240 REPORT OF THE CHEMIST OF THE 
or addition of acid, the free casein unites with acid, forming 
a casein salt of the acid, this compound, in the case of lactic 
acid, being the coagulum familiar in the ordinary souring of 
milk. | 
14. Chemical Changes in Calcium Paracasein during the Pro- 
cess of making Cheddar Cheese.—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 process of cheese-making, it 
combines with the calcium of the calcium paracasein, forming 
free paracasein and calcium lactate. It is this free paracasein 
thus formed that is soluble in warm 5 per ct. salt solution and in 
hot 50 per ct. alcohol and possesses characteristic properties of 
plasticity and ductility. 
15. Suggestions in regard to the Nomenclature of Casein and 
Paracasein and Their Compounds.—Much confusion prevails at 
present in the use of the terms casein and paracasein. It is 
suggested that the following nomenclature be used: (1) That 
the compound existing in cows’ milk be called calcium casein. 
(2) That only the free proteid be called casein. (3) That the, 
casein compound containing 2.40 per ct. of calcium oxide be 
called basic calcium casein. (4) That a compound formed by 
precipitation and combination with an acid be called a casein 
salt of the acid used. (5) That the same nomenclature be ap- 
plied to the corresponding paracasein bodies, with the following 
addition: Calcium paracasein should be applied to the uncoagu- 
lated form and the term coagulated calcium paracasein to the 
coagulated form. 
INTRODUCTION. 
For several years we have been studying the chemical changes 
that occur in the process of cheese-ripening. Early in our work 
we extracted fresh and partially ripened cheese with dilute solu- 
tion of sodium chloride, following a suggestion of Chittenden,’ 
who has shown that, in a peptic digestion of casein, heterocaseose 
was formed only in small amounts. Since we obtained by our 
extraction with dilute salt solution amounts of proteid represent- . 
ing often as much as 78 per ct. of the total nitrogen present in 
* Studies in Physiol. Chem., Yale Univ., 2:156 (1885-6). 
