The mystical practice from Tibet of generating bodily heat, so that a hermit may spend winter naked in a cave amid snow and freezing temperatures at an altitude between 11,000 and 18,000 feet. Adepts have supposedly distinguished various types of tumo: exoteric arises spontaneously in the course of mystical raptures; esoteric keeps a hermit comfortable on a snowy hill; and mystic produces experiences of paradisiacal bliss.
According to Alexandra David-Neel, tumo "is also the subtle fire with which warms the generative fluid and drives the energy in it, till it runs all over the body along the subtle channels." This has some similarity to the Hindu teachings of the nature of kundalini energy—possibly aroused in subtle physical channels, related to the energy of sexual activity, and productive of either heat or cold in the body.
David-Neel, Alexandra. Initiations and Initiates in Tibet. London, 1932. Reprint, New Hyde Park, N.Y.: University Books, 1959.