FOOD-STUFFS AND GLYCOGEN FORMATION 329 



So far all is plain, but a difficulty arises when we try to 

 explain why both Isevulose and dextrose should produce an 

 identical glycogen, for dextrose is an aldose (i.e. it contains the 

 group CHO ), whereas laevulose is a ketose (contains the 

 group CO ), and to convert the one sugar into the other is, 

 in the laboratory at least, by no means a simple process. There 

 are three possible ways by which this conversion in the body 

 could be explained : (1) that the Isevulose is first of all converted 

 into dextrose ; (2) that both dextrose and laevulose are converted 

 into some common derivative, which may possibly be a compound 

 of sugar with proteid, and which for want of a better name may 

 be called active dextrose (M. Cremer) ; (3) or that the dextrose and 

 laevulose do not form any common compound until glycogen 

 is produced, i.e. that each passes through a special synthesis. 

 Against the first possibility stands the fact, as we shall see 

 later, that in pancreatic diabetes Ia3vulose when given in the food 

 can form glycogen in the liver, whereas dextrose itself cannot. 

 The two forms of sugar must, therefore, be transformed into 

 glycogen by different processes, but whether these be entirely 

 different, or only partially so e.g. only until active dextrose is 

 formed remains an open question. 



With regard to the glycogen -forming powers of bodies closely 

 allied to the hexoses such as hexatomic alcohols (mannit, dulcit, 

 &c.), and the sugars which do not ferment with yeast, such as 

 the pentoses (which contain only five carbon atoms) there is no 

 unequivocal evidence, obtainable by the direct method at least, 

 that this is of any account. 



An elaborate series of experiments, conducted by E. Ktilz ( 6 ) 

 on rabbits and pigeons, has been considered, by most writers, to 

 point to a number of these compounds as being glycogen pro- 

 ducers, but Pfluger has conclusively shown that the results, on 

 which these important conclusions are based, are inaccurate and 

 misleading, and that, from observations by the direct method at 

 least, we cannot positively state that glycogen is formed from 

 other than the fermentable sugars. 



The two most obvious objections to Kiilz's results are : firstly, 

 that from very small variations in the amount of glycogen variations 

 which might well be due to experimental error he drew funda- 

 mental conclusions ; and secondly, that he used, as standards for 

 comparison, the average glycogen content of animals (pigeons, hens, 



