192 Report of the Chemical Department of the 



of those nitrogen compounds grouped under the names of 

 caseoses and peptones They also made cheese from milk to 

 which purified commercial pepsin had been added and found 

 similar chemical changes taking place in the cheese thus made. 

 They concluded from these experiments with normal cheese that 

 rennet exerts a digestive influence on casein, due to the presence 

 of peptic enzymes contained in rennet-extracts, the action of 

 which is intensified by the development of acid in the cheese- 

 curd. Jensen," working independently and along quite different 

 lines, reached the same conclusions at the same time. 



In the case of the work previously done here and elsewhere, 

 the effect of rennet-ferment has not been studied apart from the 

 action of other factors that are present in normal cheese-ripening. 

 So far as our present knowledge goes, the different agencies 

 taking part in the normal process of cheese-ripening are the 

 following: (i) Some acid, usually lactic; (2) enzymes present 

 in the milk before it is made into cheese; (3) an enzyme con- 

 tained in the rennet-extract added to milk in the cheese-making 

 process; and (4) micro-organisms, chiefly bacteria. In previous 

 studies of the effect of rennet-ferment on cheese-ripening, some 

 or all of these factors have been present, so that the specific 

 action of rennet has had to be inferred rather than been clearly 

 proved. It has been the special aim of our work to study the 

 action of the rennet-ferment as far as possible apart from the 

 other agencies of cheese-ripening. Under these conditions, we 

 have studied the action of rennet-extracts in cheese-ripening, — 

 (i) without acid, (2) in the presence of acid, (3) without salt, 

 and (4) with salt. In addition, we have studied the action of 

 rennet-extracts of different ages upon the casein of milk, and 

 also the proteolytic action of commercial pepsin on milk-casein 

 and in the process of cheese-ripening. We have also studied 

 the action of rennet-enzyme and pepsin on paracasein dilactate. 



DESCRIPTION OF EXPERIMENTAL WORK. 



DIFFICULTIES INVOLVED IN THE WORK. 



In order to destroy all enzymes present in milk, our general 

 plan of procedure has been to heat the milk to a temperature 



^ Landw, Jarhb. d. Schweiz., 14: 197 (1900). 



