Relations between development of lathyrism by aminoacetonitrile treatment and animal age were investigated with white rats on the following three criteria ; observations by soft X-ray photographs, changes of femur water contents, and changes of the neutral soluble collagen level in skin. All of these three indexes were observed clearly to be parallel to the development of lathyrism. The soluble collagen level in skin was found to be changed most sensitively by aminoacetonitrile treatment. When the period of aminoacetonitrile treatment was relatively shortened, lathyrism was developed more easily in immature rats than in adult ones, but the lathyrism of the same degree was recognized, regardless to animal age, by treating animals with aminoacetonitrile for 10 days or more.
