Today we unlock a laboratory door in Paris and a faint sweetness greets us—a broth of sugar and yeast, a tang of wine gone wrong, the metallic breath of steam. On one bench a row of glass vessels stands like a choir, each with a long, swan‑curved neck. On another, flasks cradle broths that were boiled and then left to cool under arches of glass that invite air but trap dust. A small flame licks at a burner; a hand adjusts it until the liquid shivers and then calms. The hand belongs to a man with a large brow, a steady gaze, and a patience that can be stern. He lifts a flask, tips it, watches nothing grow, and smiles because nothing is sometimes the most eloquent answer the world can give. The man is Louis Pasteur. Over four decades he will show that asymmetry in crystals reflects an asymmetry in life; that fermentation is the work of living agent ...