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, nor drunk, nor even inhaled the air of the plain--every one died of the nagana. How they worked, Bruce and his wife! They post-mortemed dead horses; they named a sick horse “The Unicorn” and tried to keep him alive with arsenic. To find out how long a tsetse fly can carry the trypanosomes on his stinger they put cages of flies on sick dogs and then at intervals of hours, and days, let them feed on healthy ones. They fed dying heifers hot pails of coffee, mercifully they shot dogs thinned by the nagana to sad bags of bones. Mrs. Bruce sterilized silk threads, to dip in blood swarming with trypanosomes, then sewed these threads under the hides of healthy dogs--to find out how long such blood might remain deadly.... There was now no doubt the tsetse flies, and only the flies, could carry the nagana, and now Bruce asked: