Fever (Lat. febris, probably a transposition for ferbis, from fervere, to be hot), or Pyrexia (Gr. , fromto be feverish, derived from πvp, fire), a morbid state characterized especially, as the names denote, by an increase of the temperature of the body, generally together with acceleration of the circulation, loss of appetite, thirst, muscular debility, mental weakness, lassitude, and derangement of the functions of most of the important organs of the body. The significance of the term fever has been enhanced of late by the use of the thermometer placed either in the armpit or within some one of the outlets of the body. The thermometer shows morbid increase of the heat of the body in some cases when this is not apparent to the hand placed on the skin, and when the patient may have a sensation of coldness. During the so-called cold stage of an intermittent fever, the thermometer shows the heat of the body to be moderately raised. Fever may be said to exist whenever the heat of the body is raised above the maximum of health, namely, about 99° F. Fever is distinguished as symptomatic when it is dependent upon a local inflammation; and it is said to be idiopathic, or essential, whenever it cannot be attributed to any local cause.
Asymptomatic fever, as implied in the name, is only a symptom of disease; it does not constitute per se the disease; but an idiopathic or essential fever is reckoned as a disease. In the classification of diseases there are numerous fevers, which will be separately considered under the title Fevers, excepting measles, smallpox, plague, and a few others, which are treated under their own names. In both symptomatic and idiopathic fever the increase of temperature affords not only evidence of the existence of the febrile state, but a criterion of its intensity. The fever is intense in proportion to the increase of the heat of the body, as determined by the thermometer. The range of the morbid rise is from 99° to 110°. Moreover, the temperature both in symptomatic fever and in the fevers is a criterion of the immediate danger to life. A temperature above 105°, if persisting, always denotes great gravity, and death is imminent if the temperature remains for any length of time above that point. The increase of heat is in part due to a morbid activity in the molecular changes incident to disintegration of tissue, but our existing knowledge does not enable the pathologist to give a full explanation of the rationale of fever.
At present it is an unsettled pathological question to what extent the increase of heat is causative of the various morbid phenomena which are presented in connection with symptomatic and essential fever. This question is important as bearing on the employment of drugs and other measures of treatment with a view to diminish the heat of the body. There are certain remedies which from their effect upon temperature are called antipyretics; such are quinia in full doses, digitalis, veratrum viri-de, etc. The most potent measure for diminishing temperature, however, is the employment of water externally, either in the form of the shower or plunge bath, the douche, the wet sheet, or by sponging the surface of the body. Drinking freely of cold water also has this effect. Antipyretic treatment has recently entered more largely into medical practice than formerly, from more attention having been given to the study of animal heat in different diseases by means of the thermometer.