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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:
"But where do the tsetses of the plain get the trypanosomes they stick into cows and horses? In those fly belts there are often no horses or cattle sick with nagana, for months. Surely the flies [he was wrong here] can't stay infected for months—it must be they get them from the wild animals, the big game!" That was a possibility after his heart. Here was a chance to do something else than sit at a microscope. He forgot instantly about the more patient, subtle jobs that demanded to be done—teasing jobs, for a little man, jobs like tracing the life of the trypanosomes in the flies. . . . "The microbes must be in game!" and he buckled on his cartridge belt and loaded his guns. Into the thickets he went, and shot Burchell's zebras; he brought down koodoos and slaughtered water-bucks. He slashed open the dead beasts and from their hot hearts sucked up syringes full of blood, and jogged back up the hill with them. He looked through his microscopes for trypanosomes in these bloods—but didn't find them. But there was a streak of the dreamer in him. "They may be there, too few to see," he muttered, and to prove they were there he shot great quantities of the blood from ten different animals into healthy dogs. So he discovered that the