THE ENDOC'RINAL ORGANS 



325 



hormones. Hormones act chemically upon various parts of the body. 

 Their effect generally is stimulatory. With the discovery that nerves 

 produce neurohumors which act in the manner of hormones, the contrast 

 between nervous and endocrinal action does not appear as great as was 

 formerly thought. 



The word "hormone" was first used by Bayhss and Starling in their 

 description of the chemical regulation of the secretion of the pancreatic 

 digestive juices. They discovered that, when hydrochloric acid enters 

 the intestine from the stomach, the digestive secretion of the pancreas is 

 poured into the intestine. But the same effect was produced even when 



ALVEOLUS 





i^if. 



W,l" BLOOD VESSEL 



Fig. 289. — A section of the pancreas, showing an island among the alveoli of the gland. 



X200. 



all nervous connexions had been previously cut. Therefore, they con- 

 cluded, the connexion must be chemical, by way of the blood; and they 

 were led to postulate a "chemical messenger" or hormone produced by 

 the epithelial cells lining the duodenum. They gave to this substance 

 the name Secretin. Their results have been repeatedly confirmed, and 

 endocrinologists include the duodenum in the list of endocrine organs. 



The Pancreas. General interest in endocrine organs was increased 

 by the important discovery that the pancreas has an endocrinal as w^ell as 

 a digestive function. Scattered among lobules of the pancreas are aggre- 

 gations of lightly-staining cells, the pancreatic islands or islands of Langer- 

 hans. It has been shown that these islands secrete a hormone named by 

 its discoverers insulin. Insulin poured into the blood has the function 



