كتاب الحيوان (Book of Animals)

...with certainty that the interior of a human is never devoid of blood. He said that whoever claims any animal lives without blood, or something resembling blood, is obligated to deny natural properties (taba'i) and reject the truths in their statements regarding the heating of fire, the cooling of snow, perception, sense, nourishment, and smell. That is another chapter in ignorance. Whoever claims that Divine Unity is not valid unless there is blood in the human, or unless fire does not necessarily cause burning, or that correct vision does not necessitate perception, has shown that he is in the utmost state of deficiency and stupidity, or in the utmost state of denial and obstinacy.

(Abu Ishaq said): We find that when firewood decomposes, its parts separate, and the foundations upon which it was built and the aggregates from which it was composed—which are four: fire, smoke, water, and ash—disperse. We find that fire has heat and radiance, water has sound, smoke has taste, color, and smell, and ash has taste, color, and dryness. We find that water flows from each of its companions, then we find it has species composed of simples. We find that firewood was composed of what we described; we claim it was composed of doubles and was not composed of simples.

(Abu Ishaq said): If the speaker does not know how to reason by analogy and give it its due, he might see that when wood rubs against wood, the same logic should apply to the smoke and the flowing water. If he uses analogy, he must say the same for ash as he said for smoke and water; otherwise, he is either ignorant or arbitrary. If he claims that he denied that fire was in the wood because he found the fire to be greater than the wood, and it is not permissible for the large to be within the small—and likewise with the smoke—then let him claim that the smoke was not in the firewood, or in the oil, or in the naphtha. If he claims they are equal and that he only said that because the body of the firewood could not contain the body of fire and smoke he witnessed, then one who denies their presence on this basis should not claim that the sparks of the flint and stone were not latent within the stone and the flint. He should not deny the latency of blood in humans, the latency of oil in sesame, or the latency of oil in olives. He should not deny of such things except what the body cannot contain in reality. How can they be so when they have applied this denial to everything absent from their senses—among the bodies hidden by bodies—until they return to such things as the acidity of vinegar, the sweetness of honey, the pleasantness of water, and the bitterness of aloe? He said, if they measure their speech and claim...