The co-substrate of glutathione peroxidases (GPx), glutathione (GSH), was discovered in the 19th century by de Rey-Pailhade and named “philothion”.¹  A partial elucidation of its composition was achieved in the early 1920s by Hopkins.²  The final characterization as the atypical tripeptide γ-glutamyl-cysteinyl-glycine required the evidence of the chemical synthesis by Harrington and Mead³  and du Vigneaud and Miller⁴  in the 1930s. The biosynthesis of GSH was then elucidated in the 1940s by Waelsch and Rittenberg⁵  and Bloch and Anker⁶  (for a recent review see Forman et al.).⁷  If one searches the internet for functions of glutathione, one can learn that it is a “key detoxifying molecule” or “the mother of all antioxidants”, both terms were primed early in the history of GSH and are not entirely adequate. Instead, I would recommend reading the greatly written review on the early GSH history by the late Alton Meister.⁸  Although it was published in 1988, it is still a most valuable source to find almost-forgotten knowledge and explanations of cloudy characteristics.