190 INTERMEDIATE METABOLISM 



when the pancreas is incompletely extirpated the islets 

 show signs of hyperactivity when diabetes does not occur, 

 and degeneration without corresponding changes in the 

 other tissue when diabetes supervenes. 



The Formation of Glucose and Glycogen 



In order to find out what substances are capable of 

 forming glycogen three methods are employed. The sub- 

 stance in question may (1) be perfused through the excised 

 hver, (2) be administered to the animal after the hepatic 

 glycogen store has been exhausted by strychnine convul- 

 sions, (3) be administered to an animal rendered diabetic 

 by extirpation of the pancreas or by administration of 

 phloridzin. If in the last case the sugar excretion is 

 increased it is concluded that the substance normallv 

 undergoes conversion into glycogen. 



Using these methods the following information has been 

 obtained : — 



From Carbohydrates. — Glycogen is formed not only from 

 glucose but also from lajvulose, galactose, the ordinary 

 disaccharides and from starch and cellulose ; also from 

 formaldehyde and from lactic acid. It is not formed from 

 the pentoses or from the six-carbon-atom alcohols and 

 acids, such as glycuronic acid. 



From Proteins. — In the diabetic condition there is a 

 constant ratio between the amount of glucose and nitrogen 

 excreted. This is called the D : N ratio. When protein 

 food is administered the excretion of glucose is increased. 

 In some cases as much as 58 grms. of glucose can be 

 obtained after ingestion of 100 grms. of protein. The pro- 

 duction of carbohydrate from protein is therefore proved. 



As to the individual amino-acids which can be converted 

 into carbohydrate, it might be imagined that glucosamine, 

 which contains the glucose molecule preformed, would be 

 the principal source. But this is unhkely, first, because 

 glucosamine forms only a very small part of the commoner 

 proteins; secondly, because when given to the diabetic it 



