"They wanted to prove even more surely that it was a certain kind of mosquito which really did the harm. So they built another house. Everything in this house was pure and clean. The rooms were flooded with fresh air and sunshine. Half of the house was carefully screened and shut off from the other half. The men in the half that was screened kept perfectly well. Those in the other half let themselves be bitten by mosquitoes which had been in the houses where there was yellow fever. All became dangerously ill with the fever. Two of these brave physicians died of the fever while trying to find the cause, in order that they might save the lives of thousands of people." "That is modern heroism," said Mrs. Reece, "and service of the highest sort. All humanity is indebted to those brave men. There is no doubt but that our Panama Canal could not be in progress to-day were it not for the extermination of the mosquito in the canal zone. Since we can never tell where a mosquito has been, or what kind of a mosquito it is, I suppose it is best to keep mosquitoes from biting, and always to keep them out of the house. And now, children, supper is ready, and after that games. Let us go to the dining-room!" XI CAMPING OUT At last the day, expected all summer long, had come. The children, Hope and Betty, Jack, Peter, and Jimmy, Mrs. Reece and Ben Gile, were gathered on the edge of the pond, their packs in the canoes, their paddles at bow and stern. Other guides had taken the food and tents ahead the day before. Their friends had gathered to bid them good-bye, and finally, amid the farewells, they were off, Jimmie in a canoe by himself, Jack and Peter paddling Mrs. Reece, and Ben Gile with the two little girls. Everybody was so excited that all talked at once, and nobody could hear any one else. Hope and Betty had never been camping before, and the boys meant to show the girls all the wonders of sleeping and eating out in the woods. Finally they came to a "carry"--that is, a path leading from one lake to another, across which the food and canoes have to be lugged. The girls and Mrs. Reece carried the packs and food over, making several trips in order to do so; and the boys and the guide, crossing their paddles under the thwarts of the canoes and raising the blades on their shoulders, balanced the canoes and trotted swiftly over the carry. Nothing seemed any trouble that glorious, beautiful day--nothing too heavy, nothing too hard. Betty and Hope could have skipped over every inch of the trail, and they were quite sure that they could have done all the paddling, too. And Betty did learn, in after years, not only to paddle, but also to carry her own canoe, for she grew to be a big, strong, athletic girl, with rosy cheeks and a quick, sure step.