Howell served as associate professor of physiology at Johns Hopkins in 1888 and 1889. He served as a full professor at the University of Michigan from 1889 to 1892. He then served as associate professor of physiology at
Harvard Medical School from 1892 to 1893. He then moved back to Johns Hopkins and remained there for the rest of his life. Howell served as chairman of the
National Research Council from 1932 to 1933. Howell contributed to the
London Journal of Physiology, the
Transactions of the Royal Society, the
Johns Hopkins Biological Studies, the
Journal of Morphology, and the
Journal of Experimental Medicine. He was associate editor of the
American Journal of Physiology after 1898. He wrote
Text-Book of Physiology (1905; fifth edition, 1913). And this was a standard text book for medical students for the next 50 years. ==Personal life==