THE NONNITROGENOUS SUBSTANCES 81 



Of the other monosaccharides the pentoses, C 5 H 10 O 5 , have been demonstrated 

 in animal fluids (urine) and among- the cleavage products of animal substances. 

 Arabinose, found in the urine, and xylose in the pancreas are the most important 

 pentoses. They do not ferment under the influence of the yeast plant; but 

 with a certain other fungus, not definitely determined, Salkowsky obtained a 

 large quantity of alcohol from 1-arabinose. 



B. The disaccharides are anhydric compounds of two molecules of mono- 

 saccharides e. g., 2C 6 H 12 6 = C^H^On + H 2 0. On boiling with dilute 

 mineral acids they break up with the absorption of water into monosac- 

 charides. The most important members of this group are saccharose (cane 

 sugar), lactose (milk sugar) and maltose (malt sugar), all having the 

 formula C^H^On. 



The disaccharides are crystalline bodies of a sweetish taste, readily soluble 

 in water. Lactose and maltose reduce an alkaline copper solution, saccharose 

 does not. By boiling with dilute mineral acids and by the agency of certain 

 enzymes the disaccharides take up one molecule of water and split into two 

 molecules of monosaccharides thus : saccharose into dextrose and levulose ; lactose 

 into dextrose and galactose; maltose into two molecules of dextrose. 



Saccharose is dextro-rotatory; on its cleavage into dextrose and levulose it 

 becomes, on account of the stronger rotating power of levulose, Ia3vo-rotatory. 

 For this reason the cleavage of saccharose is called inversion. 



C. The polysaccharides, ft(C 6 H 10 5 ), like the disaccharides are regarded 

 as anhydrides of the monosaccharides, but they have their origin in the union 

 of many molecules of the latter and have a high molecular weight, which 

 varies widely. 



The polysaccharides have no sweetish taste and for the most part are amor- 

 phous. Some are soluble in water, others swell up in water, while still other 

 members of this series are not visibly changed by water. By various means all 

 of them can be transformed by absorption of water into monosaccharides. 



The polysaccharides are divided into three chief groups: starches, gums, 

 and cellulose. 



1. The starches are not directly fermentable and do not reduce alkaline copper 

 solutions. To these belong : 



(a) Vegetable starches (amylum). These are found in many plant cells laid 

 down in the form of microscopic, round or oblong granules which have an organic 

 structure and are insoluble in cold water. On heating with water they swell up 

 at 50, burst and partially dissolve, forming a slimy solution, known as starch 

 paste, which can be filtered. The soluble part is called starch granulose, the in- 

 soluble part starch cellulose. On boiling with dilute acids starch is changed first 

 into dextrin (see below) and later into dextrose. By digestion with saliva or 

 pancreatic juice, or through the influence of malt-diastase it is split into dextrin 

 and maltose (cf. Chapter VII). 



(6) Glycogen is an animal starch which has a very wide distribution in the 

 animal body. It is found in almost all the tissues of the body, but in largest 

 quantities in the liver and in the muscles ; it is a constituent of embryonic tissues 

 especially and all others in which an active cell formation is taking place. Gly- 

 cogen is an amorphous, tasteless and odorless white powder ; with water it forms 

 an opalescent, dextro-rotatory solution. It is changed by diastatic enzymes into 

 maltose or dextrose according to the nature of the enzyme. 



