In recent years research into mental disorders has tended to become more and more the study of the pathology of the living. The advance of biochemistry has contributed in great measure to this practice. Although bacteriological research has, in recent years, been more extensively undertaken in connection with focal infection, it has, in the opinion of most, yielded disappointing results. The study of focal infection by bacteriological methods alone will not, I am afraid, lead us very far. Endeavour should be made to correlate its local and remote effects in disordered hæmopoiesis, disordered metabolism and disordered endocrines in relation to the internal economy of the patient. In mental disease especially this implies a knowledge of the individual's potentialities that have been predestined by heredity, and later moulded by environment—factors which largely determine the psychopathic tendencies of every one of us. The bacteriological researches of Ford-Robertson and McRae (1) strongly suggest that in mental disorders we are confronted by bacteria of a special type, which as chronic infective agents can probably only adapt themselves to a certain group of the general community having a neurotoxic susceptibility. If, then, we are to make further progress in this direction, we must search for and apply new methods of bacteriological technique, study our results, and attempt to correlate cause and effect. In this relation I shall refer to special methods which are an elaboration of my father's work, the value of which time and experience may prove. In spite of the great importance of the biochemical researches of recent years, I think it will be agreed that some of us, especially those who are clinicians, feel disappointed that so far they have not given us as much indication for scientifically applied treatment as we had hoped. May I suggest that the explanation for this is two-fold. Firstly, in forming the basis of any research the present tendency is to take mental disorders in groups, for example, dementia præcox, which has a wide range of symptoms and between which and other groups it is difficult to draw a line of demarcation. It seems to me that our knowledge of the somatic factors underlying mental disorder is as yet so limited that attempts to continue on these lines will lead us only hesitatingly along the path of progress. Are we not still at the stage where our efforts should be concentrated more on the individual as a problem in pathology which, when solved as far as our knowledge permits, can be correlated in the future with his or her psychogenic group? The second point is that in many instances our scientific work tends to run in too narrow channels; thus it must be frequently lacking in the invaluable support of parallel knowledge in other branches of laboratory and clinical experience. The most obvious example is the lack of adequate collaboration between the biochemist and bacteriologist. I know of no two sciences that can be welded together so opportunely. This combination can be taken a stage further: active and intelligent co-operation with the clinician and X-rays and therapeutic specialists should be sought to enable us to appreciate better the intricate problems we have to face. Some of you may, with reasonable grounds, accuse me of theorizing, and I should at this stage like to mention that before I attempted to put these considerations into practice in cases of mental disorder, I had had the opportunity of carrying out exactly similar lines of research on some hundreds of non-mental patients in hospital and private practice. The majority of them were cases obscure in ætiology and symptomatology. This scientific survey proved to me at least the value of comprehensive work on the individual, and how it enabled one to diagnose and treat many cases with some hope of success. During my two years at Wantage House (the new acute hospital attached to St. Andrew's), I have attempted to carry out what this experience has taught me, with the added advantage that the patients have been under my personal care. Further, there has been every facility for dental and general X-ray diagnosis, and, lastly, ample scope for treatment. The success of such a scheme is only possible by organization and the team spirit, and in this I have been singularly fortunate. The cases I am bringing to your notice are 4 out of some 120 which have been subjected to comprehensive overhaul. I will try to emphasize the salient features in each and correlate them with the mental disorder presented. In this way you can judge for yourselves if we have learnt anything that may in the future lead to a clearer conception of what may underlie at least some forms of mental disorder.