732 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



Very little is known concerning the function of the adrenal cortex, 

 although there is little doubt that it is elosely related with the develop- 

 ment of the sexual organs. The evidence for this is as follows: (1) in 

 cases of sexual precocity it is found that the adrenal cortex is much 

 hypertrophied ; (2) it becomes hypertrophied during pregnancy; (3) it 

 is ill developed in sexual deficiency; (4) changes occur in it during the 

 estrnal cycle in many animals; (5) after castration it is said to be hyper- 

 trophied; (6) the innermost portion of the cortex,- sometimes called the 

 boundary zone, is much hypertrophied in the human fetus, but this hyper- 

 trophy entirely disappears after the first year of extrauterine life. 



The other functions of the cortex are not as yet known, but there is very 

 strong evidence that they are of great importance to the welfare of the 

 animal. It has been suggested that the passage of blood through the 

 cortex before reaching the medulla indicates that some change which 

 is preparatory to the main change occurring in the medulla takes place 

 in the blood while it is in the cortex. This view is partly substantiated 

 by the observation that when an excised portion of cortex is incubated 

 at body temperature, a substance develops in it which has an action 

 like that of the hormone of the medulla — epinephrine. It is possible, 

 however, that this action is due to the fact that certain of the decomposition 

 products of protein develop an epinephrine-like action (see page 502). 



The Medulla 



Histologically the medulla is composed of masses of polygonal cells 

 with blood sinuses between them. The blood supply is derived from ves- 

 sels that have proceeded to the medulla through the capsule, and it is 

 extremely rich, being indeed the richest blood supply to any organ in the 

 body, greater even than that to the thyroid gland. The nerves form a 

 dense plexus, extending into and between the secretory cells. The most 

 characteristic feature of the cells composing the medulla is the presence 

 in them of granules which stain readily Avith chromic acid, and are hence 

 often called chromaffin cells. There are also some cells containing coarser 

 grannies that are soluble in water and do not stain with chrome salts. 



Embryologically the medulla is developed from the same neuroblastic 

 cells that give rise to the sympathetic nervous system. This evidence of 

 the close association between the medulla and the sympathetic nervous 

 system, we shall see to be substantiated by the results of experimental 

 investigation. 



On account of the anatomic relationships, it is impossible to study the 

 effect of excision of the cortex and medulla separately, or, indeed, of the 

 action of pure extracts prepared from either of these portions of the 



