DEXTRO-GLUCOSE, DEXTROSE, GRAPE-SUGAR, or DIABETIC SUGAR. One of the carbohydrates that are represented by the formula As ordi narily obtained, the crystals of dextro-glucose in clude one molecule of water for every molecule of the carbohydrate, and are therefore represented by the formula + HD. It occurs natural ly in fruits (notably in grapes, cherries, bananas, apples, pears, plums, etc.) and other vegetable tissues, usually in mixtures with other carbohy drates, among the more important of which are fruit-sugar (also called hevulose and dextro fructose), cane-sugar, and starch. It may often be observed in the crystalline state on raisins and figs, and in 'candied' honey, of which it is also a constituent. It also occurs in plants in combina tion with organic acids, the compounds, called `glucosides,' including the well-known salicin of the willow and amygdalin of bitter almonds. Glucose is one of the early products of photo synthesis (q.v.) in plants, in which it is formed from carbon dioxide and water, probably by the condensation of formaldehyde with the liberation of oxygen. As a food it is freely utilized by the plant producing it for the formation of more com plex sugars, other carbohydrates. and proteids. It may be accumulated as a reserve in many fruits, e.g. the grape. Glucose is one of the best foods for fungi and has even been fed success fully to some seed-plants, e.g. corn, which in the absence of other foods can use it in producing starch. In the animal kingdom, grape-sugar is found sometimes as a normal and sometimes as a pathological constituent of various fluids and tissues. Thus, it occurs normally in the contents of the small intestine, and in the chyle after the use of amylneemis and saccharine foods, in the blood of the hepatic veins (see LIVER), in the tissue of the liver, in both the yolk and white of birds' eggs, in the urinary secretion in minute quantity, etc. In diabetes, it exists in large quan tity in the urinary secretion, and may be de tected in nearly all the fluids of the body. The statement is frequently found in the older treatises on chemistry and medicine that grape sugar is produced by the action of ptyalin and pancreatin on starch; but later researches have shown that the principal products of the action of these enzymes on starch are dextrin and mal tose, intermediate products which are changed to glucose when treated with acids. (See further below.) Dextro-glucose seldom occurs in distinct, well formed crystals, but may be obtained in warty masses which, when examined under the micro scope, are found to consist of minute six-sided tablets. It is white when pure, melts at from SO°
to 100° C. (176°-212° F.), depending upon the manner of heating and the consequent rapidity with which it parts with its water of crystalliza tion. At higher temperatures (above 200° C.) it loses its sweetness and passes into a brown unfermentable substance called caramel, which is soluble in water and has a bitter taste. This substance is prepared on a large scale from commercial glucose and, under the name of `burnt sugar,' sugar-color,' or 'starch sugar-color,' is used for coloring foods, confectionery, liquors, etc. Grape-sugar is less sweet than ordinary cane sugar. (See SUGAR.) Its relative sweetening power has been variously estimated at one-half to three-fifths that of cane-sugar. It is very soluble in water, but is. only slightly soluble in strong alcohol. One of the most important prop erties of grape-sugar is its capacity for under going fermentation under the action of the yeast plant. It is upon this property that the use of yeast depends in the manufacture of alcohol, dis tilled liquors, beer and other malt liquors, wines, and bread. In these processes grape-sugar is de composed into alcohol and carbonic-acid gas, according to the following equation: = Grape-sugar Alcohol Carbonic-acid gas The power of decomposing grape-sugar and other carbohydrates is possessed by a number of species of the lower forms of vegetable life, the decom position products varying greatly with the species and the conditions. The action of bacteria on sugars and other carbohydrates has been found to be a very valuable means of identifying a num ber of species of these microscopic organisms. For example, one species transforms grape-sugar into lactic acid, from which the subsequent or simultaneous intervention of another species of bacteria, butyric acid, may be obtained. Grape sugar itself is produced by the hydrolysis of a number of carbohydrates which have more com molecular structure. These changes, which consist in the splitting up of the more complex molecules with the simultaneous absorption of water. may he brought about by hot dilute acids or by contact with certain enzymes (q.v.). Cane sugar is 'inverted' by treatment with dilute acid.4 (see CATALYTIC ACTION), or by invertin (an enzyme produced by the yeast-plant), the prod uct of the reaction, which is a mixture of equal parts of grape-sugar and fruit-sugar, known as `invert sugar':