Under Dr. Leo Stanley, chief surgeon at California’s San Quentin Prison from 1913 to 1951, prisoners became subjects in a wide variety of medical experiments: sterilization; testicle transplants (using testicles from executed prisoners, as well as from goats and boars); Spanish flu treatments. As historian Ethan Blue recounts in his article on Dr. Stanley’s career (may be behind a firewall for non-university readers, but cite is Pacific Historical Review 78(2), 2009):

The benefits of human experimentation in prisons were many, [Dr. Stanley] believed, because “in such a place all men are treated alike, and live under the same conditions of food, work, and general surroundings . . . .[P]atients could be under daily observation, and the ‘follow up’ conditions were ideal.” San Quentin prisoners had access to esteemed doctors from the Bay Area, and hence the benefits of medical modernity unavailable to a great many other prison inmates. The downside of this privilege was that these doctors also had access to them. (p. 227)