GUMS 139 



PARAGALACTANE. 



Paragalactane is a substance which is better termed para- 

 galacto-arabane, since on hydrolysis by weak mineral acids it 

 yields a mixture of galactose and arabinose. It occurs in the 

 cell walls of the cotyledons of many plants, e.g., Lupinus 

 luteus and other species, Phoenix dactylifera, Cocos nucifera, and 

 other palms, Sofa hispanica and Coffea arabica, where it forms 

 a reserve food-material which is digested on germination. 



Paragalactane is a white solid which is insoluble in water 

 and cuprammonia ; it dissolves in* hot potash. On heating 

 with nitric acid it is oxidized to mucic acid. Microchemically 

 it may be identified by its insolubility in the reagents men- 

 tioned, and also by the fact that with phloroglucin and hydro- 

 chloric acid it gives a red coloration on warming. JV o colour 

 is given in the cold. 



Its association with cellulose prevents the latter exhibiting 

 some of its reactions ; thus the cellulose is unacted upon by 

 cuprammonia unless the paragalactane be removed ; this may 

 be done by boiling in dilute hydrochloric acid. 



AMYLOID. 



Amyloid * is the name given to a substance occurring in 

 the seeds of paeonies and certain cresses,f which yields on 

 hydrolysis with dilute sulphuric acid a mixture of galactose, 

 glucose, and xylose. It is a colourless substance, and is in- 

 soluble in cold water, but swells up into a slimy mass in hot 

 water ; it is soluble in cuprammonia solution. Amyloid does 

 not reduce Fehling's solution, but is oxidized by nitric acid to 

 mucic and trihydroxy-glutaric acids. It gives a blue colour 

 with iodine. 



GUMS. 



The natural gums were formerly thought to be carbo- 

 hydrates of the general formula (C 6 H 10 O 5 ) n ; the researches of 

 O'Sullivan, however, have shown that they are not simple carbo- 

 hydrates, but are rather substances of a glucosidal nature, 

 since on hydrolysis they give rise to sugars mixed with complex 

 acids of high molecular weight. The gums themselves retain 



* Cf. footnote, p. 152. 



f Winterstein : "Z. physiol. Chem.," 1893, 17, 353. 



