In his paper "Ueber die Eiweissstoffe,” Dtsch. med. Wschr. 24 (1898) 581-82 and later papers German biochemist Albrecht Kossel of Berlin forecast the polypeptide nature of the protein molecule. He proposed “that amino acids and their spatial arrangement with the protein must become the chemical key to understanding of proteins” (Tanford & Reynolds, Nature's Robots, 52).
J. Norman (ed) Morton's Medical Bibliography (1991) no. 721.