152 HUMAN PHYSIOLOGY 



of this abundance of nerve elements, the suprarenal capsules 

 have been regarded as nervous organs for the inhibition of 

 peristaltic movements of the intestine. 



As extirpation of the suprarenal capsules results in a gen- 

 eral paralysis and finally death, they must be regarded as 

 vital organs. The injection of an aqueous extract of supra- 

 renal capsule is said to remove the effects of extirpation. 

 This aqueous extract contains two substances, whose chemi- 

 cal nature is not yet known. Of these the one causes a 

 considerable increase in blood pressure, while the other can 

 decrease the pressure but works more feebly than the first. 

 This increase in blood pressure caused by the first-mentioned 

 substance is due to a general contraction of the small 

 arteries. The anatomical part upon which this substance 

 acts lies in the walls of the blood vessel itself. It paralyzes 

 the central nervous system. It stimulates not only the 

 muscles of the blood vessels but also the skeletal muscles ; 

 hence its function seems to be to increase the tonus of the 

 muscles, both of the skeletal and of the blood vessels. 



Concerning the manner in which the second substance 

 acts nothing certain has yet been determined. 



Pathological changes in the suprarenal capsules are followed 

 by an abnormal coloring, bronzing, of the skin (which is also said 

 to follow the extirpation of the suprarenal capsule). This is called 

 Addison's disease. 



The active substances of the suprarenal capsule extract are 

 rendered inert by passing them through the liver. 



III. The liver. Besides functioning in the 



(1) Secretion of bile (see page 99), 



(2) formation of glycogen (see page 146), and 



(3) breaking up and formation of red blood corpuscles 



(pages 54 and 100), 



the liver also has the important function of 



(4) changing the ammonia salts, produced by proteid 



metabolism, into urea (in mammals) or into uric 

 acid (in birds and reptiles). (See pages 45 and 



47.) 



