I know that the gouty diathesis is out of date. In fact, all diatheses are out of fashion. Nobody speaks of them now. They went out with the medical philosophies of the eighteenth century. Cellular pathology with its wonderful revelation of the anatomical seat of disease and bacteriology, with its still more wonderful revelation of the external cause of disease, so dazzled the eye and the mind that we forgot that the sensitive animal body behind the attacking microbe had its changes, too, its changes in body chemistry that could not be stated in terms of cells and bacteria. The pendulum is swinging back now to a consideration of the constitution of the body on which the microbe or poison acts, its _resistance_ or _immunity_, its _anaphylaxis_ or _allergie_. With these holiday and lady terms, are we not trying to describe what our ancestors knew as _diathesis_? For what is the old conception of diathesis but just such a hereditary weakness or lack of defense or tendency to disease that our ancestors recognized clinically but could not demonstrate, elusive, difficult to detect, but nevertheless there; like the dog who has been sensitized to an otherwise harmless proteid, who seems well and is well in everything except his susceptibility to that one special cause of disease? Bacteriology, which first took away the idea of diathesis, is now giving it back. The discovery of the tubercle bacillus as the cause of tuberculosis banished the _tubercular diathesis_ apparently forever; but, step by step, through bacteria and then toxins and antitoxins and now through anaphylaxis and allergie, bacteriology is bringing back the old conception of an inherited or acquired susceptibility to attack. Call the old tubercular diathesis a _sensitization_ and you have made it the most modern of modern discoveries. So, also, step by step, through bacteriology with its toxins and antitoxins and now with anaphylaxis, from the philosophic ash-heap on which we thought to have thrown it for good and all, like an old family cat that we thought was dead, comes creeping back that old conception of a gouty diathesis or arthritism, not as dead as we thought it, to complete the explanation of the existence of hay fever. I am far from saying that calling hay fever a form of gout ends the subject. I say only that bringing such a common and puzzling disorder as hay fever in line with such a common and puzzling disorder as gout brings us a long step nearer to solving the puzzle that lies behind both of them; and I say also that, in the records of this work, the name of Gueneau de Mussy, who first recognized this relation clinically, deserves a place.