Saline is an aqueous solution of sodium chloride with a concentration of 0.9%, that is, it contains 0.9 grams of sodium chloride in 100 milliliters of saline. The main ingredient of table salt in daily life is sodium chloride, but of course it is not pure sodium chloride, but has impurities. Physiological saline is pure sodium chloride diluted into 100 ml of saline, the concentration of 0.9%, such a sodium chloride solution contains sodium ions, chloride ions and water, the concentration of 0.9% sodium chloride solution, osmotic pressure and the human body’s tissue fluid, plasma osmolarity is basically the same, isotonic solution. Injected into the human body, the cells will not occur because of osmotic pressure changes in the water to reduce, thus appearing dehydration, but also will not appear because of the increase in water edema, can effectively ensure that the cells will not rupture because of edema, but also because of the dehydration of the wrinkles, will not affect the function of the cells, so the concentration of 0.9% of the sodium chloride solution is called saline in the medical field.