t 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. 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?[35]

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