Talk:Book - Chemical embryology 1 (1900) 2

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.

42 PRELIMINARY NOTE [pt.

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

II] PRELIMINARY NOTE 43

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 I

EMBRYOLOGY IN ANTIQUITY

I -I. 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.

Ancient Indian embryology achieved a relatively high level. Structures such as the amniotic membrane are referred to in the

Fig,

I . Painted and carved door from New Guinea (de Clercq).

SECT. I] EMBRYOLOGY IN ANTIQUITY 45

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

46 EMBRYOLOGY IN ANTIQ^UITY [pt. ii

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

PLATE 1

(A) EGYPTIAN PEASANT INCUBATOR (from Cadman)

(B) CHINESE PEASANT INCUBATOR (from King)

SECT, i] EMBRYOLOGY IN ANTIQUITY 47

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.

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

48 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT, i] EMBRYOLOGY IN ANTIQUITY 49

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.

50 EMBRYOLOGY IN ANTIQUITY [pt. ii

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 . ^ , , .

. • f T^ T 1- -r. • 1 Fig- 2. Eros hatching

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

SECT. I] EMBRYOLOGY IN ANTIQUITY 51

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).

4-2

52 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT, i] EMBRYOLOGY IN ANTIQUITY 53

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

54 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT, i] EMBRYOLOGY IN ANTIQUITY 55

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

56 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT. I] EMBRYOLOGY IN ANTIQUITY 57

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

Aristotle.

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

58 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT. I] EMBRYOLOGY IN ANTIQUITY 59

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

6o EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT, i] EMBRYOLOGY IN ANTIQUITY 6i

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.

62 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

^ To the Greeks all natural foams possessed a generative virtue, and a Zeus Aphrios was worshipped at Pherae in Thrace.

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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.

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,

SECT, i] EMBRYOLOGY IN ANTIQUITY 65

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^iajoLATE II

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SECT, i] EMBRYOLOGY IN ANTIQUITY 83

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

6-2

84 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

^ For further information about the serpent's eggs of the Druids, see Kendrick; they were probably fossil echinoderms.

SECT, i] EMBRYOLOGY IN ANTIQUITY 85

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.

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

86 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT, i] EMBRYOLOGY IN ANTIQUITY 87

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."

88 EMBRYOLOGY IN ANTIQUITY [pt. ii

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

SECT, i] EMBRYOLOGY IN ANTIQUITY 89

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

go EMBRYOLOGY IN ANTIQUITY [pt. ii

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

92 EMBRYOLOGY FROM GALEN [pt. ii

^'^ 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<i TrporpeTTriKO'i Trpo? "EX\.7]va'i, has some remarks to make on embryology, but adds nothing to the knowledge previously gained. He adopts the Peripatetic view that generation results from the combination of semen with menstrual blood, and he uses the Aristotelian illustration of rennet coagulating milk. Lactantius of Nicomedia, who lived about the date of the Nicene Council (a.d. 325) perpetuated the deeply-rooted association of male with right and female with left in his book On the work of God, De opificio Dei. He also maintained that the head was formed before the heart in embryogeny, and seems to have opened hen's eggs systematically at different stages, so that to this extent he was a better embryologist than Galen. St Gregory of Nyssa, as we have already seen (p. 20), evolved a neo-vitalistic theory which he applied to the growth of the embryo.

Late Latin writers, other than the theologians, do not say much about it. There is a passage in Ausonius, however, which describes the development of the foetus {Eclog. de Rat. puerp.) but it is almost wholly astrological. Elsewhere he says:

juris idem tribus est, quod ter tribus; omnia in istis; forma hominis coepti, plenique exactio partu, quique novem novies fati tenet ultima finis.

Idyll II (Gryphus ternarii numeri), 4-6. (The power of 3, in 3 times 3 lies too, Thus 9 rules human form and human birth, And 9 times 9 the end of human life.)

But this is probably a late echo of the Pythagoreans rather than an early prelude to Leonardo da Vinci and the mathematisation of nature.

That great mass of Jewish writings known as the Talmud, which grew up between the second and sixth centuries a.d., also contains some references to embryology, and certain Jewish physicians, such as Samuel-el-Yehudi, of the second century, are said to have devoted

SECT. 2] TO THE RENAISSANCE 93

special attention to it. The embryo was called peri habbetten (fruit of the body), ]a2n ns. It grew through various definite stages:

(i) golem (formless, rolled-up thing), nbu, 0-1-5 months.

(2) shefir meruqqdm (embroidered foetus), api» T'Dit.

(3) ^ubbar (something carried), imi?, 1-5-4 months.

(4) walad (child), n*?!, 4-7 months.

(5) walad shel qaydmd (viable child), so'^^p '7tri'?i, 7-9 months.

(6) ben she-kallu khaddshdw (child whose months have been completed), rirnn I'^rir ]n.

The ideas of the Talmudic writers on the life led by the embryo in utero are well represented by the remark, "It floateth like a nutshell on the waters and moveth hither and thither at every touch"

ms o*» "rtr ':'SDn niia TUNb las •'^lan n»n n'?i rrch ity'^s •'sn lasi

And the classical passage, "Rabbi Simlai lectured: the babe in its mother's womb is like a rolled-up scroll, with folded arms lying closely pressed together, its elbows resting on its hips, its heels against its buttocks, its head between its knees. Its mouth is closed, its navel open. It eats its mother's food and sips its mother's drink: but it doth not excrete for fear of hurting"

bv rT* niioi "rsipa'!^ Q^ith las "'yan n»n n'^in rxh V^b's^^ •'in tJ^m ittNtr na» nmtyi n'?sis las:^ n»» '?2isi mns "nuai miio rsi rsin ^■'n i"?

It was thought, moreover, that the bones and tendons, the nails, the marrow in the head and the white of the eye, were derived from the father, "who sows the white", but the skin, flesh, blood, hair, and the dark part of the eye from the mother, "who sows the red". This is evidently in direct descent from Aristotle through Galen, and may be compared with the following passage from the latter writer's Commentary on Hippocrates: "We teach that some parts of the body are formed from the semen and the flesh alone from blood. But because the amount of semen which is injected into the uterus is small, growth and increment must come for the most part from the blood". It might thus appear that, just as the Jews of Alexandria were reading Aristotle in the third century B.C., and incorporating

IujILIBRAR Y

V<^XN4?AI

94 EMBRYOLOGY FROM GALEN [pt. ii

him into the Wisdom Literature, so those of the third century a.d. were reading Galen and incorporating him into the Talmud. As for God, he contributed the life, the soul, the expression of the face, the functions of the different parts. This participation of three factors in generation, male, female, and god, is exceedingly ancient, as may be read in Robertson Smith. Some Talmudic writers held that development began with the head, agreeing with Lactantius, and others that it began at the navel, agreeing with Alcmaeon. Weber has given an account of the Talmudic beliefs about the infusion of the soul into the embryo. They do not seem to have embodied any new or striking idea.

Although the Talmud contained certain references of embryological interest, the first Hebrew treatise on biology was not composed till the tenth century, when Asaph Judaeus or Asaph-ha-Yehudi wrote on embryology about a.d. 950. His MSS. are exceedingly rare, but, according to Gottheil's description, they contain several sections on embryology. Steinschneider has given another description of them. For further details on the whole subject of Jewish embryology see Macht.

Arabian science, so justly famed for its successes in certain branches, was not of great help to embryology. Abu-1-Hasan ' Ali ibn Sahl ibn Rabban al-Tabari, a Moslem physician who flourished under the Caliphate of al-Mutawakldl about a.d. 850, wrote a book called The Paradise of Wisdom, in which an entire part was devoted to embryology, all the more interesting as it is a mixture of Greek and ancient Indian knowledge. Browne gives a description of it. Ibn Rabban's contemporary, Thabit ibn Qurra, is also said to have written on embryology. The great Avicenna, or, to give him his proper name, Abu 'Ali-1-Hasan ibn 'Abdallah ibn Sina, who lived from 978 to 1036, devoted certain chapters of his Canon Medicinae to the development of the foetus, but added nothing to Galen. His contemporaries, Abu-1-Qasim Maslama ibn Ahmad al-Majriti and Arib ibn Said al-Katib, a Spanish Moslem, wrote treatises on the generation of animals, but neither has survived.

What was alchemy doing all this time? It was engaged on many curious pursuits, but among them the interpretation of embryonic development was not one. Alchemical texts before the tenth century do make reference to eggs from time to time, but it is safe to say never with any trace of an interest in the development of the embryo

SECT. 2] TO THE RENAISSANCE 95

out of them. One example taken from Berthelot's collection will suffice; it comes from the "6th book of the Philosopher" (Syriac).

To make water of eggs

Take as many eggs as you wish, break them and put the whites in a glass flask, place this in another vessel and surround it with fresh horsedung up to the neck of the vessel. Leave it so for 15 days changing the dung every 5 days. Then distil the liquid in an alembic and taking a pound of the distillate add lime of eggs 2 ozs. Shake well and distil again. Do this 4 times. Take then of elixir of arsenic, 2 parts, of sulphur i part, of pyrites and magnesia, each i part. Pound in a mortar and add to the final distillate from the eggs. Do this for 7 days always working in the sunlight, once at sunrise, once in the middle of the day, and once at sunset. When this has been done, dry the mixture, pound it, and set it aside.

I could only find one reference to the embryo in a hen's egg among the vast number of alchemical directions of this time, and then only as a constituent of the egg which must be discarded. As we shall see, it is not until after the time of Paracelsus that the notion of applying chemical methods to eggs or embryos arises at all.

2-2. St Hildegard: the Lowest Depth

Not long after the death of Avicenna, St Hildegard was born. She lived from 1098 to 1180, and was Abbess successively of Disibodenberg and Bingen in the Rhineland. Her treatises on the world, which are an extraordinary medley of theological, mystical, scientific and philosophical speculation, have been described in detail by Singer, and, though in the books. Liber Scivias and Liber Divinorum Operum simplicis hominis, there is little of embryological interest, yet she does give an account of development and especially of the entry of the soul into the foetus.

This is illustrated in Plate HI taken from the Wiesbaden Codex B of the Liber Scivias. The soul is here shown passing down from heaven into the body of the pregnant woman and so to the embryo within her. The divine wisdom is represented by a square object with its angles pointing to the four corners of the earth in symbol of stabihty. From it a long tube-Hke process descends into the mother's womb and down it the soul passes as a bright object, "spherical" or "shapeless", illuminating the whole body. The scene shows the mother in the foreground lying down ; inside her there are traces of the foetal membranes; behind this ten persons are grouped, each carrying a

96 EMBRYOLOGY FROM GALEN [pt. ii

vessel, into one of which a fiend pours some noxious substance from the left-hand corner. St Hildegard describes and expounds the scene as follows: "Behold, I saw upon earth men carrying milk in earthen vessels and making cheeses therefrom. Some was of the thick kind from which firm cheese is made, some of the thinner sort from which more porous cheese is made, and some was mixed with corruption and of the sort from which bitter cheese is made. And I saw the likeness of a woman having a complete human form within her womb. And then by a secret disposition of the most high craftsman, a fiery sphere having none of the lineaments of a human body possessed the heart of the form and reached the brain and transfused itself through all the members. . . . And I saw that many circling eddies possessed the sphere and brought it earthward, but with ever renewed force it returned upwards and wailed aloud, asking, 'I, wanderer that I am, where am I?' 'In death's shadow.' 'And where go I?' 'In the way of sinners.' 'And what is my hope? ' ' That of all wanderers.' . . . As for those whom thou hast seen carrying milk in earthen vessels, they are in the world, men and women alike, having in their bodies the seed of mankind from which are procreated the various kinds of human beings. Part is thickened because the seed in its strength is well and truly concocted and this produces forceful men to whom are allotted gifts both spiritual and carnal.. . .And some had cheeses less firmly curdled, for in their feebleness they have seed imperfectly tempered and they raise offspring mostly stupid, feeble, and useless, . . . And some was mixed with corruption . , . for the seed in that brew cannot be rightly raised, it is invalid, and makes misshapen men who are bitter distressed and oppressed of heart so that they may not lift their gaze to higher things. . . .And often in forgetfulness of God and by the mocking devil a mistio is made of the man and the woman and the thing born therefrom is deformed, for parents who have sinned against me return to me crucified in their children". We have already traced the wanderings of the cheese-analogy, which, beginning fresh with Aristotle, was taken to Alexandria and incorporated in the Wisdom Literature, and so found its way to the Arabic of 'Ali ibn a'1-Abbas al-Majusi, or Haly-Abbas, as he was known in the West, a Persian. His Liber Totius appeared in Latin in 1523, but had been translated much earlier, at Monte Cassino between 1070 and 1085, by Constantine the African, who called it Liber de Humana Natura, and gave it out to be his own work. Thus

PLATE III

AN ILLUSTRATION FROM THE LIBER SCIVIAS OF ST HILDEGARD OF BINGEN (Wiesbaden Codex B) showing the descent of the soul into the embryo {ca. 1 150 a.d.).

SECT. 2] TO THE RENAISSANCE 97

St Hildegard obtained it, and worked it up into one of her visions. At this point embryology touched, perhaps, its low-water mark. But a great man was at hand, destined to carry on the Aristotelian tradition and to add to it much of originality, in the shape of Albertus of Cologne. Before speaking of him, however, a word must be said about that very queer character, Michael Scot (i 178-1234), who, according to Gunther, "appeared in Oxford in 1230 and experimented with the artificial incubation of eggs, having got an Egyptian to teach him how to incubate ostriches eggs by the heat of the Apulian sun". That "muddle-headed old magician", as Singer rightly calls him, was not the man to profit by it, but the point is interesting, especially as an Egyptian is mentioned. Haskins, in his curious studies of the scientific atmosphere of the court of the Emperor Frederick II of Sicily, has shown Scot, newly arrived fi"om his alchemical studies in Spain, assisting that very learned and unorthodox monarch in his artificial incubation experiments.

2-3. Albertus Magnus

Albertus Magnus of Cologne and Bollstadt was born in 1206, and died in 1280, six years after his favourite disciple, St Thomas Aquinas. The greater part of his life was spent in study and teaching in one or other of the houses of the Dominican friars, to which he belonged, though for a time he was Bishop of Regensburg. Albert resembles Aristotle in many points, but principally because he produced biological work with, as it were, no antecedents. Just as Aristotle's contributions to embryology were preceded by no more than the diffuse speculations of the Ionian nature-philosophers, so Albert's came immediately after the dead period represented by the visions of St Hildegard. In many ways, Albert's position was much less conducive to good work than Aristotle's.

Albert follows Aristotle closely throughout his biological writings, quoting him word for word in large amounts, but the significant thing is that he does not follow him slavishly. He resembled Aristotle in paying much attention to the phenomena of generation, as a rough computation shows, Aristotle devoting 37 per cent, of his biological writings to this subject, and Albert 31 per cent., to which Galen's 7 per cent, may with interest be compared. Albert is extremely inferior to Aristotle, however, in point of arrangement; for Aristotle, although some of his books, such as the De Generatione Animalium,

98 EMBRYOLOGY FROM GALEN [pt. ii

are sufficiently confused and repetitive, does yet succeed in infusing a clarity and incisiveness into his style. Albert, on the other hand, allows his argument to wander through his twenty-six books De Animalibus in the most complex convolutions, so that the sections on generation and embryology are found indiscriminately in the first, sixth, ninth, fifteenth, sixteenth, and seventeenth. In Book i he gives a kind of summary or skeleton of his views on the embryo. These follow Aristotle fairly closely; thus, he accepts the AristoteHan classification of animals according to their manner of generation, and thinks still that caterpillars are immature eggs ; he derives the embryo from the white, not the yolk, and he explains why soft-shelled eggs, being imperfect, are of one colour only. But there are new observations; for instance, he describes an ovum in ovo, which he has seen, calling it a natura peccatis, and he speaks definitely of the seed of the woman, thus departing from Peripatetic opinion, and adopting the Epicurean view. The female seed, he thinks, suflfers coagulation like cheese by the male seed, and to these two humidities there must be added a third, namely, the menstrual blood (corresponding to the yolk in the case of the bird). "When these three humidities therefore have been brought into one place, all the similar members except the blood and fat are formed from the two humidities of which one generates actively but the other passively. But the blood which is attracted for the nutriment of the embryo is double in virtue and double in substance. For a certain part of the blood is united with the sperm in such a way that it takes on some of the virtue of the seed because a certain part of the spermatic humour remains in it and from this are begotten the teeth and for this reason they grow again if they are pulled out at an age near the time of sperm-making and do not grow again at an age remoter from this, at which the virtue of the first generating principle has vanished from the blood. But another part of the blood is of twofold or threefold substance and from the thick part of the blood itself is generated the flesh. And this flows in and flows out and grows again if rubbed away. From the watery part of the same blood or of the nutritive humour are generated the fat and oil and this flows in and out more easily than the flesh itself, but other parts of the blood are its refuse and impurities and are not attracted to the generation of any part of the animal, but having been collected until birth are expelled with the embryo from the uterus in the foetal membranes, like the remnants

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in the hen's egg after the chick has hatched. There is a similar virtue in the liver and heart of animals which organs after the animals are born form the flesh and fat from food in accordance with its twofold substance, and expel the refuse as we said before,"

In the sixth book, Albert contradicts Aristotle's opinion that male chick develops out of the sharp-ended egg, and one hopes that he is going to say there is no relationship between egg-shape and sex, but no, he goes on to say that the Aristotelian statement rested on a textual error (in which he was quite wrong), so that really Aristode agreed with Avicenna in saying that the males always develop from the more spherical eggs because the sphere is the most perfect of figures in solid geometry. These errors had a most persistent life : Horace has a passage in which they appear —

longa quibus facies ovis erit, ilia memento ut suci melioris, et ut magis alma rotundis ponere: namque marem cohibent callosa vitellu.m.

(When you would feast upon eggs, make choice of the long ones ; they are whiter and sweeter and more nourishing than the round, for being hard they contain the yolk of the male.)

They were finally abolished by two naturalists, Giinther and Biihle, who took the trouble to disprove them experimentally in the eighteenth century. Albertus refers here to artificial incubation: "For the alterative and maturative heat", he says, "of the egg is in the egg itself and the warmth which the bird provides is altogether external [extrinsecus est amminiculans] since in certain hot countries the eggs of fowls are put under the surface of the earth and come to completion of their own accord, as in Egypt, for the Egyptians hatch them out by placing them under dung in the sunlight". Next he speaks of monsters and of the modes of corruption of eggs which he divides into four: (i) decomposition of white, (2) decomposition of yolk, (3) bursting of the yolk-membrane, (4) antiquitas ovi. "And from the second cause it sometimes happens ", he says, "that in the corruption of the humours certain igneous parts are carried blazing to the shell of the egg and distribute themselves over it so that it shines in the dark like rotten wood; as happened in the case of that egg^ which Avicenna said he saw in the city called Kanetrizine in the country of the Gorascenes." Albert

^ See on this subject Zach.

7-2

lOO EMBRYOLOGY FROM GALEN [pt. ii

is inclined to think that astrological influences may have an effect on foetal life, but he treats the suggestion with considerable scepticism, although he believes that thunder and lightning kill the embryos of fowls (a popular belief to which Fere tried not long ago to give a scientific foundation), and he regards the embryo of the crow as especially susceptible, though on what grounds he does not say.

The fourth chapter of the first tractate of the sixth book contains Albert's description of development of the chick, and is extremely interesting. He makes two principal mistakes: {a) he describes a quite non-existent fissure in the shell by which the chick may emerge, {b) he maintains that the yolk ascends after a day or two into the sharp end of the egg, adducing as the reason that there is found there more heat and formative force than elsewhere. On the other hand, he correctly describes {a) the pulsating drop of blood on the third day, and {b) he identifies it with the heart with its systolen et dyastolen sending out the "formative virtue" to all the parts of the growing body. He notices [c) that the differentiation of the chick at first proceeds rapidly and later more slowly. But the most notable characteristic of Albert's embryology is the way in which he is hampered by his inability to invent a technical terminology. Singer has studied the way in which anatomical terms, such as "syrach", etc., came into use, but whatever the causes were which produced them, they did not operate much in Albert's mind. He represents the point beyond which embryology could not advance, until it had created a new set of terms. This is well illustrated by the following passage:

"But fi'cni the drop of blood", he says, "out of which the heart is formed, there proceed two vein-like and pulsatile passages and there is in them a purer blood which forms the chief organs such as the liver and lungs and these though very small at first grow and extend at last to the outer membranes which hold the whole material of the egg together. There they ramify in many divisions, but the greater of them appears on the membrane which holds the white of the egg within it [the allantois]. The albumen, at first quite white, is changed owing to the power of the vein almost to a pale yellow-green tint [palearem colorem]. Then the path of which we spoke proceeds to a place in which the head of the embryo is found carrying thither the virtue and purer material from which are formed the head and the brain, which is the marrow of the head. In the formation of the head also are found the eyes and because they are of an aqueous humidity which is with difficulty used up by the first heat they are very large, swelling out and bulging from the chick's head. A short

SECT. 2] TO THE RENAISSANCE loi

time afterwards, however, they settle down a little and lose their swelling owing to the digestive action of the heat — and all this is brought about by the action of the formative virtue carried along the passage which is directed to the head, but before arriving there is separated and ramified by the great vein of the albumen-membrane, as may be clearly seen by anyone who breaks an egg at this time and notes the head appearing in the wet part of the egg and at the top of the other members. For what appears first in the making of a foetus are the upper parts because they are nobler and more spiritual being compacted of the subtler part of the egg wherein the formative virtue is stronger. When this happened one of the aforementioned two passages which spring from the heart branches into two, one of them going to the spiritual part which contains the heart and divides there in it carrying to it the pulse and subtle blood from which the lungs and other spiritual parts are formed, and the other going through the diaphragm \dyqfracmd\ to enclose within it at the other end the yolk of the Qgg, around which it forms the liver and stomach. It is accordingly said to take the place of the umbilicus in other animals and through it food is drawn in to supply the flesh for the chick's body, for the principle of generation of the radical members of the chick comes from the albumen but the food from which is made the flesh filling up all the hollows is from the yolk."

After ten days, Albert goes on to say, all the constituent organs are mapped out and the head is greater then than the rest of the body put together. He observes that the yolk liquefies early in development and that slimy concretions are present in the allantoic fluid later on (uric acid). But the passage quoted does demonstrate that before further progress could be made some better name must be found than "the interior membrane to which the first vessel proceeds" for a given structure.

Albert, however, was accomplishing a good work. One of his best amplifications of Aristotle was his description of the relationship between yolk and embryo in fishes. Just as his words about the chick demonstrate that he must have opened hen's eggs at different stages during incubation, so his words about fish eggs show that he must have dissected and examined them also. Thus (Book vi, tractate 2, chap, i) he says, "Between the mode of development [anathomiam generationis] of birds' and fishes eggs there is this diflference ; during the development of the fish the second of the two veins which extend from the heart does not exist. For we do not find the vein which extends to the outer covering of the eggs of birds which some wrongly call the umbilicus because it carries the blood to the outside parts, but we do find the vein which corresponds to the yolk vein of birds, for this vein imbibes the nourishment by which the limbs increase.

102 EMBRYOLOGY FROM GALEN [pt. ii

Therefore the generation of the fish embryo begins from the sharp end of the egg like that of birds and channels extend from the heart to the head and eyes and first in them appear the upper parts. As the growth of the young fish proceeds the yolk decreases in amount being incorporated into the members and it disappears entirely when development is complete. The beating of the heart, which some call panting, is transmitted through the pulsating veins to the lower part of the belly carrying life to the inferior members. While the young fish are small and not yet fully developed they have veins of great length which take the place of the umbilicus, but as they grow these shorten till they contract into the body by the heart as has been said about birds. The young fish are enclosed in a covering just like the embryos of birds, which resembles the dura mater and beneath it another containing the foetus and nothing else, while between the two there is the moisture rejected during the creation of the embryo". Albert also described ovoviviparous fishes but it is more difficult in that case to tell whether he had himself seen and dissected them. He notes also the prodigality of nature in producing so many marine eggs only destined to be eaten.

In Books IX and xv he treats of the Galenic views on generation and insists again that there is a seed provided by the female. In Book XVI he gives his opinions about the animation of the embryo, quoting the views of the ancients as given in Plutarch, e.g. Alexander the Peripatetic, Empedocles, Anaxagoras, Theodorus and Theophrastus, the Peripatetics, Socrates, Plato, the Stoics, Avicenna, and Aristotle, "who saw the truth", but— and it is interesting to notice it — never the Christian Fathers, whose writings must have been well known to him. In discussing the Aristotelian views he compares the menstrual blood to the marble and the semen to the man with a chisel in his hand.

On the question of epigenesis and preformation, he follows Aristotle almost word for word, using the same analogies, such as the "dead eye" and the sleeping mathematician. Here his scholasticism comes out clearly, for in rejecting altogether the theory that one part being formed then forms the next part, he says, not that A would have to be in some way like B, but is not, as Aristotle had, but simply "^Generans et generatum, est simul esset et non esset, quod omnino est impossibile^ — a high-handed and very unscientific manner of settling the question. In conformity with his theology and

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in contradistinction from Aristotle he makes the vegetative and sensitive souls arrive automatically into the embryo but the rational soul only by a direct act of God.

His mammalian embryology presents some points of interest. He follows Hippocrates ("Ypocras") in an account of the co-operation of heat and cold in member-formation, and he holds very enlightened views about foetal nutrition, "It appears therefore that the embryo hangs from the cord and that the cord is joined with the vein and that the vein extends through the uterus and has blood running through it to the foetus like water through a canal. Round the embryo there are membranes and webs as we have seen. But those who think that the embryo is fed by little bits of flesh through the cord are wrong and lie, because if this were the case with man it would happen also with other animals and that it does not do so anybody can find out by investigation [per anathomyani].'"

Finally, it is typical that in Book xvii Albert repeats what he has already said in Book vi about the generation of the hen out of the tgg all over again with slight changes, but he adds the significant biochemical remark that "eggs grow into embryos because their wetness is like the wetness of yeast". The importance of Albert in the history of embryology is clear. With him the new spirit of investigation leapt up into being, and, though there were many years yet to pass before Harvey, the modern as opposed to the ancient period of embryology had begun. Albert's writings were often copied and printed in the next few centuries, and even as late as 1601 De Secretis Mulierum, an epitome of his books on generation, was published. In some sense, it still is, as it forms the backbone of the little book Aristotle's Masterpiece, of which thousands of copies are sold in England every year. The copy of the De Secretis in the Caius College Library has written across the title-page in faded ink "Simulacra sanctitas, duplex iniquitas, Nathan Emgross, Nov. 20. 161 3." But in spite of Mr Emgross, Albertus, rightly called Magnus, has had the happy fate of being beatified both by the Church and by science.

2-4. The Scholastic Period

St Thomas Aquinas (i 227-1 274) incorporated the Aristotelian theories of embryology into his Summa Theologica especially under the head De propagatione hominis quantum ad corpus. There are some striking passages, such as "The generative power of the female

104 EMBRYOLOGY FROM GALEN [pt. ii

is imperfect compared to that of the male; for just as in the crafts, the inferior workman prepares the material and the more skilled operator shapes it, so likewise the female generative virtue provides the substance but the active male virtue makes it into the finished product". How admirably this expresses the dominating sentiment of the Middle Ages! Aristotle might make a distinction between matter and form in generation, but the mediaeval mind, with its perpetual hankering after value, would at once enquire which of the two was the higher, the nobler, the more honourable.

St Thomas' theory of embryonic animation was complicated. He had a notion that the foetus was first endowed with a vegetative soul, which in due course perished, at which moment the embryo came into the possession of a sensitive soul, which died in its turn, only to be replaced by a rational soul provided directly by God, This led him into great difficulties, for, if this scheme were true, it was difficult to say that man generated man at all; on the contrary he could hardly be said to generate more than a sensitive soul which died before birth, and, on this view, what was to happen to original sin? As Harris has put it, Plato had said that the intellect was the man, using the body as a boatman uses a boat. Averroes had said precisely the opposite, namely, that the essence of humanity was in the body, and that the intellect was something extrinsic, not limited to the individual, but common to the race. Aristotle had taken the middle position, and given a soul to plants and animals, but, in doing so, he had made it into a vital rather than a psychological principle. The task of combining this -^vxv with the anima of the Fathers was what scholastic philosophy had before it. No wonder that St Thomas' account of embryonic animation was open to criticism. An echo of it appears in a poem of Jalalu'd-Din Rumi ( 1 207-1 273), the greatest of the Persian Sufi poets, and an exact contemporary of St Thomas Aquinas :

I died from mineral and plant became: Died from the plant, and took a sentient frame; Died from the beast, and donned a human dress; When by my dying did I e'er grow less?

Duns Scotus (i 266-1 308) objected to St Thomas' theory on the grounds already mentioned, and he himself abandoned the vegetative and sensitive souls altogether in his De Rerum Principio. This solution

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was no better than that of St Thomas, for, agreeing with the latter as Duns did that the rational soul was not an ordinary form "educed " from the "potentiality" of the material, but rather an ad hoc creation of God, injected by divine power into the embryo at the appropriate moment, it was difficult to see how the spiritual effects of Adam's fall could be transmitted to the men of each generation. It was as if only acquired characteristics were inherited. But the further course of theological embryology need not be pursued here ; it runs in every century parallel with true scientific embryology, and it is not my purpose to do more than take a glance at its progress from time to time. In the Speculum Naturale, which was written about 1250, by Vincent of Beauvais, the embryology of Constantine the African appears again, and the embryology of Aristotle, Galen, and the scholastics is to be found in Dante Alighieri (i 265-1 321), who dealt with the subject in his Convivio, and especially in the Divina Commedia. In Canto XXV of the Purgatorio, Statins (the personification of human philosophy enlightened by divine revelation) is made to speak to the poet thus: "If thy mind, my son, gives due heed to my words and takes them home, they will elucidate the question thou dost ask. Perfect blood which is in no case drawn from the thirsty veins, but which remains behind like food that is removed from table, receives in the heart informing power for all the members of the human body, like the other blood which courses through the veins in order to be converted into those members. After being digested a second time it descends to the part whereof it is more seemly to keep silence than to speak, and thence it afterwards drops into the natural receptacle (the uterus) upon another's blood ; there the one blood and the other mingle. One is appointed to be passive, the other to be active according to the perfect place whence it proceeds (the heart). And being united with it, it begins to operate, first by coagulating it, and then by vivifying that to which it has given consistency, so that there may be material for it to work upon [e poi avviva, Cib che per sua materia fe' constare]. The active power having become a (vegetative) soul like that of a plant — only differing from it in this, that the former is in progress while the latter has reached its goal — thereafter works so much that it moves and feels like a sea-fungus and as the next stage it takes in hand to provide with organs the faculties which spring from it. At this point, my son, the power which proceeds from the heart of the begetter is expanded and developed, that power in which

io6 EMBRYOLOGY FROM GALEN [pt. ii

Nature is intent on forming all the members, but how from being an animal it becomes a child, thou seest not yet, moreover this is so difficult a point that formerly it led astray one more wise than thou [Averroes], so that in his teaching he separated the active 'intellect' from the soul because he could not see any organ definitely appropriated by it. Open thy heart to the truth and know that as soon as the brain of the foetus is perfectly organised, the Prime Mover, rejoicing in this display of skill on the part of Nature, turns him towards it and infuses a new spirit replete with power into it which subsumes into its own essence the active elements which it finds already there, and so forms one single soul which lives and feels and is conscious of its own existence. And that thou mayst find my saying less strange, bethink thee how the heat of the sun passing into the juice which the grape distils, makes wine".

Having said this. Statins, Virgil and Dante pass on to the seventh ledge in Purgatory. It is interesting to see how Dante emphasises the dynamic teleological side of Aristotle and practically speaks of the soul enfleshing itself and arranging organs for its faculties. The reference to Averroes is explained by the fact that Averroes was a Traducianist, and held that all the soul was generated by man at the same time as the body, whereas both St Thomas and Dante, as Creationists, held that each fresh soul was a special creation of God inserted by him into the brain of the embryo. The mention of Dante's contemporary, Mondino de Luzzi (1270-1326), brings us to the more practical aspects of embryology at this period. Mondino is the most outstanding figure among the Bolognese anatomists of what is really the first period of the revival of biology. After him, as we shall see, biology languished for a couple of centuries until the advent of such men as Ulysses Aldrovandus in the sixteenth century, and Singer has shown that this was probably due to the fact that anatomy professors did not dissect in person. A fortiori embryotomy was infrequent.

But Mondino's Anathomia, published in 13 16, contained statements about the organs of generation which were rather important. He retains the notion of the seven-celled uterus, which had been introduced by Michael Scot, but he adopts a reasonable compromise between the opinions of Galen and Aristotle on the physiology of embryo formation. The distance between him and Leonardo da Vinci (1452-1519) would, however, be estimated rather at five or six centuries than at the century and a quarter that it actually was.

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2-5. Leonardo da Vinci

Leonardo was not alone among the artists of the Renaissance in his anatomical interests, for Michael Angelo, Raphael, Diirer, Mantegna, and Verrochio all made dissections in order to increase their knowledge of the human body. But he penetrated more curiously into biology than they did, and he will always remain one of the greatest of biologists, for he first introduced the quantitative outlook. In this he was some four hundred years before his time.

Leonardo's embryology is contained in the third volume of his notebooks, Quaderni d' Anatomia, published in facsimile by the admirable labours of three Norwegian scholars, Vangensten, Fohnahn and Hopstock, in 191 1. His notebooks are a remarkable, and, indeed, charming miscellany of anatomical drawings, physiological diagrams, architectural and mechanical sketches and notes such as "Shirts, hose, and shoes", "Go and see Messer Andreas", "get coal", "the supreme fool (is the) necromancer, and enchanter".

His dissections of the pregnant uterus and its membranes are beautifully depicted, as can be seen from the figures which are here reproduced (Plate IV). He was acquainted with amnios and chorion, and he knew that the umbilical cord was composed only of vessels, though he seems to have thought the human placenta was cotyledonous. There is one drawing which the editors suppose to represent the developing hen's egg, but I do not feel that this ascription is likely. Indeed, Leonardo worked with eggs much less than with mammalian embryos, though there are references to the former. "See how birds are nourished in their eggs", he says in one place, to remind himself, perhaps, of possible experiments, and, elsewhere, "Chickens are hatched by means of the ovens of the fireplace". Again, "Ask the wife of Biagino Crivelli (was she the Lucrezia Crivelli, whose portrait Leonardo painted?) how the capon rears and hatches the eggs of the hen when he is inebriated", a subject recently reopened by Lienhart. "You must first dissect the hatched egg before you show the difference between the human liver in foetus and adult." Leonardo perpetuates a persistent error in the note, "Eggs which have a round form produce males, those which have a long form produce females".

Concerning the mammalian foetus, he says, "The veins of the child do not ramify in the substance of the uterus of its mother but in the placenta which takes the place of a shirt in the interior of the

io8 EMBRYOLOGY FROM GALEN [pt. ii

uterus which it coats and to which it is connected but not united by means of the cotyledons". Thus in one sentence Leonardo falls into a mistake in saying that the human placenta is cotyledonous, but at the same time asserts a fact which it took all the ingenuity of the seventeenth century to prove to be true, namely, that the foetal circulation is not continuous with that of the mother, for the placenta is only connected to the uterine wall and not united with it. "The child", Leonardo goes on to say, "lies in the uterus surrounded with water, because heavy things weigh less in water than in the air and the less so the more viscous and greasy the water is. And then such water distributes its own weight with the weight of the creature over the whole body and sides of the uterus." The tendency towards quantitative and mathematical explanations is apparent at once.

Further notes are, "Note how the foetus breathes and how it is nourished through the umbilical cord and why one soul governs two bodies, as you see the mother desiring food and the child remaining marked (by a given amount of growth) because of it. Avicenna pretends that the soul generates the soul and the body the body. Per errata^'. The child, says Leonardo, secretes urine while still in utero, and has excrement in its intestines; at four months it has chyle in its stomach, made perhaps from menstrual blood. But it has no voice in utero, "when women say that the foetus is heard to weep sometimes within the uterus, this is rather the sound of some flatus . . . ". Nor does it breathe there (on this point Leonardo contradicts himself). "The child does not respire within the body of its mother because it lies in water and he who breathes in water is immediately drowned." "Breathing is not necessary to the embryo because it is vivified and nourished by the life and food of the mother." Nor does the embryonic heart beat. To us the statement that there is no respiration in the uterus is obviously false, but we mean by the word tissue respiration, whereas in Leonardo's time pulmonary respiration was intended; he was therefore perfectly right in denying that the embryo breathed, as certain anatomists before him had asserted.

His only reference to the soul runs thus: "Nature places in the bodies of animals the soul, the composer of the body, i.e. the soul of the mother, which first composes, in the womb, the shape of man and in due time awakens the soul which shall be the inhabitant thereof, which first remains asleep and under the tutelage of the soul of the mother which through the umbilical vein nourishes and vivifies

PLATE IV

vf Hi^l

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A PAGE FROM LEONARDO DA VINCI'S AxNATOMICAL NOTEBOOKS {QUADERNI D' ANATOMIA), ca. 1490 a.d.

SECT. 2] TO THE RENAISSANCE 109

it". This is not very revolutionary. But Leonardo was the first embryologist to make any quantitative observations on embryonic growth ; he defined, for instance, the length of a full-grown embryo as one braccio and the adult as three times that. "The child", he says, "grows daily far more when in the body of its mother than when it is outside of the body and this teaches us why in the first year when it finds itself outside the body of the mother, or, rather, in the first 9 months, it does not double the size of the 9 months when it found itself within the mother's body. Nor in 18 months has it doubled the size it was 9 months after it was born, and thus in every 9 months diminishing the quantity of such increase till it has come to its greatest height." Here Leonardo touches on one of the most modern quantitative aspects of embryology, and one almost expects to see him exemplify his words with a graph until one remembers with a shock that he lived two centuries before Descartes and five before Minot. His numerical data may also have included figures about the relative sizes of the parts, and the germ of the line of research so successfully pursued by Scammon in our own times may be found in the note "The liver is relatively much larger in the foetus than in the grown man". Other quantitative notes concern the length of the embryonic intestines as in the laconic "20 braccia of bowels" and the statement that "the length of the umbilical cord always equals the length of the foetal body in man though not in animals".^

He said little about heredity, but in one place he mentions a case of sexual intercourse between an Italian woman and an Ethiopian, the outcome of which assured him that blackness was not due to the direct action of the sun and that the "seed of the female was as potent as that of the male in generation". Finally, the best instance of the wideness of his thought appears in the note, "All seeds have an umbilical cord which breaks when the seed is mature. And similarly they have matrix and secundines as the herbs and all the seeds which grow in shells show". We have met this idea before in Hippocrates of Cos, and we shall find it again in Nathaniel Highmore.

It is no coincidence that pictures of weights and cogs and pulleys stand side by side in Leonardo's notes with anatomical drawings of the embryo. As Hopstock says, "Leonardo arrives at the conclusion that there is but one natural law which governs the world. Necessity.

^ Leonardo would have enjoyed Fog's statistical study of 8000 umbUical cords (1930).

no EMBRYOLOGY FROM GALEN [pt. ii

Necessity is Nature's master and guardian, it is Necessity that makes the eternal laws". If Aristotle is the father of embryology regarded as a branch of natural history, Leonardo is the father of embryology regarded as an exact science.

2-6. The Sixteenth Century: the Macro- Iconographers

After such a man, the writings of his contemporaries, such as the mythical Johannes de Ketham, Alessandro Achillini and Gabriele de Gerbi, appear beyond description inferior. De Ketham's embryology has been described by Ferckel. De Gerbi included in his Liber Anatomiae corporis humani et singulorum membrorum illius a section entitled De Generatione Embrjonis, but there is nothing to be said about it except that it is a verbose compilation of the views of Aristotle and Galen taken from Avicenna. The work of Nolanus in 1532 presents certain points of interest, but it is of little importance. Petrus Crescentius in his work on husbandry of 1548 mentions artificial incubation in ovens, but rather as a lost art. About this time also Hieronymus Dandinus Cesenas, a Jesuit, wrote a treatise on Galen's division of organs into white and red, those proceeding from the semen and those proceeding from the blood: it is cited by Aldrovandus, but I have not been able to consult it.

The most remarkable feature of the first half of the century was the encyclopaedic group of zoologists which now arose. Thus Belon and Rondelet, whose well-illustrated catalogues of animals were appearing from 1550 onwards, did a good service to comparative embryology in figuring the ovoviviparous selachians and viviparous cetacea. Gesner belongs to this group. All of them reproduce thin versions of Aristotle, when they speak of generation as such, and this is what differentiates them from Ulysses Aldrovandus, of whom I shall speak presently. Figs. 3 and 4 show Rondelet's pictures of a viviparous dolphin and an ovoviviparous selachian.

But the end of the twilight period was now at hand, for, within thirty years after the death of de Gerbi in 1505, four great embryologists were born as well as the greatest anatomist of any age, Andreas Vesalius (1514), of whom I shall say no more, for he had no opportunities for dissecting human embryos, and took hardly any interest in foetal development. But in 1522 Ulysses Aldrovandus was born, and in the following year Gabriel Fallopius, in 1530 Julius Caesar Arantius and in 1534 Volcher Goiter. Only three

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III

more years bring us to the birth of Andreas Laurentius and of Hieronymus Fabricius ab Aquapendente, the teacher of William Harvey.

The senior member of this group, Ulysses Aldrovandus, was the first biologist since Aristotle to open the eggs of hens regularly during

Fig. 3. A (viviparous) dolphin: from Rondelet's De piscibus marinis of 1554.

their incubation period, and to describe in detail the appearances which he found there. In his Ornithologia, published at Bonn in 1597, he set out to describe all the known kinds of birds, discussing in turn not only their zoological and physiological characteristics, but

Fig. 4. An (ovoviviparous) shark: from Rondelet's De piscibus marints of 1554.

also their significance as presages and for augury, their mystical meaning, their use as allegories and for eating, and finally all the legends respecting them, Generositas, Temperantia, Liberalitas, aquilae one finds. Beginning with the eagle, he proceeds to the vulture, the owl, the bat (the only viviparous bird!), the ostrich, the harpy (!),

112 EMBRYOLOGY FROM GALEN [pt. ii

the parrot, the crow, and so to the fowl. Side by side with a reference to the famous poem of Prudentius {Multi sunt Presbyteri, translated by J. M. Neale) about the steeple-cock, we find an excellent account of the generation of the chick in the c:gg. The book is illustrated sumptuously, but unfortunately there is only one picture of embryological interest, namely, a chick in the act of hatching.

In Aldrovandus' embryology there is much discussion of Aristotle and Galen, but traces of an independent spirit abound. Pliny's view that the heart was formed in the white is "exploded", and Aldrovandus says that it is formed on the yolk-membrane. He refutes the opinion of Galen also that the liver is first formed, in connection with which he says, "In order that I might bring to an end this controversy between the philosophers and the physicians I followed with the keenest curiosity and diligence the incubation of 22 hen's eggs, opening one each day; thus I found Aristotle's doctrine to be the truest. And because apart from the fact that these matters are most worthy of being looked into they provide also the greatest pleasure and entertainment I have thought it well to describe them as clearly and briefly as possible".

Aldrovandus also contradicts Albertus, and propounds a new theory, namely, that the spiritualia (the organs in the thorax) are formed from the seed of the cock {ex maris semine sunt). This seed he aflfirms to be present in the egg, and he identifies it with the chalazae, thus anticipating Fabricius ab Aquapendente, but not going quite so far, and explicitly opposing Gaza, who had said not long before that the chalazae were simply congealed water. Aldrovandus' admiration for Aristotle is extreme, and, though he differs from him about the chalazae, he defends the Aristotelian opinion that the chick was made from the white but nourished from the yolk. His argument for this is new, however; it is that, during incubation, the latter liquefies but the former hardens; now in all digestion liquefaction takes place, and in all growth hardening, therefore, etc. This argument is a great deal more cogent than most of those which were current between 1550 and 1650. He goes out of his way to castigate Albertus for saying that the yolk moves up into the sharp point of the egg, for experience assures him that it does not, "as I have observed by cutting open an egg after one day's incubation". A striking instance of his powers of observation was his description of the "egg-tooth" of embryonic birds, a discovery made anew in

SECT. 2] TO THE RENAISSANCE 113

the nineteenth century by Yarrell and Rose. The chick was perfect in form, according to him, on the tenth day.

The peculiarity of Aldrovandus lies in the fact that he incorporated so many elements into one book, and was able to produce a collection of chapters in which good scientific observation sat at the closest quarters with literary allusion and semi-theological homily. So wellproportioned a mixture as the Ornithologia is not often found. As a final instance three consecutive paragraphs may be mentioned, in the first of which he discusses Plutarch's arid problem about the priority of egg or hen, next he makes some very reasonable remarks about teratology, suggesting that monsters come from yolks which are physico-chemically abnormal in some way, while in the third he expresses strong scepticism concerning the tale that the basilisk is sometimes hatched out from a hen's egg — Ego ne jurantibus quidem crediderim'\ he says. This last notion is found in the fourteenthcentury poem of Prudentius alluded to above, and appears again in the Miscellaneous Exercitations of Caspar Bartholinus the younger, whose second chapter is devoted to showing "That the basilisk hatcheth not from the egg of the hen", a conclusion which has been amply confirmed in the light of subsequent experience. Bartholinus gives a bibliography of this curious legend.

Aldrovandus and his disciple Volcher Coiter the Frisian, as he described himself, were alike in not suffering from the prevailing vice of the age, verbosity. Colter's Externarum et Internarum principalium humajii corporis partium tabulae et exercitationes, which appeared at Nuremberg in 1573 — a beautifully printed book — contained a brief section entitled De ovorum gallinaceorum generationis primo exordio progressuque et pulli gallinacei creationis ordine. His Latin style betrays his German origin, for the constructions are very Teutonic, although the meaning is always perfectly clear. Coiter says, "In the year 1564 in the month of May at Bologna, being instigated by that excellent professor of philosophy outstanding in varied sciences and arts. Doctor Ulysses Aldrovandus, and by other doctors and students, I ordered 2 broody fowls to be brought and under each of them I caused 23 eggs to be placed, and in the company of these persons I opened one every day so that we could see firstly the origin of the veins and secondly what organ is first formed in the animal". What follows is practically a repetition of the facts available in Aristotle, but described with much greater clearness than either

114 EMBRYOLOGY FROM GALEN [pt. ii

Aristotle or Aldrovandus had been able to bring to the matter. On the third day, he saw the globulus sanguineus which in vitello manifeste pulsabat, and so solved his first problem. He decides that the first organ to be formed is the heart, and quotes Lactantius' experiments. He explains the large size of the eye as due to the fact that the most complicated part of the body needs the longest time for its manufacture. He correctly describes the various membranes, and the faeces subviridies in the intestines at hatching. Once he contradicts Aristotle, maintaining that on the tenth day the body as a whole is larger than the head, and once he contradicts Albertus, denying that any yolk can be found in the stomach at hatching. He concludes his tractate by a succinct and clear account of the opinions of Aristotle and Hippocrates about embryonic development. His importance is that he drew the attention of scientific thinkers to the problems arising out of the hen's egg, and assisted in the formation of that iconographic phase in embryology which was later to find its climax in the plates of Fabricius, and its close in Harvey's Exercitations.

Gabriel Fallopius, who belongs to this time, must be mentioned as the discoverer of the organs which bear his name, but his services to embryology were only indirect. A. Benedictus, who was now growing old, and Caesar Cremonius, who was still young, may be remembered as the principal upholders of pure Aristotelianism at this time. Realdus Columbus also wrote on the embryo. B. Telesius, in his De Natura Rerum of 1565, studied the hen's egg and suggested that the parts of animals were formed by the pressure of the uterus acting as a mould: he was thus the middle term between Galen and Buffon.

Julius Caesar Arantius has already been referred to. His De Humano Foetu was an important book, but, though it appeared in 1564, just at the time when the macro-iconographic school was at its height, it dealt with a rather different field and cannot be considered as a constituent of that group. He begins by relating that a pregnant woman was killed by an accident at Bologna a couple of years before, so that he had an opportunity of testing whether the opinions about certain points in generation, which he had formed on a priori grounds during the previous fifteen years, were true or not. In the first place, he found on dissection that the placenta was not cotyledonous, and he spoke thus of its formation: "Blood flows

SECT. 2] TO THE RENAISSANCE 115

out from the spongy substance of the uterus and this blood growing in bulk forms a soft and fungus-like mass of flesh, rather like the substance of the spleen, which adheres to the surface of the uterus and transmits to the foetus in proportion as it grows the nourishment for it which reaches the uterus in the form of blood and spirits". Then, going on to discuss the functions of the jecor uterinae, as he calls the placenta (with what justice may be seen by turning to Section 8-5), he devotes a chapter to De vasorum umbilicalium origine, and, contradicting Hippocrates, Galen, Erasistratus, and Aetius, says that the maternal and foetal blood-vessels do not pass into each other by a free passage. "This is repugnant to sense", he writes, "and as may be seen by ocular inspection, these vessels do not reach the inner membrane of the uterus, for the substance of the placenta is placed between their ramifications and the proper substance of the womb." He was thus the first to maintain that the maternal and foetal circulations are separate, but he naturally did not, and could not, speak of circulations, since he lived before Harvey. Nor could he have satisfactorily proved his point with the means then at his command, and, as we shall see, it was to take another century before the proof was given. Apart from this valuable contribution to embryology, Arantius gave some admirable anatomical descriptions of the foetal membranes.

Hieronymus Fabricius ab Aquapendente, the pupil of Fallopius, has always been given an important place in the history of embryology by those who have written on him. As one comes upon him in the process of tracing out that history itself, however, he does not take such a high place. With the statement, for instance, that "Fabricius carried embryology far beyond where Goiter had left it and elevated it at one bound into an independent science" I find that I cannot agree. Embryologists who called themselves that and nothing else did not appear till the end of the eighteenth century, and it seems to me doubtful whether the anatomical advances in embryology made by Fabricius are not counterbalanced by the erroneous theories which he invented at the same time. His De Formatione Ovi et Pulli pennatorum, and his De Formato Foetu of 1604 show far more scholasticism and mere argumentativeness than is to be found in Goiter, and are remarkable for their bulk. Fabricius seems to have had a genius for exsuccous and formal discussions. He spends much time, for example, in taking up the problem of whether

8-2

ii6 EMBRYOLOGY FROM GALEN [pt. ii

the yolk of the hen's egg is more earthy than the white, and looking at it from all possible angles. He disagrees at last with Aristotle and decides that the white is the more earthy. Bones, he says, are white, but also very earthy. The albumen is colder, stickier, and heavier than the yolk, "sequitur, terrestrius esse^\ And this particular example is the more flagrant because the actual matter of it is fundamentally physico-chemical. But, in addition, he introduced a number of grave errors and misleading theories into embryology, so that subsequently Harvey had to spend a large part of his time refuting them. Fabricius was, indeed, a good comparative anatomist, and it is upon that ground that he deserves praise: his plates, some of which are reproduced herewith, were far better than anything before and for a long time afterwards. He dissected embryos of man, rabbit, guinea-pig, mouse, dog, cat, sheep, pig, horse, ox, goat, deer, dogfish, and viper, a comparative study which had certainly never been made previously.

In his first tractate he begins by dealing with a question not unlike that of how the sardines got into the tin, i.e. how the contents got into the hard-shelled egg. He rejects Aristotle's idea that the egg is formed in the oviduct by a kind of umbilicus, and ascribes its growth there to transudation through the blood-vessels. He marks a definite advance upon Aristotle when he says that silkworms and other insects are born into their larval state from an egg, though he still terms the chrysalis an egg, and therefore holds that they are generated twice. Then follows his discussion of what part of the egg the chick comes from. The chalazae, he says, are not semen, for the semen is not present at all in the fertilised egg. His argument sounds peculiar when he says that both the white and yolk of the egg are the food of the embryo, for neither of them is absent at the end of incubation, therefore neither of them is its material. Hippocrates had said, "^ex luteo gigni, ex albo nutriri; Aristotle had said, "ex albo fieri, ex luteo nutrirV\ The latter was the view generally held in the sixteenth century, as may be gathered from Ambrosius Calepinus' dictionary, Scaliger's Commentary on Aristotle, and the treatise on the soul of Johannes Grammaticus.

Fabricius now says both nourish, neither makes. This distinction between food and building-materials seems to us unnecessary, but it had a great influence on later thought. Fabricius devotes much time to proving, as he thinks, that albumen and white are of the

PLATE V

ILLUSTRATIONS FROM FABRICIUS AB AQUAPENDENTE'S DE FORMATIONE OVI ET PULLI, 1604

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same nature, and adduces the fact that "in cooking the white hardens first, whether the egg be boiled or poached, but the yolk hardens also if the heat is more", comparing the heat of the kitchen to the innate heat of the chick. "But you will say", he goes on, "if the albumen and the yolk are the food of the chick in the egg, what then must we decide the material of the chick to be, since we have already said that the semen is not present in the eggs. You will find this material from an enumeration of the parts of the egg — there remains only the shell, the two membranes, and the chalazae; — nobody will assign the membranes or the shell as the material of the chick, therefore the chalazae alone are the fitting substance out of which it can be made." Having discovered this truth by the infallible processes of logic, Fabricius brings all kinds of arguments forward to support it; he adduces the three nodes in the chalazae as the precursors of brain, heart, and liver; tadpoles, he thinks, resemble significantly the chalazae, being "armless legless spines". The eyes are transparent, so are the chalazae, therefore the latter must give rise to the former. The liver is formed as soon as the heart but is practically invisible as it does not palpitate. One of his most gratuitous errors was the suggestion, now newly introduced, that the heart (and other organs) of the foetus has no proper function, no munus publicum, but beats only in order to preserve its own life. Then there is a considerable section called De Ovorum utilitatibus, which almost does for the hen's egg what Galen's De Usu Partium did for the human body, and in which such questions as Why the shell is hard and porous? and Why there are any membranes in the egg? are taken up and answered with an elaborate display of common sense. The influence of Galen is perceptible in a passage about a liver-like substance being formed if blood is freshly shed into hot water, in the usual terminology of formative faculties, and in the division of fleshes into white and red, though the former is not specifically derived fi"om the semen nor the latter from the menstrual blood. The human placenta is described as cotyledonous, and needless confusion is caused by the doctrine that the "liquors, humours, or rather, excrements, around the foetus, are two in number, sweat and urine, the former in the amnios, the latter in the allantois". But the drawings and illustrations of Fabricius' work are beautiful and accurate — so much so, indeed, that it will always remain a mystery how the man who figured the early stages of the

ii8 FROM GALEN TO THE RENAISSANCE [pt. ii

development of the chick as Fabricius did, showing the bloodvessels radiating from the minute heart, should have been able to propound the thesis that the chalazae were the material of the embryo.

The other biologist to whom Harvey was most indebted was Andreas Laurentius of Montpellier, whose Historia Anatomica (printed with his other works in 1628) contained a whole book (viii) devoted to embryology, but which presents us with nothing except a commentary on Hippocrates and Aristotle. The only evidences of life are furnished by two polemics, one of which was against Simon Petreus of Paris, who had propounded some new views about the foetal circulation. Laurentius gave also a table showing the changes which occur in the heart and lungs of the foetus at birth.

It was about this time that the embryological observations of that many-sided genius, Hieronymus Cardanus, began to attract attention. His main thesis was that the limbs of the embryo were alone derived from the yolk, while the rest of the body came from the white. This was a well-meant attempt to mediate between the two traditions headed respectively by Aristotle and Hippocrates, but the arguments in support of it were not even remarkable for ingenuity. Constantinus Varolius treated of the formation of the embryo in a book which appeared in 1591, but very inadequately. He had certainly opened hen's eggs, and describes the fourth-day embryo as forma minimi faseoli. But nearly every one of his marginal headings begins with the word Cur, and this tells its own story, for the didactic style rarely hides genuine works of research. Johannes Fernelius, a rather earlier worker, in his De Hominis Procreatione followed Aristotle and Galen in nearly all particulars, and made no real contribution to embryology. On its practical obstetrical side, the sixteenth century produced some remarkable compilations of ancient gynaecological writings. The first of these was that of Caspar Wolf, which was published at Ziirich in 1566, and, after having been enlarged by Caspar Bauhin in 1586, subsequently formed the backbone of the most important and famous one, namely, that of Israel Spach (Strassburg, 1597). Although these composite textbooks represented no real embryological progress, they yet showed that great interest in development was alive, an interest which, though doubtless utilitarian in its origin, could hardly fail to lead to advances of a theoretical nature. (See Fig. 5.)

Fig. 5. Illustration from W. H. Ryff's Anatomia of 1541.

120 FROM GALEN TO THE RENAISSANCE [pt. ii

The obstetrical literature intended for midwives is also of great interest. It was about this time that the first popular guides to their subject began to appear, founded not upon mere superstition and the remnants of ancient knowledge derived in roundabout fashion through Syriac and Arabic, but either upon a careful study of Galen and Aristotle, or upon the results of dissections and living speculation. The principal representative of the former class is that of Jacob Rueff, which appeared in 1554 and was called De Conceptu et Generatione Hominis. Although written in Latin, it was evidently a popular work, for the illustrations given in it are such as would naturally be incorporated in such a book. It is the illustrations which give it its importance, and I reproduce them in Fig. 6. I think they show very clearly what the general ideas were at this period about mammalian embryology, and thus afford us a precious insight into what was in the minds of such writers as Riolanus the elder, Mercurialis, Saxonia, Rondeletius, Venusti, Holler and Vallesius. There are many points which their expositions of foetal growth and development leave vague, and without Rueff it would be difficult or impossible to picture in what manner they imagined it to go on. Rueff 's text follows Galen and Aristotle with fidelity, as does theirs — with the exception of a few minor ideas not quite consonant with this.

In (a) of Fig. 6 Rueff portrays the mixture of semen and menstrual blood in the womb, or, as he loosely refers to it, of both seeds, coagulating into a pink egg-shaped mass surrounded with a fine pellicle, {b) shows the same mass in the uterus and wrapped round with the three coats, amnion, chorion, and allantois — a lamentable but interesting misrepresentation of the facts. Then in {c) it is shown that upon the surface of the yolk-like mass of semen and blood appear "three tiny white points not unlike coagulated milk", these being the first origins of the liver, the heart, and the brain. Next {d) shows the first blood-vessels springing from the heart, four in number, and distributing themselves over the surface of the mass. It is plain that Rueff must either have opened hen's eggs himself and seen the early growth of the blastoderm or have been told about it by some observer such as Goiter or Aldrovandus. He could not have copied his pseudo-blastoderm pictures from their works, for in 1554 none of them had appeared, and, as far as I know, there were no similar illustrations in existence at that time.

After this point the pictures grow even more fanciful, and, in (^),

Fig. 6. Illustrations from Jacob Rueff's De Conceptu et Generatione Hominis of 1554 (arranged by Singer) showing the Aristotelian coagulum of blood and seed in the uterus.

122 EMBRYOLOGY FROM GALEN [pt. ii

the first outline of the cranium is seen taking shape in the upper part of the "egg". In (/) the blood-vessels have suddenly assumed the outline of a human being, and in (g) the finished product is seen. Rueff gives what seems to be a mnemonic in hexameters :

iniectum semen, sex primis certe diebus est quasi lac : reliquisque novem sit sanguis ; at inde consolidat duodena dies; bis nona deinceps effigiat; tempusque sequens producit ad ortum talis enim praedicto tempore figura consit.

Rueff gives some excellent diagrams of the foetus in utero with relation to the rest of the body, and the various positions which are familiar to obstetricians. His teratology is less happy, for he attributes the production of monsters to the direct action of God, though he does venture upon a few speculations concerning "corrupt seed". But his principal significance for this history is that, in his picture of the yolk-like mass of mixed semen and blood and the pseudoblastoderm upon it, he throws a good light on the conceptions of the time.

Rueff 's book was subsequently translated into English, and had many editions as The Expert Midwife.

The principal representative of the second class of popular books of this period is that of Euch. Rhodion, or Rosslein, which was translated into English, and published as his own work, by Thomas Raynold, " physition ", in 1 545, under the title of The Byrth ofMankynde otherwyse named The Woman" s Book (cf. d'Arcy Power). It was the first book in the English language to contain copper engravings. They were variants of the traditional Soranus-Moschion figures. The Rosslein-Raynold book pays less attention to Galenic theory than does that of Rueff, and includes much better drawings of actual dissections. Another famous obstetrical book was that of Scipio Mercurius; for further information here see Spencer.

The minor embryologists of the sixteenth century included among them Ambroise Pare, the founder of modern surgery. His teaching on generation involved nothing original, but it seems to have been Galenism interpreted by a very intelligent and well-balanced, unspeculative mind. The three-bubble theory appears in him very clearly; thus, we read, "The seed boileth and fermenteth in the womb, and swelleth into three bubbles or bladders" — the brain, the liver, and the heart. Fare's illustrations are copied wholesale from Vesalius and Rueff, without acknowledgment. The last author to take the three-bubble theory quite seriously was A. Deusingius, who wrote in 1665, after Harvey. Others who deserve a mention, but no more, were Severinus Pinaeus, L. Bonaciolus and Felix Platter. None of them made any advance, and the illustrations of the former's De Virginitatibus notis graviditate et partu were almost ludicrous.

Hieronymus Capivaccius, F. Licetus, J. Costaeus and V. Cardelinus, who wrote in 1608, were the last true supporters of the ancient theories, such as that the male embryo was twice as hot and developed twice as quickly as the female.

SECTION 3

EMBRYOLOGY IN THE SEVENTEENTH AND EIGHTEENTH CENTURIES

3-1. The Opening Years of the Seventeenth Century

iEmilius Parisanus, a Venetian, now dealt with embryology in the fourth, fifth, and sixth books of his De Subtilitate. They were entitled as follows: "(4) Of the principles and first instruments of the soul and of innate heat, (5) Of the material of the embryo and of its efficient cause, (6) Of the part of the animal body which is first made, and of the mode and order of procreation". Parisanus is very wordy, but he has the merit of giving many quotations from the lesser known authors, and providing (as a rule) accurate references. He held that the spleen was formed in all development before the heart, and that neither heart nor lungs moved in utero. With regard to the controversy over the function of white and yolk, he was in agreement with Fabricius, but he firmly opposed the view that the chalazae were the first material of the chick, as much, it must be confessed, because of the opinion of Aristotle as from his own observation. Nevertheless, his own observations were noteworthy, and he will always be remembered for his discovery of the fact that the heart of the chick begins to beat some time before any red blood appears in it.

Parisanus was the last of the macro-iconographic group of sixteenthcentury embryologists. Their labours established the fundamental morphological facts about the developing embryo; the first great step in the history of embryology. But there were numerous errors in their work, and Harvey, who occupies a terminal or boundary position, was destined to correct them. He marks the transition from the static to the dynamic conception of embryology, from the study of the embryo as a changing succession of shapes, to the study of it as a causally governed organisation of an initial physical complexity, in a word, from Goiter and Fabricius to Descartes and Mayow. Iconography did not die : on the contrary, the improvement of the microscope gave it new life, and the micro-iconographic school emerged with its principal glory, Malpighi.

SECT. 3] THE SEVENTEENTH CENTURY 125

Harvey sums up the work of the macro-iconographic period in the historical introduction contained in Ex. xiv of his De Generatione Animalium. I give it in full in the beautiful seventeenth century English into which Harvey's Latin was translated under his guidance by the physician, Martin Llewellyn,

"We have already discovered the Formation, and Generation of the Egge; it remains that we now deliver our Observations, concerning the Procreation of the Chicken out of the Egge. An undertaking equally difficult, usefull, and pleasant as the former. For Nature's Rudiments and Attempts are involved in obscurity and deep night, and so perplext with subtilties, that they delude the most piercing wit, as well as the sharpest eye. Nor can we easier discover the secret recesses, and dark principles of Generation than the method of the fabrick and composure of the whole world. In this reciprocal interchange of Generation and Corruption consists the ^Eternity and Duration of mortal creatures. And as the Rising and Setting of the Sun, doth by continued revolutions complete and perfect Time; so doth the alternative vicissitude of Individuums, by a constant repetition of the same species, perpetuate the continuance of fading things.

"Those Authors which have delivered any thing touching this subject, do for the most part tread a several path, for having their Judgements prepossessed with their own private opinions, they proceed to erect and fashion principles proportionable to them.

"Aristotle of old, and Hieronymus Fabricius of late, have written so accurately concerning the Formation and Generation of the Foetus out of the Egge, that they seem to have left little to the industry of Posterity, And yet Ulysses Aldrovandus hath undertaken the description of the Pullulation or Formation of the chicken out of the Egge, out of his own Observations ; wherein he seems rather to have directed and guided his thoughts by the Authority of Aristotle, than by his own experience.

"For Volcherus Goiter, living at Bononia at the same time did by the advice of the said Aldrovandus (whom he calls Tutor) dayly employ himself in the opening of Egges sat upon by the Hen, and hath discovered many things truer than Aldrovandus himself, of which he also could not be ignorant. Likewise iEmilius Parisanus (a Venetian Doctor) despising other mens opinions hath fancied A new procreation of the Chicken out of the Egge.

126 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

"But because somethings, (according to our experience) and those of great moment and consequence, are much otherwise than hath been yet delivered, I shall declare to you what dayly progress is made in the egge, and what parts are altered, especially about the first dayes of Incubation; at which time all things are most intricate, confused, and hard to observe, and about which authors do chiefly stickle for their own observations, which they accomodate rather to their own preconceived perswasions (which they have entertained concerning the Material and Efficient Causes of the generation of Animals) than to truth herself.

"Aldrovandus, partaking of the same error with Aristotle, saith (which none but a blind man can subscribe to) that the Yolk doth in the first dayes, arise to the Acute Angle of the Egge ; and thinks the Grandines to be the Seed of the Cock; and that the Pullus is framed out of them, but nourished as well by the yolk as the white ; which is clean contrary to Aristotle's opinion, who conceived the Grandines to conduce nothing to the fecundity of the egge. Volcherus Goiter delivers truer things, and more consonant to Autopsie, yet his three Globuli are meer fables. Nor did he rightly consider the principle from whence the Foetus is derived in the Egg. Hieronymus Fabricius indeed contends, that the Grandines are not the seed of the cock, and yet he will have the body of the Chicken to be framed out of them (as out of its first matter) being made fruitful by the seed of the cock. He likewise saw the Original of the Chicken in the Egge; namely the Macula, or Cicatricula annexed to the membrane of the Yolke but conceived it to be onely a Relique of the stalk broken off, and an in-firmity of blemish onely of the Egge, and not a principle part of it. Parisanus hath plentifully confuted Fabricius his opinion concerning the Chalazae or Grandines, and yet himself is evidently at a loss in some certaine circles and points of the Principle parts of the Foetus (namely the Liver and the Heart) and seems to have observed a Principium or first Principle of the Foetus, but not to have known which it was, in that he saith, that the Punctum Album in the Middle of the Circles is the Cocks Seed out of which the Chicken is made. So that it comes to pass that while each of them desire to reduce the manner of the Formation of the Chicken out of the Egge to their own opinions they are all wide from the mark."

Before discussing how Harvey put them right, however, there are a number of other matters to be mentioned. Parisanus' work was

SECT. 3] AND EIGHTEENTH CENTURIES 127

published in 1623, and twenty-five years were to elapse before Harvey's Exercitations were to be put before the learned world by George Ent. In that time not a few events of importance for the history of embryology took place.

It will be convenient to speak first of Adrianus Spigelius, whose De Formato Foetu appeared in 1 63 1 . In this book the plates of the gravid uterus which had been prepared some years before for Julius Casserius were now published. They had more influence than Spigelius' text, perhaps, in contributing to the permanent fame of his book.

He gives for the most part straightforward anatomical descriptions, but he returns to the notion of a cotyledonous placenta in man, and he combats Arantius' opinions about the placenta. Arantius had said that the function of the jecor uterinae was to purify the bloodsupply to the foetus, a thoroughly modern idea, but Spigelius opposes this on two grounds, firstly, because the foetus has its own organs for purifying blood, and secondly, because, if Arantius was right, the placenta would always be as red as blood, but this is not the case in such animals as the sheep. Spigelius himself thought that the placenta was for the purpose of preventing severe loss of blood at birth, as would be the case if the embryo was joined to the mother with only one big vessel and not a great many little ones.

However, Spigelius upholds the view, taken by Rufus of Ephesus and by Vesalius, that the allantois contains the foetal urine, which has to be separated from the amniotic liquid in which the embryo is, because it would corrode the embryonic skin [ne cuti tenellae aliquod damnum urinae acrimonia inferret). This passage is interesting, as showing biochemical rudiments. The first discussion of the vernix caseosa, or sordes, as he calls it, appears in Spigelius, who, however, hazards no guess as to its nature. He is happy in his refutation of Laurentius, who had affirmed that the foetal heart did not beat in utero, and he shows some advance on all previous writers save Arantius in declaring that the umbilical vessels take vital spirits away from the foetal heart, not exclusively to it. He gave, moreover, the first denial of the presence of a nerve in the umbilical cord, and also made the first observation of the occurrence of milk in foetal breasts at birth (for the endocrinological explanation of this see Section 15). Finally, he abolished at last the notion that the meconium in the foetal intestines argued eating in utero on the part of the embryo.

128 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

Riolanus the younger, the correspondent and almost exactly the contemporary of Harvey, was Professor in Paris and published his Anthropographia in 1618. As he was a keen advocate of the ancient views, his section on the formation of the foetus has little importance. Yet it contains the first known instance of the use of the lens in embryology, the germ of that powerful instrument which was to lead in due course to so many discoveries. "In aborted embryos", said Riolanus, "the structure is damaged and can often not be properly seen, even when you make use of lenses [conspicilid] which make objects so much bigger and more complicated than they ordinarily seem."

The De Formatrice Foetus of Thomas Fienus, Professor at Louvain and a friend of Gassendi, published in 1620, is interesting because it is the middle term between Aristotle and Driesch. As the titlepage informs us, he sets out to demonstrate that the rational soul is infused into the human embryo on the third day after conception. This by itself would not be very attractive, but the most cursory inspection shows that Fienus' interests were not at all theological. He divides the book up into seven main questions, (i) What is the efficient cause of embryogeny? He concludes that it is neither God, nor Intelligence, nor anima mundi (influence of Neo-platonism here as on Galileo). (2) Is it in the uterus or in the seed? In the latter, says Fienus, adding a list of authorities who agree with this view — Haly-Abbas, Gaietanus, Zonzinas, Turisanus, Fernelius, Vallesius, Peramatus, Saxonia, Carrerius, Zegarra, Mercurialis, Massaria, and Archangelus, ^' solus Fabio Pacio utero imprudenter adscribit (!). (3) Is it heat? Fienus nearly decided that it was, and, if he had done so, would have shown a modern mind, but no, he gave his opinion against it, saying, "the process (of development) is so divine and wonderful that it would be ridiculous to ascribe it to heat, a mere naked and simple quality". After weighing various other alternatives in questions (4), (5) and (6), he asks whether it is ^'^ anima seminis post conceptum adveniens (7), and concludes that it is. It is here that he becomes really interesting, for he quotes with approval certain writers, e.g. Alexander Aphrodisias [Organicum corpus esse organicum ab anima et anima praeexistere organizationi) , Themistius {Anima fabricatur architecturaque sibi domicilium et accommodatum instrumentum) and Marsilio Ficino in his commentary on Plato's Timaeus [Priusquam adultum sit corpus, anima tota in illius fabrica occupatur), and

SECT. 3] AND EIGHTEENTH CENTURIES 129

then maintains with them that the soul is the principle which organises the body from within, arranging an organ for each of its faculties and preparing a residence for itself, not merely allowing itself to be breathed into a being which has already organised itself "The conformation of the foetus is a vital, not a natural, action", he says. He develops this idea in the remainder of the book; according to him, the seed first coagulates the menstrual blood into an amorphous cake, taking three days to do so, after which, the rational (not vegetative or sensitive) soul (entelechy), which has entered the uterus with the seed, finding a suitable mass of shapeless material, enters into it and begins to give it a shape. Fienus was attacked by several writers, and published a defence of his views.

Later writers on the same subject included Fidelis, Teichmeyer, Albertus, de Reies, Torreblanca and de Mendoza. The Spanish influence here is perhaps significant. Hieronymus Florentinus, who adopted the same standpoint as Fienus in 1658 was forced to recant it.

In 1625 Joseph de Aromatari, a Venetian, included in his epistle on plants the first definite statement of the preformationist theory since Seneca, but he did not develop the idea. He had noted that in bulbs and some seeds the rudiments of many parts of the adult plant can be seen even without glass or microscope, and this led him to suggest that probably in all animals as well as plants a similar thing was true. "And as for the eggs of fowls", he said, "I think the embryo is already roughly sketched out in the egg before being formed at all by the hen [quod attinet ad ova gallinarum, existimamus quidem pullum in ovo delineatum esse, antequam formatur a gallina]. This suggestion did not begin to bear its malignant fruits till the time of Swammerdam and Malpighi.

Johannes Sinibaldi's Geneanthropia might be mentioned as belonging to this time. It was a compilation of facts relating to the generation of man, but it expressly excluded from its field any discussion of the embryo. It is no more important for our subject than the queer Ovi Encomium of Erycius Puteanus, another of Gassendi's friends, which has already been referred to (p. 8).

3-2. Kenelm Digby and Nathaniel Highmore

Much more significant was the controversy between Sir Kenelm Digby and Nathaniel Highmore. In 1644, Sir Kenelm, whose in

I30 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

triguing personality will be sufficiently familiar to anyone even slightly acquainted with seventeenth-century England, and whose biographic details may be found in John Aubrey, published a work with the following title: Two treatises, in the one of which, The Nature of Bodies, in the other, The Nature of Man's Soule is looked into, in way of discovery of the Immortality of Reasonable Soules. It was inscribed in a charming dedication to his son, and consisted, in brief, of a survey of the whole realms of metaphysics, physics, and biology from a very individual point of view.

One of Sir Kenelm's principal objects in writing was apparently to attack the old terminology of " qualities " in physics and "faculties " in biology. To say, as contemporary reasoning did, that bodies were red or blue because they possessed a quality of redness or blueness which caused them to appear red or blue to us, or again, to say that the heart beat because it was informed by a sphygmic faculty, or, to take the famous example, that opium sent people to sleep because it contained in it a dormitive virtue, appeared mere nonsense and word-spinning to Digby, "the last refuge of ignorant men, who not knowing what to say, and yet presuming to say something, do often fall upon such expressions".

Digby, like Galileo and Hobbes, wished to explain all phenomena by reference to two "virtues" only, those of rarity and density, "working by means oflocall Motion". Chapters twenty-three, twentyfour, and twenty-five contain his opinions and experiments in embryology. He begins by opening the question of epigenesis or preformation, practically for the first time since Albert the Great. "Our main question shall be", he says, "whether they be framed entirely at once, or successively, one part after another? And if this latter way, which part first?" He declares for epigenesis, but after a manner of his own, refuting "the opinion of those who hold that everything containeth formally all things". "Why should not the parts be made in generation", he asks, "of a matter like to that which maketh them in nutrition? If they be augmented by one kind of juyce that after severall changes turneth at the length into flesh and bone; and into every sort of mixed body or similar part whereof the sensitive creature is compounded, and that joyneth itself to what it findeth there already made, why should not the same juyce with the same progresse of heat and moisture, and other due temperaments, be converted at the first into flesh and bone though none be formerly there to joyn

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it self unto?" He gives a clearly deterministic account of development. "Take a bean, or any other seed and put it in the earth, and let water fall upon it; can it then choose but that the bean must swell? The bean swelling, can it choose but break the skin? The skin broken, can it choose (by reason of the heat that is in it) but push out more matter, and do that action which we may call germinating? Can these germs choose but pierce the earth in small strings, as they are able to make their way? . . . Thus by drawing the thrid carefully along through your fingers, and staying at every knot to examine how it is tyed ; you see that this difficult progresse of the generation of living creatures is obvious enough to be comprehended and the steps of it set down; if one would but take the paines and afford the time that is necessary to note diligently all the circumstances in every change of it. . . . Now if all this orderly succession of mutations be necessarily made in a bean, by force of sundry circumstances and externall accidents ; why may it not be conceived that the like is also done in sensible creatures, but in a more perfect manner, they being perfecter substances? Surely the progresse we have set down is much more reasonable than to conceive that in the seed of the male there is already in act, the substance of flesh, bone, sinews, and veins, and the rest of those severall similar parts which are found in the body of an animall, and that they are but extended to their due magnitude by the humidity drawn from the mother, without receiving any substantiall mutation from what they were originally in the seed. Let us then confidently conclude, that all generation is made of a fitting, but remote, homogeneall compounded substance upon which outward Agents, working in the due course of Nature, do change it into another substance, quite different from the first, and do make it lesse homogeneall than the first was. And other circumstances and agents do change this second into a third, that third, into a fourth; and so onwards, by successive mutations that still make every new thing become lesse homogeneall than the former was, according to the nature of heat, mingling more and more different bodies together, untill that substance bee produced which we consider the period of all these mutations." This passage is indeed admirable, and well expresses the most modern conception of embryonic development, that of the ovum as a physico-chemical system, containing within itself only to a slight and varying degree any localisation answering to the localisation of the adult, and ready to change itself, once the

9-2

132 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

appropriate stimulus has been received, into the completed embryo by the actions and reactions of its own constituents on the one hand and the influence of the fitting factors of the environment upon the other. Digby has not received his due in the past; he stands to embryology as an exact science, much in the same relationship as Bacon to science as a whole.

"Generation is not made", he says, "by aggregation of like parts to presupposed like ones; nor by a specificall worker within; but by the compounding of a seminary matter with the juice which accrueth to it from without and with the steams of circumstant bodies, which by an ordinary course of nature are regularly imbibed in it by degrees and which at every degree doe change it into a different thing ..." (see p. 317). "Therefore to satisfie ourselves herein, it were well we made our remarks on some creatures that might be continually in our power to observe in them the course of nature every day and hour. Sir lohn Heydon, the Lieutenant of his Majesties Ordnance (that generous and knowing Gentleman, and consummate Souldier both in theory and practice) was the first that instructed me how to do this, by means of a furnace so made as to imitate the warmth of a sitting hen. In which you may lay severall eggs to hatch, and by breaking them at severall ages you may distinctly observe every hourly mutation in them if you please." Sir Kenelm then goes on to describe the events that take place in the incubating egg, which he does very accurately, though briefly. In vivipara, he says, the like experiments have been made, and the like conclusions come to by "that learned and exact searcher into nature. Doctor Harvey" — these he must have learnt of by word of mouth, for Harvey's book had not at that time been published. As regards heredity, he adopts a pure theory of pangenesis, and has more to say about it than any other writer of his time. He is sure that the heart is first formed both in ovipara and vivipara, "whose motion and manner of working evidently appears in the twinckling of the first red spot (which is the first change) in the egge".

Sir Kenelm Digby not only anticipated the outlook of the physicochemical embryologist, but he also foreshadowed with considerable accuracy Wilhelm Roux's definition of interim embryological laws. "Out of our short survey", he says, "of which (anserable to our weak talents, and slender experience) I perswade myselfe it appeareth evidently enough that to effect this worke of generation there needeth

SECT. 3] AND EIGHTEENTH CENTURIES 133

not to be supposed a forming virtue or Vis Formatrix of an unknown power and operation, as those that consider things suddenly and in grosse do use to put. Yet in discourse, for conveniency and shortnesse of expression we shall not quite banish that terme from all commerce with us; so that what we mean by it be rightly understood, which is the complex assemblement, or chain of all the causes, that concur to produce this effect, as they are set on foot to this end by the great Architect and Moderatour of them, God Almighty, whose instrument Nature is : that is, the same thing, or rather the same things so ordered as we have declared, but expressed and comprized under another name." Thus Sir Kenelm admits that it is allowable to speak of the "complex assemblement" of causes, as if it were one formative virtue, and this corresponds to Roux's "secondary components" or interim embryological laws. But that the portmanteau generalisations can be resolved into ultimate physico-chemical processes, Digby both believes and spends two entire chapters in trying to show. Digby has been one of the two seventeenth-century Englishmen most underestimated in the history of biology, but his place is in reality a very high one. How far he was in advance of his time may be gauged from the work of his contemporary Sperlingen, whose book of 1641 was thoroughly scholastic and retrograde.

His Treatise on Bodies evoked several answers. Undoubtedly the most interesting from the progressive side was that of Nathaniel Highmore, who will always be well remembered in embryological history. Highmore's The History of Generation came out in 1651, so that Harvey must have known of it, and it is one of the puzzles of this period why Harvey did not make any mention of it in his work, especially as J. D. Horst in a letter to Harvey refers to Highmore as his pupil. Harvey replying in 1655 said he had not seen Highmore for seven years. Highmore's title-page expressly states that his book is an answer to the opinions of Sir Kenelm Digby. But before discussing in what the answer consisted, we may look at the plate which is bound in immediately after the dedication (to Robert Boyle). It is interesting in that it shows again the idea initiated by Leonardo, namely, that all growing things, plants as well as animals, have an umbilical cord, and in that the drawings of the chick embryos and eggs are more quaint than accurate (Plate VI).

Highmore first describes the Aristotelian doctrine of form and matter, and then censures both it and the extensions of it with their

134 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

"qualities", etc., much as Digby himself had done. "Some of our later philosophers have showed us that those forms w'^*^ they thought and taught to bee but potentially in the matter, are there actually subsisting though till they have acquired fitting organs, they manifest not themselves. And that the effects which were done before their manifestation (as the forming and fashioning of the parts wherein they are to operate) can rise from nothing else than from the Soul itselfe. This likewise I shall leave to the Readers enquiry, and shall follow that other way of introducing Forms, and Generation of creatures (as well animals as vegetables) which gives Fortune and Chance the preheminency in that work." He then describes Sir Kenelm's opinions, quoting from him in detail, and dissents from them mainly on the ground that they do not sufficiently account for embryogeny, as it were, from a technical point of view. That they subvert the "antique principals of philosophy" does not worry Highmore, but in his view their detailed mechanisms do not explain the facts, a much more serious drawback. Highmore is himself by way of being an Atomist, and it is because embryology was first treated by him from an atomistic standpoint that he derives his importance. "The blood, that all parts may be irrigated with its benigne moisture, is forc'd by several channels to run through every region and part of the body; by which meanes every part out of that stream selects those atomes which they finde to be cognate to themselves. Amongst which the Testicles abstract some spiritual atomes belonging to every part, which had they not here been anticipated, should have been attracted to those parts, to which properly they did belong for nourishment. . . . These particles passing through the body of the Testicles, and being in this Athanor cohobated and reposited into a tenacious matter, at last passe through infinite Meanders through certain vessels, in which it undergoes another digestion and pelicanizing." Highmore objects, therefore, more to Digby 's theory of pangenesis than to his description of embryogenesis. He goes on to give a long description of the development of the chick in the egg, mentioning in passing that the albumen corresponds to the semen and the blood of vivipara and the yolk to their milk. "Fabritius, who hath taken a great deal of pains in dissections. . . supposes the chick to be formed from the chalazae, that part which by our Women is called the treddle. But this likewise is false, for then every egge should produce 2 chickens, there being one treddle

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SECT. 3] AND EIGHTEENTH CENTURIES 135

at each end of the egg, which serve for no other end than for Hgaments to contain the yolk in an equilibrium, that it might not by every moving of the egg be shakt, broke, and confused with the white." Highmore was the first to draw attention to the increase of brittleness which takes place in the egg-shell during incubation, and he holds still to the Epicurean view that the female produces a kind of seed, though he thinks that the chick embryo is nourished in the early stages by the amniotic liquid.

Perhaps the most interesting reply to Digby from the traditional angle was that of Alexander Ross. In his Philosophicall Touchstone he upheld the Galenic view that the liver must be first formed in generation, for the nourishment is in the blood and the blood requires a liver to make it : ergo, the liver must be the earliest organ. Such arguments could dispense with observations. Ross also mentions Digby's suggestion that the "formative virtue" was only a bundle of natural causes, but he claims that the notion was an old one in schoolphilosophy, being included in the phrase causa causae^ causa causati.

3-3. Thomas Browne and the Beginnings of Chemical Embryology

There are references to embryology in Sir Thomas Browne's Pseudodoxia Epidemica, or Inquiries into very many vulgar Tenents and commonly received Truths, which was published at this time. The twenty-eighth chapter of the third book contains a number of difficult problems in the embryology of the period, in most cases stated without any solution. "That a chicken is formed out of the yolk of the Egg was the opinion of some Ancient Philosophers. Whether it be not the nutrient of the Pullet may also be considered ; since umbilical vessels are carried into it, since much of the yolk remaineth after the chicken is formed, since in a chicken newly hatched, the stomack is tincted yellow and the belly full of yelk which is drawn at the navel or vessels towards the vent, as may be discerned in chickens a day or two before exclusion. Whether the chicken be made out of the white, or that be not also its aliment, is likewise very questionable, since an umbilical vessel is derived unto it, since after the formation and perfect shape of the chicken, much of the white remaineth. Whether it be not made out of the grando, gallature, germ, or tred of the egg, as Aquapendente informeth us,

136 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

seemed to many of doubt; for at the blunter end it is not discovered after the chicken is formed, by this also the white and the yelk are continued whereby it may conveniently receive its nutriment from them both.. . .But these at last and how in the Cicatricula or little pale circle formation first beginneth, how the Grando or tredle, are but the poles and establishing particles of the tender membrans firmly conserving the floating parts in their proper places, with many observables, that ocular Philosopher and singular discloser of truth, Dr Harvey hath discovered, in that excellent discourse of generation, so strongly erected upon the two great pillars of truth, Experience, and Reason.

"That the sex is discernable from the figure of eggs, or that cocks or hens proceed from long or round ones, experiment will easily frustrate.. . .Why the hen hatcheth not the egg in her belly? Why the egg is thinner at one extream? Why there is some cavity or emptiness at the blunter end? Why we open them at that part? Why the greater end is first excluded [cf p. 233]? Why some eggs are all red, as the Kestrils, some only red at one end, as those of kites and buzzards? Why some eggs are not oval but round, as those of fishes ? etc. are problems whose decisions would too much enlarge this discourse." And elsewhere, "That (saith Aristotle) which is not watery and improlifical will not conglaciate; which perhaps must not be taken strictly, but in the germ and spirited particles; for Eggs, I observe, will freeze, in the albuginous part thereof". Again, "They who hold that the egg was before the bird, prevent this doubt in many other animals, which also extendeth unto them; for birds are nourished by umbilical vessels and the navel is manifest sometimes a day or two after exclusion.. . .The same is made out in the eggs of snakes, and is not improbable in the generation of Porwiggles or Tadpoles, and may also be true in some vermiparous exclusions, although (as we have observed in the daily progress of some) the whole Magot is little enough to make a fly without any part remaining. . . . The vitreous or glassie flegm of white of egg will thus extinguish a coal."

These citations show Sir Thomas to have been more than simply the supreme artist in English prose which is his common title to remembrance. In picking his way carefully among the doubtful points and difficult problems which previous embryologists had propounded but not answered, he usually managed to give the right

SECT. 3] AND EIGHTEENTH CENTURIES 137

answer to each. But in addition to this, he was also an experimentahst, he had made both anatomical and physical experiments on eggs, and he was prepared to put any disputed point to the test of "ocular aspection", if this could be done. His experimental contributions to embryology come out more clearly in his Commonplace Books which were published by Wilkin in 1836.

"Runnet beat up with the whites of eggs seems to perform nothing, nor will it well incorporate, without so much heat as will harden the tgg. . . . Eggs seem to contain within themselves their own coagulum, evidenced upon incubation, which makes incrassation of parts before very fluid.. . .Rotten eggs will not be made hard by incubation or decoction, as being destitute of that spirit or having the same vitiated. . . . They will be made hard in oil but not so easily in vinegar which by the attenuating quality keeps them longer from concoction, for infused in vinegar they lose the shell and grow big and much heavier then before. ... In the ovary or second cell of the matrix the white comes upon the yolk, and in the later and lower part, the shell is made or manifested. Try if the same parts will give any coagulation unto milk. Whether will the ovary best?... The whites of eggs drenched in saltpeter will shoot forth a long and hairy saltpeter and the egg become of a hard substance. Even in the whole egg there seems a great nitrosity, for it is very cold and especially that which is without a shell (as some are laid by fat hens) or such as are found in the egg poke or lowest part of the matrix, if an hen be killed a day or two before she layeth. . . . Difference between the sperm of frogs and eggs, spawn though long boiled, would not grow thick and coagulate. In the eggs of skates or thornbacks the yolk coagulates upon long docoction, not the greatest part of the white. . . . In spawn of frogs the little black specks will concrete though not the other. ... In eggs we observe the white will totally freeze, the yolk, with the same degree of cold will grow thick and clammy like the gum of trees, but the sperm or tread hold its former body, the white growing stiff that is nearest to it."

The only conclusion that can be drawn from these remarkable observations is that it was in the " laboratory " in Sir Thomas' house at Norwich that the first experiments in chemical embryology were undertaken. His significance in this connection has so far been quite overlooked, and it is time to recognise that his originality and genius in this field shows itself to be hardly less remarkable than in so many

138 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

others. To have occupied himself with the chemical properties of those substances which afford the raw material of development was a great step for those times, but it was not until some twenty-five years later that Walter Needham carried this new interest into the mammalian domain, and made chemical experiments there.

3-4. William Harvey

The Latin edition of William Harvey's book on the generation of animals appeared in 1651, and the English in 1653. The frontispiece of the former which is reproduced as the frontispiece of this book is a very noteworthy picture, and derives a special interest from the fact that on the egg which Zeus holds in his hands is written, "^x ovo omnia'\ — a conception which Harvey is continually expounding (see especially the chapter, "That an egg is the common Original of all animals"), but which he never puts into epigrammatic form in his text, so that the saying, omne vivum ex ovo, often attributed to him, is only obliquely his.

The De Generatione Animalium was written at different times during his life, and not collected together for publication until George Ent, of the College of Physicians, persuaded Harvey to give it forth about 1650. As early as 1625 Harvey was studying the phenomena of embryology, as is shown among other evidences by a passage in his book where he says, "Our late Sovereign King Charles, so soon as he was become a man, was wont for Recreation and Health sake, to hunt almost every week, especially the Buck and Doe, no Prince in Europe having greater store, whether wandring at liberty in the Woods and Forrests or inclosed and kept up in Parkes and Chaces. In the three summer moneths the Buck and the Stagge being then fat and in season were his game, and the Doe and Hind in the Autumme and Winter so long as the three seasonable moneths continued. Hereupon I had a daily opportunity of dissecting them and of making inspection and observation of all their parts, which liberty I chiefly made use of in order to the genital parts". Nor was Harvey less diligent in examining the generation of ovipara. John Aubrey, in his Brief Lives, says, " I first sawe Doctor Harvey at Oxford in 1642 after Edgehill fight, but I was then too young to be acquainted with so great a Doctor. I remember that he came often to Trin. Coll. to one George Bathurst, B.D. who kept a hen in his chamber to

SECT. 3] AND EIGHTEENTH CENTURIES 139

hatch egges, which they did dayly open to discerne the progress and way of generation". Aubrey mentions a conversation he had with a sow-gelder, a countryman of Httle learning, but much practical experience and wisdom, who told him that he had met Dr Harvey, who had conversed with him for two or three hours, and "if he had been", the man remarked, "as stiff as some of our starched and formall doctors, he had known no more than they". Harvey seems also to have learnt all he could from the keepers of King Charles' forests, as several passages in his book show. Nor was the King's own interest lacking. "I saw long since a foetus", he says, "the magnitude of a peasecod cut out of the uterus of a doe, which was complete in all its members & I showed this pretty spectacle to our late King and Queen. It did swim, trim and perfect, in such a kinde of white, most transparent and crystalline moysture (as if it had been treasured up in some most clear glassie receptacle) about the bignesse of a pigeon's Ggge, and was invested with its proper coat." And, again — "My Royal Master, whose Physitian I was, was himself much delighted in this kinde of curiosity, being many times pleased to be an eye-witness, and to assert my new inventions".

Harvey's book is composed of seventy-two exercitations, which may be divided up for convenience into five divisions. In Nos. i to 10 he speaks of the anatomy and physiology of the genital organs of the fowl, and the manner of production of eggs. Nos. 11 to 13 and also Nos. 23 and 36 deal with the hen's egg in detail, describing its parts and their uses, while in Nos. 14 to 23 the process of the "generation of the foetus out of the hen egge is described. The greater part of the book, comprising Nos. 25 to 62, as well as Nos. 71 and 72, is theoretical, and treats of the embryological theories held by Aristotle on the one hand, and the physicians, following Galen, on the other, instead of which it propounds new views upon the subject. Finally, Nos. 63 to 70, as well as the two appendices^ or "particular discourses", are concerned with embryogenesis in viviparous animals, especially in hinds and does.

It will be best to refer to certain details and main points of interest in Harvey's discussions, before trying to assess his principal contributions to the science as a whole. Harvey is the first, since Aristotle, to refer to the "white yolk" of birds. "For between the yolk", he says, "which is yet in the cluster and that which is in the midst of the eg when it is perfected this is the difference in chief, that though

140 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

the former be yellowish in colour and in appearance, yet its consistence representeth rather the white, and being sodden, thickeneth like it, growing compact and viscous and may be cut into slices. But the yolk of a perfect eggc being boiled groweth friable and of a more earthy consistence, not thick and glutinous like the white." All of Harvey's observations on the formation of the egg in the oviduct contained in this chapter are interesting, and may with advantage be compared with the studies of Riddle upon the same subject, where the chemical explanation will be found for many of Harvey's simple observations. Harvey's controversy with Fabricius on the question of whether the egg is produced with a hard shell or only acquires its external hardness upon standing in the air, which follows immediately on the above citation, is interesting. "Fabricius seemeth to me to be in errour, for though I was never so good at slight of hand to surprise an egge in the very laying, and so make discovery whether it was soft or hard, yet this I confidently pronounce that the shell is compounded within the womb of a substance there at hand for the purpose, and that it is framed in the same manner as the other parts of the egg are by the plastick faculty, and the rather, because I have seen an exceeding small egge which had a shell of its own and yet was contained within another egge, greater and fairer than it, which egge had a shell too."

Harvey was the first to note that the white of the hen's egg is heterogeneous, in the sense that part of it is much more liquid than the rest, and that the more viscous part seems to be contained in an exceedingly fine membrane, so that if it is sliced across with a knife, its contents will flow out. He also set right the errors of Fabricius, Parisanus and others, by showing that the chalazae were neither the seed of the cock nor the material out of which the embryo was formed, and, most important of all, by demonstrating that the cicatricula was the point of origin of the embryo. He denied, as against popular belief, that the hen contributed anything to the developing egg but heat, "For certain it is that the chicken is constituted by an internal principle in the egge, and that there is no accession to a complete and perfect egge by the Hennes incubation, but bare cherishing and protection; no more than the Hen contributeth to the chickens which are now hatched, which is only a friendly heat, and care, by which she defendeth them from the cold, and forreign injuries and helpeth them to their meat". Whether future work will still affirm

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that nothing is given to the egg by the hen except heat is beginning now to be in doubt, if the results of Chattock are correct.

In the description of the development of the embryo in the hen's egg, which remains to this day one of the most accurate, Harvey says with regard to the spot on the yolk, which had, of course, been seen and mentioned by many previous observers, "And yet I conceive that no man hitherto hath acknowledged that this Cicatricula was to be found in every egge nor that it was the first Principle of the Egge". His description of the beginning of the heart, that "capering bloody point" or "punctum saliens'\ is too famous to need more than a reference. He thought that the amniotic liquid was of "mighty use", "For while the embryos swim there, they are guarded and skreened from all concussion, contusion, and other outward injuries, and are also nourished by it".

Thus he made no advance on the opinion which had for long been held, namely, that the amniotic liquid or colliquamentum served for sustenance. "I believe", he says, "that this colliquamentum or water wherein the foetus swims doth serve for his sustenance and that the thinner and purer part of it, being imbibed by the umbilicall vessels, does constitute and supply the primo-genital parts, and the rest, like Milk, being by suction conveyed into the stomack and there concocted or chylified, and afterwards attracted by the orifices of the Meseraick Veins doth nourish and enlarge the tender embryo." His arguments for this are, ( i ) that swallowing movements take place, and (2) that the gut of the chicken is "stuft" with excrement which could hardly arise from any other source. He was thus led to divide the amniotic liquid into two quite imaginary constituents, a purer and "sincerer" part, which could be absorbed straight into the blood without chylification, and a creamless milky part which could not be treated so simply.

"About the fourth day", says Harvey, "the egg beginneth to step from the life of a plant to that of an animall." "From that to the tenth it enjoys a sensitive and moving soul as Animals do, and after that, it is compleated by degrees and being adorned with Plumes, Bill, Clawes and other furniture, it hastens to get out." These and other passages which deal with the forerunner of the theory of recapitulation are interesting, but we have already met essentially the same idea in Aristotle. Harvey contributed nothing new to it. The first point on which he went definitely wrong was the statement that

142 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

he made that the heart does not pulsate before the appearance of the blood. No doubt his lack of microscopical facilities or of the desire to use them affords the reason for this error, but it was a very unfortunate one, for it was to a large extent upon it that he formulated his doctrine "the life is in the blood". For example, he says, "I am fully satisfied that the Blood hath a being before any other part of the body besides, and is the elder brother to all other parts of the foetus ".

The yolk, Harvey thought, supplied the place of milk, "and is that which is last consumed, for the remainder of it (after the chicken is hatched and walks abroad with the Henne) is yet contained in its belly". He thus ranged himself with Alcmaeon and Abderhalden. All his remarks about the relationships of yolk and white in nutrition are worth consideration; in noting, for instance, that the yolk is the last to be consumed, he comes very near to anticipating the knowledge of the succession of energy-sources which we now possess (see Section T"]). "In that Physitians affirme, that the Yolke is the hotter part of the ^gg&, and the most nourishing, I conceive that they understand it, in relation to us, as it is become our nourishment, not as it doth supply more congruous aliment to the chicken in the tggt. And this appeares out of our history of the Fabrick of the chicken ; which doth first prey upon and devoure the thinner part of the white, before the grosser; as it were a more proper diet, and did more easily submit to transmutation into the substance of the foetus. And therefore the yolke seems to be a remoter and more deferred entertainment than the white; for all the white is quite and clean spent, before any notable invasion is made upon the yolke." A comparison between these simple facts and our knowledge of embryonic nutrition is most interesting (see Section 6-9).

In connection with Minot's distinction of the periods of embryonic growth, it is curious that Harvey says, "And now the foetus moves and gently tumbles, and stretcheth out the neck though nothing of a brain be yet to be seen, but merely a bright water shut up in a small bladder. And now it is a perfect Magot, differing only from those kinde of wormes in this, that those when they have their freedom crawle up and down and search for their living abroad, but this worm constant to his station, and swimming in his own provision, draws it in by his Umbilicall Vessels".

Sometimes Harvey confesses himself puzzled by problems which could only be solved by chemical means, yet it does not occur to

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him that this is the case. For instance, he enquires why heat will develop a chick out of a good egg but will only make a bad one worse. "Give me leave to add something here", he writes, "which I have tried often; that I might the better discerne the scituation of the foetus and the liquors at the seventeenth day to the very exclusion. I have boiled an eggc till it grew hard, and then pilling away the shell and freeing the scituation of the chicken, I found both the remaining parts of the white, and the two parts of the yolk of the same consistence, colour, tast, and other accidents, as any other stale egge, thus ordered, is. And upon this Experiment, I did much ponder whence it should come to passe that Improlifical eggs should, from the adventitious heat of a sitting Henne, putrifie and stink; and yet no such inconvenience befall the Prolifical. But both these liquors (though there be a Chicken in them too, and he with some pollution and excrement) should be found wholesome and incorrupt; for that if you eat them in the dark after they are boyled, you cannot distinguishe them from egges that are so prepared, which have never undergone the hen's incubation." Harvey was never afraid of trying such tests on himself; in another place, for example, he says, "Eggs after 2 or 3 days incubation, are even then sweeter relished than stale ones are, as if the cherishing warmth of the hen did refresh and restore them to their primitive excellence and integrity". "And the yolke (at 14 days) was as sweet and pleasant as that of a newlaid cgge, when it is in like manner boyled to an induration." Another matter on which Harvey set Fabricius right was on the question whether at hatching the hen helps the chicken out or the chicken comes out by itself. The latter was the belief held by Harvey, who said of Fabricius' arguments on this point that they were "pleasant and elegant, but not well bottomed".

On the great question of preformation v. epigenesis, Harvey keenly argued in favour of the latter view. "There is no part of the future foetus actually in the egg, but yet all the parts of it are in it potentially. ... I have declared that one thing is made out of another two several wayes and that as well in artificial as natural productions, but especially in the generation of animals. The first is, when one thing is made out of another thing that is pre-existent, and thus a Bedstead is made out of Timber, and a Statue out of a Rock, where the whole matter of the future fabrick was existent and in being, before it was reduced into its subsequent shape, or any tittle of the

144 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

designe begun. But the other way is when the matter is both made and receiveth its form at the same time. ... So Hkewise in the Generation of Animals, some are formed and transfigured out of matter already concocted and grown and all the parts are made and distinguished together per metamorphosin, by a metamorphosis, so that a complete animal is the result of that generation; but some again, having one part made before another, are afterwards nourished, augmented, and formed out of the same matter, that is, they have parts, whereof some are before, and some after, other, and at the same time, are both formed, and grow. . . . These we say are made per epigenesin, by a post-generation, or after-production, that is to say, by degrees, part after part, and this is more properly called a Generation, than the former. . . . The perfect animals, which have blood, are made by Epigenesis, or superaddition of parts, and do grow, and attain their just future or ciKfir} after they are born. . . . An animal produced by Epigenesis, attracts, prepares, concocts, and applies, the Matter at the same time, and is at the same time formed, and augmented.. . .Wherefore Fabricius did erroniously seek after the Matter of the chicken (as it were some distinct part of the egg which went to the imbodying of the chicken) as though the generation of the chicken were effected by a Metamorphosis, or transfiguration of some collected lump or mass, and that all the parts of the body, at least the Principall parts, were wrought off at a heat or (as himselfe speaks) did arise and were corporated out of the same Matter." Nothing could be more plain than Harvey's teaching on epigenesis, so that he has precedence over Caspar Wolff on this matter.

On the relation between growth and differentiation Harvey has some valuable things to say. The term "nutrition" he restricted to that which replaces existent structures, and the term "augmentation" or "increment" to that which contributes something new. That process which led to greater diversity of form and complexity of shape he called "formation" or "framing". "For though the head of the Chicken, and the rest of its Trunck or Corporature (being first of a similar constitution) do resemble a Mucus or soft glewey substance; out of which afterwards all the parts are framed in their order; yet by the same Operatour they are together made and augmented, and as the substance resembling glew doth grow, so are the parts distinguished. Namely they are generated, altered, and formed at once,

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they are at once similar and dissimilar, and from a small similar is a great organ made." Harvey was thus very certain that the processes of growth in size and differentiation in shape went on quite concurrently, though he had no inkling of changes in the relative rapidity of each process. On this point he goes further than Fabricius. Fabricius thought that growth was a more or less mechanical process, taking its origin from the properties of elementary substances, but that differentiation was brought about by some more spiritual or subtle activity. "Fabricius", says Harvey, "affirmes amisse, that the Immutative Faculty doth operate by the qualities of the elements, namely. Heat, Gold, Moisture, and Dryness (as being its instruments) but the Formative works without them and after a more divine manner; as if (forsooth) she did finish her task with Meditation, Choice, and Providence. For had he looked deeper into the thing, he would have seen that the Formative as well as the Alterative Faculty makes use of Hot, Cold, Moist, and Dry, (as her instruments) and would have deprehended as much divinity and skill in Nutrition and Immutation as in the operations of the Formative Faculty her self." "I say the Concocting and Immutative, the Nutritive and Augmenting Faculties (which Fabricius would have to busie themselves only about Hot, Cold, Moist, and Dry, without all knowledge) do operate with as much artifice, and as much to a designed end, as the Formative faculty, which he affirms to possess the knowledge and fore-sight of the future action and use of every particular part and organ." Thus although in nearly every respect Harvey makes an advance on Fabricius, yet here he is retrograde, for, in the former's thought, the growth process at least had struggled towards a deterministic schema; with Harvey this movement is rigidly suppressed. "All things are full of deity" {Jovis omnia plena), said he, "so also in the little edifice of a chicken, and all its actions and operations, Digitus Dei, the Finger of God, or the God of Nature, doth reveal himself"

There can be no doubt that Harvey's leanings were vitalistic. In the following passage, he argues against both those who wished to deduce generation from properties of bodies (like Sir Kenelm Digby) and the Atomists ; in other words, against the outlook of those types of mind which in later times were to build up biophysics and biochemistry. Aubrey notes that Harvey was "disdainfull of the chymists and undervalued them".

"It is the usual error of philosophers of these times", says he, "to

146 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

seek the diversity of the causes of parts out of the diversity of the matter from whence they should be framed. So Physicians affirm, that the different parts of the body are fashioned and nourished by the different materials of blood or seed ; namely the softer parts, as the flesh, out of a thinner matter, and the more earthy parts as the bones, out of grosser and harder. But this error now too much received, we have confuted in another place. Nor are they lesse deceived who make all things out of Atomes, as Democritus, or out of the elements, as Empedocles. As if (forsooth) Generation were nothing in the world, but a meer separation, or Collection, or Order of things. I do not indeed deny that to the Production of one thing out of another, these forementioned things are requisite, but Generation her self is a thing quite distinct from them all. (I finde Aristotle in this opinion) and I my self intend to clear it anon, that out of the same White of the Egge (which all men confesse to be a similar body, and without diversity of parts) all and every the parts of the chicken whether they be Bones, Clawes, Feathers, Flesh, or what ever else, are procreated and fed. Besides, they that argue thus assigning only a material cause, deducing the causes of Natural things from an involuntary or casual concurrence of the Elements, or from the several disposition or contriving of Atomes ; they doe not reach that which is chiefly concerned in the operations of nature, and in the Generation and Nutrition of animals, namely the Divine Agent, and God of Nature, whose operations are guided with the highest Artifice, Providence, and Wisdome, and doe all tend to some certaine end, and are all produced, for some certaine good. But these men derogate from the Honour of the Divine Architect, who hath made the Shell of the Egge with as much skill for the egge's defence as any other particle, disposing the whole out of the same matter and by one and the same formative faculty." But although these are Harvey's theories, it is significant that in his preface he says, "Every inquisition is to be derived from its causes, and chiefly from the material and efficient", thus expressly excluding formal and final considerations. Certainly, as far as his practical work went, he was unaffected by them, and in the case of the egg-shell, for example, Harvey was not the man to say, "it is present for the protection of the embryo", and then to do or say nothing more. Such an explanation, though he might gladly accept it, was no bar to further exploration both by way of experiment and observation.

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Harvey not only follows Aristotle in his good discoveries and true statements about the egg, but also, unfortunately, in his less useful parts, as, for example, when he devotes several pages to the discussion of how far the egg itself is alive, and whether there is any soul in subventaneous or unfruitful eggs. He decides that there is only a vegetative soul. On the other hand, he admirably refutes the opinion of those physicians — who were not few in number — who declared that the foetal organs were all functionless during foetal life. "But while they contende", he says, "that the mother's Blood is the nutriment of the foetus in the womb, especially of the Partes Sanguineae, the bloody parts (as they call them) and that the Foetus is at first, as if it were a part of the mother, sustained by her blood and quickened by her spirits, in so much that the heart beats not and the liver sanguifies not, nor any part of the Foetus doth execute any publick function, but all of them make Holy-Day and lie idle; in this Experience itself confutes them. For the chicken in the egge enjoyes his own Blood, which is bred of the liquors contained within the egge, and his Heart hath its motion from the very beginning, and he borroweth nothing, either blood or spirits, from the Hen, towards the constitution either of the sanguineous parts or plumes, as those that strictly observe it may plainly perceive." We have already seen how the Stoics in antiquity believed that the embryo was a part of the mother until it was born ; from this idea the transition would be easy to the belief that all the organs in the embryo were functionless and dependent on the activity of the corresponding ones in the maternal organism.

One of Harvey's most important services to thought lay in his abolishing for good the controversy which had gone on ever since the sixth century B.C. about which part of the egg was for nutrition and which for formation. He had the sense to see that the distinction was a useless and baseless one — "There is no distinct part (as we have often said) or disposed matter out of which the Foetus may be formed and fashioned. . . . An egge is that thing, whose liquors do serve both for the Matter and the Nourishment of the foetus.. . .Both liquors are the nourishment of the foetus."

As regards spontaneous generation, Harvey considered that even the most imperfect and lowest animals came out of eggs. "We shall show", he writes, "that many Animals themselves, especially insects do germinate and spring from seeds and principles not to be discerned

148 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

even by the eye, by reason of their contract invisible dimensions (like those Atomes, that fly in the aire) which are scattered and dispersed up and down by the winds ; all which are esteemed to be Spontaneous issues, or born of Putrefaction, because their seed is not anywhere seen." Unfortunately, he never returned to this subject, for, as he himself informs us in another place, all the papers and notes in his house in London were destroyed at the time of the Civil War, so that what he had written on the generation of insects irretrievably perished.

Another point on which Fabricius had been in error was the appearance of bone and cartilage in the embryo. According to him, "Nature first stretcheth out the Chine Bone, with the ribbes drawn round it, as the Keel, and congruous principle, whereon she foundeth and finisheth the whole pile". This armchair conceit Harvey was easily able to destroy by a mere appeal to experience, but by experience also he came upon a fact less easily to be explained, namely, that the motion of the foetus began when as yet there was hardly any nervous system. "Nor is it less new and unheard of, that there should be sense and motion in the foetus, before his brain is made; for the Foetus moves, contracts, and extends himself, when there is nothing yet appears for a braine, but clear water." On the basis of this paradox Harvey may be said to be the discoverer of myogenic contraction, but he already could claim that distinction, for the first heart-beats are accomplished long before there are any nerves to the heart, as he himself points out. "We may conclude from this fact", he remarks, "that the heart and not the brain is the first principle of embryonic life", and he gives instances of physiological actions not under the conscious control of the individual, such as the reflexes, as we should call them, of the intestinal tract, and the emetic action of infusion of antimony which cannot be tasted much and "yet there passeth a censure upon it by the Stomack" and a vomit ensues. Thus, twenty-five years before Francis Glisson, Harvey had formulated, from embryological studies, the view that irritability was an intrinsic property of living tissues.

Both Harvey and Fabricius were very puzzled about the first origin of the blood. "What artificer", says Harvey, "can transform the two liquors into blood, when there is yet no liver in being?" It was to be a long time before this question was answered by Wolflf 's discovery of the blood islands in the blastoderm, and, even now, the

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chemistry of the appearance of haemoglobin is one of the most obscure corners of chemical embryology. The older observers explained it by considering the yolk to be akin to blood and ready to turn into it at the slightest inducement.

Another problem which neither Fabricius nor Harvey did anything to solve was the nature of the air-space at the blunt end of the egg. "Fabricius recounts several conveniences arising from it, according to its several magnitudes, which I shall declare in short, saying, It contains aire in it, and is therefore commodious to the Ventilation of the egge, to the Respiration, Transpiration, and Refrigeration, and, lastly, to the Vociferation of the Chicken. Whereupon, that cavity is at the first very little, afterwards greater, and at last greatest of all, according as the several recited uses do require."

As regards the placenta, Harvey took the side of Arantius and denied any connection between the maternal and foetal circulations. "The extremities of the umbilicall vessels", he said, "are no way conjoined to the extremities of the Uterine vessels by an Anastomosis, nor do extract blood from them, but are terminated in that white mucilaginous matter, and are quite obliterated in it, attracting nourishment from it." "Wherefore these caruncles may be justly stiled the Uterine Cakes or Dugs, that is to say, convenient and proportionate organs or instruments designed for the concocting of that Albuginous Aliment and for preparing it for the attraction of the veins." From this it would appear that Harvey regarded the uterine milk as the special secretion of the placenta, conveyed to the foetus through the umbilical cord. The nature of the uterine milk is still very imperfectly understood (see Section 21). Its discovery is usually attributed to Walter Needham, but various remarks in this chapter (Ex. lxx) seem to show that Harvey was well acquainted with it. In later times, it was regarded by some (Bohnius and Charleton in 1686, Zacchias in 1688 and Franc in 1722) as the sole source of foetal nourishment. Mercklin spoke of it in 1679 as materia albuginea, ovique albo non absimili". Harvey often calls the placenta the uterine liver, no doubt only for this reason, but the remarkable appropriateness of the term was to become apparent in Claude Bernard's day. As regards the matter of the continuity of the maternal and foetal circulations, he criticises van Spieghel. "There came forth a book of late", he says, "wrote by one Adrianus Spigelius, wherein he treateth concerning the use of the umbilicall arteries and doth

150 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

demonstrate by powerfull arguments that the Foetus doth not receive its Vital Spirits by the arteries from the Mother, and hath fully answered those arguments which are alledged to the contrary. But he might also as well have proved by the same arguments that the blood neither is transported into the Foetus from the mother's veines by the propagations of the umbilicall veins which is made chiefly manifest by the examples drawn from the Hen-Egge and the Caesarean Birth."

The least satisfactory parts of Harvey's book are the Exercitations Lxxi and lxxii on the innate heat and the primigenial moisture. Here he becomes very wordy and highly speculative, and gives us little but a mass of groundless arguments. He devotes many pages to proving that the innate heat is the blood and to drawing distinctions between blood and gore, the one in the body, the other shed. In one place he speaks of the processes of generation as so divine and admirable as to be "beyond the comprehension and grasp of our thoughts or understanding". Two centuries previously Frascatorius had said precisely the same thing about the motion of the heart, and it was ironical that the very man who let the light in on cardiac physiology should in his turn despair of the future of our knowledge of embryonic development.

Harvey did not say much about foetal respiration, and his few remarks are contained in one of the "additional discourses". He is puzzled exceedingly by the question. But he comes very near indeed to the truth when he says, "Whosoever doth carefully consider these things and look narrowly into the nature of aire, will (I suppose) easily grant, that the Aire is allowed to animals, neither for refrigeration, nor nutrition sake. For it is a tryed thing, that the Foetus is sooner suffocated after he hath enjoyed the Aire, than when he was quite excluded from it, as if the heat within him, were rather inflamed than quenched by the aire". Had Harvey pursued this line of thought, and looked still more narrowly into the nature of air, he might have anticipated Mayow. He does say that he proposes to treat of the subject again, but he never did.

The mainspring of Harvey's researches on the does and hinds can be realised by a reference to Rueff's figures in Fig. 6. According to the Aristotelian theory, the uterus after fertile copulation would be full of blood and semen ; according to the Epicurean theory (held by the "physitians") it would be full of the mixed semina. If this

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coagulated mass exists, said Harvey, it ought to be possible to find it by dissection, and this was what he tried to do. It soon became plain, as may be read in Ex. lxviii, not only to Harvey but to the King and the King's gamekeepers, that no such coagulum existed,

^t^^^^^jr. S>'^'^^^ ^>^T*-^^J-^ r "^ ^^^ A--r> >^r'-/f >^'^^ S" ^,-^^ ^ , ■

x> f.^^ ^^^^^/s S^^ . rr- f

Fig. 7. Manuscript notes of Dr William Harvey.

and the result was made still more certain by means of segregation experiments which the King carried out at Hampton Court. Accordingly there was nothing to be done but to abandon all the older theories completely, and have recourse to some sort of hypothesis in which an aura seminalis, an "incorporeal agent" or a "kinde of contagious property" should bring about fertilisation. This was

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a perfectly sound deduction from Harvey's experiments, and did not then appear anything like so unsatisfactory as it does now, for Gilbert of Colchester was not long dead, the "lodestone" was beginning to be investigated by the virtuosi, and even such extravagances as Sir Gilbert Talbot's Powder "for the sympatheticall cure of wounds" were only with difficulty distinguishable from the real effects of magnetic force. Harvey's idea of fertilisation by contagion has recently been in a sense revived by the work of Shearer (see Section 4*2).

But to Harvey himself the subject of the action of the seed was hid in deep night, and he confessed that, when he came to it, he was "at a stand". Some very interesting light is thrown upon his mind in this connection by a copy of the De Generatione Animalium annotated by himself, and now in the possession of Dr Pybus, by whose courtesy and by that of Dr Singer, who has transcribed the notes, I have been enabled to study it. It was given by Harvey to his brother Eliab, whose name it still bears. The notes, which are on the fly-leaves, are written in much the same way as those famous ones which Harvey used for his lectures at the College of Physicians in London, and which have been reproduced in facsimile. There is the same mixture of Latin and English, and the same signs, such as WI, to denote thoughts claimed as original. A page is reproduced in Fig. 7.

For the most part, the notes are uninteresting and nothing but a confusion of Aristotelian terms. But one page is concerned with the mode of action of the seed, and here we can, as it were, see Harvey's mind wrestling with this most difficult of problems. He sees that odour and the sense of smell may give a clue. That his thoughts on this point were doomed to frustration as soon as eggs and spermatozoa were discovered does not detract from the interest of the struggle.

Quod facit semen fecundum

What makes the seed fertile is on the analogy of an injection. In fact, the injection causes disease in many cases, and that from a distance, both by another. . .and by the same. . . A Venereal (?) disease corrupts coitus with a woman in whose uterus is the poison.

They do not [or do not yet ?] come forth in actuality but lie dormant as in fuel [? fomite]. Again, rabies in dogs lies dormant for many days on my own observation W4. Again, smallpox for days. Again, the generative seed, just as it (passes) from the male, lies dormant in the woman as infuel(?).

Or else like a . . . , like light in stone . . . , the pupil in the eye, in sense motion, ... in the body.

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Like ferment, vapour, odour, rottenness ... by rule. Or like the smell given off by flowers.

Like heat, inflammation (?) A in chalk (heat ?) both the wet form

Like what is first ... in the art of cooking . . . principles of vegetation and propagation. A Dormice by hibernating. . .cleansing by water and all kinds of lotions, again for insects, as for their seeds as well (?). Or when a soul is a god present in nature, that is divine which it brings about without an organic body by means of law.

See Aristode Marvels concerning odours and smells given off. Whether on sense and everything that can be smelt gives off something and so the objects of disperses (?) what is not without heat, or by destroying . . . sense. attracts to itself

A Amongst inflammable (objects are) fire, naphtha, paper

A WI manus et odore car . . . anatomia manair. ...

A Anat . . . post 4°"^ poras. otium inclinente die rursus quod prius et

olefrere vid. . . . Galen. ... A Mr. Boys spainel in Paris lay all ye third night and morning in getting dogg. Whelping dogg's sent (scent) are a stronger sent, vesting in vestigio alios ord . . . gr . . . lepris odore lepris esse libidine esse. Hors, the mare, hors, the cow, a bull per mutta millsa. A ... si lepra fracedo in farioli fader cupidinitus. Dogg ye otter in aquas fracedo vasorum ex sulpore?

Just as Aristotle put much of his best embryological work into his Historia Animalium and not into the work with the appropriate title, so Harvey has some admirable observations on the embryonic heart scattered through his De Motu Cordis et Sanguinis in Animalibus. Turning now to consider Harvey's influence on embryology, we must admit that it was in certain respects reactionary.

1 . He did not break with Aristotelianism, as a few of his predecessors had already done, but on the contrary lent his authority to a moribund outlook which involved the laborious treatment of unprofitable questions.

2. His opposition to atomism and to "chymistry" precluded any close co-operation between his followers and those of the DescartesGassendi tradition.

3. Fabricius had elaborated a vitalistic theory of differentiation, but had allowed growth to be "natural" or mechanical. Harvey, however, made both growth and differentiation the results of an immanent spirit, a sort of divine legate.

But these failings are far outweighed by his positive services. It must always be remembered that he had no compound microscope.

154 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

and had to rely, like Riolanus, on "perspectives", or simple lenses of very low power.

1. There can be no doubt that the doctrine omne vivum ex ovo was a tremendous advance on all preceding thought. Harvey's scepticism about spontaneous generation antedated by less than a century the experiments of Redi. It is important to note that he was led to his idea of the mammalian ovum by observations on small conceptions surrounded by their chorion and no bigger than eggs, for the true ovum itself was not discovered until the time of de Graaf and Stensen.

2. He identified definitely and finally the cicatricula on the yolkmembrane as the spot from which the embryo originated.

3. He denied the possibility of generation from excrement and from mud, saying that even vermiparous animals had eggs.

4. He discussed the question of metamorphosis (preformation) and epigenesis, and decided plainly for the latter, at any rate for the sanguineous animals.

In addition to these achievements, there are others, perhaps less striking, but equally important.

5. He destroyed once and for all the Aristotelian (semen-blood) and Epicurean (semen-semen) theories of early embryogeny. This was perhaps the biggest crack he made in the Peripatetic teaching on development; but, in spite of it, Sennertus, van Linde and Sylvius adhered to the ancient views, and Cyprianus, in 1700, had the distinction of being the last to support them in a scientific discussion, though Sterne, as late as 1 759, referred to them in a way that shows they still lived on in popular thought.

6. He handled the question of growth and differentiation better than any before, anticipating the ideas of the present century.

7. He settled for good the controversy which had lasted for 2200 years as to which part of the egg was nutritive and which was formative, by demonstrating the unreality of the distinction.

8. He set his predecessors right on a very large number of detailed points, such as the nature of the placenta.

9. He made a great step forward in his theory of foetal respiration, though here he did not consolidate the gain.

10. He affirmed that embryonic organs were active, and that the embryo did not depend on external aid for its principal physiological functions.

SECT. 3] AND EIGHTEENTH CENTURIES 155

But all these titles to remembrance, great as they are, do not account for the pecuhar fascination of Harvey. A little of it is perhaps due to his imaginative style, which comes out clearly in Martm Llewellyn's English version. A word of censure is due to Willis for transmuting it in his translation into the dull and pedestrian style of 1847. None who reads the 1653 edition of Harvey can ever forget such metaphors as this, "For the trunck of the body hitherto resembles a skiff without a deck, being in no way covered up by the anteriour parts"; or the vigour of diction which promotes such remarks as, "In a hen-egge after the tenth day, the heart admits no spectators without dissection"; or again, "For while the foetus is yet feeble. Nature hath provided it milder diet and solider meats for its stronger capacity, and when it is now hearty enough, and can away with courser cates, it is served with commons answerable to it. And hereupon I conceive that perfect eggs are not onely party-coloured, but also furnished with a double white"; or, lastly, "An egge is, as it were, an exposed womb ; wherein there is a substance concluded, as the Representative and Substitute or Vicar of the breasts".

In this connection, it would be a pity not to quote from the verses which Llewellyn prefixed to his translation of Harvey's book. After describing the controversies that followed the De Motu Cordis he wrote

A Calmer Welcome this choice Peice befall,

Which from fresh Extract hath deduced all,

And for Belief, bids it no longer begg

That Castor once and Pollux were an Egge :

That both the Hen and Houswife are so matcht,

That her Son born, is only her Son hatcht;

That when her Teeming hopes have prosp'rous bin.

Yet to conceive, is but to lay, within.

Experiment, and Truth both take thy part:

If thou canst 'scape the Women ! there's the Art.

Live Modern Wonder, and be read alone,

Thy Brain hath Issue, though thy Loins have none.

Let fraile Succession be the Vulgar Care;

Great Generation's Selfe is now thy Heire.

Curiously enough, the "calmer welcome" which Martin Llewellyn hoped for actually happened. Harvey's book was so well reasoned and based on such good observations that it produced only two

156 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

answers, and they were of little importance. Janus Orcham took exception to Harvey's finding no seed in the uterus and suggested that it had vaporised like a steam, but his Aristotelian leanings were promptly detected and castigated by Rallius. Matthew Slade, taking the pseudonym of Theodore Aides, published in 1667 his Dissertatio epistolica contra D. G. Harveium, which was, in his own words, "a detection of one or two errors in that golden book on the generation of animals of William Harvey, greatest of physicians and anatomists". The errors were purely anatomical, and ab Angelis defended Harvey against Slade's attack, claiming that the "errors" were not errors at all. A manuscript work of Slade's appears to be extant.

Harvey's influence was evidently speedily felt by his contemporaries. Strauss soon wrote a rather poor book on the bird's egg in imitation of him. But the best instance is that in 1655, very soon after the publication of Harvey's book, William Langly, "an eminent senator and physician of Dordrecht", made a great many experiments on the development of the hen's egg. Buffon says that he worked in 1635, i.e. before Harvey, but this is not the case, for in his observations which were published by Julius Schrader in 1674 the later date is given several times. Langly mentions Harvey more than once, and evidently followed his example in careful observation, for his text is concise and accurate and his drawings very noteworthy.

Julius Schrader included Langly's work in a composite volume containing a well-arranged epitome of Harvey's book on generation and some observations of his own on the hen's egg. The book was dedicated to Matthew Slade and J. Swammerdam. On the practical side Schrader added nothing memorable to Harvey and Langly, but it is noteworthy that the mammalian embryo was throughout these centuries more popular material than that of the chick. Out of fifty embryologists between Harvey and Haller, the names of Langly, Schrader, Malpighi and Maitre-Jan practically exhaust the list of those who studied the egg of the hen. This rather unfortunate orientation of mind doubtless sprang from the strong influence of medicine, and especially obstetrics, on seventeenth and eighteenth century embryology.

3-5. Gassendi and Descartes: Atomistic Embryology

Harvey's death took place in 1657. The following year saw the publication of Pierre Gassendi's Opera Omnia, and thus brought in

SECT. 3] AND EIGHTEENTH CENTURIES 157

an entirely new phase in embryology. Together with Rene Descartes' treatise on the formation of the foetus, Gassendi's De generatione animalium et de animatione foetus marks a quite different attitude to the subject. Harvey had adopted a rather contemptuous position about the "corpuscularian or mechanical philosophy", which was then coming in, and had expected even less help from it in the solution of his problems than from his equally despised "chymists". Gassendi now set out to show that the formation of the foetus could be explained on an atomistic basis: and, using the Galenic physiology and the new anatomy as a framework, he set forth his theory in full. As we read it through at the present day, however, we cannot avoid the confession that it was not a success. In spite of his frequent quotations from Lucretius and his persuasive style, it does not carry conviction. The truth of the matter was that the time was not ripe for so great a simplification. The facts were insufficiently known, and that Gassendi is not quite as interested in them as he is in his theory is shown by the circumstance that he only mentions Harvey once.

Gassendi examines in turn the Aristotelian and the Epicurean doctrines of embryogeny and rejects them both, the former on the ground that the change from tgg to hen is too great and difficult for anything so shadowy and ghost-like as a "form" to accomplish, and the latter because it leaves no room for teleology. He therefore adopts as the basis of his system atomism + preformationism, alleging that all the germs of living things were made at the creation, but that they come to their perfection as atomic congregations in an atomistic universe. Thomas' monograph is a valuable help to the study of this very interesting thinker.

At exactly the same time, Descartes was speculating on the same subject. Added to his posthumous De Homine Liber (1662) is a treatise on the formation of the foetus. He may also have written a work On the generation of animals, for a manuscript with that title was found among his papers after his death, and was believed to be in his handwriting. There is evidence, however, that it is not his, and though it was published in Cousin's edition of his works, we may safely neglect it, agreeing, in the words of that editor, that it is "a fragment in which very mediocre and often quite false ideas struggle to light through the medium of a style devoid alike of clarity and of grandeur ". It must be admitted, however, that even his main treatise is very

158 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

confused. It suffers from containing in its earlier part a great deal of matter which really belongs to the physiological text-book which immediately preceded it. Thus it begins abruptly in the middle of a disquisition on the error of attributing bodily functions to the soul. Before long, however, it warms to its theme, and a conception of growth is outlined. "When one is young, the movement of the little threads which compose the body is less slow than it is in old age, because the threads are not so tightly joined one to the other, and the streams in which the solid particles run are large, so that the threads become attached to more matter at their roots than detaches itself from their extremities, so that they grow longer and thicker, in this way producing growth." The fourth part of the book is called, strangely enough, a Digression, in which the formation of the animal is spoken of. The mixture of seeds is then described, and a theory of the formation of the heart is attempted by means of an analogy with fermentation. The explanation is unconvincing, but has a certain interest as showing chemical notions beginning to permeate biological thought. However, Descartes' way of looking at development was thoroughly novel, as is illustrated by the following citation. "How the heart begins to move.. . .Then, because the little parts thus dilated, tend to continue their movement in a straight line, and because the heart now formed resists them, they move away from it and take their course towards the place where afterwards the base of the brain will be formed, they enter into the place of those that were there before, which for their part move in a circular manner to the heart and there, after waiting for a moment to assemble themselves, they dilate and follow the same road as the aforementioned ones, etc." Descartes, in fact, with premature simplification, was trying to erect an embryology more geometrico demonstrata. That he failed in the attempt was as obvious to his contemporaries as it is to us — "We see", said Garden, "how wretchedly Descartes came off" when he began to apply the laws of motion to the forming of an animal". In doing so, he was many years before his time; Borelli had done all that could be done at that period in that direction, and, significantly enough, he left embryology alone. The rest of Descartes' book is exactly like the citations which have been given, only applied to each organ and part in turn; he practically uses the traditional teaching as a scaffolding in which to interweave his mechanical theory, and he discovers no new facts.

SECT. 3] AND EIGHTEENTH CENTURIES 159

But in the history of embryology these men and their writings have a very great significance. Impressed by the unity of the world of phenomena, they wished to derive embryology as well as physics from fundamental laws. This attempt, which resulted in a GalenEpicurus synthesis on the one hand and a Galen-Descartes synthesis on the other, must be regarded as a noble failure. Its authors did not realise what a vast array of facts would have to be discovered before a mechanical theory could with any justice be applied to explain them. Gassendi and Descartes were like the Ionian nature-philosophers, propounding general laws before the particular instances were accurately known. Their ineffectiveness arises from the fact that they did not themselves appreciate this, and consequently worked out their idea in a prolix detail, the whole of which was inevitably doomed to the scrap-heap from the very beginning. But the spark was not to die ; and if anywhere in this history we are to find the roots of physico-chemical embryology, we must pause to recognise them here.

Much less well known, but not without interest, was the Dissertatio de vita foetus in utero of Gregorius Nymmanus, which appeared in the same year as the second edition of Descartes' book, 1664. Nymmanus writes with a very beautiful Latin style, and expresses himself with great clearness. His proposition is, he says, "That the foetus in the uterus lives with a life of its own evincing its own vital actions, and if the mother dies, it not uncommonly survives for a certain period, so that it can sometimes be taken alive from the dead body of its mother". In supporting this thesis, Nymmanus answers the arguments of those who had held that the lungs and heart of the foetus were inactive in utero. Fabricius, Riolanus and Spigelius all proved, says Nymmanus, that the mother and the foetus by no means necessarily die at the same time. "The essential life", he says, "is the soul itself informing and activating the body, the accidental life is the acts of the soul which it performs in and with the body." Though the foetus cannot be said to have life in the latter sense, it can in the former. The foetus, says Nymmanus, prepares its own vital spirits and the instruments of its own soul; there is no nerve between it and its mother. If, he says, the foetal arteries got their sphygmic power from the maternal heart, they would stop pulsating when the umbilical cord was tied, but this is not the case. The pulse of the embryo is therefore due to the foetal heart itself. Galen, says Nymmanus, was

i6o EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

aware of this, but did not understand the meaning of it. Again, the foetus in utero moves during the mother's sleep, and vice versa. Nymmanus' dissertation is an interesting study in the transition from theological to scientific embryology which took place all through the seventeenth century, and may be followed in the writings of Varandaeus, de Castro, Dolaeus, Hildanus, Scultetus, Ammanus, Augerius and Garmannus. The problem of animation-time, a more metaphysical aspect of the same question, was still being handled, but less attention was being paid to it than formerly. Honoratus Faber's De Generatione Animalium of 1666 does not belong to its period. Its author, a Jesuit, proceeds in scholastic fashion to lay down four definitions, three axioms, one hypothesis, and seventy-seven propositions, in the last of which he summarises his conclusions. He is interesting in that he displayed a disbelief in spontaneous generation, thereby anticipating Redi, and he is careful to mention the work of Harvey, but nevertheless his treatise is of little value. His chief importance is that he is an epigenesist, and therefore demonstrates to us how the true opinion was becoming accepted, when Malpighi's brilliant observations and bad theory sent it out of favour, and prepared the way for the numerous controversies of the following century.

3-6. Walter Needham and Robert Boyle

It was in 1666 also that the following appeared in the Philosophical Transactions of the Royal Society :

A way of preserving birds taken out of the egge, and other small f actus' s: communicated by Mr. Boyle.

When I was sollicitous to observe the Processe of Nature in the Formation of the Chick, I did open Hens Eggs, some at such a day, and some at other daies after the beginning of the Incubation, and carefully taking out the Embryo's, embalmed each of them in a distinct Glass (which is to be carefully stopt) in Spirit of Wine; Which I did, that so I might have them in readinesse to make on them, at any time, the Observations, I thought them capable of affording; and to let my Friends at other seasons of the year, see, both the differing appearances of the chick at the third, fourth, seventh, fourteenth, or other daies, after the eggs had been sate on, and (especially) some particulars not obvious in chickens, that go about, as the hanging of the Gutts out of the Abdomen, etc. How long

sfecT. 3] AND EIGHTEENTH CENTURIES 161

the tender Embryo of the Chick soon after the Punctum saliens is discoverable, and whilst the bodie seems but a little organized Gelly, and some while after that, will be this way preserv'd, without being too much shrivel'd up, I was hindred by some mischances to satisfie myself; but when the Faetus's, I took out, were so perfectly formed as they were wont to be about the seventh day, and after, they so well retained thjeir shape and bulk, as to make me not repent of my curiosity; And some of those, which I did very early this Spring, I can yet shew you.

Boyle said in conclusion that he sometimes also "added Sal Armoniack, abounding in a salt not sowre but urinous".

In the same year that Nymmanus' book appeared, Nicholas Stensen, that great anatomist, later a Bishop, who was also to all intents and purposes the founder of geology, published his De musculis et glandulis specimen, in which Goiter's observations on the vitelline duct and the general relations between embryo and yolk in the hen's tgg were made again and confirmed. About this time also Deusingius described his case of abdominal pregnancy, and was thus the first anatomist to draw attention to this phenomenon.

In 1667 Stensen published his Elementorum myologiae specimen, in which he described the female genital organs of dogfishes. He demonstrated eggs in them and affirmed that the "testis" of women ought to be regarded as exactly the same organ as the "ovary" or "roe" of ovipara. At the time he carried the suggestion no further, but it was an extremely fruitful one, and it is surprising that it did not create more interest, for it was exactly what Harvey had been looking for. Nothing obvious having been found in the uteri of King Charles' does, and the conviction yet being very strong that viviparous conceptions really came from eggs, Stensen's minute ova supplied the fitting answer to the question. Thus Harvey and Stensen between them substituted the modern knowledge of mammalian ova for the ancient theory of the coagulum all in the space of fourteen years. The other event for which the year 1667 is remarkable is the De Formato Foetu of Walter Needham. Needham was a Cambridge physician who went to Oxford to study in the active school of physiological research which such men as Christopher Wren, Richard Lower, John Ward and Thomas Willis were making famous. His book on the formation of the embryo, written later (and dedicated to Robert Boyle), after he had been in practice in Shropshire for some time.

i62 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

is important because it is the first book in which definite chemical experiments on the developing embryo are reported, and also because it contains the first practical instructions for dissections of embryos.

Sir Thomas Browne had, as we have already seen, made experiments of a chemical nature on the constituents of birds' eggs and of the eggs of amphibia, but he did not analyse them after any development had been allowed to take place. He may therefore be regarded as the father of the static aspect of physico-chemical embryology, while Walter Needham may be regarded as the founder of the dynamic aspect. The practical difficulties of these pioneers of animal chemistry may be seen in such a book of practical instructions as Salmon's General Practise ofChymistry of 1678. They had no satisfactory glassware, no pure reagents, the methods of heating were incredibly clumsy, and there was no means of measuring either heat or atmospheric pressure.

In the review of Needham's book which is to be found in the Philosophical Transactions of the Royal Society for September 1667 there occurs the sentence, "These humors (the amniotic, allantoic, etc.) he saith, he hath examined, by concreting, distilling, and coagulating them; where he furnishes the Reader with no vulgar observations". What were these observations ? They are to be found in the chapter entitled "The nature of the humours":

"I now proceed to speak of this other nutritive liquor round about the urine itself which latter is plainly separated by the kidneys and the bladder. These liquors also proceed from the blood and seem similar to its serum but yet they are different from it. For when fire is applied to them in an evaporating basin [cochlea] they do not coagulate, as the blood-serum always does. Indeed, not even the colliquamentous liquid of the egg itself coagulates in this manner, although it is formed from juices which are evidently liable to coagulation — in the same way humours differ from themselves before and after digestion, filtration, and the other operations [mangonial of nature. All, when distilled, give over a soft and clear water [mollem et lenem] very like distilled milk. This property is common to the liquor of the allantoic space, along with the rest. Because when the salts are not yet made wild and exalted the serum of the blood remains still quite soft and does not give proof of a tartaric or saline nature. Indeed, the first urine of an infant is observed by nurses to be not at

SECT. 3] AND EIGHTEENTH CENTURIES 163

all salt, but in older animals, when I distilled it in an alembic, I seemed to observe a little volatile salt at the small end [in capitello]. Coagulations attempted by acids happened differently in respect of the different humours. For when I poured a decoction of alumina into the liquor of the cow's amnios it exhibited a few rather fine coagulations but they were clearly white. The allantoic juice, however, was precipitated like urine. Spirits of vitriol and vinegar brought about less results than alumina in each case. Spontaneous concretions I found also in the later months; these I discovered in both places. They are more frequent and larger, however, within the allantoic membrane."

From the above excerpt, which contains the account of all that Needham did on the chemical composition of the embryonic liquids, it can be seen that he treated the whole matter more dynamically than Browne. He was the first to describe the solid bodies in the amniotic fluid (see Jenkinson) and his chemical experimentation was all pioneer work.

His book has other merits, however. In the first chapter, he refutes the theory which Everard had propounded, that the uterine milk was identical with the contents of the thoracic duct, conveyed by lymphatic vessels to the uterus from the lac teals of Aselli, instead of elsewhere, and he shows that arteries must be the vessels bringing the material to the womb. The second chapter deals with the placenta "where he giveth a particular account of the double Placenta or Cake, to be found in Rabbets, Hares, Mice, Moles, etc., and examines the learned Dr Wharton's doctrine, assigning a double placenta to at least all the viviparous animals, so as one half of it belongs to the Uterus, the other to the Chorion, shewing how far this is true, and declaring the variety of these Phaenomena. Where do occur many uncommon observations concerning the difference of Milk [uterine] in ruminating and other animals, the various degrees of thickness of the uterin liquor in oviparous and viviparous creatures". He describes the human placenta very correctly indeed. "The use of the placenta is known to be to serve for conveighing the aliment to the foetus. The difficulty is only about the manner. Here are examined three opinions, of Curvey, Everhard, and Harvey. The two former do hold that the foetus is nourished only from the Amnion by the mouth ; yet with this difference, that Curvey will have it fed by the mouth when it is perfect, but whilst it is yet imperfect, by filtration

i64 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

through all the pores of the body, and by a kind of juxtaposition : but Everhard, supposing a simultaneous formation of all the instruments of nutrition together and at first, and esteeming the mass of bloud by reason of its asperity and eagerness unfit for nutrition, and rather apt to prey upon than feed the parts, maintains, that the liquor is sucked out of the amnion by the mouth, concocted in the stomack, and thence passed into the Milky Vessels even from the beginning. Meantime they both agree in this, that the embryo doth breath but not feed through the umbilicall vessels. This our Author undertakes to disprove; and having asserted the mildness of, at least, many parts of the bloud, and consequently their fitness for nutrition, he defends the Harveyan doctrine of the colliquation of the nourishing juyce by the Arteries and its conveyance to the foetus by the veins."

In the third chapter Needham gives the first really comparative account of the secondary apparatus of generation, enunciating the rather obvious rule that in any given case the number of membranes exceeds the number of separate humours by one. He affirms that all the humours are nutritive save the allantoic. It had previously been held that all fish eggs were of one humour only, but he points out that a selachian egg has its white and yolk separate. He gives the results of his chemical experiments at this point, and suggests that the noises heard from embryos in utero and in ovo may be due to the presence of air or gas in the amniotic cavity, thus forming a link between Leonardo and Mazin. In his fourth chapter he deals with the umbilical vessels and the urachus, and here he claims priority over Stensen for the discovery of the ductus intestinalis in the chick, referring to Robert Boyle, Robert Willis, Richard Lower and Thomas Millington, to whom, he says, he showed the duct before Stensen published his observations on it. The fifth chapter is concerned with the foramen ovale, and the arterial and venous canals, and with the foetal circulation in general. The sixth is about respiration or "biolychnium", and in it Needham writes against the conception of a vital flame, alleging cold-blooded animals, etc., in his favour, but here he takes a retrograde step, for he argues that the use of the lungs is not for respiration but to "comminute the bloud and so render it fit for a due circulation". "The seventh and last chapter contains a direction for the younger Anatomists, of what is to be observed in the dissection of divers animals with young, and first, of what is

SECT. 3] AND EIGHTEENTH CENTURIES 165

common to the viviparous, then, what is pecuHar to severall of them, as, a sow, mare, cow, ewe, she-goat, doe, rabbet, bitch, and a woman, lastly, what is observable in an Egg, skate, salmon, frog, etc. All is illustrated with divers accurate schemes."

The subsequent course of chemical embryology in the seventeenth century may be put in a very few words. Marguerite du Tertre incorporated in her obstetrical text-book of 1677 the results of some similar experiments to those of Needham. "If you heat the (amniotic) liquor", she says, "it does not coagulate, and if you boil it it flies away leaving a crass salt like urine, but if you heat the serosity of blood, it solidifies as if it were glue." The same observation was recorded by Mauriceau in 1687, who concluded, with some common sense, that, as there was so little solid matter present, the liquid could not be very nutritive; and by Case in 1696, who said, "In this juice the plastic and vivifying force resides, for although to our eyes it looks in colour and consistency like the serum of the blood, yet it is absolutely \toto coelo] different; for if a little of the former is slowly evaporated \si in cochleari super ignem defines] no coagulation will ever appear." Lister said this once more in 171 1, but with Boerhaave's work of 1732 the subject entered a new phase.

In 1670 Theodore Kerckring published an adequate work on foetal osteology, and, two years later, de Graaf and Swammerdam, making full use of the opportunities afforded them by the invention of the microscope, described in detail the ova of mammalia, thus demonstrating the truth of Stensen's suggestion of some years before. It is important to note that these workers mistook the "Graafian follicles" for the eggs — a mistake which was not rectified till the time of von Baer. Stensen himself published not long after an account of these eggs also, but he was by then too late to gain the priority of demonstration. Portal's claim that Ferrari da Grado, who lived in the fifteenth century, was the true discoverer of mammalian ova has been disproved by Ferrari; and, although it is true that Volcher Goiter described what we now call the Graafian follicles, he did not recognise in any way their true nature.

De Graaf 's discovery was confirmed in 1678 by Caspar Bartholinus, and, in 1674, by Langly, whose original observations had been made, so it was said, in 1657, the year of Harvey's death. If this is true, Langly has the priority of observation, Stensen of theory and de Graaf of demonstration.

i66 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

3-7. Marcello Malpighi: Micro- Iconography and Preformationism

In the year 1672, Marcello Malpighi, who had for many years previously been working on various embryological problems with the aid of the simple microscope, published his tractates De Ovo Incubato and De Formatione Pulli in Ovo. In spite of its great importance, there is not much to be said about it, for it is anything but a voluminous work. The plates in which Malpighi represented the appearances he had seen in his examination of the embryo at different stages are beautiful, and some of them are reproduced. Description of the embryo was now pushed back into the very first hours of incubation, and it is interesting to note that Malpighi could not have done his work without Harvey, whose name he mentions on his first page, and who pointed out the cicatricula as the place where development began, and therefore, as Malpighi must have reasoned, the place where microscopic study would be very profitable. Now for the first time the neural groove was described, the optic vesicles, the somites, and the earliest blood-vessels.

Malpighi opened the modern phase of the controversy preformation versus epigenesis by supporting the former view. Embryogeny, he held, is not comparable to the building of an artificial machine, in which one part is made after another part, and all the parts gradually "assembled", but takes place rather by an unfolding of what was already there, like a Japanese paper flower in water. He was led to this belief by the fact that development goes on after fertilisation as the tgg passes down the oviduct, and in the most recently laid eggs gastrulation is already over, so that in his researches he could never find an absolutely undivided egg-cell. It is curious to note that he says his experiments were done "mense Augusti, magno vigente calore'\ so that more than a usual degree of development would have taken place overnight. Had he examined the cicatriculae in hens' eggs before laying, he would very probably not have formed this theory, and the epigenesis controversy would have been settled with Harvey. Another influence which was unfavourable to the epigenetic position was that it was Aristotelian, and therefore unfashionable. Yet Malpighi's view was much more sensible than many which succeeded it, for he did not maintain a perfectly equal swelling up of all parts existing at the start, but rather an unequal unfolding,

SECT. 3]

AND EIGHTEENTH CENTURIES

167

a distribution of rate of growth at different times and in different regions of the body. Thus he says, "Now, as Tully says, Death truly belongs neither to the living nor to the dead, and I think that something similar holds of the first beginnings of animals, for when we enquire carefully into the production of animals out of their eggs, we always find the animal there, so that our labour is repaid and we see an emerging manifestation of parts successively, but never the first origin of any of them".

Ti£ JCr

I>e Cue .

^^'

1. 1? J

Ti>-ia.

Ti^ lOI.

Fig. 8. Malpighi's drawings of the early stages of development in the chick embryo.

What had been an unfounded speculation for Seneca in antiquity and for Joseph de Aromatari and Everard in late times was now set upon an apparently firm experimental basis by Malpighi.

It is most instructive to note the difference in the attitudes of Langly and Schrader respectively towards the preformation question. Langly has no doubts about it, nor has Faber; they both follow Harvey and epigenesis unquestioningly, but Schrader, although he believes in epigenesis on the whole, is not at all certain about it. His friend, Matthew Slade, he says, brought the epistle of Joseph de Aromatari to his attention, and what with that and the unexplained observations of Malpighi on the pre-existence of the embryo, he is not willing to deny all value to preformationist doctrine. Others were bolder. It was immediately seized upon by Malebranche, the

1 68

EMBRYOLOGY IN THE SEVENTEENTH [pt. n

Streeter of his age, who, in his Recherche de la Verite of 1672, reaHsed its philosophical possibilities, and gave it a kind of metaphysical sanction. That mystical microscopist, Swammerdam, made use of it as an explanation of the doctrine of original sin. In a remarkably short space of time it was a thoroughly established piece of biological theory.

Malebranche refers to it in his Recherche de la Verite in the chapter where he treats of optical illusions and emphasises the deceitfulness and inadequacy of our senses. "We see", he says, "in the germ of a fresh Qgg which has not been incubated an entirely formed chicken. We see frogs in frogs' eggs and we shall see other animals in their

B^-xh

Fig. 9. Malpighi's drawings of the chick embryo's blood-vessels.

germs also when we have sufficient skill and experience to discover them. We must suppose that all the bodies of men and animals which will be born until the consummation of time will have been direct products of the original creation, in other words, that the first females were created with all the subsequent individuals of their own species within them. We might push this thought further and belike with much reason and truth, but we not unreasonably fear a too premature penetration into the works of God. Our thoughts are, indeed, too gross and feeble to understand even the smallest of his creatures." Malebranche, who was a priest of the Oratory of the Cardinal de Berulle, took an ardent interest in the scientific life of his time — for example, in a letter to Poisson, the Abbe Daniel wrote, "Reverend Father, M. Malebranche has written to me saying that he has installed an oven in which he has hatched eggs. He has already opened

PLATE VII

I.XVI

lu Ouc

XVI.

ILLUSTRATIONS FROM MALPIGHI'S DE OVO INCUBATO OF 1672 Showing the early stages of the development of the chick, somites, area vasculosa, etc.

SECT. 3] AND EIGHTEENTH CENTURIES 169

some and has been able to see the heart formed in them and beating, together with some of the arteries" (Blampignon).

Swammerdam's support for preformation came from a different angle. He had been investigating insect metamorphosis, and, having hardened the chrysalis with alcohol, had seen the butterfly folded up and perfectly formed within the cocoon. He concluded that the butterfly had been hidden or masked {larvatus) in the caterpillar, and thence it was no great step to regard the Qgg in a similar light. Each butterfly in each cocoon must contain eggs within it which in their turn must contain butterflies which in their turn must contain eggs, and so on. Before long, Swammerdam extended this theory to man. "In nature", he said, "there is no generation but only propagation, the growth of parts. Thus original sin is explained, for all men were contained in the organs of Adam and of Eve. When their stock of eggs is finished, the human race will cease to be."

In 1684 Zypaeus reported that he had seen minute embryos in unfertilised eggs, and there were other similar claims. ^Hinc recentiores physiologV\ said Schurigius in 1732, ^^ hominem in ovulis delineatum quoad omnes partes in exiguis staminibus ante conceptionem existere statuunt"

Swammerdam cannot be regarded simply as one of the principal pillars of the preformation theory. His own embryological researches, which were made chiefly on the frog, were remarkable in many ways. He was the first to see and describe the cleavage of the eggcell and later segmentation. He said that there was a time during the development of the tadpole when its body consisted of granules {greynkens or klootkens), but as these grew smaller and much more numerous they escaped his penetration. Leeuwenhoek also saw these cells, and his account was published long before Swammerdam's, but his observations on the rotating embryos oi Anodon and the eggs of fleas were equally interesting.

3-8. Robert Boyle and John Mayow

In 1674 John Mayow, a young Oxford physician, published his tractate, De Respiratione Foetus in Utero et Ovo, which was included as one of the parts of his Tractatus Quinque medico-physici in that year. Mayow was the first worker to realise that gaseous oxygen, or, as he termed it, the " nitro-aerial " vapour, was the essential factor in the burning of a candle and the respiration of a living animal. His work

170 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

was forgotten until Beddoes drew attention to it in 1 790, but since then many have praised it and Schultze makes him the equal of Harvey.

The reason why he became interested in embryology is given in the opening sentences of his work. "Since the necessity of breathing", he says, "is so essential to the sustaining of life that to be deprived of air is the same as to be deprived of common light and vital spirit, it will not be out of place to enquire here how it happens that the foetus can live though imprisoned in the straits of the womb and completely destitute of air." He first of all gives an account of the opinions held about foetal respiration and the umbilical cord. He says that he disagrees (i) with the view that the embryo breathes per OS while it is in the womb, for there is no air in the amnion and the suctio infantuli proves nothing; and (2) with the view propounded by Spigelius that the umbilical vessels existed to supply blood to the placenta for the nourishment of the latter. If this were the case, he says, the membranes in the hen's egg could not be formed before the vitelline vein, as they are, and in cases of foetal atrophy the placenta would always die and be corrupted too, which does not happen. Nor does he support the view of Harvey (3) that the umbilical vessels supply blood for the concoction and colliquation of the food of the foetus, for why should not the embryonic body prepare its own nutritious juice before birth just as it does afterwards. He further thinks the theory (4) that the umbilical vessels are for carrying off surplus foetal nourishment quite untenable and as little likely as the theory (5) that they exist for the object of allowing a foetal circulation — for this could just as well be accomplished through the vessels which exist in the embryonic body.

Mayow decides therefore for the opinion of divino sene Hippocrate and Everard that the umbilicus is a respiratory mechanism, carefully dissociating himself, however, from the hypothesis of Riolanus that the umbilical cord with all its windings is so arranged to cool the blood passing through it. He then says, "We observe, in the first place, that it is probable that the albuminous juice exuding from the impregnated uterus is stored with no small abundance of aerial substance, as may be observed from its white colour and frothy character [Needham's uterine milk]. And in further indication of this, the primogenial juices of the egg, which have a great resemblance to the seminal juice of the uterus, appear to abound in air particles. For if the white or the yolk of an tgg be put into a glass from which

SECT. 3] AND EIGHTEENTH CENTURIES 171

the air is exhausted by the Boyhan pump these liquids will immediately become very frothy and swell up into an almost infinite number of little bubbles and into a much greater bulk than before — a sufficiently clear proof that certain aerial particles are most intimately mixed with these liquids. To which I add that the humours of an tgg when thrown into the fire, give out a succession of explosive cracks which seem to be caused by the air particles rarefying and violently bursting through the barriers which confined them. Hence it is that the fluids of the egg are possessed of so fermentative a nature. For it is indeed probable that the spermatic portions of the uterus and its carunculae are naturally adapted for separating aerial particles from arterial blood. These observations premised, we maintain that the blood of the embryo, conveyed by the umbilical arteries to the placenta or uterine carunculae, brings not only nutritious juice, but along with this a portion of nitro-aerial particles to the foetus for its support, so that it seems that the blood of the infant is impregnated with nitro-aerial particles by its circulation through the umbilical vessels quite in the same way as in the pulmonary vessels. And therefore I think that the placenta should no longer be called a uterine liver but rather a uterine lung". These splendid words, informed by so much insight and scientific acumen, show that, by the time of Mayow, chemical embryology had definitely come into being. He died at the early age of thirty-six, and we may well ponder how different the subsequent course of this kind of study would have been if he had lived a little longer.

The second part of Mayow's treatise is concerned with respiration in the hen's egg during its development, and it may be noted that his observations on the air contained in the liquids before development probably account for the facts which have been reported at one time and another concerning an alleged anaerobic life of embryos in early stages. Mayow is wrong in supposing that the gas which he pumped out from white and yolk was purely "nitro-aerial", but he shows the greatest good sense in his reminder that the amount of nitro-aerial particles required by embryos must be comparatively small owing to their small requirement for "muscular contraction and visceral concoction". His remarks on the effect of heat on the developing egg are not so clear as the remainder of the treatise, but he seems to mean that the heat will disengage the nitro-aerial particles from the liquids, and so aid in respiration, an idea which was later

172 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

used by Mazin. His fundamental mistake here was that he failed to realise that the egg-shell was permeable to air; and this vitiates all his reasoning about the respiration of the egg. "It will not be irrelevant", he says, "to enquire here whether the air which is contained in the cavity in the blunter end of every egg contributes to the respiration of the chick." He first notes that the cavity in question lies between two membranes and not between the shell-membrane and the shell as Harvey himself had supposed ; and then he goes on to say that he disagrees with the opinion of Fabricius, who had asserted that the air in the air-space serves for the respiration of the chick. His reasons are (i) that there would not be enough therein for the needs of the embryo which would use it, as it were, in one gulp, and (2) that the air in it cannot pass through the inner membrane, an error into which he was led by observing that, if an egg-shell with its contents removed and its air-space intact, was put into a vacuum, the air-space would swell up until it was as big as the egg itself. Mayow sees now what had escaped the attention of all previous observers, namely, that the egg-contents are not "rarefied or expanded, but are on the contrary condensed and forced into a narrower space than before". Such a condensation could, he thinks, take place in four ways, (a) by an increase in propinquity of discrete particles, (b) by a subsidence of motion on the part of a congregation of particles into rest, (c) by the extraction of some subtle spirit from amongst the particles, and, (d) by a decrease in elasticity on the part of some elastic substance previously present. We should at the present time choose the third alternative as being the truest, in view of the loss of water and carbon dioxide which the egg suffers as it develops, but Mayow chose the fourth, thinking it probable that the "air distributed among the juices of the egg loses its elastic force on account of the fermentation produced among these juices by incubation". Now since the egg-contents are compacted into smaller bulk by the process of incubation, a vacuum would be created somewhere if Nature had not, with her customary prudence, inserted a small amount of air into the air-space which might in due course expand and avoid this. His proof for this was an inaccurate observation; he thought he saw, in eggs at a late stage, when the contents were removed, the air-space collapse to the normal size which it occupies in unincubated eggs. He expressly says that his theory does not depend upon the conception of horror vacui, but that, by the compressive

SECT. 3] AND EIGHTEENTH CENTURIES 173

action of the imprisoned air, the fluids of the egg would be forced into the umbiHcal vessels, and the particles composing the embryonic body packed more tightly together. "The internal air appears to perform the same work as the steel plate bent round into numerous coils by which automata are set in motion."

With this ingenious but erroneous supposition Mayow concludes what is undoubtedly the first great contribution to physiological or biophysical embryology. His views on foetal respiration were soon generally accepted, as the writings of Zacchias, Viardel, Pechlin and John Ray show, but Sponius as late as 1684 was asserting that the lungs of the foetus were functional in utero, absorbing from the amniotic liquid the nitro-aerial particles which P. Stalpartius supposed the placenta to be secreting into it. It is interesting to note that by Mayow's own air-pump method Bohn found nitro-aerial particles in the uterine milk in 1686, and Lang found them in the amniotic liquid in 1 704. The problem had by then arrived at a stage beyond which it could not progress in the absence of quantitative methods.

The year 1675 saw the publication of Nicholas Hoboken's useful treatise on the anatomy of the placenta, and of the English edition of P. Thibaut's Art of Chymistry. I mention the latter here, because of a reference to the special conditions of embryonic life which is found in it. As yet no real help was being given to embryology by contemporary chemistry.

The Magistery and Calx of Egg-shells.

Obs. 2. That you must use the eggshells of hens and not of ducks, geese, or turkeys because that hens eggshells easier calcin'd being thinner by reason that a hen is a more temperate animall; waterfowl are hotter and by reason of their heat do concoct and harden their eggshells more than other fowl ; and from thence it comes that you must have a greater quantity of your Dissolvant, employ more heat, and spend more time to calcine the eggs of waterfowl than those of hens.

About this time also Francis Willoughby published his famous book on birds, an attempt to bring Aldrovandus up to date, in which a good picture is given of the embryological knowledge of the time, although no new observations or theories are given. Another contemporary review is that of Barbatus.

In 1677, spermatozoa were discovered, as announced by Hamm and Leeuwenhoek in the Philosophical Transactions of the Royal Society,

174 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

though Hartsoeker afterwards claimed that he had seen them as early as 1674, but had not had sufficient confidence to publish his results. There is a reference to this in the letters of Sir Thomas Browne, who, writing to his son, Dr Edward Browne, on December 9, 1679, said, "I sawe the last transactions, or philosophicall collections, of the Royal Society. Here are some things remarkable, as Lewenhoecks finding such a vast number of little animals in the melt of a cod, or the liquor which runnes from it ; as also in a pike ; and computeth that they much exceed the number of men upon the whole earth at one time, though hee computes that there may bee thirteen thousand millions of men upon the whole earth, which is very many. It may bee worth your reading".

At the same time as these events were taking place, Robert Boyle, at Oxford and London, was engaged in carrying out those experiments in chemistry which led him before long to write his Sceptical Chymist. It is not generally known that in this work, which appeared in 1680, and which set the key for the whole spirit of subsequent physico-chemical research, Boyle has a reference to embryology, and, curiously enough, in connection with a point which, although it is easily seen to be of the highest importance, has been quite overlooked by the commentators upon him. One of the main things he was trying to urge was that, until some system could be proposed which would give a means of quantitative estimation of the constituents of a mixture, no further progress would be made. He was asking, in fact, that chemistry should become an exact science, and his demand is only veiled by the unfamiliarity of his language. His preference for the "mechanical or corpuscularian" philosophy was mainly due to his realisation that, unless chemistry was going to start measuring something, it might as well languish in the obscurity to which Harvey would have willingly relegated it. Thus he says, "But I should perchance forgive the Hypothesis I have been all this time examining (that of the alchemists), if, though it reaches but to a very little part of the world, it did at least give us a satisfactory account of those things which 'tis said to teach. But I find not that it gives us any other than a very imperfect information even about mixt bodies themselves; for how will the knowledge of the Tria Prima discover to us the reason why the Loadstone drawes a Needle, and disposes it to respect the Poles, and yet seldom precisely points at them? how will this hypothesis teach us how a Chick is formed

SECT. 3]

AND EIGHTEENTH CENTURIES

175

in the Egge, or how the seminal principles of mint, pompions, and other vegetables, can fashion Water into various plants, each of them endow'd with its peculiar and determinate shape and with divers specifick and discriminating Qualities? How does this hypothesis shew us, how much Salt, how much Sulphur, how much Mercury must be taken to make a Chick or a Pompion? and if we know that, what principle is it, that manages these ingredients and contrives, for instance, such liquors as the White and Yolke of an Egge into such a variety of textures as is requisite to fashion the Bones, Arteries, Veines, Nerves, Tendons, Feathers, Blood and other parts of a Chick; and not only to fashion each Limbe, but to connect them altogether, after that manner which is most congruous to the perfection of the Animal which is to consist of them? For to say that some more fine and subtile part of either or all the Hypostatical Principles is the Director in all the business and the Architect of all this elaborate structure, is to give one occasion to demand again, what proportion and way of mixture of the Tria Prima afforded this Architectonick Spirit, and what Agent made so skilful and happy a mixture?" Boyle's instance of the magnetic needle pointing nearly, not exactly, at the north, and his use of the expressions "how much, how many, proportion, way of mixture", indicate that he was moving towards a quantitative chemistry, and by express implication a quantitative embryology. Elsewhere he says that he thinks the Tria Prima will hardly explain a tenth part of the phenomena which the "Leucippian" or atomistic hypothesis is competent to deal with. Thus, although Boyle made few experiments or observations on embryos, he occupies a very important position in the history of embryology. During the last two decades of this century, the Oxford Philosophical Society were occupied on a good many occasions with problems relating to embryology. It is extremely interesting to note, in connection with what we have just seen in Boyle, that John Standard of Merton College reported on February 10, 1685, "the following obbs. concerning ye weight of ye severall parts of Henn's eggs ; done with a pair of scales which turned with \ a grain.

ozs. dr.

A henn's egg weighed 2

The skin weighed

The shell The yolk The white

grns.

15

16

4

Loss in weighing

[ujf LIBRARY

176 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

ozs. dr. scr. grns.

Another raw egg of the same sort ... 2 i 2 13

Another

The former egg boiled

Lost in boiling

The skin

The shell

The yolk

The white

2 I I 19

.2 I I 18

• - - - 15

13

- I 2 19

- 5 - 7 I 2 - 13

Loss in weighing 5

Another early quantitative observation was that of Claude Perrault who found about 1680 that developing ostrich eggs lost one-ninth of their weight in five weeks. The Oxford Philosophical Society, however, preferred as a rule to consider more unusual things, such as "the egges of a parrot hatched in a woeman's bosome, a hen egg figur'd like a bottle, a hen egg that at the big ende had a fleshie excrescence, another hen-eg, monstrous, a suppos'd cocks egg, and the eggs of a puffin, an elligug, and a razor-bill". Mention of these different kinds of eggs reminds us that the systematic collection and classification of eggs had been begun some years before by Sir Thomas Browne (as may be seen in John Evelyn) and by John Tradescant. About this time R. Waller made some noteworthy observations on the "spawn of frogs and the production of Todpoles therefrom", extending the work begun by Swammerdam not long before. Mauriceau now gave a description of the phenomenon of sterile foetal atrophy. The century fittingly closes with Michael Ettmiiller's ponderous treatise, in which all the embryological work of the seventeenth century is summarised with considerable accuracy. He supported the moribund menstruation theory of embryogeny with the argument that animals do not menstruate because they are more prolific than men, and therefore all their blood is required for generation. Garmann's Oologia curiosa, which appeared in 1691, is worth mention also, as a review of the knowledge of the time. But that his work was what the booksellers' catalogues describe as "curious" is shown by the following chapter-headings: De ovo mystico, rnpthico, magico, mechanico, medico, spagyrico, magyrico, pharmaceutico.

3-9. The Theories of Foetal Nutrition

During the course of the seventeenth, and the first quarter of the eighteenth, century, many theories were propounded concerning foetal nutrition. It is convenient to classify them.

SECT. 3] AND EIGHTEENTH CENTURIES 177

I. That the embryo was nourished by the menstrual blood.

Beckher, 1633.

Plempius, 1644. (He did not deny that the umbilical cord was

functional, but insisted that the blood passing through it was

menstrual.)

In 1 65 1 Harvey's work was published. Sennertus, 1654. Seger, 1660. van Linde, 1672. F. Sylvius, 1680. Cyprianus, 1700.

II. That the embryo was nourished by its mouth. {a) By the amniotic liquid.

(A) In addition to the umbilical blood. Harvey, 1651. W. Needham, 1667. de Graaf, 1677.

C. Bartholinus, 1679. van Diemerbroeck, 1685. Ortlob, 1697.

D. Tauvry, 1700. Linsing, 1701. PauH, 1707. Barthold, 1717.

S. Middlebeek, 17 19. Teichmeyer, 17 19. Gibson, 1726.

(B) Alone; the umbilical blood being regarded as unnecessary or of minor importance, Moellenbroeck, 1672. Cosmopolita, 1686. Everardus, 1686. P. Stalpartius, 1687. Bierling, 1690.

Case, 1696. (Case thought the embryo arose entirely out of the amniotic liquid like a precipitate from a clear solution.) Berger, 1702.

These persons referred as their principal experimental basis to cases in which embryos had been born without umbilical cords, e.g. of those of: Rommelius, 1675 (in Velsch). Valentinius, 1 7 1 1 .

178 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

(b) By the uterine milk or succum lacteo-chylosum.

Mercklin, 1679. Drelincurtius, 1685. Bohnius, 1686. Zacchias, 1688. Tauvry, 1694. Franc, 1722. Dionis, 1724.

III. That the embryo was nourished through the umbiHcal cord only.

{a) By foetal blood (the circulations distinct).

Arantius, 1595.

Harvey, 1651.

W. Needham, 1667.

F. Hoffmann, 1681. (He proved the point by injection long before Hunter, who is stated by Cole to have been the first to demonstrate this.)

Ruysch, 1 70 1.

Snelle, 1705.

Falconnet, 171 1.

It is to be noted that Bierling, P. Stalpartius, Berger, Barthold, and Charleton, who supported the discontinuity theory of the circulations, were all upholders of the theory of foetal nourishment per os, so that their reasons for doing so were not those on account of which we agree with Hoffmann and Needham at the present time.

{b) By maternal blood (the circulations continuous).

Laurentius, 1600.

de Marchette, 1656.

Rallius, 1669.

Muraltus, 1672.

Blasius, 1677.

Veslingius, 1677.

Hamel, 1700.

de Craan, 1703.

Lang, 1704.

van Home, 1707.

Freind, 171 1. (Freind's Emmenologia deserves a special mention. He proved by a calculation that the amount of blood passing through the umbilical cord would be sufficient for the needs of the embryo. This is a parallel to Harvey's famous calculation about the circulation of the blood. He also quotes some experiments of

SECT. 3] AND EIGHTEENTH CENTURIES 179

Rayger and Gayant, who injected a blue dye into the foetal circulation and found it again in the maternal. Therefore he regards it as continuous.)

Mery, 171 1. (Mery combated Falconnet's view of the separate circulations. He said that he had not himself tried Falconnet's experiment, but that some students had, and could not repeat it.)

Aubert, 1 7 1 1 . (Narrative of a case in which the umbilical cord had not been tied at the maternal end and the mother had nearly bled to death through it.)

Nenterus, 17 14.

Wedel, 1 71 7.

Bellinger, 171 7. (Bellinger believed that the maternal blood was transformed by the embryonic thymus gland into proper nourishment for itself, after which it was secreted into the mouth by the salivary ducts and so went to form meconium without the necessity for deglutination. Heister's comments on this extraordinary theory are worth reading. Perhaps Bellinger was indebted to Tauvry for his idea of the importance of the thymus gland. Tauvry had drawn attention in 1700 to its diminution after birth.)

de Smidt, 17 18.

Dionis, 1724.

(c) By menstrual blood.

Plempius, 1644.

(d) By uterine milk.

Ent, 1687.

Camerarius, 17 14. {Opinio conciliatrix!)

F. Hoffmann, 1718.

{e) By the amniotic fluid.

Vicarius, 1700. Goelicke, 1723.

IV. That the embryo was nourished by pores in its skin.

Deusingius, 1660. Nitzsch, 1 67 1. Stockhamer, 1682.

This was suggested on the ground that in the earlier stages of development there is no umbilical cord. In 1684 St Romain argued against it on the ground that, if it were true, the embryo would dissolve in the amniotic liquid.

i8o EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

During this period also there were continued disputes about the origin of the amniotic liquid, van Diemerbroeck and Verheyen considered that it could not be the sweat of the embryo, for the embryo was always much too small to account for it, and, moreover, Tertre had described cases where the secundines had been formed with the membranes but in the absence of the embryo. Dionis affirmed that, whatever it was, it could not be urine, for urine will not keep good for nine days, a fortiori not for nine months. Drelincurtius put forward a theory that the embryo secreted it from its eyes and mouth by crying and salivating, while Bohn and Blancard derived it from the foetal breasts. Lang, Berger and Gofey criticised this notion without bringing forward anything constructive, and Gofey was in his turn annihilated by D. Hoffmann, who with Nenter and Konig supported the modern view, namely, that it was a transudation from the maternal blood-vessels in the decidua. The question was complicated further by the alleged discovery by Bidloo in 1 685 of glands in the umbilical cord, and by Vieussens in 1 705 of glands on the amniotic membrane. J. M. Hoffmann and Nicholas Hoboken supported the view that these were the important structures. There the problem was left during the eighteenth century, various writers supporting different opinions from time to time, and it is still under discussion (see Section 22).

Very early in the eighteenth century (1708) there appeared a work by G. E. Stahl, van Helmont's most famous follower, which struck the keynote of the whole century. Stahl's Theoria Medica Vera, divided as it was into Physiological and Pathological sections, belonged in essence to the a priori school of Descartes and Gassendi. It differed from them profoundly, of course, for, instead of trying to explain all biological phenomena, including embryonic development, from mechanical first principles, it started out from first principles of a vitalistic order, and, having combined all the archaei into one informing soul, it sought to show how the facts could be perfectly well explained on this basis. But the spiritual kinship of Stahl with Descartes and Gassendi is due to an atmosphere which can only be called doctrinaire, and which was common to them all. Like the methodist school of Hellenistic medicine, they subordinated the data to a preconceived theory, during which process any awkward facts were liable to be rather submerged than subordinated.

SECT. 3] AND EIGHTEENTH CENTURIES 181

In 1722 Antoine Maitre-Jan published his book on the embryology of the chick, the only one on this subject between Malpighi and Haller. It was an admirable treatise, illustrated with many drawings which, though not very beautiful, were as accurate as could be expected at the time. Perhaps its most remarkable characteristic is its almost complete freedom from all theory — Maitre-Jan says hardly a word about generation in general, and is far from putting forward a "system" in the usual eighteenth-century manner. He contents himself with the recital of the known facts, including those added by his own observations. He gives no references, and writes in an extremely modern and unaffected style.

The only traces of theoretical presupposition which can be found in him are Cartesian, for he speaks of the activity of ferments in blood-formation. He is an epigenesist, and long before Brooks, he gives the right explanation of Malpighi's error, affirming that the hot Italian summer was responsible for some development in Malpighi's eggs before Malpighi examined them. Maitre-Jan's book must have been accessible both to Buffon and Haller, so it is difficult to see why they should have perpetuated Malpighi's mistake till nearly the end of the century.

In technique, Maitre-Jan was pre-eminent. He was the first embryologist to make practical use of Boyle's suggestion regarding "distilled spirits of vinegar" for hardening the embryo so that it could be better dissected. He also used "weak spirits of vitriol"; after treating blastoderms with it, he said, "I saw with pleasure an infinity of little capillary vessels which had not appeared to be there before". He made a few chemical experiments also, noting that vinegar would coagulate egg-white, and estimating quantitatively the difference in oil-content of different yolks — though for this he gives no figures.

His theory he relegated to an appendix entitled Objections sur la generation des animaux par de petits vers. There were sixteen of them, but the most cogent one was that, as little worms had been found under the microscope in pond-water, vinegar, and all kinds of liquids, there was no reason to suppose that those in the semen were in any essential way connected with generation. For his time, this argument was an excellent one, and was open to no demur save on the ground of filtration experiments which had not yet been made (see p. 215).

i82 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

About this time there was some controversy over the circulation of blood, the foramen ovale, etc., in the embryo. From 1700 to 1710, Tauvry and Mery were engaged in a polemic on this subject, and the latter also corresponded with Duverney, Silvestre and Buissiere in a controversy which recalls that of Laurentius and Petreus a hundred years before. Nicholls wrote later on the same subject. Daniel Tauvry was interesting, however, for other reasons. He was an epigenesist, and wrote vigorously against the view that the soul constructed during embryogeny a suitable home for itself.

Nine years later two books appeared, which form very definite landmarks in the history of embryology. One was Martin Schurig's Embryologia, and the other the Elementa Chymiae of Hermann Boerhaave.

The former, however, gave to the world no new experiments or observations ; it was the first of what we should now call the typical "review" kind of publication. Schurig saw that he was living at the end of a great scientific movement following the Renaissance, and set himself accordingly for many years to compile large treatises on definite and restricted subjects, taking care to give all references with meticulous accuracy, and to omit no significant or insignificant work. His Spermatologia was the first to appear (in 1720), and it was followed in 1723 by Sialologia (on the saliva), Chylologia (1725), Muliebria (1729), Parthenologia (1729), Gynaecologia (1731) and Haematologia (1744). His Embryologia was the last but one of the series. In it he treated compendiously of all the theories which had been advanced about embryology during the immediately preceding two centuries, and his chapters on foetal nutrition and foetal respiration throw a flood of light on to the "intellectual climate" in which Harvey and Mayow worked, providing, as it were, the perishable background of their immortal thoughts. Schurig's bibliography is a very striking part of his book, extending to sixteen pages, and including five hundred and sixty references; it was the first attempt of its kind.

3-10. Boerhaave, Hamberger, Mazin

Hermann Boerhaave was a more prominent figure, a Professor at Leyden for many years, and renowned for his encyclopaedic learning on all subjects remotely connected with medicine. His Elementa Chymiae, which became the standard chemical book of the whole period, demonstrates throughout the exceedingly wide outlook of its

SECT. 3] AND EIGHTEENTH CENTURIES 183

author, and contains in the second volume what must be regarded as the first detailed account of chemical embryology. I reproduce here the relevant passages in full because of their great interest. It will be noted that they are cast in the form of lecture addresses, as if they had been taken down direct from the lectures of the Professor, a fact which gives them a peculiar charm when it is remembered how many great men must have listened to them, among them Albrecht von Haller and Julien de la Mettrie. In considering what follows, it should be noted that Boerhaave's interest is biological all the time, and that he does not treat the liquids of the egg, as nearly all the chemists before him had done, as substances of curious properties indeed, but quite remote from any question relating to the development of the embryo. Another interesting point is that he deals only with the white, and hardly mentions the yolk; this is perhaps to be explained by the Aristotelian theory that the embryo was formed out of the white, and only nourished by the yolk {ex alb fieri, ex luteo nutriri), a theory which was still alive, in spite of Harvey, in the first half of the eighteenth century. If this was what was at the bottom of Boerhaave's mind, then it is obvious that the egg-white would be to him the liquid inhabited more particularly by the plastic force. This, then, is what he has to say about the biochemistry of the egg.

Op. Chem. in Animalia. [Processus log.] The albumen of a fresh egg is not acid, nor alkaline, nor does it contain a fermented spirit. The white of a fresh egg, separated from the shell, the membranes, and the yolk, I enclose in clean glass vessels, and into each of these I pour different acids, and shake them up, mixing them, and no sign of ebullition appears however I treat them. Therefore I lay these vessels aside. Now in these other two vessels I have two fresh portions of albumen, and I mix with them in one case alkaline salt and in the other volatile alkali. You see they are quiet without any sign of effervescence. Now behold a remarkable thing, in this tall cylindrical vessel is half an ounce of the albumen of an egg and two drams of spirits of nitre, in this other vessel is half an ounce of egg-white, together with four and a half ounces of oil of tartar per deliquium both heated up to 92 degrees. Pray observe and behold, with one movement I pour the alkaline albumen into the acid albumen, with what fury they boil up, into what space they rarefy the mass, so that they stream out of the vessel although it is ten pints in size [decupli capace] . They have scarcely changed their colour. But when the effervescence has abated how suddenly they return to the limits of space occupied before. But now if more egg-white is heated to 100 degrees in a retort [cucurbita] an insipid water containing

i84 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

no spirit is given off. If egg-white is applied to the naked eye or naked nerve it does not give the smallest sense of pain, and scarcely affects the smell; nothing more inert and more insipid can be put on the tongue. It appears mucous and viscid to the touch, not at all penetrable. Hence in the fresh white of an egg there is no alkali or acid, or both together. It is indeed a thick, sticky, inert, and insipid liquor, yet from this truly vital liquid at a heat of 93 degrees within the space of 2 1 days the chick grows in the incubated egg from a tiny mass hardly weighing a hundredth of a grain into the perfect body of an animal, weighing an ounce or more. We have learnt therefore of a liquid distinct from all others, from which by inscrutable causes fibres, membranes, vessels, entrails, muscles, bones, cartilages, and all the other parts, tendons, ligaments, the beak, the claws, the feathers, and all the humours can be produced — and yet in this liquid we find softness, inertia, absence of acid, alkali, and spirit, and no tendency to effervesce. Indeed, if there were the slightest effervescence in it, it would certainly break the eggshell, therefore we see from how slow and inactive a mass all the solid and fluid parts of the chick are constructed. And yet this itself is rendered absolutely useless for forming the chick by greater heat. It scarcely bears 100 degrees with good effect but at a less temperature never brings forth a chick, for under 80 degrees will not suffice. But by a heat kept between these limits, there is brought about so marvellous an attenuation of the mucous inactivity that it can exhale a great part through the shell of the egg and the two membranes, the yolk and chalazae alone remaining along with the amniotic sac. For the yolk, the uterine placenta of the chick, takes little part in the nourishment. Meanwhile Malpighius has shown that this albumen is not a liquid of a homogeneous kind, as the blood-serum flowing through the vital vessels is, but that it is a structure composed of numerous membrane-like and distinct small saccules, filled with a liquid of their own, in the same way as in the vitreous humour of the eye.

[Processus 1 1 1 .] Exploration of the egg-white with alcohol. In this transparent vessel is the albumen of an egg, and into it, as you perceive, I gently pour the purest alcohol, so that it descends down the sides of the vessel and reaches the albumen. I do this deliberately and with such solicitude that you may see the surface of the albumen which, touching the alcohol, holds it up, being immediately coagulated, while the lower part remains liquid and transparent. As I now gently shake them together, it appears evident that wherever the alcohol touches the albumen a concretion is formed. Behold now, while I shake them up thoroughly together, all the egg-white is coagulated. If alcohol previously warmed is employed in this experiment, the same result is brought about but more rapidly. It appears therefore that the purest vegetable spirits immediately coagulate the plastic and nutrient material.

[Processus 112.] The fresh albumen of an egg is broken up by distillation. These fresh eggs have been cooked in pure water till they became hard. I now take the shining white, separating off all the other things, and break it up into small pieces. I put these, as you see, into a clean glass retort

SECT. 3] AND EIGHTEENTH CENTURIES 185

[cucurbita] and I duly cover it by fitting on an alembic and add a receiver. By the rules of the (chemical) art I place the whole retort in a bath of water and I apply to it successive degrees of fire until the whole bath is boiling. No vaporous streaks [^strid] of spirits are given off but simple water in dewy drops and this in incredible quantity, more than nine-tenths. I continue so with patience until by the heat of boiling water no more drops of this humour are given off. Then this water shows no trace of oil, salt, or spirit ; it is perfectly transparent and tasteless, except that it eventually grows rather sour. It is odourless, save that towards the end it gives off a slight smell of burning. It shows absolutely no sign of the presence of any alkali, when I test it in every way, as you can see for yourselves ; nor does it reveal any trace of acid, when tried how you will. Here you see pounds of this water, but in the bottom of the now open retort see, I beg of you, how little substance remains. Behold, there are fragments contracted into a very small space in comparison with the former quantity. They are endowed with a golden yellow colour, especially where they have touched the glass, but yet they are transparent after the manner of coloured glass. When I take them out I find them very light, very hard, quite fragile, and breaking apart with a crack, smelling slightly of empyreuma, with a taste rather bitter from the fire, and without any flavour of alkali or acid. This is the first part of the analysis. Now I take these remaining fragments in a glass retort [retortam] in such a way that two-thirds remain over. I put the retort into a stove of sand, first arranging a large receiver. Then thoroughly luting all the joints I distil by successive grades of fire and finally by the highest which I call suppressionis. There ascends a spirit, running in streaks [^striatim] fat and oily, and at the same time, volatile salts of solid form everywhere on the walls of the vessel, rather plentiful in proportion to the dried fragments but small in proportion to the whole albumen before the water had been removed from it. Finally an oil appears besides the light golden material mixed with the first, black, thick, and pitchy. When by the extreme force of the fire this oil is finally driven forth, then the earth in the bottom, closely united with its most tenacious oil, swells up and is rarefied and rises right up to the neck of the retort so that had the retort been overfull it would have entered into the neck and clogged it up, even causing it to burst, with danger to the bystanders. The operation is to be continued till no more comes out. That first spirit, oily and fatty, is clearly alkaline by every test, as you may tell from the way it effervesces when acid is poured on it. If we rectify it we resolve it into an alkaline volatile salt, an oil, and inert foetid water. The salt fixed to the walls is completely alkaline, sharp, fiery, oily, and volatile; and the final oil is specially sharp, caustic, and foetid. The black earth which remains in the retort is shiny, light, thin, and fragile, foetid from the final empyreumatic oil, and soft because of it. If then it is burnt on an open fire, it leaves a little fixed earth which is white, insipid, tasteless, and odourless, from which scarcely any salt can be extracted, but only a very heavy dusty powder \^pollinein\.

Cf. the dry distillation of egg-white by Pictet & Cramer in 1919.

i86 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

[Processus 113.] The fresh albumen of an egg will putrefy. Sound eggs kept at 70° for some days will become foetid and stink. . . .We have learnt then that this is the nature of the material which will shortly be changed into the structure, form, and all the parts of the animal body. Repose and a certain degree of heat produce that effect in that material. We observe therefore the spontaneous corruption and change of the material, and what is extremely remarkable, if an impregnated egg is warmed in an oven [in hypocaustis] to a heat of 92 degrees it employs these attenuated parts changed by such a heat to nourish, increase, and complete the chick for 21 days. But in this chick nothing alkaline, foetid, or putrid is found, hence observe, O doctors [medici] , the remarkable manifestations of nature ^by repose and a certain degree of heat a thick substance becomes thin, a viscous substance becomes liquid, an odourless substance becomes foetid, an insipid substance becomes sour and extremely acrid and bitter to the taste, a soothing substance becomes caustic, a non-alkali becomes alkaline, a latent oil becomes sweet and putrid. Let these results be compared with the observations of Marcellus Malpighius on the incubated egg, and we shall observe things which shall surprise us. I took care to investigate only the albumen of the egg first of all, separating the other parts off where possible, for the albumen alone forms the whole of the material which proceeds to feed [in pabulum] the embryo. The other constituents of the egg only assist in changing the albumen, so that when it is changed, it miay be applied to forming the structure of the chick.

Boerhaave's treatment of these subjects has only to be compared with that of Joachim Beccher, who wrote in 1 703, to show how thoroughly modern in outlook it is. Beccher's Physica Subterranea contains a whole section devoted to the growth of the embryo, but it is extremely confused and very alchemical in its details. The advance made in the thirty years between Beccher and Boerhaave was immense, but, if the biochemistry of development advanced so fast, its biophysics was not far behind, as is shown by the work of G. E. Hamberger and J. B. Mazin.

Hamberger's most important contributions, contained in his Physiologia medica of 1 75 1 , were his quantitative observations on the watercontent of the embryo and its growth-rate, in which he had no forerunners, Hamberger showed "that there are much less solid parts in the foetus than in the adult. The cortical substance of the brain of an embryo loses 8694 parts in 10,000 on drying but in the adult it only loses 8096 and that of the cerebellum from 81 parts is reduced to 12. The maxillary glands of the embryo lose out of 10,000 parts 8469, the liver 8047, the pancreas 7863, the arteries 8278 and even the cartilages lose four-fifths of their weight, decreasing from 10,000 to 8149I ". The

SECT. 3] AND EIGHTEENTH CENTURIES 187

corresponding figures for the adult were: liver 7192, and heart 7836. These figures do not widely diflfer fi:-om those obtained in recent times.

J. B, Mazin published his Conjecturae physico-medico-hydrostaticae de respiratione foetus in 1737 and his Tractatus medico-mechanica in 1742. In the first of these works Mazin supports what is essentially Mayow's theory of embryonic respiration, without, however, mentioning Mayow more than once. It had not been popular since 1700, though Pitcairn had defended it. Mazin put the liquids of eggs under an air-pump, and observing that air could be extracted from them affirmed that the air was hidden in them and that the embryo could therefore respire. He spoke of "aerial particles" in the amniotic liquid, and discussed the respiration of fishes in connection with this. The specific gravity of the embryo also interested him, and he did a great deal of calculation and experiment on it. His most interesting passage, perhaps, is that in which he mentions the "Eolipile" of the Alexandrians, the primitive form of the steam-engine, and says that just as the heat of the fire makes the water boil, so the heat of the viscera makes the amniotic liquid boil, giving off respirable vapours. The time-relations of this analogy are interesting, for in 1705 Thomas Newcomen had succeeded in making a steam-engine which worked with considerable precision, and the question of steampower was widely discussed. Possibly Mazin was acquainted with the Marquis of Worcester's Century of the Names and Scantlings oj Inventions, which had been published in 1663, and which had contained an aeolipile or "water-commanding machine". England was the centre of this movement and other countries employed Englishmen as engineers; Humphrey Potter, for instance, erected a steamengine for pumping at a Hungarian mine in 1 720.

As for the discovery of oxygen, it was near at hand, and Scheele in 1 773 and Priestley in 1 774 were soon to supply the knowledge without which Mazin could not proceed further.

In his second book, Mazin reported many quantitative observations on the specific gravity of the embryo. He found that it diminished as development proceeded, being to the amniotic liquid as 282 to 274 in the fourth month and as 504 to 494 in the fifth month.

Another instance of the way in which experimental physical questions now began to come in is afforded by the work of Joseph Onymos, whose De Matura Foetu of 1 745 spoke of the specific gravity of the embryo at different stages of development.

i88 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

These writers, together with Haller himself, and J. C. Heffter who handled problems of embryonic rate of growth contribute to one of the best, because most quantitative, aspects of eighteenthcentury embryology.

3*11. Albrecht von Haller and his Contemporaries

Boerhaave's greatest pupil was Albrecht von Haller. Like O. W. Holmes, at Harvard, Haller occupied a "settee" rather than a "chair", at Gottingen, and taught not only physiology but also medicine and surgery, botany, anatomy and pharmacology. Nor did he merely deal with so many subjects superficially; in each case he published what amounted to the best and most complete text-book up to then written. Haller was made Professor in 1736, and for many years worked at Gottingen, devoting much of his time to embryological researches, which, with those of his opponent Wolff, stand out as the greatest between Malpighi and von Baer. In 1 750 he published a series of dissertations and short papers on all kinds of physiological subjects, which would have been the direct ancestors of the modern compilations of groups of experts, had they been more systematically arranged. The volume on generation repays some study. The contributions relevant to the present discussion had been written at various times during the previous seventy years, and may be summarised as follows :

IV. Christopher Sturmius, De plantarum animaliumque generatione. (First published 1687.) In this paper Sturmius argues on behalf of the preformation theory "which in our times does not lack supporters", quoting Perrault, Harvey and Descartes. He contents himself with countering arguments which had been urged against it, as, {a) spontaneous generation, {b) annual recurrence of plants, {c) insect metamorphosis, {d) generation without copulation. V. Rudolf Jacob Camerarius, Specimen experimentorum physiologicotherapeuticorum circa generationem hominis et animalium. The most interesting thing about this is that Camerarius mentions the observations of D. Seiller, a sculptor, who had ascertained that the body is five times the size of the head in the embryo but seven and a half times the size of it in the adult. This is in the direct line between Leonardo and Scammon.

SECT. 3]

AND EIGHTEENTH CENTURIES

189

XV. Philip Gravel, De Super Joetatione. (First published 1738.)

XVIII. Adam Brendel, De embryone in ovulo ante conceptum praeexistante. (First published 1703.) Brendel "stands for the Graafian hypothesis. Unfortunately, he was also a preformationist and believed that every limb, organ, and function existed not potentially but actually in the unfertilised Qgg before its passage down the Fallopian tube.

XXII. Camillus Falconnet, Non est fetui sanguis maternus alimento. (First published 171 1.) This is the first of the French contributions to the book; they are all very markedly shorter than the German ones and much less heavily ornamented with irrelevant quotations. Falconnet is concerned to prove that the maternal and foetal circulations are separate, and he describes in an admirably concise manner an experiment in which he bled a female dog to death, after which, opening the uterus, he discovered that the embryonic blood-vessels were full of blood although those of the mother had none in at all. Arantius was therefore justified. Falconnet was soon confirmed by Nunn.

XXIII. Jean de Diest's Sui Sanguinis solus opifex fetus est (first published 1735) was written to prove a similar point. He refers to the experiment of Falconnet and the injections of F. Hoffmann, and criticises Cowper's experiment in which mercury had been injected into the umbilical vessels and found in the maternal circulation, on the grounds that mercury is so "tenuous and voluble" that it might pass where blood could not pass normally. He also objects to the view that the foetus is nourished by the amniotic liquid.

XXIV. Francis David Herissant, Secundinae fetui pulmonis praestant officia, et sanguine materno fetum non alitur. (First published in 1 741.) An excellent paper, in which the respiratory function of the placenta is proved by the observation that the foetal blood-vessel leading to the placenta is always full of dark venous blood, while that leading away fi-om the placenta is light and arterial [floridiori coccineoque colore, ut ipsemet observavi]. Herissant adduces also the cases of acephalic monsters, such as that of Brady, which could not possibly have drunk up any amniotic fluid, and yet were fully formed

igo THE EIGHTEENTH CENTURY [pt. ii

in all other respects. He concludes that the umbilical cord serves for respiration and nutrition.

XXV. After these three French workers, there is a great drop to Johannes Zeller, whose Infanticidas non absolvit nee a tortura liberal pulmonum infantis in aqua subsidentia (first published

1 691) is a long-winded discussion of the floating lung test in forensic medicine. His memory deserves a word of obloquy for his vigorous insistence upon torture and death for infanticide even during puerperal insanity. Perhaps it was Zeller who called forth the noble answer of de la Mettrie to this inhumanity in his Man a Machine.

XXVI. Zeller's De Vila Humana ex June pendenle (first published

1692) is no better, though at the time, perhaps because of its striking title, it was famous. It deals with the ligation of the umbilical cord at birth.

This completes the list of the papers published by Haller in his 1750 collection. He retired from the Gottingen chair three years later, and in 1757 the first volume of his Elemenla Physiologiae was published, probably the greatest text-book of physiology ever written. It appeared only by slow degrees, so that it was not until 1766 that the embryological section was available. This volume contains a discussion of a mass of literature, most of which had arisen during the preceding twenty-five years, for, although many of the names mentioned by Haller occur also in Schurig, yet many are quite new.

Haller himself published in 1 767 a volume of his collected papers on embryology, most of which were concerned with the developing heart of the chick, which he worked out very thoroughly, in collaboration with Kuhlemann. (Kuhlemann had already done for the sheep what Harvey had done for the doe.) He made a beginning with the quantitative description of embryogeny, and one of his tables showing the changing lengths of the bones is reproduced herewith (Fig. 10). He was a convinced preformationist, a fact which was largely due to his researches on the hen's egg, where he observed that the yolk had a much more intimate connection with the embryo than had previously been supposed. Since the whole yolk was part of the embryo, as it were, the preformation theory seemed to him to fit the facts better than epigenesis.

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192 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

Haller went further than Schurig, in that he usually gave an opinion of his own after summarising those of other people, but his views were by no means always enlightened, and the atmosphere of Buffon is, on the whole, more congenial to us than that of Haller. Haller, for example, believed that the amniotic liquid had nutritious properties, and that the nutrition of the embryo in mammalia was accomplished first of^ all per os and afterwards per umbilicum. He denied that the placenta had any respiratory function, and, indeed, his whole teaching on respiration was retrograde. He mentions, however, an experiment of Nicolas Lemery's, in which it had been found that indigo would penetrate the shell of a developing hen's tgg from the outside. Consequently, air might do so too, and Vallisneri had shown that, if an egg was placed in boiled water under an air-pump, the air inside would rush out through the shell and appear in the form of bubbles.

Haller was much more progressive in holding the origin of the amniotic liquid (according to him a subject of extraordinary difficulty — " solutionem non promittam'") to be a transudation from the maternal blood-vessels. He followed Noortwyck in asserting the separateness of the maternal and foetal circulations in mammalia. He opposed the existence of eggs in vivipara — "We may conclude from all this", he said, "that the ovarian vesicles are not eggs and that they do not contain the rudiments of the new animal". But he accepted it in the restricted sense that the embryonic membranes resembled an egg, thus: "If we call an egg a hollow membranous pocket full of a humour in which the embryo swims, we may admit the opinion of the older authors who derive all animals from eggs with the exception of the tiny simple animals of which we have already spoken. It was in this sense that Aristotle and Empedocles before him, said that even trees were oviparous. This has also been confirmed by the experiments of Harvey on insects, fishes, birds, and quadrupeds".

Haller's most original work was in connection with the growthrate of the embryo ; here he struck out, for once, into entirely new country. "The growth of the embryo in the uterus of the mother is almost unbelieveably rapid. We do not know what its size is at the moment of its formation, but it is certainly so small that it cannot be seen even with the aid of the best microscopes, and it reaches in nine months the weight of ten or twelve pounds. In order to clear

SECT. 3] AND EIGHTEENTH CENTURIES 193

up this speculation, let us examine the growth of the chick in the egg. We cannot in this case either measure its size at the moment when the egg is put to incubate but it cannot be more than j^ in. long, for if it were, it would be visible, and yet 25 days later it is 4 ins, long. Its relation is therefore as 64 to 64 millions or i to i million. This growth takes place in a singular manner, it is very rapid in the beginning and continually diminishes in speed. The growth on the first day is from i to gi^^ and what Swammerdam calls a worm grows in one day from one-twentieth or one-thirtieth of a grain to seven grains, i.e. it increases its weight by 140 or 240 times. On the second day the growth of the chick is from i to 5, on the third day, from i to not quite 4, on the fifth day from i to something less than 3. Then from the sixth to the twelfth day, the growth each day is hardly from 4 to 5, and on the twenty-first day it is about from 5 to 6. After the chick has hatched, it grows each day for the first 40 days at an approximately constant rate, from 20 to 2 1 on each day. The increase of the first twenty-four hours is therefore in relation to that of the last twenty-four hours as 546I to 5 or 145 to i. Now as the total increase in weight in the egg is to that of the whole growth period (up to the adult) as 2 to 24 ozs., all the post-embryonic growth is as i to 12, i.e. it is to the growth of one day alone early in incubation as i to 7|.. . .The growth of man, like that of the chick, decreases in rapidity as it advances. Let us suppose that a man, at the instant of conception, weighs a hundred-thousandth of a grain and that a one-month old embryo weighs 30 grains; then the man will have acquired in that time more than 300,000 times the weight that he had to begin with. But if a foetus of the second month weighs 3 ozs. as it approximately does, he will only now have acquired 48 times the weight he had at the beginning of the period. This is a prodigious decrease in speed, and at the end of the ninth month he will not weigh more than about 105 ozs., which is not more than an average increase of 15 per month. A child three years old is about half the size of an adult. If then the adult weighs 2250 ozs. the three-year old child only weighs 281 ozs., which is an eighth of the adult weight. Now from birth to 3 years he will grow from 105 to 281 or as 5 to 14, but in the following 22 years he will only accumulate 2250 ozs. or eight times what he had at 3 years. The growth of a man will therefore be in the first month of intrauterine life as I to 300,000, in the second as i to 48, in each of the

N E I 13

194 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

others as i to 15. In the first 3 years of extra-uterine life his growth will be from 164 to 281 and in the succeeding 22 years from 281 to 384, and the growth of the first month to the last will be as 300,000 to ^% or 136,800,000 to 28, or 4,885,717 to i. The whole growth of man will consequently be as 108,000,000 to i."

In spite of the rather unfamiliar language in which these facts are described, and the theory of the growth of the heart which Haller subsequently put forth to explain them, they remain fundamental to embryology. Their quantitative tone is indeed remarkably modern. In my opinion, when all the voluminous writings of Haller are carefully searched through, nothing more progressive and valuable than these figures can be found. Haller and Hamberger stand thus between Leonardo on the one hand and Minot and Brody on the other. That they stood so much alone is only another indication of the extraordinary reluctance with which the men of past generations assented to the truth contained in Robert Mayer's immortal words, "Eine einzige Zahl hat mehr wahren und bleibenden Wert als eine kostbare Bibliothek von Hypothesen".

Of development as a whole, Haller spoke thus, " In the body of the animal therefore, no part is made before any other part, but all are formed at the same time. If certain authors have said that the animal begins to be formed by the backbone, by the brain, or by the heart, if Galen taught that it was the liver which was first formed, if others have said that it was the belly and the head, or the spinal marrow with the brain, adding that these parts make others in turn, I think that all these authors only meant that the heart and the brain or whatever organ it was, were visible when none of the other parts yet were, and that certain parts of the embryonic body are well enough developed in the first few days to be seen while others are not so until the latter part of development; and others again not till after birth, such as the beard in man, the antlers in the stag, the breasts and the second set of teeth. If Harvey thought he descried an epigenetic development, it was because he saw first a little cloud, then the rudiments of the head, with the eyes bigger than the whole body, and little by little the viscera being formed. If one compares his description with mine, one will see that his description of the development of the deer corresponds exactly with mine of the development of the chick. If, more than twenty years ago, before I had made many observations upon eggs and the females of quadrupeds I employed this reasoning to prove

SECT. 3] AND EIGHTEENTH CENTURIES 195

that there is a great difference between the foetus and the perfect animal, and if I said that in the animal at the moment of conception one does not find the same parts as in the perfect animal, I have realised abundantly since then that all I said against preformation really went to support it". The reasons for this change of opinion become no clearer as Haller's writings are more assiduously read, and, as Dareste says, why he should have made it, will always remain a mystery.

The emboitement aspect of preformation presented no difficulties to Haller. "It follows", he said, speaking of the generation of Volvox, "that the ovary of an ancestress will contain not only her daughter, but also her granddaughter, her great-granddaughter and her greatgreat-granddaughter, and if it is once proved that an ovary can contain many generations, there is no absurdity in saying that it contains them all,"

The following passage is interesting. "We must proceed to say what is the efficient cause of the beautiful machine which we call an animal. First of all let us not attribute it to chance, as Ofrai [is this Julien Offi-ay de la Mettrie? Haller had a habit of using Christian names, e,g, Turberville for J. T. Needham] would have us do, for although he pretends that all animals come from earth, he is not attached to the ancient opinion, and nobody now believes what Aelian says, namely that frogs are born from mud. . . , Vallisneri has found the fathers and mothers of the little worms in galls, a quest of which Redi despaired, and Redi in his turn has made with exactitude and precision those experiments which Bonannus, Triumphet, and Honoratus Faber had only sketched out imperfectly. Moreover, no seed, no clover. . . . This was the received opinion but in our century a proscribed notion has been revivified and some great men have pretended that there are little animals which are engendered by an equivocal generation, without father and mother, and that all the viscera and all the parts of these animals do not exist together, but that the nobler parts are formed first by epigenesis and that then the others are formed little by little afterwards." This is an admirable illustration of how spontaneous generation and epigenesis were bound up together, "M. Needham", Haller goes on to say, "does not admit an equivocal generation but he does admit epigenesis, and a corporeal non-intelligent force, which constructs a body from a tiny little germ furnishing the necessary matter for it. He says that there are only

13-2

196 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

the primitive germs which were made at the original creation and that germs organised Hke animals do by no means pre-exist, for if they did, molae uterinae, encysted tumours, and the like, could not come into being." Haller then goes on to describe Needham's experiments with meat broths, etc., and objects to his "system", largely on the ground that "blind forces without any intelligence could hardly be able to form animals for ends foreseen and ready to take their places in the scheme of beings". He considers that Needham's theories are completely disproved by experiments such as those of Spallanzani, though, curiously enough, he does not quote the latter author in this connection. I shall return to this later.

"Nobody", he goes on to say, "has upheld epigenesis more than M. Wolff, who has undertaken an examination to demonstrate that plants and animals are formed without a mould out of matter by a certain constant force which he calls 'essential' [in his Theoria Generationis] .... I have indeed seen many of the phenomena which he describes, and it is certain that the heart seems to be formed out of a congealed humour and that the whole animal appears to have the same consistency. But it does not follow that because this primitive glue which is to take on the shape of the animal does not appear to possess its structure and all its parts, it has not effectively got them. I have often given greater solidity to this jelly by the use merely of spirits of wine and by this means I saw that what had appeared to me to be a homogeneous jelly was composed of fibres, vessels, and viscera. Now surely nobody will say that the vis essentialis of the spirit of wine gave an organic structure to an unformed matter, on the contrary it is rather in the removal of transparency and the accession of greater firmness to the extremities, as well as the making of a more obvious boundary to the contour of a viscus that one could see the structure of a cellular tissue, which was ready to be formed but which the transparency had previously hidden and the wetness not allowed to be circumscribed by lines. . . . Finally, to cut a long story short, why does this vis essentialis, which is one only, form always and in the same places the parts of an animal which are so different, and always upon the same model, if inorganic matter is susceptible of changes and is capable of taking all sorts of forms? Why should the material coming from a hen always give rise to a chicken, and that from a peacock give rise to a peacock? To these questions no answer is given." This was the

SECT. 3] AND EIGHTEENTH CENTURIES 197

case because Wolff was not a theorist, but rather an experimentalist; his writings are marked by their abstention from the discussion of speculative points. The above passage is very interesting. It reminds us of the great difficulties with which the embryologists of this epoch had to contend. Serial section cutting was unknown, the staining of thin layers and reconstruction were unheard of; even the hardening of the soft embryonic tissues was only just discovered, as is indicated by Haller above. Hertwig has excellently discussed the advances in embryological technique which took place during this and the following century. It is true that dyes were beginning to be used, as some instances already given demonstrate, and as is seen from the use of madder in the staining of bones, which began about this time, and was later much used by the Hunters. Heertodt's Crocologia is important in this connection. Heertodt, by injecting saffron into the maternal circulation, found it afterwards in the amniotic fluid, and his experiment was cited by Haller in support of that theory of the origin of the liquid. But the most important advance in technique was the progress in artificial incubation. The art, though lost throughout the Middle Ages and the seventeenth century, was now to be revived.

During this period much work was done on it. As far back as 1 600, de Serres had mentioned some experiments of this nature, but they were not successful. "The chicks", he said, "were usually born deformed, defective or having too many legs, wings, or heads, nature being inimitable by art." Birch, in his History of the Royal Society, also refers to it. "Sir Christopher Heydon [a relative of Digby's Sir John?] together with Drebell, long since in the Minories hatched several hundred eggs but it had this effect, that most of the chickens produced that way were lame and defective in some part or other." Antonelli states that similar trials were made at the court of the Grand-duke Ferdinand II at Florence about 1644, Thomas Bartholinus gives a like account with reference to the contemporary court of King Christian IV of Denmark, and Poggendorff and Antinori relate that the Accademia d. Cimento, inspired by Paolo del Buono, made trial of artificial incubation between 1651 and 1667.

But the most famous of all the attempts to make artificial as successful as natural incubation, were those of Reaumur, whose book De I' art defaire eclore les poulets of 1749 achieved a wide renown. He devotes many chapters to a detailed description of incubators of very

198 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11

various kinds : but he nowhere gives any indication of his percentage hatch. It was probably low. He speaks also of the ^^funestes effets'^ of the vapours of the dung on the developing embryos, without, however, furnishing any foundation for an exact teratology. In the second volume he describes those experiments on the preservation of eggs by varnishing them, which caught the imagination of Maupertuis and were held up to an immortal but by no means deserved ridicule by Voltaire in his Akakia. For the details of this amusing but irrelevant issue see Miall and Lytton Strachey.

After Reaumur, there were numerous continuations of the kind of work which he had done, in particular by Thevenot, La Boulaye, Nelli, Porta and Cedernhielm. Much the most interesting of these was the work of Beguelin, who attempted to incubate eggs with part of the shell removed so as to form a round window. He was not, however, successful in the carrying out of this very modern idea. Probably the most peculiar investigation made in this field at this time was that of Achard, who is mentioned in a passage of Bonnet's. "Reaumur did not suspect in 1749", says Bonnet, "that someday one would try to substitute the action of the electric fluid for his borrowed heat. This beautiful invention was reserved for M. Achard of the Prussian Academy who excels as an experimentalist. He has not so far succeeded in actually hatching a chick by means of so new a process, but he has had one develop up to the eighth day, when an unfortunate accident deranged his electrical apparatus." Bonnet goes on to say that this substitution of electricity for heat gives him hope that by electrical means an artificial fertilisation will one day become possible.

The references to these experiments and to those of many minor investigators will be found in Haller. By the beginning of the nineteenth century a great mass of literature had developed on the subject, and it had become possible to hatch out eggs more or less successfully from furnaces, though the losses were still great. Early in the nineteenth century Bonnemain and Jouard referred to the large number of monsters produced, and in 1809 Paris wrote, "During the period that I was at College, the late Sir Busick Harwood, the ingenious Professor of Anatomy in the University of Cambridge, frequently attempted to develope eggs by the heat of his hotbed, but he only raised monsters, a result which he attributed to the unsteady application of the heat".

PLATE VIII

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This is the most convenient place to mention theological embryology once again. Its place in the eighteenth century was small, and in the nineteenth, with the recognition that whatever the soul is, it is not a phenomenon, it altogether disappeared from serious general discussion. F. E. Cangiamilla's Embryologia Sacra, however, ran through several editions between 1700 and 1775. Cangiamilla {Panorm. Eccl. Can. Theol. et in toto Sicil. regno contra haereticam pravitatem Inquisitore provinciali) deals very frilly with the time of animation, quoting a host of writers such as St Gelasius, St Anselm, Hugh of St Victor and Pico della Mirandola. His mind retains a quite mediaeval conformation, as the following curious passage illustrates : '^ Quot non foetus abortivos ex ignorantia obstetricum et matrum excipit lafrina, quorum anima, si Baptismate non fraudaretur, Deum in aeternam videret, esset decentius tumulandum! " His instructions for the baptism of monsters are also very odd. But theological embryology probably reached its climax in the report of the Doctors of Divinity at the Sorbonne on March 30, 1733, in which intra-uterine baptism by means of a syringe was solemnly recommended. This is included in Deventer's book, and has been referred to by Sterne and Spencer. For other aspects of these tracts of thought see Nicholls and his anonymous antagonist. But Cangiamilla and his colleagues — Gerike, Kaltschmied, etc. — are only of decorative importance to our present theme, and for fuller information regarding them, reference must be made to the treatise of Witovski. It is interesting to note that as late as 1913, 182 days was fixed as "perfection-time", whatever that may be, by Moriani.

3*12. Ovism and Animalculism

We must now return to the beginning of the century in order to pick up the thread of the main trend of thought. By 1720 the theory of preformation was thoroughly established, not only on the erroneous grounds put forward by Malpighi and Swammerdam, but on the experiments of Andry, Hartsoeker, Dalenpatius and Gautier, who all asserted that they had seen exceedingly minute forms of men, with arms, heads, and legs complete, inside the spermatozoa under the microscope. Gautier went so far as to say that he had seen a microscopic horse in the semen of a horse (he gave a plate of it) and a similar animalcule with very large ears in the semen of a donkey; finally, he described minute cocks in the semen of a cock.

200 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

Haller remarks gently that he has searched for these phenomena in vain. Vallisneri asserted the same kind of thing about the mammahan ovum, though he admitted that, in spite of long searching, he had never seen one. Besides the main distinction between prefer mationists and epigenesists, then, there arose a division among the former group, so that the ovists regarded all embryos as being produced from smaller embryos in the unfertilised eggs, while the animalculists regarded all embryos as being produced from the smaller embryos provided by the male in his spermatozoa. The animalculists thus afforded a singular example of a return to the ancient theory mentioned by Aeschylus in the Oresteia (see p. 65). Their most conspicuous example was Nicholas Andry, who pictured each c^gg as being arranged like the Cavorite sphere in which H. G. Wells' explorers made their way to the moon, i.e. with one trap-door. The spermatozoa, like so many minute men, all tried to occupy an egg, but as there were far fewer eggs than spermatozoa, there were, when all was over, only a few happy animalcules who had been lucky enough to find an empty egg, climb in, and lock the door behind them.

The whole controversy was intimately bound up with the question of spontaneous generation, for, whatever the case might be in the higher animals, if it were true that the lower ones could arise de novo out of slime, mud, or meat infusion, for instance, then their parts at least must have been made by epigenesis, and not in any other way, for it could hardly be held that a homogeneous infusion had any structure of that kind. And if epigenesis could occur in the lower animals, then the thin end of the wedge had been driven in, and it might occur among the higher ones as well. It was in this way that the spontaneous generation controversy came to have a peculiar importance for embryology in the eighteenth century. Driesch has essayed to make the generalisation that all the supporters of epigenesis were vitalistic in their tendencies, while those who adhered to the preformation theory were not. But there are too many exceptions to this rule to make it of any use. In so far as there is truth in it.

Fig. 1 1 . Hartsoeker's drawing of a human spermatozoon.

SECT. 3] AND EIGHTEENTH CENTURIES 201

it doubtless arose from the fact that, in epigenesis, a continual production of new organs and new relationships between organs already formed would seem to require an immanent formative force of some kind, such as the vis essentialis of Wolff; while, on the preformation hypothesis, where embryogeny was little more than a swelling up of parts already there, it could be explained as simply as nutrition. The failure of the "short-cut" mechanical philosophers such as Gassendi and Descartes thus led to preformationism just as much as to epigenesis. A remark of Cheyne's throws much light on this question, for in 17 15 he wrote, unconsciously following Gassendi's line of thought, "If animals and vegetables cannot be produced from matter and motion (and I have clearly proved that they cannot), they must of necessity have existed from all eternity". Preformationism was thus the only resource if the universal jurisdiction of the mechanical theory of the world was to be retained. Stahl and, later, Wolff, saw no point in retaining it, and carefully joined together what Descartes had, with equal care, put asunder.

The original discoveries of de Graaf and Stensen were extended by Tauvry in 1690 to the tortoise, and by Lorenzini in 1678 to the Torpedo', so that the eighteenth century began with an excellent basis for ovistic preformationism. The greatest names associated with this school were Swammerdam, Malpighi, Bonnet, v. Haller, Winslow, Vallisneri, Ruysch and Spallanzani. But there were many others, some of whom did valuable work, such as Bianchi, Sterre, Teichmeyer, Weygand, Perrault, Vercelloni, Vidussi, Bussiere, Fizes and Coschwitz. The treatises of Imbert and Plonquet were written from this point of view, as was the bright little dialogue of de Houpeville. J. B. du Hamel asserted that he could see the chick embryo in the Ggg before fertilisation, and Jacobaeus made a like affirmation in the case of the frog.

On the other side, that of animalculistic preformationism, the contestants were fewer. Their greatest names were Leeuwenhoek, Hartsoeker, Leibnitz and the cardinal de Pohgnac. In England the physicians Keil and Cheque supported this position, in France Geofroi and the obstetrician la Motte, in Germany Withof and Ludwig, and in Belgium Lieutaud. De Superville wrote in favour of it in the Philosophical Transactions of the Royal Society, and an anonymous Swedish work of some fame supported it. To the argument of Vallisneri that the existence of so many animalcules must be an

202 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

illusion, since Nature could hardly be so prodigal, the animalculists retorted by instancing such observations as that of Baster, who had taken the trouble to count the eggs of a crab and had found that they amounted to 12,444. James Cooke later elaborated a theory of a world of the unborn to which the spermatozoa could retire between each attempt to find a uterus in which they could develop — this avoided Vallisneri's argument. "All those other attending Animalcula, except that single one that is then conceived, evaporate away, and return back into the Atmosphere again, whence it is very likely they immediately proceeded; into the open Air, I say, the common Receptacle of all such disengaged minute sublunary bodies; and do there circulate about with other Semina, where, perhaps, they do not absolutely die, but live a latent life, in an insensible or dormant state, like Swallows in Winter, lying quite still like a stopped Watch when let down, till they are received afresh into some other Male body of the proper kind, to be again set on Motion, and ejected again in Coition as before, to run a fresh chance for a lucky Conception ; for it is very hard to conceive that Nature is so idly luxurious of Seeds thus only to destroy them, and to make Myriads of them subservient to but a single one." But Cooke's attractive hypothesis, published in 1762, came too late, as Punnett says, to save the animalculists.

On the experimental side. Garden and Bourguet came forward with descriptions of little men inside the animalcules, thus confirming the work of Gautier and Hartsoeker. It is fair to add, however, that Garden held quite enlightened views of the mutual necessity of egg and spermatozoon. La Motte maintained that the egg (which he identified with the Graafian follicle) was too big to go down the Fallopian tube, and Sbaragli, another writer on the animalculist side, agreed with him.

Leeuwenhoek, it must be admitted, indulged in assertions no less fantastic than those of his followers. He said there were spermatic animalcules of both sexes, as one could see by a slight difference near their tails, that they copulated, that the females became pregnant and gave birth to little animalcules, that young and feeble ones could be seen, that they shed their skins, and, finally, that some had been observed with two heads. Haller, who made good use, on the whole, of his strong vein of scepticism, characterised all these remarks as "only conjectures". (See Fig. 12.)

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203

As for the supporters of epigenesis, they were few, but they included Descartes, de Maupertuis, Antoine Maitre-Jan and John Turberville Needham. Von Haller affords some evidence against the identification of epigenesis with vitaHsm and preformation with mechanism, for he says, "Various authors have taught that the parts of the human body are formed by a mechanism depending on general laws (i.e. laws not simply of biological jurisdiction) or by the virtue of some ferment, or by rest and cold making crusts out of the different juices, or in other ways. All these (mechanical) systems have some resemblance to that of M. Wolff". Haller also speaks always of Wolff's vis essentialis as "blind". Minor writers on the epigenetic side were Tauvry, Welsh, Dartiguelongue, Bouger, Drelincurtius and Mazin. After 1 750 C. F. Wolff brought an abiding victory to their opinion.

Some maintained a quite independent position, such as Buffon, who welded together an epigenetic theory

of fertilisation with a ^^S- 12. Dalenpatius' drawings of human spermatozoa.

preformationist theory of embryogeny. Pascal (not the great Jansenist) put forward the chemical view that fertilisation consisted of a combination between the acid semen of the male and the "lixivious " semen of the female, no doubt because in chemistry acids were regarded as male and alkalies female. Claude Perrault and Connor also suggested that the formation of the embryo was a fermentation set up in the egg by the spermatic animalcule. In this they were following the example of van Helmont, who had originally suggested such a theory. In 1 763 Jacobi discovered how to fertilise fish eggs with milt; a practical matter which had a good deal of influence on biological theory. Launai alone still held to the Aristotelian conception of form and matter.

There is no need here to do more than glance at the spontaneous generation controversy itself, for it has always been well known in the history of biology, especially in connection with the subsequent

204 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

work of Pasteur. J. T. Needham's books, New Microscopical Discoveries of 1745 and Observations upon the generation, composition, and decomposition of animal and vegetable substances of 1 750, exercised a considerable influence. They were written after the French fashion (Needham had been educated at Douai) very concisely, and with some brilliance of style, and it is hardly true to say, as Radl does, that their experimental foundation was meagre. That it was inadequate was proved definitely as events turned out by Spallanzani. De Kruif 's account of the controversy is false and misleading, especially in its estimate of Needham who is much more truly described in the words of Louis Pasteur (see also Prescott).

Needham's case rested upon the statement that, if meat broth was placed in a sealed vessel and heated to a high temperature so that all life was destroyed in it, it would yet be found to be swarming some days later with microscopical animals. All depended, therefore, upon the sureness with which the vessel had been sealed and the efficacy of the heat employed to kill all the animalcules initially present, and, in the ensuing controversy, Needham lost to Spallanzani entirely on a question of technique. It may be remarked here, without irrelevance, that the problem is still unsolved; for all that was proved by the experiments of Spallanzani was that animals the size of rotifers and protozoa do not originate spontaneously from broth, and all that was proved by those of Pasteur was that organisms the size of bacteria do not originate de novo in that way. The knowledge which we have acquired in recent years of filter-passing organisms, such as the mosaic disease of the tobacco-plant, and phenomena such as the bacteriophage of Twort and d'Herelle, has reopened the whole matter, so that of the region between, for example, the semi-living particles of the bacteriophage (lO"^^ gram) and the larger sized colloidal aggregates (io~^^ gram) we know absolutely nothing. The dogmatism with which the biologists of the early twentieth century asserted the statement omne vivum ex vivo was therefore, like most dogmatisms, ill-timed.

But to dwell further on this would be a digression. The important point was that Spallanzani's victory was a victory not only for those who disbelieved in spontaneous generation, but also for those who believed in the preformation theory of embryogeny. By 1 786, indeed, that viewpoint was so orthodox that Senebier, in his introduction to an edition of Spallanzani's book on the generation

SECT. 3] AND EIGHTEENTH CENTURIES 205

of animals and plants, could treat the epigenesists as no better than atheists.

Spallanzani's views on embryology were largely drawn from his study of the development of the frog's egg. Here he went far beyond Bosius, but, in spite of many careful observations, he thought he saw the embryo already present in the unfertilised ova. This led him to claim that amphibia ought to be numbered among viviparous animals. His principal step forward was his recognition of the semen as the actual agent in fertilisation on definite experimental grounds — the narrative of his artificial insemination of a bitch is too famous to quote; he said it gave him more intellectual satisfaction than any other experiment he had ever done. This demonstration finally disposed of the aura seminalis which Harvey had found himself obliged to adopt on the grounds of his dissections on does. Curiously enough Spallanzani never convinced himself that the spermatozoa themselves were the active agents.

3-13. Preformation and Epigenesis

Of all the preformationists Charles Bonnet was the most theoretical. He was an adherent of that way of thinking mainly on the theoretical ground that the organs of the body were linked together in so intimate a manner that it was not possible to suppose there could ever be a moment when one or two of them were absent from the ranks. "One needs", he said, "no Morgagni, no Haller, no Albinus to see that all the constituent parts of the body are so directly, so variously, so manifoldly, intertwined as regards their functions, that their relationship is so tight and so indivisible, that they must have originated all together at one and the same time. The artery implies the vein, their operation implies the nerves which in their turn imply the brain and that by consequence the heart, and every single condition a whole row of other conditions." Bonnet compared epigenesis to crystal-growth in which particles are added to the original mass independently of the plan or scheme of the whole, i.e. in opposition to the growth of an organism, in which particles are added on only at certain places and certain times under the guidance of "forces de rapport". Przibram has recently discussed the question of how far such a comparison is admissible, but, in Bonnet's time at any rate, it became very famous. Bonnet made reference to Haller's discovery of the intimate relationship between embryo and yolk as evidence

2o6 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

for his theory. The embryo begins, according to him, as an exceedingly fine net on the surface of the yolk, fertilisation makes part of it beat and this becomes the heart, which, sending blood into all the vessels, expands the net. The net or web catches the food particles in its pores, and Bonnet supposed that, if it were possible to abstract all the food particles at one operation from the adult animal, it would shrivel and shrink up into the original invisible web from which it originated.

Bonnet was no more afraid of the emboitement principle than was Haller; indeed, he called it "one of the greatest triumphs of rational over sensual conviction". Many of his arguments were reproductions of Haller's, and he says in his preface that he had written his book some time before Haller's papers on the chick appeared, but then, finding his own views confirmed by the more experimentally founded ones of Haller, he determined to publish what he had set down. Thus in one place he says, " I shall be told, no doubt, that the observations on the development of the chick in the tgg and the doe in the maternal uterus make it appear that the parts of an organised body are formed one after another. In the chick for instance it has been observed that during the early part of incubation the heart seems to be outside the animal and has a very diflferent form to what it will have. But the feebleness of this objection is easy to apprehend. Some people wish to judge of the time when the parts of an organised body begin to exist by the time when they become visible to us. They do not reflect that minuteness and transparency alone can make these parts invisible to us although they really exist all the time".

Bonnet was therefore what might be called an " organicistic preformationist", for his objection to epigenesis lay in the fact that it apparently did not allow for the integration of the organism as a whole. His mistake was that he assumed the capacities of the adult organism to be present all through foetal life, whereas the truth is that they grow and differentiate in exactly the same way as the physical structure itself does. Bonnet's philosophical position, which has been analysed by Whitman, seriously contradicts the generalisation of Driesch that all the epigenesists were vitalists and all the preformationists mechanists. For Bonnet an epigenetic and a mechanical theory were one and the same; he hardly distinguished, as Radl says, between Descartes and Harvey; and it was just the neo-vitalistic

SECT. 3] AND EIGHTEENTH CENTURIES 207

idea of the organism as a whole that he could not fit in with epigenesis. Needham and Wolff were undoubtedly epigenesist-vitalists, and Bonnet was undoubtedly a preformationist-vitalist, but Maupertuis was equally clearly an epigenesist-mechanist.

G. L. Leclerc, Comte de Buffon, the most independent figure in the controversy, stood alone as much because of his erroneous experiments as because of his originality of mind. As has so often been observed, Buffon was not really an experimentalist at all: he was a writer, and preferred other people to do his experiments for him. The volume on generation in his Histoire Naturelle begins with a very long historical account of the work that had been done in the previous centuries on embryology. At the beginning of the section on reproduction in general he said, "The first and most simple manner of reproduction is to assemble in one body an infinite number of similar organic bodies and to compose the substance in such a manner that every part shall contain a germ or embryo of the same species and which might become a whole of the same kind with that of which it constitutes a part". Such an idea resembles the ancient atomistic speculations, and is explicated by W. Smellie, the obstetrician, who translated Buffon into English, as follows: "The intelligent reader will perceive that this sentence, though not very obvious, contains the principle upon which the whole theory of generation adopted by the author is founded. It means no more than that the bodies of animals and of vegetables are composed of an infinite number of organic particles, perfectly similar, both in figure and substance, to the whole animal or plant of which they are the constituent parts ". This conception explains Buffon's curious attitude to the preformation question. An embryo was preformed in its germ because all the parts of the germ were each a model of the animal as a whole, but it was also formed by epigenesis because, the sexual organs being first formed, all the rest arose entirely by a succession of new origins. Buffon's "organic, living, particles" bear some resemblance to the "biogen molecules" which later generations were to discuss, and he says that an exactly similar but simpler structure is present in dead matter.

In his discussion of former theories he resolutely rejects the emboitement aspect of preformationism, giving various calculations to show its impossibility and maintaining that "every hypothesis which admits an infinite progression ought to be rejected not only as false

2o8 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

but as destitute of every vestige of probability. As both the vermicular and ovular systems suppose such a progression, they should be excluded for ever from philosophy". He completely destroys the theory which the ovists and animalculists had set up in order to explain resemblance to parents, namely, that, although the foetus might originate either from egg or spermatic animalcule originally, it was moulded into the form of its parents by the influence of the maternal organism during pregnancy. This field, which was more than once disturbed by the contestants during the course of the century, received systematic attention from time to time by medical writers. There was a memorable dispute on this point between Turner and Blondel, whose polemics, written in an exceedingly witty manner, are still very pleasant and amusing to read. Blondel was the sceptic and Turner the defender of the numerous extraordinary stories which passed for evidence on this subject. It is interesting to note that Turner believed in the continuity of foetal and maternal blood-vessels. Krause and Ens later supported the opinions of Turner, while Okes, in a Cambridge disputation, argued against them.

Buflfon's sixth chapter, in which he relates the progress of his own experiments, is unfortunate, in that his main result was to discover spermatozoa in the liquor folliculi of ovaries of female animals. The explanation of how he came to make such an enormous mistake has never been satisfactorily given, and it was not long before the truth of the observation was questioned by Ledermuller. It led him naturally to the assertion that the ovaries of mammalia were not eggproducing organs but animalcule-producing organs, and to the view that the beginning of embryonic development lay in the fusion of the male with the female spermatic animalcules — a curious revival of Epicureanism. But it is to be observed that he does not mean one male animalcule with one female animalcule, but rather all with all, in a kind of pangenesis. "All the organic particles", he says, "which were detached from the head of the animal will arrange themselves in a similar order in the head of the foetus. Those which proceeded from the backbone will dispose themselves in an order corresponding to the structure and position of the vertebrae". And so on for all the organs. The fact that for the organs common to both sexes a double set of animalcules will thus be provided does not give Buffon any difficulty and is fully admitted by him. Accordingly he could only agree to the aphorism omne vivum ex ovo in the sense of

SECT. 3] AND EIGHTEENTH CENTURIES 209

Harvey, namely, as referring to the egg-shaped chorion of vivipara, and definitely not in the sense of de Graaf and Stensen, namely, in the modern sense. "Eggs", he says, "instead of being common to all females, are only instruments employed by Nature for supplying the place of uteri in those animals which are deprived of this organ. Instead of being active and essential to the first impregnation, eggs are only passive and accidental parts, destined for the nourishment of the foetus already formed in a particular part of this matrix by the mixture of the male and female semen." Biology at this period was still labouring under the disadvantage of being without the celltheory, and therefore unable to distinguish between an egg and an egg-cell.

In spite of his leanings towards epigenesis, Buffon repeats precisely the error of Malpighi. "I formerly detected", he says, "the errors of those who maintained that the heart or the blood was first formed. The whole is formed at the same time. We learn from actual observation that the chicken exists in the egg before incubation. The head, the backbone, and even the appendages which form the placenta are all distinguishable. I have opened a great number of eggs both before and after incubation and I am convinced from the evidence of my own eyes that the whole chicken exists in the middle of the cicatrice the moment the egg issues from the body of the hen. The heat communicated to it by incubation expands the parts only. But we have never been able to determine with certainty what parts of the foetus are first fixed, at the moment of its formation." The experiment of taking a look at the cicatrices of eggs on their way down the parental oviduct is so obvious that Buffon must have thought of it, and it would be really interesting to know what factor in the intellectual climate it was that made him regard such an observation as not worth attempting. His observations on the embryo itself were good and, in some ways, new; thus he noticed that the blood first appears on the "placenta" or blastoderm, and for the first few days seems hardly to enter the body of the embryo. He gave an extremely good account of the whole developmental process in the chick and in man, and his opinions on the use of the amniotic liquid and the functions of the umbilical cord were very advanced.

J. T. Needham, however, spoke very clearly in favour of epigenesis, though he himself did no embryological experiments. His Idee sommaire of 1776, written against Voltaire, who had called him

N E I 14

2IO EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

a Jesuit and who had drawn materialistic inferences from his writings, contained the following passage: "The numerous absurdities which exist in the opinion ofpre-existent germs together with the impossibility of explaining on that ground the birth of monsters and hybrids, made me embrace the ancient system of epigenesis, which is that of Aristotle, Hippocrates, and all the ancient philosophers, as well as of Bacon and a great number of savants among the neoteriques. My observations also led me directly to the same result". Needham's embryology is mostly contained in his Observations nouvelles sur la Generation of 1750. He was explicitly a Leibnitzian and postulated a vegetative force in every monad.

Needham was not the only thoroughgoing epigenesist of this period. Maupertuis, whose Venus Physique was published anonymously in 1746, came out very clearly on the side of epigenesis. "I know too well", he said, "the faults of all the systems which I have been describing, to adopt any one of them, and I find too much obscurity in the whole matter to wish to form one of my own. I have but a few vague thoughts which I propose rather as thoughts to be examined than as opinions to be received, and I shall neither be surprised nor think myself aggrieved if they are rejected. It seems to me that both the system of eggs and that of spermatic animalcules are incompatible with the manner in which Harvey actually saw the embryo to be formed. And one or the other of these systems seems to me still more surely destroyed by the resemblance of the child, now to the father and now to the mother, and by hybrid animals which are born from two different species. ... In this obscurity in which we find ourselves on the manner in which the foetus is formed from the mixture of two liquors, we find certain facts which are perhaps a better analogy than what happens in the brain. When one mixes silver and spirits of nitre with mercury and water, the particles of these substances come together themselves to form a vegetation so like a tree that it has been impossible to refuse it the name." This was the Arbor Dianae, which played a great part in these embryological controversies of the eighteenth century. It has a great interest for us, for it was perhaps the first occasion on which a non-living phenomenon had been appealed to as an illustration of what went on in the living body. It is true that Descartes long before had said that the movements of the living body were carried out by mechanisms like clocks or watches, and that they resembled

SECT. 3] AND EIGHTEENTH CENTURIES 211

the statues in certain gardens which could be made to perform unexpected functions by the pressure of a manipulator's foot on a pedal, but these instances were all artificially constructed mechanical devices, whereas the Arbor Dianae was a natural phenomenon quite unexplained by the chemists of the time, and the lineal forerunner of Lillie's artificial nerve, and Rhumbler's drop of chloroform. We know now that its formation is a simpler process than anything which occurs in the developing embryo, but the course of research has made it undeniably clear that the same forces which operate in the formation of the Arbor Dianae are at work also in the developing embryo. To this extent Maupertuis is abundantly justified, and Driesch's comments on him are not in agreement with the facts.

"Doubtless many other productions of a like kind will be found", Maupertuis goes on, "if they are looked for or perhaps if they are looked for less. And although they seem to be less organised than the body of most animals, may they not depend on the same mechanics and on similar laws? Will the ordinary laws of motion suffice, or must we have recourse to new forces? These forces, incomprehensible as they are, appear to have penetrated even into the Academy of Sciences at Paris, that institution where so many opinions are weighed and so few admitted." Maupertuis goes on to speak of the contemporary deliberations on the subject of attraction. "Ghymistry", he says, "has felt the necessity of adopting this conception and attractive force is nowadays admitted by the most famous chymists who have carried the use of it far beyond the point which the astronomers had reached. If this force exists in nature, why should it not take part in the formation of animals?" Maupertuis was thus an epigenesist and a mechanist at the same time. His opinions have an extremely modern ring, and his only retrograde step was in suggesting that the spermatic animals had nothing else to do except to mix the two seeds by swimming about in them. But that legacy of ovism was common all through the eighteenth century, and thirty years later Alexander Hamilton could say, "From the discovery of Animalcula in semine masculino by Leeuwenhock's Glasses, a new Theory was adopted which is not yet entirely exploded".

But the real middle point and fulcrum of the whole period lay in the controversy between von Haller and Caspar Friedrich Wolflf, the former at Gottingen and the latter at St Petersburg in the Academy of the Empress Catherine. Kirchhoflf has described this polemic.

14-2

212 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

Wolff's Theoria generationis, which was a defence of epigenesis on theoretical and philosophical grounds, written in a very formal, logical, and unreadable manner, appeared when he was only twentysix years old, in 1759. Leibnitz, as Radl points out, had borrowed from the earlier preformationists the conception of a unit increasing in bulk in order to become another kind of unit; but Wolff, following Needham, borrowed from Leibnitz the idea of a monad developing into an organism by means of its own inherent force, and to this he joined the Stahlian notion of a generative supra-physical force in nature. On the practical side, Wolff's work was indeed of the highest importance. If the embryo pre-exists, he argued, if all the organs are actually present at the very earliest stages and only invisible to us even with the highest powers of our microscopes, then we ought to see them fully formed, as soon as we see them at all. In other words, at the moment at which any given organ comes into view, it ought to have the form and shape, though not the size, of the same organ when fully completed in the embryo at birth. On the other hand, if this is not the way in which development goes on, then one ought to be able to see with the microscope one shape changing into another shape, and, in fact, a series of appearances, each one different from that which had immediately preceded it, or, in other words, a series of advancing adaptations of the various parts of the primitive embryonic mass. WoliT chose as his first test case the blood-vessels of the blastoderm in the chick, for he saw that at one moment this apparatus was in existence, while the moment before it had not been. His microscopical researches led him to the conclusion that the homogeneous surface of the blastoderm partially liquefies and transforms itself at these points into a mass of islands of solid matter, separated by empty spaces filled with a colourless liquid but afterwards with a red liquid, the blood. Finally, these spaces are covered with membranes and become vessels. Consequently it was obvious that the vessels had not been previously formed, but had arisen by epigenesis.

Haller replied to this new experimental foundation for epigenesis without delay, for he was working on the development of the chick at the same time, and held closely to the opposite theory. We have already seen what his one and only argument against Wolff was. He used it time after time in all its possible variations, maintaining stoutly that the chick embryo was so fluid in the early stages that Wolff had no right to deny the presence of a given structure simply because

SECT. 3] AND EIGHTEENTH CENTURIES 213

he could not see it. Haller's explanation of Wolff's results was that the blood-vessels had been there all the time but that they had not become visible until the moment at which Wolff saw the islands forming. "After I had written the above", said Haller, "M. Wolff made new objections against the demonstration. Instructed by new researches, he denies absolutely that the yolk-membranes, which he makes two in number, exist before incubation. He pretends that they are new and that they are born at the beginning of incubation, and consequently that the continuity of their vessels with the embryo does not in the least prove that in the body of the mother the yolk received vessels from the foetus. I have compared the observations of this great man with my own and I have found that the yolk never has more than one pulpy and soft membrane, part of which is what I have called the umbilical area, and that the fine exterior membrane does not belong to the yolk but to the inner part of the umbilical membrane. ... I do not believe that any new vessels arise at all, but that the blood which enters them makes them more obvious because of the colour which it gives them, and so by the augmentation of their volume, they become longer."

Wolff replied by another extensive piece of work, which he called De Formatione Intestinorum, and which appeared in one of the publications of the Russian Academy for 1768. It ruined preformationism. In it he demonstrated that the intestine is formed in the chick by the folding back of a sheet of tissue which is detached from the ventral surface of the embryo, and that the folds produce a gutter which in course of time transforms itself into a closed tube. The intestine, therefore, could not possibly be said to be preformed, and from this as starting-point, Wolff went on to propose an epigenetic theory which applied the same process to all organs. It is interesting to note that the facts brought forward by Wolff have never been contradicted, but have been used as a foundation to which numberless morphological embryologists have added facts discovered by themselves. It is noteworthy that, although Wolff's second general principle, that of increasing solidification during embryonic development, led to no immediate results, it has been abundantiy confirmed since then (see Fig. 221). His observations on the derivation of the parts of the early embryo from "leaf-like" layers were even more important, and acteA as a very potent influence in the work of Pander and von Baer.

It happened, however, that Haller had much the greater in

214 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

fluence in the biological world at the time, so that Wolff's conceptions did not immediately yield fruit in any general advance. Looking back over the second half of the seventeenth and the first two-thirds of the eighteenth century, it is remarkable how little theoretical progress was made in view of the abundance of new facts which were discovered. Punnett, in an interesting paper, has vividly brought this out. "The controversy between the Ovists and Animalculists had lasted just a century", he says, "and it is not uninteresting to reflect that the general attitude of science towards the problem of generation was in 1775 niuch what it had been in 1675. When the period opened, almost all students of biology and medicine were Preformationists and Ovists; at its close they were for the most part Ovists and Preformationists." Ovism sprang in the first instance from de Graaf's discovery of the mammalian egg, which gave a new and precise meaning to Harvey's aphorism. Preformationism, already old as a theory, acquired an apparent factual basis in the work of Malpighi and Swammerdam, and allied itself naturally with ovism. With Leeuwenhoek and his spermatozoa, animalculism came upon the field. The main outlines of the battle which went on between the two viewpoints have already been drawn, but it is worth remembering that there were independent minds who were impressed by the obvious facts of heredity and found it difficult to call one sex essential rather than the other. Among these Needham and Maupertuis might be counted, and among the lesser men, James Handley with his Mechanical Essays on the Animal Oeconomy of 1730 ought to receive a mention. Though fond of theological arguments he upheld the common-sense attitude against ovists and animalculists alike — "We dissent in some things", he said, "both from Leeuwenhoeck and Harvey. . . . Both the semen and ova (notwithstanding all that can be said) we believe to be a causa sine qua non in every Generation". But what finally killed animalculism was the discovery in so many places of small motile living beings, flagellates, protozoa, large vibrios. It was difficult to maintain in the face of this new evidence that the spermatozoa were essential elements in generation, though the seminal fluid itself might very well be, as of course was Spallanzani's opinion. The preformation theory was what was holding up further progress, and when Wolff's arguments prevailed in the very last years of the eighteenth century, the way was open for the recognition of the true value of the spermatozoa.

SECT. 3] AND EIGHTEENTH CENTURIES 215

The otherwise unknown physician d'Aumont, who wrote the article on "Generation" in Diderot's famous Encyclopaedia, brought this out in an interesting way, for himself an ovist, he summarised the arguments, which, in 1757, were destroying the animalculist position, and reducing rapidly the number of its adherents.

1. Nature would never be so prolific as to produce such millions of spermatic animalcules, each one with its soul, unnecessarily.

2. The spermatic animalcules of all animals are the same size, no matter how large the animal is: how, therefore, can they be involved in its generation?

3. They are never found in the uterus after coitus, but only in the sperm (?).

4. How do they reproduce their kind?

5. What evidence is there that they are any different from the animalcules (of similar shape, etc.) which are to be found in hay infusion, scrapings from the teeth, etc. ? Nobody supposes that these have any relation to reproduction.

3-14. The Close of the Eighteenth Century

The last forty years of the century were not marked by any great movement in a fruitful direction for morphological embryology, an iconographic wave of some merit due to Albinus, W. Hunter, Tarin, Senffj Rosenmuller, Danz and Soemmering excepted ; and it was not until 181 2 that J. F. Meckel the younger translated Wolff's papers into German. This was one of the principal influences upon Pander and von Baer. In his introduction, Meckel describes how Wolff's work had been disregarded, and points out that Oken, writing in 1806, had apparently never even heard of it. In the very early years of the nineteenth century morphological embryology received a great impetus, however. One of the most interesting figures of the new period was de Lezerec, a Breton, whose father had been in the Russian naval service. The son, as a Russian naval cadet, no doubt stimulated by the writings of Wolff, who had lived at St Petersburg, used to incubate eggs on board ship. He eventually left the sea, studied medicine at Jena, and wrote an excellent dissertation on the embryology of the chick in 1 808, which Stieda has recently brought to light. He then went to Paris, and, taking a medical appointment at Guadeloupe, was lost to science. Very much more important was the work of Pander in 181 7 and von Baer in 1828,

2i6 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

but it belongs to the present period, and I shall not treat it historically. For data on von Baer, see Kirste, Addison and Stieda. It is interesting to note, however, that the recapitulation theory, which was first clearly formulated by von Baer, was already taking shape in various minds during the closing years of the eighteenth century. Lewes has thus described the thesis of Goethe's Morphologie, written in 1795: "The more imperfect a being is the more do its individual parts resemble each other and the more do these parts resemble the whole. The more perfect a being is the more dissimilar are its parts. In the former case the parts are more or less a repetition of the whole, in the latter case they are totally unlike the whole. The more the parts resemble each other the less subordination is there of one to the other : and subordination is the mark of high grade of organisation".

William and John Hunter belong also to the end of the century. The former, in his book on the anatomy of the gravid uterus, proved finally and completely the truth of the view that the maternal and foetal circulations are distinct. His injections left no shadow of doubt about the matter, and the way was clearly opened up for the study of the properties of the capillary endothelial membranes separating the bloods, a study which is still vigorously proceeding, especially in its physico-chemical aspect (see Section 21). There was a quarrel between the brothers over the priority of this demonstration. John Hunter's Essays and Observations also contain material important for embryology. His drawings of the chick in the &gg were very beautiful, and are still in the archives of the Royal College of Surgeons. He adopted Mayow's theory of the office of the air-space, and anticipated von Baer's theory of recapitulation much as did Goethe. "If we were capable of following the progress of increase of the number of parts of the most perfect animal as they were first formed in succession, from the very first to its state of full perfection, we should probably be able to compare it with some one of the incomplete animals themselves, of every order of animals in the creation, being at no stage different from some of the inferior orders. Or, in other words, if we were to take a series of animals, from the more imperfect to the perfect, we should probably find an imperfect animal corresponding with some stage of the most perfect." It is impossible not to reflect on the curious course which was taken by the essence of the idea of recapitulation in the history of embryology. As Aristotle first formulated it, it was as much bodily as mental, but all his sue

SECT. 3] AND EIGHTEENTH CENTURIES 217

cessors until the eighteenth century a.d. treated it as a psychological rather than a physiological or morphological theory, and lost themselves in speculations about the vegetative, sensitive, and rational souls. Yet the other aspect of the theory was only asleep, and was destined to be of the greatest value as soon as investigators began to direct their attention more to the material than to the spiritual aspect of the developing being.

Hunter did not absolutely reject preformationism, but regarded it as holding good for some species in the animal kingdom ; he therefore attached no philosophical importance to it.

Although Wolff's work did not lead to the immediate morphological advances which might have been expected, it was in many ways fruitful. It produced J. F. Blumenbach's Uber den Bildungstrieb of 1789, a work which elaborated the Wolffian vis essentialis into the nisus formativus, a directing morphogenetic force peculiar to living bodies. It is interesting to note that Blumenbach passed through an exactly opposite succession of opinions to that of Haller, i.e. he was first attracted by preformationism, but, being convinced by Wolff's work, abandoned it in favour of epigenesis. Blumenbach compares his nisus formativus with the force of gravity, regarding them as exactly similar conceptions and using them simply as definitions of a force whose constant effects are recognised in everyday experience. Blumenbach says that his nisus formativus differs from Wolff's vis essentialis because it actively does the shaping and does not merely add suitable material from time to time to a heap of material which is already engaged in shaping itself. Wolff was still alive at this time, but he did not make any comment on Blumenbach, though he might very well have said that Blumenbach had misunderstood him, and that their forces were really alike in every particular. Both Blumenbach and Wolff were mentioned by Kant in the Critique of Judgement where he adopted the epigenetic theory in his discussion of embryogeny.

A word must be said at this point about the opinions of the eighteenth century on foetal nutrition. At the beginning of it, there was, as has been shown, a welter of conflicting theories; and though, later on, writers on this subject were fewer, the progress made was no more rapid. In 1802 Lobstein was supporting the view (which had been defended by Boerhaave) that the amniotic liquid nourished the embryo per os, although Themel had shown forty years before

CHART III

igooB^

1600

1900

SECT. 3] THE EIGHTEENTH CENTURY 219

that this could be at most the very slightest source of material, from a study of acephalic monsters. These workers had obviously learnt nothing from Herissant and Brady, who had been over precisely the same ground fifty years before. On the other hand. Goods and Osiander reported the birth of embryos without umbilical cords, so that the solution of this question became, in the first year of the nineteenth century, balanced, as it were, between the relative credibility of two kinds of prodigy. Nourishment per os was defended by Kessel, Hannes and Grambs, and was attacked by Vogel, Bernhard, Glaser, Hannhard and Reichard. The idea lingered on right into the modern period, and as late as 1 886 von Ott, who was much puzzled about placental permeability, decided that a great part in foetal nutrition must be played by the amniotic liquid. WeidHch, a student of his, fed a calf on amniotic liquid for some days, and as it seemed to get on all right, he reported the amniotic liquid to have nutritive properties. The appeal to monsters was still resorted to at the end of the nineteenth century, for Opitz, in order to negative von Ott's conclusions, drew attention to a specimen in the Chemnitz Polyklinik in which the oesophagus of a well-nourished normal infant was closed at the upper third without the development of the body having been in any way restricted. The fuller possibilities of biochemistry itself have sometimes been exploited in favour of the ancient theory of nourishment />^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 white

220 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

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

SECT. 3] AND EIGHTEENTH CENTURIES 221

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

222 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

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

SECT. 3]

AND EIGHTEENTH CENTURIES

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

EMBRYOLOGY IN THE SEVENTEENTH [pt. ii

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

SECT. 3] AND EIGHTEENTH CENTURIES 227

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 1 8 14 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 1 8 14 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.

15-3