(Chapter 18) Footnote 94:

Vesalius is referring to the belief that crasis or blending of elements and qualities is a variable not only between individuals but between species. For example, animals in Aristotle may be softer or harder ( PA 644b14), dryer or wetter ( GA 733a4ff.). So too in Galen De temperamentis 1.537.5, “the dog is dryer, man wetter.” Cf. the 1555 parenthetical addition to the beginning of Chapter 20: “man is of a quite damp constitution if compared to other animals.”