30 VEGETABLE DRUGS WITHOUT ORGANIC STRUCTURE. 



Watery solutions of the gums have a slight acid reac- 

 tion; in many instances this is reinforced by the sul- 

 phuric acid which is frequently used to clean them. 

 ^ Chemically the gums are very complex. They con- 

 /tain also many included substances, such as inorganic 

 salts, tannin, sugars, coloring-matters and various pro- 

 teids. ^he salts are usually compounds of potassium, cal- 

 cium, or magnesium as carbonates, sometimes with oxalic 

 acid. The presence of the sugars is usually indicated 

 by the power of reducing copper. Of the chemical com- 

 position of the coloring-matters very little is known. The 

 nitrogenous bodies are in part ferments, which are widely 

 distributed in gums, and have had important functions in 

 the metabolism of the plant. 



Regarding the true gum substances, there is one 

 group the members of which are soluble in water. 

 These have heretofore been classified under the general 

 title of the arabins. It would appear from most re- 

 cent researches that these arabins are not simple bodies, 

 but consist of mixtures of closely related compounds. 

 Wiesner and Zeisel have recently proposed the name 

 glycosido-gummic acids to include the group.* 

 /a second group of gums is characterized by its com- 

 parative insolubility in water; these contain substances 

 which have been named cerasin and bass or in. Cerasin 

 is a colorless substance insoluble in water or alcohol. Its 

 chemical and physical composition, when freed from the 

 inorganic substances usually incorporated within it, shows 

 great similarity to an insoluble variety of arabin, which 

 is formed when arabin is heated to dryness and is termed 

 meta-arabtc acid. Cerasin acted on by enzymes, acting 

 on one type of gum alone, is said to be converted into 

 arabin. t It is perhaps better to regard cerasin as a type 



* Die Rohstoffe des Pflanzenreiches, 2d edit., 1900, p. 61. 

 t Garros: Bull. Societe Chimique. 



