26 PHYSIOLOGICAL CHEMISTRY. 



When boiled with dilute hydrochloric acid it yields furfural- 

 dehyde. 



XYLOSE, or wood sugar, is obtained by boiling wood gum 

 with dilute sulphuric acid. Its specific rotation is + 19.4. 

 Like the preceding body it is a reducing sugar, but non- 

 fermentable. The nutritive value of these substances for man 

 is low, but for the herbivora these and the antecedent pen- 

 tosans are more important, as they appear to be rather easily 

 digested in the alimentary tract of many animals. Traces of 

 pentoses have occasionally been found in human urine. 



All these bodies are distinguished from the sugars proper 

 by yielding relatively large quantities of furfuraldehyde when 

 distilled with hydrochloric acid or sulphuric acid, which reac- 

 tion may be illustrated by the following test : 



Ex. In a small retort or flask fitted with a delivery tube mix 5 gm. of 

 bran and 100 cc. of ten per cent hydrochloric acid. Connect the retort 

 or flask with a condenser, apply heat and distil over about half the liquid. 

 With a few drops of this make the Schiff furfuraldehyde test. Moisten 

 a small strip of paper with aniline acetate obtained by mixing equal vol- 

 umes of glacial acetic acid and aniline. Touch this test-paper with a glass 

 rod holding a drop of the bran distillate. A bright red color appears, due 

 to the formation of furoaniline, CJHsO.CH^CeHiNH^H The reaction is 

 extremely delicate and serves for the detection of traces of the products 

 yielding furfuraldehyde, CJHsO.CHO. 



The Hexoses. These are important substances repre- 

 sented by the general formula C 6 H 12 O 6 . Several occur 

 widely distributed in nature, being found in ripe fruits and 

 elsewhere. A few are artificial products formed by laboratory 

 operations. Complex combinations of these bodies known as 

 glucosides are also common and are essentially ethereal salts 

 of the hexoses. These hexose bodies are all sweet, soluble 

 in water, nearly insoluble in alcohol and are all reducing sub- 

 stances with oxidizing agents like Fehling's solution. They 

 undergo fermentation readily, and all the important forms 

 yield alcohol and carbon dioxide under the influence of the 

 yeast organism. Some of them yield lactic acid when acted 

 upon by the proper ferment. By partial oxidation they yield 



