[Harvey] ... begins by putting himself in some sort of harness of
     Aristotle, and taking the bit of Fabricius between his teeth; and
     then, either assuming the ideas of the former as premises, or those
     of the latter as topics of discussion or dissent, he labours on
     endeavouring to find Nature in harmony with the Stagyrite, or at
     variance with the professor of Padua--for, in spite of many
     expressions of respect and deference for his old master, Harvey
     evidently delights to find Fabricius in the wrong. Finally, so
     possessed is he by scholastic ideas, that he winds up some of his
     opinions upon animal reproduction by presenting them in the shape
     of logical syllogisms.[22]

Even Harvey's concept of the egg reveals a strong Aristotelian bias. Actually, Harvey attained
to his conclusion that all animals derive from eggs by assuming that

     on the same grounds, and in the same manner and order in which a
     chick is engendered and developed from an egg, is the embryo of
     viviparous animals engendered from a pre-existing conception.
     Generation in both is one and identical in kind: the origin of
     either is from an egg, or at least something that by analogy is
     held to be so. An egg is, as already said, a conception exposed
     beyond the body of the parent, whence the embryo is produced; a
     conception is an egg remaining within the body of the parent until
     the foetus has acquired the requisite perfection; in everything
     else they agree; they are both alike primordially vegetables,
     potentially they are animals.[23]

The ovum, for Harvey, is in essence "the primordium vegetable or vegetative incipience, understanding
by this a certain corporeal something having life in potentia; or a certain something existing
per se, which is capable of changing into a vegetative form under the agency of an internal
principle."[24] The ovum is for Harvey more a concept than an observed fact, and, as stated
by one student of generation, "The dictum ex ovo omnia, whilst substantially true in the modern
sense, is neither true nor false as employed by Harvey, since to him it has no definite or
even intelligible meaning."[25]

Harvey's treatise on generation is clearly a product of his time. It advances embryology by
its demonstration of certain facts of development, by its aggressive espousal of epigenesis
and the origin of all animals from eggs, and by its dynamic approach stressing the temporal
factors in development and the initial independent function of embryonic organs. However, the
strong Aristotelian cast of Harvey's treatise encouraged continued discussion of long outdated
questions in an outdated manner and, combined with his expressed disdain for "chymistry" and
atomism, discouraged close cooperation between embryologists of different persuasions. It is
perhaps easy to underestimate the impact and general importance of Harvey's work in view of
these qualifications, and so it should be remarked that both positive and negative features
of De Generatione influenced profoundly subsequent embryological thought.

It will be recalled that the title of The Philosophicall Touch-Stone identified Digby as the
object of Alexander Ross's ire. In comparable manner, the latter's Arcana Microcosmi, published
in 1652, declares its purpose to be "a refutation of Dr. Brown's Vulgar Errors, the Lord Bacon's
Natural History, and Dr. Harvy's book De Generatione." Let us pause a brief moment in memory
of a man so intrepid as to undertake the refutation of three of England's great intellects
in one small volume, and then proceed to examine the embryological concepts of one of the trio,
Sir Thomas Browne.

Browne's Religio Medici, composed as a private confession of faith around 1635, is known to
all students of English literature, as is his later, splendid work on death and immortality,
Hydrotaphia, Urne-Buriall. One of the greatest stylists of English prose, Browne was also a
physician and a student of generation who deserves our attention as an early chemical embryologist
pointing the way to a form of embryological investigation prominent in the last half of the
seventeenth century.

Browne's embryological opinions are found particularly in Pseudodoxia Epidemica, The Garden
of Cyrus, and in his unpublished Miscellaneous Writings. Browne, a well-read man, was educated
at Oxford, Montpellier, Padua, and Leyden, and he was thoroughly imbued with the teaching of
the prophets of the "new learning." This is evident throughout his writings, as witness his
admonition to the reader of the Christian Morals:

     Let thy Studies be free as thy Thoughts and Contemplations, but fly
     not only upon the wings of Imagination; Joyn Sense unto Reason, and
     Experiment unto Speculation, and so give life unto Embryon Truths,
     and Verities yet in their Chaos.[26]

Browne greatly admired Harvey's work on generation, considering it "that excellent discourse
... So strongly erected upon the two great pillars of truth, experience and solid reason."[27]
Browne carried out a variety of studies upon animals of all kinds, in them joining Sense unto
Reason, and "Experiment unto Speculation." Thus in his studies of generation, he made observations
and also performed certain simple chemical experiments. Noting that "Naturall bodyes doe variously
discover themselves by congelation,"[28] Browne studied experimentally the chemical properties
of those substances providing the raw material of development. He observed the effects of such
agents as heat and cold, oil, vinegar, and saltpeter upon eggs of various animals, recording
such facts as the following:

     Of milk the whayish part, in eggs wee observe the white, will
     totally freez, the yelk with the same degree of cold growe thick &
     clammy like gumme of trees; butt the sperme or tredde hold its
     former body, the white growing stiff that is nearest it.... Egges
     seem to have their owne coagulum within themselves manifested in
     the incrassations upon incubation.... Rotten egges will not bee
     made hard by incubation or decoction, as being destitute of that
     spiritt, or having the same vitiated.... How far the coagulating
     principle operateth in generation is evident from eggs wch will
     never incrassate without it. From the incrassation upon incubation
     when heat diffuseth the coagulum, from the chalaza or gallatine
     wh. containeth 3 nodes, the head, heart, & liver.[29]

It cannot be said that Browne attained to any great generalizations
regarding embryogeny on the basis of his rather naive experiments, but
they are indicative of the effects of the "new learning" in one area of
biology. Actually, Browne appears more comfortable in the search for
patterns conforming to the quincunx, as in The Garden of Cyrus, and
although he may well have been in search of something like the later
Unity of Type, he uses his amassed details of scientific knowledge most
effectively in support of nonscientific propositions. Those strange and mysticall
     transmigrations that I have observed in Silkewormes, turn'd my
     Philosophy into Divinity. As Browne himself reminds us, "a good
cause needs not to be patron'd by a passion."[31] His work and
interpretations of generation are most important for our purposes as an
indication of the rising mood of the times and an emerging awareness of
the physiochemical analysis of biological systems. Although this mood
and awareness coexist in Browne's writings with a continued reverence
for some traditional attitudes, they mark a point of departure toward a
variety of embryological thought prominent in England during the second
half of the seventeenth century.

Browne did no more than analyze crudely the reaction of the egg to various physical and chemical
agents. This static approach was later supplanted by a more dynamic one concerned primarily
with the physicochemical aspects of embryonic development. This is first apparent in a report
by Robert Boyle in the Philosophical Transactions of the Royal Society in 1666 entitled, "A
way of preserving birds taken out of the egge, and other small foetus's." Boyle, unlike Browne,
exposed embryos of different ages to the action of "Spirit of Wine" or "Sal Armoniack," demonstrating
thereby the chemical fixation of embryos as an aid to embryology. A year later, Walter Needham,
a Cambridge physician who studied at Oxford in the active School of Physiological Research,
which included such men as Christopher Wren and Thomas Willis, published a book reporting the
first chemical experiments upon the developing mammalian embryo.[32] Needham's approach and
goals are more dynamic than those of Browne, and he attempts to analyze various embryonic fluids
by coagulation and distillation procedures. His experiments reveal, for example, that "coagulations"
effected by different acids vary according to the fluid; thus, the addition of "alumina" to
bovine amniotic fluid produced a few, fine precipitations, whereas the allantoic fluid was
precipitated like urine. By such means Needham was able to demonstrate, however crudely, that
there are considerable differences in the various fluids occurring within and around the fetus.
Furthermore, it is with the results of chemical analyses that he supports his other arguments,
such as his contention that the egg of elasmobranchs is not, as believed, composed of only
one humour, but has separate white and yolk.

Needham's book contains many splendid observations, including an accurate description of the
placenta and its vessels, the relationship of the various fetal membranes to the embryonic
fluids, and rather complete directions for dissection of various mammals. These need not detain
us, since the important aspect of Needham's work relevant to our purpose is his continuation
of the chemical analysis of the developing embryo and its demonstration that, although Harvey
might have despised the "chymists" and been contemptuous of the "mechanical, corpuscular philosophy,"
this system and approach was not to be denied.

Needham's book is dedicated to Robert Boyle, whose Sceptical Chymist set the cadence for subsequent
research based upon the "mechanical or corpuscularian" philosophy and quantitative procedures.
It is appropriate for us, then, to terminate our discussion with a consideration of this current
in English embryological thought.

John Mayow was the first to realize that "nitro-aerial" vapour, or oxygen, is essential to
respiration of a living animal, and he was soon led to inquire "how it happens that the foetus
can live though imprisoned in the straits of the womb and completely destitute of air."[33]
As a consequence of this interest, the third of his Tractatus Quinque medico-physici, published
in 1674, is devoted to the respiration of the fetus in utero. He shows truly remarkable insight
when he concludes therein that

     It is very probable that the spermatic portions of the uterus and
     its carunculae are naturally suited 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 transports to the foetus not only nutritious
     juice, but also a portion of the nitro-aerial particles: so that
     the blood of the infant seems to be impregnated with nitro-aerial
     particles by its circulation through the umbilical vessels in the
     same manner as in the pulmonary vessels. Therefore, I think that
     the placenta should no longer be called a uterine liver, but rather
     a uterine lung.[34]

Although Mayow's attempted analysis of respiration of the chick embryo in ovo is less than
successful, his views on fetal respiration were soon accepted by many, and his tract stands
as a great contribution to physiological embryology.

The studies of such individuals as John Standard reporting the weight of various parts of the
hen's egg, e.g., the shell, the yolk, the white, reveal the wing of embryological investigation
that was increasingly obsessed with quantification and the physicochemical analysis of the
embryo and its vital functions. It was not, however, destined to become immediately the main
stream of embryological investigation. For even as the studies of Mayow were in progress, embryology
was embarked upon a course leading to preformationism. By the end of the seventeenth century,
the idea that the embryo was encased in miniature in either egg or sperm was elevated to a
position of Doctrine, and thereafter there was little encouragement to quantitative study of
development. Many embryological investigations were performed during the eighteenth century,
but most relate to the controversy regarding epigenesis and preformationism as the true expression
of embryonic development. Withal, the seventeenth-century embryologists, and particularly the
embryologists of seventeenth-century England, had contributed much to the progress of the discipline.
They had introduced new ideas, applied new techniques, and created new knowledge; they had
effectively advanced the study of development beyond the stage of macro-iconography; they had
freed the discipline from much of its traditional baggage of causes, virtues, and faculties.
Various English embryologists had varying success with developmental theory, but as a group
they had made great impact upon the development of embryology. In the course of their century,
they had, in the words of one of them, "called tradition unto experiment."[36]

Notes

[1] Charles Dickens, A Tale of Two Cities, London, 1859, p. 1.

[2] Kenelm Digby, Private Memoirs of Sir Kenelm Digby, Gentleman of the Bedchamber to King
Charles the First, London, 1827, Preface, p. i.

[3] Kenelm Digby, Two Treatises, in the One of Which, The Nature of Bodies; in the Other, the
Nature of Mans Soule; is Looked into, Paris, 1644, p. 213.

[4] Ibid., p. 220.

[5] Ibid., pp. 220-221.

[6] Ibid., p. 222.

[7] Ibid., p. 215.

[8] Ibid., p. 219.

[9] Ibid., p. 213.

[10] Ibid., pp. 217-219.

[11] Ibid., p. 231.

[13] Alexander Ross, Arcana Microcosmi: or, The hid secrets of Man's Body disclosed ... In
an anatomical duel between Aristotle and Galen concerning the parts thereof, London, 1652, p. 87.

[14] Nathaniel Highmore, The History of Generation, Examining the several Opinions of divers
Authors, expecially that of Sir Kenelm Digby, in his Discourse of Bodies, London, 1651, p. 4.

[15] Ibid., pp. 26-27.

[16] Ibid., pp. 27-28.

[17] Ibid., p. 45.

[18] Ibid., Pp. 90-91.

[19] William Harvey, Opera omnia: a Collegio Medicorum Londinensi edita, Londini, 1766, p. 136.

[20] William Harvey, Anatomical Excercises on the Generation of Animals, trans. Robert Willis,
London, 1847, p. 462.

[21] Ibid., pp. 336-339.

[22] Works of William Harvey, trans. Robert Willis, London, 1847, pp. lxx-lxxi.

[23] Harvey, op. cit., pp. 462-463.

[24] Ibid., p. 457.

[25] F. J. Cole, Early Theories of Sexual Generation, Oxford, 1930, p. 140.

[26] Thomas Browne, The Works, ed. Geoffrey Keynes, Chicago, 1964, I, 261-262.

[27] Ibid., II, 265.

[28] Ibid., III, 442.

[29] Ibid., III, 442-452.

[30] Ibid., I, 50.

[31] Ibid., I, 14.

[32] Walter Needham, Disquisitio anatomica de formato foetu, London, 1667.

[33] John Mayow, "De Respiratione foetus in utero et ovo," in Tractatus Quinque Medico-Physici,
Oxonii, 1674, p. 311.

[34] Ibid., pp. 319-320.