THE CARBOHYDRATES. 



The very large group of compounds termed the carbohydrates, or 

 sugars, are compounds of the nature of alcohols, primary and secondary, 

 and at the same time aldehyde or ketone. Their empirical formula 

 shows that they consist esssentially of carbon and water, C n (H 2 O) n 

 hence their name though substances other than carbohydrates, e.g. 

 formaldehyde, CH 2 O, acetic acid, C 2 H 4 O 2 , and lactic acid, C 3 H 6 O 3 , also 

 possess the same empirical formula, and some carbohydrates have em- 

 pirical formulae in which the ratio of the elements H : O is not 2: I, 

 e.g. the methyl pentose, rhamnose C 6 H 12 O 5 . 



This group of compounds contains simple and complex members. 

 The simple members contain 2, 3, 4, 5, 6, 7, 8, 9 carbon atoms in 

 their molecule, the chief physiological representatives being the 

 members with 6 carbon atoms and in a lesser degree those with 5 

 atoms of carbon. It was formerly supposed that only those mem- 

 bers containing 6 atoms of carbon belonged to the class of sugars, 

 and it is convenient to term the six carbon atom representatives 

 the sugars, whilst the whole group is termed the carbohydrates. 



The complex members consist of combinations together in an an- 

 hydride form of 2, 3, 4 and more of the simple units, generally of 

 those containing 6 carbon atoms and also of those with 5 carbon 

 atoms. Accordingly as they contain 2, 3, etc., simple units in com- 

 bination they are termed disaccharides, trisaccharides, or polysac- 

 charides, the simple unit being termed a monosaccharide. All the 

 complex members are converted into their constituent single units by 

 hydrolysis with acids. The members of the carbohydrate group are 

 'distinguished by the suffix -ose, but this suffix is not applied to some 

 of the complex compounds. 



The carbohydrates are especially abundant in plants ; the amount 

 present in animals is by comparison very small. The complex carbo- 

 hydrates form the structural basis of plants and are deposited in 

 various parts as reserve material and as food-stuffs for the young 

 plant. Both the complex reserve material and the simple carbohy- 

 drates are the chief food-stuff of animals. 



The physical properties, appearance, solubility, taste, etc., of the 

 various carbohydrates is very different and no proper classification can 

 be based upon their properties, but they are classified according to 

 their complexity 



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