286 PKACTICAL PHYSIOLOGY 



the succus entericus and in the protoplasm of many cells such as the 

 yeast plant (see p. 280). 



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 hydro- 

 lysed, and the monosaccharides thus produced then undergo alcoholic 

 fermentation. 



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

 cane, beet root, etc. It is very soluble in water and has a sweet taste. 

 It does not reduce metallic oxides in alkaline solution. 



EXPERIMENT IV. 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. 

 - By hydrolysis, reducing sugars (dextrose and laevulose) are developed. 



EXPERIMENT V. Boil some cane sugar solution with a few drops 

 of 25 % sulphuric acid. Now neutralise the acid and apply Trommer's 

 or Fehling's test and note that reduction occurs. The monosaccharides 

 developed are dextrose and laevulose, the mixture being called invert 

 sugar. 



It is often better to employ an organic acid such as citric acid to 

 produce the hydrolysis, because the organic acid does not hydrolyse 

 starch or glycogen, whereas mineral acids do. 



EXPERIMENT VI. Apply Seliwanoff s test for ketose to a solution 

 of cane sugar (Experiment IX. p. 278). The reaction is as marked as for 

 laevulose, owing to hydrolysis of the cane sugar by the hydrochloric 

 acid employed. 



EXPERIMENT VII. Heat some cane sugar solution with strong 

 hydrochloric acid. Note the reddish colour developed. This reaction 

 is given by other sugars, but not so readily. 



A solution of cane sugar is dextro-rotatory ((a)D = +66*54), but 

 after hydrolysis it is laevo-rotatory, the laevo-rotatory power of the 

 laevulose being stronger than the dextro-rotatory power of the dextrose 

 formed. On this account the process of hydrolysis is sometimes called 

 inversion, and the hydrolysing ferments in the succus entericus, etc., 

 are often called invertases. 



EXPERIMENT. Examine a ten per cent, solution of cane sugar with the polari- 

 scope. Note the rotation and calculate (a)D. Place exactly 50 c.c. of a twenty 

 per cent, solution of cane sugar in a 100 c.c. measuring flask ; add 1 gr. citric acid 

 and boil over wire gauze for five minutes. Cool, neutralise with NaOH solution, 

 and fill with distilled water to the 100 c.c. mark. Examine this solution with 

 the polariscope and calculate (a) D. 



