urposes the blood is employed,
which is formed with so much care, we have yet to discover. It seems
to answer two purposes. The parts of which the body is composed,
namely, bones, muscles, ligaments, membranes, &c. are continually
changing: in youth they are increasing in size and strength, and in
mature age they are continually acting, and, consequently,
continually liable to waste and decay. They are often exposed to
accidents, which render them unfit for performing their various
functions; and even when no such accidents happen, it seems necessary
for the health of the system that they should be perpetually renewed.
Materials must therefore be provided for repairing, increasing, or
renewing all the various organs of the body. The bones require
phosphate of lime, and gelatine, the muscles fibrine, and the
cartilages and membranes albumen; and accordingly we find all these
substances contained in the blood, from whence they are drawn, as
from a storehouse, whenever they are wanted. The process by which
these different parts of the blood become various parts of the body
is called assimilation.

Over the nature of assimilation the thickest darkness still hangs;
all that we know for certain is, that there are some conditions
necessary to its action, without which it cannot take place. These
are, 1. A sound and uninterrupted state of the nerves. 2. A sound
state of the blood vessels. 3. A certain degree of tone or vigour in
the vessels of the part.

There remains yet to be noticed another set of vessels, connected
with the circulating and nutritive systems, called lymphatics. These
vessels are very minute, and filled with a transparent fluid: they
rise by open mouths in every cavity of the body, as well as from
every part of the surface, and the course of those from the lower
extremities, and indeed from most of the lower parts of the body, is
towards the thoracic duct, which they enter at the same time with the
lacteal vessels already described. They are furnished, like the
lacteals, with numerous valves, which prevent their contents from
returning towards their extremities.

The minute arteries in every part of the body exhale a colourless
fluid, for lubricating the different parts, and other important
purposes: and the lymphatic vessels absorb the superfluous quantity
of this fluid, and convey it back to the blood.

It must be evident therefore, that, if the lymphatics in any cavity
become debilitated, or by any o