32 LIFE: ITS NATUBE, OEIGIN AND MAINTENANCE 



hormone is essential to the proper utilisation 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 utilise it as fuel. If, owing to disease of the pan- 

 creas or as the result of its removal by surgical procedure, its internal 

 secretion is not available, sugar is no longer properly utilised 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. 



Another instance of an internal secretion 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 

 Duodenum. . . . 



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 secreting 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 products, the germ- and 

 internal secretions sperm-cells (ova and spermatozoa) form hormones 

 of the reproductive which circulate in the blood and effect changes in cells 

 organs. o 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 secondary sexual characters upon the state 

 of development of the reproductive organs has been recognised 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 hormones, passed from the reproductive glands into the circulating 

 blood.* 



It has been possible in only one or two instances to prepare and isolate 

 the hormones of the internal secretions in a sufficient condition of purity to 

 subject them to analysis, but enough is known about 

 them to indicate that they are organic bodies of a not 

 very complex nature, far simpler than proteins and 

 even than enzymes. Those which have been studied are all dialysable, 

 are readily soluble in water but insoluble in alcohol, and are not destroyed 

 by boiling. One at least that of the medulla of the suprarenal capsule 



* The evidence is to be found in P. H. A. Marshall, The Physiology of Reproduction, 

 1911. 



