But when they say that an animal or a plant is hot or cold or dry or wet, they no longer mean it in the same way. For no animal, they say, can be absolutely hot like fire, or absolutely wet like water.

Here is the turn the whole book rests on. A living body is never purely hot or purely wet; it is always a blend. So "hot," said of a man or a plant, cannot mean what it means said of fire. Plants are named alongside animals on purpose. The same scheme will later grade every herb and drug, and that is the bridge from this book to Galen’s pharmacology.