The vessels of the exhalant system are too delicate to allow us to
analyze their properties of texture. Do they enlarge when the red
globules enter them? I am wholly ignorant. Haller, who admitted that
there were exhalants, thought that white fluids alone entered them,
because their diameter was disproportioned to that of the red globules.
This opinion is also that of the school of Boerhaave. Who has ever
measured comparatively the respective diameters of the vessels and the
particles of the fluids? All such expressions, as fine fluids, coarse
fluids, &c. which are still used by many physicians, have originated
from this theory and are still used, though the theory itself has been
admitted to be false. I have said twenty times, and I again repeat it,
that the only cause which prevents the red globules from passing into
vessels with white fluids, is the want of relation between the nature
of the fluid and the sensibility of the organ.
The properties of animal life have evidently no connexion with
the exhalants. Of those of organic life, they have in the highest
degree those of organic sensibility and the corresponding insensible
contractility; it is upon these that all their functions depend.
_Characters of the Vital Properties._
Though organic sensibility is everywhere given to the exhalants, it
varies however remarkably in each system; that of the mucous exhalants
is not the same as that of the serous. In general the exhalants
entering as it were like elements into the texture of each system,
partake completely of the organic properties of that system; or rather
their properties are the same. Hence, 1st, why each separates the
fluid that is peculiar to it; why consequently, when much water is
introduced into the circulation by drinking, the cutaneous exhalants,
and never the serous, appropriate it to themselves, and transmit it out
of the blood; when we run much and a general agitation is consequently
given by the heart to the mass of blood in circulation, the cutaneous
exhalants, being more powerfully excited by this impression than the
serous, the synovial, &c. separate more sweat; 2d, why the serous do
not pour out fat, the medullary serum, &c. though the mass of blood
that enters the capillaries that are continuous with these exhalants,
is everywhere the same; 3d, why when the exhalants pour out fluids that
they are not accustomed to, or when their natural fluids are altered,
these fluids differ essentially from each other; why, for example,
after inflammation, it is only upon the serous surfaces that we see
a milky serum; why nothing resembling pus flows from the inflamed
medullary membrane; why the fluids, the result of the inflammation
of the synovial membranes, are very different from those that the
serous surfaces produce, &c.; 4th, why certain exhalants have a much
greater tendency than others to admit blood and pour it out upon
their respective surfaces, of which we see an example in the mucous
exhalants, which are so disposed to suffer this fluid to pass, that a
thousand circumstances occasion hemorrhages from them; 5th, why among
the mucous exhalants themselves, some have a much greater tendency than
other to permit the blood to pass, &c. &c.
All these phenomena are evidently derived from the particular
modifications that distinguish the organic sensibility and
contractility in each kind of exhalants.