igoo-i.] The Ripening of Cheese. 113 



diastase secreted by them at the beginning of the process. The author 

 states that in experiments made by him, it was shown that the diastase 

 in question, named by Duclaux, casease, acts just as energetically in the 

 absence of the bacteria by which it is secreted as in their presence. 

 From this, it would follow that if casease is a factor in the ripening of 

 cheese, it would have to be present only in a small amount. 



Von Freudenreich's results in two series of experiments made in 

 1897, considerably strengthened the theory that the lactic acid germs 

 were the chief factors in the ripening process. He grew a number of 

 lactic acid bacteria, isolated from cheese, in sterile milk to which chalk 

 had been added to neutralize the acid formed by the bacteria. These 

 bacteria were thus able to continue their growth, and at the end of two 

 or thfee months a portion of the casein was found to be converted into 

 soluble products. Thus cultures of three different species of lactic acid 

 germs gave 5.1, 6.4, and 2.4 times as much soluble nitrogen as there was 

 present in the original milk. The reaction of these cultures was not 

 acid, but neutral or slightly alkaline. 



Von Freudenreich concludes his second paper by stating that " It 

 appears from my experiments that the lactic acid ferments, especially 

 those isolated from cheese, are endowed with the power of rendering the 

 casein soluble and decomposing it. Emmenthaler cheese, as compared 

 with the results of Bondzynski, gives even more conclusive results. 

 Thus, the latter author found in the filtrate of two emulsions made from 

 ripe Emmenthaler cheese 1.44 and 1.5 1 per cent, of soluble nitrogen. 

 The nitrogen of the amides gave 0.93 and 0.82 per cent. These figures 

 are nine to ten times higher than mine, but Bondzynski analysed cheese 

 and I milk. But it takes eleven kilograms of milk to make a kilogram 

 of cheese and the agreement is as perfect as can be when we consider 

 that the experimental conditions (temperature, etc.), were not identical. 

 These results, proved by my numerous experiments, show that the lactic 

 acid ferments are in enormous numbers in ripening cheese, whilst other 

 species, as the Tyrothrix class, are relatively rare, and this fact permits 

 us to affirm that the microbic agents in the ripening of cheese ought to 

 be looked for among the lactic acid ferments." 



A new factor in the ripening of cheese was the discovery of an 

 unorganized ferment, or enzyme, in milk by Babcock and Russell. These 

 authors kept milk in contact with an excess of chemical substances that 

 destroyed the metabolic activity of bacteria, but which did not suspend 

 entirely the action of the organized ferments. Under these conditions 

 the milk coagulated, and there was a progressive formation of soluble 



