o
its life and growth; one of these is food or sustenance, which is to be
received by the absorbent mouths of its vessels; and the other is that part
of atmospherical air, or of water, which by the new chemistry is termed
oxygene, and which affects the blood by passing through the coats of the
vessels which contain it. The fluid surrounding the embryon in its new
habitation, which is called liquor amnii, supplies it with nourishment; and
as some air cannot but be introduced into the uterus along with a new
embryon, it would seem that this same fluid would for a short time, suppose
for a few hours, supply likewise a sufficient quantity of the oxygene for
its immediate existence.

On this account the vegetable impregnation of aquatic plants is performed
in the air; and it is probable that the honey-cup or nectary of vegetables
requires to be open to the air, that the anthers and stigmas of the flower
may have food of a more oxygenated kind than the common vegetable
sap-juice.

On the introduction of this primordium of entity into the uterus the
irritation of the liquor amnii, which surrounds it, excites the absorbent
mouths of the new vessels into action; they drink up a part of it, and a
pleasurable sensation accompanies this new action; at the same time the
chemical affinity of the oxygene acts through the vessels of the rubescent
blood; and a previous want, or disagreeable sensation, is relieved by this
process.

As the want of this oxygenation of the blood is perpetual, (as appears from
the incessant necessity of breathing by lungs or gills,) the vessels become
extended by the efforts of pain or desire to seek this necessary object of
oxygenation, and to remove the disagreeable sensation, which that want
occasions. At the same time new particles of matter are absorbed, or
applied to these extended vessels, and they become permanently elongated,
as the fluid in contact with them soon loses the oxygenous part, which it
at first possessed, which was owing to the introduction of air along with
the embryon. These new blood-vessels approach the sides of the uterus, and
penetrate with their fine terminations into the vessels of the mother; or
adhere to them, acquiring oxygene through their coats from the passing
currents of the arterial blood of the mother. See Sect. XXXVIII. 2.

This attachment of the placental vessels to the internal side of the uterus
by their own proper efforts appears further illustrated by the many