308 



SCIENCE 



[N. S. Vol. XXXVI. No. 923 



are produced in the pituitary and which 

 pass from this into the blood. 



The internally secreting glands which 

 have been mentioned (thyroid, parathy- 

 roid, suprarenal, pituitary) have, so far as 

 is known, no other function than that of 

 producing chemical substances of this char- 

 acter for the influencing of other organs, to 

 which they are conveyed 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 parathyroids 

 — almost microscopic. In spite of this, 

 they are essential to the proper mainte- 

 nance of the life of the body, and the total 

 removal of any of them by disease or opera- 

 tions is in most cases speedily fatal. 



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 

 instance 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 recog- 

 nized. It was, however, discovered in 1889 

 by von Mering and Minkowski that the 

 pancreas also furnishes an internal secre- 

 tion, 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 carbo- 

 hydrates in the organism. It is well known 

 that the carbohydrates of the food are con- 

 verted into grape sugar and circulate in 

 this form in the blood, which always con- 

 tains 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 internal 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 Tiid- 

 neys, producing diabetes. 



Another instance of an internal secre- 

 tion furnished by an organ which is 

 devoted largely to other functions is the 

 "pro-secretin" found in the cells lining 

 the duodenum. When the • acid gastric 

 juice comes into contact with these cells it 

 converts their pro-secretin into ' ' secretin. ' ' 

 This is a hormone which is passed into the 

 blood and circulates with that fluid. It 

 has a specific effect on the externally secret- 

 ing cells of the pancreas, and causes the 

 rapid outpouring of pancreatic juice into 

 the intestine. This effect is similar to that 

 of the hormones of the pituitary body upon 

 the cells of the kidney and mammary gland. 

 It was discovered by Bayliss and Starling. 



The reproductive glands furnish in many 

 respects the most interesting example of 

 organs which — besides their ordinary prod- 

 ucts, the germ- and sperm-cells (ova and 

 spermatozoa) — form hormones which cir- 

 culate in the blood and effect changes in 

 cells of distant parts of the body. It is 

 through these hormones that the secondary 

 sexual characters, such as the comb and tail 

 of the cock, the mane of the lion, the horns 

 of the stag, the beard and enlarged larynx 

 of a man, are produced, as well as the many 

 differences in form and structure of the 

 body which are characteristic of the sexes. 

 The dependence of these so-called second- 

 ary sexual characters upon the state of 

 development of the reproductive organs 

 has been recognized from time immemorial, 

 but has usually been ascribed to influences 

 produced through the nervous system, and 

 it is only in recent years that the changes 

 have been shown to be brought about by 

 the agency of internal secretions and hor- 



