Fig. (17) Histogram showing the labeling index of mitochondria per each adrenal medullary cell in either adrenalin cell or noradrenalin cell of respective animals in 10 groups during the development and aging from fetal day 19 to postnatal month 24. The labeling index of mitochondria increased from perinatal stage to juvenile stage at postnatal day 14, then decreased from adult stage at month 1 to month 24.