Not until this century has it been possible to pull down a book off the shelf and find in it an up-to-date reference work on the pains and ills of the world. There were books previously on the subject---as there were on every aspect of scientific knowledge---but most were addressed effectively either to physicians or to the gullible. There was, firstly, too little known, and secondly, too much by way of speculatory garbage, for the general public to have much of a chance to learn the facts of medical progress.