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 pro- 

 portions 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 contain- 

 ing 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 glycerol we may obtain glyceryl aldehyde 

 COH CH 2 OH 



CHOH and dioxyacetone CO. Both these substances behave as 



CH 2 OH CH 2 OH 



sugars and belong to the group of trioses. They are generally 



obtained together and are called glycerose. From the hexatomic 



CH 2 OH COH 



alcohol (CHOH) 4 we may obtain either the aldehyde (CHOH) 4 or 



CH 2 OH CH.OH 



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