Jan Evangelista Purkyne, also called Johannes or Johann Evangelist Purkinje, studied cells in the cerebellum, fibers of the heart, subjective visual phenomenon, and germinal vesicle, in eastern Europe during the early nineteenth century. His investigations provided insights into various mechanisms and structures of the human body. Purkyne introduced techniques for decalcification of bones and teeth, embedding of tissue specimens, and eye examinations. He was one of the first to adopt the microtome in his experiments and to use the term protoplasm when describing the contents of young animal embryos. Purkyne identified structures in the eggs of chickens, such as the germinal vesicle, from which he hypothesized the female reproductive cell (ovum) developed, and around which he said an embryo developed. Purkyne's results helped others locate ova in mammals.