is, like diphtheria, a somewhat mysterious infectious disease. Like the latter it almost disappeared for a series of years, and then again became epidemic in 1889. The previous epidemics of influenza in the 19th century had occurred in 1803, 1833, 1837-8, and 1847-8. The causes of this recurrence of influenza are unknown. It is spread from person to person by direct infection, the infection being conveyed by the mucous discharge from the nose, throat, and lungs. Pocket-handkerchiefs probably are largely responsible for conveying the infection as dust. The disease is particularly fatal to the old; and these should not expose themselves to possible sources of infection, as in public places of assembly, during an epidemic. Every patient attacked with the disease should remain indoors for at least ten days. This is in his own interest, as he thus minimises the risk of such dangerous complications as pneumonia; and it is his duty in the interest of the rest of the community. Many lives might have been saved, had not influenzal patients “struggled about” during the early stages of the disease.

MALARIA.

Malaria, or Ague, is a generic name given to a disease caused by the invasion of the body by the plasmodium malariæ, discovered by Laveran in 1880. It occurs in two chief types, remittent fever and intermittent fever. For many generations it has been regarded as due to a marshy condition of the soil, associated with decaying vegetable matter, and a moderately high temperature. It is now clear that these conditions are necessary, only because they are necessary for the life of the mosquito. The well-known danger of being out of doors at night in a malarious country is explained by the nocturnal habits of the mosquito. The higher salubrity of the upper stories of houses is explained by the fact that the mosquito does not rise high from the ground; and of high-lying localities by their greater dryness. The value of the mosquito net, of smoke, and of fire as protections from malaria are due to their keeping mosquitos at a distance. The mosquito clings to the puddle or swamp where she was born, and where she will deposit her eggs. Hence the special danger of the immediate vicinity of such collections of water. Thus the prevention of malaria resolves itself chiefly into means for preventing the development of certain species of Anopheles (page [282]). The conditions necessary for the multiplication of these are (1), an atmospheric temperature from 75° to 104° F.; (2) collections of fresh or slightly brackish water; and (3) the presence in these of low forms of animal and vegetable life. We have already described the cycle of life of the plasmodium malariæ (page [282]). Man is the chief, if not the only source, from which the mosquito derives this parasite. In native communities the young children, even when apparently not ill with malaria, nearly always harbour these parasites in their blood corpuscles. Hence the importance of Europeans having their dwellings as remote as possible from native houses. Mosquitos do not travel far.

Instances of the prevalence of malaria in the absence of mosquitos are not substantiated. The outbreaks of malaria where the soil has been disturbed after long lying uncultivated, probably mean the formation of puddles favourable to the breeding of the larvæ of mosquitos.

The necessary preventive measures are classified by Manson as:

The suppression of mosquitos involves the draining or filling in of swamps and ponds, the cleansing and canalisation of sluggish streams, and the afforestation of hills to prevent floods. Cultivation of rice and other plants entailing the prolonged flooding of land should be restricted to fields remote from dwellings. Subsoil drainage is helpful. The “painting” of stagnant waters with petroleum, which should be renewed every week or two, frees water for a considerable time from the larvæ of mosquitos. Eucalyptus and other balsamic trees may help to dry up pools, &c.

The prevention of infection of mosquitos is secured by insisting on all malarial patients using mosquito nets. This prevents the access of mosquitos. At the same time patients should vigorously and persistently take quinine, which kills the malarial parasites in the blood, and thus diminishes and finally removes the danger to other persons produced by the intermediation of the mosquito.

The prevention of mosquito bites is secured by rendering the house mosquito-proof by filling in all openings by fine wire gauze, and by having mosquito curtains to all beds; also by fumigating the rooms occasionally with the dried flowers of the chrysanthemum, by strict cleanliness of rooms, and by flushing them with sunlight. The proof of the mosquito theory as to the causation of malaria has been recently supplied by two test experiments. (a) In the first, a number of mosquitos which had been fed on the blood of malarious patients were sent to London from Rome. These were allowed to bite Dr. Manson’s son, who had never previously had malaria. A few days later he had a characteristic attack of fever. Malarial parasites were found in his blood. He recovered in a week’s time after free dosage with quinine, and the parasites disappeared from his blood. He suffered from a slight relapse about a year later. (b) On a fever-haunted spot in the Roman Campagna a wooden hut was built, and Drs. Sambon and Low, and three others took up their abode here during the malarious season, the only precautions taken being the use of mosquito nets and wire screens in doors and windows. They went about the country daily, but were always home before sunset. They all remained at the end of the season free from malaria.