ssion chamber for several hours and
later transferred to a hospital bed. Bud Barclay came to visit him.

"We're a fine couple of fish," he said.

Tom chuckled wryly. "_Live_ fish, anyhow."

"In my case, thanks to you," Bud said.

"Forget it, pal. The score's about even, I should think," Tom said,
recalling the many life-or-death adventures they had shared.

Bud was thrilled to hear of Tom's electronic hydrolung. The young
inventor spent the evening sketching out an improved design to eliminate
future accidents.

"I'll install a special device to remove the nitrogen as the wearer
exhales," Tom explained. "Then a valve will feed in helium to replace
it. Since helium doesn't dissolve in the blood like nitrogen does, it
will not bubble out when the pressure is reduced. Should have thought of
that before!"

"But you'll need a tank for the helium, won't you?" Bud objected.

Tom shook his head. "Enough can be compressed into a small capsule to
supply the wearer's needs. Remember, it can be used over and over
again."

"Pretty neat," Bud commented.

By morning Tom felt thoroughly recovered. He insisted upon flying back
to Enterprises to make the necessary changes in his hydrolung. Bud
accompanied him, eager to get back on the job.

In a few hours Tom had added a small fitting to his power unit to
provide for helium substitution. Then the two boys hopped back to
Fearing for a second deep-water test. This time, Tom was delighted to
find that he could operate comfortably at great depths, as well as rise
or descend suddenly without ill effect.

Bud was aglow with enthusiasm. "Boy, we can really explore now!"

After the boys had returned to Enterprises, Tom phoned Arv Hanson and
asked that a duplicate of the hydrolung be turned out in the shop as
soon as possible. It was ready the following Monday morning, so Tom
suggested to his father that the two visit the proposed underwater site
and make some sample plantings.

"Great idea, son," Mr. Swift agreed. "I want to try out your new diving
apparatus myself. If it's successful, we'll be able to tackle two
problems at once--recover the Jupiter prober and start the 'sea farm.'"

They flew to Fearing, then went by boat to the farm site, about half a
mile offshore. Each carried several of the valuable Far Eastern plants.

[Illustration]

The silt beds which Mr. Swift had selected were just deep enough to
keep the plants from being discovered, yet enable them to receive