Science had recently emerged as a profession and yet it was an amateur who became a scientific celebrity throughout Europe. It was Anton van Leeuwenhoek, a Dutch merchant without university studies, who discovered microscopic life at the end of the 17th century. Leeuwenhoek was the first person to see unicellular animals, bacteria, red blood cells and sperm, and all with his homemade microscopes and an insatiable curiosity as his only instruments.
In the midst of the scientific revolution, the microscope was the fashionable technological toy among high society, who marvelled at the magnified objects that Robert Hooke drew in his book Micrographia. When Leeuwenhoek (October 24, 1632 – August 26, 1723) looked through these new devices at the fabrics he sold in his draper’s shop, he discovered his true hobby and dedicated himself to making and polishing lenses. He so perfected the art that he managed to make ones that could magnify 300 times. He built microscopes with a single lens, embedded in a brass plate to which the eye was drawn like a peephole in a door. That would have ruined anyone’s eyes, but they allowed Leeuwenhoek to see much further than Hooke, who worked with microscopes of several lenses, similar to those used today but still very primitive.
Leeuwenhoek spent the nights peering into that peephole that opened a window to an unseen world. He looked under the microscope at anything that caught his attention. He picked up a piece of rotten bread and looked at the mould fungi; he noticed the tartar of an old man who had never washed his teeth, and he saw bacteria; he thought of his blood and then discovered red blood cells; one day it occurred to him to examine his own semen… and he was the first person to see a spermatozoon wagging its tail, something that was totally surprising at a time when it was believed that semen contained miniature babies or that fleas were born from grains of sand. Leeuwenhoek took the first step to overthrow the theory of spontaneous generation, but it would take more than a hundred years until microscopes were produced superior to his own —so that other scientists could continue his work.
A curious man in the club of the great minds
He mailed his results to the most eminent scientists of the time, gathered at the Royal Society of London. Although Leeuwenhoek knew neither Latin (then the language of the scientists) nor English, that correspondence in vulgar Dutch would last for 50 years, until his death. Early on, he made the discovery for which he was admitted to the select club of Newton, Hooke and company. One day in 1676, intrigued by the spiciness of pepper, he wanted to discover the secret of that spice the navigators brought from the East. He prepared it in infusion with rainwater, let it rest for a few days and, to his surprise, saw “thousands of living creatures” moving about frantically. He calculated that millions lived in a single drop, as many as there were people in Holland.
Leeuwenhoek called these creatures “animalcules,” which today we know as protozoa and which also fascinated the King of England. Word spread through the European courts and the Tsar of Russia himself, Peter the Great, moved to see in action the great Dutch researcher in his city, Delft. There was also born the painter Jan Vermeer (the author of Girl with a Pearl Earing) and it is believed that Leeuwenhoek posed for him as a model for his painting The Geographer. What is certain is that both, besides being countrymen and born the same year, had a great interest in optics and lighting: mastering these two techniques was fundamental in the work of the painter and also in that of the scientist.