THE MONOSACCHARIDES. 67 



As stated above, most of the hexoses are capable of undergoing 

 fermentation /. e., a decomposition which is effected through the 

 activity of certain minute organisms. According to the character 

 of the specific organism present, we distinguish between alcoholic 

 and acid fermentation, such as lactic acid, butyric acid, and acetic 

 acid fermentation. The former is brought about through the 

 influence of various varieties of yeast, while the latter is referable 

 to the activity of certain bacteria, such as Bacterium lactis aerog- 

 enes, Bacillus acidi butyrici, Mycoderma aceti, etc. The decom- 

 positions which are thus effected may be represented by the equa- 

 tions : 



(1) C 6 H 12 6 = 2C 2 H 5 (OH) -f- C0 2 . 



Ethyl alcohol. 



(2) C 6 H 12 6 = 2CH 3 CH.OH-COOH. 



Lactic acid. 



(3) 2C 3 H 6 3 = C 3 H 7 .COOH + 2CO 2 + 4H. 

 Lactic acid. Butyric acid. 



Upon the readiness with which the hexoses are oxidized the so- 

 called reduction tests are based, viz., the reduction of metallic oxids 

 on heating in alkaline solution. Of the hexoses, glucose, galactose, 

 and laevulose are the only ones which occur in the animal kingdom, 

 while mannose is found only in the vegetable world. Of the first 

 three, moreover, glucose is by far the most important. 



Glucose will be considered in detail in another chapter, where the 

 methods of testing for the simple sugars in general, as also their 

 quantitative estimation, will be described. 



Laevulose (fructose) occurs in nature together with glucose, most 

 abundantly in various fruits, the roots and seeds of many vegetables, 

 and also in honey. It further results during the hydrolytic decom- 

 position of cane-sugar, inulin, and other carbohydrates. In the 

 animal body it has been found only after its introduction from without 

 (in the urine) and in rare cases of diabetes. It is readily soluble in water, 

 and its aqueous solutions, in contradistinction to common glucose, 

 are Ia3vorotatory. It may be obtained in crystalline form, but with 

 difficulty. It is fermentable, and gives the same reduction- tests as 

 glucose (which see). With phenylhydrazin Isevulose yields the 



C* TT 



same osazon, but with methyl-phenyl hydrazin pVr 5 >N.NH 2 it 



forms a fructose methyl-phenyl osazon, which cannot be obtained 

 either with glucose, mannose, or glucosamin. Its formula is : 



CH 2 .OH.(CHOH) 3 .C.CH:KN(CH 3 ).C 6 H 5 

 N.N(CH 3 ).C 6 H 6 



Galactose is formed during the hydrolytic decomposition of 

 lactose and many other carbohydrates. It is also obtained from 

 cerebrin on heating with dilute mineral acids. It is not so readily 

 soluble in water as glucose, but like it is dextrorotatory. Galactose 

 crystallizes in needles and platelets which melt at 168 C. It is 



