The present and final division of this paper contains a description of those types of mental disease which are classed by the writer under the heading “Dementia.” Under this term he includes all cases which agree, from the psychic aspect, in the possession of a decreased or decreasing mental capacity, and from the physical, in the existence of a distinct and permanent loss of cortical substance in those regions of the cerebrum which especially serve as a physical basis for the carrying on of (voluntary) psychic processes.