CHEMIC COMPOSITION OF THE HUMAN BODY. 9 



For quantitative analysis, 10 c.c. of Fehling's solution, diluted with 

 40 c.c. of water, are heated in a porcelain capsule, to which the suspected 

 solution is cautiously added from a buret until the blue color entirely dis- 

 appears. The strength of this solution is such that 10 c.c. is decolorized 

 by 50 milligrams of sugar (dextrose}. Thus if 0.8 c.c. of the suspected solu- 

 tion, e.g., urine, decolorizes 10 c.c. of Fehling's solution, then it contains 50 

 milligrams of sugar, from which the percentage of sugar in the urine can be 

 determined. 



The Fermentation Test. All the sugars with the exception of lactose 

 undergo reduction to simpler compounds, mainly alcohol and carbon dioxid, 

 under the action of the yeast plant, Saccharomyces ceremsia. The change 

 with dextrose is expressed in the following equation: 



Dextrose = Alcohol + Carbon 

 Dioxid. 



About 95 per cent, of the dextrose is so changed, the remaining 5 per 

 cent, yielding secondary products succinic acid, glycerin, etc. As a 

 means of testing any solution for the presence of sugar this method may 

 be adopted. It is generally very satisfactory. From the quantity of 

 carbon dioxid and alcohol thus produced the quantity of sugar in the solu- 

 tion may be determined. 



Levulose, or fruit-sugar, is found in association with dextrose as 

 a constituent of many fruits. It is sweeter than dextrose and more soluble 

 in both water and dilute alcohol. From alcoholic solutions it crystallizes 

 in fine, silky needles, though it usually occurs in the form of a syrup. 



Levulose is distinguished from dextrose by its property of turning 

 the plane of polarized light to the left; the extent to which it does so, how- 

 ever, varies with the temperature and concentration of the solution. For this 

 reason it is turned levulo-rotatory and has received its name from this fact. 



Under the influence of the yeast plant it slowly undergoes fermen- 

 tation, yielding the same products as dextrose. It also has a reducing 

 action on cupric hydroxid. 



Galactose is obtained by boiling milk-sugar (lactose) with dilute sul- 

 phuric acid. In many chemic relations it resembles dextrose. It is less 

 soluble in water, however, crystallizes more easily, and has a greater dextro- 

 rotatory power. It also undergoes fermentation with the yeast plant. 



3. SACCHAROSES, C 12 H 22 O n . 



Saccharose, or cane-sugar, is widely distributed throughout the vege- 

 table world, but is especially abundant in sugar-cane, sorghum cane, sugar- 

 beet, Indian corn, etc. It crystallizes in large monoclinic prisms. It is 

 soluble in water and in dilute alcohol. Saccharose has no reducing power on 

 cupric hydroxid, and hence its presence cannot be detected by Fehling's 

 solution. It is dextro-rotatory. Boiled with dilute mineral, as well as 

 with organic acids, saccharose combines with water and undergoes a change 

 in virtue of which it rotates the plane of polarized light to the left, and hence 

 the product was termed invert sugar. This latter has been shown to be a 

 mixture of equal quantities of levulose and dextrose. This inversion of 

 saccharose through hydration and decomposition is expressed in the fol- 

 lowing equation: 



