92 THE CHEMICAL COMPOSITION OF THE BODY 



ation with iodine, which disappears on heating and returns on cooling. It 

 is converted into maltose by diastase, and by boiling with dilute acids into 

 dextrose. 



Glycogen. Glycogen is a polysaccharide contained in the liver, 

 and also present in all muscles, but especially in those of very young animals, 

 in the placenta, in colorless corpuscles, and in embryonic tissues. It is 

 sometimes called animal starch and gives many reactions proper to starch 

 itself. It is freely soluble in water, and its solution looks opalescent; it 

 gives a port-wine coloration with iodine, which disappears on heating and 

 returns on cooling. It is precipitated by basic lead acetate and is insoluble 

 in absolute alcohol and in ether. It exists in the liver during life, but very 

 soon after death is changed into sugar. It may be prepared by grinding 

 muscle with sand till a pasty mass is formed, boiling the mass in water for 

 twenty minutes, filtering, and then precipitating the glycogen from the 

 filtrate by adding a little more than an equal quantity of 95 per cent alcohol. 

 It is converted into sugar by diastase ferments, or into dextrose by boiling 

 with dilute acids. 



Dextrin. This substance is made in commerce by heating dry 

 potato-starch to a temperature of 400. It is also produced in the .process 

 of the conversion of starch into sugar by diastase, and by the salivary and 

 pancreatic ferments. A yellowish amorphous powder, soluble in water, 

 but insoluble in absolute alcohol and in ether. It corresponds almost ex- 

 actly in tests with glycogen; but one variety (achroo-dextrin) does not give 

 the port-wine coloration with iodine. 



Cane-Sugar, or Saccharose. It is contained in the juices of many 

 plants and fruits, and is extracted from the sugar-cane, from beet-root, or 

 from the maple. It is crystalline and is precipitated from concentrated 

 solutions by absolute alcohol. It has no power of reducing copper salts 

 on boiling. It is dextro-rotatory. It is not subject to alcoholic fermenta- 

 tion, until by inversion it is converted into glucose, it chars on addition of 

 sulphuric acid, and on heating with potassium or sodium hydrate. 



Lactose. Lactose is the chief carbohydrate of milk. It is less 

 soluble in water than glucose; it is not sweet, and is gritty to the taste; but 

 it is insoluble in absolute alcohol. In digestion it yields a molecule of dex- 

 trose and a molecule of galactose. It undergoes alcoholic fermentation 

 with extreme difficulty; gives the tests similar to glucose, but less readily. 

 It is dextro-rotatory + 59. 



Maltose. This sugar is produced by the action of the saliva and 

 pancreatic juice on starch. It is also formed by the action of malt upon 

 starch by the action of the ferment diastase. It is converted into dextrose 

 by dilute sulphuric acid. It is dextro-rotatory; ferments with yeast; reduces 

 copper salts; and crystallizes in fine needles. 



Dextrose, or Glucose. Dextrose pccurs widely diffused in the 



