Normal temperature, resulting from balance of production and discharge of heat, regulated by a calorific centre in the brain. Limitations of power of regulation when body exposed to excessive cold or excessive heat. Causation and Forms of Pyrexia - Production from lesions of nervous system. Postmortem rise of temperature. Pyrexia from contamination of the blood, Fever proper; usually due to action of microbes; phenomena of cold stage, of fastigium, and of crisis. Theories of Pyrexia - The nervous and the metabolic theories. Arguments in favour of the latter. Other Phenomena of fever: cloudy swelling, increased rate of pulse and respirations, fall of blood-pressure and nervous disturbances. Post-mortem appearances in fevers.
UNDER the designations pyrexia and fever are included conditions of the body in which the constant phenomenon is an elevation of the temperature of the body. In order to understand this pathological change we must first consider the normal temperature of the body.
It is a remarkable fact that in man, as in other warm-blooded animals, the temperature of the body is maintained in all climates at a nearly constant level, there being in the healthy person merely slight daily variations. The normal temperature may be stated at about 99° Fahrenheit or 37° Centigrade: This fact implies that the production of heat in the body exactly balances the loss of heat by the body. The production of heat is by a process of combustion, and its amount will be equivalent to a certain quantity of oxygen absorbed and carbonic acid given off, just as any ordinary combustion may be expressed in these terms. •
The seat of heat production is in the living tissues; and their vital processes mostly involve combustion. The chief sources of heat, however, are the active muscles, the secreting glands, and the nervous system, but all the active tissues of the body seem to contribute.
Many facts render it apparent that heat is produced in much greater quantity in muscular contraction than in the performance of any other function. We are not only sensible of a great production of heat during muscular exertion, but actual measurement has shown that during contraction the muscles produce an increased amount of heat.
During severe muscular exertion the body temperature, as measured in the axilla or mouth, has been found elevated as much as from 0-5° to 1° Centigrade. Also, the amount of heat given off while prisoners were exercising on the treadmill has been found to be very excessive. Again, the measurement of the temperature of contracting muscles has shown that heat was being produced. The human biceps, even before contraction, has a temperature of about 1.5° to 2° C. above that of the surrounding connective tissue, this being due to the continual tonic contraction of the muscle; but during contraction the temperature rises 0.5° to 1° C. (Breschet 'and Becquerel, Macalister.) Bernard also found the blood of the muscular branch of the jugular vein increased in temperature during contraction of the muscles of the jaw. Then, also, there is the great rise of temperature occurring in tetanus, whether artificially produced in animals or occurring as a disease in man. In the former case, when tetanic spasm is produced by electric stimulation, the temperature of the body may rise 5° C. In man very high temperatures have been registered in tetanus. Wunderlich has found it as high as 44.75° C. (112.5° F.), and after death 45.4° C. (113.6° F.).
The muscular tissue of the body seems to be a constant source of heat production. The voluntary muscles are in a continuous state of tonic contraction, and the heart is constantly producing heat by its contractions. It has been calculated by Gr^hart that the heat produced by the heart is about equal to a twenty-fourth of that of the whole body.
Next to the muscles the Secreting glands seem to contribute most to the heat of the body. Ludwig found that when the submaxillary gland is stimulated the secreted saliva is warmer than the blood of the carotid, and Bernard found the blood leaving the glands warmer than that passing to them. The intestinal glands and the liver are also great sources of heat. Bernard found the blood of the portal vein 0-1° to 0.4° C. higher than that of the aorta, and the blood of the hepatic vein 0.2° to 0.4° higher than that of the portal, showing that heat is produced first in the glands of the intestine and then in the liver. The highest temperature in the body is said to be found in the liver.
The central Nervous system is also a heat producer. Observation in animals which had been artificially cooled and hibernating marmots showed that electric stimulation of the nervous system causes rise in temperature in the brain;
The temperature of the body rises slightly after the ingestion of food. This may be due to the activity of the glands concerned in assimilation, or to the oxidation of the products of digestion in the blood.
The production of heat is approximately measured by the consumption of oxygen and elimination of carbonic acid. In the case of a cold or tepid bath, more heat must be produced in order to compensate for its extraction by the unusually cold medium. Experiment shows that under these circumstances there is an increase in the absorption of oxygen and exhalation of carbonic acid. In man the experiment cannot be long continued, and it icannot be said that the results give more than an approximate indication of quantities. The carbonic acid produced may, for example, be retained to some extent in the body and so the results vitiated.
The living body is continually giving off heat in various ways, but chiefly by the skin and lungs. There is a constant radiation and evaporation from the surface of the body, while in the lungs there is a continual cooling of the respiratory surfaces by the inspired air, and a further loss of heat by the evaporation of moisture from these surfaces. The amount of heat lost will depend on the one hand on th,e extent of the cutaneous surface, its temperature, the activity of perspiration, and the temperature of the surrounding media,, and on the other hand on the depth of the respirations and the temperature of the inspired air.