The following translation of a letter in the “Progrès Medical” of the 2nd July, 1881, seems to me of considerable interest as showing, among other things, the powerful effect of the force of imitation in that Protean disease hysteria, and also the result of bad moral treatment. A series of somewhat similar cases, illustrating what has been well called the contagion of nervous affections in these leading to undoubted insanity with distinct delusions, is well described, and typical cases noted, by Dr. M. de Montgel, of the Marseilles Public Asylum, in the January number of the “Annales-Medico-Psychologiques.” But in almost all the cases there cited hereditary taint was distinctly made out, the weak mind being crushed by continued contact with the insane one. This folie-à-deux deserves serious attention; it may, from a medico-legal point of view, assume considerable importance; for instance, a person accused of crime may be under the domination of another's delusions. Many of the ecstatic outbreaks of seeming religion exemplify this form of insanity, often observed although seldom treated according to their deserts.