Our scientific knowledge of the subject was almost entirely created within the five years subsequent to 1898, and workers in many coun tries are constantly adding details. That sev eral species of Anopheles, and especially A. maculspennis, are the chief, and so far as known the sole disseminators of all types of malarial fever, is absolutely and thoroughly demon strated from every standpoint.
Mosquitoes and Yellow Fever.— In the case of yellow fever our knowledge is in a very different and less satisfactory state. The rela tion of mosquitoes to this disease was suspected by Dr. Finley as early as 1881, but his theory excited little interest until, upon the occupation of Cuba by the American navy, a Yellow Fever Commission of inquiry, headed by Major Reed, was appointed. By a series of very careful ex periments it has been established that mos quitoes are agents in the dispersal of this dis ease, and at the same time the old view of in fection by contact and the old practice of isola tion and fumigation for prevention have been nearly repudiated. The particular species of mosquito which transmits yellow fever is Ste gomyia fasciata, an especially fierce biter in the early afternoon, which is found in the tropical parts of both hemispheres, and in America as far north as Virginia.
The germs of the disease may be taken by the mosquito only during the first three or four days of the fever; after that time the blood of the patient cannot infect the mosquito. The germs require about 12 days to migrate from the stomach of the insect to the salivary glands, from which they may be injected through the mosquito's biting organ into the human blood stream. Mosquitos, after becoming infectious, are capable of inoculating the disease into the human at intervals of three days (period of feeding) for practically an indefinite time.
The adaptation of protective measures to this important discovery renders the prevention or suppression of an epidemic very simple, the oretically. Screening the patient from mos quitoes during the first four days of fever (be fore the diagnosis), or killing all mosquitoes in the room before the 12th day after their possi ble infection, will certainly prevent a second case.
Agency in Other Diseases.— Elephantiasis or filariasis, like malaria, results from the pres ence in the blood of an animal parasite, but one of a very different nature. The adult males and females of the Filaria, which is a slender nema tode worm, live together in the subcutaneous lymph vessels and produce enormous numbers of living, minute embryos which swarm in the blood, usually passing into the superficial capil laries at night and retreating to the deeper ves sels by day. This peculiarity first led Manson to suspect the mosquito as a means of distribu tion and as a result of his studies and those of Bancroft and others on the Filarite of man and the dog, it is now known that when infected blood is swallowed by Cules fatigans and other mosquitoes the embryos pass through certain stages of development within the intestine and malpighian tubules and then migrate through the body-cavity and tissues to the proboscis, from which human infection occurs. About three weeks are required to complete the devel opment within the mosquito, and a year before the worms become sexually mature in the final host. Elephantiasis is a dreadful and prevalent disease in tropical countries, and is frequent in the Southern States, but rare in temperate climates.
The mosquito is suspected of being instru mental in the spread of leprosy and other dis eases, and undoubtedly many important discov eries await the investigator in this field.
Restraining Local Pests of Mosquitoes.— The possibility of the control or complete ex termination of mosquitoes has received serious attention from zoologists, physicians and sani tary engineers, and is encouraged by local and national governmental grants. Wherever the 1-oblems.have been carefully considered, as in New Jersey, Long Island, the Connecticut coast and Winchester, Va., in this country, much has been already accomplished toward the mitigation of the pest. As to measures, the complete destruction of all breeding-places by the draining of swamps, pools and ditches is the most effective and permanent. This must be supplemented by emptying or suitably protect ing by screening against the access of gravid mosquitoes all artificial vessels, such as pails, rain barrels, cisterns, privies and drains, which contain standing water in which mosquitoes may breed. A most effective and simple meas ure for local application is to pour a small quantity of kerosene upon the surface of the water of possible breeding-places. This spreads as a delicate film which deters the larva and pupa from coming to the surface to breathe, so that they quickly suffocate, and at the same time kills or drives off females which come to lay their eggs. The application should be re peated at Intervals of two or three weeks. Small fishes and the other natural enemies named above may be introduced into breeding places to good purpose. The usual methods of ridding houses of 'mosquitoes by fumigation with sulphur dioxide gas; of preventing their entrance by thorough screening; and of pro tecting the person by the application to the skin of oil of citronella and other substances have a certain protective value. The most ap proved application is a mixture of one ounce each of oil of citronella and spirits of cam phor with half an ounce of oil of cedar. The effect will last longer if incorporated with vase line. It has been shown by the experiments of Grassi and others that this method alone is suf ficient to grant immunity from malaria to in habitants even of such fever-scourged districts as the Campagna of Rome. For the medical treatment of malaria we have a powerful specific in quinine, which is most effective at the tune of the paroxysms, when the sporulx are free in the blood-plasma and most susceptible to the action of the drug. See MAT-ARIA.
Bibliography.—Doty, A. H., The Mosquito: Its Relation to Disease, and Its Extermination> (New York 1912) ; Herms,. W. B., 'Malaria: Cause and Control' (New York 1913); How ard, L. 0. (et al.), 'The Mosquitoes of North Central America, and the West Indies) (4 vols., Washington, D. C., 1914-17); Smith, J. B., 'The Mosquito Investigation in New Jersey> (New York 1905) ; American Mosquito Exter mination Society 'Year Books) (New York 1904 onward); Mosquito Extermination Com mission of Hudson County, N. J., 'Annual Re ports); United States Agricultural Department Bulletin 444 (Washington 1911); California Agricultural Ex • riment Station 'Bulletin 178' (Sacramento l' ) • Connecticut Agricultural Experiment Station 'Bulletin 173' (New Haven 1912) ; New Jersey Agricultural Experiment Station Bulletin 276' (New Bruns wick, N. J., 1915).