I now come to the important, and I am sorry to say the controversial, question of the causes of insanity. After what I have already said on the etiology of the clinical forms of insanity and on the fluctuations of statistical insanity in communities, it seems to me that I might conveniently dismiss this subject by adopting the laconic style of the student who was assigned the task of writing an essay on “Snakes in Ireland” by saying in three words, as he did, “There are none.” But as the great majority of people still believe in the validity of the numerous causes which are popularly believed to create insanity somewhat in the same way as violent exercise causes fatigue or eating salt fish causes thirst, it is necessary to refer briefly to the subject.