THE POLYSACCHARIDES. 71 



to maltose, which finally yields glucose. In other cases, as with 

 glycogen, the disaccharides isomaltose and maltose are formed 

 directly. Cellulose likewise yields glucose as a final product, while 

 laevulose results from inulin, and mannose from the so-called reserve 

 celluloses, which are found in the cell-walls of many seeds. Galac- 

 tose is similarly obtained from many gums, and from a variety 

 of cellulose, which Schultze has termed galactose-cellulose, in con- 

 tradistinction to the mannose-cellulose and the true dextrose-cellu- 

 loses. In many instances, however, the exact mode of decomposi- 

 tion, as also the character and number of the intermediary products, 

 is but imperfectly understood. 



In their physical and chemical properties considerable differences 

 exist between the polysaccharides and the other carbohydrates 

 which have so far been described. They are thus (with the possible 

 exception of glycogen) non-crystallizable substances and devoid of a 

 sweet taste. In alcohol and ether they are insoluble. In water 

 most of them are more or less soluble, but as a class they are 

 incapable of diffusing through animal membranes, for which reason 

 they are termed saccharocolloids. From their solutions they can be 

 precipitated by saturation with neutral salts, and notably ammonium 

 sulphate. Like the monosaccharides and disaccharides, they are 

 optically active, but with the exception of the dextrins they do not 

 reduce metallic oxides in alkaline solution, and none of them 

 combine with phenylhydrazin to form osazons. As such, they are 

 incapable of undergoing fermentation ; but, like the disaccharides, 

 they may be inverted to monosaccharides through various ferments 

 or acids, and can then be further decomposed. 



Especially important is their behavior toward iodine, with which 

 most of the polysaccharides combine to form colored compounds that 

 are quite characteristic. Starch is thus colored blue, glycogen a 

 mahogany brown, erythrodextrin red, inulin and lichenin yellow. 



The polysaccharides which are used as food-stuffs are con- 

 veniently divided into starches, dextrins, vegetable gums, and cellu- 

 loses. Of these, the starches are by far the most important. 



Starch occurs widely distributed in the vegetable world, and con- 

 stitutes the most important reserve food of most of the higher 

 plants. It is found in the form of distinct granules, which, on 

 microscopic examination, exhibit a marked concentric striation, and 

 which differ in size and form in different plants. The individual 

 granules are enclosed in a capsule of so-called starch cellulose, which 

 is insoluble in water, but which can be made to open by heating in 

 the presence of much water. The contained starch-granulose can 

 thus be obtained, and constitutes the so-called soluble starch, amylum 

 or amylodextrin. During this process no doubt a still more complex 

 molecular group of monosaccharine anhydrides is decomposed, but 

 of the intermediary products which are formed nothing is known. 

 In the alimentary canal this change is effected through the activity of 

 diastatic ferments, which further give rise to the formation of dextrins, 



