vin] RENNET AND ITS ACTION 143 



it into lactic acid. This lactic acid coagulates the 

 milk when it reaches a certain amount. Acid coagu- 

 lation of this type, therefore, may be said to be 

 entirely dependent on the presence of milk-sugar. 



That the curds respectively produced by rennet 

 and by acid are very different, Hammarsten further 

 proved by the following experiment. He took some 

 curd which had been produced by acid coagulation, 

 and, dissolving it in a little alkali and then neutral- 

 ising the solution, he obtained a solution of casein, 

 which he found he could not coagulate with rennet. 

 From this he concluded that there was something 

 present in the original milk which was a necessary 

 condition of the action of the rennet, but which was 

 not contained in the acid-curd. This something, he 

 argued, must be present in the whey which he had 

 separated from the acid-curd. To see if this was so, 

 he added to his casein solution some of this whey 

 and then tested it with rennet, when he found that 

 it was coagulable by rennet. Further investigation 

 demonstrated that this something, which was lacking 

 in the acid-curd, was lime salts. He thus discovered 

 the further interesting fact that rennet coagulation 

 requires the presence of lime salts, and found that 

 other alkali salts can take the place of lime. In 

 fact, he came to the conclusion that the curdling by 

 rennet is similar to the clotting of blood. 



It has also been found that milk possessing an 



