When I was invited, during my last summer holiday, to read a paper on this subject, I agreed with a light heart; but on more mature reflection the glow of satisfaction at being so honoured has paled before the spectre of responsibility in addressing a body of experts on a subject peculiarly their own and remote from the paths of my usual work. I can only ask your indulgence, and—negative though most of the conclusions are—hope that they may suggest certain points in the treatment, and especially in the pathology of these conditions.