CARBOHYDRATES. 23 



causing the elimination of this substance is called, if we adopt the suggestion 

 of Salkowski, pentosuria. Up to the present time about a dozen cases 

 are known. Pentosuria is distinctly different from true diabetes. It 

 exists for years without showing the clinical indications of the latter 

 metabolic disturbance. In rare cases the elimination of pentose has been 

 detected in diabetes also, 1 but it is not known that there is any connection 

 between the two diseases. The amount of pentose eliminated varies in 

 individual cases between 0.2 and 1 per cent. 



It is a striking fact that the pentoses eliminated in urine are, as a rule, 

 optically inactive. Luzzato, 2 alone, has described an optically active 

 pentose. The question next arises as to the source of pentose in urine. 

 First of all, Bial and Blumenthal 3 have proved that pentosuria is inde- 

 pendent of the composition of the diet and especially as regards the amount 

 of pentoses in it. They have also shown that with persons afflicted with 

 the disease the combustion of carbohydrates, and thus also of Z-arabinose, 

 is perfect. Pentoses in urine, therefore, do not find their source in the 

 food. The next possibility which would suggest itself is that perhaps 

 they arise from the breaking down of tissue and especially of the 

 nuclei. If this supposition were correct, we should expect that the pentose 

 found in urine would be the same as that found in the organs, namely, 

 inactive xylose. This now is not the case, as Neuberg 4 has shown, for 

 the pentose in urine is arabinose, and curiously enough almost always the 

 inactive, racemic form. Furthermore, this pentose for the most part does 

 not exist free in the urine, but is combined with urea. For the present, we 

 can only formulate hypotheses concerning its formation. Above all, we 

 are ignorant as to why the pentose should nearly always be eliminated in 

 an inactive form. 



The five-carbon sugars are much more widely distributed in the vege- 

 table kingdom than in the animal. Up to the present time they have 

 not been identified with certainty in a free state, but on the other hand 

 they appear to be deposited in the nucleoproteids of certain plants in the 

 same manner as in animals, for Osborne and Harris 5 have isolated tritico- 

 nucleic acid from wheat flour. This manner of occurrence is inappreciable 

 as compared with that of high molecular pentosans, i.e., polysaccharides 

 of the pentoses. These substances are extremely widely distributed, and 

 take part in various ways in the building up of plants. By their hydrolytic 

 cleavage the simpler members of this series are obtained. Not only the 

 pentoses are found as pentosans, but we have methyl-pentosans as well 



Kiilz and Vogel: Z. Biol. 1895, 185. 

 Hofmeister's Beitrage, 6, 87 (1904). 

 Deut. med. Wochenschr. 22 (1901). 

 Ber. 33, 2243 (1900). 

 Z. physiol. Chem. 36, 85 (1902). 



