We preface this short communication by emphasizing that it originates as a by-product from some work that is still in progress at the Burden Institute on the balance of electrolytes in various normal psychological and neurotic conditions. This research is chiefly being conducted by McLeod, Morrison and Fosbrooke, in the Biochemical Department, and Grey Walter in the electrophysiological laboratory.

It is proposed in this review to deal only with those aspects of physiological psychology that have an immediate bearing on the problems of human behaviour. Here again two limitations must preclude consideration of much important work in this field, in that endocrinology and the study of cortical potentials have been relegated to the special articles dealing with this subject.

When Dr. Cook, who has the thankless task of organizing the papers and discussion of this meeting, told me I had let him down because I had not secured one of the most distinguished surgeons in the country, Mr. Jefferson, he put it to me that the least I could do was to fill in the gap. I was puzzled as to what to say until Prof. MacDonald gave me a clue, and instead of talking on physiology and anatomy, which, after all, you probably know better than I do, I propose to give you a few general considerations which seem to make for the defence of an operation such as this against Prof. MacDonald's criticism.

Although much work has been done on the physiological concomitants of affective states, nothing is known of any objective bodily changes accompanying thought processes, and yet the most superficial observation of lip, facial and eye movements, of unconscious gesture and restlessness furnishes indications of some of the more obvious somatic accompaniments of non-emotional mental activity.

When you did me the very great honour of calling on me to deliver the Maudsley Lecture, I was told that it had been decided that these lectures should be devoted alternately to scientific psychiatry and to subjects of general popular interest, and that the subject of my lecture was to be scientific. I decided that with a year's notice the active preparation of the lecture might well be postponed for eleven months, and that during this gestation period I might hope to fix on one of the many aspects of pathological or physiological science of sufficient interest to justify a not too technical exposition to a mainly clinical audience.

Prof. Golla, in introducing the discussion, said: I do not think there is any subject that is of greater importance at the present moment than the physiology and the pathology of the circulation of the central nervous system. I am dealing now with the physiology, with a view to putting a few facts before you which are fairly well authenticated, and pointing out how very little we know at present. I do not intend to speak of the pathological aspect, but I may remind you, in passing, of such things as the therapeutic effects of amytal and of CO2. Again, in the case of epilepsy, whatever one's ultimate view of epilepsy is, we are all agreed that circulatory disturbance plays a very large part.

In 1929 Berger (1) discovered that changes of electrical potential in the human brain could be detected through the unopened skull. Since that time the study of electro-encephalography has occupied the attention of many workers, and the literature is already too extensive for adequate review in this place. A brief description of the technique for obtaining an electro-encephalogram, or “EEG”, and a summary of its normal and pathological characters may be found in a communication by one of us (2) on the relation between the EEG and the presence of intracranial neoplasms. The cortex in the region of a tumour was found to produce abnormally slow potential waves, which were provisionally called “delta” (δ) waves to distinguish them from the normal “alpha” (α) waves which are the original “Berger rhythm”. In the same paper a case was reported in which a focus of δ waves was found in the left parieto-occipital region associated with an area of degenerating cortex. The history in this case was of occasional minor attacks and one major fit and an indefinite severe illness in infancy, the only sign being a right homonymous hemianopia in accordance with the left-sided focus. Ether and nitrous oxide anæsthesia are also accompanied by the production of slow waves, but in this condition there is no fixed focus, the whole cortex being engaged in abnormal electrical activity. Since the publication of the above-mentioned results, a case of cerebral abscess has been examined, and the EEG was found to indicate a δ focus similar in character to those which have been found in cases of new growth.

Carriers of the enteric group of organisms are apt to be a source of some administrative difficulty in mental hospitals. The Infectious Diseases Sub-Committee have therefore attempted to estimate the value of cholecystectomy in this condition.

In 1920 Marinesco and Radovici (1) described a reflex contraction of the homolateral chin muscles in response to stimulation—pricking or pinching—of the thenar surface of the hand. They record a case of amyotrophic lateral sclerosis where such a stimulus evoked a slow contraction involving the triangularis and quadratus menti of the same side. In this particular case the reflex could be elicited not only from the palmar region, but also from the skin of the arms, thorax and abdomen, also by stimulation of the perinæum, effected by passing a urethral sound. The lowest threshold of reflex excitability was, however, obtained on the palm.

Inasmuch as the following is a summary of results of investigations into the pathology of mental disorders that have been conducted at the Central Pathological Laboratory at the Maudsley Hospital during the past few years, I shall deal with the general results obtained by my co-workers in the broadest fashion, alluding only to such facts as appear to be relevant to the hypothesis I am putting before you. When the present investigations were begun we had already abundant evidence of anatomical lesions occurring in schizophrenia, worked out in this laboratory by Sir Frederick Mott (1), (2), (3), assisted by Mr. Geary. The completeness of this evidence is a matter of history and is not now seriously disputed. (A few of the slides from the collection left to the laboratory by Mott were here shown.)

The fact that intellectual effort is accompanied by an increase of muscular tonus was demonstrated by one of us in 1921 (1), the method employed being the registration, by means of a highly magnifying optical lever system, of slight displacement of a relaxed limb. It was found that those muscles which were in a state of postural tension increased in tonus during intellectual work, whilst the fully relaxed antagonists remained unaffected.

The preceding studies on the acid-base equilibrium in psychotics have made it evident that the failure to adjust must be attributed in the first instance to an inadequacy of the respiratory compensatory mechanism, and can be in no sense attributable to either a deficiency in the buffering power of the blood itself or to an increased organic acid production (acidosis). We have endeavoured to determine the excitability of the respiratory centre to the stimulus created by CO2. For this purpose a number of psychotic patients were tested as to the excitability of the respiratory centre to air containing 2% CO2 and the reaction compared with that obtaining in a number of normal subjects.