es of the parts, or coats, which constitute
these ultimate vessels, may still have greater tenuity; and that these
pores from the above analogy must posses a similar power of irritability,
and absorb by their living energy the particles of fluid adapted to their
purposes, whether to replace the parts abraded or dissolved, or to elongate
and enlarge themselves. Not only every kind of gland is thus endued with
its peculiar appetency, and selects the material agreeable to its taste
from the blood, but every individual pore acquires by animal selection the
material, which it wants; and thus nutrition seems to be performed in a
manner so similar to secretion; that they only differ in the one retaining,
and the other parting again with the particles, which they have selected
from the blood.

This way of accounting for nutrition from stimulus, and the consequent
animal selection of particles, is much more analogous to other phenomena of
the animal microcosm, than by having recourse to the microscopic
animalcula, or organic particles of Buffon, and Needham; which being
already compounded must themselves require nutritive particles to continue
their own existence. And must be liable to undergo a change by our
digestive or secretory organs; otherwise mankind would soon resemble by
their theory the animals, which they feed upon. He, who is nourished by
beef or venison, would in time become horned; and he, who feeds on pork or
bacon, would gain a nose proper for rooting into the earth, as well as for
the perception of odours.

The whole animal system may be considered as consisting of the extremities
of the nerves, or of having been produced from them; if we except perhaps
the medullary part of the brain residing in the head and spine, and in the
trunks of the nerves. These extremities of the nerves are either of those
of locomotion, which are termed muscular fibres; or of those of sensation,
which constitute the immediate organs of sense, and which have also their
peculiar motions. Now as the fibres, which constitute the bones and
membranes, possessed originally sensation and motion; and are liable again
to possess them, when they become inflamed; it follows, that those were,
when first formed, appendages to the nerves of sensation or locomotion, or
were formed from them. And that hence all these solid parts of the body, as
they have originally consisted of extremities of nerves, require an
apposition of nutritive particles of a s