“We need a bioreactor,” Ursula said to Vlad. They were working on converting one of the ectogene tanks into one, packing it with spongy animal collagen and inoculating it with cells from Nirgal’s marrow, hoping to generate an array of lymphocytes, macrophages, and granulocytes. But they didn’t have the circulatory system working right, or perhaps it was the matrix, they weren’t sure. Nirgal remained their living bioreactor.

Sax was teaching them soil chemistry during the mornings when he was teacher, and he even took them out of the schoolroom occasionally to work in the soil labs, introducing biomass to the sand and then wheelbarrowing it to the greenhouses or the beach. It was fun work, but it tended to pass through Nirgal as if he were asleep. He would catch sight of Simon outside, stubbornly taking a walk, and he would forget whatever they were doing.

Despite the treatments Simon’s steps were slow and stiff. He walked bowlegged, in fact, his legs swinging forward with very little bend to them. Once Nirgal caught up to him and stood beside him on the last dune before the beach. Sandpipers were charging up and down the wet strand, chased by white tapestries of foaming water. Simon pointed at the herd of black sheep, cropping grass between dunes. His arm rose like a bamboo crossbar. The sheep’s frosted breath poured onto the grass.

Simon said something that Nirgal didn’t catch; his lips were stiff now, and some words he was finding hard to pronounce. Perhaps it was this that was making him quieter than ever. Now he tried again, and then again, but no matter how hard he tried, Nirgal couldn’t guess what he was saying. Finally Simon gave up trying and shrugged, and they were left looking at each other, mute and helpless.

• • •

When Nirgal played with the other kids, they both took him in and kept their distance, so that he moved in a kind of circle. Sax admonished him mildly for his absentmindedness in class. “Concentrate on the moment,” he would say, forcing Nirgal to recite the loops of the nitrogen cycle, or to shove his hands deep into the wet black soil they were working on, instructing him to knead it, to break up the long strings of diatom blooms, and the fungi and lichen and algae and all the invisible microbacteria they had grown, to distribute them through the rusty clods of grit. “Get it distributed as regularly as possible. Pay attention, that’s it. Nothing but this. Thisness is a very important quality. Look at the structures on the microscope screen. That clear one like a rice grain is a chemolithotroph, Thiobacillus denitrificans. And there’s a chunk of sulphides. Now what will result when the former eats the latter?”

“It oxidizes the sulphur.”

“And?”

“And denitrifies.”

“Which is?”

“Nitrates into nitrogen. From the ground into the air.”

“Very good. A very useful microbe, that.”