CARBOHYDRATES 145 



physiological interest. The formulae given are merely empirical, and 

 the molecular weights in many instances are indefinite. In the group 

 of amyloses (starch-groups) the molecules are very large 20,000 

 to 30,000 (Brown and Morris). The various changes which substances 

 belonging to this group undergo are very complex, and it will be more 

 convenient to discuss these in connection with the physiology of diges- 

 tion. Here little more than an enumeration of some of the carbohydrates 

 will be given. The following is the usual classification. The sign + 

 indicates that the substance is dextro-rotatory and the sign , that it is 

 levo-rotatory. 



i. Glucoses 2. Saccharoses 3. Amyloses 



(C 6 H 12 6 ) (C 12 H 22 U ) (n C (; H 10 5 ) 



+ Dextrose -f Saccharose + Starch 



Levulose + Lactose -f- Glycogen 



+ Galactose + Maltose + Dextrin 



Cellulose 

 Gums 



Dextrose. This carbohydrate often called grape-sugar is found 

 in fruits, honey, and sometimes in small quantity in the blood and in 

 various tissues. Its empirical formula is C 6 H 12 O 6 . It is soluble in hot 

 and cold water and in alcohol. It reduces the copper salts and is 

 fermentible. 



Levulose. This carbohydrate is obtained by treating saccharose 

 with a dilute mineral acid. The saccharose then undergoes what is 

 known as inversion, appropriating water and changing into a mixture 

 of equal parts of levulose and dextrose. This mixture is levo-rotatory, 

 the levo-rotatory power being greater than the dextro-rotatory. It has 

 the same general reactions as dextrose. It crystallizes with difficulty. 

 Its empirical formula is the same as the formula for dextrose (C 6 H 12 O 6 ). 



Galactose. This carbohydrate is formed by the action of dilute 

 mineral acids on lactose. It is dextro-rotatory and has the same gen- 

 eral reactions as dextrose. Its empirical formula is C 6 H 12 O 6 . 



Saccharose. This carbohydrate is derived from the vegetable king- 

 dom. It crystallizes readily and is dextro-rotatory. It does not reduce 

 the salts of copper. On the addition of yeast, it first undergoes change 

 into invert-sugar and then ferments. It is by far the most important 

 of the sugars used as food. By boiling with a dilute mineral acid, it 

 undergoes inversion into equal parts of dextrose and levulose. It is 

 inverted, also, in the processes of digestion. Its empirical formula is 

 C 12 H 22 O n . 



Lactose. This is the sugar found in milk. It assumes water under 

 the same conditions as saccharose and splits into dextrose and galac- 



