12 HUMAN PHYSIOLOGY. 



color entirely disappears. The strength of this solution is such 

 that one c.c. is decolorized by five milligrams of sugar, from which 

 the percentage of sugar in any solution can be determined. 



Fermentation Test. If to a solution of dextrose a small quantity 

 of the yeast plant be added, and the solution kept at a temperature 

 of 25 C., it will gradually undergo fermentation; that is, will be 

 reduced to simpler compounds and especially to alcohol and carbon 

 dioxid. The change is expressed in the following equation : 



C 6 H 12 O 6 = 2C 2 H 6 O + 2 CO 2 . 



Dextrose. Alcohol. Carbon 



Dioxid. 



About ninety-five per cent, of the dextrose is so changed, the remain- 

 ing five per cent, yielding secondary products succinic acid, glycerin, 

 etc. 



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, however, varies with the temperature and concentration of the 

 solution. 



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

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

 ing action on cupric oxid. 



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

 sulphuric acid. In many chemic relations it resembles dextrose. It 

 is less soluble in water, however, crystallizes more easily, and has 

 a greater dextro-rotary 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 

 vegetable 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 oxid, and hence its presence can not be 



