330 THE METABOLISM OF THE CARBOHYDRATES 



and rabbits) which had been starved for a certain time without 

 regard to the period of year. For his standard estimations, Kiilz 

 gives no dates, though he gives dates for the feeding experiments ; 

 now, it is well known that the amount of glycogen in the body 

 varies considerably with the season of year, especially in such 

 animals as the rabbit. 



Max Cremer, by methods entirely analogous with those of Kiilz, 

 and indeed using Kiilz's averages for starving animals as his controls 

 (without, however, rendering his glycogen ash-free, as KLiilz did, 

 or estimating the glycogen in the whole body) tried to show that 

 pentoses are glycogen formers. In a table, No. 6, Pfliiger shows 

 that in every case in which Cramer claims a positive result, 

 the glycogen derived from tissue proteid meanwhile broken down in 

 the organism, could be held accountable for the recorded increase 

 of liver glycogen, so that, if glycogen formers at all, pentoses can 

 only be indirect ones. 



A very thorough investigation of this question has been made 

 by Frentzel ( 9 ). To clear out all the glycogen from the organism 

 he used the method described in a footnote on p. 325. He found 

 that xylose, a typical pentose, when fed to glycogen-free rabbits 

 did not cause glycogen to be formed. 1 This might mean, however, 

 not that xylose 'is incapable of being converted into glycogen, but 

 that, as a result of the action of the strychnine, the organism had 

 lost the power of producing glycogen. That such an explanation 

 does not hold, was shown by the fact that when dextrose was 

 administered to animals made glycogen-free by the same method, 

 a considerable deposition of glycogen ensued. Xylose is, therefore, 

 neither a direct nor a pseudo-glycogen former ; it can neither 

 produce glycogen itself nor can it become oxidised in place of 

 other substances, such as proteids, which, if so saved, might con- 

 ceivably become converted into glycogen. 2 



In another portion of this article it will be shown that, 

 theoretically considered, a transformation of glycerine into 

 dextrose is quite a simple process. When tested by biological 



1 The xylose was proved to be all absorbed, for the intestine was found to be 

 free of it after death, and, moreover, it was found present in the urine. 



2 With l-arabinose, another pentose, Salkowski ( 6 ), by comparing the glycogen 

 contents of rabbits fed with it with that of rabbits starved for six days, thought 

 that slight glycogen formation had occurred ; but, since his results are open to 

 the same criticism as are those of Kiilz, his statement cannot for the present be 

 accepted. 



