Just authored two books, "Basic Methods for Experiments on Eggs of Marine Animals" (1939) and "The Biology of the Cell Surface" (1939), and he also published at least seventy papers in the areas of cytology, fertilization and early embryonic development. He discovered what is known as the fast block to polyspermy; he further elucidated the slow block, which had been discovered by Fol in the 1870s; and he showed that the adhesive properties of the cells of the early embryo are surface phenomena exquisitely dependent on developmental stage. He believed that the conditions used for experiments in the laboratory should closely match those in nature; in this sense, he can be considered to have been an early ecological developmental biologist. His work on experimental parthenogenesis informed Johannes Holtfreter's concept of "autoinduction" which, in turn, has broadly influenced modern evolutionary and developmental biology. His investigation of the movement of water into and out of living egg cells (all the while maintaining their full developmental potential) gave insights into internal cellular structure that is now being more fully elucidated using powerful biophysical tools and computational methods. These experiments anticipated the non-invasive imaging of live cells that is being developed today. Although Just's experimental work showed an important role for the cell surface and the layer below it, the "ectoplasm," in development, it was largely and unfortunately ignored. This was true even with respect to scientists who emphasized the cell surface in their work. It was especially true of the Americans; with the Europeans, he fared somewhat better.