734 PHYSIOLOGY OF DIGESTION AND SECRETION. 



condition of severe glycosuria that may be produced by the use of 

 phloridzin it has been shown that the animal continues to excrete 

 sugar even when fed on proteid alone, or when starved. Under such 

 conditions the amount of dextrose in the urine bears a definite ratio 

 to the amount of nitrogen excreted. D : N :: 3.65 : 1 (Lusk), which 

 would indicate that both arise from the breaking down of the proteid 

 molecule. On this supposition 58.4 per cent, of the proteid may be 

 converted to sugar. So also the fact that during prolonged starva- 

 tion, lasting for forty or even ninety days, the blood retains a practi- 

 cally constant composition in sugar indicates that this material is 

 being formed from either the proteid or fat supply of the body. 

 Other considerations exclude the fat, and we are, therefore, led to 

 the belief that the proteid can give rise to sugar in the body. If 

 this change is part of the normal metabolism of the body it would 

 make proteid a glycogen-former, since the sugar formed from the 

 proteid may, of course, be converted to glycogen. Whether or not 

 all proteids yield glycogen or sugar in the body is not entirely de- 

 termined. Some authors have thought that only those proteids 

 that contain a carbohydrate residue have this property; but, as 

 stated above, casein and other proteids that do not possess this 

 grouping seem also to increase the glycogen supply when fed alone. 



Effect of Fats upon Glycogen Formation. A large number of 

 substances have been found by some observers to increase the store 

 of glycogen in the liver. In some of these cases at least it is evident 

 that the substance is not a direct glycogen-former in the sense that 

 the material is itself converted to glycogen. It may increase the 

 supply of liver glycogen in some indirect way, for example, by 

 diminishing the consumption of glycogen in the body. The most 

 important substance in this connection from a practical standpoint 

 is fat. Whether or not the body can convert fats into sugar or 

 glycogen is a question about- which at present there is much 

 difference of opinion, and much evidence might be cited on each side. 

 Cremer, however, has furnished apparent proof that glycerin acts 

 as a direct glycogen or sugar-former. When fed, especially in the 

 diabetic condition, it causes an increase in the sugar which can not 

 be explained as a result of proteid metabolism. Since in the body 

 neutral fats are normally split into glycerin and fatty acid, the fact 

 that glycerin can be converted to sugar seems to carry with it the 

 admission that fats may contribute directly to sugar production. 

 Whether the synthesis of sugar (or glycogen) from glycerin is, 

 so to speak, a normal process or occurs only under especial condi- 

 tions, can not be decided at present. 



The Function of Glycogen Glycogenic Theory. The mean- 

 ing of the formation of glycogen in the liver has been, and still is, 

 the subject of discussion. The view advanced first by Bernard is 



