The source of our bodily desires is one: the breath. When the breath leaves the body all desires leave it also; and as the breath changes its elements, and the elements - earth, water, fire, air, and ether - predominate in the breath by turns, this being caused by the different grades of activity in the breath, so the desires change. Therefore in a certain climate one feels hungry, and in certain weather one feels thirsty, because the influence of weather on the breath kindles in the breath more of a certain element.