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!” So Bruce went around asking everybody about tsetse flies in Uganda. He inquired of local bug experts: no, they were sure tsetse flies could not live at an altitude above three thousand feet. He asked the native headmen, even the black Prime Minister of Uganda: sorry, we have a blood-sucking fly, called Kivu--but there are no tsetse flies in Uganda. But there must be! VI And there were. One day, as they walked through the Botanical Garden at Entebbe, Bruce pushing his bulky body between the rows of tropic plants ahead of his small wife--there was a glad shriek from her.... “Why, David! There are two tsetse--on your back!” That woman was a scientific Diana. She swooped on those two tsetses, and caught them, and gave them a practical pinch--just enough to kill them, and then showed them to her husband. They had been perched, ready to strike, within a few inches of his neck. Now they knew they were on the trail. Hard work began in the laboratory; already Bruce had found an excellent experimental animal--the monkey, which he could put into a beautiful fatal sleep, just like that of a man, by injecting fluid from the spines of doomed negroes. But now to catch tsetse flies. They armed themselves with butterfly nets and the glass-windowed cages they had invented in Zululand. Then these inseparable searchers climbed into canoes; lusty crews of black boys shot them across the lake. Along the banks they walked--it was charming in the shade there--but listen! Yes, there was the buzz of the tsetse.... They tried to avoid being bitten. They were bit--and stayed awake nights wondering what would happen--they went back to the laboratory and clapped the cages on the backs of monkeys. It was a good time for them.