Denham Harman, Aging: A Theory Based on Free Radical and Radiation Chemistry. J. Gerontol. 11, 298-300 (1956).

"Aging and the degenerative diseases associated with it are attributed basically to the deleterious side attacks of free radicals on cell constituents and on the connective tissues. The free radicals probably arise largely through reactions involving molecular oxygen catalyzed in the cell by oxidative enzymes and in the connective tissues by traces of metals such as iron, cobalt, and manganese."