Within the last year a series of papers has been issued (1, 2, 3) from this laboratory indicating that in the psychotic there exists a disturbed regulation of the respiratory mechanism for the control of acid-base equilibrium, which, in the cases examined, mainly depressed psychoses, manifested itself as an inexcitability of the respiratory centre, shown by a failure of response to CO2 stimulation. The work was done on uncertified borderline cases of insanity; it has since been confirmed by Marsh (4) on certified patients, and his results in 73 cases confirm the original findings and indicate plainly that dementia præcox and depressive psychoses fall into a group showing a variable inexcitability of the respiratory centre. The question naturally arises whether this condition is a cause or an effect of the mental state, and, from the point of view of cause, whether it is due to the drug-like action of some substance arising from faulty metabolism, or is an exhaustion effect. The question of intestinal toxæmia obviously needs investigation in this respect. This subject has been freely discussed in the literature and its significance becomes of greater importance in relation to psychoses owing to the work of Buscaino (5, 6) and Scheiner (7, 8) in Italy, and of Stewart (9) in this country. Buscaino describes a reaction of the urine with silver nitrate in certain psychotic cases, alcoholic insanities and dementia præcox, and from this assumes the existence of a toxic substance from liver derangement in these cases. He further describes lesions of the small intestine of mental patients which may result in undue permeability of its walls; it is not proposed to discuss this latter aspect of his work, but to deal with his silver nitrate reaction.