70 CARBOHYDRATES MONOSACCHARIDES 



of pentoses calculated on the basis of the dry tissue, which is present 

 in various parts of the mammalian body: 



Pancreas 2.48 



Liver 0.56 



Thymus 0.56 



Submaxillary gland 0.53 



Thyroid gland 0.50 



Kidneys 0.49 



Spleen 0.46 



Brain 0.22 



Muscle 0.11 



The structural formula of d-ribose may be represented as: 



CHO 



I 



H C OH 



I 

 H C OH 



H C OH 



CH 2 OH 



d-ribose. 



it is levorotatory, the prefix d- being employed to denote its 

 relationship to d-altose and d-altrose. 



In certain very exceptional cases a pentose is formed in the urine. 

 The disease which leads to this elimination of pentoses is known as 

 Pentosuria, in contradistinction to Glycosuria, the very much more 

 common elimination of -glucose. Only a few cases of pentosuria have 

 been observed, but it is an extremely ' noteworthy fact ' that the 

 pentose which is eliminated in this disease would appear to be almost 

 invariably optically inactive, although the pentose, 1-ribose, which is 

 normally found in the tissues is, of course, optically active. Not only 

 this, but the pentose in the urine is not ribose but Arabinose, 



CHO CHO 



I I 



HO C H H C OH 



I I 



H C OH HO C H 



H C OH HO C H 



I I 



CH 2 OH CH 2 OH 



d-arabinose. 1-arabinose. 



which would seem to point to its derivation from glucose rather than 

 from the decomposition of nucleo-proteins, for it will be remembered 

 that arabinose may be derived from glucose by the oxidation of the 

 calcium salt of gluconic acid (xylose being the corresponding pentose 

 resulting from the oxidation of glucuronic acid). However this may 

 be, the pentose elimination in these cases is independent of the pentose- 



