CARBOHYDRATES 37 



through hydrolysis by acids may be transformed into pentoses. Pento- 

 ses do not ordinarily occur in the animal organism, but have been found 

 in the urine of morphine habitues and others, their occurrence some- 

 times being a, persistent condition without known cause. They may be 

 obtained from the hydrolysis of nucleoproteins being present in the 

 nucleic acid complex of the molecule. Pentoses are non-fermentable, 

 have strong reducing power and form osazones with phenylhydrazine. 

 Pentoses are an important constituent of the dietary of herbivorous 

 animals. Glycogen is said to be formed after the ingestion of these 

 sugars containing five oxygen atoms. This, however, has not been 

 conclusively proven. On distillation with strong hydrochloric acid 

 pentoses and pentosans yield furfurol, which can be detected by its 

 characteristic red reaction with aniline-acetate paper. 



CH 2 OH 



ARABINOSE, (CHOH) 3 



CHO 



Arabinose is one of the most important of the pentoses. The 

 Z-arabinose may be obtained from gum arabic, plum or cherry gum by 

 boiling for 10 minutes with concentrated hydrochloric acid. This 

 pentose is dextro-rotatory, forms an osazone and has reducing power, 

 but does not ferment. The z-arabinose has been isolated from the 

 urine and yields an osazone which melts at i66-i68C. 



EXPERIMENTS ON ARABINOSE 



i. Orcinol-Hydrochloric Acid Reaction (Bial). 1 To 5 c.c. of Bial's reagent 2 in 

 a test-tube add 2-3 c.c. of the arabinose solution and heat the mixture gently until 

 the first bubbles rise to the surface. Immediately or upon cooling the solution 

 becomes green and a flocculent precipitate of the same color may form. (For 

 further discussion see Chapter XXIII.) The test may also be performed by 

 adding the pentose to the hot reagent. 



It is claimed that this test is more delicate than the original orcinol 

 test (see 3) and more accurate, since menthol, kreosotal, etc., respond 

 to the original orcinol test but not to Bial's. Sachs 3 has offered 

 suggestions as to modification of the test in order to avoid confusion 

 with glycuronic acid. 



1 Bial: Deut. med. Woch., 28, 252, 1902, and Berl. klin. Woch., No. 18, 1903. 



2 Orcinol 1.5 gram. 



Fuming .HC1 500 grams. 



Ferric chloride (10 per cent) 20-30 drops. 



3 Sachs: Bioch. Zeit., i, 383, 1906, and 2, 245, 1906. 



