ber that," said Stanton somberly. "I won't try to race him
underwater."

"No," said Colonel Mannheim. "No, I wouldn't do that if I were you."

They both knew that there was a great deal more to it than that. In
spite of the near miracle that the staff of the Neurophysical Institute
had wrought upon Stanton's nerves and muscles and glands, they could
only go so far. They could only improve the functioning of the equipment
that Stanton already had; they could not add more.

His lungs could be, and had been, increased tremendously in efficiency
of operation, but the amount of air they could actually hold could only
be increased slightly. There was no way to add much extra volume to them
without doing so at the expense of other organs. In a breath-holding
contest, the Nipe would win easily, since his body had evolved organs
for oxygen storage, while the human body had not.

You cannot make a silk purse out of a sow's ear if you are limited to
the structures and compounds found in sows' ears. The best you can do is
make a finer, stronger, more sensitive sow's ear.

"I understand that the Nipe has his hideout pretty well bugged with all
kinds of alarms," Stanton said. "How did you get your own bugs in there
without setting off his?"

"Well, at first we didn't know for sure what he was up to; we weren't
even sure he was actually down in those tunnels. But we suspected that
if he was he'd have alarms set all over the place--perhaps even alarms
of types we couldn't recognize. But we had to take that chance. We _had_
to watch him."

He walked over to the nearby table and opened a box some twelve inches
long and five-by-five inches in cross-section.

"See this?" he said, as he took a furry object from the box.

It looked like a large rat. Dead, stiff, unmoving.

"Our spy," said Colonel Mannheim.

* * * * *

The rat moved along the rusted steel rail that ran the length of the
huge tunnel. To a human being, the tunnel would have seemed to be in
utter darkness, but the little eyes of the rat saw the surroundings as
faintly luminescent, glowing from the infra-red radiations given out by
the internal warmth of the cement and steel. The main source of the
radiations was from above, where the heat of the sun and the warmth from
the energy sources in the buildings on the surface seeped through the
roof of the tunnel. But here and there were even brighter spots of
warmth, spots that moved about