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I can see him, talking to those pests in the language of a dockforeman, to the wonder of his Zulus. Day after day this procession of Bruce, the Zulus, and the experimental horses went down into the thorns, and each afternoon, as the sun went down behind Ubombo, Bruce and his migrating experiment grunted and sweated back up the hill.

Then, in a little more than fifteen days, to the delight of Bruce and his wife, the first of those horses who had served as a fly-restaurant turned up seedy in the morning and hung his head. And in the blood of this horse appeared the vanguard of the microscopic army of finned wee devils—that tussled so intelligently with the red blood cells. . . .

So it was with every horse taken down into the mimosa—and not one of them had eaten a blade of grass nor had one swallow of water down there; one and all they died of the nagana.

"Good, but it is not proved yet, one way or another," said Bruce. "Even if the horses didn't eat or drink, they may have inhaled those trypanosomes from the air—that's the way the greatest medical authorities think malaria is passed on from one man to the next—though it sounds like rot to me." But for Bruce nothing was rot until experiment proved it rot. "Here's the way to see," he cried. "Instead of taking the horses down, I'll bring the flies up!"

So he bought more healthy horses, kept them safe on the hill, thousands of feet above the dangerous plain, then once more he went down the hill—how that man loved to hunt, even for such idiotic game as flies!—and with him he took a decoy horse. The tsetses landed on the horse; Bruce and the Zulus picked them off gently, hundreds of them, and stuck them into an ingenious cage, made of muslin. Then back up the hill, to clap the cage buzzing with flies on to the back of a healthy horse. Through a clever glass window in one of the cage-sides they watched the greedy brutes make their meal by sticking their stingers through the muslin. And in less than a month it was the same with these horses, who had never eaten,