Hypnotic and sedative drugs play such an important role in the treatment of excitement in mental diseases, that it is no exaggeration to say that the difference between the mad-house of the past and the mental hospital of the present day is largely due to the rational exhibition of these drugs in conjunction with other therapeutic measures. To say that a certain class of drugs has brought about such a great change for the better is to make a very extravagant claim, but it is also a statement which forms an equally strong plea for the more intimate knowledge of any such e x t r e m e l y u s e f u l group of d r u g s ; and it is my excuse for making a clinical research on the hypnotics and their use in mental disease the subject of this thesis. The aim of the thesis is to show, f r o m m y clinical experience of h y p n o t i c s w h i c h of these I have found satisfactory and to indicate in some measure their rational use. To use any drug rationally man y things have to be taken into consideration; indications for and contraindications to, its exhibition borne in mind, and its advantages and disadvantages carefully weighed; consequently the scope of such an investigation is proportionately wide. Thus for the sake of clarity I have divided the thesis into the following sections:- 1. Introduction || 2. I n s o m n i a in M e n t a l Diseases || 3. C l a s s i f i c a t i o n of Hypnotic Drugs || (a) The alcohol group || (b) the chloral group || (c) the Paraldehyde group || 4. Theories of the Action of Hypnotics || 5. Drugs used with Clinical Notes on Cases || 6. Summary and Conclusions || 7. Bibliography.