CELL-CONTENTS AND CELL-WALLS. 53 



monosaccharides. The liexoses are combined together as 

 units in the disaccharides, trisaccharides, and polysac- 

 charides, named according as they contain two, three, or 

 more of the monosaccharide units. Cane sugar (sucrose) 

 and malt sugar (maltose) are disaccharides ; starch, 

 dextrin, iiiulin, and cellulose are polysaccharides. These 

 complex compounds are converted into the simple mono- 

 saccharides by hydrolysis with acids, or by the action of 

 enzymes (e.g. diastase, invertase, inulase, cytase). 



Of the following general characters and reactions of the 

 carbohydrates, one or other may fail] or only be, shown 

 after the substance has been treated in some way, e.g. 

 by hydrolysing agents or by enzymes. (1) They reduce 

 alkaline solutions of copper ; (2) they are coloured yellow 

 by alkalis ; (3) they rotate the plane of polarised light 

 either to right or left ; (4) in contact with Yeast, they^are 

 split into alcohol and carbon dioxide; (5) when strongly 

 heated they are decomposed, charred, and yield various 

 products ; (6) on being heated with* mineral acids they are 

 decomposed, with formation of formic acid and other 

 substances ; (7) they give a deposit of needle-like crystals 

 with phenyl-hydrazine ; (8) some are insoluble in water, 

 while others are readily soluble, and '.those which are in- 

 soluble can be converted into soluble carbohydrates by 

 hydrolysis ; (9) in absolute alcohol most of them are 

 either insoluble or only slightly soluble. 



62. Glucose, Maltose, and Sucrose. Examine 

 specimens of these three sugars. 



(1) Glucose (grape sugar) occurs in commerce in warty 

 uncrystallised yellowish masses, but is readily crystallised 

 e.g. on dissolving it in hot alcohol and cooling the solu- 

 tion ; on being treated with caustic soda it turns yellow ; 

 it reduces various metallic oxides j. in alkaline solutions ; ^it 

 forms a characteristic osazone with phenylhydraziue. 



(2) Maltose (malt sugar) occurs as a white warty mass 

 of needle-like crystals ; it is the'chief sugar formed by the 

 action of diastase upon starch ( 74, i) it reduces metallic 

 oxides in alkaline solutions, but it does not give Barfoed's 

 test and is therefore easily distinguished from glucose. 



