roperties to isomaltose. =Cellobiose= is a disaccharide which
results from the hydrolysis of cellulose. It is a reducing sugar, forms an
osazone, and resembles maltose.

Maltose, isomaltose, gentiobiose, and cellobiose, are all
glucose-glucosides, the difference between them being undoubtedly due to
linkage being between different alcoholic groups in the glucose molecules.

The disaccharide =lactose= is a glucose-galactoside. It is the sugar which
is present in the milk of all mammals. It has never been found in plants.
=Melibiose=, which is the corresponding vegetable glucose-galactoside, may
be obtained by the partial hydrolysis of the trisaccharide _raffinose_ (see
below). It is a reducing sugar; forms a characteristic osazone; and
exhibits mutarotation. It is not fermented by ordinary top-yeasts, but is
first hydrolyzed and then fermented by the enzymes present in
bottom-yeasts.

TRISACCHARIDES

Trisaccharides, as the name indicates, consist of three hexoses (or
monosaccharides) linked together by the dropping out of two molecules of
water. Their formula is C_{18}H_{32}O_{16}. When completely hydrolyzed,
they yield three molecules of monosaccharides; when partially hydrolyzed,
one each of a disaccharide and a monosaccharide.

One trisaccharide of the reducing sugar type, namely _rhamnose_, exists in
plants as a constituent of the glucoside xanthorhamnin. It is composed of
one molecule of glucose united to two molecules of rhamnose (methyl
pentose, C_{6}H_{12}O_{5}). It is of interest only in connection with the
properties of the glucoside in which it is present (see page 84).

Three trisaccharides which are non-reducing sugars are found in plants;
namely, raffinose, gentianose, and melizitose.

=Raffinose= occurs normally in cotton seeds, in barley grains, and in
manna; also, in small quantities in the beet root, associated with sucrose.
It is more soluble in water than is sucrose and hence remains in solution
in the molasses from beet-sugar manufacture, which constitutes the
commercial source for this sugar. Raffinose crystallizes out of
concentrated solutions, with five molecules of water of crystallization, in
clusters of glistening prisms. It is strongly dextrorotatory, the anhydrous
sugar having a specific rotatory power of +185 deg., and the crystalline
form, C_{18}H_{32}O_{16}, showing a specific rotation of +104.5 deg. It
does not reduce Fehling's solution, nor form an o