The role of stress, or more generally of psychological factors, in the production of physical illness has long been a matter of interest and contention. Speaking for myself, I have found that I am more prone to viral illness when I relax after a period of exceptionally hard work than during it; but that, I concede, is no evidence.

Do The Memoirs of Sherlock Holmes constitute evidence? It is surprising how large a part stress induced disease plays in this volume.

Sherlock Holmes himself is not immune from it, though we sometimes make the mistake of supposing him to be a cold and rational calculating machine. In “The Reigate Squires” Holmes is ill. …