12 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



test, and we shall study it and other methods of estimating sugar 

 in connection with diabetic urine (see Lesson XII.). 



Levalose. — 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 pre- 

 viously 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. Similar hydrolytic changes are 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 inverting ferments on lactose or 



milk sugar. It resembles dextrose 



in being dextro-rotatory, in reducing 



cupric hydrate in Trommer's test, 



..^ // r^^-:^--,-^^ ^^^ ^'^ being directly fermentable 



^^"^^^ // \ \/^^ with yeast. When oxidised by means 



^-~-~^ // ^<^ \ ^ Qf nitric acid it, however, yields an 



acid called mucic acid (CgHioOg), 

 which is only sparingly soluble in 

 water. Dextrose when treated this 

 way yields an isomeric acid — i.e. an 

 acid with the same empirical formula, 

 called saccharic acid, which is readily 

 soluble in water. 



Fig. 2. — Inosite crystals. 



Inosite, or muscle sugar, is found in muscle, kidney, liver, and other parts 

 of the body in small quantities. It is also largely found in the vegetable 

 kingdom. It is a crystallisable substance (see fig. 2) and has the same 

 formula (CuH,„Oy) as the glucoses. It is, however, not a sugar. It gives 

 none of the sugar tests, and careful analysis has shown it has quite a different 

 chemical constitution from the true sugars. It belongs to the aromatic 

 series, and is only included here for convenience. 



DISACCHARIDE8 



Cane Sugar. — This sugar is generally distributed throughout the 

 vegetable kingdom in the juices of plants and fruits, especially the 



