Shifting the way you look at things is tough, especially when you can’t see them -- which is why what happened just about 350 years ago in the Netherlands is so remarkable. A man named Antoine van Leeuwenhoek became obsessed with a new device called a microscope. Something that gave him the chance to see things that – to most people – were invisible.

"Naturalists were using them to look at tiny insects," says Laura Snyder - author of a new book on Leeuwenhoek and his contemporary, Vermeer. "There was something remarkable to them in the idea that even these little creatures crawling around in the mud or on their food, had so many details. They were looking at the mouth of flies and lice, and they were drawn again and again to the eyes of these creatures."

Leeuwenhoek lived at the same time as Newton and Galileo, and he embraced the scientific revolution’s push to know everything and ask questions. 

"He had this incredible patience," Snyder points out. "Many of the other people who were using microscopes in this day and age moved on to other things. Initially, they thought, 'wow, this is really cool'... But after a while they would say, 'OK, well I've done that. Now let's go invent something else.'"

Leeuwenhoek stuck with it. He tried different lenses, made meticulous observations, and finally wrote to the Royal Society in London telling them about some of the almost unbelievable things he had seen.

"All he wanted to do was see what no one else had seen before - and he did. He saw sperm; he saw microscopic animals. Everywhere he went, he had a microscope, and he would look at the scrapings from people's feet and gunk from their ears. It's kind of disgusting to read about all of his observations."

Even though Leeuwenhoek had been trained to work with cloth - and did open a draper's shop in Delft - microscopes soon became his obsession. He was, many believe, the very first microbiologist. And the things he saw changed how we view the world.