The fluid secreted by the SALIVARY GLANDS into the mouth. The principal function of saliva is to aid in the initial processes of digestion, and it is essential for the process of mastication (chewing), whereby food is reduced to an homogeneous mass before being swallowed. It contains mucus and an ENZYME known as PTYALIN, which changes starch into dextrose and maltose (see DIGESTION); also many cells of different types. About 750 millilitres are produced daily. Deficiency of saliva is known as XEROSTOMIA (Latin for ‘dry mouth’).