SECTION IV 

 THE CARBOHYDRATES 



THE carbohydrates are a group of bodies of wide distribution and great 

 importance in both the vegetable and animal kingdoms. In plants the first 

 product of assimilation of carbon is a carbohydrate, and in animals these 

 substances form one of the most important sources of energy. They consist 

 of the elements carbon, hydrogen, and oxygen, the two last-named being 

 almost invariably in the proportions necessary to form water. It is on this 

 account that the term carbohydrate has been given to the group. Their 

 general formula might be expressed C n H 2n O n . Certain derivatives of the 

 group, obtained by the substitution of methyl and other radicals for a 

 hydrogen atom, though necessarily classified with carbohydrates on account 

 of their reactions, do not conform to this general formula, e.g. rhamnose, 

 C 6 H 12 5 . All the carbohydrates which are of importance in the animal 

 economy contain six carbon atoms or a multiple of this number. Analogous 

 substances however can be prepared containing less or more than this 

 number of carbon atoms. A series of compounds exist which contain in their 

 molecule 2, 3, 4, 5, 6, 7, 8, 9 carbon atoms, and are termed dioses, trioses, 

 tetroses, pentoses, hexoses, heptoses, and so on ; the termination ' ose ' with 

 the Greek numeral prefixed, indicating the number of carbon atoms, gives 

 them a distinct designation. These are all oxidation products of polyatomic 

 alcohols, being either ketones or aldehydes of these alcohols. Thus from 



COH 



I 

 jlycerol we may obtain glyceryl aldehyde CHOH and dioxy acetone 



I 

 )H 2 OH CH 2 OH 



I 



). Both these substances behave as sugars and belong to the group of 

 I 



[ 2 OH 



-ioses. They are generally obtained together and are called glycerose. 



CH 2 OH 



'rom the hexatomic alcohol (CHOH) 4 we may obtain either the aldehyde 



I 

 CH 2 OH 



59 



