The present portion of this paper deals with the subject of progressive and secondary dementia. It includes the consideration of those cases of mental disease which, owing to the existence of certain extra-neuronic encephalic morbid states, do not develop a practically stationary condition of mental enfeeblement consequent on the loss of a proportion of the higher cortical neurones, but undergo a more or less rapidly progressive process of neuronic dissolution, which, if the patient survives to such a stage, finally ends in gross dementia.