delay, but it was worse not knowing. He waited.

* * * * *

"I have it," said the robot after an interval. "There is great
difficulty feeding a city this large. In fact, there is with all of
Earth--it's greatly overpopulated."

"So I understand," mumbled Marcus.

"The trouble began forty-five or fifty years ago with the water supply,"
said the robot. "It was sanitary, but there was too great or not great
enough concentration of minerals in it. Information isn't specific on
this point. The robots in control of the tanks found that beef, pork,
lamb and chicken in all their variety would not grow fast enough. Many
tanks wouldn't grow at all.

"The robots communicated this fact to higher authorities and were told
to find out how to correct the situation. They investigated and
determined that either the entire water-system would have to be
overhauled, or a new and hardier protein would have to be developed.
Naturally, it would require incalculable labor to install a new
water-system. They didn't recommend it."

"Naturally," said Marcus.

"The situation was critical. The city had to be fed. The tank robots
were told to find the new protein. Resources were thrown open to them
that weren't hither-to available. In a short time, they solved the
problem. About half of the tanks that were not growing properly were
cleaned out and the new protein placed in them. The old animal name
system was outmoded so the new lot number system was devised and applied
to every tank regardless of its ultimate origin."

"Then nobody has any idea what they're eating," said Marcus. "But what
was that new protein? That's what I want to know."

"It was hardy. It came from the most adaptable creature on Earth," said
the robot. "And there was another factor in favor of it. The flesh of
all mammals is nearly the same. But there are differences. The ideal
protein for a meat-eating animal is one which exactly matches the
creature's own body, eliminating food that can't be fully utilized."

Marcus closed his eyes and grasped the arm of the chair.

"Do you feel ill?" inquired the managing robot. "Shall I call the
doctor? No? Well, as I was saying, there was already a supply of animal
tissue on hand. It was this that the robots used. It's funny that you're
asking this. Not many people are so curious."

"They didn't care," snarled Marcus. "As long as they were fed, they
didn't ask what it was."

"Why should they?"