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 will ultimately require considerable alteration and improvement.

It must be clearly understood, moreover, that no attempt has been made to cover the whole field of insanity. On the contrary, certain sections of that field have been more or less arbitrarily selected, mainly on the ground that they yield fruitful results to psychological methods of investigation. I confidently anticipate that in the future these methods will have a far wider application, but in the present state of our knowledge it must be frankly admitted that there are whole tracts of insanity in which they have only a very limited utility. This confession is all the more necessary on account of the tendency to unduly extensive generalisation evident in the work of many recent investigators. In view of the enormous complexity of mental processes, and the youthfulness of psychology, it is best to realise that progress must inevitably be slow, and that we must be content to feel our way to the scientific laws of the future.

A very large number of the general principles enunciated in this book are due to the genius of Prof. Freud of Vienna, probably the most original and fertile thinker who has yet entered the field of abnormal psychology. Although, however, I cannot easily express the extent to which I am indebted to him, I am by no means prepared to embrace