CHAPTER VIII
Bites and Stings
Several Kinds of Mosquitoes—Cause of Yellow Fever—Bee, Wasp, and Hornet Stings—Wood Ticks, Lice, and Fleas—Scorpions and Centipedes—Poisonous Snakes—Dog and Cat Bites.
MOSQUITOES.—The female mosquito is the offender. During or after sucking blood she injects a poison into the body which causes itching, swelling, and, in some susceptible persons, considerable inflammation of the skin. The bites of the mosquitoes living on the shores of the Arctic Ocean and in the tropics are the most virulent. The most important relation of mosquitoes to man was only recently discovered. They are probably the sole cause of malaria and yellow fever in the human being. The malarial parasite which lives in the blood of man, when he is suffering from malaria, first inhabits the body of a certain kind of mosquito. The mosquito acquires the undeveloped parasite by biting the human malarial patient, and then acts as a medium of infection by transmitting the active parasite to some healthy man, through the bite.
The more common house mosquito, the Culex, does not carry the parasite of malaria, and it is important to be able to distinguish the Anopheles which is the source of malaria. The Anopheles is more common in the country, while the Culex is a city pest. The Culex has very short palpi, the name given to the projections parallel to the proboscis; while those of Anopheles are so large that it appears to have three probosces. There are no markings on the wings of the ordinary species of Culex, while the wings of Anopheles are distinctly mottled. The Culex, sitting on a wall or ceiling, holds its hind legs above its back and its body nearly parallel to the wall or ceiling, but the Anopheles carries its hind legs either against the wall or hanging down (rarely above the back), and its body, instead of lying parallel to the wall or ceiling, hangs away at an angle of about forty-five degrees from it.
The Culex lays her eggs in sinks, tanks, cisterns, and water about houses, but the Anopheles deposits her ova in shallow pools and sluggish streams, especially those on which is a growth of green scum or algæ. Such are the main distinguishing features of the malaria-carrying mosquito, the Anopheles, and the commoner house variety, the Culex.
To prevent malaria, mosquito bites must be prevented by nettings in houses, especially for the protection of sleepers. Pools, ponds, and marshy districts must be drained in order to destroy the breeding places of Anopheles, and in the malarial season, petroleum (kerosene) must be poured on the surface of such waters to arrest the development of the immature insects (larvæ).
The mosquito is believed to be the sole cause of yellow fever, being capable of communicating the germ of the disease to man by its bite two weeks after it has itself been contaminated with the germ in feeding on the blood of a yellow-fever patient. This invaluable discovery was made by Dr. Walter Reed, U. S. A., in 1901, as a result of his labors and those of other members of the yellow-fever commission of the U. S. Army in Cuba, involving the death of one of the members of the commission (Dr. Lazear), and utilizing the heroism of a number of our young soldiers who voluntarily offered themselves to be bitten by mosquitoes that had previously bitten yellow-fever patients, and who experimentally occupied premises containing all sorts of articles infected by yellow-fever patients. The result of their research proves that yellow fever is not contagious at all, in the usual sense, but is communicated only through the medium of mosquitoes. This shows the fallacy of many quarantine rules regarding yellow-fever patients, and of the fear of nursing the sick, and will result in controlling the disease.
In the case of malaria or yellow fever, there is a vicious circle into which man and the mosquito enter; malaria and yellow-fever patients contaminate the mosquitoes which bite them, and the mosquitoes in their turn infect man with these diseases. A patient with malaria coming into a nonmalarial place, and being bitten by mosquitoes, may lead to an epidemic of the disorder which becomes endemic. To terminate this condition, it is necessary to prevent the contact of man with mosquitoes and to kill these insects. Both malaria and yellow fever will doubtless be practically eradicated before long through the result of these scientific discoveries.