376 THE METABOLISM OF THE CARBOHYDRATES 



glycogen, for Blumenthal and Wohlgemuth ( 33 ) have found that 

 if frogs be fed on proteids, such as egg albumin, which contain 

 glucosamin, glycogen becomes deposited in the organism ; whereas 

 when fed on such proteids as casein, which contains no glucosamin, 

 glycogen is not formed. 



It is possible, therefore, that, under some conditions, the 

 glucosamin present in certain proteids may be converted into 

 dextrose in the animal body ; but for various reasons, glucosamin 

 cannot be held accountable for the large amount of sugar excreted 

 by starved diabetic animals. Let us then consider in this con- 

 nection the other sugar groups which have been isolated from 

 proteid. 



We saw that pentoses were almost invariably found among the 

 decomposition products of nucleo-proteid, and we know that 

 nucleo-proteids are constantly being broken down in the organism 

 (see p. 399) ; what then becomes of the pentose thereby liberated ? 

 does it serve to build up glycogen and so become converted into 

 dextrose ; or is it excreted unchanged in the urine ? We know 

 that when pentoses are given by the mouth they appear un- 

 changed in the urine ; they are not retained in the organism as 

 glycogen, nor are they oxidised in their passage through it. 

 Taking these facts into consideration, we might expect that the 

 pentoses liberated in the break-down of nucleo-proteid would like- 

 wise pass unchanged into the urine, in which therefore traces at least 

 of pentose sugar would be constantly present. Such, however, 

 is not the case. Pentosuria is a rare condition, and the variety 

 of pentose which does appear when it is present is chemically 

 different from that which appears as a decomposition product 

 of nucleo-proteid. 1 



The dextrose group recently found in serum globulin (see p. 317) 

 is no doubt a direct glycogen former, but, at most, no more than 

 2 per cent, of dextrose can be separated from this proteid. Of 

 the other proteids which are among the constituents of our food, 

 casein and gelatin contain no carbohydrate groups, and in serum 

 albumin there is much doubt whether the 0-5 per cent of carbo- 

 hydrate which has been separated from it does not come from 

 adherent mucin. 



Pfltiger ( 6 ) has recently brought forward the view that glycogen, 



1 It is beyond the scope of this article to discuss the interesting condition 

 of pentosuria. 



