Devin Katayama

And he dedicated his early career to researching that theory.

And he dedicated his early career to researching that theory.

This is Luba Vukonsky. She's a science writer at the Weizmann Institute of Science in Israel.

This is Luba Vukonsky. She's a science writer at the Weizmann Institute of Science in Israel.

This is Luba Vukonsky. She's a science writer at the Weizmann Institute of Science in Israel.

This trip to Sicily would change everything for Metchnikoff. He and his wife were staying by the seaside in a cottage overlooking the bright blue Messina Strait. The Strait was home to all sorts of marine creatures. And while his wife went out to explore Sicily, Metchnikoff would spend long days holed up in the cottage, staring at jars filled with seawater and tiny organisms.

This trip to Sicily would change everything for Metchnikoff. He and his wife were staying by the seaside in a cottage overlooking the bright blue Messina Strait. The Strait was home to all sorts of marine creatures. And while his wife went out to explore Sicily, Metchnikoff would spend long days holed up in the cottage, staring at jars filled with seawater and tiny organisms.

This trip to Sicily would change everything for Metchnikoff. He and his wife were staying by the seaside in a cottage overlooking the bright blue Messina Strait. The Strait was home to all sorts of marine creatures. And while his wife went out to explore Sicily, Metchnikoff would spend long days holed up in the cottage, staring at jars filled with seawater and tiny organisms.

One day, he had his eye pressed up against his microscope, peering inside these minuscule starfish larvae.

One day, he had his eye pressed up against his microscope, peering inside these minuscule starfish larvae.

One day, he had his eye pressed up against his microscope, peering inside these minuscule starfish larvae.

These were cells that wandered inside the larvae, gobbling up food and other particles. Meshnikov had seen these cells in action before, but that day, watching them go about their business, it struck him. Music

These were cells that wandered inside the larvae, gobbling up food and other particles. Meshnikov had seen these cells in action before, but that day, watching them go about their business, it struck him. Music

These were cells that wandered inside the larvae, gobbling up food and other particles. Meshnikov had seen these cells in action before, but that day, watching them go about their business, it struck him. Music

If the cells attacked the thorn as a foreign invader, his theory would be correct.

If the cells attacked the thorn as a foreign invader, his theory would be correct.

If the cells attacked the thorn as a foreign invader, his theory would be correct.

Watching this unfold through his microscope, his mind was blown.

Watching this unfold through his microscope, his mind was blown.

Watching this unfold through his microscope, his mind was blown.