The Action of Rennin on Casein

The changes produced by the action of rennin in milk and solutions of casein have been the subject of many investigations. Fremy’ was probably the first to give an explanation of this phenomenon. He believed the power to coagulate milk possessed by an extract of the mucous lining of a calf’s stomach to be due to the presence of an enzyme which converted some of the lactose of the milk into lactic acid, the acid thus formed precipitating the casein. Hammarsten2 was the first to show that this coagulation of milk was due to the presence of a soluble ferment which acted directly upon the casein, producing, as he thought, two substances, the insoluble curd, Kdse, which we call paracasein and a soluble product which he called whey-protein (Molkeneiweiss). He also showed that the change of casein to paracasein was independent of coagulation, the coagulation being due to the presence of soluble calcium salts.3 A great number of papers have been published upon this subject since the early work of Hammarsten.4 As his explanation of the action of rennin has been generally accepted as correct, most of the recent investigations have been concerned with the influence of soluble salts upon the coagulation. These investigations