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some good—but no matter, they had served their purpose. The trypanosome, Castellani and Bruce now knew, was the cause of sleeping sickness!

Now—and this is rare in the dreamers who find fundamental facts in science—Bruce was a fiend for practical applications, not poetically like Pasteur, for Bruce wasn't given to such lofty soarings, nor was he practical in the dangerous manner of the strange genius I tell of in the last chapter of this story; but the moment he turned to the study of a new plague, Bruce's gray eyes would dart round, he would begin asking himself questions: What is the natural home of the virus of this disease?—How does it get from sick to healthy?—What is its fountain and origin?—Is there anything peculiar in the way this sleeping sickness has spread?

That was the way he went at it now. He had discovered the trypanosome that was the cause. There were a thousand pretty little researches to tempt the scholar in him, but he brushed all these aside. Old crafty hand at searching that he was, he fished round in his memories, and came to nagana, and screwed up his eyes: "Is there anything peculiar about the way sleeping sickness is located in this country?" He pondered.

He sniffed around. With Mrs. Bruce he explored the high-treed shores of the lake, the islands, the rivers, the jungle. Then the common-sense eye which sees things a hundred searchers might stumble over and go by—showed him the answer. It was strange—suspiciously strange—that sleeping sickness was only found in a very narrow strip of country—along the water, only along the water, on the islands, up the river—even by the Ripon Falls where Victoria Nyanza gives herself up to the making of the Nile, there were cases of it, but never inland. That must mean some insect, a blood-sucking insect, which lives only near water, must carry the disease. That was his guess, why, I cannot tell you. "Maybe it is a tsetse fly, a special one living only near lake shores and river banks!"