120 



THE VITAL PROCESSES 



(Fig. 60). From these 



Starch is the carbohydrate of greatest importance as 

 a food, and it is also the one found in the greatest abun- 

 dance. All green plants form more or less starch, and 

 many of them store it in their leaves, seeds, or roots 



sources it is obtained as food. 

 Glycogen, a substance closely 

 resembling starch, is found in 

 the body of the oyster. It is 

 also formed in the liver and 

 muscles of the higher animals, 

 being prepared from the sugar 

 of the blood, and is stored by 

 them as reserve food (Chapter 

 XI). Glycogen is, on this ac- 

 count, called animal starch. 



FIG. 60. Starch grains in Starch on being eaten is first 

 cells of potato as they appear changed to sugar, after which it 



may be converted into glycogen 

 in the liver and in the muscles. 

 Sugars. There are several varieties of sugar, but the 

 important ones used as foods fall into one or the other 

 of two classes, known as double sugars (disaccharides) and 

 single sugars (monosaccharides). To the first class belong 

 cane sugar, found in sugar cane and beets, milk sugar, found 

 in sweet milk, and maltose, a kind of sugar which is made 

 from starch by the action of malt. The important mem- 

 bers of the second class are grape sugar, or dextrose, and 

 fruit sugar, or levulose, both of which are found in fruits 

 and in honey. 



The most important of all sugars, so far as its use in 

 the body is concerned, is dextrose. To this form all the 

 other sugars, and starch also, are converted before they 

 are finally used in the body. The close chemical relation 



under the microscope 

 practical work.) 



