The reverse process, or the so-called "degradation" of a sugar into another containing fewer carbon atoms, may be readily accomplished in either one or two ways. In Wohl's process, the aldehyde group of the sugar is first converted into an _oxime_, by treatment with hydroxylamine; the oxime, on being heated with concentrated sodium hydroxide solution, splits off water and becomes the corresponding _nitrile_; this, on further heating, splits off HCN and yields an aldose having one less carbon atom than the original sugar. This process is the exact reverse of the nitrile synthesis, described above. The second method of degradation, suggested by Ruff, makes use of Fenton's method of oxidizing aldehyde sugars to the corresponding monobasic acid, using hydrogen peroxide and ferrous sulfate as the oxidizing mixture; the _aldonic acid_ thus formed is then converted into its calcium salt, which, when further oxidized, splits off its carboxyl group and one of the hydrogens of the adjacent alcoholic group, leaving an aldose having one less carbon atom than the original aldose sugar. =Enolic Forms.=--A final avenue for the interconversion of glucose, mannose, and fructose into one another, is through the spontaneous transformations which these undergo when dissolved in water containing sodium hydroxide or potassium hydroxide. This change is due to the conversion of the sugar, in the alkaline solution, into an _enol_, which is identical for all three sugars, and which may subsequently be reconverted into any one of the three isomeric hexoses. The relationships involved are illustrated in the following formulas: CHO CHO CH_{2}OH CHOH | | | ║ H-C-OH HO-C-H C=O C-OH | | | | HO-C-H HO-C-H HO-C-H HO-C-H | | | | H-C-OH H-C-OH H-C-OH H-C-OH | | | | H-C-OH H-C-OH H-C-OH H-C-OH | | | | CH_{2}OH CH_{2}OH CH_{2}OH CH_{2}OH Glucose Mannose Fructose Enolic Form The preceding technical discussion of the chemical constitution and reactions of the hexoses has been presented, not because it has any direct connection with the occurrence or functions of these compounds in plant tissues, but for the purpose of giving to the student a graphic conception of the structure and properties of these simple carbohydrates, as a basis for the understanding of the nature, properties, possible chemical reactions, syntheses, etc., of the more complex types of carbohydrates, which, along with these simple monosaccharides, constitute the most important single group of organic components of plants.