METABOLISM. 25 
Ebstein,* who was the first to investigate this subject, showed 
qualitatively the presence of pentose carbohydrates in the urine of 
man after the ingestion of arabinose and xylose even in very small 
doses, and concluded that these sugars are not assimilable. 
Salkowski f shortly afterward observed the appearance of pen- 
toses in the urine of rabbits given arabinose after five or six days of 
fasting. He found in the urine, however, only about one-fifth of 
the amount ingested, together with small amounts in the blood and 
larger ones in the muscles, but there was a considerable increase of 
the glycogen of the liver. From the latter fact Salkowski con- 
cludes that arabinose may be, either directly or indirectly, a source 
of glycogen. The glycogen found in his experiment was the ordi- 
nary six-carbon glycogen. 
Subsequent investigations by Cremer,{ Munk,§ Frentzel,|| Linde- 
mann & May, Fr. Voit,** Jacksch,tt Minch,t{ Salkowski,§§ 
and others have been directed largely to two questions, viz., 
whether the pentose carbohydrates are oxidized in the body and 
whether they serve as a source of glycogen. 
PENTOSES OXIDIZED IN THE Bopy.—As the general result of 
these investigations, it may be stated that pentoses (in particular 
arabinose and xylose), whether administered by the stomach or 
injected into the blood, are at least partially oxidized in the body. 
In the human organism the power of oxidizing the pentoses, which 
do not normally constitute any considerable portion of its food, 
appears to be quite limited, and even when they are given in small 
quantities a portion (not all) is excreted in the urine. In the rabbit 
the pentoses seem to be more vigorously oxidized, only about 
twenty per cent. being excreted unaltered, even when compara- 
tively large doses are given. ' 
In these experiments the pentose sugars were administered in 
considerable amounts at once, and the excretion of a portion unal- 
tered would seem to be a phenomenon similar to the temporary 
* Virchow’s Archiv, 129, 401; 182, 368. J Arch. klin. Med., 56, 283. 
+Centralbl. med. Wiss., 1893, p. 193. ** Ibid., 58, 524. 
t Zeit. f. Biol., 29, 536; 42, 428. ++ Zeit. f. Heilk., 20, 195. 
§Centralbl. med. Wiss., 1894, p. 83. tt Zeit. physiol. Chem., 29, 493. 
| Arch. ges. Physiol., 56, 273. 8§ Ibid., 32, 393. 
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