INTERNAL SECRETIONS 



387 



The removal of the thyroid usually leads to a train of 

 symptoms which varies somewhat in different animals, but is 

 essentially the same in nearly all. The connective tissues 

 tend to revert to the embryonic conditions, and the amount 

 of mucin increases. The temperature falls, muscular tremors 

 appear, and in dogs these may go on to convulsions. They 

 do not disappear on removing the cortex cerebri, but are 

 stopped by section of the nerves to the muscles, and 

 thus appear to be spinal in origin. The function of the 



TV, 



FIG. 152. Section through part of the Thyroid (Th.) and a Parathyroid (P.) 

 of a mammal. 



higher nervous system becomes sluggish, and the animal 

 usually dies. By administering the substance of the 

 thyroid, or by giving extracts of the thyroid, most of these 

 symptoms may be delayed or prevented. When thyroid 

 gland or extract is given to healthy animals in moderate 

 doses it causes an increased metabolism of both fats and 

 proteids, and may thus induce emaciation. It would appear 

 as if one function of the organ is to produce an internal 

 secretion, which regulates the rate of the metabolic processes 

 in the body by increasing them when such an increase is 

 desirable. It seems also to act slightly on the arterioles as a 



