Dr. Leo Stanley served as San Quentin's chief surgeon for nearly four decades. Between 1913 and 1951, he oversaw the modernization of its medical regime, shifting from Lombrosian eugenic criminology through biomedical explanations for crime, and finally into psychological treatments in the postwar period. Throughout, Stanley fixated on curing various crises of manhood. Under Stanley's scalpel, prisoners became subjects in a series of eugenic treatments ranging from sterilization to implanting "testicular substances" from executed prisoners---and also goats---into San Quentin inmates. Stanley was convinced that his research would rejuvenate aged men, control crime, and limit the reproduction of the unfit. His medical practice revealed an underside to social hygiene in the modern state, where the lines between punishment, treatment, and research were blurred.