Ethnic psychology is obliged to take into account the constant presence and powerful action of pathological mental elements. Tribes and nations have been destroyed by war or by catastrophes; but much more frequently some disease of the ethnic mind itself has prepared its own extinction. Here an important distinction is necessary. Ethnic mental disease has no relation to the frequency of individual cases of insanity. These do not affect the ethnic mind because that is the outcome of the intelligence of the community, not of its irresponsible members. For this reason ethnic psycho-pathology cannot be discussed wholly from the standpoint of insanity, although the analogies are such that we can profitably compare them in outline, and this I shall attempt. A definition is sometimes useful, so I present the following: A pathological condition of the ethnic mind is present when it is chronically incapable of directing the activities of the group correctly toward self-preservation and development. Like all definitions in natural science, this one is not to be applied literally in all cases. The incapacity may be present and yet not to such a degree as to be positively destructive. All nations have some insane tendencies, as have all individuals; and it is true, as a specialist has said: “The more one knows of insanity, the less does it seem to differ from the normal condition.” These pathological traits of the ethnic mind can be analysed and classified. They will be found to arise 1. From some intellectual deficiency or perversion; or 2. From some persistent disturbance of the emotional life. No one will demand that every member of a group should suffer from such conditions in order that its collective mind should betray morbid consequences. It is enough if a majority, or even a decided minority, providing it exerts the requisite influence on the mass, is in such a pathological state. A degenerate nobility or a dissolute priesthood has often worked the ruin of a state through the contagion of example and its control of lower classes. Before considering in detail the varied forms under which these diseased mental traits present themselves, it will be well to examine the general causes to which they are due. ETIOLOGY.—Each of such pathological conditions of the ethnic mind has a basis in some prevailing physical neurosis, the origin of which can be traced in the ethnic history, and which becomes hereditary in the stock. For of these two principles no student of the subject can doubt, (1) that every pathological mental manifestation corresponds to a neuropathic change, and (2) that whatever may be said about the transmission of acquired characters in physiology, no physician can for a moment doubt that morbid infection may be passed down from generation to generation.