We do not know the cause of yellow fever despite the claims of Sanarelli that he has isolated the specific micro-organism. Recently American physicians discovered that it is transmitted from man to man by mosquitoes that belong {186} to the genus Stegomyia, the Stegomyia Fasciata especially. If a yellow fever patient is put into a room in which the mosquitoes have been killed and the doors and windows are screened, he is as harmless, as far as contagion is concerned, as a man with a broken leg. The disease is not spread by fomites. Malaria is caused by plasmodia, which are protozoa, not bacteria, and it is carried from case to case by mosquitoes of the genus Anopheles. So certain are we that this is the mode of infection that the expression "no anopheles, no malaria" has almost become a medical axiom. A bite from an anopheles mosquito does not cause malaria unless the particular mosquito has previously bitten a malaria patient. The stegomyia flies and bites in the early afternoon and again at night, the anopheles flies and bites after sunset. In visiting a case of pernicious malaria or one of yellow fever avoid the bites of mosquitoes by gloves and a piece of netting, and there is no danger whatever. The stegomyia mosquitoes are tropical and subtropical, but they can live as far north as Philadelphia and even farther. The anopheles is especially a northern insect. The ordinary culex mosquito, when it alights upon a wall, stands with its body parallel to the wall, as a house-fly stands; the anopheles mosquito stands with its tail raised from the wall at an angle. A mosquito lays its eggs in any pool of still water, and the "wrigglers" seen in an open rain-barrel are the larvae from these eggs. The larvae come to the surface of the water to get air, and they may be smothered with petroleum; but the only effective way to get rid of malaria and yellow fever is to drain or fill pools of water and marshes. Mosquitoes will breed also in the small still bights along the edges of running streams; in old tomato cans that contain rain water; in any still water, fresh or salt. AUSTIN ÓMALLEY. {187} XV INFECTIOUS DISEASES IN SCHOOLS Cases of diphtheria, scarlet fever, measles, and even smallpox are not seldom found in schoolrooms, and much anxiety can be averted and the spread of infection can be wholly or in great part averted by a knowledge of disinfection. The laity will often follow the advice of a priest in matters of hygiene when they are inclined to rebel against the regulations of health departments and the suggestions of physicians, therefore a preliminary explanation of methods for the prevention of infection in the family will be advantageous; prevention in the family is also intimately connected with prevention in the school. Methods useful in the family are useful also in convents and boarding-schools.