-~Nrw York AGRICULTURAL EXPERIMENT STATION. 271 
of sodium chloride. This product may amount in fresh cheese 
to 75 to 80 per ct. of the proteids present. We were led by our 
former work to interpret these facts as follows: Lactic acid, 
formed by the lactic fermentation of milk-sugar, combines with 
the paracasein of the curd, forming paracasein mono-lactate, 
insoluble in water but soluble in warm dilute salt solution and. in 
hot 50: per ct. alcohol. In the light of the results of our more 
recent work, this interpretation must be modified and the observed 
facts appear to be explained correctly in the following manner: 
The coagulum following the addition of rennet enzym to milk is 
calcium paracasein, either mixed or loosely combined with soluble 
calcium salts. While lactic acid is being formed in the cheese- 
making process, it combines with the calcium of the calcium para- 
casein, forming free paracasein and calcium lactate. The con- 
ditions of manufacture are so controlled that normally not enough 
acid is produced to convert all the calcium paracasein to base- 
free paracasein. The proteids of the curd are therefore a mixture, 
in varying proportions, of calcium paracasein and free para- 
casein. It is the free paracasein that is soluble in warm 5 per ct. 
salt solution and in hot 50 per ct. alcohol; and it is this body 
that has the characteristic property of being drawn out in fine, 
silky threads, when touched with a hot iron. It is the free 
paracasein that imparts to cheese curd its peculiar plastic and 
ductile properties, exhibited in the process known as “ packing ” 
or “matting.” It is the free paracasein, therefore, that appears 
to be the body in which begin to take place the various chemical 
changes grouped under the general term cheese-ripening. 
When, in the process of cheese-manufacture, an excess of lac- 
tic acid is produced, as 0.7 or 0.8 per ct., we have the product 
familiarly known as cottage or Dutch cheese. This product is 
of a loose, granular structure and is insoluble in warm salt solu- 
tion. In this case all the calcium of the calcium paracasein com- 
bines with lactic acid, after which additional amounts of free 
lactic acid formed unite in a loose combination with the free 
paracasein producing paracasein lactate, which differs from free 
paracasein in a most marked manner in respect to its solubilities 
in dilute salt solution and hot alcohol, its plasticity and its ability 
to form fine strings when heated. 
