The word _carbohydrate_ means _carbon combined with water_; that is, the
element carbon is combined with hydrogen and oxygen, which exist in the
carbohydrate compound in the same proportion as they exist in water.
The carbohydrates are closely related chemically to the aldehydes and
the alcohols, so far as their composition is concerned (See "Aldehydes
and Ethers," Lesson III, p. 93), but this does not imply that they have
the same physiological effect in the animal body.