"Bharadwaja said, 'How does bodily fire or heat, entering the body, reside there? How also does the wind, obtaining space for itself, cause the body to move and exert itself?'
"Bhrigu said, 'I shall, O regenerate one, speak to thee of the course in which the wind moves, and how, O sinless one, that mighty element causes the bodies of living creatures to move and exert themselves. Heat resides within the head (brain) and protects the body (from perishing). The wind or breath called Prana, residing within the head and the heat that is there, cause all kinds of exertion. That Prana is the living creature, the universal soul, the eternal Being, and the Mind, Intellect, and Consciousness of all living creatures, as also all the objects of the senses. 1 Thus the living creature is, in every respect, caused by Prana to move about and exert. Them in consequence of the other breath called Samana, every one of the senses is made to act as it does. The breath called Apana, having recourse to the heat that is in the urethra and the abdominal intestines, moves, engaged in carrying out urine and faeces. That single breath which operates in these three, is called Udana by those that are conversant with science. That breath which operates, residing in all the joints of men's bodies, is called Vyana. There is heat in the bodies of living creatures which is circulated all over the system by the breath Samana. Residing thus in the body, that breath operates upon the different kinds of watery and other elementary substances and all bad humours. That heat, residing between Apana and Prana, in the region of the navel, operates, with the aid of those two breaths, in digesting all food that is taken by a living creature. There is a duct beginning from the mouth down to the anal canal. Its extremity is called the anus. From this main duct numerous subsidiary ones branch out in the bodies of all living creatures. 2 In consequence of the rush of the several breaths named above (through these ducts), those breaths mingle together. The heat (that dwells in Prana) is called Ushman. It is this heat that causes digestion in all creatures possessed of bodies. The breath called Prana, the bearer of a current of heat, descends (from the head) downwards to the extremity of the anal canal and thence is sent upwards once more. Coming back to its seat in the head, it once more sends down the heat it bears. Below the navel is the region of digested matter. Above it is that for the food which is taken. In the navel are all the forces of life that sustain the body. Urged by the ten kinds of breaths having Prana for their first, the ducts (already mentioned), branching out from the heart, convey the liquid juices that food yields, upwards, downwards, and in transverse directions. 3 The main duct leading from the mouth to the anus is the path by which yogins, vanquishers of fatigue, of perfect equanimity in joy and sorrow, and possessed of great patience, succeed in attaining to
[paragraph continues] Brahma by holding the soul within the brain. 1 Even thus is heat panted in the breaths called Prana and Apana and others, of all embodied creatures. That heat is always burning there like a fire placed in any (visible) vessel.'