The gracious act of the British Medico-Psychological Association in asking me to deliver the Maudsley Lecture for 1923 is thoroughly appreciated, not only by myself, but also by the medical profession of Canada, showing as it does a further development of the relationship steadily increasing between the Mother Country and the Dominions, I shall not say Colonies, as this term has long ago become unpopular with the rising generations beyond the seas. We feel that we occupy a modest place in the list of nations, we yield to none in our devotion to King and Country, and regard a United Empire as absolutely necessary in preserving the ideals essential for the highest development of the human race.

The material dealt with in this investigation was collected from 110 cases dying in the London County Mental Hospitals and various General Hospitals and Hospitals for consumptives.

We cannot avoid this difficult and theoretical discussion of first principles. The distinction between social and individual phenomena must be defined and shown as real, relative, abstract, etc., as the case may be. We cannot, for example, understand the inter-relations of the group and the unit unless we can form a clear idea of their respective natures. Even the literature of social psychology is not helpful or intelligible to us until the meaning and validity of such conceptions as group mind are definitely established. Hugo Munsterburg, for example, writes: “We compare the social mind with the individual mind. Such a comparison is not meant as a metaphor. It is a true, far-reaching analogy, an account of really corresponding processes.” He then works out the most elaborate parallel, even in regard to “physiological basis.” But parallels never meet, and though this one may be suggestive, it is not helpful to the understanding of the interaction of the social and individual minds—i. e. the psychogenesis of the group and the socialisation of the individual or even in forming clear ideas of these two and their relations. Other writers use group mind as a mere figure of speech, for others again it is a transcendent reality.

Urea is the compound in which the greater part of the nitrogen from protein metabolism is normally excreted, and of which it forms an important index.

Two methods are available to determine the reaction of a fluid. The first is the method of titration for acidity or alkalinity, in which a standard solution of acid or alkali is added until a certain change in the colour of a suitable indicator is detected. The second method is to determine the hydrogen-ion concentration present in the fluid. The latter is the only satisfactory method of measuring the reaction of a fluid. The hydrogen-ion concentration expresses the reaction of neutral, acid and alkaline solutions. The electrical is the standard method, but for clinical purposes is too intricate. The colorimetric method is less complicated. It is based upon the fact that each indicator has a characteristic zone of hydrogen-ion concentrations within which its colour changes occur. For details as to the theory and technique of this method, the reader may be referred to Clarke and Lubs (J. Bacteriol., 1917, ii), and Cole (Practical Physiological Chem., pp. 19–30).

The work mentioned hereunder was commenced with a view to investigating the alterations in the sugar content of the blood and urine which have been observed in the insane, and to consider whether they are necessarily pathological, or whether they are merely normal sympathetic reactions to an abnormal extra-sympathetic stimulus.

Symbiosis is systematic biological co-operation, and, whether we view it in a narrow, morphological, or in a wider yet more definite socio-physiological sense, it is a phenomenon of first-rate importance, deserving widest attention. Botany, zoology, physiology, pathology, agriculture, sociology are all vitally concerned in symbiosis.