1, physiological weight loss: about 3 ~ 4 days after birth, down to the lowest point (3% ~ 9%), and then gradually rebound. To the 7th to 10th day after birth should be restored to the weight at birth. The first period is also called physiological dehydration. If the weight loss of more than 10% growth on the 10th day has not returned to the birth weight, it is a pathological state, the cause should be analyzed. 2, physiological jaundice: jaundice appears 2 to 3 days after birth in full-term infants, peaks in 4 to 5 days, subsides in 5 to 7 days, and does not exceed 2 weeks at the latest; jaundice in preterm infants mostly appears 3 to 5 days after birth, peaks in 5 to 7 days, and subsides in 7 to 9 days. The maximum delay can be up to 4 weeks. Daily elevated serum bilirubin <85umol/L (5mg/dl); serum bilirubin <221umol/L (12.9mg/dl) in full-term infants and <257umol/L (15mg/dl) in preterm infants. 3. Physiological abnormal neurological reflexes: In fetal life, the lower end of the spinal cord is at the lower edge of the 2nd lumbar vertebra and moves up to the 1st lumbar vertebra at the age of 4 years, and the site of lumbar puncture should be noted in infancy. And the tendon reflex is weak in infancy, and the abdominal wall reflex and testicular reflex are not easily elicited, and only stabilized at 1 year of age. 3~4 months old infants have weak muscle tone, Kernig's sign can be positive, and children under 2 years of age have positive Barbinsk;s sign and can be physiological phenomenon. 4.Physiological anemia: 2~3 months after birth, the red blood cell drops to 3.0×1012/L, and Hb drops to about 100g/L. Mild anemia appears, which is called "physiological anemia", and then Hb gradually increases. The reason is that after birth, the establishment of autonomous respiration, blood oxygen content increases, erythropoietin decreases, bone marrow hematopoietic function is temporarily reduced, reticulocytes decrease; fetal red blood cell life is short, and more destruction (physiological hemolysis); coupled with rapid growth and development of infants, the rapid increase in circulating blood volume and other factors. 5, physiological leukocyte ratio changes: at birth, neutrophils account for 65%, lymphocytes about 30%. After 4-6 days of life, the proportion of both is about equal. After that, lymphocytes account for about 60% and neutrophils account for about 35%, and the two ratios are equal again at 4-6 years of age, i.e., the white blood cell fraction is similar to that of adults after 4-6 years of age. 6, physiological hemoglobin (Hb) composition changes: after birth, fetal hemoglobin (HbF) accounts for 70%, HbA accounts for about 30%, HbA2 <1%. After birth, HbF is rapidly replaced by HbA, with HbF <5% at 1 year of age and <2% at 2 years of age. 7, physiological tonsillar enlargement: tonsils include pharyngeal and palatine tonsils, the former 6 months has developed, the latter 1 year before the gradual increase in size, 3 years and 6 years of age are two stages of physiological tonsillar hypertrophy period, that is, 4 ~ 10 years of age to reach the peak of development, 14 ~ 15 years of age to measure the gradual degeneration, so tonsillitis is common in older children, infants are rare.