Saliva in the oral cavity comes from the salivary glands, also known as salivary glands. There are three pairs of salivary glands: parotid, submandibular and sublingual, as well as small salivary glands in the mucosa of the lips, cheeks, palate and tongue. The mixed fluid secreted by the above salivary glands is called saliva. In the New Story of the World, it is written that “Wei Wu lost the way to draw water when he was on a campaign, and his soldiers were all thirsty, so he ordered them to say: ‘There is a big plum forest in front of us, and it is sweet and sour to quench our thirst. When the soldiers heard this, water came out of their mouths, and they took advantage of this to get to the former source.” The story of hoping for plums to quench thirst is well known to everyone. Does saliva really have such magical power? To answer this question correctly, it is necessary to first understand saliva. Why can saliva quench thirst? It turns out that 99.4% of saliva is water and only 0.6% is solid matter (of which organic matter is about 0.4% and inorganic matter is about 0.2%). The organic matter in saliva is mainly mucin, and the inorganic matter in saliva is mainly sodium, potassium, calcium, chloride, bicarbonate and inorganic phosphate. Saliva can also be mixed with shed epithelial cells, bacteria, white blood cells and gingival sulcus fluid. The regulation of salivary secretion is entirely neuroreflexive and includes both unconditioned and conditioned reflexes. Salivary secretion caused by direct stimulation of oral mucosal nerve receptors such as mechanical, chemical and temperature stimulation of the mouth by food is unconditioned and innate. The shape, color, smell of food and the environment of eating can also cause saliva secretion through visual, auditory and olfactory stimulation, and this kind of secretion belongs to conditioned reflex. The conditioned reflexive reflection is acquired later. The typical example of conditioned reflex salivary secretion is “quenching thirst by looking at plums”. Saliva in the mouth has many positive effects on the health of the body, mainly in the following areas: 1, to help digestion: saliva contains a variety of enzymes such as amylase, these enzymes can break down the starch content of food, which helps the digestion and absorption of food. 2, to promote the role of solvents: saliva as a water solvent or carrier of food, so that it is easy to diffuse during the chewing process, and contact with the taste buds of the tongue and make the tongue easier to perceive the taste of food, increasing appetite. 3, protection and lubrication role: saliva in the mucin adsorption of oral mucosa surface formed by a thin elastic film, has a protective tissue against dehydration, to prevent exogenous irritants into the role of the mucosa, but also lubricates the lips, cheeks, tongue, etc., so that the chewing, swallowing, speech and other movements more freely and smoothly. 4, clean oral role: saliva can mechanically rinse the oral mucosa and teeth, flush out the food debris and bacteria attached to it, maintaining a clean mouth. 5, antibacterial effect: saliva contains substances such as lysozyme can stop the growth of a variety of bacteria from the air or water, other antibacterial factors in saliva such as immunoglobulins in saliva and other substances can prevent the attachment of bacteria, inhibit their growth, and even have a certain role in killing some bacteria. 6, dilution and buffering role: saliva mixed with the food entering the mouth, softening and dilution of food, saliva also plays a buffering role in terms of eating temperature. Saliva contains a higher concentration of bicarbonate, etc., to play a protective role for the digestive tract mucosa. 7, adhesion and fixation role: saliva itself has adhesion, mixed with chewed food, the food particles stick into food mass, easy to swallow. For those who need to wear full denture (scientific name for full denture), the saliva present between the tissue surface of full denture base and alveolar ridge can increase the adhesion force of full denture, thus increasing the stability and retention of denture. 8, shorten the clotting time: blood and saliva mixed, the clotting time is shortened, and the degree of shortening is related to the ratio of mixing degree. When the ratio of blood to saliva is 1:2, the clotting time is shortened the most, therefore, the clotting time and healing of the trauma in the mouth are faster than other parts …… 9, excretion: abnormal or excessive components in the blood can often be excreted through saliva. Such as excessive mercury, lead and other heavy metal elements, iodine is also excreted mainly from saliva. When the kidney function is weak and less urine, some urea, excessive glucose in the blood of diabetic patients can also often be excreted by saliva. Infectious substances in the circulating blood can also enter the saliva when there is no lesion in the gland. Hepatitis virus, AIDS virus can be transmitted through saliva. 10, other roles: submandibular glands secrete salivary gland hormones, parotid glands secrete parotid hormones, these hormones in addition to maintaining the normal secretory activities of the above glands, but also has the role of regulating calcium metabolism, promote the development of bone and dental hard tissue.