One of a large series of amorphous or crystalline
   substances, occurring very widely distributed in plants, rarely in
   animals, and regarded as influental agents in the formation and
   disposition of the sugars. They are frequently of a bitter taste, but,
   by the action of ferments, or of dilute acids and alkalies, always
   break down into some characteristic substance (acid, aldehyde, alcohol,
   phenole, or alkaloid) and glucose (or some other sugar); hence the
   name. They are of the nature of complex and compound ethers, and
   ethereal salts of the sugar carbohydrates.