Regulation Of Temperature

The fact that in healthy persons the temperature remains close to a constant normal, indicates that there are arrangements in the body whereby the production and discharge of heat are regulated in their amount. These arrangements are under the control of the nervous system, which must contain a Calorific centre, located by some observers in or above the pons, and more particularly in the cortex of the cerebrum, about the middle of its lateral or external surface (Wood, Hitzig, Hale White). The regulation of temperature takes place chiefly by modifying the discharge of heat on the one hand, and its production oil the other. That is to say, the state of the skin as regards fulness of its vessels, and activity of the sweat-glands is subject to variation according as heat requires to be economized or expended. The respiratory movements are also subject to variation, according to need. Human beings, again, assist in the regulation by clothing themselves according to the requirements of the body. By these means the central nervous system, chiefly through the vaso-motor and respiratory nerves, regulates the loss of heat. The production of heat is also to some extent controlled by the nervous system. When more heat is needed the tonicity of the muscles is increased, they become harder and more braced. Shivering is a kind of exaggerated tonicity whose rationale seems generally an increased production of heat.

The limits of the power of regulation are seldom reached in healthy persons. Almost any variation in the amount of heat produced is compensated by alterations in the state of the skin and respiration. Not even the severe muscular exertion of climbing a mountain, producing, as it does, an enormous excess of heat, is able to raise the temperature of the body appreciably. It is interesting to observe, however, that violent contraction of muscles produced by morbid influences will raise the temperature. It is so in convulsions such as those occurring in epilepsy, uraemia, or tetanus.

The power of regulation is not so great against variations in the external temperature. Prolonged exposure to cold, especially when the muscles are relaxed, frequently reduces the temperature. Some very low temperatures have been observed (Macewen, Reincke, Peter) in drunkards who have lain exposed. On the other hand a high temperature in the surrounding media will sometimes raise the body temperature. If the air be dry the body can meet a considerable elevation of temperature, compensation being effected by excessive perspiration, but if the air be moist as well as hot, or if a bath be used, then the temperature will rise.

As the actions of the body involve the production of heat, if the temperature of the surrounding media be even near, without quite reaching that of the body, then a prolonged exposure will raise the latter. When a rabbit is kept in a box at a temperature above 32° C. its temperature rises, so that when the air is at 36°, the temperature of the animal has risen to 41 or 42° (Rosenthal). In guinea-pigs Cohnheim observed a similar result. Again, Stapff found during the construction of the St. Gothard tunnel that men working in damp air at about 30° C. had their temperature raised to 40° C. (104° F.).

The regulation may be rendered inefficient by some interference with the regulating apparatus. Thus, persons in a state of starvation or antenna are not in a condition to increase the production of heat so readily as others, and hence they are less able to withstand cold. Again, interference with the vaso-motor nerves may hinder the -compensation effected through them. Thus, the division of the sympathetic nerves in the neck of rabbits, by paralysing the vaso-motor nerves of the ears, produced an active congestion in these parts, which lowered the temperature two degrees C. Animals paralyzed by curare or morphia are more readily cooled than normal ones, both because the muscles are relaxed and because the cutaneous vessels are dilated. Varnishing- the bodies of rabbits (with tar, linseed oil, collodion, etc.) causes a hyperamia of the skin and thus produces a lowering of temperature which may be fatal. Similarly, extensive burns, by producing an active congestion of the skin, lead to a lowering of temperature. In both cases, if precautions are taken against cooling, the temperature is not reduced. Hence the treatment of burns by wrapping in cotton-wool.

Post-mortem rise of temperature is not infrequently observed, especially when the temperature has been above normal at the time of death. This is explained by the fact that the tissues do not all die simultaneously, and that there may be considerable heat production after the heart has ceased to contract. The cessation of the circulation in the skin will greatly reduce the loss of heat by radiation, and the internal heat 'production may temporarily counterbalance the loss. A similar explanation is given by Cohnheim of the rise of temperature in the collapse stage of cholera. Here coldness of the surface is associated with rise of internal temperature. The former is ascribed to defective circulation in the cutaneous vessels, due to the thickening of the blood which results from the loss of fluid by the bowels, which is characteristic of cholera.

There is sometimes a rise of temperature just before death in diseases of the central nervous system, as first pointed out by Wunderlich. This is sometimes associated with convulsions or spasms, but may occur without these, and is difficult of explanation.

Causation And Forms Of Pyrexia

Among the conditions in which elevation of temperature occurs, there are two distinct classes of cases, which may indeed be used as mutually illustrative of the pathology of fever, but which in the first instance must be kept rigidly apart. There are, on the one hand, cases due to disease or injury of the central nervous system, and, on the other hand, cases in which a poison of some sort is present in the blood. It is to the latter class of cases that the term Fever is usually applied, this term including other symptoms besides mere elevation of the temperature.