He wasn't hunting for an organelle. He was trying to work out what insulin does in the liver, which meant measuring enzymes, which meant breaking liver cells open — and he'd taken to doing it gently, in a centrifuge, rather than whizzing everything to a pulp. One enzyme kept misbehaving. Fresh preparations gave a low reading. The same material left in the fridge for a few days gave a much higher one. Most of us would have blamed the assay and moved on. He asked why.

The answer is that the enzyme was in a bag. The cell keeps its digestive chemistry — the stuff that dismantles worn-out proteins and whatever's been swallowed from outside — sealed inside a membrane, the way a dishwasher tablet sits inert in its film until it's in the machine. Fresh, the bags are intact and the enzyme can't reach anything to measure. Sitting in a cold tube for days, the membranes give way and it spills out. Inside the bag it's acidic, around pH 5; the rest of the cell sits nearer 7, so even a leak does little. Which means the cell carries a strong cleaning fluid around all day and doesn't digest itself.

He called it the lysosome, and later found the peroxisome much the same way. There's a cutaway diagram attached, labelled in Azerbaijani — lizosom and peroksisom sitting among the mitochondria. He named autophagy, endocytosis and exocytosis too, apparently all in one sitting. The Nobel came in 1974, shared with Claude and Palade. He was born in 1917. I once spent most of a winter chasing a discrepancy that turned out to be a scratched cuvette, so I have some feeling for what it takes to trust an odd number instead of tidying it away.