320
D. J. BELL
accessory organs and their seminal plasma is probably devoid of detectable quantities of D-fructose, although it appears that traces may be
formed by the spermatozoa themselves (86). Traces may be present in
the hen's egg (72).
The sugar has been identified also as the sole reducing carbohydrate
in the larva of the fly (Gastrophilus) (87). D-Fructose is found in
the urine of fructosurics (88), in which its presence may be due to
a low kidney threshold or possibly excessive dephosphorylation.
2. Combined
Combined D-fructose is widespread in the higher plants. In these the
fructosyl radicals are always in the furanose form; in sucrose, the
oligosaccharides (see Section VI) derived from sucrose, and the storage
polysaccharides (89) of the inulin (Compositae), levan (Gramineae),
and irisin (certain but not all Iris spp.) or triticin (Triticum spp.)
types. "Conventional" glycosides of D-fructose (that is, ones with a
noncarbohydrate aglycone) are unknown to the writer; indeed the only
such derivative of a hexulose is the adenylpsicofuranoside synthesized
by Streptomyces hygroscopicus (49). There is no knowledge of any
glycosidic compound of fructose being synthesized in the animal kingdom with the exception of sucrose, which appears sometimes to be of
endogenous origin in the sucrosuric*
D. D-GALACTOSE
1. Free
Apart from trace amounts D-galactose has been found free, in quantity, in a single but well-substantiated instance in the plant kingdom,
namely as a crystalline exudate on ivy leaves after a severe frost (89).
In the familial human syndrome of galactosemia the sugar is present in
appreciable amounts in the blood and from thence is excreted by the
kidney with the urine (90). Galactose and xylose are cataractogenic
sugars (91); the galactosemic infant will develop cataract, and mental
defect, if sources of dietary galactose such as lactose are not withheld.
2. Combined
In glycosidic combination, D-galactose is almost universally distributed. Although it is present in but a few of the known glycosides
of the "conventional" type (91a), the sugar has recently been discovered in a variety of situations in combination with rat/o-inositol
(92) and with glycerol (93) to form O-D-galactopyranosides. The
former substance has been isolated from sugar beet (92), and the
* See reference 220.
D. J. BELL
accessory organs and their seminal plasma is probably devoid of detectable quantities of D-fructose, although it appears that traces may be
formed by the spermatozoa themselves (86). Traces may be present in
the hen's egg (72).
The sugar has been identified also as the sole reducing carbohydrate
in the larva of the fly (Gastrophilus) (87). D-Fructose is found in
the urine of fructosurics (88), in which its presence may be due to
a low kidney threshold or possibly excessive dephosphorylation.
2. Combined
Combined D-fructose is widespread in the higher plants. In these the
fructosyl radicals are always in the furanose form; in sucrose, the
oligosaccharides (see Section VI) derived from sucrose, and the storage
polysaccharides (89) of the inulin (Compositae), levan (Gramineae),
and irisin (certain but not all Iris spp.) or triticin (Triticum spp.)
types. "Conventional" glycosides of D-fructose (that is, ones with a
noncarbohydrate aglycone) are unknown to the writer; indeed the only
such derivative of a hexulose is the adenylpsicofuranoside synthesized
by Streptomyces hygroscopicus (49). There is no knowledge of any
glycosidic compound of fructose being synthesized in the animal kingdom with the exception of sucrose, which appears sometimes to be of
endogenous origin in the sucrosuric*
D. D-GALACTOSE
1. Free
Apart from trace amounts D-galactose has been found free, in quantity, in a single but well-substantiated instance in the plant kingdom,
namely as a crystalline exudate on ivy leaves after a severe frost (89).
In the familial human syndrome of galactosemia the sugar is present in
appreciable amounts in the blood and from thence is excreted by the
kidney with the urine (90). Galactose and xylose are cataractogenic
sugars (91); the galactosemic infant will develop cataract, and mental
defect, if sources of dietary galactose such as lactose are not withheld.
2. Combined
In glycosidic combination, D-galactose is almost universally distributed. Although it is present in but a few of the known glycosides
of the "conventional" type (91a), the sugar has recently been discovered in a variety of situations in combination with rat/o-inositol
(92) and with glycerol (93) to form O-D-galactopyranosides. The
former substance has been isolated from sugar beet (92), and the
* See reference 220.