190 REvort OF THE CHEMIST OF THE 
“ breaking-down ” process, in the course of which the curd under- 
goes several marked, easily discernible changes in physical 
properties. From a tough, rubber-like consistency, with a high 
water-content, the curd changes to a mass having a smooth, 
velvety appearance and feeling, and a softer, somewhat plastic 
consistency. The texture also changes so that the curd acquires 
a peculiar kind of grain and tears off somewhat like the cooked 
meat of a chicken’s breast. 
These marked changes in the physical properties of the curd 
can be most readily and satisfactorily explained by attributing 
them to the increasing quantity of the unsaturated casein lactate 
produced throughout the cheese mass, as the result of continuous 
formation of lactic acid by the fermentation of the milk-sugar 
present. These changes in the properties of curd take place 
Simultaneously with the formation of unsaturated casein lactate 
and do not take place in the absence of this compound. The 
softening of curd, or “ breaking-down ” process, is attributed by 
Duclaux to the action of vibrios, but this is certainly an error > 
so far as relates to American cheddar cheese. 
(3) Abnormal softening of curd on addition of salt, due to the 
presence of the unsaturated paracasein lactate.— It sometimes 
happens that, when curd is salted, it softens remarkably, appears 
to be slimy, and slips through the fingers when squeezed in the 
hand. This is a condition which has not been satisfactorily ex- 
plained; the usual explanation is that liquefying organisms have 
prevailed over all others and have dissolved some of the curd. 
The real explanation is as follows: When curd behaves, on salt- 
ing, in the manner described above, more than the usual amount 
of lactic acid has been formed, and, hence, more than the usual 
proportion of unsaturated paracasein lactate has resulted. When 
salt is added to such curd, we at once have a brine formed, which 
is capable of dissolving the unsaturated paracasein lactate con- 
tained in the curd, thus producing a pasty, soft, slippery mass. 
In an experiment in which we made cheese from pasteurized 
milk, we endeavored to simulate the action of lactic acid, as 
formed by fermentation in ordinary cheese-making, by substitut- 
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