DISACCHARIDES 1 1 5 



concentrated acids was found by Wohl * and by Fischer f to 

 produce exactly the opposite phenomenon, known as reversion, 

 by which the simple molecules, more especially those of levu- 

 lose, are made to condense together to form complex dextrin- 

 like substances, as well as a disaccharide iso-maltose. 



6. Sucrose is fermentable by ordinary yeast, but this has 

 been attributed to the fact that such yeast is possessed of 

 invertase which hydrolyses the sucrose previous to its fer- 

 mentation. 



TURANOSE. CiaHa^Oii. 



This is a disaccharide formed by the partial hydrolysis of 

 the trisaccharide melecitose (see p. 124) ; it reduces Fehling's 

 solution, and on hydrolysis yields glucose and levulose ; it is 

 therefore isomeric with sucrose. 



MALTOSE. Ci^H^jjOii. 



Maltose does not appear to have so wide a distribution 

 in the plant as has sucrose. The hydrolytic action of diastase 

 on starch yields maltose — 



Starch Maltose Dextrin 



From this it might be expected that where starch is stored 

 and subsequently digested, maltose would appear. But not 

 infrequently maltase also is present by the action of which 

 the maltose is converted into hexose sugars, so that if the 

 preparation of the material is such as to destroy or to preserve 

 maltase, maltose will or will not appear in the subsequent 

 analysis. It is, possibly, for this reason that discrepant 

 results have been obtained. Maltose has been described as 

 occurring in the leaves of Tropceolum, Pyrola, Populus, and 

 Linncea, whilst, on the other hand, its presence has been denied 

 in the leaves of the snowdrop, potato, and mangold.J Gillot § 

 describes the occurrence of maltose in the rhizomes and roots 

 of Mercurialis perennis and, from the variations in amount, 



* Wohl : " Ber. deut. chem. Gesells.," 1890, 23, 2092. 

 t Fischer : id., 1890, 23, 3687. 

 X See Vol. II., chapter on " Photosynthesis." 



§ Gillot : " Recherches Chimique et Biologiques sur le Genre Mer- 

 curialis," Nancy, 1925. 



8 • 



