Infection

Infection. Certain diseases are transmissible from person to person, the healthy person being affected through the medium of some infective material or contagium given off from the sick. Such diseases are said to be infectious or contagious (the latter term being sometimes limited to cases in which the disease is transmitted by direct contact). The development of the germ theory has led to the notion that the essence of infection is a living organism, and in some instances it appears clear that such organisms have been demonstrated to exist, and the group of organisms known as fission fungi, popularly known as bacteria, has had particular attention directed to it in this connection. The means by which infection is conveyed are various; thus, the sputum of phthisical patients is probably largely responsible for the transmission of consumption. The scales of epidermis from the desquamating skin are supposed to be a medium of infection in scarlet fever. The breath is probably infective in measles, whooping cough, and other diseases; the mucus from the throat in diphtheria; and there can be little doubt that the excreta from the bowels are the means of conveying infection in cholera and typhoid fever. In some diseases infection is produced by inoculation only, e.g. vaccinia, and this is the common means of transmission in other diseases, such as anthrax. When infected material is conveyed into the body of a susceptible person, there ensues a period of incubation of variable length in different diseases, from a few hours or days in the case of diphtheria to as much as three weeks in mumps; in other diseases a yet longer incubative period obtains, and in cases of hydrophobia an incubation period extending even to months is said to occur.

The incubative period is succeeded by a period of invasion, usually accompanied by symptoms of fever; and in the case of the eruptive fevers or cxanthemata, after a time fairly constant in the case of each particular disease, the characteristic rash appears. During the course of the illness the contagium undergoes development within the body, but after a time, unless death occurs, this development comes to an end, and the contagium is destroyed. It is usual to consider that a patient remains infectious for about three weeks after an attack of measles or diphtheria, and for six weeks after scarlet fever; In some cases, however, these periods of contagiousness must be extended, as, for example, in cases of scarlet fever where desquamation is protracted. The Infectious Diseases Notification Act of 1889 is now in force in most parts of the country, and requires the notification of small-pox, cholera, diphtheria, membranous croup," erysipelas, scarlet fever, typhus, enteric (or typhoid fever), continued fever, relapsing fever, and puerperal fever. Power is given to a sanitary authority, with the sanction of the Local Government Board, to include any other infectious disease within the scope of the Act.