THE CHEMISTRY OF THE BODY. 5 



or living material of the cell, for analysis necessarily involves the death 

 of the living structure. It is clear, however, that protoplasm itself is 

 largely composed of nitrogenous material, though it derives much of 

 the energy necessary for its activities from the combustion of the non- 

 nitrogenous compounds. 



THE NON-NITROGENOUS SUBSTANCES. 



These again fall into two groups : (1) those in which the combined 

 oxygen is sufficient to oxidise all the hydrogen of the molecule, and (2) 

 those in which the oxygen is insufficient to combine with the hydrogen 

 of the molecule. 



(I.) The former group consists of the Carbohydrates, and the members 

 of it which occur normally in the body are either hexoses, that is, each 

 contains six carbon atoms in its molecule, or are formed by a combina- 

 tion of two or more hexose molecules. Pentoses, with five carbon atoms 

 each, also occur ; an example is xylose, which enters into the formation 

 of the molecule of the nucleic acid derived from the pancreas. The 

 carbohydrates found in the body are dextrose, laevulose (fructose), 

 galactose, lactose, and glycogen. Others occur as constituents of 

 food, e.g. cane-sugar and starch. The first three have the formula 

 C 6 H 12 6 , and belong to the group of mono-saccharides. Lactose is a 

 disaccharide, that is, it belongs to a group of substances formed by the 

 condensation of two monosaccharide molecules with the abstraction of 

 a molecule of water. 



2C 6 H 12 6 -H 2 = C 12 H 22 O n . 



Glycogen is a polysaccharide, and is formed by the condensation of a 

 large number of monosaccharide molecules, as in the formula 



nC^A-nH.O^^H^V 



The symbol "n" may have a very high value. Thus starch is supposed 

 to have the formula 200(C 6 H 10 5 ). 



The Monosaccharides. Dextrose may be looked upon as the current 

 carbohydrate coin of the body. It is a soluble crystalline substance, 



having the formula 



CH 2 OH 



(CHOH) 4 . 



CHO 



It is an aldehyde, and, like other aldehydes, when heated with an 

 alkaline solution of a cupric salt, it reduces the latter with the forma- 

 tion of yellow cuprous oxide. This property of dextrose and other 

 ''reducing sugars " forms the basis of the tests of^Trommer, Fehling, 



