 Schwann’s “theory of the cell”, however, was much richer than his soon rejected view of cell formation. He argued that cells were the basic units in which the processes of life (he coined the term metabolism) occurred. He viewed metabolic processes as catalyzed by the specific materials that were deposited in cells as they formed. Schwann (1836) had himself recently discovered pepsin, a catalyst that breaks down egg albumin. (Pepsin operates, however, not within cells but after being secreted into digestive fluid.) When a year later he argued that fermentation could not occur without the involvement of a whole living yeast cell (Schwann 1837), some critics took Schwann to be claiming that living systems exhibited mysterious vital properties. But for Schwann this was consistent with his mechanist approach—the metabolic processes only occurred when the responsible catalysts were brought together in cells.