During an eighteen years' acquaintance with Paraguay and its inhabitants, I discovered a disease amongst the Abipones Nakaiketergehes, entirely unknown elsewhere. This disease affects the mind more than the body, though I should think it occasioned by the bad temperature of the former. They sometimes begin to rave and storm like madmen. The credulous and superstitious crowd think them reduced to this state by the magic arts of jugglers, and call them _Loapařaika_. These persons, agitated, as I think, by the intemperature of black bile, and filled with gloomy ideas, betray their madness chiefly at sun-set. The distracted persons suddenly leap out of their tents, run into the country on foot, and direct their course straight to the burying-place of their family. In speed they equal ostriches, and those who pursue them on the swiftest horses can hardly overtake and bring them home. Seized with fury in the night, they burn with the desire of committing slaughter somewhere; and for this purpose snatch up any arms they can lay hold of. Hence, as soon as a report is spread through a town of any one's being seized with this kind of madness, every body takes up a spear. The hordesmen, as they can neither calm the furious man, nor keep him at home, suffer him to go out into the street, armed with a stick, and accompanied with as many people as possible. A crowd of boys assembling to behold the spectacle, they make a circuit about all the streets. The insane person strikes the roof and mats of every tent again and again with the stick, none of the inmates daring to utter a word. If through the negligence of his guards, or his own cunning, he gets possession of arms, Heavens! what a universal terror is excited! a terror not confined to women and unwarlike boys, but felt by men who account themselves heroes; for they say it is wrong and irrational to use arms against those who are not in possession of their senses. The women, therefore, with their children used to crowd to the court-yard of our house which was fortified with stakes against the assaults of savages, and through fear of the insane person, pass hours, nay whole nights there.