58 THE CARBOHYDRATES. 



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

 saccharose, lactose, maltose, and isomaltose. They are all hexo- 

 bioses /. e.j they represent the union of the anhydrides of two 

 hexoses, and can therefore be represented by the general formula 

 C 12 H 22 O n . Of these, cane-sugar is formed through the union of 

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

 glucose and galactose; while maltose contains two molecules of 

 glucose. 



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, diiTerences 

 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 only after inver- 

 sion to monosaccharides. It is true that a solution of cane-sugar or 

 of lactose will undergo alcoholic fermentation when exposed to the 

 action of yeast; but we now know that the yeast-cell is capable of 

 furnishing certain ferments which belong to the class of the so-called 

 non-organized ferments, and which themselves are capable of bring- 

 ing about the inversion of these more complex carbohydrates. 

 Emil Fischer, moreover, has shown that for the inversion of a 

 special disaccharide a specific ferment is necessary. 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 ferments are 

 spoken of as invertin, maltase, and laetase. 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 Isevulose 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 is found in nature most abundantly in sugar-cane, in 

 the roots of the sugar beet, and in the stems of certain plants. 

 The pure substance is crystalline, and melts at 160 C. On further 

 heating it turns brown and forms so-called caramel. It is easily 

 soluble in water; and turns the plane of polarization to the right. 



