus held that the umbilicus is the first to form. This seems an amusing conclusion indeed, but the umbilicus was the place where nutriment entered and union with the mother was effected, and since Democritus inquired into the cause for the sterility of mules, we need not regard him as altogether benighted. Although Plato lived somewhat later than Democritus, he believed that semen arose from the spinal cord and his speculations on embryology seem to fall far below those of his contemporaries. It hardly seems worth while to inquire further into them as expressed in his Timaeus.
Defects in the Pre-Hippocratic Embryologic Ideas
The chief defect in the pre-Hippocratic embryologic ideas lies in their detachment from sufficient purposeful observation and experiment. This is the great step forward shown in some of the Hippocratic writings, in one of which the surprising idea is expressed that all plants and animals have to some extent the same ground plan, and that one should therefore be able to apply the story of the development of the chick to that of other animals. That purposeful experiments in embryology were undertaken in that day is indicated by the fact that an unknown author of some of the Hippocratic writings tells us that one must put twenty eggs under a hen and take one out every day, beginning with the second day, and break it open in order to confirm the above idea. This procedure constituted a great advance, and it is extremely regrettable that the name of its author remains unknown to us and especially that the novel and fruitful conception of similarity between different forms of life fell upon sterile ground and remained unproductive for almost two thousand years until an Italian, Aldrovandi, recurred to it during the time of the Renaissance. After this it formed one of the most fruitful ideas in embryology.
It is puzzling why a Hippocratic writer thought that the earliest evidence of life in the human fetus felt by the mother, or quickening, occurred as early as the third month if the conceptus be male, but not before the fourth month if it be a female. Had these Greek writers but consulted the Greek mothers they could have obtained better information, and one wonders why they did not do so, unless it be that they mistrusted their own senses, and therefore also those of others as well.
Observations of Aristotle
Online Editor - See also 1890 McRae Aristotle
Some of the observations and reflections of Aristotle upon the procreation and development of animals which are a continuation of those in the Hippocratic writings exerted a great influence on embryology up to the seventeenth century because of the authority of his great name. Indeed, some of the misconceptions found in Aristotle are still current today in other than lay circles. Aristotle, the master of them that know, as Dante called him, himself examined incubating eggs and his idea of equivocal or spontaneous generation of eels, some species of fish. insects. and worms, remained current regarding some forms of life until overthrown by the convincing experiments of Pasteur. Aristotle suggested four methods of the origin of life and believed that the organic could arise from the inorganic and also from heat. Since the ancients believed that the inorganic also had a soul, such a conception of spontaneous generation should not surprise us. Nor should we marvel that Aristotle believed in the occurrence of parthenogenesis in higher forms of life. He could not detect the two sexes in all forms of animal life.
Aristotle regarded menstrual blood, in a sense, as the equivalent of ,semen, and held that menstruation in women is comparable to estrus or heat in mammals, an error still found in contemporary literature. He also held that the menstrual flow is comparable to the eggs of other animals, and that eggs form only through the influence of the male, the female supplying the substance and the male the energizing power. somewhat as we of today still use the word “fertilization” and incorrectly regard the spermatozoon as merely supplying a ferment to the ovum to inaugurate cell division. It is true that parthenogenetic development can be started artificially in some ova by chemical means as Loeb showed for the sea urchin, or by spermatic extract which presumably also is chemical. as Lillie discovered. This has not been possible in regard to the sperm but the two cells play an equivalent role in heredity.
To Aristotle the catamenia were imperfect semen which contained no soul because the male contributed the immaterial or controlling force. This idea was held also by Harvey, who believed, after Aristotle, that the cock contributes no substance but only an influence which makes the egg perfect and so initiates development. Aristotle carried this idea so far as to hold that the female partridge could be fertilized by the breath of the male, but it is not always easy to tell whether Aristotle is speaking upon the basis of observations or hearsay, as when he says that SCOI'pl0I1S are born alive after the union of male and female. Anyone interested in Aristotle and Hippocrates will enjoy the essay by Singer.
Since the mode of reproduction of eels was not described till 1896 it is no wonder that Aristotle thought they had no generative organs. He never could find milt or roe and so concluded that eels arose from the entrails of the earth like certain worms. Aristotle was familiar with hermaphroditism in bees and with the occurrence of viviparous fishes. He knew the vitelline and allantoic vessels and the accompanying sacs and studied a twelve-day chick. He also knew something about the fate of the allantois and the yolk sac.
Since the medical school at Alexandria was known throughout the world for its enterprise in dissection of the dead, it seems as though the great men active there, such as Herophilus and Erasistratos, must also have made observations on embryology. There is no record of this, however, and one is left to pure surmise regarding this matter as regarding other things. The Alexandrians were supposed to have dissected the bodies of living men, but it has never been established that they did so. It does not seem unlikely, however, that some criminal might have been willing to take a chance on surviving an inspection of some part of his body under the knife of anatomists rather than suffer a cruel death after torture, and we must remember that dissection in that day meant something wholly different than now.
The Viewpoints of Galen
From Aristotle to Galen, during a period of about five hundred years, there does not seem to have been much of an advance in conceptions regarding embryology. Although Galen himself remained an authority in many things for a period of a thousand years, he added little of value to the ideas regarding prenatal life. He did, however, return to the idea of the existence of male and female sperm, and for a reason especially worth noting. This was because Galen found material which looked like semen in the uterine tubes of animals killed while in heat, and it is much to his credit that he carefully described this fluid. It should not surprise us that Galen confused the tubal, uterine and cervical secretions with semen, for long after Galen’s day Haller and Kuhleman, who did some experiments in embryology and made many observations on hen eggs. could find nothing but white tough slime in the tubes and uteri in mammals two weeks after coitus; at a time when the conceptuses had already implanted and were several days old. However, Haller was extremely modern in many of his ideas, for he wrote: “The extremity of the tube, therefore, surrounding and compressing the ovarium in a prolific congress, is thought to press out and swallow a mature ovum, from a fissure in the outer membrane, from whence it is continued down by the peristaltic motion of the tube, to the uterus itself ; which peristaltic motion begins from the first point of contact with the ovum, and urges the ovum downward successively to the opening into the fundus uteri, which is very manifest in brute animals. The truth of this appears from the constant observation of a sear or fissure in the ovarium, which is produced there after conception; from a foetus being certainly found in quadrupeds, both in the ovarium of the female, and in the tube; from the analogy of birds, in which the descent of the ovum from the ovarium is very manifest. Yet we must acknowledge, that a true ovum was never found in quadrupeds, unless after a long time. It is probable, that at the time of conception, the true ovum is almost fluid, very soft and pellucid, and cannot be distinguished from the mucus with which the tube is filled; likewise, that it is very small, on account of the narrowness of the tube.” Even later than this, Wolff, whose work finally established the doctrine of epigenesis, announced by Harvey, is said to have drawn the figure of a hen egg representing the developing embryo in a chalaza of the egg, fully thinking that he had seen it there. It is said that he later recognized his error and never made the drawing public. Since the idea that the sperm enters the bird egg through the chalazae and that the embryo begins to form there is a very old one, it is possible that Wolff was influenced by these older conceptions.
Galen called attention to the fact that what he regarded as comparable to pollution in the male occurs also in women, and wisely argued, as had Aristotle, that if the male and female did not, in some measure, both share equally in procreation, inheritance could not occur from both parents. He went on to say that if there were only male sperm there could only be inheritance through the male, and if only female sperm then only through the female.
Although Aristotle had regarded the ovary and testis as unimportant organs, Galen regarded them as important and as equivalent, and emphasized their role in the body as indicated by their loss in castration. However, Galen recurred to the older idea as to the origin of semen, believing that it came from the blood, because, as he reasoned, emaciation and exhaustion follow too frequent loss of it. He did not think that menstrual blood plays a role in procreation, but concluded that female semen formed the allantois and that coagulation of male and female semen in the uterus resulted in the formation of the chorion. He spoke of four stages in prenatal development, the first of which he called geniture. During this stage the conceptus was said to be unformed and white like semen. In the second stage it became a fetus, but was said to be without liver, brain, and heart although vascularized. Galen seems to have suggested no special name for the third stage, in which the heart, liver, and brain were well formed, but in which the external features still were largely unformed. In his fourth stage of prenatal life, puer, all of the organs were well formed and the joints freely movable. From this it is evident that this stage occurred relatively late in fetal life.
On the basis of their origin, Galen divided all parts of the body into two classes. One class of organs which was said to arise from sperm was called partes spermaticae, and the other class, partes sanguineae, because he believed they arose from the blood. This classification of Galen continued in use for several hundred years, and well illustrates the danger of speculation.
Galen wrongly thought that the blood of the mother circulates in the fetus, but recognized and carefully described the foramen ovale and the ductus arteriosus and venosus, the existence of which was forgotten for a long time until they were rediscovered and described by Botalli and Aranzi about the middle of the sixteenth century.
Since Galen dissected many domestic animals, he often transferred the observations made upon them directly to man, thereby misleading many who followed him. This need surprise no one and we are daily doing this very thing when we apply, without qualifications, results obtained from experiments on animals to the human being. Because of his devotion to the dissection of animals, it is surprising that Galen does not seem to have studied incubated eggs or human conceptuses, both of which he probably could. have obtained easily.
Stanford University.
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Meyer AW. 1932 - Essays on the History of Embryology: Part I | Part II | Part III | Part IV | Part V | Part VI | Part VII | Part VIII | Part IX | Part X | Part XI | Arthur Meyer | Historic Embryology Papers
Cite this page: Hill, M.A. (2024, April 23) Embryology Meyer - Essays on the History of Embryology 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Meyer_-_Essays_on_the_History_of_Embryology_2
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