[The other face of oxygen (2)].

The authors, in this second part of "The other face of Oxygen", pay attention no more to O2, the "untrustworthy" protagonist of oxidation, but to the opposite side, namely the "physiologic" antioxidative protections. Such antioxidative protections, which were being prepared and improved in cell, in interstices and in organic liquids, during millions of pears, perhaps represent the "most true" witness of the always "traumatic" cohabitation between organisms, although eukaryote, and oxygen. This, after all, in spite of the evolutive push, remained an element "foreign" to life, although, paradoxically, first protagonist of it. Similarly, "singularly foreign" appear mitochondria, namely the forges specifically entrusted with the respiratory metabolism.