Adult blood volume is equivalent to 7%-8% of body weight, for example, for a person weighing 60kg, the umbilical cord blood volume is about 4-5L, an adult male will have slightly more blood volume than an adult female under the same weight, and the composition of blood volume is mainly composed of plasma and blood cells. Plasma is mainly composed of 90% water and 6% protein, as well as the remaining low molecular substances, and blood cells are mainly divided into red blood cells, white blood cells and platelets, of which red blood cells are the most numerous. The erythrocytes of adult males in China are about (4-5.5) x 10^12, and females are (3.5-5.0) x 10^12. The function of erythrocytes is mainly to transport oxygen and carbon dioxide.