HORMONES 43 



which resulted from the action of the acid 

 food on the mucous walls of the intestine and 

 which was taken up by the blood and in this 

 way carried to the gland. Thus, what seemed 

 to be a reflex action proved in reality to be 

 the effect upon one organ of a substance 

 formed in another. The particular substance 

 in the case of the pancreas is known as secre- 

 tin. This substance is not of the nature of an 

 enzyme, for it is not destroyed by boiling 

 or by treatment with alcohol. It is, however, 

 a representative of what is probably a large 

 class of substances now recognized under the 

 general name of hormones, whose function it 

 is to excite activity in organs usually situated 

 at a distance from the region in which the 

 given hormone is produced ; in other words, 

 to enable one part of the organism to control 

 another and distant part. As is shown by the 

 pancreas, hormone action strikingly simulates 

 in its results nervous activity, and yet on an 

 entirely different principle, a principle which 

 in fact revives the discarded doctrine of the 

 humors. 



The extent to which hormones control the 

 body is only just beginning to be appreciated. 

 For a long time anatomists have recognized 



