Tom scowled. "If
so, that sub yesterday may have been observing our tests."

The telephone rang and Tom leaped to answer it. The caller was Dan
Perkins of the _Shopton Evening Bulletin_.

"You can guess why I'm calling, Tom," the editor said. "How about a
statement from you Swifts on this Brungarian sub story?"

"We found it very interesting," Tom said politely but noncommittally.
Parrying further questions, he hung up as soon as possible.

Mr. Swift approved Tom's policy of silence. Almost immediately the phone
began ringing again with a succession of calls from other newspapers and
wire services. Tom dashed off a brief, general statement and instructed
Miss Trent to give it to all further callers.

"Maybe this is a good time to make a private announcement to you
fellows," Mr. Swift said to the two boys, his eyes twinkling. "Do you
recall my telling you that Doc Simpson had isolated an unknown vitamin
from the space plants? Well, we've now discovered that this vitamin can
condition the human body to stay under water indefinitely. Doc is
putting some up in capsule form."

Both Tom and Bud gave whoops of glee at this news.

"Dad, you've helped overcome one of the big problems in our search for
the lost missile!" Tom exclaimed.

CHAPTER XV

MOUNTAIN HIKE

"After adequate doses of your space vitamin, Dad, a skin diver could
tackle almost any undersea job in my hydrolung!" Tom exclaimed. "He
wouldn't be subjected to any antiosmosis troubles with his body
tissues."

His father nodded. "For the first time, man might become a _truly marine
creature_!"

"Wow! Think of it!" Bud gasped excitedly. "With Tom's hydrolung and a
knife to hunt his own food, he could practically live in the sea!"

"That's no farfetched dream, Bud." Tom's steel-blue eyes flashed at the
thought of new fields of scientific conquest. "This discovery of Dad's
and Doc Simpson's opens up some really amazing possibilities."

Most important at the moment, the vitamin would be a great boon in
carrying out search and digging operations for the Jupiter prober. With
fresh enthusiasm, Tom returned to his laboratory to work on the new
sonar gear. In his own mind, he had already named it a "quality analyzer
sonar," since that exactly described the way it would function.

"Hmm, let's see," Tom mused as he settled down at his workbench, pencil
in hand. "Besides a regular sonarscope, I'll need at least three units
for the gear."

First, he wou