The discussion which I have been invited to open is on a subject which is new to all of us, and which may, therefore, simply on this account, claim a share of our attention. Indeed, on searching the works of Clouston, Blandford, Savage, and others, as well as the extensive periodical literature which is at our disposal in the “Journal of Mental Science,” the “West Riding Asylum Reports,” and similar publications in France and Germany, the subject of mental affections occurring subsequently to influenza has hardly been mentioned with a single word previous to the epidemics of that distemper which we have recently passed through. Nor is there anything to be found on this subject in the numerous books and papers descriptive of influenza which have appeared before 1890. All that has been written on mental disorders in connection with influenza previous to that date refers to the febrile or initial delirium which may occur at any time during the progress of the feverish attack, and may, indeed, precede all other symptoms, setting in sometimes before there is any rise of temperature. This initial delirium has been described as long ago as 1510 by Sauvages, and later on by Huxham, Ash, Haygarth, Gray, Smyth, Rush; more recently by Lombard, Bonnet, and Pétrequin, and during the last epidemics by Ewald,1 Joffroy,2 Gwynne,3 Creagh,4 Nicholson,5 Van Deventer,6 Mairet,7 and others. In the German Collective Investigation Report, edited by Leyden and Guttmann,8 no less than 276 such cases have been collated. It is, however, not this initial delirium which we have met here to consider to-day, but those better defined psychoses which are prone to occur after the feverish attack is over, during, or some time subsequently to convalescence.