CHEMIC COMPOSITION OF THE HUMAN BODY. 7 



THE CARBOHYDRATES. 



The carbohydrate compounds, which enter into the composition of the 

 animal body, are mainly starches and sugar. In many respects they are 

 closely related, and by appropriate means are readily converted into one 

 another. In composition they consist of the elements carbon, hydrogen, 

 and oxygen. As their name implies, the hydrogen and oxygen are present in 

 these compounds in the proportion in which they exist in water, or as 2:1. 

 The molecule of the carbohydrates above mentioned consists of either six 

 atoms of carbon or a multiple of six; in the latter case the quantity of 

 hydrogen and oxygen taken up by the carbon is increased, though the 

 ratio remains unchanged. 



The carbohydrates may be divided into three groups viz.: (i) amyloses, 

 including starch, dextrin, glycogen, and cellulose; (2) dextroses, including 

 dextrose, levulose, galactose; (3) saccharoses, including saccharose, lactose, 

 and maltose. According to the number of carbon atoms entering into the 

 second group (six), they are frequently termed monosaccharids; those of 

 the third group, disaccharids twice six; those of the first group, poly- 

 saccharids multiples of six. 



Though but few of the members of the carbohydrate group are con- 

 stituents of the human body, many are constituents of the foods; on 

 account of their importance in this respect, and their relation to one 

 another, the chemic features of the more generally consumed carbohydrates 

 will be stated in this connection. 



i. AMYLOSES, (C 8 H 10 O 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 many 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 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 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, the color dis- 

 appearing on heating, but reappearing on cooling. 



Boiling starch with dilute sulphuric acid (25 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 trans- 

 formation of starch into sugar (maltose) . There are at least two principal 

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

 trin j 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. 



