Part 3

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.

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. Thus, he uses the facts of embryonic development, alchemy, and insect metamorphosis as a part of his argument for the immortality of the human soul:

...for we live, move, have a being, and are subject to the actions of the elements, and the malice of diseases in that other world, the truest Microcosme, the wombe of our mother; for besides that generall and common existence wee are conceived to hold in our Chaos, and whilst wee sleepe within the bosome of our causes, wee enjoy a being and life in three distinct worlds, wherin we receive most manifest graduations: In that obscure world and wombe of our mother, our time is short, computed by the Moone, yet longer than the dayes of many creatures that behold the Sunne; our selves being yet not without life, sense, and reason; though for the manifestation of its actions it awaits the opportunity of objects; and seemes to live there but in its roote and soule of vegetation; entring afterwards upon the scene of the world, wee arise up and become another creature, performing the reasonable actions of man, and obscurely manifesting that part of Divinity in us, but not in complement and perfection, till we have once more cast our secondine, that is, this slough of flesh, and are delivered into the last world, that ineffable place of Paul, that proper ubi of spirits. The smattering I have [in the knowledge] of the Philosophers stone ... hath taught me a great deale of Divinity, and instructed my beliefe, how the immortall spirit and incorruptible substance of my soule may lye obscure, and sleepe a while within this house of flesh. Those strange and mysticall transmigrations that I have observed in Silkewormes, turn'd my Philosophy into Divinity. There is in those workes of nature, which seeme to puzzle reason, something Divine, and hath more in it then the eye of a common spectator doth discover.

To affirm that Sir Thomas Browne was the founder of chemical embryology or, indeed, to contend that he made a great impress upon the progress of embryology is to humour our fancy. As Browne himself reminds us, "a good cause needs not to be patron'd by a passion." 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. 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." 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.

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. In this they were following the injunction of Boyle, who used the developing embryo as a vehicle in an attack upon the idea that mixed bodies are compounded of three principles, the obscurities of which operated to discourage quantification:

How will this hypothesis teach us, how a chick is formed in the egg, or how the seminal principles of mint, pompions, and other vegetables ... can fashion water into various plants, each of them endowed 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, and how much mercury must be taken to make a chick or a pompion? And if we know that, what principle it is, that manages these ingredients, and contrives, for instance, such liquors, as the white and yolk of an egg into such a variety of textures, as is requisite to fashion the bones, veins, arteries, nerves, tendons, feathers, blood, and other parts of a chick? and not only to fashion each limb, but to connect them all together, after that manner, that is most congruous to the perfection of the animal, which is to consist of them?

The emphasis upon quantification and the physicochemical analysis of vital processes was to continue into the eighteenth century and to contribute to the great stress upon precision in that period. 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."

Notes

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

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

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.

Ibid., p. 220.

Ibid., pp. 220-221.

Ibid., p. 222.

Ibid., p. 215.

Ibid., p. 219.

Ibid., p. 213.

Ibid., pp. 217-219.

Ibid., p. 231.

Alexander Ross, The Philosphicall Touch-Stone; or Observations upon Sir Kenelm Digbie's Discourses of the nature of Bodies, and of the reasonable Soule, London, 1645.

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.