CHEMIC COMPOSITION OF THE HUMAN BODY. 9 



of the human body, yet on account of their importance as foods, and their 

 relation to one another, a few of their chemic features will be stated in this 

 connection. 



i. AMYLOSES (C 6 H 10 6 )n. 



Starch is widely distributed in the vegetable world, being abundant in the 

 seeds of the cereals, leguminous plants, and in the tubers and roots of some 

 vegetables. It occurs in the form of microscopic granules, which vary in 

 size, shape, and appearance, according to the plant from which they are ob- 

 tained. Each granule presents a nucleus, or hilum, around which is arranged 

 a series of eccentric rings, alternately light and dark. The granule consists 

 of an envelope and stroma of cellulose, containing in its meshes the true starch 

 material granulose. Starch is insoluble in cold water and alcohol. When 

 heated with water up to 70 C., the granules swell, rupture, and liberate the 

 granulose, which forms an apparent solution; if present in sufficient quan- 

 tity, it forms a gelatinous mass termed starch paste. On the addition of 

 iodin, starch strikes a characteristic deep blue color; the compound formed 

 iodid of starch is weak, and the color disappears on heating, but reappears 

 on cooling. 



Boiling starch with dilute sulphuric acid (twenty-five per cent.) converts 

 it into dextrose. In the presence of vegetable diastase or animal ferments, 

 starch is converted into maltose and dextrose, two forms of sugar. 



Dextrin is a substance formed as an intermediate product in the transfor- 

 mation of starch into sugar. There are at least two principal varieties 

 erythrodextrin, which strikes a red color with iodin, and achroo dextrin, which 

 is without color when treated with this reagent. In the pure state dextrin 

 is a yellow-white powder, soluble in water, in the presence of animal 

 ferments erythrodextrin is converted into maltrose. 



Glycogen is a constituent of the animal liver, and, to a slight extent, of 

 muscles 0.5 to 0.9 per cent, and of tissues generally. In the tissues of the 

 embryo it is especially abundant. When obtained in a pure state it is an 

 amorphous, white powder. It is soluble in water, forming an opalescent 

 solution. With iodin it strikes a port- wine color. In some respects it resem- 

 bles starch, in others dextrin. Like vegetable starch, glycogen or animal 

 starch can be converted by dilute acids and ferments into sugar (maltose). 



Cellulose is the basis material of the more or less solid framework of plants. 

 It is soluble only in an ammoniacal solution of cupric oxid, from which it can 

 be precipitated by acids. It is an amorphous powder; dilute acids can con- 

 vert it into dextrose. 



