497 
Enzyme of Yeast . 
From these experiments I think there can be only one 
conclusion drawn. While the yeast-cells are active they 
secrete an enzyme, as Buchner says, which enzyme can be 
extracted by appropriate means. When so extracted it sets 
up fermentation in sugar-solutions under conditions which 
prevent the activity of living yeast. All the conditions of 
such fermentation were observed — the diminution of the 
sugar, the production of C0 2 , and the coincident formation 
of alcohol. 
The enzyme is easily decomposed ; hence the necessity for 
rapid manipulation during the process of extraction. It 
possesses one of the characteristic properties of enzymes in 
general, in that it is largely thrown out of solution by 
the formation of an inert precipitate in the liquid which 
contains it. 
The secretion of the enzyme by the cell is now shown to 
be intermittent, only taking place during actual fermenta- 
tion by the yeast. It is soon decomposed when this activity 
ceases, so that resting yeast does not give it up to an extract- 
ing solvent. The completeness with which it can be extracted 
from the yeast-cell depends upon successful disintegration of 
the cell. I did not find that the enormous pressure employed 
by Buchner was necessary ; indeed, the extract obtained by the 
comparatively low pressure of five atmospheres to the square 
inch, was more active than that obtained later by the use of 
the hydraulic press. 
The Botanical Laboratory, Cambridge. 
