CARBOHYDRATES 57 



by recrystallization from water. The crystals are hard and 

 gritty, and the solution is not so sweet as that of cane sugar. 

 Lactose is composed of one molecule each of glucose and galac- 

 tose. It is manufactured in the breast gland from the glucose 

 of the blood. This is an interesting example of the conversion 

 of one sugar into another in the body, since a portion of the 

 glucose must be changed into galactose. 



Lactose responds readily to the reduction tests for the mono- 

 saccharides. It thus possesses a free aldehyde group, and is 

 represented by the accompanying formula. The solution of 

 lactose is dextrorotatory. The specific rotation is + 52.5. Lac- 

 tose does not ferment with ordinary yeast. This property is 

 serviceable in identifying it. It should be remembered that lac- 

 tose will give the mucic acid test, since it contains galactose. 



Maltose. Maltose is formed in the hydrolysis of starch or 

 glycogen by amylase. Since this enzyme is widely distributed 

 in both plants and animals, maltose may be found wherever 

 there is starch or glycogen. 



Maltose is readily soluble in water. The solution is not so 

 sweet as that of cane sugar. The solution is dextrorotatory, the 

 specific rotation being -(-137. This value varies, however, with 

 concentration and temperature. Maltose reduces Fehling's re- 

 agent, etc., and gives an osazone. Its structure is thus con- 

 sidered to be similar to that of lactose which has one free al- 

 dehyde group. On hydrolysis it yields two molecules of glu- 

 cose. Maltose ferments readily with yeast. It may easily be dis- 

 tinguished from glucose by hydrolizing with dilute acid. After 

 hydrolysis the reducing power of the solution will be found to 

 have increased, since two molecules of glucose are now present 

 for every molecule of maltose destroyed. 



Polysaccharides. 



Members of the polysaccharide group differ from one another 

 considerably in their solubilities and other properties. They 

 are found in both plants and animals in which they form reserve 

 supplies of food material, and in plants and some" of the lower 



