Członek American Academy of Arts and Sciences, Association of American Physicians; American Medico-Psychological Association (przewodniczący w 1919), American Medical Association, American Association for the Advancement of Science, American Neurological Association, American Association of Pathologists, Society of Experimental Biology; Boston Society of Neurology and Psychiatry, National Association for the Study of Epilepsy; American Psychopathological Association, American Genetic Association, Massachusetts Medical Society, New England Psychiatric Society.
Zmarł po dwudniowej chorobie, na zapalenie płuc. Był autorem ponad 150 prac naukowych. Biografię Southarda napisał jego przyjaciel, Frederick Parker Gay.
Wybrane prace Neurosyphilis. W.M. Leonard, 1917 Shell-shock and other neuropsychiatric problems presented in five hundred and eighty-nine case histories from the War literature, 1914-1918. W.M. Leonard, 1919 Elmer Ernest Southard, Mary Cromwell Jarrett, Roscoe Pound: The kingdom of evils: psychiatric social work presented in one hundred case histories. The Macmillan company, 1922