THE ENDOCRINE SYSTEM 215 



An animal can get along without the medulla of the adrenal 

 but not without the cortex. This is shown by the fact that while 

 death follows the complete removal of the adrenal glands, death 

 does not occur if only the medulla is destroyed. Death can be 

 prevented in an animal whose adrenals have been removed if an 

 extract of the cortex is given by injection. The extract of the 

 cortex is known as cortin. Cortin has been used successfully 

 in treating Addison's disease, which is an affection of the adrenal 

 cortex. It is believed by some that the essential function of 

 cortin is the regulation and maintenance of a normal circulating 

 volume of fluid within the vascular system. In a dog whose 

 adrenals have been removed the depletion of the volume of 

 circulatory fluids seems to be due to a loss of sodium salts and 

 water. The administration of sodium salts to such an animal 

 has effects similar to those produced by cortin in restoring normal 

 salt metabolism and circulatory volume, temporarily at least. 

 Ascorbic acid, the crystalline form of vitamin C has been obtained 

 from the adrenal cortex. It is generally believed that the high 

 concentration of vitamin C in the adrenal cortex is the result of 

 storage rather than of local synthesis. 



The difference in properties of epinephrine and cortin are 

 correlated with a difference in embryonic origin of the medulla 

 and cortex. The chromaffin cells, which produce epinephrine, 

 seem to be modified sympathetic nerve cells which retain close 

 anatomical relations with the sympathetic nerves innervating the 

 medulla of the gland of the adult. Isolated masses of chromaffin 

 cells also occur in connection with sympathetic ganglia in various 

 parts of the human body. In sharks, the chromaffin tissue exists 

 in the form of numerous distinct organs, completely independent 

 of what corresponds to cortical tissue of higher forms. In the 

 frog, as already mentioned, chromaffin and cortical cells are 

 intermingled. In mammals the cortical tissue is derived from 

 what are known as mesenchyme cells, which enclose the chro- 

 maffin cells and sympathetic cells to form a single organ. 



Pancreas. — The islet cells of the pancreas produce an internal 

 secretion that is also important in the metabolism of sugar. 

 Complete removal of the pancreas in a dog produces glycosuria, 

 and an increased production of urine and of urea, accompanied by 

 pronounced thirst and hunger. Acetone is also present in the 

 urine. These symptoms are the same as those shown by human 



