MRS. B.

Nor is the production of these fluids in the animal and vegetable
systems entirely different; for the absorbent vessels, which pump up the
chyle from the stomach and intestines, may be compared to the absorbents
of the roots of plants, which suck up the nourishment from the soil. And
the analogy between the sap and the blood may be still further traced,
if we follow the latter in the course of its circulation; for, in the
living animal, we find every where organs which are possessed of a power
to secrete from the blood and appropriate to themselves the ingredients
requisite for their support.

CAROLINE.

But whence do these organs derive their respective powers?

MRS. B.

From a peculiar organisation, the secret of which no one has yet been
able to unfold. But it must be ultimately by means of the vital
principle that both their mechanical and chemical powers are brought
into action.

I cannot dismiss the subject of circulation without mentioning
_perspiration_, a secretion which is immediately connected with it, and
acts a most important part in the animal economy.

CAROLINE.

Is not this secretion likewise made by appropriate glands?

MRS. B.

No; it is performed by the extremities of the arteries, which penetrate
through the skin and terminate under the cuticle, through the pores of
which the perspiration issues. When this fluid is not secreted in
excess, it is _insensible_, because it is dissolved by the air as it
exudes from the pores; but when it is secreted faster than it can be
dissolved, it becomes _sensible_, as it assumes its liquid state.

EMILY.

This secretion bears a striking resemblance to the transpiration of the
sap of plants. They both consist of the most fluid part, and both exude
from the surface by the extremities of the vessels through which they
circulate.

MRS. B.

And the analogy does not stop there; for, since it has been ascertained
that the sap returns into the roots of the plants, the resemblance
between the animal and vegetable circulation is become still more
obvious. The latter, however, is far from being complete, since, as we
observed before, it consists only in a rising and descending of the sap,
whilst in animals the blood actually _circulates_ through every part of
the system.

We have now, I think, traced the process of nutrition, from the
introduction of the food into the stomach to its finally becoming a
constituent part of the animal frame. This w