“…The pterins 2-amino-4-hydroxypteridine-6-carboxylic acid, 2-amino-4-hydroxypteridine and i8oxanthopterin are widely distributed in Nature (Forrest, Van Baalen & Myers, 1957;Viscontini, Kuhn & Egelhaaf, 1956;Forrest & Mitchell, 1955;Viscontini, Schmid & Hadorn, 1955;Viscontini, Loeser, Karrer & Hadorn, 1955;Nawa & Taira, 1954;Hama, 1953;Busnel & Drilhon, 1949; for earlier references see Blair & Graham, 1955).…”