THE ENDOCRINAL ORGANS 447 



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. 



In a sense, every organ acts as an endocrine gland toward every other. 

 All, for example, as a result of their metabolism, form CO2, which diffuses 

 into the capillaries, and is carried by the blood stream to other parts of 

 the body. But any increase in the CO2 content of the blood affects the 

 respiratory center in the medulla and increases the activity of the breath- 

 ing muscles. Strictly, however, the term endocrine organ is restricted to 

 those only which secrete hormones that act somewhat specifically and 

 usually on particular tissues. But there is no hard and fast line to be 

 drawn. 



The word "hormone" was first used by Bayliss 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 

 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 well as a digestive func- 

 tion. Scattered among lobules of the pancreas, are aggregations of 

 lightly-staining cells, the pancreatic islands or islands of Langerhans. 

 It has been shown that these islands secrete a hormone, named by its 

 discoverers insuUn. While its chemical formula remains uncertain, the 

 substance has been extracted from the pancreas of animals, and is used 

 in the treatment of diabetes. Insulin poured into the blood has the 

 function of regulating the oxidation of carbohydrates in the tissues and 

 the storage of glycogen in the liver. How this is done is an unsolved 

 problem. 



Both deficiency and excess of secretion of insulin is dangerous, and 

 often fatal. Diabetes results from too little insulin. The liver fails 

 to convert sugar into glycogen, and the excess of sugar in the blood is 

 eliminated by the kidneys, so that sugar in the urine and excessive urina- 

 tion are among the symptoms. As a result of this loss of sugar, the 

 tissues are obliged to burn their reserves of fat and protein, and the 

 patient becomes emaciated. Acidosis and death follow in the absence of 



