Fever (Lat. febris, lit. 'a trembling'), a diseased condition of the system, of which the most important characteristic is a rise in the temperature of the body. Fever should be regarded as fundamentally a symptom or group of symptoms, rather than as a disease or class of diseases, for the causes leading to it are extremely various; but it is a symptom of such importance that the term is used, with a distinguishing epithet, as the name of a number of diseases. The increase of the temperature of the body requires to be estimated according to the state of the internal parts rather than the external; the surface of the body, and particularly the extremities, being not unfrequently cold rather than warm. In many cases where fever occurs, most characteristically in Ague (q.v.), it may be considered as passing through three distinct stages more or less marked: (1) the cold or shivering stage; (2) the hot stage; (3) the sweating stage. This description, however, requires to be qualified by the remark that, even in the cold stage of fevers, it is now well ascertained that the blood and the internal organs have an elevated temperature, as estimated by the thermometer introduced into the cavities of the body. In the cold stage of fever, accordingly, and even in the most violent ague, when the teeth are chattering with cold, and the whole surface is pale and clammy, the state of the system is well expressed by the maxim of Virchow, to the effect that 'the outer parts freeze while the inner burn.' The increase of temperature is very various in different diseases and at different times in the same case. When it is over 104° F. it may be regarded as 'high'; when over 106° it is often called hyperpyrexia; and when it exceeds 107° for more than an hour or two a fatal issue is almost certain.
Elevation of temperature, though perhaps the most important, is by no means the only indication of the feverish state. It is often ushered in by a chill, or a distinct shivering, or rigor, as it is technically called; this leads through the cold stage to the hot, which usually follows pretty rapidly, and is attended by all the febrile phenomena in their highest degree. The pulse, and usually the breathing, are quickened; the appetite is lost or impaired, and the tongue furred; there is thirst, often excessive; headache and pains in the back and limbs are often present, with restlessness and general uneasiness; there is great weakness of the muscular system; all the secretions are disordered, the urine in particular being scanty, high-coloured, and loaded with sediment; when the fever is severe, delirium often comes on, especially at night. If the feverish state continue, rapid wasting takes place, especially affecting the fat and the muscles. If the case take a favourable turn, the feverish state terminates either gradually, by lysis, as in typhoid fever, or suddenly, by erisis, as in typhus fever and acute inflammation of the lungs. In the latter case there is often what is called a 'critical discharge' from skin, kidneys, or bowels. (For the features of special feverish diseases, see under their respective titles.)
The cause of the increased temperature in fever is not yet fully understood. Increased oxidation takes place in the body in almost all cases where fever is present, and must be associated with increased evolution of heat; but calculation seems to show that this is not sufficient to account in many cases for the high temperature maintained. Whether the other factors concerned depend upon obscure chemical changes in the body, or upon some peculiar disorder of the nervous system, is at present only a subject of inquiry and speculation.
Diseases in which fever occurs are separated pretty naturally into two great groups: in one of these the fever is the greatly predominating fact, and determines the specific character of the disease, the local disease (if present) being quite subordinate, and usually secondary in point of time; in the other the opposite order prevails, and the fever is obviously secondary. Hence the distinction embodied in medical language between idiopathic (i.e. 'self-originating,' 'spontaneous') and symptomatic or secondary fevers. The idiopathic fevers are distinguished with reference to their mode of diffusion, as Epidemic (q.v.) and Endemic (q.v.); or with reference to their supposed cause, as contagious, infectious, malarious, &c.; or with reference to their incidental symptoms and their peculiarities of course and termination (the presumed specific phenomena attracting, of course, particular attention), as eruptive (see EXANTHEMATA) or non-eruptive, malignant, &c. See also DISEASES (CLASSIFICATION OF).
Among these distinctions, based upon the course of the fever, one demands particular notice, as involving an important law of febrile diseases generally, and of a large class of fevers of warm climates in particular. Periodic increase and diminution, or paroxysms of longer or shorter duration, with intervals of more or less perfect relief from all the symptoms, are characteristic of most diseases of this kind, but especially of those arising from malaria—i.e. emanations from the soil, educed under the influence of solar heat. The duration of the paroxysms and of the intervals, the complete intermission, or more partial remission, of symptoms, become in such cases the characteristic facts that mark the type, as it is called, of the fever, which is accordingly distinguished as intermittent or remittent, and, according to the length of the periods, tertian, quartan, quotidian, &c. See AGUE.
Symptomatic or secondary fever occurs in a large number of diseases. Indeed, there is no condition which rules so large a part of the physician's duty, whether in the way of distinguishing diseases or of curing them, as this constitutional state. It is specially associated with acute or sub-acute inflammations of the various organs and tissues of the body. Among the diseases where it is usually most marked some of the most important are acute rheumatism, or rheumatic fever; acute abscess; meningitis, often called brain fever; acute pneumonia, or inflammation of the lungs; peritonitis.
Hectic is only distinguished from other forms of fever by the comparative mildness of its symptoms, and its slow and insidious progress. It is specially characteristic of Consumption (q.v.) and allied diseases, and of chronic forms of blood-poisoning.
The treatment of the feverish state depends so much on the cause which produces it that it can hardly be profitably treated in a general way. Some remarks, however, on the methods in use for reducing the temperature of the body may not be out of place. In very many cases of fever no such treatment is necessary; but when the temperature is so high, or so long above the normal, as to be in itself a source of danger to the patient, special means must be adopted for its reduction. Quinine has long been in use for this purpose in many diseases besides ague and other malarial fevers, in which it is the remedy par excellence. But within the last few years several new drugs have been brought into use, which have the property of reducing feverish temperature in most cases, and appear to be of great value. Of these antipyrin and antifebrin, both derivatives of coal-tar, have found most favour. Ice-bags, or coils of metal tubing through which cold water is kept flowing, are sometimes applied to the surface of the body, particularly to the neighbourhood of an organ on inflammation of which the fever depends. But the most powerful and certain of all methods, the only one hitherto found effectual in certain forms of 'hyperpyrexia,' is the use of a cold wet pack, or a bath at a temperature below that of the body. Such measures, it need hardly be said, require much caution and judgment in their application, but they have been found of great value in various forms of disease.