1. All living organisms are composed of one or more cells
2. The cell is the most basic unit of life
Schleiden's theory of free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker. In 1855, Rudolf Virchow added the third tenet to cell theory. In Latin, this tenet states Omnis cellula e cellula. This translated to:
3. All cells arise only from pre-existing cells