THE KINETIC SYSTEM 197 



ment by complete rest and the exclusion of all activat- 

 ing stimuli may, singly or in combination, cause a 

 reversion of the picture and restoration to the normal 

 state. And finally, where there is thyroid deficiency, 

 there is the antithesis of this extremely excitable con- 

 dition a reptilian sluggishness. Apparently, there- 

 fore, by the administration of a diminished, a nor- 

 mal or an excessive amount of thyroid secretion, we 

 can at will produce an adynamic, a normal or an 

 excessively dynamic state of the organism. Through 

 thyroid influence the brain threshold is lowered and 

 life becomes exquisite ; without its influence the brain 

 is an inert mass. 



The influence upon energy conversion of hyperactiv- 

 ity of the brain, the muscles or the adrenals is no less 

 significant than the effects of hyperactivity of the thy- 

 roid. We have noted that brain activity alone can 

 produce fever, and that both voluntary and electrical 

 stimulation of the muscles cause increased tempera- 

 ture ; that is, increased energy conversion. In a Mara- 

 thon race the runner's temperature may rise two de- 

 grees, and at the end of a heat, the temperature of a 

 racing horse may show an increase of four degrees. 

 In both instances the conversion of energy is above 

 normal. After a high fever the muscles show a marked 

 impairment of their power to produce motion, suggest- 

 ing that during the fever they have been involved to 

 an abnormal degree in the transformation of energy. 



We have already presented ample evidence of the 

 effect of an increased activity of the adrenals upon 

 energy transformation. The administration of large 

 doses of adrenin of itself produces fever. We have 



