CHAPTER I. 



CARBOHYDRATES. 



Chemical Relationships. These are compounds of carbon, hydrogen, 

 and oxygen, in which the latter two elements exist in the same pro- 

 portion as in water. Their general formula is therefore C m H 2n O M , 

 where m is usually of the same value as n, and in the case of the 

 simple carbohydrates is almost invariably 6 or some multiple of it. 



Carbohydrates are found chiefly in vegetables, but may also occur in 

 animal tissues. They form very important foodstuffs, for they are 

 easily digested and assimilated, and moreover are much cheaper than 

 proteids and fats. (See Diet.) The simplest form of carbohydrate 

 is called a monosaccharide, and all other carbohydrates are derived 

 from this by the condensation 1 either of two molecules of a mono- 

 saccharide (disaccharides), or of several (polysaccharides). 



I. MONOSACCHARIDES. 



Chemically, monosaccharides are either aldehydes or ketones, the 

 former are called aldoses, the latter ketoses. 



Aldoses. An aldehyde is the first oxidation product of a primary 

 alcohol, 2 and it contains the end group - CHO. 



1 Condensation is a chemical process whereby several molecules of the same 

 body (or even of different bodies) come together with the loss of one or more 

 molecules of water or some other stable body. 



2 A primary alcohol is one in which the ' OH ' or hydroxyl group is attached to 

 the last C atom of the molecule as in primary propyl alcohol, 



CH 3 -CH 2 -CH 2 OH, 



and it contains the end group - CH 2 OH. If, on the other hand, the hydroxyl 

 group be attached to a central C atom as in secondary propyl alcohol, 



CH 3 -CHOH-CH 3 , 



the alcohol is called secondary, and contains the group - CHOH. 



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