258 Report oF THE CHEMIST OF THE 
According to Hammarsten’*® and others, the action of rennet 
enzym on calcium casein of milk takes place in two distinct 
stages as follows: (1) The rennet enzym converts the milk- 
casein into paracasein, but there is no coagulation or change vis- 
ible to the eye, the paracasein remaining in the same condition 
apparently as the milk-casein. In the.absence of soluble calcium 
salts, the paracasein remains in this uncoagulated form in the 
case of normal milk. (2) In the second stage, coagulation or: 
separation of the curd takes place in the presence of soluble 
calcium salts. The conversion of milk-casein into paracasein in 
the first stage is due to the rennet enzym alone, while the coagu- 
lation of the paracasein in the second stage is due to soluble 
calcium salts alone in the case of normal milk. The term para- 
casein is commonly applied to both the coagulated and uncoagu- 
lated forms. 
Just what chemical change in the proteid, if any, takes place 
in the conversion of calcium casein into paracasein by the ren- 
net enzym, has not been clearly demonstrated. According to 
Hammarsten’s original theory'* the calcium casein of the milk 
undergoes a hydrolytic splitting by the action of rennet enzym 
into two compounds: (1) A body difficultly soluble, forming the 
chief product and closely resembling casein in composition, para- 
casein; and (2) an easily soluble, albumose-like body, called by 
him whey-proteid, produced in very small amount. ‘The para- 
casein further has not the property of holding calcium phos- 
phate in solution to the same extent that casein has. Ham- 
marsten’’ later modified these views, coming to the conclusion 
that the action of rennet enzym rearranges the casein molecule 
only in a physical way. Du Claux’® regarded casein as existing 
in milk in three different forms in equilibrium with one another; 
this equilibrium could be easily disturbed by the action of acids 
or ferments. Coagulation, according to his theory, was a purely 
physical, mechanical change. <A similar conclusion is held by 
Fuld'’, milk coagulation being regarded as a special case of the 
alternation between suspension and precipitation of a colloidal 
8 Maly Jahresber, d. Thierchem., 2:118 (1872) and 7:158, (1877). 
4 Maly Jahresber, d. Thicrchem., 4:153 (1874). 
© Zeit. f. Physiol. Chem., 28:114 (1899). 
16 Compt. Rend., 98:373. 
7 Bevtriige z. Chem. Physiol. und Pathol., 2:169 (1902). 
