ts 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 no