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 will, therefore, be a fit period to conclude our present conversation. What further remarks we have to make on the animal economy shall be reserved for our next interview.
[*] The quantity of moisture discharged by the lungs in 24 hours, may be computed at eight or nine ounces.
[*] The bulk of carbonic acid gas formed by respiration, is exactly the same as that of the oxygen gas which disappears.