In clinical lectures given between 1850 and 1852, William Pultney Alison, a senior Edinburgh physician, reflected on whether therapeutic bloodletting could be useful in some cases of pneumonia but harmful in others. If so, Alison reasoned, a change in the form of the disease—a change of type—could explain why therapeutic bloodletting had been nearly abandoned in treating a disease for which, only a few years earlier, it had been the standard therapy. In response, a young pathologist, John Hughes Bennett, denied (...) that anything like a change of type had occurred and insisted that bloodletting had never been an effective therapy. Over the next two decades, more than forty physicians debated the usefulness of bloodletting and the reasons for its decline. This debate, known as the Edinburgh Bloodletting Controversy, has attracted the attention of contemporary historians. Those who have discussed the debate side with Bennett and give Alison little serious attention. I argue that by examining the texts to determine what the issues really were, we can see that Alison may actually have been right. Moreover, this examination illuminates the practice of bloodletting and reveals one hitherto unrecognized factor that contributed to its decline. (shrink)