Secretion

Secretion is a vital process in which certain cells of the body form within themselves definite products, which accumulate and are usually discharged. The cells specialised for secreting are called glandular, and many are often united to form a Gland (q.v.). The definite products formed by the activity of the glandular cells are called secretions, this term being applied both to process and products. All the digestive juices, the silk of silkworms, the webs of spiders, the wax of bees, the nectar of flowers, and the like, are secretions. They are formed by the activity of the living matter from materials derived from the blood, or, when there is no blood, from the supplies of food which otherwise reach the glandular cells. They are discharged sometimes by a slow outpouring comparable to filtration through the free surface of the cell, sometimes by the more or less complete rupture of the cell. The process of secretion is usually periodic, intervals of quiescence alternating with those of activity. See GLANDS, PHYSIOLOGY, DIGESTION. For the secretion of plants, see VEGETABLE PHYSIOLOGY.