216 PRACTICAL PHYSIOLOGY 



By hydrolysis, reducing sugars (dextrose and laevulose) are 

 developed. 



EXPERIMENT II. Boil some cane-sugar solution with a few drops 

 of 25 per cent, sulphuric acid. Now neutralise the acid and apply 

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

 monosaccharides formed 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 III. Apply Seliwanoff's test for ketose to a solution 

 of cane sugar. The reaction is as marked as for laevulose, owing to 

 hydrolysis of the cane sugar by the hydrochloric acid employed. 



EXPERIMENT IV. 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 = -f- 66-5), but after 

 hydrolysis it is laevo -rotatory, the laevo -rotatory power of the Isevulose 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 10 per cent, solution of cane sugar with the 

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

 20 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. 



Lactose (C^^On) i g the sugar found in milk, and it has been 

 detected in the urine of nursing mothers. 



It is not very soluble in water, and is quite insoluble in alcohol 

 and ether. It has only a slightly sweet taste. It does not ferment 

 with yeast in twenty-four hours, but it undergoes a special fer- 

 mentation with the bacillus acidi lactici which develops in sour milk. 

 This fermentation results in the production of lactic acid. 



OH. 



C 12 H 22 O n + H 2 - 4CH 3 - CH 



N COOH. 



Lactose. Lactic acid. 



By hydrolysis it yields dextrose and galactose. It reduces metallic 

 oxides in alkaline solution. It is dextro-rotatory ( (a)D = -j- 52-5). 

 By oxidation with nitric acid it yields mucic acid. 



Maltose (C^H^On) is important physiologically because it is the 

 sugar produced from starch by the diastases present in the digestive 

 juices and tissues. Maltose is therefore mainly an intermediate 

 substance in the animal body. 



Maltose is also produced by the action of malt diastase, which is obtained 

 by moistening barley and allowing it to germinate in heaps at a constant 

 temperature. The diastase acts on the starch of the grain and produces 

 maltose. The product when dried is called malt. When malt is dissolved 

 in water, and the yeast plant allowed to grow on the solution, malted liquors, 



