148 COMPOSITION OF THE BODY 



220. Carbohydrates. The carbohydrates are non-nitrogenous 

 bodies of various degrees of stability, differing much in physical 

 and chemical properties, and consisting of carbon, oxygen and hy- 

 drogen. The carbohydrate molecule usually contains six or a 

 multiple of six atoms of carbon, while the hydrogen and oxygen 

 are present in the same proportion as in water, with at least five 

 atoms of oxygen to six of carbon. 1 



Carbohydrates are neutral in reaction and combine loosely With 

 other bodies, especially bases. The following properties are char- 

 acteristic of the greater number of these substances : 



(#) They reduce alkaline metallic solutions and are colored 

 yellow by alkalies. 



(b ) They rotate the plane of polarized light. 



(c ) They give characteristic crystals with phenyl-hydrazine. 



(d) Most of them in contact with yeast are broken down into 

 alcohol and carbon dioxide, i. e., they are fermentable. 



(e ) They give color reactions with acids and aromatic alcohols. . 



(/) They are mostly soluble in water. Those which are not, 

 can be dissolved by heating with an acid in which process they 

 are hydrated into soluble sugars, however. 



Most of the carbohydrates may be classified as follows : 



I. Glucoses or Monosaccharids, C 6 H 12 6 . 

 + Dextrose. 2 

 — Levulose. 

 -f- Galactose. 

 II. Saccharoses or Disaccharids, C 12 H 22 O u . 

 + Cane-sugar, 

 -f Lactose, 

 -f Maltose, 

 -f- Iso-maltose. 



1 There are some exceptions to this rule, such as bioses, trioses, tetroses, etc. . in 

 which the carbon is present in two, three, and four atoms respectively, and also such as 

 rhamnose, which has twelve atoms of hydrogen to five of oxygen. 



2 The signs -(- or — indicate that the more familiar of these substances when in 

 solution rotate the plane of polarized light to the right or left respectively. 



