Many years ago a doctor found in the blood of malaria patients tiny animals. He thought that they might be the cause of the illness, but he could not find out how they got into the blood.
Finding out how Malaria Germs get into the Blood.—It had been noticed for many years that mosquitoes were always found wherever there was malaria. In the year 1900 two men decided to find out if they could live in a malaria region and not have the disease when the mosquitoes were kept from biting them.
Fig. 73 —Position of the common humpback mosquito at rest with body full of blood sucked by thrusting the bill into the flesh.
They made their home a whole season in a cottage in the midst of many persons who were sick with malaria. They breathed the same air, ate the same kind of food, and drank the same kind of water as those who suffered from the disease, but they remained well. The only thing that they did different from those who got sick was to keep the mosquitoes out of their rooms at night by means of screens. This experiment and many other studies have shown that we catch malaria only by the bites of mosquitoes.
Fig. 74 —Position of the malaria mosquito at rest.
Only a Few Mosquitoes carry Malaria.—Malaria is not common in all regions where mosquitoes live, and it has been found that only one group of mosquitoes carries the germs. The two common groups are the straight-backed and the humped. To prove that the straight-backed ones did the harm several of them were allowed to suck blood from a man sick with malaria in Italy. They were then sent to London and let bite a healthy man. In a few days he became sick with malaria. Many experiments with the humped-back mosquitoes, found nearly everywhere in our country, show that they do not carry malaria germs.