I greatly appreciate the honour which the Society has done me in asking me to read a paper by way of introducing a general discussion on the treatment of mental disorders. My remarks will deal with the relationship of physical disorder to mental symptoms. The main point to which I will more particularly draw your attention is to the need for a closer study of the extent to which mental symptoms are the result of some auto-intoxication or infection from one or other of the free mucous surfaces of the body, the gastro-intestinal tract being, in virtue of its size and function, the most important channel. If the relationship is a close one our outlook on mental disorders necessitates greater attention being directed to the investigation and treatment of our patients with the aid of modern methods, than has hitherto been done. The literature of the subject contains many references of a general kind to what is called the toxic factor in the ætiology of insanity, but the systematic investigation of mental disorders from this point of view has not yet been carried out with the reasonable degree of completeness which modern medicine demands. In this connection it is right to refer to the valuable and suggestive work carried out by Lewis Bruce many years ago, the probable significance and value of which has, I think, been largely lost sight of. There is little new in the conception of the aetiology and treatment of mental disorders, which I am going to present for your consideration. It is, however, largely new in the sense that it has not yet been adequately tested. Prof. Robertson has lately drawn my attention to the interesting fact that the leading alienists in France more than 100 years ago entertained the view that the primary cause of mental disorders was to be found in visceral changes. Pinal in his classical text-book on mental disorders in 1809 wrote as follows: