GDMS, RESINS, A1QD VARNISHES. 175 



from date juice averages one-tenth by weight. The palm gnr, as 

 actually made, contains a large proportion of gluten, which causes 

 it to deteriorate sooner than cane gur. 



Section II. — Gums, Eesins, and Vaenishes. 



Gums are degradation products of the secondary cell- wall. The 

 essential constituents of gums are arabin, cerasin, and bassorin, 

 and according to which one of these three is present or preponder- 

 ates, we have gum arable, cherry gum, and gum tragacanth. 

 Other constituents of gums are dextrin, sugar, tannin, colouring 

 matters, and mineral ingredients. The various kinds of gum 

 arable, the type of which is obtained from several species of Acacia, 

 are readily soluble in water at all temperatures and have the same 

 composition as starch. They are the only gums which can be used 

 for adhesive purposes. Cherry gum, to which category belong the 

 exudations of Bauhinia Vahlii and Thespesia populnea, is insoluble 

 in water, but absorbs it greedily and swells up into a transparent 

 jelly-like mass. Boiled with a small quantity of some alkali, it is 

 converted into gum arable. Gum tragacanth, which is typically 

 represented by the gum (katira) of the Sterculias, of Cochlospermum 

 Gossypium, of Eriodendron anfractuosum, and of the cocoanut 

 palm, is also insoluble in water, but, above a certain low minimum 

 temperature, it absorbs water energetically, increasing enormously 

 in bulk. It, however, becomes soluble when treated with an 

 alkali. When acted upon by weak sulphuric acid, it yields a 

 sugar that is incapable of fermentation. Most of our gums are 

 mixed gums, that is to say, they contain two or all three of the 

 three main constituents. Gums have various uses besides their 

 employment as adhesive material. They are used in pharmacy 

 as a medium for medicaments and as mucilage for soothing in- 

 ternal inflammation ; also directly as a medicament itself. They 

 are also largely employed in calico printing, in sizing paper, and 

 in confectionery. 



Resins are also degradation products of the cell membrane, but 

 sometimes they are derived from fine-grained starch. In most 

 species, the change into resin is brought about in those cells the 

 vitality of which has been diminished from any cause. It is for 

 this reason that resin is found in greatest abundance in the region 

 of wounds, and that the stumps of felled pine and deodar trees 

 become almost transparent with the large proportion of resin 

 formed by the degradation of the cell-walls. Resins are soluble in 



