by some to be due to the absorption of this external heat. This, however, is certainly not true, as is shown, to omit less decisive proofs, by the experiments of Naunyn and Quincke, who exposed animals for two days to a temperature of 90°, and at the end of that time, their bodily temperature not having risen, cut their spinal cords, after which intense fever was developed in a few hours with out any change of atmosphere.
Section of the cord must therefore give rise to an increased chemical movement and heat-production in the body. As already stated, this section affects very greatly the circulation, but the fever is independent of such action. The upper end of the medulla oblongata is continuous with a nervous mass which joins the two brain hemispheres together, and hence is known as the pons or bridge. If, instead of cutting the spinal cord, we separate the medulla oblongata from the pons, an immediate rise of temperature occurs, and continues until death, whether the operation be performed in a cold or heated room.[1]
Cutting the medulla at its junction with the pons causes, then, an immediate and direct elevation of temperature, without disturbance of the circulation. What can this mean? Evidently, only one thing—namely, that by the division of the medulla there has been separated from the general tissues of the body a repressive force—a something which normally controls their chemical activity and the production in them of animal heat.
The existence of nerves whose function is to repress action is no new discovery in physiology. Readers of Lippincott's Magazine may remember my description of the pneumogastrics or brake-nerves of the heart, whose duty it is to control the action of that viscus. Nerves which repress or inhibit action are spoken of in modern physiology as inhibitory. The experiments which have been adduced prove that there are nerveswhose function it is to control the general vital chemical actions, and that the governing centre of these nerves is situated above the medulla oblongata. To this centre, whose exact location is unknown, the name of the inhibitory heat-centre has been given.
The way in which galvanization of a nerve, violent injuries and excessive pain depress the temperature, independently of any action upon the circulation, is now evident. An impulse simply passes up the irritated or wounded nerve, and excites this inhibitory heat-centre to increased action, and the temperature falls because the chemical movements of the body are repressed.
The method in which fever is produced also becomes very evident when once the existence of an inhibitory heat-centre has been established. Any poison having the power to depress, and finally paralyze, this centre must, if it find entrance to the blood, produce fever. If the poison, from its inherent properties, or from its being in very small quantity, only diminishes the activity of the inhibitory heat-centre, the controlling influence is not entirely removed from the chemical movements of the body, and only slight fever results; but if the poison actually paralyzes the inhibitory nerves, a very great rise of temperature must rapidly follow the complete removal of the brake-power.
As an illustration we may consider the intense rheumatic fever, or the so-called "cerebral rheumatism," such as affected the young Irishman whose case has been narrated in the present article. With out any apparent reason the poison of rheumatism habitually attacks one joint on one day, and another joint on an other day, and with as little apparent reason it occasionally falls of a sudden upon the inhibitory heat-centre, and actually paralyzes it. In a few minutes intense fever is developed, and the bodily temperature rapidly approaches nearer and nearer that line on the other side of which is death.
In many cases of fever, however, there is no poison in the blood: thus, the local irritation of a boil or other inflammation
- ↑ I have several times performed this experiment, and by a method, the explanation of which would require a separate article, have proved that the vaso-motor centre, as well as the respiratory centre, is situated in the medulla oblongata, and that paralysis of neither respiration nor of the vaso-motor nerves follows the operation.
