Excerpt from Immunity

In Immunity, Vikhanski tells the story of Metchnikoff's greatest discovery. He made it around Christmas of 1882, while peering through a microscope at starfish larvae in which he had inserted tiny thorns:

"Suddenly, he had a startling idea. “It struck me that similar cells must be serving the organism in its resistance against harmful agents,” he wrote in his Messina essay. In other words, he imagined he was watching no mere act of feeding but a rudimentary form of self-defense.

"Sensing that my hunch concealed something particularly interesting, I became so excited that I began striding up and down the room and even went to the seashore to collect my thoughts,” Metchnikoff wrote. “If my suggestion is true, I told myself, then a splinter in the body of the starfish larva must become quickly surrounded by encroaching mobile cells, as happens when a human being has a splinter in his finger.” . . .

“No sooner said than done. In the tiny garden of our house, where several days earlier a tangerine tree had been decorated as a ‘Christmas tree’ for the children, I picked several rose thorns and immediately inserted them under the skin of magnificent starfish larvae, clear like water.” . . .

“Naturally, I was agitated throughout the night, awaiting results,” Metchnikoff wrote. “The following day, in the early morning, I happily observed that the experiment had been a success.” A thrilling sight greeted his eyes through the microscope lens. Just as he had predicted, masses of mobile cells inside the larvae had gathered around the intruding thorns.

There was no doubt in his mind that the cells had rushed to the larva’s defense. In the same manner, they might rush to swallow another intruder, a disease-causing microbe.

The next step was almost too easy; he had no qualms about extrapolating from starfish to humans. After all, for more than twenty of his thirty-seven years, Metchnikoff had dealt with evolution of species in one way or another. He had long ago reached the conclusion that Darwin had been right. From headless mollusks to brainy mammals, all life had evolved from a common ancestor.

His daring new hypothesis was this: in all living beings, humans included, wandering cells eat up microbes, giving the organism immunity against life-threatening disease. It is these cells that are responsible for an organism’s healing power. Metchnikoff had managed to observe and define a curative force, which physicians had struggled to uncover since antiquity.

The first modern theory of immunity was born."