The subject of the present paper has occupied my attention for more than two and a half years, and during the whole of that time I have felt deeply indebted to my colleagues both at Bethlem Royal Hospital and at the Lancashire County Asylum at Prestwich for the generous way in which they have afforded me every opportunity of studying the subject. Some of these gentlemen have not only permitted me to examine their cases, but—knowing my interest in the subject—have, at inconvenience to themselves, drawn my attention to cases which would otherwise have escaped notice, and have further assisted and encouraged me by confirming my own observations. I therefore take this opportunity of most heartily thanking all these gentlemen for their valuable help and kindness.