The Other Half

The milk had to be warm, but not hot. Grandma Liv pressed the back of her wrist to the pot the way she pressed it to Soren's forehead when he said he felt sick, and she nodded.

"Now the seed," she said.

The seed was one spoonful of old yogurt, cloudy and sour, scooped from the bottom of yesterday's jar. She stirred it into the warm milk and tied a cloth over the top.

"That's it?" Soren asked. "One spoon turns a whole jar?"

"By morning," she said. "They get busy in the dark."

He put his hand around the jar. It was just barely warm. Something about that warmth bothered him, the way a sound in another room bothers you before you know what it is. He wrote a line in his notebook and set the jar by the radiator.

That night he could not sleep, so he read the book Grandma kept on the windowsill, a thick old library book with a torn jacket about the body. He liked the chapter on cells. Thirty-seven trillion of them, the book said, building him out of almost nothing, each one quiet and busy.

Then the next page.

He read it once and sat up.

He read it again with his finger under the words, the way you check a number you do not trust.

Inside a human body, the book said, there live about thirty-eight trillion bacteria. Most of them in the gut. Not invaders. Residents. And the number was close enough to the number of human cells that you could say, without lying, that a person was about half themselves and half something else.

Half.

Soren put the book down and listened to himself. His stomach made a long, slow gurgle in the dark, and for the first time in his life the sound did not feel like his.

It felt like someone else moving furniture downstairs.

He went very still and tried to feel the border, the line where Soren ended and the others began. He could not find it. His own warmth, the heat under his skin that the doctor measured, the heat Grandma checked with her wrist. Some of that was being made by them. Trillions of small lives, busy in the dark, keeping him warm the way the radiator kept the jar warm.

He got up and went down to the kitchen in his socks.

The jar was waiting by the radiator. He untied the cloth. The milk was not milk anymore. Overnight it had set thick and pale and sour, the whole jar changed by one spoonful of living things that had spent the night eating and dividing and turning one thing into another.

Nobody had stirred it. Nobody had watched. It had happened on its own, in the dark, the way the book said his stomach did, the way it had been doing inside him every night of his whole life without asking him.

"You couldn't sleep either," Grandma said from the doorway. She wasn't surprised. She was never surprised by him being awake. "Stomach?"

"Grandma," he said. "How much of me is me?"

She came in and looked at the jar, not at him. "That's a strange thing to ask a jar of yogurt."

"The book says half. Half my cells aren't human cells. They're bacteria. Thirty-eight trillion." He swallowed. "That's the same as the warm. The warm I am. Some of it's them."

Grandma Liv was a person who fixed things and did not philosophize, and he could see her deciding whether to laugh. She decided not to.

"I never finished that book," she admitted. "It's overdue by about nine years."

Soren wasn't listening. He was holding the jar and thinking about the spoonful.

One spoon of the old yogurt had become the whole new jar. That was how it worked. You didn't make the yogurt. You gave the living things a warm dark place and time, and they made it, and then a spoon of that made the next.

Which meant the yogurt in his hand came from yesterday's jar, and that from the jar before, a chain of spoonfuls going back and back.

"How old is the starter?" he asked.

Grandma actually smiled. "My mother gave me a spoon of hers. Her mother gave her one. We came from Norway with it. Kept it alive on the boat."

Soren looked at the pale thick surface in the jar. The living things in it were the great-great-grandchildren of living things that had crossed an ocean in a different jar in a different century, kept warm against somebody's body so they would not die.

And the ones inside him. Where had his come from. The first spoonful, the very first, had come from someone too. From his mother, in the first hour, the book had said that part too, that a baby gets its first residents on the way into the world and from every hand that holds it.

He was carrying a chain like the yogurt was. A line of small lives handed down, kept warm, never once stirred by him, busy in his dark every single night, half of the warmth that Grandma checked with her wrist.

"I'm a jar," he said quietly.

"You're a boy," said Grandma.

"I'm a warm dark place where things live," he said. "And so are you. And so was your mother on the boat."

Grandma Liv stood next to him and put her wrist against the jar to check it, an old habit, the same gesture she used on him. Then, without thinking, she put the back of her wrist against Soren's forehead.

"Warm," she said.

"I know," Soren said. "That's what I'm telling you."

He set the jar back by the radiator and reached for a clean spoon. He dipped it into the new yogurt, into the half of the world that had never asked him, and lifted out one full spoonful to start tomorrow's jar.