This book is not a history of leprosy down to the present day. Its main focus has been the period 1840–1920, when fears of the revival and return of leprosy became entangled with the spread of Western imperialism across the globe. Nor is it a narrative of the progressive elimination of ignorance and superstition by modern medical science. As we have seen, a mid-nineteenth-century anti-contagionist like Milroy was mainly right, but for the wrong reasons, while micro-biologists were wrong about the nature of the bacillus they rightly identified as the agent of infection.

That is, of course, always assuming that leprosy really is caused by M. leprae. It was not until 1971 that the bacillus was successfully transmitted to an experimental animal, the nine-banded armadillo, and it has still not been cultivated in vitro. Leprosy's mode of transmission remains unknown, and this, together with its very low level of infection, long latency, uncertain onset and prolonged duration means that many of the debates reviewed in this book have endured or been revived. Several modern researchers have questioned whether the disease is caused by M. leprae after all, suggesting instead that it has a metabolic origin and even returning to Jonathan Hutchinson's fish theory. The discovery that the bacilli can survive outside the body for many weeks has also seen the resurrection of telluric theories of the disease.