The act of secerting; the act of the producing from the blood substances different from the blood itself, or from any of its constituents, as bile, saliva, mucus, urineThis was considered by the older physiologists as merely separation from the blood of certain substances previously contained in it; the literal meaning of secretion. But this opinion is generally exploded. The organs of secretion are of very various form and structure, but the most general are called glands.

The matter secreted, as mucus, perspirable matter.