When he graduated from Dartmouth, Just faced the same problems all black college graduates of his time did: no matter how brilliant they were or how high their grades were, it was almost impossible for black people to become faculty members at white colleges or universities. Just took what seemed to be the best choice available to him and accepted a teaching position at historically black Howard University in Washington, D.C. In 1907, Just first began teaching rhetoric and English, fields somewhat removed from his specialty. By 1909, however, he was teaching not only English but also Biology. In 1910, he was put in charge of a newly formed biology department by Howard's president, Wilbur P. Thirkield and, in 1912, he became head of the new Department of Zoology, a position he held until his death in 1941. Not long after beginning his appointment at Howard, Just was introduced to Frank R. Lillie, the head of the Department of Zoology at the University of Chicago. Lillie, who was also director of the Marine Biological Laboratory (MBL) at Woods Hole, Massachusetts, invited Just to spend the summer of 1909 as his research assistant at the MBL. During this time and later, Just's experiments focused mainly on the eggs of marine invertebrates. He investigated the fertilization reaction and the breeding habits of species such as "Platynereis megalops", "Nereis limbata", and "Arbacia punctulata". For the next 20 or so years, Just spent every summer but one at the MBL.