shown to be quite practicable, in temperate climates at least, by the drainage of marsh lands and the filling or oiling or stocking with fish of the smaller mosquito breeding pools.
The third mode of infection, by contact, the more or less direct transfer from person to person, is by far the most important factor in the spread of communicable disease in temperate climates. Malaria is our only important insect-borne disease. Typhoid may sometimes be spread by flies and often by water or milk—diphtheria and scarlet fever and tuberculosis and tonsilitis, sometimes by milk. On the other hand, diphtheria and scarlet fever and tuberculosis and, in cities with good water supplies, even typhoid fever, are all more commonly transmitted by contact than in any other way; and contact is practically the sole cause of smallpox, measles, epidemic cerebro-spinal meningitis, influenza, common colds and the venereal diseases. It is in the nose and throat, or on the hands of a human being, that disease germs generally enter our homes, and this sort of infection is obviously most difficult to detect and control. The child infected with measles yet showing no symptoms but those of a simple cold in the head, the person with a "little sore throat" which is the beginning of an attack of diphtheria, the friend who comes in with uncleansed hands to visit the cook after nursing a sister just put to bed with typhoid fever, the visitor who is "practically all over" whooping cough; these are the dangers against which it is so difficult to guard.
The term contact is a broad one and covers a wide variety of ways in which infective material may be spread from person to person. There are all degrees between such direct contact, as occurs when one person coughs over another person's hand, and the more remote infection carried by some object which has been recently handled; no absolute line can be drawn between what may be infective and what may not. If I handle an apple with infected hands and hand it to you and you eat it, we are dealing with clear and obvious contact. If I put it on the table and you find it and eat it an hour later, the connection is almost as direct, although some of the germs will probably be dead. If twenty-four elapses, most of the infection will be gone; if two weeks, practically all of it. Objects which are supposed to remain infective after a considerable period of time, are called fomites, and fomites' infection was once held to be an important factor in the spread of disease. The recent discoveries in regard to the rapid mortality of disease germs outside the body have made it clear, however, that objects are only dangerous when they have recently been exposed to fresh infection. The old stories of toys put away in a closet and causing scarlet fever after a lapse of several years are quite apocryphal. Such mysterious cases as were once explained in this fashion are now more reasonably attributed, and very often definitely traced, to direct contact with an unrecognized carrier case.
