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



lactic acid can considerably enfeeble its action, then the amount of 

 acidity in normal Canadian Cheddar cheese might still more diminish 

 the action of galactase, as the percentage of acidity in the manufactured 

 cheese varies at different ages from 0.76 per cent, to 1.08 per cent. 



Thus, we are bound to conclude that, as far as Canadian Cheddar 

 cheese is concerned, the presence of galactase is of little importance. 



There now remains the question of the ability of rennet to cause the 

 ripening changes. 



Jensen was the first to show that curing might be accelerated by 

 incorporating pancreas with the curd, and subsequently Babcock and 

 Russell and Jensen simultaneously proved that the pepsin in rennet 

 increased the higher decomposition products, as albumose.s and peptones 

 in cheese. 



There is also the well-known fact that cheese-makers increase the 

 amount of rennet when they want a fast curing cheese. 



Now rennet acts more quickly and better in acid solutions, and 

 it seems that the role of the lactic acid bacteria, whose growth in the 

 milk is so carefully fostered by the cheese-maker, is to bring about or 

 create the requisite acidity so that the pepsin of the rennet can exercise 

 its digestive action on the cheese. 



There is practically no increase in the number of lactic acid bacteria 

 after the cheese have been taken from the press, but the amount of 

 acidity increases and Schirokich's experiments proved that the diastase 

 of Tyrothrix (which is similar to rennet in its action) was able to act on 

 the casein when the requisite amount of acid was present. 



This connection, for we can hardly call it symbiosis, between the 

 action of rennet and lactic acid bacteria will serve to harmonize the 

 results of the experiments of other investigators. Thus, if we substitute 

 the enzymes of rennet for Schirokich's bacterial enzymes, the curing 

 process may thus be explained, and Weigmann's theory that the lactic 

 acid bacteria direct the process of curing in the right direction by 

 eliminating undesirable forms of bacteria by the lactic acid formed, is 

 quite in accord with my proposal. 



Summarized, the ripening of cheese may be said to be caused by the 

 digestive action of the rennet on the insoluble nitrogenous matter of the 

 cheese, in the presence of acid formed by the lactic acid bacteria. The 

 large amount of acidity also prevents or inhibits the growth of other 

 (and perhaps undesirable) species of bacteria. 



