Saliva is a colorless, odorless and nearly neutral hypotonic liquid (Ph6.6-7. 1). Saliva is about 99%. Organic matter is mainly mucin, as well as globulin, amino acids, urea, uric acid, salivary amylase and lysozyme. Inorganic substances in saliva include sodium, potassium, calcium, thiocyanate, chlorine and ammonia. In addition, there are some gases in saliva, such as oxygen, nitrogen and carbon dioxide. Mucin in saliva is almost entirely secreted by mucus cells, which makes saliva sticky. Plasma cells secrete thin saliva, which contains almost no mucin, but the salivary amylase secreted by serous glands is four times that secreted by mucinous glands.

The osmotic pressure of saliva changes with the change of secretion rate. When the secretion rate is very low, its osmotic pressure is also low, about 50m osm/kgH2O；; ; At the maximum secretion rate, osmotic pressure can be close to plasma, and the concentration of sodium and chlorine in saliva increases and the concentration of potassium decreases. When the secretion rate is low, the opposite phenomenon occurs. At present, it is believed that the change of electrolyte composition in saliva with secretion rate is due to the different absorption of electrolyte by catheter epithelial cells when secretions flow through the catheter, but the electrolyte composition is similar to that of plasma when secretions are discharged from acinar cells.

Saliva is a part of body fluid, which comes from diet, and is formed through the "overflowing essence" of the stomach, the absorption of the intestine and the "dispersing essence" of the spleen. Body fluid is very important in human physiology, and it is also the basic substance that constitutes the human body and maintains human life activities. Body fluid refers to the thin part of body fluid, which has strong fluidity and is distributed in the skin, muscles and pores on the body surface, and can penetrate into blood vessels to play a moisturizing role. Liquid refers to the viscous part, which has little fluidity and is injected into joints, viscera, brain and marrow for nourishment. Because of the mutual transformation of body fluid, body fluid can often be called the material basis for maintaining physiological activities by gasification.

The relationship between qi and body fluid is similar to that between qi and blood. Qi plays the role of gasification, warmth, promotion and fixation on the production, distribution and excretion of body fluid, and its existence in the body needs to be attached to body fluid. Qi adheres to body fluid and moves in the body.

Both blood and body fluid are produced by Shui Gu's essence, and body fluid is a part of blood. The relationship between them is very close, so there is a saying that body fluid and blood are homologous. The interaction between blood and body fluid, such as the loss of body fluid, will inevitably affect the biochemical supplement of blood, resulting in the loss of yin blood, on the contrary, a large amount of blood loss will also lead to the lack of body fluid.

Deficiency of body fluid and functional decline will lead to deficiency of body fluid, which belongs to yin. Deficiency of body fluid is a manifestation of yin deficiency, and all causes of yin deficiency will lead to deficiency of body fluid. Symptoms of body fluid deficiency are often manifested as dryness, so symptoms of body fluid deficiency are often called internal dryness. Body fluid and body fluid in other physiological states are mutually regulated and transformed under the physiological function of viscera, so excessive blood loss, excessive sweating and excessive diuresis will lead to insufficient body fluid.

Body fluids include saliva, gastric juice, intestinal juice, tears, runny nose, sweat and urine. Saliva is an important part of body fluids. Saliva is secreted by three pairs of salivary glands around the mouth, commonly known as saliva, which contains amylase. Saliva flows to the mouth through the drainage tube, which can digest starch. In recent years, some American experts have shown that oral saliva is not only helpful for digestion, but also the first line of defense against cancer. It has a strong anti-cancer effect, even aflatoxin and nitrite, which have a strong carcinogenic effect, are not afraid. They also found that saliva can fully play its role as long as it is in contact with food for 30 seconds. Therefore, experts suggest that each bite of rice should be chewed 30 times before swallowing, which coincides with the requirement that people should "chew slowly" when eating food in China's traditional health preservation. It can be seen that our ancestors understood the mystery of body fluid to human health thousands of years ago, paid attention to strengthening and maintaining body fluid thousands of years ago, and created many training methods to strengthen and maintain body fluid-various methods of nourishing yin, promoting fluid production and swallowing body fluid. For example, there is such a set of practice methods in the popular "Ba Duan Jin" method in recent years; Shake Tianzhu slightly, stir the body fluid with red dragon, rinse the body fluid 36 times, fill it with divine water, swallow it three times, and the dragon and tiger will run by themselves ... The general idea of this method is that when practicing, stir up and down in your mouth with your tongue, stir the body fluid with your tongue, and then swallow the newborn body fluid in three bites. When swallowing body fluid, you will make a gurgling sound, but don't swallow it too hard. Give it to your abdomen with your mind ... The so-called "essence" is generally considered to be the essence of the human body and can also be regarded as the result of the sublimation of body fluid. Through practice, the body fluid is changed from quantitative to qualitative, resulting in more important and beneficial essence for human body, which lays the foundation for the next practice of essence, qi and spirit returning to deficiency.

The ancients said that body fluid refers to saliva, which ranks first among many body fluids. Most health exercises and traditional martial arts exercises need the tongue to touch the upper jaw during practice, that is, to build a bridge. One of its significance is to stimulate salivary glands and increase saliva secretion.

In addition to the above intrinsic functions, saliva can also have other uses, such as beauty. The method is as follows: after washing your face, put the newborn clean saliva in your hands, arch your hands, then apply the saliva evenly on your face and massage gently once a day in the morning and evening. After a period of time, your face will be shiny and moist. In the past, some peasant women used to lick their hair with saliva when combing their hair. The hair moistened by saliva is shiny and can be learned. Saliva is inexhaustible and has no negative effects, which can be described as a beauty product. Its mechanism of action is that saliva contains a large number of ingredients that nourish the skin, and saliva also has the effect of sterilization and disinfection. When it comes to the disinfection of saliva, it reminds us of the self-rescue of many mammals after minor injuries. They lick the wound with their tongues over and over again, licking the dirty blood clean, the wound will not be infected, and it will speed up the healing. All these phenomena and functions show that saliva can be both bactericidal and nutritious. So far, there is still a simple method to treat mild trauma with saliva in China.