Yellow Fever.—Until 1901 yellow fever was the scourge of many cities in the South. Thousands of persons lost their lives from it. Wherever the dread disease broke out in a city many persons would flee to the country because they thought that they could not breathe the air without getting the germs.
Some persons thought that mosquitoes might cause the disease, and in 1900 experiments were carried out in Cuba to learn whether mosquitoes really did carry yellow fever germs. Seven men made their home in a room well screened to keep out the mosquitoes. They used clothing which had been worn by others sick with the fever and even slept on pillows and blankets on which yellow fever victims had died. Many persons thought that these bedclothes were full of fever germs and that all the men would surely get the disease. Not one of them, however, got sick although they lived in the midst of these soiled materials for three weeks.
Fig. 75 —The yellow fever mosquito biting the finger. Note how the lower lip is bent.
Seven other men were chosen for another experiment. A large room was prepared and made thoroughly clean. Only clean bedding and clean clothes were used. The men were given pure food and pure water, but into the room were let loose mosquitoes which had been sucking blood from a person sick with the fever. In a few days six of the seven men became sick with the fever and one of them died. From these experiments and other studies we now know that this dreadful fever is carried from the sick to the well only by the bites of mosquitoes.
Fig. 76 —A bunch of mosquito eggs floating on the surface of the water. Enlarged about fifteen times.
How Mosquitoes Live.—Before we can get rid of any pests we must know where the eggs are hatched and the young pass their early life. The eggs of mosquitoes are laid on standing water. The water may be in an old tomato can, a rain barrel, a cistern, or a large pond. A day or two after the mother lays one or two hundred eggs, they hatch into dark, wriggling objects called wigglers. In from ten to twenty days later they change into flying mosquitoes. These habits of life show that the easiest time to kill them is when they are young.