SECTION XIII 



GUMS 



Under this name a number of substances resembling in their 

 properties acacia gum, tragacanth, or cherry gum have been 

 grouped together. They are all insoluble in alcohol, ether, &c., 

 but dissolve or at least swell in water, yielding either viscous adhesive 

 solutions or gelatinous mixtures. 



When submitted to carefully regulated hydrolysis with dilute 

 mineral acids various sugars are produced, but the gum is not 

 entirely converted into sugars, about 20 per cent, resisting such 

 treatment. This residue has proved in each gum investigated to be 

 an organic acid with which the various sugars separated during the 

 hydrolysis have been combined. Hence the gums must be regarded 

 as consisting of glucosidal acids of high molecular weight. In some 

 gums these acids exist almost wholly in the free state, but in the 

 majority of gums they are partly combined with potassium, mag- 

 nesium, or calcium in the form of salts. 



Amongst the sugars that have been obtained from gums are the 

 pentoses, arabinose, xylose, and tragacanthose, and the hexose, 

 galactose. In addition to the glucosidal organic acid gums contain 

 mineral matter (up to 5 per cent.) together with small quantities 

 of sugars and of nitrogenous substances. 



Gums are yielded by trees and shrubs belonging to a number of 

 natural orders, but especially Leguminosce, Eosacece, Rutacece, Ana- 

 cardiacece, Combretacece, and Sterculiacece. They are produced by 

 the conversion of the cell- walls of the tissues into gum (gummosis), 

 doubtless by means of a diastasic enzyme of the origin of which 

 nothing definite is known. Typical gums (acacia gum, cherry gum) 

 are formed as a protective coating after the infliction of injury on 

 the tree, and are to be regarded as pathological products. Mucilages, 

 on the other hand, are normal products of the plant and are secreted 

 in certain cells. Tragacanth occupies an intermediate position as it 

 is not a pathological product. 



The so-called artificial gum (dextrin) produced from starch differs 

 essentially from the gums in being entirely converted into dextrose 



