=Detection.=--To the well-educated physician is now open an exact method of determining the existence of malaria, and of distinguishing it from all similar diseases, by the examination of the patient's blood for the malarial parasite--its presence or absence deciding the presence or absence of the disease. For the layman the following points are offered: intermittency of chills and fever, or of fever alone, should suggest malaria, particularly in a patient living in or coming from a malarial region, or in a previous sufferer from the disease. In such a case treatment with quinine will solve the doubt in most cases, and will do no harm even if the disease be not malaria. Malaria is one of the few diseases which can be cured with certainty by a drug; failure to stop the symptoms by proper amounts of quinine means, in the vast majority of cases, that they are not due to malaria. There are many other diseases in which chills, fever, and sweating occur at intervals, as in poisoning from the presence of suppuration or formation of pus anywhere in the body, but the layman's ignorance will not permit him to recognize these in many instances. The quinine test is the best for him. =Prevention.=--Since the French surgeon, Laveran, discovered the parasite of malaria in 1880, and Manson, in 1896, emphasized the fact that the mosquito is the medium of its communication to man, the way for the extermination of the disease has been plain. "Mosquito engineering" has attained a recognized place. This consists in destroying the abodes of mosquitoes (marshes, ponds, and pools) by drainage and filling, also in the application of petroleum on their surface to destroy the immature mosquitoes. Such work has already led to wonderful results.[11] Open water barrels and water tanks prove a fruitful breeding place for these insects, and should be abolished. The protection of the person from mosquito bites is obtained by proper screening of habitations and the avoidance of unscreened open air, at or after nightfall, when the pests are most in evidence. Dwellings on high grounds are less liable to mosquitoes. Persons entering a malarial region should take from two to three grains of quinine three times a day to kill any malarial parasites which may invade their blood, and should screen doors and windows. Patients after recovery from malaria must prolong the treatment as advised, and renew it each spring and fall for several years thereafter. A malarial patient is a direct menace to his entire neighborhood, if mosquitoes enter.