Robert Hooke and Microscopy
1665
Robert Hooke was a 17th century scientist working mainly in physics but his work changed the way scientists approached medicine and other biological sciences. In the Micrographia (Small Drawings), he shocked the world with his drawings of flea and other life forms magnified many times over. He coined the term "cell" while studying cork with a microscope; the structure reminded him of monks' cells. He was not describing the cell as the term is used today, but he established both a terminology and an awareness that life forms are made up of parts not visible to the naked eye.

Illustration from:
Micrographia: or, The Copper-Plates of Dr. Hooke's Wonderful Discoveries by the Microscope, Reprinted and Fully Explained. Printed for and sold by John Bowles, London, 1745. The Linda Hall Library also owns the edition published in 1665.