CARBOHYDRATES. 41 



posed of x-molecules of sugar anhydrides. The attempt has frequently 

 been made to determine the molecular weight of many of these compounds. 

 Thus with starch, the formula derived in this way has been given as 

 CigHsoOis on the one hand, and as CseoHeooOaoo on the other. We will 

 meet with the same difficulty when we come to study the proteins. 



The following substances belong to this group : starch, inulin, cellulose, 

 gums, vegetable mucilages, and glycogen. They are, with the possible 

 exception of glycogen and inulin, all known only in the amorphous state. 

 Water dissolves some of them completely, others merely swell, while the 

 remainder are unaffected. The solutions do not taste sweet, but are 

 optically active. In general they will not diffuse through a parchment 

 membrane, and for this reason they are also called saccharo-colloids. 

 Chemically they are indifferent compounds, and will not combine, for 

 example, with phenyl-hydrazine. With the exception of dextrin, they will 

 not reduce metallic oxides in alkaline solution. 



These various higher polysaccharides differ widely in biological signifi- 

 cance. Thus starch and glycogen, which on account of their similar 

 nature may be designated as vegetable and animal glycogens, are found 

 to be the most important reserve-substances of the carbohydrate group 

 that occur in the vegetable and animal kingdoms respectively. Inulin 

 has a similar nature. The gums and vegetable mucilages, on the other 

 hand, fulfill an entirely different purpose. They serve, at least to some 

 extent, to close up injuries, and correspond to the wound-secretions of 

 animals. Then again, those substances classed together under the name of 

 cellulose have a still different significance. They are found extensively 

 in the vegetable world, and form in general the chief constituents of the- 

 walls of plant cells; or at least this is true from the mosses and ferns up 

 through the whole order of phanerogams, while in the studies concerning 

 bacteria, fungi, and algae, the conclusions drawn have not been uniform. 1 

 A peculiar position is occupied by the dextrins, which it is now certain 

 are not individual substances, but very complicated mixtures. As we 

 have already seen, they are to be looked upon as the decomposition 

 products of starch. 



Now, after this brief introduction, we shall turn our attention to the indi- 

 vidual representatives of this class. Sharply distinct in its entire behavior 

 from all the other higher polysaccharides, is cellulose. It is perfectly insol- 

 uble in the ordinary solvents, water, alcohol, ether, etc. There is, in fact, 

 only one good solvent known for cellulose, and this is an ammoniacal 

 solution of copper oxide (Schweitzer's reagent). If cellulose is treated 

 with concentrated sulphuric acid at ordinary temperatures, first of all the 

 sulphuric acid ester of cellulose is formed. If this sulphuric acid solution 



1 For the chemical composition of the cell membranes of different cryptogams, see 

 Karl Miiller: Z. physiol. Chem. 45, 265 (1905). 



