Complex sentence: Ehrlich had used mixtures of acidic and basic dyes for this purpose in 1879: in 1891 Ernst Malachowski and Dmitri Leonidovich Romanowsky independently developed techniques using a mixture of Eosin Y and oxidated Methylene Blue that was also useful for this purpose.
Split into simpler sentences: Ehrlich had used mixtures of acidic and basic dyes for this purpose in 1879. In 1891 Ernst Malachowski and Dmitri Leonidovich Romanowsky independently developed techniques using a mixture of Eosin Y and oxidated Methylene Blue that was also useful for this purpose.