New YoRK AGRICULTURAL EXPERIMENT STATION, 167 
I. INTRODUCTION. 
Fermentation, or the breaking down of complex organic com- 
pounds into simpler ones, was first looked upon as a purely 
chemical process. Later it was studied from the standpoint 
of germ life and now we are coming to see that most of the work 
of fermentation is accomplished by the action of unorganized 
ferments commonly called enzymes. Enzymes are chemical sub- 
stances, without life, capable of causing deep-seated changes in 
certain substances, the enzymes themselves undergoing little or 
no change. They are produced by the activity of plant or animal 
cells. 
As we shall see, Cheddar cheese as ordinarily manufactured, 
contains enzymes derived from three sources—(1) bacteria, (2) 
milk glands of cows arfd (3) rennet. 
During the past three years, in which we have constantly been 
- working upon the problem of cheese ripening, it has been our 
hope to determine what proportion of the casein decomposition 
in normal cheese can be justly ascribed to the activity of 
enzymes. <A direct determination under normal conditions is 
rendered impossible by the continued activity of germ life 
within the cheese mass. A separation of the activities of the 
various groups of enzymes is also rendered difficult under 
ordinary circumstances, owing to the intimate way in which the 
enzymes are mingled during the process of manufacture. 
Work on these lines is going forward under more satisfactory 
conditions than before and this report is to be considered only 
as a record of a portion of the data secured. 
The difficulties attending an investigation of this kind have 
been reduced to a minimum by the convenient location of all the 
departments and supplies concerned in the work. Our _ bae- 
teriological laboratory, cheese-curing rooms and dairy are in one 
building, while the chemical laboratory and the cattle barns are 
only a few rods distant. 
In making the cheese used in our investigation, we have had 
the valuable assistance of Mr. George A. Smith, Dairy Expert, 
