390 THE CHEMICAL COMPOSITION OF THE BODY [CH. XXV. 



meter, 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. 



Levulose. 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 levulose. The previously 

 dextro-rotatory solution of cane sugar then becomes levo-rotatory, the 

 levo-rotatory power of the levulose being greater than the dextro- 

 rotatory power of the dextrose formed. Hence the term inversion. 

 The same hydrolytic change is produced by certain ferments, such as 

 the invert ferment of the intestinal juice. 



Pure levulose can be crystallised, but so great is the difficulty of 

 obtaining crystals of it that one of its names was uncrystallisable 

 sugar. Small quantities of levulose have been found in blood, urine, 

 and muscle. It has been recommended as an article of diet in diabetes 

 in place of ordinary sugar ; in this disease it does not appear to have 

 the harmful effect that other sugars produce. Levulose gives the same 

 general reactions as dextrose. 



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

 verting ferments 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 iso- 

 meric acid i.e., an acid with the same empirical formula, called sac- 

 charic 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 ferments such as that occurring in the 

 intestinal juice. It then takes up water, and is split into equal parts 

 of dextrose and levulose. 



C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 



[Cane sugar.] [Dextrose.] [Levulose.] 



With yeast, cane sugar is first inverted by means of a special soluble 

 ferment secreted by the yeast cells, and then there is an alcoholic 

 fermentation of the glucoses so formed. 



Lactose, or Milk Sugar, occurs in milk. It is occasionally 

 found in the urine of women in the early days of lactation, or after 



