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 from Switzerland.
"Mammalian blood," pronounced the chemist, "probably human—rather a curious thing about it, too."
"What's that?" asked the Professor.
"Why," his friend answered, "I was able to identify the distinctive bacillus——" He named the rare bacillus of an unusual and obscure disease. And this disease was that from which the Professor's cousin had died.
The professor was a man interested in all phenomena. In other circumstances he would have observed keenly that which now occurred, when the hair of his head underwent a curious involuntary stiffening and bristling process that in popular but sufficiently accurate terms, might be described as "standing on end." But at the moment he was in no state for scientific observations.
He got out of the house somehow. He said he did not feel well, and his friend, the chemist, agreed that his holiday in Switzerland did not seem to have done him much good.
The Professor went straight home and shut himself up in his study. It was a fine room, ranged all round with books. On the shelves nearest to his hand stood volumes on mathematics, the theory of mathematics, the study of mathematics, pure mathematics, applied mathematics. But there was not any one of these books that told him anything about such a thing as this. Though, it is true, there were many references in them, here and there, to X, the unknown quantity.
The Professor took his pen and wrote a large X upon the sheet of paper in front of him.
"An unknown quantity!" he muttered. "An unknown—quantity!"
The days passed peacefully. Nothing was out of the ordinary except that the Professor developed an odd trick of continually glancing at his right hand. He washed it a good deal, too. But the first of the month was not yet.