Career
In 1861 he emigrated with his family to Hamburg. In 1879 he received his doctorate from the University of Kiel, where he worked as an assistant to Arnold Ludwig Gotthilf Heller and Friedrich von Esmarch. In 1919 he was named an honorary professor at the newly established University of Hamburg.
His special field of interest was the endocrine glands.
His name is associated with "Simmonds" disease", defined as a form of hypopituitarism in which all pituitary secretions are lacking. In 1914 he was the first to describe the diseases" clinical features that were associated with destruction of the anterior lobe.