New York AGRICULTURAL EXPERIMENT STATION. QA1 
the cheese, it became apparent that we were dealing with some 
compound other than heterocaseose. The first suggestion throw- 
ing any light on the method of formation of this salt-soluble sub- 
stance came in the following manner: In studying the action 
of galactase in cheese-ripening, we made cheddar cheese from 
milk containing chloroform, added for the purpose of inhibiting 
bacterial action. Under these conditions no lactic acid was 
present. In order to approximate more closely the conditions 
present in normal cheddar cheese, we added in a parallel experi- 
ment a small quantity of lactic acid, the other conditions of 
experiment being kept uniform. We noticed at once that when no 
acid was present in the cheese, we found little or no salt-soluble 
substance; while in the cheese containing a little added lactic 
acid there were present marked quantities of the salt-soluble 
product. This fact suggested that lactic acid was a necessary 
agent in forming the salt-soluble proteid found by us in cheese. 
Working along the line furnished by this clue, we were led to 
believe that there is a chemical combination between the para- 
casein of fresh cheese-curd and the lactic acid formed from milk- 
sugar during the cheese-making process. We were able to form 
salt-soluble proteids also by treating paracasein with such acids 
as acetic, hydrochloric and sulphuric. In each case definite 
amounts of acid disappeared and the proteid treated with acid 
underwent marked and definite changes in properties. By treat- 
ing the salt-soluble compound with about the amount of acid re- 
quired to convert paracasein into the salt-soluble substance, we 
obtained a body insoluble in salt solutions and differing also in 
other properties. We were thus led to conclude that two sets of 
salts were formed by treating paracasein with acids, one contain- 
ing twice as much acid in combination as the other. We there- 
fore called the salt-soluble compound found in normal cheese para- 
casein monolactate, and the one insoluble in salt solution, para- 
casein dilactate. We also found the same behavior in the case 
of milk-casein when treated by acids. The two series of com- 
pounds varied in respect to many of their properties. The details 
of this work were described in Bulletin No. 214. Our conclusions 
were based upon the fact that when paracasein or casein is 
treated with an acid in definite quantities, we obtain compounds 
of definitely characteristic properties. 
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