It has been my good fortune to be able to secure data of this sort, pertaining to certain curious nervous attacks which occur among the primitive races of the Fuegian Archipelago. These facts were supplied me, following along the lines of a questionnaire, by the well known explorer Charles Wellington Furlong, F. R. G. S., who in 1907-1908, was in charge of the first scientific expedition to cross through the heart of Tierra del Fuego. Mr. Furlong's keen powers of observation, have made the data unusually complete. While he had no theory to offer in explanation of the attacks as seen among these primitive tribes, yet it is interesting to note, that certain of the facts corroborate the well-known ideas of sexual repression as elaborated by Freud. The mental organization of these people likewise, seems to substantiate certain psychoanalytic conceptions. For a clear comprehension of these attack, certain preliminary anthropological and geographical data are necessary. The following data relates to the running amuck or outburst, among the Yahgan and Ona tribes of the Fuegian Archipelago. This data was obtained in 1907 and 1908 during expeditions through the regions of the Fuegian Archipelago. The Yahgans, some forty years ago, numbered perhaps 2,500 but in 1908 had been reduced through contact with civilization and principally through an epidemic of measles to 173. These peoples are canoe Indians and inhabit today the island coasts from Beale Island to the Wollastons inclusive, in the neighborhood of Cape Horn; from about 54 degrees 50' S. Lat. to about 55 degrees 56' S. Lat., making them the southern-most inhabitants of the world. The Ona Indians, a taller and finer race physically, who are foot Indians, occupy the mountain and forest regions of southern Tierra del Fuego from approximately 53 degrees 50' S. Lat. to 55 degrees 3' S. Lat. The Onas formerly occupied the entire northern half of Tierra del Fuego and possibly numbered some 3,000, but through contact and warfare with the whites, who drove them south off the open lands of the north, they have been reduced to about 300. These peoples are of a light cinnamon colored skin, black haired, and of a decided Amerindian type. The Onas are above average stature, the Yahgans below it.