THE DISACCHARWES. 69 



gous to the formation of ethers from alcohols. On hydrolytic de- 

 composition they accordingly yield two monosaccharine molecules, 

 which represent either one and the same substance or two isomeric 

 bodies : 



C 12 H 22 O n = [C 6 H 12 6 ] 2 - H 2 or 



C 12 H 22 O n + H 2 O = 2C 6 H 12 6 . 



Some of the disaccharides occur in nature as such, while others 

 result from the decomposition of still more complex carbohydrates, 

 viz., the polysaccharides proper. 



The most important members of the group are cane-sugar or 

 saccharose, lactose, and maltose. They are all hexo-bioses i. e., 

 they represent the union of the anhydrides of two hexoses, and can 

 therefore be represented by the general formula C 12 H22O n . Of these, 

 cane-sugar is formed through the union of one molecule of glucose 

 and one molecule of laevulose ; lactose from glucose and galac- 

 tose; while maltose contains two molecules of glucose. Other 

 members of the group which, however, do not occur in the animal 

 body are trehalose, gentiobiose, cellose (cellobiose), and melibiose. 



In their general properties the disaccharides closely resemble the 

 monosaccharides. Like these, they have a sweet taste. They are 

 crystallizable, capable of passing through animal membranes, and 

 are optically active. In certain particulars, however, differences 

 exist. Lactose, maltose, and isomaltose are thus capable of reducing 

 metallic oxides in alkaline solution, and yield osazons with phenyl- 

 hydrazin, while saccharose does not react in this manner. 



The disaccharides as such are not fermentable, but become so 

 after inversion to monosaccharides. Emil Fischer has shown that 

 for the inversion of a special disaccharide a specific ferment is neces- 

 sary. As the various fermentative agents, however, possess a varying 

 number of inverting ferments, it is clear that a certain disaccharide 

 may be inverted by one form of yeast, but not by another; while, on 

 the other hand, one special form may be capable of inverting all forms 

 of the disaccharides. This is actually the case, and we thus find that 

 the so-called kefir granules, as also the Bacterium lactis, can invert 

 cane-sugar as well as maltose and lactose. Common yeast, on the 

 other hand, inverts only cane-sugar and maltose, while lactose is not 

 attacked. According to their specific power of inversion, these fer- 

 ments are spoken of as invertm, maltase, and lactose. The derivation 

 of the two latter names is, of course, apparent. The significance of 

 the term invertin, however, is not so clear. It has reference to the 

 mixture of glucose and laevulose which is obtained from cane-sugar 

 by inversion, and which was originally spoken of as invert-sugar. 

 Invertin is thus a ferment which inverts cane-sugar. 



After inversion the disaccharides undergo fermentation, like the 

 monosaccharides, and here, as there, we may distinguish between 

 alcoholic, lactic acid, butyric acid, and acetic acid fermentation. 



Cane-sugar (saccharose, saccharobiose) is found in nature most 



