PEXTOSHS 649 



logic importance, is virtually a clean page. Tlicy have never l)een 

 found iu the urine, since there are at present no established methods 

 for their detection, and ett'orts have been lacking. 



PENTOSES 



Chemical theory demands the existence of fourteen pentoses, i. e., 

 six aldo-pentoses, four 2-keto-pentoses and four 3-keto-pentoses. Only 

 those better known to cliemists have received biological study, e. g., 

 arabinose and xylose.'"* Of these the optically inactive or d- 1-arabin- 

 ose, tlie 1-arabinose and 1-xylose are the best known. When even 

 small quantities of pentose gain access to the circulating blood, pentose 

 is excreted in the urine. Ebstein ^'■' reports the appearance of traces 

 in the urine of a man (in which none had been previously demon- 

 strated), after the administration of so little as 0.25 gram of 1-ara- 

 binose b}' mouth. Bergell -" found reactions for pentose in the urine 

 seven to ten minutes after ingestion of the same sugar, and when given 

 subcutaneously, Fr. Voit -^ saw about 50 per cent, excreted. Neu- 

 berg and "Wohlgemuth -- gave a normal man 15 grams of d- 1-ara- 

 binose and recovered 4.5 grams of d-, and only 1.04 grams of 1-ara- 

 binose in the urine. On the other hand 1-arabinose becomes converted 

 in part into the dextro-form, since both forms appear in the urine 

 when only one is given. Xylose has been found to behave in general 

 like arabinose.-^ 



Since all writers agree that 10 to 50 per cent, of administered pen- 

 toses are excreted in the urine even when given per os in very small 

 quantities, and since pentoses occur in many foods (plums, cherries, 

 apples, etc.) or result from the bacterial decomposition of other carbo- 

 hydrates, it is inevitable that alimentary pentosurias should occasion- 

 ally occur in nearly everj' normal individual, and, as a matter of fact, 

 most normal urines give reactions wdiicli indicate the presence of 

 some pentose { Cremer, Funaro, Cominotti). Vice versa, one may 

 conclude that very little pentose normally occurs in the blood, since 

 otherw'ise more of it w'ould appear in the normal urine than does ; and 

 finally, that pentoses must play but a minor role in the general metabo- 

 lism of the carbohydrates. Therefore it is highly improbable tiiat 

 during the breakdown or synthesis of glucose in the body the hexoses 

 split to any extent into a pentose and formaldehyde. The same holds 

 good for the behavior of hexoses in the presence of alkali. They 

 split almost exclusively into chains of 2, 3 and 4 carbon atoms (Nef). 



18 Rhamnose is a methyl pentose, representing a elass of substances closely 

 related to the pentoses. 



i9Vircho\v"s Archiv., 18n2 (120), 401. 



2oFestschr. f. E. v. Levden, 1<)02 (2), 401. 



2iDeut. Arch. f. klin.'Med., ISO? (58), ,523. 



22Zeit. f. physiol. C'hem., 1002 (35), 41. 



23 For literature, see Xeuberg. "Der Harn sowie die iibrigen Ausscheidiingen, 

 etc." (Springer, Berlin, 1911), I, p. 370. 



