On a New Sjjecies of Manna. 241 



is brought in and kept for a few hours in a warm apart- 

 ment, the perfect insects disengage themselves and are seen 

 to flit about in numbers. — J.M.] 



On a New Species of Manna from New Soutpi Wales. 

 By Thomas Anderson, M.D. F.R.S.E. 



(From the Edinburgh New Philosophical Journal for July, 1849.) 



The saccharine exudations of plants which have been classed 

 und«r the generic term of Mannas, present, in all instances, 

 a close resemblance in their chemical constitution. Their 

 principal constituents are, gum, sugar, and the peculiar 

 principle called mannite, which derives its name from its 

 source, and has been considered as the characteristic con- 

 stituent of a manna. All the varieties of manna obtained 

 from European 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 Honey-dew. 

 At least, this is certainly the case under certain circum- 

 stances, as it was observed by Langlois* in the honey-dew 

 of the lime, Avhicli, during the hot summer of 1842, occurred 

 in such abundance in the neighbourhood of Strasburg, that 

 it fell from the trees in the form of small rain. 



About 30 years since, a species of manna Vv'as brought to 

 this country from New South Wales, which was obtained 

 from the Eucalyptus mamiifera, and differed in many of its 

 properties from the European mannas. This substance was 

 examined by Dr. Thomas Thomsonf, who ascertained it to 

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

 mannite. It was afterwards examined by Professor Johnston^ 

 who confirmed Dr. Thomson's observation, and by analysis 

 obtained for this new species of sugar the formula C12 H^ O14, 

 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, it 



* Journal fiir Practische Chimie, vol. xxix,, p. 444. 



f Organic Chemistry, Veigretables, p. 642. 



i Journal liir Practische Chimie, vol. xxix., p. 485. 



