520 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



exactly in the same manner, influence the contraction of tlie heart 

 and arteries. Its extracts are also instrumental in promoting the 

 secretion of certain glands. When injected mto the blood they cause 

 a free secretion of water from the kidneys and of milk from the mam- 

 mary glands, neither of which organs are dii'ectly influenced (as most 

 other glands are) through the nervous system. Doubtless under 

 natural conditions these organs are stimulated to activity by hormones 

 which are produced in tlie pituitary and which pass from this into the 

 blood. 



The internalh'' secreting glands which have been mentioned (thy- 

 roid, parathyroid, suprarenal, pituitary) have, so far as is known, no 

 other function than that of j)roducmg chemical substances of this 

 character for the influencmg of other organs, to which they are con- 

 veyed by the blood. It is interesting to observe that these glands 

 are all of very small size, none being larger than a walnut, and some — 

 the paratiiyroids — almost microscopic. In spite of this, tliey are 

 essential to the proper maintenance of the life of the body, and the 

 total removal of any of them by disease or operation is in most cases 

 speedily fatal. 



PANCREAS. 



There are, however, organs in the body yielding internal secretions 

 to the blood in the shape of hormones, but exercising at the same time 

 other functions. A striking mstance is furnished by the pancreas, the 

 secretion of which is the most important of the digestive juices. 

 This — the pancreatic juice — forms the external secretion of the gland, 

 and is poured into the intestine, where its action upon the food as it 

 passes out from the stomach has long been recognized. It was, liow- 

 ever, discovered m 1889 by Von Alering and Minkowski that the pan- 

 creas also furnishes an internal secretion, containing a hormone which 

 is passed from the pancreas into the blood, by which it is carried first 

 to the liver and afterwards to the body generally. This hormone is 

 essential to the proper utilization of carbohydrates in the organism. 

 It is well known that the carbohydrates of the food are converted 

 into grape sugar and circulate in this form in the blood, which always 

 contains a certain amount; the blood conveys it to all the cells of the 

 body, and they utilize it as fuel. If, owing to disease of the pancreas 

 or as the result of its removal by surgical procedure, its uiternal secre- 

 tion is not available, sugar is no longer properly utilized by the cells 

 of the body and tends to accumulate in the blood; from the blood the 

 excess passes off by the kidneys, producing diabetes. 



DUODENUM. 



Another instance of an internal secretion furnished by an organ 

 which is devoted largely to other functions is the "prosecretin" 

 found in the cells lining the duodenum. When the acid gastric juice 



