Historical background of the cell concept

Advances in the knowledge of the cell and its discovery have been related to technological advances in vision instruments, such as the microscope.

In 1665, Robert Hooke observed a thin section of cork with a simple microscope and noticed that it was formed by small cavities similar to cells in a honeycomb, which he called cellulae, from which the word cell arose. It was about the first observation of dead cells. Of course, what Hooke observed were not living cells but the cavities that they leave when they die.

The first to study living tissue under a microscope was Marcello Malpighi, who a few years later observed living cells.

In the middle of the seventeenth century, the Dutch Anton Van Leeuwenhoek (1632-1723) manufactured microscopes of up to 275 magnifications, which allowed him to describe red blood cells, bacteria, protozoa, and even discovered that in semen there were some "animals" that later they were called sperm. Then came compound microscopes, which had two sets of lenses.

The cytology began when they were first compound microscopes that combine two sets of convex lenses:

• An objective lens that is placed close to the specimen, and creates a magnified inverted image.
• An ocular lens, located at such a distance that its effect is to increase the size of the inverse image, multiplying the effect of the objective lens.

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Other important discoveries about the cell were the following:

• 1830s: Matthias Schleiden says that all plants are made up of cells, and Theodor Schwann said the same about animals. Ferdinand Cohn, a few years later, discovered that microorganisms were also made up of cells.
• 1831:  Robert Brown that plant cells had a nucleus.
• 1839: Purkinje observed cell cytoplasm, the fluid that filled cells, which he called protoplasm.
• 1857: Kölliker identified the mitochondria.
• 1858: Rudolf Virchow postulated that all cells come from other cells.
• 1860: Spallanzani and Pasteur demonstrated with experiments that every cell comes from another cell, thus denying reproduction by spontaneous generation.
• In 1861: Brucke defined the cell as the “anatomical and functional unit of a living being”.
• 1905: Harrison managed to cultivate cells of a multicellular being "in vitro".
• 1931: Ernst Ruska  built the first transmission electron microscope. Four years later, he obtained an optical resolution twice that of the light microscope.
• 1981: Lynn Margulis publishes his hypothesis on endosymbiosis, which explains the origin of the eukaryotic cell.