148 GROWTH 



Perhaps a further illustration from the physiology of an 

 adult animal would serve to clarify the functional interdepend- 

 ence of organs which has been discussed. The illustration ap- 

 plies to man, but the facts have been developed in the study of 

 rabbits, dogs, and man. 



There is a widespread common knowledge of the nervous 

 system and its normal functions, of the physiology of the liver, 

 of the pancreas and its digestive functions, and of the physical 

 nature, the chemistry, and the physiology of the blood. Per- 

 haps you remember that in the blood there is a very constant 

 amount of sugar, varying only slightly from 0.12 per cent from 

 hour to hour throughout the day. Among other great functions 

 the liver always contains an excess of stored sugar in the form 

 of glycogen. During the absorption of a meal the sugar princi- 

 ples are entering the blood stream in greater amount than nor- 

 mal to the blood and are rapidly abstracted, polymerized, and 

 deposited in the liver as glycogen. During fasting, when no 

 sugars are absorbed from foods, the liver glycogen is slowly 

 redissolved and reenters the blood stream at a rate just ade- 

 quate to keep up a constant blood sugar. 



The nervous and muscular tissues consume these sugars, and 

 their normal behavior absolutely depends on the constancy of 

 the sugar supply. It is not so generally known that the pan- 

 creatic gland, which is so important for the digestion of food, is 

 of very great importance in that it produces a group of chemi- 

 cals which also enter the blood and which are absolutely essen- 

 tial to enable the body to use its sugars. If the pancreas is surgi- 

 cally removed from an animal, or destroyed by disease in man, 

 then sugars cannot be used by the muscles and the nervous 

 system, the animal quickly often in a few hours becomes uncon- 

 scious, has nervous-muscular convulsions and promptly dies. 

 The animal cannot utilize the sugar present in abundance with- 

 out the internal secretion of the pancreas. 



If, on the other hand, the liver is removed from an animal, 

 thus taking away the stored source of sugars so that no sugar 



