"Working with arsenical compunds, Ehrlich and his Japanese laboratory assistent, Hata, carried out six hundred and five experiments before reaching the one compound which satisfied all requirements. This was the famous '606', later modified to eliminate some remaining side effects and renamed neo-salvarsan. The experiments and the discovery of the new compound are discribed in the book cited ('Experimental Chemotherapy of Spirochaetal Diseases')." PMM 402.