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atized body by the nervous system。 We have seen that adrenalin causes activation of the body connected with its brain by the nervous system； and histologic changes in the brain acted on directly by the adrenalin； but we found no notable brain…cell changes in the other brain through which the products of metabolism have circulated。
In the foregoing we find direct evidence that the products of metabolism are not the principal cause of the brain…cell changes。 We shall now present evidence to show that for the most part the brain…cell changes are 〃work〃 changes。 What work？ We postulate that it is the work by which the energy stored in the brain…cells is converted into electricity or some other form of transmissible energy which then activates certain glands and muscles； thus converting latent energy into beat and motion。 It has chanced that certain other studies have given an analogous and convincing proof of this postulate。 In the electric fish a part of the muscular mechanism is replaced by a specialized structure for storing and discharging electricity。 We found 〃work〃 changes in the brain…cells of electric fish after all their electricity had been rapidly discharged （Fig。 61）。 We found further that electric fish could not discharge their electricity when under anesthesia； and clinically we know that under deep morphin narcosis； and under anesthesia； the production both of heat and of muscular action is hindered。 The action of morphin in lessening fever production is probably the result of its depressing influence on the brain…cells； because of which a diminished amount of their potential energy is converted into electricity and a diminished electric discharge from the brain to the muscles should diminish heat production proportionally。 We found by experiment that under deep morphinization brain…cell changes due to toxins could be largely prevented （Fig。 62）； in human patients deep morphinization diminishes the production of muscular action and of fever and conserves life when it is threatened by acute infections。 The contribution of the brain…cells to the production of heat is either the result of the direct conversion of their stored energy into heat； or of the conversion of their latent energy into electricity or a similar force； which in turn causes certain glands and muscles to convert latent energy into heat。
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
In our crossed circulation experiments we found that neither waste products nor metabolic poisons could be considered the principal cause of the brain…cell changes。 We found that in the production both of muscular action and of fever there were brain…cell changes which showed a quantita…tive relation to the temperature changes or to the muscular work done。 We observed that under deep morphinization the febrile response or the muscular work done was either diminished or eliminated and that the brain…cell changes were correspondingly diminished or eliminated。 We found also that brain…cell changes and muscular work followed electric stimulation alone。 I conclude； therefore； that the brain…cell changes are work changes。
We shall next consider other organs of the kinetic system in their relation to muscular activity； to emotion； to consciousness； to sleep； to hibernation； and to heat production。
The Adrenals
In our extensive study of the brain in its relation to the production of energy and the consequent exhaustion caused by fear and rage； by the injection of foreign proteins； of bacterial toxins； and of strychnin； by anaphylaxis； by the injection of thyroid extract； of adrenalin； and of morphin； we found that； with the exception of morphin； each of these agents produced identical changes in the brain…cells。 As we believed that the adrenals were intimately associated with the brain in its activities； we concluded that the adrenals also must have been affected by each of these agents。 To prove this relation； we administered the above…mentioned stimuli to animals and studied their effects upon the adrenals by functional； histologic； and surgical methods； the functional tests being made by Cannon's method。
Functional Study of the Adrenals。Our method of applying the Cannon test for adrenalin was as follows： （_a_） The blood of the animals was tested before the application of the stimulus。 If this te