10 HUMAN PHYSIOLOGY. 



i. AMYLOSES, (C 6 H ]0 5 )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 obtained. 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 en- 

 velope 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 solu- 

 tion ; if present in sufficient quantity, 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 

 transformation of starch into sugar. There are at least two principal 

 varieties ery thro dextrin, which strikes a red color with iodin, and 

 achr oo 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 

 maltose. 



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

 extent, of muscles 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 resembles 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 



