Increase Of Temperature In Inflammation

Calor is one of the cardinal signs of inflammation, and a feeling of heat is usually experienced when external parts are the seat of acute inflammation. In regard to internal parts, their nerves are not capable of conveying impressions of differences of temperature; a hot substance swallowed gives a sensation of pain. Many experiments have been made with a view to determining whether a part which is in a state of acute inflammation is the seat of increased production of heat.

There is no doubt that the temperature of external parts is increased in inflammation. John Hunter determined this by actual observation. He had a case of hydrocele to deal with, and undertook its treatment by the old operation of laying open the sac and inserting lint dipped in an irritating salve with a view to producing inflammation. At the time of the operation he found that the temperature in the tunica vaginalis was 92°, but next day, inflammation having been induced, the temperature had risen to 98 3/4°. The question here arises whether this increase of temperature is due to an actual production of heat in the inflamed part, or to an increased supply of .hot blood, due to dilatation of the arteries.

That there is a greatly increased supply of blood to inflamed external parts has been proved by experiment and observation. Cohnheim found that in a recent inflammation produced by scalding the foreleg of a dog in hot water, or by painting with croton oil, the amouut of blood issuing from a cannula inserted into a vein was greatly increased, sometimes reaching nearly double that issuing from a corresponding vein on the other side. It may even be as great as when the arteries have been relaxed in a limb by dividing the axillary plexus of nerves. This extreme degree of difference may not continue long, but even for some days it is frequently very considerable.

It is an every-day observation of surgeons that an incision in an inflamed part is accompanied by a much greater escape of blood than in a normal part, and if an artery be incised it spouts more blood and to a greater distance than a similar artery in a non-inflamed part. It is similar with the veins; Lawrence performed venesection in both arms in a person who had an acute inflammation of one hand, and he found that the blood flowed two or three times more rapidly from the vein on the side affected. The relaxation of the arteries in acute inflammation evidently produces a determination of blood which extends beyond the immediate focus of the inflammation, and is not counterbalanced by the retardation.

John Hunter, having determined the great increase in temperature above referred to, yet came to the conclusion that it was due alone to the determination of blood, for he found that the temperature of an inflamed external part never exceeded or even quite reached that of a normal internal part, or, in other words, of the blood in internal organs. Since Hunter's time, Simon has asserted that there is some development of heat in inflamed parts. His experiments seemed to show that the arterial blood passing to an inflamed external part is not so warm as the focus of inflammation, and that the venous blood returning from the part is warmer than the arterial blood, although not so warm as the focus of inflammation. But the experiments of Jacobsen, made with more exact instruments, entirely confirm the views of Hunter. It appears that the most intense inflammations of the skin or of muscles never cause an elevation of temperature sufficient to reach that of the rectum, vagina, or abdomen, the difference being generally 1° to 2° C. Again, in inflammations induced in internal parts, as the peritoneum or the pleura, the temperature was never raised to that of the blood in the left ventricle, being always from .2° to .5° C. under it. This means that in these parts, where the temperature is already near that of the blood in the left ventricle of the heart, inflammation, leading to an increased supply of blood of a similar temperature, causes virtually no elevation above the normal heat. Again, Cohnheim has found that, when in one fore-paw of a dog a state of acute inflammation is induced, while in the other active hypersemia is produced by dividing the axillary plexus of nerves, the temperature in the inflamed foot is always slightly less than that in the other. We may safely infer, then, that in inflammation there is no local production of heat.

Fever often accompanies inflammation, but it only does so when the blood is affected. This may happen in one of two ways. The agent which caused the inflammation may be primarily in the blood, and it may produce both the general manifestations of fever and the local manifestations of inflammation. This applies to many infective agents. On the other hand, a local inflammation may give rise to products whose absorption into the blood will cause fever. (See under Fever).