INFECTIOUS diseases may at any period of their evolution create psychotic disorders of various characters. But they may also have a favorable influence, even of years' duration, on preexisting mental disorders. It is the latter aspect of the relationship that will be considered here.
As far back as 1844 Jacobi,1 and in the next few years von Rienecker, Griesinger, Neumann, Kraft-Ebing, Régis, Kraepelin, Fielder2 and others, reported a satisfactory influence of incidental disease on the course of the original psychosis.
The psychotic disorders which have thus been benefited are of wide variety; mental depression; hyperkinetic and expansive states of manicdepressive psychosis; persecutory delusions of the paranoid type; delusive and hallucinatory states of dementia precox; agitated states of involutional melancholia, and psychasthenic episodes. Of the incidental disorders influencing the original psychoses, the following have been recorded: exanthematous diseases, acute inflammatory rheumatism, suppurative conditions and trauma to the cranium. As