 Some figures concerned with the natural sciences, especially medicine, are thought to have regarded organic bodies as composed of particles. Galen (2nd c. CE), in On the Natural Faculties, divides medical theorists into two groups, following the division of natural philosophers. On the one side are continuum theorists, who hold that all matter is infinitely divisible but that all the matter in things subject to generation and corruption is susceptible to qualitative alteration. On the other are those who suppose that matter is composed of tiny, unchangeable particles separated by void spaces, and explain qualitative change as produced only in compound bodies, by rearrangement of the particles alone. In Galen’s view, qualitative alteration is needed to produce the powers whereby beneficent Nature directs change: Galen credits the first group with asserting the priority of Nature and its beneficent order, and the latter with denying this.