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MONOSACCHARIDES. 197
Correspondingly the carbohydrates can he divided into three chief
groups, namely, 1. Simple sugars or monosaccharides, 2. Complex sugars
or disaccharides, trisaccharides and crystalline polysaccharides, and
3. Non-crystalline or colloid polysaccharides. Of these groups the mono-
saccharides, disaccharides and colloid polysaccharides are of special
physiological importance.
Our knowledge of the carbohydrates and their structural relation-
ships has been very much extended by the pioneering investigations of
Killiani ’ and especially those of E. Fischer.2
As the carbohydrates occur chiefly in the plant kingdom it is naturally
not the place here to give a complete discussion of the numerous carbo-
hydrates known up to the present time. According to the plan of this
work it is only possible to give a short review of those carbohydrates
which occur in the animal kingdom or are of special importance as food
for man and animals.
1. Monosaccharides.
All varieties of sugars are characterized by the termination " ose,"
to which a root is added signifying their origin or other relations. Accord-
ing to the number of carbon atoms contained in the molecule the mono-
saccharides are divided into, trioses, tetroses, pentoses, hexoses, heptoses,
and so on.
All monosaccharides are either aldehydes or ketones of polyhydric
alcohols. The former are termed aldoses and the latter ketoses. Ordinary
glucose is an aldose, while ordinary fruit sugar (fructose) is a ketose.
The difference may be shown by the structural formula? of these two
varieties of sugar:
Glucose = CH2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CHO;
Fructose = CH2 (OH).CH(OH).CH(OH).CH(OH).CO.CH2 (OH).
A difference is also observed on oxidation. The aldoses can be con-
verted into oxyacids having the same quantity of carbon, while the ketoses
yield acids having less carbon. On mild oxidation the aldoses yield
monobasic oxyacids, and dibasic acids on more energetic oxidation. Thus
ordinary glucose yields gluconic acid in the first case and saccharic
acid in the second.
1
Ber. d. deutsch. chem. Gesellsch., 18, 19, and 20.
2
See E. Fischer’s lecture, Synthesen in der Zuckergruppe, Ber. d. deutsch. chem.
Gesellsch., 23, 2114. Excellent works on carbohydrates are Tollen’s Kurzes Hand-
buch der Kohlehydrate, Breslau, 2 (1895), and 1, 2. Auflage, 1898, which gives a
complete review of the literature, and E. O. v. Lippmann, Die Chemie der Zucker-
arten, Braunschweig, 1904.
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