Although physicians had some expectation that radium exposure might have effects similar to those of x-rays, no one knew exactly how radium would impact the human body. In setting rules for therapeutic experimentation, professional medical associations in the late-19th and early 20th-century United States emphasized that each doctor was expected to make his or her own moral judgments about treatment. This did not mean, however, that medical associations advised doctors to experiment on patients without considering the consequences; rather, they emphasized that decisions about therapeutic experimentation were a tricky business, bounded by complicated, idiosyncratic factors, such as the particulars of a given case, the overall health, age, and status of the patient, and the doctor’s own comfort or discomfort with a particular type of therapy. To navigate this morass of factors, most medical organizations suggested that doctors abide by the “golden rule” when contemplating experimental therapies: a doctor should not use a treatment on a patient without first trying it out on the physician’s own body, family members, or friends. In theory, the golden rule had a self-limiting quality, since doctors presumably would want to avoid unnecessarily harming themselves or their loved ones.