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 deg.  Fahrenheit, this species also became unconscious when the locally-heated brain attained a temperature of 110 deg.; or if death occurred by arrest of the respiration in the hot box at 114 deg., 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.  Anaesthetizing 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.