CHAPTER III. 

 THE CARBOHYDRATES AND RELATED BODIES. 



Under the term carbohydrate it has long been customary to 

 include a number of bodies with closely related properties and 

 similar composition, which may be expressed by such simple 

 formulas as C 6 H 10 O 5 , C 6 H 12 O G , or multiples of these. The 

 term carbohydrate came into use long before the structure of 

 the bodies in question was known. It is now possible to 

 describe these substances in their relations to the fundamental 

 hydrocarbons or alcohols and this classification will be there- 

 fore briefly explained. 



NATURE OF THE CARBOHYDRATES. 



In their chemical behavior these bodies resemble aldehydes 

 or ketones in certain important characteristics. Like the 

 latter they are often strong reducing substances and most 

 of them form combinations with phenyl hydrazine. These 

 and other properties suggest that they may be considered as 

 aldehyde or ketone derivatives of the polyhydric alcohols, 

 which relationship is shown by the following table, which con- 

 tains also some acid derivatives for further illustration. 



Some of the bodies in the table are naturally occurring sub- 

 stances and are highly important, but most of them are arti- 

 ficial. The aldohexoses and the ketohexoses are closely 

 related to two groups of more complex bodies, in which cane 

 sugar and starch are the best illustrations, and with them form 

 the important class of carbohydrates in the more restricted 

 sense. 



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