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D. J. BELL
amounts in plant sap, in the tissue fluids and excreta of animals, and
even in soils. These trace amounts must almost certainly be regarded
as "escapes" from normal mechanisms of anabolism and catabolism.
Nonetheless, the presence of such sugars does provide some confirmation of their participation in physiological metabolic pathways. The
value of some of the older work on the assay of glucose (and other
reducing sugars) in tissue fluids must be accepted with some caution
since the methods used are not always entirely specific. It must be
borne in mind, also, that preparations of glucose oxidase, which
are of fungal origin, may contain glucosidases such as trehalase. In
most organisms it seems that nearly all the carbohydrate of their tissues
is present in combined states. An interesting survey of fungal polysaccharides has been made (65a).
A. D-GLUCOSE
1. Free
This sugar is, of course, a characteristic component of the blood
and tissue fluids of vertebrate animals and has also been found in the
tissue fluids of many kinds of plant. In a number of invertebrates—
limpets (66), snails (66, 66a), nematodes (67), and insects (68)—
little or no free glucose can be detected. In arthropods—crabs (66a,
68a) and crayfishes (68b)—and in species of Arenicola and Sipunculus
D-glucose has been detected, by reliable procedures, in the body fluids
(68a, 68b). In locusts (69) and in some other insects (68) the nonreducing disaccharide trehalose (Section VI,A) seems to be the major
carbohydrate component of low molecular weight.
In vertebrate blood, species differences occur with respect to the
relative distribution of D-glucose between the water of the plasma and
the water of the erythrocytes (70). Man is at one end of the scale, with
approximately equal concentrations of the sugar in both erythrocytes
and plasma, whereas the domestic fowl carries virtually all its blood
glucose in the plasma (71). The hen's egg (72) and its 11-day embryonic allantoic fluid (73) both contain a little D-glucose.
2. Combined
Among oligosaccharides, polysaccharides (74), and natural glycosides (74a),* examples containing moieties of D-glucose are too numerous to mention. There are, however, one or two instances of somewhat
unusual character which may be brought to the reader's notice.
Nervous tissue of vertebrates normally contains certain mixed, lipid* The isolation of 0-methyl-/?-D-glucoside from Scabiosa succtsa (mentioned
in reference 74a, p. 554) may be an artifact. (See reference 23.)
D. J. BELL
amounts in plant sap, in the tissue fluids and excreta of animals, and
even in soils. These trace amounts must almost certainly be regarded
as "escapes" from normal mechanisms of anabolism and catabolism.
Nonetheless, the presence of such sugars does provide some confirmation of their participation in physiological metabolic pathways. The
value of some of the older work on the assay of glucose (and other
reducing sugars) in tissue fluids must be accepted with some caution
since the methods used are not always entirely specific. It must be
borne in mind, also, that preparations of glucose oxidase, which
are of fungal origin, may contain glucosidases such as trehalase. In
most organisms it seems that nearly all the carbohydrate of their tissues
is present in combined states. An interesting survey of fungal polysaccharides has been made (65a).
A. D-GLUCOSE
1. Free
This sugar is, of course, a characteristic component of the blood
and tissue fluids of vertebrate animals and has also been found in the
tissue fluids of many kinds of plant. In a number of invertebrates—
limpets (66), snails (66, 66a), nematodes (67), and insects (68)—
little or no free glucose can be detected. In arthropods—crabs (66a,
68a) and crayfishes (68b)—and in species of Arenicola and Sipunculus
D-glucose has been detected, by reliable procedures, in the body fluids
(68a, 68b). In locusts (69) and in some other insects (68) the nonreducing disaccharide trehalose (Section VI,A) seems to be the major
carbohydrate component of low molecular weight.
In vertebrate blood, species differences occur with respect to the
relative distribution of D-glucose between the water of the plasma and
the water of the erythrocytes (70). Man is at one end of the scale, with
approximately equal concentrations of the sugar in both erythrocytes
and plasma, whereas the domestic fowl carries virtually all its blood
glucose in the plasma (71). The hen's egg (72) and its 11-day embryonic allantoic fluid (73) both contain a little D-glucose.
2. Combined
Among oligosaccharides, polysaccharides (74), and natural glycosides (74a),* examples containing moieties of D-glucose are too numerous to mention. There are, however, one or two instances of somewhat
unusual character which may be brought to the reader's notice.
Nervous tissue of vertebrates normally contains certain mixed, lipid* The isolation of 0-methyl-/?-D-glucoside from Scabiosa succtsa (mentioned
in reference 74a, p. 554) may be an artifact. (See reference 23.)