288 PENTOSURIA 



PENTOSURIA 



Another abnormality of carbohydrate metabolism, of 

 rare occurrence it is true, but of considerable physiological 

 interest, is pentosuria, 55 which was discovered by Salkowski 

 in 1892. 



\-xylose. Attention has been called in a previous lec- 

 ture (v. Vol. I of this series, p. 117, et seq., Chemistry of the 

 Tissues) to the importance of the pentoses in the construc- 

 tion of animal and vegetable tissue. Carl Neuberg's fine 

 researches leave no doubt that the sugar which exists so 

 widely in the nucleoproteins of animals is A-xylose. The 

 discovery of Neuberg and Salkowski, who observed 

 glycuronic acid pass over into A-xylose in putrefaction, 

 COOH.[CH(OH)] 4 .COH -- C0 2 CH 2 .OH. [CH(OH)] 3 . 

 COH, has cleared up the obscurity which previously involved 

 the origin of tissue pentoses. One cannot make any serious 

 mistake in supposing that glucose under certain physio- 

 logical circumstances can be changed by oxidation into 

 glycuronic acid and that the latter by having C0 2 split off 

 can be transformed into tissue pentose, even though up to 

 the present this series of changes has not been proved 

 beyond peradventure. 



Another important connection which the pentoses have 

 with the processes of animal metabolism is seen in the fact 

 that pentosans, the primary substances of the pentoses, 

 occur widely in the vegetable kingdom. What their part is 

 in the nutrition of herbivora can be easily appreciated if 

 one considers that many types of forage contain twenty-five 

 per cent, or more of pentosans. Although there is but little 

 probability that the pentoses are directly changed into 

 glucose, that is to say, into glycogen (vide supra, p. 230), 

 and that this is conceivable only when aided by complicated 



08 Literature upon Pentosuria: C. Neuberg, Ergebn. d. Physiol., 3', 405^410, 

 1904, and v. Noorden's Handb. d. Pathol. d. Stoffwechs., 2d ed., 2, 219-224, 1907; 

 A. Magnus-Levy, Handb. d. Biochem., 4' 395-406, 1909; F. Umber, Lehrb. d. 

 Ernahr., pp. 242-248, 1909. 



