and some time or other you'd be caught bathing."

"Not much chance for bathing out there when we were away from the Nile,
eh?"

"Well, having a sand-bath; and then they'd see that the rest of your
skin was white."

"Oh, no, they wouldn't," cried Frank. "I should do as that amateur did
who wanted to play Othello properly--black myself all over."

The professor took off his fez, laid it upon his knees, and with both
hands gave his shaggy hair a vicious rub, which, however, did not
disorder it in the least, seeing that it was as rough as could be
before.

"Yes," said the doctor; "he has an answer for all objections, Fred, old
fellow."

"Yes, yes, yes," cried the professor, putting on his fez again, and
making a vicious dab at the tassel, which was tickling his neck, but
subsided quietly between his shoulders after it had done swinging. "He
has something to say to everything. Too much talk. It wouldn't do.
The Baggara are as keen as their swords: they'd see through it
directly."

"Then I'd dye it blacker," said Frank.

"Oh, the colour would be right enough, boy," cried the professor, "but
that's what would let the cat out of the bag."

"What do you mean?"

"That tongue of yours, my lad. Your speech would betray you directly."

"Oh, no, it would not," said Frank. "Mutes are common enough in the
East, are they not?"

"Oh, yes, but--"

"Well, I would not talk."

"Pooh!" cried the professor contemptuously. "You wouldn't talk? Why,
you've got a tongue as long as a girl's. You not talk? Why, you'd be
sure to burst out with something in plain English just when our lives
were depending upon your silence."

"_Urrr_!" growled the young fellow angrily. "Give me credit for a
little more common-sense. Do you think, with the success of our
expedition and poor Hal's life and happiness at stake, I couldn't make a
vow to preserve silence for so many months, and keep it?"

"I do think so," said the professor, clapping one hand down upon the
other. "You would find it impossible. What do you say, Bob?"

"Humph!" grunted the doctor.

"Come, there's no need for you to hold your tongue," cried the professor
petulantly. "Say something."

"Very well, I'll say something," replied the doctor: "I don't know."

"Yes, you do. You know it's impossible."

"No," said the doctor thoughtfully; "I know it would be very hard, but
seeing what a stubborn, determined fellow Frank is, I should not be
surprised if he suc