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.[559] 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 Brahma by holding the soul within the brain.[560] 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.’

SECTION CLXXXVI

“Bharadwaja said, ’If it is the wind that keeps us alive, if it is the wind that causes us to move and exert, if it is the wind that causes us to breathe and to speak, then it seems that life is worth little.  If the animal heat (that digests all food) be of the nature of fire, and if it is that fire which assists at digestion by dissolving the food we take, then life is worth little.  When an animal dies, that which is called its life is never seen leaving it.  Only the breath leaves it, and the internal heat becomes extinguished.  If life were nothing else, than wind, or if life depended only on the wind, then it could have been seen like the external sea of air, and when passing out it would have mingled with that air.  If life dependest upon air, and if it ended with the escape of that air from the body, it would then mingle with another portion of air (that exists externally) like a portion of water escaping into the great ocean and thereby only changing the place of its residence.  If a quantity of water be thrown into a well, or if the flame of a lamp be thrown into a blazing fire, either of them, entering a homogeneous element, loses its independent or separate existence.  If life were air, it also, when the animal died, would mingle with the great ocean of air outside.  How can we say that there is life in this animal body which is made up of the five (primal) elements?  If one of those elements disappear, the union of the other four becomes dissolved.  The element of water drieth up if food be not taken.  The element of air disappears if the breath be restrained.  The element of space disappears if the excretions cease.  So also the element of fire becomes extinguished if food does not go in.  The element of earth breaks in pieces