The temperature of human body is relatively constant. Normal people's body temperature fluctuates slightly within 24 hours, and generally the difference is not more than 65438 0 degrees. Physiologically, the body shape is slightly lower in the morning and slightly higher in the afternoon. After exercise, after eating, before menstruation or before pregnancy, the body temperature of women is slightly higher, while that of the elderly is lower. If the body temperature is higher than normal, it is called fever, 37.5 ~ 38 degrees is low fever, 38 ~ 39 degrees is moderate fever, 39 ~ 40 degrees is high fever, and above 40 degrees is ultra-high fever. Relatively constant human body temperature is one of the important conditions for maintaining normal human life activities. For example, when the body temperature is higher than 4 1 degree or lower than 25 degrees, it will seriously affect the functional activities of various systems (especially the nervous system) and even endanger life. The heat production and heat dissipation of human body are regulated by nerve center, and many diseases will cause problems in the normal regulation of body temperature and make it change. It is of great significance to check the patient's temperature and observe its changes in clinic for diagnosing diseases or judging the prognosis of some diseases.