If a small animal, such as a dog, cat or rabbit, be placed in a chamber heated by means of the sun's rays falling upon a slanting glass roof or by some artificial method to a temperature of considerably over one hundred degrees, a very constant series of phenomena is developed. The breathing becomes hurried and the pulse greatly quickened, whilst the restless movements of the body indicate nervous distress. After a time, if the exposure be continued, the symptoms are intensified, and restlessness passes into the weakness of partial paralysis; then suddenly or gradually, with or without convulsions, stupor sets in, deepening into coma, and death from arrested respiration is the final result. If the temperature of the animal be tested from time to time during the exposure, it will be found to rise steadily, and the severity of the symptoms will be directly, and in any one species constantly, proportional to the intensity of the bodily heat.
The nervous system of man apparently resists the action of heat, but in reality it does not do so. Man, it is true, is the only animal that can thrive almost equally amidst arctic snows and in tropical jungles. This is not, however, because his nervous system lacks sensitiveness, but because he has the power of heating or cooling his body in such a manner that its temperature is comparatively unaffected by that of the surrounding air. Man might be well defined as the naked sweating animal. In the north he strips the bear and the fox of their coat to keep him warm; in the south his own skin acts as a refrigerator. The dog has a few sweat-glands about the mouth—man has two millions densely covering his body. In the horse exposed to heat the hair soon becomes wet and matted, interfering very greatly with evaporation; in man the bare skin offers an excellent surface, from which the perspiration passes off almost as fast as formed. Evaporation, conversion of a liquid into a vapor, means a steady conversion of sensible heat into what was formerly called latent heat, but what we now know to be repulsive force: the heat-energy of the body is lost in driving the particles of sweat asunder in the form of vapor.
It is possible, however, to have a temperature which even a Hindoo cannot resist. When a man is exposed to such a heat his bodily temperature rises, and as it rises the symptoms of fever develop precisely as they do in the lower animals—sometimes slowly, sometimes suddenly—with disturbances of the respiration, circulation and innervation precisely similar to those already noticed as occurring in the dog, the cat and the rabbit. Sunstroke, or thermic fever, is generally believed to be instantaneous in its onset, but the wide experience of the English in India has shown that whilst in some cases it is thus sudden in its development, in others it is a slow process, and probably in almost all cases close observation would have revealed the existence of premonitions.
External heat, by producing an internal rise of temperature, may thus cause all the phenomena of fever. Of these phenomena the most prominent is disturbance of the nervous system and of the circulation. In order to determine whether the heat itself directly causes the nervous disturbance, or whether it produces it indirectly by causing changes in the blood, I applied caloric directly to the brains of animals. This was done by fitting a hog's bladder like a bonnet over the head and allowing hot water to run through it. It was found that stupor, coma, convulsions, and finally death from arrest of the respiration, were produced, sometimes gradually, sometimes suddenly, precisely as in the case of exposure of the animal in a hot chamber. Moreover, on opening the skull and plunging a thermometer into the cerebrum immediately after death or the supervention of unconsciousness, it was found that these phenomena were developed at the same brain-temperature when the heat was locally applied as when the animal was exposed in the hot box. Thus, if any given species in the hot box became unconscious when the temperature reached 110° Fahrenheit, this species also became unconscious when the locally-heated brain attained a temperature of 110°; or if death occurred by arrest of the respiration in the hot box at 114°, so did it when the locally-heated brain reached that point.
Dr. Lauder Brunton of England has performed a series of experiments upon the circulation parallel to those just narrated. Anæsthetizing animals and exposing the heart, he has found that the action of that organ is accelerated and weakened by the local application of heat, precisely as occurs in fever.
In order to test the effect of the withdrawal of heat, I have taken a rabbit out of the hot chamber, in which it lay upon its side totally unconscious, and plunged it into a bucket of cold water. The temperature of the water rose rapidly, whilst that of the rabbit fell even more rapidly. As soon as the bodily heat approached its normal intensity consciousness returned, and in a few moments the animal, which had just before been at the point of death, was running about the grass.
Some months since I had an opportunity of repeating this experiment upon a human being.
In acute inflammatory rheumatism it sometimes happens that the swelling and pain of the joints suddenly disappear, and the patient becomes comatose or wildly delirious. It has been customary to explain these symptoms as the result of the rheumatism leaving the joints and attacking the brain. Evidently, this being the case, the proper thing to do was to irritate the joints so as to draw the rheumatism back to them. This method was formerly practiced, and the almost invariable result was death in a few hours.
In most if not all of these frightful cases of sudden accession of severe nervous symptoms in rheumatism the temperature will be found, on testing it, to be exceedingly high—108°, 109° or even 110° Fahrenheit. If the views advocated in this paper be correct, it is not the rheumatism, but the intense bodily heat, which causes the severe symptoms, and finally death. The joints lose their sensitiveness, not because the disease has left them, but because the heat so overpowers the brain that it has lost its power of perception: the patient's leg might be cut off without his feeling it. In such a case the proper treatment is to take away the heat by plunging the patient into a cold bath. But can there be anything more shocking to the universal belief and prejudices than to put a patient dying of acute rheumatism into an almost ice-cold bath?
Last spring there was in my ward in the Philadelphia Hospital a stout young Irishman who had passed through an acute attack of inflammatory rheumatism, and was suffering from a sharp relapse. Entering the ward one day, I saw at once that the man was unconscious, and turning to the resident physician asked, "What is the matter with James?" "Nothing," was the reply: "I saw him an hour and a half ago, and he was doing very well, except that the fever was very high." "He is dying now, at any rate," was my rejoinder. On going to the bedside the patient was found perfectly unconscious, the skin dry and intensely hot, the affected joints pale and devoid of sensibility, the breathing irregular and jerking, the pulse 170 and scarcely perceptible, every muscle relaxed as in death, every power of perception abolished. A thermometer placed in the armpit registered 108-4/5° Fahrenheit.