In his works on natural sciences, primarily in the Physics, Aristotle focuses on different forms of metabolē and distinguishes movement in general from substantial change. The On generation and corruption deals with the latter. When reading this treatise, one should pay particular attention to the concept of mixture. Apart from being the subject of a specific chapter (I 10), the problem of mixture permeates the whole work. But what exactly is mixture? Is it a simple combination of small parts? Can a compound of water and wine be called mixture? If so, is this mixture and nothing more? In the course of the discussion, it is argued that the Aristotelian idea of mixis does not correspond to the concept that is usually associated with it. Rather, it is shown that mixis is fundamental for comprehending the physical world and constitutes not only the term per quem the first elements of all material bodies originate, but also plays a fundamental role in all natural sciences, particularly, in biology.