PECTINS 197 



arabinose, i molecule of methyl pentose, i molecule of galac- 

 tose, and 8 molecules of galacturonic acid. 



On the other hand, Schryver * and his colleagues, who 

 worked on turnips, onions, and pea pods, hold somewhat 

 divergent views from those of the previous authors. Thus 

 they disagree with von Fellenberg's statement that pectins 

 contain any methyl pentose residue — a view which is sup- 

 ported by Nanji, Paton, and Ling.f Moreover, the insoluble 

 form of pectin as it occurs in the cell wall, to which they 

 give the name pectinogen rather than protopectin, they 

 regard as a pectic acid in which three carboxyl groups are 

 methylated and one is in loose combination with calcium ; 

 they obtain their pectinogen by extracting the cell wall material 

 with 0-5 per cent solutions of either ammonium oxalate or 

 oxalic acid ; the methoxyl content of their extracts varies 

 according to the period of extraction ; the shorter the time 

 required the more nearly does the composition correspond to 

 that of the pectinogen as it occurs in the cell wall. 



Alkalis, such as lime water, convert pectinogen into pectic 

 acid with Hberation of methyl alcohol, but accompanying this 

 hydrolysis there is also the separation of a second substance 

 of the nature of a hemicellulose ; no mention is made of the 

 araban obtained by Ehrlich in the sugar beet pectins, and it is 

 not clear whether this is identical with the above hemicellulose. 



As is stated previously, the formula assigned to the pectic 

 acid obtained by Schryver and Haynes J by the action of 

 caustic soda on pectic substances, is C17H24OX6, while that 

 assigned by von Fellenberg to his acid was C70H104O68. The 

 discrepancy may be explained by assuming that the latter 

 formula is that of the normal acid containing eight carboxyl 

 groups, while the formula of Schryver and Haynes represents 

 an anhydride of this acid resulting by the elimination of 

 4 molecules of water, thus § : — 



4Cj,H240ie or QgHggOg^ ^ C7oHi„4C)68 ~ 4H2O or CjgHggOgi 

 [Schryver & [v. Fellenberg] 



Haynes] 



* Norris and Schryver : " Biochem. Journ.," 1925, 19, 676. 

 t Nanji, Paton, and Ling : " J. Soc. Chem. Ind.," 1925, 44, 253T. 

 I Schryver and Haynes : " Biochem. Journ.," 1916, 10, 539. Carre 

 and Haynes : id., 1922, 16, 60. 



§ Carr6 : " Ann. Bot.," 1925, 36, 818. 



