New York Agricultural Experiment Station. 189 



IV. The action of rennet-extract in cheese was studied in com- 

 parison with commercial pepsin. In these experiments (55 to 57), 

 the milk-enzymes were destroyed by heat and commercial pepsin 

 was added in different amounts. No chloroform was used and there 

 were present, therefore, such organisms' as were introduced during 

 the process of making cheese. Acid was furnished by addition of 

 hydrochloric acid. 



V. The action of rennet-extract on paracasein dilactate was studied 

 in comparison with commercial pepsin. In these experiments, rennet- 

 enzyme and commercial pepsin, sterilized by formaldehyde, were 

 allowed to act upon sterile paracasein dilactate. 



VI. The action of rennet-extract was studied in cheese containing 

 acid-forming and some proteolytic organisms. In these experiments 

 (52 and 53), the milk-enzymes were destroyed by heat, acid was 

 fiu-nished by a lactic-acid " starter," but no chloroform was used. 

 We thus had as our only proteolytic agents rennet-enzyme in the 

 presence of acid and such organisms as were introduced in the 

 " starter " or that got into the milk or curd during the operation of 

 cheese-making. 



VII. Special work was done to show that all milk-enzymes were 

 destroyed by heat. Bacteriological examinations were made of the 

 cheese and milk, 



VIII. In the case of every experiment made, there was little or 

 no digesting action by either rennet-enzyme or commercial pepsin in 

 the absence of acid, while the action was marked in the presence 

 of acid. 



IX. In the absence of acid in cheese, no paracasein lactate is found 

 and little or no proteolysis occurs; in the presence of acid in the 

 cheese, paracasein monolactate is formed and digestion takes place, 

 the rennet-ferment being the active agent. The ability of rennet- 

 enzyme to convert paracasein into soluble nitrogen compounds ap- 



