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Period: 400 BCE to
SPONTATNEOUS GENERATION
Prior to the 17th Century, the theory of 'Spontaneous Generation' was developed by biologists. It was the idea that life could emerge from things not alive. E.g. maggots developing from rotting meat. -
Hans and Zacharias Janssen
In the early 1600, the first compound microscope was constructed by Hans and Zacharias Janssen- two spectacle makers using two lenses inside a tube. -
Robert Hooke (1635–1703)
Robert Hooke further developed the compound microscope, including the use of the iris diaphragm. Under the microscope, he observed thin slices of cork and first described cells. He described it as ‘... all perforated and porous, much like a honeycomb... the pores or cells... consisted of a great many little boxes...’ -
Anton van Leeuwenhoek (1632–1723)
Making his own compound telescope, Leeuwenhoek observed a drop of stagnant rainwater and described unicellular organisms, he called 'amimalcules'. He also soaked pepper in water, when he examined a drop of this water under his microscope he found more more unicellular organisms, instead of the little needles he expected that made pepper ‘hot’. -
Robert Brown (1773–1858)
Brown discovered and described the nucleus under a microscope. He observed that the cells of orchids contained a structure inside the cells. -
Matthias Schleiden (1804–1881) and Theodor Schwann (1810–1882)
Schlieden was a botanists that discovered that all plant tissue he looked under a microscope were composed of cells. Schwann was a physiologist who discovered after observing animals for some time, that all animal cells were made of cells. After reaching out to each other, Schleiden and Schwann formulated the cell theory that all living matter is composed of small units called cells. -
Rudolf Virchow (1821–1902)
Virchow formulated the third point of the cell theory by stating ‘where a cell exists there must have been a pre-existing cell, just as the animal arises only from an animal and the plant only from a plant.’ i.e. all cells come from pre-existing cells. He believed all cells divide and that is how new cells are made. -
Louis Pasteur (1822-1895)
Louise Pasteur disproved the theory of spontaneous generation. His experiment where meat broth was put in a flask with an S-shaped neck and one without. Over time, dust particles from the air fell into the one without the S-shape and became cloudy- a sign of microbial life, whereas the broth in the unbroken flasks remained clear. The idea was that the bend in the neck prevented falling particles from reaching the broth, thus showing that that microorganisms arose only from other microorganisms. -
Carl Zeiss and Ernst Abbe
Carl Zeiss and Ernst Abbe produced the first oil immersion objectives which meant images could be magnified over 1000×. -
Walther Flemming (1843–1905)
Flemming used biological stains to view cells dividing and verified the ideas of Virchow. By staining cells, it adds contrast to the microscopic image, making it easier to see.