THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 731 



and by observing the pathological changes in the various endocrine organs 

 in diseased conditions. Embryological and histological studies are also of 

 the greatest importance. A difficulty in investigating the function of 

 an endocrine organ lies in the fact that the secretion of no one gland 

 acts independently of those from other glands. On the contrary, there is 

 undoubtedly a close association of function, so that we can not tell 

 whether a change of function observed after removal of some gland or 

 administration of some extract is a direct consequence of the experi- 

 mental procedure, or is induced by some secondary effect developed on 

 another endocrine organ. It will no doubt take many years before suf- 

 ficient data have been collected to enable us definitely to state what the 

 particular function of each endocrine organ may be. Since most progress 

 has been made in connection with the adrenal gland, it will be advan- 

 tageous to consider the functions of this gland first. 



ADRENAL GLAND 



In mammals the adrenal gland is composed of two parts, the cortex and 

 the medulla. In other groups of animals however, these two are more or 

 less separate, being completely so in fishes. This not infrequent separa- 

 tion of cortex and medulla suggests a different function for the two 

 structures. Experimental investigation supports this view. 



The Cortex 



The cortex on microscopic examination is seen to be composed of rows 

 of epithelial cells arranged more or less in columns except at the 

 periphery, where they form glomerular masses, and next the medulla, 

 where they assume a reticular formation. The cells of the greater part 

 of the cortex, unlike those of the medulla, contain no granules with 

 special staining qualities, but they do contain particles which are be- 

 lieved to be composed of cholesterol esters and lecithin. In the cells of 

 the reticular portion of the cortex, however, pigment particles are not 

 infrequently observed. The blood supply of the cortex is not relatively so 

 rich as that of the medulla, being represented by fine arterioles which 

 run inwards from the capsule towards the medulla in the connective tis- 

 sue that lies between the columns of cortical cells. Nerves similarly 

 penetrate into the cortex, some supplying its blood vessels and cell 

 columns, but most of them proceeding to the medulla. They are derived 

 from a network of nerve fibers in the capsule of the organ, and the nerve 

 supply of this network comes partly from the suprarenal plexus, and 

 partly from the splanchnic nerve. Embryologically the cortex is de- 

 veloped from the cells of the genital ridge, that is, from mesodermic 

 cells. 



