es of monsieur the Professor had shown signs of failing on the
lower glacier, for example, they might all have been in difficulties.
The Professor thrilled with pleasure at the head guide's implied praise.
He was glad to know on such good authority that his nerves were all
right, and the incidents that had driven him there began to fade in his
memory.

Nevertheless, he found himself watching the calendar with a certain
interest, and when he woke on the morning of the first day of the next
month he glanced quickly at his right hand. There was nothing there.

He dressed and spent, as he had planned, a quiet day, busy with his
correspondence. His spirits rose as the day passed. He was still
watchful, but more confident; and, after dinner, though he had meant to
go straight to his room, he agreed to join in a suggested game of
bridge. They were cutting for partners when one of the ladies who was to
take part in the game dropped with a little cry the card she had just
lifted.

"Oh, there is blood upon your hand," she cried, "on your right hand,
Professor!"

Upon the Professor's right hand there showed now a drop of blood, larger
still then those other three had been. Yet the very moment before it had
not been there. The Professor put down his cards without a word, and
left the room, going straight upstairs.

The drop of blood was still standing on his hand. He soaked it up
carefully with some cotton-wool he had, and was not surprised to find
beneath no sign or trace of any cut or wound. The cotton-wool he made up
carefully into a parcel and addressed it to an analytical chemist he
knew, inclosing with it a short note.

He rang the bell, sent the parcel to the post, and then he got out pen
and paper and set himself to solve this problem, as in his life he had
solved so many others.

Only this time it seemed somehow as though the data were insufficient.

Idly his pen traced upon the paper in front of him a large _X_, the sign
of the unknown quantity.

But how, in this case, to find out what was the unknown quantity? His
hand, his firm and steady hand, shook so that he could no longer hold
his pen. He rang the bell again and ordered a stiff whisky-and-soda. He
was a man of almost ascetic habits, but to-night he felt that he needed
some stimulant.

Neither did he sleep very well.

The next day he returned to England. Almost at once he went to see his
friend, the analytical chemist, to whom he had sent the parcel fr