THE SUPRARENAL SYSTEM 265 



dependence is shown by the fact that, at a very early develop- 

 mental stage, a portion of the adrenal system attaches itself to 

 the embryonal interrenal and, in the higher vertebrates, combines 

 with it to form an apparently homogeneous organ, the suprarenal. 

 The medullary substance of the suprarenal is merely a somewhat 

 considerable, intracapsular portion of the adrenal system and, as 

 Kohn aptly remarks, is to be regarded as a large ganglion, the 

 suprarenal paraganglion, formed by the fusion of several smaller 

 ganglia. 



In order to understand the functional significance of the 

 adrenal system, an accurate knowledge of the quantitative value of 

 the suprarenal medulla is essential. The fact that the medullary 

 substance of the suprarenal was earlier recognized and has become 

 altogether better known than the extracapsular portions of the 

 adrenal system, produced this result, that morphological and 

 physiological investigation has been almost exclusively con- 

 fined to the intracapsular adrenal tissue. Investigation re- 

 vealed the existence of an important internal secretory 

 process, and this was at first regarded as a function of the 

 suprarenal as a whole. But even later, after the peculiar 

 position of the chromaffine tissue had been recognized, the 

 physiological importance of the suprarenal medulla was very 

 much over-estimated. There was an inclination to ascribe to the 

 suprarenal medulla all the functions which are the property of 

 the chromaffine system in general, for the sole reason that these 

 functions had been proved to be attributes of the medullary por- 

 tion of the system. For this reason it is very important to re- 

 member that the free portions of the adrenal system are not only 

 genetically and structurally identical with the medullary substance 

 of the suprarenal, but that they possess the same functional signifi- 

 cance and that there is definite proof of this (the survival of animals 

 without suprarenal medulla, compensatory hypertrophy of the 

 extra-capsular chromaffine tissue, the similar effects of para- 

 ganglion extract). Not only is the suprarenal medulla not the 

 sole active portion of the adrenal system, but it is not even the 

 most important part of it. When we remember the wide distribu- 

 tion of the nervous system in the body, and consider that large 

 and small groups of chrome-brown cells are attached to every one 

 of its ganglia, that they lie in many plexuses and are found almost 

 everywhere where sympathetic fibres and cells occur ; and that, in 

 addition to these, the adrenal system includes a number of in- 

 dependent structures we can hardly doubt that the free portions 

 collectively present a far larger mass of active, functional tissue 

 than that section of the system which is enclosed in the supra- 

 renals. These are facts which must not be lost sight of in any 

 attempt to estimate the physiological significance of the activity 

 of the adrenal system. 



Functionally, the adrenal system belongs to the group of the 



