Book - Chemical embryology 1 (1900) 2
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Needham J. Chemical Embryology Vol. 1. (1900)
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Part II The Origins of Chemical Embryology
DII LABORIBUS OMNIA VENDUNT
Nobilissimo juveni Medico Philippo
de Glarges, amicitiae ergo libenter
Gulielmus Harveus scripsit, Anglus,
Med. Reg. et Anat. Prof. Londin.
Mai. 8 1641
From the commonplace book of Philip de Glarges.
Not to prayse or disprayse : all did well.
William Harvey's MS. notes, Canones Anatomiae Generalis, 6.
Preliminary Note
It is open to anyone to say with some appearance of truth that physico-chemical embryology has no history, since the attempt to unravel the causes of embryological phenomena by physico-chemical means has only recently begun. But such a statement would betray a superficial and jejune mentality. Physico-chemical embryology has its roots in the history of embryology as a whole, and it is those roots which I shall try to uncover in what follows. It must be remembered that morphological must theoretically precede biophysical analysis, as it has actually preceded it chronologically, and to that extent physico-chemical embryology cannot be properly understood without reference to its descriptive husks, and their historical growth. Moreover, even in antiquity there are hints that the chemistry of the embryo was dimly envisaged (as in Aristotle, see p. 70). Again, that philosophical problem which we have already considered, plays a great part in the history of embryology, and as we watch the pendulum swinging from Democritus to Aristotle, back again over to Herophilus, and back once more to Galen, we almost feel as if we were spectators looking on, like Hardy's spirits, at a great drama, with the movement of which we are powerless to interfere, but knowing that the existence of exact biology depends upon which side wins. Lastly, such unmorphological questions as the respiration and nutrition of the embryo were discussed from the most ancient times, and it is surely no unduly wide interpretation of the word which leads us to include an account of these opinions under the heading of chemico-embryological history. Nor could the present moment be more appropriate for such an historical survey. Embryology is entering a new phase: and on the threshold it is very fitting that some retrospective attention should be paid to the phases which it has already passed through. The events of the past, moreover, throw Hght on those of the future, and this is true not necessarily in Spengler's sense but also because the historical approach to problems actually unsolved protects them, by a kind of gentle scepticism, from too severe a subjection to doctrinaire presentations. "Die Geschichte einer Wissenschaft ist der Hort ihrer Freiheit; sie duldet ihr keine einseitige Beherrschung", said Louis Choulant in 1842. Theoretical bhnd alleys, such as the final cause, practical blind alleys, such as preformationism and phlogiston, are always able to remind us that we may be mistaken.
No exhaustive treatise on the history of embryology at present exists. The nearest approach to it is the very valuable memoir of Bruno Bloch with its epitome but this only covers the era of the Renaissance with thoroughness. Hertwig's account, which he printed at the beginning of his great Handbuch der Entwicklungslehre, does not deal very fully with any aspect of the subject before 1800, nor do the much shorter ones of Henneguy and Minot. The latter paper is interesting in that it ends with an emphasis on the need for a physicochemical attitude in the future. The introduction to Keibel's book is much slighter, but contains some useful information. There are various monographs and papers on special points, such as Pouchet's rather untrustworthy treatment of the embryology of Aristotle, and Lones' discussion of it, which is worse. Camus' notes are still the best commentary on the Historia Animalium. Again, useful information on some cultural points is to be had from the treatise of Ploss & Bartels. The introductions to certain books also contain valuable information, and in this class comes Dareste's remarkable book on teratology. The bibliographies contained in v. Haller's eighth volume and in Heffter's book, are, naturally, of the greatest assistance.
These reservations made, the principal reviews of the subject are chiefly to be found in histories of science in general, such as Sarton's; histories of biological theory, such as Radl's; histories of obstetrics, such as V. Siebold's, Spencer's and Fasbender's; histories of gynaecology, such as McKay's; and histories of anatomy, such as Singer's and V. Toply's. Histories of medicine as a whole are numerous and helpful: I have found those of Garrison and NeuburgerPagel most useful. Those which deal with special periods are also of assistance, such as Schrutz and Browne on Arabian, Bloch on Byzantine, and Harnack on Patristic medicine. Histories of chemistry provide no help, for ancient chemistry was so oriented towards "practical" results, such as the lapis philosophorum and elixir vitae, that the egg was only considered as a raw material for various preparations. The investigation of its change of properties during the development of the embryo did not occur to the alchemists. Detailed studies of particular subjects, such as those contained in Singer's two excellent volumes The History and Method of Science, may also be of some assistance. Again, there are books which give a wonderful orientation and an articulate survey of vast tracts : of these Clifford Allbutt's Greek Medicine in Rome, with its mass of references, is among the most valuable. And Miall's Early Naturalists must not be omitted, for, apart from the peculiar charm of style which marks it, it contains some singularly helpful bibliographical data. But the study of the original sources, so far as that is possible, is a duty which cannot be avoided, and in what follows I have been careful to copy down no statement from a previous review when it was possible to read the actual words of the writer himself.
This practice of going to the originals is made peculiarly necessary in a case such as the present one, when the history of a subject is to be regarded from an entirely new angle. My intention is to give here the sketch of a history of embryology consistently from the physico-chemical angle, and to show, at one and the same time, how our knowledge of the development of the embryo has come into being, and how throughout the process what we now call the physicochemical foundations of embryonic growth have from time to time received attention, even though it was largely speculative. Since few have previously examined the history of the subject, and none from this angle, I have in many cases come upon interesting facts which have remained unknown owing to the very attitude of mind previously adopted.
Finally, I would defend the arrangement of my Sections only on the ground that it is suitable in the present state of historical knowledge. I say little about embryology in ancient China and ancient India, because on the basis of what we know there is little to say, not because it was intrinsically less interesting than the embryology of Mediterranean antiquity and the later West, though this may turn out to be the case. I do not propose a framework for historical facts in what follows ; I only attempt to bring them together, and to reveal some of the relationships between them. If the traditional framework turns out to be badly constructed — and there are many signs that it may — the facts can be rearranged.
The history of single forms of scientific knowledge is in a way happier because containing more of continuity than that of civilisation as a whole. The assiduity with which men of different periods in the rise and decHne of a culture pursue the different forms of human experience may, as Spengler has shown, vary much, but those forms remain fundamentally the same, even if their manifestations are profoundly changed. That science, at any rate, does maintain some sort of continuity whatever gaps there may be between the phases of its progress, is a belief agreeable with all the available facts, and one which no criticism will easily shake.
Section 1 Embryology in Antiquity
1-1. Non-Hellenic Antiquity
Since biological science as a whole was little cultivated in ancient Egypt and the ancient civilisations of Babylonia, Assyria and India, the study of embryology, we may assume, was equally little pursued. Doubtless the undeveloped embryo, whether in egg or uterus, carried with it, for these persons of remote antiquity, some flavour of the obscene in the literal sense of the word. But embryology stands in a peculiar relation to the history of humanity, in that even at the most remote times children were being born, and, though the practitioners of ancient folk-medicine might confine their ideas for the most part to simple obstetrics, they yet could hardly avoid some slight speculation on the growth and formation of the embryo. Fig. I illustrates this level of culture. It is a painted and carved door from a house in Dutch New Guinea, taken from de Clercq's book; the original was of yellowish brown wood. The male embryo is clearly shown, but the artist evidently had a hazy conception of the umbilical cord. The line passing from the uterus to the head may or may not be merely ornamental. The movement of the foetus in utero played and still plays a large part in the folklore of primitive peoples, as may be read in the exhaustive treatise of Ploss & Bartels. For information concerning god-embryos in primitive religion see Briffault.
Fig, I . Painted and carved door from New Guinea (de Clercq).
Ancient Indian embryology achieved a relatively high level. Structures such as the amniotic membrane are referred to in the Bhagavad-Gitd. Susriita believed that the embryo was formed of a mixture of semen and blood, both of which originated from chyle. In the third month commences the differentiation into the various parts of the body, legs, arms and head, in the fourth follows the distinct development of the thorax, abdomen and heart, in the sixth are developed hair, nails, bones, sinews and veins, and in the seventh month the embryo is furnished with any other things that may be necessary for it. In the eighth there is a drawing of the vital force to and from mother and embryo (is this comparable with the Hippocratic eXKeiv? see Peck) which explains why the foetus is not yet viable. The hard parts of the body are derived from the father, the soft from the mother. Nourishment is carried on through vessels which lead chyle from mother to foetus. (For further details see Vullers.) Ancient Chinese embryology was very similar, if we may judge from Hureau de Villeneuve; Maxwell & Liu and von Martuis.
Egyptian medicine did not venture on embryological speculation, or so it would seem from the writings which have come down to us — the Ebers medical papyrus does not once mention the embryo (Brugsch) . But there are points of interest as regards Egypt in this connection. The Egyptians were responsible for one of the greatest helps in systematic embryological study, namely, the discovery of the artificial incubation of the eggs of birds. The success of this process was to have so obvious an effect on embryology and the abortive attempts to bring it to completion were so frequent in the West right up to the nineteenth century a.d. that it is remarkable to find artificial incubation practised "probably", in Cadman's words, "as far back as the dawn of the Old Kingdom, about 3000 B.C." It is doubtful whether the very remote date could be supported by Egyptological evidence, for, according to Hall and Lowe, hens were not introduced into Egypt from Mesopotamia or India until the time of the eighteenth dynasty {ca. 1400 b.g.) when there was much intercourse with the East (cf Queen Tiy and the Tell-el-Amarna correspondence) : before then the Egyptians had only goose or duck's eggs. Artificial incubation is certainly as old as Diodorus Siculus and Pliny, for both of them refer to the practice, the latter in connection with a curious piece of ancient sympathetic magic. " Livia Augusta, theEmpresse," says Pliny, "wife sometime of Nero, when she was conceived by him and went with that child (who afterwards proved to be Tiberius Caesar) being very desirous (like a yong fine lady as she was) to have a jolly boy, practised this girlish experiment to foreknow what she should have in the end; she tooke an egge, and ever carried it about her in her warme bosome; and if at any time she had occasion to lay it away, she would convey it closely out of her own warme lap into her nurses for feare it should chill. And verily this presage proved true, the egge became a cocke chicken, and she was delivered of a sonne. And hereof it may well be came the device of late, to lay egges in some warme place and to make a soft fire underneath of small straw or light chaffe to give a kinde of moderate heate ; but evermore the egges must be turned with a mans or womans hand, both night and day, and so at the set time they looked for chickens and had them" (Philemon Holland's translation).
Pliny also says, "Over and besides there be some egs that will come to be birds without sitting of the henne, even by the worke of Nature onely, as a man may see the experience in the dunghills of Egypt. There goeth a prettyjeast of a notable drunkard of Syracusa, whose manner was when hee went into the Taverne to drinke to lay certaine egges in the earth, and cover them with moulde, and he would not rise nor give over bibbing untill they were hatched. To conclude, a man or a woman may hatch egges with the very heate onely of their body". This story occurs also in Aristotle.
The Emperor Hadrian — curiositatum omnium explorator as Tertullian calls him — writing in a.d. 130 to his brother-in-law, L. Julius Servianus, from Egypt, says, "I wish them no worse than that they should feed on their own chickens, and how foully they hatch them, I am ashamed to tell you". In the Description de VEgypte, written by the members of the scientific staff of Napoleon's Egyptian expedition, and published at Paris in 1809, Roziere and Rouyer wrote on the artificial incubation of the Egyptians. They conjecture very probably that the Emperor was shocked owing to a misunderstanding shared by Aristotle, PUny, de Pauw and Reaumur, namely, that the "gelleh" or dung was used to heat the eggs by its fermentation, and not, as is and was actually the case, by being slowly burnt in the incubation ovens. Bay gave an account of the ovens in modern times, but the best one is that of Lane. "The Egyptians", said Lane in 1836, "have long been famous for hatching fowls' eggs by artificial heat. This practice, though obscurely described by ancient authors, appears to have become common in ancient Egypt from an early time. In Upper Egypt there are over fifty establishments, and in Lower Egypt more than a hundred. The furnace is constructed of sun-dried bricks and consists of two parallel rows of small ovens and cells for fire divided by a narrow vaulted passage, each oven being about 9 or 10 feet long, 8 feet wide and 5 or 6 feet high, and having above it a vaulted fire-cell of the same size but rather less in height. The eggs are placed upon mats or straw, one tier above another usually to the number of three tiers and the burning fuel is placed upon the floors of the fire-cells above. The entrance of the furnace is well closed. Each furnace consists of from twelve to 24 ovens and receives about 150,000 eggs during the annual period of its continuing open, one quarter or one third of which generally fail. The peasants supply the eggs and the attendants examine them and afterwards generally give one chicken for every two eggs that they have received. The general heat maintained during the process is from 100 to 103 of Fahrenheit's thermometer. The manager, having been accustomed to the art from his youth, knows from long experience the exact temperature that is required for the success of the operation without having any instrument like our thermometer to guide him. The eggs hatch after exactly the same period as in the case of natural incubation. I have not found that the fowls produced in this manner are inferior in point of flavour or in other respects to those produced from the egg in the ordinary way." The accompanying picture (Plate I a), taken from Cadman, shows the interior of a modern peasant's incubator. There is reason to beheve that its construction and operation vary very little, if at all, from that of the ovens used in dynastic Egypt.
PLATE 1
(A) EGYPTIAN PEASANT INCUBATOR (from Cadman)
(B) CHINESE PEASANT INCUBATOR (from King)
When Bay visited the native incubators in 191 2 he took with him a flask of lime water and a thermometer. The former showed a large precipitation of calcium carbonate and the latter stood at 40° C. He was led to speculate on the value of a high CO2 tension in the atmosphere, and concluded that it must have a beneficial effect, since the loss in the native incubator was not more than 4 per cent., while that in the oil-heated agricultural incubators of his time was as much as 40 per cent. Cadman, writing in 1921, suggests that the well-known non-sitting instinct of Egyptian poultry is an effect of the ancient practice of artificial incubation. But enough has been said of the Egyptian "Ma'mal al katakeet", or chicken factory. In spite of the remarkable opportunity thus afforded for acquiring facts in experimental embryology, no use was apparently ever made of it, though there seems to be a certain amount of traditional information current among the peasant operators, as, for example, that the "ruh" or life enters into the egg at the eleventh day. It w^ould be interesting to investigate this aspect of the subject further.
In ancient China also it would appear that artificial incubation was successfully carried on in remote antiquity, if we may judge by the account given by King. Native incubation in China is carried on in wicker baskets, heated with charcoal pans (Plate Ib). The attendants sleep in the incubator itself, and use the same thermometer as the Egyptians, namely, their eyelids, to which they apply the blunt end of the egg. The Egyptian success was known generally in the West in later times though it could not be imitated. ' ' The Aegyptians ' ' , said Sir Thomas Browne, "observed a better way to hatch their Eggs in Ovens, than the Babylonians to roast them at the bottom of a sling, by swinging them round about, till heat from motion had concocted them; for that confuseth all parts without any such effect." Browne's slightly rueful tone suggests that he tried it himself. It is interesting that this quaint experiment was the cause of a controversy between Sarsi, who asserted on the authority of Suidas that it was possible, and GaHleo, who thought the idea ridiculous. Modern work on the instability of albumen solutions, such as that of Harris, lends some colour to the legend. (See p. 275.)
Ancient Egypt supplies the starting-point for another and profounder train of thought which recurs constantly throughout the history of embryology, and to which I shall have to refer again more than once. This was concerned with the problem of deciding at what point the immortal constituent universally regarded as existing in living beings took up its residence in the embryo. Some fragments of ancient Indian philosophy assure us that the Vedic writers occupied themselves with this question, and according to Crawley the Avesta theorises upon it. But as early as 1400 B.C., i.e. during the eighteenth dynasty in Egypt, something was said regarding this, for we have extant at the present day a very beautiful hymn to the sun-god, Aton, written by no less a person than Akhnaton (Nefer-kheperu-Ra Ua-en-Ra, Amen-hetep Neter heq Uast), generally known as Amenophis IV or the "heretic" king, who abandoned the traditional worship of the Theban god Amen-Ra and established an Aton-cult, as has been described by Baikie and others. One of his hymns, which bears considerable resemblance to the one hundred and fourth psalm, runs as follows (in Breasted's translation) :
{the sun- god is addressed)
Creator of the germ in woman,
Maker of seed in man,
Giving life to the son in the body of his mother,
Soothing him that he may not weep,
Nurse (even) in the womb.
Giver of breath to animate every one that he maketh
When he cometh forth from the womb on the day of his birth.
Thou openest his mouth in speech. Thou suppliest his necessity.
When the fledgling in the egg chirps in the shell Thou givest him breath therein to preserve him alive. When thou hast brought him together To the point of bursting out of the egg, He cometh forth from the egg To chirp with all his might.
He goeth about upon his two feet When he hath come forth therefrom.
The important point here is that life = soul. At this early period there is no trace of the notions which appear later, such as the idea that embryos are not aUve until the time of birth or hatching, or the idea that the soul is breathed into the embryo at some particular point in development. But in later times these considerations carried great weight, and with the rise of theology a definite stand had to be taken about them, for otherwise no ethical status could be assigned to abortion. Speculation on these matters has continued without cessation since the time of Akhnaton, reaching a climax perhaps in Christian times with Cangiamilla's Embryologia Sacra, and living on embedded in Roman Catholic theology up to our own era. In the last century the subject seems to have had a special fascination for Ernst Haeckel, who frequently mentioned it. But the future holds no place for the discussion of such themes, and what has been called "theological embryology" is already dead, though we may perhaps descry its successor, psychological embryology, in such researches as those of Teuscher, Cesana, y Gonzalez, Swenson and Coghill.
Fig- 2. Eros hatching
Ancient Greek thought shows many evidences of appreciation of the mystery of embryonic growth, as for example in the Orphic cosmogonies, which had their origin about the seventh or eighth century b.g. In these rehgious and legendary descriptions of the world, which have been exhaustively discussed by A. B. Cook and F. Lukas, the cosmic egg plays a large part, and has been shown to occur also in the ancient cosmogonies ot Lgypt, India, Persia and from the cosmic egg. Phoenicia. A familiar reference to this cosmic (A Hellenistic gem deegg, out of which all things were produced at ^^^^ ^ y . . oo .j the beginning of the world, is in Aristophanes' comedy. The Birds, where the owl, as leader of the Chorus, says in the Parabasis (J. T. Sheppard's translation) :
Chaos was first, and Night, and the darkness of Emptiness, gloom
tartarean, vast ; Earth was not, nor Heaven, nor Air, but only the bosom of Darkness ;
and there with a stirring at last Of wings, though the wings were of darkness too, black Night was inspired
a wind-egg to lay. And from that, with the turn of the seasons, there sprang to the light
the Desired, Love, and his wings were of gold, and his spirit as swift as the wind when
it blows every way. Love moved in the Emptiness vast, Love mingled with Chaos, in spite of
the darkness of Night, Engendering us, and he brought us at last to the light.
And perhaps another reference to the place of the egg in ancient cosmogony occurs in The Arabian Nights, where Aladdin's request for a roc's egg is treated as a blasphemy by the genie. Still more fantastic is the speculation of C. H. Rice (in Psyche, 1929!) that the world is an egg; living matter being the embryo and inorganic matter the yolk. But none of the facts which have so far been mentioned bears more than obliquely upon the main centre of interest, the study of embryology. For its direct ancestry, Greece, as might be expected, is responsible.
1-2. Hellenic Antiquity: the Pre-Socratics
The pre-Socratic philosophers nearly all seem to have had opinions upon embryological phenomena, many of which are worth referring to. These investigators of nature who Hved in Greece from the eighth century onwards are only known to us through the writings of others, or in some cases in the form of fragments, for all their complete books have perished. Diels' collection of the Fragmente der Vorsokratiker is the most convenient source for what is left, but the assembling of their opinions has not been left to modern times, for a collection of them occurs in the writings of Plutarch of Chaeronea^ (3rd century a.d.). It is necessary to make use of some caution in describing their views, for Aristotle, as an instance, frequently gives the most unfair versions of the views of his predecessors. The account which follows is based upon Plutarch, in Philemon Holland's translation, and Diels. Empedocles of Akragas, who lived about 444 B.C., believed that "the embryo derives its composition out of vessels that are four in number, two veins and two arteries, through which blood is brought to the embryo". He also held that the sinews are formed from a mixture of equal parts of earth and air, that the nails are water congealed, and that the bones are formed from a mixture of equal parts of water and earth. Sweat and tears, on the other hand, are made up of four parts of fire to one of water. Empedocles also had opinions about the origin of monsters and twins, and asserted that the influence of the maternal imagination upon the embryo was great so that its formation could be guided and interfered with. "Empedocles", says Plutarch, "saith that men begin to take forme after the thirtie-first day and are finished and knit in their parts within 50 dales wanting one. Asclepiades saith that the members of males because they are more hot are joynted and receive shape in the space of 26 dales, and many of them sooner, but are finished and complet in all limbes within 50 dales but females require two moneths ere they be fashioned, and fower before they come to their perfection, for that they want naturall heat. As for the parts of unreasonable creatures they come to their accomplishment sooner or later, according to the temperature of their elements." Empedocles did not consider that an embryo was fully alive. "Empedocles ", says Plutarch, "denieth it to be a creature animall, howbeit that it hath life and breath within the bellie, mary the first time that it hath respiration is at the birth, namely, when the superfluous humiditie which is in such unborne fruits is retired and gone, so that the aire from without entreth into the void vessels lying open."
- It is now certain that this collection is not by Plutarch himself but by an earlier compiler, Aetius (see Burnet).
Anaxagoras of Clazomenae (500-428 B.C.) may have said that the milk of mammals corresponded to the white of the fowl's egg, but that observation is also attributed to Alcmaeon of Croton. It is more certain that he spoke of a fire inside the embryo which set the parts in order as it developed, and that the head was the part to be formed first in development. This thesis was supported by Alcmaeon, and by Hippon of Samos, a Pythagorean, in the fifth century B.C., but Diogenes of Apollonia maintained about the same time that a mass of flesh was formed first, and afterwards the bones and nerves were differentiated. Plutarch remarks about this: "Alcmaeon affirmeth that the head is first made as being the seat of reason. Physicians will have the heart to be the first, wherein the veines and arteries are. Some thinke the great toe is framed first, others the navill".
The other contributions of Diogenes to this primitive embryology, were the view that the placenta is the organ of foetal nutrition, and the view that the male embryo was formed in four months but the female embryo not till five months had elapsed — a notion also found in Asclepiades and Empedocles, as we have seen. He also associated heat with the generation of little animals out of slime, and compared this with the heat of the uterus. He agreed with Empedocles that the embryo was not alive. "Diogenes saith that infants are bred within the matrice inanimate, howbeit in heat, whereupon it commeth that naturall heat, so soon as ever the infant is turned out of the mother's wombe, is drawen into the lungs." But the principal pre-Socratic embryologist was, as Zeller points out, Alcmaeon of Croton, who lived in the sixth century B.C., a disciple of Pythagoras, though apparently an independent one. He is said to have been the first man to make dissections. The fragments of Alcmaeon (who is not to be confused with Alcman, the Lacedaemonian poet) have been collected together by Wachtler; the most important are xviii and xix. Athenaeus in the Deipnosophists says, in his usual chatty way, "Now with respect to eggs Anaxagoras in his book on natural philosophy says that what is called the milk of the bird is the white which is in the eggs". This may be a wrong ascription; it may refer to Alcmaeon, for Aristotle says in his book on the generation of animals, "Nature not only places the material of the creature in the egg but also the nourishment sufficient for its growth, for since the mother-bird cannot protect the young within herself she produces the nourishment in the egg along with it. Whereas the nourishment which is called milk is produced for the young of vivipara in another part, in the breasts, Nature does this for birds in the egg. The opposite, however, is the case to what people think and what is asserted by Alcmaeoii of Croton. For it is not the white that is the milk, but the yolk, for it is this that is the nourishment of the chick, whereas they think it is the white because of the similarity of the colour". Whether Aristotle was led to this conclusion because of his erroneous ideas about the part played in foetal nutrition by yolk and white respectively or whether he recognised a similarity between yolk and milk on account of their fatty nature, we cannot tell. In any case, his correction of Alcmaeon was in the right direction, and it is interesting to compare the amino-acid distribution in the casein of milk and the vitellin of yolk, as has been done by Abderhalden & Hunter (see p. 261).
Parmenides asserted a connection between male embryos and the right side of the body and between female embryos and the left side of the body — an idea which, considering its total lack of foundation, has had a very long lease of life in the world of thought. There was much controversy on the question of how foetal nutrition went on ; the atomists, Democritus (born about 460 b.c.) and Epicurus (born about 342 B.C.), said that the embryo ate and drank/>^r 0^. "Democritus and Epicurus hold", says Plutarch, "that this unperfect fruit of the wombe receiveth nourishment at the mouth; and thereupon it commeth that so soon as ever it is borne it seeketh and nuzzeleth with the mouth for the brest head or nipple of the pappe : for that within the matrice there be certain teats; yea, and mouths too, whereby they may be nourished. But Alcmaeon affirmeth that the infant within the mother's wombe, feedeth by the whole body throughout for that it sucketh to it and draweth in maner of a spunge, of all the food, that which is good for nourishment." It would appear also that Democritus believed the external form of the embryo to be developed before the internal organs were formed.
1-3. Hippocrates: the Beginning of Observation
But the foregoing fragments of speculation do not really amount to much. The first detailed and clear-cut body of embryological knowledge is associated with the name of Hippocrates, of whom nothing certain is known save that he was born probably in the forty-fifth Olympiad, about 460 b.c, that he lived on the island of Cos in the Aegean Sea, and that he acquired greater fame as a physician than any of his predecessors, if we may except the legendary names of Aesculapius, Machaon and Podalirius. It has not been believed for many centuries past that all the writings in the collection of Hippocratic books were actually set down by him, and much discussion has taken place about the authenticity of individual documents.
Most of the embryological information is contained in a section which in other respects (style, etc.) shows homogeneity. We are therefore rather interested in that unknown biological thinker who wrote the books in this class, for he could with considerable justice be referred to as the first embryologist. Littre discusses his identity, but there is no good evidence for any of the theories about it, though perhaps the most likely one is that he was Polybus, the son-in-law of Hippocrates. That the writings on generation are only slightly later than the time of Hippocrates is more or less clear from the fact that Bacchius knew of them, and actually mentions them.
For the most part the embryological knowledge of Hippocrates is concerned with obstetrical and gynaecological problems. Thus in the Aphorisms, d(f)opicr/iioi, the books on epidemics, eirchrifxiai, the treatise on the nature of women, irepl rywaLKelr)'? (f)V(rio'?, the discussions of premature birth, Trepl eirraixrjvov, the books on the diseases of women, irepl 'yvvaixeiaiv, and the pamphlet on superfoetation, there are many facts recorded about the embryo, but all with obstetrical reference. There are some curious notions to be found there, such as the association of right and left breasts with twin embryos and a prognostic dependent on this.
But the three books which are most important in the history of embryology are the treatise on Regimen, irepl StaLTr}<;, the work on generation, irepl jovr]<;, and the book about the nature of the infant, Trepl ^vaio<; TraiZiov. The two latter really form one continuous discussion, and it is not at all clear how they came to be split up into separate books. In the Regimen the writer expounds his fundamental physiological ideas, involving the two main constituents of all natural bodies, fire and water. Each of these is made up of three primary natures, only separable in thought and never found isolated, heat, dryness and moisture, and each of them has the power of attracting, eXKeiv, their like, an important feature of the system. Life consists in moisture being dried up by fire and fire being wetted by moisture alternately, rpo^-i'i, the nourishment (moisture) coming into the body, is consumed by the fire so that fresh rpocfir] is in its turn required.
It is important to note that the Hippocratic school was far more akin in its general attitude to living things to modern physiology than the Aristotelian and Galenic physiology. For no considerations of final causes complicate the causal explanations of the Hippocratic school, and the author of the irepl SmtV?/? indeed devotes seven chapters to a detailed comparison of the processes of the body {a) with the processes of the inorganic world both celestial and terrestrial, and (b) with the processes used by men in the arts and crafts, such as iron-workers, cobblers, carpenters and confectioners. These discussions present distinct mechanistic features.
He then in Section 9 sets forth his theory of the formation of the embryo. "Whatever may be the sex", he says, "which chance gives to the embryo, it is set in motion, being humid, by fire, and thus it extracts its nourishment from the food and breath introduced into the mother. First of all this attraction is the same throughout because the body is porous but by the motion and the fire it dries up and solidifies — vtto Be r?)? Kivijcno^; Koi tov irvpoii ^rfpaiveTai koI arepeovraL — as it solidifies, a dense outer crust is formed, and then the fire inside cannot any more draw in sufficient nourishment and does not expel the air because of the density of the surrounding surface. It therefore consumes the interior humidity. In this way parts naturally solid being up to a point hard and dry are not consumed to feed the fire but fortify and condense themselves the more the humidity disappears — these are called bones and nerves. The fire burns up the mixed humidity and forwards development towards the natural disposition of the body in this manner ; through the solid and dry parts it cannot make permanent channels but it can do so through the soft wet parts, for these are all nourishment to it. There is also in these parts a certain dryness which the fire does not consume, and they become compacted one to another. Therefore the most interior fire, being closed round on all sides, becomes the most abundant and makes the most canals for itself (for that was the wettest part) and this is called the belly. Issuing out from thence, and finding no nourishment outside, it makes the air pipes and those for conducting and distributing food. As for the enclosed fire, it makes three circulations in the body and what were the most humid parts become the venae cavae. In the intermediate part the remainder of the water contracts and hardens forming the flesh." In this account of the formation of the embryo, which seems at first sight a Httle fantastic, there are several interesting things to be remarked. Firstly, there is to be noted throughout it a remarkable attempt at causal explanations and not simply morphological description. The Hippocratic writer is out to explain the development of the embryo from the very beginning on machine-like principles, no doubt unduly simplified, but related directly to the observed properties of fire and water. In this way he is the spiritual ancestor of Gassendi and Descartes. The second point of interest is that he speaks of the embryo drying up during its development, a piece of observation which anyone could make by comparing a fourth-day chick with a fourteenth-day one, and which we express to-day in graphical form (see Fig. 220). Thirdly, the ascription of the main driving force in development to fire has doubtless no direct relation to John Mayow's discovery, two thousand years later, that there is a similarity between a burning candle and a living mouse each in its bell-jar, and may mean as much or as little as Sir Thomas Browne's remark, "Life is a pure flame, and we live by an invisible sun within us". Yet the essential chemical aspect of living matter is oxidation, and the development of the embryo no less than the life of the adult is subject to this rule, so that what may have been a mere guess on the part of the Hippocratic writer, may also have been a flash of insight due to the simple observation which, after all, it was always possible to make, namely, that both fires and li\dng things could be easily stifled.
Preformationism is perhaps foreshadowed in Section 26 of the same treatise. "Everything in the embryo is formed simultaneously. All the limbs separate themselves at the same time and so grow, none comes before or after other, but those which are naturally bigger appear before the smaller, without being formed earlier. Not all embryos form themselves in an equal time but some earlier and some later according to whether they meet with fire and food, some have everything visible in 40 days, others in 2 months, 3, or 4. They also become visible at variable times and show themselves to the light having the blend (of fire and water) which they always will have."
The work on Generation is equally interesting. The earlier sections deal with the differences between the male and the female seed, and the latter is identified with the vaginal secretion. Purely embryological discussion begins at Section 14, where it is stated that the embryo is nourished by maternal blood, which flows to the foetus and there coagulates, forming the embryonic flesh. The proof alleged for this is that during pregnancy the flow of menstrual blood ceases; therefore it must be used up on the way out. In Section 15 the umbiHcal cord is recognised as the means by which foetal respiration is carried on. Section 1 7 contains a fine description of development with a very interesting analogy. "The flesh", it is said, "brought together by the spirit, TO TTvevfia, grows and divides itself into members, hke going to like, dense to dense, flabby to flabby, humid to humid. The bones harden, coagulated by the heat." Then a demonstration experiment follows : "Attach a tube to an earthen vessel, introduce through it some earth, sand, and lead chips, then pour in some water and blow through the tube. First of all, everything will be mixed up, but after a certain time the lead will go to the lead, the sand to the sand, and the earth to the earth, and if the water be allowed to dry up and the vessel be broken, it will be seen that this is so. In the same way seed and flesh articulate themselves. I shall say no more on this point". Here again was an attempt at causal explanation, rather than morphological description, in complete contrast to the later work of
Section 22 contains a suggestive comparison between seeds of plants and embryos of animals, but the identification of stalk with umbihcal cord leads to a certain confusion. Perhaps the most interesting passage of aU is to be found in Section 29. "Now I shall speak", says the unknown Hippocratic embryologist, "of the characters which I promised above to discuss and which show as clearly as human intelligence can to anyone who will examine these things that the seed is in a membrane, that the umbilicus occupies the middle of it, that it alternately draws the air through itself and then expels it, and that the members are attached to the umbilicus. In a word, all the constitution of the foetus as I have described it to you, you will find from one end to the other if you wiU use the following proof Take 20 eggs or more and give them to 2 or 3 hens to incubate, then each day from the second onwards tiU the time of hatching, take out an egg, break it, and examine it. You will find everything as I say in so far as a bird can resemble a man. He who has not made these observations before will be amazed to find an umbihcus in a bird's egg. But these things are so, and this is what I intended to say about them." We see here as clearly as possible the beginnings of systematic embryological knowledge, and from this point onwards, through Aristotle, Leonardo, Harvey and von Baer, to the current number of the Archivf. Entwicklungsmechanik, the line runs as straight as Watling Street.
In Section 30 there is an important passage in which the author discusses the phenomena of birth. "I say", he says, "that it is the lack of food which leads to birth, unless any violence has been done; the proof of which is this ; — the bird is formed thus from the yolk of the egg, the egg gets hot under the sitting hen and that which is inside is put into movement. Heated, that which is inside begins to have breath and draws by counter-attraction another cold breath coming from the outside air and traversing the egg, for the egg is soft enough to allow a sufficient quantity of respiration to penetrate to the contents. The bird grows inside the egg and articulates itself exactly like the child, as I have previously described. It comes from the yolk but it has its food from, and its growth in, the white. To convince oneself of this it is only necessary to observe it attentively. When there is no more food for the young one in the egg and it has nothing on which to live, it makes violent movements, searches for food, and breaks the membranes. The mother, perceiving that the embryo is vigorously moving, smashes the shell. This occurs after 20 days. It is evident that this is how things happen, for when the mother breaks the shell there is only an insignificant quantity of liquid in it. All has been consumed by the foetus. In just the same way, when the child has grown big and the mother cannot continue to provide him with enough nourishment, he becomes agitated, breaks through the membranes and incontinently passes out into the external world free from any bonds. In the same way among beasts and savage animals birth occurs at a time fixed for each species without overshooting it, for necessarily in each case there must be a point at which intra-uterine nourishment will become inadequate. Those which have least food for the foetus come quickest to birth and vice versa. That is all that I had to say upon this subject."
The theory underlying this passage evidently is that the main food of the fowl embryo is the white and that the yolk is there purely for constructional purposes. Had the author not been strongly attached to this erroneous view he could not have failed to notice the unabsorbed yolk-sac which still protrudes from the abdomen of the hatching chick, and if he had given this fact a little more prominence he could hardly have come to enunciate the general theory of birth which appears in the above passage. Moreover, had he been acquainted with the circulation of the maternal and foetal blood in viviparous animals, he could hardly have held that there was less food in a given amount of maternal blood at the end of development than at the beginning. At any rate, his attempted theory of birth was a worthy piece of scientific effort, and we cannot at the present moment be said to understand fully the principles governing incubation time (see p. 470).
The treatises on food and on flesh, trepl Tpo(f>rj<i and irepl aapKcovy are both late additions to the Hippocratic corpus, but contain points of embryological interest. Section 30 of the former contains some remarks on embryonic respiration, and Section 3 of the latter has a theory of formation of nerves, bones, etc. by difference of composition of glutinous substances, fats, water, etc. Section 6 supports the view that the embryo is nourished in utero by sucking blood from the placenta, and the proof given is that its intestine contains the meconium at birth. Moreover, it is argued, if this were not so, how could the embryo know how to suck after it is born?
1-4. Aristotle
After the Hippocratic writings nothing is of importance for our subject till Aristotle. It is true that in the Timaeus Plato deals with natural phenomena, eclectically adopting opinions from many previous writers and welding them into a not very harmonious or logical whole. But he has hardly any observations about the development of the embryo. The four elements, earth, fire, air, and water, are, according to him, all bodies and therefore have plane surfaces which are composed of triangles. Applying this semi-atomistic hypothesis to the growth of the young animal, he says, "The frame of the entire creature when young has the triangles of each kind new and may be compared to the keel of a vessel that is just ofT the stocks ;^ they are locked firmly together and yet the whole mass is soft and delicate, being freshly formed of marrow and nurtured on milk. Now when the triangles out of which meats and drinks are composed come in from without, and are comprehended in the body, being older and weaker than the triangles already there, the frame of the body gets the better of them and its newer triangles cut them up and so the animal grows great, being nourished by a multitude of similar particles." This is as near as Plato gets to embryological speculation. His description has a causal ring about it, which is in some contrast with the predominantly teleological tone of the rest of his writings ; for instance, only a few pages earlier he has been speaking of the hair as having been arranged by God as "a shade in summer and a shelter in winter". It is also true that Plato may have said more about the embryo than appears in the dialogues. Plutarch mentions various speculations about sterility, and adds, "Plato directly pronounceth that the foetus is a living creature, for that it moveth and is fed within the bellie of the mother".
But all this was only the slightest prelude to the work of Plato's pupil, Aristotle. Aristotle's main embryological book was that entitled Trepl ^mcov yeveaeco'i, On the Generation of Animals, but embryological data appear in irepl ^axop, The History of Animals, irepl ^wmv fjLopicov, On the Parts of Animals, Trepl dva7rvofj<i, On Respiration, and Trepl ^Mcov Ktvrjcr€(o<i, On the Motion of Animals. All these were written in the last three-quarters of the fourth century B.C.
With Aristotle, general or comparative biology came into its own. That almost inexhaustible profusion of living shapes which had not attracted the attention of the earlier Ionian and Italo-Sicilian philosophers, which had been passed over silently by Socrates and Plato, intent as ever upon ethical problems, but which had been for centuries the inspiration of the vase-painters and other craftsmen {(^coypdcjioL), was now for the first time exhaustively studied and reduced to some sort of order. The Hippocratic school with their "Coan classification of animals", which Burckhardt has discussed, had indeed made a beginning, but no more. It was Aristotle who was the first curator of the animal world, and this comparative outlook colours his embryology, giving it, on the whole, a morphological rather than a physiological character.
The question of Aristotle's practical achievements in embryology is interesting, and has been discussed by Ogle. There is no doubt that he diligently followed the advice of the author of the Hippocratic treatise on generation and opened fowl's eggs at different stages during their development, but he learnt much more than the unknown Hippocratic embryologist did from them. It is also clear that he dissected and examined all kinds of animal embryos, mammalian and cold-blooded. The uncertain point is whether he also dissected the human embryo. He refers in one place to an "aborted embryo", and as he was able to obtain easily all kinds of animal embryos without waiting for a case of abortion, it is likely that this was a human embryo. Ogle brings forward six or seven passages which all contain statements about human anatomy and physiology only to be explained on the assumption that he got his information from the foetus. So it is probable that his knowledge of biology was extended to man in this way, as would hardly have been the case if he had lived in later times, when the theologians of the Christian Church had come to very definite conclusions about the sanctity of foetal as well as adult life.
The Trept i^wcov ^eveaeoo<;^ the first great compendium of embryology ever written, is not a very well-arranged work. There are a multitude of repetitions, and the order is haphazard, so that long digressions from the main argument are common. The work is divided into five books, of which the second is much the most important in the history of embryology, though the first has also great interest, and the third, fourth, and fifth contain much embryological matter mixed up among points of generation and sexual physiology.
Book I begins with an introduction in which the relative significance of efficient and final causes is considered, and chapters i to 7 deal with the nature of maleness and femaleness, the nature and origin of semen, the manner of copulation in different animals and the forms of penis and testes found in them. Chapter 8 continues this, and describes the different forms of uterus in different animals, speaks of viviparity and oviparity, mentions the viviparous fishes (the selachians) and draws a distinction between perfect and imperfect eggs. Chapter 9 discusses the cetacea; 10, eggs in general; and 11 returns to the differences between uteri. In chapter 12 the question is raised why all uteri are internal, and why all testes are not, and in chapter 13 the relations between the urinary and the genital systems are discussed. Copulation now receives attention again, in 14 with regard to Crustacea, in 15 with regard to cephalopoda, and in 16 with regard to insecta. After this point the argument Hfts itself on to a more theoretical plane, and opens the question of pangenesis, into which it enters at length during the course of chapters 17 and 18, refuting eventually the widely-held view that the semen takes its origin from all the parts of the body so as to be able to reproduce in the offspring the characteristics of the parent.
The nature of semen receives a long discussion; it is decided at last that it is a true secretion, and not a homogeneous natural part (a tissue) nor a heterogeneous natural part (an organ) nor an unnatural part such as a growth, nor mere nutriment, nor yet a waste product. It is here that the theory is put forward that the semen supplies the "form" to the embryo and whatever the female produces supplies the matter fit for shaping. The obvious question has next to be answered, what is it that the female supplies? Aristotle concludes in chapters 19 and 20 that the female does not produce any semen, as earlier philosophers had held, but that the menstrual blood is the material from which the seminal fluid, in giving to it a form, will cause the complete embryo to be produced. This was not a new idea, but had already been suggested by the author of the Hippocratic ire pi yovi]^. What was quite new here, was the idea that the semen supplied or determined nothing but the form. Chapters 21 and 22 are rather confused ; they contain more arguments against pangenesis, and considerations upon the contrast between the active nature of the male and the passive nature of the female. Chapter 23, which closes the first book, compares animals to divided plants, for plants in Aristotle's view fertilise themselves.
Book II opens with a magnificent chapter on the embryological classification of animals, showing Aristotle, the systematist, at his best — his classification is reproduced in Chart I. But the chapter also includes a brilliant discussion of epigenesis or preformation, fresh development or simple unfolding of pre-existent structures, an antithesis which Aristotle was the first to perceive, and the subsequent history of which is almost synonymous with the history of embryology. The question in its acutest form was not settled until the eighteenth century, but since then it has become clear that there were elements of truth in the opinion which was the less true of the two. Chapter 2 is not so important, though it has some interesting chemical analogies; it compares semen to a foam, and suggests that it was this foam, like that of the sea, which gave birth to the goddess Aphrodite^. But chapter 3 returns to the high level of speculation and thought found in the opening part of the book, for it deals with the degree of aliveness which the embryo has during its passage through its developmental stages. Aristotle does not here anticipate the form of the recapitulation theory, but he certainly suggests the essence of it in perfectly clear terms. This chapter has also an interest for the history of theological embryology, for its description of the entry of the various souls into the embryo was afterwards made the basis for the legal rulings concerning abortion. This chapter also discusses embryogeny as a whole, as does the succeeding one. Chapter 5 is a digression into the problem of why fertilisation is necessary by the male, but it has also some curious speculations as to what extent the hen's egg is alive, if it is infertile. The main thread is resumed in chapters 6 and 7, two very fine ones, in which embryogeny and foetal nutrition are thoroughly dealt with, but dropped again in the last section, chapter 8, which is devoted to an explanation of sterility. This ends the second book.
- To the Greeks all natural foams possessed a generative virtue, and a Zeus Aphrios was worshipped at Pherae in Thrace.
The third book is chiefly concerned with the application of the general embryological principles described in the previous book to the comparative field, and the fourth book contains a collection of minor items which Aristotle has not been able to speak of before.
But if the work as a whole tails off in a rather unsatisfactory manner, its merits are such that this hardly matters. The extraordinary thing is that, building on nothing but the scraps of speculation that had been made by the Ionian philosophers, and the exiguous data of the Hippocratic school, Aristotle should have produced, apparently without effort, a text-book of embryology of essentially the same type as Graham Kerr's or Balfour's. It is even very possible that Aristotle was unacquainted with any of the Coan school, for, though he often mentions Democritus, Anaxagoras, Empedocles and even Polybus, yet he never once quotes Hippocrates, and this is especially odd, for Aristotle is known to have collected a large library. Probably Hippocrates was only known to Aristotle as an eminent medical man; if this is so, Aristotle's achievements are still more wonderful.
The depth of Aristotle's insight into the generation of animals has not been surpassed by any subsequent embryologist, and, considering the width of his other interests, cannot have been equalled. At the same time, his achievements must not be over-estimated. Charles Darwin's praise of him in his letter to Ogle (which is too well known to quote) is not without all reservations true. There is something to be said for Lewes as well as Piatt. Aristotle's conclusions were sometimes not warranted by the facts at his disposal, and some of his observations were quite incorrect. Moreover, he stood at the very entrance into an entirely unworked field of knowledge ; he had only to examine, as it were, every animal that he could find, and set down the results of his work, for nobody had ever done it before. It was like the great days of nineteenth-century physiology, when, as the saying was, "a chance cut with a scalpel might reveal something of the first importance".
As has already been said, Aristotle regarded the menstrual blood as the material out of which the embryo was made. "That, then, the female does not contribute semen to generation", says Aristotle, "but does contribute something, and that this is the matter of the catamenia, or that which is analogous to it in bloodless animals, is clear from what has been said, and also from a general and abstract survey of the question. For there must needs be that which generates and that from which it generates, even if these be one, still they must be distinct in form and their essence must be different; and in those animals that have these powers separate in two sexes the body and nature of the active and passive sex also differ. If, then, the male stands for the effective and active, and the female, considered as female, for the passive, it follows that what the female would contribute to the semen of the male would not be semen but material for the semen to work upon. This is just what we find to be the case, for the catamenia have in their nature an affinity to the primitive matter." Thus the male dynamic element {t6 appev iroLn^TtKov) gives a shape to the plastic female element {to OrjXv TradrjTiKov). Aristotle was right to the extent that the menstrual flow is associated with ovulation, but as he knew nothing of the mammalian ovum, and indeed, as is shown in his embryological classification, expressly denied that there was such a thing, his main menstruation theory is wrong. Yet it was not an illegitimate deduction from the facts before him.
These views of Aristotle's about the contribution of the female to the embryo are in striking contrast with certain conceptions of a century before which were probably generally held in Greece. There is a most interesting passage relating to them in the Eumenides of Aeschylus, when, during the trial scene, Apollo, defending Orestes from the charge of matricide, brings forward a physiological argument. "The mother of what is called her child", Apollo is made to say, "is no parent of it, but nurse only of the young Hfe that is sown in her (jpo(f)6<; 8e Kv^iaj
PLATE II
serves for nourishment; whiles the chick is unhatched and within the egge, the head is bigger than all the bodie besides; and the eies that be compact and thrust together be more than the verie head. As the chick within growes bigger, the white turneth into the middest, and is enclosed within the yolke. By the 20 day (if the eggs be stirred) ye shall heare the chick to peepe within the verie shell; from that time forward it beginneth to plume and gather feathers ; and in this manner it lies within the shell, the head resting on the right foot, and the same head under the right wing, and so the yolke by little and little decreaseth and faileth". But the best way to illustrate Pliny's embryology is to copy out some of his index, as follows :
The Table to the first Tome of Plinies Naturall Historie.
Egs diverse in colour 298
Egs of birds of 2 colours within the shell ibid.
Egs of fishes of i colour ibid.
Egs of birds, serpents, and fishes, how they differ ibid.
Egs best for an hen to sit upon 299
Egs hatched without a bird, onely by a kind heat ibid.
Egs how they be marred under an hen ibid,
wind-egs, called Hypenemia 300
how they be engendred 301
wind-egs, Zephyria ibid.
Egs drawne through a ring ibid.
Egs how they be best kept ibid.
The Table to the second Tome of Plinies Naturall Historie,
Egs of hens and their medicinable properties 351
yolke of hens egs, in what cases it is medicinable 352
Egs all yolke, and without white, be called Schista ibid,
skinne of an Hens egge-shell, good in Physicke ibid.
Hens Eggeshell reduced unto ashes, for what it serveth ibid,
the wonderfull nature of Hens Eggeshels ibid.
Hens Egges, all whole as they be, what they are good for 353
the commendations of Hens Egges, as a meat most medicinable ibid. Hens Egge, a proper nourishment for sicke folks, and may go
for meat and drinke both ibid.
Egge-shels, how they may be made tender and pliable ibid,
white of an Egge resisteth fire ibid,
of Geese Egges a discourse 354 the serpents egge, which the Latines call Anguinum, what it
is, and how engendred 355
This last item exhibits Pliny at his worst. It is worth quoting, apart from its intrinsic value, for it shows to what depths embryological knowledge descended within four hundred years after Aristotle collected his specimens on the shores of the lagoon of Pyrrha, and talked with the fishermen of Mitylene. "I will not overpasse one kind of eggs besides, which is in great name and request in France, and whereof the Greeke authors have not written a word ; and this is the serpents egg, which the Latins call Anguinum. For in Summer time yerely, you shall see an infinit number of snakes gather round together into an heape, entangled and enwrapped one within another so artificially, as I am not able to expresse the manner thereof; by the means therefore, of the froth or salivation which they yeeld from their mouths, and the humour that commeth from their bodies, there is engendred the egg aforesaid. The priests of France, called Druidae^, are of opinion, and so they deliver it, that these serpents when they have thus engendred this egg do cast it up on high into the aire by the force of their hissing, which being observed, there must be one ready to catch and receive it in the fall again (before it touch the ground) within the lappet of a coat of arms or souldiours cassocks. They affirme also that the party who carrieth this egg away, had need to be wel mounted upon a good horse and to ride away upon the spur, for that the foresaid serpents will pursue him still, and never give over until they meet with some great river betweene him and them, that may cut off and intercept their chace. They ad moreover and say that the only marke to know this egg whether it be right or no, is this, that it will swim aloft above the water even against the stream, yea though it were bound and enchased with a plate of gold." But one must not be too severe upon Pliny, for he and his translator, Philemon Holland, provide an entertainment unequalled anywhere else.
To some extent the same applies to Plutarch of Chaeronea, who lived about the same time. Plutarch's writings, inspired as they were throughout by the desire to commend the ancient religion of Greece to a degenerate age, represent no milestone or turning-point in the history of embryology, yet there is a passage in the Symposiaques, or Table-questions which bears upon it. The third question of book 2 is "Whether was before, the hen or egg?" "This long time", says Plutarch, "I absteined from eating egges, by reason of a certaine dream I had, and the companie conceived an opinion or suspition of me that there were entred into my head the fantasies and superstitions of Orpheus or Pythagoras, and that I abhorred to eat an egge for that I believed it to be the principle and fountaine of generation." He then makes the various characters in the dialogue speak to the motion, and one of them, Firmus, ends his speech thus, "And now for that which remaineth (quoth he and therewith he laughed) I will sing unto those that be skilfull and of understanding one holy and sacred sentence taken out of the deepe secrets of Orpheus, which not onely importeth this much, that the cgge was before the henne, but also attributeth and adjudgeth to it the right of eldership and priority of all things in the world, as for the rest, let them remaine unspoken of in silence (as Herodotus saith) for that they bee exceeding divine and mysticall, this onely will I speake by the way; that the world containing as it doth so many sorts and sundry kinds of living creatures, there is not in manner one, I dare well say, exempt from being engendred of an egge, for the egge bringeth forth birdes and foules that fiie, fishes an infinit number that swimme, land creatures, as lizards, such as live both on land and water as crocodiles, those that bee two-footed, as the bird, such as are footlesse, as the serpent, and last of all, those that have many feet, as the unwinged locust. Not without great reason therefore is it consecrated to the sacred ceremonies and mysteries of Bacchus as representing that nature which produceth and comprehendeth in itselfe all things". This emphatic passage looks at first sight as if it was a statement of the Harveian doctrine omne vivum ex ovo. But the fact that no mammals are mentioned makes this improbable. Firmus then sits down and Senecius opposes him with the well-worn argument that the perfect must precede the imperfect, laying stress also on the occurrence of spontaneous, i.e. eggless, generation, and on the fact that men could find no "row" in eels. Three hundred years later, Ambrosius Macrobius handled the question again (see Whittaker), and the progress in embryological knowledge could be strikingly shown by the difference in treatment. It would be an interesting study to make a detailed comparison of them.
- For further information about the serpent's eggs of the Druids, see Kendrick; they were probably fossil echinoderms.
1-6. Galen
Another fifty years brings us to Galen of Pergamos, second in greatness among ancient biologists, though in spite of his multitudinous writings he does not quite take this high rank in embiyology. That knowledge of the development of the foetus was at this time specially associated with Peripatetic tradition appears from a remark of Lucian of Samosata, Galen's contemporary. In the satire called, The Auction of the Philosophies, Hermes, the auctioneer, referring to the Peripatetic who is being sold, says, "He will tell you all about the shaping of the embryo in the womb". But Galen was now to weld together all the biological knowledge of antiquity into his voluminous works, and so transmit it to the Middle Ages.
Most of Galen's writing was done between a.d. 150 and 180. Out of the twenty volumes of Kiihn's edition of 1829, l^^s than one is concerned with embryology, a proportion considerably less than in the case of Aristotle. Galen's embryology is to be found in his Trepl (f)V(nKcov Svvdfiecov, On the Natural Faculties, which contains the theoretical part, and in his On the Formation of the Foetus, which contains the more anatomical part. There is also the probably spurious treatise et ^mov to Kara <yaa-Tp6<i, On the Question of whether the Embryo is an Animal.
It is important to realise at the outset that Galen was a vitalist and a teleologist of the extremest kind. He regarded the living being as owing all its characteristics to an indwelling Physis or natural entity with whose "faculties" or powers it was the province of physiology to deal. The living organism according to him has a kind of artistic creative power, a t6xvv> which acts on the things around it by means of the faculties, Swd/xei's, by the aid of which each part attracts to itself what is useful and good for it, rb oUelov, and repels what is not, to aXXorptov. These faculties, such as the "peptic faculty" in the stomach and the "sphygmic faculty" in the heart, are regarded by Galen as the causes of the specific functions or activity of the part in question. They are ultimate biological categories, for, although he admits the theoretical possibility of analysing them into simpler components, he never makes any attempt to do so, and evidently regards such an effort as doomed to failure, unlike Roux, whose "interim biological laws" are really conceived of as interim. "The effects of Nature", says Galen, "while the animal is still being formed in the womb are all the different parts of the body, and after it has been born an effect in which all parts share is the progress of each to its full size and thereafter the maintenance of itself as long as possible." Galen divides the effects of the faculties into three. Genesis, Growth, and Nutrition, and means by the first what we mean by embryogeny. "Genesis", he says, "is not a simple activity of Nature, but is compounded of alteration and of shaping. That is to say, in order that bone, nerve, veins, and all other tissues may come into existence, the underlying substance from which the animal springs must be altered; and in order that the substance so altered may acquire its appropriate shape and position, its cavities, outgrowths, and attachments, and so forth, it has to undergo a shaping or formative process. One would be justified in calling this substance which undergoes alteration the material of an animal, just as wood is the material of a ship and wax of an image." In this remarkable passage, Galen expresses modern views about chemical growth and chemical differentiation.
Galen then goes on to treat of embryogeny in more detail. "The seed having been cast into the womb or into the earth — for there is no difference — ", he says (see p. 65), "then after a certain definite period a great number of parts become constituted in the substance which is being generated; these differ as regards moisture, dryness, coldness and warmth, and in all the other qualities which naturally derive therefrom", such as hardness, softness, viscosity, friability, lightness, heaviness, density, rarity, smoothness, roughness, thickness, and thinness. "Now Nature constructs bone, cartilage, nerve, membrane, ligament, vein, and so forth at the first stage of the animal's genesis, employing at this task a faculty which is, in general terms, generative and alterative, and, in more detail, warming, chilHng, drying and moistening, or such as spring from the blending of these, for example, the bone-producing, nerve-producing, and cartilageproducing, faculties (since for the sake of clearness these terms must be used as well) .... Now the peculiar flesh of the liver is of a certain kind as well, also that of the spleen, that of the kidneys and that of the lungs, and that of the heart, so also the proper substance of the brain, stomach, oesophagus, intestines and uterus is a sensible element, of similar parts all through, simple and uncompounded. . . . Thus the special alterative faculties in each animal are of the same number as the elementary parts, and further, the activities must necessarily correspond each to one of the special parts, just as each part has its special use. . . . As for the actual substance of the coats of the stomach, intestine, and uterus, each of these has been rendered what it is by a special alterative faculty of nature; while the bringing of these together, the combination therewith of the structures that are inserted into them, etc. have all been determined by a faculty which we call the shaping or formative faculty; this faculty we also state to be artistic — nay, the best and highest art — doing everything for some purpose, so that there is nothing ineffective or superfluous, or capable of being better disposed."
Thus the alterative faculty takes the primitive unformed raw material and changes it into the different forms represented by the different tissues, while the formative faculty, acting teleologically from within, organises these building-stones, as it were, into the various temples which make up the Acropolis of the completed animal. Galen next goes on to speak of the faculty of growth. "Let us first mention", he says, "that this too is present in the foetus in utero as is also the nutritive faculty, but that at that stage these two faculties are, as it were, handmaids to those already mentioned, and do not possess in themselves supreme authority."
Later on, until full stature is reached, growth is predominant, and finally nutrition assumes the hegemony.
So much for Galen's embryological theory. But before leaving the treatise On the Natural Faculties, it may be noted that he ascribes a retentive faculty to the uterus as well as to the stomach, and explains birth as being due to a cessation of action on the part of the retentive faculty, "when the object of the uterus has been fulfilled", and a coming into action of a hitherto quiescent propulsive faculty. This wholesale allotting of faculties can obviously be made to explain anything, and is eminently suited to a teleological account such as Galen's. It was not inconvenient as a framework within which all the biological knowledge of antiquity could be crystallised, but it was utterly pernicious to experimental science. Fifteen hundred years later it received what would have been the death-blow to any less virile theory, at the hands of Moliere in his immortal Malade Imaginaire :
Bachelirius. Mihi a docto doctore
Demandatur causam et rationem quare Opium facit dormire A quoi respondeo Quia est in eo Virtus dormitiva Cujus est nature Sensus assoupire. Chorus. Bene, bene, bene, bene respondere. Dignus, dignus est entrare In nostro docto corpore. Bene, bene, respondere.
But to return to Galen. The book on the formation of the embryo opens with a historical account of the views of the Hippocratic writers with whom Galen was largely in agreement. It goes on to describe the anatomy of allantois, amnios, placenta, and membranes with considerable accuracy. The embryonic life consists, it says, of four stages: (i) an unformed seminal stage, (2) a stage in which the tria principia (a concept here met with for the first time) are engendered, the heart, liver and brain, (3) a stage when all the other parts are mapped out and (4) a stage when all the other parts have become clearly visible. Parallel with this development, the embryo also rises from possessing the life of a plant to that of an animal, and the umbilicus is made the root in the analogy with a plant. The embryo is formed, firstly, from menstrual blood, and secondly, from blood brought by the umbilical cord, and the way in which it turns into the embryo is made clearer as follows: "If you cut open the vein of an animal and let the blood flow out into moderately hot water; the formation of a coagulum very like the substance of the liver will be seen to take place". And in effect this viscus, according to Galen, is formed before the heart.
Galen also taught that the embryo excreted its urine into the allantois, and was acquainted with foetal atrophy. He gave a fairly correct account of the junction of the umbilical veins with the branches of the portal vein, and the umbilical with the iliac arteries, of the foramen ovale, the ductus Arantii and the ductus Botalli. He maintained that the embryo respired through the umbilical cord, and said that the blood passed in the embryo from the heart to the lungs and not vice versa. The belief that male foetuses were formed quicker than female ones he still entertained, and explained as being due to the superior heat and dryness of the male germ. He also associated the male conception with the right side and the female with the left and asserted that the intra-uterine movements are sooner felt in the case of the male than in the case of the female. Dry foods eaten by the mother, he thought, would lead to a more rapid development of the foetus than other kinds.
In this account of the Galenic embryology I have drawn not only upon the book on the formation of the foetus, but also upon his v7r6fMV7]/jba, Commentary on Hippocrates, his Trepl alricov av/jLTTTco/naTcov, On the Causes of Symptoms, and his book Trepl %peta? tmv fjuoplcor, On the Use of Parts. It is this latter work that had the greatest influence on the ages which followed Galen's Hfe. In the course of seventeen books, he tries to demonstrate the value and teleological significance of every structure and function in the human and animal body, and to show that, being perfectly adapted to its end, it could not possibly be other in shape or nature than what it is. At the conclusion of this massive work with all its extraordinary ingenuity and labour, he says, "Such then and so great being the value of the argument now completed, this section makes it all plain and clear like a good epode — I say an epode, but not in the sense of one who uses enchantments (eVwSat?) but as in the melic poets whom some call lyric, there is as well as strophe and antistrophe, an epode, which, so it is said, they used to sing standing before the altar as a hymn to the Gods. To this then I compare this final section and therefore I have called it by that name". This is one of the half-dozen most striking paragraphs in the history of biology ; worthy to rank with the remarks of Hippocrates on the " Sacred Disease". Galen, as he wrote the words, must have thought of the altar of Dionysus in the Athenian or Pergamene theatre, made of marble and hung about with a garland, but they were equally applicable to the altar of a basilica of the Christian Church with the bishop and his priests celebrating the liturgy at it. What could be more charged with significance than this? At the end of the antique epoch the biology of all the schools, Croton, Akragas, Cos, Cnidus, Athens, Alexandria, Rome, is welded together and as it were deposited at the entrance into the sanctuary of Christendom. It was the turning-point, in Spengler's terminology, between ApoUinian civilisation and Faustian culture. Galen's words are the more extraordinary, for he himself can hardly have foreseen that the long line of experimentalists which had arisen in the sixth century B.C. would come to an end with him. But so it was to be, and thenceforward experimental research and biological speculation were alike to cease, except for a few stray mutations, born out of due time, until in 1453 the city of Byzantium should burst like .a ripe pod and, distributing her scholars all over the West, as if by a fertilising process, bring all the fruits of the Renaissance into being.
Section 2 Embryology from Galen to the Renaissance
2-1. Patristic, Talmudic, and Arabian Writers
We are now at the beginning of the second century a.d. The next thousand years can be passed over in as short a time as it has taken to describe the embryology of Galen alone. The Patristic writers, who on the whole were careful to base their psychology on the physiology of the ancients, had little to say about the developing embryo. Most of their interest in it was, as would naturally be expected, theological; Tertullian, for instance, held that the soul was present fully in the embryo throughout its intra-uterine life, thus denying that kind of psychological recapitulation which had been suggested by Aristotle. "Reply," he says in his De Anima, "O ye Mothers, and say whether you do not feel the movements of the child within you. How then can it have no soul? " These views were not held by other Fathers, of whom St Augustine of Hippo {De Immortalitate et de quantitate ahimae) may serve as a representative, for he thought that the embryo was "besouled" in the second month and "besexed" in the fourth. These various opinions were duly reflected in the law, and abortion, which had even been recommended theoretically by Plato and defended practically by Lysias in the fourth or fifth century B.C., now became equivalent to homicide and punishable by death. This fact leads Singer to the view that the Hippocratic oath is late, perhaps early Christian. The late Roman law, which, according to Spangenberg, regarded the foetus as not Homo'", not even Infans'\ but only a Spes animantis'\ was gradually replaced by a stern condemnation of all pre-natal infanticide. "And we pay no attention", said the Bishops of the Quinisext Council, held at Byzantium in 692, "to the subtle distinction as to whether the foetus is formed or unformed." Other authorities, following St Augustine, took a more liberal view, and the canon law as finally crystallised recognised first the fortieth day for males and the eightieth day for females as the moment of animation, but later the fortieth day for both sexes. The embryo informatus" thus had no soul, the embryo formatus" had, and as a corollary could be baptised. St Thomas Aquinas was of opinion that embryos dying in utero might possibly be saved : but Fulgentius denied it. As for the ancient belief that male embryos were formed twice as quickly as female ones, it lingered on until Goelicke took the trouble to disprove it experimentally in 1723.
Clement of Alexandria, in his book \6<yo^r os\ thus Kottnitz in 1889 collected some data about the presence of peptones and protein in the human amniotic liquid with this object in view. That the foetus swallows the liquid which surrounds it towards the end of gestation in all amniota, can hardly be disputed, and as there are known to be active proteolytic enzymes in the intestinal tract, no doubt some of the protein which it contains is digested — but to maintain that any significant part is played in foetal nutrition by this process has become steadily more and more impossible since 1600.
But to return to the eighteenth century; all was not repetition; occasionally somebody brought forward a few facts. Thus the deglutition of the amniotic Hquid was discussed by Flemyng in 1 755 in a paper under the title " Some observations proving that the foetus is in part nourished by the amniotic liquor". "I believe", he said, "that very few, if any at all, will maintain now-a-days with Claudius de la Courvee and Stalpartvan-der-Wiel, that the whole of its nourishment is conveyed by the mouth." But he himself had found whiten hairs in the meconium of a calf embryo with a white hide. Both Aides and Swammerdam had found the same thing, but Aides did not think it of any significance, and Swammerdam merely remarked that the calf must lick itself in utero.
More interesting was W. Watson's "Some accounts of the foetus in utero being differently affected by the Small Pox". This was the earliest investigation of the permeability of the placenta to pathological agents. "That the foetus", said Watson, "does not always partake of the Infection from its Mother, or the Mother from the Foetus, is the subject of this paper." Two of his cases, he said, "evince that the Child before its Birth, though closely defended from the external Air, and enveloped by Fluids and Membranes of its own, is not secure from the variolous Infection, though its Mother has had the Distemper before. They demonstrate also the very great Subtility of the variolous Effluvia". But other cases "are the very reverse of the former, where though from Inoculation the most minute portion of Lint moisten'd with the variolous Matter and applied to the slightly wounded Skin, is generally sufficient to propagate this Distemper; yet here we see the whole Mass of the Mother's Blood, circulating during the Distemper through the Child, was not sufficient to produce it. . . . From these Histories it appears that the Child before its Birth ought to be consider'd as a separate, distinct Organization; and that though wholly nourish'd by the Mother's Fluids, with regard to the Small Pox, it is liable to be affected in a very different Manner and at a very different Time from its Mother". Doubtless the modern explanation of Watson's discordant results would be that! in one case there were placental lesions, destroying the perfect barrier between the circulations, and in others there were not.
In the last year of the century (but the seventh of the Republic) Citizens Leveille & Parmentier contributed an interesting paper to I the Journal de Physique in which they observed the increase in size] of the avian yolk on incubation and spoke of a current of water yolkwards (see Fig. 225).
3-15. The Beginning of the Nineteenth Century
At the beginning of the new century a fresh influence came in! with the work of Lamarck, though it did not have such a great effect on his contemporaries as on later generations. Its relations with] biochemistry are so remote that there is no need to deal in any detail with it here, but Lamarck's opinions on embryology may perhaps be given in the words of Cuvier, written in 1836.
"In 1802 he pubUshed his researches on living bodies, containing a physiology peculiar to himself, in the same way that his researches on the principal facts of physics contained a chemistry of that character. In his opinion the egg contains nothing prepared for life before being fecundated, and the embryo of the chick becomes susceptible of vital motion only by the action of the seminal vapour; but, if we admit that there exists in the universe a fluid analogous to this vapour, and capable of acting upon matter placed in favourable circumstances, as in the case of the embryon, which it organises and fits for the enjoyment of life, we will then be able to form an idea of spontaneous generations. Heat alone is perhaps the agent employed by nature to produce these incipient organizations, or it may act in concert with electricity. M. de Lamarck did not believe that a bird, a horse, nor even an insect, could directly form themselves in this manner; but, in regard to the most simple living bodies, such as occupy the extremity of the scale in the different kingdoms, he perceived no difficulty; for a monad or a polypus are, in his opinion, a thousand times more easily formed than the embryo of a chick. But how do beings of a more complicated structure, such as spontaneous generation could never produce, derive their existence? Nothing, according to him, is more easy to be conceived. If the orgasm, excited by this organizing fluid, be prolonged, it will augment the consistency of the containing parts, and render them susceptible of reacting on the moving fluids which they contain, and an irritability will be produced, which will consequently be possessed of feeling. The first efforts of a being thus beginning to develope itself must tend to procure it the means of subsistence and to form for itself a nutritive organ. Hence the existence of an alimentary canal. Other wants and desires, produced by circumstances, will lead to other efforts, which will produce other organs : for, according to a hypothesis inseparable from the rest, it is not the organs, that is to say, the nature and form of the parts, which give rise to habits and faculties ; but it is the latter which in process of time give birth to the organs. It is the desire and the attempt to swim that produces membranes in the feet of aquatic birds; wading in the water, and at the same time the desire to avoid getting wet, has lengthened the legs of such as frequent the sides of rivers; and it is the desire of flying that has converted the arms of all birds into wings, and their hairs and scales into feathers. In advancing these illustrations, we have used the words of our author, that we may not be suspected either of adding to his sentiments or detracting any thing from them."
If the latter part of the eighteenth century did not produce the move forward in the morphological direction which might have been expected from the work of Wolff, a remarkable amount of work was accomplished on the chemical side. This mass of work did not spring from any one source, it was not due to a great discovery on the part of one man, but rather it came about that, as the technique of chemistry itself improved, a number of otherwise undistinguished investigators, such as Dehne, Macquer and Bostock, applied physicochemical methods to the embryo, though it is true that among the names are those of certain great chemists, such as Scheele and Fourcroy. The results of this movement were summarised in the work of J. F.John, whose Chemische Tabellen des Tierreichs appeared in 1814. With this date I propose to bring my historical assessment to an end. The work that was done in physico-chemical embryology after 181 4 will be considered in the appropriate sections dealing with the problems of the present time; for Gobley, as an example, who gave the name to the substance still called vitellin, was working only a dozen years after the date of the publication of John's Tabellen.
In this translation of the Tables, I have made one alteration only. John groups together a number of data which are contained in von Haller's Elementa Physiologiae, and attributes them to that great man. But actually they were obtained by earlier investigators and only came to John through the medium of Haller and Fourcroy — I have therefore allotted them to their true originators.
EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814
Substance or liquid
investigated Composition
Amniotic liquid (man) It contains a substance which can be precipitated with tincture of gall, phosphate of lime and muriatic salts „ It is salt
„ It is sweet
,, It coagulates on boiling
Investigator
Date
Rhades
1753
Schrader
1674
Vieussens
1705
Rhades
1753
Roederer
1750
Barbati &
1676
Heertodt
223
EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814 {cont.)
Substance or liquid investigated
Amniotic liquid (man)
Cheesy material, given off into the amniotic liquid by the body of the foetus (man)
Embryonic tissue-juice (man)
Amniotic liquid (cow)
Amniotic and allantoic liquids (cow)
Composition
It is miscible with water It is coagulable by tincture of gall It is coagulable by alcohol It is coagulable by alumina It is coagulable by spirits of nitre Free mineral alkali, water, albuminous substance, common salt Much water, very little common salt, fire-stable alkali, phosphoric acid, some earth, and oxyde of iron
Much water, a lymphatic coagulum, common salt, salmiac, a trace of phosphate of lime Sp. g. 1-005. Albuminous matter, soda, muriate of soda, phosphate of lime, the rest is water
Animal slime, and a characteristic fatty material, or rather an albuminous material tending to fat, carbonate of lime
It contains hydrofluoric acid
Water, much sulphate of soda, phosphate of lime and talc, an animal substance soluble in water, insoluble in spirits of wine, and not forming a combination with tannic acid, a crystalline amniotic acid
The liquid of the allantois is very different quantitatively in the different periods of pregnancy, as also in the qualitative aspect of its composition. First it is crystalline and colourless, then it gets yellowish, and finally a dark reddish-brown. But it remains watery all the time and never has the property possessed by the amniotic liquid, of becoming at last quite slimy even to the point of showing fibres in it. During the last months the hippomanes appear in it, these are soft and yet tough. The quantity of this liquid is much greater at the end than at the beginning. Alcohol precipitates from it a very large amount of a reddish substance; sulphate of baryta, tartaric acid, and carbonate of lime give a large precipitate. These reagents do not change the amniotic fluid at all. 1000 gm. Uq. allant. gave 20-25 gm. solid residue, 1000 gm. liq. amnii gave lo-i i gm. solid residue
Investigator
Date
Longfield
1759
Rhades
1753
Spielmann
1753
Tauvry
1690
Langly
1674
Gmelin &
1796
Ebermaier
van den Bosch
1792
Scheele
Vauquelin & Buniva
Vauquelin & Buniva
Berzelius
Buniva & Vauquelin
Dzondi
1807
1806
224
EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814 {cont.)
Substance or liquid investigated
Blood of embryo (man)
Blood of embryo (rabbit)
Foetal urine (man) Meconium (man)
Meconium (cow)
Eggs (wild birds) Air-space
Shells
Shell-membranes Egg-white
Yolk
Shell-membranes Shell
Composition Investigator
Soda, much serum, and some leathery Fourcroy
fibrous threads, which made up
only ^ grain out of 3 gros 6 grains
of cruor . They were jelly-like in consistency. No phosphoric acid. It
differed from the blood of an adult
(i) in not giving a red flush when
shaken up with air, (2) in not clotting in air, (3) in the fibres being
more jelly-like Does not coagulate in the cold but Fourcroy
gives rise to a red serum tending
towards brown. It was not as solid
as usual except when heated, then
it went grey though the supernatant
liquor was red It is odourless and colourless and of Fourcroy
a slimy nature Water f , ^r> spirituous extract similar Bay en
to gall, a black residue dissolving
partially in water to give a yellow
colour. He holds it to be a milky
excrement Contains true gall-like substances
Date 1790
1803
Does not contain air of different composition from atmospheric air
Phosphate of lime, animal glue, and some combustible substance which escapes with a sulphurous smell from shells when they are softened in acid. Ferrous particles. Sometimes some common salt. An egg, which weighed 2 ozs. 2 scruples 15 grains, had white which weighed 10 qentchen 2 scruples, yolk ^ oz. \ scruple, and shell and membranes 2 drachms 5 grains
An animal material insoluble in acids
6 qentcfwn 2 scruples 7 grains lost practically 6 qentchen in drying, it contains no caustic salts, the ash is an earthy insipid dust
Albuminous matter, water, muriate of soda, phosphate of lime, and sulphur
Albuminous matter, oil, yellow pig- Adet ment
From 60 eggs, 5^ ozs. oil Dehne
Albuminous matter with much Adet oxygen
Carbonate of lime, phosphate of lime, Adet and very oxydised albuminous matter
Buniva & — Vauquelin
Hehl 1 796
von Wasserberg 1 780
von Wasserberg 1 780 von Wasserberg 1 780
Adet
SECT. 3]
AND EIGHTEENTH CENTURIES
225
EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814 {cent.) Substance or liquid
Composition
investigated Eggs (domestic hen) Shell
Investigator Date
Shell-membranes
A fine earth and a gelatinous material True lime, containing perhaps phosphoric acid \ oz. of pulverised clean shell, digested with spirits of wine, gave i \ grains of an extract which smelt and tasted rancid. The same amount of shell gave i scruple of a yellow watery extract which tasted salt Carbonate and phosphate of lime, traces of a jelly, which can be used as gum. Phosphoric acid can be had from the ash Carbonate and phosphate of lime, bitter earth and iron, a jelly which can be used as gum Carbonate of Hme 72 parts, phosphate of lime 2, jelly 3, water and loss 23 Carbonate of lime 89-6 parts, phosphate of lime 5-7, animal substance 4-7, traces of sulphur. As a hen lays 130 eggs in six months and as an egg weighs on an average 58-117 grams, 7486-226 grams of solid must be used for egg-production in that time, i.e. since the shells would weigh 64-685 gm., 7333-793 gm., 14 pounds 15 ounces 7 gros 8 grains. The secretion of the lime is probably accomplished by means of the kidneys Carbonate and phosphate of lime, and jelly Very much carbonate of lime, very little phosphate. Traces of phosphate of iron, earthy carbonates, rnuriates, albuminous and gelatinous substance to hold it together. I cannot find any uric acid in it, as Vauquelin says is there, nor is he right in saying that the sulphur is in the shell — it is in the membranes only, and under the form of sulphuric acid
Consist of an animal material Have the properties of the fibrous
part of blood A jelly-like material, soluble in hot
water An animal substance with traces of
phosphate of lime, carbonate of
lime, muriates, and a sulphurous
body An albuminous substance containing
traces of sulphur and soluble in
caustic potash
Macquer Leonhardi
Neumann
Berniard
Hatchett
1 781
1780
1800
Merat-Gaillot —
Vauquelin 1 799
Fourcroy John
1811
Macquer Jordan
Fourcroy
John
178:
1811
Vauquelin —
15
226 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii
EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814 {cont.)
Substance or liquid investigated
Chalazae
Egg-white
Yolk-membrane
Yolk
Egg (Snipe, Tringa vanellus) Shell
Composition
An agglutinative substance insoluble in water, apparently like dried tragacanth gum
A white lymphatic transparent sticky slimy material
Soda, albuminous matter, water, sulphur
Water, albuminous matter, with some free alkali, phosphate of lime, muriate of soda, and sulphur
Contains benzoic acid
Water 80 parts, uncoagulable substance 4-5 parts, albuminous matter 15-5 parts, traces of soda, sulphuretted hydrogen gas, and benzoic acid
Contains sulphur
Water, albuminous matter, a little jelly, soda, sulphate of soda, muriate of soda, phosphate of lime, oxyde of iron (?)
An oxydised albuminous substance Apparently an albuminous substance
Consists of a lymphatic material and
a fatty oil Water, oil, albuminous matter, jelly Water, oil, albuminous matter, jelly, phosphates of lime and soda, with other salts Water, oil, albuminous matter Water, a mild oil, albuminous matter, a colouring matter which is perhaps iron Water, a yellow mild oil, traces of free (phosphoric?) acid, a small amount of a reddish-brown material, not fatty, and soluble in ether and warm alcohol, a jelly-like substance, a great deal of a modified albuminous substance, and sulphur
Egg (lizard, Lacerta viridis) Yolk
White
Egg (fish, salmon)
Is composed of the same constituents as that of the hen, but the dark green pigment and the dark brown splashes are probably oxyde of iron
A yellow oil, an albuminous material, and salts
Diflfers from that of fowls in being granular and greasy when hardened by boiling
420 grains contained of pure dry albuminous matter 26 grains, of a viscous oil 18 grains, insoluble albuminous matter 102 grains, mu
nvestigator John
Date
Macquer
—
Jordan
—
Fourcroy
—
Proust Bostock
—
Scheele John
Fourcroy —
John —
Macquer 1781
Thomson —
Hatchett —
Jordan —
Fourcroy —
John
i
John
John John
John
EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814 {cont.)
Substance or liquid
investigated Composition Investigator Date
riate of soda and sulphuric alkali 28 grains, jelly, phosphate of lime, and oxyde of iron 2 grains, water 242 grains
Egg (fish, Cyprinus barbiis) Contains a substance dangerous for Crevelt —
man, the nature of which is unknown
Egg (insect, Locusta viridissima, and migratoris)
Shell An animal combustible substance John —
and phosphate of lime
Contents Albuminous matter, a yellow fluid John —
fatty oil, a little jelly and a characteristic substance, acid, phosphates, and sulphuric alkali
The most interesting of the investigators in this table is Dzondi, whose work in 1806 was the first in which definite chemical characteristics were systematically followed throughout embryonic development. It is surprising that so long a time should have elapsed between Walter Needham and John Dzondi: no less than 139 years.
After 1814 events were to move so rapidly in the world of science that it would not be possible to follow all the embryological work that was done, and at the same time maintain the proper proportion between the historical part of this book and the other parts. The eighteenth century was the period during which the chemical side of embryology began to differentiate and split itself off from the rest. After 1814 it pursued a course of its own, the individual tracks of which I shall mention under their appropriate heads. But another century had yet to pass before the value of the physico-chemical approach to embryology could become generally recognised, and we are ourselves only at the very beginning of this new period.
A certain contrast may appear between the critical treatment which I have given to the investigators whose work I have been discussing, and the saying of William Harvey's — "all did well", which stands prefixed to this Part of the book. Yet history without criticism is a contradiction in terms, and the praise and dispraise, which I have tried to allot as accurately and justly as I could, is, as it were, technical, rather than spiritual. All the workers who have been mentioned, and others besides them who left no special marks on their time, are worthy of our respect and of our fullest praise, for they preferred wisdom before riches and, according to their several abilities and generations, diligently sought out truth.
Cite this page: Hill, M.A. (2024, April 24) Embryology Book - Chemical embryology 1 (1900) 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Chemical_embryology_1_(1900)_2
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
