Elementary biology : descriptive and experimental / by John Thornton.

  • Thornton, John
Date:
1907
Catalogue details

Licence: In copyright

Credit: Elementary biology : descriptive and experimental / by John Thornton. Source: Wellcome Collection.

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    Glucose or grape-sugar (CGH1206) occurs very widely in the cell-sap of many vegetables, especially in the juice of the grape, cherry, pear, and other sweet fruits. It is also found in honey. Glucose is less sweet than cane-sugar, as may be found by comparing the taste of two or three granular masses from a raisin (a dried grape) with two or three similar pieces of common sugar. It is also less soluble than common sugar. Glucose is further distinguished from cane-sugar by the fact that under the influence of yeast it readily ferments, yielding mainly alcohol and carbon dioxide.1 Cane-sugar does not directly ferment with yeast. Glucose is now prepared artificially in large quantities for the use of brewers and confectioners by the action of sulphuric acid on grains that contain a large proportion of starch. As it is difficult to crystallize, commercial glucose is in the form of a syrup or pasty mass. Sugar is formed by plants from the food materials taken in, and it is afterwards used in the construction of proto- plasm, or transferred from one part of the plant to the other to be kept as reserve food. It is stored either as sugar or after being converted into starch. During the growing summer season sugar is transported from leaves to roots in many plants, and then from roots to stem and leaves when growth begins again in spring after the winter’s rest. The sugar of plants in the form of nectar also serves to attract insects (par. 62). Sugar is largely used as food by man, the supply being chiefly obtained from the beet-root, the sugar-cane, and the sugar-maple. As already stated, all these give saccharose or cane-sugar. The special value of sugar as a food is due to the fact that it is, after slight change, readily and directly absorbed into the blood in the alimentary canal, and thus becomes a nutritive substance at once. 1 Another distinguishing test for grape-sugar is described on page 237- D
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