from Xew South irales. 133 



principal constituents are, gum, sugar, and the peculiar prin- 

 ciple called mannite, which derives its name from its source, 

 and has been considered as the characteristic constituent of 

 a manna. All the varieties of manna obtained from Euro- 

 pean or Asiatic plants which have been examined contain this 

 substance in greater or less abundance, and it appears also 

 to be a common constituent of the fluid exudation of the leaves 

 known by the name of Hone3'-dew. At least, this is cei'tainly 

 the case under certain circumstances, as it was observed by 

 Langlois* in the honey-dew of the lime, which, during the 

 hot summer of 1842, occurred in such abundance in the neigh- 

 bourhood of Strasburg, that it fell from the trees in the form 

 of small rain. 



About 30 years since, a species of manna was brought to 

 this country from New South Wales, which was obtained 

 from the Eucalyptus mannifera, and differed in many of its 

 properties from the European mannas. This substance was 

 examined by Dr Thomas Thomsont, who ascertained it to 

 contain a species of sugar resembling, and yet diflPerent from, 

 mannite. It was afterwai'ds examined by Professor Johnston:[: 

 who confirmed Dr Thomson's observation, and by analysis 

 obtained for this new species of sugar the formula 0,2 Hj^ 0^^, 

 which removes it altogether from mannite, and brings it into 

 the class of the true sugars, containing hydrogen and oxygen 

 in the proportion to form water, and further establishes its 

 isomerism with grape-sugar, from which, however, itmanifestly 

 differs in all its properties. This was the first manna ex- 

 amined which contained no mannite ; and I have now to add 

 to tlie list another, similar in this respect, but differing in 

 evei'y other, and peculiarly remarkable from its possessing a 

 regularly-organised structure. 



The specimen subjected to analysis, I owe to the kindness 

 of Mr Sheriff Cay, by whose son, Mr Robert Cay, the sub- 

 stance was originally discovered in the interior of Australia 

 Felix, to the north and northwest of Melbourne. An immense 



* .Journal fur Practische C'hiniie, vol. xxix., \t. 444. 



t Organic Chemistry, Vegetables, p. 642. 



\ Journal fiir Practische Chimie, vol. xxix., p. 485. 



