Discovery

The idea that living things are built of small, discrete units took shape gradually over two millennia. Aristotle (384-322 BC) was the first to sense that plants and animals are made of organised structural units, though he could not describe what those units actually were. It took until the 1660s for Robert Hooke, examining a thin slice of cork under his own microscope, to see rows of small empty boxes that reminded him of a honeycomb - he called them 'cells', from the Latin cella meaning a small chamber or compartment, and published the observation in his 1665 book Micrographia. What Hooke had actually seen were the dead, empty cell walls of cork tissue, not living cells, but the name stuck. Soon after, Antonie van Leeuwenhoek, grinding his own remarkably powerful lenses, became the first person to observe living single-celled organisms swimming in pond water, which he called 'animalcules'. In 1831, Robert Brown identified a dense, roughly spherical body inside plant cells and named it the nucleus. The first real theoretical leap came from the French scientist H. J. Dutrochet in 1824, who was the first to propose the outline of a cell theory, an idea that Matthias Schleiden (a German botanist) and Theodor Schwann (a German zoologist) formalised in 1833 by stating that all plants and animals are built o …