216 Ingvar Jorgensen and Walter Stiles. 
(ii.) The completeness of the inversion of cane sugar. 
(iii.) The completeness of the fermentation of sugars other than 
pentoses by bakers’ yeast. 
(iv.) The completeness of the fermentation of sugars other than 
maltose and pentoses by maltase-free yeasts. 
Finally the accuracy of the glucose and fructose determinations 
depends upon the accuracy of the following determinations:— 
(i.) The reducing power of the original plant extract. 
(ii.) The optical rotation of the original plant extract. 
(iii.) The reducing power of the extract after inversion. 
(iv.) The reducing power of the extract after fermentation 
with maltase-free yeasts. 
(v.) The reducing power of the extract after fermentation 
with bakers’ yeast. 
(vi.) The estimation of pentoses by the Krober-Tollens method. 
As the accuracy of the glucose and fructose determinations thus 
depends on the accuracy of 13 separate assumptions, operations and 
determinations, it is not to be expected that the results given for 
glucose and fructose are likely to have a high order of accuracy. 
Indeed, Davis (1916) points out that the extracts probably contain 
optically active substances other than sugars, e.g., amino-acids and 
amides. As Davis himself says, “the values given as dextrose 
and laevulose probably do not, in most cases, represent real values ” ; 
he therefore prefers to designate them as “ apparent dextrose ” and 
“apparent laevulose.” 
A method by which it may be possible to make more 
satisfactory estimations of fructose is suggested in a recent 
publication of Miss Wilson and Atkins (1916). The sucrose is first 
estimated by measuring the reducing power and optical rotation of 
the solution of mixed sugars before and after treatment with 
invertase. After inversion, fructose may then be estimated by 
oxidising other sugars (glucose and maltose) by means of bromine. 
Under certain definite conditions, the glucose and maltose are 
destroyed by this means, and the fructose remains almost entirely 
unchanged. The method is not very exact, but it is possible that 
further research on it may render it more accurate, and in any case, 
the results obtained by its means are not open to all the objections 
of the indirect method previously described. It is, moreover, 
considerably more rapid. 
Although Miss Wilson and Atkins worked out the method in 
order to apply it to the analysis of leaf extracts, no account of work 
involving its use is as yet available. 
