A further support to the postulate that the brain-cells contribute to the production of fever by sending impulses to the muscles is found in the effect of muscular exertion, or of other forms of motor stimulation, in the presence of a fever-producing infection. Under such circumstances muscular exertion causes additional fever, and causes also added but identical changes in the brain-cells. Thyroid extract and iodin have the same effect as muscular exertion and infection in the production of fever and the production of brain-cell changes. All this evidence is a strong argument in favor of the theory that certain constituents of the brain-cells are consumed in the work performed by the brain in the production of fever.
That the stimulation of the brain-cells without gross activity of the skeletal muscles and without infection can produce heat is shown as follows:
(a) Fever is produced when animals are subjected to fear without any consequent exertion of the skeletal muscles.
(b) The temperature of the anxious friends of patients will rise while they await the outcome of an operation (Fig. 63).
(c) The temperature and pulse of patients will rise as a result of the mere anticipation of a surgical operation (Fig. 64).
(d) There are innumerable clinical observations as to the effect of emotional excitation on the temperature of patients. A rise of a degree or more is a common result of a visit from a tactless friend. There is a traditional Sunday increase of temperature in hospital wards. Now the visitor does not bring and administer more infection to the patient to cause this rise, and the rise of temperature occurs even if the patient does not make the least muscular exertion as a result of the visit. I once observed an average increase of one and one-eighth degrees of temperature in a ward of fifteen children as a result of a Fourth of July celebration.
Is the contribution of the brain to the production of heat due to the conversion of latent energy directly into heat, or does the brain produce heat principally by converting its latent energy into electricity or some similar form of transmissible energy which, through nerve connections, stimulates other organs and tissues, which in turn convert their stores of latent energy into heat?
According to Starling, when the connection between the brain and the muscles of an animal is severed by curare, by anesthetics, by the division of the cord and nerves, then the heat-producing power of the animal so modified is on a level with that of cold-blooded animals. With cold the temperature falls, with heat it rises. Such an animal has no more control over the conversion of latent energy into heat than it has over the conversion of latent energy into motion.
Electric stimulation done over a period of time causes brain-cell changes, and electric stimulation of the muscles causes a rise in temperature.
Summary of Brain-cell Studies