fford another means of conversion of one sugar into another.

From the standpoint of physiological processes, _glucuronic acid_ is the
most interesting and important oxidation product of glucose. It is often
found in the urine of animals, as the result of the partial oxidation of
glucose in the animal tissues. Normally, glucose is oxidized in the body to
its final oxidation products, carbon dioxide and water. But when many
difficultly oxidizable substances, such as chloral, camphor, turpentine
oil, aniline, etc., are introduced into the body, the organism has the
power of combining these with glucose to form glucosides. These so-called
"paired" compounds are then oxidized to the corresponding glucuronic acid
derivatives and eliminated from the body in the urine. No phenomenon
similar to this occurs in plants, however, and glucuronic acid has never
been found in plant tissues.

=Synthesis and Degradation of Hexoses.=--Monosaccharides of any desired
number of carbon atoms can be produced from aldoses having one less carbon
atoms, by way of the familiar "nitrile" reaction. Aldoses, like all other
aldehydes, combine directly with hydrocyanic acid, forming compounds known
as nitriles, which contain one more carbon atom than was present in the
original aldehyde; the cyanogen group can easily be converted into a COOH
group; and this, in turn, reduced to an aldehyde, thus producing an aldose
with one more carbon atom than was present in the initial sugar. These
changes may be illustrated by the following equations:

(1) CHO + HCN CHOH.CN CN
| | |
(CHOH)_{3} = (CHOH)_{3} or (CHOH)_{4}
| | |
CH{2}OH CH_{2}OH CH_{2}OH
Aldopentose Nitrile

(2) CN + H_{2}O COOH + NH_{3}
| |
(CHOH)_{4} = (CHOH)_{4}
| |
CH_{2}OH CH_{2}OH
Nitrile Acid

(3) COOH - O CHO
| |
(CHOH)_{4} = (CHOH)_{4}
| |
CH_{2}OH CH_{2}OH
Acid Aldohexose

It is possible, by this process, to advance step by step from formaldehyde