When the flask was full of millions of cells, Jafarov drew them up into a tiny needle, about as thick as two strands of human hair, and injected them into the knee joints of mice. He’d been working on the procedure for months and perfected it slowly: he had to enter the joint with the needle causing no injury, like a perfect diver slicing into water without causing a splash. A few weeks later, he showed me the knee. The cells had formed a thin layer of cartilage at the joint. We had made a chimeric knee, with a jellyfish protein in its cells, glowing silently within the mouse. It was far from
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