CHEMIC COMPOSITION OF THE HUMAN BODY. 25 



elements which are thus obtained, and the percentages in which they 

 exist in the body, are as follows viz., oxygen, 72 per cent.; hydrogen, 

 9.10; nitrogen, 2.5; carbon, 13.50; phosphorus, 1.15; calcium, 1.30; 

 sulphur, 0.147; sodium, o.io; potassium, 0.026; chlorin, 0.085; 

 fluorin, iron, silicon, magnesium, in small and variable amounts. 



THE CARBOHYDRATES. 



The carbohydrates constitute a group of organic bodies, con- 

 sisting mainly of starches and sugars, having their origin for the 

 most part in the vegetable world. ""TrTmany 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 the majority of these compounds in the pro- 

 portion to form water, or as 2 : i. The molecule of the carbo- 

 hydrates just 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 fre- 

 quently termed monosaccharids ; those of the third group, disaccharids 

 twice six; those of the first group, polysaccharids multiples of six. 



Though but few of the members of the carbohydrate group are 

 constituents 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 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 



