352 THE METABOLISM OF THE CARBOHYDRATES 



bacteria for the half -digested starch lies several days in the 

 intestines leaving only a small proportion to be absorbed as 

 dextrose and pass into the urine. Dextrose is the only sugar 

 which thus appears. 



With maltose also, only dextrose appears in the urine. 



The most interesting results in this direction are with Icevulose, 

 for, as Ktilz has shown, this sugar is often oxidisable in the 

 tissues of patients suffering from Diabetes mellitus, whereas 

 dextrose and dextrose-yielding carbohydrates are not. If large 

 quantities of Isevulose be given to depancreated dogs on constant 

 diet and therefore with a constant D:N ratio arise in the 

 dextrose excretion will be noticed, and a small amount of Isevulose 

 itself will appear in the urine. If only small amounts of Isevulose 

 be given no Isevulose will appear in the urine, and the increase 

 in dextrose excretion will be very slight, since a large part of 

 the Isevulose becomes utilised in metabolism. It is only when 

 excess is given that some of the Isevulose leaks as such through 

 the kidney filter or becomes converted into dextrose, which, 

 as we have seen above, cannot be destroyed, and is likewise 

 excreted. 



The dextrose, however, might possibly be derived from proteid, 

 the Isevulose having induced a more active break-down of this. 

 That it is nob so derived, but comes from the Ia3vulose itself, 

 is proved by the fact that the D:N ratio has in some cases been 

 seen to rise to 11 or 13- 5, a figure far above what could be 

 obtained were proteids the source of the sugar. 



How then is this transformation of Isevulose into dextrose 

 brought about ? Lsevulose, it will be remembered, is, in its 

 chemical structure, quite different from dextrose ; it is a ketose, 

 whereas dextrose is an aldose. 



An examination of the glycogen contents of the liver and 

 muscles furnishes us with an answer to this question. After 

 feeding Isevulose to depancreated dogs, a high percentage of 

 glycogen (8' 14 in the liver and 0*81 in the muscles) has been 

 found, and in its chemical reactions, this glycogen is indis- 

 tinguishable from normal glycogen. From this result we must 

 assume that, in depancreated dogs at least, a direct transforma- 

 tion of Isevulose into glycogen occurs. This transformation is not 

 effected by the Isevulose being first of all changed into dextrose ; 

 for we have found dextrose to form no glycogen under such 



