The starting-point for a physiological understanding of the above-mentioned diseases consisted in some new laboratory facts obtained in the course of the study of conditioned reflexes in dogs.

While, during the last thirty years, great advances have been made in our knowledge of inhibition, its properties and its interactions with excitation, yet little progress has been made in elucidating the precise nature of inhibition itself. Pavlov (67), for instance, has discovered many of the principles of inhibition, its interaction with excitation, its irradiation, its extinction and so on. But all the time he is dealing with inhibition simply as a phenomenon which shows itself in the end-reaction. With regard to what is actually happening in the cortex, he admits that it is unknown. Yet the phenomenon of inhibition is one of prime importance in the organization of the central nervous system. Perhaps, at times, while watching, say, a dog chasing a ball, one is apt to forget the many reactions which are not happening in one's interest in what is happening. Yet an overdose of strychnine to the dog will soon remind one that every movement of each limb, every twitch of a muscle is surrounded, as it were, by a wall of inhibition, checking, controlling and timing so as to produce the final smooth and graceful co-ordination.

The periods under review were selected according to the availability of suitable material. Before the year 1907 and during the years of the Great War the number of deaths divided into suitable age-groups are not readily obtainable. The years immediately following the end of the war were considered to be unsuitable owing to the occurrence of epidemics of influenza.

The following examination of the clinical features of depressive states is based on the detailed study of 61 cases examined and treated by the writer at the Maudsley Hospital, London.

It has been stated that in schizophrenia the usual specific dynamic action (S.D.A) of foodstuffs is not shown. In order to be certain that the S.D.A. of foodstuffs is less in schizophrenics than in normal subjects, it was considered desirable to attempt a form of examination in which information would be available not only concerning the rate of absorption of the ingested material, but also concerning the excretion of products of metabolism which would be increased during and after the period in which the S.D.A. was evident. Accordingly the results dealt with in this paper are based entirely on the findings of chemical changes in the blood and urine of the subjects investigated after administration of the selected agent.

Caterham Mental Hospital accommodates upwards of 2,000 patients, the great majority of whom are defectives. The medical staff numbers 7, and all other staff about 500. The patients are of all ages, and are described as “unimprovable adults” and “children of school age”. The type of patient has altered very little in the past five years, but a hostel has been added which accommodates 34 high-grade boys. These are selected from the other institutions of the London County Council, and, as a certain number prove unsuitable and do not wish to return to the institutions they came from, a number of higher grade patients have accumulated in the main institution. There are also, on the female side, laundry workers of high grade who have been sent for that specific work.