grown outside of the body. He published the results of his studies in 1907. This part of Harrison's research was the first step toward current research on precursor and stem cells. While Harrison himself didn't develop this area of research any further, he encouraged others to. He was considered for a Nobel prize for his work on nerve-cell outgrowth, which helped form the modern functional understanding of the nervous system, and he contributed to surgical tissue transplant technique. During the first world war, Harrison studied embryology and the symmetries of development. By means of the dissection of embryos followed by transplantation and rotation of the limb bud he demonstrated that the main axes of the developing limb are determined independently and at slightly different times, determination of the anteroposterior (anterior-posterior) axis preceding that of the dorsoventral (dorsal-ventral) axis. Harrison dissected Ambystoma puncatatum (salamander) embryos and transplanted limb buds to determine whether the limbs developed independently or according to instructions from host cells. When the limb buds were transplanted in halves or doubled, they still developed into normal limbs. Harrison concluded that the information from the host (the surrounding embryo cells) directed the cells to develop normally even though they were transplanted in halves or doubles. Therefore, the limb buds were all equipotential, meaning they all developed the same way, and the tissue around the limb buds determined their dorsoventral orientation. However, when a left limb was put on the right side of the body, a left limb grew anyway despite its relocation. The same pattern occurred when a right disk was placed on the left side of the body—a right limb grew. Harrison also transplanted inverted limbs. When a left disk was inverted, it grew a right limb (and vice versa). Harrison then concluded by this data that the buds determined anteroposterior orientation independent of the surrounding host tissue. Harrison's research lead him to assume that the development of limbs is not determined exclusively by the limb buds or by the environment, but that both of these factors influence how an embryo develops. Harrison published the results of this study in 1921 in the Journal of Experimental Zoology in a paper titled "On relations of symmetry in transplanted limbs". Personal life Harrison married Ida Lange (1874-1967) in Altona, Germany on January 9, 1896, and they had a family of five children. One of them is the cartographer Richard Edes Harrison.