410 THE CHEMICAL COMPOSITION OF THE BODY [CH. XXY1II. 



brown colour. This constitutes Moore's test for sugar. In alkaline solu- 

 tions dextrose reduces salts of silver, bismuth, mercury, and copper. 

 The reduction of cupric to cuprous salts constitutes Trommer's test, 

 which is performed as follows : put a few drops of copper sulphate 

 into a test-tube, then solution of dextrose, and then strong caustic 

 potash. On adding the potash a precipitate is first formed which 

 dissolves, forming a blue solution. On boiling this, a yellow or red 

 precipitate (cuprous hydrate or oxide) forms. 



On boiling a solution of dextrose with an alkaline solution of 

 picric acid, a dark red opaque solution due to reduction to picramic 

 acid is produced. 



Another important property of grape sugar is that under the 

 influence of yeast it is converted into ethyl alcohol and carbonic 

 acid (CeH 12 6 = 2 C 2 H 6 + 2C0 2 ). 



Dextrose may be estimated by the fermentation test, by the polar- 

 imeter, and by the use of Fehling's solution. The last method is the 

 most important : it rests on the same principles as Trommer's test, 

 and we shall study it in connection with diabetic urine. 



Laevulose or Fructose. When cane sugar is treated with dilute 

 mineral acids it undergoes a process known as inversion i.e., it 

 takes up water and is converted into equal parts of dextrose and 

 laevulose. The previously dextro-rotatory solution of cane sugar 

 then becomes laevo-rotatory, the laevo-rotatory power of the Isevulose 

 being greater than the dextro-rotatory power of the dextrose formed. 

 Hence the term inversion. The same hydrolytic change is produced 

 by certain enzymes, such as the invertase of the intestinal juice and 

 of yeast. Pure Isevulose can be crystallised with difficulty. It gives 

 the same general reactions as dextrose. 



Galactose is formed by the action of dilute mineral acids or of 

 inverting enzymes on lactose. It resembles dextrose in its action on 

 polarised light, in reducing cupric salts in Trommer's test, and in 

 being directly fermentable with yeast. When oxidised by means of 

 nitric acid it yields an acid called mucic acid (C 6 H 10 8 ), which is 

 only slightly soluble in water. Dextrose when treated in this way 

 yields an isomeric acid i.e., an acid with the same empirical formula, 

 called saccharic acid, which is very soluble in water. 



Cane Sugar is generally distributed in the vegetable kingdom, 

 but especially in the juices of the sugar cane, beetroot, mallow, and 

 sugar maple. It is a substance of great importance as a food. It 

 undergoes inversion in the alimentary canal. It is crystalline, and 

 dextro-rotatory. With Trommer's test it gives a blue solution, but 

 no reduction occurs in boiling. After inversion it is, of course, 

 strongly reducing. 



Inversion may be accomplished by boiling with dilute mineral 

 acids, or by means of inverting enzymes such as that occurring in the 



