Abstract
1. Uranium nitrate is relatively more toxic for old animals than for young animals. 2. This relative toxicity is not only expressed in the old animals by a greater functional disturbance of the kidney, but is also shown by an inability on the part of these animals to repair the kidney injury and reestablish its functional capacity. 3. The intoxication in younger animals has been followed by a repair of the renal injury and a partial restoration of kidney function. 4. In these animals the processes of repair lead to the development of a chronic diffuse type of nephropathy in which the acid-base equilibrium of the blood may be maintained at the point of normality. In these animals renal functional tests indicate the presence of severe kidney injury.