كتاب الحيوان (Book of Animals)

And from that wrinkling, the moistures of his body appear, such as phlegm from the mouth, mucus flowing from the nose, and rheum and tears from the eyes. They thought that this was due to the abundance of parts of moisture within him, and they wanted to divide childhood, youth, maturity, and old age into four categories, just as they manage to do in other matters. When those moistures appear, it is only because dryness has rejected them and squeezed them out of the strong body. If what they mentioned were true, then the tears of a child would be more abundant, his mucus more flowing, and his moistures more apparent. Yet in vegetables, aromatic herbs, branches, and trees, they are more moist in their youth, and as years and days pass, they become drier. The rajiz said:

Listen, I will tell you the signs of aging * Sleep in the late afternoon and coughing at dawn

And speed of back-bending i.e., stooping and weakness in sight * And leaving the beautiful woman while still in purity

And caution that increases into anxiety * And people wear out just as trees wear out

He used to express wonder at the talk of hayula prime matter. He would say: We have already known the measure of the gravity of moisture, and we will grant you that cold has a weight. Is it not the case that you do not doubt that heat is light and has no weight, and that when it enters a body that has weight, it becomes lighter? You cannot prove for dryness a weight equal to what you prove for moisture. Moreover, many of you claim that cold, which freezes water, is actually the driest thing. Some of them claimed that cold often accompanies dryness, and that dryness alone, if it reached water, would not freeze it; and cold alone, if it reached water, would not freeze it; rather, water only freezes because they both combine upon it. In this statement, if two things combined have united to cause freezing, why do you deny that two things might combine to cause melting? If it is permissible for the qabas brand/fire to freeze, it is permissible for moisture to melt.

Abu Ishaq said: If some of these substances are ascending and some are descending, and we find gold heavier than an equal amount of these descending things, how can it be heavier than them when it contains ascending things? If they claim that lightness only comes from rarefaction, porosity, and an abundance of air parts in the body, then it should be that air is lighter than fire. Yet fire is in the stone just as air is in it, and fire is more powerful at lifting the stone than the air within it. He used to say: Evidence that fire is latent in firewood is that firewood burns with a specific amount of burning, and the wood prevents all the fire within it from coming out. So it creates a barrier; whenever you wish to extract the remainder of the fire, you extract it. You see that the fire then has a flame without the fuel. Whenever you have extracted that remaining fire and then kindled it for a thousand years, it will not ignite. The interpretation of "it will not ignite" is merely the appearance of the fire that was in it. If there is nothing in it, how could it ignite?