Rudolf Virchow was the first to suggest that new cells are formed from the division of the preexisting cells - omnis-cellula-e-cellula (every cell is derived from a previous cell). Robert Hooke was the first to coin the term "cell" for small structures in a piece of cork under a microscope. His observations were published in a book named micrographia. Leeuwenhoek was the first person to observe and describe microscopic organisms and living cell. He observed nucleus in RBC of salmon fish and used simple lens and observed nuclei and unicellular organisms including bacteria. In 1676, he described the bacteria and gave the term animalcules. His observations laid the foundations for the science of bacteriology and microbiology. Robert Brown (1831) described and named nucleus.