26 APPLIED PHYSIOLOGY 



Conversely, Graves' disease is a condition characterized 

 by an increased rate of tissue metabolism, and many 

 pathologists believe that the essential fact in its etiology 

 is an over-activity of the thyroid gland. It is interesting 

 in the light of these facts to speculate on the question 

 whether variations in the metabolism of individuals 

 may not be due to a varying degree of activity of their 

 thyroids. Is the sluggish and obese person one whose 

 thyroid is functionally rather inactive, and the alert 

 spare man one whose metabolism is constantly being 

 stimulated by an exceptionally abundant outpouring of 

 iodothyrin? Again, is the tendency to accumulate fat 

 after the middle period of life to be ascribed to a natural 

 decline of thyroid activity about that time ? It would 

 take us too far afield to consider these questions in 

 detail, but they are full of interesting suggestion to the 

 clinician. 



Of the influence, if any, of the suprarenals on general 

 metabolism we know nothing. Even assuming that 

 adrenalin is a true secretion, its action is exerted upon 

 the vascular system, and not upon the tissues at large, 

 and upon the phenomena of Addison's disease experi- 

 mental physiology has not yet thrown any clear light. 



It is commonly assumed that the reproductive glands 

 exert a marked influence upon general metabolism. 

 Physiological experiments upon this subject have yielded 

 rather discordant results, but there is a considerable 

 amount of evidence to show that castration in either 

 sex results in a diminution of oxidation, and a tendency 

 to the accumulation of fat. This tendency is well shown 

 in many women after the menopause. Whether this is 



