The second class of toxic agents affecting the community at large includes the various forms of disease-germs. No one can doubt the debilitating influence of malaria on the mental faculties of the population exposed to its poisonous action. Vast tracts of the earth’s surface are by it rendered incapable of sustaining the highest types of humanity. Their energy is sapped, their vitality lowered, by the insidious miasm. No race or nationality is immune. Though the white race is most liable to its attacks, the African blacks are so far from being exempt that in the more intense malarial districts of their continent nearly one-third of the natives suffer from the disease. Marsh poison is usually confined to the lowlands. But the mountain valleys also generate a noxious agent, most unfriendly to mental growth. It displays itself in a threefold form, embracing goitre, cretinism, and deaf-mutism, the three closely related and bringing with them a positive debility of psychical powers. The mountains have not only been the refuge of the feeble, escaping from the plains, but they have worked to render these outcasts feebler still by reducing them in stature and viability. Goitre is not confined to Alpine regions, though more prevalent there. It is distinctly hereditary, and the offspring of goitrous parents are predisposed to cretinism and allied forms of imbecility. The southern and western slopes of the Alps, the Pyrenees, the Himalayas, and the Cordilleras are especially the homes of this class of diseases. Another series of toxic agents which calls for consideration in this connection are the so-called “constitutional diseases.” These are contagious and transmissible, the poison of the blood being handed down from generation to generation. The most noteworthy of these is syphilis. Its extreme prevalence among lower classes of the community and in some of the darker races is a present and potent cause of their mental inferiority. It is well known to specialists that children born of syphilitic parents are deficient in mental energy and physical stamina. They are liable to scrofulous symptoms and tubercular degenerations, and are deficient in ambition and love of labour. Less widely distributed, but yet affecting whole communities, are ergotism and pellagra, due to the consumption of diseased grain, and leprosy which is undoubtedly hereditary and vitiates the blood of whole families. Certain stocks are especially liable to it, notably the African blacks and next to them the Semites, both Jews and Arabs. 4. _Mental Shock._—History presents many instructive examples of the destructive power of mental shock on the ethnic mind. It is brought about by some great, sudden, unexpected catastrophe, which breaks asunder the associations or institutions in which the community has lived its mental life. Such a disruption may arise from an intensely malignant epidemic, from war, or from a natural catastrophe.