CHAPTER XVIII 



feementation of polysacchaeides and fats 

 The Gums — Hemicelluloses and Celluloses 



Characteristics. — The gums, hemicelluloses and cellu- 

 loses are the most complex of the carbohydrates known to 

 occur in nature. They all have much the same empirical 

 formula, in most eases represented by (C6Hio05)n. They 

 differ in their action toward various reagents. The gums 

 will swell in water and are soluble in hot water. The hemi- 

 celluloses may be softened and even put into solution by hot 

 water. Celluloses, however, are soluble only in strong 

 sulphuric acid and in ammoniacal copper sulphate. All 

 may be broken down by hydrolysis with hot acids through 

 a series of intermediate compounds to simple sugars having 

 the formula CeHjaOa, or in a few cases to pentoses, 

 (CA„0,)._ 



Distribution. — The gums occur commonly in nature as 

 products of plant growth. The agar-agar used in the bac- 

 teriological laboratory is a gum derived from various mem- 

 bers of the group of red or purple seaweeds. The gum 

 tragacanth and the gum arable of commerce are examples of 

 gums produced by higher plants. Gums may frequently be 

 observed upon certain trees, such as the cherry. The hemi- 

 celluloses are relatively abundant in certain seeds. The 

 date seed, for example, consists for the most part of com- 

 pounds belonging to this group. The true celluloses make 

 up most of the cell wall of higher plants. 



Fermentation. — It is evident from even casual observa- 

 tion in nature that cellulose and plant bodies rapidly decay 

 and disappear, particularly when incorporated into the soil. 



220 



