Studies on Enzyme Action. 593 
sugar, as the synthetic product is completely fermented by bottom yeast, a 
yeast having no action on milk sugar; moreover, as the solution has no 
reducing action after the removal of this product by fermentation, the 
presence of milk sugar is precluded. 
This observation is scarcely compatible with the statement made by Croft 
Hill in his latest communication that, whilst a large number of isomeric 
bioses are conceivably possible, “one would expect that with any particular 
enzyme or group of enzymes only those would be formed which are capable 
of being hydrolysed back to glucose by the same enzyme:” the very opposite 
would appear to be the case, as will be shown later on. 
If the argument made use of in previous communications be correct, the 
action of acids and of enzymes, both as hydrolytic and as condensing agents, 
is similar, except that, and in so far as, differences arise owing to the non- 
selective activity of the former and the strictly selective activity exercised by 
the latter. 
The key to the interpretation of the changes which attend condensation 
must be looked for in the behaviour of glucose itself in solution. It is now 
abundantly proved that glucose can exist in two stereoisomeric forms, differ- 
ing only in the position which the hydroxyl group occupies relatively to the 
oxygen atom in the ring, viz. :— 
(aes Seg 
Hace. (c< A 8 
NA a 
a-Glucose.* B-Glucose. 
The term glucose, in fact, has a double connotation and these two 
substances must usually be thought of under the single name. As crystal- 
lised from alcohol, it consists almost entirely of the «-form; but this changes 
over into the 8-form if maintained during several days at about 105°. If 
either form be dissolved in water, change takes place of the one into the 
other: ultimately, the two forms exist in solution in equilibrium, in propor- 
tions which depend on the conditions, the @-compound predominating.t 
* The two positions are labelled arbitrarily. 
+ Cf. Tanret, ‘ Bull. Soc. Chim.,’ 1905, vol. 33, p. 337. 
{ Tanret, who was the first to recognise that glucose existed in several forms, has been 
led by the results recorded in No. 1 of this series to reconsider the conclusion he origin- 
ally came to that three isomerides are obtainable. He now agrees that there are but two,, 
corresponding to the two a- and B-methylglucosides, and that his supposed third 
modification was an equilibrated mixture of these two forms. Calculating from the 
rotatory power ([a]jp = +110°) of the pure a- and [a]p = +19° of the pure @-form, he 
