A Full account of the cases on which this paper is founded cannot now be given, as some of them are still under observation; and in others, which have ended fatally, the histological examination of the tissues is not yet complete. We think, however, that sufficient data have been collected to make a preliminary communication desirable. The condition to be considered may be described as “encephalitis,” or “encephale myelitis,” rather from the want of a better term than from any conviction on our part that it is essentially inflammatory in origin.