The functions of the absorbents are not at the present day a subject
of doubt with any anatomist; but the manner in which these functions
are performed, are far from being so well agreed upon. The first
idea has been to compare the action of the absorbents with that of
capillary tubes. But if we reflect a little upon this action, it is
easy to see that these phenomena are wholly different from those of
inert, capillary tubes. I think that we never should be able to say
precisely, how an absorbent orifice, being immersed in a fluid, takes
it up, seizes its particles and makes them ascend in its tube. But what
is undoubted in absorption is that the vessels derive this faculty
from the vital forces which they have; that it is only the relation
existing between the particular kind of organic sensibility with which
they are endowed, and the fluids with which they are in contact, that
is the immediate cause of the phenomenon. Do you wish numerous proofs
of this? See the lacteals choosing only chyle from among the variety
of matter contained in the intestinal canal; see the absorbents of the
bladder and the gall-bladder leaving many of the elements of the urine
and the bile, to take only the aqueous part of these fluids; see the
cutaneous absorbents, the mucous ones of the bronchiæ, &c. selecting
only certain principles from the air and leaving others. Often inactive
for a long time, they immediately recommence action when any substances
in relation with their sensibility are presented to them. Observe the
fluids injected or effused into the cellular texture, they are taken
up or left by the absorbents of this texture, disappear promptly, or
remain and occasion suppuration, according as they agree with or are
repugnant to their sensibility.
We cannot deny that in the natural state the sensibility of the
absorbents has a particular type, to which certain substances are
alone accommodated, and which alone on this account can be absorbed.
The exercise of the organic sensibility then always pre-exists in
absorption, as it does in secretion, nutrition, &c. Thus in the
physical phenomena, the exercise of gravity always precedes the fall of
heavy bodies. Thus the power of attracting is put into exercise before
the motion of the planets takes place, &c. &c.