230 REPORTS ON THE STATE OF SCIENCE. 



metagummic acid to the insoluble acid, and gummic acid to the soluble 

 aeid produced by the action of alkalies on metagummic acid and also 

 existing in soluble gum. He remarks that these experiments modified all 

 the ideas then held concerning gum arable, which up to then had been 

 considered as a neutral substance comparable to dextrin, but that it 

 now appeared that the natural gum was a lime salt of an acid. It was, 

 iu fact, gummate of lime, and the insoluble natural gum cerasin was 

 metagummate of lime. It should be mentioned that the term ' gummic 

 acid ' has also been used for quite a different substance, prepared by 

 Reichardt. 



Arabic Acid. — That gum arable was largely composed of an acid had 

 already been discovered by Neubauer and announced in 1854 and 1857, 

 although Fremy was not aware of this. Neubauer made analyses of the 

 acid obtained by freeing gum arable of its ash constituents and also of the 

 salts of this acid, to which he gave the name Arahinsaure. 



Metarabic Acid. — Fr^my's term metagummic acid seems to have 

 been changed into metarabic acid by later writers, no doubt because his 

 gummic acid was the same as the arable acid previously described by 

 Neubauer. 



As early as 1810 Gay-Lussac and Th(5nard had analysed gum, and had 

 put it in the same class as sugar and starch, stating that these substances 

 were composed of cai-bon united to hydrogen and oxygen, which were in 

 the same proportions as in water ; that is to say, they put it in the class 

 of compounds now called ' carbohydrates.' 



An important step in the elucidation of the problem of the constitution 

 of gums was Scheibler's discovery, published in 1868 and in 1873, of a 

 new sugar, arabinose, obtainable both from gum arable and from a gummy 

 substance yielded by sugar beet. He also noticed the concurrent libera- 

 tion of an acid with the sugar, but does not seem to have investigated it 

 further. As early as 1832, however, Gu^rin had obtained a sugar from 

 gum arable by the action of sulphuric acid. 



Arabinon, galactose, xylose, fucose, and tragacanthose are other sugars 

 which have been obtained from gums by hydrolysis. 



Up till comparatively recently the gums have been placed among the 

 carbohydrates, together with cellulose, starch, and dextrin, and have had 

 the forraulaj (Cf.HioO,),, and Ci^HioOii assigned to them, and, in fact, 

 this view has not yet been abandoned by the text-books. O'Sullivan, 

 however, has shown that this view of their nature is mistaken, and that 

 the gums are really acids of high molecular weight, and are constituted 

 of an acid grouping forming a nucleus, to which are attached a number 

 of the residues of various hexoses, pentoses, and bioses ; these residues 

 being linked on to the acid nucleus by an ethereal oxygen attachment, 

 just as the dextrose and Isevulose are joined in cane sugar. In some cases 

 the linking is by two oxygen atoms, and reaction with two molecules of 

 water occurs when the sugar residue is broken off by hydrolysis. 



He first dealt with gum arable, and in 1884 showed that it contained 

 an acid nucleus of the formula C13H38O22, to which in a later paper he 

 gives the name arabic acid ; it is the X- arabinosic acid of the 1884 paper. 

 The gum substance itself is an acid composed of this nucleus joined to 

 +^^he residues of a number of galactose and arabinose or arabinon mole- 

 cules ; arabinon, CioHigOg, being a biose or disaccharide formed by the 

 union of the residues of two arabinose molecules. On submitting the 

 gum to hydrolytic action of varying degrees of intensity, more and more 



