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New York AGRICULTURAL EXPERIMENT STATION. 209 
VIII. ENZYMS IN RELATION TO CHEESE-MAKING AND 
CHEESE-RIPENING. 
Enzyms are substances without life, capable of causing deep- 
seated chemical changes in certain other substances, the enzyms 
themselves undergoing little or no change. They are produced by 
the activity of plant or animal cells. Certain enzyms are inti- 
mately connected with the manufacture of cheddar cheese. We 
have (Ist) an enzym or, perhaps, a collection of enzyms, ‘present 
in the milk itself as drawn from the cow, known as galactase; (2d) 
one Or more enzyms contained in rennet-extract, and (3d) en- 
zyms produced by bacteria which get into the milk after it is drawn. 
We have studied particularly the relation of the first two kinds 
of enzyms to cheese-making and cheese-ripening. (Bulletin No. 
203, “A Study of Enzyms in Cheese” and Bulletin 233, ‘“ Rennet- 
Enzyms as a Factor in Cheese-Ripening.”) Such studies are at- 
tended with untsual difficulties, because it is as yet practically im- 
possible to obtain enzyms in an absolutely pure condition. Then, 
too, it is necessary to exclude in such experiments all possible 
‘ chance for action of organisms and, in order to accomplish this, 
conditions must be introduced which are more or less abnormal. - 
I. CHANGES IN CHEESE CAUSED BY ENZYMS IN MILK AND RENNET. 
In order to study the combined action of galactase and rennet- 
enzym, chloroform was successfully used to exclude bacterial action 
and the cheese was kept in an atmosphere of chloroform during 
ripening for periods varying from a few months to two years. 
“Under such conditions no lactic acid was formed and in some of 
the experiments lactic acid to the amount of 0.2 per ct. was intro- 
duced into the milk to stimulate the normal cheese-making process. 
The amounts of water-soluble nitrogen compounds formed in the 
cheese under the conditions of the experiments represent work done 
by the enzyms present as galactase and in rennet-extract. At the 
end of one year the normal cheese contained 37 per ct. of its nitro- 
gen in water-soluble form, while the chloroformed cheese contained 
23 per ct. The character of the water-soluble nitrogen was quite 
different under the two sets of conditions. In normal cheese the 
proportion of amido compounds is large in comparison with al- 
bumoses and peptones; in chloroformed cheese, the reverse is true. 
Again, in chloroformed cheese, little or no ammonia is formed, 
while in normal cheese ammonia appears early and increases steadily. 
These results show that there is some nitrogen-digesting agent at 
