[Illustration: FIG. 78.--Resting positions for ordinary mosquito (left) and malarial mosquito (right).] In the year 1900, however, English scientists, working in the Roman Campagna, demonstrated conclusively that which had been vaguely suggested before, namely, that the cause of malaria is a parasite composed of little more than an unformed mass of protoplasm, not floating in the air at all, but transmitted only by the bite of a mosquito. By a series of most interesting experiments, conducted by them and by other scientists in other parts of the world, it has been definitely proved that when a mosquito bites an individual suffering from malaria, the mosquito draws up into his body, along with the blood of the bitten person, some of the malarial parasites. In the body of the mosquito, the parasite develops, requiring for a full-grown specimen about seven days; then, if the mosquito bites another person, the parasite is injected into the skin of the victim, and in the course of about a week a good case of malaria ensues. Fortunately, only a small proportion of the number of mosquitoes in the world are capable of nourishing the malaria parasite. Under ordinary conditions about 5 per cent of all mosquitoes found are malarial, and a particular name has been given to those capable of transmitting the disease. The ordinary mosquito is known as the "culex," while the malarial kind is known as "anopheles." Figure 78 shows the characteristic attitude of the two kinds by which the one can be distinguished from the other when resting on a wall or ceiling. As will be noticed in the drawing, the culex carries his body parallel to the wall with his hind legs crossed over his back. The harmful mosquito, the female anopheles, always hangs on by her front legs and has her body at an angle of about forty-five degrees to the surface to which she clings, her hind legs hanging down. The wings of the harmless mosquito are usually mottled, while the wings of the malarial mosquito are of an even color. The details of the behavior of the parasite on its long journey from the original malarial patient through the body of the mosquito and into the body of the person bitten is full of interest to the scientist, who must, however, be provided with a good microscope to follow such minute bodies; but the methods of avoiding the disease are more pertinent to our present purpose.