The children had been slapping the mosquitoes buzzing about on the _piazza_. "And now," said the guide, "before we go into supper, I will tell you a real and a true story. Mosquitoes sometimes carry sickness from one person to another until it spreads throughout a large city. We didn't realize how dangerous mosquitoes were till a short time ago. People had malaria, and were very ill with it. In some countries many died. Every one thought, however, that the malaria came in some mysterious way from the mists of the low-lying swamps and marshes. But one day some one happened to think it might not be in the marshes, after all; rather that it might be a certain little two-winged insect with a short, piercing instrument, which spent its babyhood days in these same marshes. "And so two English doctors determined to find out the truth of the matter. In the faraway land of Italy was a place where thousands of people were suffering from this disease. There these doctors went and built a comfortable little house in the very worst place they could find. They were careful to screen every door and window, and to leave not a crack for a mosquito to crawl in. "There they lived, always going into the house at sundown, shutting all the screen doors, but allowing the damp night air to pour in. It was this night air which every one supposed gave people malaria. But the two physicians in the snug little house, free from mosquitoes, kept well, strong, and happy, although the people outside in the other houses were very ill and suffering with chills and fever. "You see, these little Anopheles, for that is their name, bite some one ill with malaria. Perhaps the next person they stab with their sharp needle is well. In this way they leave some of the poisoned blood in the wound. There is another illness which is a hundred times worse than malaria. This is called yellow fever. In some countries thousands of people died from this every year, and doctors did not know just how it was carried from place to place. "Our Government appointed a commission to study the matter. Dr. Walter Reed, a surgeon of the United States Army, with three assistants, went to Havana and built a house, carefully screened, just like that of the English physicians in Italy. People thought that the fever was carried in the clothes and on the sheets of those who were ill. To prove that this was not so, these men wore the clothes of sick people, and even slept on the sheets taken from the sickbed. They did this disagreeable thing for twenty days, keeping the little house very warm, and shutting out the fresh air and sunshine. But in spite of all these things the men continued well and strong.