604 Dr. E. F. Armstrong. [July 29, 
The results recorded in the table allow of a definite answer being given to 
the two questions propounded in the introduction. It will be noticed that, 
without exception, all the twenty typical yeasts tested were able to ferment 
glucose, mannose and fructose; and it should be added that they did so, 
apparently, with equal ease. 
But quite a number of the yeasts were incapable of fermenting galactose, 
including even S. Pombe, which acts very powerfully on glucose. In this 
connection it may be mentioned that Dienert* has stated that of 89 yeasts 
examined by him, all of which fermented glucose, as many as 21 were 
unable to fermeut galactose. As a rule, galactose was fermented less easily 
than the three other sugars; but in this connection it should be mentioned 
that Mazet has described several yeasts which, he states, ferment galactose 
more readily than glucose. 
Whatever may be the mechanism of alcoholic fermentation, it is beyond 
doubt that inability to ferment galactose has nothing to do with the absence 
from the yeast of any one of the sucroclastic enzymes, since yeasts are to be 
found which are without action on galactose in each of the four classes. It 
must therefore be supposed that this sugar is not merely somewhat less 
readily fermented than the other three sugars but that the process is in itself 
a distinct one; that, in fact, the fermentation of glucose and galactose is 
brought about by different mechanisms. 
The power of a yeast to ferment mannose or glucose or fructose is clearly 
in no way conditioned by the presence of a particular sucroclastic enzyme ; 
indeed, taking the experiments with S. apiculatus into account, it would seem 
that the occurrence of alcoholic fermentation is altogether independent of the 
presence of an enzyme—whether free or fixed—able to induce the hydrolysis 
elther of maltose or of sucrose. The same argument is applicable to the 
fermentation of galactose. 
But although it must be concluded that the process of enzymo-hydrolysis 
and of fermentation are different in some essential respects, it is apparently 
none the less certain that they are cognate phenomena; otherwise it would 
be difficult to understand why it is that the only hexoses to undergo fermenta- 
tion are those which have been shown to be compatible with the sucroclastic 
enzymes (compare No. III of these Studies). It is conceivable that the 
enzyme is potentially present, in a more or less modified form, in the 
protoplasmic structure of the cell, in a condition in which it can induce 
fermentation; and that it is only on liberation from the protoplasmic 
structure that it assumes sucroclastic functions, whilst, at the same time, it 
loses its fermentative activity. 
* © Ann. Inst. Pasteur,’ 1900, p. 39. 
t+ Jbid., 1903, p. 11. 
