Virchow is credited with many important discoveries. His most widely known scientific contribution is his cell theory, which built on the work of Theodor Schwann. He was one of the first to accept the work of Robert Remak, who showed the origins of cells was the division of pre-existing cells. He did not initially accept the evidence for cell division, believing it only occurs in certain types of cells. When it dawned on him that Remak might be right, in 1855, he published Remak's work as his own, which caused a falling out between the two. This work, Virchow encapsulated in the epigram Omnis cellula e cellula, id est, All cells (come) from cells, which he published in 1855. (The epigram was actually coined by François-Vincent Raspail, but popularized by Virchow.) It is a rejection of the concept of spontaneous generation, which held that organisms could arise from nonliving matter. For example, maggots were believed to spontaneously appear in decaying meat; Francesco Redi carried out experiments which disproved this notion and coined the maxim Omne vivum ex ovo ("Every living thing comes from a living thing" — literally "from an egg"); Virchow (and his predecessors) extended this to state that the only source for a living cell was another living cell.