ELEMENTARY CHEMICAL PHYSIOLOGY 215 



Glucose readily combines with alcohols, acids, phenols, etc., to form 

 glucosides. These are resolved into their constituent groups by hydrolysis 

 with acid. 



Lsevulose (C 6 H 12 6 ) is found along with dextrose in fruits and 

 honey and results from the hydrolysis of cane sugar (see 

 Disaccharides). It is very rarely found in animal tissues. It is 

 crystallisable with great difficulty, being usually obtained as a 

 putty-like mass. It is laevo -rotatory ( (a)D == 93). 



Galactose (C 6 H 12 O 6 ) is a dextro-rotatory sugar produced, along 

 with dextrose, by hydrolysing lactose (see Disaccharides). Certain 

 lipoid substances in brain tissue, yield galactose on hydrolysis. 

 It differs but slightly from dextrose in its reactions. Its presence 

 can be detected by the fact that when oxidised, as by boiling with 

 nitric acid, it yields mucic acid which forms characteristic crystals. 



EXPERIMENT. Test for galactose. Add 3 c.c. pure HNO 3 (con.) to 10 c.c. 

 of a strong solution of lactose in a small evaporating dish. Boil gently over 

 a free flame for three minutes, and then lower the flame and allow to evap- 

 orate till the volume is reduced to about 3 c.c. Transfer to a test tube, cool 

 under the tap, add 2 c.c. water, and allow to stand. Crystals of mucic acid 

 separate out. 



II. Disaccharides 



Chemically, each molecule of a disaccharide consists of two 

 molecules of a monosaccharide less one molecule of water, 



2C 6 H 12 6 H 2 r =C 12 H 22 11 . 



Their structure can be demonstrated by hydrolysing them, i.e. 

 by causing them to take up a molecule of water, in consequence of 

 which they split up into two monosaccharides. In disaccharides 

 the two monosaccharide molecules are linked together in the same 

 manner as glucose and the other constituent radicle in glucosides. 



The chief means of hydrolysing include boiling with dilute acid 

 and the action of certain ferments called invertases, which are 

 contained in the succus entericus and in the protoplasm of many 

 cells such as the yeast plant (see p. 210). 



The members of this class are cane sugar, maltose and lactose, 

 and of these cane sugar does not reduce metallic oxides in alkaline 

 solution, nor does it form an osazone, whereas lactose and maltose 

 give both these reactions. With yeast maltose and cane sugar are 

 first hydrolysed, and the monosaccharides thus produced then 

 undergo alcoholic fermentation. 



Cane Sugar or Sucrose (C 12 H 22 O n ) is the common sugar obtained 

 from sugar cane, beetroot, etc. It is very soluble in water and 

 has a sweet taste. It does not reduce metallic oxides in alkaline 

 solution. 



EXPERIMENT I. Perform Trommer's test with some cane sugar 

 solution. Notice that, although no reduction occurs, the cane sugar, 

 like other sugars, is capable of holding the cupric hydroxide in 

 solution, so that a clear blue colour is produced. 



