I20 Transactions of the Canadian Institute. [Vol. VII. 



Babcock and Russell, in 1900, experimented upon the action of 

 rennet on cheese, and concluded from a number of experiments : 



1. That an increase in the amount of rennet extract used in making 

 cheese does increase the amount of soluble nitrogenous products, which 

 measure the progress of cheese ripening. 



2. Increase in amount of rennet used does not increase the water 

 content of cheese ; and, therefore, the ripening of cheese cannot be 

 indirectly affected in this way. 



3. The products of peptic digestion in milk and cheese are confined 

 to the higher decomposition products, viz., albumoses and peptones 

 precipitated by tannin. 



4. The increase in soluble nitrogenous products and also in milk due 

 to an increase in amount of rennet extract used are confined to those 

 bye-products that are peculiar to pepsin, thus indicating that the 

 digestive action of rennet extract is attributable to the action of the 

 pepsin incorporated with rennet extract. 



5. The crucial test of this conclusion was made by adding purified 

 pepsin to milk and making the same into cheese, where rennet extract 

 was or was not added to curdle the milk. In such cheese digestion has 

 been increased in those cases to which pepsin has been added, and this 

 increase has been confined to those bye-products that are characteristic 

 of pepsin, and which also appear in cheese made with high quantities of 

 rennet. 



6. The digestion in cheese incident to pepsin is determined mainly 

 by the degree of acidity developed in the milk and curd. In Cheddar 

 cheese, peptic digestion probably does not begin until the acidity of the 

 milk is approximately 0.3 per cent, lactic acid. 



7. x^cid salts as phosphates, etc., favour peptic digestion in milk in a 

 manner comparable to free acids. 



8. Free acid does not normally exist in Cheddar cheese, the 

 apparent acidity being due to acid salts. 



The results of the first researches of Chodat and Hofman-Bang were 

 published in 1898, and their conclusions were as follows : 



1. A single species of bacterium can produce the digestion of the 

 casein and the characteristic odour of cheese. 



2. That contrary to the opinion of de Freudenreich but in agreement 



