444
NATURE OF THE
of similar organisation. The nature of the secretion depends there¬
fore solely on the peculiar vital properties of the organic substance
which forms the secreting canals, and which may remain the same
however different the conformation of the secreting cavities may be;
while it may vary extremely although the form of the canals or ducts
remains unchanged. The variety of secretions is due to the same
cause as the variety of the formation and vita*l properties of organs
generally; the only difference being that, in nutrition, the part of the
blood which has undergone the peculiar change is incorporated with
the organ itself, while in secretion it is eliminated from it.
Several chemists, and especially Chevreul, have recently laboured
to prove that all secretions are formed independently of any change
effected by the organ in the components of the blood; that all the
materials of the different secretions pre-exist in the blood itself; and
that the principal action of the secreting organ is merely to attract
these matters from the blood and to transfer them to the fluid
secreted. As circumstances favouring this view very strongly,
Gmelin mentions, that the salts of the blood and those of the secre¬
tions are nearly identical; that, both in the blood and in the secre¬
tions, osmazome, and a substance resembling salivary matter, occur;
and that many of the substances which were formerly believed to
exist only in the secretions, namely, casein, Cholesterine, Stearine,
elain, and elaic acid, have been discovered in the blood. The ex¬
istence of cholesterine in the blood has been recently confirmed
anew by Boudet. (Essai critique et expérimental sur le Sang.
Paris, lé33.)(a) Nevertheless the theory appears to me to be founded
on a very erroneous view; for, in the first place, neither horn, mucus,
biliary matter, picromel, semen, true casein, true salivary matter,
nor the poisonous matters secreted by animals, are contained in the
blood; and secondly, components of the secretions may accidentally
re-enter the blood by imbibition, so that their presence in it is no
proof of their being part of its natural constituents; and, in fine, the
existence of all the secreted matters in the blood would not do away
with the difficulty, for it would remain to explain how they were
formed in it,—for instance, in the blood of herbivorous animals. It
is, indeed, quite certain that the “true secretions,” as distinguished
from the “excretions,” are, like the solid parts of the body, formed
from the more simple constituents of the blood by the organs which
secrete them.
The chemical process of secretion is not at all understood. The
simple problem to be solved is, how the secreting membranes can,
at the same time, and from the same blood, nourish themselves,—
that is, attract analogous particles and add them to their own sub¬
stance,—and also secrete or eliminate non-analogous particles; for
the secreted fluid is in its chemical properties wholly different from
the secreting organ. The glandular substance, generally, consists
merely of uncoagulated albumen, which, when reduced to a state of
minute division, is readily soluble in water. The elementary parts
(a) See on this subject Liebig’s Mnmal or Organic Chemistry.