Cell the Unit of Life

In 1837, Matthias Jakob Schleiden viewed and stated that new plant cells are formed from

the nuclei of old plant cells. While dining that year with Schwann, the conversation turned on the nuclei

of plant and animal cells. Schwann remembered seeing similar structures (nuclei) in the cells of the

notochord and instantly realized the importance of connecting the two phenomena (presence of nuclei

and new cell formation). The resemblance was confirmed without delay by both observers, and the

results soon appeared in Schwann's famous microscopic investigations on the accordance in the

structure and growth of plants and animals, in which he declared that "All living things are

composed of cells and cell products". This became cell theory.

 In 1855, pathologist Rudolf Virchow posed the maxim Omnis cellula e cellula that

every cell arises from pre-existing cells.